Modeling And Optimization Of Batch Autoclave Bulk Propylene Polymerization Process

With the deepening of the domestic petrochemical integration process,the utilization of propylene has become the key to the benefits of refineries and petrochemicals.The basic brand of polypropylene market has become saturated,and there is still room for development in the polypropylene special product market,and the price is significantly better than the basic brands.Intermittent operation is adopted for the batch bulk polypropylene process,which can flexibly switch product scheme,and has a natural advantage in special polypropylene brands production compared to other continuous process processes.Moreover,the amount of the batch catalyst used is small,and a variety of high value-added polypropylene products can be produced.However,the process has poor stability of the product batch,so the process research on the process is of great significance.Based on the Aspen Polymer Plus platform,a batch bulk polypropylene process model was established,combined with industrial data fine-tuning reaction kinetic data to obtain a reactor model that can reflect the actual polymerization process.According to the characteristics of the process,the high-pressure propylene recovery and low-pressure propylene recovery process of propylene is modeled using modules such as flash tanks and condensers.The deviation between the simulation results and the actual scenario is less than 5%,which can be used to guide industrial actual production and model prediction.Based on the established model,the sensitivity analysis of the process parameters that may affect the product performance of the reaction process is carried out.The results show that the polymerization temperature and the amount of hydrogen added can significantly affect the molecular weight distribution of the polymerized product.As the polymerization temperature increases,the amount of hydrogen added increases.The weight average molecular weight decreased significantly;the heating time had little effect on the reaction parameters,the heating time increased,and the weight average molecular weight of the product increased slightly.The catalyst and reaction temperature can significantly accelerate the reaction rate and shorten the reaction time.According to the analysis of the influence of the process parameters on the polymerization products,the process of the polymerization process may be fluctuating.The main reason for the poor stability of the product batch is that the dissolved hydrogen in the high-pressure recovery propylene cannot be measured and the temperature is uncontrollable at the peak of the exothermic reaction.Aiming at the problem that the dissolved hydrogen in propylene can not be measured in high pressure recovery,a soft-reduction model of propylene concentration based on phase equilibrium is proposed.The propylene and hydrogen in the high-pressure recovery propylene storage tank are in phase equilibrium,and the dissolved hydrogen is calculated by the temperature and pressure of the storage tank.Improve the accuracy of hydrogen prediction concentration by 66.7%,and reduce the weight average molecular weight deviation of the brand during production by 80%.The root cause of the difficulty in controlling the constant temperature stage is that the design of the polymerization reactor is designed based on the empirical rule of average polymerization heat,and it is difficult to respond to the peak heat release and the problem that the heat transfer efficiency is lowered by the polypropylene particles in the later stage of the reaction.In order to solve the problem of heat removal in the reaction process,a design scheme based on the exothermic peak calculated by reaction model is proposed.Under the same working condition,the heat transfer area required for the design based on the exothermic peak calculated by reaction model is 108% more than the heat transfer area based on the average polymerization heat rule.,Aiming at the difficulty of heat removal in the existing polymerization reactor,the heat removal by propylene external circulation process was proposed.The gas phase external circulation process and the original jacket heat removal process were compared and analyzed.It is considered that the propylene gas phase external circulation process is more suitable for the efficient heat removal of this process.The process only increases the two devices of the gas phase condenser and the non-condensable gas compressor and the 0.12 KW·h/batch electric work,reducing the power consumption of the circulating water pump by 80.0%.