Method and system for purifying helium from helium-rich gas

Abstract

The present invention relates to the technical field of helium purification, and specifically discloses a method and system for purifying helium from helium-rich gas. The method provided by the present invention comprises the following steps: (1) contacting the helium-rich gas with oxygen so that the hydrogen in the helium-rich gas reacts with the oxygen to obtain a catalytically dehydrogenated gas; (2) chemically dehydrogenating the catalytically dehydrogenated gas in the presence of a metal oxide to obtain a chemically dehydrogenated gas; (3) sequentially subjecting the chemically dehydrogenated gas to cryogenic separation, membrane separation and pressure swing adsorption to obtain ultrapure helium. The present invention efficiently integrates processes such as precious metal catalytic dehydrogenation separation (hydrogen and oxygen react), chemical dehydrogenation (hydrogen reacts with metal oxides at high temperature), cryogenic separation, membrane separation, and pressure swing adsorption, and has the advantages of low energy consumption, low investment cost, stable operation, mild conditions, etc., solves the problem of helium purification, and has broad application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of helium purification, and in particular to a method and system for purifying helium from helium-rich gas. Background Art

[0002] Due to its unique properties, helium is widely used in cryogenics, aerospace, electronics, biomedicine, nuclear facilities and other fields, and is one of the important basic materials for the development of high-tech industries. With the continuous development of the economy, my country's demand for helium is growing rapidly, and it is urgent to develop a method for preparing high-concentration helium with low energy consumption.

[0003] Cryogenic process is a commonly used method in industrialization. In the process of extracting helium from natural gas by cryogenic process, there are stringent requirements for equipment design and manufacturing. The construction and operation costs of cryogenic process alone are high, the equipment is complicated, the energy consumption is high, and the economic benefits are not competitive.

[0004] Membrane separation is simple to operate, saves energy, and can significantly reduce construction and operating costs.

[0005] The combination of cryogenics and high-performance membranes will greatly improve the efficiency of natural gas helium extraction and reduce energy consumption. However, in order to ensure the intake requirements and purification effects of cryogenics and membranes, it is necessary to 2 , H 2 S.H. 2 O、CO 2 Impurity gases with greater impacts also need to be combined with appropriate impurity removal processes to meet the air intake and outlet requirements of the purification process to ensure the purified concentration. Summary of the invention

[0006] In order to solve the technical problems existing in the prior art, the present invention provides a method and system for purifying helium from helium-rich gas.

[0007] A first aspect of the present invention provides a method for purifying helium from helium-rich gas, the method comprising the following steps:

[0008] (1) contacting the helium-rich gas with oxygen so that the hydrogen in the helium-rich gas reacts with the oxygen to obtain a catalytically dehydrogenated gas;

[0009] (2) chemically dehydrogenating the catalytically dehydrogenated gas in the presence of a metal oxide to obtain a chemically dehydrogenated gas;

[0010] (3) The gas after chemical dehydrogenation is subjected to cryogenic separation, membrane separation and pressure swing adsorption in sequence to obtain ultra-pure helium.

[0011] A second aspect of the present invention provides a system for purifying helium from helium-rich gas, the system comprising a catalytic dehydrogenation separation unit, a chemical dehydrogenation unit, a cryogenic separation unit, a membrane separation unit and a pressure swing adsorption unit connected in sequence;

[0012] Preferably, a decarbonization drying device is included between the chemical dehydrogenation unit and the cryogenic separation unit.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] Traditional cryogenic technology needs to cool helium to a low temperature below -190°C to separate methane, nitrogen and other gases. In addition, once hydrogen exists in the raw gas, the condensation temperature of hydrogen and helium is very low, so the separation effect is poor and it is difficult to prepare high-purity helium. The present invention combines noble metal catalytic dehydrogenation (hydrogen and oxygen react) and chemical dehydrogenation (hydrogen reacts with metal oxides at high temperature) to convert hydrogen, methane and light hydrocarbons in the raw gas (helium-rich gas) into carbon dioxide and water vapor, and sets a decarbonization and drying link after the two-step dehydrogenation unit to prevent carbon dioxide and water vapor from entering the cryogenic process and causing freezing. After the cryogenic separation process, the helium-rich gas still contains a small amount of methane, oxygen, nitrogen and other gases with large differences in physical and chemical properties from helium. At this time, a primary or multi-stage membrane separation process is used for efficient separation to prepare a product with high helium purity, and finally the pressure swing adsorption technology is used to adsorb the remaining impurity gas to obtain ultra-pure helium. The present invention efficiently integrates precious metal catalytic dehydrogenation separation, chemical dehydrogenation, cryogenic separation, membrane separation, pressure swing adsorption and other processes, and has the advantages of low energy consumption, low investment cost, stable operation, mild conditions, etc., which can greatly reduce the energy consumption of the helium separation process; and the prepared helium concentration will not be affected by hydrogen, and can reach a higher concentration. The present invention solves the problem of helium purification, and can achieve efficient utilization of helium resources including natural gas, oil field associated gas, etc. The prepared high-purity helium has broad application prospects. DETAILED DESCRIPTION

[0015] 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.

[0016] A first aspect of the present invention provides a method for purifying helium from helium-rich gas, the method comprising the following steps:

[0017] (1) contacting the helium-rich gas with oxygen so that the hydrogen in the helium-rich gas reacts with the oxygen to obtain a catalytically dehydrogenated gas;

[0018] (2) chemically dehydrogenating the catalytically dehydrogenated gas in the presence of a metal oxide to obtain a chemically dehydrogenated gas;

[0019] (3) The gas after chemical dehydrogenation is subjected to cryogenic separation, membrane separation and pressure swing adsorption in sequence to obtain ultra-pure helium.

