Electrochemical reactor for catalytic hydrogenation and product isolation, and method thereof

Abstract

The invention relates to an electrochemical reactor comprising a cathode chamber comprising a cathode, one or more inlets, and one or more outlets; an anode chamber comprising an anode, one or more inlets, and one or more outlets; a separator positioned between the cathode chamber and the anode chamber; and a fibrous carrier material being coated with a hydrogenation catalyst, wherein the fibrous carrier material is arranged in the cathode chamber between the cathode and the separator. Further, the invention pertains to a method of a catalytic hydrogenation in aqueous solution, comprising the steps of provision of such an electrochemical reactor; supply of an aqueous solution into the anode chamber via the respective inlet(s), and supply of an aqueous solution containing a reagent of a hydrogenable organic compound into the cathode chamber via the respective inlet(s); adsorption of the reagent on the fibrous carrier material; electrolysis of water in the electrochemical reactor such that hydrogen is formed at the cathode and oxygen is formed at the anode; diffusion of hydrogen to the hydrogenation catalyst positioned on the fibrous carrier material; catalytic hydrogenation of the reactant to a product, which is a hydrogenated compound; desorption of the product from the fibrous carrier material; accumulation of the product in the cathode chamber; and discharge of the aqueous solution from the anode chamber via the respective outlet(s) and discharge of an aqueous solution containing the product from the cathode chamber via the respective outlet(s). Furthermore, the invention refers to a fibrous carrier material being coated with a hydrogenation catalyst.

Description

[0001] Electrochemical Reactor for Catalytic Hydrogenation and Product Isolation, and Method thereof

[0002] Embodiments of the present invention relate to an electrochemical reactor designed for catalytic hydrogenation of a hydrogenable organic compound. Another embodiment of the present invention refers to a method of a catalytic hydrogenation in aqueous solution containing a reagent of a hydrogenable organic compound. Furthermore, the present invention pertains to a fibrous carrier material being coated with a hydrogenation catalyst.

[0003] Technological Background

[0004] The synthesis of basic and fine chemicals is of crucial importance for the manufacture of industrial goods. Especially for compounds being produced on a large scale, it is desirable that efficient synthesis routes with no or as few impurities as possible are known. In particular reaction conditions should be as mild as possible and the product should be easily purified and isolated.

[0005] Electrochemistry is of great importance in the field of preparative chemistry. For example, the preparation of metals such as lithium, sodium, potassium, magnesium and aluminum proceeds via fused-salt electrolysis. In addition, halogens and organic compounds are produced electrochemically on a large scale. For the latter, the Simons fluorination process, the Monsanto adiponitrile processes and the BASF Lysmeral synthesis via anodic benzylic oxidation may be taken as possible examples. One advantage of electrochemical reaction processes is that redox reactions are only driven by electricity and may take place without the addition of reducing or oxidizing agents. For this reason, electrochemical reactors have been and are constantly being further developed. Contemporary electrochemical reactor designs emphasize enhanced energy sufficiency, scalability and selectivity in catalytic processes. Advancements in materials science have led to the development of novel catalysts and electrode materials, optimizing reaction kinetics and durability. Additionally, there is a growing focus on integrating innovative reactor configurations, such as flow cells and membrane reactors, to improve mass transport and overall performance.

[0006] A wide variety of electrochemical processes and devices has been developed enriching the state of art. US 10 577 698 B2 relates to an electrochemical process which is based on the reduction of at least one chemical compound in a multiphase catholyte solution, wherein the catholyte solution is formed by feeding a gas through a gas distributor into the cathode chamber. In the same way as the gas distributor is permeable to gas particles, the separator may also be permeable to the electrolyte or further components contained therein as reported in US 11 318 455 B2. Herein, a battery is disclosed comprising at least one electrochemical cell with an anode, an electrolyte, a cathode, and a separator comprising a polymer of intrinsic porosity. Furthermore, in addition to or instead of the separator, at least one electrode material may also be porous. In this context, KR 10 1858760 B1 describes an electrode of an electrochemical cell having a porous structure with a plurality of voids containing sulfur. Finally, also complex compounds of biochemical importance may be produced ex vivo by using an electrochemical reactor. An example for this is the hydrogenation of nicotinamide adenine dinucleotide by an indirect electrochemical reduction, wherein the electrolysis is carried out in the presence of an electron carrier as reported in US 4 526 661 A.

[0007] Independent of electrochemical processes, the separation of products and reactants has been subject of numerous investigations. The technical teachings enriching the state of art have in common that the separation and purification of products take place in a second process step after the reaction. The following disclosures can be taken as examples. EP 1 159 290 B1 describes a separation method in aqueous phase systems with at least one aqueous phase containing a thermo-separating micelle-polymer. The separation method comprises partitioning the compound in a two-phase system wherein at least one of the phases is rich and the other is poor in a thermo-separating polymer; collecting one phase containing the predetermined compound and if desired, further working up said compound from the collected phase. Beyond that, US 9 370 749 B2 discloses a porous multi-component material for the capture and separation of species of interest comprising a substrate and a porous composite thin film. As reported in US 10239 044 B2 also metal-organic frameworks are suitable to purify compounds of interest. More precisely, the disclosure relates to a method of separating an aromatic compound from a mixture of hydrocarbons wherein a separation medium consisting of a crystalline cyclodextrin metal-organic framework is provided. The separation medium is in contact with the mixture of hydrocarbons and an aromatic compound from the mixture of hydrocarbons is isolated by resolving the hydrocarbons. Further, it is possible to utilize different adsorption affinities of the products and the reagents for purification. For example, in US 6 887 386 B2, the separation of products and reagents is based on ionic interactions of different strengths. Further, US 4 147 624 A describes the use of adsorbents in the purification and removal of impurities from fluid streams in industrial processes. For example, small amounts of organic compounds, including aliphatic and aromatic compounds, may be removed by being adsorbed on activated carbon or polymeric adsorbents in the treatment of wastewaters.

[0008] Hence, a common challenge of conversion processes reported in the state of art persists in that a separate and distinct step for the isolation and separation of products from reactants is required. A two-step process does not only introduce additional complexity but also raises concerns about efficiency and overall system integration.

[0009] The present invention is therefore based on the task of providing an alternative electrochemical reactor system, whereby catalytic conversions are optimized as far as possible and the isolation of the resulting products is enabled through the strategic manipulation of adsorption affinities. The method including such an electrochemical reactor system may offer a streamlined and efficient process with potential applications in diverse industries, from renewable energy to industrial manufacturing.

[0010] Summary of the Invention

[0011] This task is solved by the electrochemical reactor according to claim 1 . The electrochemical reactor comprises: a cathode chamber comprising a cathode, one or more inlets, and one or more outlets; an anode chamber comprising an anode, one or more inlets, and one or more outlets; a separator positioned between the cathode chamber and the anode chamber; and a fibrous carrier material being coated with a hydrogenation catalyst, wherein the fibrous carrier material is positioned between the cathode and the separator.

[0012] A further aspect of the invention relates to a method of a catalytic hydrogenation in aqueous solution according to claim 10. The method comprises the steps of: a) provision of the afore-mentioned electrochemical reactor; b) supply of an aqueous solution into the anode chamber via the respective inlet(s), and supply of an aqueous solution containing a reagent of a hydrogenable organic compound into the cathode chamber via the respective inlet(s); c) adsorption of the reagent on the fibrous carrier material; d) electrolysis of water in the electrochemical reactor such that hydrogen is formed at the cathode and oxygen is formed at the anode; e) diffusion of hydrogen to the hydrogenation catalyst positioned on the fibrous carrier material; f) catalytic hydrogenation of the reagent to a product, which is a hydrogenated organic compound; g) desorption of the product from the fibrous carrier material; h) accumulation of the product in the cathode chamber; and i) discharge of the aqueous solution from the anode chamber via the respective outlet(s) and discharge of an aqueous solution containing the product from the cathode chamber via the respective outlet(s).

[0013] Yet another aspect of the present invention pertains to a fibrous carrier material being coated with a hydrogenation catalyst according to claim 15.

[0014] Further preferred embodiments of the invention can be found in the dependent claims and the following description.

