Kinetics of Coffee Oil Ethanolysis Catalyzed By an Immobilized Lipase Enzyme to Produce Biodiesel

As supplies of fossil fuels are depleted, the need for alternative sources of fuel becomes evident. Biodiesel is an attractive alternative to petroleum-based fuel; however, cost of the feedstock, mainly vegetable oils, makes biodiesel a costly product. In the search for alternative feedstocks, spent coffee grounds were revealed to be a largely available and economical source of vegetable oil. To design a process for biodiesel production, a kinetic rate model was necessary. Immobilized lipase was found to be an optimal catalyst for the ethanol transesterification of coffee. Tests were performed in batches, a differential packed bed reactor, and a recycle reactor. Reactor effluents were analyzed by GC-MS. Results indicated significant external mass transfer limitations and stability of the immobilized enzyme catalyst at temperatures less than or equal to 45^oC. A modified Michaelis-Menten equation for two substrates provided a good fit for the reaction kinetics in the range of 30^o to 45^oC.