Communication pubs.acs.org/EF
Enhanced Acid-Catalyzed Biomass Conversion to Hydroxymethylfurfural Following Cellulose Solvent- and Organic Solvent-Based Lignocellulosic Fractionation Pretreatment Barron B. Hewetson,†,‡ Ximing Zhang,‡ and Nathan S. Mosier*,†,‡ †
Laboratory of Renewable Resources Engineering and ‡Department of Agricultural and Biological Engineering, Purdue University, West Lafayette, Indiana 47907, United States S Supporting Information *
biomass characterization by acid hydrolysis. In both biomass samples, the glucan portions remain comparable to the raw material with only slight increases in apparent acid-insoluble lignin. The crystallinity indices confirm that crystallinity within the substrates was significantly reduced after COSLIF treatment. Among them, the Avicel relative crystallinity index (RCI) decreased from 79 to 41%, while that of herbaceous corn stover was only mildly reduced from 39 to 32%. Poplar, a hardwood, demonstrated a greater reduction of RCI from 41 to 19%. The significant alterations of crystallinity found within both biomasses indicate different levels of disruption in the cellulose structure. To examine the effect of COSLIF on cellulose conversion, we used a combination of maleic acid and aluminum chloride (25 mM each) to both hydrolyze cellulose and dehydrate the resulting glucose to HMF. To the best of our belief, this is the first report on using COSLIF-treated biomass to make valueadded chemicals in a single-pot biphasic system. For Avicel, results (Figure 1) reveal that, after COSLIF treatment, HMF yields was enhanced significantly in comparison to the initial raw Avicel. Total C6 product (HMF, levulinic acid, and glucose) conversion was improved by 16%. A similar improvement for both poplar and corn stover was achieved but with lower overall yields. The COSLIF treatment conditions used here have previously been shown to dramatically enhance enzymatic hydrolysis of cellulose from 90% yields.17−21 The results from acid conversion of COSLIF treatment is somewhat surprising, but the results may suggest that factors other than cellulose crystallinity have a significant effect on acid-catalyzed conversion. However, even with a similar sugar content after COSLIF treatment, the C6 product yields of poplar are better than corn stover, which follows the pattern of greater reduction in the crystallinity index for poplar compared to corn stover. Notably, the yields of furfural from dehydration of xylose hydrolyzed from hemicellulose in the biomass remained unaffected with the addition of COSLIF treatment and were measured between 53 and 60% for both biomass samples. These results are consistent with the yields reported by Kim et al.23 In this communication, the COSLIF process was applied to different lignocellulosic materials to examine the impact of a
Cellulose is a promising, sustainable source of reduced carbon for producing fuels and chemicals to displace petroleumderived products.1 One hurdle to realizing this potential is the recalcitrance of cellulose to enzymatic and acid catalytic depolymerization.2,3 Numerous pretreatments to enhance the reactivity of cellulose prior to enzymatic hydrolysis have been developed for the production of fermentatively derived biofuels.4−8 However, little work has been published on the effects of pretreatment on acid-catalyzed hydrolysis of cellulose combined with the catalytic conversion of the resultant glucose to products [e.g., 5-hydroxymethylfurfural (HMF), γ-valerolactone (GVL), etc.].9−12 We report the effectiveness of a cellulose solvent- and organic solvent-based lignocellulosic fractionation (COSLIF) for pretreating pure cellulose and lignocellulosic biomass for subsequent catalytic conversion. In COSLIF, concentrated phosphoric acid and ethanol are used as the cellulose solvent and organic anti-solvent, respectively, to significantly reduce the crystallinity of cellulose, which has been demonstrated to significantly enhance the reactivity of