WO2021013652A1

WO2021013652A1 - Catalyst, catalyst carrier or absorbent monolith of stacked strands having zig-zag or helical longitudinal channels

Info

Publication number: WO2021013652A1
Application number: PCT/EP2020/070006
Authority: WO
Inventors: Marco Oskar KENNEMA; Jasper LEFEVERE; Bart MICHIELSEN; Christian Walsdorff; Fred BORNINKHOF; Florian SCHARF
Original assignee: Basf Se
Priority date: 2019-07-19
Filing date: 2020-07-15
Publication date: 2021-01-28

Abstract

A three-dimensional porous catalyst, catalyst carrier or absorbent monolith of stacked strands of catalyst, catalyst carrier or absorbent material, composed of layers of linear spaced-apart parallel strands that are rotated against one another, wherein part of the layers of the same orientation are congruent and part of the layers of the same orientation are not congruent to one another, wherein in the not congruent layers of the same orientation at least part of the parallel strands are laterally offset to one other.

Description

Catalyst, catalyst carrier or absorbent monolith of stacked strands having zig-zag or helical lon gitudinal channels

Description

The invention relates to a three-dimensional porous catalyst, catalyst support or absorbent monolith of stacked strands, a method for producing the monolith and the use of the monolith.

Typically, inorganic catalysts, catalyst supports or absorbents are produced as extruded strands or extruded monolith or honeycomb structures.

Alternative processes which allow for a greater variety of shapes in comparison to a linear stretched honeycomb structure can be prepared e.g. by rapid prototyping processes. The pro cess described in US 8,119,554, for example, involves the production of a shaped body by means of a powder-based rapid prototyping process, in which a binder material is selectively introduced in an inorganic catalyst powder to form the three-dimensional structure.

A further production process often named robocasting can be employed. In this method, a paste of the catalyst material particles is extruded into strands which are deposited in stacked layers to form the desired three-dimensional structure. Subsequently, the structure is dried and sin tered. The production of regenerable diesel soot particulate filters by robocasting methods is disclosed in US 7,527,671.

This method has also been employed for preparing Cu/A Ch catalytic systems with a wood pile porous structure. Journal of Catalysis 334 (2016), 1 10 to 115, relates to the 3D printing of a heterogeneous copper-based catalyst. AI₂O₃ powder with a mean particle size of 0.5 pm was added to an aqueous solution of copper(ll) nitrate, and the viscosity of the resulting suspension was adjusted by adding hydroxypropyl methyl cellulose as viscosity modifier. The resulting ink was concentrated by the removal of water by evaporation until suitable for extrusion. The aque ous ink was loaded into a syringe attached by a nozzle with a diameter of 410 pm. A robotic deposition system was used to create the woodpile structures. The structure was dried at room temperature for 24 h and subsequently sintered at 1400 °C for 2 h in air.

Ni/AhCh-coated structured catalysts are disclosed in Catalysis Today, 273 (2016), pages 234 to 243. To prepare the catalyst, stainless steel supports were prepared using the robocasting pro cess. The resulting 3D structures were sintered at 1300°C for 4 h and a coating slurry of boehmite powder with nickel loading was applied. Thus, only the stainless steel support struc ture was prepared by robocasting.

All the above-mentioned processes need a sintering step at temperatures well above 1000°C. For a number of catalysts employing catalytically active metals, such sintering at high tempera tures is detrimental to the catalyst properties. Typically, the dispersion of the catalytically active metal on a catalyst support deteriorates upon this temperature treatment.

To obtain high external surface areas for the catalysts, e.g. for diffusion limited reactions, or high packing fractions with low void volume, in fixed-bed catalyst reactors, the use of smaller catalyst extrudates is necessary. In mass transfer limited reactions the performance of small catalyst extrudates is better than that of larger extrudates, especially in mass-transfer limited reactions. A disadvantage, however, is that smaller extrudates show a higher pressure drop in the packed bed. Furthermore, the mechanical strength of these small extrudates is typically not sufficient to form a packed bed reactor.

