WO2019072597A1

WO2019072597A1 - Process for producing catalyst shaped bodies by microextrusion

Info

Publication number: WO2019072597A1
Application number: PCT/EP2018/076485
Authority: WO
Inventors: Christian Walsdorff; Marco Oskar KENNEMA; Esther GROENEVELD; Peter BERBEN; Bernard Reesink
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2017-10-09
Filing date: 2018-09-28
Publication date: 2019-04-18
Anticipated expiration: 2020-04-09
Also published as: EP3466648A1

Abstract

The invention relates to a process for producing catalyst shaped bodies by microextrusion in which a pasty suspension of a catalyst shaped body precursor material in a liquid diluent is extruded through a movable microextrusion nozzle and by moving the microextrusion nozzle a catalyst shaped body precursor is generated layerwise and the catalyst shaped body precursor is subsequently subjected to a thermal treatment, wherein on a movable platform via a plurality of microextrusion nozzles a plurality of catalyst shaped body precursors are generated simultaneously.

Description

Process for producing catalyst shaped bodies by microextrusion Description

The invention relates to a process for producing catalyst shaped bodies by microextrusion. Processes for additive manufacturing of chemical catalysts by micro-extrusion are also referred to as "robocasting" or "direct-ink-writing" (DIM). Many processes employ chemical catalysts in the form of shaped bodies. Such shaped bodies are often in the form of cylinders, hollow cylinders or spheres. Shaped bodies having for example trilobal or star-shaped cross sections or having a plurality of hollow cylindrical openings are also used. Such shaped bodies are produced by extrusion,

tabletizations or in the case of spheres also by agglomerization on spinning plates.

However, the topological degrees of freedom of shaped bodies that may be produced with such classical methods are generally limited.

EP 1 127618 A1 describes hollow cylinders produced by tabletization having rounded end faces. DE 102 26 729 A1 describes cylinders produced by extrusion having notches parallel to the extrusion direction. WO 2016/156042 A1 describes shaped bodies produced by extrusion having four parallel hollow cylindrical openings.

A greater diversity of shaped body topologies is producible by additive manufacturing process- es, often also referred to as 3D printing processes.

The umbrella term additive manufacturing processes subsumes a series of different processes. Common to these is that a three-dimensional shaped body is constructed by additive means, i.e. by successive addition of material.

For the production of chemical catalysts two types of additive manufacturing processes in particular have been described.

US 8,1 19,554 describes a so-called powder bed printing process for producing chemical cata- lysts. US 9,278,338 likewise describes a so-called powder bed printing process for producing chemical catalysts. Both documents also describe catalyst shaped bodies having geometries which would not be obtainable by classical tabletization or extrusion processes. WO

2016/166526 and WO 2016/166523 also describe the production of catalyst shaped bodies having geometries which would not be achievable by classical

tabletization or extrusion processes. However, powder printing processes are of only limited suitability for producing chemical catalysts. Difficulties arise for example when constituents of the powder react with the liquid adhesive or are soluble therein. The thus obtained shaped bodies must generally also be calcined at high temperatures to achieve a sufficient

mechanical stability, which can have a strong influence on the catalytic properties. The specific density and thus also the active composition available in a volume element are often low.

C.R. Tubio et al. describe in Journal of Catalysis 334 (2016) 1 10 to 1 15 the production of a chemical catalyst shaped body by means of a robocasting process. The thus obtained catalyst shaped bodies having a structure described by the authors as "wood-pile" would not be obtainable with classical extrusion and tabletization processes either. One advantage of such robocasting methods is that the starting materials are treated in a manner similar to classical extrusion processes which imbues the methods with a relatively broad applicability. Catalyst shaped bodies may be employed individually or in small numbers, for example in the form of monoliths such as in automotive exhaust gas catalysts. In processes for producing chemicals catalyst shaped bodies are often not employed individually but rather in the form of dumped packings, so-called catalyst beds. Shaped bodies having geometries obtainable by additive manufacturing technologies can have various advantages for chemical catalysts compared to classical geometries as are obtainable by tabletization or extrusion. In particular

shaped bodies having macroscopic channel structures may have a relatively high geometric surface area per catalyst bed volume at relatively low pressure drop.

