Catalyst body for anhydrous formaldehyde production

Abstract

The present invention relates to a catalyst body comprising: (A) a porous monolith and (B) an alkali metal comprising compound, such as sodium carbonate, wherein the porous monolith (A) is an electrically conducting material, such as Si-infiltrated silicon carbide, and wherein the alkali metal comprising compound (B) is distributed in the porous monolith. The present invention further relates to a process for producing said catalyst body, to a process for preparing anhydrous formaldehyde by contacting a feed gas comprising methanol with said catalyst body, to a process for preparing a chemical compound or a polymer comprising said process step for preparing anhydrous formaldehyde, and to a reactor for preparing anhydrous formaldehyde comprising a fixed bed built up by at least one said catalyst body.

Description

[0001] Catalyst body for anhydrous formaldehyde production

[0002] Description

[0003] The present invention relates to a catalyst body comprising:

[0004] (A) a porous monolith and

[0005] (B) an alkali metal comprising compound, wherein the porous monolith (A) is an electrically conducting material and wherein the alkali metal comprising compound (B) is distributed in the porous monolith.

[0006] The present invention further relates to a process for producing said catalyst body, to a process for preparing anhydrous formaldehyde by contacting a feed gas comprising methanol with said catalyst body, to a process for preparing a chemical compound or a polymer comprising said process step for preparing anhydrous formaldehyde, and to a reactor for preparing anhydrous formaldehyde comprising a fixed bed built up by at least one said catalyst body.

[0007] Highly endothermic reactions are frequently at the start of the value creation chain in the chemical industry, for example in the cracking of mineral oil fractions such as liquefied petroleum gas (LPG for short), naphtha, diesel or gas oil, the reforming of natural gas or naphtha, the dehydrogenation of propane, the dehydroaromatization of methane to benzene, or the pyrolysis of hydrocarbons. Temperatures between 500° C. and 1700° C are required to achieve yields of industrial and economic interest. The main reason for this lies in the thermodynamic limitation of the equilibrium conversion. Most of these highly endothermic reactions are heated by firing fossil carbon-based fuels such as natural gas, heating oil or other, fossil-based fuel gases, including fossil-based off-gases that are generated as a by-product in the respective processes.

[0008] Due to the advancing climate change and the commitment of the chemical industry to reduce its carbon footprint it is necessary to replace firing fossil carbon-based fuels for generation of heat in chemical production by more environmentally friendly decarbonized sources of heat, in particular by heat generated from electricity which is obtained from renewable energy resources such as sunlight, wind, the movement of water, or geothermal heat.

[0009] Formaldehyde is one of the most widely used chemicals in the world. Today, it is consumed as a feedstock in more than 50 different processes in the chemical industry, mainly in the form of aqueous solutions and resins containing formaldehyde. The demand for formaldehyde has been growing steadily. In 2011 , global output was 31.4 million tons / year, rising to 46.6 million tons / year in 2022 and was estimated to reach 70.8 million tons / year in 2030. Industrially produced formaldehyde is normally consumed in the form of an aqueous solution. Yet for many processes, it is advantageous to use highly concentrated gaseous formaldehyde, for example, in the production of diesel fuel alternatives, namely oxymethylene ethers (OME), or in the formation of polyacetal resin. For this purpose, water must be separated from formaldehyde, which is a costly and energy-intensive process. Therefore, alternative approaches have been sought for decades, one of which is the direct dehydrogenation of methanol to water-free formaldehyde. Many studies have been carried out to test different process concepts and catalysts. Nonetheless, a viable method for industrial-scale implementation has not yet been found. A. Meyer and A. Renken, Chem. Eng. Technol., vol. 13, no. 1 , pp. 145-149, 1990 ‘describe sodium compounds as catalysts for methanol dehydrogenation to water-free formaldehyde. An electrical heating concept is not disclosed.

[0010] DE 102 36 019 A1 describes a reactor for performance of endothermic reactions which is equipped with one or more heating blocks that completely fill the reactor cross section and are electrically insulated from the reactor inner wall and optionally from one another, wherein the heating blocks are formed from open-cell foam. The presence of an alkali metal comprising compound as a catalyst is not described.

[0011] L. Zheng et al., I nt J Hydrogen Energy 2023; 48: 14681-96 describe a process for electrified methane steam reforming by using Rh / AhCh washcoated SiSiC foams as catalyst and heating device.

[0012] L. Zheng et al., Chem. Eng. J. 2023, 466, 143154 describe processes for electrified CO2 reforming of methane (eCRM) and the electrified reverse water-gas shift (eRWGS) reactions by direct Joule heating of catalytically-activated open-cell SiC foams.

[0013] An electrified dehydrogenation of methanol to anhydrous formaldehyde and hydrogen is not disclosed or suggested by any of the above-mentioned documents.

[0014] DE 198 14 285 discloses a process for the synthesis of anhydrous formaldehyde by catalytic dehydrogenation of methanol in the gas phase at 700 - 1000 °C in a tube reactor. The tube reactor is heated by placing it in an electrically heated oven. The catalyst precursor is placed in a zone of the tube reactor before the zone where methanol is introduced into the tube reactor and where the dehydrogenation takes place. The thermal energy needed for the dehydrogenation of methanol is generated outside of the reactor.

[0015] C. J. Baranowski et al., ChemCatChem, 2021 , vol. 13, no. 17, pages 3864 - 3877 also disclose a process for the synthesis of anhydrous formaldehyde by catalytic dehydrogenation of gaseous methanol. A 10 mm quartz-tube equipped with a heating element is loaded with alkali metal- grafted silica powder, which is supported on quartz wool for fixing it in the quartz-tube as catalyst bed. There is no hint that the heating element is located inside of the quartz tube.

[0016] L. Zheng et al., AIChE Journal, A / ChE J. 2023; 69(1): e17620. doi:10.1002 / aic.17620; available from the internet: https: / / aiche.onlinelibrary.wiley.com / doi / epdf / 10.1002 / aic.17620, describe methane steam reforming catalyzed by Rh / AhCh, which is supported on a SiSiC foam. The SiSiC foam serves as catalyst carrier and as directly electrically heatable device (direct Joule heating).

[0017] E. Meloni et al., Renewable Energy 211 , 2023, pages 336 - 346 describe dry reforming of methane catalyzed by a nickel compound, which is supported on a monolith carrier, which is directly electrically heatable.

[0018] Neither Zheng et al. nor Meloni et al. disclose or suggest as an endothermic reaction the dehydrogenation of methanol to anhydrous formaldehyde and hydrogen catalyzed by sodium species in the gas phase instead of an endothermic reforming reaction of methane taking place on the surface of a solid catalytically active compound.