WO 2017/055565 A1 discloses a method of building a bulk catalytic structure, comprising: shaping a composition comprising a ceramic material to obtain a green structure, wherein said ceramic material comprises a catalytic material and a first and a second inorganic binder; firing the green structure to obtain the bulk catalytic structure, wherein the structure comprises first channels having a length extending in a flow direction and second channels having a length extending in a radial direction, wherein the shaping step comprises extruding the suspension, slurry or paste as fibers by three-dimensional fiber deposition, wherein the fibers form a layered network.

The layered network comprises alternating layers of fibers parallel to one another, wherein the fibers in successive layers are arranged orthogonal or oblique to one another.

In a preferred embodiment, the alternating layers comprise first alternate layers and second alternate layers, wherein the fibers in successive ones of the first alternate layers are aligned and wherein the fibers in successive ones of the second alternate layers are aligned.

US 9,597,837 B1 discloses a method for making a three-dimensional porous fluidic device comprising: depositing struts and walls in the three-dimensional geometry using a rapid-proto- typing method to construct a three-dimensional porous fluidic device, the three-dimensional po rous fluidic device comprising: a fluidic inlet side and an outlet side; a wall surrounding the fluid ic device; within the wall of the fluidic device a lattice of a plurality of struts positioned in layers forming a network of pores wherein the struts in the first layer are separated from the struts in a third layer by struts in a second layer which are arranged at an angle to the struts in the first layer and the third layer and wherein the struts in the third layer and the first layer are offset in spacing and wherein the struts within a layer are separated from an adjacent strut within the layer by a space such that channels having a tortuous pathway of interconnecting pores are formed.

EP 3 381 546 A1 discloses a device for through-flow of a fluid, comprising a fluid inlet and a fluid outlet, wherein the fluid inlet and the fluid outlet define an overall flow direction, a porous structure with interconnected pores arranged between the fluid inlet and the fluid outlet, wherein the porous structure is coupled to a wall to provide for heat conduction between the porous structure and the wall, and wherein the porous structure comprises a porosity gradient along a first direction which is cross to the overall flow direction, and wherein the porosity gradient de velops along the first direction between a first porosity at a first location proximal to the wall and a second porosity larger than the first porosity at a second location remote from the wall. The porous structure comprises an arrangement of fibers which are attached to one another, where in the fibers are arranged in parallel layers, the layers being stacked.

Current catalysts prepared through robocasting have a large surface area. However, they also have a high pressure drop across the individual monolith bodies, which in turn results in a high pressure drop across a reactor where these monolith bodies would be placed.

The object underlying the present invention is to provide a catalyst including a catalytically ac tive metal which has a high external surface area. The catalyst structure should be sufficiently mechanically stable so that packed catalyst beds can be formed in a reactor. In particular, the catalyst structure should give a low pressure drop in a structured packing of a reactor bed.

The object is achieved by a three-dimensional porous catalyst, catalyst carrier or absorbent monolith of stacked strands of catalyst, catalyst carrier or absorbent material, composed of lay ers of linear spaced-apart parallel strands, the layers being rotated against one another, where in part of the layers of the same orientation are congruent and part of the layers of the same orientation are not congruent with one another, wherein in the not congruent layers of the same orientation at least part of the parallel strands are laterally offset to one another.

Current state of the art monolith structures have parallel channels parallel to the primary direc tion of flow within the monolith structure and thus have no cross-channel flow pattern. The in ventive catalyst shape allows for multiple flow directions of the gas through the monolith struc ture with a preferential path, but also secondary and tertiary cross-channel flows through the structure. In the case of the inventive monolith, a helical or zig-zag primary flow pattern through the monolith provides a significantly lower pressure-drop, a higher turbulent flow with a minimal decrease in surface area per volume.

