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.

Comparison of Pretreatment Methods for Production of Ethanol from Sugarcane Bagasse

“…The content of lignin decreased sharply from 21.12% to 5.54%, and a preferable amount of glucan increased from 50.74% to 62.59% when 1.5 mL of GL/g-DS was applied during GL-Ethanol pretreatment with the use of anthraquinone (AQ) (1%, w/w), better than the two steam explosion pretreatment methods. Previous studies have shown that AQ can be used in soda pulping processes to improve delignification and reduce carbohydrate decomposition (Jiménez et al 2009;Kanungo et al 2011). Approximately 74% of active lignin could be recovered from the GL-Ethanol pretreatment.…”

Trapping of p-Coumaryl and Coniferyl Alcohol during Soda–Anthraquinone Treatment: A Means of Estimating Uncondensed β-O-4 Structures in Native Lignin

“…1 Products expected from the condensation between EG and sinapyl alcohol were not observed. 2 There was evidence from the prior data to suggest a positive correlation between the concentration of uncondensed guaiacyl A rings (as defined in Figure 1) and the extent of SAQ delignification. 11 It is known that most of the syringyl rings (∼90%) in hardwood lignin are uncondensed.…”

“…2,10 The prior data also suggested that uncondensed β-O-4 structures in sugar maple (Acer saccharum) and three eucalypti were cleaved at a high rate during SAQ cooking at 165 °C. 2,11 Also, EG appeared to trap coniferyl alcohol and its transformation products, vinylguaicol and isoeugenol, to form dimers 1−3 (Figure 2) at high yields. 2 The reactions schemes for the transformation of coniferyl alcohol (CA) to vinylguaicol (VG) and isoeugenol (IE) are in the literature.…”

“…In alkaline pulping of biomass to generate papermaking fibers, the β-O-4 bond connecting uncondensed aromatic rings is known to be cleaved at a relatively high rate. 1,2 The bond is also labile during thermochemical treatments of lignin for chemical and fuel syntheses. 3,4 An uncondensed aromatic ring is defined as one not containing a C−C bond at any ring position except for C-1 (side chain) nor connected to another C 9 unit by a diaryl ether linkage.…”

“…2,11 Also, EG appeared to trap coniferyl alcohol and its transformation products, vinylguaicol and isoeugenol, to form dimers 1−3 (Figure 2) at high yields. 2 The reactions schemes for the transformation of coniferyl alcohol (CA) to vinylguaicol (VG) and isoeugenol (IE) are in the literature. 1 Products expected from the condensation between EG and sinapyl alcohol were not observed.…”