Lignin degradation in neutral sulphite pulping with anthraquinone catalysis

Abstract

Neutral sulphite pulping cannot be utilized for producing chemical pulp, due to its insufficient lignin removal. Lignin is more efficiently degraded with the addition of anthraquinone. This catalyst enables the neutral sulphite process to produce a high quality pulp with higher yields than conventional kraft. However, anthraquinone is not currently used, due to its carcinogenicity. Although alternatives have been investigated, neither viable substitutes nor the details of the catalytic mechanism have been found.

This study aims at identifying key mechanisms of anthraquinone in neutral sulphite pulping promoting delignification. Several isolation methods were tested, and resin exchange was most effective in isolating lignosulphonates from the spent liquor. Anthraquinone was shown to modify certain lignin structures, such as β-O-4 ethers and resinol, enabling a more efficient sulphonation of lignin. These findings reveal the importance of sulphonation in removing larger lignin molecules over degradation. Targeted research into catalysts for high-yield neutral sulphite pulping should focus on exhibiting the same effect on these structures.