Process for the preparation of gamma-butyrolactone

Abstract

Disclosed is a process for the preparation of gamma-butyrolactone, which comprises converting furan acid into said gamma-butyrolactone in a membraneless tank free of mediators for paired electrolysis, said process comprising the steps of: a) electrochemically oxidizing said furan acid to 2(5H)-furanone; and b) electrochemically reducing said 2(5H)-furanone to said gamma-butyrolactone.

Description

Technical Field

[0001] This invention belongs to the field of chemical synthesis and relates to an electrochemical method for preparing γ-butyrolactone, wherein the γ-butyrolactone is, for example, particularly but not exclusively, a biomass-derived γ-butyrolactone. Background Technology

[0002] Biomass is an attractive carbon source for the production of sustainable fuels and chemicals. Therefore, the high-value utilization of biomass—the conversion of various lignocellulosic feedstocks into biofuels and bio-derived chemicals—has garnered considerable attention over the past few decades. In particular, gamma-butyrolactone (also known as γ-butyrolactone) (GBL) has become an important biorefining compound due to its versatility; it is a non-toxic solvent and chemical precursor that can be used in various industries, including the fragrance, pharmaceutical, and perfume industries. The global market size for GBL is believed to have reached US$3.61407 billion in 2022 and is projected to exceed US$4.90437 billion by 2032.

[0003] GBL preparation can be divided into two main routes: the petroleum-based route and the biomass-based route. In the petroleum-based route (for example, see...),... Figure 1A This typically involves oxidizing benzene to maleic anhydride at 200-600°C and 1-3 bar of oxygen (O2), and then hydrogenating the maleic anhydride to GBL at 160-280°C and 6-8 MPa of hydrogen (H2). Alternatively, it may involve condensing acetylene with formaldehyde at 90-110°C and 0.5-2.0 MPa of H2 to form 1,4-butanediol, followed by dehydrogenation and ring closure at 180-300°C to obtain GBL.

[0004] In a biomass-based route, it may involve the thermal catalytic conversion of furan precursors such as furfural (FAL) or furoic acid (FA) to GBL, which typically involves a two-stage process: (1) oxidizing FAL or FA to 2(5H)-furanone (2-FO); and (2) hydrogenating the isolated 2-FO to produce GBL. However, such a thermal method is believed to involve any of the following: stoichiometric oxidants (e.g., H2O2, peroxymonosulfate, etc.), metal catalysts (e.g., CuMoO4, Pd / SiO2, etc.), or harsh reaction conditions (e.g., high pressure (e.g., >2 MPa) and high temperature (e.g., >100 °C)), and all of the above conditions are believed to reduce selectivity for 2-FO, resulting in the production of various oxidation or ring-opening products, such as maleic acid (MA), 5-hydroxy-2(5H)-furanone (HFO), and CO2, etc.

[0005] Therefore, it is believed that achieving a simple conversion of furan precursors such as FAL and FA to GBL with considerable yield and efficiency remains challenging.

[0006] This invention seeks to eliminate or at least mitigate such problems by providing a new or improved method for producing GBL. Summary of the Invention

[0007] In a first aspect of the invention, a method for preparing γ-butyrolactone is provided, the method comprising the step of converting furoic acid to γ-butyrolactone in a diaphragmless tank free of mediators for paired electrolysis, the method comprising the steps of: a) electrochemically oxidizing furoic acid to 2(5H)-furanone; and b) electrochemically reducing 2(5H)-furanone to γ-butyrolactone. Optionally, the mediator comprises TEMPO, an organic co-solvent, or a separator.

[0008] Optionally, the diaphragmless tank includes an electrode pair made of any one of platinum, nickel, palladium, ruthenium, rhodium, lead, lead oxide, manganese, manganese oxide, molybdenum, iridium oxide, iridium, fluorine-doped tin oxide, indium tin oxide, carbon-based materials (especially carbon cloth), zinc, copper, or gold.

[0009] In an optional embodiment, the electrode pair includes an anode made of platinum, palladium, fluorine-doped tin oxide, or gold.

[0010] In an optional embodiment, the electrode pair includes a cathode made of any one of platinum, nickel, palladium, ruthenium, rhodium, lead, lead oxide, manganese, manganese oxide, molybdenum, iridium oxide, iridium, fluorine-doped tin oxide, indium tin oxide, carbon-based materials (especially carbon cloth), zinc, copper, or gold.

[0011] Optionally, the step of converting furoic acid to γ-butyrolactone is carried out at pH 2-6.

[0012] Optionally, the step of converting furoic acid to γ-butyrolactone is carried out in an atmosphere of 0.5 to 3 atm.

[0013] Optionally, the step of converting furoic acid to γ-butyrolactone is carried out at a temperature of about 20°C to about 100°C.

[0014] Optionally, the step of converting furoic acid to γ-butyrolactone is carried out at an applied voltage of about 1.4 V to about 3.0 V relative to Ag / AgCl.

[0015] Optionally, the method further includes the step of separating γ-butyrolactone after completing step b).

[0016] In an optional embodiment, the step of converting furoic acid to γ-butyrolactone is carried out in a separatorless, diaphragmless tank under an ambient atmosphere of 1 atm, at pH 3 to 6, at a temperature of about 35°C to about 80°C, and at an applied voltage of about 1.8V to about 2.0V relative to Ag / AgCl.

[0017] Optionally, the separatorless diaphragmless tank includes a platinum anode, a nickel cathode, an Ag / AgCl counter electrode, and a phosphate buffer solution containing approximately 1 mM to approximately 200 mM furoic acid.

[0018] In one optional embodiment, furoic acid is biomass-derived furoic acid.

[0019] Optionally, furoic acid is electrochemically oxidized to 2(5H)-furanone with a selectivity of about 40% to about 95%. In an optional embodiment, furoic acid is electrochemically oxidized to 2(5H)-furanone with a selectivity of 84.2%.

[0020] Optionally, furoic acid is electrochemically oxidized to 2(5H)-furanone in a yield of about 40% to about 95%. In one optional embodiment, furoic acid is electrochemically oxidized to 2(5H)-furanone in a yield of 74.8%.

[0021] Optionally, furoic acid is electrochemically oxidized to 2(5H)-furanone, with a carbon balance of about 40% to about 95%. In an optional embodiment, furoic acid is electrochemically oxidized to 2(5H)-furanone, with a carbon balance of 89.0%.

