UBC Theses and Dissertations
Empirical process modeling of the acid catalyzed steam pretreatment of radiata and lodgepole pine Olsen, Colin Andreas Dupont
Ethanol, an alternative liquid fuel, can be produced from sugars derived from lignocellulosic biomass in a bioconversion process that involves pretreatment, enzymatic hydrolysis, and fermentation. Among the different types of biomass investigated for bioconversion, softwoods are readily available in Canada, the US, and Scandinavia. Acid catalyzed steam pretreatment is a preferred method for softwoods due to its ability to effectively recover hemicellulose-derived sugars at moderate operating conditions. More severe conditions are generally required to produce a substrate readily hydrolyzed by enzymes, but because sugar degradation also occurs at these conditions, steam pretreatment is essentially a compromise. Prediction of sugar recoveries from steam pretreated and enzymatically hydrolyzed softwood is desirable for the purposes of process control and steam pretreatment reactor design. In this thesis, efforts were made to determine whether response surface methodology or the thermal severity factors Ro and CS were better suited to the development of empirical models of steam pretreatment. The construction of the thermal severity factor models highlighted the predominance of temperature and time in determining the direct outcomes of the acid catalyzed steam pretreatment of radiata pine. Within a comparison of several response surface methodology models, a hybrid experimental design produced the most robust model because it was developed in conjunction with a narrow process space. Moreover, it was apparent that the response surface methodology models possessed the greater capacity for predicting the direct outcomes of steam pretreatment. In an attempt to overcome limitations identified in the first portion of this thesis, the predictive capability of response surface methodology was further tested using lodgepole pine ranging in chip size and moisture content. The additional model created demonstrated that response surface methodology could successfully account for feedstock characteristics as well as steam pretreatment operating conditions. Moisture content, but not chip size, was shown to have a significant influence on the combined sugar recovery obtained after SO2 catalyzed steam pretreatment and subsequent enzymatic hydrolysis. In addition, model development was conducted in this portion of the thesis such that the model could form the basis of a more dynamic simulation of the entire softwood to bioethanol process.
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