Desulfurization of biodiesel produced from waste fats, oils and grease using β-cyclodextrin

Abstract

Making biodiesel from the fat, oil and grease in wastewater is attractive for sustainable biofuel production, waste management and public health. Sulfur reduction is a critical problem in biofuel production from low grade feedstocks containing high levels of sulfur contamination. Traditional desulfurization methods face challenges due to the financial and environmental costs of required catalysts, reagents or energy. This paper presents a new desulfurization method applied to biodiesel that uses β-cyclodextrin as the adsorbent. Biodiesel was produced from brown grease decanted from the FOG delivered to a local wastewater treatment plant. The equilibrium and kinetic behavior of the adsorption process were quantified with experimental measurements using the produced biodiesel and commercially available β-CD. A convection/diffusion model was then developed to simulate the adsorption process in a fixed bed adsorber. A 3-column design is presented based on the model results and compared with a sulfur reduction system based on vacuum distillation. The β-CD system operates at ambient temperature and pressure, whereas the vacuum distillation system operates at less than 0.01 Atm and near 200 C. The initial cost of the β-CD system is expected to be less than half the cost of the distillation system, but the operating costs may be similar. The β-CD system does not require the addition of hydrogen as in hydrodesulfurization but does require regeneration and periodic replacement of β-CD. Process intensification strategies such as polymerizing the β-CD or using more innovative process designs than fixed bed adsorbers may further increase the advantages of a β-CD based desulfurization system.