Study On Steady-state Design And Dynamic Control Of Separation Of Coal-to-ethylene Glycol By-products By Dividing Wall Column

Dimethyl carbonate（DMC）-methanol azeotrope is the main component of crude DMC,the by-product of coal-to-ethylene glycol.Because crude DMC contains various impurities and azeotropes,it is difficult to obtain high-purity products by ordinary distillation.As an important organic synthesis intermediate,DMC is widely used and is a green chemical raw material that meets the requirements of the modern"clean process".The separation of crude DMC can effectively improve the economic benefits of coal-to-ethylene glycol.For the separation of crude DMC,the methylal and methyl formate are removed with a pre-separation distillation column after dehydration,and then methanol-dimethyl carbonate azeotrope with a amount of ethanol are separated by a traditional extractive distillation column and extractive dividing wall column.In this paper,the steady-state design and dynamic control of crude DMC separation process are studied by using chemical process simulation software Aspen Plus and dynamic process simulation software Aspen Plus Dynamics.The optimal operating conditions and design parameters are obtained by optimizing the sensitivity analysis and the minimum annual total cost value as the objective function,while the thermal integration design of the separation process is carried out.Then,on the basis of the steady-state simulation design,the dynamic control of the extractive dividing wall column was studied and the feed flow disturbance was added for testing.The main conclusions are as follows:（1）Aspen Plus software is used in the Sensitivity analysis module to calculate and optimize extractive dividing wall column and extractive distillation column,and optimize the process design parameters in the steady-state process,which is on the basis of satisfying the purity of the target product.The obtained product purity DMC is 99.95%,methanol is 99.5%,and the recovery rate all reaches 99%.The theoretical plate number of the extractive distillation column is 42,the theoretical plate number of the rectification recovery column is18,the ratio of the feed position to the theoretical plate number is about 0.71,and the ratio of the extraction agent feed position to the theoretical plate number is about 0.29.At the same time,it is obtained that the theoretical plate number of the main column of the next-wall extractive distillation column is 28,the theoretical plate number of the auxiliary column is 9,the solvent ratio is 0.4～0.45,and the ratio of the fresh material feeding position to the theoretical plate number is 0.5～0.53,The ratio of the extraction agent feeding position to the number of theoretical plates is 0.15,and the optimal gas phase distribution ratio is 0.7～0.75.The total annual cost of the extractive distillation column is 0.89×10⁶$,the total annual cost of the next-wall extractive distillation tower is 0.606×10⁶$,the TAC can be saved by 31.91%,the energy consumption of the reboiler can be saved by 30.36%,and the energy consumption of the condenser can be saved by 34.51%,the CO₂ emissions were saved by 31.13%.（2）With the goal of energy saving,the thermal integration design of the crude DMC separation process is carried out,and the heat exchange between the bottom material of the pre-separation tower and the top material of the auxiliary tower of the extractive dividing wall column can save the energy consumption of the reboiler by 425.73k W,and the energy saving efficiency was 18.9%.（3）Three control structures are designed for the dynamic control of the extractive dividing wall column.The feed flow is set to±10%and±20%of the feed disturbance,and the response curve is analyzed.It is found that the third control structure is the improved one.The gas phase distribution control structure can reach steady state faster and with less fluctuation.