Effect of Heating Rate on Yields and Distribution of Oil Products from the Pyrolysis of Pubescen

摘要

The effect of heating rate on both the yields and the distribution of the oil products obtained from the pyrolysis of pubescen was studied. The molecular weight of the liquid products was mainly distributed in the range 200-500Da [about 77% from gel-permeation chromatography (GPC)]. At 15 degrees C min(-1), the total yield of small-molecular products from degradation of carbohydrate was 9.53wt% and the total yield of identified monophenols reached a maximum of 3.57 wt%. Thus, the liquid products were predominantly present as oligomers. Lignin in pubescen was degraded to stable tetramers. The formation of monophenols and/or oligophenols mostly involved the cleavage of the C-C (C-alpha-C-beta, C-beta-C-gamma, C-1-C-alpha) and C-O bonds (beta-O-4, beta-O-5, C-alpha-O, C-gamma-O, and 4-aryl ether linkages). Carbohydrate-derived species interacted with each other and then produced oligomers, the formation pathways of which are explained. A decrease of relative content of the species with molecular weight M-n=200-500 Da and an increase of relative content of the species with M-n=500-1000Da were observed as the heating rate was increased from 2.5 to 15 degrees C min(-1). With further increasing the heating rate from 15 to 25 degrees Cmin(-1), the molecular-weight distribution remained almost unchanged. Increase of the heating rate promoted the cleavage of C-1-C-alpha bonds, C-beta-C-gamma bonds in lignin, and the dehydration of C-alpha-OH units of lignin into C-alpha=C-beta.