Enhanced pyrolysis of lignocellulosic biomass by room-temperature dilute sulfuric acid pretreatment

In the present work, the effects of dilute sulfuric acid (0.2 wt%) pretreatment at room temperature (30 degrees C) on the pyrolytic behaviors of pubescens, rice straw, willow, and cypress were studied. For herbaceous biomass, the degradation temperatures (Ta) of cellulose increased by around 20 degrees C, and the yields of bio-char in slow pyrolysis decreased by around 4 % after the pretreatment. For the pretreated softwood biomass, a decreased Ta and an increased yield of bio-char were found for willow, while little variation for cypress was detected. Regarding the typical small molecular products in the bio-oil after the pretreatment, levoglucosan (LGA) was only found in those of the pretreated pubescens (14.3 %, 400 degrees C) and cypress (4.5 %, 400 degrees C; 9.3 %, 500 degrees C), whereas levoglucosenone (LGO) was only found in that of the pretreated willow (9.7 %, 400 degrees C; 10.5 %, 500 degrees C). Increased yield of the small lignin-derived compounds was found for rice straw (from 7.9 % to 14.5 %), while decreased yields were found for willow and cypress. For the oligomeric part in bio-oil, significantly promoted production of holocellulose-derived oligomers was found with slightly increased proportions of heavy oligomers (>1300 Da). Meanwhile, the production of lignin-derived oligomers was apparently promoted as well, especially for rice straw. In the 500 degrees C pyrolysis of the two woody biomass samples, in addition to more complete degradation (higher yields of bio-oil and small-molecular compounds, and lower yield of bio-char), it was also found that the proportion of the oligomers in 256-500 Da increased significantly, and more holocellulose-derived oligomers were found. It was, therefore, speculated that a higher pyrolysis temperature would mainly promote the pyrolysis of cellulose and hemicellulose.