[0015] Brief Description of the Figures

[0016] Features will become apparent to those of ordinary skill in the art by describing in detail exemplary embodiments with reference to the attached drawings in which:

[0017] FIG.1 shows an exploding drawing of an electrochemical reactor according to an embodiment of the present disclosure;

[0018] FIG. 2 illustrates an exploding drawing of an electrochemical reactor according to another embodiment;

[0019] FIG. 3 schematically represents a fibrous carrier material being coated with a hydrogenation catalyst according to another embodiment of the present disclosure;

[0020] FIG. 4 shows an image of a section of a fibrous carrier material as illustrated in FIG. 3 taken with a field-emitting scanning electron microscope with Bruker Quantax XFIash Flat Quad energy-dispersive X-ray spectrometer (Zeiss Merlin VP Compact);

[0021] FIG. 5 illustrates an exploding drawing of an electrochemical reactor according to another embodiment;

[0022] FIG. 6 illustrates the procedural steps of the method for catalytic hydrogenation in aqueous solution containing a reagent of a hydrogenable organic compound according to a further embodiment of the disclosure;

[0023] FIG. 7 shows the maximum adsorption capacity (qm) of phenol and cyclohexanol on 4 fibrous carrier materials obtained by fitting the experimental adsorption isotherms of phenol and cyclohexanol with Langmuir adsorption equation;

[0024] FIG. 8 shows experimental isotherms data in adsorption of phenol and cyclohexanol on 2 fibrous carrier materials fitted with Freundlich equation; and

[0025] FIG. 9 shows the results from electrochemical hydrogenation of phenol to cyclohexanol in the electrochemical reactor by means of various fibrous carrier materials coated with Raney Nickel.

[0026] Detailed Description of the Invention

[0027] Functions and possible variations of the invention are explained in more detail below using examples. The present disclosure, however, may be embodied in various different forms, and should not be construed as being limited to only the illustrated embodiments herein. Rather, these embodiments are provided as examples so that this disclosure will be thorough and complete, and will fully convey the embodiments and features of the present disclosure to those skilled in the art.

[0028] Accordingly, processes, elements, and techniques that are not considered necessary to those having ordinary skill in the art for a complete understanding of the aspects and features of the present disclosure may not be described. In the drawings, the relative size of elements, layers, and regions may be exaggerated for clarity.

[0029] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. Further, the use of “may” when describing embodiments of the present disclosure refers to “one or more embodiments of the present disclosure”. In the following description of embodiments of the present disclosure, the terms of a singular form may include plural forms unless the context clearly indicates otherwise.

[0030] It will be further understood that the terms “include”, “comprise”, “including” or “comprising” specify a property, a region, a fixed number, a step, a process, an element, a component, and a combination thereof but do not exclude other properties, regions, fixed numbers, steps, processes, elements, components, and combinations thereof. The term “consisting essentially of” means that specific further components can be present, namely those not materially affecting the essential characteristics of a composition.

[0031] Moreover, it will be understood that when a film, a region, or an element is referred to as being “above” or “on” another film, region, or element, it can be directly on the other film, region, or element, or intervening films, regions, or elements may also be present.

[0032] General Concepts

[0033] The electrochemical reactor according to the invention comprises: a cathode chamber comprising a cathode, one or more inlets, and one or more outlets; an anode chamber comprising an anode, one or more inlets, and one or more outlets; a separator positioned between the cathode chamber and the anode chamber; and a fibrous carrier material being coated with a hydrogenation catalyst, wherein the fibrous carrier material is arranged between the cathode and the separator.

[0034] In other words, the disclosure relates to a two-chambered electrochemical reactor comprising a cathode chamber, an anode chamber, and a separator being positioned between the electrode chambers. The separator may preferably be an ion-exchange membrane, wherein the ion-exchange membrane may be configured to be preferentially permeable to ions like H+, OH- and H3O+and preferentially impermeable to hydrogen and oxygen. Further, there is an electrode arranged in each electrode chamber. More precisely, there is a cathode in the cathode chamber and an anode is in the anode chamber, wherein each electrode may consist of one or more electrodes being connected in series. Both electrode chambers have each one or more inlets and one or more outlets enabling supply into and discharge from the electrode chambers. In the cathode chamber, a fibrous carrier material is positioned between the cathode and the separator. Furthermore, the fibrous carrier material is coated with a hydrogenation catalyst.

[0035] Thus, the electrochemical reactor is designed for the catalytic conversion of an organic compound to be hydrogenated (such as aromatic and / or unsaturated compounds) with simultaneous isolation and concentration of the obtained product based on partition coefficient disparities. Further, the specific design of the electrochemical reactor may enable the use of solutions containing other compounds in addition to a targeted hydrogenable reagent without deactivating the catalyst or causing yield losses in the hydrogenation reaction. The electrochemical reactor employs a separator to delineate its two electrode chambers. Preferably, the separator may be an ion-selective membrane. A core element of the electrochemical reactor is the cathode chamber, where a fibrous carrier material, hosting catalytic nanoparticles, possesses high adsorption affinity for reagents (i.e. reactants or substrates), facilitating rapid adsorption due to thin fibers and enhanced mass transfer. The reaction occurs with electrochemically produced hydrogen on a fibrous cathode, leading to the hydrogenation of reagents on the catalyst-coated fibrous carrier material. Crucially, products are characterized by low affinity for the carrier material, and hence efficiently desorb and exit the reactor, accumulating in the outflow chamber. In summary, this novel reactor design addresses challenges in conversion, offering a streamlined and efficient process with potential applications in diverse industries, from renewable energy to industrial manufacturing.

[0036] An electrochemical reactor according to the invention is advantageous with regard to the following aspects: firstly, the presence of inlets and outlets at both electrode chambers makes it possible for electrolyte solutions and reaction mixtures to be supplied into and discharged from the electrode chambers independently of one another enabling a more flexible process. In particular, the electrolyte solution in the cathode chamber containing a reagent of a hydrogenable organic compound may be exchanged more frequently than the electrolyte solution in the anode chamber. The exchange of the electrolyte solution in the cathode chamber may depend on the reaction turnover. Secondly, since the aim is to electrolyze water, the separator may be an ion-exchange membrane, wherein the ion-exchange membrane may preferentially be permeable to ions selected from the group comprising H+, OH- and H3O+contributing to a charge balance and a decrease of concentration gradients of OH- and H3O+between the electrode chambers. Further, the ion-exchange membrane may practically be impermeable to hydrogen and oxygen for safety reasons. As H2and O2are essentially formed during the electrolysis of water, the mixing of these compounds leads to the risk that the exothermic reverse reaction forming water takes place. The reaction is kinetically inhibited, so that the activation barrier is only exceeded by a spark, for example. However, the reaction is catalyzed by, for example, platinum, wherein water formation takes place sufficiently quickly, even at 25°C, such that in worst case an explosion-like formation of water from the elements occur. Therefore, mixing of the electrolysis products H2and O2must be avoided. This would be ensured by the ion-exchange membrane being practically impermeable to hydrogen and oxygen. Therefore, during electrolysis oxygen may remain in the anode chamber and hydrogen may remain in the cathode chamber. Thirdly, the fibrous carrier material being coated with a hydrogenation catalyst may enable sufficiently rapid completion of the hydrogenation reaction and thus keeping the partial pressure of H2low. The use of a suitable fibrous carrier material has the effect that the organic compounds to be hydrogenated adsorb on the fibrous carrier material such that they are attached in close proximity to the catalytic sites before being catalytically hydrogenated in the presence of H2. In absence of a catalyst, the hydrogenation reaction does not proceed sufficiently quickly at 25°C. In contrast to homogeneously catalyzed reactions, the use of a heterolytic catalyst allows for less complex processing of the reaction mixture in the sense that the catalyst may easily be separated mechanically from the reaction mixture, for example through filtration.

[0037] According to an embodiment, the cathode may essentially consist of stainless steel felt. The use of such a cathode has the benefits that the material is ubiquitous and cost-effective compared to, for example, copper. Moreover, such a stainless-steel felt cathode is suitable for producing hydrogen by electrolysis of water since the cathode material is corrosion-resistant.

[0038] According to another embodiment, the anode may essentially consist of one or more compounds selected from the group of platinum, titanium, nickel, and niobium. The advantage of an anode made of one or more of these compounds is that, for example, platinum is chemically inert, corrosion-resistant, and the noble metal catalyzes the anodic formation of oxygen in water electrolysis. To reduce the costs of anode materials, the core of the anode may be made of more inexpensive materials like, for example, titanium. The core of the anode may be coated with a thin layer of platinum enabling oxygen formation.

