Synergistic effect of hydrothermal Co-liquefaction of Spirulina platensis and Lignin: Optimization of operating parameters by response surface methodology

Abstract

Hydrothermal liquefaction (HTL) of biomass is an effective technology to transform and utilize wet biomass feedstocks. Significant synergistic effects were found during HTL of two species of wet biomass-Spirulina platensis and Spartina alterniflora. In this study, the lignin, a main compound of Spartina alterniflora and much other terrestrial biomass were chosen for hydrothermal co-liquefaction with Spirulina platensis. The effect of HTL Spirulina platensis, lignin, and the blend was optimized through response surface methodology. The results explicitly showed that the highest bio-oil yield was 33.1 wt% at 340 °C, 40 min with the Spirulina platensis -lignin blending mass ratio of 2:1, which is much higher than that of lignin (22 wt%) and a bit lower than that of Spirulina platensis (36 wt%) under the same reaction conditions. The synergistic enhance effects on the bio-oil yield were observed at relatively severe reaction conditions (higher temperatures, longer residence times, and larger Spirulina platensis to lignin mass ratios). The co-liquefaction process has upgraded the quality of bio-oil, as confirmed by GCMS analysis. By which, the content of nitrogen-containing heterocyclic compounds in bio-oil was significantly decreased, whereas the content of fatty acid compounds such as hexadecanoic acid was significantly increased. Such an improvement would greatly reduce the energy consumption required for post-treatment.