Acid Hydrolysis of Hemicellulose in Green Liquor Pre-Pulping Extract of Mixed Northern Hardwoods

Abstract

Forest biomass is a promising resource for future biofuels and bioproducts. Pre-pulping extraction of hemicellulose by alkaline (Green Liquor) pretreatment produces a neutral-pH extract containing hemicellulose-derived oligomers. A near-term option for use of this extract is to hydrolyze the oligomers to fermentable monomer sugars. Chips of mixed northern hardwoods were cooked in a rocking digester at 160 degrees C for 110 min in Green Liquor at a concentration of 3% Na2O equivalent salts on dry wood. The mass of wood extracted into the Green Liquor extract was approximately 11.4% of the debarked wood mass, which resulted in a dilute solution of oligomeric hemicelluloses sugars. The concentration of the extract was increased through partial evaporation prior to hydrolysis. Dilute sulfuric acid hydrolysis was applied at conditions ranging from 100 to 160 degrees C, 2% to 6% (w/v) H2SO4, and 2- to 258-min residence time. The maximum fermentable sugar concentration achieved from evaporated extract was 10.7 g/L, representing 90.7% of the maximum possible yield. Application of the biomass pretreatment severity function to the hydrolysis results proved to offer a relatively poor prediction of temperature and reaction time interaction. The combined severity function, which incorporates reaction time, temperature, and acid concentration, did prove to provide a useful means of trading off the combined effects of these three variables on total sugar yields.

Evaluation of Enzyme Mixtures in Releasing Fermentable Sugars from Pre-pulping Extracts of Mixed Northeast Hardwoods

“…The milled wood chips were used for determination of total solids/moisture and carbohydrate content in biomass. The sugar composition of un-extracted wood chips was 42.1% glucan, 23.1% XMG, and 1.8% arabinan [16,27]. Note that XMG (capitalized) represents the sum total of the three oligomeric sugars xylan, mannan, and galactan while xmg (small letters) represents the sum of the corresponding hydrolyzed sugars xylose, mannose, and galactose.…”

“…The enzymatic process offers some advantages, such as minimization of the formation of decomposition products that inhibit the subsequent microbial fermentation, reduction of acid and base consumption, as well as reduction in gypsum disposal costs, and a more environmentally friendly process [14,15]. In a previous study, we were able to optimize the xylose yield from acid hydrolysis of the extract with respect to the temperature, residence time, and concentration of the acid catalyst [16]. For the case of enzymatic hydrolysis, optimal conditions depend on all of these factors, as well as substrate composition and enzyme activities.…”

Statistical methodology for optimizing the dilute acid hydrolysis of sugarcane bagasse

“…The hemicellulosic fraction of lignocellulosic residues can be hydrolyzed with dilute acids and the yield of xylose recovered depends on the acid concentration, temperature, and residence time during hydrolysis [5,6]. Previous research has indicated that the formation of the sugar degradation products furfural and 5-hydroxymethylfurfural (5-HMF) is taking place in proportion to the severity of the acid hydrolysis [7,8]. The kinetics of these reactions has been described by different models evaluated by Jacobsen and Wyman [9].…”

A study on the economic analysis and optical project model of woodchip cogeneration systems

“…Various environmental and economic benefits have been claimed for the application of biomass such as energy security, reduction of greenhouse gas emissions, and availability of a renewable source for increasing energy demand. Especially, forest residues are a viable option because they are abundant, relatively cheap and not edible [1,2]. The recovery of forest residues reduces the chance of forest fires, increases forest health by reducing competition for resources, generates additional revenue by utilizing forest by-products, and reduces the burden of disposal of waste material [3][4][5]13].…”