H3PW12O40/ZrO2 and 1-Butyl-3-methylimidazolium Chloride: A Double-Effect Catalyst for the Degradation of Alkali Lignin.

Abstract

Alkali lignin is a component of the waste black liquor produced by the paper-making industry that is difficult to degrade. In recent years, the biological activities of lignin, such as free-radical scavenging and antioxidant capacity, have received increasing attention. Here, we prepared H3PW12O40/ZrO2 and used this catalyst together with the ionic liquid 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) as a double-effect catalyst for the degradation of alkali lignin. Single-factor and orthogonal tests showed that the best degradation conditions were as follows: reaction time, 2 h; reaction temperature, 100 °C; mass ratio of H3PW12O40/ZrO2 to lignin, 1:4; and substrate concentration, 2.5%. The phenolic hydroxyl group content of the lignin degradation product increased by 231.2% and the total hydroxyl group content increased by 337.1% when the double-effect catalyst was used rather than [BMIM]Cl alone. Analysis by gel permeation chromatography showed that both the weight-average molecular weight and the number-average molecular weight of the product were reduced and that the lignin was degraded into small-molecular-weight compounds by the macromolecule. The product after the catalytic degradation of lignin showed a markedly increased antioxidant capacity, which was similar to that of the commercial antioxidant, 2,6-ditert-butyl-4-methylphenol. The study opens up a new direction for the better utilization of lignin.