MEMBRANE CONTACTOR COMPRISING A COMPOSITE MEMBRANE OF A POROUS LAYER AND A NON-POROUS SELECTIVE POLYMER LAYER FOR CO2 SEPARATION FROM A MIXED GASEOUS FEED STREAM

Abstract

A membrane contactor system for separating CO.sub.2 from a mixed gaseous feed stream comprising CO.sub.2, said contactor system comprising: (i) a composite membrane, said membrane having a permeate side and a retentate side; (ii) said retentate side being exposed to a mixed gaseous feed stream comprising carbon dioxide; (iii) said permeate side being exposed to a carbon dioxide capture organic solvent; (iv) said composite membrane comprising a porous layer and a non-porous selective polymer layer, said non-porous selective polymer layer selectively allowing transport of CO.sub.2 across the composite membrane from said mixed gaseous feed stream so that it dissolves in said capture solvent whilst limiting the transport of said capture solvent across the composite membrane.

Claims

1. A membrane contactor system for separating CO.sub.2 from a mixed gaseous feed stream comprising CO.sub.2, said contactor system comprising: (i) a composite membrane, said membrane having a permeate side and a retentate side; (ii) said retentate side being exposed to a mixed gaseous feed stream comprising carbon dioxide; (iii) said permeate side being exposed to a carbon dioxide capture organic solvent; (iv) said composite membrane comprising a porous layer and a non-porous selective polymer layer, said non-porous selective polymer layer selectively allowing transport of CO.sub.2 across the composite membrane from said mixed gaseous feed stream so that it dissolves in said capture solvent whilst limiting the transport of said capture solvent across the composite membrane.

2. The system as claimed in claim 1, wherein the porous layer is nearest the retentate side of the composite membrane and the non-porous selective polymer layer is nearest the permeate side of the composite membrane.

3. The system as claimed in claim 1, wherein the polymer of the non-porous selective polymer layer comprises the residue of a fluorocarbon monomer.

4. The system as claimed in claim 1, wherein the polymer of the non-porous selective polymer layer is a copolymer.

5. The system as claimed in claim 4, wherein the copolymer comprises monomer residues of fluorinated monomers.

6. The system as claimed in claim 1, wherein the polymer of the non-porous selective polymer layer is chemically compatible with an amine-based organic capture solvent.

7. The system as claimed in claim 1, wherein the non-porous selective polymer layer has a selectivity towards CO.sub.2 over capture solvent of larger than 100 times.

8. The system as claimed in claim 1, wherein the non-porous selective polymer layer is less than 5 microns in thickness.

9. The system as claimed in claim 1, wherein the porous layer is a polypropylene or PTFE.

10. The system as claimed in claim 1, wherein the porous layer has an MWCO of 25,000 or more.

11. The system as claimed in claim 1, wherein the organic capture solvent comprises an amine.

12. The system as claimed in claim 1, wherein the organic capture solvent has a Mw of 300 g/mol or less and consists of the atoms N, H, C and optionally O.

13. The system as claimed in claim 1, wherein the organic capture solvent comprises: diethylethanolamine (DEEA), N-methyl-1,3-propane diamine (MAPA), highly concentrated monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP), 2-dimethylaminoethanol (DMMEA), modified imidazoles, 1-(2-hydroxyethyl)piperidine (12HE-PP), 3-(diethylamino)-1,2-propanediol (DEA-12PD), 2-[2-(diethylamino)ethoxy]ethanol (DEA-EO), 2-Amino-2-methyl-1,3-propanediol (AMPD), 2-amino-2-hydroxymethyl-1,3-propanediol (AHPD), or 2-Amino-2-ethyl-1,3-propanediol (AEPD).

14. The system as claimed in claim 1, wherein the organic capture solvent comprises a mixture of at least two amine-based solvents.

15. The system as claimed in any preceding claim 1, wherein the organic capture solvent comprises a mixture of an organic base and an amine, a combination of amines or an amine functionalized ionic liquid.

16. The system as claimed in claim 1, wherein the organic capture solvent is a mixture that undergoes demixing when mixed with CO.sub.2.

17. The system as claimed in claim 1, wherein the organic capture solvent comprises a blend of a primary amine and a secondary or tertiary amine.

18. The system as claimed in claim 1, wherein the solvent is a blend of N-methyl-1,3-propane diamine (MAPA) and diethylethanolamine (DEEA).

19. The system as claimed in claim 1, wherein the composite membrane is in the form of a hollow fiber membrane.

20. The system as claimed in claim 1, wherein the non-porous selective polymer layer comprises a polymer and an inorganic component.

21. The system as claimed in claim 20, wherein the inorganic component comprises a nanoparticle such as a zeolite, MOF or is a nanostructure comprising graphene or derivative thereof.

