Continuous hydrocarbon fuels production by photoenzymatic decarboxylation of free fatty acids from waste oils

Fatty acid photodecarboxylase, recently found in Chlorella variabilis NC64A (CvFAP), could efficiently catalyze C16-C18 fatty acids into C1-shortened hydrocarbons under visible light. This provides an alternative approach for hydrocarbon fuels production in mild conditions compared with hydrotreating of oils. In this study, a cascade system integrating lipase hydrolysis and CvFAP decarboxylation was demonstrated for the efficient production of hydrocarbon fuels from waste oils. The continuous CvFAP-catalyzed decarboxylation characteristics and performance of free fatty acids derived from waste oil were investigated for the first time. A hydrocarbon fuel production rate of 18.4 mM/h was obtained at a residence time of 50 min. The regulation of pH value from 6.8 to 8.5 significantly improved the activity of CvFAP, thereby obtaining an optimal conversion of 61.2%. The precipitation of palmitic acid caused a low conversion (37.9%) compared with the other fatty acids, further inhibiting hydrocarbon production. In such a cascade system, various oils can be converted to hydrocarbon fuels with a concentration of 8.97-15.3 mM. A high energy production rate of 204.3 kJ/L/h was achieved, which exhibited the advancement in high-quality biofuel production.