Hydrothermal liquefaction of rice straw: Effect of reaction environment

• Effect of N2, O2 and CO2 on hydrothermal liquefaction of rice straw.
• Maximum bio-oil yield (17 wt%) and conversion (78%) was achieved using N2.
• Maximum organic carbon conversion (TOC) (77%) was achieved using N2.
• Bio-oil was composed of derivatives of phenol, guaiacol, catechol, syringol.
• Use of O2 led to oxidation of some phenolic derivatives.

Hydrothermal liquefaction of rice straw was performed at temperatures from 280 to 320 °C under different reaction environments viz., N2, O2 and CO2. N2 and CO2 did not show any significant change in the product distribution, however, in case of liquefaction using O2, the bio-oil yield was very low. Maximum bio-oil yield (17 wt%) as well as conversion (78%) was observed in case of liquefaction using N2. TOC analysis indicated that the maximum organic carbon conversion (77%) was under N2 environment. Ether soluble bio-oil obtained under O2 environment showed higher aliphatic proton content than N2 and CO2, whereas, aromatic proton content was higher in case of N2 and CO2 than O2. 1H and 13C NMR showed that bio-oil obtained at all the conditions was highly aliphatic and aromatic in nature. GC/MS showed that bio-oil (ether and acetone soluble) obtained under different reaction conditions was composed of phenol, guaiacol, catechol, syringol and their derivatives.

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