基于聚合物分子量分布的乙烯淤浆聚合工艺优化

分子量及分布是聚合物生产过程中极其重要的质量指标,但目前的技术水平并不能实现分子量及其分布的实时测量,基于反应机理的动态建模是实现其软测量的重要方法。以乙烯淤浆聚合工艺为研究对象,基于聚合机理,分别以聚合物的平均分子量和分子量分布为目标,以循环气中氢气乙烯比为决定变量,采用稳态优化方法求取聚合物生产的工艺条件。结果表明:以平均分子量为优化目标所得的结果与分析值的偏差较大,虽然聚合物的平均分子量符合要求,但聚合物的分子量分布曲线与所需产品的分子量分布曲线之间的最大误差可达0.092;而以分子量分布曲线为目标所得的最大误差只有0.069。因此,以分子量分布曲线作为目标的优化方法明显比常规的以平均分子量为目标的优化方法优越。

Optimization of ethylene slurry polymerization conditions based on molecular weight distribution

Molecular weight and its distribution are extremely important quality indices in the polymer production process,however real-time measurement of molecular weight and its distribution cannot be achieved.Dynamic modeling based on polymerization mechanism is an important method for implementing soft measurement.In this study, the polymerization conditions of the ethylene slurry polymerization plant (HDPE) were investigated based on polymerization mechanism, with polymer average molecular weight and its distribution curve as the target, the ratio of hydrogen to ethylene in recycle gas as the decision variable.The results showed large deviation between the simulation results with the average molecular weight as the optimizing target and those of plant analysis.Although the average molecular weight of the polymer could reach the desired quality, the maximum error between the molecular weight distribution curve from simulation and the desired polymer product could be up to 0.092.However, the maximum error was only 0.069 with the molecular weight distribution curve as the target.Therefore,the optimization method with the molecular weight distribution curve as the target is significantly superior to the conventional optimization method with average molecular weight as the target.