Influence of pretreatment condition on the fermentable sugar production and enzymatic hydrolysis of dilute acid-pretreated mixed softwood

doi:10.1016/j.biortech.2013.04.103

Bioresource Technology

Volume 140, July 2013, Pages 306-311

https://doi.org/10.1016/j.biortech.2013.04.103 Get rights and content

Highlights

•
The fermentable sugar production from softwood differed depending on the acid catalysts.
•
On dicarboxylic acid, pH was important factor on the fermentable sugar production.
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Reaction temperature was the next significant factor.
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The highest enzymatic hydrolysis yield was found following maleic acid pretreatment.

Abstract

In this study, the effects of different acid catalysts and pretreatment factors on the hydrolysis of mixed softwood were investigated over a range of thermochemical pretreatments. Maleic, oxalic, and sulfuric acids were each used, under different pretreatment conditions. The most influential factor for fermentable sugar production in the dicarboxylic acid pretreatment of softwood was the pH. Reaction temperature was the next significant factor. However, during sulfuric acid pretreatment, fermentable sugar production was more dependent on reaction temperature, than time or pH. Enzymatic hydrolysis yields differed, depending on acid catalyst and pretreatment factor, regardless of lignin content in pretreated biomass. The highest enzymatic hydrolysis yield was found following maleic acid pretreatment, which reached 61.23%. The trend in enzymatic hydrolysis yields that were detected concomitantly with pretreatment condition or type of acid catalyst was closely related to the fermentable sugar production in the hydrolysate.

Introduction

Lignocellulosic biomass is the most abundant organic material on earth, and various studies have reported that enough such materials could be collected from waste streams and future dedicated crop plantations to produce alternative energy, such as bioethanol (Wyman, 1996, World Watch Institute, 2007). The carbohydrate composes about 65–75% of the overall lignocellulosic biomass composition. Therefore, the biomass can be converted to fermentable sugar by physical, chemical or biological process, much as for starch conversion to fermentable sugars. However, producing fermentable sugar from carbohydrate at high yields is far more difficult than deriving sugars from corn or sugar cane, because the biomass is highly recalcitrant (Yang and Wyman, 2008, Zhu and Pan, 2010). Therefore, a pretreatment step is necessary to promote hydrolysis of carbohydrate. Many pretreatment techniques have been investigated, and they are grouped into physical, chemical, biological, and combinations of these approaches (Pan et al., 2005, Schilling et al., 2012, Soderstrom et al., 2003). Depending on the pretreatment process, the yield of degradation product such as fermentable sugar and inhibitors differ. In addition, structural change of biomass occurs by different pretreatment process. The structural and compositional change of biomass, depending on the pretreatment process, can affect the enzyme digestibility or fermentability for bioethanol production (Bansal et al., 2012, Nakagame et al., 2011).

Softwoods are one of the major lignocellulosic biomass, and have potential as biomass source for bioconversion (Mabee et al., 2006). Softwoods are mainly comprised of cellulose, hemicelluloses, and lignin. They have a unique chemical composition that differs from hardwood. They have more hemicelluloses with a lower xylose content, and higher mannose content, relative to hardwood. The lignin content is usually higher than that of hardwoods. Interestingly, lignin structure and the high concentration in softwood hinder delignification and enzymatic hydrolysis (Sjostrom, 1993).

In this study, we investigated the degradation properties of a mixed softwood using sulfuric, maleic, and oxalic acid, during pretreatment at different combinations of reaction temperature, time, and pH, while maintaining the combined severity factor (CSF) constant. We hypothesized that the catalytic rates and degradation product yields would be attributable to the catalysts properties and pretreatment parameters. Finally, we drew results, which are highly significant differences among the three acids and pretreatment parameters. The dicarboxylic acids exhibit much higher hydrolytic efficiencies than those of sulfuric acid. Furthermore, the effect of enzymatic hydrolysis on the pretreated biomass was examined, to compare the effectiveness of various acid catalysis systems and pretreatment parameters.

Section snippets

Biomass and pretreatment conditions

Mixed softwood (Pinus rigida and Pinus densiflora) chips were purchased from Poong Lim Inc. (Daejeon, Korea). The mixed softwood was milled and screened to a 40∼60 mesh size, using a J-NCM Wiley mill (JISICO, Seoul, Korea) and stored at 4 °C with less than 10% moisture content.

