Method and system for purifying helium by using two-stage membrane combined with alloy adsorption

Abstract

The present invention relates to the technical field of helium extraction and refining, and specifically discloses a method and system for purifying helium by using a two-stage membrane combined with alloy adsorption. The method provided by the present invention comprises: subjecting the raw gas to catalytic dehydrogenation separation, first-stage polymer membrane separation, alloy adsorption and second-stage polymer membrane separation in sequence to obtain ultrapure helium. The present invention effectively combines processes such as catalytic oxidative dehydrogenation (preliminary dehydrogenation), polymer membrane separation (one-stage membrane separation and two-stage membrane separation), and alloy adsorption (deep dehydrogenation), and uses natural gas, shale gas, multi-stage flash gas, etc. as raw gas to prepare high-purity helium (5N or 6N grade helium), and the conditions of each process are stable and controllable; combining the advantages of the above process technologies, especially considering the specific arrangement between the processes, the helium preparation process is simple, economical, continuous and stable, and the problem of preparing and purifying ultrapure helium is well solved, and it has a very broad application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of helium extraction and purification, and in particular to a method and system for purifying helium by using a two-stage membrane combined with alloy adsorption. Background Art

[0002] Helium is widely used in aerospace, refrigeration, medical, optical fiber, leak detection, deep-sea diving, high-precision welding production and other fields due to its low density, low boiling point and inert properties. Some groundwater and some natural gas contain a small amount of helium. In particular, after LNG products are produced from natural gas, the helium concentration in the tail gas (BOG) increases to 1-10%. At present, the widely used separation technologies include cryogenic technology, membrane technology, adsorption technology, and distillation technology. The combination of these technologies can effectively enrich, separate and purify helium. However, the extremely low boiling point and small size of hydrogen in the gas is difficult to be efficiently separated from helium. With the increase of the target helium concentration, the complexity and energy consumption of the process or equipment increase significantly, especially the process with cryogenic technology as the core. Efficient dehydrogenation has become a key step in the preparation of ultra-pure helium. Most helium refinements use catalytic dehydrogenation technology. The principle of dehydrogenation is to convert hydrogen into water more gently under the action of a catalyst, but its catalytic oxidation efficiency, reaction conditions and reaction energy consumption are mainly restricted by the performance of the catalyst, and the removal effect of trace hydrogen is limited. Therefore, how to economically and efficiently extract ultrapure helium remains an urgent problem to be solved. Summary of the invention

[0003] The purpose of the present invention is to overcome the technical problems of harsh conditions and high cost for preparing helium in the prior art, and to provide a method and system for purifying helium by using a two-stage membrane combined with alloy adsorption.

[0004] In order to achieve the above-mentioned object, the first aspect of the present invention provides a method for purifying helium using a two-stage membrane combined with alloy adsorption, the method comprising: subjecting the raw gas to catalytic dehydrogenation separation, first-stage polymer membrane separation, alloy adsorption and second-stage polymer membrane separation in sequence to obtain ultrapure helium.

[0005] A second aspect of the present invention provides a system for purifying helium, the system comprising a catalytic dehydrogenation separation unit, a first-stage polymer membrane separation unit, an alloy adsorption unit and a second-stage polymer membrane separation unit connected in sequence;

[0006] Preferably, the catalytic dehydrogenation separation unit comprises a catalytic oxidation device and a dehydration drying device.

[0007] Compared with the prior art, the present invention effectively combines catalytic oxidative dehydrogenation (preliminary dehydrogenation), polymer membrane separation (one-stage membrane separation and two-stage membrane separation), alloy adsorption (deep dehydrogenation) and other processes together, and uses natural gas, shale gas, multi-stage flash gas, etc. as raw gas to prepare high-purity helium (5N or 6N grade helium), and the conditions of each process are stable and controllable. Compared with the conventional cryogenic process, the present invention has the advantages of compact structure and low energy consumption. In addition, the present invention can purify helium under lower temperature and milder conditions (for example, helium is raised to 5N level or 6N level). The present invention combines the advantages of the above process technologies, especially considering the specific arrangement between each process, so that the helium preparation process is simple, economical, continuous and stable, and the problem of ultra-pure helium preparation and purification is better solved. It can realize efficient utilization of gases containing helium resources such as natural gas, oil field associated gas, chemical industry and other waste gases, and the prepared helium is of very high value and has a very broad application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is an infrared spectrum of the polyimide random copolymer prepared in Preparation Example 1;

[0009] Figure 2 is a scanning electron microscope image of a cross section of the polyimide-based hollow fiber membrane prepared in Preparation Example 1;

[0010] Figure 3 is a scanning electron microscope image of a cross section of a polyimide-based hollow fiber membrane prepared in Preparation Example 2;

[0011] Figure 4 The polyimide-based hollow fiber membrane prepared in Example 1 is 1 H NMR spectrum. DETAILED DESCRIPTION

[0012] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0013] In the present invention, "C1-C4 alkyl" includes methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl. "C6-C10 aryl" includes benzene, toluene, xylene (o, m, p), ethylbenzene, methylethylbenzene ... etc. "C1-C4 halogenated alkyl" includes monofluoromethyl, difluoromethyl, trifluoromethyl, monofluoroethyl, difluoroethyl, trifluoroethyl, monochloromethyl, dichloromethyl, trichloromethyl ... etc. "C1-C4 saturated monohydric alcohol" includes methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol. "C3-C5 alkane" includes straight-chain alkane (e.g. n-propane, isopropane ... n-pentane, isopentane, etc.) with 3-5 carbon atoms, branched alkane or cycloalkane (cyclopropane, cyclobutane, cyclopentane). "C5-C7 alkane" is similar thereto.

[0014] The first aspect of the present invention provides a method for purifying helium using a two-stage membrane combined with alloy adsorption, the method comprising: subjecting the raw gas to catalytic dehydrogenation separation, first-stage polymer membrane separation, alloy adsorption and second-stage polymer membrane separation in sequence to obtain ultrapure helium.

[0015] According to some embodiments of the present invention, the raw gas is a mixed gas containing helium, hydrogen and other impurity gases, and can be selected from at least one of natural gas, shale gas, helium-rich hydrogen-containing gas and liquefied natural gas flash steam (BOG). The natural gas or shale gas can be subjected to multi-stage flash evaporation and then used as raw gas for helium purification.

[0016] According to some embodiments of the present invention, the catalytic dehydrogenation separation includes catalytic oxidation and dehydration drying, and the catalyst used in the catalytic oxidation is a precious metal catalyst selected from at least one of Pt, Pd, Rh, Ru and Au.

[0017] According to some embodiments of the present invention, the conditions for the catalytic oxidation may include: a temperature of 40-150°C (such as 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C or any value between the above values), preferably 50-120°C; the space velocity of the feed gas is 1-10000m 3 / m 3 h, preferably 10-1000m 3 / m 3 ·h.

[0018] According to some embodiments of the present invention, the conditions for the catalytic oxidation are such that 90-100% by volume of the hydrogen in the feed gas is converted into H 2 O, for example, can make the volume fraction of hydrogen in the raw gas less than 0.1%.

[0019] The present invention has no particular limitation on the conditions for dehydration and drying, as long as the water generated during the catalytic dehydrogenation process can be removed.

[0020] According to some embodiments of the present invention, the polymer membranes used in the first stage polymer membrane separation and the second stage polymer membrane separation can be independently selected from at least one of a hollow fiber membrane, a flat membrane and a tubular membrane; more preferably a hollow fiber membrane.

[0021] In the present invention, there is no particular limitation on the polymer membranes used in the first-stage polymer membrane separation and the second-stage polymer membrane separation, as long as they can meet the requirements of the present invention. They can be commercially available or prepared by conventional methods in the art such as phase separation, solution phase separation, melt stretching, interfacial polymerization, coating polymerization, and in-situ polymerization.

[0022] According to some embodiments of the present invention, the materials of the polymer membranes used in the first stage polymer membrane separation and the second stage polymer membrane separation may be the same or different, and each is independently selected from at least one of polyimide, polybenzimidazole and polysulfone, more preferably polyimide.

[0023] According to some embodiments of the present invention, the first stage polymer membrane separation adopts a one-stage or multi-stage (two to five-stage) separation method. Among them, the two-stage membrane separation refers to the polymer membrane separation in which the gas on the permeate side is pressurized and then used as the inlet of the membrane again. Tertiary membrane separation, four-stage membrane separation and five-stage membrane separation have similar meanings. Among them, the process of polymer membrane separation can be one to five stages. Preferably, multi-stage membrane separation is separation through multiple membranes or membrane components. Among them, the first-stage membrane separation, the second-stage membrane separation, the third-stage membrane separation, the fourth-stage membrane separation and the fifth-stage membrane separation are respectively carried out in the first-stage membrane separation unit, the second-stage membrane separation unit, the third-stage membrane separation unit, the third-stage membrane separation unit and the fourth-stage membrane separation unit.

[0024] According to some embodiments of the present invention, the conditions for the first stage polymer membrane separation may include: before performing the first stage polymer membrane separation, the gas pressure obtained by catalytic dehydrogenation separation is controlled to 0.01-10MPa (such as 0.01MPa, 0.1MPa, 0.2MPa, 0.3MPa, 0.5MPa, 0.8MPa, 1MPa, 2MPa, 3MPa, 4MPa, 5MPa, 6MPa, 7MPa, 8MPa, 9MPa, 10MPa or any value between the above values), preferably 0.1-8MPa, and the temperature is controlled to be less than or equal to 50°C, preferably 0-50°C.

