Method for preparing gamma-butyrolactone

Abstract

Disclosed is a process for the preparation of gamma-butyrolactone comprising the conversion of furoic acid to said gamma-butyrolactone in a diaphragm-free tank free of a mediator for paired electrolysis, said process comprising the steps of: a) electrochemical oxidation of said furoic acid to 2 (5H)-furanone; and b) the electrochemical reduction of said 2 (5H)-furanone to said gamma-butyrolactone.

Description

Technical Field

[0001] The present invention belongs to the field of chemical synthesis and relates to an electrochemical method for preparing gamma-butyrolactone, such as particularly but not exclusively biomass-derived gamma-butyrolactone. Background Art

[0002] Biomass is an attractive carbon source for the production of sustainable fuels and chemicals. Therefore, biomass conversion, i.e., the conversion of various lignocellulosic feedstocks into biofuels and bio-derived chemicals, has attracted considerable attention over the past few decades. In particular, gamma-butyrolactone (also known as γ-butyrolactone) (GBL) has emerged as an important biorefining compound due to its versatility; it is a non-toxic solvent and chemical precursor that can be used in a variety of industries, including the flavor, pharmaceutical, and fragrance industries. The global market size of GBL is believed to be worth USD 3,614.07 million in 2022 and is expected to exceed USD 4,904.37 million by 2032.

[0003] The preparation of GBL can be divided into two main routes: petroleum-based route and biomass-based route. In the petroleum-based route (e.g., see Figure 1A ), which may generally involve oxidation of benzene to maleic anhydride at 200°C-600°C, 1-3 bar oxygen (O2), and hydrogenation of maleic anhydride to GBL at 160°C-280°C, 6-8 MPa hydrogen (H2). Alternatively, it may involve condensation of acetylene with formaldehyde at 90°C-110°C, 0.5-2.0 MPa H2 to form 1,4-butanediol, which is dehydrogenated and ring-closed at 180°C-300°C to obtain GBL.

[0004] In the biomass-based route, it may involve thermal catalysis of furan precursors such as furanaldehyde (FAL) or furoic acid (FA) to GBL, which generally involves a two-stage process: (1) oxidation of FAL or FA to 2(5H)-furanone (2-FO); and (2) hydrogenation of the separated 2-FO to produce GBL. However, it is believed that this thermal method may 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 it is believed that all of the above conditions may reduce the selectivity to 2-FO, resulting in the production of various oxidation products 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 facile conversion of furanic precursors such as FAL and FA to GBL with respectable yield and efficiency remains challenging.

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

[0007] In a first aspect of the present invention, there is provided a method for preparing γ-butyrolactone, the method comprising the step of converting furoic acid to γ-butyrolactone in a diaphragmless cell without a mediator for paired electrolysis, the method comprising the following steps: a) electrochemically oxidizing furoic acid to 2(5H)-furanone; and b) electrochemically reducing 2(5H)-furanone to γ-butyrolactone. Optionally, the mediator includes TEMPO, an organic co-solvent or a separator.

[0008] Optionally, the diaphragmless cell 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, a carbon-based material (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, a carbon-based material (especially carbon cloth), zinc, copper or gold.

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

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

[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 1.4V to about 3.0V relative to Ag / AgCl.

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

[0016] In an optional embodiment, the step of converting furoic acid to γ-butyrolactone is carried out in a diaphragmless cell without a separator, in an ambient atmosphere of 1 atmosphere, at a pH of 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 separator-free diaphragmless cell comprises a platinum anode, a nickel cathode, an Ag / AgCl counter electrode, and a phosphate buffer solution containing from about 1 mM to about 200 mM furoic acid.

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

[0019] Optionally, furoic acid is electrochemically oxidized to 2(5H)-furanone with a selectivity of from 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 with a yield of from about 40% to about 95%. In an optional embodiment, furoic acid is electrochemically oxidized to 2(5H)-furanone with a yield of 74.8%.

[0021] Optionally, furoic acid is electrochemically oxidized to 2(5H)-furanone with a carbon balance of from 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 from about 40% to about 99% of γ-butyrolactone. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present 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 a petroleum-derived substrate is shown;

[0025] Figure 1B is a table summarizing different systems for oxidizing furfural to produce furoic acid;

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

[0027] Figure 2A A cyclic voltammogram of a forward scan using Pt as the working electrode in the presence and absence of 20 mM 2-FO is shown;

[0028] Figure 2B A cyclic voltammogram of a reverse scan using Ni as the working electrode in the presence and absence of 20 mM FA is shown;

