Response surface optimization of product yields and biofuel quality during fast hydrothermal liquefaction of a highly CO2-tolerant microalgae

The effects of biochemical components and processing variables (e.g., temperatures, solid-liquid ratio, ethanol concen-tration, and time) during fast hydrothermal liquefaction of a highly CO2-tolerant microalgae (Micractinium sp.) on the product yields and biofuel quality were explored using response surface methodology coupled with central composite design. Results showed that the maximum bio-oil yield (51.4 %) was obtained at 321 degrees C for 49 min at ethanol concen-tration of 75 % and solid-liquid ratio of 15.3 %. Among different studied parameters, ethanol concentration showed the highest significant impact on the bio-oil yield due to the low P-value and high F-value in ANOVA analysis. Further-more, the chemical compositions of bio-oils were determined, which showed that the increase of ethanol concentra-ti on in the solvent not only increased the bio-oil yield but also promoted the bio-oil quality by reduction of carboxylic acids and nitrogen-containing compounds with simultaneous enhancement of esters in the bio-oil. The present results show that fast hydrothermal liquefaction is a promising approach to convert the microalgae into high quality biofuels rich in esters.

Automated summary

The effects of biochemical components and processing variables on the product yields and biofuel quality during fast hydrothermal liquefaction of CO2-tolerant microalgae were investigated. Results showed that the maximum bio-oil yield was obtained at specific conditions, and ethanol concentration had the highest impact on bio-oil yield. Furthermore, the increase of ethanol concentration improved the bio-oil quality by reducing carboxylic acids and nitrogen-containing compounds while enhancing the esters content. Fast hydrothermal liquefaction is a promising approach to produce high-quality biofuels from microalgae.