Efficient Fractionation of Spruce by SO₂‐Ethanol‐Water Treatment: Closed Mass Balances for Carbohydrates and Sulfur

Abstract

SO(2)-ethanol-water (SEW) lignocellulosic fractionation has the potential to overcome the present techno-economic barriers that hinder the commercial implementation of renewable transportation fuel production. In this study, SEW fractionation of spruce wood chips is examined for its ability to separate the main wood components, hemicelluloses, lignin, and cellulose, and the potential to recover SO(2) and ethanol from the spent fractionation liquid. Therefore, overall sulfur and carbohydrate mass balances are established. 95-97 % of the charged SO(2) remains in the liquid and can be fully recovered by distillation. During fractionation, hemicelluloses and lignin are effectively dissolved, whereas cellulose is preserved in the solid (fibre) phase. Hemicelluloses are hydrolysed, producing up to 50 % monomeric sugars, whereas dehydration and oxidation of carbohydrates are insignificant. The latter is proven by the closed carbohydrate material balances as well as by the near absence of corresponding by-products (furfural, hydroxymethylfurfural (HMF) and aldonic acids). In addition, acid methanolysis/GC and acid hydrolysis/high performance anion exchange chromatography (HPAEC) methods for the carbohydrate determination are compared.

Lignosulfonate and elevated pH can enhance enzymatic saccharification of lignocelluloses

“…Reported studies indicate that these two mechanisms produced negative effects on enzymatic saccharification of lignocelluloses. Pretreatment of lignocelluloses such as Organosolv [8,9] and SPORL [10] is able to partially remove lignin physical blockage by solubilizing a fraction of lignin into the hemicellulosic sugar stream (pretreatment spent liquor). However, further processing lignocelluloses to remove lignin blockage such as by delignification is not only expensive but also may not be necessary in terms of improving cellulose accessibility.…”

“…Sulfonated lignin, has good hydrophilic properties. We can hypothesize that sulfonated lignin such as lignosulfonate in the sulfite pretreatment hydrolysates (spent liquor) [9,10] may produce less nonspecific binding (adsorption) to cellulase enzymes. This hypothesis is indirectly corroborated by the excellent enzymatic digestibility of lignocellulosic substrates after sulfite pretreatment such as SPORL[10], sulfite pulping [22], and lignin sulfonation [23].…”

Purification of cellulosic pulp by hot water extraction

“…An alternative to the acid sulfite-HCE process for the production of viscose-grade pulps may be the SO 2 -Ethanol-Water (SEW) pulping. In addition to a good quality rayon pulp, the SEW process allows high flexibility in terms of raw materials, short cooking times, and a significant recovery of sugars from the pulping liquor (Iakovlev and Heiningen 2012;Sixta et al 2013). The production of viscose-grade pulps has also been investigated by applying a CCE stage to paper-grade pulps, which allows the removal of substantial amounts of shortchain hemicellulosic sugars while preserving the yield of cellulose (Gehmayr et al 2011;Schild and Sixta 2011).…”

Comparison of Two Acid Hydrotropes for Sustainable Fractionation of Birch Wood

“…However,e conomic and sustainable biomass preprocessing methods are neededt of ractionate lignocelluloses into easily processable building blocks such as sugars, lignin precursors, and lignocellulosic nanomaterials for efficient downstream conversion to av ariety of biobased products.O nly limited success has been achievedd espite many research efforts in the last severald ecades. Traditional fractionation processes, including commercial wood pulping, dilute acid, [1,2] steam explosion, [3] al-kaline, [2] organosolv, [4][5][6] and sulfite, [7,8] are primarily focused on obtaining polysaccharides by dissolving hemicelluloses and/or lignin and are conducted at high temperatures resulting in condensed lignin, [9,10] which is not suitable for value-added utilization other than as boiler fuel. [11] Recent advances such as reductive catalytic fractionation, [12] organic solvents, [5,[13][14][15][16] and ionic-liquid-based systems [17] have not fully addressed chemical recovery, chemical toxicity, or value-added uitlization of all components of the lignocelluloses.…”