cellulose to enzymatic hydrolysis.13 Instead of enzymes, we use a combination of maleic acid and aluminum chloride to catalyze the hydrolysis of cellulose and the conversion of resultant glucose in a single processing step to make value chemicals HMF and levulinic acid. Both HMF and levulinic acid are known as vital building blocks for biofuels and biopolymers.9,10 We have shown that Brønsted acids are all equally effective at hydrolyzing cellulose at equivalent pH.14 However, we have also shown that maleic acid combined with AlCl3 exhibits superior selectivity compared to HCl with AlCl3 on converting glucose to HMF.9,10 In this study, we use maleic acid combined with AlCl3 to hydrolyze cellulose, purified and in intact biomass, and also simultaneously catalyze the conversion of the cellulose-derived glucose to HMF. The effect of COSLIF on cellulose conversion was investigated by examining three different substrates. Avicel, microcrystalline cellulose, served as pure cellulose with no xylose present. Poplar and corn stover were representative of a hardwood and herbaceous crops, respectively. The substrate composition analyses before and after COSLIF treatment are reported in Table 1. The composition is within the range of values reported by others.15,16,22 The glucan portion of Avicel is decreased from 97.5 to 83.9% after swelling. This may have been caused by the formation of water-insoluble macromolecular components that precipitate in ethanol and are measured as acid-insoluble lignin (pseudo-lignin) during © XXXX American Chemical Society
Received: August 2, 2016 Revised: October 24, 2016 Published: October 26, 2016 A
DOI: 10.1021/acs.energyfuels.6b01910 Energy Fuels XXXX, XXX, XXX−XXX
Communication
Energy & Fuels Table 1. Biomass Composition and RCI with and without COSLIF Treatment composition (%) Avicel cellulose (glucan) hemicellulose (xylan) hemicellulose (arabinan) acetyl acid-soluble lignin acid-insoluble lignin other relative crystallinity (%)
corn stover
untreated
treated
untreated
95.7 ± 0.8 0 0 0 1.2 ± 0.1 0.8 ± 0.9 2.4 79
83.9 ± 3.2 0 0 0 0.8 ± 0.1 9.1 ± 1.6 6.3 41
39.6 ± 2.8 24 ± 1 0.7 ± 0.1 0.6 ± 0.1 1.4 ± 0.1 15.9 ± 0.1 17.8 39
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poplar treated
41.1 29.2 0.9 0.9 1.3 18.9
± 1.7 ±1 ± 0.1 ± 0.1 ± 0.03 ± 1.6 7.8 32
untreated
treated
48.4 ± 0.3 23.6 ± 0.7 0 2 ± 0.1 6.6 ± 0.3 17.2 ± 0.2 2.1 41
43.7 ± 2.3 21.9 ± 0.5 0 1.5 ± 0.04 4.1 ± 0.03 20.3 ± 0.9 8.6 19
ACKNOWLEDGMENTS This research is supported by the Center for Direct Catalytic Conversion of Biomass to Biofuels (C3Bio), an Energy Frontier Research Center (EFRC) funded by the Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy (DOE), under Award DE-SC000097.
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Figure 1. Yields (percentage of theoretical) for cellulose-derived products with and without COSLIF treatment.
cellulose solvent (concentrated phosphoric acid) on simultaneous hydrolysis and conversion of the resultant glucose using maleic acid and aluminum chloride. We believe that this is the first demonstration of COSLIF to enhance the catalytic conversion of cellulose to HMF. Although COSLIF has little effect on biomass composition, the significant decrease in the crystallinity index of cellulose results in significantly higher HMF yields. However, the increase in yield is not as dramatic as previously reported for enzymatic conversion of COSLIFtreated biomass.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.energyfuels.6b01910. Materials and methods (PDF)
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REFERENCES
AUTHOR INFORMATION
Corresponding Author
*Telephone: +1-765-494-7022. Fax: +1-765-494-7023. E-mail:
[email protected]. Notes
The authors declare no competing financial interest. B
DOI: 10.1021/acs.energyfuels.6b01910 Energy Fuels XXXX, XXX, XXX−XXX
Communication
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DOI: 10.1021/acs.energyfuels.6b01910 Energy Fuels XXXX, XXX, XXX−XXX
