Method for producing transition alumina catalyst monoliths

Abstract

A method for producing a three-dimensional porous transition alumina catalyst monolith of stacked catalyst fibers, comprising: a) Preparing a paste in a liquid diluent of hydroxide precursor particles and/or oxyhydroxide precursor particles of transition alumina particles, all particles in the suspension having a number average particle size in the range of from 0.05 to 700 μm, b) extruding the paste nozzle(s) to form fibers, and depositing the extruded fibers to form a three-dimensional porous catalyst monolith precursor, c) drying the precursor to remove the liquid diluent, d) performing a temperature treatment of the dried porous catalyst monolith precursor to form the transition alumina catalyst monolith, wherein no temperature treatment of the porous catalyst monolith precursor or porous catalyst monolith at temperatures above 1000° C. is performed and wherein no further catalytically active metals, metal oxides or metal compounds are applied to the surface.

Claims

1. A method for producing a three-dimensional porous transition alumina catalyst monolith of stacked catalyst fibers, comprising the following steps: a) preparing a suspension paste in a liquid diluent of hydroxide precursor particles or oxy-hydroxide precursor particles of transition alumina particles or mixtures thereof and which suspension can furthermore comprise a binder material selected from organic materials in a maximum amount of 20 wt %, based on the amount of hydroxide precursor particles or oxyhydroxide precursor particles of transition alumina particles or mixtures thereof and/or a plasticizer chosen from organic materials in a maximum amount of 10 wt %, based on the amount of hydroxide precursor particles or oxyhydroxide precursor particles of transition alumina particles or mixtures thereof, all particles in the suspension having a number average particle size in the range of from 0.05 to 700 μm, b) extruding the paste of step a) through one or more nozzles to form fibers, and depositing the extruded fibers to form a three-dimensional porous catalyst monolith precursor, c) drying the porous catalyst monolith precursor to remove the liquid diluent, d) performing a temperature treatment of the dried porous catalyst monolith precursor of step c) at a temperature in the range of from 500 to 1000° C., to form the transition alumina catalyst monolith, wherein no temperature treatment of the porous catalyst monolith precursor or porous catalyst monolith at temperatures above 1000° C. is performed and wherein no further catalytically active metals, metal oxides or metal compounds are applied to the surface of the transition alumina precursor particles, the catalyst monolith precursor or transition alumina catalyst monolith, wherein no dopants are added to the suspension paste and wherein the amount of impurities, selected from Li.sub.2O, Na.sub.2O, K.sub.2O, CaO, MgO, BaO, B.sub.2O.sub.3, Ga.sub.2O.sub.3, SiO.sub.2, TiO.sub.2, ZrO.sub.2, ZnO, Fe.sub.2O.sub.3, as well as chlorides, nitrates and sulfates in the transition alumina particles and hydroxide precursor particles and oxyhydroxide precursor particles thereof, is not higher than 2.5 wt %, based on the transition alumina in the monolith.

2. The method of claim 1, wherein transition alumina is the sole phase forming the catalyst monolith.

3. The method of claim 1, wherein the transition alumina is eta-, gamma- or delta-alumina, and wherein eta-, gamma- and/or delta-alumina particles are present in the suspension paste; and/or wherein gibbsite, bayerite, nordstrandite, doyleite, diaspore, boehmite, pseudoboehmite, akdalaite or tohdite, or mixtures thereof are present in the suspension paste and wherein in step d) a temperature treatment in the range of from 500 to 925° C. is performed to effect the transformation.

4. The method of claim 1, wherein in step b) the nozzles have a maximum diameter of less than 5 mm.

5. The method of claim 1, wherein the monolith of stacked catalyst fibers is three-dimensionally structured by depositing the extruded fibers in a regular, recurring stacking pattern to form a three-dimensionally structured porous catalyst monolith precursor.

6. The method of claim 1, wherein the monolith is formed from one continuous extruded fiber or from multiple individual extruded fibers.

