Soda/AQ Pulping of a Hardwood with Trapping of the Generated Coniferyl Alcohol

Abstract

Coniferyl alcohol is generated from the cleavage of β-O-4 bonds during alkaline pulping of hardwoods and softwoods. Once formed, some of the coniferyl alcohol (CA) is transformed into vinylguaiacol (VG) and isoeugenol (IE). All three of these compounds (CA, VG, and IE) can rearrange to quinone methides (QMs) under alkaline conditions and become involved in condensation reactions with lignin and carbohydrate moieties. The aim of this investigation was to see if ethylguaiacol (EG) addition to soda-AQ (SAQ) pulping systems would lead to its reaction with the QMs from CA, VG, and IE to form dimers that are unreactive towards further condensation. Sugar maple wood meal was delignified by the SAQ process with EG added at 5.0 wt% on wood meal. Three dimers were detected in the pulping effluent and identified as a combination of EG with CA, VG, and IE. The total yield of the three dimers corresponded to ∼80% of the estimated CA that would have been generated. Conventional kraft, SAQ, and SAQ+EG pulping of the maple chips were then performed. The bleachability of the SAQ+EG pulp was significantly improved as compared to the SAQ pulp and it was estimated to be superior to the kraft pulp as well.