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Fractionation of pulp mill waste to produce hemicellulose oligomers for adsorption onto NBSK pulp Rangu, Varun 2017

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  FRACTIONATION OF PULP MILL WASTE TO PRODUCE HEMICELLULOSE OLIGOMERS FOR ADSORPTION ONTO NBSK PULP  by Varun Rangu  B.Tech., National Institute of Technology, Warangal, 2012  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF  MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Chemical and Biological Engineering)  THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver)  December 2017  © Varun Rangu, 2017ii  Abstract Non-renewable fossil fuels and the dangers of climate change have drawn significant research into the forest biorefinery. The pulp and paper industry is positioned to lead the implementation of new technologies from such research.  Northern Bleached Softwood Kraft (NBSK) pulp is one of the chief products of the pulp and paper industry in British Columbia (B.C). It is primarily used as reinforcing pulp.  Hemicellulose present in mill waste streams such as hog fuel, primary sludge, and chip fines, can be separated and utilized as a strength additive to improve physical strength properties of NBSK pulp, and reduce refining energy.   This study investigated the influence of operating variables on the separation of hemicellulose oligomers from these lignocellulosic waste streams, and the adsorption of these oligomers onto NBSK pulp. Reaction temperature and residence time were studied for the separation of hemicellulose, while adsorption temperature, time, fibre consistency, oligomer-to-pulp percentage, and weight average molar mass Mw, were studied for the adsorption of hemicellulose onto NBSK pulp. Hog fuel and primary sludge were found to contain 58.98% and 67.90% polysaccharides respectively. Hemicellulose oligomer yields greater than 90% were obtained from hog fuel via liquid hot water treatment, and from primary sludge via dilute acid hydrolysis. A maximum total oligomer mass of 3.25g was obtained from 25g oven-dry hog fuel. Oligomer-to-pulp percentage and fibre consistency showed a linear effect on the adsorption yield, while adsorption temperature showed a nonlinear effect.  The results are encouraging, and suggest the potential of these waste streams to produce a green hemicellulose-based paper strength additive. iii  Lay Summary Pulp and paper companies in Canada are facing multiple challenges such as reduced product demand due to digitization, slow growth of feedstock and high labor costs compared to tropical countries like Brazil, and increased competition from low cost producers. Therefore, there is a need to develop solutions which can help tackle these challenges. This study investigates the separation of hemicellulose sugars from waste streams produced by saw, pulp and paper mills. The separated hemicellulose sugars can potentially be used as strength additive to Northern Bleached Softwood Kraft (NBSK) pulp, which is one of the primary products of the pulp and paper industry in British Columbia. This will add value to the waste streams, and reduce the energy required for refining, a mechanical process employed to improve the strength properties of pulp.                 iv  Preface The research work presented in this thesis was conducted under the direct supervision of Dr. Heather Trajano and Dr. Rodger Beatson in the Department of Chemical and Biological Engineering at the University of British Columbia (UBC). I have conducted literature review, defined research goals, designed and conducted experiments, analyzed and compiled data, and wrote this thesis.    Liquid hot water treatment of chip fines for high-low tests (Section 5.2) was conducted by Jingqian, a PhD student. Operation of the Dionex ICS 5000 High Performance Liquid Chromatography system for sugar analyses was done by Xue Feng Chang, at British Columbia Institute of Technology (BCIT). Hydrolysis of hog fuel and primary sludge, and adsorption experiments were done in the Clean Energy Research Centre at UBC, while milling of raw biomass was done at BCIT.                v  Table of Contents  Abstract ........................................................................................................................................... ii Lay Summary ................................................................................................................................. iii Preface............................................................................................................................................ iv Table of Contents ............................................................................................................................ v List of Tables ................................................................................................................................. ix List of Figures ................................................................................................................................ xi List of Abbreviations ................................................................................................................... xiv Acknowledgements ....................................................................................................................... xv Dedication ................................................................................................................................... xvii Chapter 1: Introduction ............................................................................................................... 1 1.1 Background ................................................................................................................... 1 1.2 Composition of Lignocellulosic Biomass..................................................................... 3 1.2.1 Cellulose ................................................................................................................ 5 1.2.2 Hemicellulose ........................................................................................................ 6 1.2.3 Lignin .................................................................................................................... 7 1.2.4 Additional Components....................................................................................... 10 1.3 Saw & Pulp Mill Waste Streams for Obtaining Hemicellulose ................................. 10 1.3.1 Hog Fuel .............................................................................................................. 11 1.3.2 Primary Sludge .................................................................................................... 12 1.3.3 Chip Fines ........................................................................................................... 13 1.4 Fractionation of Lignocellulosic Biomass .................................................................. 13 1.4.1 Recalcitrance of Lignocellulosic Biomass .......................................................... 13 1.4.2 Fractionation Techniques .................................................................................... 14 1.4.2.1 Liquid Hot Water Treatment ........................................................................... 14 1.4.2.2 Fractionation with Acidic Solutions ................................................................ 15 1.4.2.3 Fractionation under Alkaline Conditions ........................................................ 16 1.4.2.4 Steam Explosion .............................................................................................. 16 1.4.2.5 Other Techniques ............................................................................................. 16 1.4.3 Hemicellulose Removal from Waste Streams ..................................................... 17 vi  1.5 Adsorption of Hemicellulose Oligomers onto Pulp ................................................... 20 1.5.1 Effect on Pulp Properties..................................................................................... 20 1.5.2 Influence of Operating Parameters ...................................................................... 24 1.6 Present Investigation................................................................................................... 26 1.6.1 Significance ......................................................................................................... 27 1.6.2 Research Objectives ............................................................................................ 27 Chapter 2: Experimental Procedure .......................................................................................... 29 2.1 Production of Hemicellulose Oligomers from Hog Fuel and Primary Sludge ........... 29 2.1.1 Compositional Analysis of Raw Biomass ........................................................... 29 2.1.1.1 Procurement and Preparation........................................................................... 29 2.1.1.2 Determination of Extractives ........................................................................... 30 2.1.1.3 Determination of Structural Carbohydrates, Lignin and Ash .......................... 31 2.1.2 Separation of Hemicellulose Oligomers ............................................................. 34 2.1.2.1 Procedure ......................................................................................................... 34 2.2 Adsorption of Hemicellulose Oligomers onto NBSK Pulp ........................................ 37 2.2.1 Compositional Analysis of NBSK Pulp .............................................................. 37 2.2.2 High-Low Experiments ....................................................................................... 38 2.2.3 Full-Scale Experiments ....................................................................................... 41 2.2.3.1 Experiment Design .......................................................................................... 42 2.2.3.2 Methodology .................................................................................................... 43 2.2.3.2.1 Recovery of Hemicellulose Oligomers from Chip Fines ........................... 43 2.2.3.2.2 Adsorption.................................................................................................. 44 Chapter 3: Liquid Hot Water Treatment of Hog Fuel ............................................................... 46 3.1 Introduction ................................................................................................................ 46 3.2 Composition of Hog Fuel ........................................................................................... 46 3.3 Separation of Hemicellulose Oligomers ..................................................................... 48 3.3.1 pH of Hydrolysate ............................................................................................... 50 3.3.2 Percentage Solids Removed ................................................................................ 51 3.3.3 Percentage Oligomers ......................................................................................... 54 3.3.3.1 Arabinan .......................................................................................................... 54 3.3.3.2 Galactan and Xylan ......................................................................................... 56 3.3.3.3 Glucan and Mannan ......................................................................................... 58 vii  3.3.4 Total Mass of Oligomers ..................................................................................... 60 3.4 Conclusion .................................................................................................................. 61 Chapter 4: Dilute Acid Hydrolysis of Primary Sludge ............................................................. 63 4.1 Introduction ................................................................................................................ 63 4.2 Composition of Primary Sludge ................................................................................. 64 4.2.1 Composition of Ash ............................................................................................ 66 4.3 Separation of Hemicellulose Oligomers ..................................................................... 66 4.3.1 pH of Hydrolysate ............................................................................................... 67 4.3.2 Percentage Solids Removed ................................................................................ 69 4.3.3 Percentage Oligomers ......................................................................................... 70 4.3.3.1 Arabinan .......................................................................................................... 71 4.3.3.2 Galactan ........................................................................................................... 72 4.3.3.3 Xylan ............................................................................................................... 73 4.3.3.4 Glucan and Mannan ......................................................................................... 74 4.3.4 Total Mass of Oligomers ..................................................................................... 75 4.4 Conclusion .................................................................................................................. 76 Chapter 5: Adsorption of Hemicellulose Oligomers onto NBSK Pulp ..................................... 77 5.1 Introduction ................................................................................................................ 77 5.2 High-Low Experiments .............................................................................................. 77 5.3 Full-Scale Investigation .............................................................................................. 79 5.3.1 Effects of Operating Variables ............................................................................ 81 5.3.1.1 Individual Effects ............................................................................................ 82 5.3.1.1.1 Hemicellulose Oligomer-to-Pulp Percentage ............................................ 82 5.3.1.1.2 Fibre Consistency....................................................................................... 84 5.3.1.1.3 Adsorption Temperature ............................................................................ 85 5.3.1.2 Interactive Effects ............................................................................................ 87 5.3.1.2.1 Fibre Consistency and Oligomer-to-Pulp Percentage ................................ 87 5.3.1.2.2 Adsorption Temperature and Fibre Consistency ....................................... 88 5.3.1.2.3 Adsorption Temperature and Oligomer-to-Pulp Percentage ..................... 90 5.4 Conclusion .................................................................................................................. 91 Chapter 6: Conclusions and Future Work ................................................................................. 92 6.1 Summary ..................................................................................................................... 92 viii  6.2 Recommendations for Future Work ........................................................................... 93 Bibliography ................................................................................................................................. 94 Appendix A: Mass Balance for Compositional Analysis ........................................................... 100 Appendix B: Additional Data from JMP .................................................................................... 102                           ix  List of Tables Table 1. 1. Composition of cellulose, hemicellulose and lignin in several lignocellulosic materials on dry basis (Sun & Cheng, 2002) .................................................................................................. 4 Table 1. 2. Percentage of typical linkages of lignin in softwood and hardwood (Z. Chen & Wan, 2017) ............................................................................................................................................... 9 Table 1. 3. Examples of biorefineries converting lignocellulosic feedstocks to valuable products (S I Mussatto & Dragone, 2016) ................................................................................................... 15  Table 2. 1. Temperature and residence time used for hydrolysis experiments. ............................ 36 Table 2. 2. Minimum and maximum values for the five operating variables studied in high-low test. ................................................................................................................................................ 39 Table 2. 3. Operating conditions used to obtain hemicellulose oligomers with Mw values indicated in Table 2.2 ................................................................................................................................... 39 Table 2. 4. Operating conditions for each case in high-low test ................................................... 41 Table 2. 5. Classification of operating variables based on adsorption yield ................................. 41 Table 2. 6. Experimental conditions obtained using a central composite design with JMP 13 .... 43  Table 5. 1. Mw of hemicellulose, and mass of oligomers per ml of hydrolysate. ......................... 78 Table 5. 2. Adsorption yield results of high-low experiments ...................................................... 79 Table 5. 3. Characteristics of hydrolysate obtained at 170 C and 0 minutes for chip fines .......... 80 Table 5. 4. Adsorption yield and predicted adsorption yield for each run in the full-scale investigation .................................................................................................................................. 80  x  Table B. 1. PValues for indivisual operating variables, and for the product of the variables. ... 102                            xi  List of Figures Figure 1. 1. Illustration showing the similarities and differences between an oil refinery and biorefinery. ...................................................................................................................................... 1 Figure 1. 2. Structure of lignocellulosic material (Chaturvedi & Verma, 2013) ............................ 4 Figure 1. 3. Molecular chain structure of cellulose (H. Chen, 2014) ............................................. 5 Figure 1. 4. Structure of Galactoglucomannan (Laine, 2005) ........................................................ 7 Figure 1. 5. Basic structural units of lignin. (Fengel and Wegner, 1984) ....................................... 8 Figure 1. 6. SEM image of handsheet ........................................................................................... 21 Figure 1. 7. SEM image of handsheet ........................................................................................... 21 Figure 1. 8. Influence of process factors on adsorption yield (Ban & van Heiningen, 2011) ...... 25  Figure 2. 1 Hog fuel ...................................................................................................................... 30 Figure 2. 2 Primary sludge ............................................................................................................ 30 Figure 2. 3. Convection oven (VWR) ........................................................................................... 30 Figure 2. 4. Dionex ASE 350 Accelerated Solvent Extractor ....................................................... 31 Figure 2. 5. Midmark M11UltraClave .......................................................................................... 32 Figure 2. 6. Dionex ICS 5000 High Performance Liquid Chromatography ................................. 33 Figure 2. 