Two‐stage dilute acid‐catalyzed hydrolytic conversion of softwood sawdust into sugars fermentable by ethanologenic microorganisms

Abstract

Softwood hemlock residues generated in a sawmill were tested as a feasible agricultural feedstock for the production of high-value bio-based products using the concept of two-stage dilute acid hydrolysis. To convert the carbohydrate contained in the hemlock sawdust, two-stage dilute-acid catalyzed hydrolysis was conducted. In the first stage, sawdust was hydrolyzed at 190 • C for 150 s with 1.1wt% sulfuric acid and 46.0 wt% total solids. As a result, 69.3% mannose, 74.2% galactose, 67.7% xylose, and 17.4% glucose of their theoretical maximum yields were achieved, which reveals that hemicellulose was the major target in the first-stage hydrolysis. After recovering soluble sugars by washing from the first-stage hydrolysate with water, the washed first-stage hydrolysate solids were hydrolyzed again in the second stage at more severe conditions, such as 2.6 or 3.5 wt% H 2 SO 4 , 205 or 210 • C, and 80-135 s. After the two stages, the highest overall yields from 100 g of dry hemlock sawdust were a total of 39.3 g of fermentable sugars (36.0 and 3.3 g of hexose and pentose sugars, respectively). These results indicate that hemlock sawdust could be used to produce fermentable sugars which can be converted into other value-added bio-based products.

Hemicellulose extraction from slash pine sawdust by steam explosion with sulfuric acid

“…By contrast, water-soluble hemicellulose sugars in the liquor behaved quite differently, reaching a maximum value at CS ∼3 and then dropping considerably due to sugar degradation at the most severe pretreatment conditions. These results agree with those obtained by other authors [6,17,19,20,31]. Both HMF and furfural contents increased along with an increase in CS but their concentrations were lower than 0.1% at CS lower than 3 (Fig.…”

“…On the basis of these, many authors have suggested the application of a two-stage pretreatment method, with the first step operating at lower temperatures (170 °C-190 °C) to maximize hemicellulose recovery and the second stage at a higher temperature (200 °C-230 °C) to modify the cellulose structure and increase its accessibility. With the application of steam explosion in two stages, the resulting hemicellulose extraction yields were similar to those obtained in this work but higher glucan yields were achieved upon EH (34 %-40% glucans in 72 h) [19,20]. However, the use of a two-stage process would increase both capital and operational costs that are associated with the overall biomass conversion process [17].…”

“…Previous studies have shown that SO 2 is the most effective catalyst for the steam treatment of softwoods [17], but it is highly toxic to human health and may cause a negative environmental impact [18]. Several authors have obtained high hemicellulose extraction yields (60 %-90%) from softwoods that were pretreated by high-pressure steam after impregnation with dilute sulfuric acid [17,[19][20][21]. Moreover, likewise other acid pretreatment methods, most of the lignin component remain in the water-insoluble fraction after SE.…”

Two-Stage Acidic–Alkaline Hydrothermal Pretreatment of Lignocellulose for the High Recovery of Cellulose and Hemicellulose Sugars

“…To achieve maximum multiple sugar yields simultaneously, pretreatment streamline was suggested to be divided into separate stages [6,7]. It was well known that the severity of pretreatment conditions greatly affects the hydrolysis of lignocellulose components, especially hemicellulose [8].…”

Oxidação de lignina proveniente de resíduos lignocelulósicos agroindustriais para obtenção de compostos químicos aromáticos de maior valor agregado

“…Quando se encontram altamente ordenadas são conhecidas como cristalinas. Da mesma maneira, as regiões com menor grau de ordenamento são denominadas de amorfas (GÓMEZ et al, 2008 (KARIMI et al, 2006;TUCKER et al, 2003;CHUNG et al, 2005;KIM, 2005 SADDLER, 1988;CONVERSE;WARE, 1994). O grau de cristalinidade da celulose varia de acordo com sua origem e processamento.…”