[0029] Figure 3Shows the electrochemical oxidation of FA at pH 2. 10 mM FA, 1 mA constant current, pH 2 buffer, 80 °C, through 0 - 86.4 C charge (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 Shows the stability of 2 - FO at 80 °C from pH 2 to 9 Reaction conditions: 10 mM 2 - FO in 10 mL of 0.5 M potassium phosphate buffer of different pH at 80 °C;

[0031] Figure 4B Shows the yield of MA from pH 2 to 9. Reaction conditions: 10 mM 2 - FO in 10 mL of 0.5 M potassium phosphate buffer of different pH at 80 °C;

[0032] Figure 5A Shows the ECO of FA on Pt or Au at pH 1 or 5.5. Reaction conditions: 10 mM FA in 10 mL of pH 5.5 buffer; Applied voltage: +1.8 V Ag / AgCl ; Through charge, 100 C; Platinum foil as working electrode and counter electrode. Experiments were performed in triplicate, and error bars correspond to the standard deviation of three independent measurements

[0033] Figure 5B Is a table summarizing the conversion rate, product yield, selectivity, and carbon balance after electrocatalytic oxidation of FA at different anodes and pH;

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

[0035] Figure 7 Shows the maximum UV - Vis absorbance of FA from pH 2 to 9 (λ max );

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

[0037] Figure 9A Shows the LSV study at pH 1 with or without 50 mM FA. Reaction conditions: Scan rate 50 mV / s; 80 °C; WE: Pt; CE: Pt;

[0038] Figure 9B Shows the LSV study at pH 5.5 with or without 50 mM FA. Reaction conditions: Scan rate 50 mV / s; 80 °C; WE: Pt; CE: Pt;

[0039] Figure 10A Shows the ECO of FA at temperatures in the range of 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 ; by charge, 100 C; platinum foil as the working electrode and counter electrode. The experiments were carried out in triplicate, and the error bars correspond to the standard deviation of three independent measurements;

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

[0041] Figure 11A Shows the linear sweep voltammetry (LSV) curves of the electrode in pH 5.5 buffer at 20 °C in the presence and absence of 50 mM FA. The potential difference was measured at j = 7.5 mA cm -2 . WE: Pt; CE: Pt;

[0042] Figure 11B Shows the linear sweep voltammetry (LSV) curves of the electrode in pH 5.5 buffer at 40 °C in the presence and absence of 50 mM FA. The potential difference was measured at j = 7.5 mA cm -2 . WE: Pt; CE: Pt;

[0043] Figure 11C Shows the linear sweep voltammetry (LSV) curves of the electrode in pH 5.5 buffer at 60 °C in the presence and absence of 50 mM FA. The potential difference was measured at j = 7.5 mA cm -2 . WE: Pt; CE: Pt;

[0044] Figure 11D Shows the linear sweep voltammetry (LSV) curves of the electrode in pH 5.5 buffer at 80 °C in the presence and absence of 50 mM FA. The potential difference was measured at j = 7.5 mA cm -2 . WE: Pt; CE: Pt;

[0045] Figure 12 is a schematic diagram showing the proposed mechanistic pathway for the ECO of FA to GBL in pH 5.5 electrolyte at 80 °C;

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

[0047] Figure 14Shows the ECH of 20 mM 2-FO on a Ni cathode paired with a Pt anode as the counter electrode in 20 mL of 0.5 M buffer (pH 5.5) at 80 °C, electrolyzed at 10, 20, and 30 mA cm -2 and a total of 360 C passed through;

[0048] Figure 15 is a table summarizing the d-band centers and widths of bulk electrocatalysts;

[0049] Figure 16A Shows cyclic voltammograms (CVs) of 20 mM 2-FO in the presence and absence of 20 mM 2-FO at 80 °C in 20 mL of pH 5.5 electrolyte using Ni, Pd, and Cu as working electrodes, respectively;

[0050] Figure 16B Shows cyclic voltammograms (CVs) of 20 mM 2-FO in the presence and absence of 20 mM 2-FO at 80 °C in 20 mL of pH 5.5 electrolyte using Pt, Pb, and Au as working electrodes, respectively;

[0051] Figure 16C Shows cyclic voltammograms (CVs) of 20 mM 2-FO in the presence and absence of 20 mM 2-FO at 80 °C in 20 mL of pH 5.5 electrolyte using carbon cloth, Mo, and Zn as working electrodes, respectively;

[0052] Figure 17 Shows the electrochemical reduction (ECH) of 2-FO at 20 °C - 80 °C. The experiments were 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; 2.0 V Ag / AgCl ; WE: Pt, CE: Ni;

[0053] Figure 18 Shows the conversion and yield at pH 2 - 6 (2.0 V Ag / AgCl ; WE: Pt, CE: Ni) with a total of 100 C passed through;