[0020] The present invention has no particular limitation on the type of the helium-rich gas, as long as it can be purified by the method of the present invention. For example, the helium-rich gas can be selected from at least one of natural gas, shale gas and liquefied natural gas flash steam (BOG).

[0021] In the present invention, in order to deeply remove hydrogen and further ensure the separation effect of the membrane, before deep cold separation, the helium-rich gas is subjected to noble metal catalytic dehydrogenation (hydrogen and oxygen react) and chemical dehydrogenation (hydrogen reacts with metal oxides at high temperature) in sequence.

[0022] According to some embodiments of the present invention, in step (1), the catalyst used for the reaction of hydrogen and oxygen is a precious metal catalyst, and the precious metal catalyst can be selected from at least one of Pt, Pd, Rh, Ru and Au.

[0023] According to some embodiments of the present invention, the contact conditions may include: a temperature of 30-300°C (30°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 120°C, 140°C, 160°C, 180°C, 200°C, 250°C, 280°C, 300°C or any value between the above values), preferably 50-120°C; the space velocity of the raw gas is 1-10000 h -1 , preferably 10-1000 h -1 ;

[0024] The present invention has no particular limitation on the amount of oxygen used. Preferably, as long as more than 99% of the hydrogen in the system can be converted into water, it can be used. In order to make the hydrogen react more thoroughly, preferably, pure oxygen is used as a combustion aid during the reaction of hydrogen and oxygen.

[0025] According to some embodiments of the present invention, in step (2), the conditions of the chemical dehydrogenation include: the temperature of the chemical dehydrogenation is 100°C to 1000°C (100°C, 200°C, 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C or any value between the above values), and the space velocity of the chemical dehydrogenation is 50-400h -1 .

[0026] In the present invention, when the helium-rich gas also contains methane or other hydrocarbon gases, CO can also be generated under the conditions of step (1). 2 and water, and are removed by subsequent steps.

[0027] According to some embodiments of the present invention, the metal oxide is selected from at least one of copper oxide, iron oxide and chromium oxide. During chemical dehydrogenation, the metal oxide undergoes a redox reaction with hydrogen, thereby removing the remaining hydrogen in the system.

[0028] According to some embodiments of the present invention, decarbonization and drying are further included between the chemical dehydrogenation and the cryogenic separation to remove water and carbon dioxide.

[0029] Preferably, the adsorbent may be selected from at least one of potassium hydroxide, sodium hydroxide and soda lime.

[0030] Preferably, the decarburization drying space velocity is 200-800h -1 .

[0031] According to some embodiments of the present invention, the conditions for the cryogenic separation may include: a temperature of -220°C to -100°C and a pressure of 0.1 MPa to 10 MPa.

[0032] According to some embodiments of the present invention, the membrane used in the membrane separation can be selected from at least one of a hollow fiber membrane, a flat membrane and a tubular membrane. The membrane can be a homogeneous membrane, a heterogeneous membrane or a composite membrane. The membrane can be commercially available or prepared by methods such as thermally induced phase separation, solution induced phase separation, melt stretching, interfacial polymerization, coating polymerization, in-situ polymerization, etc.

[0033] According to some embodiments of the present invention, the material of the membrane used in the membrane separation is selected from at least one of polysulfone, polyethersulfone, polyimide, polypropylene, polyethylene, synthetic resin, polyvinylidene fluoride, polytetrafluoroethylene, polyetheretherketone, polybenzimidazole, polydimethylsiloxane, cellulose acetate membrane, polycarbonate membrane, polymethyl methacrylate membrane, zeolite molecular sieve membrane, carbon molecular sieve membrane and metal organic framework material, more preferably polyimide.

[0034] According to some embodiments of the present invention, the 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 membrane separation in which the permeate side gas is pressurized and then used as the inlet gas of the membrane again. Tertiary membrane separation, four-stage membrane separation and five-stage membrane separation have similar meanings. Among them, the membrane separation process 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.

[0035] According to some embodiments of the present invention, the membrane separation conditions may include: before membrane separation, controlling the gas pressure obtained by cryogenic separation to 0.1-15 MPa and the gas temperature to -20°C to 100°C.

[0036] According to some embodiments of the present invention, the membrane used in the membrane separation may be a polyimide-based hollow fiber membrane.

[0037] 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%.

[0038] Preferably, the thickness of the dense layer is 100-500 nm, and the porosity of the hollow fiber membrane is 50-70%.

[0039] Preferably, the hollow fiber membrane is made of polyimide random copolymer.

[0040] According to some embodiments of the present invention, the polyimide random copolymer has a structure shown in formula (I): (I),

[0041] In formula (I), m and n are each independently an integer of 10-2000;

[0042] X has a structure represented by any one of formula (X1) to formula (X3);

[0043] (X1), (X2), (X3),

[0044] In formula (X1)-formula (X3), R 1 , R 2 , R 3 , R 4 , R 5 and R6 Each is independently H, C1-C4 alkyl, C6-C10 aryl, amino, hydroxyl or carboxyl;

[0045] Y has a structure represented by any one of formula (Y1) to formula (Y5);

[0046] (Y1), (Y2), (Y3), (Y4), (Y5),

[0047] 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;

[0048] Z and Z' each independently have a structure represented by formula (Z1) or formula (Z2);

[0049] (Z1), (Z2),

[0050] In formula (Z2), Ra and Rb are each independently H, C1-C4 alkyl or C1-C4 halogenated alkyl.