[0019] Proceeding from this prior art, an object of the invention was to provide a catalyst body, which is first electrically heatable to evaporate sodium species out of a sodium comprising compound and which secondly allows to heat up the methanol comprising gas phase for the direct dehydrogenation of methanol to water-free formaldehyde. Additionally, the catalyst body should allow the easy scale-up of the concept from laboratory scale to industrial scale and should further allow an easy adjustment of important reaction parameters such as the temperature for an optimized yield and selectivity of the desired products which are dry formaldehyde and hydrogen.

[0020] This object is achieved by a catalyst body comprising:

[0021] (A) a porous monolith and

[0022] (B) an alkali metal comprising compound, wherein the porous monolith (A) is an electrically conducting material and wherein the alkali metal comprising compound (B) is distributed in the porous monolith.

[0023] The inventive catalyst body comprises as a first component a porous monolith, also referred to hereinafter as porous monolith (A), for short, and as a second component an alkali metal comprising compound, also referred to hereinafter as alkali metal comprising compound (B).

[0024] The porous monolith (A), which is an electrically conducting material, is preferably an open-cell foam.

[0025] In one embodiment of the present invention, the inventive catalyst body is characterized in that the porous monolith (A) is an open-cell foam.

[0026] The alkali metal comprising compound (B) can be selected from a wide range of known alkali metal compounds, including the alkali metals themselves including mixtures thereof. Preferably the alkali metal comprising compound (B) is a salt or the metal itself, in particular a salt. From the group of the alkali metals, consisting of lithium, sodium, potassium, rubidium and caesium and mixtures thereof, preference is given to sodium and potassium and mixtures thereof, in particular to sodium. Preferred alkali metal comprising compounds (B) are sodium salts. A wide variety of sodium salts are known to the person skilled in the art. Suitable sodium salts can be selected from the group consisting of Na2COs, Na2B4O?, Na3PC>4, Na2MoC>4, Na2SC>4, NaCI, NaOCb , NaOCF^CHs, NaSi, NaH, Na2O2, NaBF , NaxWC>3 and Na2WC>4 and mixtures thereof. Preferably the alkali metal comprising compound (B) is sodium carbonate.

[0027] Non-limiting examples of mixtures of alkali metal compounds, which might be comprised by the catalyst body are sodium / potassium, Na2CC>3 / NaOCH3, Na2CC>3 / KOCH3, Na2CO3 / NaC>2CH, Na2CO3 / KOC(CH3) / LiOH, NaOH / KOH / LiOH, Na2CO3 / NaOH or Na2CO3 / CH3CO2Na / Na2SO4. In one embodiment of the present invention, the inventive catalyst body is characterized in that the alkali metal comprising compound (B) is sodium or a sodium salt, preferably a sodium salt, wherein the sodium salt is selected from the group consisting of Na3CO3, Na2B4O?, Na3PO4, Na2MoO4, Na2SO4, NaCI, NaOCH3, NaOCH2CH3, NaSi, NaH, Na2O2, NaBH4, NaxWO3and Na3WO4and mixtures thereof.

[0028] In another embodiment of the present invention, the inventive catalyst body is characterized in that the alkali metal comprising compound (B) is sodium carbonate.

[0029] In another embodiment of the present invention, the inventive catalyst body is characterized in that the alkali metal comprising compound (B) is a mixture of at least two different alkali metals and / or alkali metal salts.

[0030] The porous monolith (A), which is made of an electrically conducting material, is preferably resistance-heatable.

[0031] In one embodiment of the present invention, the inventive catalyst body is characterized in that the electrically conducting material is resistance-heatable.

[0032] Suitable electrically conducting materials, which are resistance-heatable, are known to the person skilled in the art. Examples of such electrically conducting materials are metals such as nickel, carbon such as graphite or ceramics such as metal carbides. The electrically conducting material comprises or consists, preferably consists, of a material selected from the group consisting of carbons, silicon carbides including modified silicon carbides, molybdenum disilicide (MoSi2), FeCrAI-alloy and tin oxides including antimony-doped tin oxide. The porous monolith, which is preferably an open cell foam, is preferably an electrically conducting material, which comprises or consists, preferably consists, of a material selected from the group consisting of carbons, silicon carbides including modified silicon carbides, molybdenum disilicide (MoSi2), FeCrAI-alloy and tin oxides including antimony-doped tin oxide. A particular preferred electrically conducting material comprises Si-infiltrated silicon carbide or consists of Si-infiltrated silicon carbide.

[0033] In one embodiment of the present invention, the inventive catalyst body is characterized in that the electrically conducting material comprises or consists, preferably consists, of a material selected from the group consisting of carbons, silicon carbides including modified silicon carbides, molybdenum disilicide (MoSi2), FeCrAI-alloy and tin oxides including antimony-doped tin oxide.

[0034] In another embodiment of the present invention, the inventive catalyst body is characterized in that the electrically conducting material comprises Si-infiltrated silicon carbide.

[0035] Si-infiltrated silicon carbides are very suitable as electrically conducting materials for porous monoliths due to their remarkable heat transfer properties as well as exceptional oxidation resistance. Further advantageous properties of Si-infiltrated silicon carbides are temperature resistance up to 1400 °C, high thermal conductivity, excellent shock resistance, low-pressure drop, high-surface area and low coefficient of thermal expansion. In a further embodiment of the present invention, the inventive catalyst body is characterized in that the electrically conducting material is Si-infiltrated silicon carbide.

[0036] The amount of the alkali metal comprising compound (B), which is distributed in the porous monolith (A) of the inventive catalyst body can be varied in a wide range, depending on the nature of the porous monolith (A) and the nature of the alkali metal comprising compound (B).The ratio of the mass of the alkali metal of the alkali-metal comprising compound, preferably the mass of sodium, to the mass of the porous monolith is in the range of from 0.01 to 0.2, preferably in the range of from 0.02 to 0.12.

[0037] In one embodiment of the present invention, the inventive catalyst body is characterized in that the ratio of the mass of the alkali metal of the alkali-metal comprising compound (B) to the mass of the porous monolith (A) is in the range of from 0.02 to 0.12.

[0038] The geometric properties of porous monoliths suitable for the inventive catalyst body are known and can be varied in a wide range depending on the material of the porous monoliths and the respective production processes. Ceramic sponges can be produced for instance by the method of “direct foaming of a liquid slurry”, by the method of “burning out fugitive pore formers” and by the method of “replication of a sacrificial foam template”.