[0022] Optionally, 2(5H)-furanone is electrochemically reduced by olefin hydrogenation to produce about 40% to about 99% of γ-butyrolactone. Attached Figure Description

[0023] The invention will now be described more specifically by way of example only with reference to the accompanying drawings, in which:

[0024] Figure 1A A schematic diagram of the synthesis of GBL from petroleum-derived substrates is shown;

[0025] Figure 1B It is a table summarizing the different systems used to oxidize furfural to produce furoic acid;

[0026] Figure 1C This is a schematic diagram illustrating the production of GBL from biomass-related precursors according to an embodiment of the present invention;

[0027] Figure 2A Cyclic voltammograms with and without 20 mM 2-FO are shown using Pt as the working electrode in a forward scan.

[0028] Figure 2B Cyclic voltammograms with negative scans are shown using Ni as the working electrode, with and without 20 mM FA.

[0029] Figure 3The electrochemical oxidation of FA in pH 2 is illustrated. 10 mM FA, 1 mA constant current, pH 2 buffer, 80 °C, through a charge of 0–86.4 C (24 h). WE:Pt, CE:Pt. Experiments were performed in triplicate, and error bars correspond to the standard deviation of three independent measurements.

[0030] Figure 4A The stability reaction conditions of 2-FO at 80 °C and pH 2 to 9 are shown: 10 mM 2-FO in 10 mL of 0.5 M potassium phosphate buffer at different pH values ​​at 80 °C;

[0031] Figure 4B The yields of MA at pH 2 to 9 are shown. Reaction conditions: 10 mM 2-FO in 10 mL of 0.5 M potassium phosphate buffer at different pH values ​​at 80 °C;

[0032] Figure 5A The ECO reactions of FA on Pt or Au at pH 1 or 5.5 are shown. Reaction conditions: 10 mM FA in 10 mL pH 5.5 buffer; applied voltage: +1.8 V Ag / AgCl The experiment was conducted with a charge of 100°C; platinum foil was used as both the working and counter electrodes. The experiment was performed in triplicate, and the error bars corresponded to the standard deviation of the three independent measurements.

[0033] Figure 5B It is a table summarizing the conversion, product yield, selectivity, and carbon balance of FA after electrocatalytic oxidation under different anodes and pH conditions;

[0034] Figure 6 This is a schematic diagram of anodic interface events at pH 1 and above 40°C;

[0035] Figure 7 The maximum UV-Vis absorbance (λ) of FA at pH 2 to 9 is shown. max );

[0036] Figure 8 This is a schematic diagram of anodic interface events at pH 5.5 and above 40°C;

[0037] Figure 9A The study of LSV at pH 1 with and without 50 mM FA is shown. Reaction conditions: scan rate 50 mV / s; 80 °C; WE: Pt; CE: Pt;

[0038] Figure 9B The study of LSV at pH 5.5 with and without 50 mM FA is shown. Reaction conditions: scan rate 50 mV / s; 80 °C; WE: Pt; CE: Pt;

[0039] Figure 10A The ECO of FA is shown at temperatures ranging from 20°C to 80°C. Reaction conditions: 10 mM FA in 10 mL of pH 5.5 buffer; applied voltage: +1.8 V. Ag / AgCl The experiment was conducted with a charge of 100°C; platinum foil was used as both the working and counter electrodes. The experiment was performed in triplicate, and the error bars corresponded to the standard deviation of the three independent measurements.

[0040] Figure 10B This is a table summarizing the conversion rate and product yield of FA after electrocatalytic oxidation at different temperatures;

[0041] Figure 11A Linear sweep voltammograms (LSV) of the electrode are shown at 20°C in pH 5.5 buffer with and without 50 mM FA. At j = 7.5 mA cm⁻¹ -2 The potential difference is measured below. WE: Pt; CE: Pt;

[0042] Figure 11B Linear sweep voltammograms (LSVs) of the electrode are shown at 40°C in pH 5.5 buffer with and without 50 mM FA. At j = 7.5 mA cm⁻¹ -2 The potential difference is measured below. WE: Pt; CE: Pt;

[0043] Figure 11C Linear sweep voltammograms (LSVs) of the electrode are shown at 60 °C in pH 5.5 buffer with and without 50 mM FA. At j = 7.5 mA cm⁻¹ -2 The potential difference is measured below. WE: Pt; CE: Pt;

[0044] Figure 11D Linear sweep voltammograms (LSV) of the electrode are shown at 80 °C in pH 5.5 buffer with and without 50 mM FA. At j = 7.5 mA cm⁻¹ -2 The potential difference is measured below. WE: Pt; CE: Pt;

[0045] Figure 12 This is a schematic diagram illustrating the proposed mechanism pathway for the conversion of FA to GBL in an electrolyte at 80°C in pH 5.5 electrolyte.

[0046] Figure 13 This is a schematic diagram of anodic interface events at pH 5.5 and below 40°C;

[0047] Figure 14The ECH of 20 mM 2-FO in 20 mL of 0.5 M buffer (pH 5.5) at 80 °C on a Ni cathode paired with a Pt anode as the counter electrode is shown at 10, 20, and 30 mA cm⁻¹. -2 Electrolysis was performed at a total temperature of 360°C.

[0048] Figure 15 This is a table summarizing the d-band center and width of bulk electrocatalysts;

[0049] Figure 16A Cyclic voltammograms (CVs) are shown at 80 °C with and without 20 mM 2-FO in 20 mL of pH 5.5 electrolyte, using Ni, Pd, and Cu as working electrodes, respectively.

[0050] Figure 16B Cyclic voltammograms (CVs) are shown at 80 °C with and without 20 mM 2-FO in 20 mL of pH 5.5 electrolyte, using Pt, Pb, and Au as working electrodes, respectively.

[0051] Figure 16C Cyclic voltammograms (CVs) are shown at 80 °C with and without 20 mM 2-FO in 20 mL of pH 5.5 electrolyte, using carbon cloth, Mo, and Zn as working electrodes, respectively.

[0052] Figure 17 The electrochemical reduction (ECH) of 2-FO was demonstrated at 20°C–80°C. The experiment was performed in triplicate, and the error bars correspond to the standard deviation of three independent measurements. Reaction conditions: 20 mM 2-FO in 20 mL pH 5.5 buffer; 2.0 V Ag / AgCl ;WE: Pt, CE: Ni;

[0053] Figure 18 The results showed that at pH 2-6 (2.0V) Ag / AgCl Conversion rate and yield at WE:Pt, CE:Ni, total at 100°C;

[0054] Figure 19 The results were shown at 80°C and a scan rate of 50 mV / s. -1 CV analysis of 20 mM 2-FO (WE: Ni, RE: Ag / AgCl, CE: Pt);

[0055] Figure 20 Cyclic voltammograms (CVs) are shown at 80 °C with or without 20 mM 2-FO in an electrolyte at pH 5.5. WE: Ni; CE: Pt;

[0056] Figure 21AIt shows the range from 1.6 to 2.2V. Ag / AgCl Electrochemical reduction (ECH) of 2-FO under an applied anodic potential. Experiments were performed in triplicate, and error bars corresponded to the standard deviation of three independent measurements. Reaction conditions: 20 mM 2-FO in 20 mL pH 5.5 buffer at 80 °C; WE: Pt, CE: Ni;

[0057] Figure 21B This is a table summarizing the corresponding cathode potentials and average current densities. The experiment was performed in triplicate, and the error bars correspond to the standard deviation of three independent measurements. Reaction conditions: 20 mM 2-FO in 20 mL of pH 5.5 buffer at 80 °C; WE: Pt, CE: Ni;

[0058] Figure 22 The results show that 2-FO (2.0V) under optimized conditions (pH 5.5 buffer, 80°C) were tested. Ag / AgCl Time-resolved electrolysis of (WE: Pt, CE: Ni). The experiment was conducted in triplicate, and the error bars corresponded to the standard deviation of the three independent measurements.

