A study aimed at understanding the AQ/polysulfide synergistic effect in alkaline pulping

Abstract When polysulfide (PS) and anthraquinone (AQ) are employed together during alkaline pulping, the yield gain and the extent of delignification during pulping are more than expected based on simple additive effects. The reactions of two lignin model compounds were studied in an attempt to better understand the PS/AQ synergism chemistry. Diagnostic products were not observed with an “electron detector” compound; instead, it appears that PS preferentially oxidized the compound. Reactions of a “clock” compound indicated that PS could not reduce AQ to anthrahydroquinone (AHQ) at 140°C. However, the data indicated that β-aryl ether fragmentation efficiencies for PS were better than sodium sulfide, the lignin active reagent in kraft pulping. In addition, AQ was observed to fragment the clock model by nonquinone methide chemistry.