[0039] Preferred porous monoliths (A) which can preferably be described as open-cell foams are characterized by cells with a cell diameter in the range of from 1 mm to 6 mm, a window diameter in the range of from 0.15 mm to 3.5 mm, and a strut diameter in the range of from 50 pm to 2000 pm, preferably in the range of from 150 pm to 1500 pm, wherein cell diameter, window diameter and strut diameter of the porous monolith are mean values determined by averaging more than 25 measurements obtained by means of optical microscopy.

[0040] The term “window diameter” refers to the size of the openings or "windows" between adjacent pores or cells in the open-cell foam as shown in figure 1. Figure 1 shows an enlarged cut-out of an open-cell foam showing beside an example of the window diameter (abbreviated as dw) also examples for a cell diameter dcand a strut diameter dst. Strut diameter (dst) is the measurement of the size of the structural elements (struts) that make up the framework of a porous material. Struts are the solid parts that provide support and stability to the structure. Window diameter (dw) describes the size of openings or pores in a porous material, often referred to as "windows" that connect adjacent cells. The cell diameter (dc) refers to the measurement of the distance across a cell in a porous material. It should be noted that - due to the irregular nature of sponge structures - these quantities are not evenly distributed, therefore they are characterised in the present invention by their mean values. In the present invention the measured values were taken by means of optical microscopy. In the present invention the mean values were determined by averaging more than 25 measurements of each the three diameters obtained by means of optical microscopy. Preferably the mean values were determined by averaging between 30 to 100 measurements of each of the three diameters. In one embodiment of the present invention, the inventive catalyst body is characterized in that the porous monolith (A) is an open-cell foam which is characterized by cells with a cell diameter in the range of from 1 mm to 6 mm, a window diameter in the range of from 0.15 mm to 3.5 mm, and a strut diameter in the range of from 50 pm to 2000 pm, wherein cell diameter, window diameter and strut diameter of the porous monolith are mean values determined by averaging more than 25 measurements of each of the three diameters obtained by means of optical microscopy.

[0041] Preferably the porous monolith (A) is an open-cell foam which is characterized by a pore per inch (PPI) value being in the range of from 5 to 50, preferably in the range of from 10 to 30, a porosity being in the range of from 0.6 to 0.95, preferably the range of from 0.7 to 0.85, and a specific surface area being in the range of from 500 m2 / m3to 1800 m2 / m3.

[0042] The porosity of the porous monolith is defined as the ratio of the volume of the porous monolith which is accessible by fluids that penetrate the porous monolith from outside (Vaccessibie voids) to the geometric volume of the porous monolith (Vgeometric). In the present case the porosity was determined by first measuring the water displacement by the porous monolith. The porosity was then calculated by subtracting the water displacement volume (V ispiacement) from the geometric volume of the porous monolith (Vgeometric body) and dividing the difference by the geometric volume of the porous monolith.

[0043] PorOSity — Vaccessibie voids / Vgeometric body—(Vgeometric body " Vdispiacement ) / Vgeometric body

[0044] The specific surface area of the porous monolith is herein determined by optical microscopy data by applying the dense packing model as described in the literature and discussed by Buci- uman and Kraushaar-Czarnetzki, Ind. Eng. Chem. Res., 2003, 42, 1863-1869. The specific surface area (SA) is calculated by the following formula, wherein E is the porosity of the porous monolith, dwis the window diameter of the porous monolith and dst is the strut diameter of the porous monolith as described above.

[0045] In one embodiment of the present invention, the inventive catalyst body is characterized in that the porous monolith (A) is an open-cell foam which is characterized by a pore per inch (PPI) value being in the range of from 5 to 50, and a porosity being in the range of from 0.6 to 0.95, wherein the porosity is determined by first measuring the water displacement by the porous monolith, followed by calculating the porosity by subtracting the water displacement volume (Vdispiacement) from the geometric volume of the porous monolith (Vgeometric body) and dividing the difference by the geometric volume of the porous monolith, and a specific surface area SA being in the range of from 500 m2 / m3to 1800 m2 / m3, wherein the specific surface area SA given in the unit of m2 / m3is calculated by the formula wherein E is the porosity of the porous monolith, dwis the window diameter and dst is the strut diameter as defined above.

[0046] In case the porous monolith has a rough outer surface characterized by the above-mentioned open pores the external shape of the porous monolith corresponds to the theoretical convex hull of the considered porous monolith. That means, that in the present invention, the geometric volume of a porous body, such as the porous monoliths shown in figure 1 , refers to the volume of the porous body enclosed by the convex hull of the porous body.

[0047] In the present invention, the term “outer surface of the porous monolith” is defined as the part of the monolith surface that is completely visible from outside with the naked eyes. The monolith surface is the surface of the porous monolith, which is accessible by fluids such as liquids or gases, when immersing the porous monolith in said fluids.

[0048] Open cell foams can show different arrangements of the individual pores or cells. In particular, 3D-printed foams can show many different internal structures which are not obtainable by processes such as “burning out fugitive pore formers” or by the method of “replication of a sacrificial foam template”. The internal structures can be regular or irregular. The porous monolith (A), which is an open-cell foam shows preferably a regular continuous porous structure selected from the group of structures consisting of tetrakaidecahedron / Kelvin cell structure, Weaire Phelan cell structure and lattice structure.

[0049] In one embodiment of the present invention, the inventive catalyst body is characterized in that the porous monolith (A) has an internal structure showing a regular continuous porous structure selected from the group of structures consisting of tetrakaidecahedron / Kelvin cell structure, Weaire Phelan cell structure and lattice structure.

[0050] The dimension and external shape of the catalyst body is mainly determined by the dimension and external shape of the used porous monolith.

[0051] The dimensions of the porous monolith (A), which is an open-cell foam, as well as its external shape can be varied in a wide range depending on its production method and the requirements for its installation in the cavity of a selected reactor.

[0052] The shape of the porous monolith is preferably selected from the group consisting of a cylinder, a rectangular cuboid, a triangular prism and a hexagonal prism. In one embodiment of the present invention, the inventive catalyst body is characterized in that the porous monolith (A) has a shape selected from the group consisting of a cylinder, a rectangular cuboid, a triangular prism and a hexagonal prism.

[0053] The smallest dimension of the inventive catalyst body is preferably in the range of from 1 cm to 500 cm, more preferably in the range from to 2 cm to 20 cm, in particular from 2.5 cm to 10 cm. The largest dimension of the inventive catalyst body is preferably in the range of from 1 cm to 500 cm, more preferably in the range from to 2 cm to 20 cm, in particular from 2.5 cm to 10 cm.

[0054] In one embodiment of the present invention, the inventive catalyst body is characterized in that the smallest dimension of the catalyst body is in the range of from 1 cm to 500 cm.

[0055] In a further embodiment of the present invention, the inventive catalyst body is characterized in that the ratio of the largest dimension of the catalyst body to the smallest dimension of the catalyst body is in the range of from 1 to 10, preferably 1 to 5, more preferably 1 to 3.

