WITH ENHANCED GAS PERMEANCE

Cross-Reference to Related Applications

[0001] This application claims priority to U.S. Provisional Application No. 62/307,173, filed March 1 1 , 2016, the disclosure of which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

[0002] The invention relates to a process for making SAPO-34 zeolite membranes.

Description of Related Art

[0003] Because of their moiecular-sized pores, adsorption properties, and high thermal and chemical stabilities, zeolite membranes have been extensively studied for molecular separations. Substantial efforts have been made in developing hb-permseiective inorganic membranes for H ₂ separation from various gas mixtures. One potential application of H ₂ - selective membranes is in membrane reactors to achieve increased conversion in alkane dehydrogenation for the production of olefins. For example, H2-selective membranes may be used in propane dehydrogenation (PDH) processes for producing propylene. Conversion enhancement in this equilibrium-limited reaction can lead to significantly enhanced productivity and lower downstream separation requirements to produce pure olefins. A recent theoretical assessment of PDH membrane reactors has shown that small-pore (< 0.5 nm) H ₂ - selective zeolitic membranes with H ₂ permeances in the range of 2-6 ^χ 10 ^~7 mol.m ² s ¹ Pa- ¹ are needed for significantly increased PDH conversion (> 55%) at temperatures around 600 °C. However, the current state of the art provides nanoporous H ₂ permeation membranes that have considerably lower permeances (e.g., in the range of 0.1-2.0 ^χ 10 ^~7 moi.nr ² s ¹ Pa or suffer from low stability at high temperature.

[0004] SAPO-34 is a promising nanoporous zeolite candidate due to its high H2 selectivity over hydrocarbons combined with a good H ₂ permeability of ~3 ^χ 10 ^~13 mol.m ^"1 s- ¹ Pa ^_1 at 600 °C. Several reports have focused on the synthesis of small-pore SAPO-34 zeolite membranes (effective pore diameter ~ 0.38 nm) to achieve dramatically increased H ₂ or C0 ₂ selectivity over relatively larger molecules such as CH ₄ , C3H6, and C3H8 through the size exclusion effect. Although several groups reported H ₂ -selective SAPO-34 membranes, such membranes were several microns thick (> 5-10 m) and thus do not meet the permeance requirement. A SAPO-34 membrane having thickness less than 2 microns while maintaining good H2 seieciiviiy would be exceedingly useful as a H2-selective zeoliie membrane in the PDH process.

SUMMARY OF THE INVENTION

[0005] The invention relates to processes for making SAPO-34 membranes with less than 2 micron thickness and good H2 selectivity, and the use of these membranes as H2-selective zeolite membranes in the PDH process.

[0006] The invention provides methods for making silicoaluminophosphate (SAPO) membranes on a porous support, the methods comprising:

coating SAPO seeds on a porous support;

providing a zeolite membrane on the seeded support from an aqueous templating solution comprising an alkali templating agent and a non-alkali templating agent; and

calcining the zeolite membrane to remove the templating agents,

wherein the SAPO seeds have a size of 2 μηι or less.

[0007] The invention also provides SAPO membranes made by the methods described above.

[0008] The invention also provides methods for separating a first gas component from a gas mixture comprising a first gas component and a second gas component, the methods comprising:

providing a porous silicoaluminophosphate (SAPO) membrane having

a first side and a second side, wherein the first gas component selectively passes from the first side to the second side over the second gas component, and

a thickness of 2 μνη or less;

applying a feed stream containing the gas mixture to the first side of the membrane at a temperature in the range of about 500 °C to about 700 °C; and

applying a sweep stream to the second side of the membrane, wherein the sweep stream maintains a lower partial pressure of the first gas component on the second side of the membrane than on the first side of the membrane, thereby producing a feed stream enriched in the second gas component on the first side of the membrane.

[0009] The invention also provides methods for the dehydrogenation of an alkane, e.g., propane, and the separation of resulting hydrogen from the resulting alkene, e.g., propylene. The methods comprise: providing a porous silicoaluminophosphate (SAPO) membrane having a first side and a second side, wherein the resulting hydrogen selectively

passes from the first side to the second side over the alkane, a thickness of 2 m or less, and

a dehydrogenation catalyst on the first side of the membrane; applying a feed stream containing a mixture of the hydrogen and alkane to the first side of the membrane at a temperature in the range of about 500 °C to about 700 °C;

applying a sweep stream to the second side of the membrane, wherein the sweep stream maintains a lower partial pressure of the resulting hydrogen on the second side of the membrane than on the first side of the membrane, thereby producing a feed stream enriched in the alkane on the first side of the membrane.

[0010] These and other features and advantages of the present invention will be more fully understood from the following detailed description of the invention taken together with the claims. It is noted that the scope of the claims is defined by the recitations therein and not by the specific discussion of features and advantages set forth in the present description.

