Hot-water Extraction of Hemicelluloses by Microwave Heating: A Study of Sugarcane Bagasse and Sawmill Shavings of Norway Spruce and Scots Pine as Raw Materials for Hemicellulose Extraction

Abstract

In light of the increasing focus on sustainability and bio-mass as feedstock for energy and chemicals, extraction of hemicelluloses from different kinds of lignocellulosic materials has received much attention. This thesis has focused on the use of microwave heating in hemicellulose hot water extraction of sugarcane bagasse and softwood sawmill shavings. The effects of raw material particle size, extraction time and extraction temperature on yields and degree of polymerization in hemicellulose extraction have been investigated. A comparison of microwave and conventional heating has been performed separately. Analysis of sugar content by the phenol-sulfuric acid method indicated that use of microwaves in hemicellulose extraction gives higher yields than conventional heating. As analyzed by HPLC, this effect seems to be less pronounced, and requires further investigation. The degree of polymerization (DP) of the extracted hemicelluloses by the two methods was similar. Investigation of two different size fractions of sawmill shavings (0.9-3.0 mm and >3.0 mm), with microwave heated extraction showed no difference between the fractions in terms of yield or DP. The similarity between responses for both fractions can be explained by the small difference in size of the smallest dimension and thus equal limitations for mass transfer. The effects of extraction temperature and time on hemicellulose yield and degree of polymerization (DP) were analyzed through a 4x4 factorial setup (T=175-180-185-190°C, t=2-6-10-20 min). Optimization analysis by statistical software (Minitab) with equal weighting of responses determined optimal trade-off between yield and DP at conditions T=183°C, t=12 min for extraction of sugarcane bagasse and T=183°C, t=5 min for sawmill shavings. Results from analyses at the closest corresponding experimental conditions (T=185°C, t=10 min and T=185°C, t=6 min respectively) gave hemicellulose yield of 60% and DP=111 (Mw=38400 g/mol) for sugarcane bagasse and 55% yield and DP=23 (Mw=5700 g/mol) for sawmill shavings.