Synthesis of a novel amphoteric copolymer and its application as a dispersant for coal water slurry preparation

In this work, a novel amphoteric copolymer was synthesized via free radical polymerization, named Poly(sodium p-styrenesulfonate–co-acrylic acid-co-diallyldimethylammonium chloride) (P(SS-co-AA-co-DMDAAC)). Afterwards, P(SS-co-AA-co-DMDAAC) was explored for use as a dispersant in coal water slurry (CWS) preparation. The structure of P(SS-co-AA-co-DMDAAC) was verified by Fourier transform infrared spectroscopy (FTIR) and Nuclear magnetic resonance (NMR). The synthetic conditions were optimized as the feed ratio of AA to SS was 1:1 (for Yulin coal) or 1.5:1 (for Yili coal), and DMDAAC dosage was 4.0 wt% (for Yulin coal) and 6.0 wt% (for Yili coal) toward total monomers. The performances of P(SS-co-AA-co-DMDAAC) as a dispersant for CWS were evaluated by various technologies, such as apparent viscosity, Zeta potential, static stability and contact angle measurements. The results revealed that the optimized dosage of P(SS-co-AA-co-DMDAAC) in CWS preparation was 0.3 wt% and 0.4 wt% for Yulin coal and Yili coal respectively. In this optimum condition, CWS prepared using P(SS-co-AA-co-DMDAAC) as dispersant showed a typical shear thinning behavior and excellent stability, which are desired in industry. The rheological models also confirmed the pseudo-plastic characteristics of CWS. Finally, as compared to the widespread used anionic dispersant Poly(sodium p-styrenesulfonate) (PSS), P(SS-co-AA-co-DMDAAC) developed in this work exhibited better slurry making performance. Introduction of cationic functional groups promoted the adsorption of dispersant, which further enhanced the electrostatic repulsion among coal particles. Accordingly, the viscosity of CWS decreased and static stability enhanced.