EP3649278A1

EP3649278A1 - Electrochemical process for synthesizing diaryl carbonates

Info

Publication number: EP3649278A1
Application number: EP18750100.2A
Authority: EP
Inventors: Vinh Trieu; Stefanie Eiden; Dana KAUBITZSCH; Jan HEIJL; Niklas Meine
Original assignee: Covestro Deutschland AG
Current assignee: Covestro Intellectual Property GmbH and Co KG
Priority date: 2017-07-03
Filing date: 2018-06-29
Publication date: 2020-05-13
Also published as: CN110809649A; WO2019007831A1; TW201920769A; KR20200026916A

Abstract

The invention relates to an electrochemical process for electrochemically synthesizing diaryl carbonates, characterized in that a formula of formula R-OH (1), where R is an aryl group, preferably a tert-butylphenyl, cumyl-phenyl, naphthyl or phenyl group, especially preferably a phenyl group, is anodically reacted with CO on a gas diffusion electrode comprising at least one flat, electrically conductive substrate and a gas diffusion layer which is applied to the substrate and which contains a mixture of an electrocatalyst and a hydrophobic polymer, the electrocatalyst being in the form of a powder selected from among the series consisting of gold, copper, silver, ruthenium, iridium, copper oxide, ruthenium oxide and iridium oxide, preferably gold, ruthenium, copper, copper oxide and ruthenium oxide, or the electrocatalyst being in the form of metal particles or metal oxide particles selected from among the series consisting of gold, copper, silver, ruthenium, iridium, copper oxide, ruthenium oxide and iridium oxide, preferably gold, ruthenium, copper, copper oxide and ruthenium oxide, supported on a carbon support selected from among activated carbon, carbon black, graphite, graphene or carbon nanotubes, in particular carbon black.

Description

Electrochemical process for the preparation of diaryl carbonates

The invention relates to an electrochemical process for the preparation of diaryl carbonates.

Diaryl carbonates are important precursors in the production of polycarbonates and are therefore of great economic importance. The preparation of aromatic polycarbonates by the melt transesterification method is known and described, for example, in "Schnell", Chemistry and Physics of Polycarbonates, Polymer Reviews, Vol. 9, Interscience Publishers, New York, London, Sydney 1964, in D.C. Prevorsek, B.T. Debona and Y. Kersten, Corporate Research Center, Allied Chemical Corporation, Moristown, New Jersey 07960, "Synthesis of Poly (ester) Carbonate Copolymer" in Journal of Polymer Science, Polymer Chemistry Edition, Vol. 19, 75-90 (1980). , in D. Freitag, U. Grigo, PR

Müller, N. Nouvertne, BAYER AG, "Polycarbonates" in Encyclopedia of Polymer Science and Engineering, Vol. 11, Second Edition, 1988, pp. 648-718, and finally in Dres. U. Grigo, K. Kircher and P.R. Müller "Polycarbonates" in Becker / Braun, Kunststoff-Handbuch, Volume 3/1, polycarbonates, polyacetals, polyesters, cellulose esters, Carl Hanser Verlag Munich, Vienna 1992, pages 117-299.

The preparation of the diaryl carbonates used in the melt transesterification process for aromatic polycarbonates, e.g. through the interfacial process is described in principle in the literature, see e.g. in Chemistry and Physics of Polycarbonates, Polymer Reviews, H. Schnell, Vol. 9, John Wiley and Sons, Inc. (1964), p. 50/51. The diaryl carbonate is prepared by reacting phenol with a carbonyl dihalide (e.g., phosgene) prepared from carbon monoxide.

The preparation of diaryl carbonates can also be based on carbon dioxide. It is advantageous here that in this way conventional fossil raw materials can be replaced, and the greenhouse gas carbon dioxide can be recycled back into the material cycle, which is generally referred to as closing the carbon cycle. Overall, this would reduce the carbon footprint, which would contribute to global climate change goals. Carbon dioxide is a waste product in many chemical Processes available and can therefore be considered as a sustainable raw material. It is also advantageous that carbon dioxide as a non-combustible gas is easy to handle.

For the preparation of diaryl and dialkyl carbonates, carbon dioxide is already used industrially as a raw material, described in Green Chemistry, 2003, 5, 497-507. A major disadvantage here is that numerous synthetic steps are required for the synthesis described therein:

It is assumed that ethylene oxide, which is produced from ethylene. After reaction of ethylene oxide with carbon dioxide, ethylene carbonate is then obtained, which is then transesterified with methanol to give dimethyl carbonate. Subsequently, a further transesterification with phenol to the arylalkyl carbonate. This is then disproportionated in a final reaction to the diaryl carbonate.

