The Study On Multi-objective Collaborative Optimization Of Continuous Polymerization Grade Transition

Change with diversiform market demand of the polymer,since several grades of polymer need to be generated in one continuous polymerization reactor,the grade transition operation occurs frequently and thus it is desirable to establish a flexible operation strategy.The frequent grade transition operation,inevitably,results in the production of considerable amount of off-specification polymer,decrease of production time and reduction of production efficiency.Therefore,the optimization of polymer grade transition becomes an important research field in the polymerization industry.We study the optimization of continuous polymerization grade transition,propose multi-objective collaborative optimization and perform related research:1.We study the grade transition operation of the styrene polymerization in a pilot continuous stirred tank reactor(CSTR)and establish the polymerization process model based on polymerization mechanism,mass conservation and energy conservation.We calculate the polymer molecular as the quality indexes by the method of moments,solve the dynamic optimization problem with the segmented optimization strategy,control variable parameterization and Ronge-Kutta method.2.Polymerization grade transition operation need to simultaneously satisfy multiple requirements e.g.safe operation,short transition time,low operating cost and so on,and therefore it is a multi-objective optimization problem with constraints.Result from the limitations of traditional weighting methods,the constrained multi-objective particle swarm optimization algorithm(CMOPSO)presented is used to solve this multi-objective optimization problem.Considered about Multi-objective handling mechanism and Constraints handling mechanism,on the one hand it ensures the good distribution of Pareto solution set and prevents algorithms from local optimum,on the other hand,it enhances target searching ability of the algorithm and improve the efficiency of the algorithm without any increase in the algorithm's complexity.We selecte multi-objective test functions with different features to prove the effectiveness and applicability of the proposed algorithm.3.In a pilot CSTR of styrene polymerization,we establish a multi-objective function on the polymer transition time and transition materials to address the grade transition economic collaboration.The weights of quality indicators function are ensured by biogeography-based optimization(BBO).By adding endpoint constraints to the quality indexes of polystyrene,we propose two different schemes,one with the endpoint constraints and the other without endpoint constraints.Calculated by the CMOPSO,the simulation results confirm that the optimization method can reduce fluctuations of variables,reduce the raw materials consumption and shorten the transition time.4.We describe and analyzed the slurry process polymerization grade transition of high density polyethylene in serial configuration,propose the quality collaborative objective functions based on the instantaneous index and cumulative index of quality.The introduction of the path constraints on the manipulated variables can ensure the stability of the operating variables in the reaction process.Two strategies calculated by CMOPSO are proposed,one with the path constraints and the other without path constraints.We propose the indexes based on the instantaneous rate of operating variables change to evaluate the Pareto solution set,it can guide the choice of the decision maker.The simulation results confirm the effectiveness of the optimization method.