The current state of the art additive manufactured catalysts prepared using the layer by layer addition of fibers allow for cross-channel flow of gas, however the primary direction of flow of the gas is in the direction perpendicular to the deposition of the fibers of the layer. In some cas es, the fibers are laid in such a way as to allow for a primary flow in a zig-zag pattern across the monolith, this zig-zag pattern being known to improve the activity of the catalyst in comparison to the straight-channeled state of the art catalysts.

The inventive catalyst shape geometry further builds on the fact that the zig-zag or helical flow pattern through the monolith structure increases the catalytic activity by providing a high degree of turbulence in the monolith while providing a decrease in the pressure drop across the struc- ture when compared to the state of the art manufactured catalyst prepared by layer fiber addi tion.

Preferably, the parallel strands in the not congruent layers of the same orientation are laterally offset to one another by 1 to 3 strand diameters.

The monolith may have a square, octagonal, round, elliptical or hexagonal shape. However, in a preferred embodiment, the monolith has a hexagonal cross-section and is composed of layers of parallel strands that are rotated at 60° and 120°, respectively, against one another.

Preferably, every third layer of spaced-apart parallel strands has the same orientation.

In a particular preferred embodiment, the layers of parallel strands comprise pairs of closely spaced-apart parallel strands, wherein vicinal pairs have a larger separation.

In one embodiment, the closely spaced-apart parallel strands are separated by 0.3 to 2 strand diameters, and vicinal pairs are separated by 3 to 6 strand diameters.

In a preferred embodiment, the monolith resulting from this construction principle has helical channels extending in longitudinal direction.

In a further embodiment, the monolith resulting from this construction principle has zigzag- channels extending in longitudinal direction.

In a further embodiment, in some or all of the layers a strand is arranged that forms a frame of the layer defining the outer periphery of the catalyst monolith.

The invention is further illustrated by the Figures.

Figure 1 shows a first sequence of layers 1 a - 1 c giving a first substructure 1 d.

Figure 2 shows a second sequence of layers 2a - 2c giving a second substructure 2d.

Figure 3 shows a third sequence of layers 3a - 3c giving a third substructure 3d.

Figure 4 shows a fourth sequence of layers 4a - 4c giving a fourth substructure 4d.

Figure 5 shows a fifth sequence of layers 5a - 5c giving a fifth substructure 5d.

Figure 6 shows a sixth sequence of layers 6a - 6c giving a sixth substructure 6d.

Figure 7 shows a seventh sequence of layers 7a - 7c giving a seventh substructure 7d. Figure 8 shows an eighth sequence of layers 8a - 8c giving a eighth substructure 8d.

Figures 1 to 8 illustrate how the tortuous monolithic structure having helical channels in longitu dinal direction is created by superposition of layers 1 a - 1 c, 2a - 2c, 3a - 3c, 4a - 4c, 5a -5c,

6a - 6c, 7a - 7c and 8a - 8c. Each layer is composed of pairs of parallel spaced-apart strands, the distance between a pair of strands being for example 1 strand diameter and the distance between vicinal pairs being for example 5 strand diameters. In part of the layers of the same orientation, the strands are laterally offset to one another by for example 2 strand diameters.

The triples of layers 1 a - 1 c, 2a - 2c, 3a - 3c, 4a - 4c, 5a - dc, 6a - 6c, 7a - 7c and 8a - 8c give substructures 1 d, 2d, 3d, 4d, 5d, 6d, 7d and 8d having short channel segments formed by the superposition of the each three consecutive layers of different orientation. The channel seg ments in consecutive substructures 1 d, 2d, 3d, 4d, 5d, 6d, 7d and 8d are slightly laterally offset to one another along the symmetry axis of the hexagon. The superposition of substructures 1d - 8d having slightly laterally offset channel segments gives the overall monolithic structure having tortuous or helical channels in longitudinal direction.

Figure 9 illustrates the parameters r and m2 as well as a vicinal pair of strands (a) for one lay er of the inventive monolith design.