DESCRIPTION OF THE DRAWINGS

[0011] FIGURE 1a shows a SEM image of a typical SAPO-34 seed layer obtained by the mechanical-coating process on the inner surface of a-alumina supports, using a 1 wt% seed suspension of ~1 μιη SAPO-34 seeds.

[0012] FIGURE 1b shows a SEM image of a typical SAPO-34 seed layer obtained by the dip-coating process on the inner surface of a-alumina supports, using a 1 wt% seed suspension of -220 nm SAPO-34 seeds.

[0013] FIGURE 2 shows the C3H8 selectivity as a function of temperature in the separation of a H2 C3H8 equimolar mixture by the tubular SAPO-34 zeolite membranes.

[0014] FIGURE 3a shows the propane conversion for different weight hourly space veiocities (WHSVs) of a PDH reaction using a packed-bed membrane reactor (PBMR) containing SAPO-34 membranes T1 , T2, T4, and T5 at 600 °C.

[0015] FIGURE 3b shows the propylene selectivity for different weight hourly space velocities (WHSVs) of a PDH reaction using a packed-bed membrane reactor (PBMR) containing SAPO-34 membranes T1 , T2, T4, and T5 at 600 °C.

[0016] FIGURE 3c shows the propylene yield for different weight hourly space velocities (WHSVs) of a PDH reaction using a packed-bed membrane reactor (PBMR) containing SAPO-34 membranes T1 , T2, T4, and T5 at 600 °C, medium-pore membranes (MR MFI), and packed-bed reactor (PBR).

[0017] FIGURE 4 shows a membrane reactor system and PBMR configuration according to an embodiment of the invention.

[0018] FIGURE 5 shows SEM images of the secondary grown SAPO-34 zeolite membranes; T1 (a1 and a2), T2 (b1 and b2), T3 (d and c2), T4 (d1 and d2) and T5 (e1 and e2).

DETAILED DESCRIPTION OF THE INVENTION

[0019] The term "SAPO" refers to a micro pore zeolite containing silicon, aluminum, phosphorous and oxygen.

[0020] The term "dip coating" refers to a method of coating the surface of a substrate with a material by immersing the substrate into a mixture containing the material or a precursor of the material, removing the substrate from the mixture, and then drying the coated substrate.

[0021] The term "rub coating" refers to a method of coating the surface of a substrate with a material by physically rubbing the substrate with a mixture containing the material or a precursor of the material, and then drying the coated substrate.

[0022] The term "size" of a SAPO seed refers to a seed in which all dimensions conform to the stated size. For example, a seed having a size of 1 or less has no dimension greater than 1 μηι.

[0023] The term "templating agent" refers to a species added to the synthesis media to aid in and/or guide the polymerization and/or organization of the building blocks that form the crystal framework.

[0024] The term "calcining" refers to a thermal treatment process to bring about a thermal decomposition, phase transition, or removal of a volatile fraction. As used herein, "calcination" and "calcining" refer to a process carried out in air, i.e., in the presence of oxygen, at a temperature of between about 500°C and 700°C, and more preferably at about 600 °C. Calcination is carried out for a period of time sufficient to effect the desired reaction. Typically, calcination is carried out for at least about 4 hours. In other embodiments, calcination is carried out for from about 6 hours, and in other embodiments, about 8 hours, or 10 hours.

[0025] The term "permeance" refers to the degree to which a material (e.g., a gas) passes or is transmitted through another substance (e.g., a membrane). Thus, in the context of this disclosure, permeance can refer to the degree to which a gas flows through a membrane. Permeance is determined according to the ratio of flux (the quantity of mass diffusing through and perpendicular to a unit cross-sectional area of material per unit time) under an applied pressure difference.

[0026] The term "selectivity" or "permselectivity" refers to the ratio of the permeance of two materials (e.g., gases).

[0027] The invention provides methods for making a silicoaluminophosphate (SAPO) membrane on a porous support. The methods comprise:

coating SAPO seeds on a porous support;

providing a zeolite membrane on the seeded support from an aqueous templating solution comprising an alkali templating agent and a non-alkali templating agent; and

calcining the zeolite membrane to remove the templating agents,

wherein the SAPO seeds have a size of 2 m or less, preferably less than 1 .5 μιη, more preferably less than 1 μιη, and even more preferably less than 750 nm.

[0028] The size of the SAPO seeds may influence the thickness of the resulting SAPO membrane. Typically, the thickness of the SAPO membrane will not exceed the size of the SAPO seed. Thus, to provide a membrane with a thickness of 2 μηι or less, the size of the SAPO seed is 2 μηι or less. In some embodiments, the SAPO seeds have a size less than 2 μιη. In other embodiments, the SAPO seeds have a size pf 500 nm or less, of 400 nm or less, or of 300 nm or less.

[0029] The SAPO seeds may be coated on the porous support according to any applicable method known in the art. In some embodiments, the seeds are dip-coated. In other embodiments, the seeds are rub-coated.