[0056] The inventive catalyst body comprises a porous monolith (A), which is an electrically conducting material, which heats up by passing an electric current through it. The specific electrical resistivity of the inventive catalyst body can vary in a wide range depending on the nature of the electrically conducting material. Depending on usually available voltages and currents of electrical energy the catalyst body has a specific electrical resistivity at 20 °C in the range of from 10'3to 104Q m, preferably in the range of from 10'2to 101Q m.

[0057] In one embodiment of the present invention, the inventive catalyst body is characterized in that the catalyst body has a specific electrical resistivity at 20 °C in the range of from 10'3to 104Q m.

[0058] The present invention further also provides a process for producing the inventive catalyst body as described in detail above, comprising the process steps of:

[0059] (a) contacting a porous monolith of an electrically conducting material, preferably an open-cell foam of an electrically conducting material with an alkali metal comprising compound, preferably with a solution of an alkali metal comprising compound, more preferably with a solution of a sodium salt, in particular with an aqueous solution of sodium carbonate,

[0060] (b) optionally drying the porous monolith for removing any solvent or solvents applied in step a) at a temperature in the range of from 30 °C to 300 °C,

[0061] (c) optionally repeating step (a) and (b) until the desired amount of alkali metal comprising compound in the porous monolith is reached,

[0062] (d) optionally removing the alkali metal comprising compound at least partly from the outer surface of the porous monolith by treating the outer surface of the porous monolith with a mechanical means for cleaning smooth or rough surfaces, wherein the outer surface of the porous monolith is defined as the part of the monolith surface that is completely visible from outside with the naked eyes, and (e) optionally drying the catalyst body at a temperature in the range of from 150 °C to 300 °C.

[0063] The description and preferred embodiments of the catalyst body, its properties with respect to composition and components including the properties of said components such as the porous monolith of an electrically conducting material and the alkali metal comprising compound, correspond to the above description of these features for the inventive catalyst body.

[0064] In process step (a) the porous monolith of an electrically conducting material is contacted with an alkali metal comprising compound. Methods for contacting the porous monolith with an alkali metal comprising compound are known to the person skilled in the art. For example, the impregnation of the porous monolith with a solution or suspension of the alkali metal comprising compound is a common method. Alternatively, a vaporizable alkali metal comprising compound, such as the alkali metal itself, can be deposited in the porous structure via any of the known vapor deposition processes. In a further alternative the porous monolith can be filled with the alkali metal comprising compound in form of a dry fine powder, which can be baked on the monolith surface by heating the monolith to temperatures up to 1000 °C. Afterwards, excess powder can be shaken off.

[0065] In the optional process step (b) the porous monolith, which was treated in process step (a) with an alkali metal comprising compound in the presence of any solvent or solvents, is dried at a temperature in the range of from 30 °C to 300 °C for removing said solvent or solvents. After performing process step (b), the porous monolith can be again contacted with a solution of suspension of the alkali metal comprising compound.

[0066] The optional process step (c) represents the repeating of process step (a) and process step (b) until the desired amount of alkali metal comprising compound in the porous monolith is reached.

[0067] In the optional process step (d) the alkali metal comprising compound deposited on the outer surface of the porous monolith during the preceding process steps is at least partly removed for allowing sufficient electrical contact of the catalyst body with an appropriate electrode, if the alkali metal comprising compound has a higher electrical resistivity at 20 °C than the electrically conducting material of the porous monolith itself, preferably if the electrical resistivity at 20 °C of the alkali metal comprising compound is by a factor of at least 10, more preferably by a factor of at least 103, in particular by a factor of at least 105higher than the electrical resistivity at 20 °C of the electrically conducting material of the porous monolith itself.

[0068] In another embodiment of process step (d) the alkali metal comprising compound deposited on the outer surface of the porous monolith is preferably not completely removed from said outer surface, but preferably from such parts of the outer surface, which are needed for sufficient electrical contact of the catalyst body with an appropriate electrode or with one or more further inventive catalyst bodies. This goal can be reached by choosing appropriate means for cleaning extending no further than completely into the pores of the porous monolith, which are visible from the outside, preferably no further than 1 / 2 of the average pore size into the pores of the porous monolith, more preferably no further than 1 / 3, in particular no further than 1 / 5, of the average pore size into the pores of the porous monolith, which are visible from the outside, wherein the extension of the cleaned outer surface in depth of the porous monolith and the average pore size of the pores visible from outside is determined by averaging more than 25 measurements obtained by means of optical microscopy.

[0069] In view of the above-described pore dimensions, in particular in view of the preferred cell diameter range of the preferably used porous monolith, the mechanical means for cleaning smooth or rough surfaces used in process step (d) can be further specified in that the means for cleaning extending no further than 3 mm, preferably 2 mm, into the pores of the porous monolith, which are visible from the outside, preferably in the range of from 0.02 mm to 2 mm, in particular from 0.05 mm to 1 mm, into the pores, wherein the extension of the cleaned outer surface in depth of the porous monolith is determined by averaging more than 25 measurements obtained by means of optical microscopy.

[0070] In one embodiment of the present invention process step d) is characterized in that the mechanical means for cleaning smooth or rough surfaces extending no further than completely into the pores of the porous monolith, which are visible from the outside, preferably no further than 1 / 2 of the average pore size into the pores of the porous monolith, more preferably no further than 1 / 3, in particular no further than 1 / 5, of the average pore size into the pores of the porous monolith, which are visible from the outside, wherein the extension of the cleaned outer surface in depth of the porous monolith and the average pore size of the pores visible from outside is determined by averaging more than 25 measurements obtained by means of optical microscopy.

[0071] In another embodiment of the present invention process step d) is characterized in that the mechanical means for cleaning smooth or rough surfaces extending no further than 3 mm, preferably 2 mm, into the pores of the porous monolith, which are visible from the outside, preferably in the range of from 0.02 mm to 2 mm, in particular from 0.05 mm to 1 mm, into the pores, wherein the extension of the cleaned outer surface in depth of the porous monolith is determined by averaging more than 25 measurements obtained by means of optical microscopy.

[0072] Mechanical means for cleaning smooth or rough surfaces are known to the person skilled in the art. Examples of mechanical means for cleaning smooth or rough surfaces are sponges, such as household sponges or sponge cloths, nonwoven fabrics, or woven fabrics, such as cotton cloth, linen fabrics or microfiber cloths. Cotton cloths or linen fabrics are preferably moistened with a suitable solvent such as demineralized water. The surface roughness of the mechanical means for cleaning rough surfaces is usually significantly lower than the surface roughness of the surface to be cleaned. In case of 3D-printed monoliths, which comprise smooth outer surfaces, a soft brush can be used as mechanical means to clean said smooth outer surfaces. Also fine sandpapers are suitable mechanical means for cleaning the outer surface of porous monoliths having preferably convex hulls with flat surfaces.