7. Shimadzu UV Spectrophotometer ............................................................................. 33 Figure 2. 8. Thermolyne muffle furnace ....................................................................................... 33 Figure 2. 9. Parr 4520 bench top batch reactor with temperature control, used for the biomass hydrolysis. ..................................................................................................................................... 35 Figure 2. 10. Incubator .................................................................................................................. 40  xii  Figure 3. 1. Compositional analysis results for hog fuel. ............................................................. 47 Figure 3. 2. Representation of temperature vs time graph for fractionation of biomass .............. 49 Figure 3. 3. pH of hog fuel hydrolysate as a function of temperature. Error bars represent the range........................................................................................................................................................ 51 Figure 3. 4. Percentage solids removed by hog fuel hydrolysis as a function of temperature. Error bars represent the range. ............................................................................................................... 52 Figure 3. 5. Percentage oligomers of arabinan from hog fuel hydrolysis as a function of residence time. Error bars represent the range. ............................................................................................. 55 Figure 3. 6. Trend of percentage of arabinan monomers with respect to initial hog fuel, with increase in residence time at 180o C. Error bars represent the range. ........................................... 56 Figure 3. 7. Percentage oligomers of galactan from hog fuel hydrolysis as a function of residence time. Error bars represent the range. ............................................................................................. 57 Figure 3. 8. Percentage oligomers of xylan from hog fuel hydrolysis as a function of residence time. Error bars represent the range. ............................................................................................. 57 Figure 3. 9. Percentage oligomers of glucan from hog fuel hydrolysis as a function of residence time. Error bars represent the range. ............................................................................................. 59 Figure 3. 10. Percentage oligomers of mannan from hog fuel hydrolysis as a function of residence time. Error bars represent the range. ............................................................................................. 59 Figure 3. 11. Total mass of oligomers removed from hog fuel as function of temperature. Error bars represent the range. ............................................................................................................... 60  Figure 4. 1. Compositional analysis for primary sludge. .............................................................. 64 Figure 4. 2. XRD analysis of ash obtained from primary sludge. ................................................ 66 Figure 4. 3. pH of primary sludge hydrolysate as a function of temperature ............................... 68 xiii  Figure 4. 4. Percentage solids removed by dilute acid hydrolysis of primary sludge, as a function of temperature. .............................................................................................................................. 70 Figure 4. 5. Percentage oligomers of arabinan from primary sludge hydrolysis as a function of residence time ............................................................................................................................... 72 Figure 4. 6. Percentage oligomers of galactan from primary sludge hydrolysis as a function of residence time ............................................................................................................................... 73 Figure 4. 7. Percent oligomers of xylan from primary sludge hydrolysis as a function of residence time ............................................................................................................................................... 74 Figure 4. 8. Total mass of oligomers removed from primary sludge as function of temperature 75  Figure 5. 1. Variation of predicted adsorption yield with oligomer-to-pulp percentage, at a fibre consistency of 2.5%, and temperature of 37.5o C. ........................................................................ 83 Figure 5. 2. Variation of predicted adsorption yield with fibre consistency at an oligomer-to-pulp percentage of 2%, and temperature of 37.5o C. ............................................................................ 84 Figure 5. 3. Variation of predicted adsorption yield with temperature, at a fibre consistency of 2.5%, and an oligomer-to-pulp percentage of 2%. ....................................................................... 86 Figure 5. 4. Surface plot showing the variation of predicted adsorption yield with variation in oligomer-to-pulp percentage and fibre consistency, at a temperature of 37.5o C ......................... 88 Figure 5. 5. Surface plot showing the variation of predicted adsorption yield with variation in temperature and fibre consistency, at an oligomer-to-pulp percentage of 2%. ............................ 89 Figure 5. 6. Surface plot showing the variation of predicted adsorption yield with variation in temperature and oligomer-to-pulp percentage, at a fibre consistency of 2.5%. ........................... 90  xiv  List of Abbreviations AIA Acid Insoluble Ash AIL Acid Insoluble Lignin ASA Acid Soluble Ash ASE Accelerated Solvent Extractor  ASL Acid Soluble Lignin B.C British Columbia BKP Bleached Kraft Pulp BOD Biochemical Oxygen Demand DP Degree of Polymerization DS Degree of Substitution GGM Galactoglucomannan GM Galactomannan HMF Hydroxy-methyl furfural HPLC High Performance Liquid Chromatography NBSK Northern Bleached Softwood Kraft NREL National Renewable Energy Laboratory OD Oven Dry ODW Oven Dry Weight UV Ultra Violet WRV Water Retention Value       xv  Acknowledgements I would like to start by thanking my advisors, Dr. Heather Trajano and Dr. Rodger Beatson. Dr. Trajano and Dr. Beatson have both been very encouraging and understanding advisors. In addition to supporting and providing valuable guidance for this research project, they have encouraged me in my extracurricular endeavors, and supported my career goals. I admire them immensely for their dedication, and they inspire me to work hard. I am extremely glad to have had them as my advisors. I am extremely grateful to my committee members Dr. Mark Martinez and Dr. Anthony Lau for their valuable comments and inputs regarding my research.  I am thankful to Jingqian, a PhD student in our research group. She was usually the first person who I would ask questions about my research, which she has always answered patiently. CHBE faculty, fellow graduate students, Co-op students in our laboratory, and postdoctoral researchers at BCIT, have all played a vital role in my success both directly and indirectly, and I am grateful for the help they have given me. I would also like to acknowledge the support, and sincerely thank Mitacs Inc and Canfor Pulp Limited for providing funding for this project. My friends Fuhar, Gaurav, Lakshana, Shubham, Charu, Payel and Aarya, aunt Dominga and uncle Hari, have been like family to me in Vancouver. They made my time in Vancouver more enjoyable, and have always been by my side. I can’t thank them enough for their love and support. Lastly, but most importantly, I would like to express my gratitude to my parents, Rajyalaxmi Rangu and Satish Rangu, who have always believed in me, and without whom I would not have xvi  been able to accomplish as much as I have. I feel extremely fortunate to have received all their love and affection.                 xvii  Dedication         To my beloved parents and my late grandparents  1  Chapter 1: Introduction 1.1 Background Factors such as reduced newsprint demand, high labor costs, and competition from low cost producers are making it challenging for Canadian pulp and paper companies to be profitable. Companies which innovate and develop new products and unique markets will be able to meet these challenges (Thorp, 2005; Wising & Stuart, 2006).  Working on similar principles as that of a petrochemical refinery (Figure 1.1), biorefinery facilities fractionate biomass into valuable products such as fuels, chemicals and valuable materials. A few of these products have been identified by the National Renewable Energy Laboratory (NREL) (Werpy & Petersen, 2004). Biorefinery technologies offer pulp and paper companies options for the production of new high-value products from their mills, and the improvement of the quality of existing products (Wising & Stuart, 2006). Employment of these options may open doors to new revenue streams.  Figure 1. 1. Illustration showing the similarities and differences between an oil refinery and biorefinery. 2  There are several emerging biorefinery technologies for the pulp and paper industry. Some biorefinery technologies have been well studied, and their integration into existing facilities evaluated (Paleologou et al., 2011). Since each facility is unique in terms of the technologies employed and products produced, choosing the right combination of biorefinery technologies to integrate with existing technologies depends on numerous factors. These include availability of a market for the new products, supply chain, impact of implementing new technologies on the entire mill, and undesirable process issues that may arise due to the integration (Wising & Stuart, 2006).  With about 55 million hectares of its 95 million hectares of land area covered by forests (The State of British Columbia’s Forests, 3rd edition, 2010), British Columbia (B.C) is home to a substantial pulp and paper industry. Though B.C’s forests have diverse growing stock, softwood constitutes the major portion. Therefore, the majority of British Columbian pulp producers utilize softwood.  One of B.C’s primary products is Northern Bleached Softwood Kraft (NBSK) pulp from white spruce, lodgepole pine, and alpine fir. NBSK pulp is characterized by long, slender, flexible and strong fibres, which give excellent strength properties to NBSK pulp, and therefore it is used as reinforcement pulp. However, in view of increasing competition from pulp mills in tropical countries, which have the advantage of low labor costs, and significantly larger mills, there is a need to find ways to make NBSK pulp more competitive in the market (Van Heiningen A., 2006). Drying of pulp fibres leads to reduction in the internal fibre volume, making the fibres stiffer and thinner than never dried fibres. This is called hornification, and is believed to be due to increased coalescence of cellulose fibrils in the fibre wall. As a result, the fibres lose their capacity to regain their original water swollen state upon rewetting (Minor, 1994; Palme, Theliander, & Brelid, 2016). This can be denoted in terms of water retention value (WRV), which is an empirical 3  measure of the capacity of pulp fibres to hold water. Pulp is subjected to mechanical treatment called beating, to reverse the effects of hornification. Though beating improves WRV, it also consumes significant energy, and results in fibre shortening and formation of fines (Laivins & Scallan, 1996; Lumiainen, 2000).      Previous studies show that adsorption of hemicelluloses such as glucomannans and xylans onto pulp reduces the coalescence of cellulose fibrils (Palme et al., 2016), thus improving the strength properties of pulp, reducing hornification, and reducing the energy required for beating (Ban, Chen, & Andrews, 2011; Ren, Peng, Sun, & Kennedy, 2009; Salmen, 2015; Silva et al., 2011). Oligomers, which are longer chain molecules having multiple monomers, have been found to have better adsorption ability (Ban et al., 2011), and to form stronger bonds with cellulose fibres in pulp. Therefore, hemicellulose oligomers can act as strength additive for pulp. There are several process streams in the pulp mill which can be used to obtain hemicellulose, of which, process waste streams such as chip fines, hog fuel and primary sludge, are very attractive. Value could be added to these waste steams by extraction and utilization of hemicellulose. 1.2 Composition of Lignocellulosic Biomass Lignocellulosic biomass is a complex material. It can be categorized based on its source, such as industrial waste, forestry waste, agricultural residues, domestic wastes, and municipal solid wastes. These include sawdust, pulp mill residues, food industry residues, hard and soft woods, different grasses, non-food seeds, nutshells, waste paper, wheat straw and rice straw (Behera, Arora, Nandhagopal, & Kumar, 2014).  Chemical and physical interactions between the three major components of lignocellulosic biomass, cellulose, hemicellulose, and lignin, result in a complex lignocellulosic matrix (Figure 1.2). In addition to these three components, minor quantities of proteins, pectins, extractives and 4  ash are also found in lignocellulosic biomass (H. Chen, 2014). The composition and chemical nature of these components varies from one plant to another, and from one tissue to another. For example, as can be seen in Table 1.1, softwood has more lignin content when compared to hardwood (Kumar, Barrett, Delwiche, & Stroeve, 2009; Schädel, Blöchl, Richter, & Hoch, 2010).  Figure 1. 2. Structure of lignocellulosic material (Chaturvedi & Verma, 2013) As the most abundant source of renewable organic matter on Earth (H. Chen, 2014), lignocellulosic biomass has garnered immense attention, especially in recent decades, with a variety of studies focussing on converting it to value added products with applications ranging from pharmaceuticals to fuels. Table 1. 1. Composition of cellulose, hemicellulose and lignin in several lignocellulosic materials on dry basis (Sun & Cheng, 2002)  5  1.2.1 Cellulose Cellulose is present in large quantities in higher plants and other biomass including bacteria and marine algae. It is the most important structural constituent of a plant cell wall. It is a linear homopolymer consisting of D-glucose units linked to each other by β-(1,4)-glycosidic bonds. Cellobiose, as shown in Figure 1.3, is the repeating unit in cellulose. The chemical formula of cellulose can thus be written as (C6H10O5)n, where ‘n’ is the degree of polymerization (DP), which can be as high as thousands or tens of thousands (Kumar et al., 2009; H. Chen, 2014; Haghighi Mood et al., 2013).  Figure 1. 3. Molecular chain structure of cellulose (H. Chen, 2014) The majority of cellulose in biomass exhibits a crystalline structure, and a small fraction is amorphous (Kumar et al., 2009). The large number of hydroxyl groups result in formation of intra- and inter-molecular hydrogen bonds, contributing to the compact crystalline structure of cellulose. This crystalline structure of cellulose gives it the characteristics of being insoluble in water, dilute acids and dilute alkaline solutions at room temperature (H. Chen, 2014; Zhang et al., 2015). The cellulose fibrils are intertwined with lignin and hemicellulose, to form the lignocellulose matrix (Figure 1.2). Cellulose has been in use for centuries, and through developing technology, new applications for cellulosic food, chemicals and fuels are emerging (Kramer et al., 2006). 6  1.2.2 Hemicellulose Hemicellulose is also a polysaccharide and constitutes a significant portion of lignocellulosic biomass, in some cases second only to cellulose (Table 1.1). However, unlike cellulose, hemicellulose is an amorphous branched copolymer comprising of several different sugar units instead of only D-glucose. The monosaccharides which make up hemicellulose include pentoses: xylose and arabinose, hexoses: glucose, galactose and mannose, and uronic acids like D-glucuronic and D-galacturonic acids (Fengel and Wegner, 1984; Kumar et al., 2009). The monomers are linked by a combination of ether bonds and weak hydrogen bonds. It also has shorter chain lengths compared to cellulose, in the range of two hundred monomers (Fengel and Wegner, 1984). Unlike cellulose, hemicellulose is easily hydrolysable under acidic or alkaline conditions, due to its amorphous nature.  Based on the structure and monomer units present, hemicelluloses can be divided into four different classes: xylans, mannans, xyloglucans and β-glucans with mixed linkages. The variations between these four classes include distribution, localization, types of side-chains, and types and distribution of glycoside linkages present in the backbone (Ebringerová & Thomas, 2005). Different plants have different types and concentrations of hemicellulose. The concentration of hemicellulose also varies between different tissues within a single plant (Schädel et al., 2010). Softwoods primarily have D-mannose derived hemicelluloses such as galactoglucomannans (GGM), and hardwoods primarily consist of D-xylose derived hemicelluloses such as arabinoglucuronoxylan (Li & Liu, 2010; Ebringerová & Thomas, 2005). Figure 1.4 shows the typical structure of galactoglucomannan. Since Northern Bleached Softwood Kraft pulp is produced from softwood, the mill waste streams used for this study contain softwood hemicelluloses. 7  Hemicelluloses form different kinds of bonds with other components in the lignocellulosic matrix, such as hydrogen bonds with cellulose, covalent bonds with lignin, and ester linkages with acetyl units and hydroxycinnamic acids, and therefore present a complicated scenario to be selectively separated. In addition, due to their relative sensitivity to operating conditions, parameters such as residence time and temperature must be controlled to avoid the formation of degradation products such as hydroxy-methyl furfural (HMF) (Zhang et al., 2015; Jun Li Ren et al., 2009).    Figure 1. 4. Structure of Galactoglucomannan (Laine, 2005)  1.2.3 Lignin Lignin is an amorphous organic polymer, and is the most abundant organic polymer on Earth, after cellulose (Sjostrom, 1993). It is present in the primary cell wall, and imparts structural support, resistance against microbial attack, and water impermeability (Kumar et al., 2009).  8  Lignin is a complex compound having a large molecular structure formed by the cross linking of polymers consisting of phenylpropane monomeric units. There are three common phenylpropane units which constitute lignin: p-hydroxyl (derived from coumaryl alcohol), guaiacyl (derived from coniferyl alcohol) and syringyl (derived from sinapyl alcohol) (Figure 1.5). The proportions of these phenylpropane units in lignin vary between different lignocellulosic feedstocks. In softwoods, lignin is generally dominated by guaiacyl units, while in hardwoods lignin contains syringyl and guaiacyl units (Chen, 2014). These phenylpropane units are linked to each other by means of alkyl and ether linkages. There are seven types of typical interlinkages: β-O-4, α-O-4, 5-5, β-5, β-1, 4-O-5 and β-β (Table 1.2). β-O-4 linkage is the dominant kind of linkage in both softwood and hardwood, constituting about 50-60% (Chen & Wan, 2017). Recalcitrance, which is lignin’s resistance to undergo chemical transformations (Calvaruso, Clough, Rechulski, & Rinaldi, 2017),  depends on the type of phenylpropane units that make up lignin, and the type of linkages between these units (Li & Liu, 2010).                              Coumaryl alcohol            Coniferyl alcohol               Sinapyl alcohol                          p-hydroxyl lignin               Guaiacyl lignin                   Syringyl lignin  Figure 1. 5. Basic structural units of lignin. (Fengel and Wegner, 1984)   9  Table 1. 