The use of carbon dioxide as a raw material is a challenge because carbon dioxide is an inert molecule. So it takes an energy input to convert carbon dioxide into a higher quality chemical. In order to produce a product with a low carbon footprint, the generation of the input energy should in turn be associated with as little carbon dioxide emissions as possible. For example, electric power obtained from renewable energy sources is suitable for this purpose.

Despite the advantageous use of carbon dioxide as a raw material, this process has several disadvantages. Thus, numerous synthesis steps are required, which make the process consuming. Furthermore, ethylene oxide is used, the use of which requires special safety measures with increased expenditure. Due to the low equilibrium constant of the transesterification reaction to dimethyl carbonate, a large excess of methanol is necessary (Catal Surv Asia, 2010, 14, 146-163). In addition, continuous multi-stage distillation columns are required. The individual steps of the transesterification with phenol to arylalkyl carbonate are also carried out in reactive distillation columns which have a high energy requirement and require the use of several catalysts such as Pb (OPh) ₂ and Bu ₂ SnO (Catal. Surv. Asia, 2010, 14, 146-163 ). In addition, the reactive distillation apparatuses used in the prior art have large amounts of heterogeneous and at the same time homogeneous catalysts.

For the preparation of dialkyl carbonates electrochemical processes are already known and, for example, in J Chem Technol Biotechnol 2016; 91: 507-513, Electrochimica Acta 54 (2009) 2912-2915 and Journal of C02 Utilization 3-4 (2013) 98-101. Here, C0 _{2 is used} as a precursor. The disadvantage here is that expensive platinum electrodes and high concentrations of expensive ionic liquids are needed. US 2003/070910 A1 also describes the preparation of dialkyl carbonates. In contrast, the production of diaryl carbonates differs by another thermodynamics. Results with respect to dialkyl carbonates are not readily transferable to diaryl carbonates. For example, Comparative Examples 4 and 8 show that dimethyl carbonate, but not diphenyl carbonate, can be obtained with the same palladium electrode. Also, Comparative Example 7 shows that with a heterogeneous palladium electrode, the formation of diphenyl carbonate can not be detected.

An electrochemical process for preparing diaryl carbonates is further described in J. Phys. Chem. C, 2012, 116, 10607-10616, ACS Catal., 2013, 3, 389-392 and Res. Chem. Intermed., 2015, 41, 9497-9508, wherein carbon monoxide is reacted here for the oxidative carbonylation reaction of phenol , In this electrochemical oxidative carbonylation for the preparation of diaryl carbonates, the selection of suitable electrocatalysts is limited to palladium-based materials. No example of this reaction was found in the prior art which could be successfully carried out without a palladium-based electrocatalyst. The practical limitation of electrocatalysts on expensive palladium-based materials is of great disadvantage. The electrochemical oxidative carbonylation for the preparation of diaryl carbonates has hitherto not been applied industrially. In the publication J. Phys. Chem. C, 2012, 116, 10607-10616 it is pointed out that only palladium nanoparticles in the range <2 nm are sufficiently catalytically active. If the nanoparticles are> 6 nm, the electrocatalyst is inactive. The further limitation of the electrocatalyst to the particle size <2 nm may be disadvantageous, as this affects the required long-term stability of the electrocatalyst.

To address this limitation of electrocatalyst size, the same group has further reduced the size of the palladium-based electrocatalyst in subsequent work by using only homogeneous palladium complexes, described in

ACS Catal., 2013, 3, 389-392, Res. Chem. Intermed., 2015, 41, 9497-9508 and Catal. Be. Technol., 2016, 6, 6002-6010. The use of homogeneous catalysts is disadvantageous because they must be separated from the product and thus represent an increased cost factor.

The oxidative carbonylation of phenol is also known as a chemical variant without electricity, as described, for example, in Journal of Molecular Catalysis A: Chemical, 1999, 139, 109-119. Also for this non-electrochemical variant of the oxidative carbonylation of phenol, the choice of catalyst appears to be limited to palladium-based materials. No example of reaction of the oxidative carbonylation of phenol which could be successfully carried out without a palladium-based catalyst has been found in the prior art. WO 2011/024327 A1 describes the preparation of diaryl carbonates via homogeneous catalysis with palladium. This application focuses on making the reaction as efficient as possible and describes exclusively the use of a dissipation or reoxidation electrode, which converts the catalytically inactive Pd ° back into the catalytically active homogeneously dissolved Pd ²⁺ . The actual catalyst is here, as already described above, the homogeneous Pd ²⁺ .

