Copolymerization Kinetics of Itaconic Acid and Acrylamide for the Application of Flocculants in Wastewater Treatment

Abstract

The objective of this thesis was to identify and evaluate a replacement for acrylic acid in the production of anionic polymer flocculants, which are used for treating inorganic contaminants such as silts and clays in wastewater. The replacement monomer that was investigated was itaconic acid (IA), which is produced from the fermentation of sugars instead of through petroleum-derived products. A design framework [1] was employed to determine whether itaconic acid could be utilized in the development of novel polymeric materials for the wastewater treatment industry.

The poly(itaconic acid-co-acrylamide) samples were successfully synthesized via aqueous solution polymerization using free radical polymerization. Design of experiments using the error-in-variables model [2] was employed to determine which comonomer ratios would provide the most information for reactivity ratio estimation. However, due to experimental challenges, additional comonomer ratios between 10 and 50 mol% itaconic acid were also tested. These polymer samples were then characterized using gravimetric analysis for conversion determination, elemental analysis for cumulative copolymer composition, gel permeation chromatography for molecular weight distribution and weight-average molecular weights, and zeta potential for net surface charge. Reactivity ratios were estimated using both the instantaneous and cumulative error-in-variables models, with the composition determined through elemental analysis. The cumulative reactivity ratios were found to be 1.4577 and 0.2914 for itaconic acid and acrylamide, respectively. These followed a similar trend to the literature [3, 4], which showed that itaconic acid has a reactivity ratio > 1 and acrylamide has a reactivity ratio < 1 for this copolymer system. In the current work, only two feed compositions (10 mol% and 20 mol% IA) yielded enough data to be used in reactivity ratio estimation; this limits the amount of information that can be gained about this copolymer system from the reactivity ratio estimates.

The highest feed fraction of itaconic acid to be successfully polymerized under the specific experimental parameters was 20 mol% itaconic acid (with the balance acrylamide), which translated to 35 mol% cumulative copolymer composition in the polymer product. A maximum weight-average molecular weight of 706 981 g/mol was achieved for this formulation at a conversion of 54.8 mass percent, which had a corresponding zeta potential of -31 mV. These itaconic acid / acrylamide copolymer samples were also compared to commercial anionic flocculant samples, which were tested to provide benchmark values for the novel polymer flocculants. The commercial samples all had weight-average molecular weights above 10 million g/mol and zeta potentials above -100 mV. These values are much larger than those of the novel itaconic acid and acrylamide copolymers, meaning there is still room for improvement of these new polymer flocculants. Recommendations for future work include investigating emulsion polymerization techniques to eliminate itaconic acid solubility challenges, and increasing the total monomer concentration. This could help drive the molecular weight averages closer to the commercial benchmarks as well as provide an easier scale-up, since emulsion polymerization is used more often in the industrial production of polymer flocculants. This research will help further the development of new climate-friendly flocculants that can be tailored to specific contaminants.