[0073] In the optional process step (e) the catalyst body is finally dried at a temperature in the range of from 150 °C to 300 °C.

[0074] The above-described catalyst body can be applied as part of an electrically heatable catalyst bed or as the electrically heatable catalyst bed itself for endothermic reactions, which are catalyzed by an alkali metal comprising compound. The inventive catalyst body are preferably usable in a process for preparing anhydrous formaldehyde from methanol. io The present invention further also provides a process for preparing anhydrous formaldehyde by contacting a feed gas comprising methanol with the inventive catalyst body as described in detail above, collecting a product gas comprising anhydrous formaldehyde and hydrogen, and optionally isolating the anhydrous formaldehyde from the product gas.

[0075] The feed gas comprising methanol gas is contacted with the inventive catalyst body, which is usually electrically heated to a temperature of at least 500 °C, preferably to a temperature in the range of from 600 °C to 700 °C, more preferably in the range of from 640 °C to 670 °C.

[0076] In one embodiment of the present invention the process for preparing anhydrous formaldehyde by contacting a feed gas comprising methanol with the inventive catalyst body is characterized in that the catalyst body is electrically heated to a temperature in the range of from 600 °C to 700 °C, preferably in the range of from 640 °C to 670 °C.

[0077] It is known that the initially existing amount of the alkali metal comprising compound supported on the catalyst body is reduced during running the process for preparing anhydrous formaldehyde due to its transport out of the reactor by the gas flow through the porous monolith. In order to keep the amount of the of the alkali metal comprising compound on the catalyst body in the required range, the catalyst body is preferably contacted with additional alkali metal comprising compound in a continuous or batchwise manner during running the process.

[0078] Therefore, the inventive catalyst body as described in detail above can also be prepared in situ directly in a reactor comprising one or more porous monoliths of an electrically conducting material by contacting said porous monolith(s) with said alkali metal comprising compound directly in the reactor, preferably in a reactor which is already heated internally by the electrically resistance heated porous monolith(s).

[0079] In a further embodiment of the present invention the process for preparing anhydrous formaldehyde by contacting a feed gas comprising methanol with the inventive catalyst body is characterized in that the catalyst body is contacted with additional alkali metal comprising compound in a continuous or batchwise manner during running said process.

[0080] The mole fraction of methanol in the feed gas can be varied in a wide range. The other components of the feed gas beside methanol are usually inert gases such as nitrogen or argon. The mole fraction of methanol in the feed gas is usually in the range of from 0.01 to 1 , preferably in the range of from 0.02 to 0.7, more preferably in the range of from 0.05 to 0.5.

[0081] In a further embodiment of the present invention the process for preparing anhydrous formaldehyde by contacting a feed gas comprising methanol with the inventive catalyst body is characterized in that the mole fraction of methanol in the feed gas is in the range of from 0.05 to 0.5.

[0082] The pressure of the process for preparing anhydrous formaldehyde by contacting a feed gas comprising methanol can be run in a wide pressure range. The process is usually performed under a pressure in the range of from 0.1 to 100 bar, preferably in the range of from 0.2 to 50 bar, more preferably in the range of from 0.5 to 5 bar, in particular in the range of from 1 to 1 .5 bar. In another embodiment of the present invention the process for preparing anhydrous formaldehyde by contacting a feed gas comprising methanol with the inventive catalyst body is characterized in that the process is performed under a pressure in the range of from 1 to 1.5 bar.

[0083] The amperage of the electric current which is applied to heat up the invention catalyst body during the above-described process can be varied in a wide range, depending on the available voltage and the needed amount of energy in form of heat.

[0084] The above-described catalyst body can be applied as part of an electrically heatable catalyst bed or as the electrically heatable catalyst bed itself in a reactor for endothermic reactions, preferably in a fix bed reactor for preparing anhydrous formaldehyde.

[0085] The present invention further provides a reactor for preparing anhydrous formaldehyde comprising a fixed bed built up by at least one inventive catalyst body as described in detail above or a plurality of said catalyst bodies.

[0086] Chemical reactors, which are electrically heated up by passing a current through an electrically heatable catalyst bed are known and have been described. At least one pair of electrodes is in contact with the catalyst bed to allow passing an electric current through the catalyst bed. The electrodes are designed and integrated in the reactor in such a way that the gas flow through the reactor is not hindered.

[0087] In one embodiment of the present invention the reactor for preparing anhydrous formaldehyde is characterized in that the fixed bed is contacted on opposite sides by at least one pair of electrodes, which are permeable to the feed gas and the product gas in each case.

[0088] The gas stream which leaves the heated reaction zone is usually introduced in a quenching or cooling zone, such as a gas cooler or a water-cooled bundle reactor, and / or a scrubber comprising a liquid phase such water, methanol, oxymethylene ethers. For the production of anhydrous formaldehyde any contact of the anhydrous formaldehyde formed in the inventive reactor with water must be avoided.

[0089] In a further embodiment of the present invention the reactor for preparing anhydrous formaldehyde is characterized in that the reactor comprises a product outlet that is connected to a cooling zone and / or a scrubber comprising a water-free solvent.

[0090] The anhydrous formaldehyde which is prepared according to the above-describe process can be used in the production of a chemical compound or a polymer, preferably in the production of a chemical compound or a polymer selected from the group consisting of trioxane, polyoxymethylene dimethyl ethers, 1 ,4-butanediol, methylene diphenyl diisocyanate, pentaerythritol, 2,2-dimethylpropane-1 ,3-diol, urea formaldehyde resins, melamine resins, phenol formaldehyde resins and polyoxymethylene plastics. The present invention further provides the use of anhydrous formaldehyde prepared according to the process for preparing anhydrous formaldehyde as described above in the production of a chemical compound or a polymer.

[0091] Chemical compounds or polymers, which are prepared by using formaldehyde during their syntheses are well known.

[0092] Preferably these chemical compounds or polymers are selected from the group consisting of trioxane, polyoxymethylene dimethyl ethers, 1 ,4-butanediol, methylene diphenyl diisocyanate, pentaerythritol, 2,2-dimethylpropane-1 ,3-diol, urea formaldehyde resins, melamine resins, phenol formaldehyde resins and polyoxymethylene plastics.

