PURIFICATION OF HYDROGEN GAS

TECHNICAL FIELD

Various embodiments disclosed herein generally relate to recovery and purification of H ₂ gas from mixed gas streams. More specifically, this disclosure pertains to compositions, methods of preparation of the compositions, and use of the compositions for recovery and purification of H ₂ gas from mixed gas streams.

BACKGROUND

Major barriers to the commercialization of biologically produced hydrogen gas (H ₂ ) by fermentation of carbohydrates such as sugars, starch and/or cellulose) include optimization of the bioprocess using high concentrations of a low cost substrate, as well as purification and storage of the H ₂ produced. H ₂ produced by fermentation of biomass is a mixture of H ₂ , carbon dioxide (C0 ₂ ), water vapour, and nitrogen gas (N ₂ ) which is commonly used as a carrier gas. The ¾ may also contain trace amounts of hydrogen sulphide (H ₂ S). Since H ₂ is usually produced at low rates and low pressures, it must be accumulated and stored in a storage vessel to enable transportation. Currently available storage materials require high purity H ₂ at high pressures in the range of 100 atm to 200 arm to adsorb the ¾, and contaminants exemplified by C0 ₂ , water, and N ₂ and H ₂ S can "poison" the storage materials. H ₂ produced as a bi-product of fermentation processes utilizing high substrate concentrations, for example in the range of 10% to 20%, may increase the volumetric production of H ₂ , but this approach will increase the amount of contamination that will have to be removed in order to make the H ₂ commercially useful.

The combustions of 1 kg of H ₂ can release up to 120 megajoules (MJ) of energy, not- with-standing amount of 20 MJ/kg of energy taken up by residual water vapour present in the H ₂ gas. The equivalent of this amount of energy production from oil and natural gas requires about 2.5 to about 2.75 kg of fuel. Therefore, it is apparent that on a gravimetric basis, H ₂ is one of the most efficient fuels commercially available. However, H ₂ is also the lightest element. Methane gas (CH ₄ ) is eight times heavier than H ₂ , while gasoline is ten items heavier than liquid H ₂ . Thus, despite having the largest heat of combustion per unit of mass, H ₂ exhibits a very low volumetric energy density. Advances in gas separation technologies, exemplified by improved separation membrane systems, resulting from the need to recover pure ¾ from a mixed gas stream, have the potential to improve efficiency and recovery while decreasing the costs of hydrogen production. Palladium-based (Pd) membranes appear to be viable candidates for use in membrane reactors because of their very high H permeability and catalytic activity with respect to H ₂ dissociation. However, Pd membranes are veiy expensive and are rapidly deactivated by trace concentrations of sulphur and other contaminants. Binary Pd-M alloys wherein M may be one of silver (Ag), nickel (Ni) or copper (Cu), have been proposed to improve the PD membranes' resistance to inactivation and/or deactivation by contaminants.

SUMMARY OF THE INVENTION This section provides a general summary of the disclosure and is not a comprehensive disclosure of its full scope.

Disclosed herein is are exemplary cationic zeolite compositions for use in absorbing impurities and /or selected gases from mixed gas streams. Some exemplary cationic zeolite compositions selectively sequester one of hydrogen gas, nitrogen gas, carbon dioxide, hydrogen sulphide among others. Also disclosed herein are methods for preparing the exemplary cationic zeolite compositions. Also disclosed herein are methods for the use of the exemplary cationic zeolites for separation, recovery, and purification of hydrogen gas from mixed gas streams.

BRIEF DESCRIPTION OF THE FIGURES: The drawings described herein are for illustrative purposes only of selected embodiments and are not intended to limit the scope of the present disclosure.

Figs. 1(A)- 1(D) show exemplary zeolites wherein 1(A) is Zeolite A (LTA), 1(B) is Zeolite LTL, 1(C) is Zeolite BEA, 1(D) is Gismondine GIS, 1(E) is Zeolite MFI, and 1(F) is Mordenite MOR; Fig. 2 shows an exemplary H ₂ purification system;

Fig. 3(A) is a chart showing the composition of a feroientation gas before ingress to a column packed with a cationic Zeolite 13X, while Fig. 3(B) shows the composition of the fermentation gas after it had passed through the cationic Zeolite 13X; Fig. 4 is a chart showing separation and adsorption of ¾ and N ₂ gases from a mixed gas stream. Bracketed numbers (1) and (2) refer to a modified zeolite having different mass ratios of cations to zeolite (cross-reference with Tables 2 and 3);

