CN115872373A - Method and system for purifying helium from helium-rich gas - Google Patents

Abstract

The invention relates to the technical field of helium purification, and particularly discloses a method and a system for purifying helium from helium-rich gas. The method provided by the invention comprises the following steps: (1) Contacting the helium-rich gas with oxygen to enable hydrogen in the helium-rich gas to react with the oxygen to obtain gas after catalytic dehydrogenation; (2) In the presence of metal oxide, carrying out chemical dehydrogenation on the gas subjected to catalytic dehydrogenation to obtain a gas subjected to chemical dehydrogenation; (3) And carrying out cryogenic separation, membrane separation and pressure swing adsorption on the gas subjected to chemical dehydrogenation in sequence to obtain the ultrapure helium. The invention carries out high-efficiency fusion on the processes of catalytic dehydrogenation separation (hydrogen and oxygen react), chemical dehydrogenation (hydrogen reacts with metal oxide at high temperature), cryogenic separation, membrane separation, pressure swing adsorption and the like of noble metals, has the advantages of low energy consumption, low investment cost, stable operation, mild conditions and the like, solves the problem of helium purification, and has wide application prospect.

Description

Method and system for purifying helium from helium-rich gas

Technical Field

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

Background

Due to the unique property of helium, the helium is widely applied in the fields of low temperature, aerospace, electronic industry, biomedical science, nuclear facilities and the like, and is one of important basic materials for the development of national safety and high-tech industries. With the continuous development of economy and the rapid increase of helium demand in China, helium in China mainly depends on import at present, and in order to meet the demand of economic development of China on helium resources and the strategic demand of national defense safety, a method for preparing high-concentration helium with low energy consumption is urgently needed to be developed.

The deep cooling process is a common method for industrialization at present. The design and manufacturing requirements of equipment are strict in the process of extracting helium from natural gas by using the cryogenic process, the problems of high construction and operation cost, equipment responsibility, high energy consumption and the like of the cryogenic process are solved, and the economic benefit is not competitive.

The membrane separation has the advantages of simple operation, energy consumption saving and capability of greatly reducing the construction and operation cost; the design and preparation method has higher selectivity and permeation capacity to helium/methane, and has great strategic significance for realizing the helium stripping of economic natural gas, reducing the helium import dependence and realizing the independence of helium production and use.

The combination of the cryogenic process and the high-performance membrane greatly improves the efficiency of extracting helium from natural gas and reduces energy consumption, but in order to ensure the gas inlet requirement and purification effect of the cryogenic process and the membrane process, the method can be used for extracting H in gas ₂ 、H ₂ S、H ₂ O、CO ₂ And the impurity gases with larger influence need to be combined with a proper impurity removal process to meet the gas inlet and outlet requirements in the purification process and ensure the purification concentration.

Disclosure of Invention

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

In a first aspect, the present invention provides a method for purifying helium from a helium-rich gas, the method comprising the steps of:

(1) Contacting the helium-rich gas with oxygen to enable hydrogen in the helium-rich gas to react with the oxygen to obtain gas after catalytic dehydrogenation;

(2) In the presence of metal oxide, carrying out chemical dehydrogenation on the gas subjected to catalytic dehydrogenation to obtain a gas subjected to chemical dehydrogenation;

(3) And carrying out cryogenic separation, membrane separation and pressure swing adsorption on the gas subjected to chemical dehydrogenation in sequence to obtain the ultrapure helium.

The invention provides a system for purifying helium from helium-rich gas, which 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 sequentially communicated;

preferably, a decarburization drying device is arranged between the chemical dehydrogenation unit and the cryogenic separation unit.

Compared with the prior art, the invention has the following beneficial effects:

in addition, once hydrogen exists in raw material gas, the separation effect is poor because the condensation temperature of the hydrogen and the helium is very low, and the helium with high purity is difficult to prepare. The invention converts hydrogen, methane and light hydrocarbon in raw material gas (helium-rich gas) into carbon dioxide and water vapor by combining noble metal catalytic dehydrogenation (hydrogen and oxygen react) and chemical dehydrogenation (hydrogen reacts with metal oxide at high temperature), sets a decarburization drying link after two dehydrogenation units to prevent the carbon dioxide and the water vapor from entering a cryogenic process to cause freezing blockage, and the helium-rich gas subjected to the cryogenic separation process still contains a small amount of gases with large physical and chemical property difference with helium, such as methane, oxygen, nitrogen and the like, at the moment, the helium-rich gas is efficiently separated by a one-stage or multi-stage membrane separation process to prepare a product with high helium purity, and finally, the residual impurity gas is adsorbed by a pressure swing adsorption technology to prepare the ultra-pure helium. The invention carries out high-efficiency fusion on the processes of catalytic dehydrogenation separation, chemical dehydrogenation, cryogenic separation, membrane separation, pressure swing adsorption and the like of the noble metal, has the advantages of low energy consumption, low investment cost, stable operation, mild conditions and the like, and can greatly reduce the energy consumption in the helium gas separation process; and the prepared helium concentration is not influenced by hydrogen, and higher concentration can be achieved. The invention solves the problem of helium purification, can realize high-efficiency utilization of helium resources such as natural gas, oilfield associated gas and the like, and has wide application prospect.