[0059] Figure 23 This is a schematic diagram of the electrochemical redox stage combination of GBL from furoic acid (FA) to 2(5H)-furanone (2-FO) to γ-butyrolactone (GBL) in a one-pot process according to an embodiment of the present invention;

[0060] Figure 24 This demonstrates a one-pot electrochemical conversion of 20 mM FA in 20 mL (pH 5.5) buffer; 80 °C; 2.0 V. Ag / AgCl Through different charges. WE: Pt, CE: Ni. The experiment was conducted in triplicate, and the error bars corresponded to the standard deviation of the three independent measurements;

[0061] Figure 25 The one-pot electrochemical conversion of 100 mM FA in 20 mL (pH 5.5) buffer is demonstrated; 80 °C; 2.0 V. Ag / AgCl Through different charges. WE: Pt, CE: Ni. The experiment was conducted in triplicate, and the error bars corresponded to the standard deviation of the three independent measurements; and

[0062] Figure 26 The one-pot electrochemical conversion of 150 mM FA in 20 mL (pH 5.5) buffer is demonstrated; 80 °C; 2.0 V. Ag / AgCl The experiment was conducted using different charges. WE: Pt, CE: Ni. The experiment was performed in triplicate, and the error bars corresponded to the standard deviation of the three independent measurements. Detailed Implementation

[0063] As used herein, unless the context clearly indicates otherwise, the forms “a” and “the” are intended to include both singular and plural forms.

[0064] The terms “example” or “exemplary” as used in this invention are intended to be used as examples, instances, or illustrations. Any aspect or design described as “exemplary” in this disclosure is not necessarily to be construed as being more preferred or advantageous than other aspects or designs. Rather, the use of the terms “example” or “exemplary” is intended to present concepts in a specific manner. As used in this application, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or.” That is, unless otherwise specified or the context clearly indicates, “X adopts A or B” is intended to mean any natural inclusive permutation. That is, “X adopts A or B” holds true if X adopts A; X adopts B; or X adopts both A and B.

[0065] As used herein, the term “approximately” is intended to refer to values ​​that deviate slightly from those described herein. For example, “approximately 20°C” can mean 18 to 22°C (e.g., 18.9, 19.5, 20, 21.1, 21.9°C, etc.); “approximately 1.8V” can mean 1.7 to 1.9V (e.g., 1.72, 1.78, 1.8, 1.85, 1.88, 1.9, etc.); “approximately 100mM” can mean 98 to 102mM (e.g., 98.1, 98.6, 99.3, 99.8, 100, 100.6, 101.2, 101.9, etc.), and so on.

[0066] One believed alternative approach for the synthesis of γ-butyrolactone (GBL) from furan precursors is electrocatalysis, particularly those involving specific pairwise electrolysis (i.e., combining specific oxidation and specific reduction to obtain the desired product). Typically, such electrocatalysis can utilize an applied potential bias to simultaneously achieve electrochemical redox reactions at each electrode. However, in most cases, the pairwise electrolysis setup involves separating the redox reactions using ion-exchange membranes or porous glass frits to minimize yield loss from the reverse reaction, and the product streams are collected separately or combined for subsequent reactions.

[0067] Unwilling to be bound by theory, the inventors have developed, through their own research, experimentation, and verification, an electrochemical synthesis of GBL that can be carried out in a one-pot paired electrolytic unit without separators. Specifically, the synthesis can comprise multiple electrochemical reactions under mild conditions, such as ambient pressure and low temperatures (e.g., below 100°C), in which furoic acid (FA) is converted to GBL without the separation of any intermediates during the reaction. Furthermore, in some exemplary embodiments, the synthetic method of the present invention has been found to provide considerably high conversion selectivity and yield. Therefore, it is believed that the present invention can provide a simple, efficient, green, and sustainable method for the high-value conversion of furan precursors such as FA to GBL.

[0068] In a first aspect of the invention, a method for preparing γ-butyrolactone is provided, the method comprising the step of converting furoic acid to γ-butyrolactone in a diaphragmless tank free of mediators for paired electrolysis, the method comprising the steps of: a) electrochemically oxidizing furoic acid to 2(5H)-furanone; and b) electrochemically reducing 2(5H)-furanone to γ-butyrolactone.

[0069] As used herein, the term "diaphragmless tank" generally refers to an electrochemical cell having a single chamber / compartment in which electrochemical oxidation and electrochemical reduction occur. In other words, both electrochemical oxidation and reduction occur within the same chamber / compartment of the diaphragmless tank. Specifically, a diaphragmless tank, as used herein, can be a diaphragmless tank that does not contain mediators such as (2,2,6,6-tetramethylpiperidin-1-yl)oxy (TEMPO), organic cosolvents, or separators (e.g., ion exchange membrane separators). It is believed that, compared to a diaphragm tank, a diaphragmless tank minimizes pH fluctuations and thus promotes the selective oxidation of FA to 2-FO. Diaphragmless tanks can take the form of small glass cups, beakers, round-bottom flasks, etc. It should be understood that those skilled in the art can choose the appropriate form based on practical needs.

[0070] In some embodiments, the diaphragmless tank may comprise an electrode pair (i.e., an anode and a cathode) made of any of platinum, nickel, palladium, ruthenium, rhodium, lead, lead oxide, manganese, manganese oxide, molybdenum, iridium oxide, iridium, fluorine-doped tin oxide (FTO), indium tin oxide (ITO), a carbon-based material (e.g., carbon cloth), zinc, copper, or gold. For example, in some embodiments, the anode may be made of platinum, palladium, fluorine-doped tin oxide, or gold. In some embodiments, the cathode may be made of any of platinum, nickel, palladium, ruthenium, rhodium, lead, lead oxide, manganese, manganese oxide, molybdenum, iridium oxide, iridium, fluorine-doped tin oxide, indium tin oxide, carbon cloth, zinc, copper, or gold.

