Castor Oil Transesterification Catalysed by Liquid Enzymes: Feasibility of Reuse under Various Reaction Conditions

In the present work, biodiesel production by reaction of non-edible castor oil with methanol under enzymatic catalysis is investigated. Two liquid enzymes were tested: Eversa Transform and Resinase HT. Reactions were performed at 35 °C and with a molar ratio of methanol to oil of 6:1. The reaction time was 8 hours. Stepwise addition of methanol was necessary to avoid enzyme inhibition by methanol. In order to minimize the enzyme costs, the influence of enzyme activity loss during reuse of both enzymes was evaluated under two distinct conditions. In the former, the enzymes were recovered and fully reused; in the latter, a mixture of 50 % reused and 50 % fresh enzymes was tested. In the case of total reuse after three cycles, both enzymes achieved only low conversions. The biodiesel content in the oil-phase using Eversa Transform was 94.21 % for the first cycle, 68.39 % in the second, and 33.35 % in the third cycle. Resinase HT gave 88.05, 86.60 and 58.24 %, respectively. For the partial enzyme reuse, after three cycles, the biodiesel content was 88.36 and 88.05 % respectively for the Eversa Transform and Resinase HT, showing that partial reuse of enzymes could be beneficial for enzymatic transesterification reactions.