22. A process for separating CO.sub.2 from a mixed gaseous feed stream containing CO.sub.2, said process comprising contacting said mixed gaseous feed stream with a composite membrane comprising a non-porous, selective polymer layer for separating CO.sub.2 from a mixed gaseous feed stream, said layer being carried on a porous support layer: allowing CO.sub.2 to pass through said porous support layer and said non-porous selective polymer layer to make contact with an organic capture solvent which dissolves said CO.sub.2; wherein said non porous, selective polymer layer is impermeable or of limited permeability to said capture solvent.

23. The process as claimed in claim 22 wherein the gas stream is flue gas, biogas, natural gas, or syngas.

24. The process as claimed in claim 22, wherein the solvent and gas stream are at a temperature of less than 100? C.

25. The process as claimed in claim 22, wherein the gaseous feed stream is supplied at a pressure of less than 5 bars.

Description

DESCRIPTION OF FIGURES

[0139] FIG. 1. Illustrates the process of the invention. Flue gas enters composite membrane unit (1) via a conduit (2). It can enter the unit (1) under pressure generated by fan (10). Flue gas passes through the unit (1) from bottom to top as shown. Carbon dioxide is transported across composite membrane (3), into the solvent on the permeate side of the membrane. Lean solvent enters via inlet (11) and rich solvent is removed via outlet (12). Purified gas can then be collected from outlet (4). Solvent and gas are forced in counter current flow. Heat exchange (5) is used to ensure that the solvent is piped to the unit (1) at a desired temperature. Rich solvent that has absorbed CO.sub.2 can be passed back to the heat exchange (5) and moved to stripper (6) where CO.sub.2 is separated from the solvent via heating. CO.sub.2 is removed from the top of the stripper via condenser (7) and captured. Lean solvent is removed through the bottom of the stripper for recycling either to the stripper via reboiler (8) or back to heat exchanger (5) for recycling into the separation unit (1).

[0140] FIGS. 2 to 4 show the results of the immersion experiments of the examples showing compatibility between polymer materials and the solvents of primary interest in the invention.

[0141] FIG. 5 is a theoretical scheme of the composite membrane of the invention in operation. The gas feed stream containing carbon dioxide passes in a first direction and liquid phase, i.e. solvent, passes in a counter direction. Carbon dioxide passes from the gas stream through the porous layer and then dense membrane layer to the solvent. Solvent however cannot pass through the dense layer.

[0142] FIG. 6 shows the CO.sub.2 permeability data for free standing films of Teflon AF2400 and AF1600.

[0143] FIG. 7 shows the comparison between the fluxes obtained through a Teflon AF2400 (thickness 53 ?m) for CO.sub.2, H.sub.2O, DEEA and MAPA. In particular the CO.sub.2 flux has been scaled on the real process conditions (flue gas pressure 1 bar, 13 vol % CO2), whereas the flux for the vapors have been obtained exposing the upstream side of the membrane to the pure liquids.

[0144] FIG. 8 shows the ideal selectivity (Hp: flux of amines scaled linearly with their molar concentration in the aqueous solution) achievable by using a Teflon AF2400 dense membrane based on the results reported in FIG. 11. Different concentrations of amines have been considered (e.g. xDyM=xM DEEA yM MAPA).

[0145] FIG. 9 shows the comparison between the fluxes obtained through a Teflon AF1600 (thickness 41 ?m) for CO.sub.2, H.sub.2O, DEEA and MAPA. In particular the CO.sub.2 flux has been scaled on the real process conditions (flue gas pressure 1 bar, 13 vol % CO.sub.2), whereas the flux for the vapors have been obtained exposing the upstream side of the membrane to the pure liquids.

[0146] FIG. 10 reports the selectivity which can be ideally achieved by Teflon AF1600 in the real process conditions for different amines concentrations. The same assumptions mentioned for FIG. 8 apply.

[0147] FIG. 11 reports SEM picture of the composite hollow fibers membrane obtained by coating Teflon AF2400 on a commercial porous polypropylene hollow fiber. Fluorinert FC72 produced by 3M has been used as a solvent for the fluorine-based copolymer.

[0148] FIGS. 12 to 14 summarise the carbon dioxide capacity per cycle for blends of MAPA with various solvents.

[0149] FIGS. 15a and b show the effect of adding 7.5 wt % ZIF8 to the Teflon AF2400 polymeric matrix on the amines (DEEA and MAPA) flux through a 10 ?m thick membrane. It is clear that the addition of nanoparticles is able to reduce the amine flux, due to the sieving mechanism of the ZIF-8 nanoparticles. Indeed, they have a pore size that allows CO2 permeation but prevent the permeation of larger penetrants, such as the DEEA and MAPA. In addition, larger permeability fluxes compared to the pure AF2400 have been obtained: permeability as high as 4200 Barrer has been achieved in case of AF2400+ZIF8 membrane, which represents a significant enhancement compared to the permeability of the pure polymeric phase (about 3000 Barrer).

