PROCESS FOR THE REMOVAL OF CARBON DIOXIDE FROM A GAS MIXTURE CONTAINING HYDROGEN

Abstract

A process is described for the removal of carbon dioxide from a gas mixture containing hydrogen by contacting the gas mixture with a shaped sorbent comprising a plurality of layers of photopolymerized resin containing particles of a molecular sieve carbon dioxide sorbent material.

Claims

1. A process for the removal of carbon dioxide from a gas mixture containing hydrogen by contacting the gas mixture with a shaped sorbent comprising a plurality of layers of photopolymerized resin containing particles of a molecular sieve carbon dioxide sorbent material.

2. The process according to claim 1, wherein the molecular sieve carbon dioxide sorbent material comprises a zeolite material.

3. The process according to claim 1, wherein the maximum particle size (Dv100) of the molecular sieve carbon dioxide sorbent material in the shaped sorbent is less than the layer thickness.

4. The process according to claim 1, wherein the photopolymerised resin is derived from a photopolymer comprising a mixture of multifunctional monomers and oligomers functionalized by an acrylate.

5. The process according to claim 4, wherein the photopolymer is a urethane-based photopolymer.

6. The process according to claim 1, wherein the shaped sorbent comprises from 1 to 70% by volume of molecular sieve carbon dioxide sorbent material.

7. The process according to claim 1, wherein the shaped sorbent is foamed.

8. The process according to claim 1, wherein the shaped sorbent comprises 5 to 5000 layers.

9. The process according to claim 1, wherein each layer of the plurality of layers in the shaped sorbent has a thickness in the range of from 10 to 300 μm.

10. The process according to claim 1, wherein the shaped sorbent is a particulate material with a cross-sectional length width or height, in the range of from 0.3 mm to 100 mm.

11. The process according to claim 1, wherein the shaped sorbent is a flow-through monolith with a cross-sectional length width or height, in the range of from 10 to 200 cm.

12. The process according to claim 1, wherein the gas mixture containing hydrogen is derived from an electrolysis process or from a process that converts a hydrocarbon or carbonaceous fossil fuel, biomass or municipal waste to synthesis gas containing hydrogen and carbon dioxide.

13. The process according to claim 1, wherein the hydrogen-containing gas mixture is a synthesis gas stream comprising hydrogen and carbon dioxide having a carbon dioxide content in the range 1 to 50% by volume.

14. The process according to claim 1, wherein the adsorption of carbon dioxide from the gas mixture is performed at a temperature in the range and at a pressure in the range of 1 to 100 bar abs.

15. The process according to claim 1, wherein the adsorption of carbon dioxide from the hydrogen-containing gas mixture is performed in a pressure-swing adsorption (PSA) process, a vacuum swing adsorption (VSA) process, a temperature swing adsorption (TSA) process, or a combination of two or more of these.

16. The process according to claim 1, wherein the molecular sieve carbon dioxide sorbent material comprises a zeolite material selected from zeolite 13X and zeolite 5A.

17. The process according to claim 1, wherein the maximum particle size (Dv100) of the molecular sieve carbon dioxide sorbent material in the shaped sorbent is less than a half the layer thickness.

18. The process according to claim 1, wherein the maximum particle size (Dv100) of the molecular sieve carbon dioxide sorbent material in the shaped sorbent is no less than a fifth of the layer thickness.

19. The process according to claim 1, wherein each layer of the plurality of layers in the shaped sorbent has a thickness in the range of from 20 to 100 μm.

20. The process according to claim 1, wherein the shaped sorbent is a particulate material with a cross-sectional length width or height, in the range of from 0.3 mm to 50 mm.

21. The process according to claim 1, wherein the hydrogen-containing gas mixture is a synthesis gas stream comprising hydrogen and carbon dioxide having a carbon dioxide content in the range 1 to 50% by volume, also containing water vapour, carbon monoxide and methane each in the range of 0 to 1% by volume, with the remainder of the gas mixture consisting of hydrogen.

Description

[0048] The invention will now be further described by reference to the following examples and figures in which:

[0049] FIG. 1 is a depiction of vat photopolymerisation additive-layer manufacture (VP-ALM) equipment used to prepare shaped sorbents,

[0050] FIG. 2 is a depiction of a shaped unit produced for CO.sub.2 adsorption using an additive layer manufacturing technique, and

[0051] FIG. 3 is a depiction of another shaped unit produced for CO.sub.2 adsorption using an additive layer manufacturing technique.

Example 1. Preparation of Shaped Zeolite Sorbents by Digital Light Processing

[0052] Materials and Equipment.

[0053] Sorbent Materials: 13X and 5A Zeolite Powder (Commercially Available).