2. Percentage of typical linkages of lignin in softwood and hardwood (Z. Chen & Wan, 2017) Linkages Dimer structure Softwood (%) Hardwood (%) β-O-4 (Phenylpropane β-aryl ether)  ~ 50 60 5-5 (Biphenyl and dibenzodioxocin)  9.5-11 6-8 β-5 (Phenylcoumaran)  9-12 6 β-1 (1,2-Diaryl propane)  7 7 α-O-4 (Phenylpropane α-aryl ether)  6-8 6-8 4-O-5 (Diaryl ether)  3.5-4 6.5 β-β (β-β linked structures)  2 3  10  1.2.4 Additional Components While cellulose, hemicellulose, and lignin constitute the major portion of lignocellulosic biomass, there are other chemical components which are present in minor quantities. These include extractives and ash.  Extractives are present in various locations of a wood structure, and some extractives protect the wood from wood-boring insects and fungal attacks (Challinor, 1996). Extractives are compounds such as glycerides, waxes, fatty acids, resin acids and oxidized compounds, which are soluble in water or neutral organic solvents, and are therefore generally identified by the solvent they are soluble in (Fengel and Wegner, 1984).  Ash, constituted by inorganic compounds, is the residue remaining after subjecting lignocellulosic biomass to incineration. Ash includes elements such as calcium, potassium, magnesium, manganese, zinc, iron and phosphorous in different forms, such as carbonate, oxide, sulphate and chloride (Anglès et al., 1997). Similar to other components in lignocellulosic biomass, the percentage of these elements varies based on the plant species, growth environments and even the tissue of a plant (Pitman, 2006; H. Chen, 2014). Some of the pulp mill waste streams such as primary sludge may contain high amounts of ash, as they are obtained after the biomass has been subjected to chemical treatments. High ash content may interfere with the ease of hydrolysis of hemicellulose polysaccharides, as it can alter the pH of the hydrolysate. 1.3 Saw & Pulp Mill Waste Streams for Obtaining Hemicellulose According to Canada Report on Bioenergy, 2010 (Bradley, 2010) British Columbia has the largest forest industry in Canada. Annually, 11 million dry tons of surplus softwood derived residues are available in British Columbia (Burkhardt, Kumar, Chandra, & Saddler, 2013). A major portion of these residues are produced by saw and pulp mills in the province. 11  There are 3 primary methods of pulping: chemical, mechanical (including thermomechanical) and chemimechanical. The yield of chemical pulp (≈ 45-55%) is lower than that of mechanical pulp (≈ 85-95%), as the objective in chemical pulping is to obtain pure cellulose fibres by removing the non-cellulose components. This results in process streams within the pulp mill containing hemicellulose, lignin, extractives, and inorganic chemicals, along with small amounts of cellulose (Bajpai, 2011). These waste streams can be utilized as sources of hemicellulose. Kraft (Sulphate) pulping is the predominant chemical pulping method world-wide, because of its compatibility with all types of wood species and the superior strength properties of Kraft pulp (Bajpai, 2011). Northern Bleached Softwood Kraft pulp is produced by subjecting softwood from British Columbia’s forests to Kraft pulping. Hog fuel and primary sludge waste streams from these mills are studied as potential sources of hemicellulose oligomers for this research. In addition, hemicellulose oligomers obtained from chip fines are used for the adsorption study, as detailed in chapter 5. 1.3.1 Hog Fuel Hog fuel is a heterogeneous mixture of saw mill by-products such as bark, sawdust and shavings. However, the relative proportion of these components depends on the mill’s marketing strategies for these residues (Briggs, 1994; Carrasco et al., 2017). Though hog fuel has non-structural polysaccharides due to the presence of extractive-rich bark,  Burkhardt et al., (2013) determined that it also contains significant quantity of cellulose and hemicellulose (≈ 45-55%). The hemicellulose content will vary from one mill to the other, due to varying proportions and composition of component residues. 12  Previously, surplus hog fuel in the saw mills of British Columbia, Alberta and Manitoba was required to be incinerated. However, due to increasing mill residue cost and potential for hog fuel to be used as an energy source, mills began utilizing hog fuel as a fuel source (Bradley, 2010). In a modern pulp mill, hog fuel is typically burned to produce heat and power for the mill.  1.3.2 Primary Sludge Primary sludge is a heterogeneous material consisting of chemically modified wood fibres and chemical contaminants, which depend on the type of chemical treatments being used in the mill (Jackson & Line, 1997). Sludge is obtained after treatment of mill effluent water, which aims to abate the impact of effluent water on the environment by means of separating suspended solids and other waste. The objective of waste water treatment in pulp and paper mills is to prevent the effluent water from having properties unallowably different from receiving water. Various sources within the pulp and paper mill contribute to generation of effluent water. These sources include condensates from digester and evaporator, and white waters obtained from thickening, cleaning and screening. Additives such as coagulants and/or flocculants are added during effluent treatment to enhance the efficiency of removal of undesirable material, and thus reduce the toxicity and biochemical oxygen demand (BOD). In mills employing lime coagulation for decolourization of effluent water, calcium related compounds may also end up in sludge. The exact composition of sludge varies from one mill to another, due to differences in treatment processes and chemicals (Smook, 2002).  After dewatering, sludge is often landfilled or in some cases incinerated. It has been found that incineration of sludge yields less heat, and in cases where it is mixed with hog fuel or bark, it reduces the capacity for steam generation. Landfilling can result in leachate contamination of 13  ground and surface water (Smook, 2002; Veluchamy & Kalamdhad, 2017). Utilizing sludge to produce hemicellulose sugars is a potential alternative to landfilling and incineration. 1.3.3 Chip Fines Chip fines are those wood chips which have short and fragmented fibres when compared to desirable chips for pulp production. Usually, these are the particles which pass through 3mm diameter holes in a classifier, i.e., the particles which are smaller than 3mm in size. They reduce the yield of pulp, and result in poor strength properties in comparison to the desired chips. In addition, chip fines also lead to handling problems such as blinding of screens (Smook, 2002).  For this study, hemicellulose oligomers were obtained from chip fines, and were adsorbed onto NBSK pulp at different oligomer loadings, adsorption temperatures and fibre consistencies. The results, as detailed in chapter 5, have been used to study the impact of varying operating parameters on the extent of adsorption. 1.4 Fractionation of Lignocellulosic Biomass 1.4.1 Recalcitrance of Lignocellulosic Biomass Selective separation of any one component from lignocellulosic biomass is challenging due to compositional and physicochemical factors, which resist fractionation. Complex interactions between cellulose, hemicellulose, and lignin act as hindrance for selective separation of one particular component (Kumar et al., 2009). The possibility of a multitude of reactions during fractionation may result in separation of an undesired component, degradation of the desired component, and incomplete removal of the desired component. Depending on the lignocellulosic feedstock being used, the complexity of selective separation may increase or decrease. For example, the presence of chemical contaminants in primary sludge may hinder the ease of hemicellulose removal, as they may interfere with the pH of the hydrolysate during fractionation. 14  1.4.2 Fractionation Techniques Ability to fractionate lignocellulosic biomass into its individual components is the key driver which promotes the utilization of lignocellulosic biomass for production of valuable products. Various fractionation methods have been developed for this purpose, some of which are implemented at an industrial scale, as shown in Table 1.3. Several studies are being conducted to develop better methods, or to improvize the existing methods. Since bioethanol from cellulose has been one product from lignocellulosic biomass which has received immense attention, a major portion of the fractionation methods have been developed to improve the accessibility of cellulose to enzymes. Nevertheless, all the fractionation methods result in separation of one or more of the individual components, hemicellulose, lignin and cellulose (Mussatto & Dragone, 2016; Jiang et al., 2016). Depending on the desired outcome, cost effectiveness, and environmental impact, a fractionation method can be selected, and customized if necessary. 1.4.2.1 Liquid Hot Water Treatment In liquid hot water treatment, also known as hydrothermal pretreatment or aqueous fractionation, lignocellulosic biomass is broken down using water at elevated temperatures (160oC - 240oC) and pressures. High pressures facilitate maintaining water in liquid phase to promote separation of the components after disintegration of the lignocellulosic matrix (Brodeur et al., 2011). This process results in two main products, a slurry which is rich in solubilized hemicellulose, and a solid fraction rich in cellulose (Pérez et al., 2008). Liquid hot water treatment is one of the simplest ways to fractionate lignocellulosic biomass, and is one of the mildest methods. It helps avoid the usage of expensive and corrosive chemicals such as acids and bases, and helps avoid additional postprocessing steps, such as separation of residual salts. This makes it a cost effective and environmentally friendly process (Nitsos et al., 2016). 15  1.4.2.2 Fractionation with Acidic Solutions In fractionation using acidic solutions, acids such as sulphuric acid, hydrochloric acid, oxalic acid and nitric acid are used. Both concentrated and dilute acids can be used for fractionation, based on the desired outcome of fractionation. Dilute acids (< 5% w/v) result in significant hydrolysis of hemicellulose present in the lignocellulosic matrix, as well as mild hydrolysis of cellulose. Concentrated acids (> 30% w/v) result in efficient hydrolysis of both hemicellulose and cellulose fractions. Operating temperatures and pressures for dilute acid fractionation are generally higher than those for concentrated acid fractionation, with mostly atmospheric pressures employed for concentrated acid fractionation (Solange & Mussatto, 2016; Bensah & Mensah, 2013; Pandey et al., 2014). Table 1. 3. Examples of biorefineries converting lignocellulosic feedstocks to valuable products (S I Mussatto & Dragone, 2016)  16  1.4.2.3 Fractionation under Alkaline Conditions In fractionation under alkaline conditions, lignocellulosic biomass is treated with reagents such as NaOH, Ca(OH)2, KOH and NH3OH. It has been found to improve the efficiency of lignin removal. Though low temperature and pressure are usually used for this method, selection of operating parameters including concentration of the reagent and treatment time, is done based on factors such as type of lignocellulosic biomass used and the extent of fractionation desired. However, high treatment times, which extend from several hours to sometimes days, and necessity of a downstream process to separate the residual salts are drawbacks of this process (Kumar et al., 2009; Zaafouri & Romero, 2016).   1.4.2.4 Steam Explosion Steam explosion, which has chemical, mechanical and physical impacts on lignocellulosic biomass, is one of the most widely used methods for fractionation (Duque et al., 2016). In this method, lignocellulosic biomass is introduced into a reactor at moderate to high temperatures (180oC – 260oC), and at pressures ranging from 1-5 MPa. This is followed by a sudden depressurization step to ambient conditions, resulting in solubilization of hemicellulose sugars, softening of lignin, and partial depolymerization of cellulose (Jiang et al., 2016; Sassner et al., 2008).  1.4.2.5 Other Techniques There are several other fractionation methods such as ionic liquids fractionation, organosolv fractionation and oxidative delignification. Though all these methods result in fractionation of lignocellulosic biomass in one way or the other, some of the differences between them include product composition, total time of operation, environmental impact, economics, ease of operation, and requirement of secondary separation processes. 17  1.4.3 Hemicellulose Removal from Waste Streams Methods such as liquid hot water treatment (aqueous fractionation), fractionation using acidic solutions and steam explosion can assist in selectively separating hemicellulose from lignocellulosic biomass (Pérez et al., 2008; Solange I, Mussatto, 2016; Bensah & Mensah, 2013; Pandey, Negi, Binod, & Larroche, 2014; Jiang et al., 2016; Sassner, Mårtensson, Galbe, & Zacchi, 2008).  For this study, hog fuel and chip fines were subjected to liquid hot water treatment, and primary sludge was subjected to dilute acid hydrolysis to remove hemicellulose oligomers. These methods were selected to reduce the cost of operation, and enhance the ease of operation. In addition, absence of chemical agents makes liquid hot water treatment a greener method.  Liquid hot water treatment is catalysed by the formation of hydronium ions, which are initially generated by water ionization. These hydronium ions assist in the hydrolysis of ether bonds, and cleavage of acetyl groups in hemicellulose, resulting in its depolymerization. In later stages, hydronium ions generated from acetyl groups help catalyze the hydrolysis of hemicellulose. This mechanism is similar to that of a dilute acid hydrolysis (Moniz, Carvalheiro, & Duarte, 2016). Liu, (2010) presented a model for the hydrolysis of lignocellulosic biomass during liquid hot water treatment, by proposing a mechanism, which considers mass transfer along with the chemistry. As proposed by the authors, the steps involved in the mechanism are: 1. Migration of hydrogen ions and/or hydrogen bond-forming molecules from the liquor phase to the surface of the solid particle. 2. Chemisorption on the solid surface. 3. Hydrolysis reactions with hemicellulose and other accessible molecules. 4. Cleavage of hemicellulose oligomers from the solid surface. 5. Migration of hemicellulose oligomers to the bulk liquor. 18  Proposed reaction steps during the above proposed mechanism are as following: Formation of proton and/or hydronium ion: H2O (aq) ⇌ H+ (aq) + OH- (aq)                                                                                                          (1.1) H+ (aq) + H2O (aq) ⇌ H3O+ (aq)                                                                                                        (1.2) R—POAc (s) + H+ (aq) ⇌ R—POAc●H+ (s)                                                                                   (1.3) R—POAc●H+ (s) + H2O ⇌ R—POH●H+ (s) + HOAc (aq)                                                                (1.4) R—POAc●H+ (s) + H2O ⇌ R—OH●H+ (s) + HPOAc (aq)                                                                   (1.5) HOAc (aq) ⇌ H+ (aq) + OAc— (aq)                                                                                                     (1.6) R—POH●H+ (s) ⇌ R—POH (s) + H+ (aq)                                                                                             (1.7) R—OH●H+ (s) ⇌ R—OH (s) + H+ (aq)                                                                                                         (1.8) Solubilization of hemicellulose: R—XnOH (s) + H+ (aq) ⇌ R—XnOH●H+ (s)                                                                                             (1.9) R—XnOH●H+ (s) + H2O (aq) → R—XmOH●H+ (s) + HXsOH (aq)                                                          (1.10) Reduction of hemicellulose chain length in the liquor: HXnOH (aq) + H+ (aq) ⇌ HXnOH●H+ (aq)                                                                                           (1.11) HXnOH●H+ (aq) + H2O (aq) → HXmOH●H+ (aq) + HXsOH (aq)                                                            (1.12) Where m+s = n, R represents cellulose and/or lignin bonded to biomass, and P represents a segment/subunit of hemicellulose or lignin. Xn represents the middle group in a hemicellulose oligomer having n monomers. HOAc is acetic acid molecule, where Ac = CH3CO. 19  Eqs. (1.3) and (1.9) represent adsorption of hydrogen ions onto the surface of lignocellulosic biomass. Eqs (1.4), (1.5), and (1.10) represent the reaction on the surface of lignocellulosic biomass, where cleavage of one acetyl group, one acetylated group, or hemicellulose oligomer happens from the lignocellulosic biomass.  The ion participating in the hydrolysis reactions can be either H+ or H3O+. Other possible reactions: Dehydration of monomeric sugars to products such as furfural, humic acid and levulinic acid:  HXnOH●H+ (aq) → H+ + H2O + furfural and other dehydration products.                                           (1.13) Condensation of polysaccharides: R—XnOH●H+ (s) + HXsOH (aq) → R—Xn+sOH●H+ (s) + H2O (aq)                                                (1.14) Or R—XnOH (s) + HXsOH●H+ (aq) → R—Xn+sOH●H+ (s) + H2O (aq)                                                   (1.15) Dehydration polymerization of hemicellulose oligomers. HXnOH●H+ (aq) + HXmOH (aq) → HXn+mOH●H+ (aq) + H2O (aq)                                                  (1.16) Operating conditions are the key to regulating the extent of hydrolysis during liquid hot water treatment, as variations in operating conditions result in varying degree of hydrolysis. Inappropriate operating conditions may lead to undesirable results such as hydrolysis of hemicellulose oligomers into monomers and degradation products such as hydroxymethylfurfural (HMF), and condensation of polysaccharides. Some of the operating conditions which influence the extent of hydrolysis are treatment temperature, treatment time, particle size, and pH of the hydrolysate (Haghighi Mood et al., 2013).  20  Decrease in the particle size generally results in increased hydrolysis and hemicellulose removal, due to increased surface area of exposure. Influence of particle size becomes even more significant in situations where the liquid-to-solid ratio is low. In this case, majority of the hydrolysis may occur on the external surface of the particle, with minimum effect to the interior (Moniz et al., 2016).   The combined effect of temperature and time can be represented by the severity factor, log (Ro), defined as:  log (Ro) = log (t × e[(T - 100)/14.75]),                                                                                  (1.17) where t is the treatment time in minutes, and T is the temperature of the treatment in oC (Hendriks & Zeeman, 2009; Nitsos et al., 2016; Overend & Chornet, 1987).  Since pH of the hydrolysate indicates the acidity of the hydrolysate, and thus the availability of H+ ions, lower pH, which indicates higher H+ ion concentration, results in higher hydrolysis of lignocellulosic biomass.    1.5  Adsorption of Hemicellulose Oligomers onto Pulp 1.5.1 Effect on Pulp Properties  Strengthening of paper products is generally done either by mechanical processes, which increase the hydrogen bond formation between fibres, or by adding paper strength additives (Hartmans et al., 2004). Polysaccharides such as guar gum and starch are currently used as wet-end papermaking additives (Ren et al., 2009). However, the availability and abundance of hemicellulose prompts the study of its use as a wet-end additive, as the addition of hemicellulose oligomers and their derivatives has been found to enhance the physical strength properties of hand sheets (Gruenhut 1953; Dugal and Swanson 1972; Ren et al., 2009). Other advantages such as 21  reduction in hornification and beating energy also motivate the study of hemicellulose as a wet-end additive (Ban et al., 2011; Laffend and Swenson 1968).  