Effect of pretreatment and biomass blending on bio-oil and biochar quality from two-step slow pyrolysis of rice straw

This study investigated biomass blending and water washing to improve product quality from two-step pyrolysis of rice straw. Rice straw (RS) was mixed with groundnut shells (GNS) and wheat straw (WS) in different weight ratios. Blending RS with GNS/WS in a 1:1 ratio increased the total bio-oil yields by 7-9% and reduced the py-rolysis gas and char yields by 5-7% and < 2%, respectively. RS was washed with water separately to examine the effect of removing water-soluble ash elements. The optimum washing duration was 60 min; the ash removal efficiency was then 26%. The bio-oil yields from washed straw increased by 4% over unwashed straw, and pyrolysis gas yields decreased. Combining the washing and blending processes increased the levoglucosan yield by 1.6-2.1 times compared to unwashed RS, and the water content in bio-oil was reduced by -10%. Moreover, the biochar samples obtained after pyrolysis of washed biomass blends had potential fuel appli-cations owing to low fouling or slagging propensity. They also had possible use in the soil for adsorption of soil contaminants and increasing acidic soil pH, with likely stability of -1000 years in the ground. These results provide a promising alternative for efficiently converting rice straw to multiple value-added products.

Automated summary

This study investigated biomass blending and water washing as methods to improve the product quality of two-step pyrolysis of rice straw. The results showed that blending rice straw with groundnut shells/wheat straw increased the bio-oil yields, while washing rice straw reduced the ash content and increased the levoglucosan yield.