[0039] According to a yet another embodiment, the anode may be a dimensionally stable anode (DSA). In particular, the DSA electrode may be structured in such a way that a noble mixed metal oxide catalyst comprising metals selected from the group of iridium, ruthenium, tantalum, platinum, and rhodium, is coated on a substrate essentially consisting of at least one of titanium and niobium. The use of such an electrode may be beneficial since in addition to sufficiently high catalytic activity, the costs of the anode material may be minimized. Furthermore, DSA electrodes are commercially available and may further be modified according to the specific reaction conditions.

[0040] According to a further embodiment, at least one of a first separating element may be placed in the cathode chamber between the fibrous carrier material and the cathode; and a second separating element may be placed in the cathode chamber between the fibrous carrier material and the separator. At least the first separating element may be formed of an electrically isolating material so as to suppress electric contact between the cathode and the fibrous carrier material, in particular the hydrogenation catalyst coated thereon. The first separating element may have a sieve-shaped structure through which the aqueous solution entering the cathode chamber flows. Also, the second separating element may have such a sieve-shaped structure through which the aqueous solution may pass to the separator. The additional presence of the separating elements may also improve mechanical stability of the fibrous carrier material and thus may be advantageous for the longevity of the electrochemical reactor.

[0041] According to another embodiment, the first separating element between the fibrous carrier material and the cathode may be configured to distribute supplies entering the cathode chamber. This is beneficial since both, the aqueous solution containing the organic compound to be hydrogenated, and hydrogen, are distributed by the first separating element such that as many catalytic sites as possible take part in the hydrogenation reaction and the reaction rate of the hydrogenation is as high as possible.

[0042] A fibrous carrier material contains or essentially consists of fibers. A fiber is a linear, elementary structure consisting of a fibrous material. There is a distinction between biogenic and mineral fibers that occur naturally and those that are created, whether organic or inorganic. The external shape of the fiber can be either longitudinal (plain or curly) or cross-sectional (round, angular, etc.). A fiber can be solid or hollow. The fibrous carrier material may be a woven fabric or a nonwoven fabric. A nonwoven fabric is defined as a structure comprising fibers, which have been joined together in any way to form a nonwoven and bonded together in any way except for the crossing or interlacing of yarns, as occurs in weaving, knitting, lace-making, braiding and the manufacture of tufted products.

[0043] According to another embodiment, the fibrous carrier material may be configured to adsorb organic compounds due to attractive interactions. The organic compounds may include at least one of an unsaturated group and aromatic group. Aromatic and unsaturated compounds are characterized by the presence of at least one TT-electron system. It is therefore advantageous if the fibrous carrier material either also has a ir-like framework or is at least capable of interacting with the n-system in unsaturated and / or aromatic organic compounds. In this context, a possible interaction may be for example TT-TT- stacking. According to a further embodiment, the fibrous carrier material may be based on carbon fibers (coated with the hydrogenation catalyst). Carbon fibers are industrially manufactured fibers made from carbon-containing raw materials that are converted into graphite-like carbon by chemical reactions adapted to the raw material. The fibers can be further processed into semifinished woven or nonwoven products. For example, the fibrous carrier material may be an activated carbon textile or a graphite felt. An advantage of these materials is their commercial availability and high affinity to aromatic compounds which are adsorbed at the surface of the fibers. Further, these materials may easily be chemically processed, for example by treatment with an aqueous hydrogen peroxide solution. Such a treatment may lead to a fine-tuning of their chemical properties with regard to interactions with the organic compounds to be hydrogenated and the hydrogenated products. More precisely, treatment of a fibrous carrier material with a hydrogen peroxide solution may lead to an increased oxygen content on the surface of the fibrous carrier material, resulting in an increased hydrophilicity and wettability of the fibrous carrier material and offering reaction sites for the deposition of the hydrogenation catalyst.

[0044] According to another embodiment, the hydrogenation catalyst may essentially consist of one or more compounds selected from the group comprising Raney Nickel (RNi), platinum, iridium, rhodium, and platinum on carbon (Pt / C). In particular, the use of RNi is advantageous since it represents a cost-effective alternative to noble metals in catalyzed hydrogenations. Specifically, the fibrous carrier material may be based on carbon fibers and these hydrogenation catalysts are coated on, or disposed on the surface of the fibers.

[0045] The coating of the fibrous carrier material with the hydrogenation catalyst may be carried out via spray coating. This makes it possible to distribute the catalyst particles homogeneously all over the fibrous carrier material maximizing the active surface of the catalyst. Moreover, the intrinsic porosity of the fibrous carrier material enables efficient diffusion of the starting materials to the catalyst particles enabling high reaction rates. The mass of the coated catalyst may correspond to one to twenty times the mass of the bare fibrous carrier material. For example, the mass of the coated catalyst may correspond to three to four times the mass of the bare fibrous carrier material. Nevertheless, even a greater mass of RNi compared to the bare fibrous carrier material may be coated on the fibrous carrier material. If the mass of the coated catalyst amounts less than twice the mass of the bare fibrous carrier material, there may be too few catalyst particles and therefore too few active catalytic sites to ensure the desired reaction rate. The catalysts coated on the fibers of the fibrous carrier material may serve as fixed reaction sites, continuously exposing active sites for the reaction. This design contrasts with conventional reactors that use suspended catalysts, which often suffer from catalyst agglomeration and a resulting decrease in active surface area for reactions.

[0046] Further, the invention relates to a method of catalytic hydrogenation in aqueous solution. The invention is based on the knowledge that reaction mixtures can be easily separated if the present compounds have different adsorption affinities towards, for example, carrier materials. In a more precise way, the invention discloses a method for combined catalytic hydrogenation of a reagent of a hydrogenable organic compound with simultaneous isolation and concentration of the products carried out in an electrochemical reactor. The reagent may include for example at least one of an unsaturated group and aromatic group. The method comprises the steps of: a) provision of an electrochemical reactor as outlined above; b) supply of an aqueous solution into the anode chamber via the respective inlet(s), and supply of an aqueous solution containing a reagent of a hydrogenable organic compound into the cathode chamber via the respective inlet(s); c) adsorption of the reagent on the fibrous carrier material; d) electrolysis of water in the electrochemical reactor such that hydrogen is formed at the cathode and oxygen is formed at the anode; e) diffusion of hydrogen to the hydrogenation catalyst positioned on the fibrous carrier material; f) catalytic hydrogenation of the reagent to a product, which is a hydrogenated organic compound; g) desorption of the product from the fibrous carrier material; h) accumulation of the product in the cathode chamber; and i) discharge of the aqueous solution from the anode chamber via the respective outlet(s) and discharge of an aqueous solution containing the product from the cathode chamber via the respective outlet(s).

[0047] Thus, the electrochemical reactor initiates the process as an aqueous solution containing a hydrogenable reagent is introduced into the electrochemical system. The reagent swiftly adsorbs onto the fibrous carrier material functionalized chemically due to its high partition coefficient coming from high adsorption affinity on the fibrous carrier material. Meanwhile, electrochemically produced hydrogen within the cell, derived from the electrolysis of the aqueous solution on the cathode, facilitates the catalytic hydrogenation of the reagent adsorbed on the surface of the nanoparticle catalysts. The distinct partition coefficients of reagent and product play a pivotal role in the subsequent stages of the process. The hydrogenated product that preferentially has low affinity for staying on the fibrous carrier material, readily disengages and exits the reactor. The liberated product is then accumulating in the outflow chamber for convenient extraction.

[0048] In other words, after provision of the electrochemical reactor in step a), an aqueous solution is supplied into the anode chamber via one or more inlets of the anode chamber and an aqueous solution containing a reagent of a hydrogenable organic compound (for example, a compound including at least one of an unsaturated group and aromatic group) is supplied into the cathode chamber via one or more inlets of the cathode chamber in step b). A sufficient solubility of the organic compound in water may be beneficial for high reaction rates if the process is used for synthesis of compounds. However, the process can also be used to treat water that is contaminated with one or more hydrogenable organic compounds.