Ren et al. (2009) studied the effect of addition of different degrees of substitution (DS) cationic hemicelluloses and carboxymethyl hemicelluloses, on bleached spruce kraft pulp. They synthesized these derivatives, and measured the effect of their addition to pulp. When cationic hemicelluloses were applied independently, tear index, burst index and breaking length of the hand sheets improved. While burst index and breaking length increased with increase in DS, tear index showed a decrease. On the other hand, when carboxymethyl hemicelluloses were applied, tear index, burst index and breaking length of the handsheets increased compared to the control group, but no effect of DS on physical properties was identified. When a mixture of cationic hemicelluloses with DS 0.37, and carboxymethyl hemicelluloses with DS 0.35 was applied at 1% w/w (based on dry pulp weight) and 1% w/w respectively, breaking length, tear index and burst index increased by 21.1%, 54.6% and 19.1% respectively.          Figure 1. 6. SEM image of handsheet  before addition of hemicelluloses  (Ren et al., 2009)  Figure 1. 7. SEM image of handsheet  after addition of hemicelluloses (Ren et al., 2009) 22  The scanning electron microscope (SEM) images of the hand sheet (Figure 1.6 and Figure 1.7) before and after the addition of hemicelluloses, shows the fibre intertexture. The majority of the spaces present between fibres in the handsheet without hemicelluloses (Figure 1.6), appear to be occupied by hemicellulose polysaccharides. Jun-Li Ren et al (2009) suggested that this resulted in chemical and physical interactions between the hemicellulose polysaccharides and the fibres in the pulp, thus enhancing the physical properties of hand sheets. Ban et al. (2011) studied the effect of adsorption of xylan extracts obtained from hardwood, on both hardwood and softwood kraft pulps. They observed improvements in beatability and physical strength properties after the adsorption of xylan extracts. Hemicellulose adsorbed pulp showed rapid development of freeness, which indicates reduced beating time, energy and thus increased beating efficiency. Both hardwood and softwood pulps exhibited improvements in physical strength properties, with softwood pulp showing an increase of 10-20% in tensile strength and 10% in tear strength when compared to conventional softwood kraft pulp. They attributed the improvements in physical strength properties of pulp to the increased free hydroxyl groups on the fibre surface due to the adsorbed hemicellulose polysaccharides, which would increase hydrogen bond formation between fibres. Silva et al. (2011) studied the effect of addition of three different birchwood-based xylans: 4-O-methylglucuronic acid xylan (MeGlcA-xylan), hexenuronic acid xylan (HexA-xylan) and low uronic acid content xylan (LowUrA-xylan) to bleached eucalyptus kraft pulp. Water retention values (WRV) increased for both never-dried and once-dried bleached kraft pulp, reduced hornification and reduced beating energy. As much as 40% reduction in beating energy was observed for pulp treated with LowUrA-xylan. Silva et al. (2011) cited the hydrophilic nature of hemicelluloses, which favours inter-fibre bonding and promotes better swelling of cell walls in 23  water, for these improvements, and that diminished aggregation of fibrils resulted in reduced hornification. However, no significant changes in physical strength properties were observed, except for a small increase in tensile index and sheet density. It was concluded that the already significant presence of xylans (14.2%) in the pulp resulted in a minimal change to physical strength properties upon addition of new xylans.  Conversely, the effect of hemicellulose removal on pulp and paper strength properties has also been studied. Liu et al. (2013) studied the loss of hemicellulose from bleached eucalyptus kraft pulp on the properties of paper and its printability. Sodium hydroxide solution was used to selectively remove parts of hemicellulose from pulp. Hemicellulose loss resulted in an increase in the bulk, surface roughness and air permeability of paper, and improved the opacity and brightness.  A decrease in strength indices was observed, as expected Hodge et al. (2010) studied the impact of hemicellulose preextraction on the properties of birch kraft pulp. Silver birch wood chips were subjected to hemicellulose extraction, using water and kraft white liquor (NaOH, Na2S and Na2CO3). Treated wood chips were subjected to kraft pulping, and subsequently the pulp was used to make handsheets. Water extraction resulted in higher removal of hemicellulose compared to white liquor, and resulted in a decrease in strength properties such as burst strength, tensile strength, compression strength and tensile stiffness, when compared to the handsheets prepared from pulp not subjected to preextraction.  Depending on the type of hemicelluloses, factors such as time of adsorption and temperature, and the type of pulp being used as adsorbent, the extent of improvement of physical strength properties of pulp, and other factors such as reduction in hornification and beating energy has varied. Regardless, adsorption of hemicelluloses onto pulp has also shown to have a positive effect on pulp yield, softening of paper (Olsson & Salmén, 2003), and dust reduction (US 20040206464). 24  1.5.2 Influence of Operating Parameters  The extent of adsorption of hemicelluloses onto pulp is influenced by factors such as time, temperature, fibre consistency, hemicellulose oligomer to pulp ratio, type of hemicellulose applied and type of pulp used as adsorbent. It is important to understand the effect of each factor on the adsorption process to be able to achieve desired rate and extent of adsorption.   Ban & Van Heiningen (2011) studied the effect of adsorption process factors: fibre consistency (%), adsorption time and temperature, and extracts to fibre ratio (g extracts/g fibre), on hemicellulose adsorption to cellulose fibres. Hemicelluloses were obtained from US southern mixed hardwood. Adsorption yield was used as a metric to measure the extent of adsorption, where adsorption yield was defined as “the cellulosic pulp weight gain through adsorption, calculated by the weight difference between adsorbed and original pulp” (Ban & van Heiningen, 2011). The authors observed that adsorption time and temperature had a linear effect on the adsorption yield. Therefore, with increasing time and temperature, adsorption yield was found to increase all the time. However, the effect of time was not significant. Fibre consistency and extracts to fibre ratio had a non-linear effect. After reaching a maximum level, adsorption yield began to drop with an increase in fibre consistency. The rate of increase of adsorption yield decreased with increasing extracts-to-fibre ratio (Figure 1.8). 25                     Figure 1. 8. Influence of process factors on adsorption yield (Ban & van Heiningen, 2011) Since softwoods primarily have D-mannose derived hemicelluloses, the effect of operating parameters may be different for the adsorption of mannans onto NBSK pulp. Hydrogen bonding between hemicelluloses, and the hydroxyl groups of cellulose is expected to be the reason for adsorption of mannans onto fibre surfaces (Clayton and Phelps, 1965).   Hannuksela et al (2002) studied the adsorption of galactoglucomannans (GGM) obtained from thermomechanical pulp and galactomannans (GM) obtained from guar gum onto bleached kraft pulp (BKP). Effect of acetyl groups present on galactoglucomannans, temperature, pH, molar mass and the degree of beating of pulp on adsorption were studied. Differences in the adsorption of galactoglucomannans and galactomannans were observed. Deacetylation of GGM’s and the addition of salt increased the adsorption of GGM’s onto BKP, while temperature had little effect. Adsorption of GM’s onto BKP was not affected by temperature, salt addition, pH and the degree to which the pulp was beaten. However, unbeaten pulp showed lower adsorption. Reduced side                 Variables change range Adsorption yield (%) 26  groups on the GM’s increased the adsorption onto BKP, and GM’s with a low molar mass adsorbed at a higher rate onto unbeaten pulp, compared to high molar mass GM’s. Ribe et al. (2010) investigated the influence of operating parameters on the rate and extent of adsorption of birch black liquor xylan onto unbleached softwood kraft pulp. With sufficient xylan availability in the liquor, and appropriate process conditions, the yield of unbleached pulp increased up to 40%. Increase in temperature, decrease in pH and increase in ionic strength improved the total adsorption as well as initial adsorption rate. Increased loading of xylan oligomers from 5g/liter to 10 g/liter, increased adsorption by 20-30%. There is a possibility of operating parameters such as temperature and time of adsorption, hemicellulose oligomer-to-pulp percentage and fibre consistency, exhibiting a unique influence on the adsorption of hemicellulose oligomers onto Northern Bleached Softwood Kraft (NBSK) pulp. In addition, though there have been significant investigations on the impact of hemicellulose addition to different types of pulps, there are few studies which tried to understand the impact of operating parameters on the adsorption of softwood hemicellulose to softwood kraft pulp. This necessitates an experimental study to establish the effect of these parameters. 1.6 Present Investigation The present investigation can be briefly classified into two parts:  1. Hemicellulose removal from hog fuel and primary sludge (chapters 3 & 4) 2. Adsorption of hemicellulose obtained from chip fines onto NBSK pulp (chapter 5) The first part of the investigation is focused on identifying the operating parameters for hemicellulose removal, which result in maximum yield of hemicellulose oligomers, with minimum degradation of oligomers to monomers. The objective is to maximize hemicellulose oligomer 27  yield, and minimize monomer yield, as oligomers result in better improvements in physical strength properties of pulp when compared to monomers.  The hemicellulose removal technique used for hog fuel was liquid hot water treatment, while that used for primary sludge was dilute acid hydrolysis, using H2SO4. The second part of the investigation focuses on the individual and interactive effects of operating parameters: adsorption temperature, fibre consistency and oligomer-to-pulp percentage on the adsorption yield. Adsorption yield is defined by equation 2.3 (section 2.2). The objective is to maximize the adsorption yield. Hemicellulose oligomers used for the adsorption were obtained by subjecting chip fines to liquid hot water treatment. 1.6.1 Significance This study will help understand the potential of saw and pulp mill waste streams, hog fuel, primary sludge and chip fines produced in British Columbia, as feedstocks for biorefinery. The overall significance of this work was to contribute knowledge about the suitable operating parameters to maximize hemicellulose oligomer yield from waste streams, and to maximize hemicellulose adsorption yield onto NBSK pulp. The results from this study can then be used for investing the impact of hemicellulose oligomers obtained from hog fuel, primary sludge and chip fines on the physical strength properties and hornification of NBSK pulp. Improvement in strength properties of pulp, and reduction in hornification, can potentially reduce the energy requirement for beating, which may benefit the overall economics of NBSK pulp manufacturing. 1.6.2 Research Objectives The following research objectives have been defined for this investigation of hemicellulose removal and adsorption onto NBSK pulp. 28  1. Determine the impact of treatment temperature, residence time, and pH of the hydrolysate on the hemicellulose yield and oligomer content during liquid hot water fractionation of hog fuel. Identify the operating parameters which maximize hemicellulose yield, while minimizing oligomer conversion to monomers. 2. Determine the impact of treatment temperature, residence time, and pH of the hydrolysate on the hemicellulose yield and oligomer content during dilute acid hydrolysis of primary sludge. Identify the operating parameters which maximize hemicellulose yield, while minimizing oligomer conversion to monomers. 3. Determine the individual and interactive effects of adsorption temperature, hemicellulose oligomer-to-pulp percentage and fibre consistency on the adsorption yield of hemicellulose obtained from chip fines, onto NBSK pulp.          29  Chapter 2: Experimental Procedure 2.1 Production of Hemicellulose Oligomers from Hog Fuel and Primary Sludge 2.1.1 Compositional Analysis of Raw Biomass 2.1.1.1 Procurement and Preparation  Hog fuel and primary sludge were generously provided by Canfor Pulp Limited. These materials were provided in a wet condition, with hog fuel having a moisture content of 33.12% and primary sludge having a moisture content of 73.44%. They were sealed in polythene bags, and stored in a cold storage room at 4oC, until use. When required, these materials were prepared for compositional analysis using the procedure described by Sluiter et al (2008a).  Primary sludge was present in the form of large chunks, while hog fuel was present mostly in the form of chips with varying sizes (Figures 2.1 and 2.2). To prepare samples for compositional analysis, both materials were shredded by hand into pieces smaller than 5 by 5 by 0.6 cm (Sluiter et al., 2008a). The pieces were then evenly spread in a single layer on an aluminum plate, and dried in a constant temperature and humidity (CTH) room, at a temperature of 23 ± 1oC and a relative humidity (RH) of 50% ± 2%, until the moisture content was less than 10%. Moisture content was determined by drying 2 samples of biomass in a convection oven (VWR) at 105o C (Figure 2.3), using the procedure described by  Sluiter et al., (2008b). After the moisture content was below 10%, the material was milled using a Wiley mill, until it passed through a 1 mm mesh screen. Overly large pieces were discarded. This dried, milled raw biomass was collected in sealed polythene bags and stored at 4o C until use.   30             2.1.1.2 Determination of Extractives  Water and ethanol soluble extractives in the milled hog fuel and primary sludge were quantified using a Dionex ASE 350 Accelerated Solvent Extractor (Figure 2.4), according to the procedure described by Sluiter et al (2008e). Moisture content determination of the samples was done at the same time, using the procedure described by Sluiter et al. (2008b). HPLC grade water, and 190 proof ethanol were used for the extraction. The samples were placed in 22 ml extraction cells with 27 mm cellulose filters, and 60 ml collection tubes were used to collect the extracts. No inert fillers were used inside the extraction cell, as the sample size was chosen in order to avoid any significant dead volume after filling the samples. This was primarily due to the necessity to Figure 2. 2 Primary sludge Figure 2. 1 Hog fuel Figure 2. 3. Convection oven (VWR) 31  further analyze the solid sample after removal of extractives. The extractive free biomass i.e., the solid residue obtained after the removal of extractives, was air dried in aluminum plates of known weight to a moisture content below 10%. The percentage of extractives present in the biomass was calculated using the change in dry mass of biomass after extraction.   Figure 2. 4. Dionex ASE 350 Accelerated Solvent Extractor 2.1.1.3 Determination of Structural Carbohydrates, Lignin and Ash  Structural carbohydrates bound in the matrix, lignin, and ash in the extractive-free biomass were quantified by the two stage acid hydrolysis procedure described by Sluiter et al (2011). A 0.3 g sample of air-dried, extractive-free biomass was subjected to the procedure, while another portion of the air-dried sample was used to determine the moisture content, and thus the oven dry weight of the sample subjected to two stage hydrolysis. Autoclaving of the samples was done at 121o C for one hour with a Midmark M11UltraClave (Figure 2.5) automatic sterilizer, under liquids setting. After autoclaving, porcelain crucibles were used to separate the liquid hydrolysate Solvent reservoir Operating Console Collection tubes Extraction cells 32  from the solid residue. The hydrolysate was used to quantify the amount of acid soluble lignin, and structural carbohydrates. The acid insoluble solid residue, was used to quantify the acid insoluble lignin, and acid insoluble ash.   Figure 2. 5. Midmark M11UltraClave  Dionex ICS 5000 High Performance Liquid Chromatography (HPLC), with a Dionex CarboPac SA10 column was used to quantify arabinose, xylose, glucose, galactose and mannose (Figure 2.6). HPLC samples were prepared by passing 1 ml of hydrolysate through 0.22 μm filters (Chromatographic Specialties Inc). Samples were diluted as necessary, to bring the expected concentrations of sugars into the range of sugar concentration in calibration standards. Fucose was added as an internal standard. Acid soluble lignin was determined by using a Shimadzu UV Spectrophotometer (Figure 2.7) with a background of deionized water. Samples were diluted as necessary to bring the absorbance into the range of 0.7-1.0 (Sluiter et al., 2011). This was measured at a wavelength of 240 nm, and an absorptivity of 12 L/g cm, corresponding to Pinus radiata, a softwood, was used for conversion of absorbance to acid soluble lignin concentration.  33  Total ash content was determined according to the procedure described by Sluiter et al.,(2008c). This was particularly important in the case of primary sludge, which contained a significant amount of acid soluble ash. A Thermolyne muffle furnace (Figure 2.8) without a ramping program was used for the determination of acid insoluble ash, whereas a muffle furnace with a ramping program was used to determine total ash. Acid insoluble lignin content was determined by subtracting the mass of acid insoluble ash content from the oven dry mass of acid insoluble residue.                Control panel   Sample  holder  Figure 2. 6. Dionex ICS 5000 High Performance Liquid Chromatography Figure 2. 7. Shimadzu UV Spectrophotometer  (source: www.coleparmer.ca)  Figure 2. 8. Thermolyne muffle furnace  34  2.1.2 Separation of Hemicellulose Oligomers  Hemicellulose oligomers were produced from biomass by subjecting the biomass to hydrolysis. Milled raw biomass prepared by the method described in section 2.1.1 was used for the hydrolysis. In the case of hog fuel, liquid hot water treatment was used as the final hydrolysate pH was acidic, ranging from 3.26 to 4.6. Due to the high ash content of primary sludge, especially calcite (CaCO3), as discussed in section 4.2, the pH of the hydrolysate obtained from liquid hot water treatment of primary sludge was ~ 10. This resulted in limited hydrolysis of primary sludge, and low production of hemicellulose oligomers. As a result, dilute acid hydrolysis was employed for the removal of hemicellulose oligomers from primary sludge, using H2SO4.  A pH test was conducted to determine the quantity of H2SO4 to be used for the hydrolysis of primary sludge. Primary sludge slurry samples, representative of the actual slurry used for the hydrolysis, were prepared by addition of different quantities of H2SO4. The objective was to lower the starting pH below 7. This was achieved when the mass of 98% w/w H2SO4 added to the biomass slurry was equal to 1.25% of the total slurry mass. The initial slurry pH reached 5.71 to 6.06 after 24 hours. This resulted in the final pH of the hydrolysate ranging from 2.44 to 6.67 and in measurable production of hemicellulose oligomers from primary sludge. 2.1.2.1 Procedure Hydrolysis was conducted in a 1 L batch reactor (Parr 4520), as shown in Figure. 2.9. The reactor setup enables control of reaction temperature and residence time. Prior to starting hydrolysis, the moisture content in biomass was determined by drying biomass samples at 105o C to constant weight in an oven. Hydrolysis experiments were conducted at 5% biomass consistency and the total mass of the reactant mixture was 500 g. Sufficient deionized water and H2SO4 were added to the reactor. Sludge hydrolysis was conducted using 6.25 g of 98% w/w H2SO4; this 35  represents 1.25% of the total mass of the biomass slurry. Acid addition was accomplished by measuring 6.25 grams of 98% w/w H2SO4 in a tared flask, using an analytical balance. Complete acid transfer was ensured by rinsing the flask multiple times using deionized water.                               