Figure 10 illustrates the vertical overlap between 3 layers of a microextruded monolith structure (b) is the strand diameter, (d) is the vertical overlap between the layers indicated in Examples 1 - 3.

Figure 1 1 shows the top view of an actual example of the inventive monolith with b = 1.2 mm, rm = 0.5 mm and m2 = 4.16 mm.

Figure 12 shows a perspective view of the monolith of figure 1 1.

The object of the invention is further achieved by a method for producing a three-dimensional porous catalyst, catalyst carrier or absorbent monolith of stacked strands, comprising catalyst, catalyst carrier or absorbent material, comprising the following steps: a) Preparing a paste of metal, metal alloy, metal compound particles of catalytically active metal or catalyst support particles in a liquid diluent, in which the metal, metal alloy or metal compound particles can be supported on or mixed with catalyst support particles, and which paste can optionally comprise a binder material, b) extruding the paste of step a) through one or more nozzles having a diameter larger than 500 pm to form strands, and depositing the extruded strands in consecutive layers of linear spaced-apart parallel strands having the same or a different orientation and being congruent or not congruent with one another, to form a three-dimensional porous monolith precursor, c) drying the porous monolith precursor to remove the liquid diluent, d) if necessary, reducing metal oxide(s) in the porous monolith precursor to form the catalyti- cally active metal or metal alloy, or additional heat treatment to produce a catalytically active material.

The layer pattern and layer organization of the monolith structures of the invention leads to a significant decrease in pressure drop across each individual monolith body. This results in a lower pressure drop across a reactor filled with the monoliths of the invention and a more ho mogeneous flow through the reactor bed filled with a random packing of individual monoliths.

In this respect, a three-dimensional monolith is a one-piece structure made of at least two stacked layers of strands.

In general, the strands are deposited orthogonal or oblique to each other in alternating layers. The orientation of the strands in each consecutive layer can be rotated by a certain angle, e.g. by 60°, 45° or 36°, clockwise or anti-clockwise, with respect to the preceding layer. Channels are formed in the monolith by superposition of individual layers of parallel strands having differ ent orientations.

Preferably, the strands are deposited in consecutive layers comprising a multitude of first layers, second layers and third layers, respectively, wherein the strands in the first layers, in the second layers and in the third layers, respectively, have the same orientation, and wherein the first, se cond and third layers are oriented at 0°, 60° and 120°, respectively, to one another. Preferably, the catalyst monolith has a hexagonal cross-section in this case, but it may also have a circular cross section.

In a further embodiment, the strands are deposited in consecutive layers comprising first, second, third and fourth layers, wherein the strands in the first layers, in the second layers, in the third layers and in the fourth layers are oriented at 0°, 45°, 90° and 135°, respectively, to one another. Preferably, the catalyst monolith has an octagonal cross-section in this case, but it may also have a circular cross section.

The monolith can have any other suitable cross-section, for example a triangular, pentagonal or circular cross-section. A triangular catalyst monolith can have sequences of layers oriented at 0°, 60° and 120°, respectively, to one another. A pentagonal monolith may have a sequences of layers, oriented at 0°, 36°, 12°, 108° and 144°, respectively, to one another.

In one embodiment, the parallel strands in each layer are partial strands deposited in a continu ous manner as part of one single individual strand, the one single individual strand having cor ners and changing its direction in the plane of the layer.

In preferred embodiments, the outer periphery of the catalyst monolith is created by depositing in some or all of the layers, preferably in all of the layers, a strand that forms a frame of the lay- ers defining the outer perimeter of the monolith. The outermost strands are thus part of the frame. The stacked frames of each layer result in a solid lateral wall of the catalyst monolith.

In further preferred embodiments, in some or all of the layers a strand is arranged that forms a frame of the layer defining the outer periphery of the catalyst monolith.

Formulations also used in standard extrusion processes are in principle suitable as pasty sus pensions. It is a prerequisite that the particle size of the catalyst precursor material is sufficiently small for the microextrusion nozzle. The largest particles (d99 value) should preferably be at least five times smaller, in particular at least ten times smaller, than the nozzle diameter.