In contrast, JP H673582 describes heterogeneous electrocatalysis on a palladium electrode, but only dialkyl carbonates are prepared. As Comparative Example 7 shows, using such an electrode, the formation of a diaryl carbonate could not be detected.

WO2014 / 046796 A2 describes inter alia the preparation of (phosgene) COCh. as the starting material for carbonyls with electrochemical conversion of CO ₂ to CO and a hydrogen halide or halogen salt to a halogen. This is not an in-situ production of CO from CO ₂ in the preparation of diaryl or arylalkyl, since initially phosgene is formed, which is then converted to the carbonates.

The present invention has for its object to provide an electrochemical process for the preparation of diaryl carbonates, in which electricity can be used directly as an energy source, and carbon dioxide as a precursor, with fewer reaction steps than in the prior art are required. Furthermore, a heterogeneous electrocatalyst, which is not limited to platinum or palladium-based material, and also should be used

Particle sizes> 2 nm may have to improve the long-term stability of such a material. Furthermore, the process for the preparation of diaryl carbonates with a gas diffusion electrode should be carried out, which is the prerequisite of the higher current density for a technical application. The object is achieved with a method for the electrochemical production of

Diaryl carbonates, which is characterized in that a compound of formula (1)

(1) R-OH where the radical R is an aryl radical, preferably tert-butylphenyl, cumylphenyl, naphthyl or phenyl, particularly preferably a phenyl radical, is anodically reacted with CO at a gas diffusion electrode, wherein the gas diffusion electrode at least one comprising planar, electrically conductive carrier and a gas diffusion layer applied to the carrier, wherein the gas diffusion layer contains a mixture of an electrocatalyst and a hydrophobic polymer,

wherein the electrocatalyst is present in the form of powder selected from the series gold, copper, silver, ruthenium, iridium, copper oxide, ruthenium oxide and iridium oxide, preferably gold, ruthenium, copper, copper oxide and ruthenium oxide

or

the electrocatalyst being in the form of metal particles or metal oxide particles selected from the group consisting of gold, copper, silver, ruthenium, iridium, copper oxide, ruthenium oxide and iridium oxide, preferably gold, ruthenium, copper, copper oxide and ruthenium oxide supported on a carbon support selected from activated carbon, Carbon black, graphite, graphene or carbon nanotubes, in particular carbon black.

The particular advantage of the method according to the invention is that it allows the electrochemical preparation of diaryl carbonates with little effort and a small number of reaction steps. The inventively provided gas diffusion electrode is an electrode in which the three states of matter - solid, liquid and gaseous - are in contact and the solid, electron-conducting catalyst catalyzes an electrochemical reaction between the liquid and the gaseous phase. In this case, the electrocatalyst is preferably heterogeneous and preferably free of palladium. According to the invention can be based on palladium-based in the gas diffusion electrode

Catalyst materials are dispensed with. As the inventors have discovered, in a first alternative the electrocatalyst may be in the form of powder selected from the group consisting of gold, copper, silver, ruthenium, iridium, copper oxide, ruthenium oxide and iridium oxide, preferably gold, ruthenium, copper, copper oxide and ruthenium oxide. In a second alternative, electrocatalysts can be used which are present in the form of metal particles or metal oxide particles selected from the series gold, copper, silver, ruthenium, iridium, copper oxide, ruthenium oxide and iridium oxide, preferably gold, ruthenium, copper, copper oxide and ruthenium oxide. The metal particles or metal oxide particles according to the invention are supported on a carbon support selected from activated carbon, carbon black, graphite, graphene or carbon nanotubes, in particular carbon black.

The heterogeneous electrocatalyst used in turn allows easy reuse in a wide range of particle sizes, since complex separation processes of catalytically active metal complexes can be omitted. By eliminating the size limitation of the electrocatalyst to the range <2 nm results in a greater freedom in the design of the electrodes. Also can be increased by a larger particle size of the electrocatalyst its long-term stability.

As explained in the introduction to the specification of this patent application, in the prior art both for the chemical and the electrochemical oxidative carbonylation reaction of phenol only palladium-based catalysts are known in which the reaction could be carried out successfully. It is all the more surprising that the feasibility of the reaction on other materials such. As gold or ruthenium oxide could be shown.