[0071] The process disclosed herein for converting FA to GBL specifically includes sequentially oxidizing FA to 2-FO (step a) and then reducing 2-FO to GBL (step b). Therefore, the yield of 2-FO is believed to be one of the factors controlling the subsequent yield of GBL. It is also believed that alkaline pH conditions (such as pH greater than 6) may cause an irreversible ring-opening reaction of 2-FO, producing maleic acid (MA), which reduces the amount of 2-FO reduced to GBL. Therefore, it is preferred that the step of converting furoic acid to γ-butyrolactone is carried out in an acidic environment. In some embodiments, the step of converting furoic acid to γ-butyrolactone can be carried out at pH 2 to 6, 2.1 to 6, 2.1 to 5.9, 2.5 to 6, 2.8 to 6, 2.8 to 5.9, 3 to 6, 3 to 5.8, 3 to 5.5, 3.8 to 6, 4 to 6, 4 to 5.8, 4 to 5.5, 4.5 to 5.5, 4.8 to 5.5, 5 to 5.5, etc.

[0072] The conversion of furoic acid to γ-butyrolactone can also be carried out under mild pressure conditions and / or temperature. For example, in some embodiments, the conversion step can be carried out in an ambient atmosphere of 0.5 atmospheres to 3 atmospheres, such as 1 atmosphere. In some other embodiments, the conversion step can be carried out at temperatures of about 20°C to about 100°C, such as about 22°C to about 101°C, about 21°C to about 100°C, about 20°C to about 99°C, about 20°C to about 90°C, about 21°C to about 89°C, about 22°C to about 81°C, about 20°C to about 79°C, about 28°C to about 80°C, about 28°C to about 79°C, about 30°C to about 80°C, about 30°C to about 81°C, about 31°C to about 80°C, about 31°C to about 79°C, about 35°C to about 80°C, about 35°C to about 81°C, etc.

[0073] In some embodiments, the conversion of furoic acid to γ-butyrolactone can be carried out at an applied voltage of about 1.4 V to about 3.0 V relative to Ag / AgCl, particularly at an anodic voltage. In other words, the conversion step can be carried out accordingly at a cathode voltage of about -0.2 V to about -2.0 V relative to Ag / AgCl.

[0074] In some optional or additional embodiments, the method of the present invention further includes the step of separating γ-butyrolactone after step b). For example, γ-butyrolactone can be separated from the electrochemical reaction mixture by solvent extraction with a suitable solvent, particularly an organic solvent such as dichloromethane. The organic phase containing the extracted GBL can then be dried with anhydrous Na₂SO₄, MgSO₄, etc., followed by removal of the organic solvent by, for example, rotary evaporation to obtain GBL. In some other optional or additional embodiments, the GBL obtained from the extraction can be further purified by column chromatography.

[0075] In some specific embodiments, the step of converting furoic acid to γ-butyrolactone can be carried out in a separatorless diaphragmless tank, i.e., a tank without a separator between the anode and cathode. In these embodiments, the separatorless diaphragmless tank may include a platinum anode, a nickel cathode, an Ag / AgCl counter electrode, and a phosphate buffer solution containing about 1 mM to about 200 mM furoic acid.

[0076] Furoic acid can be biomass-derived, such as those derived from / obtained from hemicellulose. Alternatively or optionally, furoic acid can be obtained under various reported conditions, such as Figure 1B The conditions shown are obtained from the oxidation of furfural (FAL). As described herein, it is preferred to use FA instead of FAL as a feedstock for the production of GBL because acidic conditions (such as those with an acidic pH as described herein) are believed to favor the conversion of FA to 2-FO, while FAL tends to be unstable under such acidic conditions (e.g., FAL may tend to form humic substances and / or be readily reduced to furfuryl alcohol).

[0077] In operation, the conversion of furoic acid to γ-butyrolactone can be carried out under an ambient atmosphere of 1 atmosphere, at pH 3 to 6, at a temperature of about 35°C to about 80°C, and at an applied voltage of about 1.8V to about 2.0V relative to Ag / AgCl. Specifically, the operating temperature in these embodiments may be higher than the boiling point of the furan radical intermediate, thereby promoting its escape from the electrode (anodide) surface and reaction with the surrounding H2O to produce 2-hydroxyfuran, which is then tautomerized to produce 2-FO.

[0078] In some embodiments, furoic acid can be electrochemically oxidized to 2(5H)-furanone with a selectivity of about 40% to about 95%, such as about 40.5% to about 95%, about 40.5% to about 95.1%, about 45% to about 90%, about 50% to about 90%, about 55% to about 88%, about 60.2% to about 84%, about 60% to about 84.2%, about 65% to about 84%, about 65.5% to about 84.1%, about 68% to about 83.9%, about 70% to about 80%, about 80% to about 84%, etc. In some specific embodiments, furoic acid can be electrochemically oxidized to 2(5H)-furanone with a selectivity of 84.2%.

[0079] In some embodiments, furoic acid can be electrochemically oxidized to 2(5H)-furanone in yields of about 40% to about 95%, such as about 40.5% to about 95%, about 40.5% to about 95.1%, about 45% to about 90%, about 50% to about 90%, about 55% to about 88%, about 55.5% to about 80.1%, about 54.9% to about 79%, about 55% to about 79.8%, about 55% to about 74.8%, about 65% to about 80%, about 68% to about 80%, about 68.2% to about 7%, about 68.4% to about 79%, etc. In some specific embodiments, furoic acid can be electrochemically oxidized to 2(5H)-furanone in yield of 74.8%.

[0080] In some embodiments, furoic acid can be electrochemically oxidized to 2(5H)-furanone with a carbon balance of about 40% to about 95%, such as about 40.5% to about 95%, about 40.5% to about 95.1%, about 45% to about 90%, about 50% to about 90%, about 55% to about 88%, about 50.5% to about 90%, about 55% to about 89%, about 55.5% to about 90%, about 62.8% to about 89%, about 68% to about 89%, about 68.4% to about 80.5%, about 68.4% to about 84.2%, etc. In some specific embodiments, furoic acid can be electrochemically oxidized to 2(5H)-furanone with a carbon balance of 89.0%.

[0081] In addition to the operating temperatures described above, the operating pH in these embodiments can promote the hydrogenation of 2-FO olefins to produce GBL. Specifically, it is believed that within this pH range, the onset potential of the hydrogen evolution reaction (HER) may become more negative than that of 2-FO, thus minimizing competition from HER. In some embodiments, 2(5H)-furanone can be electrochemically reduced via olefin hydrogenation to produce about 40% to about 99% (e.g., about 40.5% to about 98.9%, about 43% to about 98.2%, about 47.8% to about 97%, about 47% to about 96.5%, about 57% to about 97%, about 57.4% to about 96.5%, about 47% to about 69.1%, about 47.8% to about 93.5%, etc.) of γ-butyrolactone.