[0051] Preferably, m and n are each independently an integer of 50-1000.

[0052] Preferably, 0.9≥n / (m+n)≥0.3, preferably, 0.7≥n / (m+n)≥0.5.

[0053] In the present invention, X has one of the following structures:

[0054] , , .

[0055] In the present invention, Y has one of the following structures,

[0056] , , ,

[0057] , .

[0058] In the present invention, Z and Z' both have the structure shown by Z1 or Z3,

[0059] , .

[0060] Preferably, X is Xa, Y is Ya, and Z and Z' are both Z1;

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

[0062] Or, X is Xa, Y is Yd, and Z and Z' are both Z1;

[0063] Or, X is Xb, Y is Ya, and Z and Z' are both Z1;

[0064] Or, X is Xb, Y is Yb, and Z and Z' are both Z1;

[0065] Or, X is Xb, Y is Yd, and Z and Z' are both Z1;

[0066] Or, X is Xc, Y is Ya, and Z and Z' are both Z1;

[0067] Alternatively, X is Xc, Y is Yb, and Z and Z' are both Z1;

[0068] Or, X is Xc, Y is Yc, and Z and Z' are both Z1;

[0069] Alternatively, X is Xc, Y is Y4, and Z and Z' are both Z1;

[0070] Or, X is Xc, Y is Yd, and Z and Z' are both Z1;

[0071] Or, X is Xb, Y is Ya, and Z and Z' are both Z3;

[0072] Or, X is Xb, Y is Yb, and Z and Z' are both Z3;

[0073] Or, X is Xb, Y is Yd, and Z and Z' are both Z3;

[0074] Or, X is Xc, Y is Ya, and Z and Z' are both Z3;

[0075] Or, X is Xc, Y is Yb, and Z and Z' are both Z3;

[0076] Alternatively, X is Xc, Y is Yd, and Z and Z' are both Z3.

[0077] 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".

[0078] In the present invention, based on the principle of first subjecting the dianhydride monomer (dianhydride shown in formula (II) and dianhydride shown in formula (III)) and diamine monomer to polycondensation to obtain polyamic acid, and then imidizing (intramolecular dehydration) the polyamic acid, the dianhydride monomer and diamine monomer can be subjected to polycondensation to obtain polyamic acid by a one-pot method, or the dianhydride monomer (i.e., the dianhydride shown in formula (II) and the dianhydride shown in formula (III)) can be first mixed evenly and then subjected to polycondensation reaction with the diamine monomer. However, in order to better control the reaction, it is preferred to react in the latter manner. Therefore, the present invention also provides a method for preparing a polyimide random copolymer, the method comprising the following steps:

[0079] (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, and performing a polycondensation reaction to obtain a material containing polyamic acid,

[0080] (II), (III);

[0081] (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;

[0082] In formula (II) and formula (III), X and Y have the same meanings as described above.

[0083] 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),

[0084] (Z1), (Z2),

[0085] In formula (Z2), Ra and Rb are each independently H, C1-C4 alkyl or C1-C4 halogenated alkyl.

[0086] Preferably, X is Xa, Y is Ya, and Zp is Z1;

[0087] Alternatively, X is Xa, Y is Yb, and Zp is Z1;

[0088] Or, X is Xa, Y is Yd, and Zp is Z1;

[0089] Or, X is Xb, Y is Ya, and Zp is Z1;

[0090] Or, X is Xb, Y is Yb, and Zp is Z1;

[0091] Or, X is Xb, Y is Yd, and Zp is Z1;

[0092] Or, X is Xc, Y is Ya, and Zp is Z1;

[0093] Or, X is Xc, Y is Yb, and Zp is Z1;

[0094] Or, X is Xc, Y is Yc, and Zp is Z1;

[0095] Or, X is Xc, Y is Y4, and Zp is Z1;

[0096] Or, X is Xc, Y is Yd, and Zp is Z1;

[0097] Or, X is Xb, Y is Ya, and Zp is Z3;

[0098] Or, X is Xb, Y is Yb, and Zp is Z3;

[0099] Or, X is Xb, Y is Yd, and Zp is Z3;

[0100] Or, X is Xc, Y is Ya, and Zp is Z3;

[0101] Or, X is Xc, Y is Yb, and Zp is Z3;

[0102] Alternatively, X is Xc, Y is Yd, and Zp is Z3.

[0103] 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).

[0104] In the present invention, M and N satisfy 0.9≥N / (M+N)≥0.3, preferably, 0.7≥N / (M+N)≥0.5.

[0105] 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).

[0106] 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.

[0107] In the present invention, the polycondensation reaction is carried out under an inert atmosphere, which is preferably provided by nitrogen.

[0108] 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.

[0109] In the present invention, the usage of the first solvent is 1000-3000 mL relative to 1 mmol of the diamine monomer.

[0110] 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 conditions for mechanical stirring can include: 20-40°C, 2000-15000rpm, 2-12h; the conditions for ultrasound can include: 20-40°C, 0.5-2.0h; the conditions for shaking can include: 20-40°C, 260-800rpm, 12-36h.

[0111] 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.

[0112] In the present invention, the dehydrating agent is selected from at least one of dichlorobenzene, toluene, acetic anhydride and xylene.

[0113] In the present invention, the catalyst is selected from pyridine and / or diquinoline.

[0114] 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.

[0115] 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.

[0116] In the present invention, the method further comprises: before obtaining the polyimide copolymer, diluting the material after the imidization treatment in step (S2) and contacting it 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.

