Effects of Chloride Ions in Acid-Catalyzed Biomass Dehydration Reactions in Polar Aprotic Solvents Max A

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Effects of Chloride Ions in Acid-Catalyzed Biomass Dehydration Reactions in Polar Aprotic Solvents Max A Chemical and Biological Engineering Publications Chemical and Biological Engineering 3-8-2019 Effects of chloride ions in acid-catalyzed biomass dehydration reactions in polar aprotic solvents Max A. Mellmer University of Wisconsin–Madison Chotitath Sanpitakseree University of Minnesota Benginur Demir University of Wisconsin–Madison See next page for additional authors Follow this and additional works at: https://lib.dr.iastate.edu/cbe_pubs Part of the Catalysis and Reaction Engineering Commons, and the Sustainability Commons The ompc lete bibliographic information for this item can be found at https://lib.dr.iastate.edu/ cbe_pubs/363. For information on how to cite this item, please visit http://lib.dr.iastate.edu/ howtocite.html. This Article is brought to you for free and open access by the Chemical and Biological Engineering at Iowa State University Digital Repository. It has been accepted for inclusion in Chemical and Biological Engineering Publications by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Effects of chloride ions in acid-catalyzed biomass dehydration reactions in polar aprotic solvents Abstract The use of polar aprotic solvents in acid-catalyzed biomass conversion reactions can lead to improved reaction rates and selectivities. We show that further increases in catalyst performance in polar aprotic solvents can be achieved through the addition of inorganic salts, specifically chlorides. Reaction kinetics studies of the Brønsted acid-catalyzed dehydration of fructose to hydroxymethylfurfural (HMF) show that the use of catalytic concentrations of chloride salts leads to a 10-fold increase in reactivity. Furthermore, increased HMF yields can be achieved using polar aprotic solvents mixed with chlorides. Ab initio molecular dynamics simulations (AIMD) show that highly localized negative charge on Cl− allows the chloride anion to more readily approach and stabilize the oxocarbenium ion that forms and the deprotonation transition state. High concentrations of polar aprotic solvents form local hydrophilic environments near the reactive hydroxyl group which stabilize both the proton and chloride anions and promote the dehydration of fructose. Keywords Catalytic mechanisms, Chemical engineering, Heterogeneous catalysis Disciplines Catalysis and Reaction Engineering | Chemical Engineering | Sustainability Comments This article is published as Mellmer, Max A., Chotitath Sanpitakseree, Benginur Demir, Kaiwen Ma, William A. Elliott, Peng Bai, Robert L. Johnson, Theodore W. Walker, Brent H. Shanks, Robert M. Rioux, Matthew Neurock, and James A. Dumesic. "Effects of chloride ions in acid-catalyzed biomass dehydration reactions in polar aprotic solvents." Nature Communications 10, no. 1 (2019): 1132. DOI: 10.1038/s41467-019-09090-4. Posted with permission. Creative Commons License This work is licensed under a Creative Commons Attribution 4.0 License. Authors Max A. Mellmer, Chotitath Sanpitakseree, Benginur Demir, Kaiwen Ma, William A. Elliott, Peng Bai, Robert L. Johnson, Theodore W. Walker, Brent H. Shanks, Robert M. Rioux, Matthew Neurock, and James A. Dumesic This article is available at Iowa State University Digital Repository: https://lib.dr.iastate.edu/cbe_pubs/363 ARTICLE https://doi.org/10.1038/s41467-019-09090-4 OPEN Effects of chloride ions in acid-catalyzed biomass dehydration reactions in polar aprotic solvents Max A. Mellmer1,2, Chotitath Sanpitakseree3, Benginur Demir 1,2, Kaiwen Ma1, William A. Elliott4, Peng Bai 3, Robert L. Johnson5, Theodore W. Walker1, Brent H. Shanks5, Robert M. Rioux4,6, Matthew Neurock3 & James A. Dumesic 1,2 The use of polar aprotic solvents in acid-catalyzed biomass conversion reactions can lead 1234567890():,; to improved reaction rates and selectivities. We show that further increases in catalyst performance in polar aprotic solvents can be achieved through the addition of inorganic salts, specifically chlorides. Reaction kinetics studies of the Brønsted acid-catalyzed dehy- dration of fructose to hydroxymethylfurfural (HMF) show that the use of catalytic con- centrations of chloride salts leads to a 10-fold increase in reactivity. Furthermore, increased HMF yields can be achieved using polar aprotic solvents mixed with chlorides. Ab initio molecular dynamics simulations (AIMD) show that highly localized negative charge on Cl− allows the chloride anion to more readily approach and stabilize the oxocarbenium ion that forms and the deprotonation transition state. High concentrations of polar aprotic solvents form local hydrophilic environments near the reactive hydroxyl group which stabilize both the proton and chloride anions and promote the dehydration of fructose. 