[0030] in some embodiments, the SAPO membranes produced by the methods disclosed herein have a thickness of about 2 μίη or less. In other embodiments, the membranes have a thickness of about 2 μιη to about 1.5 μιτι, or about 1.5 μιη to about 1 .0 μιη, or about 1.8 μιτι to about 1 .4 μιη, or about 1.6 μιη to about 1.2 μιη, or about 1.4 μιη to about 1.0 μηι, or about 1 .2 μιη to about 0.8 μιη, or about 1.0 μιη to about 0.6 μιη, or about 1.5 μιη to about 0.9 μιη, or about 1 .4 μιη to about 0.9 μίπ, or about 1.3 μιη to about 0.9 μηι, or about 1.2 μΓΠ to about 0.9 μιη, or about 1 .1 μπ to about 0.9 μηι, or 1.5 μπι to about 1.0 μηι, or about 1.4 μιη to about 1.0 μιη, or about 1 .3 μιη to about 1.0 μιη, or about 1.2 μηι to about 1 .0 μιη, or about 1 .1 μηι to about 1.0 μιη, or 1 .5 μηι to about 1.1 μιη, or about 1.4 μηι to about 1 .1 μηι, or about 1 .3 μιη to about 1.1 μηι, or about 0.9 μηι to about 0.5 μιη, or about 1.2 μηι to about 1 .1 μιτι. In some embodiments, the SAPO membranes produced by the disclosed methods have a thickness of about 2 μιτι to about 0.8 μιη, or about 2 μιη to about 0.9 μιτι, or about 2 μιη to about 1 .0 μιη, or about 2 μηι to about 1.1 μιη. In some embodiments, the SAPO membranes produced by the disclosed methods have a thickness of about 1.6 μιη to about 0.8 μιτι, or about 1.6 μιη to about 0.9 μιη, or about 1.6 μιη to about 1.0 μιη, or about 1.6 μιη to about 1.1 μίη.

[0031] In some embodiments, the membranes produced by the methods disclosed herein are assessed based on characteristics other than membrane thickness. The membrane may also be useful for the separation of gas mixtures if it has certain permeance and selectivity characteristics. In some embodiments, the SAPO membrane has a single gas permeance of about 1 *10 ⁷ mol/(m ² *s*Pa) to about 1 *10 ⁶ mol/(m ² *s*Pa) and/or a separation selectivity of about 5 to about 100 at a temperature in the range of about 15 °C to about 700 °C. Permeance and selectivity measurements are typically performed according to the procedure described in Example 3 below.

[0032] In some embodiments, the SAPO membranes have a permeance of about 1*10 ⁷ mol/(m ² *s*Pa) to about 1 ^* 10 ⁶ moi/(m ² *s*Pa). In other embodiments, the SAPO membranes have a permeance of about 1 ^* 10 ⁷ mol/(m ^2* s ^* Pa) to about 5 ^* 10 ⁷ mol/(m ² *s*Pa), or about 5*10 ^"7 mol/{m ² *s*Pa) to about 1 ^* 10 ⁶ mol/(m ² *s*Pa). In other embodiments, the SAPO membranes have a permeance of about 1*10 ⁷ mol/(m ² *s ^* Pa) to about 3 ^* 10 ^~7 mol/(m ^2* s*Pa), about 2*10 ^"7 mol/(m ² *s*Pa) to about 3 ^* 10 ⁷ moi/(m ² *s*Pa), about 3*10 ⁷ mol/(m ^2* s ^* Pa) to about 5*10 ^"7 mol/(m ² *s*Pa), about 5*10 ⁷ mol/(m ² *s ^* Pa) to about 7 ^* 10 ⁷ mol/(m ² *s*Pa), about 6*10 ⁷ mol/(m ^2* s*Pa) to about 8*10 ⁷ mol/(m ² *s*Pa) or about 8*10 ⁷ moi/(m ² *s*Pa) to about 110- ⁶ moi/(m ² *s*Pa).

[0033] In some embodiments, the SAPO membranes have a separation selectivity of about 5 to about 100 at a temperature in the range of about 15 °C to about 700 °C. In other embodiments, the SAPO membranes have a separation selectivity of about 5 to about 75, or about 5 to about 50, or about 5 to about 25, or about 5 to about 15, or about 5 to about 10, or about 10 to about 75, or about 10 to about 50, or about 10 to about 25, or about 10 to about 15, about 25 to about 75, or about 25 to about 50, or about 50 to about 75, or about 75 to about 100 at a temperature in the range of about 15 °C to about 700 °C. In certain embodiments, the SAPO membranes have a separation selectivity of about 15 to about 25 at a temperature in the range of about 15 °C to about 700 °C. In other embodiments, the SAPO membranes have a separation selectivity of any of the above ranges at a temperature in the range of about 15 °C to about 100 °C, or about 100 °C to about 200 °C, or about 200 °C to about 300 °C, or about 300 °C to about 400 °C, or about 400 °C to about 500 °C, or about 500 °C to about 600 °C, or about 600 °C to about 700 °C.