Fig. 5(A) is a chart showing the composition of a fermentation gas before ingress to a column packed with an exemplary cationic Zeolite A cationized with Ca ²⁺ , while Fig. 5(B) shows the composition of the fermentation gas after it had passed through the Zeolite A cationized with Ca ²⁺ ;

Fig. 6(A) is a chart showing the composition of a fermentation gas before ingress to a column packed with an exemplary cationic Zeolite Y cationized with Mg ²⁺ , while Fig. 6(B) shows the composition of the fermentation gas after it had passed through the Zeolite Y cationized with M ² ^

Fig. 7(A) is a chart showing the composition of a fermentation gas before ingress to a column packed with an exemplary cationic Zeolite A cationized with Mg ²⁺ , while Fig. 7(B) shows the composition of the fermentation gas after it had passed through the Zeolite A cationized with Mg ^2"1" ;

Fig. 8(A) is a chart showing the composition of a fermentation gas before ingress to a column packed with an exemplary cationic Zeolite 4A that was dried at 130° C, but not calcined, and cationized with Ca ²⁺ , while Fig. 8(B) shows the composition of the fermentation gas after it had passed through the cationic zeolite; Fig. 9(A) is a chart showing the composition of a fermentation gas before ingress to the column packed with an exemplary cationic Zeolite 4A that was dried at 130° C but not calcined, and cationized with Ca ²⁺ , while Figs. 9(B) and 9(C) show the composition of the fermentation gas after it had passed through the cationic zeolite;

Fig. 10(A) is a chart showing the composition of a fermentation gas before ingress to the column packed with the cationic zeolite from Fig. 8 from which previously sequestered H ₂ had lias recovered, while Fig. 10(B) shows the composition of the fermentation gas after it has passed through the cationic zeolite;

Fig. 11 is a chart showing a BET plot for the pore size distribution of Ca ²⁺ exchanged Zeolite A(2), Ca ²⁺ exchanged Zeolite A(l), and Zeolite A. BET measurement was carried out at 77K with N ₂ gas. "a" is Zeolite A, "b" is Ca ²⁺ exchanged Zeolite A(l), and "c" is Ca ²⁺ exchanged Zeolite A(2) (open circles show the adsorption curve; solid circles show the desorption curve);

Fig. 12 is a chart showing the relation between pore size and surface area of Ca ²⁺ exchanged Zeolite A(2), Ca ²⁺ exchanged Zeolite A(l) ₅ and Zeolite A by density function theory (DFT) method, "a" is Zeolite A, "b" is Ca ²⁺ exchanged Zeolite A(l), ^1L c" is Ca ²⁺ exchanged Zeolite A(2);

Fig. 13 is a chart showing XRTJ patterns for the crystallinity of two Ca ²⁺ exchanged Zeolites with Zeolite A. These patterns were carried out using four samples such as, Zeolite A, before calcination, after calcination at 500° C, and after H ₂ adsorption. Fig. 13(A) "a" is Zeolite A, "b" is Ca ²⁺ exchanged Zeolite A(l) before calcination, "c" is Ca ²⁺ exchanged Zeolite A(l) after calcination at 500° C, and "d" is Ca ^2÷ exchanged Zeolite A(l) after adsorption of H ₂ . Fig. 13(B) "a" is Zeolite A, "b" is Ca ²⁺ exchanged Zeolite A(2) before calcination, "c" is Ca ²⁺ exchanged Zeolite A(2) after calcination at 500° C, and "d" is Ca ²⁺ exchanged Zeolite A(2) after adsorption of H ₂ ; and Fig. 14 is a chart showing XRD patterns for the crysl^linity of two Mg ²⁺ exchanged

Zeolites with Zeolite Y. Mg ^2"1" exchanged Zeolites were calcinated at 500° C. "a" is Zeolite Y, "b" is Mg ²⁺ exchanged Zeolite Y(0), and V is Mg ²⁺ exchanged Zeolite Y(l).

DETAILED DESCRIPTION

The present disclosure pertains to separation, recovery and purification of H ₂ gas from mixed gas streams.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In order that the invention herein described may be fully understood, the following terms and definitions are provided herein. The word "comprise" or variations such as "comprises" or "comprising" will be understood to imply the inclusion of a stated integer or groups of integers but not the exclusion of any other integer or group of integers.