Suitable formulations exhibit the rheological properties necessary for microextrusion. The abovementioned literature describes in detail how suitable rheological properties may be estab lished. If necessary, binders and viscosity-modifying additions such as starch or carboxymethyl- cellulose may be added to the formulations.

The microextrudable pasty suspension preferably contains water as liquid diluent but organic solvents may also be employed. The suspension may contain not only catalytically active com positions or precursor compounds for catalytically active compositions but also an inorganic support material or inert material. Examples of commonly used support or inert materials, which may also be catalytically active per se in certain reactions, are silicon dioxide, aluminum oxide, diatomaceous earth, titanium dioxide, zirconium dioxide, magnesium oxide, calcium oxide, hydrotalcite, spinels, perovskites, metal phosphates, metal silicates, zeolites, steatites, cordie- rites, carbides, boron nitrides, metal-organic frame works and mixtures thereof.

The process according to the invention may also be used to produce shaped bodies essentially comprising only a support material or an inert material. Such shaped bodies produced by the process according to the invention may then be converted into catalyst shaped bodies in further process steps, for example by impregnation or coating and optionally further thermal treatment steps.

Metal, metal alloy or metal oxide particles of catalytically active metals or metal alloys can be employed in a robocasting process, wherein no treatment or sintering step at temperatures above 1000°C is necessary in order to obtain mechanically stable catalytically active structures.

When employing metals, metal alloys or metal oxides, supported on or mixed with inorganic oxide catalyst support particles, a high dispersion of the catalytically active metal or metal alloy can be achieved since no temperature treatment at temperatures above 1000°C is necessary. Often, such temperature treatment leads to a lowering of the dispersion of the catalytically ac tive metal or alloy.

Powders of prefabricated supported catalysts, with catalytically active metals being in oxide form, if appropriate, can be formed in a robocasting process without significantly changing their properties, e.g. active metal dispersion on the catalyst support. According to the above-mentio ned known processes, supported catalysts were obtained at the end of the robocasting and sin tering only.

The robocasting process allows for the manufacture of three-dimensional porous catalyst mono lith structures of stacked catalyst fibers, which have an increased external surface area in com parison to normal extrudates.

This leads to higher activity and selectivity due to increased external surface area in diffusion- limited reactions, like hydrogenation reactions, oxidation reactions, or dehydration reactions.

An example of a hydrogenation reaction is that of butanal to butanol or butyne diol hydrogena tion.

Furthermore, heat transport limited reactions like oxidation reactions, e.g. ethylene oxide reac tion, can be envisaged.

A low pressure drop is possible, thus allowing to work with smaller fiber diameters compared to single extrudates.

The invention also relates to a randomly packed catalyst bed, comprising the porous catalyst monoliths of stacked catalyst strands of the invention.

When starting from powders of prefabricated catalysts, the original active metal (oxide) disper sion on the catalyst support can be maintained.

The 3D robocasting technique employed according to the present invention is well established and can be performed as described in US 7,527,671 , US 6,027,326, US 6,401 ,795, Catalysis Today 273 (2016), pages 234 to 243, or Journal of Catalysis 334 (2016), pages 1 10 to 1 15, or US 6,993,406.

The 3D robocasting technique can be used with catalyst formulations which can be based on pastes that are currently used in standard extrusion techniques provided the particle size is small enough to pass the extrusion nozzle. The extrusion formulation or paste contains pre formed catalytic materials, e.g. nickel precipitates, in which the nickel oxide particles are already present. If necessary, a binder can be added to the extrusion mixture.

