Accepted Manuscript Pretreating lignocellulosic biomass by the concentrated phosphoric acid plus hydrogen peroxide (PHP) for enzymatic hydrolysis: Evaluating the pretreatment flexibility on feedstocks and particle sizes Qing Wang, Zhanghong Wang, Fei Shen, Jinguang Hu, Fubao Sun, Lili Lin, Gang Yang, Yanzong Zhang, Shihuai Deng PII: DOI: Reference:
S0960-8524(14)00796-2 http://dx.doi.org/10.1016/j.biortech.2014.05.088 BITE 13496
To appear in:
Bioresource Technology
Received Date: Revised Date: Accepted Date:
1 April 2014 21 May 2014 22 May 2014
Please cite this article as: Wang, Q., Wang, Z., Shen, F., Hu, J., Sun, F., Lin, L., Yang, G., Zhang, Y., Deng, S., Pretreating lignocellulosic biomass by the concentrated phosphoric acid plus hydrogen peroxide (PHP) for enzymatic hydrolysis: Evaluating the pretreatment flexibility on feedstocks and particle sizes, Bioresource Technology (2014), doi: http://dx.doi.org/10.1016/j.biortech.2014.05.088
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Pretreating lignocellulosic biomass by the concentrated phosphoric acid plus hydrogen peroxide (PHP) for enzymatic hydrolysis: Evaluating the pretreatment flexibility on feedstocks and particle sizes Qing Wanga,b 1, Zhanghong Wanga,b 1, Fei Shena,b, Jinguang Huc, Fubao Sund, Lili Linb, Gang Yangb, Yanzong Zhangb, Shihuai Denga,b a Institute of Ecological and Environmental Sciences, Sichuan Agricultural University-Chengdu Campus, Chengdu, Sichuan 611130, P. R. China; b Engineering & Technology Center for Rural Environment Protection of Sichuan Province, Sichuan Agricultural University-Chengdu Campus, Chengdu, Sichuan 611130, P. R. China; c Forest Products Biotechnology, Department of Wood Science, the University of British Columbia, 2424 Main Mall, Vancouver, BC, Canada; d Key Laboratory of Industrial Biotechnology &Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi 214122, P.R. China;
Abstract: In order to seek a high-efficient pretreatment path for converting lignocellulosic feedstocks to fermentable sugars by enzymatic hydrolysis, the concentrated H3PO4 plus H2O2 (PHP) was attempted to pretreat different lignocellulosic biomass for evaluating the pretreatment flexibility on feedstocks. Meanwhile, the responses of pretreatment to particle sizes were also evaluated. When the PHP-pretreatment was employed (final H2O2 and H3PO4 concentration of 1.77% and 80.0%), 71-96% lignin and more than 95% hemicellulose in various feedstocks (agricultural residues, hardwood, softwood, bamboo, and their mixture, and garden wastes mixture) can be removed. Consequently, more than 90% glucose conversion was uniformly achieved indicating PHP greatly improved the pretreatment flexibility to different feedstocks. Moreover, when wheat straw and oak chips were PHP-pretreated with different sizes, the average glucose conversion reached 94.9% and 100% with lower coefficient of variation (7.9% and 0.0%), which implied PHP-pretreatment can significantly weaken the negative effects of feedstock sizes on subsequent conversion.
Corresponding author; Present address: 211 Huimin Road, Wenjiang District, Chengdu, Sichuan, 611130, P. R.
China; Tel.(Fax): +86 28 86291390; E-mail: [email protected]; 1 These authors contributed equally to this work.