The term "about" or "approximately" means within 20%, preferably within 10%, and more preferably v thin 5% of a given value or range. Natural zeolites belong to a family of naturally occurring volcanic rocks and ash layers with unique physiochemical properties. Zeolites are crystalline hydrated alumino- silicates with a three-dimensional tnicroporous framework of [SiO] ^4" and [AIO] ^5' tetrahedralinked to each other by shared oxygen atoms thereby forming an open crystal lattice structure that can widely accept a variety of cations and molecules. These tetrahedral structures are connected via their comers thereby forming the crystal structures of the individual specific types of zeolites. The framework types do not depend of the composition or the distribution of the T-atoms exemplified by Al, P, As, Ga, Ge, B, Be, and the like, cell dimensions or symmetries. Typical zeolite framework structures are shown in Figs 1(A)- 1(F) wherein Fig.1(A) is a Zeolite A commonly referred to as LTA, Fig. 1(B) is Zeolite A commonly referred to as LTL, Fig.1(C) is a Zeolite beta commonly referred to as BE A, Fig.1(D) is a Gismondine commonly referred to as GIS, Fig.1(E) is a Zeolite Socony Mobile No. 5 commonly referred to as ZSM-5 and/or MFI, and Fig.1(F) is a Mordenite commonly referred to as MORThe negative charge in the zeolite framework is produced by aluminum (Al ³⁺ ) atom substitution for silicon (Si ⁴⁺ ), and is balanced by exchangeable cations exemplified by Na ⁺ , K ⁺ , Ca ²⁺ ₌ Mg ²⁺ . These cations play a role in determining the adsorption and gas-separation properties of the individual zeolites based on the size, charge density and distribution of cations in the zeolite porous structures. Zeolite adsorption capacity is dependent on several factors including the Si/Al ration, pore shape, pore size, the polarizing power, distribution and number of cations in the zeolite porous structures. The polarities and sizes of adsorbed molecules, the presence of water, carbonates, and other impurities on the surfaces of zeolites are other factors that can effect adsorption.

The Al ³⁺ content affects both the physical and the chemical properties of zeolites since the Si/Al ratio is an important property of zeolites. Generally, there are three classes of zeolites based on the Si/Al ratios, i.e., (i) low-silica zeolites wherein the ratio is 5<Si/Al<5, (ii) medium-silica zeolites wherein the ratio is 5<Si/A 10, and high-silica zeolites wherein the ratio is Si Al>10. The Si/Al ratio also has an effect on C0 ₂ adsorption. As the Si/Al ratio increases, the cation content and the thermal conductivity decreases. Zeolites have a greater cation exchange capacity and higher absorption for polar molecules when the Si Al ratio decreases.

Zeolites possess properties that make them ideal as strong selective adsorbents for separation of gases exemplified by N¾, I ₂ S, CO, C0 ₂ , water vapour, 0 ₂ , N ₂ , CH _2> S0 ₂ , and the like. Zeolite pore sizes range from about 2.4A to about 4.3A in diameter, which varies with zeolite type. Zeolites act as sieves on a molecular scale with respect to adsorption of chemical species. Molecules of an appropriate size and shape are adsorbed within a pore, whereas molecules that are too large or too small are excluded. Consequently, zeolites have excellent selective adsorption capacities for gases. However, it is apparent that different types of zeolites adsorb different types of gases. For example, Zeolite A, Zeolite 13X and Zeolite TRl-PE-MCM-41 have good adsorption affinities for C0 ₂ . Zeolites 5A, Zeolite 13X, Zeolite MCM-41, and Zeolite MCM-48 have good adsorption affinities for water and N ₂ .

