Model-Based Optimization of Semibatch Emulsion Polymerization of Styrene

Emulsion polymerization reactors usually operate under starved conditions to better control the polymer properties and keep a safe operation. The main drawback is the low productivity obtained. In this work, we optimize offline the flow rates for the semibatch emulsion polymerization of styrene under starved conditions and keeping the reaction under diffusion limitation in order to maximize the reaction rate. To achieve this, we impose the maximal concentration of monomer in the particles as a path constraint. This results in a higher reaction rate compared to starved conditions close to saturation. At the same time, it enables safe operation by avoiding accumulation of monomer that may react hazardously at the end of the reaction, once the gel effect occurs. Therefore, we show that high productivity can be obtained by operating the reactor under starved conditions. We compare the optimal recipe under diffusion limitations with the benchmark of keeping the concentration of monomer in the polymer particles close to saturation and with constant feeding flow rates. We find consistent improvement of both the average reaction rate and the amount of polymer produced in the optimized strategy.

乳液聚合（emulsion polymerization）反应器通常在饥饿态工况（starved conditions）下运行，以更好地调控聚合物性能并保障安全操作。其主要弊端为所得生产率偏低。本研究针对饥饿态工况下的半间歇苯乙烯乳液聚合过程，以最大化反应速率为目标，离线优化进料流量，并将反应维持在扩散限制（diffusion limitation）条件下。为达成该目标，我们将颗粒内单体最大浓度作为路径约束。与接近饱和的饥饿态工况相比，该策略可获得更高的反应速率；同时，可避免反应末期凝胶效应（gel effect）发生时因单体过度积累引发的危险反应，从而保障操作安全。由此可见，在饥饿态工况下运行反应器同样可实现高生产率。我们将扩散限制条件下的最优配方，与维持聚合物颗粒内单体浓度接近饱和且采用恒定进料流速的基准工况进行对比，结果显示优化策略在平均反应速率与聚合物总产量两方面均实现了显著提升。