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

[0055] Figure 20 Shows cyclic voltammograms (CVs) of 20 mM 2-FO in the presence or absence of 20 mM 2-FO at 80 °C in pH 5.5 electrolyte. WE: Ni; CE: Pt;

[0056] Figure 21AShows the electrochemical reduction (ECH) of 2-FO at an applied anodic potential of 1.6 to 2.2 V Ag / AgCl The experiments were 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;

[0057] Figure 21B is a table summarizing the corresponding cathode potentials and average current densities. The experiments were 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 Shows the time-resolved electrolysis of 2-FO (2.0 V Ag / AgCl ; WE: Pt, CE: Ni) under optimized conditions (pH 5.5 buffer, 80 °C). The experiments were performed in triplicate, and the error bars correspond to the standard deviation of three independent measurements;

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

[0060] Figure 24 Shows the one-pot electrochemical conversion of 20 mM FA in 20 mL (pH 5.5) buffer; 80 °C; 2.0 V Ag / AgCl , by different charges. WE: Pt, CE: Ni. The experiments were performed in triplicate, and the error bars correspond to the standard deviation of three independent measurements;

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

[0062] Figure 26 Shows the one-pot electrochemical conversion of 150 mM FA in 20 mL (pH 5.5) buffer; 80 °C; 2.0 V Ag / AgCl , by different charges. WE: Pt, CE: Ni. The experiments were performed in triplicate, and the error bars correspond to the standard deviation of three independent measurements. Detailed Description

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

[0064] The terms “example” or “exemplary” as used in this invention are intended to be examples, instances, or illustrations. Any aspect or design described as “exemplary” in this disclosure is not necessarily to be construed as more preferred or advantageous than other aspects or designs. Instead, the use of the terms “example” or “exemplary” is intended to present concepts in a concrete fashion. 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 employs A or B” is intended to mean any natural inclusive arrangement. That is, if X employs A; X employs B; or X employs both A and B, then “X employs A or B” holds in any of the foregoing cases.

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

[0066] It is believed that one of the alternative methods for synthesizing γ-butyrolactone (GBL) from furan precursors can be electrocatalysis, especially those methods involving specific paired electrolysis (i.e., combining specific oxidation and specific reduction to obtain the desired product). Generally, such electrocatalysis can use an applied potential bias to simultaneously achieve electrochemical redox reactions at each electrode. However, in most cases, the paired electrolysis setup includes using an ion exchange membrane or a porous frit to separate the redox reactions to minimize the yield loss of the reverse reaction, and the product streams are collected separately or combined for subsequent reactions.

[0067] Not wishing to be bound by theory, the inventors have developed, through their own research, experimentation, and testing, an electrochemical synthesis of GBL that can be carried out in a one-pot paired electrolysis device without a separator. In particular, the synthesis can include a plurality of electrochemical reactions under mild conditions, such as at ambient pressure and low temperature (e.g., below 100 °C), in which furfural acid (FA) is converted to GBL in such a setup without separating any intermediates during the reaction. At the same time, in some exemplary embodiments, it has been found that the synthesis method of the present invention can provide a relatively high conversion selectivity and yield. Therefore, it is believed that the present invention can provide a simple, effective, green, and sustainable method for valorizing furan precursors such as FA to GBL.

[0068] In a first aspect of the present invention, there is provided a method for preparing γ-butyrolactone, the method comprising the step of converting furfural acid to γ-butyrolactone in a diaphragm-free cell without a mediator for paired electrolysis, the method comprising the following steps: a) electrochemically oxidizing furfural acid to 2(5H)-furanone; and b) electrochemically reducing 2(5H)-furanone to γ-butyrolactone.

[0069] As used herein, the term "diaphragm-free cell" generally refers to an electrochemical cell having one chamber / compartment in which both the electrochemical oxidation and the electrochemical reduction occur. In other words, both the electrochemical oxidation and the reduction occur in the same chamber / compartment of the diaphragm-free cell. In particular, the diaphragm-free cell as used herein can be a diaphragm-free cell without a mediator such as (2,2,6,6-tetramethylpiperidin-1-yl)oxy (TEMPO), an organic co-solvent, or a separator (e.g., an ion exchange membrane separator). It is believed that, compared with a diaphragm cell, a diaphragm-free cell can minimize pH fluctuations and thus promote the selective oxidation of FA to 2-FO. The diaphragm-free cell can be in the form of a small glass, a beaker, a round-bottom flask, etc. It should be understood that a person skilled in the art can select a suitable form according to actual needs.