Additive manufacturing processes are often also described as "rapid prototyping". They were thus often developed to be able to produce prototypes of particular shaped bodies typically as a one-off or in small batches. However, chemical catalyst shaped bodies for use in commercial reactors are often required on a scale of several tons up to several hundred tons for filling a single reactor line. This corresponds to millions of shaped bodies.

The present invention accordingly has for its object the provision of a process for producing large numbers of catalyst shaped bodies for chemical processes having geometries not obtainable by classical tabletization or extrusion processes.

The object is achieved by a process for producing catalyst shaped bodies by microextrusion in which a pasty suspension of a catalyst shaped body precursor material in a liquid diluent is extruded through a movable microextrusion nozzle and by moving the microextrusion nozzle a catalyst shaped body precursor is generated layerwise and the catalyst shaped body precursor is subsequently subjected to a thermal treatment, characterized in that on a movable platform via a plurality of microextrusion nozzles a plurality of catalyst shaped body precursors are generated simultaneously. According to the invention shaped bodies are produced from a catalyst precursor material by means of a robocasting process on a movable base (platform). The platform may be moved continuously or discontinuously relative to the microextrusion nozzles. The thus produced catalyst shaped bodies may comprise only the support material, the support material and one or more active components or only active components, depending on the type of the employed extrudable formulation. It is preferable when by microextrusion and joining of (discontinuous or continuous) strands macroscopically porous catalyst shaped bodies are produced. However, it is also possible to generate solid catalyst shaped bodies.

3D-microextrusion technology (3D-robocasting technology) is known per se and described for example in US 7,527,671 , US 6,027,326, US 6,401 ,795, Catalysis Today 273 (2016), pages 234 to 243, Journal of Catalysis 334 (2016), pages 1 10 to 1 15 or US 6,993,406. The microextrusion nozzles generally have a diameter of less than 5 mm, preferably of less than 4 mm, particularly preferably of 0.05 to 3 mm, in particular of 0.2 to 2 mm.

The geometric resolution of catalyst shaped bodies produced by the process according to the invention is naturally defined by the diameter of the microextrusion nozzles. Preferably pro- duced by the process according to the invention are catalyst shaped bodies having a minimum diameter of at least 3 mm, particularly preferably of at least 5 mm and in particular of at least 10 mm.

The maximum size of the shaped bodies produced according to the invention is substantially defined by the dimensions of the platform according the invention and any enclosures and also the movement range of the microextrusion heads. For shaped bodies that are large relative to the spacing of the microextrusion nozzles a plurality of nozzles may also be employed simultaneously for construction of a common shaped body. The maximum diameter of the catalysts produced according to the invention is preferably not more than 1 m, particularly preferably not more than 30 cm and in particular not more than 10 cm.

Dimensions greater than 10 cm are contemplated in particular for monolithic shaped bodies which are generally fitted very precisely into an apparatus for performing catalytic reactions. Examples of such applications include many processes for exhaust gas treatment.

Dimensions of not more than 10 cm, preferably of not more than 5 cm and in particular of not more than 3 cm are contemplated in particular for shaped bodies which are not individually fitted into an apparatus for performing catalytic reactions but rather are used as a so-called dumped packing in a catalyst bed. Examples of such apparatuses are adiabatic or isothermal reactors or any desired intermediate forms, in particular in the form of tube-bundle, plate, dumped packing or tray reactors. Examples of such processes include many chemical industry processes for producing chemical compounds. Drying or further thermal treatment can also bring about a shrinking of the catalyst shaped bodies produced according to the invention which may need to be taken into account in the dimensioning of the microextrusion nozzles and the freshly microextruded ("green") shaped bodies. Formulations also used in standard extrusion processes are in principle suitable as pasty suspensions. 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 established. If necessary, binders and viscosity-modifying additions such as starch or carbox- ymethylcellulose 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 compositions or precursor compounds for catalytically active compositions but also an inorganic support material or inert material. Examples of commonly used support or inert materials are silicon dioxide, aluminum oxide, diatomaceous earth, titanium dioxide, zirconium dioxide, mag- nesium oxide, calcium oxide, hydrotalcite, spinels, perovskites, metal phosphates, metal silicates, zeolites, steatites, cordierites, carbides 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.

