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High-yield catalysed organosolv pulping of non-wood fiber sources

University of British Columbia

Global demand of pulp, paper and paperboard increases by the year. In contrast, shortages in wood supply were reported in many countries. On the other hand, large quantities of available non-wood fibrous materials are under-utilized. Furthermore, reduction of the environmental impacts by the pulp industries is now enforced in many parts of the world. Diversification of the raw material to non-wood fiber sources and introduction of new pulping and bleaching technologies, which are environmentally friendly, are seen as alternatives to alleviate the problems mentioned above. Therefore, in this study neutral alkali earth metal (NAEM) salt catalysed organosolv pulping was used to pulp some nonwood fibrous materials (sugarcane rind, sisal and tebu-tebu), in addition to spruce (softwood) and mangrove (hardwood). The bleaching agent employed was alkaline acetone peroxide, a T C F (totally chlorine-free) bleaching process. Under the specified pulping conditions, the screened pulp yields were 56 %, 58 %, 54 %, 63 % and 47 % for spruce, mangrove, sugarcane rind, sisal and tebu-tebu, respectively. In using flow-through and batch cooking, the type of cook did not affect the pulp yield of mangrove and sugarcane rind but affected that of spruce, sisal and tebu-tebu. The pulp yield of spruce was higher (^ 5 %) in batch type of cooks than in percolation type of cooks, but that of sisal and tebu-tebu was slightly lower (^ 3 %) in the batch type of cooks. Contrary to expectations, the rate of deUgnification was found to be higher in batch type cooks for all species. Therefore, the cooking times required to achieve fiber liberation were found to be shorter in batch type of cooks than in percolation type of cooks. The total cooking time required to liberate the fibers in batch cooks was only 25 to 30 min for mangrove and all non-wood fibers, and 40 min for spruce. Surprisingly, it was found that complete fiber liberation, as per definition used in this study (less than 1 % screen rejects), could not be obtained in percolation type cooking of spruce although the cook had been extended to 90 min. In a 60 min cook, 96.4 % of all fibers were liberated. Employing extended cooking beyond the fiber liberation point in N A E M pulping remarkably reduced the Kappa numbers at the expense of pulp yield and viscosity. On interrupting the process at fiber liberation provides maximum fiber yield. In addition, pulping to fiber liberation (high yield) is justified by the fact that the N A E M pulps were found to be easily bleachable even at high Kappa number (> 50). This is demonstrated by the TCF bleaching trial in this study. Furthermore, the non-wood pulps were easier to bleach than the softwood (spruce). Bleachability of the pulps was species dependent. In this series, softwood (spruce) was found to be the most difficult to bleach. Brightness, viscosity and degree of deUgnification were found to be affected by the concentration of hydrogen peroxide, acetone, alkali (KOH) charge and pulp consistency. The presence of acetone, especially at 50 % concentration by weight, in the bleaching system was found to improve the brightness and degree of deUgnification, and possibly to some extent, reduced the degradation of the fibers. The strength properties of the pulps varied by species and were somewhat affected by the bleaching process. Spruce pulp was found to be the strongest pulp among the selected species, while sugarcane rind was the strongest and sisal the weakest pulp among the non-wood pulps. Bleaching was found to improve the tensile strength of wood pulps but reduced that of the non-wood fiber pulps. Bleaching also reduced the tear and burst strengths and folding endurance of spruce and all non-wood pulps. The strength losses were more severe for the non-wood pulps and less so for the wood (spruce) pulp. Folding endurance was affected most by bleaching among the other strength properties. The bleaching conditions applied in this study were not fully optimized. On comparing these results with some literature values of the strength properties for the species pulped by the N A E M process, it can be concluded that the N A E M process can produce non-wood pulps as good as, or even better than, those produced by the conventional pulping processes (kraft or soda). Except for spruce, for which the strength values are between sulfite and kraft pulps of the same species.

Thesis/Dissertation

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2009-02-06

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http://hdl.handle.net/2429/4245

Forestry

University of British Columbia

UBCV

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