[0117] 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 method may be as follows: the imidization-treated material in step (S2) (after dilution) is added to the precipitant to precipitate polyimide, and then the precipitated polyimide is eluted with the precipitant (3-5 times), and finally filtered and dried (70-150° C., 24-48 hours) to obtain a polyimide random copolymer.

[0118] In the present invention, the polyimide-based hollow fiber membrane is prepared according to a method comprising the following steps:

[0119] (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;

[0120] (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;

[0121] (3) The hollow fiber membrane precursor is rolled up and extracted to obtain the polyimide-based hollow fiber membrane.

[0122] 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%.

[0123] 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%.

[0124] 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.

[0125] 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.

[0126] In the present invention, the poor solvent for the second polyimide is at least one selected from C3-C5 alkanes, tetrahydrofuran, acetone and chloroform.

[0127] 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.

[0128] 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).

[0129] In the present invention, the additive may be a lithium salt, preferably selected from lithium nitrate and / or lithium chloride.

[0130] 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).

[0131] 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.

[0132] In the present invention, 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.

[0133] In the present invention, the solvent A accounts for 50-99wt%, preferably 60-95wt%, of the total weight of the inner core liquid.

[0134] According to some embodiments of the present invention, the extrusion is performed in a spinneret, wherein the extrusion temperature (temperature of the spinneret) is 40-75°C, preferably 60-70°C.

[0135] In the present invention, during the extrusion process, the flow rate of the casting solution is 6-30 mL / min.

[0136] According to some embodiments of the present invention, during the extrusion process, the flow rate of the core liquid is 2-10 mL / min.

[0137] 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.

[0138] In the present invention, the height of the air gap is 5-30 cm.

[0139] In the present invention, the air gap is heated by an annular sleeve, and the temperature is preferably controlled to be 70-150°C.

[0140] 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.

[0141] In the present invention, the solvent C is selected from at least one of a C1-C4 saturated monohydric alcohol, γ-butyrolactone and water.

[0142] In the present invention, in step (3), the winding rate is 0.5-2 m / s.

[0143] In the present invention, the purpose of the extraction is to remove the diluent and additives in the hollow fiber membrane precursor.

[0144] 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.

[0145] 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.

[0146] 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.

[0147] In the present invention, the extraction further includes a drying step.

[0148] In the present invention, the drying conditions include: temperature of 20-35° C. and time of 2-15 h.

[0149] The present invention has no particular limitation on the adsorbent for pressure swing adsorption, as long as it can meet the requirements of the present invention. For example, the adsorbent for pressure swing adsorption can be selected from at least one of molecular sieves, activated carbon and metal organic framework materials (MOFs).

[0150] According to some embodiments of the present invention, the conditions for the pressure swing adsorption may include: the pressure of the pressure swing adsorption is 0.1-15 MPa, preferably 2-4.5 MPa; the space velocity of the pressure swing adsorption is 10-550 h -1 .

[0151] A second aspect of the present invention provides a system for purifying helium from helium-rich gas, the system comprising a catalytic dehydrogenation separation unit, a chemical dehydrogenation unit, a cryogenic separation unit, a membrane separation unit and a pressure swing adsorption unit connected in sequence;

[0152] Preferably, a decarbonization drying device is included between the chemical dehydrogenation unit and the cryogenic separation unit.

[0153] The present invention will be described in detail below through examples.

[0154] 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.

[0155] In the following embodiments, the test method for the volume fraction of each gas is as follows: gas chromatography. In the embodiments, primary membrane separation represents one membrane separation, secondary membrane separation represents the gas after primary membrane separation is used as the inlet gas for membrane separation again (using fresh membrane components), and tertiary membrane separation, quaternary membrane separation and quintuple membrane separation are similar.

[0156] The following preparation examples are used to illustrate the polyimide random copolymer

[0157] Preparation Example 1

[0158] (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 polycondensed for 12 h to obtain a material containing polyimide acid;

[0159] (2) A mixture of acetic anhydride (0.36 mmol) and pyridine (0.36 mmol) was added to the polyimide acid material obtained in step (1), and intramolecular dehydration was performed at 200°C for 24 hours 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 rinsed with a mixed solution of water and ethanol (1500 mL: 1500 mL) (3 times), and a polyimide random copolymer was obtained after 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 were detected in the remaining liquid phase after the polyimide was precipitated, indicating that all raw materials participated in the reaction.

[0160] The following preparation examples are used to illustrate the preparation of polyimide-based hollow fiber membranes.

[0161] Preparation Example 1

[0162] (1) Add 20 wt % of the random copolymer of polyimide obtained in Preparation Example 1, 50 wt % of NMP, 10 wt % of ethanol (boiling point 78° C.), 10 wt % of THF (boiling point 68.28° C.) and 10 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, speed 30 r / min for 24 hours, and then filter at 50° C. through a filter screen (pore size 100 mesh) to obtain a casting solution;

[0163] (2) A metering pump was used 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 were extruded through the spinneret together to obtain a hollow fiber. The hollow fiber was 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. The spinneret temperature (extrusion temperature) was 75°C. The flow rates of the casting liquid and the inner core liquid entering the hollow spinneret were 6mL / min and 2mL / min, respectively.

[0164] (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.

[0165] The obtained hollow fiber membrane was characterized by mercury intrusion porosimetry, and the porosity was 80% and the thickness of the dense layer was 135 nm.

[0166] The following examples are used to illustrate the process of purifying helium using the method of the present invention.