An exemplary embodiment of the present disclosure pertains to cationized zeolites suitable for use in the separation, recovery, and purification of H ₂ from mixed gas streams. An exemplary method for cationizing zeolites generally comprises the steps of: (i) heating a selected zeolite at an elevated temperature to remove impurities from the zeolite, (ii) cationizing the purified zeolite by mixing with a selected cation solution, (iii) washing the cationized zeolite with water to remove excess cations, and (iv) calcining the cationized zeolite. A suitable temperature for removing impurities from the zeolite is selected from a range of about 120° C to about 450° C, about 130° C to about 400° C, about 140° C to about 350° C, about 150° C to about 300° C, about 160° C to about 250° C, about 170° C to about 200° C, for a period of time from a range of about 2 h to about 24 h, 4 h to about 20 h, 6 h to about 1 h ₃ 8 h to about 12 h. The purified zeolite is then cationed by mixing with a selected cation solution. Suitable cations for cationizing zeolites are exemplified by Ca ²⁺ , Mg ²⁺ , and Li ⁺ . A suitable process for cationizing a zeolite comprises mixing a purified zeolite in a cation solution at a temperature from a range of about 50° C to about 180° C, about 60° C to about 150° C, about 70° C to about 120° C for a period of time from the range of about 24 h to about 96 h, about 36 h to about 84 , about 48 hr to about 72 h. It is suitable to mix or agitate the zeolite-cation mixture during the cationizing process. After the cationizing step is concluded, the catiomzed zeolites are washed with water to remove excess cations. The cationized zeolites may be washed several times with dionized water or alternatively, with distilled water. The washed cationized zeolites are then thoroughly dried. The dried cationized zeolites are then calcined at a temperature from the range of about 400° C to about 1,000° C, 450° C to about 800° C, 500° C to about 600° Cf or a period of time from a range of about 18 h to about 72 h, about 24 h to about 60 h, about 36 h to about 48 h.

An exemplary embodiment of the present disclosure pertains to systems for separating, recovery and purification of H ₂ from mixed gas streams exemplified by gas streams such as produced in bioreactors, biorefineries, municipal waste treatment facilities, industrial waste treatment facilityes, and by industrial processes utilizing combustion of hydrocarbon liquid fuels, carbonaceous solid fuels, lignocellulosic feedstocks, and the like. The systems generally comprise a supply of a mixed gas stream which flows sequentially through a series of columns wherein: (i) the first column(s) houses silica and or silica gel for separation of water and other vapours e.g., ethanol from the mixed gas stream, (ii) a second column(s) houses a non-cationized Zeolite selected for separation of C0 ₂ from the mixed gas stream, (iii) a third column(s) houses a cationized Zeolite selected for separation of H ₂ S from the mixed gas stream, (iv) a fourth column(s) houses a cationized Zeolite selected for separation of 0 ₂ from the mixed gas stream, and (v) a hydrogen capture and purification component for recovering H ₂ from the gas stream egressing from the fourth column(s). It is to be understood that the sequence of cationized Zeolites housed within the third and fourth columns can be varied so that either one of rfcS, and 0 can be separated out from the mixed gas stream firstly or alternatively, secondly. The gas stream egressing from the fourth column and ingressing the hydrogen capture and purification component will comprise a mixture of H ₂ and N ₂ . The hydrogen capture and purification component generally comprises a column(s) housing a calciurn-cationized Zeolite A(2) which will bind H ₂ while the N ₂ will flow un-impeded through the column(s) and will egress the hydrogen capture and purification component. After a selected period of time during ingress of the H ₂ and N ₂ gas mixture into and through the hydrogen capture and purification component, the ingressing gas flow into and the egressing gas flow out of the hydrogen capture and purification component will be stopped by closure of valves thus sealing the hydrogen capture and purification component. The hydrogen capture and purification component will then be heated with a temperature from a range of about 175° C to about 450° C, 200° C to about 400° C, 225° C to about 350° C, for a period of time ranging from about 2 h to about 24 h to release H ₂ sequestered within the Ca-Zeolite A(2). The valve on the conduit egressing the capture and purification component is opened to enable recovery of the released H ₂ .

An exemplary embodiment of the present disclosure pertains to methods of separation, recovery, and purification of H ₂ from mixed gas streams. The methods generally comprise tire steps of flowing a mixed gas stream through silica gel and/or pure silica for removal of water vapours and/or ethanol vapours from the gas stream, flowing the de-watered mixed gas stream through Zeolite 13X for sequestering and removing C0 ₂ from the gas stream, then flowing the gas stream through Ca-Zeolite A(2) for sequestering and removing H ₂ from the gas stream, shutting off the flow of the mixed gas stream into the Ca-Zeolite A(2), heating the Ca-Zeolite A(2) to temperatures from the range about 225° C to about 350" C for a period of time ranging from about 2 h to about 24 h to release H ₂ sequestered within the Ca-Zeolite A(2), and recovering the released H ₂ .