The robocasting technique implies the extruding through one or more nozzles having a diameter of more than 0.2 mm, preferably more than 0.5 mm. Particularly preferably, the diameter of the nozzle should be in the range of from 0.75 mm to 2.5 mm, most preferably from 0.75 mm to 1.75 mm. The nozzle can have any desired cross-section, e.g. circular, elliptical, square, star shaped, lobed. The maximum diameter is the largest diameter of a non-circular cross-section. One of the main criteria for microextruding is the use of an extrudable paste that has the correct rheological properties for the microextruding technique. The above-mentioned literature gives detailed advice as to how to obtain the required rheological properties.

If necessary, in the process according to the present invention, a viscosity adjusting agent can be employed. Typical viscosity adjusting agents are celluloses like carboxymethyl cellulose. Preferably, no viscosity adjusting agent or polymer is employed.

All commercially employed inorganic oxide catalyst support particles may be employed accor ding to the present invention. Preferably, the inorganic oxide catalyst support is selected from the group consisting of diatomaceous earth, silicon dioxide, aluminium oxide, titanium dioxide, zirconium dioxide, magnesium oxide, calcium oxide, mixed metal oxides, hydrotalcites, spinels, perovskites, metal phosphates, silicates, zeolites, steatite, cordierite, carbides, nitrides or mix tures or blends thereof.

In addition to the above mentioned commercially employed inorganic oxide catalyst support particles (or mixtures thereof), a catalytically active material may be added as part of the inor ganic oxide support (or mixtures thereof) or as an additional coating on the support structure or as several consecutive coatings. This catalytically active material may be composed of an num ber of the following elements: Na, K, Mg, Ca, Ba, Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Sn, Sb, La, Hf, W, Re, Ir, Pt, Au, Pb, and Ce, even if not all compo nents are catalytically active.

The amount of catalytically active metal or metal alloy, which is based on the amount of support, is preferably in the range of from 0.1 to 95 wt.-%, more preferably 3 to 75 wt.-%, most preferably 8 to 65 wt.-%.

The suspension paste prepared in step a) of the process according to the present invention preferably has a solids content of 1 to 95 wt.-%, more preferably 10 to 65 wt.-%.

If necessary, a binder material for binding metal (oxide) and/or support particles together can be employed in the suspension paste. Preferred binder materials are selected from the group of inorganic binders such as clays, alumina, silica or mixtures thereof.

The amount of binder material in the suspension paste is preferably in the range of from 0.1 to 80 wt.-%, more preferably 1 to 15 wt.-%, based on the suspension paste.

Often, it is not necessary to additionally use organic binder materials in the suspension although their use is possible according to the invention. Therefore, preferably no organic binder material is present in the suspension.

The term“porous” employed here defines that the monolith is not a solid block of material but contains channels and/or pores. The porosity is preferably at least 20%, more preferably at least 30% and can preferably be in the range of from 20 to 90%, and can be determined by Hg-PV and He-density. It can be de termined by the following formula. Porosity(%) = 100 - [(density of total microextruded struc ture/density of fiber material)x100]. The density of the total microextruded structure is deter mined by dividing its total weight by its total volume. The density of the fiber material can be determined by measuring Hg-PV and He-density.

Since the lattices or scaffolds formed from the fibers are self-supporting, open space remains between the fibers which leads to the porosity. Respective structures can be seen in the above- mentioned literature.

The robocasting process employed according to the present invention can also be described as 3D fiber deposition.

General description of the microextrusion process also known as 3DFD

3D Fiber Deposition (3DFD) is used to shape powder of a catalyst, catalyst carrier or absorbent material. The 3DFD method is an adaptive manufacturing method whereby a highly loaded paste is extruded by a moving nozzle. By computer controlling the movement of the extrusion head in x, y and z-direction, a porous material can be produced from the extruded fibers or strands layer by layer. After drying, the porous material can be thermally dried.

The main benefit of this technology is the degree of freedom with regard to the porous parame ters (fiber thickness, inter strand distance and stacking design).

