Enhancement of Enzymatic Saccharification of Poplar by Green Liquor Pretreatment

Abstract

Green liquor (Na 2 S + Na 2 CO 3 , GL) pretreatment is an effective pathway for improving the enzymatic digestibility of lignocellulosic biomass for the production of bioethanol. In this work, GL was employed as a pretreatment to enhance the enzymatic saccharification of poplar. During pretreatment, the increase of H-factor and TTA charge resulted in enhanced delignification and increased degradation of polysaccharides. The sugar yield of enzymatic hydrolysis increased rapidly with increasing TTA charge in GL pretreatment, while the effect of different H-factors (from 400 to 800) on sugar yield was unnoticeable. The pretreated solid recovery was 75.5% at a lignin removal rate of 29.2% under optimized conditions of total titratable alkali (TTA) charge 20%, sulfidity 25%, and H-factor 400. The sugar yield of glucan, xylan, and total sugar of GLpretreated poplar in enzymatic hydrolysis reached up to 89.9%, 65.5%, and 82.8%, respectively, at a cellulase loading of 40 FPU/g-cellulose. Keywords INTRODUCTIONThe economic and environmental benefits that can be derived from bioethanol have led to extensive research in the bioconversion of lignocellulosic feedstocks into ethanol (Christersson 2008). Bioethanol is a renewable energy source produced through the fermentation of sugars and can reduce greenhouse gas emissions (Yang et al. 2013). Although current research and development attention have focused mainly on agricultural residues and dedicated energy crops, wood biomass (hardwood and softwood) is still an important feedstock for bioethanol production (Zhu and Pan 2010). Large quantities of wood biomass are also sustainably available in various regions of the world.The major differences between wood biomass and agricultural biomass are based on both physical properties and chemical components. Wood biomass is physically larger, structurally stronger, and denser than agricultural biomass. Its higher density significantly reduces transportation cost. Wood biomass has a higher lignin content than agricultural biomass. The lignin is one of the major hurdles for cellulase access to carbohydrate fraction in woody biomass and thus reduces the effectiveness of enzymatic hydrolysis. Therefore, more effort is required to overcome the recalcitrance of wood biomass through pretreatment for an efficient enzymatic saccharification.Poplar has been widely planted in temperate zones because of its rapid growth and ease of stock establishment through stem-or root-cuttings (Kang et al. 1996). Since the introduction of clones in the 1970s, poplar has been incorporated into many managed PEER-REVIEWED ARTICLE bioresources.com Meng et al. (2014). "Green liquor saccharification," BioResources 9(2), 3236-3247. 3237systems for the production of timber and fiber throughout south temperate central China, which has an area of roughly 600,000 km 2 (Fang et al. 1999). Poplar has many characteristics that make it suitable for plantation culture, which enables the production of large quantities of wood in short periods of time.Lignocellulosic biomas...

Novel Approach to Prepare Ultrathin Lignocellulosic Film for Monitoring Enzymatic Hydrolysis Process by Quartz Crystal Microbalance

“…The wood chips were sealed in plastic bags and stored in a refrigerator at 4 °C before use. GL-pretreated poplar (GL-poplar) was prepared according to the method described by Meng et al 18 The total titratable alkali charge (TTA, the sum of Na 2 S and Na 2 CO 3 as Na 2 O) on the basis of bone dry material was 24%. The sulfidity of the pretreatment liquor, defined as the percentage of Na 2 S as Na 2 O to TTA, was 25%.…”

“…Poplar is a typical and resource-rich hardwood species. The effects of green liquor (GL) pretreatment on the chemical composition and enzymatic hydrolysis of poplar have been investigated in our previous works. , In this work, a novel method for the preparation of even and smooth ultrathin lignocellulosic films on QCM gold sensors was investigated using solutions of ball-milled poplar and GL-pretreated poplar in LiCl/DMSO solvent system. The obtained films were used to monitor the processes of cellulase adsorption and enzymatic hydrolysis in situ and in real time by a QCM instrument.…”

Chemical Pretreatments of Wood Chips Prior to Alkaline Pulping - A Review of Pretreatment Alternatives, Chemical Aspects of the Resulting Liquors, and Pulping Outcomes

“…Alkaline pretreatment can shorten the cooking times and lower the need for alkali charge of the subsequent pulp cooking process. Also, alkaline pulping liquors, such as white and green liquors, can be used for pretreatments as such (Ban et al 2003a(Ban et al ,b, 2004Lucia 2003, 2005;Ban et al 2009;Walton et al 2010a;Wu et al 2010;Yoon and van Heiningen 2010;Gonzalez et al 2011;Jun et al 2012;Meng et al 2014;Kim et al 2015;Wang et al 2015). Pretreatments conducted with white and green liquors utilize proven technologies for the sophisticated recovery of all the used chemicals at a very high efficiency, and they can be easily integrated into existing pulp mill operations (Jin et al 2010).…”

Effect of delignification on hemicellulose extraction from switchgrass, poplar, and pine and its effect on enzymatic convertibility of cellulose-rich residues

“…Alkaline treatment can be an effective process to remove hemicellulose, and it has been used in many studies for the extraction of hemicellulose from different types of biomass (Lawther et al 1996;Vena et al 2013) or used as a pretreatment method to increase the enzymatic convertibility of cellulose substrate (Zhao et al 2008b;Meng et al 2014). Alkali treatment can disrupt the cell wall of biomass efficiently through hydrolyzing uronic and acetic esters; it also can cleave the α-ether linkages between lignin and hemicellulose and the ester bonds between lignin and/or hemicellulose and hydroxycinnamic acids (Jackson 1977).…”