Distillation Sequence Optimization For Comprehensive Utilization Of C4 Mixture From MTBE Plant

Catalytic cracking and steam cracking processs produce a large amount of mixture by product C4.Isobutylene is a high value-added intermediate widely used in the preparation of butyl rubber,polyisobutylene,methyl tert-butyl ether,methacrylonitrile,etc.Heyungroup C₄comprehensive utilization device mainly includes three units:MTBE synthesis,C4 separation and butene isomerization.With MTBE as the main product,n-butene is converted to isobutylene by isomerization reaction,and the utilization degree of C₄ is improved.Due to the low relative volatility of n-butene and n-butane,the Hexun group uses MEK+NFM solvent system for extraction and separation.Even so,there are still complex processes and high energy consumption in the C₄ separation process.In the thesis,the synergistic coupling characteristics of extraction separation and isomerization process were studied,improves the C4 comprehensive utilization device from the perspective of separation sequence,and uses Aspen Plus chemical process simulation software to optimize the improvement process and economic feasibility analysis.First,the simulation process,the main process of the Heyun Group's C4 comprehensive utilization device,was established in the Aspen Plus software platform.The simulation results of key operating units?extractive distillation,isomerization,MTBE synthesis?were compared with actual production data.The relative error of n-butane product purity was 1.46%,and the relative error of butene product purity was 0.76%.The relative error of MTBE product purity is 0.01%.The simulation results show that the simulation process of the C₄ comprehensive utilization device established in this study has high accuracy,which provides a good simulation tool for the improvement and optimization of the device.On the basis of Aspen Plus process simulation,the distillation separation sequence used in the existing C₄ comprehensive utilization device was analyzed.The existing distillation separation sequences first remove isobutane and n-butane from raw materials to obtain high concentration butene,then isomerize butene into isobutene,isobutene etherify to generate MTBE,and the unreacted butene is used as the separation raw material again.High olefin content in the separation raw materials requires large extraction dose and high energy consumption.Butane product concentration is 85%and butene loss result in the low butene utilization rate.To solve this problem,the optimization process was proposed.Firstly,the butene in the raw material was transformed into isobutene,which was further etherified into MTBE,and then the unreacted butene mixture was extracted and distilled.The process parameters were optimized by Aspen Plus software.The content of butene in the extractive distillation materials decreased from 71.3%to 52.97%,and the demand for extraction agent decreased from 340 t/h to 240 t/h.The concentration of butane was increased from 29.22%to 45.15%,and the purity index of butane products was increased from 85%to 95%,which reduced the loss of butene and increased the output of MTBE products by 3.5%.The 1.2 MPaG steam energy consumption of the process was reduced from 62 t/h to 52 t/h.As the purity of butene in the reaction system decreased,the isomerization and load of MTBE process increased.The flow rate of isobutene product increased from 41.79 t/h to 51.14 t/h.During the reforming process 4 tons of isomerization catalyst was added,and the investment cost was 7.73 million yuan.The actual increase in income was 28.32 million yuan per year after commissioning.Compared with the original process,the optimized process has been optimized in terms of material loss and energy consumption,with less process change and transformation,obvious benefits obtained,and the process optimization is feasible.