Microwave-assisted two-stage hydrothermal liquefaction of Spirulina to produce high-quality bio-oil with low-carbon ketones

Due to the aggravation of environmental pollution and the massive consumption of fossil fuels, exploring renewable resources has become an important research topic. It is one of the research hotpots to convert algae into bio-oil by hydrolysis. This study studies the preparation of bio-oil with high content of low-carbon ketones by typical algae (Spirulina) using microwave-assisted heating through two-stage hydrothermal liquefaction (HTL). The effects of pre-treatment temperature, pre-treatment time, reaction temperature, reaction time, and reaction environment on the content of low-carbon ketones in the hydrolysate were discussed by setting up the orthogonal experiments. The changes of algae caused by pre-treatment were observed by elemental analysis, TEM and SEM. The samples obtained from the experiment were analyzed by gas chromatography/mass spectrometry (GC/MS) to find the best experimental conditions. Through the research in this study, it is found that the pre-treatment temperature of 80 °C is conducive to the formation of the target product (low-carbon ketones). The pre-treatment time of 20 min is more favorable. At the same time, it is found through experiments that the reaction temperature of 180 °C and the reaction time of 30 min are more conducive to the formation of the ketones. In addition, the weak acid solution environment significantly increases the relative content of the ketones. This study provides the basis for algae to prepare high-quality bio-oil and scientific support for the energy utilization of abundant algae resources.