Preparation and evaluation of dispersants for gypsum from acid hydrolysis lignin

摘要

We investigated the chemical conversion of guaiacyl sulfuric acid lignin (SAL), one of the acid hydrolysis lignins, into water-soluble sulfonated products with high dispersibitity. At first, SAL was phenolated (P-SAL) to enhance the solubility and reactivity. Sulfonated products were prepared from P-SAL by three methods: hydroxymethylation followed by neutral sulfonation (two-step method), sulfomethylation with sodium hydroxymethylsulfonate (one-step method) and arylsulfonation with chlorosulfonic acid. These three methods yielded water-soluble sulfonated preparations. The gel filtration curves and sulfur contents suggested that the products obtained by the two-step method have an abundance of higher molecular weight sulfonates and that the products by the one-step method have similar properties in average molecular weight and in their sulfonate group contents to those of commercial lignosulfonates. Among arylsulfonation products, the molecular weight tended to be higher with the increase of reaction temperature. This is probably due to the reaction intermediate with sulfonyl chloride groups (-SO_2Cl) formed by chlorosulfonation with chlorosulfonic acid participate in the condensation reaction between other aromatic nuclei. We investigated the dispersibility for gypsum paste of prepared sulfonate products. Surprisingly, all products possessed 30-70% higher dispersibility than the commercial lignosulfonate. The results of gel chromatography and elemental analysis suggested that the higher molecular weights and sulfur contents of the preparations increased their ability.