[0049] In the following step c), the reagent of a hydrogenable organic compound adsorbs on the fibrous carrier material in the cathode chamber due to attractive interactions between the organic compound and the fibrous carrier material. During water electrolysis in step d), hydrogen is formed at the cathode and oxygen is formed at the anode. The separator being practically impermeable to hydrogen and oxygen may prevent the compounds from mixing. The favored permeability of the separator to ions selected from the group comprising H+, OH- and H3O+may contribute to a charge balance and a reduction of concentration gradients of OH- and H3O+between the electrode chambers.

[0050] The formed hydrogen diffuses in step e) through the cathode chamber and the fibrous carrier material being coated with a hydrogenation catalyst. Subsequently, in step f) of the method, the hydrogenation of the reagent is catalyzed at the catalytic sites on the fibrous carrier material consuming hydrogen and the reagent.

[0051] In other words, the reagent to be hydrogenated is adsorbed onto the fibrous carrier material prior to catalytic hydrogenation. However, it may also possible that the adsorption of the reagent and the catalytic hydrogenation thereof take place simultaneously, i.e. in a single step. After hydrogenation, the product has a lower adsorption affinity towards the fibrous carrier material compared to the reagent, and therefore tends to desorb from the fibrous carrier material in step g). Consequently, in step h) the hydrogenated product accumulates in the aqueous solution in the cathode chamber. Finally, in step i), the anode chamber containing an aqueous solution and the cathode chamber containing an aqueous solution of the hydrogenated product are discharged via the outlets of the respective electrode chamber.

[0052] The method according to the invention enables catalytic hydrogenation in aqueous solution of hydrogenable organic compounds including for example at least one of an unsaturated group and aromatic group. Inter alia, the use of a fibrous carrier material being coated with a hydrogenation catalyst is crucial. Due to higher adsorption affinities of the organic compounds to be hydrogenated towards the fibrous carrier material compared to the hydrogenated product compounds, the hydrogenation reaction is accelerated, as on average a greater amount of the reagent than of the product is adsorbed on the fibrous carrier material being coated with a hydrogenation catalyst. Further, the proximity between the cathode and the fibrous carrier material being coated with a hydrogenation catalyst minimizes the diffusion distance and ensures that hydrogen can quickly reach the catalyst particles. This reactor design allows hydrogen to be available immediately at the catalyst surface upon generation, reducing the time lag between hydrogen formation and utilization, and thus increasing the space-time yield (STY). The STY describes the mass of a target product produced per time unit and reactor volume.

[0053] Moreover, the fibers of the fibrous carrier material ensure a large interstitial space for the gas flow, facilitating the rapid movement of hydrogen through the fibrous carrier material. Another advantage is that, the product accumulates in the aqueous solution in the cathode chamber due to its lower adsorption affinity towards the fibrous carrier material compared to the reagent. This results in a simultaneous purification and separation of the hydrogenated product compound from the starting material.

[0054] The electrode chambers may be supplied and discharged independently from each other. This may enable a more flexible electrolysis process such that the aqueous solution containing the reagent of a hydrogenable organic compound and the hydrogenated product may be supplied and discharged more frequently than the aqueous solution in the anode chamber, since the aqueous solution in the anode chamber mainly serves as an oxygen source.

[0055] Furthermore, the fibrous carrier material may be configured such that attractive interactions between the fibrous carrier material and the reagent including for example at least one of an unsaturated group and aromatic group occur. Aromatic and unsaturated compounds are characterized by the presence of a TT-electron system. It is therefore advantageous if the fibrous carrier material either also has a ir-like framework or is at least capable of interacting with the TT-system of an unsaturated or aromatic organic compound, for example via TT-iT-stacking. Such interactions may be enabled, for example, by carbon fibers provided in the form of activated carbon textiles or graphite felts.

[0056] According to a specific embodiment, phenol may be catalytically hydrogenated forming at least one product compound selected from cyclohexanone and cyclohexanol (see reaction scheme 1).

[0057] Reaction scheme 1: Catalytic hydrogenation of phenol forming at least one product compound selected from cyclohexanone and cyclohexanol.

[0058] Thereby an aqueous solution of phenol is supplied into the cathode chamber. The solution may additionally contain further compounds like humic acids, fulvic acids and other organic molecules derived from the decomposition of plant and microbial material. The phenol molecules also diffuse through the cathode chamber and tend to adsorb on the fibers of the fibrous carrier material due to their high adsorption affinity towards the fibrous carrier material. Meanwhile hydrogen is generated electrochemically by water electrolysis at the cathode and diffuses to the catalytic sites on the surface of the fibrous carrier material. At these catalytic sites the hydrogenation of phenol takes place. The formation of cyclohexanol may either proceed directly, i.e. without an isolable intermediate (see reaction scheme 1 , path A). On the other hand, cyclohexanone may be formed as an isolable intermediate during hydrogenation of phenol. Depending on the reaction conditions, i.e. ratio of amounts of hydrogen, phenol and cyclohexanone, cyclohexanone may be at least partially further hydrogenated forming cyclohexanol (see reaction scheme 1 , path B). In other words, the hydrogenation of phenol preferably yields at least one of the product compounds selected from cyclohexanone and cyclohexanol. Finally, the hydrogenated product leaves the fibrous carrier material since the fibrous carrier material has a lower adsorption affinity towards both, cyclohexanone and cyclohexanol, compared to phenol. Phenol represents a suitable reagent to be hydrogenated since phenol is highly soluble in water (84 g / L at 20°C - taken from the GESTIS database). Further, neither cyclohexanone nor cyclohexanol have a TT-scaffold anymore leading to weaker interactions towards the fibrous carrier material compared to the interactions between the fibrous carrier material and phenol. Phenol has a higher adsorption affinity to, for example, graphene-based fibrous carrier materials due to TT-iT-electron interactions between the TT- electrons of the aromatic ring and the electron-rich regions of the basal plane of the fibrous carrier material, whereas the hydrogenated products have no more TT-electrons available for this interaction with the fibrous carrier material. Therefore, cyclohexanone and cyclohexanol have smaller partition coefficients within the fibrous carrier material compared to phenol and are enriched in the aqueous solution.

[0059] Another aspect of the invention pertains to a fibrous carrier material being coated with a hydrogenation catalyst. The fibrous carrier material may be configured such that attractive interactions between the fibrous carrier material and a reagent of a hydrogenable organic compound occur. In particular, the fibrous carrier material may be based on a carbon fiber and semi-products formed thereof, for example, activated carbon textile and graphite felt. In principle, any hydrogenation catalyst, which can be applied to the fibrous carrier material and is stable in aqueous solution, may be suitable. Especially, catalysts selected from the group comprising Raney Nickel (RNi), platinum, iridium, rhodium, and platinum on carbon (Pt / C) may be preferred.

[0060] Specific Embodiments

[0061] FIG. 1 shows an exploded drawing of an electrochemical reactor 100 according to an embodiment. The electrochemical reactor 100 comprises a cathode chamber 10 comprising a cathode 12, an inlet 20 and an outlet 22; an anode chamber 70 comprising an anode 72, an inlet 80 and an outlet 82; a separator 60 positioned between the cathode chamber 10 and the anode chamber 70, and a fibrous carrier material 30 being coated with a hydrogenation catalyst 40 (not shown), wherein the fibrous carrier material 30 is arranged in the cathode chamber 10 between the cathode 12 and the separator 60. The inlet 20 and outlet 22 are passing through a first wall 24 of the cathode chamber 10, wherein the wall 24 is opposite to the separator 60. The inlet 80 and outlet 82 are passing through a first wall 84 of the anode chamber 70, wherein the wall 84 is opposite to the separator 60. This arrangement of the inlets 20, 80 and outlets 22, 82 is particularly beneficial for efficient supply into and discharge from the electrode chambers 10, 70. The electrodes 12, 72 are electrically connected to a voltage source (not shown). The cathode 12 is made of stainless steel felt and the anode 72 essentially consists of a titanium core layered with platinum. Furthermore, the separator 60 is an ion-exchange being preferentially permeable to ions selected form the group comprising H+, OH- and H3O+, and being preferentially impermeable to hydrogen and oxygen.

