Research On New Technology Of Battery-grade Dimethyl Carbonate Purification

Dimethyl carbonate(DMC)is widely used in lithium-ion battery electrolyte solvent for its excellent physical properties,such as good intermiscibility,low viscosity and high dielectric constant.Battery-grade DMC requires a concentration of DMC to be higher than 99.99%,and the content of moisture,methanol and ethanol to be less than 20ppm.At present,distillation technology is widely used to purify DMC to battery-level products,which need high energy consumption while the high content of impurities in the products seriously reduces the battery life.Based on DMC content system,we improve the quality of the product and make the content of moisture,methanol and ethanol to be less than 20ppm.On the other hand it also largely reduces the process energy consumption.According to the research results,the production line of 3500 tons/a is built.The main research content consists of the following aspects:(1)The basic physical properties date such as melting point,specific heat,crystallization heat of DMC and the thermal conductivity of the crystal layer were measured to provide data support for the research of crystallization process.(2)The mathematical model of heat conduction with a moving boundary has been adopted to simulate the static layer melt crystallization process.Integrating the effects of the temperature of the cooling fluid on solid-liquid interface,the analytical iterative method was adopted to solve the model.The calculated results fit well with experimental values.(3)The effects of falling film flow rate,the initial superheat of the feed liquid,the cooling rate,the final crystallization temperature,the sweating rate,the final sweating temperature and so on were systemically studied by a small test of DMC single-tube falling film crystallization process.Furthermore,the orthogonal experimental design method was applied to determine the optimal crystallization condition.The falling film flow rate is 0.0023m/s,superheat degree of DMC is 1K,the cold material was crystallized at 271.15K with cooling rate of 1.5 K/h and sweated at 277.65K with heating rate of 2 K/h.The result indicated that the purity of DMC reached to 99.993%with the yield of 59.68%,the content of moisture,methanol and ethanol are 18ppm,9ppm and lOppm.All of these research results provide basic data and the oretical guidance for the engineering magnification and industrialization design of the new process.(4)Combined with the advantages of falling film melt crystallization and distillation process,the crystallization-distillation coupling process was simulated to optimize the energy consumption and product quality.On this basis,the industrial design of the falling film crystallization-distillation coupling process was conducted.By comparing with the traditional distillation process,the result shows that the cost of new process is less than the old one for 57.88%.