[0034] In embodiments where the membranes produced by the disclosed methods are assessed based on their permeance and selectivity characteristics, the permeance characteristics may be defined by the permeance of H2 and its selectivity characteristics may be defined by the selectivity of the membrane for permitting passage of H2 over C3H8.

[0035] In certain embodiments the membranes produced by the methods disclosed herein are free or substantially free of defects. As used herein the term defect refers to holes or other imperfections in the membrane. Further, the term defect refers to holes in the membrane that are larger than pores and lead to elevated or significantly elevated permeance values. Without being bound by any particular theory, it is believed that the lack of defects in the disclosed membranes leads to their useful and desirable permeance characteristics.

[0036] The porous support for use in the present invention is not particularly limited as long as it is porous and chemically stable to enable crystallization of a zeolite membrane on the its surface. The porous support is typically inorganic, and can be, for example, a ceramic sintered body such as silica, a-a!umina, γ-alumina, mullite, zirconia, titania, yttria, silicon nitride or silicon carbide, a sintered metal such as iron, bronze and stainless steel or glass, or a carbon molding. The porous support should have a higher permanence value that the SAPO membrane that it supports. In some embodiments, the porous support has a permeance greater than 3x the permeance of the SAPO membrane it supports.

[0037] In some embodiments, the porous support comprises a ceramic or metallic material. In other embodiments, the porous support comprises alpha-alumina, silica, mullite or stainless steel.

[0038] In some embodiments, the SAPO is SAPO-34. The SAPO-34 may be a silicoaluminophosphate having a molecular formula of Si _x Al _y Pz02, wherein 0 < x < 1 , 0 < y < 1 , and 0 < z < 1.

[0039] The seeded support is immersed in the templating solution and the templating solution is heated. The temperature of the templating solution may be varied according to the type of templating agent(s) used, and the desired characteristics of the resulting SAPO membrane. In some embodiments, the templating solution is heated to between about 100 °C and 300 °C. In other embodiments, the temperature is between about 150 °C and about 250 °C.

[0040] The amount of time seeded support is immersed in the templating solution may be varied according to the type of templating agent(s) used, and the desired characteristics of the resulting SAPO membrane. In some embodiments, the seeded support is immersed for about 1 to about 48 hours. In some embodiments, the seeded support is immersed for about 2 to about 24 hours, while in other embodiments, the time may be about 6 to about 12 hours or about 12 to about 24 hours. In some embodiments, the seeded support is immersed in the templating solution and the templating solution is heated to between about 150 and 250 °C for about 2 to about 24 hours.

[0041] The aqueous templating solution can comprise an alkali templating agent and a non- alkali templating agent. The pH of the templating solution, and the concentration and ratio of the templating agents can be independently adjusted to control the thickness of the resulting SAPO membrane. In some embodiments, the ratio of the templating agents is sufficient to provide a templating solution with a pH of about 8 or less. In some embodiments, the pH of the templating solution is about 5.0 to about 8.0, or about 6.0 to about 8.0, or about 7.0 to about 8.0, or about 5.0 to about 7.0, or about 5.0 to about 6.0, or about 6.0 to about 8.0, or about 7.0 to about 8.0, or about 6.5 to about 8.0, or about 6.5 to about 7.5, or about 6.5 to about 7.0, or about 6.0 to about 7.5, or about 6.0 to about 6.5, or about 7.5 to about 8.0.

[0042] In certain embodiments, the ratio of alkali templating agent to non-alkali templating agent is about 3.0:1.0 to about 1.0 to 1.0. In some embodiments, the ratio is about 2.0:1.0 to about 1.0 to 1.0, or about 2.0:1.0 to about 1.5 to 0.5, or about 1.0:1.0 to about 1.5 to 0.5. In other embodiments, each of the above ratios may include about 100 to about 200 parts water. In some embodiments, the water is present in about 120 to about 180 parts, or about 120 to about 160 parts, or about 100 to about 150 parts, or about 150 to about 200 parts.

[0043] The templating agent can be any organic compound capable of directing the construction of the zeolitic structure, or as is known in the art, the pore dimension. Because the arrangement of the atoms in the lattice of the zeolite is influenced by the type, dimension and structure of the templating agent, the templating agent can direct the structure of the pores and channels in the zeolite.

[0044] Typical templating agents include salts and bases of quaternary ammonium. Examples may include alkylammonium salts and hydroxides. Other compounds such, as for example, corona ethers, tri-, di- and mono-a!ky!amines, diamines, cyclic and polycyclic amines, amines and po!yamines can also be conveniently used in the preparation of zeolites which can be treated according to the process of the invention.

[0045] The alkali templating agent can be a tempiating agent known in the art capable of producing an alkaline environment in aqueous solution. For example, the alkali templating agent may be an ammonium hydroxide salt. In some embodiments, the alkali templating agent can be a tetralkylammonium hydroxide. For example, the alkali templating agent can be a tetrapropylammonium hydroxide (TPOH).