[0062] FIG. 2 is an exploded drawing of an electrochemical reactor 100 according to another embodiment. The electrochemical reactor 100 shown in FIG. 2 differs from the electrochemical reactor shown in FIG. 1 in that the fibrous carrier material 30 is additionally surrounded by two separating elements 50, 52 such that the first separating element 50 is arranged between the cathode 12 and the fibrous carrier material 30 and the second separating element 52 is arranged between the fibrous carrier material 30 and the separator 60. According to another embodiment, the first separating element 50 is further configured to distribute the supply entering the cathode chamber 10. This configuration may lead to an increased reaction rate of the hydrogenation due to better mixing of the aqueous solution containing the organic compound to be hydrogenated.

[0063] FIG. 3 schematically illustrates the fibrous carrier material 30 in the form of a woven product being coated with a hydrogenation catalyst 40 according to another embodiment. For example, the fibrous carrier material 30 essentially consists of carbon fibers, which have been spray coated with Raney Nickel (RNi). Particles of RNi are distributed over the fibers 32 of the fibrous carrier material 30. Particularly high reaction rates for the hydrogenation of phenol are found if the mass of the coated RNi corresponds to three to four times the mass of the bare fibrous carrier material 30.

[0064] FIG. 4 shows the image of a section of a fibrous carrier material 30 based on carbon fibers taken with a field-emitting scanning electron microscope with Bruker Quantax XFIash Flat Quad energy-dispersive X-ray spectrometer (Zeiss Merlin VP Compact). It can be seen that RNi particles are attached to the fibers 32 of the fibrous carrier material 30. The image is only for illustrative purposes, scaling is not indicated. Fig. 5 illustrates another exemplary embodiment the electrochemical reactor 100 in an exploded view. The cathode chamber 10 is located on the left-hand side of the drawing. To the right is the anode chamber 70. The separator 60 is an ion-exchange membrane being assembled between the cathode chamber 10 and anode chamber 70.

[0065] The outermost parts of cathode chamber 10 and anode chamber are plate-like reactor holders 102, 104 including inlet and outlet holes for a reaction solution. The reactor holders 102, 104 serve to mechanically stabilize the electrochemical reactor 100. The cathode chamber 10 further includes a cathode solution chamber 14 which, when assembled, defining the reaction space available in the cathode chamber 10. Similar, the anode chamber 70 includes an anode solution chamber 74 which, when assembled, defining the reaction space available in the anode chamber 70.

[0066] Within the cathode solution chamber 14, the cathode 12 is positioned, which is in form of a stainless steel felt. The assembly further includes a solution distributor 54, which directs the solution fed into the cathode solution chamber 14 onto the cathode 12 over a large area. Furthermore, a fibrous carrier material 30 being coated with the catalyst 40 (not shown) is provided in the cathode chamber 10. The fibrous carrier material 30 may be an activated carbon textile or a graphite felt and the catalyst may be Raney Nickel (RNi) or platinum on carbon (Pt / C).

[0067] The fibrous carrier material 30 coated with a hydrogenation catalyst is provided between a first separating element 50 and a second separating element 52. The first separating element 50 and second separating element 52 are formed of an electrically isolating material so as to suppress electric contact between the cathode 12, the fibrous carrier material 30, and the separator 60, respectively. The first separating element 50 and second separating element 52 have a sieve-shaped structure which can be passed by the solution.

[0068] A first gasket 16, a second gasket 17, and a third gasket 18 ensure the required tightness of the cathode chamber 10 and stabilize the position of the elements arranged in the cathode chamber 10.

[0069] The anode chamber 70 includes an anode 72 made of Pt / Ti. A fourth gasket 76, a fifth gasket 77, and a sixth gasket 78 ensure the required tightness of the anode chamber 70 and stabilize the position of the anode 72 arranged in the anode chamber 74.

[0070] During operation of the electrochemical reactor 100, an aqueous solution to be treated is fed into the anode chamber 74 and the cathode chamber 14. In case, the aqueous solution includes, for example, aromatic compounds, these compounds are adsorbed on the surface of the fibrous carrier material 30. When a voltage is applied to the anode 72 and cathode 12, hydrogen is formed at the cathode 12 and oxygen at the anode 72. The hydrogen produced by electrolysis is carried along by the solution and is finely distributed via the first separating element 50 onto the coated fibrous carrier material 30. At the hydrogenation catalyst, hydrogen and the adsorbed aromatic compounds are reacted, i.e. a hydrogenation reaction is performed. The resulting products of the process, i.e. the hydrogenated compounds, show less affinity to the surface of the fibrous carrier material 30 and are carried out of the cathode chamber 14 with the flowing solution. For example, water contaminated with aromatics can be continuously purified in this way, producing non-aromatic compounds. Specifically, polycyclic aromatic hydrocarbons are carcinogenic, can alter the genome and have reprotoxic properties. They are difficult to break down in the environment and accumulate in organisms. Hydrogenation produces compounds with a significantly lower hazard potential. The method can therefore support wastewater treatment or groundwater remediation.

[0071] FIG. 6 schematically shows the procedural steps of the catalytic hydrogenation in aqueous solution containing a reagent of a hydrogenable organic compound according to an embodiment. More precisely, phenol is electrochemically hydrogenated to cyclohexanone and cyclohexanol.

[0072] Step S1 of the method according to the invention consists in the provision of an electrochemical reactor as depicted above. In a preferred embodiment, the fibrous carrier material 30 is an activated carbon textile, for example an activated carbon textile of the brand ACC-5092-15, delivered by Kynol Europe GmbH, which is further functionalized by treatment with an aqueous hydrogen peroxide solution. Further, Raney Nickel is chosen as hydrogenation catalyst 40 and the fibrous carrier material 30 is coated via spray coating with the hydrogenation catalyst 40.

[0073] In step S2, an aqueous solution is supplied into the anode chamber 70 via the inlet 80 and an aqueous solution containing phenol is supplied into the cathode chamber 10 via the inlet 20. For example, a 0.1 M aqueous solution of phenol is supplied into the cathode chamber 10.

[0074] In step S3, phenol molecules adsorb on the fibrous carrier material 30. Adsorption is essentially driven by interactions between the TT-system of phenol and the fibrous carrier material 30. Of particular relevance is TT-iT-stacking. In particular, the activated carbon textiles are found to adsorb phenol efficiently. In step S4, the electrolysis of water takes place. For this purpose, a voltage is applied to the electrodes such that oxygen is formed at the anode 72 and hydrogen is formed at the cathode 12. The separator 60 is an ion-exchange membrane being preferentially permeable to H+, OH- and H3O+and therefore enabling charge balancing between the electrode chambers 10, 70 such that the pH value in both electrode chambers 10, 70 remains as constant as possible. The practical impermeability of the separator 60 to hydrogen and oxygen prevents mixing of the two compounds in the electrochemical reactor and thus reduces the risk of exothermic formation of water.

[0075] In step S5, hydrogen diffuses to the catalytic sites positioned on the fibrous carrier material 30. The fibrous carrier material 30 is arranged in close proximity to the cathode 12 minimizing the diffusion distance and ensuring that hydrogen can quickly reach the catalytic sites. H2is prevented by the ion-exchange membrane from diffusing into the anode chamber 70.

[0076] In step S6, phenol is catalytically hydrogenated to cyclohexanone and cyclohexanol. The hydrogenation reaction takes place at the catalytic sites positioned on the fibrous carrier material 30. Raney Nickel is particularly suitable as hydrogenation catalyst 40. The reaction is favored by the fact that the phenol molecules are in close proximity to the catalytic sites due to their adsorption on the fibrous carrier material 30. Especially the activated carbon textile ACC- 5092-15 being pretreated with an aqueous hydrogen peroxide solution shows an adsorption selectivity in favor of phenol.

[0077] In step S7, cyclohexanone and cyclohexanol desorb from the fibrous carrier material 30 due to their lower adsorption affinities towards the fibrous carrier material 30 compared to phenol. According to Le Chatelier’s principle, the desorption of the hydrogenated products has a favorable effect on the equilibrium of the hydrogenation reaction since the products are removed from the reaction mixture by desorption from the fibrous carrier material 30 and thus the product formation is favored.

[0078] In step S8, the hydrogenated products accumulate in the aqueous solution in the cathode chamber 10. As cyclohexanone and cyclohexanol predominantly desorb from the fibrous carrier material 30, they accumulate in the aqueous solution surrounding the fibrous carrier material 30 in the cathode chamber 10. In this way, the hydrogenated products are separated from phenol, as the latter adsorbs preferentially on the fibrous carrier material 30.