[0082] Details of the reaction mechanism and the efficiency of the synthetic method will be discussed in later parts of this disclosure.

[0083] The invention is described in more detail below by way of examples, but is not limited thereto.

[0084] Example

[0085] Materials and methods

[0086] All solutions were prepared using ultrapure deionized water (>18.2 MΩcm).-1 Preparations were made using reagents from Millipore. Potassium hydrogen phosphate (K₂HPO₄, 99%), potassium dihydrogen phosphate (KH₂PO₄, 99.8%), 2(5H)-furanone (2-FO, 98%), and maleic acid (MA, >99%) were purchased from Aladdin. Phosphoric acid (85%–87%), methanol (ACS grade), and dichloromethane (DCM, ACS grade) were purchased from Anaqua. Butyric acid (BA, 99%) and furoic acid (FA, 98%) were purchased from Dieckmann. Formic acid (>99%) and 5-hydroxy-2(5H)-furanone (HFO, 98%) were purchased from Macklin. All reagents and electrodes purchased from commercial sources were used without additional purification or modification.

[0087] Electrocatalytic reaction

[0088] An electrochemical workstation (CHI 660E, CH Instruments Co., Ltd., Shanghai, China) was used. All electrolysis experiments were performed in a 30 mL diaphragmless tank with a three-electrode configuration. All metal electrodes were cleaned in acetone and water for 5 minutes under ultrasonic conditions, and then immersed in 0.5 M H₂SO₄ for 2 minutes. All potentials reported in this work are referenced to an Ag / AgCl reference electrode without iR compensation. Electrolyte solutions with different pH values ​​were prepared by mixing 0.5 M H₃PO₄, KH₂PO₄, and K₂HPO₄ (i.e., 0.5 M phosphate buffer). Unless otherwise specified, each electrolysis experiment used an anode and cathode with dimensions of 10 × 10 × 0.1 mm and no covering on either side.

[0089] Electrolysis scale-up and product separation

[0090] The reaction was scaled up in a 1000 mL single tank with two electrodes (3 × 3 cm nickel cathode; 3 × 3 cm platinum anode) at 50 mA cm⁻¹. -2 The reaction mixture was run under constant current. The same electrolyte as described above was used, except that 5 g to 20 g (e.g., 5.6 g) of FA was used in 500 mL of electrolyte. After electrolysis for 24 hours, the reaction mixture was extracted with 1000 mL of DCM, the organic layer was dried with anhydrous sodium sulfate, and then the DCM was removed by rotary evaporation for 1 hour to obtain GBL.

[0091] Product Analysis

[0092] All products were quantitatively analyzed using a Waters Breeze HPLC instrument. A reversed-phase column (C18, Atlantis) running at 30 °C was used to separate the product mixture. The mobile phase was a 10 mM aqueous solution of H3PO4 / KH2PO4 and methanol in a 90:10 (v / v) ratio, with an isocratic flow rate of 1 mL / min. The concentrations of FA and its products were quantified using external standards with a photodiode array and refractive index detector. Infrared spectra were collected using a Fourier transform infrared spectrometer (Perkin Elmer) in the range of 4500–600 cm⁻¹. -1 Four scans were performed. UV-Vis spectrophotometric measurements were conducted in the 220-300 nm range using a UV-3600 spectrophotometer (Shimadzu, Japan). 1 The purity of GBL was determined by 1H NMR spectroscopy (Bruker Advance-III) using a 400-MHz instrument equipped with a broadband probe and with reference to an external standard of formic acid.

[0093] calculate

[0094] Calculate the conversion (Conv.), selectivity (Sel.), carbon balance (CB), Faraday efficiency (FE), and yield using the following equations:

[0095]

[0096]

[0097]

[0098]

[0099]

[0100] Among them mol 初始反应物 and mol 反应物 These represent the number of moles of the corresponding reactants before and after the reaction; mol x It is related to the number of moles of product; n and F are the electron transfer number and Faraday constant at 96,485 C / mol, respectively. The total charge is calculated as the integral of the current (I, A) over the operating time in seconds.

[0101] Example 1

[0102] Furoic acid (FA) is electrochemically oxidized to 2(5H)-furanone (2-FO).

[0103] The electrocatalytic conversion of FA to GBL in this invention involves sequentially oxidizing FA to 2-FO in a membrane-free tank, followed by reducing 2-FO to GBL. Figure 1C It is believed that a key factor promoting these two reactions in a diaphragmless tank is that, due to the mild conditions, the substances involved (e.g., FA, 2-FO, and GBL) do not undergo undesirable redox reactions. Controlled experiments using cyclic voltammetry (CV) analysis and bulk electrolysis confirmed that FA cannot be electrochemically reduced and can only be oxidized to 2-FO, which in turn can only be hydrogenated to GBL. Figure 2A and 2B It is believed that this appropriate inertia of each chemical participant enables the one-pot electrochemical conversion of FA to GBL.

[0104] Time-resolved electrochemical oxidation (ECO) galvanometer electrolysis of 2-furfuric acid (FA) was performed at 1 mA and pH 2 using a Pt anode paired with a Pt cathode to investigate changes in Faradaic efficiency (FE) and product distribution. Figure 3 Pt cathode was chosen because control experiments showed it could produce H₂. + The reduction to H2, i.e., the hydrogen evolution reaction (HER), almost completely replaces 2-FO in pH 2, making the analysis of the 2-FO product more accurate. As the charge transport increases from 0 to 43.2 C (2.24 equivalents of oxidative charge), the FA conversion reaches 89.6%, producing 73.7% 2-FO. The reaction also produces 12.1% HFO and 2.6% MA. When the charge transport increases to 86.4 C (4.5 equivalents of oxidative charge), all FA is consumed, producing 83.6% 2-FO, accompanied by small amounts of HFO (11.6%) and MA (2.8%). This result indicates that at this low current density (1 mA cm⁻¹), [the reaction is effective]. -2 At acidic pH and FA levels, side reactions include the peroxidation of 2-FO to HFO and MA. As FA decreases, FE decreases, which changes the electrochemical reaction from FA oxidation to water oxidation.

[0105] pH stability tests showed that at pH greater than 6, 2-FO can undergo an irreversible ring-opening reaction to produce MA ( Figure 4A and 4B Therefore, it is believed that the ECO of FA needs to be carried out in an acidic environment to maximize the retention of 2-FO.

[0106] At pH 1, the conversion of FA reached 100%, but the yield of 2-FO decreased to 28.3%, while the yield of HFO increased to 14.7% (from 11.6% at pH 2). Figure 5A and 5BThe decreased 2-FO yield may be due to the weaker directional adsorption of FA by the furan ring, which promotes its over-oxidation and mineralization. Figure 6 This will increase HFO yield and oxidative mineralization activity, as indicated by the low carbon balance (CB).

