Hydrothermal liquefaction of rice straw with NiO nanocatalyst for bio-oil production

Abstract

In this study, rice straw as an abundant agricultural waste was subjected to hydrothermal liquefaction for production of bio oil. The series of batch experiments were conducted at different temperatures (200 °C, 230 °C, 260 °C, 280 °C and 300 °C) for reaction time of 120 min with and without NiO nanocatalyst. The resulting bio-oil was categorized into light and heavy oils (LO and HO). In presence of nanocatalyst, the yields of LO and HO were maximized up to 13.2% and 17.2% at 300 °C, respectively. The carbon recovery of bio oil was significantly improved to 52.8% with 46.6% energy recovery in catalyzed reaction. Typical H/C and O/C atomic ratio of catalyzed HO are 1.2 and 0.3 respectively. The highest calorific values of LO and HO are 24.9 MJkg−1 and 31.9 MJkg−1 respectively. The tested nanocatalyst increased the yield of bio oil, but could not incite the elemental compositions and heating values of bio oil. The valuable chemical compounds in bio-oil had been analyzed by GC-MS. The LO samples mainly contained phenols, alcohols and ketones while HO consisted alkanes and organic acids. Additionally, aldehydes and other organic compounds were also found in products.