[0070] In some embodiments, the diaphragm-free cell can include an electrode pair (i.e., an anode and 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 (FTO), indium tin oxide (ITO), a carbon-based material (e.g., carbon cloth), zinc, copper, or gold. For example, in some embodiments, the anode can be made of platinum, palladium, fluorine-doped tin oxide, or gold. In some embodiments, the cathode can be 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 cloth, zinc, copper, or gold.

[0071] The process of converting FA to GBL disclosed herein particularly includes sequentially oxidizing FA to 2-FO (step a), and then reducing 2-FO to GBL (step b). Therefore, it is believed that the yield of 2-FO may 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 and produce maleic acid (MA), which reduces the amount of 2-FO reduced to GBL. Therefore, preferably, 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 step of converting 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 atm to 3 atm, such as 1 atm. In some other embodiments, the conversion step can be carried out at the following temperatures: 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 step of converting furoic acid to γ-butyrolactone can be carried out at an applied voltage, particularly an anodic voltage, of about 1.4 V to about 3.0 V relative to Ag / AgCl. In other words, the conversion step can be carried out at a cathodic 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 a step of separating γ-butyrolactone after step b) is completed. 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, for example, anhydrous Na2SO4, MgSO4, etc., and subsequently the organic solvent is removed 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 diaphragm-free cell without a separator, i.e., in a diaphragm-free cell without a separator between the anode and the cathode. In these embodiments, the diaphragm-free cell without a separator may include a platinum anode, a nickel cathode, an Ag / AgCl counter electrode, and a phosphate buffer solution containing from about 1 mM to about 200 mM furoic acid.

[0076] The furoic acid can be biomass-derived furoic acid, such as those derived from / obtained from hemicellulose. Alternatively or optionally, the furoic acid can be obtained from the oxidation of furfural (FAL) under various reported conditions, such as Figure 1B those shown in. As described herein, it is preferred to use FA instead of FAL as the raw material for producing GBL because it is believed that acidic conditions (such as those with an acidic pH as described herein) are favorable for 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 easily reduced to furfuryl alcohol).

[0077] In operation, the step of converting furoic acid to γ-butyrolactone can be carried out under an ambient atmosphere of 1 atmosphere, at a pH of 3 to 6, at a temperature of about 35 °C to about 80 °C, and at an applied voltage of about 1.8 V to about 2.0 V 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 (anode) surface and reacting with the surrounding H2O to produce 2-hydroxyfuran, which then tautomerizes 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 with a yield 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 with a yield of 74.8%.

[0080] In some embodiments, in which furoic acid can be electrochemically oxidized to 2(5H)-furanone, the carbon balance is 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 temperature as described above, the operating pH in these embodiments can promote the olefin hydrogenation of 2-FO to produce GBL. In particular, 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, so the competition from HER is minimized. In some embodiments, 2(5H)-furanone can be electrochemically reduced by 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 synthesis method will be discussed in later parts of this disclosure.

[0083] Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited thereto.

[0084] Examples

[0085] Materials and Methods

[0086] All solutions were prepared using ultrapure deionized water (>18.2 MΩcm-1 , prepared by 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 carried out in a 30 mL undivided cell 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 were 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 stated, each electrolysis experiment used an anode and a cathode with dimensions of 10×10×0.1 mm and uncovered on both sides.

[0089] Electrolysis scale-up and product separation

[0090] The scale-up reaction was carried out in a 1000 mL single cell with two electrodes (3×3 cm nickel cathode; 3×3 cm platinum anode), operating at a constant current of 50 mA cm -2 under. The same electrolyte as above was used, except that 5 g to 20 g (such as 5.6 g) of FA was used in 500 mL of the electrolyte. After 24 hours of electrolysis, the reaction mixture was extracted with 1000 mL of DCM, the organic layer was dried over 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) operating 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 ratio of 90:10 (v / v), and the isocratic flow rate was 1 mL / min. The concentrations of FA and its products were quantified using a photodiode array and a refractive index detector with an external standard. Infrared spectra were collected using a Fourier transform infrared spectrometer (Perkin Elmer) and were scanned four times in the range of 4500 - 600 cm -1 at. UV-visible spectrophotometry was performed in the range of 220 - 300 nm using a UV-3600 spectrophotometer (Shimadzu, Japan). The purity of GBL was determined by 1 H NMR spectroscopy (Bruker Advance-III) using a 400-MHz instrument equipped with a broadband probe and referring to an external standard of formic acid.

[0093] Calculation

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

[0095]

[0096]

[0097]

[0098]

[0099]

[0100] where mol 初始反应物 and mol 反应物 are the number of moles of the corresponding reactants before and after the reaction, respectively; mol x is related to the number of moles of the product; n and F are the number of electron transfers and the Faraday constant at 96,485 C / mol, respectively. The total charge was calculated based on the integration of the current (I, A) with respect to the operating time in seconds.

