Thermodynamic analysis based on simultaneous chemical and phase equilibrium for dehydration of glycerol with methanol

Highlights: • The thermodynamic analysis over the wider ranges of temperature, pressure and feed ratio. • Gibbs free energy minimization method was adopted. • Application of the improved genetic algorithm. • Distribution of equilibrium composition in vapor and liquid phase. -- Abstract: Glycerol can be dehydrated with methanol to produce tri-methyl glyceryl ethers (TMGE) and di-methyl glyceryl ethers (DMGE) as excellent diesel additives. Based on the simultaneous chemical and phase equilibrium, the thermodynamic equilibrium for dehydration of glycerol with methanol was studied in a wide range of reaction conditions (T = 40–300 °C, P = 0.5–7.5 atm and methanol/glycerol = 4:1–8:1 mol/mole). The improved genetic algorithm was applied to minimize Gibbs free energy of system corrected by UNIFAC model, which will provide an alternative of thermodynamic equilibrium analysis for the similar systems containing multi-phases, multi-components and multi-reactions. It was found that glycerol conversion is about 99.9% in the whole study range. The TMGE selectivity decreases with temperature due that the reaction is exothermic, but increases after the temperature rises to a certain value due to endothermic effect of components evaporation. In addition, the effects of pressure and the mole ratio of glycerol to methanol were investigated in this paper. Increasing the feed ratio of methanol to glycerol leads to the TMGE selectivity of 99.7%. More water ranging from 56% to 33% of equilibrium content, is generated with the mole ratio of methanol/glycerol from 4:1 to 8:1. Phase distribution of the equilibrium composition was demonstrated in this paper.