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Electrochemical conversion of biomass-derived intermediate compounds to high-value products has emerged as a promising approach in the field of biorefinery. Biomass upgrading allows for the production of chemicals from non-fossil-based carbon sources and capitalization on electricity as a green energy input. Amino acids, as products of biomass upgrading, have received relatively little attention. Pharmaceutical and food industries will benefit from an alternative strategy for the production of amino acids that does not rely on inefficient fermentation processes. The use of renewable biomass resources as starting materials makes this proposed strategy more desirable. Herein, we report an electrochemical approach for the selective oxidation of biomass-derived α-hydroxyl acids to α-keto acids, followed by electrochemical reductive amination to yield amino acids as the final products. Such a strategy takes advantage of both reactions at the anode and cathode and produces amino acids under ambient conditions with high energy efficiency. A flow electrolyzer was also successfully employed for the conversion of α-hydroxyl acids to amino acids, highlighting its great potential for large-scale application.
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Electrohydrodimerization of biomass-derived furfural generates a jet fuel precursor
Despite the increasing interest in upgrading biomass-derived molecules to value-added products, the electrochemical conversion of biomass platform chemicals to highly valuable biofuels, such as jet fuel, has not yet received wide attention. Herein, we report a catalyst-free electrochemical route for the production of a jet fuel precursor, hydrofuroin, from the electrohydrodimerization of furfural, which can be readily derived from lignocellulose and already has an industrial production of 300 000 tons per year. Detailed electrochemical studies using carbon and copper electrodes at various pH values enabled us to probe the reduction mechanism of furfural and obtain the kinetic details, such as the diffusion constant and electron transfer rate. Preparative electrolysis in a batch electrolyzer achieved a high yield of hydrofuroin (94%) with an excellent faradaic efficiency of 93%. Finally, a flow electrolyzer was employed to demonstrate the great promise of large-scale production of hydrofuroin from the electrohydrodimerization of furfural.
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- PAR ID:
- 10205265
- Date Published:
- Journal Name:
- Green Chemistry
- Volume:
- 22
- Issue:
- 16
- ISSN:
- 1463-9262
- Page Range / eLocation ID:
- 5395 to 5401
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)The increasing demand for green chemical products calls for the exploration of sustainable and renewable carbon resources beyond fossil-based materials, whose utilization inevitably results in environmental concerns. As such, biomass valorisation has attracted increasing attention because biomass is the most widely available and sustainable carbon source. Among the available biomass-derived platform chemicals, 5-hydroxymethylfurfural (HMF) has long been regarded as an attractive candidate for the production of numerous value-added products. Nevertheless, the poor stability, and difficult separation and purification of HMF from fructose dehydration significantly inhibit its large-scale application. Herein, we report a two-step process for the direct production of two biopolymer precursors, 2,5-furandicarboxylic acid (FDCA) and 2,5-bis(hydroxymethyl)furan (BHMF), from fructose, bypassing the isolation of HMF. FDCA and BHMF are much easier to separate and purify from the reaction mixture than HMF, and they both can replace petroleum-based counterparts in the syntheses of many industrially important polymers, ranging from polyesters to polyamides. Optimized fructose dehydration under microwave irradiation achieved a high HMF yield (83%) using a biphasic strategy. The subsequent electrocatalytic conversion of the resulting microwave reaction mixture allowed us to carry out either oxidation or reduction via readily tuning the electrochemical parameters to yield FDCA or BHMF, respectively. The integration of microwave irradiation and electrocatalysis in a flow electrolyzer enabled the direct conversion of readily available fructose to highly valuable FDCA and BHMF without the expensive and challenging step of HMF isolation, suggesting an economically attractive approach for upgrading carbohydrates.more » « less
