Decarboxylation of microalgal oil without hydrogen into hydrocarbon for the production of transportation fuel

A catalytic decarboxylation process following pyrolysis was developed for the production of transportation fuels from microalgae. The pyrolysis of Chlorella sp. KR-1, which has a triglyceride content of 36.5%, was carried out at 600 °C to obtain feedstock oil for decarboxylation. The major compounds in the pyrolysis oil were free fatty acids with carbon numbers of 16 and 18. Decarboxylation of the pyrolysis oil was performed using a type of hydrotalcite (MG63) as a catalyst at temperatures of 350 °C and 400 °C. Due to the selective reaction by MG63, hydrocarbons with carbon numbers of 15 and 17 were the most abundant compounds in the liquid product. The product yield at a reaction temperature of 400 °C was 78.6% and the degree of oxygen removal was 78.0%. Inert or less active oxygenates for hydrotalcite, such as phenolic compounds and fatty acid alkyl ester, may prevent the complete removal of oxygen. The diesel fraction in the product obtained under the given reaction condition was 83.8%, whereas that of the pyrolysis oil was 35.5%.

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► Catalytic decarboxylation process following pyrolysis of microalgal biomass has been developed for the production of transportation fuels.
► Microalgae pyrolysis produced free fatty acids and hydrocarbons.
► Pyrolysis oil was successfully converted into hydrocarbons.
► Diesel fraction in product drastically increased from 35.5% of pyrolysis oil to 83.8% of reaction product by decarboxylation reaction.