The typical flow chart for the 3DFD technology consists of the following subsequent steps:

Preparation of highly viscous paste

Extrusion through thin nozzle

Computer controlled deposition of fibers to form a porous periodic structure

Drying and if necessary reducing

The powder is mixed together with the solvent/diluent (e.g. water), if necessary binder and addi tives, thus obtaining a viscous paste. A good mixing to achieve a homogeneous paste (minimi zing agglomerates or the incorporation of air bubbles) is a prerequisite for a smooth and repro ducible process. The powder loading of the functional material depends on the specific surface area, the particle size distribution and the powder morphology. Generally, as the particle size of the powder decreases, the viscosity of the paste will increase. Therefore the solid loading needs to be lowered for these powders. Apart from organic or, preferably, inorganic binder(s), rheology modifiers can be added to control the rheological behavior of the paste. In some cases a defoamer is also added to avoid air bubbles in the paste. After drying at room conditions (or under controlled atmosphere and temperature), the 3DFD structure is reduced, if necessary. No calcining or sintering at temperatures above 1000 °C is necessary.

The monolith of stacked fibers may shrink due to the heat treatment. This shrinkage could be in the range of 5-50% of the printing size of the“green” catalyst body.

The monolith of stacked catalyst fibers is three-dimensionally structured by depositing the ex truded fibers in regular, recurring stacking pattern (periodically structured catalyst), to form a three-dimensionally structured porous catalyst monolith precursor.

The points where the direction of the extrudate is changed or the layer in which the extrudate is deposited may have a larger diameter than the desired strand diameter. Though undesired, the diameter of an individual strand may also change in a parallel section of the shaped body due to a change in the printing speed.

The fibers or strands preferably have a thickness of 0.2 mm to 2.5 mm, more preferably of 0.5 mm to 2 mm, most preferably 0.75 mm to 1.75 mm.

They are preferably spatially separated from each other by a smaller first (primary) and one larger second (secondary) distance, wherein the first distance is determined by the formula: mi= b^*d wherein (mi), the primary distance between the fibers is determined by the strand diameter b multiplied by a factor d, wherein d is from 0.25 to 2. d = 1 in Example 2 and d = 0.5 in Figure 11.

The larger secondary distances are calculated by the formula: itΐ2= rrii^*e wherein m2 is at least one of the secondary inter-strand distances, e is from 3 to 6, preferably 3 to 5. In Example 2, e = 3; In Figure 11 , e = 4.16

Further (tertiary etc.) inter-strand distances may be present in the monolith structure as de scribed by the formula:

m_x= mi^*f wherein m_x is at least one of the subsequent inter-strand distances, f is from 2 to 10, preferably from 2 to 6.

The invention is further illustrated by the following examples. Pressure drop simulations

Examples 1 to 3

The correlation between pressure drop and catalyst monolith shape was calculated via numeri cal flow simulation (computational fluid dynamics - CFD), which completely resolves the flow in the void spaces between the solid catalyst structures. CFD simulations are a standard tool to calculate the pressure drop in complex 3D geometries. First, the geometry of the 3D micro- extruded (robocasted) catalyst monolith is created. For this purpose, a CAD (Computer Aided Design) model of a single catalyst body is created with a CAD program. For the calculation of the internal pressure drop, the porous monoliths were virtually placed in tubes with the exact same cross-section, to exclude bypass flow around the monoliths. Pressure drop calculations were performed by simulating air flow at ambient temperature and different gas space velocities (GFISV, gas hourly space velocity). Values for the thermodynamic and transport properties of air at a constant operating pressure of 1 bar and a temperature of 20°C were taken from the scien tific literature.

Example 1 : state of the art additive manufactured monolith structure

Example 2: Inventive additive manufactured monolith structure

Example 3: comparison of pressure drop between Example l and Example 2

Claims

1. A three-dimensional porous catalyst, catalyst carrier or absorbent monolith of stacked strands of catalyst, catalyst carrier or absorbent material, composed of layers of linear spaced-apart parallel strands, the layers being rotated against one another, wherein part of the layers of the same orientation are congruent and part of the layers of the same ori entation are not congruent with one another, wherein in the not congruent layers of the same orientation at least part of the parallel strands are laterally offset to one another.