7. The method of claim 1, wherein the regular, recurring stacking pattern is composed of stacked layers of extruded fibers, wherein in each layer at least 50 wt % of the extruded fibers are deposited parallel to each other and spatially separated from each other, or in a cobweb pattern.

8. The method according to claim 7, wherein at least 50 wt % of the extruded fibers are deposited as linear strands parallel to each other and spatially separated from each other, or wherein multiple cobweb patterns are stacked, wherein the direction of the strands in each layer is different from the direction in neighboring layers, so that a porous structure with contact points of strands of neighboring layers results.

9. The method according to claim 1, wherein the transition alumina particles, hydroxide precursor particles or oxyhydroxide precursor particles or mixtures thereof or the transition alumina catalyst monolith have an acidity in the range of from 100 to 2000 μmol/g.

10. The method according to claim 1, wherein the transition alumina catalyst monolith consists of eta-, gamma- or delta-alumina, or mixtures thereof.

11. The method of claim 1, wherein the transition alumina catalyst monolith has a BET surface area in the range of from 50 to 350 m.sup.2/g.

12. The method according to claim 1, wherein the transition alumina catalyst monolith has a porosity of at least 20%, determined by nitrogen physisorption.

13. The method according to claim 1, wherein the transition alumina catalyst monolith has a pore volume in the range of from 0.05 to 2.0 ml/g, determined by mercury porosimetry measurements.

14. The method according to claim 1, wherein the transition alumina catalyst monolith contains no dopants and the content of impurities is below 0.1 wt %.

15. The method according to claim 1, wherein the transition alumina catalyst monolith has a monomodal or polymodal pore size distribution.

16. A three-dimensional porous catalyst monolith of stacked catalyst fibers, obtainable by the method according to claim 1.

17. The monolith according to claim 16, which has a side crushing strength of at least 60 N, determined as disclosed in Oil and Gas Science and Technology-Riv. IFP, vol 55 (2000) No 1, pages 67-85.

18. A dehydration reaction which comprises utilizing the three-dimensional porous transition alumina catalyst monolith of stacked catalyst fibers according to claim 16.

19. The reaction according to claim 18, wherein methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol, tert-butanol, pentanol, hexanol, 1-phenylethanol, 2-phenylethanol, cumyl alcohol (2-phenyl-2-propanol) or glycerol are dehydrated.

20. A process for the isomerization of double bonds, cis/trans isomerization and skeletal isomerization reactions utilizing the three-dimensional porous transition alumina catalyst monolith of stacked catalyst fibers according to claim 16.

21. A method for producing a three-dimensional porous transition alumina catalyst monolith of stacked catalyst fibers, comprising the following steps: a) preparing a suspension paste in a liquid diluent of hydroxide precursor particles or oxy-hydroxide precursor particles of transition alumina particles or mixtures thereof and which suspension can furthermore comprise a binder material selected from organic materials in a maximum amount of 20 wt %, based on the amount of hydroxide precursor particles or oxyhydroxide precursor particles of transition alumina particles or mixtures thereof and/or a plasticizer chosen from organic materials in a maximum amount of 10 wt %, based on the amount of hydroxide precursor particles or oxyhydroxide precursor particles of transition alumina particles or mixtures thereof, all particles in the suspension having a number average particle size in the range of from 0.05 to 700 μm, b) extruding the paste of step a) through one or more nozzles to form fibers, and depositing the extruded fibers to form a three-dimensional porous catalyst monolith precursor, c) drying the porous catalyst monolith precursor to remove the liquid diluent, d) performing a temperature treatment of the dried porous catalyst monolith precursor of step c) at a temperature in the range of from 500 to 1000° C., to form the transition alumina catalyst monolith, wherein no temperature treatment of the porous catalyst monolith precursor or porous catalyst monolith at temperatures above 1000° C. is performed and wherein no further catalytically active metals, metal oxides or metal compounds are applied to the surface of the transition alumina precursor particles, the catalyst monolith precursor or transition alumina catalyst monolith, wherein no dopants are added to the suspension paste and wherein the amount of impurities, selected from Li.sub.2O, Na.sub.2O, K.sub.2O, CaO, MgO, BaO, B.sub.2O.sub.3, Ga.sub.2O.sub.3, SiO.sub.2, TiO.sub.2, ZrO.sub.2, ZnO, Fe.sub.2O.sub.3, as well as chlorides, nitrates and sulfates in the transition alumina particles and hydroxide precursor particles and oxyhydroxide precursor particles thereof, is not higher than 2.5 wt %, based on the transition alumina in the monolith; wherein the transition alumina catalyst monolith has a BET surface area in the range of from 50 to 350 m.sup.2/g.