The geometric resolution of catalyst shaped bodies produced by the process according to the invention is naturally defined by the diameter of the microextrusion nozzles. Preferably produced by the process according to the invention are catalyst shaped bodies having a minimum diameter of at least 3 mm, particularly preferably of at least 5 mm and in particular of at least 10 mm. Examples for the use of the process according to the invention may be monolithic shaped bodies for treatment of exhaust gases, for example nitrogen oxides or laughing gas.

Examples for the use of the process according to the invention also include shaped bodies typically employed as a dumped packing in a catalyst bed, for example in processes for producing synthesis gas, for oxidation of nitrogen dioxide to nitrogen trioxide or for oxidation of ethylene to ethylene oxide. Suitable extrudable formulations for producing catalysts for oxidation of SO2 to SO3 are described for example in WO 2016/156042 A1 , see in particular example 1 of WO 2016/156042 A1. In one embodiment the inventive

process for producing catalyst shaped bodies is used for the oxidation of SO2 to SO3.

In one embodiment of the invention the platform is moved discontinuously after generation of a plurality of catalyst shaped body precursors. For example after robocasting of a plurality of shaped bodies the platform may be moved sufficiently far forward that for the next robocasting step a free region of the platform is available again.

However, in a preferred embodiment of the invention the platform is moved continuously during the layerwise generation of the catalyst shaped bodies, wherein the movement of the micronoz- zles compensates for the movement of the platform. To this end the electronic control means of the microextrusion nozzles in the three spatial directions is configured such that the translation movement of the platform is compensated by an additional translation movement of the microextrusion nozzles. Such a control compensation by vectorial movement components which compensate the movement of the platform is known to those skilled in the art.

The geometric resolution (accuracy) of the catalyst shaped body produced with the process according to the invention is also defined by the accuracy of the movement and positioning of the microextrusion nozzles and the platform, in particular also by the accuracy of the relative movements between the microextrusion nozzles and the platform. An estimate of the accuracy of the movement and positioning of the microextrusion nozzles and the platform necessary for a desired resolution of the shaped bodies according to the invention is possible for those skilled in the art according to the prior art using general mathematical knowledge.

According to the invention the microextrusion step is performed not only with a one the microextrusion nozzle

but rather with a plurality of microextrusion nozzles. Said nozzles may be attached perpendicu- larly in a row or obliquely displaced against the direction of motion of the platform.

They may particularly preferably also be arranged staggeredly one behind the other in a plurality of rows.

In a preferred embodiment the majority of the microextrusion nozzles are fixed against one an- other such that they may be moved in the three spatial directions simultaneously with one common motive apparatus. This also includes movement components for compensation of a continuous platform movement. In this embodiment a plurality of microextrusion nozzles is thus interconnected and moves synchronously. After formation of a plurality of shaped bodies with a plurality of microextrusion nozzles is complete the plurality of microextrusion nozzles is positioned over regions of the platform that are still free where further shaped bodies are subsequently formed. The microextrusion nozzles may be moved such that any gaps present in an arrangement of previously formed shaped bod- ies may be filled to increase the occupancy and capacity of the platform. However, the microextrusion nozzles may also be moved to a section of the platform on which no shaped bodies are yet present. It is preferable when the platform moves continuously or discontinuously from a region in which the robocasting steps are performed to a region in which a thermal treatment is performed. In a preferred embodiment the movable platform is a circulating belt. The circulating belt may be a continuous belt, for example a hard rubber belt. It is preferable to employ a chain belt or a plate belt made of a metallic material of construction. Ceramic materials of construction for example may also be employed as the platform and the segments of a belt structure. Plastics too, for example Teflon, may be employed provided this is permitted by the temperatures of the thermal treatment. This belt structure is preferably arranged like the track of a tracked vehicle so that segments of the belt structure return to their starting point after one circulation. In a preferred embodiment on the circulating belt the catalyst shaped bodies are subjected to a drying as the thermal treatment, wherein the belt traverses at least one drying zone. The drying may be effected in a plurality of drying zones at different temperatures. It is preferable when the circulating belt exhibits perforations and a drying by means of a heated gas which flows through the perforations in the at least one drying zone is effected. However, generation of the catalyst shaped body precursors by microextrusion and thermal treatment of same may also be effected on different circulating belts.