Some embodiments of the present invention relate to lowing examples are provided to more fully describe the invention and are presented for non-limiting illustrative purposes. EXAMPLES Example 1 :

An exemplary H ₂ purification system 10 is shown in Fig. 2 and generally comprises a testbed 30 consisting of a series of five 30-cm long stainless steel columns 31, 32, 33, 34, 35 each having a 1.2-cm diameter. A bioreactor 20 was provided for containing biomass fermentation. A first conduit 40 interconnected the top of the bioreactor 20 with the bottom for the first column 31 in the testbed 30. A second conduit 41 interconnected the top of the first column 3 l ith the bottom of the second column 32 in the testbed 30. A third conduit 42 interconnected the top of the second column 32 with the bottom of the third column 33 in the testbed 30. A fourth conduit 43 interconnected the top of the third column 33 with the bottom of the fourth column 34 in the testbed 30. A fifth conduit 44 interconnected the top of the fourth column 34 with the bottom of the fifth column 35 in the testbed 30. A sixth conduit 45 interconnected the top of the fifth column 35 with a H ₂ purification and storage chamber 50 containing therein two columns 51, 52 connected in series by a conduit 46. The sixth conduit 45 was interconnected with the top of the first column 51 in the H ₂ purification and storage chamber 50. The bottom of the first column 51 was interconnected with the bottom of the second column 52 in the H ₂ purification and storage chamber 50 by a conduit 46. The top of the second column 52 in the ¾ purification and storage chamber 50 was interconnected with a gas output delivery conduit 47. The H ₂ purification and storage chamber 50 was provided with a temperature sensor 64. The first conduit 40 interconnecting the bioreactor 20 with the bottom of the first column 31 in the testbed 30 was provided with: (i) a valve 60 to open and shut-off the flow of gases from the bioreactor 20 into the columns in the testbed 30, (ii) a pressure regulator 61 to control the flow of gases during conveyance, (iii) a mass flow meter 62 for momtoring the flow of gases out of the bioreactor, and (v) a condensation trap (not shown) for recovery of ethanol from the flow of gases. The sixth conduit 45 interconnecting the top of the fifth column 35 in the testbed 30 and the top of the first column 51 in the H purification and storage chamber 50 was provided with a pair of valves 65, 66 with a mass flow meter 67 interposed the two valves 65, 66 for controlling the flow of gas from the testbed 30 into the H ₂ purification and storage chamber 50. The gas output delivery conduit 47 egressing from the H ₂ purification and storage cliamber 50 was also provided with a valve 67 to open, to shut-off, and to control the flow of gas out of the H ₂ purification and storage chamber 50.

The H purification and storage chamber 50 was an insulated vessel i.e., an oven, capable of maintaining temperatures within the vessel for extended periods of time, in a range of about 225° C to about 350° C.

Prior to packing the first and second columns 31, 32, the silica was heated to 350° C under vacuum to remove impurities. Zeolite 13X and Zeolite Y were heated to 180° C and 450° C respectively to remove impurities. Samples of the two zeolites were then cationized with one of Ca ²⁺ , Mg ²⁺ , and Li ⁺ at temperatures maintained between about 75° C and 120° C while the being spun at about 700 rpm to about 1,000 rpm for three days. Then, the samples were washed with deionized water to remove excess salts, and dried at about 120° C and 140° C for about 2 days. The cationized zeolites were then calcined at about 500° C for 4 h. After cooling, the cationic Zeolite 13X was used to pack the third column 33. Cationic Zeolite NaY was blended with alkaline-activated charcoal and then used to pack the fourth column 34. Cationic Zeolite Zr-Al was used to pack the fifth column 35. Cationic Zeolite A-Ca ²⁺ was used to pack the two columns 1 , 52 in the H ₂ purification and storage chamber 50.

A simulated fermentation gas comprising 10% ¾, 15% C0 _2; and 75% N ₂ was fed through the columns 31, 32, 33, 34, 35 in the testbed 30 at different flow rates. Gas samples were collected at the inlet and the outlet of each column and were analyzed by gas chromatography. The results indicated that the columns 1, 32 packed with silica gels removed all of the water vapour from the fermentation gas prior its ingress into the third column 33 in the testbed 30. The data in Figs. 3(A) collected at the inlet to the third column 33 and 3(B) collected at the outlet of the third column 33 , show that the cationic Zeolite 13X removed essentially all of the C0 ₂ from the bioreactor gas resulting in increased concentrations of the H ₂ , 0 ₂ , and N ₂ at the outlet of the third column 33 (Table 1). Table 1.

Sample site C0 ₂ H ₂ o ₂ N ₂

Column inlet.

