Further development of chemical and biological processes for production of bioethanol: Optimisation of pre-treatment processes and characterisation of products

摘要

The efficiency of several processes for pre-treatment of lignocellulose has been investigated to provide suitable feedstock for enzymatic hydrolysis and fermentation. Wet oxidation (with and without alkaline) has been investigated for wheat straw,birchwood, and willow treating 60 g/L. The conditions for willow and birchwood was selected based on the optimal conditions for wheat straw. Three different harvest years of wheat straw were included to evaluate the effect of crop variation from year toyear. Comparative studies were made using steaming and steam explosion of wheat straw. Alkaline wet oxidation fractionated wheat straw efficiently into solubilised hemicellulose and a highly convertible cellulose fraction. High oxygen (12 bar) duringtreatment and low lignin in treated fibres resulted in highly convertible cellulose. Different optimal reaction conditions were found for different harvest years. For straw 1993 and 1997, the conditions were 185°C, 15 minutes resulting in 9-10 g/Lsolubilised hemicellulose and 63-67% cellulose convertibility. For straw 1994, the conditions were 195°C, 5 minutes resulting in 7.5 g/L solubilised hemicellulose and 96% cellulose convertibility. For willow, the optimal pre-treatment was wet oxidationwithout alkaline using 185°C, 15 minutes (from 60 g willow/L). These conditions gave 8.2 g/L hemicellulose in solution and 50% cellulose convertibility, which was lower than that of wheat straw. High recoveries were obtained for willow compared to wheatstraw. Addition of alkaline significantly decreased fractionation and degree of convertible cellulose. For birchwood, the best process conditions were hydrothermal treatment (without oxygen and alkaline). At 200°C and 15 minutes, 8 g/L hemicellulose wassolubilised with high recoveries for both polysaccharides, however, poor cellulose convertibility was found (