WO2018052287A1

WO2018052287A1 - Method for additive manufacturing of a 3d structure

Info

Publication number: WO2018052287A1
Application number: PCT/NL2017/050597
Authority: WO
Inventors: Hendricus Adrianus Johannes Van Dijk; Franciscus Petrus Felix Van Berkel; Paul Dean Cobden
Original assignee: Stichting Energieonderzoek Centrum
Priority date: 2016-09-13
Filing date: 2017-09-12
Publication date: 2018-03-22
Also published as: WO2018052287A8; EP3512619A1

Abstract

Method of additive manufacturing of a 3D structure (1) extending in an axial direction (7), wherein the 3D structure (1) comprises a plurality of channels (6) extending from an input surface to an output surface. Additive manufacturing is applied to obtain the 3D structure (1) using a base material which results in the 3D structure (1) being composed of an active material, wherein the active material is a porous material. The 3D structure (1) is a functional structure having a non-uniform axial geometry, wherein variations in the non-uniform axial geometry are provided in subsequent additive manufactured layers of the functional structure.

Description

Method for additive manufacturing of a 3D structure

Field of the invention

The present invention relates to a method of additive manufacturing of a 3D structure extending in an axial direction, wherein the 3D structure comprises a plurality of channels extending from an input surface to an output surface.

Background art

International patent publication WO2012/032325 discloses a method of producing a shaped catalyst unit. One of the disclosed methods is stereo-lithography, wherein a powdered catalyst dispersed in a monomer binder, which is cured in subsequent layers using photo-polymerization. A heat treatment is then performed to remove the polymer and provide the three dimensional object from the catalytic material. The catalyst shaped unit is disclosed as possibly having one or more through holes, running parallel, or non-parallel (e.g. curved) through the shaped unit at various angles to the longitudinal axis of the shaped unit.

International patent publication WO02/32545 discloses a multicellular or a honeycomb structure for application as a diesel particulate filter (DPF) in an automotive engine. The structure has an inlet end and an outlet end and a multiplicity of cells extending from the inlet end to the outlet end through which engine exhaust stream passes. The honeycomb structure is manufactured using an ink jet printing process, involving providing a powder layer on a supporting bed, and depositing a liquid binder using (a row of) ink jet heads.

Summary of the invention

The present invention seeks to provide an improved method for manufacturing compact and effectively working porous components for use in sorption and catalytic processes.

According to the present invention, a method as defined above is provided, wherein the method comprises additive manufacturing of the 3D structure using a base material which results in the 3D structure being composed of an active material. The 3D structure is a functional structure having a non-uniform axial geometry, wherein variations in the non-uniform axial geometry are provided in subsequent additive manufactured layers of the functional structure. A 3D structure manufactured according to the present invention embodiments, can be applied in a sorption or catalytic process because of the plurality of channels in combination with the active material used in the functional structure. By applying such a 3D structure in a sorption or catalytic process, the active (sorption and/or catalyst) material is more efficiently used for the process. This results in size reduction of the process and possibly in improved performance with respect to separation performance, conversion and selectivity. Shaping of the 3D structure allows optimization of the fluid-dynamic, heat transport and mass transport properties of the structure as such, since the axial (and radial) geometry can be freely chosen using such an additive manufacturing technique which inherently provides freedom in dimensions and position in both axial and radial direction. Short description of drawings

The present invention will be discussed in more detail below, with reference to the attached drawings, in which

Fig. 1A-D shows cross sectional views of sections of a 3D structure manufactured according to an embodiment of the present invention;

Fig. 2 shows a side cross sectional view of a part of the 3D structure of Fig. 1 A-D;

Fig. 3A-C shows cross sectional views of sections of a 3D structure manufactured according to a further embodiment of the present invention; and

Fig. 4 shows a perspective view of yet another embodiment of a 3D structure.