Detailed Description

The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and these ranges or values should be understood to encompass values close to these ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.

In a first aspect, the present invention provides a method for purifying helium from a helium-rich gas, the method comprising the steps of:

(1) Contacting the helium-rich gas with oxygen to enable hydrogen in the helium-rich gas to react with the oxygen to obtain gas subjected to catalytic dehydrogenation;

(2) In the presence of metal oxide, carrying out chemical dehydrogenation on the gas subjected to catalytic dehydrogenation to obtain a gas subjected to chemical dehydrogenation;

(3) And carrying out cryogenic separation, membrane separation and pressure swing adsorption on the gas subjected to chemical dehydrogenation in sequence to obtain the ultrapure helium.

The present invention is not particularly limited in the kind of the helium-rich gas as long as the purification thereof can be accomplished by the method of the present invention, and for example, the helium-rich gas may be selected from at least one of natural gas, shale gas, and flash Boil Off Gas (BOG) of liquefied natural gas.

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

According to some embodiments of the present invention, the catalyst used for the reaction of hydrogen and oxygen in step (1) is a noble metal catalyst, and the noble metal catalyst may be at least one selected from the group consisting of Pt, pd, rh, ru, and Au.

According to some embodiments of the invention, the conditions of the contacting may comprise: the temperature is 30-300 deg.C (30 deg.C, 50 deg.C, 60 deg.C, 70 deg.C, 80 deg.C, 90 deg.C, 100 deg.C, 120 deg.C, 140 deg.C, 160 deg.C, 180 deg.C, 200 deg.C, 250 deg.C, 280 deg.C, 300 deg.C or any value of above values), preferably 50-120 deg.C; the space velocity of the feed gas is 1-10000h ^-1 Preferably 10-1000h ^-1 ；

The amount of oxygen used in the present invention is not particularly limited, but preferably is such that more than 99% of hydrogen in the system is converted into water. In order to make the reaction of hydrogen more complete, it is preferable to use pure oxygen as the combustion improver during the reaction of hydrogen and oxygen.

According to some embodiments of the invention, in step (2), the conditions of the chemical dehydrogenation comprise: the temperature of chemical dehydrogenation is 100 deg.C to 1000 deg.C (100 deg.C, 200 deg.C, 300 deg.C, 400 deg.C, 500 deg.C, 600 deg.C, 700 deg.C, 800 deg.C, 900 deg.C, 1000 deg.C or above), and the space velocity of chemical dehydrogenation is 50-400h ^-1 。

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

According to some embodiments of the invention, the metal oxide is selected from at least one of copper oxide, iron oxide and chromium oxide. In chemical dehydrogenation, the metal oxide and hydrogen undergo redox reaction, so that residual hydrogen in the system is removed.

According to some embodiments of the invention, a decarbonization drying is further included between the chemical dehydrogenation and the cryogenic separation to remove water and carbon dioxide.

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

Preferably, the space velocity of the decarburization drying is 200 to 800h ^-1 。

According to some embodiments of the invention, the conditions of the cryogenic separation may comprise: the temperature is-220 ℃ to-100 ℃, and the pressure is 0.1MPa to 10MPa.

According to some embodiments of the present invention, the membrane used in the membrane separation may be selected from at least one of a hollow fiber membrane, a flat sheet membrane, and a tubular membrane. Wherein the membrane may be a homogeneous membrane, a non-homogeneous membrane or a composite membrane. The film can be obtained commercially, or can be prepared by thermal phase separation, solution phase separation, melt stretching, interfacial polymerization, coating polymerization, in-situ polymerization, and the like.

According to some embodiments of the present invention, the membrane used in the membrane separation is made of at least one material selected from 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, and more preferably polyimide.

According to some embodiments of the invention, the membrane separation is in one or more stages (two to five stages) of separation. The two-stage membrane separation is a membrane separation in which the gas on the permeation side is pressurized and then reused as the feed gas to the membrane. Three-stage membrane separation, four-stage membrane separation and five-stage membrane separation have similar meanings. Wherein, the membrane separation process can be one to five stages. Preferably, the multistage membrane separation is a separation by a plurality of membranes or membrane modules. Wherein, 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 and the fourth-stage membrane separation unit.

