Enhancement of enzymatic biodiesel production: influence of reaction conditions, type of alcohol and lipase

Biodiesel is gaining importance as renewable fuel to reduce greenhouse gas emissions and dependence on fossil fuels. Enzymatic biodiesel production offers a more sustainable alternative to conventional chemical processes, operating under milder conditions and with lower energy requirements. This study evaluated the influence of temperature (30-50ºC), oil/alcohol molar ratio (1/3-1/30), alcohol type, reaction time and lipase formulation on enzymatic biodiesel production by transesterification. Cod liver oil was used as model substrate to compare reaction conditions before applying the most favourable conditions to microalgae oil. Response surface methodology was used to model the combined effects of the reaction variables. Biodiesel yield generally increased with reaction time, although decreases occurred after maximum values were reached. Lower temperatures favoured methanol-based reactions, whereas the temperature effect was less pronounced with ethanol. The highest yield, 99.94%, was obtained using ethanol and the solid immobilised lipase after 24 hours at 40ºC with a 1/18 oil/ethanol molar ratio. Stepwise methanol addition reduced enzyme inhibition in the immobilised lipase, increasing conversion from 17.02% to 45.97% after 48 hours. The liquid lipase produced comparable maximum yields with both alcohols at 1/18. Reusability experiments showed lower efficiency loss with ethanol than methanol for solid immobilised lipase. Finally, biodiesel production from microalgae reached 55.47%, with 33.11% of the fatty acid ethyl ester profile corresponding to desirable C16-C18 fatty acids. The estimated cetane number for microalgae biodiesel was 55.86, complying with the UNE-EN 14214:2013 standard.