Aromatic polyamide (PA) reverse-osmosis (RO) membranes have been the gold standard for seawater and brackish water purification for more than three decades. Thin-film composite (TFC) membranes of this class typically consist of a thin (~0.2 µm), highly-crosslinked film that is formed via the interfacial polymerization of trimesoyl chloride (TMC) with <i>m</i>-phenylenediamine (mPD) on a polysulfone ultrafiltration support. The DuPont Water Solutions RO Membrane R&D organization has recently developed a predictive tool that unites the underlying thermodynamic, kinetic, and diffusive processes governing PA formation via interfacial polymerization into a single, integrated model predicting how membrane yield, composition, and network structure are affected by recipe and process variables. However, key model parameters that describe the primary kinetics of PA formation–i.e., those reactions involving monomers and small oligomers–were not available from existing kinetic data. Rather than directly measuring various rate constants, a series of solution-phase model studies were designed that enabled estimation of reactivity ratios derived from observed product ratios for competition experiments run under pseudo first-order conditions. Application of these dimensionless reactivity ratios to the known rate constant for the reaction of TMC and mPD enabled determination of all relevant monomer–monomer and monomer–oligomer rate constants. This presentation will describe the evolution of this strategy in the broader context of development of the integrated membrane formation model.

Estimation of polyamide interfacial polymerization reactivity ratios via solution-phase model studies

2019 Fall National Meeting

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