[0046] The a non-alkali templating agent can be a templating agent known in the art in that does not produce an alkaline environment in aqueous solution. In some embodiments, the non-alkali templating agent can be a tetralkylammonium salt, such as, for example, tetralkylammonium bromide. For example, the non-alkali templating agent can be a tetrapropylammonium bromide (TPABr).

[0047] The aqueous templating solution may comprise a mixture of a tetralkylammonium hydroxide and a tetralkylammonium bromide. In some embodiments, the templating solution comprises an aqueous mixture of tetrapropylammonium hydroxide (TPAOH) and tetrapropylammonium bromide (TPABr).

[0048] Following SAPO crystal synthesis, the SAPO membranes can be calcined in air to substantially remove the organic template material. In some embodiments, the calcination temperature is between about 500 K and about 700 K. In other embodiments, the calcination temperature is between about 450 K and about 550 K. The calcination time is between about 4 hours and about 24 hours. In some embodiments, the zeolite membrane is calcined in air for less than 12 hours. The calcination time may be adjusted according to the composition of the SAPO membrane and the templating agents used. Longer times may be required at lower temperatures in order to substantially remove the template material. In some embodiments, the calcination time may be between 5 and 7 hours, in other embodiments, the calcination time may be less than 12 hours. The heating rate (i.e., the time in which the temperature is increased from ambient to the calcination temperature) during calcination should be slow enough to limit formation of defects such as cracks, in some embodiments, the heating rate is less than about 2.0 °C/min. In other embodiments, the heating rate is less than about 1 °C/min. Similarly, the cooling rate must be sufficiently slow to limit membrane defect formation. In some embodiments, the cooling rate is less than about 2.0 °C/min. In other embodiments, the cooling rate is less than about 1 °C/min.

[0049] The invention also provides methods for separating a first gas component from a gas mixture comprising a first gas component and a second gas component, the method comprising:

providing a porous silicoalumtnophosphate (SAPO) membrane having

a first side and a second side, wherein the first gas component selectively passes from the first side to the second side over the second gas component, and

a thickness of 2 μνη or less;

applying a feed stream containing the gas mixture to the first side of the membrane at a temperature in the range of about 500 °C to about 700 °C; and

applying a sweep stream to the second side of the membrane, wherein the sweep stream maintains a lower partial pressure of the first gas component on the second side of the membrane than on the first side of the membrane, thereby producing a feed stream enriched in the second gas component on the first side of the membrane.

[0050] In some embodiments of the method, the SAPO membrane is provided on one side of a porous support. In other embodiments, the membrane has a first gas component permeance of about 1*10 ⁷ mol/(m ² *s ^* Pa) to about 1*10 ⁶ mol/(m ² *s ^* Pa). In certain embodiments, the membrane has a separation selectivity of about 5 to about 100 for the first gas component over the second gas component at a temperature in the range of about 15 ^C' C to about 30 °C. in certain embodiments, the membrane has a separation selectivity of about 5 to about 100 for the first gas component over the second gas component at a temperature in the range of 600-700 °C. In other embodiments, the membrane has a permeance and a separation selectivity of any membrane described herein.

[0051] The methods for separating a first gas component from a second gas component may be carried out in a propane dehydrogenation (PDH) reactor, such as, for example, the system as described in Figure 4. The methods may involve placing the membrane in a vessel, typically on a porous support. The porous support may be any known in the art, for example, an a-alumina tube. As used herein, the thickness between the first and second side represents a measurement of the thickness of the membrane without the porous support.

[0052] The feed stream containing the gas mixture is applied to the first side of the membrane, and the first gas component selectively permeates through the membrane (i.e., from the first side to the second side), while the second gas component remains on the first side of the membrane. The feed stream may comprise a gas mixture having components to be separated. The gas mixture comprises two or more gas components. In some embodiments, the gas mixture comprises a first gas component and a second gas component. In some embodiments, the first gas component is H2 and the second gas component is C ₃ H ₈ , C3H5, Ar, or N ₂ . In some embodiments, the first gas component is H ₂ and the second gas component is CsHs. In other embodiments, the first gas component is N ₂ and the second gas component is CH ₄ or other light hydrocarbons associated with natural gas. In embodiments where the first gas component is N ₂ and the second gas component is CH ₄ , the applying a feed stream containing the gas mixture to the first side of the membrane may be performed at room temperature.

[0053] The sweep stream is applied to the second side of the membrane and maintains a lower or equal partial pressure of the first gas component on the second side of the membrane than on the first side of the membrane. This produces sweep stream that is enriched with the first component on the second side of the membrane and a feed stream enriched in the second gas component on the first side of the membrane. The sweep stream may comprise an inert gas such as argon.

[0054] In some embodiments, a packed catalyst is provided on the first side of the membrane. The packed catalyst may be any catalyst known in the art that is compatible with the method described herein. In some embodiments, the catalyst mediates reaction between two of more components in the gas mixture. In other embodiments, the catalyst may catalyze a reaction that produces one of the gas components of the gas mixture that is to be separated from the other components of the mixture.