[0101] Example 1

[0102] Electrochemical oxidation of furoic acid (FA) to 2(5H)-furanone (2-FO)

[0103] The electrocatalytic conversion of FA to GBL in the present invention involves the sequential oxidation of FA to 2-FO in a diaphragmless cell, followed by the reduction of 2-FO to GBL( Figure 1C ). It is believed that the key factor promoting these two reactions in a diaphragmless cell is that, due to mild conditions, none of the substances involved (such as FA, 2-FO, and GBL) undergo unwanted redox reactions. Control experiments using cyclic voltammetry (CV) analysis and bulk electrolysis confirmed that FA cannot be electrochemically reduced and can only be oxidized to 2-FO, while 2-FO can only be hydrogenated to GBL( Figure 2A and 2B ). It is believed that this appropriate inertness of each chemical participant enables the one-pot electrochemical conversion of FA to GBL.

[0104] Time-resolved electrochemical oxidation (ECO) amperometric electrolysis of 2-furoic acid (FA) was carried out at 1 mA at pH 2 using a Pt anode paired with a Pt cathode to study the changes in Faradaic efficiency (FE) and product distribution( Figure 3 ). The Pt cathode was chosen because control experiments showed that it carried out the reduction of H + to H2, i.e., the hydrogen evolution reaction (HER), almost completely instead of 2-FO in pH 2, which made the analysis of 2-FO products more accurate. As the charge passed increased from 0 to 43.2 C (2.24 equivalents of oxidation charge), the FA conversion reached 89.6%, and 73.7% of 2-FO was produced. The reaction also produced 12.1% of HFO and 2.6% of MA. When the charge delivery increased to 86.4 C (4.5 oxidation equivalent charges), all FA was consumed and 83.6% of 2-FO was produced, accompanied by a small amount of HFO (11.6%) and MA (2.8%). This result indicates that at this low current density (1 mA cm -2 ) and acidic pH, side reactions include the peroxidation of 2-FO to HFO and MA. As FA decreased, the FE decreased, which shifted the electrochemical reaction from oxidizing FA to oxidizing water.

[0105] The pH stability test 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%, and the yield of HFO increased to 14.7% (from 11.6% at pH 2)( Figure 5A and 5B)。The decrease in 2-FO yield may be due to the weak directional adsorption of the furan ring to FA, which promotes its over-oxidation and mineralization( Figure 6 )。This will increase the HFO yield and oxidative mineralization activity, as indicated by the low carbon balance (CB).

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

[0108] In addition, it was found that using a gold (Au) electrode instead of a Pt electrode provided a poor 2-FO yield (6.5%)( Figure 5A and 5B )。Density functional theory (DFT) calculations show that this is because the Au surface is more easily "poisoned" by upright furoate than the platinum surface, thus hindering the decarboxylation or oxidation step of furoate. In summary, the above preliminary experiments show that using a Pt electrode at pH 5.5 is optimal for the ECO of FA to 2-FO.

[0109] In an experiment where potentiometry was carried out at a silver / silver chloride (Ag / AgCl) voltage (V Ag / AgCl ) of +1.8 V, the temperature was changed from 20 °C to 80 °C and the same coulombic charge was used to examine the effect of temperature( Figure 10A and 10B)。At 20 °C, FA was completely consumed, but only 37.5% of 2-FO, 5.0% of MA, and trace amounts of HFO were formed, resulting in poor CB. When the temperature was increased from 20 °C to 40 °C, the yield of 2-FO increased to 68.4%, the formation of MA decreased significantly, and the CB increased to 70.6%. At 60 °C, the yield of 2-FO increased slightly to 79.0%, and the same was true for the yields of MA and HFO, which increased the selectivity of 2-FO to 80.5%. In summary, although the increase in temperature increased the yield of 2-FO, it decreased the conversion rate of FA, which may be because the electrocatalytic oxidation changed from FA oxidation to oxygen evolution reaction (OER), as the OER activity is believed to be temperature-dependent.

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

[0111] In addition, it was determined whether the decrease in FA conversion rate at elevated temperatures was due to weakened adsorption of FA, as it is believed that higher temperatures can promote its desorption. Therefore, the change in the OER onset potential in the presence and absence of FA was examined separately by LSV at the specified temperatures. At j = 7.5 mA cm -2 −2, the OER onset potential differences in the presence and absence of FA were +168, +156, +120, and +77 mV at 20, 40, 60, and 80 °C, respectively ( Figure 11A - 11D ). At a positive potential bias, the furoate anion can form an inhibitory film on the positively charged anode, thus shifting the OER onset potential to a more positive value than before. However, as the temperature increased, the onset potential shift decreased, indicating a weakened inhibitory effect of the FA film on OER. Therefore, it can be concluded that the lower FA conversion rate at higher temperatures is due to enhanced competition with OER and weakened FA adsorption. Although elevated temperatures decrease the conversion rate of FA, they are believed to still play a crucial role in promoting 2-FO production and improving CB, as it is believed that low temperatures (e.g., 20 °C) promote the polymerization of FA rather than its oxidation to 2-FO.