[0025] In the present invention, according to a preferred embodiment, the gas obtained by catalytic dehydrogenation separation enters the first polymer membrane separation stage, wherein the permeate gas of the first membrane (first membrane separation unit) is pressurized to 0.01-10Mpa by a compressor and enters the next membrane after heat exchange by a heat exchanger, and the retentate gas enters the inlet of the first membrane or refluxes to the inlet of the catalytic oxidation dehydrogenation unit;

[0026] The permeate gas of the secondary membrane (second-stage membrane separation unit) is pressurized to 0.1-10Mpa by a 1^^ compressor and then enters the tertiary membrane or directly enters the next unit after heat exchange in a heat exchanger. The residual gas of the secondary membrane enters the inlet of the secondary membrane or the primary membrane or flows back to the inlet of the catalytic oxidation dehydrogenation unit;

[0027] The permeate gas of the tertiary membrane (third-stage membrane separation unit) is pressurized to 0.1-5Mpa by a 1^^^ compressor and enters the quaternary membrane or directly enters the next unit after heat exchange by a heat exchanger. The residual gas of the tertiary membrane enters the inlet of the first or second membrane or refluxes to the inlet of the catalytic oxidation dehydrogenation unit;

[0028] The permeate gas of the quaternary membrane (fourth-stage membrane separation unit) is pressurized to 0.01-5Mpa by a 1^^^^ compressor and enters the fifth-stage membrane or directly enters the next unit after heat exchange by a heat exchanger. The residual gas of the quaternary membrane enters the inlet of the first, second or third-stage membrane or flows back to the inlet of the catalytic oxidation dehydrogenation unit;

[0029] The permeate gas of the five-stage membrane (fifth-stage membrane separation unit) is pressurized to 0.1-5Mpa by a 1^^^^^ compressor and enters the four-stage membrane or directly enters the next unit after heat exchange through a heat exchanger. The residual gas of the three-stage membrane enters the inlet of the first, second, third or fourth membrane or refluxes to the inlet of the catalytic oxidation dehydrogenation unit.

[0030] Among them, "1^^" stands for "one-stage membrane and two-stage membrane", "1" is a stage and "^^" is a level; "1^^^", "1^^^^" and "1^^^^^" have similar meanings.

[0031] According to some embodiments of the present invention, the polymer membrane used in the polymer membrane separation is a polyimide-based hollow fiber membrane, preferably a polyimide hollow fiber membrane having a triptycene structure.

[0032] Preferably, the polyimide-based hollow fiber membrane comprises a support layer and a dense layer attached to the outer surface of the support layer, the thickness of the dense layer is less than 1000 nm, and the porosity of the hollow fiber membrane is 40-80%. The porosity of the support layer is greater than the porosity of the dense layer. The porosity of the dense layer cannot be obtained by mercury intrusion characterization.

[0033] Preferably, the thickness of the dense layer is 100-500 nm, more preferably 100-300 nm (such as 100 nm, 150 nm, 200 nm, 250 nm, 300 nm or any value therebetween); the porosity of the hollow fiber membrane (support layer) is 50-70%.

[0034] Preferably, the hollow fiber membrane is made of polyimide random copolymer.

[0035] In the present invention, the polyimide random copolymer has a structure shown in formula (I):

[0036]

[0037] In formula (I), m and n are each independently an integer of 10-2000;

[0038] X has a structure represented by any one of formula (X1) to formula (X3);

[0039]

[0040] In formula (X1) to formula (X3), R 1 , R 2 , R 3 , R 4 , R 5 and R 6 Each is independently H, C1-C4 alkyl, C6-C10 aryl, amino, hydroxyl or carboxyl;

[0041] Y has a structure represented by any one of formula (Y1) to formula (Y5);

[0042]

[0043] In formula (Y1) to formula (Y5), R 7 , R 8 , R 9 , R 10 , R 11 , R 12 , R 13 , R 14 , R 15 and R 16 Each is independently H, C1-C4 alkyl, C6-C10 aryl, amino, hydroxyl or carboxyl;

[0044] Z and Z' each independently have a structure represented by formula (Z1) or formula (Z2);

[0045]

[0046] In formula (Z2), Ra and Rb are each independently H, C1-C4 alkyl or C1-C4 halogenated alkyl. Preferably, m and n are each independently an integer of 50-1000.

[0047] Preferably, 0.9≥n / (m+n)≥0.3, preferably, 0.7≥n / (m+n)≥0.5.

[0048] In the present invention, X has one of the following structures:

[0049]

[0050] In the present invention, Y has one of the following structures,

[0051]

[0052] In the present invention, Z and Z' both have the structure shown by Z1 or Z3,

[0053]

[0054] Preferably, X is Xa, Y is Ya, and Z and Z' are both Z1;

[0055] Alternatively, X is Xa, Y is Yb, and Z and Z' are both Z1;

[0056] Or, X is Xa, Y is Yd, and Z and Z' are both Z1;

[0057] Or, X is Xb, Y is Ya, and Z and Z' are both Z1;

[0058] Or, X is Xb, Y is Yb, and Z and Z' are both Z1;

[0059] Or, X is Xb, Y is Yd, and Z and Z' are both Z1;

[0060] Or, X is Xc, Y is Ya, and Z and Z' are both Z1;

[0061] Alternatively, X is Xc, Y is Yb, and Z and Z' are both Z1;

[0062] Or, X is Xc, Y is Yc, and Z and Z' are both Z1;

[0063] Alternatively, X is Xc, Y is Y4, and Z and Z' are both Z1;

[0064] Or, X is Xc, Y is Yd, and Z and Z' are both Z1;

[0065] Or, X is Xb, Y is Ya, and Z and Z' are both Z3;

[0066] Or, X is Xb, Y is Yb, and Z and Z' are both Z3;

[0067] Or, X is Xb, Y is Yd, and Z and Z' are both Z3;

[0068] Or, X is Xc, Y is Ya, and Z and Z' are both Z3;

[0069] Or, X is Xc, Y is Yb, and Z and Z' are both Z3;

[0070] Alternatively, X is Xc, Y is Yd, and Z and Z' are both Z3.

[0071] Although according to a preferred embodiment of the present invention, X, Y, and Z have a specific structure, the present invention does not exclude the situation that "X is taken from two or three different structures, Y is taken from two, three, four or five different structures, and Z is taken from two different structures".

[0072] In the present invention, based on firstly carrying out polycondensation reaction of dianhydride monomer (dianhydride shown in formula (II) and dianhydride shown in formula (III)) and diamine monomer to obtain polyamic acid, then imidization (intramolecular dehydration) is carried out to polyamic acid, dianhydride monomer and diamine monomer can be carried out polycondensation reaction to obtain polyamic acid by one-pot method, or dianhydride monomer (i.e. dianhydride shown in formula (II) and dianhydride shown in formula (III)) can be mixed uniformly before carrying out polycondensation reaction with diamine monomer. However, in order to better control the reaction, it is preferred to react in the latter mode. Therefore, the present invention also provides a method for preparing polyimide random copolymer, and the method comprises the following steps:

[0073] (S1) in the presence of a first solvent, mixing a mixture of a dianhydride monomer represented by formula (II) and a dianhydride monomer represented by formula (III) with a diamine monomer to carry out a polycondensation reaction to obtain a material containing polyamic acid,

[0074]

[0075] (S2) imidizing the material containing polyamic acid obtained in step (S1) to cause intramolecular dehydration of the polyamic acid to obtain a polyimide random copolymer;

[0076] In formula (II) and formula (III), X and Y have the same meanings as described above.

[0077] Wherein, the diamine monomer is selected from the structure such as H 2 N-Zp-NH 2 At least one of the compounds shown, wherein Zp has a structure shown in formula (Z1) or (Z2),

[0078]

[0079] In formula (Z2), Ra and Rb are each independently H, C1-C4 alkyl or C1-C4 halogenated alkyl.

[0080] Preferably, X is Xa, Y is Ya, and Zp is Z1;

[0081] Alternatively, X is Xa, Y is Yb, and Zp is Z1;

[0082] Or, X is Xa, Y is Yd, and Zp is Z1;

[0083] Or, X is Xb, Y is Ya, and Zp is Z1;

[0084] Or, X is Xb, Y is Yb, and Zp is Z1;

[0085] Or, X is Xb, Y is Yd, and Zp is Z1;

[0086] Or, X is Xc, Y is Ya, and Zp is Z1;

[0087] Or, X is Xc, Y is Yb, and Zp is Z1;

[0088] Or, X is Xc, Y is Yc, and Zp is Z1;

[0089] Or, X is Xc, Y is Y4, and Zp is Z1;

[0090] Or, X is Xc, Y is Yd, and Zp is Z1;

[0091] Or, X is Xb, Y is Ya, and Zp is Z3;

[0092] Or, X is Xb, Y is Yb, and Zp is Z3;

[0093] Or, X is Xb, Y is Yd, and Zp is Z3;

[0094] Or, X is Xc, Y is Ya, and Zp is Z3;

[0095] Or, X is Xc, Y is Yb, and Zp is Z3;

[0096] Alternatively, X is Xc, Y is Yd, and Zp is Z3.

[0097] In the present invention, the molar amounts of the dianhydride monomer represented by formula (II) and the dianhydride monomer represented by formula (III) are defined as M and N, respectively, and the ratio of M to N is (10-2000):(10-2000), more preferably 1:(0.5-15), and further preferably 1:(1-9).