The process according to the invention uses compounds of the formula (1). Preferred starting compounds of the formula (1) are those selected from the series:

especially preferred is:

The reaction equation of the electrochemical process according to the invention for the preparation of diaryl carbonates is exemplified by the reaction of schematically shown with carbon monoxide: anodic reaction:

According to a first advantageous embodiment of the invention, it is provided that the CO is produced cathodically in an upstream reaction electrochemically from CO 2, in particular at a gas diffusion electrode:

C0 ₂ + 2e + H ₂ 0 - ^ CO + 2 OH ^" The OH ^" ions formed here are neutralized with the protons from the anodic reaction to water: 2 OH ^" + 2 H ⁺ -> 2 H ₂ 0

The use of carbon dioxide in a cathodic reduction reaction to provide the carbon monoxide has the advantage that the greenhouse gas carbon dioxide can thus be recycled back into the material cycle, which is generally also known as closing the carbon monoxide

Carbon cycle is called. Carbon dioxide is available as a waste product in many chemical processes and can thus be used as a sustainable raw material. It is also advantageous that carbon dioxide as a non-combustible gas is easy to handle. The method according to the advantageous embodiment described above is thus characterized by particular sustainability. This is preferably an in-situ generation of the carbon dioxide. In particular, the CO thus obtained is preferably reacted directly in the process according to the invention for the electrochemical preparation of diaryl carbonates in the anodic reaction at the gas diffusion electrode.

The reaction for the cathodic formation of carbon monoxide can basically be carried out in an analogous manner as described by way of example in Bull, Chem. Soc. Jpn, 1987, 60, 2517-2522. be described described.

According to a further advantageous embodiment of the invention, the anodic electrochemical reaction at a current density in the range of 0.1 to 5000 mA / cm ² , preferably 0.1 to 500 mA / cm ² , more preferably 0.1 to 100 mA / cm ² and most preferably 0.2 to 50 mA / cm ² . As a result, a realization on an industrial scale industrial scale is possible.

According to a further advantageous embodiment of the invention is used as the solvent phenol as the alcohol of formula (1), or a mixture of the alcohol of formula (1) with other solvents, in particular a solvent selected from acetonitrile, propylene carbonate, dimethylformamide, dimethyl sulfoxide, 1, 2nd -Dimethoxyethane, dichloromethane and N-methyl-2-pyrrolidone, more preferably acetonitrile.

According to a further embodiment of the process according to the invention, lithium chloride, lithium bromide, lithium perchlorate, lithium bis (trifluoromethylsulfonyl) imide, sodium phenolate, lithium phenolate, tetrabutylammonium chloride, preferably lithium chloride and lithium perchlorate, or imidazolium, aammonium, phosphonium or pyridinium can be used as electrochemical conductive salts. based ionic liquids, preferably 1-ethyl-3-methylimidazolium tetrafluoroborate can be used. Most preferably, the ionic liquids comprise cations as imidazolium, ammonium, phosphonium or pyridinium. According to an advantageous embodiment of the invention, it is provided that the anodically carried out electrochemical reaction at a temperature in the range of 10 to 250 ° C, in particular in the range of 20 to 100 ° C and particularly preferably in the range of room temperature is performed. According to a further advantageous embodiment of the invention, the reaction can be carried out at atmospheric pressure or elevated pressure, in particular at up to 1 bar overpressure. In particular, in an operation with elevated pressure can be achieved at the electrode higher local concentrations and thus better productivity.

According to an advantageous embodiment of the invention, it is provided that the gas diffusion layer of the gas diffusion electrode contains a mixture of electrocatalyst, hydrophobic polymer and other carbon materials, wherein the hydrophobic polymer is a fluorine-substituted polymer, preferably polytetrafluoroethylene (PTFE).

According to an advantageous embodiment of the invention it is preferably provided that the proportion of electrocatalyst in the form of powder is 80 to 97 wt .-%, preferably 90 to 95 wt .-%, based on the total weight of electrocatalyst and hydrophobic polymer, or that

Proportion of electrocatalyst in the form of metal or metal oxide particles on a carbon support 40 to 60 wt .-%, based on the total weight of electrocatalyst and hydrophobic polymer.

According to a further advantageous embodiment of the invention, it is provided that the metal or metal oxide powder has an average particle diameter in the range of 1 to 100 μm, preferably in the range of 2 to 90 μm, or in that the mean particle diameter of the metal material supported on carbon materials. or metal oxide particles 2 nm to 100 μιη, preferably 2 nm to 1 μιη.

