Method for electrolytic dicarboxylation of at least one alkene with carbon dioxide CO2 in the presence of hydrogen H2

Abstract

To provide a method for dicarboxylating alkenes, more particularly dienes, which can prevent the formation of salts in the product phase and thus avoid the associated costly and inconvenient isolation work to the greatest extent possible. A method for forming at least one unsaturated dicarboxylic acid by electrolytic dicarboxylation of at least one alkene, more particularly at least one diene, with carbon dioxide CO2 in the presence of hydrogen H2 is provided, the reaction being carried out in a reactor having at least one cathode as a working electrode for cathodic activation of CO2 and at least one anode as a counter electrode for anodic oxidation of H2, the volume ratio of hydrogen H2:carbon dioxide CO2 being 1:1 to 1:3, and the total pressure p g is 2 to 4 MPa, particularly preferably 3 to 4 MPa, and the average current density j is 5 to 15 mA / cm 2 , and particularly preferably 10 to 12.5 mA / cm 2 It is characterized in that:

Description

[Technical field]

[0001] The present invention relates to a process for the electrolytic dicarboxylation of at least one alkene, more particularly at least one diene, with carbon dioxide CO2 in the presence of hydrogen H2, and to a reactor for carrying out such a process. [Background technology]

[0002] Among other uses, adipic acid is the starting material for the large-scale production of polyamide 6.6 (nylon). It is industrially produced in quantities of around 2.5 million metric tons per year by partial oxidation of "KA oil". Nitrous oxide, an inevitable by-product of the acid's production, is a greenhouse gas with 298 times the greenhouse potential of CO2. The process also requires the stoichiometric use of nitric acid, produced, for example, by the energy-intensive Ostwald process. KA oil is produced by partial oxidation of fossil-derived cyclohexanone and cyclohexanol. One of the difficulties here is the low conversion rate per pass through the reactor (4-11%). This requires a reuse step or downstream steps after the production of adipic acid.

[0003] Other approaches include, among others, the biotechnological and photocatalytic production of adipic acid (US Pat. No. 7,799,545; Hwang, KC and Sagadevan, A., “2014, One-pot room-temperature conversion of cyclohexane to adipic acid by ozone and UV light. Science, 346, 1495-1498”). There are also patents on the production of adipic acid by double hydroesterification and dicarboxylation (US Pat. No. 3,778,466, US Pat. No. 4,552,976 and US Pat. No. 3,876,695).

[0004] Loveland et al. ("Electrolytic production of acyclic carboxylic acids from hydrocarbons"; US 3,032,489 (Patent Document 5)) and Tyssee et al. ("Electrolytic carboxylation of substituted olefins"; US 3,864,225 (Patent Document 6)) have already shown a route to produce adipic acid by electrochemical coupling (electrolytic dicarboxylation) of 1,3-butadiene and CO2. Subsequently, Tilborg et al. ("Electrochemical conversion of conjugated dienes into alkanedienedioic acids"; US 4,377,451 (Patent Document 7)) conducted various case parameter studies and initial consideration of the macro-reaction kinetics of the reaction. Building on this work, a study by Grinberg et al. ("Electrochemical reduction of CO2 in the presence of 1,3-butadiene using a hydrogen anode in a non-aqueous medium; Russian Chemical Bulletin," 1999, 48(2), 294-299) demonstrated the feasibility of electrolytic dicarboxylation using hydrogen, albeit to a limited extent. Adding to these considerations, a recent study by Li et al. (Electrochim. Acta 2011, 56, 1529-1534) added a complete route for the production of adipic acid without hydrogen.

[0005] The electrochemical approach is shown in Scheme 1 below:

[0006] [ka] [Prior art documents] [Patent documents]

[0007] [Patent Document 1] U.S. Patent No. 7,799,545 [Patent Document 2] U.S. Pat. No. 3,778,466 [Patent Document 3] U.S. Pat. No. 4,552,976 [Patent Document 4] U.S. Pat. No. 3,876,695 [Patent Document 5] U.S. Pat. No. 3,032,489 [Patent Document 6] U.S. Pat. No. 3,864,225 [Patent Document 7] U.S. Pat. No. 4,377,451 [Non-patent literature]