[0098] In the present invention, M and N satisfy 0.9≥N / (M+N)≥0.3, preferably, 0.7≥N / (M+N)≥0.5.

[0099] In the present invention, the molar ratio of the total amount of the dianhydride monomer represented by formula (II) and the dianhydride monomer represented by formula (III) to the diamine monomer is 1:(0.6-1.5), preferably 1:(0.8-1.2).

[0100] In the present invention, in step (S1), the polycondensation reaction conditions may include: reaction temperature of -20°C to 60°C, preferably -10°C to 40°C; reaction time of 5-30h, preferably 8-24h.

[0101] In the present invention, the polycondensation reaction is carried out under an inert atmosphere, which is preferably provided by nitrogen.

[0102] In the present invention, the first solvent can be selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide and N-methylpyrrolidone (NMP), preferably selected from N-methylpyrrolidone and / or N,N-dimethylformamide.

[0103] In the present invention, the usage of the first solvent is 1000-3000 mL relative to 1 mmol of the diamine monomer.

[0104] In the present invention, the dianhydride monomer represented by formula (II) and the dianhydride monomer represented by formula (III) can be mixed to obtain a mixture by the following methods: mechanical stirring, shaking or ultrasound. The mechanical stirring conditions may include: 20-40°C, 2000-15000rpm, 2-12h; the ultrasound conditions may include: 20-40°C, 0.5-2.0h; the shaking conditions may include: 20-40°C, 260-800rpm, 12-36h.

[0105] In the present invention, the imidization treatment is carried out by adding a dehydrating agent and a catalyst to the amic acid-containing material obtained in step (S1), and reacting at 170-200° C. for 12-24 hours.

[0106] In the present invention, the dehydrating agent is selected from at least one of dichlorobenzene, toluene, acetic anhydride and xylene.

[0107] In the present invention, the catalyst is selected from pyridine and / or diquinoline.

[0108] In the present invention, the amount of the dehydrating agent used may be 2-15 mol, preferably 3-8 mol, relative to 1 mol of the diamine monomer.

[0109] In the present invention, the amount of the catalyst used may be 2-15 mol, preferably 3-8 mol, relative to 1 mol of the diamine monomer.

[0110] In the present invention, the method further comprises: before obtaining the polyimide copolymer, the material after the imidization treatment in step (S2) is diluted and contacted with a precipitant to obtain the polyimide copolymer. Wherein, the precipitant can be a poor solvent for polyimide, selected from at least one of ethanol, acetone and water, and more preferably selected from at least two of ethanol, acetone and water. Equivalent to 1 mol of diamine monomer, the total amount of the precipitant can be 10-50L. Wherein, the solvent for dilution can be N-methylpyrrolidone. Preferably, relative to 1 mol of diamine monomer, the amount of the solvent for dilution can be 5-8L.

[0111] In the present invention, there is no particular limitation on the manner in which the imidization-treated material in step (S2) is contacted with the precipitant, as long as the requirements of the present invention are met. For example, the following manner may be used: the imidization-treated material in step (S2) (after dilution) is added to the precipitant to precipitate the polyimide, and then the precipitated polyimide is eluted with the precipitant (the elution may be 3-5 times), and finally filtered and dried (70-150° C., 24-48 hours) to obtain a polyimide random copolymer.

[0112] In the present invention, the polyimide-based hollow fiber membrane is prepared according to a method comprising the following steps:

[0113] (1) preparing a casting solution containing a polyimide, a diluent and an additive, wherein the diluent contains a good solvent for the polyimide, a poor solvent for the first polyimide and a poor solvent for the second polyimide, wherein the boiling point B1 of the poor solvent for the first polyimide is higher than the boiling point B2 of the poor solvent for the second polyimide;

[0114] (2) extruding the inner core liquid and the casting liquid at a temperature T, and then curing to obtain a hollow fiber membrane precursor, wherein B2≤T<B1;

[0115] (3) The hollow fiber membrane precursor is rolled up and extracted to obtain the polyimide-based hollow fiber membrane.

[0116] In the present invention, in step (1), based on the total weight of the casting solution, the content of the polyimide is 20-40wt%, the content of the diluent is 50-75wt%, and the content of the additive is 0.5-10wt%.

[0117] Preferably, based on the total weight of the casting solution, the content of the polyimide is 25-35wt%, the content of the diluent is 60-70wt%, and the content of the additive is 1-5wt%.

[0118] In the present invention, in order to facilitate the formation of the dense layer of the hollow fiber membrane, the boiling point B1 of the first polyimide poor solvent is 5-200° C. higher than the boiling point B2 of the second polyimide poor solvent, preferably 10-20° C. higher. Wherein, the boiling point refers to the normal pressure boiling point unless otherwise specified.

[0119] In the present invention, the poor solvent for the first polyimide is at least one selected from the group consisting of a C2-C4 saturated monohydric alcohol, γ-butyrolactone and water.

[0120] In the present invention, the poor solvent for the second polyimide is at least one selected from C3-C5 alkanes, tetrahydrofuran, acetone and chloroform.

[0121] In the present invention, the good solvent for the polyimide is at least one selected from N-methylpyrrolidone, N,N-dimethylacetamide and N,N-dimethylacetamide.

[0122] In the present invention, in order to obtain better effects, the present invention has certain requirements on the usage ratio of the good solvent of the polyimide, the poor solvent of the first polyimide and the second polyimide. Preferably, the weight ratio of the good solvent of the polyimide, the poor solvent of the first polyimide and the poor solvent of the second polyimide is 1:(0.1-0.5):(0.1-0.5), preferably 1:(0.15-0.3):(0.15-0.3).

[0123] In the present invention, the additive may be a lithium salt, preferably selected from lithium nitrate and / or lithium chloride.

[0124] In the present invention, in step (1), the casting solution is prepared according to a method comprising the following steps: stirring polyimide, a diluent and an additive at 20-50°C and 100-1200 r / min for 12-48 hours, and then removing impurities by vacuum degassing and filtering (20-50°C).

[0125] In the present invention, the vacuum degassing conditions include: pressure of -0.1MPa to -0.095MPa, temperature of 20-30°C, rotation speed of 10-50r / min, and time of 12-24h.

[0126] In the present invention, in step (2), the inner core liquid includes solvent A and solvent B, wherein the solvent A is selected from at least one of N-methylpyrrolidone, N,N-dimethylacetamide and N,N-dimethylacetamide, and the solvent B is selected from at least one of a saturated monohydric alcohol of C1-C4, γ-butyrolactone and water.

[0127] In the present invention, the solvent A accounts for 50-99wt%, preferably 60-95wt%, of the total weight of the inner core liquid.

[0128] According to some embodiments of the present invention, the extrusion is carried out in a spinneret, wherein the extrusion temperature (temperature of the spinneret) is 40-75°C, preferably 60-70°C.

[0129] In the present invention, during the extrusion process, the flow rate of the casting solution is 6-30 mL / min.

[0130] According to some embodiments of the present invention, during the extrusion process, the flow rate of the core liquid is 2-10 mL / min.

[0131] In the present invention, before solidification, the hollow fibers obtained by extrusion are passed through an air gap to promote the formation of a dense layer and better control the thickness of the dense layer.

[0132] In the present invention, the height of the air gap is 5-30 cm.

[0133] In the present invention, the air gap is heated by an annular sleeve, and the temperature is preferably controlled to be 70-150°C.

[0134] In the present invention, the solidification is carried out in a coagulation bath. Preferably, the bath liquid used in the coagulation bath is solvent C and / or water, and the temperature of the coagulation bath is 40-70°C.

[0135] In the present invention, the solvent C is selected from at least one of a C1-C4 saturated monohydric alcohol, γ-butyrolactone and water.

[0136] In the present invention, in step (3), the winding rate is 0.5-2 m / s.

[0137] In the present invention, the purpose of the extraction is to remove the diluent and additives in the hollow fiber membrane precursor.

[0138] In the present invention, the extractant used for extraction is selected from at least one of water, C1-C4 saturated monohydric alcohol and C5-C7 alkane. There is no particular limitation on the amount of the extractant, as long as it can meet the requirements of the present invention.

[0139] In the present invention, the extraction conditions include: a temperature of 20-35° C. and a time of 3-48 hours. The extraction time refers to the time for the membrane fibers (hollow fiber membrane precursors) to be immersed.

[0140] In the present invention, preferably, the extraction method is preferably: extracting in water, C1-C4 saturated monohydric alcohol and C5-C7 alkane in sequence for 2-5 times respectively.

[0141] In the present invention, the extraction further includes a drying step.

[0142] In the present invention, the drying conditions include: temperature of 20-35° C. and time of 2-15 h.

[0143] According to some embodiments of the present invention, the conditions for alloy adsorption may include: before the alloy adsorption, the temperature of the gas obtained by the first stage polymer membrane separation is controlled to 10-50°C, preferably 20-30°C.

[0144] According to some embodiments of the present invention, the adsorption material for alloy adsorption is a hydrogen storage alloy material, which can be selected from at least one of rare earth alloys, titanium alloys, zirconium alloys, vanadium alloys and magnesium alloys.

[0145] In the present invention, the alloy adsorption can be carried out in an alloy adsorption separator.

[0146] According to some embodiments of the present invention, the second stage polymer membrane separation adopts a one-stage or multi-stage separation method.

[0147] The present invention has no special restrictions on the conditions of the second polymer membrane separation, as long as they can meet the requirements of the present invention. For example, the conditions of the second polymer membrane separation may include: controlling the temperature (inlet temperature) of the gas after alloy adsorption to 0-50°C and the pressure (inlet pressure) to 0-5MPa.