In addition, it can be provided that the electrocatalyst and hydrophobic polymer are applied and compressed in powder form on the carrier and form the gas diffusion layer.

It is further preferred that the gas diffusion electrode based on a metal or metal oxide powder as electrocatalyst a total loading of catalytically active component in a range of 5 mg / cm ² to 300 mg / cm ² , preferably from 10 mg / cm ² to 250 mg / cm ² , or that the gas diffusion electrode based on carbon supported metal or metal oxide particles has a total loading of catalytically active component in a range of

0.5 mg / cm ² to 20 mg / cm ² , preferably from 1 mg / cm ² to 5 mg / cm ² .

According to an advantageous embodiment of the invention, the electrically conductive carrier as mesh, woven, knitted, knitted, non-woven, expanded metal or foam, preferably as a fabric, particularly preferably as a network, be formed and nickel, gold, silver or a combination of nickel with gold or silver included.

According to DE 10.148.599A1, the gas diffusion electrode can be produced by applying the catalyst / powder mixture directly to a carrier. The powder mixture is produced in a particularly preferred embodiment by mixing the catalyst powder and the binder and optionally other components.

The mixing is preferably done in a mixing device which mixes rapidly rotating mixing elements, e.g. Have flywheel. To mix the components of the powder mixture, the mixing elements rotate preferably at a speed of 10 to 30 m / s or at a speed of 4000 to 8000 U / min. After mixing, the powder mixture is preferably sieved. The sieving is preferably carried out with a sieve device, which with networks o-the like. equipped, whose mesh size 0.04 to 2 mm.

By mixing in the mixing device with rotating mixing elements energy is introduced into the powder mixture, whereby the powder mixture heats up strongly. If the powder is excessively heated, a deterioration of the electrode performance is observed, so that the temperature during the mixing process is preferably 35 to 80 ° C. This can be done by cooling during mixing, e.g. by adding a coolant, e.g. liquid nitrogen or other inert heat-absorbing substances. Another way of controlling the temperature may be that the mixing is interrupted to allow the powder mixture to cool or by selecting suitable mixing units or changing the fill in the mixer.

The application of the powder mixture to the electrically conductive carrier takes place, for example, by scattering. The spreading of the powder mixture onto the carrier can e.g. done by a sieve. Particularly advantageously, a frame-shaped template is placed on the carrier, wherein the template is preferably selected so that it just covers the carrier. Alternatively, the template can also be chosen smaller than the surface of the carrier. In this case remains after sprinkling the powder mixture and the pressing with the carrier an uncoated edge of the carrier free of electrochemically active coating. The thickness of the template can be selected according to the amount of powder mixture to be applied to the carrier. The template is filled with the powder mixture. Excess powder can be removed by means of a scraper. Then the template is removed.

In the subsequent step, the powder mixture is pressed in a particularly preferred embodiment with the carrier. The pressing can be done in particular by means of rollers. Preferably, a pair of rollers is used. However, it is also possible to use a roller on a substantially flat base, wherein either the roller or the base is moved. Furthermore, the pressing can be done by a ram. The forces during pressing are in particular 0.01 to 7 kN / cm.

Another aspect relates to the use of the diaryl carbonates obtained from the process according to the invention for the production of polycarbonate, preferably by the melt transesterification process.

The transesterification reaction can be described by way of example according to the following equation:

The abovementioned advantages of the process according to the invention also apply analogously to the proposed use of the diaryl carbonates in the production of polycarbonate, preferably by the melt transesterification process

The invention is explained in more detail below by the examples, which, however, do not represent a limitation of the invention.

Examples

Analytical Methods Used: Gas Chromatography (GC)

Gas chromatographic (GC) analyzes were performed using the 7890A Gas Chromatograph and the 7639 Autosampler from Agilent Technologies. The interaction of the sample with the stationary phase takes place in a quartz capillary column DB-1701 from Agilent Technologies, USA (length: 30 m, internal diameter: 0.25 mm, film thickness of the covalently bonded stationary phase: 0.25 μm, precaution column: 5 m) , Carrier gas: hydrogen, injector temperature: 150 ° C, detector temperature: 310 ° C) Measuring program: starting temperature of 150 ° C for 1 min, heating rate: 50 ° C / min, 260 ° C final temperature for 5 min) for the analysis of

Diphenyl carbonate. For the analysis of DMC, the following parameters were used: starting temperature of 40 ° C and held for 1.5 min, heating rate: 50 ° C / min, 200 ° C final temperature would not be maintained. The amount of substance obtained was determined by an external standard. For a known amount of substance of the diphenyl carbonate or dimethyl carbonate of the electrolyte solution was added. The area of the obtained standard electrolytic solution signal was related to the area of the obtained signal of the sample. From this, the amount of substance of the methylphenyl carbonate formed was determined. The yield was determined on the basis of the Farady equation and the amount of substance obtained via the external standard.