[0054] Photopolymer: Genesis Flexible Development Base Resin is a commercially available photocurable resin that is composed of acrylated monomers/oligomers (urethane acrylate resin and urethane acrylate), dispersant, and photoinitiator. The photo-polymer viscosity at 20° C. is 45 mPa.Math.s. This photo-polymer was supplied and used as received from Tethon Corporation Inc.

[0055] Dispersant: Hypermer KD1 is a commercially available cationic polymeric dispersant designed for creating stable solvent-based dispersions of inorganic particulates. This dispersant was supplied by Croda International Plc.

[0056] Light blocker: LB1 and 2,5-Bis(5-tert-butyl-2-benzoxazolyl)thiophene (referred to below as BBOT) are commercially available agents for preventing over-penetration of light into the photocurable resin. These agents improve feature reproduction for the designed parameters with respect to the VP-AM shaped product. LB1 was supplied by Resyner Technologies S.L. 2,5-Bis(5-tert-butyl-2-benzoxazolyl)thiophene was supplied by Alfa Aesar.

[0057] Particle size analysis: A Malvern Mastersizer 3000 with Aero S attachment was used to measure the particle size distribution of the zeolite powders with a dispersion pressure of 2 bar. 13X powder had a particle size distribution of d.sub.10=2.7 μm, d.sub.50=5.7 μm, d.sub.90=11.6 μm. 5A powder had a particle size distribution of d.sub.10=5.0 μm, d.sub.50=11.7 μm, d.sub.90=28.2 μm.

[0058] Computer-aided design equipment: A desktop computer running “Blender” open-source software.

[0059] Vat photo-polymerisation additive-layer manufacture (VP-ALM) equipment: Bison 1000 DLP available from Tethon Corporation Inc. The equipment is similar to that depicted in FIG. 1. The equipment comprises a computer control unit (not shown) that controls the equipment, a vat or reservoir 10 for liquid photo-polymer or adsorbent mixture having a thin, transparent polymer window 14 at its base to allow light 28 from a computer-controlled digital light processor light source 16 to be projected using a mirror 18 onto the liquid layer at the bottom of the reservoir 10. The transparent polymer window is non-stick to permit detachment of the layers of cured material. A build platform 22 may be placed in the liquid photo-polymer or adsorbent mixture 24 such that there is a layer of liquid between the lower face of the build platform 22 and the non-stick polymer window 14. Once a cured layer 26 has been formed, the platform 22 and vat 10 are separated by a layer thickness and the process repeated.

[0060] Sorbent Mixtures for Thick Sheet Preparation:

[0061] Sorbent Mixture 1: 52.1% by weight Zeolite 13X in Genesis Flexible Development Base Resin (referred to below as Base Resin).

[0062] 4.60 g of Base Resin was weighed out. 5.01 g of 13X zeolite was weighed out and added to the resin within a Hauschild Speedmixer™ pot. The mixture was then mixed at 2000 rpm for 60 s. After mixing any residue of powder was returned from the sides of the container and mixed into the bulk mixture. The mixture was then mixed again at 3000 rpm for 60 s. Following this mixing procedure, the sorbent mixture was poured into the resin tank of the Bison 1000 equipment ready to produce cured material.

[0063] Sorbent Mixture 2: 50.4% by weight Zeolite 5A in Genesis Flexible Development Base Resin (referred to below as Base Resin).

[0064] 4.95 g of Base Resin was weighed out. 5.04 g of 5A zeolite was weighed out and added to the resin within a Hauschild Speedmixer™ pot. The mixture was then mixed at 2000 rpm for 60 s. After mixing any residue of powder was returned from the sides of the container and mixed into the bulk mixture. The mixture was then mixed again at 3000 rpm for 60 s. Following this mixing procedure, the sorbent mixture was poured into the resin tank of the Bison 1000 equipment ready to produce cured material.

[0065] Sorbent Mixture for Thin Sheet Preparation:

[0066] Sorbent mixture 3: 58.0% by weight Zeolite 13X in 38.9% Genesis Flexible Development Base Resin (referred to below as base resin), 3.0% Hypermer KD1, and 0.1% BBOT.

[0067] 0.6 g of Hypermer KD1 was weighed out and added to a Hauschild Speedmixer™ pot. 0.02 g of BBOT was weighed out and added to the dispersant. 11.6 g of 13X was weighed and added to the mixture. 7.78 g of Base Resin was weighed out and added to the pot. The pot was heated to 50° C. for 30 minutes prior to mixing. The mixture was then mixed at 3000 rpm for 120 s using a Hauschild Speedmixer™. After mixing any residue of powder was returned from the sides of the container and mixed into the bulk mixture. The mixture was then mixed again at 3000 rpm for 120 s. Following this mixing procedure, the sorbent mixture was formed into a thin sheet structure as set out below.