[0055] In some embodiments, the catalyst may be a hydrogenation or dehydrogenation catalyst. The catalyst may be used for propane dehydrogenation (PDH), that when combined with the methods for separating components from a gas mixture as described herein, provides, through selective permeation of product hb, enhanced propane conversion.

[0056] The vessel is placed in a heater or furnace to maintain the desired temperature at which the separation of the gas mixture occurs. Optionally, the first and/or second sides of the membrane can be connected to an analytical instrument for analyzing the composition of the resulting gases. For example, the vessel may be connected to chromatographic and/or mass spectrum instruments.

[0057] The invention also provides methods for separating a first gas component from a gas mixture comprising a first gas component and a second gas component, the methods comprising:

providing a porous silicoaluminophosphate (SAPO) membrane having

a first side and a second side, wherein the first gas component selectively passes from the first side to the second side over the second gas component,

a thickness of 2 μιη or less, and

a first gas component permeance of about 1 ^* 10 ⁷ mol/(m ^2* s ^* Pa) to about 1 *10- 6 mol/(m ² *s*Pa) and/or a separation selectivity of about 5 to about 100 for the first gas component over the second gas component at a temperature in the range of about 15 °C to about 700 °C;

applying a feed stream containing the gas mixture to the first side of the membrane at a temperature in the range of about 500 °C to about 700 °C; and

applying a sweep stream to the second side of the membrane, wherein the sweep stream maintains a lower partial pressure of the first gas component on the second side of the membrane than on the first side of the membrane, thereby producing a feed stream enriched in the second gas component on the first side of the membrane.

[0058] In some embodiments of the method, the SAPO membrane is provided on one side of a porous support. In other embodiments, the membrane has a first gas component permeance of about 1*10 ⁷ mol/(m ² *s ^* Pa) to about 1*10 ⁶ mol/(m ² *s ^* Pa). In certain embodiments, the membrane has a separation selectivity of about 5 to about 100 for the first gas component over the second gas component at a temperature in the range of about 15 ^C 'C to about 30 °C. in certain embodiments, the membrane has a separation selectivity of about 5 to about 100 for the first gas component over the second gas component at a temperature in the range of 600-700 °C. In other embodiments, the membrane has a permeance and a separation selectivity of any membrane described herein.

[0059] The invention also provides methods for the dehydrogenation of an alkane and the separation of product hydrogen from the residual alkane and product alkene, the methods comprising:

providing a porous silicoaluminophosphate (SAPO) membrane having

a first side and a second side, wherein the resulting hydrogen selectively

passes from the first side to the second side over the alkane, a thickness of 2 m or less, and

a dehydrogenation catalyst on the first side of the membrane; applying a feed stream containing a mixture of the hydrogen and alkane to the first side of the membrane;

applying a sweep stream to the second side of the membrane, wherein the sweep stream maintains a lower partial pressure of the resulting hydrogen on the second side of the membrane than on the first side of the membrane, thereby producing a feed stream enriched in the alkane on the first side of the membrane.

[0060] In some embodiments of the methods described herein, the catalyst can be the packed catalyst as described herein, and the dehydrogenation can be performed in a reactor or vessel as described herein.

EXAMPLES

Example 1 : SAPO-34 seed synthesis and seed layer

[0061] To prepare a pure-silica micron-sized (~1 μιη) SAPO-34 seed suspension, the synthesis solution was prepared to grow the seed crystals. It had a molar ratio of 1.0 AI2O ₃ : 1.0 P2O5: 0.32 Si0 ₂ : 1.0 TEAOH: 0.8 DPA: 52 H ₂ 0 (TEAOH = tetra-ethyl ammonium hydroxide; DPA = dipropylamine) (Li, S. G.; Carreon, M. A.; Zhang, Y. R; Funke, H. H.; Noble, . D.; Falconer, J. L. J. Membr. Sci. 2010, 352, 7-13). To prepare the seeds, the AI(i-C ₃ H ₇ 0)3 (98%, Sigma-Aldrich), H3PO4 (85 wt.% aqueous solution, Sigma-Aldrich), and deionized water were stirred for 3 h to form an homogeneous solution, and then Ludox AS-40 colloidal silica (40 wt.% S1O2 suspension in water, Sigma-Aldrich) was added, and the resulting solution was stirred for another 3 h. The TEAOH template (35 wt.% aqueous solution, Sigma- Aldrich) was then added, and the solution was stirred for 1 h. After the addition of DPA (99%, Sigma-Aidrich), the solution was stirred at room temperature for 4 days. The solution was then placed in the Teflon-lined stainless steel autoclave and heated at 210 °C for 6 h. After the solution cooled to room temperature, it was centrifuged to separate the seeds, and then washed with deionized water. This centrifugation and washing procedure was repeated three times, and the resulting precipitate was dried at 70 °C overnight.