[0079] In step S9, the aqueous solution is discharged from the anode chamber 70 via the outlet 82 and the aqueous solution containing cyclohexanone and cyclohexanol is discharged from the cathode chamber 10 via the outlet 22. The electrode chambers 10, 70 are supplied and discharged independently of each other such that in particular, the cathode chamber 10 is supplied and discharged depending on the progress of the hydrogenation.

[0080] Properties of the Fibrous Carrier Materials and Experimental Procedures

[0081] Essential functions of the fibrous carrier materials are to adsorb hydrogenable organic compounds in close proximity to the catalytic sites and to desorb the products. To optimize these properties, various commercial fibrous materials are examined and, in some cases, chemically modified. The fibrous carrier material is selected from the group of activated carbon textile and graphite felt. Two activated textiles, namely ACN-305-15 and ACC-5092-15, which are produced by Kynol and supplied by Kynol Europe GmbH, and a graphite felt (SIGRACELL felts) which is produced and supplied by SGL Carbon GmbH (Germany) are used as fibrous carrier materials. In particular, it is observed that the two activated carbon textiles ACN-305-15 and ACC-5092-15 are suitable for the use as fibrous carrier materials in an electrochemical reactor according to the present disclosure. For sake of clarity, the fibrous carrier materials are named as follows: FB1 (ACN-305-15), FB2 (graphite felt), FB3 (ACC-5092-15) and FFB3 (the functionalized FB3).

[0082] Modification of Activated Carbon Textile FB3 with Hydrogen Peroxide

[0083] 0.5 g of the activated carbon textile FB3 are placed in 100 mL of an aqueous 30wt% solution of hydrogen peroxide for 24 h at 25°C under mild shaking. After that, the fibrous carrier material is removed from the H2O2solution and is placed in 500 mL of deionized water. The fibrous carrier material is washed five times with deionized water to remove the remaining H2O2from the fibrous carrier material. Finally, the fibrous carrier material is dried at 50°C for 14 hours at ambient pressure.

[0084] Structural and Textural Properties of the Fibrous Carrier Materials

[0085] In order to better understand the relationship between the chemical and structural properties of the fibrous carrier materials and their adsorption capacity towards various chemical compounds, the fibrous carrier materials are investigated in more detail. The fibrous carrier materials are characterized by an arithmetic mean fiber diameter lying between 11 pm and 14 m measured by means of a digital light microscope equipped with a high-resolution zoom lens (KEYENCE VH-Z500). Further, the nitrogen adsorption and desorption isotherms for the fibrous carrier materials are measured at -196°C on a Belsorp MINI (BEL Japan, Ltd.). For this purpose, the sample is heated at 200°C for three hours and then degassed for 14 hours. The specific surface area is determined by the Brunauer-Emmet-Teller (BET) method over a range of N2relative partial pressure p / po varying from 0.01 to 0.30. The total pore volume is obtained using the adsorbed nitrogen at a relative pressure p / po of approximately 0.99. The Barrett- Joyner-Halenda (BJH) method is then applied to the desorption isotherm to calculate the mean pore size by assuming a cylindrical pore model and using the Kelvin equation to relate the pore size to the relative pressure. Table 1 lists textural and physical characteristics of the fibrous carrier materials.

[0086] Table 1: Textural and physical characteristics of the commercial and the functionalized fibrous carrier materials.

[0087] 1reported by the supplier

[0088] As it can be seen in Table 1 , the properties of the graphite felt FB2, besides the mean arithmetic fiber diameter, are completely different to the properties of the fibrous carrier materials based on activated carbon textiles. This is due to the fact that the graphite felt FB2 has a different structure compared to FB1 , FB3 and FFB3. Comparing the (functionalized) activated carbon textiles, it is noticeable that physical and textural properties differ only slightly between the fibrous carrier materials FB1 , FB3 and FFB3. For example, the surface area of these fibrous carrier materials is lying between 1308 and 1505 m2 / g. In particular, for the surface area, values ranging from 1000 to 1800 m2 / g are particularly preferred. In case of smaller surface area values, the attachment area for the catalyst particles is smaller, which consequently means that there are fewer catalyst particles attached on the fibrous carrier material and thus lowering the reaction rate. If the surface area exceeds values of 1800 m2 / g, loss of stability of the fibrous carrier material may occur. The same considerations also apply to the total pore volume ranging from 0.54 cm3 / g for FFB3 to 0.66 cm3 / g for FB1. Surprisingly, the surface area as well as the total pore volume of FFB3 are smaller compared to FB3. This illustrates that the functionalization of the fibrous carrier material, for example by treatment with an aqueous hydrogen peroxide solution, has a significant impact on the structural properties of the materials and, in the present case, leads to a reduction of the surface area and the total pore volume. In contrast, the mean pore diameter of the fibrous carrier materials calculated by using the BJH method is invariant and amounts to 1.6 nm for each of the fibrous carrier materials based on an activated carbon textile. This calculated mean diameter of the idealized cylindrical pores has a particularly suitable size. If the mean pore diameter is too small, for example smaller than 0.5 nm, the starting materials might not reach the catalyst particles in the cavities which is accompanied by a reduction in the yield and an extension of the reaction time. Another possibility is that the starting materials may pass the pores and reach the catalyst particles, but the product compounds are too sterically demanding so that these compounds may not leave the fibrous carrier material. If the pore diameter is too big, for example greater than 5 nm, the stability of the fibrous carrier material and the reaction selectivity may be reduced. The mean pore diameters of the fibrous carrier materials FB1 , FB3 and FFB3 are lying in the preferred range of 0.5 nm to 5 nm. This optimizes the stability of the fibrous carrier material and at the same time ensures that the starting materials diffuse freely to the catalyst particles and that possible selectivity may arise during product formation, as particularly sterically demanding product compounds may no longer be able to leave the cavities.

[0089] Further experiments are carried out to determine chemical surface characteristics of the fibrous carrier materials. The temperature-programmed decomposition (TPD) is performed using a BELCAT-B chemisorption analyzer (BEL Japan, Osaka) connected with a mass spectrometer (MKS Cirrus 2). For these measurements, the samples are first pretreated at 150°C for 30 minutes in an argon atmosphere and then heated up from 150°C to 1100°C in a helium flow of 50 mL / min with a heating rate of 10 K / min, whereby the evolved gases CO2 and CO are determined. The point of zero charge (PZC) of the activated carbon textiles FB1 , FB3 and FFB3 is determined by application of an immersion method. Therefore, 0.05 g of each fibrous carrier material is put into 10 mL of an aqueous 10 mM Na2SO4electrolyte solution and agitated for 48 hours in glass vessels by a reciprocal shaker (HS 260 basic - 1 KA) at 120 swivel motion per minute. Initial pH values of the solution before adding the fibrous carrier materials are adjusted with 0.1 M HCI and 0.1 M NaOH solutions. The point in which the initial pH is equal to the final pH is considered as the point of zero charge (PZC). Table 2 lists the chemical surface characteristics of the commercial fibrous carrier materials and the functionalized fibrous carrier material.

[0090] Table 2: Chemical surface characteristics of the commercial and the functionalized fibrous carrier materials. The mass proportions (O-, CO2- and CO-content) are given in relation to the mass of the bare fibrous carrier materials.

[0091] 1calculated from released CO2and CO

[0092] As it can be seen in Table 2, the functionalization of the fibrous carrier material FB3 leads to distinct changes in its surface chemistry. In particular, the oxygen content in the functionalized fibrous carrier material FFB3 exceeds the oxygen content in FB1 or FB3 by a factor of almost two leading to higher hydrophilicity and wettability of FFB3. Further, the amount of CO2- and CO-containing functional groups, which are in particular acidic groups, is significantly larger in FFB3 than in FB1 or FB3. In other words, FFB3 contains a larger amount of acidic functional groups compared to the other fibrous carrier materials. By modifying the surface of the fibrous carrier materials, different interaction strengths, in particular different adsorption affinities, may occur towards chemical compounds. Further, the point of zero charge of FFB3 is decreased compared to FB1 and FB3 by a factor of three. Thus, FFB3 has a negative net charge in solution with a pH value of 6-7, while FB1 and FB3 have a positive net charge under the same conditions.