[0068] Sorbent Mixture 4: 54.7% by weight Zeolite 13X with 34.8% Genesis Flexible Development Base Resin (referred to below as base resin), 9.95% Hypermer KD1, and 0.5% LB1.

[0069] 39.8 g of Hypermer KD1 was weighed out and added to a Hauschild Speedmixer™ pot. 2.0 g of LB1 was weighed out and added to the dispersant. 218.8 g of 13X was weighed and added to the mixture. 139.2 g of Base Resin was weighed out and added to the pot. The pot was heated to 50° C. for 60 minutes prior to mixing. The mixture was then mixed at 1400 rpm for 120 s using a Hauschild Speedmixer™. After mixing any residue of powder was returned from the sides of the container and mixed into the bulk mixture. The mixture was then mixed again at 1400 rpm for 120 s. Following this mixing procedure, the sorbent mixture was poured into the resin tank of the Bison 1000 equipment ready to produce cured material.

[0070] The zeolites 13X and 5A were not pre-conditioned and so contained adsorbed water and CO.sub.2.

[0071] DLP Printer Preparation.

[0072] Methods and software are available commercially from the DLP printer providers or open-source.

[0073] The Method Used Here was as Follows: [0074] 1. Draw/Create a structure design using computer-aided design (CAD) software. [0075] 2. Import the structure design into the DLP printer equipment software for positioning on the virtual build platform and generation of automatic support structures. [0076] 3. Generate a slice file in which the design is divided up into a plurality of layers. [0077] 4. Send the slice file to the DLP printer equipment (it is necessary to ensure at this point that there is sorbent material mixture in the vat and the build platform is fixed if required).

[0078] The Genesis Flexible Development photopolymer solidifies upon exposure to 405 nm wavelength light. The Bison 1000 has a variable power light source. At the curing surface the power output is a minimum of 2.24 mW.Math.cm.sup.−2 and a maximum of 9.05 mW.Math.cm.sup.−2. This was calibrated for a peak wavelength of 405 nm.

[0079] Prior to forming the shaped sorbents, a working curve was determined to identify the exposure to the light source required to produce the desired resolution by exposing the photopolymer to a known amount of energy and then measuring the thickness of the solidified polymer. A description of photopolymerisation including how to determine the working curve may be found in “Additive Manufacturing Technologies—Rapid Prototyping to Direct Digital Manufacturing” by Ian Gibson, David W. Rosen and Brent Stucker, Spring (2010), pages 61-102.

[0080] The fully assembled reservoir was loaded with adsorbent mixture without the build platform. The pre-prepared slice file was then processed using the DLP equipment. Light was projected through the windows into the layer of liquid from the digital light processor in a pattern according to the first layer of the shaped adsorbent, thereby causing it to solidify. The light switched off after a set exposure time and the process repeated using a pattern according to a second layer of the shaped adsorbent, and so on, building up the layers until the fully-formed shaped adsorbent was realized.

[0081] The number of exposures was determined by designing an input file that, when processed by the software into slices, gave shaped adsorbents of increasing thickness depending on the corresponding number of exposures. Each exposure was 5 s at the respective power setting.

[0082] The layer thickness for each exposure is a function of the material properties of the formulation and output power of the light projector. The thickness of each area corresponding to a specific power was plotted to create a working curve.

[0083] Complex-Shape Sorbents.

[0084] Shaped sorbents comprising 55% wt zeolite 13X in the Printing Resin, prepared using this method are depicted in FIG. 2 and FIG. 3. The shaped sorbents are in the form of a triply periodic minimal surface (designated as Type #1 and Type #2 for FIG. 2 and FIG. 3, respectively). Both structures are cuboid and comprise interconnected undulating layers 30 having a plurality of through-holes 32. Type #2 has a frame 34 formed along the edges of the cube. Type #1 has outer dimensions of about 7.5 mm×7.5 mm×7.5 mm and a wall thickness of about 0.25 mm. Type #2 has outer dimensions of about 5.2 mm×5.2 mm×5.2 mm and a wall thickness of about 0.20 mm.

[0085] Thin Sheet Preparation.

[0086] A 3D Systems LC-3D Print Box (referred to below as Curing Box) was used as the UV light source to cure thin sheets of 58% 13X sorbent mixture.

[0087] An excess (1.0-2.0 g) of 58% 13X sorbent mixture was evenly deposited in a line across one end of a fluorinated ethylene polymer (referred to below as FEP) film supported by a glass pane. A ‘wet’ film of 58% 13X sorbent mixture was spread with 50 μm and 100 μm k-bars, respectively (commercially available from RK PrintCoat Instruments Ltd). Each of the wet films was then placed in the Curing Box for 1 minute and 3 minutes for the 50 μm and 100 μm thick films, respectively. After removal from the Curing Box, the sheets were rinsed with isopropyl alcohol and dried with compressed air. The sheets were carefully removed from the FEP film to produce cured sheets of and 60 μm for the 50 μm and 100 μm wet films, respectively.