Figure 2. 9. Parr 4520 bench top batch reactor with temperature control, used for the biomass hydrolysis. The slurry was heated to the target temperature by means of the heating coil (Figure 2.9). During cooling, the heating coil was turned off and removed from the reactor, and the slurry was cooled by means of natural cooling until it reached 100oC. After this, the slurry was quenched using ice. During the reaction, the slurry was continuously stirred at 180 RPM.  The effect of reaction temperature and residence time on hydrolysate pH, percentage solids removed by hydrolysis, percentage oligomers, and total mass of oligomers was evaluated. Residence time represents isothermal heating time, i.e., the time for which the slurry was maintained at the target temperature by means of external heating. Table 2.1 summarizes the tested temperature and Control panel for temperature and stirrer Stirrer Heating coil Cooling water reservoir Reactor  Thermocouple Pressure gauge  36  residence time combinations. The range within which temperature was varied was 120oC to 180oC, while the range of residence time was 0 minutes to 60 minutes. As seen in Table 2.1, 16 conditions were tested. Duplicates were obtained in the case of hog fuel, and single runs were conducted in the case of primary sludge. Table 2. 1. Temperature and residence time used for hydrolysis experiments.  After the completion of hydrolysis, the biomass slurry was separated by vacuum filtration with a Whatman ashless filter paper (grade 41). The liquor or hydrolysate was collected in sealable polyethylene flasks (Fisherbrand), and was stored at 4oC. The solid residue was collected on an aluminum plate of known weight, and air dried. Compositional analysis of the solid residue was conducted according to the procedure described in section 2.1.1.3.  The percentage solids removed by hydrolysis was calculated as: Percentage solids removed = W1−W2W1× 100                   (2.1) Where W1 is the oven dry weight of biomass before hydrolysis, and W2 is the oven dry weight of solid residue after hydrolysis. The quantity of carbohydrates present in monomer form in the raw liquor was analyzed using the same Dionex ICS 5000 HPLC system described in section 2.1.1.3.  Post-hydrolysis of the liquor was conducted using a 5 mL sample according to the procedure described by Sluiter et al (2008d); this process converts any oligomers present into their monomeric form. The amount of 0   minutes20 minutes40 minutes60 minutes120oC0   minutes20 minutes40 minutes60 minutes140oC0   minutes20 minutes40 minutes60 minutes160oC0   minutes20 minutes40 minutes60 minutes180oC37  72% w/w H2SO4 added to the liquor before subjecting it to post-hydrolysis was determined from the pH of the raw liquor.  The presence of sugar monomers after post-hydrolysis was quantified with the Dionex ICS 5000 HPLC system (section 2.1.1.3).  The difference in the quantity of monomeric sugars in the raw liquor and the liquor after post-hydrolysis was used to calculate the percentage of sugars present in oligomeric form. This is an important parameter which influences the final impact of hemicellulose adsorption on the pulp physical strength properties, and was calculated as: Percentage oligomers = M1−M2M1× 100                                   (2.2) Where M1 is the sugar monomer percentage in the hydrolysate after post-hydrolysis, and M2 is the sugar monomer percentage in the raw hydrolysate. 2.2 Adsorption of Hemicellulose Oligomers onto NBSK Pulp 2.2.1 Compositional Analysis of NBSK Pulp NBSK pulp was generously provided by Canfor Pulp Limited, and was stored at 4oC in a tightly sealed container. Moisture content of NBSK pulp in the container was determined by taking 3 samples from three different locations in the container, and then applying the procedure described by Sluiter et al., (2008b).  Based on the moisture content of NBSK pulp, 5 g (oven-dried basis) pulp sample was collected from the container to perform compositional analysis. The sample was air dried to a constant moisture content below 10%, and was then milled using a benchtop Wiley mill, to pass through a 20 mesh screen. This milled sample was subjected to the two stage acid hydrolysis procedure described by Sluiter et al (2011) to determine composition. Details regarding the two-38  stage acid hydrolysis can be found in section 2.1.1.3. Dionex ICS 5000 HPLC system was used for the quantification of sugars. 2.2.2 High-Low Experiments An initial high-low test was conducted to determine the significance of influence of 5 operating variables on the adsorption of hemicellulose sugars onto NBSK pulp. The operating variables were: adsorption temperature, adsorption time, hemicellulose oligomers-to-pulp percentage, fibre consistency, and weight average molar mass (Mw) of the hemicellulose oligomers present in the hydrolysate. The high and low values tested for each of these operating variables can be found in Table 2.2. The response variable which was used to evaluate the influence of these operating variables is the adsorption yield, defined by the following equation: Adsorption yield = S1 – S2                                                       (2.3) Where, S1 = Total mass of sugar in raw hydrolysate (mg)              S2 = Total mass of sugar in adsorption liquid (mg) The objective was to assess the change in adsorption yield of hemicellulose sugars onto NBSK pulp, between the high and low values of each operating variable, and classify the operating variables into high impact and low impact categories. The high and low values of Mw correspond to the Mw values of hemicellulose oligomers obtained from the liquid hot water treatment of chip fines at two different operating conditions, as indicated in Table 2.3.  The raw hydrolysate/liquor from the liquid hot water treatment of chip fines was collected in sealable polyethylene flasks (Fisherbrand), and was stored at 4oC. The quantity of carbohydrates present in monomer and oligomer form in the raw liquor was analyzed using the Dionex ICS 5000 HPLC system (section 2.1.1.3). The difference in the quantity of monomeric sugars between the 39  raw liquor and hydrolyzed liquor was used to calculate the quantity of sugars present in oligomeric form. mg of oligomers per ml of hydrolysate = (Q1 – Q2)                            (2.4) Where, Q1 is the mg of monomers per ml of hydrolysate subjected to post hydrolysis, and Q2 is the mg of monomers per ml of raw hydrolysate. Table 2. 2. Minimum and maximum values for the five operating variables studied in high-low test. Factor Low High Adsorption time 5 minutes 60 minutes Adsorption temperature 25 C 50 C Fibre consistency 1% 4% Hemicellulose oligomer-to-pulp percentage 1% 3% Weight average molecular weight (Mw) 1.43 kg/mol 8.98 kg/mol  Table 2. 3. Operating conditions used to obtain hemicellulose oligomers with Mw values indicated in Table 2.2 Operating condition Mw Value 140oC and 27 minutes 1.43 kg/mol 170oC and 0 minutes 8.98 kg/mol  Experiments were conducted by classifying them into 6 different cases, each with a unique set of operating variables. These sets of operating variables were obtained by varying one single variable for each set, as indicated in Table 2.4.  40  Raw hydrolysate, NBSK pulp and deionized water were separately brought to the desired temperature. Based on the oligomer content in the raw hydrolysate obtained from the liquid hot water treatment of chip fines, desired quantity of raw hydrolysate was added to 2.5 grams (oven-dried basis) NBSK pulp. Sufficient water was added to the mixture of pulp and raw hydrolysate to obtain a final mixture with desired fibre consistency and hemicellulose oligomer-to-pulp percentage. This mixture was shaken in an incubator shaker (Figure 2.10) at 140 rpm, for required amount of time. After the completion of adsorption, the liquid phase and solid phase were separated by vacuum filtration with a Whatman ashless filter paper of grade 41. 50 ml of the liquid was collected in a plastic centrifuge tube (Fisherbrand), and stored at 4oC. The solid was collected in an aluminum plate of known mass, and air dried to a constant moisture level. Compositional analysis of the liquid samples was done similar to that of the raw hydrolysate obtained from the liquid hot water treatment of chip fines (Sluiter et al., 2008d).         Figure 2. 10. Incubator  41  Table 2. 4. Operating conditions for each case in high-low test  Time (minutes) Temperature (oC) Fibre consistency (%) Oligomer-to-pulp (%) Mw (kg/mol) Case 1 5  25 4 3 8.98 Case 2 60 25 4 3 8.98 Case 3 5 50 4 3 8.98 Case 4 5 25 1 3 8.98 Case 5 5 25 4 1 8.98 Case 6 5 25 4 3 1.43  2.2.3 Full-Scale Experiments Based on the adsorption yield results obtained from high-low experiments, the 5 operating variables were classified into two groups (discussed further in Chapter 5):  1. High impact 2. Low impact  Table 2. 5. Classification of operating variables based on adsorption yield High impact Low impact 1. Adsorption temperature 2. Fibre consistency 3. Hemicellulose oligomer-to-pulp percentage 4. Mw 1. Adsorption time  The high impact operating variables resulted in a difference in the adsorption yield, on changing the value of the variable. On the other hand, the low impact operating variable, adsorption time, did not show any significant impact on the adsorption yield, with its variation. Due to the 42  low impact of adsorption time, it was excluded from the full-scale study. Due to the challenges in precisely obtaining hemicellulose oligomers with a desired Mw value, effect of Mw on the adsorption yield was excluded from the full-scale study. Better adsorption yield was obtained for the Mw value of 8.98 kg/mol, which corresponds to the hydrolysate/liquor obtained at 170oC and 0 minutes. Therefore, hydrolysate/liquor obtained at 170oC and 0 minutes, from liquid hot water treatment of chip fines was used for the full-scale experiments.  2.2.3.1 Experiment Design Design of experiments was performed using JMP 13 (SAS Institute INC., 2016). A central composite design (CCD) with two center points was applied for the current investigation. Three factors were selected as adsorption variables: adsorption temperature, fibre consistency and hemicellulose oligomer-to-pulp percentage. The high and low values for these variables are same as those for the high-low tests (Table 2.2). Adsorption yield was selected as the response variable. The experimental conditions generated using JMP 13 are tabulated in Table 2.6. The design consisted a total of 16 experimental conditions, each of which was replicated.         43  Table 2. 6. Experimental conditions obtained using a central composite design with JMP 13  Adsorption temperature (oC) Fibre consistency (%) Hemicellulose Oligomer-to-pulp Percentage (%) 1 37.50 2.50 1.00 2 37.50 4.00 2.00 3 25.00 2.50 2.00 4 45.00 1.61 2.60 5 45.00 3.40 2.60 6 37.50 2.50 3.00 7 30.00 1.61 1.40 8 37.50 2.50 2.00 9 50.00 2.50 2.00 10 45.00 3.40 1.40 11 30.00 1.61 2.60 12 37.50 1.00 2.00 13 30.00 3.40 1.40 14 37.50 2.50 2.00 15 30.00 3.40 2.60 16 45.00 1.61 1.40  2.2.3.2 Methodology 2.2.3.2.1 Recovery of Hemicellulose Oligomers from Chip Fines Chip fines were milled using a Wiley mill, until the milled biomass passed through a 1 mm mesh screen. Overly large pieces were discarded. Milled material was collected in sealable polythene bags and stored at 4o C until use. Compositional analysis of the milled chip fines was done to quantify extractives, structural carbohydrates, lignin and ash. The method used for the determination of extractives, and the method used for the determination of structural carbohydrates, lignin and ash are the same as the methods described in section 2.1.1.2 and 2.1.1.3 respectively. Liquid hot water treatment was used to obtain hemicellulose oligomers from chip fines, similar to hog fuel, as described in section 2.1.2. The treatment was carried out at 170oC and 0 minutes. A 1 L batch reactor (Parr 4520) was used for carrying out the liquid hot water treatment. 44  Since each run could only generate 475 ml of hydrolysate, a total of 9 runs were conducted to obtain sufficient quantity of hemicellulose oligomers for the full-scale adsorption experiments. The hydrolysates from all the 9 runs were mixed to generate a single, large volume of hydrolysate. This ensured that the hydrolysate samples taken for adsorption experiments were identical to each other. 2.2.3.2.2 Adsorption Adsorption experiments were conducted according to the procedure described for the high-low experiments. Samples of raw hydrolysate, NBSK pulp and deionized water were separately brought to the desired temperature. Once the temperature was reached, appropriate quantity of hydrolysate, based on the desired hemicellulose oligomer-to-pulp percentage, was added to 5 g (oven-dried basis) NBSK pulp. Deionized waster was then added to bring the mixture to the desired fibre consistency. This mixture was placed in an incubator shaker (Figure 2.10), and shaken at140 rpm for 60 minutes, at the desired temperature.  The resulting mixture consisted of a liquid phase containing hemicellulose oligomers, and a solid phase containing NBSK pulp with adsorbed hemicellulose oligomers. This mixture was separated by vacuum filtration with a Whatman ashless filter paper of grade 41. The quantity of carbohydrates present in monomer form in the liquid phase was analyzed using the Dionex ICS 5000 HPLC system (section 2.1.1.3). 5 ml of liquid was subjected to acid hydrolysis as described by Sluiter et al., (2008d) to convert the sugars present in oligomeric form to their monomeric form. The amount of 72% w/w H2SO4 added to the raw liquor before subjecting it to hydrolysis was determined by the pH of the raw liquor, to bring the final acid concentration to 4% w/w. These samples were then analyzed using the Dionex ICS 5000 HPLC system (section 2.1.1.3) to quantify 45  the monomeric sugars present. Compositional analysis of the solid residue, containing NBSK pulp and adsorbed hemicellulose oligomers was done using the procedure described in section 2.2.1.                   46  Chapter 3: Liquid Hot Water Treatment of Hog Fuel   3.1 Introduction Hog fuel produced in saw mills is a form of lignocellulosic biomass, and thus contains all the components of lignocellulosic biomass: cellulose, lignin, hemicellulose, extractives and ash. Presence of extractive-rich bark in hog fuel results in high amounts of extractives. Researchers such as Burkhardt et al. (2013) have studied the composition of hog fuel, and found that it contains 45-55% of structural carbohydrates, a portion of which is hemicellulose.  Hog fuel produced in the saw mills of British Columbia (B.C) is primarily derived from softwoods obtained from the forests in B.C. Therefore, it contains softwood hemicelluloses which primarily are D-mannose derived hemicelluloses, such as galactoglucomannans (GGM). Currently, hog fuel is burnt to produce heat and generate electricity in the mill. It may be possible to utilize this hog fuel to produce hemicellulose oligomers. These hemicellulose oligomers can be used to improve the physical strength properties of NBSK pulp, reduce hornification, and reduce the energy required for beating. In this study, the effect of operating parameters: temperature and residence time, on the pH of hydrolysate, percentage solids removed, percentage oligomers present, and total mass of oligomers removed after liquid hot water treatment of hog fuel was investigated. The results of this study are presented in this chapter.  3.2 Composition of Hog Fuel Composition of hog fuel varies from one mill to the other, due to varying proportions of components such as bark, sawdust and shavings, which constitute hog fuel. This can also be noticed in the results obtained by Burkhardt et al. (2013), for the compositional analysis of two 47  different types of hog fuel, where one was more bark intensive than the other. In this study, compositional analysis of hog fuel was performed to quantify water and ethanol soluble extractives, structural carbohydrates, acid soluble and insoluble lignin, and ash. Methods described in section 2.1.1 were used for this purpose.  Figure 3.1 shows the results for compositional analysis of hog fuel. Errors bars indicate the standard deviation for 28 samples.   Figure 3. 1. Compositional analysis results for hog fuel. As seen in Figure 3.1, structural carbohydrates constitute 58.98% of oven-dried hog fuel. Glucan is the dominant polysaccharide, constituting 38.90%. This is expected, as the glucan content represents glucan obtained from hemicellulose, as well as cellulose present in the lignocellulosic matrix of hog fuel. If we assume all the hemicellulose to be present in form of galactoglucomannan (GGM), which contains 1 glucose monomer for 3 mannose monomers, we can estimate the glucan content contributed by hemicellulose, which would be 3.24%. Lignin is 1.84 2.7338.95.799.725.2427.1417.860102030405060708090100Arabinan Galactan Glucan Xylan Mannan ASL AIL Ash ExtractivesPercentage of oven dry hog fuel (%)Component48  the dominant component after structural carbohydrates, constituting 32.38%, of which 5.24% is acid soluble lignin (ASL), while 27.14% is acid insoluble lignin (AIL). AIL was obtained as a portion of acid insoluble residue after the two-stage acid hydrolysis of hog fuel. Hog fuel has shown significant presence of extractives, 7.86%, likely due to the presence of bark (section 1.3.1). Total ash content, which is only about 1%, is the smallest constituent of hog fuel. This implies that the effect of ash on the pH of hydrolysate will be insignificant, since ash is usually constituted by inorganic compounds such as CaCO3, which increase the pH of hydrolysate, restricting the hydrolysis of biomass. 3.3 Separation of Hemicellulose Oligomers  The amorphous and hydrophilic nature of hemicellulose means that it can be easily removed from the cell walls of lignocellulosic biomass, when compared to cellulose, which is crystalline in nature. Hydrolysis facilitates the fractionation of lignocellulosic biomass into its individual components by providing H+ ions, which result in disrupting the molecular interactions between hemicelluloses and other components in the lignocellulosic matrix, and within hemicellulose polysaccharides. In the case of hog fuel, liquid hot water treatment (also known as autohydrolysis, or hydrothermal treatment) was used for the separation of hemicellulose oligomers. The objective of the liquid hot water treatment of hog fuel was to study the effect of temperature and residence time on the removal of hemicellulose oligomers, and to identify operating parameters which maximize the oligomer content, and minimize the degradation of oligomers to monomers. As mentioned in section 2.1.2.1, residence time represents isothermal heating time, i.e., the time for which the slurry was maintained at the target temperature by means of external heating. The range of reaction temperature tested for the study is 120o C to 180o C, and the range of residence times tested is 0 49  minutes to 60 minutes, and the combinations of these parameters used for the study can be found in Table 2.1. Duplicates were obtained for each run, resulting in a total of 32 runs. Since heating time and cooling time contribute to the fractionation of hog fuel, a pseudo-time (eq 3.1) was calculated to represent the time of reaction for each run. For this purpose, it was assumed that fractionation was occurring above 100oC. A graph was generated as represented in Figure 3.2, and pseudo-time was calculated using equation 3.1. The denominator in equation 3.1 denotes the difference between the target temperature and 100oC.   Figure 3. 