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Keywords: Concentrated phosphoric acid; Hydrogen peroxide; Pretreatment; Enzymatic hydrolysis;
1. Introduction Second generation biofuels refer to those produced from lignocellulosic feedstocks, including agricultural and forestry residues, perennial woody and herbaceous energy crops and other lignocellulose-based wastes (Rigdon et al., 2013). Lignocellulosic feedstocks can have positive environmental outcomes and make up a substantial proportion in future energy portfolios (Gelfand et al., 2013). Moreover, lignocellulose as the most abundant renewable biomass has a huge year-supply of approximately 200 billion metric tons worldwide (Li et al., 2014; Percival Zhang et al., 2006; Ragauskas et al., 2006). In the last few decades, several ways of utilizing lignocellulosic biomass for biofuel production in different types, including biogas, bio-diesel, pyrolytic bio-oil, and bioethanol, have been considered thoroughly by researchers worldwide, in which refining lignocellulosic ethanol substantially plays the great important roles in aspects of improving energy security, reducing greenhouse gas emission and maintaining the price stability of petroleum (Singh et al., 2014). Technically, ethanol production from lignocellulosic feedstocks by biological routes should generally undergo three key steps including pretreatment, fermentable monosaccharides conversion, and fermentation. Actually, the steps of fermentable sugar production and ethanol fermentation are still seriously restricted because the digestibility of cellulose is hindered by the physico-chemical, structure and composition of lignocellulose (Alvira et al., 2010). Thus, pretreatment is an essential step to obtain potentially fermentable sugars by the enzymatic hydrolysis for
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subsequent ethanol fermentation. The general aims of pretreatment on lignocellulosic biomass are to break down the lignin or hemicellulose and disrupt the crystalline structure of cellulose for enhancing the accessibility to enzymes during hydrolysis step (Mosier et al., 2005) Currently, a large number of pretreatment approaches have been widely investigated on various feedstock sources. The characteristics of these pretreatment technologies have been systematically summarized and overviewed in many review articles, which actually indicated that different pretreatment technologies presented distinguished advantages and disadvantages to different feedstocks since some typical physico-chemical characteristics existed in various lignocellulosic biomass. For example, alkaline-based pretreatment approaches, including lime, NaOH, and ammonia recycling percolation (ARP), can effectively reduce lignin content in most agricultural residues but less satisfactory for processing the recalcitrant biomass such as softwoods (Chandra et al., 2007). Typically low pH pretreatments (e.g., dilute acid, uncatalyzed and catalyzed steam explosion with either acid or SO2 as a catalyst) can remove most of the hemicellulose from lignocellulosic feedstocks but a small portion of biomass lignin (Kumar et al., 2009). Moreover, it was not profitable that current pretreatment technologies always consumed excessive energy to obtain enough severity for better effectiveness. Additionally, there are some evidences to support that the size-reduction of lignocellulosic feedstocks can facilitate the pretreatment (Sun & Cheng, 2002). However, milling or grinding the biomass to small particle sizes before pretreatment
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is energy-intensive and costly expensive (Alvira et al., 2010). Thus, it makes sense to develop some new pretreatment methods, which can be widely suitable for pretreating different lignocellulosic feedstocks with gentle severity, high efficiency and no excessive size-reduction. Recently, concentrated phosphoric acid (H3PO4) pretreatment has been investigated on the feedstocks of microcrystalline cellulose and cotton-based biomass, in which the cellulose could be well dissolved and decrystallized, and superior enzymatic hydrolysis could be achieved (Shen et al., 2013; Zhang et al., 2010; Zhang et al., 2009). However, when the lignocellulosic feedstocks were pretreated, the lignin can not be efficiently removed, resulting in lower cellulose digestibility and slower hydrolysis rates (Zhang et al., 2007). This may partially because the concentrated H3PO4 typically lacks oxidizability in contrast to the traditionally-employed concentrated acid for pretreatment such as sulfuric acid (Sun et al., 2011). Thus, is it possible to achieve better pretreatment effectiveness by enhancing the oxidization of the concentrated H3PO4-pretreatment? In this context, based on the potential oxidizability of hydrogen peroxide (H2O2) to lignin and the concentrated H3PO4 dissolvability to the insoluble carbohydrates in lignocelluloses, the concentrated phosphoric acid plus hydrogen peroxide (PHP) was employed to investigate the possibility of efficiently pretreating various lignocellulosic feedstocks. Concretely, the flexibilities of PHP-pretreatment to lignocellulosic sources and particle sizes of feedstocks were evaluated according to the lignin and hemicellulose removal, and subsequently enzymatic hydrolysis.