[0167] Example 1

[0168] In a certain helium-rich gas, the volume fraction of helium is 8.5%, and the composition of other gases includes: 35% of methane, 37.3% of nitrogen, 2.1% of hydrogen, 7.5% of carbon dioxide, 9.5% of oxygen and 0.1% of water;

[0169] (1) The above helium-rich gas (space velocity is 300h -1 ) is introduced into a catalytic dehydrogenation separation unit to react hydrogen with oxygen (pure oxygen is used as a combustion aid) to obtain a catalytically dehydrogenated gas, wherein the catalyst used is Pt, and the temperature at which hydrogen and oxygen react is 120°C;

[0170] (2) The gas after catalytic dehydrogenation is directly sent to a chemical dehydrogenation reactor through a pipeline (the catalyst used for chemical dehydrogenation is copper oxide) for chemical dehydrogenation reaction to obtain chemical dehydrogenated gas, wherein the temperature of the chemical dehydrogenation is 500°C and the space velocity is 80h -1 ;

[0171] (3) The gas after chemical dehydrogenation is passed into a decarbonization drying device (the adsorbent used is soda lime) at an air velocity of 310 h -1 The gas after decarbonization and drying was introduced into the cryogenic separation unit, where the temperature of cryogenic separation was -150°C and the pressure was 6MPa. After the temperature was raised to -20°C, it was introduced into the polybenzimidazole hollow fiber membrane assembly (Zhongke Energy Materials Technology (Dalian) Co., Ltd., PBI membrane) for primary, secondary and tertiary membrane separation operations (the pressure was 5MPa). The gas after membrane separation was sent to the pressure swing adsorption unit (13XAPG4×8 zeolite molecular sieve as adsorbent, purchased from Shanghai Bojing Molecular Sieve Co., Ltd.), the adsorption pressure was 5MPa, and the adsorption space velocity was 250h -1 , ultrapure helium is obtained. The volume fractions of the gas components after separation at each stage are shown in Table 1.

[0172] Table 1

[0173]

[0174] Example 2

[0175] In the produced gas from a gas field, the volume fraction of helium is 20%, and the composition of other gases includes: 18% methane by volume, 60% nitrogen by volume, 1% hydrogen by volume, 0.5% carbon dioxide by volume, and 0.5% oxygen by volume.

[0176] (1) The above gas field was mined (space velocity was 800 h -1 ) is introduced into a catalytic dehydrogenation separation unit to react hydrogen with oxygen (pure oxygen is used as a combustion aid) to obtain a catalytically dehydrogenated gas, wherein the catalyst used is Pd, and the temperature at which hydrogen and oxygen react is 106°C;

[0177] (2) The gas after catalytic dehydrogenation is directly sent to a chemical dehydrogenation reactor through a pipeline (the catalyst used for chemical dehydrogenation is copper oxide) for chemical dehydrogenation reaction to obtain gas after chemical dehydrogenation, wherein the temperature of the chemical dehydrogenation is 350°C and the space velocity is 400h -1 ;

[0178] (3) The gas after chemical dehydrogenation is passed into a decarbonization drying device (the adsorbent used is soda lime) at an air velocity of 750 h -1 The gas after decarbonization and drying was introduced into the cryogenic separation unit, where the temperature of cryogenic separation was -140°C and the pressure was 6MPa. After the temperature was raised to -20°C, it was introduced into the hollow fiber membrane assembly using polybenzimidazole (Zhongke Energy Materials Technology (Dalian) Co., Ltd., PBI membrane) for primary, secondary, tertiary, quaternary and quintuple membrane separation operations (the pressure was 11MPa). The gas after membrane separation was sent to the pressure swing adsorption unit (13XAPG4×8 zeolite molecular sieve as adsorbent, purchased from Shanghai Bojing Molecular Sieve Co., Ltd.), the pressure swing adsorption pressure was 10MPa, and the pressure swing adsorption space velocity was 300h -1 , ultrapure helium is obtained. The volume fractions of the gas components after separation at each stage are shown in Table 2.

[0179] Table 2

[0180]

[0181] Example 3

[0182] In the flash steam (BOG) gas of the LNG station, the volume fraction of helium 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 6.66%, and carbon dioxide with a volume fraction of 0.01%;

[0183] (1) The flash steam (BOG) gas (space velocity 290 h -1) is introduced into a catalytic dehydrogenation separation unit to react hydrogen with oxygen (pure oxygen is used as a combustion aid) to obtain a catalytically dehydrogenated gas, wherein the catalyst used is Au, and the temperature at which hydrogen and oxygen react is 74°C;

[0184] (2) The gas after catalytic dehydrogenation is directly sent to a chemical dehydrogenation reactor through a pipeline (the catalyst used for chemical dehydrogenation is copper oxide) for chemical dehydrogenation reaction to obtain gas after chemical dehydrogenation, wherein the temperature of the chemical dehydrogenation is 600°C and the space velocity is 360h -1

[0185] (3) The gas after chemical dehydrogenation is passed into a decarbonization drying device (the adsorbent used is potassium hydroxide) at an air velocity of 200 h -1 The gas after decarbonization and drying is introduced into a cryogenic separation unit, wherein the temperature of the cryogenic separation is -135°C and the pressure is 0.5MPa. After the temperature rises to 20°C, the polyimide-based hollow fiber membrane assembly prepared in the above-mentioned Preparation Example 1 is introduced to perform primary, secondary and tertiary membrane separation operations (the pressure is 2MPa). The gas after membrane separation is sent to a pressure swing adsorption unit (13XAPG4×8 zeolite molecular sieve is used as an adsorbent, purchased from Shanghai Bojing Molecular Sieve Co., Ltd.), the pressure swing adsorption pressure is 1MPa, and the pressure swing adsorption space velocity is 10h -1 , ultrapure helium is obtained. The volume fractions of the gas components after separation at each stage are shown in Table 3.