Peak area (25μν*≤) 568.5 2380.4 28.4 2822.9

Norm (%) 9.8 41.0 0.5 48.7

Column outlet

Peak area (25μν*≤) 9.7 2931.4 63.2 3702.2

Norm (%) 0.001 43.7 LI 55.2

Example 2;

Fourteen cation exchange zeolites and two modified activated carbon materials were synthesized and tested to determine their absorption capacity for H ₂ and/or N ₂ . The zeolites tested were Zeolite A, Zeolite Y ₇ and 2eolite X ₇ each in combination with one of exchangeable cations Ca ²⁺ , Mg ²⁺ , or Li ⁺ ions. The activated carbon was modified with exchangeable cations Na and Li . The cation exchange zeolites were synthesized as follows. First, the selected individual combinations of zeolites and cations were mixed together at 700 rpm at temperatures from a range of about 70° C to about 125° C for 3-4 days. The individual combinations were then washed with deionized water and then dried at 130° C for 1-2 days. Each of the individual combinations was then calcined at temperatures from the range of about 450° C to about 550° C at a rate of temperature increase of 5° C/rmn for 4 h under vacuum. After cooling, each cation exchange zeolite was packed into a 30-cm long stainless steel column with a 1.2-cm diameter. The modified activated carbon combinations were synthesized following the same steps.

Simulated fermentation gases comprising 10% H ₂ , 15% C0 ₂ , and 75% N ₂ were fed into the catalyst-packed columns at a rate of 5 mL/min at a temperature from a range of about 18° C to about 30° C at ambient atmospheric pressure. Samples of the mixed gases were collected at each column's inlet and outlet, and were analyzed by gas chromatography. The mass ratio of cations to zeolite (gr-cation/gr-zeolite) in selected modified materials is shown in Table 2. Table 2:

„ . Mass composition

(cation:zeolite)

1 Mg-Y 2.9 g : 16.9 g

2 Mg-Y(l) 7.1 g : 30.0 g

3 Mg-A 2.9 g : 12.3 g

4 Li-Y 5.0 g : 20.0 g

5 Li A 2.0 g : 10.0 g

6 Li-Ca-Y 1.0 g : 1.5 g : 25.0 g

7 Li-Ca-Y(l) 2.5 g : 5.0 g : 20.0 g

8 Li-4a-Y 5.0 g : 10.0 g : 10.0 g

9 Ca-A 4-9 g : 12.5 g

10 Ca-A(l) 8.0 g : 12.8 g

11 Ca-A(2) 13.6 g : 13.6 g

Ca-4A

12 Ca-4A(dry) 12.0 g : 16.0 g

Ca-4A(desorption)

13 Na-Ac 4.0 g : 18.9 g

14 Li-Ac 5.0 g : 19.0 g

Of the fourteen modified materials tested, Ca-Zeolite A(2) demonstrated the greatest capacity to adsorb H ₂ (Table 3; Fig. 5). Ca-Zeolite A(2) removed over 90% of the ¾ initially present in the gas stream, and also, adsorbed a small amount ie. _s 1.74% of N ₂ . The seven best performing catalysts in this study were: (i) Ca-Zeolite A(2) over 90%, (ii) Ca-Zeolite 4A, 77%, (iii) Ca-Zeolite 1A, 76%, (iv) Mg-Zeolite A, 75%, (v) Mg-Zeolite Y, 74%, (vi) Li- Zeolite 4A-Zeolite-Y, 58%, and (vii) Li-Zeolite Y, 55% (Table 3; Fig. 4). The H ₂ adsorption capacity per g of catalyst was determined by dividing the total amount of H ₂ adsorption by the total amount of catalyst used in the column. The H ₂ adsorption capacity per g of each catalyst was: (i) Ca-Zeolite A(2), 9-5%, (ii) Ca-Zeolite A(l) , 8.68%, (iii) Mg-Zeolite A, 8.28%, (iv) Mg-Zeolite Y, 8.13%, and (v) Ca-Zeolite 4A, calcination, 7.19% (Table 3; Fig. 4).

Table 3:

H ₂ adsorption N ₂ adsorption Amount of adsorption (%) Amount of adsorption (%)

(Adsorption capacity per g of zeolite used in % g) (Adsorption capacity per g of zeolite used in % g)

Ca-A(2) 90.0 (9.45) Li-A 43.0 (4.48)

Ca-4(A) 77.2 (7.19) Mg-Y(l) 30.2 (1.97)

Ca-A(l) 75.7 (8.68) Mg-A 28.0 (3.11)

Mg-A 74.6 8.28) Ca-A 23.1 (1.97)

Mg-Y 74.0 (8.13) Li-Ca-Y 16.9 (1.68)

