(370b) A Comprehensive Kinetic Investigation of the Inverse Suspension Copolymerization of Acrylamide: Theoretical and Experimental Studies

Due to their excellent properties, polyacrylamide products are suitable in several applications like water treatment, oil-field and mining as well as paper chemicals. High molecular-weight homopolymers of acrylamide are used as pushing fluids in tertiary oil recovery, as drag reduction agents and as drilling fluids. Copolymers with various cationic monomers such as diallyldimethylammonium chloride (DADMAC) are used for fines retention in paper making, as flocculants, and, in general, wherever aqueous solid liquid separations are required.

Since acrylamide is solid at normal reaction temperatures it is usually polymerized in aqueous solutions. The polymerization of acrylamide is characterized by a very high polymerization heat (ΔH_p = 19.5 kcal/mo1) and the formation of a highly viscous reaction medium. Moreover, the polymerization has to be carried out in pH neutral solutions, at moderate temperatures (i.e., less than 70°C, to avoid intermolecular imidization. Thus, in industry the polymerization of acrylamide is commonly carried out in a hetero-phase process (e.g. inverse-suspension or inverse-emulsion). The inverse suspension process involves the emulsification of a water-soluble monomer, in a continuous organic phase. A water-in-oil steric stabilizer is used and the polymerization is carried out in the presence of either a water- or an oil-soluble initiator. The resulting (micro-) suspensions exhibit lower viscosities and, thus,   higher heat removal rates (due to the presence of the continuous organic phase). As a result, the polymerization can be carried out at higher monomer concentrations than the solution process.

In the present work, a comprehensive theoretical and experimental kinetic investigation of the inverse suspension copolymerization of acrylamide is presented. Experimental kinetic studies, including both the homo-polymerization of acrylamide and its copolymerization with sodium acrylate or DADMAC at various compositions, were carried out in a 1 Liter jacketed batch reactor. Paraffin oil was employed as the oil phase and different surfactants were used in order to optimize the HLB of the surfactant blend.

A comprehensive mathematical model was developed based on a detailed kinetic mechanism to simulate the dynamic evolution of the monomer conversion and molecular weight developments (i.e., M_n, M_w, CC, etc.). The proposed kinetic mechanism of the acrylamide copolymerization comprises a series of elementary reaction steps, including initiator decomposition, chain initiation, propagation, chain transfer to monomer, termination by disproportionation and reaction with terminal double bond. The key kinetic rate constants were estimated from a series of solution polymerization experiments. The developed comprehensive polymerization model has been evaluated against experimental data for both homo- and co-polymerizations of acrylamide. It is shown that model predictions are in good agreement with experimental data (both reported in the open literature and obtained in the present study).

Acknowledgment

This research has been financed by the European Commission under the FP7-NMP-2011-SMALL-5 Project (OPTICO G.A. No 280813).