2. Representation of temperature vs time graph for fractionation of biomass  Pseudo-time = 𝐴1+𝐴2+𝐴3(Target−100)                                       (3.1) The pseudo-time values calculated for each run are tabulated in Table 3.1.   50  Table 3. 1. Pseudo-time values for all the runs Target temperature (oC) Residence time (minutes) Pseudo-time (seconds) 120 0  770 120 20 1970 120 40 3170 120 60 4370 140 0  1411 140 20 2611 140 40 3811 140 60 5011 160 0  1950 160 20 3150 160 40 4350 160 60 5550 180 0  2695 180 20 3895 180 40 5095 180 60 6295  3.3.1 pH of Hydrolysate Figure 3.3 shows the final pH as a function of hydrolysis temperature. pH of the hydrolysate decreased with increase in temperature from 120o C to 180o C, for all residence times. However, at 60 minutes, the rate of decrease in pH with increasing temperature, dropped. Increasing residence time also caused the pH of the hydrolysate to decrease. At 160o C and 180o C, the decrease in pH of hydrolysate with increase in residence time is negligible. These trends indicate that with increase in severity of operating parameters, the pH of the hydrolysate decreases, implying greater release of H+ ions. The lowest pH, 3.26, was obtained after hydrolysis at 180o C for 60 minutes. The highest pH, 4.60, was obtained after hydrolysis at 120o C for 0 minutes. In addition, with increasing severity, the magnitude of influence of increasing the severity of operating parameters further, reduces.  51   Figure 3. 3. pH of hog fuel hydrolysate as a function of temperature. Error bars represent the range. Operating parameters resulting in a lower pH indicate a higher concentration of H+ ions in the hydrolysate, and thus higher ease of removal of hemicellulose oligomers present in the lignocellulosic matrix. Such conditions also facilitate higher conversion of hemicellulose oligomers to monomers. However, the possibility of the rate of separation of hemicellulose oligomers from hog fuel exceeding the rate of degradation of hemicellulose oligomers can result in an increase in the percentage of oligomers present in the hydrolysate. This is verified from the compositional analysis results of the liquid hydrolysate.  3.3.2 Percentage Solids Removed  Among several factors, percentage solids removed from hog fuel by liquid hot water treatment represents one of the simplest ways to determine the extent of hydrolysis. This is because of the direct proportionality between the extent of hydrolysis, and the percentage solids removed 2.63.13.64.14.65.1110 120 130 140 150 160 170 180 190pH of hydrolysateTemperature (T, oC)0 min 20 min 40 min 60 min52  from hog fuel. As mentioned in section 2.1.2.1, the percent solids removed by hydrolysis was calculated as: Percentage solids removed = W1−W2W1× 100                   (3.2) Where w1 is the oven dry weight of biomass before hydrolysis, and w2 is the oven dry weight of solid residue after hydrolysis.   The percentage solids removed from hog fuel is shown in Figure 3.4 as a function of hydrolysis temperature.  The highest average percentage solids removed from hog fuel is 23.10 % at 180o C and 60 minutes, and the lowest average percentage solids removed is 2.87% at 120o C and 0 minutes. These high and low values correspond to the lowest and highest pH of the hydrolysate shown in Figure 3.3, confirming the relationship between extent of hydrolysis and pH.    Figure 3. 4. Percentage solids removed by hog fuel hydrolysis as a function of temperature. Error bars represent the range. 0.005.0010.0015.0020.0025.00110 120 130 140 150 160 170 180 190Percentage solids removed (%)Temperature (T, oC)0 min 20 min 40 min 60 min53  The trend of percentage solids removed with respect to temperature and residence time reflects the trend of pH of hydrolysate with respect to these operating parameters. With an increase in temperature at a constant residence time, the percentage solids removed from hog fuel increased. Similarly, with an increase in residence time at constant temperature, the percentage solids removed increased. At 120o C, percentage solids removed at different residence times are very similar, indicating that the effect of residence time on the percentage solids removed is minor at 120o C. This may be due to the insufficient generation of H+ ions at 120o C, resulting in suppression of the influence of residence time on improving the extent of hydrolysis. In addition, the effect of temperature on the percentage solids removed is greater in comparison to the effect of residence time.  Though percentage solids removed is a good measure of the extent of hydrolysis, it doesn’t provide information regarding the oligomer content available in the hydrolysate. This is because, along with solubilization of biomass, high severity conditions enhance conversion of oligomers to monomers and degradation products. This might result in a low oligomer content at high severity conditions, despite higher percentage solids removed. Oligomer content is a key parameter for this study, as oligomers result in better enhancement of the strength properties of NBSK pulp relative to monomers. Additionally, percentage solids removed represents the fraction of acid soluble lignin, acid soluble ash, and extractives, which are separated from hog fuel during liquid hot water treatment, along with the solubilized sugars. In view of this, percentage oligomers obtained for each individual sugar: arabinan, galactan, glucan, xylan and mannan, and the total oligomer mass obtained after liquid hot water treatment, are discussed in sections 3.3.3 and 3.3.4. 54  3.3.3 Percentage Oligomers Percentage oligomers was determined by quantifying the sugar monomers present in the raw hydrolysate/liquor obtained after the hydrolysis of hog fuel, and sugar monomers present in the hydrolysate after subjecting it to acid hydrolysis as described by Sluiter et al. (2008d). These values were used to calculate the percentage of sugar obtained in oligomer form by using the equation below: Percentage oligomers = M1−M2M1× 100                                   (3.3) Where M1 is the sugar monomer percentage in the hydrolysate, after post-hydrolysis, and M2 is the sugar monomer percentage in the raw hydrolysate. Figures 3.5, 3.7, 3.8, 3.9 and 3.10 present the percentage oligomers obtained for sugars: arabinan, galactan, xylan, glucan and mannan, respectively, as a function of residence time. 3.3.3.1 Arabinan For arabinan, as shown in Figure 3.5, in general, low severity conditions resulted in a high percentage of oligomers, and high severity conditions reduced the percentage of oligomers. To elaborate, with increase in temperature from 120oC to 180oC at any residence time, there is a decrease in the percentage of oligomers. Hydrolysis at 120oC resulted in highest percentage of oligomers at each residence time. The rate of degradation of oligomers to monomers with increasing residence time increased with increase in temperature. Almost no degradation, but an irregular increase in oligomer percentage is observed with increasing residence time at 120o C. This reflects the low concentration of H+ ions at 120oC.  At 180oC, the percentage of oligomers becomes zero at 40 minutes and 60 minutes. This indicates that arabinan is present only in monomer form at these conditions. This indicates that arabinan is easily removed relative to other 55  polysaccharides, since no other sugar exhibits zero oligomer presence under the range of operating conditions used for this study. The smaller quantity of arabinan in hog fuel (Figure 3.1) when compared to other polysaccharides, may also be the reason for its faster degradation. This can be seen from the reduction of total monomer content of arabinan in the hydrolysate after posthydrolysis, with increase in residence time at 180oC (Figure 3.6)  Figure 3. 5. Percentage oligomers of arabinan from hog fuel hydrolysis as a function of residence time. Error bars represent the range.  020406080100120-10 0 10 20 30 40 50 60 70Percentage oligomers of arabinan (%)Residence time (minutes)120˚ C 140˚ C 160˚ C 180˚ C56   Figure 3. 6. Trend of percentage of arabinan monomers with respect to initial hog fuel, with increase in residence time at 180o C. Error bars represent the range. 3.3.3.2 Galactan and Xylan Galactan and xylan showed similar trends. As seen in Figure 3.7, at 120o C and 140o C, there is no significant variation in the percentage of galactan oligomers both with change in residence time and temperature. However, xylan showed slight increase in the percentage of oligomers with increase in temperature from 120oC to 140oC. This can be attributed to the low generation of H+ ions at 120o C. At 160oC and 180oC, the percentage oligomers decreased with increase in residence time. It also decreased with increase in temperature from 160oC to 180oC, at each residence time.  00.20.40.60.811.21.41.61.80 10 20 30 40 50 60 70Percentage of arabinan monomers (%)Residence time (minutes)57   Figure 3. 7. Percentage oligomers of galactan from hog fuel hydrolysis as a function of residence time. Error bars represent the range.   Figure 3. 8. Percentage oligomers of xylan from hog fuel hydrolysis as a function of residence time. Error bars represent the range. 020406080100120-10 0 10 20 30 40 50 60 70Percentage oligomers of galactan (%)Residence time (minutes)120˚ C 140˚ C 160˚ C 180˚ C020406080100120-10 0 10 20 30 40 50 60 70Percentage oligomers of xylan (%)Residence time (minutes)120˚ C 140˚ C 160˚ C 180˚ C58  Percentage of xylan oligomers was more responsive to changing operating parameters than galactan. The lowest percentage of xylan oligomers obtained was 12.73%, which is significantly lower than that obtained for galactan, 45.67%. 3.3.3.3 Glucan and Mannan Glucan and mannan showed similar trends (Figures 3.9 and 3.10). At 120oC, 140oC and 160oC, there is no significant variation in the percentage of oligomers, with change in residence time. With increase in temperature from 120oC to 160oC, the percentage oligomers increased for each residence time. This increase is more noticeable in the case of mannan. This is again due to the insufficient availability of H+ ions at low temperatures such as 120oC. At 180oC, with increase in residence time, we can see a moderate drop in the percentage oligomers. Between glucan and mannan, the lowest oligomer percentage is observed for mannan, at 180oC and 60 minutes, 74.86%. The lowest oligomer percentage observed in the case of glucan is 82.2%. The response of oligomer percentage to changing operating parameters in the case of glucan and mannan is significantly lower compared to other sugars. This may be partially due to the higher quantities of glucan and mannan in hog fuel (Figure 3.1), and may mean that glucan and mannan are difficult to hydrolyze compared to other sugars. Consequently, glucan and mannan produce oligomers with lesser tendency to breakdown to monomers. Since the total quantity of sugars obtained in each run is different, the percentage of oligomers does not provide information regarding which run resulted in the maximum quantity of oligomers. Therefore, it is important to look at the total mass of oligomers obtained for each run. 59   Figure 3. 9. Percentage oligomers of glucan from hog fuel hydrolysis as a function of residence time. Error bars represent the range.   Figure 3. 10. Percentage oligomers of mannan from hog fuel hydrolysis as a function of residence time. Error bars represent the range. 020406080100120-10 0 10 20 30 40 50 60 70Percentage oligomers of glucan (%)Residence time (minutes)120˚ C 140˚ C 160˚ C 180˚ C020406080100120-10 0 10 20 30 40 50 60 70Percentage oligomers of mannan (%)Residence time (minutes)120˚ C 140˚ C 160˚ C 180˚ C60  3.3.4 Total Mass of Oligomers The total mass of oligomers present in the hydrolysate was calculated as: Total mass of oligomers =  (M1−M2)×(𝑊1−𝑊2)100                               (3.4) Where W1 is the oven dry weight of biomass before hydrolysis, W2 is the oven dry weight of solid residue after hydrolysis, M1 is the monomer percentage after post-hydrolysis, and M2 is the monomer percentage in raw hydrolysate. These monomer percentages are with respect to mass of hog fuel removed by liquid hot water treatment.  Figure 3. 11. Total mass of oligomers removed from hog fuel as function of temperature. Error bars represent the range. Figure 3.11 presents the total mass of oligomers obtained as a function of temperature. At 0, 20 and 40 minutes residence time, with increase in temperature, the total mass of oligomers increased. The rate of increase slows after 160oC for 40 minutes residence time. At 60 minutes residence time, the total mass of oligomers increased until 160oC, but decreases significantly on 00.511.522.533.54110 120 130 140 150 160 170 180 190Total mass of oligomers (g)Temperature (T, oC)0 min 20 min 40 min 60 min61  further increase of temperature to 180oC. At 120oC, 140oC, and 160oC, the total mass of oligomers increased with increase in residence time. However, at 180oC, the oligomer mass increased with increase in residence time only from 0 minutes to 20 minutes, reaching a maximum average oligomer mass of 3.25 g at 20 minutes. With further increase in residence time at 180oC, total oligomer mass began decreasing, indicating the increased conversion of oligomers to monomers and degradation products. The lowest average oligomer mass, 0.30 g, was obtained after hydrolysis at 120oC for 0 minutes.  These results show that, though the percentage oligomers generally showed significant decrease at high severity conditions (section 3.3.3), due to increased hydrolysis, supported by reduced pH (section 3.3.1), the total oligomer mass obtained increased with increase in severity of operating parameters. The exceptions to this are hydrolysis at 180oC for 40 minutes and 60 minutes, where the total oligomer mass has shown a decrease. Additionally, we can note the difference in the percentage solids removed and the total mass of oligomers obtained. For example, the percentage solids removed from hog fuel after treatment at 180oC for 20 minutes, is 19.90%, which is equivalent to 4.98g of oven-dry hog fuel. However, the total mass of oligomers obtained for this run is 3.25g. Therefore, the difference, i.e., 1.73g represents the solubilized extractives, acid soluble lignin and acid soluble ash. 3.4 Conclusion The results of compositional analysis of hog fuel reinforce the potential of hog fuel as a source of hemicellulose oligomers, which can act as a green paper strength additive. Though a portion of the glucan obtained from hog fuel came from cellulose present in the lignocellulosic matrix, a considerable portion of hog fuel is constituted by hemicellulose. The study of the effect of operating parameters on the separation of hemicellulose oligomers from hog fuel can be used 62  as a guide in choosing appropriate operating conditions, which enhance the separation of hemicellulose oligomers, and prevent the degradation of hemicellulose oligomer to monomers and degradation products.                           63  Chapter 4: Dilute Acid Hydrolysis of Primary Sludge 4.1 Introduction Primary sludge generated in pulp and paper mills is another form of lignocellulosic biomass. It is obtained after the treatment of mill effluent water from various sources such as condensates from digester and evaporator, and white waters obtained from thickening (Smook, 2002). As a result, primary sludge contains chemically modified fibres and chemical contaminants. These chemical contaminants include papermaking chemicals, fillers or dirt from chips cleaning, and their composition depends on factors such as the type of chemical treatment processes employed in the mill, and the waste handling procedures used (Jackson & Line, 1997). Due to the presence of chemical contaminants in primary sludge, it generally contains high ash content, in the range of 20-50%. However, a significant portion of primary sludge is cellulose and hemicellulose (Meyer & Edwards, 2014; Veluchamy & Kalamdhad, 2017; Migneault et al., 2011). Primary sludge produced in the pulp and paper mills of British Columbia (B.C), is primarily derived from softwoods obtained from the forests in B.C. Therefore, it contains softwood hemicelluloses which primarily are D-mannose derived hemicelluloses, such as galactoglucomannans (GGM). Some of the traditional primary sludge management techniques include landfilling and incineration. However, landfilling of primary sludge contaminates ground and surface water due to leachate formation, while incineration yields less heat, and releases greenhouse gases (Smook, 2002; Veluchamy & Kalamdhad, 2017). It may be possible to utilize primary sludge to produce hemicellulose oligomers. These hemicellulose oligomers can be used as a green strength additive to improve the physical strength properties of NBSK pulp, reduce hornification, and reduce the energy required for beating. 64  In this study, the effect of operating parameters: temperature and residence time, on the pH of hydrolysate, percentage solids removed, percentage oligomers present, and total mass of oligomers removed after dilute acid hydrolysis of primary sludge was investigated. The results of this study are presented in this chapter. 4.2 Composition of Primary Sludge The composition of primary sludge used for this study was determined using the methods described in section 2.1.1. Water and ethanol soluble extractives, structural carbohydrates, acid soluble and insoluble lignin, and ash were quantified.  Figure 4.1 shows the compositional analysis results for primary sludge. Errors bars indicate the standard deviation of 11 samples.   Figure 4. 1. Compositional analysis for primary sludge. From Figure 4.1 structural carbohydrates account for 67.90% of oven dried primary sludge. Similar to hog fuel, glucan is the dominant sugar, constituting 56.50% on an average. This glucan 0.42 0.3656.55.94 4.68 5.01 3.3827.392.140102030405060708090100Arabinan Galactan Glucan Xylan Mannan ASL AIL Ash ExtractivesPercentage of oven dry primary sludge (%)Component65  content represents both hemicellulose and cellulose. If we assume all the hemicellulose to be present in form of galactoglucomannan (GGM), which contains 1 glucose monomer for 3 mannose monomers, we can estimate the glucan content contributed by hemicellulose, which would be 1.56%. Xylan and mannan are the only other sugars present in significant quantities at 5.94% and 4.68%, respectively. Arabinan and galactan constitute only 0.42% and 0.36%, respectively. Ash is the second largest component after structural carbohydrates in primary sludge, constituting 27.39 %. This includes both acid soluble ash (ASA) and acid insoluble ash (AIA). This a significant difference when compared to hog fuel, which contained only 1 % ash. Primary sludge has 2.14% extractives, due to the absence of extractive-rich bark content. The amount of lignin in primary sludge is 8.39%: 5.01 % of acid soluble lignin (ASL) and 3.38 % of acid insoluble lignin (AIL). This is substantially less than the 32.38 % lignin observed in hog fuel. The major difference is the quantity of acid insoluble lignin (AIL), which is 27.14% in the case of hog fuel, while only 3.38% in the case of primary sludge. Primary sludge represents fibre that has been subjected to various chemical treatment processes including pulping and bleaching. Therefore, lignin has been removed, resulting in a smaller presence when compared to hog fuel or fresh wood.  Though the compositions of primary sludge and hog fuel differed from each other with respect to every component, the difference in ash content played a key role in altering the response of primary sludge to liquid hot water treatment. Liquid hot water treatment of primary sludge resulted in a hydrolysate with high pH (~ 10) reflecting reduced availability of H+ ions and thus marginal hydrolysis of primary sludge. To enhance the hydrolysis of primary sludge and the production of hemicellulose oligomers, 6.25 g of 98% w/w sulphuric acid was added to the reactant mixture, which represents 1.25 % of total slurry weight (section 2.1.2). This reduced the pH of hydrolysate to 2.44 to 6.67, and increased the extent of hydrolysis of primary sludge.  