[0062] The synthesis solution used to grow the nano-sized (-220 nm) seed crystals had a molar ratio of 1.0 Al ₂ 0 ₃ : 0.6 P ₂ 0 ₅ : 0.6 Si0 ₂ : 6.0 TEAOH: 111 H ₂ 0 (van Heyden, H.; Mintova, S.; Bein, T. Chem. Mater. 2008, 20, 2956-2963). To prepare the seeds, the AI(i-C ₃ H ₇ 0)3, Ludox AS-40 colloidal silica, TEAOH template and deionized water were stirred for 2 h to form an homogeneous solution, and H3PO4 was added dropwise over a period of 2 h to avoid the formation of dense gel particles. The solution was then placed in the Teflon-lined stainless steel autoclave and heated at 180 °C for 3 h. After the solution cooled to room temperature, it was centrifuged to separate the seeds, and then washed with deionized water. This centrifugation and washing procedure was repeated three times, and the resulting precipitate was dried at 70 °C overnight.

[0063] The SAPO-34 seeds were deposited on the inner surfaces of the support tubes by either rub-coating or dip-coating. Membrane T1 was seeded by rub-coating with ~1 μιη seeds, and membranes T2-T6 were seeded by dip-coating with -220 nm seeds. Rub-coating was then carried out by rubbing 1.0 wt.% seed suspension (-1 μηη) evenly onto the inside surface of the tube supports for about 2 min with cotton swabs. The rub-coating process was repeated once and the supports were then dried at 70 °C for overnight. For dip-coating, the outer surface of tube supports were first wrapped in Teflon tape and then immersed for about 60s in deionized water that contained 1.0 wt% SAPO-34 seeds (-220 nm). The dip-coating process was repeated once to ensure the uniform distribution of seeds on the inner surfaces. The supports were lifted out of the seed suspension and then dried at 70 °C for overnight.

Example 2: SAPO-34 membrane synthesis by seeded growth

[0064] The SAPO-34 zeolite membrane was synthesized on the inner surface of a porous a- alumina tube (Ceramco) that was first seeded with SAPO-34 seed crystals. The tube is 80- mm long with I.D. and O.D. of 8 mm and 11 mm, respectively. The two ends of the tube are glazed with dense glass covering 5-mm length on each end to leave a 70-mm long active membrane section in the middle of the tube. The zeolite membrane was synthesized on the inner surface of tube support by the seeded growth. Usually two seeded supports were placed in an autoclave, which was then filled with the synthesis gel to about 0.5 cm above the top of the supports.

[0065] For membrane T1 , the synthesis gel for membrane preparation had a molar ratio of 1.0 Al ₂ 0 ₃ : 1.0 P2O5: 0.32 Si0 ₂ : TEAOH: 1.6 DPA: 150 H ₂ 0. The Al(i-C ₃ H ₇ 0) ₃ , H3PO4, and deionized water were stirred for 3 h to form an homogeneous solution, and then Ludox AS-40 colloidal silica was added, and the resulting solution was stirred for another 3 h. The TEAOH was then added, and the solution was stirred for 1 h. After the addition of DPA, the solution was stirred at room temperature for 4 days before membrane synthesis. The outer surface of the seeded (-1 μιη) supports were then wrapped with Teflon tape and placed in the Teflon- lined stainless steel autoclave (Parr), which was then filled with the synthesis gel. Hydrothermal synthesis was carried out in a conventional oven at 210 °C for 6 h. After the hydrothermal reaction, the tubular zeolite membrane was washed thoroughly with deionized water, dried, and calcined in air at 550 °C for 6 h to remove the template.

[0066] For membranes T2-T6, The synthesis solution for membrane preparation had a molar ratio of 0.85 Al ₂ 0 ₃ : 1.0-2.0 P ₂ 0 ₅ : 0.3 Si0 ₂ : 1.0-2.0 TEAOH: 0.0-1.0 TEABr: 120-155 H ₂ 0, where TEABr is tetraethylammonium bromide. The AI(OH)3 (50%, Sigma-Aldrich), H3PO4, and deionized water were stirred for 2 h to form an homogeneous solution, Ludox AS-40 colloidal silica was added, and the resulting solution was stirred for another 30 min. Then, TEAOH and TEABr (99%, Sigma-Aldrich) were added, and the solution was stirred for an additional 30 min and these solution was aged for 12-15 h at room temperature. The outside of the seeded (-220 nm) supports were then wrapped with Teflon tape and placed vertically in the Teflon-lined stainless steel autoclave, which was then filled with the synthesis solution. Hydrothermal synthesis was carried out in a conventional oven at 220 °C for 6 h. After the reaction, the membrane was washed thoroughly with deionized water, dried, and calcined in air at 550 °C for 6 h to remove the template. The synthesis conditions for SAPO-34 membranes T1-T6 are summarized in Table 1. Table 1. Synthesis conditions for SAPO-34 membranes

Example 3: Characterization

Membrane Thickness

[0067] Scanning Electron Microscopy (SEM) images and energy dispersive X-ray spectroscopy (EDX) analyses (elemental mapping and line scanning) were obtained on a JEOL LEO-1530 at a landing energy of 15kV using the 'InLens' mode detector. The membrane samples were coated with gold to prevent surface charging effects.