2. The monolith of claim 1 , wherein the parallel strands in the not congruent layers of the same orientation are laterally offset to one another by 1 to 3 strand diameters.

3. The monolith of claim 1 or 2 having a hexagonal cross-section composed of layers of par allel strands that are rotated against at 60° and 120°, respectively, against one another.

4. The monolith of claim 3, wherein every third layer has the same orientation.

5. The monolith of any one of claims 1 to 4 comprising pairs of closely spaced-apart parallel strands, wherein vicinal pairs have a larger separation.

6. The monolith of claim 5, wherein closely spaced-apart parallel strands are separated by 0.25 to 2 strand diameters, and vicinal pairs are separated by 3 to 6 strand diameters.

7. The monolith of any one of claims 1 to 6 having helical channels or zig-zag channels in longitudinal direction.

8. The monolith of any one of claims 1 to 7, wherein in some or all of the layers a strand is arranged that forms a frame of the layer defining the outer periphery of the catalyst mono lith.

9. A method for producing a three-dimensional porous catalyst, catalyst carrier or absorbent monolith as claimed in claims 1 to 8, comprising the following steps: a) Preparing a paste of metal, metal alloy, metal compound particles of catalytically active metal or catalyst support particles in a liquid diluent, in which the metal, metal alloy or metal compound particles can be supported on or mixed with catalyst support particles, and which paste can optionally comprise a binder material, b) extruding the paste of step a) through one or more nozzles having a diameter larger than 500 pm to form strands, and depositing the extruded strands in consecutive layers of linear spaced-apart parallel strands having the same or a different orientation and being congruent or not congruent with one another, to form a three-dimensional porous monolith precursor, c) drying the porous monolith precursor to remove the liquid diluent, d) if necessary, reducing metal oxide(s) in the porous monolith precursor to form the catalytically active metal or metal alloy, or additional heat treatment to produce a catalyti- cally active material.

10. The method according to any one of claims 9, wherein parallel strands are deposited con tinuously as partial strands of one single individual strand in each layer.

11. The method according to any one of claims 9 or 10, wherein more than one layer of the catalyst monolith is deposited continuously as one single individual strand.

12. The method according to any one of claims 9 to 11 , wherein the outer periphery of the catalyst monolith is created by depositing in some or all of the layers a strand that forms a frame of the layer defining the outer periphery of the catalyst monolith.

13. The method according to any one of claims 9 to 12, wherein no temperature treatment of the porous catalyst monolith precursor or porous catalyst monolith at temperatures above 1000 °C is performed.

14. The method according to one of claims 9 to 13, wherein the inorganic oxide catalyst

support is selected from the group consisting of silicon dioxide, aluminium oxide, titanium dioxide, zirconium dioxide, magnesium oxide, calcium oxide, mixed metal oxides, hydro- talcites, spinels, perovskites, metal phosphates, silicates, zeolites, steatite, cordierite, car bides, nitrides or mixtures or blends thereof.

15. The method according to one of claims 9 to 14, wherein the catalytically active metal is selected from the group consisting of Na, K, Mg, Ca, Ba, Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Sn, Sb, La, Hf, W, Re, Ir, Pt, Au, Pb, and Ce and mixtures or alloys thereof.

16. The method according to one of claims 9 to 15, wherein a binder material is employed, selected from the group consisting of inorganic binders, preferably clays, alumina, silica or mixtures thereof.

17. The use of the three-dimensional porous catalyst monolith of stacked catalyst strands according to claims 1 to 8 in oxidation, hydrogenation and dehydration reactions.

18. A randomly packed catalyst bed, comprising porous catalyst monoliths of stacked catalyst strands according to claims 1 to 8.

19. A structured packing of a catalyst bed, comprising porous catalyst monoliths of stacked catalyst strands according to claims 1 to 8.