Recycling Process Design Of 5000 Tons/Year Of N-methylpyrrolidone In Polyphenylene Sulfide Production

Due to its good chemical stability,high thermal stability,high boiling point,low viscosity,no corrosion,low toxicity,low volatility and biodegradability,N-methylpyrrolidone(NMP)is widely used in petrochemical extractants and coatings,pesticides and so on.Not only the NMP is widely used as a solvent in the process of the synthesis of polyphenylene sulfide(PPS)by sodium sulfide method,but also the price of NMP is expensive,relatively.Therefore,it is particularly important to study the recovery process of NMP.In this paper,the experimental study was conducted on the plugging of the distillation tower and the problem of low NMP recovery due to decomposition of NMP in an alkaline environment.These problems exist in the current NMP recycling process.According to the analysis of the possible components in the filtrate after PPS polycondensation reaction and the experimental data,this article adopted the method of water washing to remove the PPS oligomer in the filtrate,thereby it solved the plugging of phenomenon of the distillation tower blocks during the process of recycling of NMP by distillation;Then,hydrochloric acid(1 mol/L)was added to the filtrate from which the PPS oligomer was removed to adjust the mixture to a neutral environment,and NMP was recovered by vacuum distillation,which effectively reduced the decomposition of NMP.The recovery rate of NMP was greatly improved by moisture detector and gas chromatography(GC)after the process improving.The specific process is as follows: First,the PPS oligomer in the filtrate after the PPS polycondensation reaction was removed by the method of water washing,and then removal of water from feed solution that pH of the filtrate after removal of the PPS oligomer was adjusted to neutral by vacuum distillation.The solvent NMP was left in the kettle liquid and the auxiliary LiCl can also be recovered and recycled.This process does not require the NMP to be distilled out,but needs to remove the water in the treated liquid,and also recycles the catalyzer LiCl in the feed liquid,thereby greatly reducing the production cost of PPS.In this work,the recovery process of NMP was simulated and analyzed by Aspen Plus software.The simulation data of the production liquid(containing 95.44% NMP)produced in 5000 tons PPS industrial production was simulated at the start time of 300 days/year.Under the working conditions,the equipment in the NMP recovery process was calculated and selected,and the main equipment distillation tower was calculated and verified in details.The detailed technical and economic evaluation of the entire recycling process was carried out,and the production cost was reduced on the basis of ensuring the safety of production.The flow chart of the NMP recycling process and the workshop layout are drawn through the software Auto CAD.