[0008] [Non-Patent Document 1] Hwang, KC, and Sagadevan, A. 2014, One-pot room-temperature conversion of cyclohexane to adipic acid by ozone and UV light. Science, 346, 1495-1498 [Non-Patent Document 2] Grinberg et al., Electrochemical reduction of CO2 in the presence of 1,3-butadiene using a hydrogen anode in a non-aqueous medium; Russian Chemical Bulletin, 1999, 48(2), 294-299 [Non-Patent Document 3] Li et al., Electrochim. Acta 2011, 56, 1529-1534 Summary of the Invention [Problem to be solved by the invention]

[0009] In addition to a cathode where the reduction of CO2 proceeds, a counter reaction is required that releases the necessary electrons. This can be achieved, for example, by a sacrificial component, which must be oxidized stoichiometrically for this purpose. The sacrificial components and substances used can be, for example, aluminum, zinc, redox systems, etc., which must be reduced in a tandem process or subsequently isolated and recovered. The product phase after the reaction therefore contains the target substance, hexa-3-enedioic acid (dihydromuconic acid), in the form of a sacrificial anode salt (product 1 in the scheme). Isolating this product part and developing a method for industrially implementing the process is extremely complex and expensive, which is a hindrance to industrial practical use, especially the sacrificial anode salt.

[0010] It is therefore desirable to prevent the formation of these salts in the product phase and to avoid, as far as possible, the costly and inconvenient isolation operations associated therewith.The object of the present invention is therefore to provide a process for the dicarboxylation of alkenes, and more particularly dienes, which avoids the above-mentioned drawbacks. [Means for solving the problem]

[0011] The above object is achieved by a method according to claim 1 and a reactor according to claim 13 or 14.

[0012] That is, a method for producing at least one unsaturated dicarboxylic acid by electrolytic dicarboxylation of at least one diene with carbon dioxide CO2 in the presence of hydrogen H2 is provided, the reaction being carried out in a reactor comprising at least one cathode as a working electrode for the cathodic activation of CO2 and at least one anode as a counter electrode for the anodic oxidation of H2, and optionally comprising at least one reference electrode.

[0013] The method in question is -The volume ratio of hydrogen H2:carbon dioxide CO2 is 1:1 to 1:3, - the total pressure p of the reactor g is set to 2 to 4 MPa, preferably 3 to 4 MPa, for example, 3.4 MPa, 3.5 MPa, 3.7 MPa, etc., -Average current density j is 5 to 15 mA / cm 2 , preferably 10 to 12.5 mA / cm 2 As, It will be executed.

[0014] According to the present method, the anode side is optimized by using an anode reaction (counter reaction) that includes hydrogen H2. This makes it possible to greatly simplify all industrial operations. Taking the dicarboxylation of 1,3-butadiene as an example, the reaction is summarized in the following Scheme 2:

[0015] [ka]

[0016] In the first step (marked "1."), CO2 is electrochemically cathodically activated. At the same time, H2 is oxidized anodically. The resulting protons then complete the current circuit, directly producing unsaturated dicarboxylic acids such as hexa-3-enedioic acid, the precursor of adipic acid. In other words, the electrochemically activated CO2 can be used to convert two carboxyl groups (-COO - ) is introduced into the unsaturated alkene system.

[0017] Following the dicarboxylation, in one embodiment, the unsaturated dicarboxylic acid can be converted to a saturated dicarboxylic acid, for example hex-3-enedioic acid to the target product adipic acid, by homogeneously or heterogeneously catalyzed hydrogenation. For this purpose, alternatively, standard catalysts such as platinum metal supported on activated carbon, silica or titanium dioxide, or the very well-known Wilkinson catalyst, can be used under suitable reaction conditions. For this purpose, it has been found that it is first necessary to remove the electrolyte from the electrolytic dicarboxylation (1.). Then, to reach adipic acid, it is necessary to remove the hydrogenation catalyst and hydrogenation medium, as well as by-products from said electrolytic dicarboxylation, if present.

[0018] The method has various advantages over existing approaches, for example, the use of anodic sacrificial materials and sacrificial electrodes is not required, which means that not only the use of aluminum but also the generation of aluminum salt products, which are difficult to purify, is avoided, which means that various cost savings are achieved in the corresponding method. The savings here relate to the fact that, by not using aluminum as a component, which is a certain high cost, the method steps for the above-mentioned separation of the product aluminum salts and also the frequent maintenance of the reactor due to the replacement of consumed sacrificial electrodes are avoided. The purification steps of the industrial operation, which are being developed, are greatly simplified. In addition, the conversion of dienes to the corresponding dicarboxylic acids is improved while the formation of by-products, especially monocarboxylic acids, is reduced.