Example 1 Preparation of a carbon monoxide gas diffusion electrode based on gold

The gas diffusion electrode was produced by the dry process, wherein 93% by weight gold powder SPF 1775 from Ferro, 7% by weight PTFE from DYNEON TF2053 were mixed in an IKA mill AI 1 basic. Subsequently, the powder mixture was pressed with a roller press at a force of 0.5 kN / cm on a nickel carrier network. For an electrode of size 24 cm ² , 7.7 g of the powder mixture were needed.

Example 2

Preparation of diphenyl carbonate on a carbon monoxide gas diffusion electrode based on gold Examples 2a-f were in a commercially available filter press cell (Model Micro Flow Cell volume: 0.001 m ²⁾ manufactured by Electro Cell in a 2-electrode structure or 3- electrodes on au (reference electrode Leakless Ag / AgCl electrode, commercially available from eDAQ model ET072 ) carried out. The carbon monoxide gas diffusion electrode was switched anodically based on gold according to Example 1, as the counter electrode was an Ir-MMO electrode (luediu -Mixed-metal-oxide-electrode, commercially available from ElectroCell). The electrolysis was carried out at a carbon monoxide flow rate of 0.5 L / h for 1 h (current density in each case 0.2 mA / cm ² ). During this time, the electrolyte was pumped in a circle at a rate of 2 mL / min.

An overview of the experimental details is given in Table 1.

Table 1. Overview of Examples 2a-f for the preparation of diphenyl carbonate on a carbon monoxide gas diffusion electrode based on gold.

Comparative Example 3

Preparation of a CO gas diffusion electrode based on palladium

Carbon black activation of Ketjenblack carbon black KB6OOJD

30.80 g of KB600JD was stirred in 5 mol / L HCl (600 mL) for 1 h at room temperature followed by filtration and washing with FLO (1.5 L). Now KB6OOJD was suspended in 65% HNO3 and refluxed for 2 h at 85 ° C. After that, KB6 OOJD was _branded with a filter

Merk (Stericup 250 mL Durapore 0.22 μιη PVDF) filtered off and washed with FLO acid-free (pH = 7). The resulting KB6OOJD was oven dried at 110 ° C for 72 h. PdCLr3H20 (1.37 g, 12.4 mmol / L) was dissolved in H2O (664 mL) and added to the solution following KB600JD (5.0 g). The suspension was evaporated with vigorous stirring for 6 h at 90 ° C. The black mass was dried at 110 ° C for 48 h. 6.3 g of the impregnated carbon black Pd_KB6oojD were obtained.

The gas diffusion electrode was produced by the dry process, wherein 60 wt .-% Pd-KBeooro and 40 wt .-% PTFE from DYNEON TF2053 were mixed in an IKA mill Al l basic. Subsequently, the powder mixture was pressed with a roller press at a force of 0.5 kN / cm on a nickel carrier network. For a 120.8 cm ² electrode, 4.9 g of the powder mixture was needed.

Comparative Example 4

Preparation of dimethyl carbonate on a carbon monoxide gas diffusion electrode based on palladium soot

The experiment was carried out in a commercially available Electrocell Model Micro Flow Cell volume (0.001 m ² ) from Electrocell in a 2-electrode run. The gas diffusion electrode prepared according to Comparative Example 3 was anodically switched, and as the counterelectrode, an iridium-MMO electrode (iridium mixed metal oxide electrode, commercially available from Eelctrocell) was used. The electrolysis was carried out at 2.5 V for 31 min (current density each 0.5 mA / cm ² ) during which time 30 mL of electrolyte and CO were passed through the cell. For the electrolyte, 2.66 g of L1CIO4 (0.1 mol / L) were dissolved in MeOH (250 mL).