[0093] In one embodiment of the present invention the use of anhydrous formaldehyde prepared according to the process for preparing anhydrous formaldehyde as described above in the production of a chemical compound or a polymer is characterized in that the chemical compound or polymer is selected from the group consisting of trioxane, polyoxymethylene dimethyl ethers, 1 ,4-butanediol, methylene diphenyl diisocyanate, pentaerythritol, 2,2-dimethylpropane-1 ,3-diol, urea formaldehyde resins, melamine resins, phenol formaldehyde resins and polyoxymethylene plastics.

[0094] The present invention further provides a process for preparing a chemical compound or a polymer comprising the above-described inventive process step for preparing anhydrous formaldehyde.

[0095] In one embodiment of the present invention the process for preparing a chemical compound or a polymer comprising the above-described inventive process step for preparing anhydrous formaldehyde is characterized in that the chemical compound or polymer is selected from the group consisting of trioxane, polyoxymethylene dimethyl ethers, 1 ,4-butanediol, methylene diphenyl diisocyanate, pentaerythritol, 2,2-dimethylpropane-1 ,3-diol, urea formaldehyde resins, melamine resins, phenol formaldehyde resins and polyoxymethylene plastics.

[0096] The invention is illustrated by the examples which follow but do not restrict the scope of the invention.

[0097] Figures in percent are each based on % by weight, unless explicitly stated otherwise.

[0098] Materials and equipment:

[0099] Sponges:

[0100] The studied 10, 20 and 30 PPI silicon-infiltrated silicon carbide ceramic sponges (Figure 2) were produced by Engicer SA based in Switzerland. The sponges were manufactured using the replication technique. 20 PPI Sponge (Figure 3) with a solid layer (5 mm) was 3D printed by Engicer SA.

[0101] Reactor concept for direct resistance heating (DRH) and the Experimental Set up for Methanol Dehydrogenation to Formaldehyde by a direct resistance heating (DRH) concept:

[0102] The experimental tests of methanol dehydrogenation were conducted in a self-constructed laboratory setup equipped with a direct resistance heating reactor (material: 2.4663, ID 44 mm, OD 54 mm).

[0103] A special design is required to place the directly heated sponge inside a reactor. In Figure 4, the technical drawing of the concept, which was developed at KIT Technik Haus, is shown.

[0104] On the upper left of figure 4 a front plate of the reactor is shown with the holes for the pipe for the supply lines to the thermocouples (T2 6x1) and for the pipe for the gas inlet and outlet (T 1 12x2). On the upper right side of figure 4 the A-A cut shows the electrical bushing (EB), the shell (1), the isolator (2) and the sponge D38x30 (3). In the lower part of figure 4 the electrical contacting of the sponge via cables insulated with ceramics (C I) and via two nickel plates (Ni - P) is shown. The nickel plates (Ni -P) are placed on the side of the sponge and are pressed together by macro-insulation material. The electrical resistivity was 10 Ohm cm, which was measured at the KIT's Technik Haus. There are two thermocouples at distance of ca. 3 cm from the sponge. The maximum overpressure in this reactor may be 0.5 bar. In order to place a sponge with macro-insulation material in the reactor in the most careful way, a zirconium foil was used as a buffer between the reactor wall and the insulation to ensure that the macro material was not damaged.

[0105] Temperatures inside the reactor were measured with thermocouples (Type K, class 1 in accordance with I EC 60584, Inconel 600, insulation MgO, OD 3 mm) protected by a macro material insulation sleeve. There are two nickel HELICOFLEX sealings in the reactor provided by Tech- netics Group. Power was supplied using Voltcraft DPPS- 32-30, possible output: 1-32 VDC - 0- 30 A, with the input of 220-240 V, 50 / 60 Hz., max. 4.7 A. Feedthrough power adapters (pin / con- ductor material - nickel, for temperature range: -269 °C to 450 °C, withstanding max. pressure at 20 °C: 103 bar; max. current: 31.5 A; manufactured by Hositrad) were used in order to supply current from the power supply to the nickel wires. Pressure in the system was measured using Rosemount 2051 In-Line Pressure Transmitter from Emerson. There is also a back-pressure controller (P-502C-1 K1 R-PGD-39-K + F-001AV-LFU-33-K) provided by Bronkhorst, which allows pressure to be controlled in the plant.

[0106] The product stream was analyzed using a gas chromatograph (ARNEL 6453, Perkin Elmer) equipped with a main column (molecular sieve 5A) that is protected by a pre-column (Plot II), that efficiently removes contaminants from the gas stream by a backflush-to-vent system, that uses a two-valve-switch in an external, heated oven. The GC consisted of a thermal conductivity detector, a methanizer and a flame ionization detector. Argon (99.9999 %, Air Liquide) as the carrier gas was passed through an oxygen, moisture and hydrocarbon trap (Restek) for an additional purification. A flow controller (F-201CV-050-PGD-33-K) provided by Bronkhorst was installed in order to provide a constant flow through the gas chromatograph’s valving system. The experimental uncertainty is estimated to be 15% (up to 20% for higher flows (>2 std. liter / min)) due to the varying pressure in the system.

[0107] Methanol (99.9%, extra dry, AcroSeal) was supplied using a mass flow controller (ML120V00- PGD-33-0-S-DA-000, Bronkhorst) and an evaporator (W-202A-330-K, Bronkhorst) in which methanol and argon were heated to 120 °C. The maximum methanol flow is 100 g / h. SS 316 pipes for methanol stream were coated with Silcolloy 1000. It is a hydrogenated amorphous silicon coating manufactured by SilcoTek® GmbH.

[0108] Argon (99.9999 %, Air Liquide) was dosed by F-201CV-2K0-PGD-33-K Bronkhorst) and it was used as a dilutant gas. Moreover, it was passed through 0.5 Micron Pore Size Particulate Filter provided by Swagelok. Sodium carbonate (anhydrous granular ACS 1 , Merck) was used as the material to impregnate ceramic sponges for the catalytic tests.

[0109] In Figure 5, the process flow diagram of the mini-plant is shown, in which the most important elements of the system are presented, including, among others, a methanol dosing and evaporation unit on the left side, a directly resistance-heated reactor (DRH) in the lower middle, a gas analytic system (GC) with hydrogen generator (H2-G), argon gas cylinder (Ar) and synthetic air gas cylinder (N2, O2, Ar 78-21-1) on the lower right side and an off-gas purification system including a gas scrubber (G SC), a water cooling system (W C S) and an exhaust system (EX) on the upper right side.

