Two-Stage Dilute-Acid Pretreatment of Softwoods

Abstract

Whole tree chips obtained from softwood forest thinnings were pretreated via single- and two-stage dilute-sulfuric acid pretreatment. Whole-tree chips were impregnated with dilute sulfuric acid and steam treated in a 4-L steam explosion reactor. In single-stage pretreatment, wood chips were treated using a wide range of severity. In two-stage pretreatment, the first stage was carried out at low severity to maximize hemicellulose recovery. Solubilized sugars were recovered from the first-stage prehydrolysate by washing with water. In the second stage, water-insoluble solids from first-stage prehydrolysate were impregnated with dilute sulfuric acid, then steam treated at more severe conditions to hydrolyze a portion of the remaining cellulose to glucose and to improve the enzyme digestibility. The total sugar yields obtained after enzymatic hydrolysis of two-stage dilute acid-pretreated samples were compared with sugar yields from single-stage pretreatment. The overall sugar yield from two-stage dilute-acid pretreatment was approx 10% higher, and the net enzyme requirement was reduced by about 50%. Simultaneous saccharification and fermentation using an adapted Saccharomyces cerevisiae yeast strain further improved cellulose conversion yield and lowered the enzyme requirement.

Effects of Dilute Acid Pretreatment on Enzyme Adsorption and Surface Morphology of Liriodendron tulipifera

“…Moreover, pretreatment using dilute acid increased the relative lignincontent due to holocellulose removal. This result agreed with other studies, indicating that pretreatment with dilute sulfuric acid led to a decrease of residual xylan content and an increase of lignin content [11,24,25] …”

The chemistry involved in the steam treatment of lignocellulosic materials

“…A wide variety of chemicals have been suggested in the literature and these include sodium hydroxide [19][20][21] , sulfur dioxide [22][23][24][25][26] , aqueous ammonia 27,28 , calcium hydroxide plus calcium carbonate 27 , phosphoric acid [29][30][31] , alkaline hydrogen peroxide 32 , inorganic salts with acidic properties 33 , ammonium salts 21,33,34 , Lewis acids and organic acid anhydrides 34 , acetic acid 21,33,34 , formic acid 33 , sulfuric acid [35][36][37] , n-butylamine 38 , n-propylamine 39 and alcohols (methanol, ethanol or butanol) in the presence of an acid or alkaline catalyst 40 .…”

Characterization of cellulolytic activities of Bjerkandera adusta and Pycnoporus sanguineus on solid wheat straw medium

“…Because sugar production from biomass is a key limiting step in industrial processes, harsh physical-chemical pretreatments (such as steam explosion, with or without diluted sulfuric acid) are used to loosen lignin and release fibrils of cellulose and monomers of hemicellulose components (Wyman et al 2005). Pre treatment also decreases the recalcitrance of crystalline cellulose by generating pores on its structure making it more accessible to hydrolytic enzymes (Nguyen et al 2000;Nagle et al 2002;Söderström et al 2002). The holocellulose (cellulose and hemicellulose) can be then completely saccharified by a number of enzymes due to the synergism displayed by combinations of endo-and exo glucanases and β-glucosidases (Nidetzky et al 1994).…”