Description of embodiments

The major part of sorption and catalyst processes are based on fixed beds consisting of individual shaped particles through which a fluid passes. Classic solutions for improving the efficient use of material are based on using specific shaped particles, such as ring-shaped tablets, tablets with holes, multi-lobe extrudates, etc. Moreover, the active components can be specifically located at the outer part of the particle.

Alternatively, shaped structures such as monoliths and honeycombs, generally obtained by extrusion, can be used. These shapes are inherently symmetrical and/or periodical in axial direction and are limited in the number of cells per square inch.

For the state of the art sorption and catalyst systems containing a packed bed of adsorbent/catalyst material, the pellet size is usually limited by two conflicting interests:

- Small pellets will increase the sorbent/catalyst utilization. This, however comes at an increased pressure drop and increased chance of (local) fluidization and associated particle attrition.

- Larger pellets lead to a bed with lower pressure drop and decreased chance of (local) fluidization, thereby allowing for larger throughput. The adsorbent/catalyst material is, however, used less efficiently, leading to decreased separation performance and/or conversion efficiency.

Other means to incorporate structured adsorbent materials are coating of adsorbent/catalyst material on rolled metal sheets, that might be perforated or otherwise machined, coating of adsorbent/catalyst material on extruded ceramic structures (monolith or honeycomb), or extrusion of the adsorbent/catalyst material itself. For these solutions, coating procedures need to be developed and furthermore, extrusion only allows to create an axially symmetric shape.

According to the present invention embodiments, a method is provided of additive manufacturing of a 3D structure extending in an axial direction 7, wherein the 3D structure comprises a plurality of channels extending from an input surface to an output surface. The method comprises additive manufacturing of the 3D structure 1 using a base material which results in the 3D structure 1 being composed of an active material. The 3D structure 1 is a functional structure having a non-uniform axial geometry, wherein variations in the non-uniform axial geometry are provided in subsequent additive manufactured layers of the functional structure. This allows to manufacture a 3D structure which can be applied in a sorption or catalytic process. Note that the porous material may be porous as such, but is also understood to include non-porous primary parts, which in the eventually produced 3D structure form channels in between the primary parts (e.g. because of their individual shape, or by agglomeration effects). Furthermore, the active material may be non-porous material having a specific activity and/or associated properties, such as catalytic activity, sorbent activity, heat transport properties, electron conductance properties, piezoelectric properties, etc. The non-porosity of such material may be observed on micron scale, as such material may even be porous on a sub-micron scale.

In a specific group of embodiments, the base material is a slurry comprising the active material and a radiation hardening (e.g. polymer) solution. The radiation hardening polymer solution is removed after additive manufacturing of the 3D structure. As in the other embodiments, the 3D structure has a non-uniform axial geometry. A radiation hardening polymer is used to shape the entire 3D structure for proper functioning using the functional material, and a mild heat treatment is sufficient to remove the polymer and allows the functional material to remain in its original state, e.g. porous.

In a further embodiment, the non-uniform axial geometry is obtained using layer-by-layer variations in macro dimensions related to the functional structure and micro dimensions related to the porous material along the axial direction of the 3D structure.

The functional structure as described in the present invention embodiments is a structure wherein the plurality of channels 6 are arranged for one or more of fluid transfer, heat transfer, mass transfer. The geometry of the functional 3D structure (3D shaped body) results in a more efficient use of the active material and thus may lead to a more compact sorption and/or catalyst process. In addition the compact 3D structure (e.g. in the form of a shaped adsorbent and/or catalyst body) can be modular and it is possible to form building blocks for small to large-scale adsorbent and/or catalyst reactor sizes. The present invention embodiments e.g. allow to manufacture micro-reactor or integrated reactor types of process designs, optimized for specific applications. E.g. the functional structure may be arranged to mix and redistribute multi-phase streams (fluid dynamics functionality), arranged for heat exchange, heat conduction, quenching (heat management functionality), or arranged for adding/removing reactants/products, minimize diffusion lengths (mass transfer functionality), or combinations thereof.

