Energy-efficient Conversion of Castor Oil for Biodiesel Production: Investigate Novel Energy-Efficient Biodiesel Production Technologies such as Enzymes and Membranes

Thalles Allan Andrade

Publikation: AfhandlingPh.d.-afhandling


Biodiesel production is a field of continuous interest due to the search for alternative renewable fuels to replace the use of fossil fuels. Generally produced from the transesterification of vegetable oils and animal fats, the enzyme-catalyzed route is an alternative for the use of chemical catalysts. The process catalyzed by enzymes is less energy-intensive and more environmentally friendly, assuring higher compatibility with different raw materials and better product separation. The biggest drawback for the use of enzymatic processes is the higher costs of enzymes compared to chemical catalysts. Non-edible castor oil is a renewable alternative for biodiesel production with unique properties due to the presence of ricinoleic acid in its composition.
The biodiesel production was optimized evaluating the influence of the temperature, alcohol-to-oil molar ratio, enzyme loading and water content in the reaction yield. Even though excess alcohol should shift the reaction towards the formation of products, high concentration of alcohol inhibits the enzyme activity. Liquid lipases Eversa Transform and Resinase HT were tested. Methyl esters content of 94.3 % was obtained after 8 hours, at 35 °C, 6:1 methanol-to-oil molar ratio, 7 wt% water and 3 wt% Eversa Transform solution by weight of castor oil, while Resinase HT showed lower enzyme activity on the castor oil transesterification.
Reaction mechanisms were evaluated for reactions at 35, 40 and 50 °C, with 6:1 methanol-to-oil molar ratio, 5 wt% water and 5 wt% Eversa Transform loading by weight of castor oil. Matlab v8.5 was used to evaluate the proposed mechanisms and estimate their respective kinetic parameters. According to the mechanism able to fit the experimental data, it was concluded that, in presence of water, reactions of transesterification and hydrolysis of triglycerides happen simultaneously.
From the kinetic parameters, process simulation and economical evaluation for the biodiesel production process catalyzed by Eversa Transform were investigated. For comparison purposes, a process catalyzed by immobilized lipase Novozym 435 was also simulated. For a biodiesel production of 250,000 tons per year, the process with liquid enzyme resulted in a production cost of 0.76 US$/kg and annual profit of US$ 56 million. Concerning the process catalyzed by the immobilized enzyme, at least 300 times enzyme reuse was required to achieve the same annual profit. Environmental impact assessment showed that the liquid lipase-catalyzed process is more environmentally friendly than the other process.
Recovery and reuse of liquid lipases Eversa Transform and Resinase HT were tested. Partial enzyme reuse, with 50 % fresh and 50 % reused enzyme, assured high biodiesel production for three batches. While Eversa Transform showed higher overall methyl esters content, Resinase HT seemed to be more resistant. Ultrafiltration with ceramic membrane reduced glycerol and methanol contents in the lipases solution to less than 1 %. Compared to enzyme recovery by centrifugation, the use of diafiltration increased the methyl esters content when the lipases were reused.
StatusUdgivet - 2018

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