Medium-low temperature hydrothermal hydrolysis kinetic characteristics of concentrated wet microalgae biomass

To improve microalgae biomass utilization efficiency during biofuel production process, medium-low temperature hydrothermal hydrolysis pretreatment was adopted in this study. The pretreatment kinetic characteristics of concentrated wet microalgae Chlorella vulgaris biomass (50 g/L) under medium-low temperature hydrolysis (100°C-200°C) were experimentally investigated. The hydrothermal hydrolysis kinetics describing the coupled effects of temperature, initial pressure and retention time then were proposed using response surface methodology (RSM). The maximum carbohydrate yield reached 327.3 mg/g dried biomass under initial pressure of 4 MPa at reaction temperature of 150°C for 120 min. The maximum protein yield (321.5 mg/g dried biomass) was obtained under initial pressure of 4 MPa at reaction temperature of 200°C for 60 min. Based on the hydrothermal hydrolysis kinetic models, it was confirmed that temperature was the most important factor affecting both carbohydrate and protein release during hydrothermal hydrolysis process. Hydrothermal initial pressure and retention time were significant to carbohydrate release, but not to protein release. While, lipid was mainly distributed in microalgae residual and almost did not exist in supernatant (about 8.03 mg/g). And with assistance of mixed hexane and methanol (the ratio of hexane to methanol was 7:3), 67.69% of microalgae lipid was extracted out from hydrothermal hydrolysed microalgae residual (123.3 mg/g dried biomass).