Example 2. CO.SUB.2 .Capacity Measurements

[0088] Single layer “thick” sheet shaped sorbents were created using Sorbent Mixtures 1 and 2 from Example 1 to characterise adsorption properties of the materials. The fully assembled reservoir was loaded with adsorbent mixture without the build platform. The pre-prepared slice file was then processed using the Bison 1000 DLP equipment. Light was projected through the windows into the layer of liquid from the digital light processor in a pattern according to the area of the shaped adsorbent, thereby causing it to solidify. The light switched off after a set exposure time of 30 s-60 s at a power of 8.33 mW.Math.cm.sup.−2.

[0089] The shaped adsorbent was removed from the base of the reservoir and washed with isopropanol to remove unreacted sorbent mixture. The washed shaped adsorbent was then placed in a UV Curing Box and post-treated at 375-405 nm to fully cure the polymer.

[0090] Sheets of 11 cm×6 cm with thicknesses ranging between 0.15 mm and 0.25 mm were prepared by this method. Sheets were sectioned to produce small fragments to fit into a sample holder for characterisation.

[0091] Single layer “thin” sheet sorbents were created to using Sorbent Mixtures 3 from Example 1 characterise adsorption properties of the material. The adsorbent mixture was spread on a non-stick substrate with a k-bar spreader to produce ‘wet’ films of known thickness. The ‘wet’ films were placed in a Curing Box for 60-180 s and treated with 375-405 nm light.

[0092] The cured sorbent sheets were washed with isopropanol and removed from the non-stick substrate. Sheets with a final thickness of 35 μm and 60 μm were sectioned to produce smaller fragments to fit into a sample holder for characterisation

[0093] Multi-layered, complex shaped sorbents (FIG. 2 and FIG. 3) were created from Sorbent Mixture 4 to characterise adsorption properties of the material. The fully assembled reservoir was loaded with adsorbent mixture with the build platform. The pre-prepared slice file was then processed using the Bison 1000 DLP equipment. Light was projected through the windows into the layer of liquid from the digital light processor in a pattern according to the area of the shaped adsorbent, thereby causing it to solidify. The first layer was exposed for 10 s at 4.1 mW.Math.cm.sup.−2 with subsequent layers (up to the maximum required for each respective structure) being exposed for at 4.1 mW.Math.cm.sup.−2. The shaped adsorbent was removed from the build platform and washed with isopropanol to remove unreacted adsorbent mixture. The washed shaped adsorbent was then placed in a UV Curing Box and post-treated at 375-405 nm to fully cure the polymer.

[0094] Tests were performed on the cured sorbent mixtures described in example 1 (50.4% by weight Zeolite 5A in Genesis Flexible Development Base Resin, 52.1% by weight Zeolite 13X in Genesis Flexible Development Base Resin, 55% Zeolite 13X in printing resin, and 58% Zeolite 13X in “thin” sheet resin mixture).

[0095] Carbon dioxide uptake of samples was measured using a Chemisorb 2480 volumetric chemisorption analyser. Accurately weighed aliquots of approximately 0.2-1 g of material were used. Activation of samples was achieved by heating under vacuum from ambient to 120° C. at 10° C. per minute, and held at this temperature for 2 hours, followed by cooling to the analysis temperature of 35° C. The sample was then held under vacuum for a further 60 minutes. The uptake of pure carbon dioxide was measured at 100, 150, 200, 300, 400, 500, 600, 700 and 760 mmHg using an equilibration time of 10 seconds to generate an equilibrium isotherm. Using the post activation sample weight, the total gas uptake was recorded at 760 mmHg. The results were as follows:

TABLE-US-00001 Particle Thickness Size Solids CO.sub.2/g Sample Shape Zeolite (μm) (d.sub.90, μm) (%) (%) Sorbent Thick 13X 250 11.6 52 3.3% Mixture 1 Sheet Sorbent Thick 5A 150 28.2 50 9.9% Mixture 2 Sheet Sorbent Thin 13X 35 11.6 58 11.7% Mixture 3 Sheet Sorbent Thin 13X 60 11.6 58 8.2% Mixture 3 Sheet Sorbent Figure 13X 210 11.6 55 3.0% Mixture 4 2 Sorbent Figure 13X 280 11.6 55 3.5% Mixture 4 3

[0096] The results indicate that the photopolymerised samples containing 13X zeolite and 5-A zeolite are able to effectively capture carbon dioxide. The efficacy of the sorbent is improved by ensuring that the particle size embedded in the polymer is less than the layer thickness and in particular less than about ⅕.sup.th of the thickness of the composite. Complex structures made with a DLP printer have been demonstrated (FIG. 2 and FIG. 3) and characterised to confirm uptake of CO.sub.2.