Thus, after traversing a first region in which the robocasting steps are performed and at least a second region in which a thermal treatment is performed the belt is deflected such that the shaped bodies fall off and for example are passed into a further process step while the belt is guided back in the opposite direction and after a renewed deflection is passed back into the region in which the robocasting steps are performed.

After leaving the belt structure the shaped bodies may be subjected to one or more further pro- cess steps, for example a further thermal treatment, in particular at higher temperatures, or a finishing or packaging step.

The deflection of the belt structure according to the invention a be effected for example via rollers,

wheels or cogwheels.

The platform and belt structure is preferably perforated, i.e. provided with openings so that the gas stream may be guided vertically through the belt structure, in particular in order to ensure a uniform thermal treatment or drying of the shaped bodies.

The platform and belt structure may be in the form of a net or braid or in the form of plates connected with hinges. It is preferable when the belt, or the individual segments of the belt, is/are made of a metallic material of construction. The heat input in the thermal treatment step may be effected for example by means of microwave radiation, electrically or steam powered assemblies, direct heating with a fuel gas or by introduction of a preheated gas.

In the process according to the invention a rapid forming of the shaped bodies in the

robocasting step is desired. The most uniform possible outflow velocity at the microextrusion nozzles is advantageous. It may in particular be advantageous after formation of a shaped body is complete not to reduce the outflow velocity or to interrupt the outflow completely. On the con- trary preference is given to a continuous flow velocity, so that shaped bodies formed successively by a microextrusion nozzle may be connected by a thin material bridge or corresponding flash-like fragments may be present on the shaped bodies. This is generally unproblematic. Such excess material is generally separated from the shaped bodies by abrasion, for instance during

falling off from the platform, and may then be removed from the shaped bodies in a sieving step preferably operated continuously upstream of a bagging step. After a pretreatment, for example a grinding step, this removed material may be reused, preferably as admixture to fresh starting materials, for producing the microextrudable paste for the robocasting. In the process according to the invention it is preferable when at least individual regions of the platform (belt structure) are arranged in a largely closed or at least aspiratable housing (chamber). Particularly the thermal treatment step is generally performed in a closed system such as in a belt dryer or a belt calciner. The terms belt drier and belt calciner may overlap and a belt calciner may thus be constructed similarly to a belt dryer but is operated at relatively higher temperatures. Drying steps and further thermal treatment steps (calcining steps) may also be performed in a common apparatus which may then preferably be operated with a series of more or less sharply separated temperature zones.