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null (Ed.)Organic electrosynthesis is emerging as a cost-effective and environmental-friendly chemical production strategy by utilizing renewable electricity. Paired electrolysis cogenerates valuable chemicals at both electrodes can optimize the energy efficiency and economic feasibility. We report pairing hydrogenation and oxidation of 5-(hydroxymethyl)furfural (HMF) or furfural to desired chemicals at a single electrolysis cell. Electrocatalytic hydrogenation of HMF to 2,5-bis(hydroxymethyl)furan (BHMF) and furfural to furfural alcohol (FA) with high selectivity of >90% can be operated at near-neutral pH on Ag-based and Pb-based catalysts, respectively. In addition, oxidizing HMF to 2,5-furandicarboxylic acid (FDCA) and furfural to furoic acid can both be realized at TEMPO mediated process by using carbon-based catalysts or at Ni-based catalyst in an alkaline medium. Taken together, HMF or furfural can be performed in a single electrolysis cell with a minimized cell voltage only around 1.6 V. Products selectivity and faradaic efficiency are highly related to the reaction conditions, including potential or current density, architectures of the reactor, type of catalysts. By optimizing the single flow reactor, a three-electrode system, two-electrode membrane assembly architecture, and pH-symmetric and pH-asymmetric structure can be designed to reduce the capital expense, minimize required energy, and simplify processing steps. Finally, a complete electrons economy can be achieved by pairing two electrochemical reactions, and the overall charge efficiency can attain over 170% without any crossover issue detected. As a result, the continuous cogeneration of high value-added BHMF or FA and FDCA or furoic acid can be performed in a single electrolyzer.more » « less
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Biomass is abundant, inexpensive and renewable, therefore, it is highly expected to play a significant role in our future energy and chemical landscapes. The US DOE has identified furanic compounds (furfural and 5-(hydroxymethyl)furfural (HMF)) as the top platform building-block chemicals that can be readily derived from biomass sources [1]. Electrocatalytic conversion of these furanic compounds is an emerging route for the sustainable production of valuable chemicals [2, 3]. In my presentation, I will first present our recent mechanistic study of electrochemical reduction of furfural through a combination of voltammetry, preparative electrolysis, thiol-electrode modifications, and kinetic isotope studies [4]. It is demonstrated that two distinct mechanisms are operable on metallic Cu electrodes in acidic electrolytes: (i) electrocatalytic hydrogenation (ECH) and (ii) direct electroreduction. The contributions of each mechanism to the observed product distribution are clarified by evaluating the requirement for direct chemical interactions with the electrode surface and the role of adsorbed hydrogen. Further analysis reveals that hydrogenation and hydrogenolysis products are generated by parallel ECH pathways. Understanding the underlying mechanisms enables the manipulation of furfural reduction by rationally tuning the electrode potential, electrolyte pH, and furfural concentration to promote selective formation of important bio-based polymer precursors and fuels. Next, I will present electrocatalytic conversion of HMF to two biobased monomers in an H-type electrochemical cell [5]. HMF reduction (hydrogenation) to 2,5-bis(hydroxymethyl)furan (BHMF) was achieved under mild electrolyte conditions and ambient temperature using a Ag/C cathode. Meanwhile, HMF oxidation to 2,5-furandicarboxylic acid (FDCA) with ~100% efficiency was facilitated under the same conditions by a homogeneous nitroxyl radical redox mediator, together with an inexpensive carbon felt anode. The selectivity and efficiency for Ag-catalyzed BHMF formation were sensitive to cathode potential, owing to competition from HMF hydrodimerization reactions and water reduction (hydrogen evolution). Moreover, the carbon support of Ag/C was active for HMF reduction and contributed to undesired dimer/oligomer formation at strongly cathodic potentials. As a result, high BHMF selectivity and efficiency were only achieved within a narrow potential range near –1.3 V. Fortunately, the selectivity of redox-mediated HMF oxidation was insensitive to anode potential, thus allowing HMF hydrogenation and oxidation half reactions to be performed together in a single cathode-potential-controlled cell. Electrocatalytic HMF conversion in a paired cell achieved high molar yields of BHMF and FDCA, and nearly doubled electron efficiency compared