Dealkaline lignin–The waste from the pulp and paper industry as acid catalyst in biorefinery

Abstract

Dealkaline lignin, a by-product from the pulp and paper industry, can be transformed into lignosulfonic acid catalysts with a simple ion exchange method. The catalyst exhibited much superior catalytic performance to the commercial resin catalyst for the conversion of furfuryl alcohol to ethyl levulinate and fructose to 5-hydroxymethylfurfural (yield: 97% over lignosulfonic acid catalyst versus 20% over the commercial resin catalyst under the similar reaction conditions). The excellent catalytic activity was due to the synergistic effects of carboxyl, hydroxyl and sulfonic acid groups. The abundant carboxyl and hydroxyl groups in catalyst could form hydrogen bond in local area of SO3H sites with the oxygen-containing substrates, facilitating their acid-catalyzed reactions, but only in the aprotic solvents. In protic solvents, the substrate will preferably form hydrogen bond with the solvent but not lignosulfonic acid, and thus the lignosulfonic acid catalyst is more advantageous for catalyzing the acid catalyzed reactions in aprotic solvents.