Modeling of the Inhibition Mechanism of Acrylic Acid Polymerization

Inhibitors such as MEHQ (monomethyl ether hydroquinone) and PTZ (phenothiazine) are added to acrylic acid in the shipping and storage process to prevent its spontaneous polymerization. Dissolved oxygen is also an strong inhibitor, and its presence in the solution enhances the inhibition effects of MEHQ. In this work, we developed a comprehensive mathematic model for the inhibition of acrylic acid polymerization and simulated the inhibition effects of oxygen and MEHQ on the polymerization of acrylic acid in batch and semibatch processes. The key kinetic parameters were obtained from the literature or estimated from experimental data in the literature. The model was able to predict most of the effects of inhibitors. Although the literature data we used failed to predict the synergistic inhibition effects of oxygen and MEHQ, the model was able to predict the effects. Simulation results show that oxygen is a strong inhibitor in both batch and semibatch reactors and does not act as a retarder as expected. MEHQ has a much stronger effect on polydispersity than on polymerization rate, especially in a semibatch reactor. Thus, MEHQ can be used to narrow the molecular weight distribution (MWD) without compromising too much on the monomer conversion and weight average molecular weight.