[0019] A particularly surprising finding is that increasing pressure, and in particular increasing CO2 partial pressure, does not necessarily have a linear effect on the faradaic efficiency, i.e. there is no linear relationship between pressure and faradaic efficiency. Rather, specifically, special adjustments must be made to the CO2 partial pressure. Both very high (above 4 MPa) and very low (below 2 MPa) total pressures are found to have a negative effect on the faradaic efficiency. Here, no direct relevance to kinetic models is apparent. The dependencies are complex and not directly predictable (e.g. by simulation) and do not lend themselves to prediction or extrapolation once other input parameters are changed.

[0020] An increase in total pressure does not necessarily result in an increase in the Faradaic efficiency. The equilibria and dependencies here are complex and are not yet clear. For example, increasing the pressure to 5 MPa for a ratio of 1:3 (hydrogen / carbon dioxide) results in a rapid decrease in the Faradaic efficiency to 15%.

[0021] While the method of the present invention uses a gas diffusion electrode (GDE) at a pressure slightly above atmospheric pressure, the method of the present invention omits the GDE and increases the total pressure. A gas mixture is used. Moreover, the faradaic efficiency of the method of the present invention is relatively low.

[0022] In one embodiment of the method, hydrogen H2 is introduced into the reactor at a partial pressure p 0,H2 It exists in.

[0023] In another embodiment of the process, carbon dioxide CO2 is introduced into the reactor at a partial pressure p 0,CO2 It exists in.

[0024] In yet another embodiment of the method, at least one diene is metered into the reactor in liquid form. This results in a high diene concentration in the reaction mixture. That is, the diene concentration after metering can be 1-5 mol / L, preferably 1.5-3 mol / L, particularly preferably 1.5-2 mol / L. Liquid diene can be, for example, charged into the reactor in a concentration of 1.62 mol / L.

[0025] In the present case, diene is a general term for a group of compounds having two or more double bonds in conjugated or isolated form. Thus, the at least one diene may be, for example, a linear conjugated diene including 1,3-butadiene, pentadiene, hexadiene, 1,3,5-hexatriene, or cyclohexadiene.

[0026] It is also possible to use polyunsaturated non-conjugated dienes. Such dienes can include, for example, linear dienes with non-conjugated double bonds. Such dienes can, for example, have at least one terminal (end-located) double bond. Examples include α,ω-dienes such as 1,7-octadiene (OD), 1,9-decadiene, 1,11-dodecadiene, and 1,13-tetradecadiene.

[0027] The process parameters presented for the present electrolytic dicarboxylation allow for an increase in the faradaic efficiency, which is the stoichiometric ratio of the current contributed to the desired product or by-product relative to the total current, e.g., "Faraday efficiency for component X".

[0028] According to the present method, the Faraday efficiency FE for the sum of all dicarboxylation products ECcan be 10-55%, preferably 15-30%, particularly preferably 20-25%. The faradaic efficiency depends on the selected electrode geometry, partial pressure and butadiene concentration, as well as whether a mediator is used, which will be described in detail later. A mediator here refers to a component added to the reaction from the metal-organic compound group that can affect the faradaic efficiency in an unknown manner.

[0029] In this case, the Faraday efficiency FE for the sum of all dicarboxylation products available for the preparation of linear unbranched dicarboxylic acids is EC is in the range of 5 to 30%, preferably 10 to 25%, and particularly preferably 15 to 20%, for example, 13.3%, 26.2%, and the like.

[0030] In one embodiment of the method, the reaction is carried out in an anhydrous organic solvent containing at least one conductive salt, the organic solvent being selected from dimethylformamide (DMF), dimethylpropyleneurea (DMPU) and N-methyl-2-pyrrolidone (NMP), preferably DMF being used, and the at least one conductive salt being an alkyl ammonium bromide, preferably tetra-n-butyl ammonium bromide (TBAB).

[0031] In another preferred embodiment of the method, the electrolytic dicarboxylation is carried out in the presence of a mediator. The component referred to as the mediator is a metal-organic compound, such as a transition metal complex. Surprisingly, an effect on the reaction was identified that was unexpected. Mediators are commonly encountered in electrochemistry, but they are unusual in that they are highly specific to a particular reaction and can be generalized between similar reactions.