The 3D structure manufactured according to the present invention embodiment also may result in size reduction of the process and possibly in improved performance with respect to separation performance, conversion efficiency, selectivity, conversion stability, etc. For sorption processes, this means that e.g. the mass transfer zone is reduced and that sorbent regeneration is more efficient, opening possibilities for fast cycles for sorption based separations. For catalytic processes this means that the reaction can be operated outside the diffusion limited regime, effectively requiring less catalyst material. For both type of processes, this can lead to cost reductions.

In all of the present invention embodiments, the non-uniform axial geometry of the 3D structure allows to optimize the fluid dynamic and heat management properties such that the active (adsorbent and/or catalyst) material is more efficiently used than via conventional methods, since the axial geometry can be freely chosen.

In a specific embodiment of the present invention method, the macro dimensions comprise a wall thickness of the plurality of channels. This can have advantageous effects in the field of improved heat and/or mass transfer properties.

Furthermore, the plurality of channels may have one of the following cross sectional shapes: rectangular, hexagonal, polygonal, circular, ellipsoid. The additive manufacturing process allows to have this flexibility of cross sectional shapes, and allows to further improve the efficiency of the 3D structure in a sorption or catalytic process, by combining the shaping freedom on a macro and a micro scale with the use of an (active) functional material.

Further embodiments of the present invention method allow for further optimisation by also exploiting the possibility that the 3D structure furthermore has a non-uniform radial geometry. E.g. a density of channels of the plurality of channels varies as a function of a radial distance from a central axis of the 3D structure. As a further example, cross sectional dimensions of channels of the plurality of channels may vary as a function of a radial distance from a central axis of the 3D structure.

In one exemplary group of embodiments, the additive manufacturing process is specifically based on using a slurry as the base material with a radiation hardening (e.g. polymer) solution. The (cured) radiation hardening solution is then removed after the actual additive manufacturing of the 3D structure 1 . E.g., the slurry comprises a liquid polymer having a photo-initiator (e.g. 2-4 weight%), and further comprises the active material in a dispersed powder form. This ensures that the active material is present everywhere in the 3D structure during the manufacturing process, and remains present after removing the hardened polymer from the semi-product.

In a further group of embodiments, the base material is a solution comprising a precursor material for the active material. Proper processing steps then allow to build up the functional structure by properly transforming the precursor material into the active material.

In an even further group of embodiments, the base material comprises the active material in a granulate form (or equivalent in a powder or particle form), and the 3D structure 1 is formed by connecting the granulates of active material in a predetermined pattern. This may be accomplished using a (generic) bonding process or a selective laser sintering/melting process. In view of the additive manufacturing process as used in the present invention embodiments, it is advantageous when the functional material is a non-water soluble material, as this is not affected when preparing the slurry.

As opposed to prior art methods for additive manufacturing of a 3D structure e.g. in dental applications, where non-porous ceramic materials are used, a further embodiment of the present invention comprises that the functional material is a porous ceramic material. This allows the specific application of the 3D structure provided by the present invention embodiments to be used in specific applications, such as sorption processes (where the functional material is then an acid gas adsorbing active material, such as hydrotalcite, or more specifically a K2CO3 promoted hydrotalcite of magnesium- and aluminiumoxide). Alternatively, a specific application may be catalytic processes (where the functional material is a catalytic active material). Examples of such catalytic active material are readily known to the person skilled in the art (e.g. from the prior art document WO2012/032325 mentioned in the introductory part above. E.g., a non-catalytic support material (such as alumina, hydrotalcites, and other materials in oxidic form) mixed with a catalytic active material may be used as functional material to provide a catalytic active 3D structure according to the present invention.

In a further embodiment, the method further comprises assembling a plurality of 3D structures 1 into a reactor structure, or even into an entire reactor unit. This may be accomplished by stacking several 3D structures 1 in a proper configuration (with the channels of adjacent and stacked 3D structures 1 aligned). Alternatively, or additionally, the plurality of 3D structures are each specifically designed in order to form the parts of a reactor unit, e.g. by stacking the individual 3D structures. Furthermore, the 3D structures used for assembling a reactor structure may be provided with additional assembly elements as part of the (individual) 3D structures 1 , such as fitting elements (e.g. co-operating jig-saw type of external form, to make assembly easier), lifting hooks or other handling features for individual 3D structures 1 .

