Study On Melting Crystallization Separation Process And Simulation Of Non Phosgene Isocyanate Carbamate Intermediate And Isocynante Product

In the process of synthesizing isocyanate by non phosgene pyrolysis,the key problem is to separate isocyanate products and carbamate intermediates.In the traditional separation of MDI isomers,high vacuum distillation was used to separate two substances.The traditional separation of 4,4’-diphenylmethane diisocyanate（4,4’-MDI）/2,4’-diphenylmethane diisocyanate（2,4’-MDI）system adopts high vacuum distillation,which has important problems such as high number of trays and large pressure drop in the tower body,resulting in high loss rate of 4,4’-MDI.In addition,as the traditional separation technology of Ethyl phenylmethylene dicarbamate（XDC）/Ethyl carbamate（EC）system,distillation separation has the problem of EC crystallization at the top outlet of the distillation column.Melt crystallization technology has great development potential with the advantages of solvent-free participation,low energy consumption and environmental friendliness.Therefore,this paper studies the melt crystallization separation process of 4,4’-MDI/2,4’-MDI and XDC/EC systems.The specific research contents are as follows:（1）The separation of 4,4’-MDI/2,4’-MDI system by melt crystallization was studied.Firstly,the phase diagram of 4,4’-MDI/2,4’-MDI system was measured by differential scanning calorimetry,which showed that the system was a low eutectic system.Secondly,the key parameters in the crystallization and sweating process were optimized by dynamic falling film melt crystallization method.The optimization results showed that under the optimal conditions,the purity of 4,4’-MDI in the product was 99.3%and the yield was 50.8%.While ensuring the product quality,the technical problems existing in the traditional process were solved.（2）The separation and purification of 4,4’-MDI/2,4’-MDI system by melt crystallization technology was simulated by Material Studio software.The structures of 4,4’-MDI and 2,4’-MDI molecules were analyzed from the perspective of population analysis.Secondly,the solid-liquid equilibrium of MDI isomer mixed amorphous cell was studied by molecular dynamics.The separation phenomenon was successfully observed by Radial distribution function（RDF）.The results of orientation correlation function analysis showed that compared with2,4’-MDI,4,4’-MDI preferentially grew on the crystal surface to form a stable crystal structure,and the main force in the crystal structure of 4,4’-MDI was the interaction between different molecular isocyanates.（3）The separation of XDC/EC system by static melt crystallization technology was studied.Firstly,the phase diagram of the system was measured by differential scanning calorimetry,and the system was determined as low eutectic system;The basic physical properties of XDC/EC system were tested.The results showed that the temperature of crystallization experiment should be kept below100℃and the time should be controlled within 7 h.Finally,after secondary crystallization separation,the purity of XDC in the product reaches 99.2%,which meets the requirements of industrial production.The separation performance K_Cand crystal stacking structure parameters are adoptedτandΦto describe the separation process and promote the understanding of the melting crystallization separation process.