[0148] In the present invention, the method further comprises: desorbing the adsorbed alloy material at 200-500° C. to obtain regenerated adsorbed material and desorbed gas, and returning (eg, reflux) the obtained desorbed gas to the catalytic oxidative dehydrogenation unit.

[0149] A second aspect of the present invention provides a system for purifying helium, the system comprising a catalytic dehydrogenation separation unit, a first-stage polymer membrane separation unit, an alloy adsorption unit and a second-stage polymer membrane separation unit connected in sequence;

[0150] Preferably, the catalytic dehydrogenation separation unit comprises a catalytic oxidation device and a dehydration drying device.

[0151] In the present invention, the meanings of abbreviations are:

[0152] PMDA: Pyromellitic anhydride

[0153] BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride

[0154] ODPA: 4,4'-diphenyl ether dianhydride

[0155] 6FDA: 4,4'-(Hexafluoroisopropylene) diphthalic anhydride

[0156] BTDA: 3,3',4,4'-Benzophenone tetracarboxylic dianhydride

[0157] TPDAn (a compound represented by formula (III), wherein Y is Yd): triptylenyl dianhydride (prepared by referring to “LUO SJ, WIEGAND JR, KAZANOWSKA B, et al. Finely Tuning the Free Volume Architecture in Iptycene-Containing Polyimides for Highly Selective and Fast Hydrogen Transport. Macromolecules 2016, 49, (9): 3395-3405”)

[0158] mPDA: meta-phenylenediamine

[0159] PPDA (structural formula: ): Pentiptycene diamine (prepared according to “LUO SJ, LIU Q, ZHANG BH, et al. Pentiptycene-based polyimides with hierarchically controlled molecular cavity architecture for efficient membrane gasseparation. J Membrane Sci 2015, 480: 20-30”)

[0160] The present invention will be described in detail below through examples.

[0161] In the following preparation examples, the mechanical stirring conditions are: 10000 rpm at room temperature, 5 h; the ultrasonic conditions are: room temperature, 1 h; the shaking conditions are: 30°C, 600 rpm, 15 h;

[0162] In the following preparation examples, unless otherwise specified, all examples were commercially available; the hollow spinneret was purchased from Shanghai Zhanxin; the porosity of the hollow fiber membrane support layer was measured by mercury intrusion; and the thickness of the dense layer was measured by scanning electron microscopy.

[0163] In the following embodiments, the test method for the volume fraction of each gas is as follows: gas chromatography. In the embodiments, the primary membrane separation represents a polymer membrane separation, the secondary membrane separation represents the gas after the primary polymer separation is used as the inlet gas for polymer membrane separation again (using a fresh membrane assembly), and the tertiary membrane separation, the quaternary membrane separation and the quintuple membrane separation are similar.

[0164] The following preparation examples are used to illustrate the preparation of polyimide random copolymers and polyimide flat films.

[0165] Preparation Example 1

[0166] (1) Under nitrogen protection, 200 mL of anhydrous N-methylpyrrolidone and m-phenylenediamine (10.81 g, 0.1 mmol) were added to a 1 L three-necked flask in sequence and stirred until the materials were completely dissolved; 4,4-diphenyl ether dianhydride (ODPA) (12.4138 g, 0.04 mmol) and 4,4'-(hexafluoroisopropylene) diphthalic anhydride (6FDA) (26.6544 g, 0.06 mmol) were mixed under mechanical stirring, and then added to the above system at 20° C. and polycondensed for 12 h to obtain a material containing polyimide acid;

[0167] (2) A mixture of acetic anhydride (36.7524 g, 0.36 mmol) and pyridine (28.4760 g, 0.36 mmol) was added to the polyimide acid material obtained in step (1), and intramolecular dehydration was performed at 180° C. for 18 h to obtain a material containing polyimide; then 600 mL of N-methylpyrrolidone (NMP) was added to the polyimide-containing material for dilution, and the diluted material was poured into a mixed solvent of water and ethanol (500 mL: 500 mL) under stirring to precipitate polyimide to obtain polyimide, and then the mixture was rinsed with a mixed solution of water and ethanol (1500 mL: 1500 mL) (3 times), and a polyimide random copolymer was obtained after suction filtration and drying. The polyimide random copolymer was subjected to infrared testing using a Fourier transform infrared spectrometer (Thermo Nicolet 380), and the infrared spectrum is shown in FIG. Figure 1 Infrared testing shows that the polyimide random copolymer has a structure shown in formula (I), wherein X is Xc, Y is Ya, and Z and Z' are both Z1. In addition, no raw materials are detected in the remaining liquid phase after the polyimide is precipitated, indicating that all raw materials participate in the reaction.

[0168] Figure 1 Medium, 1784cm -1 and 1730cm -1 The peaks at 1357 cm-1 are the symmetric stretching vibration peaks and asymmetric stretching vibration peaks of the two carbonyl groups on the five-membered imine ring in polyimide. -1is the stretching vibration of CN in polyimide, 721 cm -1 is the deformation vibration peak of the imine ring, 1255cm -1 The stretching vibration of the ether bond in aromatic ether is 1144 cm -1 The peak at is the stretching vibration peak of CF, that is, the appearance of the above characteristic peaks indicates the successful synthesis of PI-1.

[0169] The polyimide obtained above is used to prepare a gas separation membrane:

[0170] The above-mentioned polyimide random copolymer is added to NMP at a solid content of 15wt%, and stirred in a shaking table at 50°C until the above-mentioned polyimide random copolymer is completely dissolved to obtain a uniform and stable casting liquid; the casting liquid is cooled to room temperature, ultrasonically degassed, and then uniformly coated on the surface of a clean glass plate, placed in a blast oven at 70°C for 6 hours to remove a large amount of solvent, and then moved to a vacuum oven (dried at 120°C for 12 hours) to further remove the solvent; after cooling to room temperature, the glass plate with the membrane is immersed in deionized water until the membrane falls off the surface of the glass plate to obtain a gas separation membrane (flat membrane).

[0171] Preparation Example 2

[0172] (1) Under nitrogen protection, 200 mL of anhydrous N-methylpyrrolidone and m-phenylenediamine (10.81 g, 0.1 mmol) were added to a 1 L three-necked flask in sequence, and stirred until the materials were completely dissolved; 4,4-diphenyl ether dianhydride (ODPA) (0.01 mmol) and 4,4'-(hexafluoroisopropylene) diphthalic anhydride (6FDA) (0.09 mmol) were mixed under mechanical stirring, and then added to the above system at 0°C, and polycondensation reaction was carried out for 12 hours to obtain a material containing polyimide acid;

[0173] (2) Add a mixture of acetic anhydride (0.36 mmol) and pyridine (0.36 mmol) to the polyimide acid material obtained in step (1), and perform intramolecular dehydration at 200°C for 24 hours to obtain a material containing polyimide; then add 600 mL of N-methylpyrrolidone (NMP) to the polyimide-containing material for dilution, and pour the diluted material into a mixed solvent of water and ethanol (500 mL: 500 mL) under stirring to precipitate polyimide to obtain polyimide, and then rinse with a mixed solution of water and ethanol (1500 mL: 1500 mL) (3 times), and obtain a polyimide random copolymer after suction filtration and drying. Infrared testing shows that the polyimide random copolymer has a structure shown in formula (I), wherein X is Xc, Y is Ya, and Z and Z' are both Z1. In addition, no raw materials can be detected in the remaining liquid phase after the polyimide is precipitated, indicating that all raw materials participate in the reaction.

[0174] The polyimide obtained above is used to prepare a gas separation membrane:

[0175] The above-mentioned polyimide random copolymer is added to NMP at a solid content of 40wt%, and stirred in a shaking table at 50°C until PI-2 is completely dissolved to obtain a uniform and stable casting liquid; the casting liquid is cooled to room temperature, ultrasonically degassed and evenly coated on the surface of a clean glass plate, placed in a 70°C forced air oven for 6 hours to remove a large amount of solvent, and then moved to a vacuum oven (dried at 120°C for 12 hours) to further remove the solvent; after cooling to room temperature, the glass plate with the membrane is immersed in deionized water until the membrane falls off the surface of the glass plate to obtain a gas separation membrane (flat membrane).

[0176] Preparation Example 3

[0177] (1) Under nitrogen protection, 200 mL of anhydrous N-methylpyrrolidone and m-phenylenediamine (10.81 g, 0.1 mmol) were added to a 1 L three-necked flask in sequence and stirred until the materials were completely dissolved; 4,4'-biphenyl ether dianhydride (0.05 mmol) and tripterycene dianhydride (0.05 mmol) were mixed under mechanical stirring, and then added to the above system at 20° C. and polycondensed for 12 h to obtain a material containing polyimide acid;

[0178] (2) Add a mixture of acetic anhydride (0.36 mmol) and pyridine (0.36 mmol) to the polyimide acid material obtained in step (1), and perform intramolecular dehydration at 180°C for 18 hours to obtain a material containing polyimide; then add 600 mL of N-methylpyrrolidone (NMP) to the polyimide-containing material for dilution, and pour the diluted material into a mixed solvent of water and ethanol (500 mL: 500 mL) under stirring to precipitate polyimide to obtain polyimide, and then rinse with a mixed solution of water and ethanol (1500 mL: 1500 mL) (3 times), and obtain a polyimide random copolymer after suction filtration and drying. Infrared testing shows that the polyimide random copolymer has a structure shown in formula (I), wherein X is Xc, Y is Yd, and Z and Z' are both Z1. In addition, no raw materials can be detected in the remaining liquid phase after the polyimide is precipitated, indicating that all raw materials participate in the reaction.

