Novel Process for Generating Cationic Lignin Based Flocculant

Kraft lignin is currently under-utilized since it is primarily used as fuel in pulping processes. However, it can be used as a raw material to prepare a functional polymer such as flocculant. A cationic lignin polymer was synthesized via graft polymerization of lignin and [2- (methacryloyloxy)­ethyl] trimethylammonium chloride (METAC) in an acidic environment (i.e., a heterogeneous system). The reaction, which was optimized under the conditions of pH 4.0, METAC/lignin ratio of 1.8 mol/mol, 3 h, 80 °C, 0.3 mol/L of lignin concentration, and 1.5 wt % of initiator dosage, generated a lignin-graft-PMETAC polymer having 2.93 mequiv/g charge density and 1.53 × 106 g/mol molecular weight. The lignin-graft-PMETAC polymer can be dissolved in water (at 10 g/L concentration) and a pH range of 0.5–13. The flocculation performance of the polymer was evaluated in a 0.25 wt % kaolin suspension using a particle dispersion analyzer, and the results demonstrated the superiority of the lignin-graft-PMETAC polymer to unmodified lignin and PMETAC. These results confirmed that lignin-graft-PMETAC polymer could replace PolyMETAC (i.e., PMETAC, a synthetic polymer) as a flocculant, which promotes the use of sustainable products in industry. This paper introduces a new process for inducing a cationic lignin-based flocculant.