| In recent years,due to the growing expansion of the biodiesel industry,glycerol has been produced on a large scale as a by-product of the biodiesel production process.In a context of global energy shortage,the transformation of excess glycerol into downstream products with high added value has become a global concern.The etherification of glycerol with alkenes to produce alkyl glycerol ethers can not only convert excess glycerol into useful chemicals,but the process is green and clean.Therefore,it gotten much more attentions than before.Because heterogeneous reactions involve complex phase equilibrium systems,it is difficult to find the optimal reaction conditions for conversion and utilization in actual production.In this article,the thermodynamics study of the heterogeneous reaction between glycerol and olefin etherification will be carried out to provide powerful theoretical guidance for improving raw material conversion and reducing resource waste.Through literature research,it is found that the theoretical data about this aspect was not systematic enough.In order to complete the theoretical data relating to the reaction between glycerol and olefins,the thermodynamic properties of glycerol and olefin are studied in detail from the following aspects.(1)Based on the equilibrium of heterogeneous and multi-component reactions,the thermodynamic data related to the etherification of glycerol and ethylene,propene,isobutene and isopentene,and the simultaneous etherification of glycerol with isobutene and tert-butanol to alkyl glycerol ether were estimated by Benson method,Joback group contribution method and Rozicka-Domalsk method.The UNIFAC activity co-efficient model was used to correct the non-ideality of liquid mixtures.By adapting the modified genetic algorithm to the real Gibbs free energy minimization reaction system,a thermodynamic model was established which belongs the simultaneous etherification of glycerol and tert-butanol with isobutene,glycerol and isobutene.(2)Using the thermodynamic calculation model of chemical reaction equilibrium system,the etherification process of glycerol and olefin was analyzed in the wide range of temperature(313-573 K),pressure(0.1-0.8 MPa)and molar ratio of olefin(ethylene,propene,isobutene and isopentane)/glycerol feed(4:1-8:1).Effects of reaction conditions on the entire reaction system and on the distribution of gas-liquid equilibrium components were included.It is showed that the selectivities of alkyl glycerol ether were the highest when glycerol and olefin etherize under low temperature,high pressure and low molar ratio of glycerol and olefin feed.(3)A thermodynamic calculation model of an equilibrium system of chemical reactions was used to analyze the equilibrium process of a complex heterogeneous system composed of glycerin + isobutylene + tert-butanol.In the temperature range of 313-573 K,the gas-liquid equilibrium composition of glycerol + isobutene + tert-butanol reaction system,the equilibrium conversion of raw materials and the equilibrium selectivity of three tert-butyl glycerol ethers were studied.Based on the fixed ratio of glycerol feed,the feed ratio of tert-butanol and isobutene was gradually increased to explore the changing trend of isobutene conversion.In the triangular phase diagram composed of glycerol,isobutene and tert-butanol,the different etherification reactions on both sides of the critical curve were investigated.The results show that the synthesis of tert-butyl glycerol ethers includes two processes: dehydration of glycerol with tert-butanol and co-etherification of glycerol with isobutene and tert-butanol.When the temperature gradually increased,the proportion which belongs glycerol to isobutene and tertbutanol co-etherification reduced by degrees,and the proportion of glycerol to tert-butanol dehydration gradually increased.When the initial ratio of glycerol: isobutene: tert-butanol was1:3:1,the glycerol conversion and tert-butyl glycerol ether selectivities were the highest. |
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