22. The method according to claim 21, wherein the transition alumina catalyst monolith has a porosity of at least 20%, determined by nitrogen physisorption.

23. A method for producing a three-dimensional porous transition alumina catalyst monolith of stacked catalyst fibers, comprising the following steps: a) preparing a suspension paste in a liquid diluent of hydroxide precursor particles or oxy-hydroxide precursor particles of transition alumina particles or mixtures thereof and which suspension can furthermore comprise a binder material selected from organic materials in a maximum amount of 20 wt %, based on the amount of hydroxide precursor particles or oxyhydroxide precursor particles of transition alumina particles or mixtures thereof and/or a plasticizer chosen from organic materials in a maximum amount of 10 wt %, based on the amount of hydroxide precursor particles or oxyhydroxide precursor particles of transition alumina particles or mixtures thereof, all particles in the suspension having a number average particle size in the range of from 0.05 to 700 μm, b) extruding the paste of step a) through one or more nozzles to form fibers, and depositing the extruded fibers to form a three-dimensional porous catalyst monolith precursor, c) drying the porous catalyst monolith precursor to remove the liquid diluent, d) performing a temperature treatment of the dried porous catalyst monolith precursor of step c) at a temperature in the range of from 500 to 1000° C., to form the transition alumina catalyst monolith, wherein no temperature treatment of the porous catalyst monolith precursor or porous catalyst monolith at temperatures above 1000° C. is performed and wherein no further catalytically active metals, metal oxides or metal compounds are applied to the surface of the transition alumina precursor particles, the catalyst monolith precursor or transition alumina catalyst monolith, wherein no dopants are added to the suspension paste and wherein the amount of impurities, selected from Li.sub.2O, Na.sub.2O, K.sub.2O, CaO, MgO, BaO, B.sub.2O.sub.3, Ga.sub.2O.sub.3, SiO.sub.2, TiO.sub.2, ZrO.sub.2, ZnO, Fe.sub.2O.sub.3, as well as chlorides, nitrates and sulfates in the transition alumina particles and hydroxide precursor particles and oxyhydroxide precursor particles thereof, is not higher than 2.5 wt %, based on the transition alumina in the monolith; wherein the transition alumina catalyst monolith has a porosity of at least 20%, determined by nitrogen physisorption.

Description

EXPERIMENTAL PROCEDURE OF 3DFD PROCESS

(1) Obtaining a smooth process and a narrow control on the extrusion of thin filaments often re-quires adjustments of both the formulation of the paste and the experimental set-up. The main process parameters which have to be addressed are listed below.

(2) Parameters

(3) Particle size distribution of starting material

(4) Preparation and mixing procedure of the paste

(5) Paste formulation

(6) De-airing & paste reservoir filling

(7) Design of deposition platform

(8) Height control of nozzle

(9) Programming of turns and transition between layers

(10) Tuning extrusion speed versus movement speed

(11) Drying conditions during deposition

(12) For a further description of the process, reference can be made to the above-listed documents.