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2. Materials and Methods 2.1 Lignocellulosic feedstocks The employed lignocellulosic feedstocks were typically sorted as agricultural residues (wheat straw, corn stalk, and Jerusalem artichoke stalk), softwood (spruce chips), hardwood (oak chips), bamboo residues and the garden wastes mixture (GWM). Agricultural residues of wheat straw and corn stalk were collected from the local farm. Jerusalem artichoke stalk was harvested from the farm of Sichuan Agricultural University. Woody sawdusts of oak and spruce, and bamboo residues were collected from the local furniture factories in Chengdu city, Sichuan, China. The mixed garden wastes were locally collected from the campus of Sichuan Agricultural University. The collected feedstocks were all air-dried (the determined moisture content of 0.042-0.155, dry basis) and chopped into 5 mesh (2 mesh (0.8-1.5cm, Large), 2-5 mesh (0.4cm-0.8cm, Medium) and
S0960-8524(14)00796-2 http://dx.doi.org/10.1016/j.biortech.2014.05.088 BITE 13496
To appear in:
Bioresource Technology
Received Date: Revised Date: Accepted Date:
1 April 2014 21 May 2014 22 May 2014
Please cite this article as: Wang, Q., Wang, Z., Shen, F., Hu, J., Sun, F., Lin, L., Yang, G., Zhang, Y., Deng, S., Pretreating lignocellulosic biomass by the concentrated phosphoric acid plus hydrogen peroxide (PHP) for enzymatic hydrolysis: Evaluating the pretreatment flexibility on feedstocks and particle sizes, Bioresource Technology (2014), doi: http://dx.doi.org/10.1016/j.biortech.2014.05.088
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
Pretreating lignocellulosic biomass by the concentrated phosphoric acid plus hydrogen peroxide (PHP) for enzymatic hydrolysis: Evaluating the pretreatment flexibility on feedstocks and particle sizes Qing Wanga,b 1, Zhanghong Wanga,b 1, Fei Shena,b, Jinguang Huc, Fubao Sund, Lili Linb, Gang Yangb, Yanzong Zhangb, Shihuai Denga,b a Institute of Ecological and Environmental Sciences, Sichuan Agricultural University-Chengdu Campus, Chengdu, Sichuan 611130, P. R. China; b Engineering & Technology Center for Rural Environment Protection of Sichuan Province, Sichuan Agricultural University-Chengdu Campus, Chengdu, Sichuan 611130, P. R. China; c Forest Products Biotechnology, Department of Wood Science, the University of British Columbia, 2424 Main Mall, Vancouver, BC, Canada; d Key Laboratory of Industrial Biotechnology &Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi 214122, P.R. China;
Abstract: In order to seek a high-efficient pretreatment path for converting lignocellulosic feedstocks to fermentable sugars by enzymatic hydrolysis, the concentrated H3PO4 plus H2O2 (PHP) was attempted to pretreat different lignocellulosic biomass for evaluating the pretreatment flexibility on feedstocks. Meanwhile, the responses of pretreatment to particle sizes were also evaluated. When the PHP-pretreatment was employed (final H2O2 and H3PO4 concentration of 1.77% and 80.0%), 71-96% lignin and more than 95% hemicellulose in various feedstocks (agricultural residues, hardwood, softwood, bamboo, and their mixture, and garden wastes mixture) can be removed. Consequently, more than 90% glucose conversion was uniformly achieved indicating PHP greatly improved the pretreatment flexibility to different feedstocks. Moreover, when wheat straw and oak chips were PHP-pretreated with different sizes, the average glucose conversion reached 94.9% and 100% with lower coefficient of variation (7.9% and 0.0%), which implied PHP-pretreatment can significantly weaken the negative effects of feedstock sizes on subsequent conversion.
Corresponding author; Present address: 211 Huimin Road, Wenjiang District, Chengdu, Sichuan, 611130, P. R.
China; Tel.(Fax): +86 28 86291390; E-mail: [email protected]; 1 These authors contributed equally to this work.