66  4.2.1 Composition of Ash To better understand the impact of ash on the pH of hydrolysate, XRD analysis (Figure 4.2) was conducted on ash, to determine its composition. Ash was recovered from primary sludge by removing all organic matter according to the procedure described by Sluiter et al., 2008c. Calcite (CaCO3) was the dominant component of ash, constituting 85.28 % of the total mass. Quartz, lime, albite, talc, illite/muscovite and orthoclase are also present, but in minor quantities. Based on this composition, the high pH of hydrolysate in the case of primary sludge can be attributed to the presence of calcite.   Figure 4. 2. XRD analysis of ash obtained from primary sludge.  4.3 Separation of Hemicellulose Oligomers Similar to liquid hot water treatment of hog fuel, the objective of dilute acid hydrolysis of primary sludge was to study the effect of temperature and residence time on the removal of hemicellulose oligomers from the lignocellulosic matrix, and identify operating parameters which 67  maximize the oligomer content. As described in section 2.1.2.1, the range of temperature tested was 120oC to 180oC, and the range of residence time was 0 minutes to 60 minutes. The combinations tested in this study are reported in Table 2.1. Single runs were conducted for each combination, resulting in a total of 16 runs. Pseudo-time values for each run were calculated using equation 3.1, as described in section 3.3, and are tabulated in Table 3.1. 4.3.1 pH of Hydrolysate       Figure 4.3 shows the pH of the hydrolysate as a function of temperature, at each residence time. The pH of the hydrolysate significantly increased with increase in residence time from 0 minutes to 60 minutes, at each temperature. The only exception is 180o C; the pH began to decrease after 40 minutes. The increase in hydrolysate pH is due to neutralization by the ash. Thus, increasing residence time results in increased neutralization. This suggests that the rate of recovery of hemicellulose polysaccharides from the lignocellulosic matrix will decrease with increasing residence time. The lower pH after hydrolysis at 180oC for 60 minutes relative to 40 minute hydrolysis may indicate that sufficient H+ ions were generated to exceed the ash neutralizing capacity.  No clear trend regarding the effect of temperature on the pH of the hydrolysate was identified.  However, the pH after hydrolysis at 180oC was lower than the pH after hydrolysis at 120oC for equivalent residence times. Hydrolysis at 120oC for 60 minutes, the lowest temperature and longest residence time in the operating range, resulted in the highest hydrolysate pH (6.67), while hydrolysis at 140oC and 0 minutes resulted in the lowest hydrolysate pH (2.44). The next lowest hydrolysate pH, 2.74, was obtained after hydrolysis at 180oC for 0 minutes, the highest temperature and lowest residence time in the operating range.  These observations demonstrate the complexity of hydrolyzing high ash content materials such as primary sludge.   68   Figure 4. 3. pH of primary sludge hydrolysate as a function of temperature Operating parameters resulting in a lower pH indicate a higher concentration of H+ ions in the hydrolysate, and thus greater ease of hydrolysis of primary sludge. Since pH of the hydrolysate increased with increase in residence time of the run, it is less likely that oligomers which initially separated from the lignocellulosic matrix at lower pH are hydrolysed to monomers or degradation products. Simultaneously, it is less likely that additional hemicellulose oligomers will be generated from the lignocellulosic matrix. However, when temperature is increased, due to the fluctuations in the pH of the hydrolysate, the possibility of removal of hemicellulose polysaccharides from the lignocellulosic matrix, and degradation of oligomers to monomers and degradation products is also variable. 22.533.544.555.566.57110 120 130 140 150 160 170 180 190pH of hydrolysateTemperature (T, oC)0 min 20 min 40 min 60 min69  4.3.2 Percentage Solids Removed  Among several factors, percentage solids removed by dilute acid hydrolysis represents the simplest measurement of extent of hydrolysis of primary sludge. As stated in section 2.1.2.1, the percentage solids removed by hydrolysis was calculated as: Percentage solids removed = W1−W2W1× 100                   (4.1) Where W1 is the oven dry weight of primary sludge before hydrolysis, and W2 is the oven dry weight of solid residue after hydrolysis.   The percentage solids removed from primary sludge is shown in Figure 4.4 as a function of temperature. The fluctuations in pH (Figure 4.3) with increasing temperature were not reflected by the percentage solids removed (Figure 4.4). The percentage solids removed increased with increase in temperature from 120oC to 180oC, at each residence time. This may be because the fluctuations in pH may only impact the ease or rate of hydrolysis of primary sludge without causing precipitation of products back onto the lignocellulosic matrix.  With increase in residence time from 0 minutes to 60 minutes, percentage solids removed decreased in most cases. In detail, at 120oC and 140oC, the percentage solids removed at 0 minutes and 20 minutes are similar, and percentage solids removed at 40 minutes and 60 minutes are similar and slightly lower. At 160oC and 180oC, percentage solids removed increases as residence time increases from 0 minutes to 20 minutes.  Increasing the residence time beyond 20 minutes reduces the percentage solids removed at 160oC. However, at 180oC, increasing residence time from 40 minutes to 60 minutes increases the percentage solids removed.  This coincides with the exception observed in the case of pH of hydrolysate at 180oC and 60 minutes.  This suggests that increased solids removal reflects increased hydrolysis of carbohydrates due to decreased pH. 70   Figure 4. 4. Percentage solids removed by dilute acid hydrolysis of primary sludge, as a function of temperature.  Similar to hog fuel, the effect of temperature on the percentage solids removed is greater than the the effect of residence time.  Although percentage solids removed is a good measure of the extent of hydrolysis, it doesn’t provide information regarding the oligomer content available in the hydrolysate as it also includes solubilized ASL, acid soluble ash, and extractives. In addition, as solubilization of biomass increases, the possibility of conversion of oligomers to monomers and degradation products also increases. In view of this, percentage oligomers obtained in the case of each individual sugar for each run, and the total oligomer mass obtained for each run are discussed in sections 4.3.3 and 4.3.4. 4.3.3 Percentage Oligomers The percentage of each sugar in oligomer form calculated for each run was determined by quantifying the monomers present in the raw hydrolysate obtained after the dilute acid hydrolysis 012345678110 120 130 140 150 160 170 180 190Percentage solids removed (%)Temperature (T, oC)0 min 20 min 40 min 60 min71  of primary sludge, and quantifying the monomers present in the hydrolysate after subjecting it to acid hydrolysis as described by Sluiter et al (2008d). These values were used to calculate the percentage of sugar obtained in oligomer form: Percent oligomers = M1−M2M1× 100                                   (4.2) Where M1 is the monomer percentage after post-hydrolysis, and M2 is the monomer percentage in raw hydrolysate.  Figures 4.5, 4.6 and 4.7 show the percentage oligomers obtained for arabinan, galactan and xylan respectively. 4.3.3.1 Arabinan In the case of arabinan (Figure 4.5), percentage of the sugar present in oligomer form increased with increasing residence time, at 160oC and 180oC. At 120oC and 140oC, the percentage of oligomers decreases suddenly at 40 minutes before increasing at 60 minutes. Aside from the sudden drop at 40 minutes for 120oC and 140oC, the increase in percentage oligomers with increasing residence time can be attributed to the increase in pH of sludge hydrolysate with increasing residence time, as discussed in section 4.3.1. No particular trend can be established with varying temperature; this likely reflects the fluctuations in pH observed with increasing temperature at each residence time.    72   Figure 4. 5. Percentage oligomers of arabinan from primary sludge hydrolysis as a function of residence time 4.3.3.2 Galactan The varying influence of ash can also be seen in the case of galactan (Figure 4.6). On increasing temperature from 120oC to 180oC for 0 minutes and 20 minutes, the percentage oligomers of galactan increases from 120oC to 160oC, before decreasing. At 40 minutes, the percentage oligomers of galactan increased with increasing temperature. At 60 minutes, the percentage oligomers increased with increase in temperature from 120o C to 140oC, before decreasing. The trend of percentage oligomers with increasing residence time from 0 minutes to 60 minutes is unique at each temperature.  020406080100120-10 0 10 20 30 40 50 60 70Percentage oligomers for arabinan (%)Residence time (minutes)120 degree C 140 degree C 160 degree C 180 degree C73   Figure 4. 6. Percentage oligomers of galactan from primary sludge hydrolysis as a function of residence time 4.3.3.3 Xylan In the case of xylan (Figure 4.7), the percentage oligomers increased with increase in temperature from 120oC to 180oC, for each residence time. There is one exception, an intermediate drop in percentage oligomers at 160oC for 20 minutes. However, this trend does not align with pH of the hydrolysate, which has shown the pH ultimately decreasing with increasing temperature from 120oC to 180oC. This is due to the high quantity of xylan in primary sludge, compared to arabinan and galactan (Figure 4.1), which ensured the dominance of removal of xylan oligomers from the lignocellulosic matrix, over degradation, even at lower pH.  There is no significant impact of residence time, on the percentage oligomers of xylan, with a unique trend in the case of each temperature. With an increase in residence time, percentage oligomers decreased moderately at 120oC and 140oC, and increased moderately at 160o C and 180o C, when comparing the extremes in residence time, 0 minutes and 60 minutes. 020406080100120-10 0 10 20 30 40 50 60 70Percentage oligomers for galactan (%)Residence time (minutes)120 degree C 140 degree C 160 degree C 180 degree C74   Figure 4. 7. Percent oligomers of xylan from primary sludge hydrolysis as a function of residence time 4.3.3.4 Glucan and Mannan No glucan or mannan was detected in the hydrolysate except for a small quantity of mannan in the hydrolysate obtained at 180oC after 0 and 20 minutes. This mannan was present fully in oligomer form. The difficulty in establishing trends for percentage oligomers in the case of primary sludge can be attributed to two reasons. One is the varying influence of ash with varying operating parameters, and the other is the presence of arabinan and galactan in minute quantities (Figure 4.1), which result in increased error. Since the total quantity of sugars obtained in each run differs, the total mass of oligomers obtained for each run must also be considered.   020406080100120-10 0 10 20 30 40 50 60 70Percentage oligomers for xylan (%)Residence time (minutes)120 degree C 140 degree C 160 degree C 180 degree C75  4.3.4 Total Mass of Oligomers The total mass of oligomers was calculated using the following equation: Total mass of oligomers =  (M1−M2)×(𝑊1−𝑊2)100                       (4.3) Where W1 is the oven dry weight of primary sludge before hydrolysis, W2 is the oven dry weight of solid residue after hydrolysis, M1 is the monomer percentage after post-hydrolysis, and M2 is the monomer percentage in raw hydrolysate. Figure 4.8 shows the total mass of oligomers obtained after each run, as a function of temperature. Oligomer mass increased with increasing temperature from 120oC to 180oC, for each residence time. The only exception to this trend was the decrease in total mass of oligomers produced by hydrolysis at 180oC for 60 minutes.   Figure 4. 8. Total mass of oligomers removed from primary sludge as function of temperature 00.050.10.150.20.250.30.35110 120 130 140 150 160 170 180 190Total mass of oligomers (g)Temperature (T, oC)0 min 20 min 40 min 60 min76  There is no significant effect of residence time, except at 180oC. Nearly equal oligomer mass is obtained for all residence time conditions at 120oC, 140oC and 160oC.  At 180oC oligomer mass initially increased with increasing residence time to a maximum of 0.31 g at 20 minutes, before starting to decrease. 4.4 Conclusion With 67.90% of its total oven-dried mass occupied by polysaccharides, primary sludge represents a possible source to obtain hemicellulose as a green strength additive. Although a portion of glucan, the sugar with the highest presence in primary sludge, comes from cellulose, there is still a measurable quantity of sugars which can possibly be used as pulp strength additives.  However, the high quantity of ash in primary sludge (27.39%), primarily calcite, resulted in neutralization of hydrolysate during dilute acid hydrolysis. This reduced the extent of hydrolysis of primary sludge, and thus limited the sugars released into the hydrolysate. This is evident from the absence of glucan and mannan in the hydrolysate from almost every run. This also resulted in a low total oligomer mass, where the maximum oligomer mass obtained (0.31 g) is comparable to the lowest oligomer mass obtained from hog fuel (0.3 g) and is more than 10 times smaller than the maximum oligomer mass (3.25 g) obtained from hog fuel.  It may be possible to improve the removal of hemicellulose oligomers from primary sludge by changing the operating conditions of hydrolysis, changing the hydrolysis technique, or by pre-processing primary sludge to separate ash.      77  Chapter 5: Adsorption of Hemicellulose Oligomers onto NBSK Pulp 5.1 Introduction Adsorption of hemicellulose onto pulp has shown benefits such as improvement in physical strength indices, reduction in hornification, reduction in beating energy requirement, increase in pulp yield, and reduction of dust (Gruenhut 1953; Dugal and Swanson 1972; Ren et al. 2009; Ban et al., 2011; Laffend and Swenson 1968; US 20040206464). Researchers studied the effect of operating variables such as temperature, time, pH, molar mass and fiber consistency on the adsorption of hemicellulose to pulp. The nature and extent of the influence of these operating variables has varied from one study to another depending on the type of hemicellulose and pulp used for the study (Ribe et al., 2010; Hannuksela et al., 2002; Ban & Van Heiningen 2011).  In this study, the influence of operating variables: adsorption temperature, adsorption time, hemicellulose oligomer-to-pulp percentage, fibre consistency and Weight average molar mass (Mw) of the hemicellulose oligomers, on the adsorption of hemicellulose oligomers onto NBSK pulp was studied. Hemicellulose oligomers used in this study were obtained by liquid hot water treatment of chip fines. Chip fines were used instead of hog fuel to minimize the impact of extractives on the strength enhancement of NBSK pulp in later stages, and primary sludge was not used due to the low yield of hemicellulose oligomers after fractionation. 5.2 High-Low Experiments High-low experiments were performed as described in section 2.2.2, to determine the operating variables of greatest influence prior to a full parametric study. The hydrolysates obtained from liquid hot water extraction of chip fines at 140oC for 27 minutes, and 170oC for 0 minutes, were used to conduct the 6 cases of the high-low experiments (Table 2.4). The Mw and mass of hemicellulose oligomers obtained for these hydrolysate samples are indicated in Table 5.1. 78  Table 5. 1. Mw of hemicellulose, and mass of oligomers per ml of hydrolysate. Hydrolysis condition Weight average molar mass, Mw Hemicellulose oligomer mass per ml of hydrolysate 140 oC and 27 minutes 1.43 kg/mol 2.42 mg/ml 170 oC and 0 minutes 8.98 kg/mol 2.50 mg/ml  The response variable of interest, adsorption yield, was defined as: Adsorption yield = S1 – S2                                                                                         (5.1) Where  S1 = Total mass of sugar in raw hydrolysate (mg)              S2 = Total mass of sugar in adsorption liquid (mg) Adsorption liquid is the liquid recovered via filtration of the pulp, hydrolysate and water mixture following adsorption.  The adsorption yield results obtained for each of the 6 cases are presented in Table 5.2. From the results, increasing the time from 5 minutes (case 1) to 60 minutes (case 2) while keeping other operating variables constant, did not result in a significant difference in the adsorption yield.  However, increasing temperature, decreasing fibre consistency, decreasing oligomer-to-pulp percentage, and decreasing Mw, all caused adsorption yield to decrease.      79  Table 5. 2. Adsorption yield results of high-low experiments  Run Time (minutes) Temperature (o C ) Fibre consistency (%) Oligomer-to-pulp (%) Mw (kg/mol) Adsorption Yield (mg) Case 1 5  25 4 3 8.98 35.80  Case 2 60 25 4 3 8.98 35.71  Case 3 5 50 4 3 8.98 32.54  Case 4 5 25 1 3 8.98 30.95  Case 5 5 25 4 1 8.98 10.45  Case 6 5 25 4 3 1.43 28.35   Due to its marginal impact on adsorption yield, time was excluded from the list of operating variables for full-scale investigation. Mw was also excluded from the full-scale investigation, because this investigation considered Mw to be a continuous input variable, therefore, requiring the production of hydrolysate containing hemicellulose oligomers with a targeted Mw value. As reduction in Mw resulted in a reduced adsorption yield, the hydrolysate used for the full-scale investigation was produced at 170oC for 0 minutes. Therefore, full-scale investigation was used to evaluate the influence of temperature, fibre consistency, and hemicellulose oligomer-to-pulp percentage, on adsorption yield. 5.3 Full-Scale Investigation A full-scale investigation was conducted according to the procedure described in section 2.2.3. The hydrolysate obtained for the full-scale investigation, from the liquid hot water treatment of chip fines at 170oC for 0 minutes, showed an average total monomer mass, total oligomer mass and Mw as indicated in Table 5.3.  80  Table 5. 3. Characteristics of hydrolysate obtained at 170 C and 0 minutes for chip fines Operating parameters Total monomer mass after post hydrolysis per ml (mg/ml) Total oligomer mass per ml (mg/ml) Mw (kg/mol) 170 C and 0 minutes 3.24 2.84 7.95  Adsorption yield values obtained during the full-scale investigation are reported in Table 5.4. Table 5. 4. Adsorption yield and predicted adsorption yield for each run in the full-scale investigation  Adsorption temperature (oC) Fibre consistency (%) Hemicellulose Oligomer-to-pulp Percentage (%) Experimental adsorption yield (mg) Predicted adsorption yield (mg) 1 37.50 2.50 1.00 28.29  27.57  2 37.50 4.00 2.00 27.45  39.25  3 25.00 2.50 2.00 53.94  56.54  4 44.93 1.61 2.59 70.88  68.89  5 44.93 3.39 2.59 67.12  58.16  6 37.50 2.50 3.00 61.41  70.22  7 30.07 1.61 1.41 40.63  43.87  8 37.50 2.50 2.00 46.45  46.45  9 50.00 2.50 2.00 49.52  55.01  10 44.93 3.39 1.41 41.86  37.36  11 30.07 1.61 2.59 75.02  73.80  12 37.50 1.00 2.00 60.05  56.34  13 30.07 3.39 1.41 38.01  34.28  14 37.50 2.50 2.00 47.83  46.45  15 30.07 3.39 2.59 61.52  54.23  16 44.93 1.61 1.41 36.54       38.11    81  A second order model was fit to this data using JMP 13 (SAS institute INC., 2016). The equation obtained from the fit is as follows: Predicted adsorption yield = 46.45 - [0.76 × ((T-37.5) / 12.5)] - [8.54 × ((F-2.5) / 1.5)] + [21.33 × (O-2)] + [((T-37.5) / 12.5) × ((F-2.5) / 1.5) × 6.25] + [((T-37.5) / 12.5) × (O-2) × 0.60] - [((F-2.5) / 1.5) × (O-2) × 7.06] + [((T-37.5) / 12.5)2 × 9.33] + [((F-2.5) / 1.5)2 × 1.35] + [(O-2)2 × 2.45]                                                                                                                                                   (5.2) In the above equation, T is the adsorption temperature in oC, F is the fibre consistency in percentage, and O is the hemicellulose oligomer-to-pulp percentage. The predicted adsorption yield values obtained using equation 5.2 are reported as predicted adsorption yield in Table 5.4. The R2 value obtained for this model fit is 0.86.  