[0186] Table 3

[0187]

[0188] Example 4

[0189] After the natural gas produced from a gas field is pretreated (multi-stage flash evaporation), the volume fraction of helium in the flash 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%, hydrogen with a volume fraction of 10.65%, and carbon dioxide with a volume fraction of 0.05%.

[0190] (1) The flash gas (space velocity is 10h -1 ) is introduced into a catalytic dehydrogenation separation unit to react hydrogen with oxygen (pure oxygen is used as a combustion aid) to obtain a catalytically dehydrogenated gas, wherein the catalyst used is Pd, and the temperature at which hydrogen and oxygen react is 83°C;

[0191] (2) The gas after catalytic dehydrogenation is directly sent to a chemical dehydrogenation reactor through a pipeline (the catalyst used for chemical dehydrogenation is chromium oxide) for chemical dehydrogenation reaction to obtain gas after chemical dehydrogenation, wherein the temperature of the chemical dehydrogenation is 800°C and the space velocity is 286h -1 ;

[0192] (3) The gas after chemical dehydrogenation is passed into the decarbonization drying process (using sodium hydroxide as a desiccant) at an air velocity of 600 h -1 The gas after decarbonization and drying is passed into the cryogenic separation unit, where the temperature of cryogenic separation is -120°C and the pressure is 0.35MPa. After the temperature rises to 25°C, it is passed into the hollow fiber membrane component made of polysulfone (PRISM) for primary and secondary membrane separation operations (both pressures are 6MPa). The gas after membrane separation is sent to the pressure swing adsorption unit (13XAPG4×8 zeolite molecular sieve is used as adsorbent, purchased from Shanghai Bojing Molecular Sieve Co., Ltd.), the adsorption pressure is 2MPa, and the pressure swing adsorption space velocity is 20h -1 , ultrapure helium is obtained. The volume fractions of the gas components after separation at each stage are shown in Table 4.

[0193] Table 4

[0194]

[0195] Example 5

[0196] In a certain helium-rich gas, the volume fraction of helium is 17%, and the composition of other gases includes: 35% by volume of methane, 35% by volume of nitrogen, 2% by volume of hydrogen, 5% by volume of carbon dioxide, 5% by volume of oxygen and 1% by volume of water;

[0197] (1) The above helium-rich gas (space velocity 1000 h -1 ) is introduced into a catalytic dehydrogenation separation unit to react hydrogen with oxygen (pure oxygen is used as a combustion aid) to obtain a catalytically dehydrogenated gas, wherein the catalyst used is Pt, and the temperature at which hydrogen and oxygen react is 59°C;

[0198] (2) The gas after catalytic dehydrogenation is directly sent to a chemical dehydrogenation reactor through a pipeline (the catalyst used for chemical dehydrogenation is copper oxide) for chemical dehydrogenation reaction to obtain chemical dehydrogenated gas, wherein the temperature of the chemical dehydrogenation is 300°C and the space velocity is 150h -1 ;

[0199] (3) The gas after chemical dehydrogenation is cooled and pressurized to 10 MPa and then passed into the decarbonization drying process (using soda lime as a desiccant) at an air velocity of 710 h -1The gas after decarbonization and drying is passed into the cryogenic separation unit, where the temperature of cryogenic separation is -115°C and the pressure is 10MPa. After the temperature rises to -20°C, it is passed into the hollow fiber membrane assembly made of polysulfone (PRISM) for primary, secondary and tertiary membrane separation operations (the pressure is 10MPa). The gas after membrane separation is sent to the pressure swing adsorption unit (using coconut shell activated carbon as adsorbent, purchased from Tianjin Lvjing Environmental Protection Technology Co., Ltd.), the pressure swing adsorption pressure is 2MPa, and the pressure swing adsorption space velocity is 83h -1 , ultrapure helium is obtained. The volume fractions of the gas components after separation at each stage are shown in Table 5.

[0200] Table 5

[0201]

[0202] Example 6

[0203] In the natural gas multi-stage flash steam (BOG) produced from a gas field, the volume fraction of helium is 10%, and the composition of other gases includes: 45% methane, 40% nitrogen, 2.5% hydrogen, 0.5% carbon dioxide and 2% oxygen;

[0204] (1) The above gas field is mined (space velocity is 410h -1 ) is introduced into a catalytic dehydrogenation separation unit to react hydrogen with oxygen (pure oxygen is used as a combustion aid) to obtain a catalytically dehydrogenated gas, wherein the catalyst used is Au, and the temperature at which hydrogen and oxygen react is 115°C;

[0205] (2) The gas after catalytic dehydrogenation is directly sent to a chemical dehydrogenation reactor through a pipeline (the catalyst used for chemical dehydrogenation is iron oxide) for chemical dehydrogenation reaction to obtain gas after chemical dehydrogenation, wherein the temperature of the chemical dehydrogenation is 930°C and the space velocity is 50h -1 ;

[0206] (3) The gas after chemical dehydrogenation is cooled and pressurized to 1 MPa and then passed into the decarbonization drying process with soda lime as a desiccant), with an air velocity of 300 h -1 The gas after decarbonization and drying is passed into the cryogenic separation unit, where the temperature of cryogenic separation is -120°C and the pressure is 7MPa. After the temperature rises to -20°C, it is passed into the hollow fiber membrane assembly made of polysulfone (PRISM) for primary and secondary membrane separation operations (both at a pressure of 5MPa). The gas after membrane separation is sent to the pressure swing adsorption unit (using 13XAPG4×8 zeolite molecular sieve as adsorbent, purchased from Shanghai Bojing Molecular Sieve Co., Ltd.), the pressure swing adsorption pressure is 5MPa, and the pressure swing adsorption space velocity is 10 -1Ultrapure helium is obtained. The volume fractions of the gas components after separation at each stage are shown in Table 6.