[0032] Preferably, the mediator is a transition metal complex, more particularly a complex of Rh, Pt, Pd, Ru or Fe. Particularly preferred mediators are platinum metal complexes with phosphane ligands (e.g., xantphos) and ferrocene. The use of a mediator reduces the electropolymerization tendency and improves the faradaic efficiency. Preferably, any applied mediator does not show any catalytic function in the reaction itself, but may reduce the macroscopic polymerization tendency of 1,3-butadiene and affect the electrocarboxylation efficiency.

[0033] As already mentioned above, the dicarboxylation can be followed by the reaction of the unsaturated dicarboxylic acid to form a saturated dicarboxylic acid, which can be carried out by homogeneously or heterogeneously catalyzed hydrogenation under suitable reaction conditions using known catalysts such as homogeneous catalytic complexes such as platinum metal on a suitable support or platinum metal in the form of a metal-phosphine complex (one example being Wilkinson's catalyst).

[0034] As previously mentioned, the method is carried out in a reactor comprising at least one cathode as a working electrode for the cathodic activation of CO2, at least one anode as a counter electrode for the anodic oxidation of H2, and at least one reference electrode.

[0035] In one variant of the reactor, the anode and cathode are arranged parallel to each other.

[0036] In another variant of the reactor, the anode and cathode are arranged concentrically with respect to one another, in which the anode is arranged concentrically around the cathode, i.e. the cathode may be centrally located within, for example, an annular anode and may consist, for example, of a narrow polished nickel plate.

[0037] Surprisingly, the selectivity of electrocarboxylation is 44% in the parallel configuration, whereas the selectivity is improved to 73% in the concentric configuration. The values ​​given here for the selectivity of electrocarboxylation are based on the amount of dicarboxylic acid moieties relative to the total amount of electrocarboxylation product produced.

[0038] The anode may be composed of platinum metal, one or more alloys of platinum metal, or a heterometallic support that is platinized (i.e. coated with platinum metal). Platinum is preferably used here and may take the form of a coil, net, woven fabric, or platinum particles immobilized on a suitable support or plate (e.g. planar, flat, concentric plate, etc.). Platinum anode material is highly inert and does not cause contamination of the system as described above.

[0039] The cathode may be constructed of graphite or a transition metal (preferably platinum metal, preferably nickel) and may take the form of a flat plate. The cathode material is preferably subjected to a pretreatment process which includes the successive steps of grinding, polishing, washing and drying.

[0040] The anode and cathode spaces may be separated (eg by a membrane or the like) or not, preferably not.

[0041] In another embodiment of the reactor of the present case, the anode and cathode spaces are separated from each other, more particularly by a membrane body, for example made of Nafion.

[0042] The invention will now be described by way of example with reference to the drawings. [Brief description of the drawings]

[0043] [Figure 1] FIG. 2 is a schematic diagram showing an electrode arrangement (parallel arrangement) of the first embodiment. [Diagram 2] FIG. 11 is a schematic diagram showing an electrode arrangement (concentric arrangement) of the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] (Description of the device) The equipment configuration used includes a pressure-stabilized stirred vessel with an in-vessel electrode, a 1,3-butadiene metering system, and a gas mixing system. The pressure-rated reactor used has an inert inner shell, internals, and electrode placement structure. Convective mixing was achieved by a magnetically coupled stirrer at a fixed distance below the cathode.

[0045] To carry out electrochemical reactions under pressure, the electrode arrangement must be integrated into a pressure-rated vessel made of a mechanically robust material, such as stainless steel. However, as the material is inherently conductive, it must not come into contact with the electrodes and the electrode medium. This is achieved by the aforementioned inner skin. Here, the use of highly corrosion-resistant stainless steels such as 1.4435, 1.4462 is particularly recommended. In the case of stainless steels such as 1.4301, 1.4306, a strong tendency to chemical corrosion was recorded due to the inevitable droplets of electrolyte. However, it is possible to isolate the affected parts with an inner skin made of PEEK, Teflon or other materials with sufficient mechanical stability and chemical inertness.

[0046] A PTFE insert and PEEK lid with corresponding passages for the power feed lines and electrodes allow maximum electrical isolation of the components. During the reaction, the arrangement consisting of the inner shell, inner structure and electrodes is introduced into the PTFE insert, completely closing the reactor. Electrically insulated contacts allow the application of voltage to the electrodes through the pressure-stabilized stainless steel jacket.

