Simulation and optimization of crude glycerol refining process as a co-product of biodiesel

Abstract

Glycerol is an essential chemical raw material widely used in industries such as food, pharmaceuticals, cosmetics, tobacco, and textiles. With the increasing production of biodiesel, a considerable amount of crude glycerol co-product is generated. Purification of crude glycerol by separating it from biodiesel co-products can lead to the production of high-purity glycerol, thus enabling the synthesis of high-value-added chemicals to reduce the production cost of biodiesel. This paper proposes a new glycerol purification process based on the acidification of potassium oleate soap using sulphuric acid. The composition of crude glycerol is complex. The presence of salts can affect the binary interaction parameters of glycerol and water. The ion forms resulting from the ionization of potassium fatty acid soaps are not available in the database and require important data to be provided through physical property estimation. Additionally, the dissociation of sulphuric acid is involved in the system. These issues make it challenging to propose a complete process based on the characteristics of crude glycerol. In this study, the vapor–liquid equilibrium data of the glycerol-water system containing potassium sulphate under reduced pressure were experimentally determined, and the binary interaction parameters of the glycerol-water system were regressed and used in the subsequent process simulation. The entire process of crude glycerol refining from biodiesel co-products was simulated and optimized using Aspen Plus software, proposing an optimized complete refining process for crude glycerol and designing a crude glycerol refining process with a production scale of 100,000 tons per year. The potassium oleate soap is first acidified with sulphuric acid, then removed by centrifugation, with the resulting lower layer entering the distillation process. We compared two different distillation processes and identified the more optimal separation sequence. Glycerol products with a mass concentration of 99.2% were obtained, with glycerol and methanol yields of 98.83% and 99.79%, respectively. Based on the above research, energy integration and optimization of the process were further investigated through pinch analysis. Overall, energy savings of 7.192 Gcal/h were achieved, resulting in a reduction in energy consumption of 40.65%. This paper proposes a new purification scheme for crude glycerol and an energy integration scheme to reduce the purification cost of high-purity glycerol. This is significant for the rational utilization of crude glycerol, a co-product of biodiesel.