(13) The stacking design is preferably as depicted in FIGS. 1 and 2 of U.S. Pat. No. 7,527,671. Most preferred is a 1-3-1 pattern.

(14) The liquid diluent employed can be chosen from water and organic liquid diluents. Preferably, the liquid diluent contains mainly or is water.

(15) The drying is preferably performed at a temperature in the range of from −100 to 500° C., more preferably 0 to 300° C., most preferably 20 to 150° C.

(16) No treatment of the porous catalyst monolith precursor or porous catalyst monolith at temperatures above 1000° C., preferably above 975° C., more preferably above 925° C., is performed.

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

(18) The monolith can be formed from one continuous extruded fiber or from multiple individual extruded fibers.

(19) Preferably, the regular, recurring stacking pattern is composed of stacked layers of extruded fibers, wherein in each layer at least 50 wt %, more preferably at least 90 wt % of the extruded fibers or each of the fibers are deposited parallel to each other and spatially separated from each other. The parallel deposition can be in straight or curved lines. As an alternative, they can be deposited/stacked in a circular pattern with radial interlayers, like in a cobweb pattern.

(20) More preferably, at least 50 wt %, most preferably at least 90 wt % of the extruded fibers or each of the fibers are deposited as linear strands parallel to each other and spatially separated from each other, wherein the direction of the strands in each layer is different from the direction in neighboring layers, so that a porous structure with contact points of strands of neighboring stacks result. As an alternative, multiple cobweb patterns can be stacked, each pattern layer preferably rotated relative to its neighboring pattern layers.

(21) One example of stacks of layers alternating by 90° in the direction is depicted in FIGS. 1 and 2 of U.S. Pat. No. 7,527,671.

(22) The fibers or strands preferably have a thickness of 10 to 5000 μm, more preferably 10 to 1000 μm, most preferably 150 to 500 μm.

(23) They are preferably spatially separated from each other by 10 to 5000 μm, more preferably 100 to 1000 μm, most preferably 200 to 800 μm.

(24) One example is a stacking of 360 μm strands being spaced by 650 μm.

(25) Typical monolith sizes are 1 mm.sup.3 and above, preferably 1 mm.sup.3 to 100 m.sup.3, more preferably 3 mm.sup.3 to 300 m.sup.3.

(26) The monolith can have any desired shape. Preferably, it is in the form of a cylinder with circular or ellipsoidal cross section, a cuboid, a sphere, an ellipsoid, a tablet or a polygon.

(27) In comparison to this, typical extrusion processes for transition alumina catalyst extrudates yield extrudates with a minimum diameter of 1.2 mm. Depending on the formulation, these extrudates have a strength of lower than 10 N or lower than 100 N as measured by the SCS method (side crush strength).

(28) Structures made from 360 μm fibers and 650 μm interfiber distance and ABAB or ABC stacking show a side crushing strength of a 1.5 cm-1.5 cm-1.5 cm structure of more than 100 N.

(29) Thus, the process according to the present invention leads to catalyst structures having a high strength combined with high porosity and high geometric surface area and high packing density.

(30) The invention also relates to a three-dimensional porous catalyst monolith of stacked catalyst fibers, obtainable by the above process.

(31) The invention furthermore relates to the use of these monoliths as catalysts in dehydration reactions. Preferably, the reactions involve a gas phase, a liquid phase or mixed liquid/gas phase.

(32) In some embodiments the use of these monoliths as catalysts involves the dehydration of an aliphatic or benzyl alcohol to form an ether or an olefin.

(33) The term “dehydration” encompasses all chemical reactions, in which water is liberated from a chemical compound while forming a covalent bond. Preferably, alcohols or ethers are dehydrated.

(34) In some further embodiments the use of these monoliths as catalysts involves the isomerization of double bonds, cis/trans isomerization and skeletal isomerization reactions.

(35) These reactions are described for example in Ullmann's Encyclopedia of Industrial Chemistry, 2012, in the section “Aluminum Oxide”.