[0110] Examples

[0111] 1 . Catalyst Preparation

[0112] Before the impregnation procedure sponges were cleaned in a sonic bath for 3 hours. 20 PPI and 30 PPI standard sponges were impregnated by using 3 mol Na2COs solution (500 ml) and a small amount of ethylene glycol (25 ml). They were dried after every series (in total 5 times) at 250 °C for 45 minutes. No current flows through fully impregnated sponges as Na2COs acts as an isolator. The active material was dissolved from the outer surface of the sponge by carefully cleaning the sponge with a cotton cloth moistened with demineralized water. The mass of the sponge after the partial removal of the washcoat was 10.182 g (drying for 2 hours at 250 °C). In that way, it was possible to use the sponge for further tests successfully. The obtained impregnation values are presented in Table 1. Table 1

[0113] The 3D-printed sponge was impregnated with use of 3 mol Na2CO3 solution (500 ml) and a small amount of ethylene glycol (25 ml). The sponge was dried after every series of impregnation (in total 10 times) at 250 °C for 45 minutes. In case of the 3D-printed sponge the partial removal of the washcoat was not necessary. An electrical current passed through the sponge. Table 2 presents the mass of the sponge before and after the impregnation procedure.

[0114] Table 2

[0115] 2. Tests of the directly resistance heated (DRH) reactor concept

[0116] 2.1 Blank tests

[0117] 2.1.1 Blank tests for a standard sponge

[0118] The tests were conducted with a methanol flow of 10 g / h in a total gas flow of 1 .3 std. liter / min, resulting in a mole fraction xmolMeon of 0.09, the pressure in the system was 1.1 bar. The thermal decomposition of methanol starts at 445 °C without a catalyst. A methanol conversion of 75% was reached at 609 °C. Table 3 shows the results of blank tests for standard 20 PPI sponge.

[0119] Table 3 2.1.2 Blank tests for a 3D-printed sponge

[0120] The tests were conducted for a methanol flow of 12 g / h, which gives an xmolMeon of 0.1 and the total flow = 1.4 std. liter / min, the pressure in the system was 1.4 bar, and the back pressure in the setup was set at 1 .2 bar. The thermal decomposition of methanol starts at 443 °C without a catalyst for 3D- printed sponge. At 617 °C methanol conversion was 60%.

[0121] 2.2 Catalytic Tests

[0122] The experimental tests were carried out to prove that a direct resistance heating (DRH) concept can be used for the dehydrogenation of methanol to anhydrous formaldehyde and hydrogen. The main objectives of these experiments were to determine the durability of the reactor elements in the presence of methanol and sodium carbonate, and to find the optimum values of applied electric current to perform the endothermic reaction. Furthermore, several different mass flows of methanol and its content in the stream were tested. One of the objectives was to achieve a high methanol conversion with sufficient selectivity towards formaldehyde. As formaldehyde is unstable and tends to decompose into hydrogen and carbon monoxide, the various gas velocities in the reactor were also investigated in order to minimize formaldehyde decomposition. Catalytic tests were carried out using 20 PPI-impregnated ceramic sponges. Several detailed experimental findings are described in the following.

[0123] 2.2.1 Standard sponge

[0124] The tests for the sponge with 0.6 g catalyst were conducted for methanol flows as follows:

[0125] • 12 g / h, which gives an xmolMeon of 0.15 and the total flow = 0.95 std. liter / min, the pressure in the system was 1.1 bar

[0126] The tests for the sponge with 0.3 g catalyst were conducted for methanol flow as follows:

[0127] • 12 g / h, which gives an xmolMeon of 0.10 and the total flow = 1.4 std. liter / min, the pressure in the system was 1.1 bar

[0128] • 12 g / h, which gives an xmolMeon of 0.15 and the total flow = 0.95 std. liter / min, the pressure in the system was 1.1 bar

[0129] • 18 g / h, which gives an xmolMeon of 0.10 and the total flow = 2.1 std. liter / min, the pressure in the system was 1.1 bar

[0130] The selected results are presented below in Table 4. Table 4. Results of standard impregnated sponges

[0131] In the majority of the experiments, traces of CO2, CH4, HCOOH, and HCOOCH3 were detected. Presumably, water has also been produced, but the analytical equipment has no means of detecting it. After the experiments some carbon deposits were found on the sponge. In case of higher methanol mass flow and its content in the stream higher temperature is necessary to achieve the comparable conversion. After the experiments some carbon deposits were found on the sponge.

[0132] 2.2.2 3D-printed sponge

[0133] The tests were conducted for methanol flows as follows:

[0134] • 12 g / h, which gives an xmolMeon of 0.085 and the total flow = 1.7 std. liter / min, the pressure in the system was 1 .3 bar

[0135] • 12 g / h which gives an xmolMeon of 0.10 and the total flow = 1.4 std. liter / min, the pressure in the system was 1 .3 bar

[0136] • 10 g / h, which gives an xmolMeon of 0.05 and the total flow = 2.3 std. liter / min, the pressure in the system was 1 .5 bar • 20 g / h, which gives an xmolMeon of 0.10 and the total flow = 2.3 std. liter / min, the pressure in the system was 1 .5 bar

[0137] The selected results are presented below in Table 5.

[0138] Table 5. Results of 3D-printed impregnated sponge

[0139] In case of higher methanol mass flow and its content in the stream higher temperature is necessary to achieve the comparable conversion. In most of the experiments, traces of CO2, CH4, HCOOH, and HCOOCH3 were detected. Presumably, water has also been produced, but the analytical equipment has no means of detecting it. After the experiments some carbon deposits were found on the sponge. In case of higher methanol mass flow and its content in the stream higher temperature is necessary to achieve the comparable conversion. Table 6 presents the results for the lower temperature range of experiments.

[0140] Table 6. Selected results for xmolMeOH = 0.05, VTot = 2.3 std. liter / min, MeOH = 10 g / h

[0141] Catalyst recovery in case of 3D-printed sponge

[0142] The regeneration tests with 2.5 vol% oxygen in argon were conducted. The reactor was heated up from 200 °C to 450 °C for 2.5 hours, and then temperature was kept at 500 °C for 1 hour. The regeneration took 3.5 hour and was carried out until only traces amount of CO2 and CO were detectable. The successful catalytic tests were performed; however, the selectivity values were dropping faster in comparison to the tests before the regeneration. One of the possible reasons is that the amount of the catalyst was not sufficient for more detailed tests already before the regeneration attempt. After tests, the sponge weighed 41.5 g after removing solid residues. Nevertheless, this set of experiments proved that regeneration with oxygen gas is possible and the elements of the reactor are not damaged.

[0143] Stability tests in case of 3D-printed sponge

[0144] The 3D-printed impregnated sponge was on a stream in the reaction temperature for more than 30 hours (in total 7 sets of experiments). The setup with the catalyst was stable over time (at least 2.5 hour) at comparable temperatures. Some selected results are shown below in Table 7 and Table 8.