The present invention embodiments thus allow to obtain a compact sorption or catalytic reactor unit in the form of a functional structure of active material by means of applying structured adsorbent/catalyst materials in the manufacturing of the 3D structures, for which the geometry can be adapted in all dimensions by applying additive manufacturing to produce such a 3D structure. The macro dimensions of the functional structure and the micro dimensions of the (porous) active material can be uncoupled, and additive manufacturing allows shape freedom in the axial direction 7, allowing increased freedom in the geometry than conventional techniques such as extrusion. Moreover, compacting of such a sorption/catalyst reactor is additionally achieved by increasing the utilization of the adsorbent/catalyst material, resulting from the improved fluid- dynamics that can be achieved when using additive manufacturing for providing the 3D structure. Additionally, multiple functions can be combined in a single 3D structure, such as heat management functions via heat exchange or conduction via the solid material, and fluid-dynamic functions, such as e.g. mixers and redistributors.

The present invention embodiments in a further aspect thus also relate to a 3D structure 1 extending in an axial direction 7, wherein the 3D structure 1 comprises a plurality of channels 6 extending from an input surface to an output surface, the 3D structure 1 being composed of an active material. The 3D structure 1 is a functional structure having a non-uniform axial geometry, wherein variations in the non-uniform axial geometry are provided in subsequent additive manufactured layers of the functional structure.

As mentioned above, a 3D structure manufactured according to the present invention can be used in the field of catalysis and/or sorption. For catalysis the field can be very wide, e.g. from large scale bulk chemical production to smaller scale fine chemical production. For the sorption application the use in Pressure Swing Adsorption (PSA) and Temperature Swing Adsorption (TSA) systems is of particular interest. For example PSA is a commonly applied separation process for the separation of gaseous components. The largest application is in the production of H2, where a PSA unit downstream a e.g. Steam-Methane Reformer (SMR) and a water-gas shift unit (WGS) separates high purity hb frorn a syngas. For h -purification in an ammonia plant, PSA is used to remove CO and CO2. Other applications are the fractionation of air into an 02-rich product and the fractionation to obtain Ar and other noble gasses from air (non-cryogenic air separation), CO2 separation in CCS schemes and CO recuperation from CO-rich feeds.

An exemplary example of a 3D structure manufactured according to the present invention embodiments, relates to a 3D structure made of a slurry (or paste, as this composition has a high viscosity), having a K2C03-promoted hydrotalcite as functional material. A 3D structure is designed having large macro-dimensions (in the order of a few cm), as well as having micro-dimensions tuned to optimize the material use (meaning minimization of diffusion resistances), to decrease axial dispersion effects, and to avoid increasing the void-fraction (e.g. a current prior art packed bed has a total void fraction of typically 0.70 m³void/m³reactor, with an inter-particle void fraction of 0.40 m³void/m³bed). If the material use and axial dispersion are improved, the void fraction can be increased somewhat, allowing to decrease the total reactor volume (and hence a costs savings).

The 3D structure manufactured is e.g. a square-channelled honeycomb consisting of multiple layers in axial direction 7 that are shifted with respect to the x-y plane, as shown and described below with reference to the exemplary embodiment of the 3D structure 1 having walls 2- 5 as shown in Fig. 1 A-D. The axial direction 7 is directed perpendicular to the views of Fig. 1 A-D, in this exemplary case parallel to the channels 6. The channel width X of the plurality of channels 6 can be chosen smaller than possible with conventional extrusion (i.e. <0.7mm).