[0112] Based on the above, it is believed that the oxidation of FA in an aqueous environment generally involves the formation of 2-FO, which begins with the electrocatalytic decarboxylation of FA, resulting in the formation of a furan radical intermediate. If the reaction temperature is low, this intermediate can be converted to hydroxyfuran, which tautomerizes to 2-FO, or undergo anodic polymerization or mineralization, thus reducing the CB ( Figure 12)。Therefore, 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 mainly polymerized into polyfuran, resulting in low CB. Changing the temperature from 20 °C to 40 °C significantly improved CB because the yield of 2-FO almost doubled, increasing from 37.5% to 68.4%. However, further increasing the temperature to 60 °C and 80 °C only led to a slight increase in the yield of 2-FO, 79.0% and 74.8% respectively. The significant increase in the yield of 2-FO at 40 °C but not at 60 °C and 80 °C can be attributed to the boiling point of furan being 31.3 °C. That is, at 20 °C, the furan radicals remained on the electrode surface, leading to their polymerization ( Figure 13 ). However, at temperatures above 40 °C, the volatility of the furan radicals dominated, 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 exceeded the boiling points of furan and its radicals. Similar temperature-dependent observations were made in studies on the (electro)chemical oxidation formation of polyfuran in organic solvents (not shown). It was found that when the temperature was raised to the boiling point of furan, the formation of polyfuran increased, but at temperatures above 32 °C, the yields of polyfuran and oligofuran decreased significantly. In the aqueous electrolyte system at high temperatures, the volatile furan radicals may escape from the electrode surface and react with the surrounding H2O to produce 2-hydroxyfuran and 2-FO. Therefore, increasing the temperature prevented the polymerization of the furan radical intermediate, leading to the formation of 2-FO.

[0115] In summary, the electrocatalytic oxidation of FA to 2-FO has been demonstrated above, and it has also been suggested above that the reaction should be catalyzed by Pt at pH 5.5 and 80 °C to achieve a balance between a good yield (74.8%), selectivity for 2-FO (84.2%), and good CB (89.0%). At the same time, alkaline pH should be avoided because 2-FO is unstable at pH above 6. Similarly, strongly acidic electrolytes (such as pH 1) should be avoided because they cause over-oxidation of FA. At pH 5.5, the carboxylate groups are adsorbed vertically on the surface in a bidentate manner, and thus decarboxylation (-CO2) occurs through radical rearrangement after oxidation. This process generates furan radicals, which then react with H2O from the bulk electrolyte to form hydroxyfuran. Subsequently, the hydroxyfuran tautomerizes to form 2-FO. Increasing the temperature above 40 °C promotes the thermal desorption of furan radicals, thus 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, as 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 adsorbate ( 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 good 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 ( Figure 16A - 16C ). Only the CV of Ni showed observable current differences in the presence and absence of 2-FO, which is consistent with the aforementioned d-band width model of 2-FO C═C adsorption onto Ni.

[0122] Secondly, the influence of temperature from 20 °C to 80 °C was examined ( Figure 17 ). As the temperature increased from 20 °C to 80 °C, the conversion rate 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 promoted the desorption of 2-FO from the surface, thus allowing the regeneration of the adsorbed H2 required for surface C═C hydrogenation. The high GBL yield observed at 80 °C is ideal for coupling the ECO of FA with the ECH of 2-FO, as both reactions are promoted by high temperatures.

[0123] The influence 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 at pH values above 6, as was evident in earlier control experiments ( Figure 4A and 4B ). As the pH decreased, the yield of GBL decreased, from 68.1% at pH 6 to 57.4% at pH 4 and to 6.8% at pH 2. This decrease in the GBL yield can be attributed to the increased coverage of surface-adsorbed hydrogen (H ads ) on the Ni cathode in an acidic environment, which shifted the selectivity from the ECH of 2-FO to HER.