The characterization with the GC 7809A from Agilent Technologies showed the following: Sample content DMC = 5.3 ng corresponds to a yield of 0.17%. Comparative Example 5

Preparation of dimethyl carbonate on a carbon monoxide gas diffusion electrode based on gold

The experiment was carried out in a commercially available Electrocell Model Micro Flow Cell volume (0.001 m ² ) from Electrocell in a 2-electrode run. The gas diffusion electrode prepared according to Example 1 was anodically switched, and as the counterelectrode an iridium-MMO electrode (iridium mixed metal oxide electrode, commercially available from Electrocell) was used. The electrolysis was carried out at 1.5 V for 31 min (current density each 0.5 mA / cm ² ) during which time 30 mL of electrolyte and CO were passed through the cell. For the electrolyte, 2.66 g of L1CIO4 (0.1 mol / L) were dissolved in MeOH (250 mL).

The characterization with the GC 7809A from Agilent Technologies showed the following: Sample content DMC = 0.9 ng corresponds to a yield of 0.92%. Comparative Example 6

Preparation of a palladium-based carbon monoxide gas diffusion electrode. The gas diffusion electrode was produced by the dry process, wherein 93 wt .-% palladium powder M8039 from Ferro, 7 wt .-% PTFE from DYNEON TF2053 were mixed in an IKA mill Al l basic. Subsequently, the powder mixture was pressed with a roller press at a force of 0.29 kN / cm on a nickel carrier network. For a 32 cm ² electrode, 4.3 g of the powder mixture was needed. Comparative Example 7

Preparation of dimethyl carbonate on a carbon monoxide gas diffusion electrode based on palladium

The experiment was carried out in a commercially available Electrocell Model Micro Flow Cell volume (0.001 m ² ) from Electrocell in a 2-electrode run. The gas diffusion electrode prepared according to Comparative Example 6 was anodically switched, and as the counterelectrode, an iridium-MMO electrode (iridium mixed metal oxide electrode, commercially available from Electrocell) was used. The electrolysis was carried out at a current density of 0.2 mA / cm ² for one hour. The flow rate of CO was 0.5 L / h and the electrolyte (30 mL) was circulated at a flow rate of 2 mL min ¹ . For the electrolyte, PhOH (14.11 g, 0.15 mol, 0.75 mol L ¹ ) and LiCl (114.5 mg, 2.7 mmol, 0.014 mol L ¹ ) were dissolved in CH 3 CN (200 mL). No DPC was found by GC-HS analysis. In this case, the following analysis was performed:

The experiment was performed on the devices, GC7890A with a column (HP-5: Stationary phase: 5% - phenylmetylpolysiloxane, length: 30 mx 320 μm x 0.25 μm, carrier gas: helium) and a headspace (HS) sample application system 7697 , executed by Angilent Technologies. In each case, 3 mL samples were placed in 20 mL vials in the HS-Sampler and these were heated in the oven for 15 min at 80 ° C, brought to a pressure of 15 psi. Subsequently, 1 mL of the gas phase was applied via a transfer line (200 ° C) to the column with a split of 10: 1. The FID (Flame Ionization Detector) was operated at 300 ° C and a hydrogen flow rate of 40 mL / min Column program: Start temperature was 90 ° C and held for 2 min, then the temperature was raised by 50 ° C / min up to 250 ° C The final temperature 250 ° C was again held for 2 minutes.

Comparative Example 8 Preparation of diphenyl carbonate on a carbon monoxide gas diffusion electrode based on palladium and Ketjenblack

The experiment was carried out in a commercially available Electrocell Model Micro Flow Cell volume (0.001 m ² ) from Electrocell in a 2-electrode run. The gas diffusion electrode prepared according to Comparative Example 3 was anodically switched, and as the counter electrode, an iridium mixed metal oxide (MMO) electrode, commercially available from Electrocell, was used. The electrolysis was carried out at a current density of 0.2 mA / cm ² for one hour. The flow rate of CO was 0.5 L / h and the electrolyte (30 mL) was circulated at a flow rate of 2 mL min ¹ . For the electrolyte, PhOH (14.1 g, 0.15 mol, 0.75 mol L ¹ ) and LiCl (1 14.5 mg, 2.7 mmol, 0.014 mol L ¹ ) were dissolved in CH ₃ CN (200 mL).

No DPC was found by GC-HS analysis.