[0047] (Explanation of experimental considerations) Prior to each experiment, a pre-prepared Ni electrode 1 was inserted into the electrode arrangement. A Luggin tube 3 was filled with 1 molar TBAB-DMF solution and the reactor was assembled accordingly with a magnetic stirring core. Multiple evaluation cycles were performed with repeated flushing with nitrogen to remove moisture, oxygen and any solvent residues from the previous cleaning steps.

[0048] The reactor was then pressurized to the desired pressure using a pre-prepared CO2 / H2 mixture. A metering system equipped with a high-pressure pump, an expansion section, and a mixer was used to feed the reactants and an aprotic dehydrated organic solvent together with a conductive salt soluble in the solvent. At this time, a predetermined amount of 1,3-butadiene was accurately metered.

[0049] After metering the reactants into the reactor to the target volume, an equilibration phase of approximately 30 minutes was used to fully saturate the reactants with CO2 and H2. Mixing was ensured by magnetically coupled stirring with a magnetic stir core. The pressure was automatically maintained at the target pressure by closed loop control.

[0050] To ensure that reaction conditions were consecutively identical, a computer-controlled standard procedure was used for the entire reaction, including the electrode activation cycle, the reaction itself, and further electrochemical characterization steps.

[0051] After each reaction run, the reactor was gradually depressurized according to standard automated procedures and the closed reaction chamber was purged with slight nitrogen overpressure for approximately 1 hour to ensure removal of any remaining 1,3-butadiene. The removed reaction materials were concentrated to dryness on a rotary evaporator.

[0052] The products were analyzed by gas chromatography with associated mass spectrometry (GC / MS). For this purpose, samples of the crude material were quantitatively silylated and measured against standards. On the basis of the labelling alone, it was then possible to identify some isomers of the by-products. The dried products were then analysed for their organic carbon content (TOC: total organic carbon), with the aim of making it possible to determine the inhibition of polymerization by the mediator. For this purpose, the products were completely dissolved and combusted, after which measurements were made by IR spectroscopy of the gas phase.

[0053] The product composition was then determined by GC / MS. Consistency checks were performed with multiple samples from each reaction run by measuring the same sample multiple times and analyzing the total amount of coupling product separately by HPLC / DAD / ELSD (High Performance Liquid Chromatography (HPLC), Diode Array Detector (DAD) and Evaporative Light Scattering Detector (ELSD)).

[0054] As preparation for the reaction, the organic solvent used was dehydrated with a drying agent (e.g., diphosphorus pentoxide, sodium hydride, etc.) and distilled under reduced pressure. The dehydrated solvent was added to the pre-dried conductive salt under an argon atmosphere and stored using freshly calcined molecular sieves (4A).

[0055] There are several solvents suitable for the reaction of interest, including dimethylformamide (DMF), dimethylpropyleneurea (DMPU), and N-methyl-2-pyrrolidone (NMP). However, DMF was primarily used due to its superior results. Specifically, the conductive salt used was tetra-n-butylammonium bromide (TBAB).

[0056] To prepare the working electrode, a nickel plate was first cut to size and ground to a certain shape. The plate was then attached to a corresponding holder by TIG welding to prevent contamination with dissimilar metals. The electrode was then subjected to successive steps of grinding, polishing, cleaning and drying before it was ready for use. Micrographs (AFM) of the electrode after the pretreatment process showed that the initial surface roughness (peak-to-valley roughness) of the working electrode was 68 nm.

[0057] The counter electrodes were platinum coils or plates that were first cleaned and cut to a certain shape, and all electrodes were electrically insulated with a Teflon sleeve at the part that did not want to be exposed to the electrolyte.

[0058] Before each experiment, the Teflon reactor insert was thoroughly cleaned by rinsing with aqua regia and then dried.

[0059] The working and counter electrodes were pretreated as described above and inserted into the reactor. The reference electrode bridge (Luggin capillary) was prepared and filled with electrolyte, then inserted into the reactor insert and the reactor was closed. After checking the contacts for shorts or insufficient electrical resistance, the reactor was filled with the required amount of electrolyte solution and 1,3-butadiene via a metering system. The total amount of electrolyte and 1,3-butadiene for each experiment was 28.00 mL.

[0060] To ensure a steady supply of gas during the reaction, a gas mixture of target composition of hydrogen and carbon dioxide was prepared in a pressure-stabilized storage vessel (500 mL).