Li-4A-Y 58.4 (5.29) Li-Y 19.0 (1.83)

Li-A 55.2 (5.75) Ca-4A 13.2 (1.23)

Mg-Y(l) 53.8 (2.19) Na-AC 11.8 (0.98)

Li-AC 44.6 (3.64) Mg-Y 10.4 (1.14)

Na-AC 31.4 (2.60) Li-Ca-Y(l) 6.4 (0.63)

Li-Y 29.4 (1.90) L1-4A-Y 6.4 (0.58)

Li-Ca-Y(l) 25.8 (2.53) Ca-A(l) 2.5 (0.29)

Li-Ca-Y 16.9 (1.68) Li-AC 2.2 (0.18)

Ca-A 13.6 (1.16) Ca-A(2) 1.8 (0.19)

Ca ²⁺ ion-exchanged Zeolite 4A (Ca-Zeolite 4A) rapidly adsorbed H ₂ but the adsorption was unstable. In contrast, adsorption of of H ₂ by Ca-Zeolite A(l) and Ca-Zeolite A(2) was slower but more stable. Ca-Zeolite A(l) and Ca Zeolite A(2) bound much greater amounts of H ₂ .

Example 3:

Simulated fermentation gases comprising 10% H ₂ , 15% C0 ₂ , and 75% N ₂ were fed into selected individual catalyst-packed columns at a rate of 5 mL/min at a temperature from a range of about 18° C to about 30° C at ambient atmospheric pressure. Samples of the mixed gases were collected at each column's inlet and outlet, and were analyzed by gas chromatography. The cationic zeolites assessed were: (i) Zeolite A canonized with Ca ²⁺ , (ii) Zeolite Y cationized with Mg ⁱ⁺ , (iii) Zeolite 4A catio ized with Mg ²⁺ , (iv) Zeolite 4A that was dried at 130° C, and then cationized with Ca (not calcined), (v) Zeolite 4A that was dried at 130° C, then cationized with Ca ²⁺ , and then calcined, (vi) the C0 ₂ sequestration performance of the Zeolite 4A sample from (v) was assessed during the flow of gas, had been released by heating and recovered from the column. Figs. 5(A) and 5(B) show the performance of the Zeolite A cationized with Ca ²⁺ (sample i). The C0 ₂ sequestration performance of the Zeolite Y cationized with Mg ²⁺ (sample ii) is shown in Figs. 6(A) and

V849-3WO\VAN_LAW\ 1216572\4 6(B). For each of the assessments, samples were taken from the mixed gas ingressmg the column (A) ₌ and egressing from the column (B). Figs. 7(A) and 7(B) show the performance of the Zeolite Y cationized with g ^2"1" . Figs. 8(A) and 8(B) show the performance of Zeolite 4A that was dried at 130° C and cationized with Ca2+, but not calcined. Fig. 8(A) shows the gas composition before ingressing into the column and Fig. 8(B) shows the gas composition after egressing the column. Fig. 9(A) shows the gas composition before ingressing into Zeolite 4A that was dried at 130° C but not calcined, and cationized with Ca ^z+ ₃ Fig. 9(B) shows the gas composition after egressing the column, and Fig. 9(C) shows the gas composition egressing from the column (B) after 1 hr. Figs. 10(A) and 10(B) show the "second-time use" performance of the Zeolite 4A cationized with Ca ²⁺ that was retested after desorption at 350° C.

Example 4:

A BET (Brunauer, Emmett, and Teller) test was carried out for pore size analysis. All BET data were obtained from the N ₂ adsorption measurements of samples and all isotherm curves exhibited the N ₂ adsorption and desorption isotherms at 77K. The degassing time was performed for under about 8 hrs to about 12 hrs to remove impurities, including water, from the pores before carrying out BET analysis. BET analysis was carried out under a relative pressure (P Po) range between 0.05 and 0.35. The pressure range is dependent on the adsorbate gas molecule (N ₂ ) and the adsorbent material. The N ₂ adsorption/desorption isotherms of all samples show type-I and IV sorption behavior, pointing to the microporous structure characteristic. Ca-Zeolite A(2) and Ca-Zeolite A(l) showed hysteresis, but Zeolite A did not (Fig. 11).

The surface areas, pore sizes, and pore volumes by nitrogen adsorption isotherms at 77 K are shown in Table 4. The data show the order of surfaces being Zeolite A less than Ca- Zeolite A(l), which in turn, is less than Ca- Zeolite A(2). It appears that surface areas of Ca- Zeolite A (2) was higher than those of Ca-Zeolite A(l), which may be due to the differing amounts of Ca .

