Design of a low-cost process for the production of biodiesel using waste oil as raw material

Biodiesel is a promissory candidate to partially replace the use of fossil diesel in engines and other devices for energy production; it is composed by a combination of alkyl esters. It can be produced mainly from vegetable oils; which cost represents around 60-80% of the total production cost of biodiesel, affecting the selling price of the biofuel. Thus, the use of waste oils as raw material has been studied in the last years, because they are a cheaper alternative. However, they usually have a high content of free fatty acids, thus its conversion into alkyl esters require additional steps; since alkaline transesterification of oils with a high composition of free fatty acids is accompanied by saponification reactions. Usual pre-treatments involve the use of acid, homogeneous catalysts to transform the fatty acids into alkyl esters. On the other hand, the conversion of the oil into biodiesel is performed by reactions with alcohols, usually methanol which is produced commonly from petrochemical routes; this fact makes the production of biodiesel less sustainable. An alternative alcohol to produce biodiesel is ethanol, which can be obtained from other bioprocesses. In this work, the design of a low-cost biodiesel production process is reported, using waste cooking oil as raw material. Simulations of the process are performed in the process simulator Aspen Plus. Sensitivity analysis are performed to the equipment with degrees of freedom, to determine the design with the lowest energy requirement. Total annual costs and environmental impact are evaluated for the process.