to the unpaired cell. Finally, I will briefly introduce our recent work on the development of a three-electrode flow cell with an oxide-derived Ag (OD-Ag) cathode and catbon felt anode for paring elecatalytic oxidation and reduction of HMF. The flow cell has a remarkable cell voltage reduction from ~7.5 V to ~2.0 V by transferring the electrolysis from the H-type cell to the flow cell [6]. This represents a more than fourfold increase in the energy efficiency at the 10 mA operation. A combined faradaic efficiency of 163% was obtained to BHMF and FDCA. Alternatively, the anodic hydrogen oxidation reaction on platinum further reduced the cell voltage to only ~0.85 V at 10 mA operation. These paired processes have shown potential for integrating renewable electricity and carbon for distributed chemical manufacturing in the future.more » « less
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Biomass is abundant, inexpensive and renewable, therefore, it is highly expected to play a significant role in our future energy and chemical landscapes. The US DOE has identified furanic compounds (furfural and 5-(hydroxymethyl)furfural (HMF)) as the top platform building-block chemicals that can be readily derived from biomass sources [1]. Electrocatalytic conversion of these furanic compounds is an emerging route for the sustainable production of valuable chemicals [2, 3]. In my presentation, I will first present our recent mechanistic study of electrocatlytic hydrogenation (ECH) of furfural through a combination of voltammetry, preparative electrolysis, thiol-electrode modifications, and kinetic isotope studies [4]. It is demonstrated that two distinct mechanisms are operable on metallic Cu electrodes in acidic electrolytes: (i) electrocatalytic hydrogenation (ECH) and (ii) direct electroreduction. The contributions of each mechanism to the observed product distribution are clarified by evaluating the requirement for direct chemical interactions with the electrode surface and the role of adsorbed hydrogen. Further analysis reveals that hydrogenation and hydrogenolysis products are generated by parallel ECH pathways. Understanding the underlying mechanisms enables the manipulation of furfural reduction by rationally tuning the electrode potential, electrolyte pH, and furfural concentration to promote selective formation of important bio-based polymer precursors and fuels We further studied the mechanisms on the Pb electrode, based on the potential regulated ECH and ER products. Isotopic incorporation studies and electrokinetics have confirmed ECH process to alcohol and alkyl product followed different pathways: alcohol was generated from Langmuir Hinshelwood step through surface-bound furfural and hydrogen, which is sensitive to surface structures. In contrast, alkyl product was formed through an Eley–Rideal step via surface-bound furfural and the inner-sphere protons. By modifying the electrode/electrolyte interface, we have elucidated H2O and H3O+ matters in forming alcohol and alkyl products, respectively. Dynamic oscillation studies and electron paramagnetic resonance (EPR) finally confirmed that the alcohol and dimer products shared the same intermediate. The dimer was formed through the intermediate desorption from the surface to form radicals and the self-coupling of two radicals at the bulk electrolyte. Next, I will present electrocatalytic conversion of HMF to two biobased monomers in an H-type electrochemical cell [5]. HMF reduction (hydrogenation) to 2,5-bis(hydroxymethyl)furan (BHMF) was achieved under mild electrolyte conditions and ambient temperature using a Ag/C cathode. Meanwhile, HMF oxidation to 2,5-furandicarboxylic acid (FDCA) with ~100% efficiency was facilitated under the same conditions by a homogeneous nitroxyl radical redox mediator. We recently developed a three-electrode flow cell with an oxide-derived Ag (OD-Ag) cathode and catbon felt anode for paring elecatalytic oxidation and reduction of HMF [6]. The flow cell has a remarkably low cell voltage: from ~7.5 V to ~2.0 V by transferring the electrolysis from the H-type cell to the flow cell. This represents a more than fourfold increase in the energy efficiency at the 10 mA operation. A combined faradaic efficiency of 163% was obtained to BHMF and FDCA. Alternatively, the anodic hydrogen oxidation reaction on platinum further reduced the cell voltage to only ~0.85 V at 10 mA operation. These paired processes have shown potential for integrating renewable electricity and carbon for distributed chemical manufacturing in the future.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/d0gc01720e