[0124] A series of CV experiments were conducted to observe the changes in the onset HER and 2-FO ECH potentials ( Figure 19 ). At pH 2, the ECH efficiency of 2-FO was low, and thus the CV analysis only had a HER curve starting at approximately 0.44 V Ag / AgCl . However, starting from pH 3, the ECH of 2-FO became effective, with an obvious peak reflecting the electrochemical reduction of 2-FO appearing at 0.65 V Ag / AgCl . This peak was not observed in the absence of 2-FO ( Figure 20 ). As the pH increased, the HER onset potential and the 2-FO reduction peak became increasingly negative until pH 5.5. Compared with 2-FO, the HER onset potential became increasingly negative, indicating minimal competition from HER. This explains why the Faradaic efficiency (FE) of the ECH of 2-FO increased with increasing pH ( Figure 18 ).

[0125] The compatibility between the ECO of FA and the ECH of 2-FO was evaluated by examining the reduction efficiency of 2-FO in relation to the working potential of the Pt anode ( Figure 21A and 21B ). In particular, the cathode potential was recorded using a multimeter (measured between the cathode and the reference electrode), while the working potential of the anode was monitored by an electrochemical workstation. By applying at +1.6 VAg / AgCl The Pt operated below this started to be evaluated, which was the lowest potential to generate a reasonable current of about 3.5 mA cm -2 The CV analysis showed that +1.6 V Ag / AgCl was close to the onset potential of HER ( Figure 20 ). When Pt was operated at +1.6 V Ag / AgCl , the working potential of the Ni cathode reached -0.6 V Ag / AgCl and 38.3% of GBL was produced. When the Pt working potential increased to +1.8 and +2.0 V Ag / AgCl , the Ni reduction potential increased to -0.8 and -1.0 V Ag / AgCl respectively, and the GBL yields were 70.5% and 68.6% respectively. After that, at +2.2 V Ag / AgCl , the corresponding cathode working potential became too high, favoring HER of 2-FO to GBL rather than ECH, so the GBL yield and FE started to decline.

[0126] Therefore, the above results indicate that the ECH tolerance range of 2-FO is an extensive range of anodic potentials from +1.8 to +2.0 V Ag / AgCl , which is very favorable for the successful combination of ECO and ECH reactions.

[0127] Time-resolved electrolysis was carried out under optimized conditions to study the product distribution of 2-FO reduction and the change of FE ( Figure 22 ). From 0 to 150 C, all 2-FO was converted to GBL without forming by-products, as indicated by the overlapping curves of 2-FO conversion rate and GBL yield. However, beyond 150 C, the two curves started to diverge, indicating the loss of GBL due to hydrolysis. At the end of electrolysis, all 2-FO was consumed and hydrogenated at the olefin position with a selectivity of 98.5%. This led to the production of 94.1% GBL and 4.4% GHB. GHB was formed by the ring-opening hydrolysis of GBL, which is a side reaction that usually occurs at pH greater than 2. Trace amounts of over-oxidized products such as HFO and MA were also detected (data not shown). The FE was calculated based on the detected products, and as 2-FO decreased, the FE gradually decreased, indicating a shift in selectivity from the ECH of 2-FO to HER.

[0128] In summary, the ECH of 2-FO showed high efficiency in a series of working potentials, temperatures, and pH ranges. Using a Ni cathode, the ECH of the C═C bond in 2-FO had a high selectivity (98.5%) and was completely converted. Time-resolved electrolysis showed that the selectivity for 2-FO C═C hydrogenation remained constant throughout the electrolysis, but the FE gradually decreased as 2-FO was consumed. The ECH of C═C was highly compatible with the ECO of FA, enabling the one-pot conversion of FA to GBL.

[0129] Example 3

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

[0131] Under optimized conditions of 80 °C and +2.0 V Ag / AgCl , one-pot electrochemical conversion of FA to GBL was carried out 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 on the Pt anode. Then, 2-FO was reduced to GBL on the Ni cathode ( Figure 23 ). When the initial concentration of FA was 20 mM, after passing 150 C, the 2-FO yield reached a peak of 25.9%, and then gradually decreased as the GBL yield increased, consuming 2-FO ( Figure 24 ). After passing 500 C, the GBL yield reached 71.9%, and then gradually decreased due to the long-term hydrolysis ring-opening reaction. When using an initial FA concentration of 100 mM ( Figure 25 ), 2-FO initially grew rapidly and was then hydrogenated to GBL. After passing 1600 C, the GBL yield reached 69.1%, with 38.3% FE and 80.1% CB. When the initial FA concentration was 150 mM, the GBL yield reached 98.9 mM ( Figure 26 ). Experiments involving the use of 150 mM FA produced a dark yellow electrolyte, indicating that furan polymerization occurred and no products were detected by gas chromatography-mass spectrometry. Therefore, the initial concentration of FA should be within 100 mM.

