Kinetics of extraction and in situ transesterification of oils from spent coffee grounds

Abstract

Resource limits, environmental concerns and unstable petroleum costs have led to an increased effort to develop alternative liquid fuels. Purpose grown feedstocks are expensive and demand additional resources such as land and water. Spent coffee grounds (SCGs) are a good potential low-cost feedstock, however, processing times and costs must be lowered in order to be cost competitive with fossil fuels. In this work, we investigated the kinetics of oil extraction from SCGs to explore if current methods of oil extraction could be hastened and if an integrated process which couples oil extraction and conversion to biodiesel stages in one single step (in situ transesterification) was viable. Kinetics of oil extraction from SCGs using n-hexane as solvent was studied as a function of temperature, solvent to solid ratio and water content. We have found that oil extraction times could be as low as 10 min due to higher diffusion coefficients of oils from SCGs. Further, we demonstrate, for the first time, the successful in situ transesterification of SCGs using different concentrations of sodium hydroxide as a catalyst and methanol to oil mole ratios. Both of these outcomes show promise for lowering biodiesel production costs from SCGs, a ubiquitous waste product around the world.