[0061] The partial pressures for the reactions presented here were p0(H2) = 1.0 MPa and p0(CO2) = 3.0 MPa. The reactor filling pressure was p = 3.4 MPa and maintained for a saturation period of 30 min by a pressure regulator. The voltage was controlled to maintain a current of -50 mA ± 0.1 mA during the reaction time. The reaction time was constant at 43857 s with a corresponding charge of 2193 A·s. The current used was 50 mA and the electrode area = 5 cm 2 So, the current density j = 10mA / cm 2 It became.

[0062] Several examples of the feasibility of reactions with given amounts of 1,3-butadiene in a pressure vessel are given below.

[0063] 1 and 2 show the electrode arrangement structure used in these reactions. Fig. 1 shows a parallel arrangement using a Pt coil 1 as the anode, a polished Ni plate 2 as the cathode, a Luggin capillary 3 with a frit, and a silver-silver bromide electrode 4. Fig. 2 shows a parallel arrangement using a Pt plate 1 as the anode, a polished Ni plate 2 as the cathode, a Luggin capillary 3 with a frit, and a Ag / Ag + A concentric arrangement with electrode 4 is shown.

[0064] Table 1 contains the faradaic efficiencies measured for the reaction runs. The first input data in Table 1 represents the plane-parallel geometry, and the second input data represents the concentric geometry. All experiments with additives were performed in the concentric geometry.

[0065] As can be seen from the same table 1, depending on the additive (mediator) used, the faradaic efficiency can be significantly increased, up to 51.8% in the case of ferrocene and 29.5% in the case of the combination of PdCl2 and Xantphos. Surprisingly, in the latter case, a decrease in the tendency of 1,3-butadiene to polymerize is observed. The combinations RhCl3 and Xantphos and PdCl2 and Xantphos have the same inhibition of polymerization (TOC), but the latter shows an overall higher faradaic efficiency. When ferrocene is used, there is no inhibition whatsoever on the faradaic efficiency for the target product.

[0066] Table 1: Results [Table 1]

[0067] The various products in the reaction run include a range of different dicarboxylation products as shown in Table 2:

[0068] Table 2: Analysis of product phases [Table 2]

[0069] The results shown in Table 2 show that in order to significantly improve the very limited faradaic efficiency of the electrolytic dicarboxylation of Non-Patent Document 2 (from 3.8% to 20%), a higher CO2 partial pressure is required.

[0070] Furthermore, a suitably high CO2 partial pressure and a sufficiently high current density (10 mA / cm 2It was also demonstrated that the use of 4-pentenoic acid, which is a significant inhibitor, can be avoided to the greatest extent possible by terminating the polymerization of adipic acid and adiponitrile to form nylon.