EXAMPLES

[0150] Immersion tests

[0151] Different materials have been immersed in H.sub.2O, DEEA, MAPA and an aqueous mixture of 3M DEEA, 3M MAPA (hereinafter refereed as 3D3M) and stored at 60? C. The uptake of solvent was compared for each material.

PTFE

[0152] The PTFE (ePTFE, Gore, Porous) was initially immersed as a composite membrane (porous PTFE+porous Polyester as support layer) but the polyester was easily dissolved by the pure amines and the 3D3M solution. Thus, the test was repeated using only the porous PTFE layer. As expected the material showed a high hydrophobic behavior (negligible water uptake), but also a high affinity with the amine, especially DEEA. In case of MAPA the uptake kinetics resulted to be much slower, affecting the behavior of the mixture as well. Results are shown in FIG. 5. However, after 5 weeks of immersion, the samples appeared to show a good compatibility with the absorbent solutions. The retrievement of the initial weight of the samples after the monitoring campaign have been obtained within an error of 3%.

Polypropylene

[0153] The Polypropylene (Celgard 2400, porous) also showed hydrophobic character as expected. In addition, the amines uptake was relatively high, leading to a 3D3M solution uptake of about 0.6 g/gpol. However, no sign of relevant swelling has been observed over time, since the uptake remained stable over the entire monitoring campaign. Results are shown in FIG. 3. Furthermore, after 5 weeks of immersion the initial weight was retrieved with an error always below 6%, suggesting a good compatibility with the considered solvents.

Teflon AF2400

[0154] The Teflon AF2400 (DuPont, dense) showed the very good performance. Indeed, a negligible uptake has been observed for all the different solutions and no macroscopic changes have been detected on the immersed samples after 5 weeks, suggesting also that the material is able to ensure certain selectivity between CO.sub.2 and the absorbent solution. Results are shown in FIG. 4. Good compatibility has been observed as well, since the initial weight was retrieve within an error of 3%.

Permeability Tests

[0155] Pure gas permeability tests at different operative temperature and approximately 1.5 bar as upstream side pressure have been performed using a pure gas permeation apparatus. At 23? C. the permeability of Teflon AF2400 is about 3000 Barrer and it decreases at higher operative temperatures, although the temperature influence on this parameter is rather small (activation energy for permeation is ?3.84 kJ/mol). In case of Teflon AF1600 the permeability is smaller, due to the larger amount of PTFE monomers in the polymer chain and corresponds to 500 Barrer at room temperature operating conditions. However, the operative temperature has an opposite effect on the polymer transport properties, being the activation energy of the permeation process calculated as equal to 1.68 kJ/mol. Permeation tests of the pure liquids which are part of the third generation solvent considered as reference (H.sub.2O, DEEA and MAPA) have been carried out on thick films of the considered polymers (AF2400 and AF1600). In FIG. 7 the results obtained for a 53 ?m thick Teflon AF2400 membrane are shown. In particular the figure reports the transmembrane flux obtained for the pure chemicals (CO.sub.2, H.sub.2O, DEEA and MAPA): in case of CO.sub.2 the flux value is already scaled on the real process conditions (flue gas pressure 1 bar and 13 vol % CO.sub.2 in the stream), whereas the vapors flux are the ones obtained exposing the upstream side of the membrane to the pure liquids. Based on these data and assuming that the amine flux scales linearly with their molar concentration in the aqueous solution, the selectivities achievable by Teflon AF2400 have been calculated for different amine concentrations in the third generation solvents at room temperature conditions (FIG. 8), resulting to be always larger than 250. In case of Teflon AF1600 (FIG. 9, membrane thickness 41 ?m) lower fluxes have been achieve despite the smaller thickness compared to the AF2400 sample, likely due to the lower free volume of the polymer matrix. The flux values obtained have been used also for the calculation of the ideal selectivity which can be achieved in the real conditions of the permeation process (same assumptions considered for the AF2400 grade apply) and in this case slightly lower selectivity has been achieved, which varies between 140 and 170 in the considered concentration range of amines.

Composite Membranes

[0156] A proper procedure to obtain a composite membrane with a thin dense layer of Teflon AF2400 has been identified. In view of the good compatibility showed, porous polypropylene (PP) has been chosen as support layer. The Teflon AF2400 has been coated on porous polypropylene hollow fibers (Membrana Oxyphan, Type PP 50/200), based a literature procedure. The obtained results are reported in FIG. 10.