Conversion of rice straw into valuable products by hydrothermal treatment and steam gasification

Abstract

In order to obtain valuable products such as monosaccharides and hydrogen from rice straw (RS), the two-stage processing, hydrothermal treatment in the first stage and steam gasification in the second stage, was carried out. In the hydrothermal treatment, influence of hydrothermal treatment conditions and pretreatments to the raw RS sample on the product distribution was examined. Maximum yield of monosaccharides from the raw RS sample was 1.1wt.% (C basis), which was obtained by the hydrothermal treatment at 220°C for 5min. A water treatment of raw RS sample was carried out before hydrothermal treatment to increase the yield of monosaccharides, so that 9.4wt.% (C basis) of formic acid was extracted. Furthermore, in the subsequent hydrothermal treatment, the yield of monosaccharides increased up to approximately 4.5wt.% (C basis). Simultaneously, 7.9wt.% (C basis) of acids and furfural and 45.1wt.% (C basis) of other water-soluble products were also formed. In the second stage, conversion of hydrothermal-treated rice straw residue (HT-RSR) into hydrogen was performed by steam gasification using fixed-bed reactor and influence of nickel catalyst was examined. Hydrogen from HT-RSR sample without catalyst was produced above 800°C, while hydrogen from the 7.5wt.% nickel-loaded sample was evolved at lower temperature (500°C). The peak top temperature of the hydrogen evolution was shifted from 850°C for the 1.5wt.% nickel-loaded sample to 750°C for the 7.5wt.% nickel-loaded sample. Total amount of hydrogen evolved from the samples loaded with nickel more than 2wt.% was 50–60mmol/g-RSR and about three times larger than that from HT-RSR sample without catalyst. In addition, e.g. for the 2.3wt.% nickel-loaded sample, the CO, CO2, and other gaseous products were also evolved and their yields were 9.4, 21.1, and 3.1wt.% (C basis), respectively.