(36) The invention furthermore relates to a control system data set containing a plurality of control instructions which when implemented on an additive production facility prompt the additive production facility to produce a three-dimensional porous catalyst monolith or three-dimensional porous catalyst monolith precursor as described above.

(37) Additive production facilities are for example 3D fiber deposition (3DFD), 3D printing, stereolitography, fused filament fabrication (FFF) or laser sintering. These facilities or equipments are used to shape the powder or paste in order to form the three-dimensional catalyst monolith or its precursor. Thus, the additive production facility can be a 3D fiber deposition printer, 3D printer, stereolitography device or laser sintering device. These production facilities or production equipments are typically computer-controlled using a CAD file (computer aided design file). The CAD file contains the information on the three-dimensional structure of the porous catalyst monolith or its precursor and is needed to operate the additive production facility.

(38) This CAD file which can also be described as a control system data set contains a plurality of control instructions which drive the additive production facility, for example the moving nozzle in a 3D fiber deposition apparatus. The control system data set can also be described as control system data record or data drive set. The control system data set or CAD file contains all information necessary to drive the additive production facility in order to produce the monolith or monolith precursor. This meaning is encompassed by the term “prompt” as used above. The control system data set and control instructions are typically electronic data stored on appropriate data storing device which can be a CD, DVD, USB stick, hard drive or SSD drive of a computer or attached to a computer.

(39) The control system data set is typically loaded to the computer controlling the additive production facility prior to printing or extruding the 3D structure. Thus, the term “implementing” typically means loading the control system data or control instructions in a computer system which operates the additive production facility. Thus, the additive production facility then has the control instructions implemented thereon.

(40) The gamma-alumina catalyst monoliths of the present invention show a lower pressure drop, a higher activity and a higher selectivity when compared to normal extrudates. Since more external surface of the catalyst is facing reactants, more of the catalyst is immediately available. Thus, the residence time of the reactant in the catalyst can be shortened due to the faster transport. Consequently, less side products are formed.

(41) The robocasting process allows for the manufacture of three-dimensional porous catalyst monolith structures of stacked catalyst fibers, which have an increased external surface area and/or increased side crushing strength of preferably at least 50 N, more preferably at least 60 N in comparison to normal extrudates.

(42) Furthermore, higher catalyst densities in the reactor can be achieved due to well-ordered stackings of fibers. A packing density of up to 70% is possible by employing regularly stacked catalyst fibers prepared according to the present invention.

(43) The low pressure drop allows to work with smaller fiber diameters compared to single extrudates.

(44) The invention will be further illustrated by the following examples.