[0068] Membrane thickness was measured at multiple points in the EDX/SEM images. The membrane thickness was measured at total 25 to 30 points along the individual membranes and the average was provided in Table 1. The standard deviations of membrane thickness obtained from membranes and reported in Table 1 are within 0.3 nm.

Permeance and Permselectivity

[0069] Before calcination, the integrity of the zeolite membrane was checked via He permeation measurements, for which a transient permeation setup with upstream pressure of 25-30 psi at room temperature was employed. The membranes had very low He permeances (less than 1.0 * 10 ^"10 mol rrr ² s ¹ Pa ¹ ).

[0070] After calcination, H2 C3H8 binary gas permeation was performed at 25 - 650 °C. The tubular SAPO-34 membranes were mounted in a stainless steel cell, placed in a temperature-programmable oven, and maintained under Ar gas flow (10 cm ³ /min) on both the feed and permeate side for 2 h at 23°C. Then the feed stream (either single-component hydrogen or propane, or binary mixtures of hydrogen and propane), and an Ar sweeping flow on the permeate side, were introduced into the membrane cell. The permeate stream (composed of the Ar sweep gas and the molecules that permeated through the membrane) was analyzed by an online GC system (Shimadzu GC2014) equipped with a molecular sieve 13X column for the thermal conductivity detector (TCD) and an alumina plot column for the flammable ionization detector (FID). H2 and C3H8 single gas permeation measurements were performed at 23 °C (Table 2), and H2 C ₃ H ₈ equimolar mixture gas separation was measured in the temperature range of 23-650 °C (Figure 2). The membrane permeance for component is calculated as:

P,„ , =— , (i = , H, ...) where Q, (mol) is the amount of gas permeated over a time period t (s), A = 17.6 cm ² is the active membrane area, and ΔΡ, (Pa) is the transmembrane pressure. The H2 C3H8 permseiectivity (a°H2/c3Hs) is defined as the ratio of their pure gas permeances:

P

¹ m,C3H8 ^2)

The H2 C3H8 separation factor (aH2/c3Hs) for the binary mixture is given by

(}'H 2 / C3 Hg ) permeate

a H 2IC5HS

feed (3) where «2 and yc3H8 are mole fractions of H2 and C3H8, respectively. Example 4: Propane Dehydrogenation (PDH) reaction

[0071] The propane dehydrogenation packed bed membrane reactor (PDH PBMR) system is schematically shown in Figure 4. The membrane tube was mounted in a stainless steel permeator sealed by soft graphite gaskets (Mercer Gasket & Shim). A total amount of 1.2 g of catalyst particles were packed in the 70-mm membrane section. The catalyst bed was packed with quartz chips and was held by plugs of quartz wool on both ends, which had a height of about 70 mm. The membrane section surrounding the catalyst bed thus had an area of 17.6 cm ² which gave a catalyst load of 68.2 mg-catalyst/cm ² -membane. The catalyst used in this work was 1 % Na ₂ 0-doped 20% Cr ₂ O ₃ /80% AI2O3 from the Dow Chemical Company. Before the PDH reaction, the paced bed membrane reactor (PBMR) was maintained at 23 - 500 °C under Ar gas flows (10 cm ³ /min) on both the catalyst side and the permeate side. During the PDH reaction, the propane feed stream and the Ar sweeping flow were introduced into the membrane reactor. The retentate and permeate gases were analyzed by an online GC (Shimadzu, 2014) equipped with an molecular sieve 13X column for the thermal conductivity detector (TCD) and an alumina plot column for the flammable ionization detector (FID). The PDH reaction was also performed in a conventional PBR for comparison. The PBR was made of an impermeable a-alumina tube having the same dimensions as the porous tubes used in the PBMR. The amount of catalyst used in the PBR was also 1.2 g.

[0072] The propane conversion was calculated based on the total propane feed flow rates entering as feed and exiting the reactor in both permeate and retentate streams:

F, out

C3HS

C3 /78 1 pin (4)

1 CiHH

The selectivity for gas component / ^' is defined as:

The yield for gas component is calculated by:

Y. = 3HS (i = C ₃ H ₆ , CH ₄ ...) (6)

100

[0073] Table 1 shows the H2 C3H8 separation performance of SAPO-34 membranes T1-T6. Table 2 H2 C3H8 and N2/CH4 separation performance of SAPO-34 membranes

³ Helium permeances of uncalcined membranes were measured at room temperature. b Single gas permeance and permselectivity of calcined membranes were measured at room temperature.

c Separation of N2/CH4 equimolar mixture by calcined membranes were performed at room temperature.