5.3.1 Effects of Operating Variables  Both individual and interactive effects of operating variables on the adsorption yield were obtained using equation 5.2. Individual effects of operating variables are elucidated in section 5.3.1.1; in this section one operating variable is changed while the other two operating variables are kept constant at their mid-levels. Interactive effects of operating variables are explained in section 5.3.1.2 by means of response surfaces. In this section, the effect of varying two operating variables at the same time, on the adsorption yield is shown. The third operating variable is kept constant at its mid-level.    82  The ranking of the three operating variables in terms of their impact on the adsorption yield, as given by JMP is: 1. Hemicellulose oligomer-to-pulp percentage  2. Fibre consistency 3. Temperature 5.3.1.1 Individual Effects Individual effects show the influence of an operating variable when the other two variables are kept constant. In sections 5.3.1.1.1, 5.3.1.1.2 and 5.3.1.1.3, the individual effects of oligomer-to-pulp percentage, fibre consistency and adsorption temperature are discussed. While the effect of one operating variable is discussed, the other two variables are fixed at their mid-values in the experimental range.   5.3.1.1.1 Hemicellulose Oligomer-to-Pulp Percentage Figure 5.1 shows the variation of predicted adsorption yield with changes in oligomer-to-pulp percentage in the region of the experimental design. The values of fibre consistency and temperature are fixed at their mid-levels, 2.5% and 37.5oC, respectively. The predicted adsorption yield (in mg) at mid-level for oligomer-to-pulp percentage, and the mid value for oligomer-to-pulp percentage, 2%, are indicated in red, on the y-axis and x-axis respectively. Oligomer-to-pulp percentage was ranked the highest impact operating variable amongst the three variables studied in this investigation. The trend shown in Figure 5.1 indicates a linear effect of oligomer-to-pulp percentage on the adsorption yield, in the region of experiment design, i.e., between an oligomer-to-pulp percentage of 1% and 3%. The adsorption yield increased with an increase in the oligomer-to-pulp percentage. This is expected, as the higher presence of 83  hemicellulose oligomers in the slurry will increase contact between pulp fibres and hemicellulose oligomers, resulting in a higher adsorption yield. Although the trend obtained in the experimental region is completely linear, there is a possibility that increasing the hemicellulose oligomer-to-pulp percentage beyond a certain point may not result in any further increase in the adsorption yield. This was observed by Ban & Van Heiningen (2011), who obtained a flat curve, beyond a certain oligomer-to-pulp dosage, indicating a saturation of the pulp surface with hemicellulose oligomers.    Figure 5. 1. Variation of predicted adsorption yield with oligomer-to-pulp percentage, at a fibre consistency of 2.5%, and temperature of 37.5o C.     (mg) 84  5.3.1.1.2 Fibre Consistency Figure 5.2 shows the variation of predicted adsorption yield with changes in fibre consistency in the region of the experiment design. The values of oligomer-to-pulp percentage and temperature are fixed at their mid-levels, 2% and 37.5 oC, respectively. The predicted adsorption yield (in mg) at mid-level for fibre consistency, and the mid value for fibre consistency, 2.5%, are indicated in red, on the y-axis and x-axis respectively.   Figure 5. 2. Variation of predicted adsorption yield with fibre consistency at an oligomer-to-pulp percentage of 2%, and temperature of 37.5o C. After oligomer-to-pulp percentage, fibre consistency was ranked the highest impact operating variable. The trend shown in Figure 5.2 indicates a linear effect of fiber consistency on  (mg) Fibre Consistency (%) 85  the adsorption yield, in the region of experiment design, i.e., between a fibre consistency of 1% and 4%. With an increase in fibre consistency, the adsorption yield decreases, reaching a minimum value at a fibre consistency of 4%. This demonstrates that as the mixture of pulp, oligomer, and water thickens, the adsorption yield reduced. The thicker the pulp slurry, the greater the restriction to the diffusion of hemicellulose oligomers in the slurry. Thus, a reduced surface area of pulp is exposed to hemicellulose oligomers, resulting in decreased adsorption yield. However, this trend may only be appropriate in the experiment design region used in this study. Reducing fibre consistency far below 1% may also reduce the probability of contact between the pulp and hemicellulose oligomers, by increasing the distance between them. This will reduce the adsorption yield (Ban & Van Heiningen., 2011). In this study, a fiber consistency of 1% has resulted in the best possible adsorption yield. 5.3.1.1.3 Adsorption Temperature Figure 5.3 shows the variation of predicted adsorption yield with changes in temperature in the region of the experiment design. The values of fibre consistency and oligomer-to-pulp percentage are fixed at their mid-levels, i.e., 2.5% and 2% respectively. The predicted adsorption yield (in mg) at mid-level for temperature, and the mid value for temperature, 37.5oC, are indicated in red, on the y-axis and x-axis respectively. Temperature was ranked the least impact operating variable amongst the three variables studied as a part of this investigation. Unlike fibre consistency and oligomer-to-pulp percentage, the trend shown in Figure 5.3 indicates a non-linear effect of temperature on the adsorption yield, in the region of experiment design, i.e., between 25oC and 50oC.  86   Figure 5. 3. Variation of predicted adsorption yield with temperature, at a fibre consistency of 2.5%, and an oligomer-to-pulp percentage of 2%. With the increase in temperature from 25oC, the adsorption yield decreases until it reaches a minimum at approximately 38oC. Increasing temperature beyond 38oC resulted in an increase in the adsorption yield. This result is unlike the effect observed by Ban & Van Heiningen (2011), who observed an increase in the adsorption yield with increase in temperature. However, the experimental range of temperature used by Ban & Van Heiningen (2011) was between 40oC and 95oC. In contrast, Hannuksela et al (2002) did not find any significant effect of temperature on the adsorption of galactoglucomannans (GGM) and galactomannans (GM) onto bleached kraft pulp (BKP), and applied a similar temperature range as the current investigation. Interestingly,  (mg)  (oC) 87  adsorption yields obtained in this study at 25oC and 50oC are very close to each other, at 56.54 mg and 55 mg respectively. This, combined with the ranking of temperature as the least impactful operating variable, indicate the insignificant influence of temperature on the adsorption yield, in the range from 25oC to 50oC.   5.3.1.2 Interactive Effects Interactive effects of operating variables on the adsorption yield are equally important as the individual effects, because the interactive effects may enhance or dampen individual effects. Figures 5.4, 5.5 and 5.6 are surface plots generated using JMP 13. Each of these figures represents the effect of two operating variables on the adsorption yield, while the third operating variable is fixed at its mid-level. The color of the surface plot changes from blue to green to red, as the adsorption yield values increase from a minimum to a maximum.  5.3.1.2.1 Fibre Consistency and Oligomer-to-Pulp Percentage Figure 5.4 shows the surface plot indicating the effect of fibre consistency and oligomer-to-pulp percentage on the predicted adsorption yield. The temperature is kept constant at its mid-level, 37.5 o C. Fiber consistency and oligomer-to-pulp percentage were the most influential operating variables amongst the three variables studied. Their interactive effects on the predicted adsorption yield are also interesting. Both high oligomer-to pulp percentage and low fibre consistency are required to achieve high oligomer yield. The impact of fibre consistency on the adsorption yield increased with increasing oligomer-to-pulp percentage. Though high oligomer-to-pulp percentage always results in better adsorption yield, high fibre consistency hindered the possibility of achieving maximum oligomer yield. On the other hand, at low oligomer-to-pulp percentage, the 88  adsorption yield is almost independent of fibre consistency. This again emphasizes the extent of influence of oligomer-to-pulp percentage on the adsorption yield.   Figure 5. 4. Surface plot showing the variation of predicted adsorption yield with variation in oligomer-to-pulp percentage and fibre consistency, at a temperature of 37.5o C 5.3.1.2.2 Adsorption Temperature and Fibre Consistency Figure 5.5 shows the surface plot indicating the effect of fibre consistency and adsorption temperature on the predicted adsorption yield. The oligomer-to-pulp percentage is kept constant at its mid-level, 2%. High adsorption temperature hindered most of the influence of fibre consistency on adsorption yield. Reduction in the fibre consistency did not result in any significant improvement in the adsorption yield at high temperatures. However, at low temperatures, adsorption yield 89  increased with a decrease in fibre consistency, reaching a maximum at the lowest fibre consistency. Therefore, low temperatures seem to complement the influence of fibre consistency. The nonlinear influence of adsorption temperature on adsorption yield is shown both at low and high fibre consistencies. The combination of the conditions which resulted in minimum adsorption yield values in the case of individual effects, resulted in a minimum adsorption yield under interaction as well. In other words, a combination of high fibre consistency and median adsorption temperature resulted in the lowest adsorption yield on the surface.    Figure 5. 5. Surface plot showing the variation of predicted adsorption yield with variation in temperature and fibre consistency, at an oligomer-to-pulp percentage of 2%.    90  5.3.1.2.3 Adsorption Temperature and Oligomer-to-Pulp Percentage Figure 5.6 shows the surface plot indicating the effect of oligomer-to-pulp percentage and adsorption temperature on the predicted adsorption yield. The fibre consistency is kept constant at its mid-level, 2.5%.   Figure 5. 6. Surface plot showing the variation of predicted adsorption yield with variation in temperature and oligomer-to-pulp percentage, at a fibre consistency of 2.5%. The strong influence of oligomer-to-pulp percentage when compared to that of adsorption temperature is evident from Figure 5.6. Unlike fibre consistency, increase in oligomer-to-pulp percentage resulted in an increase in the adsorption yield, regardless of the temperature. The nonlinear effect of temperature on the adsorption yield existed at all oligomer-to-pulp percentanges, however at different levels of adsorption yield. A minimum adsorption yield region 91  resulted from median temperature and low oligomer-to-pulp percentage, and a maximum adsorption yield region resulted from a high oligomer-to-pulp percentage and temperature values lying on the extremes of the experimental range. However, a portion of the median temperature and high oligomer-to-pulp percentage region, also results in maximum adsorption yield, confirming the influence of high oligomer-to-pulp percentage. Overall, in view of minimum influence on each other, the interactive effects of adsorption temperature and oligomer-to-pulp percentage are not as significant as that of the other two interactive effects.  5.4 Conclusion This study has provided insight into the influence of various operating variables on the adsorption of softwood hemicellulose oligomers onto NBSK pulp. Temperature was shown to have an unexpected effect on adsorption yield, in the experiment region used for this investigation. A high oligomer-to-pulp dosage is essential to obtain high adsorption yield, while low fibre consistency and low temperature can help enhance adsorption yield further.           92  Chapter 6: Conclusions and Future Work 6.1 Summary The results of compositional analysis of hog fuel and primary sludge reinforce the potential of these waste streams as a source of hemicellulose oligomers, which can act as a green paper strength additive. Hog fuel and primary sludge were found to contain 58.98% and 67.90% polysaccharides respectively. Glucan is the dominant component in both these waste streams, constituting 38.90% of hog fuel, and 56.50% of primary sludge. Though a portion of the glucan came from cellulose present in the lignocellulosic matrix, a considerable portion of the sugars is constituted by hemicellulose. The high content of ash in primary sludge played a vital role in altering the behavior of primary sludge to fractionation using liquid hot water treatment. Employing dilute acid hydrolysis reduced the pH of the hydrolysate and resulted in separation of a measurable quantity of polysaccharides.  The study of the effect of operating parameters on the separation of hemicellulose oligomers from these waste streams can be used as a guide in choosing appropriate operating conditions, which enhance the separation of hemicellulose oligomers and prevent the degradation of hemicellulose oligomer to monomers and degradation products. The identification of the nature of influence of operating conditions on the removal of hemicellulose oligomers from these waste streams was simple in the case of hog fuel. However, the presence of high ash content increased the complexity in the case of primary sludge. Glucan and mannan were the most difficult sugars to hydrolyze in both hog fuel and primary sludge. A maximum oligomer mass of 3.25g was obtained from the liquid hot water treatment of hog fuel at 180o C for 20 minutes, while a maximum oligomer mass of 0.31g was obtained from the dilute acid hydrolysis of primary sludge 93  at 180o C for 20 minutes. Interestingly, the same operating conditions resulted in the highest oligomer mass from both hog fuel and primary sludge. The adsorption study helped understand the individual and interactive effects of operating variables on the adsorption of softwood hemicellulose oligomers onto NBSK pulp. Temperature showed an unexpected effect on the adsorption yield, in the experiment region used for this investigation. A high oligomer-to-pulp dosage is essential for a high adsorption yield, while low fibre consistency and low temperature can help enhance the adsorption yield further.  6.2 Recommendations for Future Work Though dilute acid treatment of primary sludge improved its hydrolysis, the maximum oligomer mass obtained was 10 times smaller than the maximum oligomer mass obtained from hog fuel. There may be a possibility to improve this by increasing acid loading, or by pre-processing primary sludge to separate ash.  The adsorption studies have provided insight into the response of adsorption yield with varying operating variables. The impact of softwood hemicellulose adsorption on the physical strength properties of NBSK pulp needs to be evaluated. Additionally, widening of the experimental region for the operating variables may also help observe any unidentified trends in this study.       94  Bibliography Anglès, M. N., Reguant, J., Martinez, J. M., Farriol, X., Montané, D., & Salvadó, J. 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State of British Columbia’s Forests, 3rd Edition, 2010. Sun, Y., & Cheng, J. (2002). Hydrolysis of lignocellulosic materials for ethanol production: A review. Bioresource Technology, 83(1), 1–11. http://doi.org/10.1016/S0960-8524(01)00212-7 Thorp, B. (2005). Biorefinery offers industry leaders business model for major change. Pulp and Paper, 79(11), 35–39. Veluchamy, C., & Kalamdhad, A. S. (2017). Influence of pretreatment techniques on anaerobic digestion of pulp and paper mill sludge: A review. Bioresource Technology, 245(June), 1206–1219. https://doi.org/10.1016/j.biortech.2017.08.179 Werpy, T., & Petersen, G. (2004). Top value-added chemicals from biomass volume i — results of screening for potential candidates from sugars and synthesis gas. Other information: PBD: 1 Aug 2004, Medium: ED; Size: 76 pp. pages.  Wising, U., & Stuart, P. (2006). Identifying the Canadian forest biorefinery. Pulp and Paper Canada, 107(6), 25–30. Zaafouri, K., & Romero, L. I. (2016). Recent advances in alkaline pretreatment of lignocellulosic biomass. Biomass Fractionation Technologies for a Lignocellulosic Feedstock Based Biorefinery, 431-459. 99  Zhang, N., Li, S., Xiong, L., Hong, Y., & Chen, Y. (2015). Cellulose-hemicellulose interaction in wood secondary cell-wall. Modelling and Simulation in Materials Science and Engineering, 23(8), 85010.                         100  Appendix A: Mass Balance for Compositional Analysis Note: All mass values are in grams. Assuming, M1 is the amount of oven-dry mass of raw lignocellulosic biomass taken for the determination of extractives. If, after the removal of extractives, the oven-dry mass of the solid residue is M2. Quantity of extractives = M1 – M2 Percentage of extractives in oven-dry raw biomass = ((M1 – M2)/M1) × 100. 0.3g air-dried solid residue was then subjected to the two-stage acid hydrolysis according to the procedure described by Sluiter et al (2011). If S is the percentage solids in the air-dried solid residue, then the oven-dry mass of the sample (M3) subjected to two-stage acid hydrolysis is   M3 = (S×0.3)/100 g After obtaining the concentration of each sugar in g/ml using HPLC, it is multiplied by the total volume of the liquid phase, which is calculated as below: Density of 72% H2SO4 = ρ 72% H2SO4= 1.6338 g/ml  Density of H2O= ρ H2O= 1.00 g/ml  Density of 4% H2SO4 = ρ 4% H2S04 = 1.025 g/ml  1. The weight of 3.00 ml 72% H2SO4 is:  3.00 ml 72% H2SO4 x ρ 72% H2S04= 4.90 g 72% H2SO4  2. The composition of 3 ml of 72% H2SO4 is:  4.90 g 72% H2SO4 x 72% (acid wt) = 3.53 g acid  4.90 g 72% H2SO4 x 28% (water wt) = 1.37 g water  3. The concentration of H2SO4 after dilution is:  101  3.53 g acid / (84.00 g H20 + 4.90 g 72% H2SO4) = 3.97 % H2SO4 (w/w)  4. The total volume of solution present after dilution is:  (4.90 g H2SO4 + 84.00 g H20) x (ρ 4% H2S04)-1 = 86.73 ml   These calculations are also provided in Sluiter et al (2011). Multiplying the concentrations in g/ml with 86.73 ml gives the mass of each sugar, which can be denoted by Ma, Mga, Mgl, Mx, and Mm for arabinan, galactan, glucan, xylan and mannan respectively. These mass values can be used to calculate the percentage of these sugars in the oven-dry raw biomass. If the oven-dry mass of solid residue remaining after the two-stage acid hydrolysis is M4, and the oven-dry mass of residue obtained after ashing M4, is M5. Quantity of acid insoluble lignin = M4 – M5 M5 is the quantity of acid insoluble ash. The amount of acid soluble lignin (ASL) on an extractives free basis can be calculated as: %ASL = (100 x Dilution x Volume of filtrate x UVabs)/(oven-dry mass of sample × ε × path length) where:  UVabs = average UV-Vis absorbance for the sample at appropriate wavelength  Volume of hydrolysis liquor = Volume of filtrate, 86.73 mL  Dilution = (Volumesample + Volumedilutingsolvent)/Volumesample  ε = Absorptivity of biomass at specific wavelength  Pathlength = pathlength of UV-Vis cell in cm    102  Appendix B: Additional Data from JMP Table B. 1. PValues for indivisual operating variables, and for the product of the variables. Operating variable PValue T 0.85344 F 0.07474 O 0.00170 T×T 0.29335 F×F 0.87322 O×O 0.77264 T×O 0.94728 T×F 0.50034 F×O 0.44917  In Table B.1,  T = adsorption temperature F = fibre consistency, and O = oligomer-to-pulp percentage. 

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