engleski

Synthesis of fatty acid octyl esters combined with glycerol extraction and reuse of acid catalyst

The transesterification of triglycerides is an equilibrium reaction catalyzed by base, acid or enzymatic catalysts. When fatty acid octyl esters are synthesized, the reaction mixture has one phase, unlike the synthesis of fatty acid methyl esters where methanol is not miscible with triglycerides and/or fatty acid octyl esters. The monophasic characteristic of this reaction mixture creates difficulties with the separation of glycerol and residual octanol. Transesterification with base catalysts is susceptible to the presence of free fatty acids and water in feedstocks such as waste cooking oil and waste animal fat. In this study, octanol and waste animal fat or waste cooking oil comprised one phase, while the acid catalyst (20 wt% H2SO4) is dissolved in water and represents the second phase. This way, octanol (log Kow = 3.00) is mixed with the triglycerides, while the formed glycerol (log Kow = -1.76) is extracted in the water phase, shifting the equilibrium towards the formation of fatty acid octyl esters. As the catalyst (H2SO4) is predominantly present in the water phase (log Kow = -2.20), when the water phase is removed, so is most of the catalyst and glycerol. Even at full conversion, the formed glycerol represents a small percentage of the reaction mixture (4.6 wt%). Therefore, the water phase with the catalyst could be reused and the fatty acid octyl esters can be washed with water and octanol can be evaporated. This study examined the reaction kinetics (9:1 alcohol triglyceride molar ratio, 80 °C, different ratio of triglyceride/oil to water), and reusability of the water phase (with the catalyst) by adding glycerol.

biodiesel, octanol, transestrification, acid catalysis

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