[0179] The polyimide obtained above is used to prepare a gas separation membrane:

[0180] The above-mentioned polyimide random copolymer is added to NMP at a solid content of 15wt%, and stirred in a shaking table at 50°C until PI-3 is completely dissolved to obtain a uniform and stable casting liquid; the casting liquid is cooled to room temperature, ultrasonically degassed and evenly coated on the surface of a clean glass plate, placed in a blast oven at 70°C for 6 hours to remove a large amount of solvent, and then moved to a vacuum oven (dried at 120°C for 12 hours) to further remove the solvent; after cooling to room temperature, the glass plate with the membrane is immersed in deionized water until the membrane falls off the surface of the glass plate to obtain a gas separation membrane (flat membrane).

[0181] Preparation Example 4

[0182] The method of Preparation Example 1 is followed, except that 4,4'-(hexafluoroisopropylene) diphthalic anhydride (6FDA) is replaced with an equimolar amount of tripterylenyl dianhydride, and m-phenylenediamine is replaced with a molar amount of pentaterylenyl diamine. A polyimide random copolymer is prepared. The specific reaction conditions are shown in Table 1. Infrared testing shows that the above-mentioned polyimide random copolymer has a structure shown in formula (I), wherein X is Xc, Y is Yd, and Z and Z' are both Z3. In addition, no raw materials are detected in the remaining liquid phase after the polyimide is precipitated, indicating that all raw materials participate in the reaction.

[0183] A separation membrane (flat membrane) was prepared in the same manner as in Preparation Example 1.

[0184] The following preparation examples are used to illustrate the preparation of polyimide-based hollow fiber membranes.

[0185] Preparation Example 1

[0186] (1) Add 30 wt % of the random copolymer of polyimide obtained in Preparation Example 2, 45 wt % of NMP, 10 wt % of ethanol (boiling point 78° C.), 10 wt % of THF (boiling point 68.28° C.) and 5 wt % of lithium nitrate into a kettle with a stirring device, heat to 50° C., and stir (speed 600 r / min) for 36 hours under nitrogen protection. After stopping stirring, degas at 25° C., -0.1 MPa, and speed 30 r / min for 24 hours, and then filter through a filter screen (pore size 100 mesh) at 50° C. to obtain a casting solution;

[0187] (2) using a metering pump to deliver the casting liquid and the inner core liquid (NMP: water = 95wt%: 5wt%) to the hollow spinneret, respectively, the inner core liquid and the casting liquid are extruded through the spinneret together to obtain a hollow fiber, the hollow fiber is passed through an air gap of 10 cm, and then placed in 50°C water for solidification to obtain a polyimide-based hollow fiber membrane precursor; wherein the spinneret temperature (extrusion temperature) is 75°C; the flow rates of the casting liquid and the inner core liquid entering the hollow spinneret are 6mL / min and 2mL / min, respectively;

[0188] (3) The polyimide hollow fiber membrane precursor obtained in step (2) is wound up by a winding machine, and then extracted twice in water, ethanol, and n-hexane in sequence, and the extraction time is 3 hours; then the extracted hollow fiber membrane is placed in a fume hood at room temperature and air-dried for 12 hours to obtain a polyimide-based hollow fiber membrane. The winding speed is 1 m / s.

[0189] The obtained hollow fiber membrane was characterized by mercury intrusion method, and the porosity was 65.5%. The thickness of the dense layer was 150nm. The mechanical properties were characterized (the characterization method refers to "Determination of tensile properties of plastics GB / T1040.1-2006"), the membrane wire breaking force was 6N, and the elongation at break was 50%; the electron microscope scanning image of the cross section of the hollow fiber membrane is shown in Figure 2 The membrane fibers were dissolved in deuterated reagent DMSO and then 1 H NMR spectroscopy analysis, see Figure 4 .

[0190] Preparation Example 2

[0191] (1) Add 27.5 wt % of the random copolymer of polyimide obtained in the above-mentioned Preparation Example 1, 48.5 wt % of DMF, 10 wt % of ethanol (boiling point 78° C.), 10 wt % of THF (boiling point 68.28° C.) and 4 wt % of lithium nitrate into a kettle with a stirring device, heat to 50° C., and stir (speed 1200 r / min) for 36 hours under nitrogen protection. After stopping stirring, degas at 25° C., -0.1 MPa, and speed 50 r / min for 24 hours, and then filter through a filter screen (pore size 100 mesh) at 50° C. to obtain a casting solution;

[0192] (2) using a metering pump to deliver the casting liquid and the inner core liquid (NMP: water = 95wt%: 5wt%) to the hollow spinneret, respectively, the inner core liquid and the casting liquid are extruded through the spinneret together to obtain a hollow fiber, the hollow fiber is passed through an air gap of 5 cm, and then placed in 50°C water for solidification to obtain a polyimide-based hollow fiber membrane precursor; wherein the spinneret temperature is 70°C; the flow rates of the casting liquid and the inner core liquid entering the hollow spinneret are 8mL / min and 2.5mL / min, respectively;

[0193] (3) The polyimide hollow fiber membrane precursor obtained in step (2) is wound up by a winding machine, and then extracted twice in water, ethanol, and n-hexane in sequence, and the extraction time is 3 hours; then the extracted hollow fiber membrane is placed in a fume hood at room temperature and air-dried for 12 hours to obtain a polyimide-based hollow fiber membrane. The winding speed is 1 m / s.

[0194] The obtained hollow fiber membrane was characterized by mercury intrusion method, and the porosity of the support layer was 67.5%. The thickness of the dense layer was 400nm. The electron microscope scanning image of the cross section of the hollow fiber membrane is shown in Figure 3 .

[0195] Preparation Example 3

[0196] The preparation was carried out in the same manner as in Preparation Example 1, except that the polyimide copolymer obtained in Preparation Example 3 was used instead of the polyimide random copolymer obtained in Preparation Example 2.

[0197] The obtained hollow fiber membrane (polyimide hollow fiber membrane with triptycene structure) was characterized by mercury intrusion porosimetry, and the porosity was 63.5% and the thickness of the dense layer was 140 nm.

[0198] The following example is used to illustrate the process of purifying helium.

[0199] Example 1

[0200] The natural gas extracted from a gas field is subjected to multi-stage flash evaporation to obtain raw gas 1#, wherein the volume fraction of helium in the raw gas is 8.5%, and the composition of other gases includes: 35% by volume of methane, 37.3% by volume of nitrogen, 2.1% by volume of hydrogen, 7.5% by volume of carbon dioxide and 9.5% by volume of oxygen.

[0201] The raw gas (space velocity 95m 3 / m 3 h) passing into a catalytic dehydrogenation unit, wherein Pt is used as a catalyst in the oxidative dehydrogenation process, the temperature of the catalytic oxidation reaction is 60° C., and the volume fraction of oxygen is maintained at greater than 8%; the gas from the outlet of the catalytic oxidation device is passed into a dehydration drying unit; the gas 2# after catalytic dehydrogenation (temperature controlled at 25° C.) enters the polyimide hollow fiber membrane assembly prepared by the above-mentioned Preparation Example 1 for the first stage polymer membrane separation (primary membrane separation and secondary membrane separation operations are performed in sequence (the first stage membrane inlet pressure is increased to 3 MPa, and the secondary membrane pressure is increased to 2 MPa)) , the permeate gas 3# after the first stage of polymer membrane separation is heat exchanged to 50°C and then enters the alloy adsorption separator for deep dehydrogenation to obtain ultra-pure helium product. The adsorbent uses magnesium-based hydrogen storage alloy (Xi'an Qiyue Biotechnology Co., Ltd.). The adsorbent after hydrogen adsorption is desorbed at a desorption temperature of 300°C, and the desorbed gas obtained is refluxed to the entrance of the oxidative dehydrogenation unit; the gas (high-purity helium) 4# after adsorption dehydrogenation is then separated by the second stage of polymer membrane (the polyimide hollow fiber membrane prepared in the above-mentioned Preparation Example 1), and the permeate gas is the product gas (ultra-pure helium 5#). Among them, the volume fractions of the gas components after separation at each stage are shown in Table 1.

[0202] Table 1 (In Table 1, "one-stage membrane separation" refers to "first-stage polymer membrane separation", and "two-stage membrane separation" refers to "second-stage polymer membrane separation")

[0203] Table 1

[0204] No.\composition mol% Helium Methane Nitrogen <![CDATA[CO 2 ]]> hydrogen oxygen Raw gas 1# 8.5 35 37.3 7.5 2.1 9.5 Gas after oxidative dehydrogenation 2# 8.78 35.16 38.55 7.75 0.02 8.74 One-stage membrane separation (first stage) permeate gas 35.39 25.59 27.27 5.48 0.08 6.19 First stage membrane separation (secondary) permeate gas 3# 90.18 3.83 4.08 0.82 0.17 0.92 Gas 4 after alloy adsorption 90.33 3.83 4.09 0.82 0.002 0.93 Second stage membrane separation permeate steam 5# 99.998 0 0 0 0.002 0

[0205] Example 2

[0206] The natural gas extracted from a gas field is subjected to multi-stage flash evaporation to obtain raw gas 1#, wherein the volume fraction of helium in the raw gas is 15.73%, and the composition of other gases includes: methane with a volume fraction of 19.9%, nitrogen with a volume fraction of 57.7%, hydrogen with a volume fraction of 6.62% and oxygen with a volume fraction of 0.05%.

