Process Research For Diethyl Carbonate Synthesis By Transesterification In A Reactive Column

Diethyl carbonate (DEC) is a kind of green solvent with excellent performance, and is also an important organic intermediate. It is widely used in the organic synthesis industry, fuel additives, and lithium battery industry. At present, there are several routes to produce DEC, these methods through like phosgene, oxidative carbonylation, transesterification and urea alcoholysis. DEC can be synthesized by the trasesterification reaction of dimethyl carbonate (DMC) and ethanol (EtOH) in the present of sodium methoxide, the process that implement in a reactive distillation column is not only economic but also security. It is found that the trasesterification reaction consists two parts, the first one generates ethyl methyl carbonate (EMC) and methanol (MeOH), and the second one generates DEC and MeOH. In order to improve the reaction conversion rate, product yield and purity of DEC, some basic and engineering research was made for the reactive distillation method to synthesize DEC. These research combining experiments with simulations were based on the previous studies. In addition, the research provided great evidences and guidance for the optimization and design of the synthesis process.Firstly, the reaction of synthesizing DEC using DMC and EtOH, catalyzed by sodium methoxide was studied experimentally in a batch stirred tank reactor, with the effect of catalyst dosage, temperature, molar ratio of EtOH to DMC on the transesterification was investigated. After data reconciling, a mathematical model was used to process the experimental data. And the model with reliable parameters had passed strict test. The results show that the reaction is a consecutive reaction, and the intermediate product is EMC. Its reaction heat is -1.595 kJ·mol-1 for the first transesterification reaction, along with a reaction heat of 0.809 kJ·mol-1 for the second transesterification reaction. Both of them are reversible ones. The two reactions’forward activation energies are 45.633 kJ·mol-1 and 55.058 kJ·mol-1, respectively.Secondly, on the basis of equilibrium stage model, kinetic equation and UNIQUAC thermodynamic model, Aspen Plus software was used to calculate the process of synthesis of DEC by reactive distillation. The simulation values were good matched with the industry experimental data which means the established model was credible. Then a lot of simulations were done to examine the impact of different operating conditions on the DMC conversion rate, DEC yield and the concentration of DEC in the product. It was found that the theory number of the plate for rectifying section and the reaction section were 5 and 28, and it was suitable to feed a single strand mixed stream at 19th plate. The appropriate molar ratio of EtOH/DMC in the feed stream was 2.5:1, and each plate’s liquid holdup was not less than 70 L. The appropriate reflux ratio of 4.5～5.5 was obtained, while the operation at the atmospheric pressure was favorable.Finally, on the base of original equipment in a chemical enterprise, the industry-scale installation producing DEC was conducted combined with the simulation research. The flowsheet, a start-up and operating plan was put forward. The reactive distillation device worked well and making the industrialization of the reactive distillation method realized. At the same time, many industrial experiment parameters were achieved, which support some basis for the design and optimization of a new project.