[0107] It is believed that, such as ultraviolet-visible spectroscopy (UV-Vis spectroscopy) Figure 7 As shown, using pH 5.5, FA is almost completely deprotonated, which solves the above problem. At pH 5.5, CB is 89.0%, while at pH 1 it is only 46.1%. Figure 5A and 5B The carboxylate form of FA, namely the furoate anion, tends to adsorb onto the Pt surface in a bidentate manner and with a perpendicular orientation. Figure 8 It promotes the ECO of carboxyl groups. Linear sweep voltammetry (LSV) analysis showed that the current density difference (with and without FA) at pH 5.5 was greater than that at pH 1, indicating stronger inhibition of Pt furoate at pH 5.5, thus confirming enhanced surface adsorption of furoate anions at higher pH. Figure 9A and 9B Therefore, pH 5.5 was chosen for the ECO of FA. It is believed that a high pH can also suppress cathode hydrogen evolution and promote the electrochemical hydrogenation (ECH) of organic compounds, which is beneficial for the ECH of 2-FO to GBL.

[0108] Furthermore, it was found that using a gold (Au) electrode instead of a Pt electrode resulted in a poorer 2-FO yield (6.5%). Figure 5A and 5B Density functional theory (DFT) calculations indicate that this is because Au surfaces are more susceptible to "poisoning" by upright furoate ions than platinum surfaces, thus hindering the decarboxylation or oxidation steps of furoate ions. In summary, the above preliminary experiments demonstrate that using a Pt electrode at pH 5.5 is optimal for the ECO conversion of FA to 2-FO.

[0109] By using a silver / silver chloride (Ag / AgCl) voltage (V) of +1.8V... Ag / AgCl In an experiment to measure the potential, the temperature was changed from 20℃ to 80℃, and the same coulomb charge was used to test the effect of temperature. Figure 10A and 10BAt 20 °C, FA was completely consumed, but only 37.5% 2-FO, 5.0% MA, and trace amounts of HFO were formed, resulting in poor CB. When the temperature increased from 20 °C to 40 °C, the yield of 2-FO increased to 68.4%, the formation of MA decreased significantly, and CB increased to 70.6%. At 60 °C, the yield of 2-FO increased slightly to 79.0%, as did the yields of MA and HFO, which increased the selectivity of 2-FO to 80.5%. In summary, although increasing the temperature improved the yield of 2-FO, it reduced the conversion of FA, which is likely because the electrocatalytic oxidation shifted from FA oxidation to the oxygen evolution reaction (OER), since OER activity is believed to be temperature-dependent.

[0110] The most significant improvement in CB was observed at 80 °C, reaching 89.0%. FA conversion decreased slightly, from 98.0% at 60 °C to 88.9% at 80 °C. This reduction can be attributed to the increasingly competitive nature of OER. However, the yield of 2-FO decreased only slightly to 74.8%. Therefore, 2-FO selectivity and overall CB were considered to be highest at 80 °C.

[0111] Furthermore, to determine whether the decrease in FA conversion at elevated temperatures was due to weakened FA adsorption, as higher temperatures are believed to promote desorption, the change in OER onset potential was examined by LSV at specified temperatures in the presence and absence of FA. At j = 7.5 mA cm⁻¹ -2 At 20, 40, 60, and 80 °C, with and without FA, the initial potential differences of OER were +168, +156, +120, and +77 mV, respectively. Figure 11A-11D Under a positive bias, furoate anions can form an inhibitory film on the positively charged anode, thereby shifting the OER onset potential to a more positive value than before. However, the onset potential shift decreases with increasing temperature, indicating a weakening inhibitory effect of the FA film on the OER. Therefore, it can be concluded that the lower FA conversion at higher temperatures is due to increased competition with the OER and weakened FA adsorption. Although increased temperature reduces FA conversion, they are believed to still play a crucial role in promoting 2-FO production and improving CB, as lower temperatures (e.g., 20°C) are believed to promote the polymerization of FA rather than its oxidation to 2-FO.

[0112] Based on the above, it is believed that FA oxidation in aqueous environments typically involves the formation of 2-FO, which begins with the electrocatalytic decarboxylation of FA, leading to the formation of a furan radical intermediate. If the reaction temperature is low, this intermediate can be converted to hydroxyfuran, with a tautomerism of 2-FO, or undergo anodic polymerization or mineralization, thereby reducing CB ( ). Figure 12Therefore, it is believed that the yield of 2-FO depends on the fate of the furan radical intermediate.

[0113] At 20°C, FA was completely consumed, but it primarily polymerized into polyfuran, resulting in low CB. Changing the temperature from 20°C to 40°C significantly improved CB, as the yield of 2-FO almost doubled, increasing from 37.5% to 68.4%. However, further increases in temperature to 60°C and 80°C only resulted in slight increases in the 2-FO yield, to 79.0% and 74.8%, respectively. The yield of 2-FO was significantly improved at 40°C, but not at 60°C and 80°C, which can be attributed to the boiling point of furan at 31.3°C. That is, at 20°C, furan radicals remained on the electrode surface, leading to their polymerization. Figure 13 However, at temperatures above 40°C, the volatility of furan radicals predominates, leading to an increase in the formation of 2-hydroxyfuran and 2-FO. Figure 8 ).

[0114] At 60°C and 80°C, the yields of 2-FO were similar because both temperatures exceed the boiling points of furan and its radicals. Similar temperature-dependent observations were made in studies of the (electro)chemical oxidation formation of polyfurans in organic solvents (not shown). It was found that polyfuran formation increased with increasing temperature to the boiling point of furan, but the yields of both polyfurans and oligofurans decreased significantly above 32°C. In aqueous electrolyte systems at high temperatures, volatile furan radicals may escape from the electrode surface and react with surrounding H₂O to produce 2-hydroxyfurans and 2-FO. Therefore, increased temperature inhibits the polymerization of furan radical intermediates, leading to the formation of 2-FO.

[0115] In summary, the electrocatalytic oxidation of FA to 2-FO has been confirmed above, and it is also suggested that the reaction should be catalyzed by Pt at pH 5.5 and 80 °C to achieve a balance between good yield (74.8%), 2-FO selectivity (84.2%), and good CB (89.0%). Meanwhile, alkaline pH should be avoided, as 2-FO is unstable above pH 6. Similarly, strongly acidic electrolytes (such as pH 1) should be avoided, as they lead to over-oxidation of FA. At pH 5.5, the carboxylate groups are adsorbed vertically on the surface in a bidentate manner, thus undergoing decarboxylation (-CO2) via radical rearrangement after oxidation. This process generates furan radicals, which then react with H2O from the host electrolyte to form hydroxyfuran. Subsequently, the hydroxyfuran undergoes tautomerism to form 2-FO. Increasing the temperature above 40 °C promotes the thermal desorption of furan radicals, thereby enhancing the selectivity for 2-FO.