[0207] The raw gas (space velocity 410m 3 / m 3 h) into a catalytic dehydrogenation unit, wherein Ru is used as a catalyst in the oxidative dehydrogenation process, the temperature of the catalytic oxidation reaction is 50° C., and the volume fraction of oxygen is maintained at greater than 8%; the gas from the outlet of the catalytic oxidation device is passed into a dehydration drying unit; the gas 2# after catalytic dehydrogenation (temperature controlled at 10° C.) enters the polyimide hollow fiber membrane assembly prepared by the above-mentioned Preparation Example 2 for the first stage polymer membrane separation (first stage membrane separation and second stage membrane separation operations are performed in sequence (first stage membrane inlet pressure is increased to 8 MPa, and second stage membrane pressure is increased to 10 MPa)), after the first The permeate gas 3# after separation by the first polymer membrane is heat exchanged to 20°C and then enters the alloy adsorption separator for deep dehydrogenation to obtain an ultra-pure helium product. The adsorbent is a magnesium-based hydrogen storage alloy (Xi'an Qiyue Biotechnology Co., Ltd.). The adsorbent after hydrogen adsorption is desorbed at a desorption temperature of 400°C. The desorbed gas obtained is refluxed to the entrance of the oxidative dehydrogenation unit; the gas (high-purity helium) 4# after adsorption and dehydrogenation is then separated by the second polymer membrane (using the polyimide hollow fiber membrane with a triptycene structure prepared in the above-mentioned preparation example 3), and the permeate gas is the product gas (ultra-pure helium 5#). The volume fractions of the gas components after separation at each stage are shown in Table 2.

[0208] Table 2 (In Table 2, "one-stage membrane separation" refers to "first-stage polymer membrane separation", and "two-stage membrane separation" refers to "second-stage polymer membrane separation")

[0209] Table 2

[0210]

[0211]

[0212] Example 3

[0213] The natural gas extracted from a gas field is subjected to two-stage flash evaporation to obtain raw gas 1#, wherein the volume fraction of helium in the raw gas is 19.7%, and the composition of other gases includes: methane with a volume fraction of 15.9%, nitrogen with a volume fraction of 53.7%, carbon dioxide with a volume fraction of 10.65%, hydrogen with a volume fraction of 0.05%, oxygen with a volume fraction of 0.05%, and other impurity gases.

[0214] The raw gas (space velocity 760m 3 / m 3 h) into a catalytic dehydrogenation unit, wherein Pd is used as a catalyst in the oxidative dehydrogenation process, the temperature of the catalytic oxidation reaction is 100° C., and the volume fraction of oxygen is maintained at greater than 8%; the gas from the outlet of the catalytic oxidation device is passed into a dehydration drying unit; the gas 2# after catalytic dehydrogenation (temperature controlled at 25° C.) enters the polyimide tubular membrane assembly with a triptycene structure prepared in the above-mentioned Preparation Example 3 for the first stage polymer membrane separation (first stage membrane separation, second stage membrane separation operation, third stage membrane separation, fourth stage membrane separation (first stage membrane inlet pressure increased to 2MPa, second stage membrane pressure increased to 3MPa, third stage membrane inlet pressure increased to 1MPa, fourth stage membrane pressure increased to 2MPa, fourth stage membrane pressure increased to 3MPa, fourth stage membrane pressure increased to 1MPa, fifth stage membrane pressure increased to 2MPa, fifth stage membrane pressure increased to 3 ... The permeate gas 3# after separation by the first polymer membrane is heat exchanged to 20°C and then enters the alloy adsorption separator for deep dehydrogenation to obtain ultra-pure helium products. The adsorbent is a magnesium-based hydrogen storage alloy (Xi'an Qiyue Biotechnology Co., Ltd., customized magnesium-based hydrogen storage alloy). The adsorbent is desorbed after hydrogen adsorption, and the desorption temperature is 420°C. The desorbed gas is refluxed to the inlet of the oxidative dehydrogenation unit; the gas (high-purity helium) 4# after adsorption dehydrogenation is separated by the second polymer membrane (polysulfone, Permea, PRISM○R), and the permeate gas is the product gas (ultra-pure helium 5#). The volume fractions of the gas components after separation at each stage are shown in Table 3.

[0215] Table 3 (In Table 3, "one-stage membrane separation" refers to "first-stage polymer membrane separation", and "two-stage membrane separation" refers to "second-stage polymer membrane separation")

[0216] Table 3

[0217] No.\composition mol% Helium Methane Nitrogen <![CDATA[CO 2 ]]> hydrogen oxygen Raw gas 1# 19.7 15.9 53.7 10.65 0.05 0 Gas after oxidative dehydrogenation 2# 18.16 14.65 49.49 9.82 0 7.88 One-stage membrane separation (first stage) permeate gas 53.15 8.39 28.33 5.62 0 4.51 One-stage membrane separation (secondary) permeate gas 90.96 1.62 5.47 1.08 0 0.87 First stage membrane separation (three-stage) permeate gas 99.47 0.1 0.32 0.06 0 0.05 First stage membrane separation (fourth stage) permeate gas 3# 99.982 0.003 0.011 0.002 0 0.002 Gas 4 after alloy adsorption 99.982 0.003 0.011 0.002 0 0.002 Second stage membrane separation permeate steam 5# 99.999 0 0.001 0 0 0

[0218] Example 4

[0219] The volume fraction of helium in the raw gas 1# of the flash steam 1# (BOG) of the liquefied natural gas station is 22.32%, and the composition of other gases includes: 17.8% by volume of methane, 52.5% by volume of nitrogen, 7.32% by volume of hydrogen, 0.06% by volume of oxygen and other impurity gases.

[0220] The raw gas (space velocity 500m3 / m 3 h) into a catalytic dehydrogenation unit, wherein Pd is used as a catalyst in the oxidative dehydrogenation process, the temperature of the catalytic oxidation reaction is 80° C., and the volume fraction of oxygen is maintained at greater than 8%; the gas from the outlet of the catalytic oxidation device is passed into a dehydration drying unit; the gas 2# after catalytic dehydrogenation (temperature controlled at 12° C.) enters the polyimide tubular membrane assembly with a triptycene structure prepared in the above-mentioned Preparation Example 3 for the first stage polymer membrane separation (first stage membrane separation, second stage membrane separation operation, third stage membrane separation (first stage membrane inlet pressure is increased to 0.3 MPa, second stage membrane is controlled to 0.1 MPa, The three-stage membrane inlet is pressurized to 0.3MPa), and the permeate gas 3# after separation by the first stage polymer membrane is heat exchanged to 20°C and then enters the alloy adsorption separator for deep dehydrogenation to obtain ultra-pure helium product. The adsorbent uses titanium-based hydrogen storage alloy (Xi'an Qiyue Biotechnology Co., Ltd.). The adsorbent desorbs hydrogen at a desorption temperature of 350°C, and the desorbed gas is refluxed to the inlet of the oxidative dehydrogenation unit; the gas (high-purity helium) 4# after adsorption dehydrogenation is separated by the second stage polymer membrane (the polyimide flat membrane prepared in the above Preparation Example 1), and the permeate gas is the product gas (ultra-pure helium 5#). The volume fractions of the gas components after separation at each stage are shown in Table 4.

[0221] Table 4 (In Table 4, "one-stage membrane separation" refers to "first-stage polymer membrane separation", and "two-stage membrane separation" refers to "second-stage polymer membrane separation")

[0222] Table 4

[0223] No.\composition mol% Helium Methane Nitrogen hydrogen oxygen Raw gas 1# 22.32 17.8 52.5 7.32 0.06 Gas after oxidative dehydrogenation 2# 22.88 18.24 53.81 0.07 5.0 One-stage membrane separation (first stage) permeate gas 60.07 9.41 27.76 0.18 2.58 One-stage membrane separation (secondary) permeate gas 95.91 0.91 2.69 0.24 0.25 First stage membrane separation (three-stage) permeate gas 3# 99.7 0.03 0.08 0.18 0.01 Gas 4 after alloy adsorption 99.998 0 0 0.002 0 Second stage membrane separation permeate steam 5# 22.32 17.8 52.5 7.32 0.06

[0224] Example 5

[0225] The volume fraction of helium in natural gas No. 1 produced from a shale gas field is 0.6%, and the composition of other gases includes: 75% by volume of methane, 15.3% by volume of nitrogen, 5.5% by volume of carbon dioxide, 2.1% by volume of hydrogen, 1.5% by volume of oxygen and other impurity gases.

[0226] The raw gas (space velocity 17m 3 / m 3h) into a catalytic dehydrogenation unit, wherein Pd is used as a catalyst in the oxidative dehydrogenation process, the temperature of the catalytic oxidation reaction is 120° C., and the volume fraction of oxygen is maintained at greater than 8%; the gas from the outlet of the catalytic oxidation device is passed into a dehydration drying unit; the gas 2# after catalytic dehydrogenation (temperature controlled at 50° C.) enters the polyimide flat homogeneous membrane assembly obtained in the above Preparation Example 2 for the first stage polymer membrane separation (first stage membrane separation, second stage membrane separation operation, third stage membrane separation, fourth stage membrane separation, fifth stage membrane separation (first stage membrane inlet pressure increased to 2.5 MPa, second stage membrane pressure increased to 2.5 MPa, third stage membrane pressure increased to 3M Pa, four-stage membrane pressurization to 3MPa, four-stage membrane pressurization to 4MPa), the permeate 3# after the first stage polymer membrane separation is heat exchanged to 30°C and then enters the alloy adsorption separator for deep dehydrogenation to obtain ultra-pure helium product, the adsorbent uses titanium series hydrogen storage alloy (Xi'an Qiyue Biotechnology Co., Ltd.), the adsorbent after hydrogen adsorption is desorbed, the desorption temperature is 500°C, and the desorbed gas obtained is refluxed to the entrance of the oxidative dehydrogenation unit; the gas (high-purity helium) 4# after adsorption dehydrogenation is separated by the second stage polymer membrane (the polyimide flat homogeneous membrane component prepared in the above preparation example 2), and the permeate gas is the product gas (ultra-pure helium 5#). Among them, the volume fractions of the gas components after separation in each stage are shown in Table 5.