A suitable belt calcining apparatus is disclosed in EP 1 889 657 A1 for example. Said apparatus comprises as a means for generating the gas circulation a ventilator which is suitably arranged above the conveyor belt and the chamber (the chambers). In suitable embodiment the means for generating the gas circulation also comprise gas guiding devices for guiding the gas circulation inside the chamber, wherein the gas guiding devices extend inside the chamber in each case at the edge of the conveyor belt substantially in a plane perpendicular to the contact sur- face of the conveyor belt. The means for generating the gas circulation and/or the gas guiding devices are advantageously configured such that the gas ascends through the gas-permeable conveyor belt and the particulate catalyst precursors present thereupon and descends again at the walls of the chamber. Conversely, however, a gas circulation in the opposite direction is also conceivable. If the belt calcining apparatus comprises at least two heatable chambers, said chambers are preferably delimited from one another such that essentially no gas exchange between the chambers takes place. To remove decomposition gases and the like it is preferable when a portion of the gas recirculated in the chamber is continuously or periodically removed and replaced by fresh gas. The supply of fresh gas is controlled such that the temperature con- sistency in the chamber is not impaired. The volume of the gas circulated in the chamber per unit time is generally greater than the volume of the gas supplied or discharged from the chamber per unit time and is preferably at least five times the amount thereof. It is also possible for a plurality, for example two or three, of the above-described belt calcining apparatuses to be traversed successively. The catalyst precursor may optionally be collected and intermediately stored after traversing one apparatus and before traversing a further apparatus. The region in which the robocasting step is performed may also be surrounded by an aspirata- ble housing. This is required in particular when the catalyst materials comprise health- hazardous substances or flammable solvents are employed in the production of the extrudable pastes. Also optionally provided in case of use of organic additives or other substances which may form explosive gas atmospheres, for example ammonia, is a configuration of the housing and the offgas aspiration as an explosion control area. Treatment of the waste air aspirated from the enclosure by means of filters, scrubbers, incineration plants or DeNOx devices may also be required. In case of aspiration of the housing a corresponding feed air supply is preferably also provided. In one embodiment of the process according to the invention a continuous or discontinuous cleaning of the platform (belt structure) of any deposits also takes place. This may be effected for example mechanically through brushes or using a cleaning liquid, for example by means of spray nozzles. A cleaning is thus preferably performed automatically in a section of the belt structure outside the region of the robocasting or the thermal treatment step.

The invention is more particularly elucidated in figures 1 to 8.

Figure 1 shows a schematic representation of an exemplary embodiment of the microextrusion process according to the invention A) in side view and B) in plan view. Here, the multiextrusion head comprising a plurality of individual microextrusion nozzles, for example 12 individual microextrusion nozzles, is moved from the starting position (1 ) to the end position (2) along the conveyor belt (7) moving in the direction (3) during the microextrusion step. The microextruded shaped bodies made of catalyst precursor material traverse on the perforated conveyor belt (7) the belt dryer or calcining oven having for example 3 temperature zones (4), (5) and (6).

Figure 2 shows a schematic representation of a further exemplary embodiment of the microextrusion process according to the invention in plan view. Here, a belt dryer or

calciner is fed by a plurality of feed conveyor belts with microextruded shaped bodies made of catalyst precursor material. Here, per feed conveyor belt, a multiextrusion head comprising a plurality of individual microextrusion nozzles, for example 12 individual microextrusion nozzles, is moved from the starting position (1 ) to the end position (2) along the feed conveyor belt moving in the direction (3) during the microextrusion step. At the transition point (4) at which the feed conveyor belt is laterally moveable in the direction of the double arrow the platforms with the microextruded shaped bodies are transferred from the feed conveyor belt to the conveyor belt of a belt dryer or

calciner. The microextruded shaped bodies traverse on the perforated conveyor belt moving in the direction (5) for example the temperature zones (6), (7) and (8).

Figure 3 shows various arrangements of the individual microextrusion nozzles in a microextru- sion head. These may be arranged (1 ) strictly in parallel, (2) displaced in the longitudinal direction or (3) displaced in the horizontal direction. (4) reproduces in schematic form the 3 spatial directions x, y and z of the movement of the individual microextrusion nozzles/of the entire mi- croextrusion head.

Figure 4 shows (right-hand side) various options for moving the microextrusion nozzles for layerwise construction of for example a hollow cylindrical shaped body (left-hand side): (1 ) axial- ly and radially; (2) perpendicularly to the axis; (3) circularly.