1 Department of Chemical and Biological Engineering, University of Wisconsin–Madison, Madison, WI 53706, USA. 2 DOE Great Lakes Bioenergy Research Center, University of Wisconsin–Madison, Madison, WI 53706, USA. 3 Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455, USA. 4 Department of Chemical Engineering, Pennsylvania State University, State College, PA 16801, USA. 5 Department of Chemical and Biological Engineering, Iowa State University, Ames, IA 50011, USA. 6 Department of Chemistry, Pennsylvania State University, State College, PA 16801, USA. Correspondence and requests for materials should be addressed to J.A.D. (email: [email protected]) NATURE COMMUNICATIONS | (2019) 10:1132 | https://doi.org/10.1038/s41467-019-09090-4 | www.nature.com/naturecommunications 1 ARTICLE NATURE COMMUNICATIONS | https://doi.org/10.1038/s41467-019-09090-4 cid catalysis is ubiquitous in biomass-conversion pro- HCl. Rate constant values increased by over an order of cesses to produce chemicals and fuels. It has been magnitude and HMF yields increased by 15% when GVL was A fl shown recently that the use of organic solvents for such used as the solvent with H2SO4 and tri ic acid compared biomass-upgrading reactions leads to increased catalytic activity with using water as the solvent. Similar improvements in and selectivity compared with reactions in aqueous media1–25. reactivity and HMF yields were also observed using dioxane Accordingly, we explored the processing strategies using and THF as solvents. γ-valerolactone (GVL) solvent mixtures with water to produce We observe a substantial difference in the fructose conversion 2 concentrated streams of C5 and C6 sugars as well as valuable rate constant values as well as HMF yield when HCl is used as platform chemicals3 and high-value products4 from biomass the acid catalyst in these polar aprotic solvent systems compared using dilute concentrations of mineral acids. In subsequent with other strong acids. For example, in GVL with HCl, a rate studies on acid-catalyzed dehydration of xylose to furfural, we constant value of 62 M−1 ks−1 and HMF yield of 80% were reported a 30-fold increase in reactivity and a 25% increase in achieved, a threefold increase in rate constant value, and a 25% selectivity (furfural yield increased from 50% to 75%) using GVL increase in HMF yield compared with using H2SO4 and triflic as a solvent compared with the reaction carried out in water5. acid in GVL. Similar improvements using HCl compared with Similar solvent enhancement effects have been reported using H2SO4 and triflic acid were observed in THF and dioxane other polar aprotic solvents, such as tetrahydrofuran (THF)6,7, solvents, with a 5-fold and 10-fold increase in rate, respectively. dimethyl sulfoxide8–11, 1,4-dioxane12, and sulfolane13. Despite This increased reaction performance using HCl compared with the potential advantages of using polar aprotic solvents for other strong Brønsted acid catalysts is not observed using H2Oas biomass-upgrading reactions, fundamental understanding of the solvent under these conditions. these solvation effects in acid-catalyzed processes using nonaqu- As shown in Table 2, the improved performance of the fructose eous solvents is limited at present. dehydration reaction can also be achieved with the addition of Herein, we show that the addition of catalytic concentrations equimolar concentrations (i.e., 5 mM) of chloride-containing fi fl (e.g., < 5 mM) of inorganic salts, speci cally chloride salts, in polar salts (e.g., KCl) with H2SO4 and tri ic acid in GVL solvent, aprotic solvents, such as GVL, can further enhance the reactivity and yield for acid-catalyzed reactions related to biomass conver- sion. The dehydration of fructose to 5-hydroxymethylfurfural Table 2 Fructose conversion experimental results in 90% (HMF) is a Brønsted acid-catalyzed reaction, which is recognized GVL using homogeneous acid/salt systemsa as a promising biomass utilization platform. In addition, this extensively characterized reaction serves as a model system to Acid catalyst Salt Rate constant (M−1 ks−1)b study the mechanisms behind observed solvent effects. Based −c KCl 3.2 ± 1 on fundamental reaction kinetics studies and ab initio molecular H2SO4 KCl 53 ± 9 dynamics studies, we show that chloride ions participate in Triflic acid KCl 64 ± 5e stabilizing protonated transition states for these acid-catalyzed HCl KCl 78 ± 8f reactions, leading to improvements in reaction rates and H2SO4 NaCl 55 ± 20 selectivities. Triflic acid NaCl 53 ± 6 Triflic acid LiCl 69 ± 10 d Triflic acid CaCl2 71 ± 10 HBr − 28±3 Results Triflic acid KBr 22 ± 3 Experimental reaction kinetics studies.Table1 compares Triflic acid NaBr 25 ± 2 fructose conversion reaction rate constant values
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