Shortcut design of sulfur reduction distillation system using pseudo-component description of biodiesel and the sulfur contaminants

Abstract A critical factor in environmental degradation is the coupled problem of world population growth and waste management, including wastewater management. Making biodiesel from the FOG (fat, oil and grease) in the wastewater system is an attractive path for sustainable biofuel production, waste management and public health. High sulfur content is the biggest challenge in biodiesel produced with the brown grease extracted from FOG. The purpose of this paper is to present a new method to design the sulfur reduction process based on a pseudo-component approach that greatly reduces the effort required to characterize the complex mixture of methyl esters and sulfur containing contaminants. To demonstrate this method, biodiesel was produced from decanted brown grease using several combinations of acid and base catalysts in a two-step esterification/ transesterification process. Vacuum batch distillation was applied to the crude biodiesel product to generate volatility and sulfur distribution data. An easily applied vapor/liquid equilibrium model was then developed using 7 pseudo-components, each with an assigned sulfur content. A principal result is that the pseudo-component model very accurately simulated the batch distillation data. These pseudo-components were then used in the ASPEN software to design a continuous distillation system for a FOG to biodiesel system being installed at a wastewater treatment plant. The second principal result is the ASPEN based design predicts a biodiesel product containing sulfur lower than 10 ppm, satisfying sulfur requirements worldwide. In conclusion, the pseudo-component design method is a versatile and easily applied approach to design sulfur reduction processes.