Figure 5 shows in plan view options for microextrusion strand guiding in layerwise construction of a hollow cylindrical shaped body from figure 4. The extrusion may be effected continuously (1 ) in an endless strand, wherein (A) denotes schematically the transition of the endless strand to the next shaped body after completion of a shaped body. The extrusion may be effected dis- continuously (2), wherein discrete strands of extruded material are joined together to afford one shaped body. The extrusion may be effected continuously in a circular

pattern (3). Any desired hybrid forms of these strand guiding schemes are possible in inventive construction of a shape body. It may in principle be advantageous for inventive manufacture of the shaped bodies at high speed and precision in the layerwise construction of the shaped body to implement the extrusion within a layer or plane either only in the x-direction or only in the y-direction depending on the movement options of the microextrusion nozzles, i.e. without vectorial movement components in the respective other spatial direction. In figure 5 (2) the extrusion sections within the plane are implemented exclusively thus. In figure 5(3) the extrusion is implemented with constantly changing vectorial components in the x-direction and the y-direction. In figure 5(1 ) the extrusion within a layer was implemented partly in only one spatial direction x or y and partly in the direction of motion with vectorial components in the x-direction and the y-direction. A macroporosity of the shaped bodies produced according to the invention may be established by the spacing of different sections of continuously or discontinuously implemented extrusion strands to one another. However, the spacing of different sections of continuously or discontinuously implemented extrusion strands within a shaped body produced according to the invention need not be uniform or regular.

Figure 6 shows in schematic form and by way of example an embodiment of a catalyst produced according to the invention in the form of a hollow cylinder. Figure 7 shows in cross section and in schematic form examples of catalysts produced according to the invention in the form of hollow cylinders having rounded end faces: 7(1 ) cylinder having rounded outer edges described by the angles (A) and (B); 7(2) cylinder having rounded inner and outer edges described by the angles (A), (B), (C) and (D).

Figure 8 shows further examples of possible shaped body geometries in cross section. All shaped bodies may be constructed as per figure 5 (1 ) cylinder having longitudinal recesses; (2) 5-membered cogwheel shape having central opening; (3) four-leafed clover shape having 4 central openings; (4) triangular shape having central opening; (5) 7-vertice star shape having central opening; (6) three-leafed clover shape having 3 central openings. Such shaped bodies are preferably produced by the process according to the invention such that the cross sectional plane shown in figure 8 is oriented parallel to the plane of the movable base (platform). The shaped bodies may have a mirror plane parallel to these cross sectional planes as is also the case in a hollow cylinder according to figure 6(1 ).

Claims

1 . A process for producing catalyst shaped bodies by microextrusion in which a pasty suspension of a catalyst shaped body precursor material in a liquid diluent is extruded through a movable microextrusion nozzle and by moving the microextrusion nozzle a catalyst shaped body precursor is generated layerwise and the catalyst shaped body pre- cursor is subsequently subjected to a thermal treatment, wherein on a movable platform via a plurality of microextrusion nozzles a plurality of catalyst shaped body precursors are generated simultaneously.

2. The process according to claim 1 , wherein the platform is moved continuously or discon- tinuously relative to the microextrusion nozzles.

3. The process according to claim 2, wherein after generation of a plurality of catalyst

shaped body precursors the platform is moved discontinuously.

4. The process according to claim 2, wherein during generation of the catalyst shaped body precursors the platform is moved continuously, wherein the movement of the microextrusion nozzles compensates the movement of the platform.

5. The process according to any of claims 1 to 4, wherein a plurality of microextrusion noz- zles is interconnected and moved synchronously.

6. The process according to any of claims 1 to 6, wherein the movable platform is a circulating belt.

7. The process according to claim 6, wherein the circulating belt is a continuous belt.

8. The process according to claim 6, wherein the circulating belt comprises individual segments.

9. The process according to any of claims 6 to 8, wherein on the circulating belt the catalyst shaped bodies are subjected to a drying as the thermal treatment, wherein the belt traverses at least one drying zone.

10. The process according to claim 9, wherein the circulating belt is part of a belt dryer or belt calciner.

1 . The process according to claim 9 or 10, wherein the circulating belt comprises perforations and a drying by means of a heated gas which flows through the perforations in the at least one drying zone is effected.

2. The process according to any of claims 9 to 1 1 , wherein the drying is effected in a plurality of drying zones at different temperatures.