[0132] Example 4

[0133] Scale-up production of GBL

[0134] Under optimized conditions, a scale-up volume of 500 mL of 100 mM FA (5.6 g, 500 mL) was used to produce sufficient GBL for product separation while delivering 38,880 C to maximize the conversion of FA to GBL. After dichloromethane (DCM) extraction and subsequent removal of DCM in vacuo, 2.1 g (47.8% isolated yield) of GBL with a purity of 98.1% was obtained (as determined by 1 1H NMR). This optimal isolated yield may be due to the extended electrolysis time and GBL loss during the removal of DCM in vacuo, resulting in GHB hydrolysis. As FA and 2-FO were depleted, GHB and succinic acid (SA) were also detected near the end of the reaction, 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 the ring-opening of 2(3H)-furanone, which generates 4-oxobutyric acid, followed by the ECO of its aldehyde group. It can also be formed by the ECH of the C═C bond of MA, which is derived from the Figure 12 HFO described in. Trace amounts of butyric acid (BA) were also observed, which may be produced by the reduction of GHB. DCM extraction was highly selective for GBL, as shown by the high purity mentioned above.

[0135] It is believed that the FA-to-GBL method of the one-pot process as described herein produces high-purity GBL at a rate comparable to that of existing FAL-to-FA technologies. Based on the conversion rate, this scaled-up reaction consumes 5.6 g of FA every 24 h, which is equivalent to 2083.3 μmol / h. It is believed that this conversion rate is far superior to some reported thermal catalytic 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 of O2 was determined to be 750 μmol / h. At the same time, it was 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 a conversion rate of approximately 2425 μmol / h. Therefore, it is believed that the electrosynthesis of FA-to-GBL by the one-pot process as described herein shows good compatibility with some existing FAL-to-FA technologies in terms of reaction rate, suggesting the potential integration of these systems.

[0136] The present invention is given by way of example only, and various other modifications and / or changes 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 into said γ-butyrolactone in a diaphragm-free cell without a mediator for paired electrolysis, the method comprising the following steps: a) electrochemically oxidizing the furoic acid to 2(5H)-furanone; and b) electrochemically reducing 2(5H)-furanone to the γ-butyrolactone.

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

3. The method of claim 1, wherein the diaphragm-free cell comprises 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 cloth, zinc, copper or gold.

4. The method of claim 3, wherein the electrode pair comprises an anode made of platinum, palladium, fluorine-doped tin oxide or gold.

5. The method of claim 3, wherein the electrode pair comprises 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 cloth, zinc, copper or gold.

6. The method of claim 1, wherein the step of converting furoic acid to the gamma-butyrolactone is performed at a pH of 2 to 6.

7. The method of claim 1, wherein the step of converting furoic acid to the gamma-butyrolactone is performed under an ambient atmosphere of 0.5 atmosphere to 3 atmospheres.

8. The method of claim 1, wherein the step of converting furoic acid into the gamma-butyrolactone is performed at a temperature of 20°C to 100°C.

9. The method of claim 1, wherein the step of converting furoic acid to the γ-butyrolactone is performed at an applied voltage of 1.4 V to 3.0 V vs. Ag / AgCl.

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

11. The method of claim 1, wherein the step of converting furoic acid to the γ-butyrolactone is carried out in a diaphragmless cell without a separator under ambient atmosphere at 1 atmosphere, at pH 3 to 6, at a temperature of 35°C to 80°C, at an applied voltage of 1.8 V to 2.0 V relative to Ag / AgCl.

12. The method of claim 11, wherein the separator-free diaphragm-free cell comprises a platinum anode, a nickel cathode, an Ag / AgCl reference electrode, and a phosphate buffer solution containing 1 mM to 200 mM of the furoic acid.

13. The method of claim 11, wherein the furoic acid is biomass-derived furoic acid.

14. The method of claim 12, wherein the furoic acid is electrochemically oxidized to the 2(5H)-furanone with a selectivity of 40% to 95%.

15. The method of claim 14, wherein the furoic acid is electrochemically oxidized to the 2(5H)-furanone with a selectivity of 84.2%.

16. The method of claim 12, wherein the furoic acid is electrochemically oxidized to the 2(5H)-furanone in a yield of 40% to 95%.

17. The method of claim 16, wherein the furoic acid is electrochemically oxidized to the 2(5H)-furanone with a yield of 74.8%.

18. The method of claim 12, wherein the furoic acid is electrochemically oxidized to the 2(5H)-furanone with a carbon balance of 40% to 95%.

19. The method of claim 18, wherein the furoic acid is electrochemically oxidized to the 2(5H)-furanone with a carbon balance of 89.0%.

20. The method of claim 14, wherein the 2(5H)-furanone is electrochemically reduced by olefin hydrogenation to produce 40% to 99% of gamma-butyrolactone.

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