Application of heterogeneous catalysis to biodiesel synthesis using microalgae oil

• Microalgae oil application for biodiesel synthesis is discussed. • Catalytic effectiveness of ferment preparations and chemical catalyst is disputed. • Application of heterogeneous catalysts for biodiesel synthesis is reviewed. • Possibilities of catalyst regeneration is shown. Recently, there is a growing interest in the use of microalga in various fields. Microalgae have properties such as rapid reproduction and high biomass accumulation, and under certain conditions, some are able to accumulate a large amount of oil. However, microalgae oil often contains more free fatty acids than the vegetable oil and is therefore unsuitable for biodiesel synthesis using alkaline catalysts. For this reason, some authors suggest the application of heterogeneous catalysis. A particular interest in the use of immobilized enzymes has developed. Other solid substances can also be used as heterogeneous catalysts are usually metal oxides, carbonates or zeolites. The use of these catalysts results in simpler biodiesel synthesis, especially purification processes, a cleaner end product and a less polluted environment. The molar ratio of alcohol to oil is lower during enzymatic transesterification, and more than 90% ester yield is obtained using a molar ratio of alcohol to oil of 3:1 to 4.5:1. The alcohols do not have a negative effect on the effectiveness of chemical catalysts, so it is possible to use alcohols in molar ratio from 4:1 to 12:1. The optimal temperature of enzymatic process is 30℃‒50℃. An ester yield of more than 95% was obtained in 12‒48 h. Using chemical catalysts, greater than a 95% yield of esters was obtained at higher temperatures in a shorter time. Material costs of enzymatic catalysis can be reduced by reusing the catalysts directly or after regeneration.