The pretreatment was conducted in 500 ml cylindrical stainless steel reaction vessels. Mixed softwood and acid solutions were placed in the stainless steel vessels, which were in turn placed into a larger tumbling digester,

Effects of pretreatment conditions on fermentable sugar production from mixed softwood

Pretreatment was performed at the same CSF of 2.50, to investigate different catalytic properties and pretreatment factors on hydrolysis of the mixed softwood. The compositional analysis of the hydrolysate under different pretreatment conditions is shown in Table 2, Table 3. Galactoglucomannans are the principal hemicelluloses in softwood, and their monomeric components are galactose, glucose, and mannose. Their backbone is a linear or possibly slightly branched chain built up by 1–4 linked

Conclusion

This study investigated the effect of different acid catalysts and pretreatment factors on the hydrolysis of a biomass during pretreatment. The pretreatment factors for fermentable sugar production differed, depending on the kind of acid catalyst. A high concentration of dicarboxylic acids seemed to favor the production of fermentable sugars. In contrast, sulfuric acid pretreatment demanded a high reaction temperature. Enzymatic hydrolysis yields differed, depending on the acid catalyst and

Acknowledgements

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2012-0008177) and by Priority Research Centers Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2010-0020141).

References (34)

P. Bansal et al.
Elucidation of cellulose accessibility, hydrolysability and reactivity as the major limitations in the enzymatic hydrolysis of cellulose
Bioresour. Technol.
(2012)
C. Cara et al.
Conversion of olive tree biomass into fermentable sugars by dilute acid pretreatment and enzymatic hydrolysis
Bioresour. Technol.
(2008)
J.R. Jensen et al.
Effects of dilute acid pretreatment conditions on enzymatic hydrolysis monomer and oligomer sugar yields for aspen, balsam, and switchgrass
Bioresour. Technol.
(2010)
M.A. Kabel et al.
Complex xylo-oligosaccharides identified from hydrothermally treated Eucalyptus wood and brewery’s spent grain
Carbohydr. Polym.
(2002)
M.A. Kabel et al.
Effect of pretreatment severity on xylan solubility and enzymatic breakdown of the remaining cellulose from wheat straw
Bioresour. Technol.
(2007)
A.M. Kootstra et al.
Comparison of dilute mineral and organic acid pretreatment for enzymatic hydrolysis of wheat straw
Biochem. Eng. J.
(2009)
L. Kumar et al.
The lignin present in steam pretreated softwood binds enzymes and limits cellulose accessibility
Bioresour. Technol.
(2012)
J.W. Lee et al.
Efficiencies of acid catalysts in the hydrolysis of lignocellulosic biomass over a range of combined severity factors
Bioresour. Technol.
(2011)
J.W. Lee et al.
Simultaneous saccharification and ethanol fermentation of oxalic acid pretreated corncob assessed with response surface methodology
Bioresour. Technol.
(2009)
W.S. Lim et al.
Effects of pretreatment factors on fermentable sugar production and enzymatic hydrolysis of mixed hardwood
Bioresour. Technol.
(2013)

S. Monavari et al.

Impact of impregnation time and chip size on sugar yield in pretreatment of softwood for ethanol production

Bioresour. Technol.

(2009)

C.A. Mooney et al.

The effect of fiber characteristics on hydrolysis and cellulase accessibility to softwood substrate

Enzyme Microb. Technol.

(1999)

S. Nakagame et al.

The isolation, characterization and effect of lignin isolated from steam pretreated Douglas-fir on the enzymatic hydrolysis of cellulose

Bioresour. Technol.

(2011)

N. Nichols et al.

Fungal metabolism of fermentation inhibitors present in corn stover dilute acid hydrolysate

Enzyme Microb. Technol.

(2008)

K. Ohgren et al.

Effect of hemicellulose and lignin removal on enzymatic hydrolysis of steam pretreated corn stover

Bioresour. Technol.

(2007)

L. Qin et al.

Mass balance and transformation of corn stover by pretreatment with different dilute organic acids

Bioresour. Technol.

(2012)

L.P. Ramos et al.

Effect of enzymatic-hydrolysis on the morphology and fine-structure of pretreated cellulosic residues

Enzyme Microb. Technol.

(1993)

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View full text

Influence of pretreatment condition on the fermentable sugar production and enzymatic hydrolysis of dilute acid-pretreated mixed softwood

Highlights

Abstract

Introduction

Section snippets

Biomass and pretreatment conditions

Effects of pretreatment conditions on fermentable sugar production from mixed softwood

Conclusion

Acknowledgements

Bioresour. Technol.

Bioresour. Technol.

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Carbohydr. Polym.

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Biochem. Eng. J.

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Bioresour. Technol.

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Enzyme Microb. Technol.

Bioresour. Technol.

Enzyme Microb. Technol.

Bioresour. Technol.

Bioresour. Technol.

Enzyme Microb. Technol.