Example of 3D Microextruded Catalyst

(45) 3D Microextruded Porous Transition Alumina Catalyst Monolith

(46) Suspensions were made from catalyst transition alumina precursor particles, water and acid (HNO.sub.3). The ingredients were manually added and mixed to obtain the right rheological properties for extruding through a 400 μm sized nozzle. The particle size of the powder was selected to allow for this extrusion. The suspension is brought in a dispensing unit consisting of a syringe vessel and a nozzle. The unit is mounted on a micro-extruder machine. The micro-extruder is a computer numerical control (CNC) machine that is programmed to move according to a well-defined pattern and within a well-defined form. The CNC machine is programmed to continuously deposit filaments layer by layer in a predefined pattern. The deposition parameters, e.g. the distance between the nozzle and the surface of the structure, the speed of the nozzle movement, the air pressure and the temperature and airflow of the environment, etc. are regulated. A 3D-structure is built in a box by depositing the filaments layer by layer according to the programmed pattern and according to the required dimensions. All 3D structures were afterwards dried at 80° C. A) A temperature treatment at 850° C. was applied to form a porous transition alumina catalyst monolith. The dimensions of the monolithic structure after calcination were 1.91 cm×1.90 cm×0.74 cm (length, width, height). The porous properties of the monolith were found to be: BET surface area 184 m.sup.2/g, total pore volume 0.73 mL/g and SCS>720 N. B) A temperature treatment of 680° C. was applied to form a porous transition alumina catalyst monolith. Cube-type structures for experimental testing were cut out from a larger monolithic structure. The dimensions of the cube-type structures after calcination were 6.0 mm×6.0 mm×6.0 mm (length, width, height). The porous properties were found to be: BET surface area 217 m.sup.2/g, total pore volume 0.74 mL/g. SCS was measured on a representative sample of 2.17 cm×2.17 cm×0.89 cm (length, width, height) and it was found to be 400 N. C) A temperature treatment of 680° C. was applied to form a porous transition alumina catalyst monolith. Cylinder-type structures for experimental testing were cut out from a larger monolithic structure. The dimensions of the cylinder-type structures after calcination were 2.08 cm×7.0 cm (diameter, total height). The porous properties were found to be: BET surface area 217 m.sup.2/g, total pore volume 0.74 mL/g. SCS was measured on a representative sample of 2.17 cm×2.17 cm×0.89 cm (length, width, height) and it was found to be 400 N.
Ethanol Dehydration Experiments

(47) For ethanol dehydration testing of 3D-microextruded alumina catalysts, 25 cc of catalyst was loaded into a 1″ OD (0.834″ ID)×4 ft stainless steel fixed-bed downflow reactor.

(48) The reactor was equipped with a thermowell that housed five thermocouples.

(49) The reactor was heated by a furnace, with the catalyst loaded such that its location was in the middle furnace section.

(50) Catalyst mass loading was determined by multiplying catalyst bulk density by 25 cc.

(51) In the case of the cubes [Example 1B], an equal volume of inert 14×28 mesh α-alumina granules was loaded with the catalyst and served as interstitial packing.

(52) In the case of the cylinders [Example 1C], bulk density was determined based on normal packing density of cylinder elements with the following nominal dimensions: OD=20.8 mm, ID=5.56 mm, h=16.74 mm with a nominal particle mass of 2.814 g. The cylinders were formed such that they could be stacked single file in the reactor with the thermowell protruding through a center hole which was cut out.

(53) In all cases, ⅛″ Denstone spheres were used as bed support and in the pre-heat zone above the catalyst bed to provide surface area for the feedstock to vaporize.

(54) Once loaded, the reactor was purged with 300 sccm N.sub.2 for approximately 30 minutes to remove air and subsequently heated to 400° C. under flowing N.sub.2 and held for at least 4 hours.

(55) Once pretreatment of the catalyst was completed, the reactor was cooled to 375° C. and pressurized to 118 psig. Once pressure and temperature were stable, N2 flow was stopped and feed consisting of 90 wt % ethanol/10 wt % water was introduced to the reactor at a rate of LHSV.sub.EtOH=1.926 hr.sup.−1, where LHSV.sub.EtOH is defined as volumetric flow rate of ethanol per catalyst volume. The reactor was held at these conditions for approximately 24 hours.

(56) Product analysis was performed with an online gas chromatograph equipped with a flame ionization detector (FID), a heated sample injection valve, and an HP-PLOT Q capillary column (30 m×0.320 mm×20 μm). The reaction effluent was delivered to the GC through heated sample lines at ˜180-200° C. and injected approximately every 15 min.

(57) The following quantities were calculated and used to assess and compare catalyst performance: percent ethanol conversion and percent selectivity to ethylene.
Percent conversion is defined as [(molar flow rate of ethanol in−molar flow rate of ethanol out)/(molar flow rate of ethanol in)]×100.
Percent selectivity is defined as [moles ethylene produced/moles ethanol consumed]×100.

(58) The catalyst [Example 1B] displayed 87.09% conversion and 85.64% selectivity.

(59) The catalyst [Example 10] displayed 78.5% conversion and 56.32% selectivity.