[0227] Table 5 (In Table 5, "one-stage membrane separation" refers to "first-stage polymer membrane separation", and "two-stage membrane separation" refers to "second-stage polymer membrane separation")

[0228] Table 5

[0229] No.\composition mol% Helium Methane Nitrogen <![CDATA[CO 2 ]]> hydrogen oxygen Raw gas 1# 0.6 75 15.3 5.5 2.1 1.5 Gas after oxidative dehydrogenation 2# 0.57 71.79 14.65 5.27 0.02 7.7 One-stage membrane separation (first stage) permeate gas 1.76 70.91 14.46 5.2 0.06 7.61 One-stage membrane separation (secondary) permeate gas 6.1 67.67 13.81 4.96 0.2 7.26 First stage membrane separation (three-stage) permeate gas 22.98 55.11 11.24 4.04 0.72 5.91 One-stage membrane separation (fourth stage) permeate gas 70.79 19.66 4.01 1.44 1.99 2.11 First stage membrane separation (five-stage) permeate gas 3# 94.88 2.02 0.41 0.15 2.32 0.22 Gas 4 after alloy adsorption 97.12 2.07 0.42 0.15 0.02 0.22 Second stage membrane separation permeate steam 5# 99.98 0 0 0 0.02 0

[0230] Example 6

[0231] The volume fraction of helium in the raw gas 1# of the flash steam 1# (BOG) of the liquefied natural gas station is 15.73%, and the composition of other gases includes: 19.9% ​​by volume of methane, 57.7% by volume of nitrogen, 6.62% by volume of hydrogen, 0.05% by volume of oxygen and other impurity gases (the volume fraction of various light hydrocarbons is <0.001%, which can be ignored).

[0232] The raw gas (space velocity 320m 3 / m 3h) passing into a catalytic dehydrogenation unit, wherein Au is used as a catalyst in the oxidative dehydrogenation process, the temperature of the catalytic oxidation reaction is 99° C., and the volume fraction of oxygen is maintained at greater than 8%; the gas from the outlet of the catalytic oxidation device is passed into a dehydration drying unit; the gas 2# after catalytic dehydrogenation (temperature controlled at 44° C.) enters the polyimide hollow fiber membrane assembly with a triptycene structure prepared in the above-mentioned Preparation Example 3 for the first stage polymer membrane separation (first stage membrane separation, second stage membrane separation operation, and third stage membrane separation (first stage membrane inlet pressure is increased to 2MPa, second stage membrane pressure is increased to 1.5MPa, and third stage membrane inlet pressure is increased to 1.5MPa)), and then The permeate gas 3# after the first stage polymer membrane separation is heat exchanged to 20°C and then enters the alloy adsorption separator for deep dehydrogenation to obtain an ultra-pure helium product. The adsorbent is a zirconium-based hydrogen storage alloy (Xi'an Qiyue Biotechnology Co., Ltd.). The adsorbent after hydrogen adsorption is desorbed at a desorption temperature of 210°C, and the desorbed gas obtained is refluxed to the inlet of the oxidative dehydrogenation unit; the gas (high-purity helium) 4# after adsorption and dehydrogenation is then separated by the second stage polymer membrane (the polyimide hollow fiber membrane component with a triptycene structure prepared in the above Preparation Example 3, and the permeate gas is the product gas (ultra-pure helium 5#). The volume fractions of the gas components after separation at each stage are shown in Table 6.

[0233] Table 6 (In Table 6, "one-stage membrane separation" refers to "first-stage polymer membrane separation", and "two-stage membrane separation" refers to "second-stage polymer membrane separation")

[0234] Table 6

[0235] No.\composition mol% Helium Methane Nitrogen hydrogen oxygen Raw gas 1# 15.73 19.9 57.7 6.62 0.05 Gas after oxidative dehydrogenation 2# 15.87 20.08 58.21 0.07 5.77 One-stage membrane separation (first stage) permeate gas 59.35 9.65 27.99 0.23 2.78 One-stage membrane separation (secondary) permeate gas 96.8 0.7 2.02 0.28 0.2 First stage membrane separation (three-stage) permeate gas 3# 99.62 0.03 0.1 0.25 0 Gas 4# after alloy adsorption 99.86 0.03 0.1 0.002 0.01 Second stage membrane separation permeate steam 5# 99.998 0 0 0.002 0

[0236] Comparative Example 1

[0237] The method of Example 1 is followed, except that no catalytic oxidative dehydrogenation unit is provided. The volume fractions of the gas components after separation at each stage are shown in Table 7.

[0238] Table 7

[0239] No.\composition mol% Helium Methane Nitrogen <![CDATA[CO 2 ]]> hydrogen oxygen Raw gas 1# 8.5 35 37.3 7.5 2.1 9.5 One-stage membrane separation (first stage) permeate gas 32.42 26.70 25.75 2.85 7.21 5.07 First stage membrane separation (secondary) permeate gas 2# 78.72 4.32 1.39 0.42 14.59 0.57 Gas after alloy adsorption 3# 92.03 5.05 1.62 0.49 0.14 0.67 Second stage membrane separation permeate steam 4# 99.84 0.00 0.00 0.00 0.15 0.00

[0240] Comparative Example 2

[0241] The method of Example 1 was followed, except that the first polymer membrane separation unit was not provided. The volume fractions of the gas components after separation at each stage are shown in Table 8.

[0242] Table 8

[0243] No.\composition mol% Helium Methane Nitrogen <![CDATA[CO 2 ]]> hydrogen oxygen Raw gas 1# 8.5 35 37.3 7.5 2.1 9.5 Gas after oxidative dehydrogenation 2# 8.73 35.93 38.39 7.70 0.02 9.24 Gas after alloy adsorption 3# 8.73 35.93 38.40 7.70 0.00 9.24 Polymer membrane separation permeate vapor 4# 99.80 0.04 0.04 0.01 0.00 0.11

[0244] Comparative Example 3

[0245] The method of Example 1 was followed, except that the order of the catalytic dehydrogenation unit and the first stage polymer membrane separation unit was replaced. The volume fractions of the gas components after separation at each stage are shown in Table 9.

[0246] Table 9

[0247] No.\composition mol% Helium Methane Nitrogen <![CDATA[CO 2 ]]> hydrogen oxygen Raw gas 1# 8.5 35 37.3 7.5 2.1 9.5 One-stage membrane separation (first stage) permeate gas 32.42 26.70 25.75 2.85 7.21 5.07 First stage membrane separation (secondary) permeate gas 2# 78.72 4.32 1.39 0.42 14.59 0.57 Gas after oxidative dehydrogenation #3 92.00 5.05 1.62 0.49 0.17 0.67 Gas 4 after alloy adsorption 92.16 5.06 1.62 0.49 0 0.67 Second stage membrane separation permeate steam 5# 99.993 0 0 0 0.004 0

[0248] The polymer films of the preferred embodiments used in the present invention can achieve better results. For details, please refer to the contents recorded in (Application No. 202110864549.5).

[0249] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for purifying helium by using a two-stage membrane combined with alloy adsorption, It is characterized in that The method comprises: subjecting the raw gas to catalytic dehydrogenation separation, first-stage polymer membrane separation, alloy adsorption and second-stage polymer membrane separation in sequence to obtain ultrapure helium; Wherein, the polymer membrane used in the first stage polymer membrane separation and the second stage polymer membrane separation is a polyimide-based hollow fiber membrane; the material of the hollow fiber membrane is a polyimide random copolymer; The polyimide random copolymer has a structure shown in formula (I): （I）， In formula (I), m and n are each independently an integer of 10-2000; X has a structure represented by any one of formula (X1) to formula (X3); (X1)、 (X2)、 (X3), In formula (X1)-formula (X3), R 1 , R 2 , R 3 , R 4 , R 5 and R 6 Each is independently H, C1-C4 alkyl, C6-C10 aryl, amino, hydroxyl or carboxyl; Y has a structure represented by any one of formula (Y1) to formula (Y5); <h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> (Y1)<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> (Y2)<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> (Y3)<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> (Y4)<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> (Y5) In formula (Y1) to formula (Y5), R 7 , R 8 , R 9 , R 10 , R 11 , R 12 , R 13 , R 14 , R 15 and R 16 Each is independently H, C1-C4 alkyl, C6-C10 aryl, amino, hydroxyl or carboxyl; Z and Z' each independently have a structure represented by formula (Z1) or formula (Z2); (Z1)、 (Z2), In formula (Z2), Ra and Rb are each independently H, C1-C4 alkyl or C1-C4 halogenated alkyl.

2. The method according to claim 1, in, The raw gas is selected from at least one of natural gas, shale gas, helium-rich hydrogen-containing gas and liquefied natural gas flash steam (BOG).