[0145] Table 7. Selected results for xmolMeOH = 0.085, VTot = 1.7 std. liter / min, MeOH = 12 g / h

[0146] Table 8. Selected results for xmolMeOH = 0.05, VTot = 2.3 std. liter / min, MeOH = 10 g / h

[0147] 2.2.3 Summary of the Catalytic Tests

[0148] Some characteristic features can be concluded for 3D-printed ceramic sponge and standard ceramic sponges. They are listed in Table 9 below.

[0149] Table 9. Comparison between standard and 3D-printed ceramic sponges Although the results for the standard sponges and the 3D-printed sponge are comparable in terms of selectivity, the overall performance of the 3D-printed sponge is more promising. Owning to the solid layer around it, the nickel plates are not damaged during the experiments, even at higher temperatures. The possibility of 3D printing ceramic sponges provides the opportunity to create a unique and suitable structure for the further development of this concept.

[0150] Visual inspection of DRH elements, the 3D-printed sponge and the macro insulation with nickel plates and wires connected to the copper adapter, after ca. 50 hours of experiments proves that these elements are almost intact and may be used for further tests.

[0151] Excellent durability of the system confirms that the DRH concept is suitable for anhydrous formaldehyde production with co-generation of valuable hydrogen gas. It is possible to heat up the sponge to the sufficient temperature for the endothermic reaction. The maximum temperature reached is 665 °C for the standard sponge and 650 °C for the 3D-printed sponge measured at a distance of 3 cm from the surface. The use of a directly heated sponge with the catalyst on its structure definitely supports the trend towards electrification of the chemical industry. The key issue is to find the appropriate gas velocity in the reactor to minimize formaldehyde decomposition to CO and H2. The decrease in selectivity with increasing conversion is also significant. By modifying the catalyst, the selectivity towards formaldehyde can be improved. The DRH concept with Na2COs as the catalyst at 480 °C enables to convert 30% of methanol and without catalyst at ca. 480 °C converts only ca. 10% of methanol. Significant changes can be seen in the temperature range ca. 600 °C, where the methanol conversion on the sponge with catalyst is always above 85% and without catalyst around 60%. To conclude, a direct resistance heating reactor was created, and ceramic sponges impregnated with Na2COs were tested as the catalyst support. Owing to the implementation of the novel reactor type, sodium carbonate catalyzes the dehydrogenation reaction at 31.6 A, 8.3 V and 262 Wwith the selectivity of 60% and conversion 92%.

[0152] Figure 1: Enlarged cut-out of an open-cell foam showing cell diameter dc, strut diameter dst and window diameter dw.

[0153] Figure 2: Pictures of 10, 20 and 30 PPI SiSiC sponges.

[0154] Figure 3: Picture of 3D-printed sponge

[0155] Figure 4: Scheme of direct resistance heating (DRH) concept

[0156] Figure 5: Process flow diagram of the mini-plant for methanol dehydrogenation

Claims

Claims1 . A catalyst body comprising:(A) a porous monolith and(B) an alkali metal comprising compound, wherein the porous monolith (A) is an electrically conducting material and wherein the alkali metal comprising compound (B) is distributed in the porous monolith.

2. The catalyst body according to claim 1 , wherein the alkali metal comprising compound (B) is sodium carbonate.

3. The catalyst body according to claim 1 or 2, wherein the electrically conducting material is resistance-heatable.

4. The catalyst body according to any of claims 1 to 3, wherein the electrically conducting material comprises Si-infiltrated silicon carbide.

5. The catalyst body according to any of claims 1 to 4, wherein the electrically conducting material is Si-infiltrated silicon carbide.

6. The catalyst body according to any of claims 1 to 5, wherein the ratio of the mass of the alkali metal of the alkali-metal comprising compound (B) to the mass of the porous monolith (A) is in the range of from 0.02 to 0.12.

7. The catalyst body according to any of claims 1 to 6, wherein the porous monolith (A) is an open-cell foam which is characterized by cells with a cell diameter in the range of from 1 mm to 6 mm, a window diameter in the range of from 0.15 mm to 3.5 mm, and a strut diameter in the range of from 50 pm to 2000 pm, wherein cell diameter, window diameter and strut diameter of the porous monolith are mean values determined by averaging more than 25 measurements of each of the three diameters obtained by means of optical microscopy.

8. The catalyst body according to any of claims 1 to 7, wherein the porous monolith (A) is an open-cell foam which is characterized by a pore per inch (PPI) value being in the range of from 5 to 50, and a porosity being in the range of from 0.6 to 0.95, wherein the porosity is determined by first measuring the water displacement by the porous monolith, followed by calculating the porosity by subtracting the water displacement volume (Vdispiacement) from the geometric volume of the porous monolith (Vgeometric body) and dividing the difference by the geometric volume of the porous monolith, and a specific surface area SA being in the range of from 500 m2 / m3to 1800 m2 / m3, wherein the specific surface area SA given in the unit ofm2 / m3is calculated by the formulaSA = 4.82wherein E is the porosity of the porous monolith, dwis the window diameter and dst is the strut diameter as defined in claim 7.

9. The catalyst body according to any of claims 1 to 8, wherein the porous monolith (A) has a shape selected from the group consisting of a cylinder, a rectangular cuboid, a triangular prism and a hexagonal prism.

10. The catalyst body according to any of claims 1 to 9, wherein the smallest dimension of the catalyst body is in the range of from 1 cm to 500 cm.

11. A process for producing a catalyst body according to any of claims 1 to 10 by comprising the process steps of:(a) contacting a porous monolith of an electrically conducting material with an alkali metal comprising compound,(b) optionally drying the porous monolith for removing any solvent or solvents applied in step a) at a temperature in the range of from 30 °C to 300 °C,(c) optionally repeating step (a) and (b) until the desired amount of alkali metal comprising compound in the porous monolith is reached,(d) optionally removing the alkali metal comprising compound at least partly from the outer surface of the porous monolith by treating the outer surface of the porous monolith with a mechanical means for cleaning smooth or rough surfaces, wherein the outer surface of the porous monolith is defined as the part of the monolith surface that is completely visible from outside with the naked eyes, and(e) optionally drying the catalyst body at a temperature in the range of from 150 °C to 300 °C.

12. A process for preparing anhydrous formaldehyde by contacting a feed gas comprising methanol with the catalyst body according to any of claims 1 to 10, collecting a product gas comprising anhydrous formaldehyde and hydrogen, and optionally isolating the anhydrous formaldehyde from the product gas.

13. A reactor for preparing anhydrous formaldehyde comprising a fixed bed built up by at least one catalyst body according to any of claims 1 to 10 or a plurality of said catalyst bodies.

14. Process for preparing a chemical compound or a polymer comprising the process step for preparing anhydrous formaldehyde according to claim 12.

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