[0207] Table 6

[0208]

[0209] Example 7

[0210] In a certain helium-rich gas, the volume fraction of helium is 20%, and the composition of other gases includes: 18% of methane by volume, 60% of nitrogen by volume, 1% of hydrogen by volume, 0.5% of carbon dioxide by volume, and 0.5% of oxygen by volume.

[0211] (1) The above helium-rich gas (space velocity 600 h -1 ) is introduced into a catalytic dehydrogenation separation unit to react hydrogen with oxygen (pure oxygen is used as a combustion aid) to obtain a catalytically dehydrogenated gas, wherein the catalyst used is Rh, and the temperature at which hydrogen and oxygen react is 260°C;

[0212] (2) The gas after catalytic dehydrogenation is directly sent to a chemical dehydrogenation reactor through a pipeline (the catalyst used for chemical dehydrogenation is copper oxide) for chemical dehydrogenation reaction to obtain gas after chemical dehydrogenation, wherein the temperature of the chemical dehydrogenation is 660°C and the space velocity is 360h -1 ;

[0213] (3) The gas after chemical dehydrogenation is pressurized to 6 MPa and then passed into the decarbonization drying process (soda lime is used as a desiccant) at an air velocity of 200 h -1 The gas after decarbonization and drying is passed into the cryogenic separation unit, where the temperature of cryogenic separation is -220℃ and the pressure is 8MPa. After the temperature rises to -20℃, it is passed into the hollow fiber membrane component using polybenzimidazole (Zhongke Energy Materials Technology (Dalian) Co., Ltd., PBI membrane) for primary membrane separation operation (pressure of 15MPa). The gas after membrane separation is sent to the pressure swing adsorption unit (Tianjin Lvjing Environmental Protection Technology Co., Ltd., coconut shell activated carbon), the pressure of pressure swing adsorption is 12MPa, and the pressure swing adsorption space velocity is 200h -1 , ultrapure helium is obtained. The volume fractions of the gas components after separation at each stage are shown in Table 7.

[0214] Table 7

[0215]

[0216] Example 8

[0217] In the secondary flash gas of a certain LNG, the volume fraction of helium is 5%, and the composition of other gases includes: 40% methane, 20% nitrogen, 10% hydrogen, 15% carbon dioxide, 8% oxygen and 2% water;

[0218] (1) The flash gas (space velocity is 20 h -1 ) is introduced into a catalytic dehydrogenation separation unit to react hydrogen with oxygen (pure oxygen is used as a combustion aid) to obtain a catalytically dehydrogenated gas, wherein the catalyst used is Pd, and the temperature at which hydrogen and oxygen react is 110°C;

[0219] (2) The gas after catalytic dehydrogenation is directly sent to a chemical dehydrogenation reactor through a pipeline (the catalyst used for chemical dehydrogenation is copper oxide) for chemical dehydrogenation reaction to obtain gas after chemical dehydrogenation, wherein the temperature of the chemical dehydrogenation is 520°C and the space velocity is 146h -1 ;

[0220] (3) The gas after chemical dehydrogenation is cooled and pressurized to 8 MPa and then passed into the decarbonization drying process (the desiccant used is potassium hydroxide) at an air velocity of 350 h -1 The gas after decarbonization and drying is introduced into a cryogenic separation unit, wherein the temperature of the cryogenic separation is -145°C and the pressure is 6MPa. After the temperature rises to -20°C, the hollow fiber membrane assembly made of polyimide prepared in the above-mentioned Preparation Example 1 is introduced to perform primary and secondary membrane separation operations (both at a pressure of 12MPa). The gas after membrane separation is sent to a pressure swing adsorption unit (using 13XAPG4×8 zeolite molecular sieve as an adsorbent, purchased from Shanghai Bojing Molecular Sieve Co., Ltd.), the pressure swing adsorption pressure is 5.5MPa, and the pressure swing adsorption space velocity is 60h -1 , ultrapure helium is obtained. The volume fractions of the gas components after separation at each stage are shown in Table 8.

[0221] Table 8

[0222]

[0223] Example 9

[0224] In the produced gas from a gas field, the volume fraction of helium is 15%, and the composition of other gases includes: 15% methane, 30% nitrogen, 6% hydrogen, 30% carbon dioxide, 3.5% water and 0.5% oxygen;

[0225] (1) The above gas field is mined (space velocity is 400h -1) is introduced into a catalytic dehydrogenation separation unit to react hydrogen with oxygen (pure oxygen is used as a combustion aid) to obtain a catalytically dehydrogenated gas, wherein the catalyst used is Pt, and the temperature at which hydrogen and oxygen react is 99°C;

[0226] (2) The gas after catalytic dehydrogenation is directly sent to a chemical dehydrogenation reactor through a pipeline (the catalyst used for chemical dehydrogenation is copper oxide) for chemical dehydrogenation reaction to obtain gas after chemical dehydrogenation, wherein the temperature of the chemical dehydrogenation is 550°C and the space velocity is 130h -1 ;

[0227] (3) The gas after chemical dehydrogenation is passed into the decarbonization drying device (soda lime is used as a desiccant) at an air velocity of 800 h -1 The gas after decarbonization and drying is introduced into a cryogenic separation unit, wherein the temperature of the cryogenic separation is -220°C and the pressure is 10MPa. After the temperature rises to -20°C, the polyimide-based hollow fiber membrane assembly prepared in the above-mentioned Preparation Example 1 is introduced to perform primary, secondary and tertiary membrane separation operations (the pressure is 15MPa). The gas after membrane separation is sent to a pressure swing adsorption unit (coconut shell activated carbon is used as an adsorbent, purchased from Tianjin Lvjing Environmental Protection Technology Co., Ltd.), the pressure of the pressure swing adsorption is 14MPa, and the adsorption space velocity is 110h -1 , ultrapure helium is obtained. The volume fractions of the gas components after separation at each stage are shown in Table 9.