The thickness of each of the layers applied in the additive manufacturing process should be in the mm scale to prevent building-up of laminar flow patterns. Moreover, x-y shifting of the channels means the centre of the flow pattern in the upper channel transfers to the wall in the channel below. The cross-sectional open area should be maintained in order not to create constant contraction/expansion as is the case for fluid flow through a packed bed, since this creates a lower degree of axial dispersion.

In the exemplary 3D structure 1 layers 2 and 3 (left and right hatched, respectively) are applied subsequently as shown in Fig. 1A and Fig. 1 B and share the x-direction walls. The layers 3 and 4 (cross hatched) see Fig. 1 C) then share the y-direction walls, and layers 4 and 5 (honeycomb hatching) share the x-direction walls again (as shown in Fig. 1 D). This ensures that the 3d structure 1 has its maximum strength when shifting the channel spacing in layers. Going from layer 2 to layer 3, the flow is split in half in the x-direction, whereas it is split in half in the y-direction going from layer 3 to 4. This prevents the build-up of a laminar flow pattern and plug-flow behaviour is enhanced.

This 3D structure shown is an exemplary embodiment, in more general terms, the nonuniform axial geometry of the 3D structure 1 comprises a section (layers 2-5 as described above) in an axial direction 7 having one or more channel cross connections between the plurality of channels 6. The channel cross connections allow to have a proper 3D structure wherein the walls are made of the functional material as described above, i.e. allowing efficient channel mixing. As shown in the embodiment of Fig. 1A-D, the 3D structure 1 comprises a plurality of channels parts (layers 2-5), each having channels extending from an input surface to an output surface of the associated channel part, wherein the channel alignment between two consecutively formed channel parts is shifted over a distance of less than half of an individual channel width X.

In case the thickness of the stands is significant with respect to the channel spacing in one channel part 2-5, some spacing of the stands in axial direction 7 is required not to disturb the cross- sectional area for flow too much (contraction/expansion). This is exemplified in the embodiment shown in a partial cross section in Fig. 2, showing a partial cross sectional view of two adjacent channel parts (i.e. layers 2 and 3). For thick stands (with respect to the printing resolution), the stands can have a sharp edge 2a, 3a so that the cross-sectional area for flow is constant (as indicated by 1/2 in Fig. 2). In the generic wording used above, this embodiments comprises that the ends of two consecutively formed channel parts 2, 3 are formed with a sharp edge 2a, 3a.

A further example of a 3D structure additive manufacturing process is shown in the schematic views of Fig. 3A-C. In this embodiment, the 3D structure 1 has a plurality of channel parts (layers 2-4), each having channels 6 extending from an input surface to an output surface of the associated channel part 2-4, added on top of each other as shown in the sequence of Fig. 3A to Fig. 3C, similar to the embodiment described above with reference to Fig. 1 . In this embodiment, the plurality of channels 6 in each channel part 2-4 have a hexagonal shaped cross section, and subsequent sections 2, 3, 4 are laterally shifted. To allow a proper additive manufacturing process, the 3D structure 1 is printed along a printing direction 8 as indicated (i.e. to have continuously connected layers and prevent 'hanging' or 'loose' walls of the 3D structure 1).

Fig. 4 shows a perspective view of yet another embodiment of a 3D structure 1 that can be manufactured according to the present invention. Similar to the embodiments described with reference to Fig. 1A-D and Fig. 3A-C, the 3D structure is made up of sequentially added channel parts 2-5, wherein the cross section of the associated channels 6 vary non-uniformly in the axial direction 7. Note that in this embodiment the printing direction 8 may be parallel to the axial direction 7.

When stacking shifted layers 2-5 of a square honeycomb version of the 3D structure (see description of Fig. 1A-D above), horizontal stands would appear if the printing direction 8 is parallel to the axial direction 7. These, however, cannot be easily printed using the additive manufacturing process because printing inherently means that changes in the axial direction 7 have to be smooth and not abrupt. Therefore, the whole exemplary 3D structure 1 as shown in Fig. 1 A-D and Fig. 2 is stretched in the axial direction 7 by its opposite corners such that the top view is still represented by a square. This may be accomplished in a further embodiment of the present invention, wherein the axial direction 7 of the 3D structure 1 is at an angle to a printing direction 8 of the additive manufacturing process. This would allow additive manufacturing of a 3D structure 1 with horizontal stands by ensuring all walls of the 3D structure 1 are printed in a smooth and non-abrupt manner.