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Keywords: Concentrated phosphoric acid; Hydrogen peroxide; Pretreatment; Enzymatic hydrolysis;
1. Introduction Second generation biofuels refer to those produced from lignocellulosic feedstocks, including agricultural and forestry residues, perennial woody and herbaceous energy crops and other lignocellulose-based wastes (Rigdon et al., 2013). Lignocellulosic feedstocks can have positive environmental outcomes and make up a substantial proportion in future energy portfolios (Gelfand et al., 2013). Moreover, lignocellulose as the most abundant renewable biomass has a huge year-supply of approximately 200 billion metric tons worldwide (Li et al., 2014; Percival Zhang et al., 2006; Ragauskas et al., 2006). In the last few decades, several ways of utilizing lignocellulosic biomass for biofuel production in different types, including biogas, bio-diesel, pyrolytic bio-oil, and bioethanol, have been considered thoroughly by researchers worldwide, in which refining lignocellulosic ethanol substantially plays the great important roles in aspects of improving energy security, reducing greenhouse gas emission and maintaining the price stability of petroleum (Singh et al., 2014). Technically, ethanol production from lignocellulosic feedstocks by biological routes should generally undergo three key steps including pretreatment, fermentable monosaccharides conversion, and fermentation. Actually, the steps of fermentable sugar production and ethanol fermentation are still seriously restricted because the digestibility of cellulose is hindered by the physico-chemical, structure and composition of lignocellulose (Alvira et al., 2010). Thus, pretreatment is an essential step to obtain potentially fermentable sugars by the enzymatic hydrolysis for
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subsequent ethanol fermentation. The general aims of pretreatment on lignocellulosic biomass are to break down the lignin or hemicellulose and disrupt the crystalline structure of cellulose for enhancing the accessibility to enzymes during hydrolysis step (Mosier et al., 2005) Currently, a large number of pretreatment approaches have been widely investigated on various feedstock sources. The characteristics of these pretreatment technologies have been systematically summarized and overviewed in many review articles, which actually indicated that different pretreatment technologies presented distinguished advantages and disadvantages to different feedstocks since some typical physico-chemical characteristics existed in various lignocellulosic biomass. For example, alkaline-based pretreatment approaches, including lime, NaOH, and ammonia recycling percolation (ARP), can effectively reduce lignin content in most agricultural residues but less satisfactory for processing the recalcitrant biomass such as softwoods (Chandra et al., 2007). Typically low pH pretreatments (e.g., dilute acid, uncatalyzed and catalyzed steam explosion with either acid or SO2 as a catalyst) can remove most of the hemicellulose from lignocellulosic feedstocks but a small portion of biomass lignin (Kumar et al., 2009). Moreover, it was not profitable that current pretreatment technologies always consumed excessive energy to obtain enough severity for better effectiveness. Additionally, there are some evidences to support that the size-reduction of lignocellulosic feedstocks can facilitate the pretreatment (Sun & Cheng, 2002). However, milling or grinding the biomass to small particle sizes before pretreatment
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is energy-intensive and costly expensive (Alvira et al., 2010). Thus, it makes sense to develop some new pretreatment methods, which can be widely suitable for pretreating different lignocellulosic feedstocks with gentle severity, high efficiency and no excessive size-reduction. Recently, concentrated phosphoric acid (H3PO4) pretreatment has been investigated on the feedstocks of microcrystalline cellulose and cotton-based biomass, in which the cellulose could be well dissolved and decrystallized, and superior enzymatic hydrolysis could be achieved (Shen et al., 2013; Zhang et al., 2010; Zhang et al., 2009). However, when the lignocellulosic feedstocks were pretreated, the lignin can not be efficiently removed, resulting in lower cellulose digestibility and slower hydrolysis rates (Zhang et al., 2007). This may partially because the concentrated H3PO4 typically lacks oxidizability in contrast to the traditionally-employed concentrated acid for pretreatment such as sulfuric acid (Sun et al., 2011). Thus, is it possible to achieve better pretreatment effectiveness by enhancing the oxidization of the concentrated H3PO4-pretreatment? In this context, based on the potential oxidizability of hydrogen peroxide (H2O2) to lignin and the concentrated H3PO4 dissolvability to the insoluble carbohydrates in lignocelluloses, the concentrated phosphoric acid plus hydrogen peroxide (PHP) was employed to investigate the possibility of efficiently pretreating various lignocellulosic feedstocks. Concretely, the flexibilities of PHP-pretreatment to lignocellulosic sources and particle sizes of feedstocks were evaluated according to the lignin and hemicellulose removal, and subsequently enzymatic hydrolysis.
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2. Materials and Methods 2.1 Lignocellulosic feedstocks The employed lignocellulosic feedstocks were typically sorted as agricultural residues (wheat straw, corn stalk, and Jerusalem artichoke stalk), softwood (spruce chips), hardwood (oak chips), bamboo residues and the garden wastes mixture (GWM). Agricultural residues of wheat straw and corn stalk were collected from the local farm. Jerusalem artichoke stalk was harvested from the farm of Sichuan Agricultural University. Woody sawdusts of oak and spruce, and bamboo residues were collected from the local furniture factories in Chengdu city, Sichuan, China. The mixed garden wastes were locally collected from the campus of Sichuan Agricultural University. The collected feedstocks were all air-dried (the determined moisture content of 0.042-0.155, dry basis) and chopped into 5 mesh (2 mesh (0.8-1.5cm, Large), 2-5 mesh (0.4cm-0.8cm, Medium) and
