Hydrothermal co-liquefaction of rice straw and Nannochloropsis: The interaction effect on mechanism, product distribution and composition

Catalytic co-liquefaction of rice straw and Nannochloropsis has been investigated in this study, using alkali catalyst (K2CO3) in glycerol-water solvent at different temperature, residence time and raw material mass ratios. The distribution of co-liquefaction products was examined in relation to the main reaction conditions. The synergistic effect of rice straw and Nannochloropsis co-liquefaction was confirmed. The yield of bio-crude increased from 32.49% of pure rice straw to 42.22% of a mixture with rice straw/Nannochloropsis mass ratio 1:1 under reaction conditions of 350 degrees C for 10 min with K2CO3, resulting in a synergistic effect on encouraging bio-crude production of 8.86%. GC-MS results indicated that co-liquefaction affected the mechanism of bio-crude production. The formation of ketones and phenols in bio-crude were weakened but fatty acids, esters, and nitrogenous compounds were improved under co-liquefaction. Rice straw and Nannochloropsis co-liquefaction was beneficial to improve the quality of bio-crude. Co-liquefaction increased H/C and decreased N element content as compared to liquefaction of pure rice straw and Nannochloropsis, respectively. Meanwhile, co-liquefaction decreased the bio-crude O/C ratio. By recycling aqueous phase by-products in the co-liquefaction process, the yield and HHV of the bio-crude as well as the fractions of phenols and hydrocarbons were also increased.