[0093] Spray Coating of the Fibrous Carrier Material with Raney Nickel (RNi)

[0094] The spray coating process essentially comprises the two steps of producing a suspension containing the hydrogenation catalyst and applying it to the fibrous carrier material. Surprisingly, the investigations revealed that the addition of various binders of up to 1wt% (relative to the mass of the catalyst) - comprising PTFE micro powder, Nation and polyurethane - drastically reduces the catalytic activity of RNi. As a result, a new binder-free spray coating is developed and applied to prevent the adverse impact of binder on catalytic activity of RNi. In a first step of the spray coating process, a suspension is produced by mixing 10 mL of deionized water and 1000 mg of RNi (supplied by Sigma-Aldrich) at a pH value of 6-7. After shaking the suspension for 30 minutes, it is placed in an ultrasonic bath for additional 30 minutes. In a second step of the procedure, the RNi is applied to the fibrous carrier material having a crosssection of 4 cm x 2 cm by using a smart airbrush supplied by Redoxme AB company (Sweden) with a pressure of 25 psi and an air flow rate of 8 L / min. This method has the advantage that the RNi is coated uniformly on the fibrous carrier materials, wherein the RNi particles are deposited on the fibers. Preferably, the mass of the coated RNi corresponds to twice to four times the mass of the bare fibrous carrier material. Nevertheless, RNi may also be coated with more than four times the mass of the bare fibrous carrier material.

[0095] Pt / C (10%wt from Sigma-Aldrich®) was coated on FFB3 by spray coating. To prepare the coating slurry, a mixture was made containing 250 mg of Pt / C, Nation (5% in mixture of lower aliphatic alcohols and water, Sigma Aldrich, USA) at 10 wt% relative to Pt / C, deionized water (5 vol% relative to isopropanol), and 10 mL of isopropanol. The slurry was shaken for 30 minutes and then treated in an ultrasonic bath for an additional 30 minutes. It was then sprayed onto a 4 cm x 2 cm fibrous carrier material (0.33 g) using the airbrush described above. After coating, the fibrous carrier material was dried in an oven at 50°C for 2 hours under ambient pressure, followed by 14 hours of drying at room temperature. In total, 176 mg of Pt / C was coated on FFB3.

[0096] Adsorption Experiments

[0097] With the aim of investigating the suitability of the fibrous carrier materials for the catalyzed electrochemical hydrogenation of phenol and the purification of the reaction mixture, batch adsorption experiments with phenol and cyclohexanol are carried out using 25 mL and 50 mL vessels containing 10 mL to 50 mL of the solution to be examined. All chemicals are of at least analytical grade. All solutions are prepared with deionized water (Milli-Q IQ 7000, Merck KGaA, Germany). Phenol is supplied by Merck KGaA (Germany) and cyclohexanol (99%) is purchased from Alfa Aesar (US). After adding the fibrous carrier materials to the vessels containing an aqueous 10 mM Na2SO4 solution (Merck, 99%) fulfilling the function of a background electrolyte solution, the pH value is adjusted to 6-7 by adding a 0.1 M HCI (Merck, 99%) solution or a 0.1 M NaOH (Merck, 99%) solution. The mass of the fibrous carrier materials per liter of the electrolyte solution lies between 1 g and 10 g. Afterwards, the vessels are shaken for 14 hours by a reciprocal shaker (HS 260 basic - 1 KA) at 120 swivel motion per minute. The pH value is checked and readjusted to 6-7 if necessary. Then, specific concentrations of phenol and cyclohexanol, each varying from 100 mg / L to 2 g / L, are added to the mixtures from their respective stock solutions.

[0098] The amount of phenol and cyclohexanol adsorbed by the fibrous carrier materials is calculated from the differences between the initial concentration of the solutes and their final concentration in the aqueous supernatant after two hours according to equation 1 where qeis the concentration of adsorbed solutes at equilibrium, co and ceare the initial concentration and concentration of the freely dissolved solute at equilibrium, V is the volume of the solution and m is the mass of the bare fibrous carrier material.

[0099] The single point adsorption coefficient Kd of the adsorbates on the fibrous carrier materials is calculated by means of equation 2

[0100] Kd=q(2). e

[0101] The maximum adsorption capacity is obtained by fitting adsorption experimental data with the Langmuir isotherm according to equation 3 where qmdenotes the maximum adsorption capacity of the fibrous carrier materials and KL is a constant related to the affinity between the adsorbate and the adsorbent.

[0102] In course of the experiments it is revealed, that FB2 shows lowest performance. In particular, FB2 has the smallest adsorption capacity and affinity for both phenol and cyclohexanol among the fibrous carrier materials. Therefore, FB2 does not seem to be a suitable fibrous carrier material for the catalytic hydrogenation of phenol. Compared to this, the application of FB1 , FB3 or FFB3 in the electrochemical reactor results in higher cyclohexanol formation. In the cases of FB1 and FB3, the values of qmfor phenol are about three times higher than for cyclohexanol. For FFB3, the value of qmfor phenol is slightly smaller, but still in the same order of magnitude as for FB1 and FB3, while the value of qmfor cyclohexanol for FFB3 is significantly smaller compared to FB1 and FB3. In other words, while both FB1 and FB3 adsorb well phenol and cyclohexanol, FFB3 adsorbs phenol slightly worse, but essentially cyclohexanol adsorbs only poorly on FFB3. Therefore, in the case of FFB3, cyclohexanol accumulates to a greater extent in the aqueous phase compared to the other fibrous carrier materials making FFB3 more suitable to carry out the electrochemically catalyzed hydrogenation of phenol and to be involved in the purification of the resulting cyclohexanol. The adsorption selectivity of FFB3 in favor of phenol is also clearly quantified by the corresponding single point adsorption coefficient values Kd of phenol and cyclohexanol (see Table 3). For FFB3, the value of Kdfor cyclohexanol is very low (58.0 L / kg) while the value of Kdfor phenol amounts to 1765 L / kg. This difference illustrates the selectivity of FFB3 in favor of the adsorption of phenol compared to the adsorption of cyclohexanol. In the case of FB3, the value of Kdfor phenol is just under three times as large as the value of Kd for cyclohexanol demonstrating the lower selectivity of FB3 towards phenol.

[0103] Table 3: Single point adsorption coefficient Kdof phenol and cyclohexanol applying FB3 and FFB3.

[0104] FIG. 7 shows the maximum adsorption capacity (qm) of phenol and cyclohexanol on 4 fibrous beds obtained by fitting the experimental adsorption isotherms with Langmuir equation. The experiments were performed in 10 mM Na2SO4solution at pH 6-7. The results show that FB2 has very low maximum adsorption capacity for both phenol and cyclohexanol. FB1 and FB3 have much higher qmfor phenol than cyclohexanol. FFB3 keeps its high adsorption capacity towards phenol, it has very low adsorption capacity for cyclohexanol though: adsorption of cyclohexanol on FFB3 is lower than adsorption of phenol on FFB3 by a factor of 12. This difference for FB1 and FB3 are around 3 times. FIG. 8 shows experimental isotherms data in adsorption of phenol and cyclohexanol on FB3 and FFB3 fitted with Freundlich equation. Based on the isotherms fitted with Freundlich, FFB3 shows much lower adsorption towards cyclohexanol in a wide range of concentrations than FB3. This high difference can be used in the electrochemical reactor for separation of phenol (as reagent) and cyclohexanol (as product).

[0105] Further investigations are carried out with regard to the kinetics of the adsorption of phenol on the fibrous carrier materials. The adsorption kinetics may be studied with the empirical pseudo- first-order equation (4) ln(,qe- qt) = -k1X t + Zn(qe) (4), where qeand qtare the amounts of adsorbate uptake per mass of adsorbent at equilibrium and at any time t (in min) and ki is the rate constant of the model with the start condition qt=o = 0.

[0106] Comparing the fibrous carrier materials FB3 and FFB3, it is observed that the adsorption of phenol on FFB3 is faster than the adsorption of phenol on FB3 (see Table 4). This finding once again emphasizes the suitability of FFB3 as fibrous carrier material, as more phenol molecules adsorb in the same time period than in the case of FB3.

[0107] Table 4: Kinetic parameters in adsorption of phenol on the fibrous carrier materials FB3 and FFB3.