[0228] Table 9

[0229]

[0230] From the above data, it can be seen that the two-stage dehydrogenation process of catalytic oxidation and chemical dehydrogenation can convert two types of small molecular combustible gases, hydrogen and a small amount of methane, which are difficult to separate from helium in the mixed gas, into CO 2 and water, the volume fraction of hydrogen is greatly reduced, and through cooling and decarbonization drying (compression drying adsorption to remove water), CO 2 The volume fraction of nitrogen, oxygen, methane and carbon dioxide is gradually separated from helium after further membrane separation, and the volume fraction of helium can be increased to 99.99%. Finally, after molecular sieve pressure swing adsorption, the volume fraction of helium can reach 99.999%.

[0231] 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).

[0232] 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 from helium-rich gas, It is characterized in that The method comprises the following steps: (1) contacting the helium-rich gas with oxygen so that the hydrogen in the helium-rich gas reacts with the oxygen to obtain a catalytically dehydrogenated gas; (2) chemically dehydrogenating the catalytically dehydrogenated gas in the presence of a metal oxide to obtain a chemically dehydrogenated gas; (3) subjecting the gas after chemical dehydrogenation to cryogenic separation, membrane separation and pressure swing adsorption in sequence to obtain ultrapure helium; Wherein, the membrane used in the 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 helium-rich gas is selected from at least one of natural gas, shale gas and liquefied natural gas flash steam (BOG).

3. The method according to claim 1 or 2, in, In step (1), the catalyst used for the reaction of hydrogen and oxygen is a precious metal catalyst, and the precious metal catalyst is selected from at least one of Pt, Pd, Rh, Ru and Au; And / or, the contact conditions include: temperature of 30-300°C; space velocity of the feed gas of 1-10000 h -1 .

4. The method according to claim 3, in, The contact conditions include: a temperature of 50-120°C; a space velocity of the raw gas of 10-1000 h -1 .

5. The method according to claim 1 or 2, in, In step (2), the conditions for chemical dehydrogenation include: the temperature of chemical dehydrogenation is 100°C to 1000°C, the space velocity of chemical dehydrogenation is 50-400h -1 ; And / or, the metal oxide is selected from at least one of copper oxide, iron oxide and chromium oxide.

6. The method according to claim 5, in, Decarbonization and drying are also included between the chemical dehydrogenation and the cryogenic separation, and the adsorbent is at least one of potassium hydroxide, sodium hydroxide and soda lime.

7. The method according to claim 6, in, The decarburization drying space velocity is 200-800h -1 .

8. The method according to claim 1 or 2, in, The conditions for the cryogenic separation include: a temperature of -220°C to -100°C and a pressure of 0.1 MPa to 10 MPa.

9. The method according to claim 1 or 2, in, The membrane separation adopts a one-stage or multi-stage separation method; And / or, the membrane separation conditions include: before membrane separation, the gas pressure obtained by cryogenic separation is controlled to be 0.1-15 MPa, and the gas temperature is controlled to be -20°C to 100°C.

10. The method according to claim 1, 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%.

11. The method according to claim 10, in, The thickness of the dense layer is 100-500 nm, and the porosity of the hollow fiber membrane is 50-70%.

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

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

3.

14. The method according to claim 13, in, 0.7≥n / (m+n)≥0.

5.

15. The method according to any one of claims 1, 12, 13 and 14, 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, 、 。 16. The method according to claim 15, 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.

17. The method according to any one of claims 10, 11, 12, 13, 14 and 16, 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.

18. The method according to claim 17, 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 the polyimide, diluent and 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, before solidification, passing the extruded hollow fiber 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.

19. The method according to claim 18, 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 of the polyimide, the poor solvent of the first polyimide and the poor solvent of 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, 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 with 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.

20. The method according to claim 19, in, In step (2), the solvent A accounts for 60-95% 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.

21. The method according to claim 1 or 2, in, The adsorbent for pressure swing adsorption is selected from at least one of molecular sieves, activated carbon and metal organic framework materials.

22. The method according to claim 21, in, The conditions of the pressure swing adsorption include: the pressure of the pressure swing adsorption is 0.1-15MPa; the space velocity of the pressure swing adsorption is 10-500 h -1 .

23. The method according to claim 22, in, The conditions for the pressure swing adsorption include: the pressure of the pressure swing adsorption is 2-4.5 MPa.

24. A system for purifying helium from a helium-rich gas, It is characterized in that The system comprises a catalytic dehydrogenation separation unit, a chemical dehydrogenation unit, a cryogenic separation unit, a membrane separation unit and a pressure swing adsorption unit which are connected in sequence; Wherein, the membrane used in the membrane separation unit is the membrane in the method described in any one of claims 1-23.

25. The system according to claim 24, in, A decarbonization and drying device is included between the chemical dehydrogenation unit and the cryogenic separation unit.

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