Monomeric Products Formed from the Lignin of Sugi Wood During Alcohol Sulfite Pulping

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Abstract
Isopropanol bisulfite treatment of sugi (Cryptomeria japonica D. Don) MWL yielded a significant amount of lipophilic low-molecular-weight products as well as water-soluble high-molecular-weight lignin whereas with an aqueous bisulfite treatment a very small amount of lipophilic products was formed and about half of the MWL was changed to insoluble and probably condensed products. Seven monomeric and one dimeric lignin degradation products as well as two carbohydrate-derived products were found in the spent liquor from isopropanol bisulfite pulping of sugi wood of which eugenol and isoeugenol were the major products. After cooking for 50–100 minutes at 165°C, the combined yield of these two products reached a maximum of 4.5% based on lignin, which is ten times as high as the yield of a phenolic fraction previously obtained from aqueous bisulfite pulping of Pinus radiata. Formation of the other products such as stilbene and coniferaldehyde increased gradually after 100 minutes and the combined yield was less than 0.5%. The high yield of eugenol and isoeugenol as byproducts may increase the viability of the alcohol sulfite pulping process.