[0108] Selectivity of the hydrogenation

[0109] Finally, a further criterion for the suitability of the fibrous carrier material is the selectivity of the hydrogenation, in this case the hydrogenation of phenol. The selectivity can be estimated by considering the columbic efficiency (CE) defined by equation 5:

[0110] In equation 5, Q denotes the number of electrons consumed in the electrochemically catalyzed hydrogenation of phenol and Qtotai is the number of theoretically produced electrons. Q can be obtained by equation 6:

[0111] Q = n x z x F (6).

[0112] In equation 6, n is the amount of the substance, z is the number of transferred electrons per molecule (i.e. 6 electrons for the formation of cyclohexanol), and F is the Faraday constant.

[0113] Qtotai can be derived by integrating the current l(t) of the electrochemical hydrogenation with integration over time t leading to equation 7:

[0114] Qtotai = Jo / (t) dt (7).

[0115] For determining the selectivity of the hydrogenation, samples from the electrochemical cell are taken before and after the reaction. The samples are filtered with 0.2 pm PTFE filters and subsequently prepared for analysis by diluting aliquots of acidified water (1 mL concentrated H2SO4in 1000 mL milliQ water, pH = 2). The diluted samples are analyzed via gas chromatography-mass spectrometry (GC-MS, GC 7890A and MSD 5975C InertXL, Agilent, Santa Clara, US) by using a DB-FATWAX capillary column (30 m x 250 pm x 0.25 pm, Agilent, Santa Clara, US) with Helium as carrier gas and 1 -butanol as internal standard. The initial temperature is 50°C. After holding the initial temperature of 50°C for two minutes, the temperature is increased to 250°C with a temperature ramp of 15 K / min. The compounds are identified using retention times and mass spectra of pure reference compounds, and quantified using external standards.

[0116] In the experiments, an aqueous 60 mL solution containing 0.1 M phenol as reagent is prepared and used as feed in each case. The feed is circulated through the cathode chamber of the electrochemical reactor with a flow rate of 10 mL / min. The residence time inside the cathode chamber without the fibrous carrier material (so-called empty carrier material residence time) is around 115 seconds, meaning that the volume of the empty cathode chamber amounts to 19.2 mL. The concentration of cyclohexanol in the aqueous phase is measured by taking samples from the solution after 24 hours. The amount of phenol and cyclohexanol adsorbed on the fibrous carrier material is obtained by transferring the fibrous carrier material into a flask containing 60 mL of a mixture of 80vol% ethanol and 20vol% water, and by placing the flask in an ultrasonic bath for two hours. After filtration, the sample is taken for analyzing phenol and cyclohexanol initially adsorbed on the fibrous carrier material. The two hours of sonification proved to be sufficient for extracting phenol and cyclohexanol adsorbed on the fibrous carrier material since extending the duration of the sonification did not result in additional extraction of phenol and cyclohexanol.

[0117] Reference Signs

[0118] 10 cathode chamber

[0119] 12 cathode

[0120] 14 cathode solution chamber

[0121] 16 - 18 gaskets

[0122] 20 inlet of cathode chamber

[0123] 22 outlet of cathode chamber

[0124] 24 first wall of cathode chamber

[0125] 30 fibrous carrier material

[0126] 32 fiber of fibrous carrier material

[0127] 40 hydrogenation catalyst

[0128] 50 first separating element

[0129] 52 second separating element

[0130] 54 solution distributor

[0131] 60 separator

[0132] 70 anode chamber

[0133] 72 anode

[0134] 74 anode solution chamber

[0135] 76 - 78 gaskets

[0136] 80 inlet of anode chamber

[0137] 82 outlet of anode chamber

[0138] 84 first wall of anode chamber

[0139] 100 electrochemical reactor

[0140] 102, 104 reactor holders provision of an electrochemical reactor according to claim 1 supply of an aqueous solution into the anode chamber via the respective inlet, and supply of an aqueous solution containing phenol into the cathode chamber via the respective inlet adsorption of phenol on the fibrous carrier material water electrolysis such that hydrogen is formed at the cathode and oxygen is formed at the anode diffusion of hydrogen to the catalytic sites positioned on the fibrous carrier material hydrogenation of phenol on the catalytic sites forming cyclohexanone and cyclohexanol desorption of cyclohexanone and cyclohexanol from the fibrous carrier material accumulation of cyclohexanone and cyclohexanol in water in the cathode chamber discharge of the aqueous solution from the anode chamber via the respective outlet and discharge of an aqueous solution containing cyclohexanone and cyclohexanol from the cathode chamber via the respective outlet

Claims

Claims1 . An electrochemical reactor (100) comprising: a cathode chamber (10) comprising a cathode (12), one or more inlets (20), and one or more outlets (22); an anode chamber (70) comprising an anode (72), one or more inlets (80), and one or more outlets (82); a separator (60) positioned between the cathode chamber (10) and the anode chamber (70); and a fibrous carrier material (30) being coated with a hydrogenation catalyst (40), wherein the fibrous carrier material (30) is positioned in the cathode chamber (10) between the cathode (12) and the separator (60).

2. The electrochemical reactor (100) according to claim 1 , wherein the cathode (12) essentially consists of stainless steel felt.

3. The electrochemical reactor (100) according to claims 1 and 2, wherein the anode (72) essentially consists of one or more compounds selected from the group of platinum, titanium, nickel, and niobium.

4. The electrochemical reactor (100) according to any one of the preceding claims, wherein the anode (72) is a dimensionally stable anode (DSA) such that a substrate essentially consisting of at least one of titanium and niobium is coated with a noble mixed metal oxide catalyst comprising at least one metal selected from the group of iridium, ruthenium, tantalum, platinum, and rhodium.

5. The electrochemical reactor (100) according to any one of the preceding claims, wherein at least one of a first separating element (50) is placed in the cathode chamber (10) between the fibrouscarrier material (30) and the cathode (12); and a second separating element (52) is placed in the cathode chamber (10) between the fibrous carrier material (30) and the separator (60).

6. The electrochemical reactor according to claim 5, wherein the first separating element (50) between the fibrous carrier material (30) and the cathode (12) is configured to distribute supplies entering the cathode chamber (10).

7. The electrochemical reactor (100) according to any one of the preceding claims, wherein the fibrous carrier material (30) is configured to adsorb organic compounds due to attractive interactions.

8. The electrochemical reactor (100) according to any one of the preceding claims, wherein the fibrous carrier material (30) is based on carbon fibers.

9. The electrochemical reactor (100) according to any one of the preceding claims, wherein the hydrogenation catalyst (40) essentially consists of one or more compounds selected from the group comprising Raney Nickel (RNi), platinum, iridium, rhodium and platinum on carbon (Pt / C).

10. A method of a catalytic hydrogenation in aqueous solution, comprising the steps of: a) provision of an electrochemical reactor (100) according to claim 1 ; b) supply of an aqueous solution into the anode chamber (70) via the respective inlet(s) (80), and supply of an aqueous solution containing a reagent of a hydrogenable organic compound into the cathode chamber (10) via the respective inlet(s) (20); c) adsorption of the reagent on the fibrous carrier material (30); d) electrolysis of water in the electrochemical reactor (100) such that hydrogen is formed at the cathode (12) and oxygen is formed at the anode (72);e) diffusion of hydrogen to the hydrogenation catalyst (40) positioned on the fibrous carrier material (30); f) catalytic hydrogenation of the reagent to a product, which is a hydrogenated organic compound; g) desorption of the product from the fibrous carrier material (30); h) accumulation of the product in the cathode chamber (10); and i) discharge of the aqueous solution from the anode chamber (70) via the respective outlet(s) (82) and discharge of an aqueous solution containing the product from the cathode chamber (10) via the respective outlet(s) (22).

11. The method according to claim 10, wherein the electrode chambers (10, 70) are supplied and discharged independently of each other.

12. The method according to claims 10 and 11 , wherein in step c) the reagent adsorbs on the fibrous carrier material (30) due to attractive interactions.

13. The method according to claims 10 through 12, wherein in step g) the product has a lower adsorption affinity towards the fibrous carrier material (30) than the respective reagent such that desorption of the product from the fibrous carrier material (30) is favored.

14. The method according to claims 10 through 13, wherein phenol is catalytically hydrogenated forming at least one product compound selected from the group of cyclohexanone and cyclohexanol.

15. A fibrous carrier material (30) being coated with a hydrogenation catalyst (40).

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