[0071] The strong influence of the electrode configuration on the selectivity was also confirmed. Examples 1 and 2 are presented for this purpose. When a parallel configuration was used, the formation of branched products was increased. The concentric electrode configuration significantly reduced the formation of the undesired methyl-pentenedioic acid derivatives. The present invention includes the following embodiments. [Aspect 1] Hydrogen H 2 In the presence of carbon dioxide CO 2 1. A process for forming at least one unsaturated dicarboxylic acid by electrolytic dicarboxylation of at least one alkene, more particularly at least one diene, by CO 2 At least one cathode as a working electrode for cathodic activation of H 2 The reaction is carried out in a reactor having at least one anode as a counter electrode for the anodic oxidation of -Hydrogen H 2 : Carbon dioxide CO 2 The volume ratio is 1:1 to 1:3, - the total pressure p of the reactor g is 2 to 4 MPa, particularly preferably 3 to 4 MPa; -Average current density j is 5-15mA / cm 2 , and particularly preferably 10 to 12.5 mA / cm 2 That is, A method comprising: [Aspect 2] In the method according to embodiment 1, hydrogen H 2 In the reactor, a partial pressure p0,H of 0.75 to 2 MPa, preferably 1 to 1.5 MPa is applied. 2 5. The method of claim 1, wherein [Aspect 3] In the method according to aspect 1 or 2, carbon dioxide is introduced into the reactor at a partial pressure p of 2 to 4 MPa, particularly preferably 3 to 4 MPa. 0,CO2 5. The method of claim 1, wherein [Aspect 4] 4. The method of any one of the preceding aspects, wherein at least one diene is metered into the reactor in liquid form. [Aspect 5] The method according to any one of the preceding aspects, wherein the at least one diene is a linear conjugated diene. [Aspect 6] In the method according to any one of the preceding aspects, the Faraday efficiency F for the sum of all dicarboxylation products is EC is 10 to 55%, preferably 15 to 30%, and particularly preferably 20 to 25%. [Aspect 7] In the method according to any one of the first to sixth aspects, the Faraday efficiency FE for the sum of all dicarboxylation products available for the preparation of linear unbranched dicarboxylic acids is EC is 5 to 30%, preferably 10 to 25%, and particularly preferably 15 to 20%. [Aspect 8] 8. The method according to any one of the preceding aspects, characterized in that the reaction is carried out in a dehydrated organic solvent containing at least one conductive salt. [Aspect 9] The method according to embodiment 8, characterized in that the organic solvent is selected from dimethylformamide (DMF), dimethylpropyleneurea (DMPU) and N-methyl-2-pyrrolidone (NMP), preferably DMF. [Aspect 10] The method according to embodiment 8 or 9, characterized in that the at least one conductive salt is an alkylammonium bromide, preferably tetra-n-butylammonium bromide (TBAB). [Aspect 11] 11. The method according to any one of the preceding aspects, characterized in that the electrolytic dicarboxylation is carried out in the presence of a mediator. [Aspect 12] The method according to embodiment 11, wherein the mediator is a transition metal complex, more particularly a complex of Rh, Pt, Pd, Ru or Fe. [Aspect 13] 13. A reactor for carrying out the method according to any one of the preceding embodiments, characterized by a concentric arrangement of the anode and the cathode, with the anode being concentrically arranged around the cathode. [Aspect 14] 13. A reactor for carrying out the method according to any one of the preceding aspects, characterized in that the anode and cathode spaces are not separated or are separated by a membrane body.

Claims

1. Hydrogen H ２ In the presence of carbon dioxide CO ２ 1. A process for forming at least one unsaturated dicarboxylic acid by electrolytic dicarboxylation of at least one diene by CO ２ At least one cathode as a working electrode for cathodic activation of H ２ The reaction is carried out in a reactor comprising at least one anode as a counter electrode for the anodic oxidation of - Hydrogen H ２ : Carbon dioxide CO ２ The volume ratio of - the total pressure of the reactor p ｇ is 2 to 4 MPa, the average current density j is between 5 and 15 mA / cm 2 , A method comprising:

2. 2. The method of claim 1, wherein the hydrogen ２ In the reactor, a partial pressure p ０，Ｈ２ 5. The method of claim 1, wherein

3. 3. The method according to claim 1 or 2, wherein carbon dioxide is introduced into the reactor at a partial pressure p of 2 to 4 MPa. ０，ＣＯ２ 5. The method of claim 1, wherein

4. 4. The process according to any one of claims 1 to 3, characterized in that at least one diene is metered into the reactor in liquid form.

5. 5. The process according to any one of claims 1 to 4, characterized in that the at least one diene is a linear conjugated diene.

6. 6. The method according to claim 1, wherein the Faraday efficiency FE for the sum of all dicarboxylation products is ＥＣ is 10-55%.

7. In the process according to any one of claims 1 to 6, the Faraday efficiency FE for the sum of all dicarboxylation products available for the preparation of linear unbranched dicarboxylic acids is ＥＣ is 5-30%.

8. 8. The method according to claim 1, wherein the reaction is carried out in an anhydrous organic solvent containing at least one conductive salt.

9. 9. The method according to claim 8, wherein the dehydrated organic solvent is selected from dimethylformamide (DMF), dimethylpropyleneurea (DMPU) and N-methyl-2-pyrrolidone (NMP).

10. 10. The method according to claim 8 or 9, characterized in that at least one conductive salt is an alkylammonium bromide.

11. 11. The method according to any one of claims 1 to 10, characterized in that the electrolytic dicarboxylation is carried out in the presence of a mediator.

12. 12. The method of claim 11, wherein the mediator is a transition metal complex.

13. 13. A reactor for carrying out the method according to any one of claims 1 to 12, characterized by a concentric arrangement of anodes and cathodes, with at least one anode concentrically arranged around at least one cathode.

14. 13. A reactor for carrying out the method according to any one of claims 1 to 12, characterized in that the anode and cathode spaces are not separated or are separated by a membrane body.

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