Abstract
The process of prehydrolysis followed by soda-anthraquinone (AQ) cooking and totally chlorine-free (TCF) bleaching with peroxymonosulfuric acid (Psa) was investigated to develop a biorefinery process. Eucalyptus globulus, showing a high syringaldehyde (Sa) to vanillin (Va) molar ratio after nitrobenzene oxidation, was utilized. Xylooligosaccharide yield in the prehydrolysate (PHL) obtained at 150 °C for 2.5 h reached 7.2% of wood weight, indicating 47% extraction of xylan. Furfural yields increased with acid catalytic dehydration of the PHL to 1.0–1.8% of wood weight; adding an earlier acid post-hydrolysis of the PHL to generate monomeric xylose enhanced furfural production to 4.0%. Soda-AQ cooking, a non-sulfur process affording simpler alkali lignin isolation than kraft cooking, was utilized. Active alkali dosage increment decreased both Sa to Va molar ratio (S/V ratio) and Sa and Va yields of dissolved lignin. Gel permeation chromatography indicated decreased or increased purified lignin weight-average molecular weight (Mw) upon increased active alkali dosage or prehydrolysis temperature, respectively (e.g., 150 to 170 °C at 18% alkali increased Mw 1653 to 2050). Chlorine dioxide (0.083% and 0.042% as active chlorine) inclusion during the 1st and 2nd Psa stages with Psa (0.2% and 0.1% as H2SO5 weight, respectively) improved final bleached pulp viscosity from 6.0 to 7.2 mPa s.
Highlights
In the biorefinery concept, it is important that cellulose, hemicellulose, and lignin are effectively separated from lignocellulosic raw materials; these three main biopolymers are converted to basic sources for other value-added materials, chemicals, and fuels
By increasing the AA dosage to 18%, we observed an improvement of α-cellulose content to 94.0% along with a small viscosity loss to 6.0 mPa s (Table 4 and Fig. 5). These results demonstrated that the combined process of prehydrolysis soda-AQ and totally chlorine-free (TCF) bleaching with sequence of O-peroxymonosulfuric acid treatment (Psa)-EpPsa-alkali extraction with hydrogen peroxide bleaching (Ep) requires some modification, especially an increment of viscosity to produce a high-quality Dissolving pulp (DP)
In this study, the yield of xylooligosaccharide in the PHL obtained by prehydrolysis at 150 °C for 2.5 h reached 7.2% based on wood weight, indicating that 47% of the xylan in the wood was extracted
Summary
It is important that cellulose, hemicellulose, and lignin are effectively separated from lignocellulosic raw materials; these three main biopolymers are converted to basic sources for other value-added materials, chemicals, and fuels. DP needs to be produced in a high-quality range, with a high degree of purity (> 94% α-cellulose), an acceptable level of viscosity (> 6.2 mPa s), and an extremely low lignin content (0.05%) [1]. Meeting such requirements renders the yield of the overall. The severity of the prehydrolysis conditions and an extent of hydrolytic cleavage of glycosidic bonds control the Salaghi et al J Wood Sci (2019) 65:10 remaining amount of partly hydrolyzed cellulose in the raw material residue and its final degree of polymerization [6]
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