The BET results shown in Table 4 indicate that the surface areas of Ca- Zeolite A(2) are higher than those of Ca- Zeolite A(l), but much higher than those of Zeolite A (276.6 m2/g , 245.6 m2/g, and 68.74 m2/g, respectively). These results suggest that Na ⁺ atoms in Zeolite A were replaced by Ca atoms. Both Zeolite A and Ca- Zeolite A(l) had lower half pore widths than Ca-Zeolite A(2). The half pore width of Ca-Zeolite A(2) was 9.420 A, while

V84923WO\VAN_LAW\ 1216572\4 the half pore widths of both Zeolite A and Ca- Zeolite A(l) were 6.365 . The micropore volumes of Ca- Zeolite A(2), Ca- Zeolite A(l) and Zeolite A were 0.204 cc/g, 0.l94cc/g, and 0.0111 cc/g, respectively, based on a Density Function Theory (DFT) method. External surfaces of Zeolite A, Ca- Zeolite A(2) and Ca- Zeolite A(l) were not significantly different as measured by the t-method; 44.47 dimVg, 46.49 m ² /g, and 43.86 m ² /g, respectively. However, the micropore surface areas determined by t-method did have great differences. The micropore surface area of Zeolite A was 24.27 m ² /g, while the micropore surface areas of Ca- Zeolite A(2) and Ca- Zeolite A(l) were 230.12 m ² /g and 201.7 m ² /g, respectively.

Table 4

CaA(2) CaA(l) Zeolite A

Surface Area

Multipoint bet (m ² /g) 276.6 245.6 68.74

t-method external surface area (m ² /g) 46.49 43.86 44.47

t-method micropore surface area (m ² /g) 230.12 201.7 24.27

Pore Volume

t-method micropore volume (cc/g) 0.1117 0.9835 0.01163

DR. method micropore volume (cc/g) 0.1349 0.1205 0.03421

DFT method micropore volume (cc/g) 0.204 0.194 0.111

Pore Size

DFT method Half pore width(A) 9.420 6.365 6.365

DFT method Half pore width(A) 7.302 7.649 1.543

Fig. 12 shows the pore size distributions of Zeolite A and two types of Ca exchanged Zeolite A by the DFT method. Ca-Zeolite A(2) has a pore size range of about 20.545 A to about 29.48 A, while Ca-Zeolite A(l) had a pore size of about 18.36 A to about 27.475 A. It is apparent that Ca-Zeolite A(2) has a broader pore size range than CaA(l). However, neither Ca-Zeolite A(l) nor Ca-Zeolite A(2) displayed large differences in their external surface areas. The formation of new pores on these Ca exchanged Zeolites were observed through X-Ray Diffraction (XRD) patterns. Example 5:

Figs. 13 and 14 show the XRD patterns obtained and the crystallinity of cation exchanged zeolites based on Zeolite A and Zeolite Y. Intensities of the main peaks (100, Miller index) increased in the following order; Ca-Zeolite A(l) before calcinations was less than Ca-Zeolite A(l) after calcination, which was less than Ca-Zeolite A(l) after H ₂ adsorption and Ca-Zeolite A(2) before calcinations, which were less than Ca-Zeolite A(2) after calcinations, which was less than Ca-Zeolite A(2)-after ¾ adsorption (Figs. 13(A) and 13(B)). Peaks in the range 10-27° 2Θ vary when comparing Zeolite A. Ca-Zeolite A(l) after H ₂ adsorption displayed minimal differences in the vicinity of 6.7°, 17-18°, 25°, 28.6°, 36- 37°, and 53-55° 2Θ. Ca-Zeolite A(2) after H ₂ adsorption displayed similar results and there were minimal differences in the vicinity of 6.8°, 11.5°, 2 , 26°, 28.5°, 35-38°, and 53-72° 2Θ. Peaks after H ₂ adsorption shifted marginally to the right side from 40° 2Θ.

X-ray diffraction patterns of Mg ²⁺ exchanged Zeolite Y by ion exchange were carried out by XRD analysis (Fig.14). The crystallinity of the Zeolite Y after ion-exchange clearly was identified with that of the Zeolite A. The (220) peak of zeolite Y decreased with increasing Mg ^2* ions, while the (311) peak of zeolite Y increased with increasing Mg ²⁺ ions (note that over 43°, 2Θ represents very slight variations).