3. The method according to claim 1 or 2, in, The catalytic dehydrogenation separation includes catalytic oxidation and dehydration drying, and the catalyst used in the catalytic oxidation is a precious metal catalyst selected from at least one of Pt, Pd, Rh, Ru and Au; And / or, the conditions of the catalytic oxidation include: a temperature of 40-150°C; a space velocity of the feed gas of 1-10000 m 3 / m 3 ·h.

4. The method according to claim 3, in, The conditions of the catalytic oxidation include: a temperature of 50-120°C; a space velocity of the raw gas of 10-1000 m / s; 3 / m 3 ·h.

5. The method according to claim 3, in, The conditions of the catalytic oxidation are such that 90-100% by volume of the hydrogen in the feed gas is converted into H 2 O.

6. The method according to claim 1 or 2, in, The first stage polymer membrane separation adopts a one-stage or multi-stage separation method; And / or, the conditions of the first stage polymer membrane separation include: before the first stage polymer membrane separation, the pressure of the gas obtained by catalytic dehydrogenation separation is controlled to be 0.01-10 MPa, and the temperature is controlled to be less than or equal to 50°C.

7. The method according to claim 6, in, The conditions for the first stage polymer membrane separation include: before the first stage polymer membrane separation, the pressure of the gas obtained by catalytic dehydrogenation separation is controlled to be 0.1-8 MPa and the temperature is controlled to be 0-50°C.

8. The method according to claim 1 or 2, in, The polyimide-based hollow fiber membrane comprises a support layer and a dense layer attached to the outer surface of the support layer, the thickness of the dense layer is less than 1000nm, and the porosity of the hollow fiber membrane is 40-80%.

9. The method according to claim 8, in, The thickness of the dense layer is 100-500 nm, and the porosity of the hollow fiber membrane is 50-70%.

10. The method according to claim 1, in, In the formula (I), m and n are each independently an integer of 50-1000.

11. The method according to claim 1, in, 0.9≥n / (m+n)≥0.

3.

12. The method according to claim 11, in, 0.7≥n / (m+n)≥0.

5.

13. The method according to any one of claims 1, 10, 11 and 12, in, The X has one of the following structures, 、 、 ； And / or, Y has one of the following structures, 、 、 、 、 ； and / or, Z and Z' both have the structure shown by Z1 or Z3, 、 。 14. The method according to claim 13, in, X is Xa, Y is Ya, and Z and Z' are both Z1; Alternatively, X is Xa, Y is Yb, and Z and Z' are both Z1; Or, X is Xa, Y is Yd, and Z and Z' are both Z1; Or, X is Xb, Y is Ya, and Z and Z' are both Z1; Or, X is Xb, Y is Yb, and Z and Z' are both Z1; Or, X is Xb, Y is Yd, and Z and Z' are both Z1; Or, X is Xc, Y is Ya, and Z and Z' are both Z1; Alternatively, X is Xc, Y is Yb, and Z and Z' are both Z1; Or, X is Xc, Y is Yc, and Z and Z' are both Z1; Alternatively, X is Xc, Y is Y4, and Z and Z' are both Z1; Or, X is Xc, Y is Yd, and Z and Z' are both Z1; Or, X is Xb, Y is Ya, and Z and Z' are both Z3; Or, X is Xb, Y is Yb, and Z and Z' are both Z3; Or, X is Xb, Y is Yd, and Z and Z' are both Z3; Or, X is Xc, Y is Ya, and Z and Z' are both Z3; Or, X is Xc, Y is Yb, and Z and Z' are both Z3; Alternatively, X is Xc, Y is Yd, and Z and Z' are both Z3.

15. The method according to claim 1, in, The polyimide-based hollow fiber membrane is prepared according to a method comprising the following steps: (1) preparing a casting solution containing a polyimide, a diluent and an additive, wherein the diluent contains a good solvent for the polyimide, a poor solvent for the first polyimide and a poor solvent for the second polyimide, wherein the boiling point B1 of the poor solvent for the first polyimide is higher than the boiling point B2 of the poor solvent for the second polyimide; (2) extruding the inner core liquid and the casting liquid at a temperature T, and then curing to obtain a hollow fiber membrane precursor, wherein B2≤T<B1; (3) The hollow fiber membrane precursor is rolled up and extracted to obtain the polyimide-based hollow fiber membrane.

16. The method according to claim 15, in, In step (1), based on the total weight of the casting solution, the content of the polyimide is 20-40wt%, the content of the diluent is 50-75wt%, and the content of the additive is 0.5-10wt%; and / or the boiling point B1 of the poor solvent for the first polyimide is 5-200° C. higher than the boiling point B2 of the poor solvent for the second polyimide; and / or, the poor solvent of the first polyimide is selected from at least one of a C2-C4 saturated monohydric alcohol, γ-butyrolactone and water; and / or, the poor solvent for the second polyimide is selected from at least one of C3-C5 alkanes, tetrahydrofuran, acetone and chloroform; And / or, the good solvent of the polyimide is selected from at least one of N-methylpyrrolidone, N,N-dimethylacetamide and N,N-dimethylacetamide; and / or, the weight ratio of the good solvent for the polyimide, the poor solvent for the first polyimide and the poor solvent for the second polyimide is 1:(0.1-0.5):(0.1-0.5); And / or, the additive is a lithium salt; And / or, the casting solution is prepared according to a method comprising the following steps: stirring polyimide, a diluent and an additive at 20-50° C. and 100-1200 r / min for 12-48 hours, and then removing impurities by vacuum degassing and filtering; and / or, in step (2), the inner core liquid comprises solvent A and solvent B, wherein the solvent A is selected from at least one of N-methylpyrrolidone, N,N-dimethylacetamide and N,N-dimethylacetamide, and the solvent B is selected from at least one of C1-C4 saturated monohydric alcohol, γ-butyrolactone and water; And / or, the extrusion is carried out in a spinneret, wherein the extrusion temperature is 40-75°C; And / or, during the extrusion process, the flow rate of the casting solution is 6-30 mL / min; and / or, during the extrusion process, the flow rate of the inner core liquid is 2-10 mL / min; and / or, prior to solidification, passing the extruded hollow fibers through an air gap; and / or, the solidification is carried out in a coagulation bath; And / or, in step (3), the winding speed is 0.5-2 m / s; And / or, the extractant used for extraction is selected from at least one of water, C1-C4 saturated monohydric alcohol and C5-C7 alkane; And / or, the extraction conditions include: temperature of 20-35°C and time of 3-48h; And / or, the extraction further includes a drying step.

17. The method according to claim 16, in, In step (1), based on the total weight of the casting solution, the content of the polyimide is 25-35wt%, the content of the diluent is 60-70wt%, and the content of the additive is 1-5wt%; and / or the boiling point B1 of the poor solvent for the first polyimide is 10-20° C. higher than the boiling point B2 of the poor solvent for the second polyimide; and / or, the weight ratio of the good solvent for the polyimide, the poor solvent for the first polyimide and the poor solvent for the second polyimide is 1:(0.15-0.3):(0.15-0.3); and / or, the additive is selected from lithium nitrate and / or lithium chloride; And / or, the vacuum degassing conditions include: pressure of -0.1MPa to -0.095MPa, temperature of 20-30°C, rotation speed of 10-50r / min, and time of 12-24h; And / or, the filtering temperature is 20-50°C; and / or, in step (2), the solvent A accounts for 50-99wt% of the total weight of the inner core liquid; And / or, the extrusion is carried out in a spinneret, wherein the extrusion temperature is 60-70°C; And / or, the height of the air gap is 5-30 cm; And / or, the air gap is heated by an annular sleeve, preferably at a controlled temperature of 70-150°C; And / or, the bath liquid used in the coagulation bath is solvent C and / or water, and the temperature of the coagulation bath is 40-70°C; And / or, the drying conditions include: temperature of 20-35° C. and time of 2-15 h.

18. The method according to claim 17, in, In step (2), the solvent A accounts for 60-95wt% of the total weight of the inner core liquid; And / or, the solvent C is selected from at least one of a C1-C4 saturated monohydric alcohol, γ-butyrolactone and water.

19. The method according to claim 1 or 2, in, The conditions for alloy adsorption include: before the alloy adsorption, the temperature of the gas obtained by the first stage polymer membrane separation is controlled to be 10-50°C; And / or, the adsorption material for alloy adsorption is a hydrogen storage alloy material, selected from at least one of rare earth alloys, titanium alloys, zirconium alloys, vanadium alloys and magnesium alloys.

20. The method according to claim 19, in, The alloy adsorption conditions include: before the alloy adsorption, the temperature of the gas obtained by the first stage polymer membrane separation is controlled to be 20-30°C.

21. The method according to claim 1 or 2, in, The second stage polymer membrane separation adopts a one-stage or multi-stage separation method; And / or, the conditions for the second polymer membrane separation include: controlling the temperature of the gas after alloy adsorption to 0-50° C. and the pressure to 0-5 MPa.

22. A system for purifying helium, It is characterized in that The system comprises a catalytic dehydrogenation separation unit, a first-stage polymer membrane separation unit, an alloy adsorption unit and a second-stage polymer membrane separation unit which are connected in sequence; Wherein, the polymer membrane used in the first stage polymer membrane separation and the second stage polymer membrane separation is the polymer membrane in the method according to any one of claims 1 to 21.

23. The system according to claim 22, in, The catalytic dehydrogenation separation unit comprises a catalytic oxidation device and a dehydration drying device.

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