The present invention has been described above with reference to a number of exemplary embodiments as shown in the drawings. Modifications and alternative implementations of some parts or elements are possible, and are included in the scope of protection as defined in the appended claims.

Claims

1 . A method of additive manufacturing of a 3D structure (1) extending in an axial direction (7), wherein the 3D structure (1) comprises a plurality of channels (6) extending from an input surface to an output surface,

the method comprising additive manufacturing of the 3D structure (1 ) using a base material which results in the 3D structure (1) being composed of an active material,

and wherein the 3D structure (1) is a functional structure having a non-uniform axial geometry, wherein variations in the non-uniform axial geometry are provided in subsequent additive manufactured layers of the functional structure.

2. The method according to claim 1 , wherein the non-uniform axial geometry is obtained using layer-by-layer variations in macro dimensions related to the functional structure and micro dimensions related to the active material along the axial direction (7) of the 3D structure (1).

3. Method according to claim 1 or 2, wherein the functional structure is a structure wherein the plurality of channels (6) are arranged for one or more of fluid transfer, heat transfer, mass transfer.

4. Method according to any one of claims 1 -3, wherein the active material is a sorption and/or catalytic active material.

5. The method according to any one of claims 1 -4, wherein the non-uniform axial geometry of the 3D structure (1) comprises a section in an axial direction (7) having one or more channel cross connections between the plurality of channels (6).

6. The method according to any one of claims 1 -4, wherein the 3D structure (1 ) comprises a plurality of channels parts (2-5), each having channels extending from an input surface to an output surface of the associated channel part, wherein the channel alignment between two consecutively formed channel parts (2-5) is shifted over a distance of less than half of an individual channel width (X).

7. The method according to any one of claims 1 -6, wherein the plurality of channels (6) have one of the following cross sectional shapes: rectangular, hexagonal, polygonal, circular, ellipsoid.

8. The method according to any one of claims 1 -7, wherein the 3D structure (1) furthermore has a non-uniform radial geometry.

9. The method according to claim 8, wherein a density of channels of the plurality of channels (6) varies as a function of a radial distance from a central axis of the 3D structure (1).

10. The method according to claim 8, wherein cross sectional dimensions of channels of the plurality of channels (6) vary as a function of a radial distance from a central axis of the 3D structure (1)·

1 1 . The method according to any one of claims 1 -10, wherein the axial direction (7) of the 3D structure (1 ) is at an angle to a printing direction (8) of the additive manufacturing process.

12. The method according to any one of claims 1 -1 1 , wherein the base material is a slurry comprising the active material and a radiation hardening solution.

13. The method according to claim 12, wherein the slurry comprises a liquid polymer having a photo-initiator, and further comprises the active material in a dispersed powder form.

14. The method according to claim 12, wherein the active material is a porous ceramic material and/or a non-water soluble material.

15. The method according to any one of claims 1 -1 1 , wherein the base material is a solution comprising a precursor material for the active material.

16. The method according to any one of claims 1 -1 1 , wherein the base material comprises the active material in a granulate form, and the 3D structure (1) is formed by connecting granulates in a predetermined pattern.

17. The method according to any one of claims 1 -16, further comprising assembling a plurality of 3D structures (1) into a reactor structure.

18. A 3D structure (1 ) extending in an axial direction (7), wherein the 3D structure (1) comprises a plurality of channels (6) extending from an input surface to an output surface,

the 3D structure (1) being composed of an active material, and wherein the 3D structure (1) is a functional structure having a non-uniform axial geometry, wherein variations in the nonuniform axial geometry are provided in subsequent additive manufactured layers of the functional structure.