[0116] Example 2

[0117] Electrocatalytic hydrogenation of 2-FO to γ-butyrolactone (GBL)

[0118] At elevated temperatures, the electrocatalytic oxidation of FA to 2-FO is selective. However, the Pt cathode cannot effectively reduce 2-FO because it preferentially promotes HER. Therefore, potential cathode materials were investigated that might be able to selectively hydrogenate the olefin of 2-FO rather than its carbonyl group ( Figure 14 ). In particular, the performance of eight common ECH metals and carbon cloth (CC) as cathodes was investigated at current densities of 10, 20, and 30 mA cm -2 , which correspond to the estimated current generated between anode potentials of +1.7 to +2.0 V Ag / AgCl . In addition, 360 C (4.6 times the reduction equivalent) was used to maximize the completion of the reaction. The 2-FO conversion and GBL yield were measured to examine the relative performance of various electrocatalysts.

[0119] As Figure 14 shown, Ni is the most effective catalyst for ECH of the olefin in 2-FO, providing 84.0%, 93.5%, and 96.5% GBL at 10, 20, and 30 mA cm -2 respectively. The GBL yield is comparable to the 2-FO conversion at 30 mA cm -2 , indicating that GBL is produced with a relatively high selectivity (i.e., 98.2%). This can be attributed to the favorable adsorption of C═C on its surface, since the desorption of C═O is easier than that of C═C. The high C═C ECH efficiency can be explained by the reported designed d-band model.

[0120] According to this model, a short distance between the d-band center and the Fermi level enhances the binding energy between the metal surface and the adsorbent ( Figure 15 ). Among the top five most active metal catalysts, the binding energy of 2-FO follows the trend of Ni < Pd < Pt < Cu < Au, which is in close agreement with the GBL yield observed in the experiment ( Figure 14 ). It has been reported that a decrease in the d-band width increases the interaction between the C═C bond and the metal surface, resulting in an increase in the selectivity of C═C hydrogenation relative to C═O reduction. Among the five metal catalysts, Ni has the narrowest d-band, which is consistent with the current experimental observations for C═C hydrogenation.

[0121] To verify the electrocatalytic reduction activity of 2-FO hydrogenation, CV analysis was performed on all cathode materials ( Figures 16A-16C ). Only the CV of Ni showed an observable current difference with and without 2-FO, which is consistent with the aforementioned d-band width model of 2-FO C═C adsorption onto Ni.

[0122] Secondly, the effects of temperatures ranging from 20°C to 80°C were examined. Figure 17 When the temperature increased from 20 °C to 80 °C, the conversion of 2-FO increased from 12.8% to 69.8%, and the yield of GBL reached 68.4%. These results indicate that the increase in temperature promotes the surface desorption of 2-FO, thereby allowing the surface regeneration of adsorbed H2 required for C=C hydrogenation. The high GBL yield observed at 80 °C is ideal for the combined ECO of FA with the ECH of 2-FO, as both reactions are promoted by high temperatures.

[0123] The effect of pH on the reduction of 2-FO was investigated from pH 2 to pH 6 at 80 °C. Figure 18 Neutral and alkaline conditions were not considered because 2-FO is chemically unstable above pH 6, as was evident in early control experiments. Figure 4A and 4B As pH decreased, the yield of GBL decreased from 68.1% at pH 6 to 57.4% at pH 4, and further to 6.8% at pH 2. This decrease in GBL yield can be attributed to surface adsorption of hydrogen (H₂O) in acidic environments. ads The increased coverage on the Ni cathode will shift the ECH selectivity from 2-FO to HER.

[0124] A series of CV experiments were conducted to observe changes in the initial HER and 2-FO ECH potentials. Figure 19 At pH 2, the ECH efficiency of 2-FO is low, and therefore CV analysis only has an efficiency of approximately 0.44 V. Ag / AgCl The HER curve starts at pH 3. However, starting at pH 3, the ECH of 2-FO becomes effective at 0.65V. Ag / AgCl A distinct peak reflecting the electrochemical reduction of 2-FO appeared at the [location name missing]. This peak was not observed in the absence of 2-FO. Figure 20 As pH increases, the HER onset potential and the 2-FO reduction peak become increasingly negative until pH 5.5. The increasingly negative HER onset potential compared to 2-FO indicates minimal competition from HER. This explains why the Faraday efficiency (FE) of the ECH of 2-FO increases with increasing pH. Figure 18 ).

[0125] The compatibility between the ECO of FA and the ECH of 2-FO was assessed by examining the reduction efficiency of 2-FO in relation to the Pt anodic operating potential. Figure 21A and 21B Specifically, the cathode potential was recorded using a multimeter (measured between the cathode and reference electrode), while the anode operating potential was monitored via an electrochemical workstation. This was achieved at +1.6V.Ag / AgCl The evaluation of Pt under running conditions begins, which produces an average of approximately 3.5 mA cm⁻¹. -2 The lowest potential for a reasonable current. CV analysis shows +1.6V. Ag / AgCl Approximately the onset potential of HER ( Figure 20 When Pt is at +1.6V Ag / AgCl During operation, the Ni cathode operating potential reaches -0.6V. Ag / AgCl And it produces 38.3% GBL. This occurs when the Pt operating potential increases to +1.8 and +2.0V. Ag / AgCl At that time, the Ni reduction potential increased to -0.8 and -1.0 V, respectively. Ag / AgCl The GBL yields were 70.5% and 68.6%, respectively. Then, at +2.2V... Ag / AgCl At this point, the corresponding cathode operating potential becomes too high, favoring the HER of 2-FO to GBL instead of ECH, thus causing GBL yield and FE to begin to decline.

[0126] Therefore, the above results indicate that 2-FO has an ECH tolerance range of +1.8 to +2.0 V. Ag / AgCl The wide range of anodic potentials is highly advantageous for the successful combination of ECO and ECH reactions.

[0127] Time-resolved electrolysis was performed under optimized conditions to study the product distribution and FE variation of 2-FO reduction. Figure 22 From 0 to 150°C, all 2-FO was converted to GBL without the formation of byproducts, as indicated by the overlapping curves of 2-FO conversion and GBL yield. However, above 150°C, the two curves began to bifurcate, indicating the loss of GBL due to hydrolysis. At the end of electrolysis, all 2-FO was consumed and hydrogenated at the olefin site with a selectivity of 98.5%. This resulted in the production of 94.1% GBL and 4.4% GHB. GHB was formed via ring-opening hydrolysis of GBL, a side reaction that typically occurs at pH greater than 2. Trace amounts of over-oxidation products, such as HFO and MA (data not shown), were also detected. Fe was calculated based on the detected products, and the FE gradually decreased with decreasing 2-FO, indicating a shift in selectivity from the ECH of 2-FO to the HER.