Claims

claims

1. Process for the electrochemical preparation of diaryl carbonates, characterized in that a compound of the formula (1)

(1) R-OH where the radical R is an aryl radical, preferably tert-butylphenyl, cumylphenyl, naphthyl or phenyl, particularly preferably a phenyl radical, is anodically reacted with CO at a gas diffusion electrode, wherein the gas diffusion electrode at least one comprising planar, electrically conductive carrier and a gas diffusion layer applied to the carrier,

wherein the gas diffusion layer contains a mixture of an electrocatalyst and a hydrophobic polymer,

wherein the electrocatalyst is in the form of powder selected from the group consisting of gold, copper, silver, ruthenium, iridium, copper oxide, ruthenium oxide and iridium oxide, preferably gold, ruthenium, copper, copper oxide and ruthenium oxide or

wherein the electrocatalyst is present in the form of metal particles or metal oxide particles selected from the group consisting of gold, copper, silver, ruthenium, iridium, copper oxide, ruthenium oxide and iridium oxide, preferably gold, ruthenium, copper, copper oxide and ruthenium oxide, supported on a carbon support selected from activated carbon, Carbon black, graphite, graphene or carbon nanotubes, in particular carbon black.

2. The method according to claim 1, characterized in that the CO is generated cathodically in an upstream reaction electrochemically from CO ₂ , in particular on a gas diffusion electrode.

3. The method according to claim 1 or 2, characterized in that the anodic electrochemical reaction at a current density in the range of 0.1 - 5000 mA / cm ² , preferably 0.1 - 500 mA / cm ² , more preferably 0.1 - 100 mA / cm ² and most preferably 0.2 - 50 mA / cm ² , is performed.

4. The method according to any one of claims 1 to 3, characterized in that a mixture of the alcohol of formula (1) with other solvents, in particular a Solvent selected from acetonitrile, propylene carbonate, dimethylformamide, dimethyl sulfoxide, 1, 2-dimethoxyethane, dichloromethane and N-methyl-2-pyrrolidone, particularly preferably acetonitrile is used.

5. The method according to any one of claims 1 to 4, characterized in that as electrochemical conductive salts lithium chloride, lithium bromide, lithium perchlorate, sodium perchlorate, lithium bis (trifluoromethylsulfonyl) imide, sodium phenolate, lithium phenolate, tetrabutylammonium chloride, preferably lithium chloride and lithium perchlorate, or imidazolium, Aammonium- , Phosphonium, or pyridinium-based ionic liquids, preferably 1-ethyl-3-methyl-imidazolium-tetrafluoroborate.

6. The method according to any one of claims 1 to 5, characterized in that the anodically carried out electrochemical reaction at a temperature in the range of 10 to 250 ° C, in particular in the range of 20 to 100 ° C and more preferably in the range of room temperature performed becomes.

7. The method according to any one of claims 1 to 6, characterized in that the reaction at atmospheric pressure or higher pressure, in particular at up to 1 bar pressure is performed.

8. The method according to any one of claims 1 to 7, characterized in that the gas diffusion layer comprises a mixture of electrocatalyst, hydrophobic polymer and other carbon materials, wherein the hydrophobic polymer is a fluorine-substituted polymer, preferably polytetrafluoroethylene (PTFE).

9. The method according to any one of claims 1 to 8, characterized in that the proportion of electrocatalyst in the form of powder 80 to 97 wt .-%, preferably 90 to 95 wt .-%, based on the total weight of electrocatalyst and hydrophobic polymer or that the proportion of electrocatalyst in the form of metal or metal oxide particles on a carbon support is 40 to 60% by weight, based on the total weight of electrocatalyst and hydrophobic polymer.

10. The method according to any one of claims 1 to 9, characterized in that the metal or metal oxide powder has a mean particle diameter in the range of 1 to 100 μιη, preferably in the range of 2 to 90 μιη, or that the mean particle diameter the supported on carbon materials metal or metal oxide particles 2 nm to μηι, preferably 2 nm to 1 μιη.

Method according to one of claims 1 to 10, characterized in that the electrocatalyst and the hydrophobic polymer are applied in powder form on the support and compressed and form the gas diffusion layer.

Method according to one of claims 1 to 11, characterized in that the gas diffusion electrode based on a metal or metal oxide powder as electrocatalyst, a total loading of catalytically active component in a range of 5 mg / cm ² to 300 mg / cm ² , preferably from 10 mg / cm ² to 250 mg / cm ² , or that the gas diffusion electrode based on carbon-supported metal or metal oxide particles has a total loading of catalytically active components in a range from 0.5 mg / cm ² to 20 mg / cm ² , preferably from 1 mg / cm ² to 5 mg / cm ² .

.Method according to one of claims 1 to 12, characterized in that the electrically conductive carrier as a network, woven, knitted, knitted fabric, non-woven, expanded metal or foam, preferably as a fabric is formed and nickel, gold, silver or a combination of nickel containing gold or silver.