Study On Production Process And Energy Saving Process Of Dimethyl Carbonate

As a green organic solvent,dimethyl carbonate(DMC)has a good market prospect because of its wide application and biodegradability.At present,PC transesterification is the most widely used process in domestic manufacturers.The basic process includes four parts: reactive distillation,stripping distillation,vacuum distillation and pressure swing distillation.Based on the basic process,focusing on the key point of energy saving and consumption reduction,this paper makes a detailed discussion and research on process optimization,so as to provide some theoretical guidance for energy saving and consumption reduction in the actual production process.The parameters of the model library built in the process simulation software are used to simulate the production process of DMC,and the calculation results are quite different from the actual production data and experimental data.Therefore,first of all,the kinetic model,thermodynamic model and binary interaction parameters of the reaction and separation process of this process are modeled and optimized.According to the characteristics of the material system in the process,the UNIQUAC-RK equation is selected as the thermodynamic model of the simulation calculation,and the experimental data in the literature are used to fit the parameters of the material interaction.The error between the fitting results and the experimental data is within 2%.For the reaction involved in the process,the appropriate kinetic equation is selected to describe the process.The process parameters of the basic process were optimized by Aspen Plus simulation.The conversion rate of PC was 98.5%.DMC products with purity of 99.7% and PG by-products with purity of 99.7% were obtained.In order to reduce the energy consumption,the thermal integration of the process is carried out.Compared with the basic process,TAC is reduced by 35.32%.In order to further reduce the energy consumption and solve the problem of over temperature in the distillation tower and vacuum distillation tower,an improved process is proposed.To reduce energy consumption,the pressure of high-pressure tower is raised to 18 bar so that the material flow on the top of the tower is directly returned to the reactive distillation tower for reaction,and then the atmospheric tower in the basic process is removed to reduce the use of low-pressure steam.To solve the problem of over temperature in the tower bottom,the boiling temperature at the bottom of the tower is lowered by reducing the recovery rate at the top of the stripper.The side stream of PG product with purity of 99% is withdrawed for the vacuum distillation tower,and then the top stream of the vacuum distillation tower is returned to the stripper to recover methanol.After these improvements,the cost of utility is decreased by 27.90% than the basic process.The bottom temperature of the stripper was 148.2 ? and vacuum distillation tower was 148.6 ?both were lower than the temperature limit of 150 ?.Then,the heat integration of the process is carried out so that the latent heat of condensation on the top of the high-pressure tower and the vacuum distillation tower is used reasonably,which saves a lot of heating steam.The utility cost is reduced by 42.72%,and the TAC is reduced by 39.76%.In order to ensure the operation stability of the process,the dynamic control of the high-pressure tower was studied,and the dynamic behavior under different control schemes was evaluated.Based on the analysis of the cost of heat integration process,the cost of medium pressure steam accounts for 83.35% of the total annual cost.The middle reboiler flash heat pump distillation process is proposed by adding an intermediate reboiler in the stripping section of the high-pressure tower and using the steam from the top of the tower as the heat source,so that the consumption of medium pressure steam at the bottom of the tower can be reduced.After the thermal integration of this process,the consumption of medium pressure steam can be reduced by 5273.27 kw compared with the improved thermal integration process.Finally,the economy of the three kinds of heat integration processes above is compared.The TAC of the heat integration improved process and the heat pump process is 33.85% and 37.85% respectively less than the basic heat integration process.