[0128] In summary, the ECH of 2-FO exhibits high efficiency across a range of operating potentials, temperatures, and pH values. Using a Ni cathode, high selectivity (98.5%) was achieved for the ECH of the C=C bonds in 2-FO, resulting in complete conversion. Time-resolved electrolysis showed that the selectivity for C=C hydrogenation of 2-FO remained constant throughout the electrolysis process, but the FE gradually decreased with the consumption of 2-FO. The C=C ECH is highly compatible with the ECO of FA, enabling one-pot conversion of FA to GBL.

[0129] Example 3

[0130] FA oxidation and 2-FO reduction coupling for one-pot production of GBL

[0131] At 80℃ and +2.0V Ag / AgCl Under optimized conditions, a one-pot electrochemical conversion of FA to GBL was performed using a Pt anode. Three initial FA concentrations (20, 100, and 150 mM) were examined. All experiments showed that FA was oxidized to 2-FO at the Pt anode. Then, 2-FO was reduced to GBL at the Ni cathode. Figure 23 When the initial concentration of FA was 20 mM, the 2-FO yield reached a peak of 25.9% after passing through 150°C, and then gradually decreased with increasing GBL yield, consuming 2-FO ( Figure 24 After passing through 500°C, the GBL yield reached 71.9%, then gradually decreased due to the prolonged hydrolysis and ring-opening reaction. When using an initial FA concentration of 100 mM ( Figure 25 2-FO initially grows rapidly and is then hydrogenated to GBL. After passing through 1600°C, the GBL yield reaches 69.1%, with 38.3% FE and 80.1% CB. When the initial FA concentration is 150 mM, the GBL yield reaches 98.9 mM. Figure 26 The experiment involving 150 mM FA produced a dark yellow electrolyte, indicating furan polymerization, and no product was detected by gas chromatography-mass spectrometry. Therefore, the initial concentration of FA should be below 100 mM.

[0132] Example 4

[0133] GBL expands production.

[0134] Under optimized conditions, a scale-up of 500 mL of 100 mM FA (5.6 g, 500 mL) was used to generate sufficient GBL for product separation, while simultaneously delivering the product at 38,880 °C to maximize the FA-to-GBL conversion. Following dichloromethane (DCM) extraction and subsequent removal of DCM under vacuum, 2.1 g (47.8% separation yield) of GBL with a purity of 98.1% was obtained (e.g., by...). 1 (H NMR determination). The optimal separation yield was likely due to the prolonged electrolysis time and GBL loss during DCM removal under vacuum, leading to GHB hydrolysis. GHB and succinic acid (SA) were also detected near the end of the reaction as FA and 2-FO were depleted, and based on pre-extraction... 1¹H NMR analysis showed that the yields of GHB and SA were 12% and 5%, respectively. SA may be formed by ring-opening of 2(3H)-furanone, which yields 4-oxobutyric acid, followed by ECO of its aldehyde group. It can also be formed by ECH of the C=C bond of MA, which originates from... Figure 12 HFO as described above. Trace amounts of butyric acid (BA) were also observed, likely from the reduction of GHB. DCM extraction showed high selectivity for GBL, as demonstrated by the high purity mentioned above.

[0135] It is believed that the one-pot FA to GBL method described herein produces high-purity GBL at a rate comparable to existing FAL to FA technologies. Based on the conversion rate, this scaled-up reaction consumes 5.6 g of FA per 24 h, which is equivalent to 2083.3 μmol / h. This conversion rate is believed to be significantly superior to some reported thermocatalytic methods with harsh reaction conditions; for example, in one instance, the conversion rate of FAL to FA using MnO2 / CeO2 at 130 °C and 8 bar O2 was determined to be 750 μmol / h. Meanwhile, it is noted that the conversion rate of this scaled-up reaction is comparable to some other biocatalytic methods with high FAL to FA conversion rates, such as those with conversion rates of approximately 2425 μmol / h. Therefore, the electrosynthesis of FA to GBL using the one-pot method described herein is believed to exhibit good compatibility with some existing FAL to FA technologies in terms of reaction rate, suggesting potential integration of these systems.

[0136] The invention is given by way of example only, and various other modifications and / or alterations may be made to the described embodiments by those skilled in the art without departing from the scope of the invention as specified in the appended claims.

Claims

1. A method for preparing γ-butyrolactone, comprising the step of converting furoic acid to said γ-butyrolactone in a separatorless, membrane-free tank without a separator for paired electrolysis, the method comprising the following steps: a) Electrochemically oxidize the furoic acid to 2(5) H )-Furfuralone; and b) 2(5) H )-Furfuralone is electrochemically reduced to the γ-butyrolactone; The step of converting furoic acid to the γ-butyrolactone is carried out in a separatorless diaphragmless tank under an ambient atmosphere of 1 atmosphere, at a pH of 3 to 6, at a temperature of 40°C to 80°C, and at an applied voltage of 1.8 V to 2.0 V relative to Ag / AgCl. The separatorless diaphragmless tank includes a platinum anode, a nickel cathode, an Ag / AgCl reference electrode, and a phosphate buffer solution containing 20 mM to 100 mM furoic acid.

2. The method of claim 1, wherein the mediator comprises TEMPO and an organic co-solvent.

3. The method of claim 1, further comprising the step of separating the γ-butyrolactone after step b) is completed.

4. The method of claim 1, wherein the furoic acid is biomass-derived furoic acid.

5. The method of claim 1, wherein the furoic acid is electrochemically oxidized to the 2(5) H )-Furfural, with a selectivity of 40% to 95%.

6. The method of claim 5, wherein the furoic acid is electrochemically oxidized to the 2(5) H )-Furfural, with a selectivity of 84.2%.

7. The method of claim 1, wherein the furoic acid is electrochemically oxidized to the 2(5) H )-Furfural, with yields ranging from 40% to 95%.

8. The method of claim 7, wherein the furoic acid is electrochemically oxidized to the 2(5) H )-Furfural, with a yield of 74.8%.

9. The method of claim 1, wherein the furoic acid is electrochemically oxidized to the 2(5) H )-Furfural, with a carbon balance of 40% to 95%.

10. The method of claim 9, wherein the furoic acid is electrochemically oxidized to the 2(5) H )-Furfural, with a carbon balance of 89.0%.

11. The method of claim 5, wherein the 2(5) H )-Furfural is electrochemically reduced via olefin hydrogenation to produce 40% to 99% γ-butyrolactone.

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