According to some embodiments of the invention, the conditions of the membrane separation may comprise: before membrane separation, the pressure of the gas obtained by cryogenic separation is controlled to be 0.1-15MPa, and the temperature of the gas is controlled to be-20-100 ℃.

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

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 1000nm, and the porosity of the hollow fiber membrane is 40-80%.

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

Preferably, the material of the hollow fiber membrane is polyimide random copolymer.

According to some embodiments of the invention, the polyimide random copolymer has a structure represented by formula (I):

in the formula (I), m and n are each independently an integer of 10 to 2000;

x has a structure represented by any one of formula (X1) to formula (X3);

in the formula (X1) -formula (X3), R ¹ 、R ² 、R ³ 、R ⁴ 、R ⁵ And R ⁶ Each independently is H, C1-C4 alkyl, C6-C10 aryl, amino, hydroxyl or carboxyl;

y has a structure represented by any one of the formulae (Y1) to (Y5);

in the formula (Y1) -formula (Y5), R ⁷ 、R ⁸ 、R ⁹ 、R ¹⁰ 、R ¹¹ 、R ¹² 、R ¹³ 、R ¹⁴ 、R ¹⁵ And R ¹⁶ Each independently is 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);

in the formula (Z2), ra and Rb are each independently H, C1-C4 alkyl or C1-C4 haloalkyl.

Preferably, m and n are each independently an integer from 50 to 1000.

Preferably, 0.9. Gtoreq.n/(m + n). Gtoreq.0.3, preferably, 0.7. Gtoreq.n/(m + n). Gtoreq.0.5.

In the present invention, the X has one of the structures shown below,

in the present invention, Y has one of the structures shown below,

in the present invention, Z and Z' each have a structure represented by Z1 or Z3,

preferably, X is Xa, Y is Ya, and Z' are both Z1;

or X is Xa, Y is Yb, and Z' are both Z1;

or X is Xa, Y is Yd, and Z' are both Z1;

or X is Xb, Y is Ya, and Z' are both Z1;

or X is Xb, Y is Yb, and Z' are both Z1;

or X is Xb, Y is Yd, and Z' are both Z1;

or X is Xc, Y is Ya, and Z' are both Z1;

or X is Xc, Y is Yb, and Z' are both Z1;

or X is Xc, Y is Yc, and Z' are both Z1;

or X is Xc, Y is Y4, and Z' are both Z1;

or X is Xc, Y is Yd, and Z' are both Z1;

or X is Xb, Y is Ya, and Z' are both Z3;

or X is Xb, Y is Yb, and Z' are both Z3;

or X is Xb, Y is Yd, and Z' are both Z3;

or X is Xc, Y is Ya, and Z' are both Z3;

or X is Xc, Y is Yb, and Z' are both Z3;

alternatively, X is Xc, Y is Yd, and Z' are both Z3.

Although according to a preferred embodiment of the invention X, Y, Z have a specific certain structure, the invention does not exclude the case where "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".

In the invention, based on the principle that firstly dianhydride monomers (dianhydride represented by formula (II) and dianhydride represented by formula (III)) and diamine monomers are subjected to polycondensation reaction to obtain polyamic acid, and then the polyamic acid is subjected to imidization (intramolecular dehydration), the dianhydride monomers and the diamine monomers can be subjected to polycondensation reaction by a one-pot method to obtain the polyamic acid, or the dianhydride monomers (namely dianhydride represented by formula (II) and dianhydride represented by formula (III)) can be uniformly mixed and then subjected to polycondensation reaction with the diamine monomers. However, in order to better control the progress of the reaction, it is preferable to carry out the reaction in the latter manner. Accordingly, the present invention also provides a method for preparing a polyimide random copolymer, the method comprising the steps of:

(S1) in the presence of a first solvent, mixing a mixture containing a dianhydride monomer shown in a formula (II) and a dianhydride monomer shown in a formula (III) with a diamine monomer for a polycondensation reaction to obtain a material containing polyamic acid,

(S2) imidizing the polyamic acid-containing material obtained in the step (S1) to dehydrate the polyamic acid intramolecularly to obtain a polyimide random copolymer;

in the formulae (II) and (III), X and Y have the same meanings as described above.

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

in the formula (Z2), ra and Rb are each independently H, C1-C4 alkyl or C1-C4 haloalkyl.

Preferably, X is Xa, Y is Ya, zp is Z1;

or X is Xa, Y is Yb, and Zp is Z1;

or X is Xa, Y is Yd, and Zp is Z1;

or X is Xb, Y is Ya, and Zp is Z1;

or X is Xb, Y is Yb, and Zp is Z1;

or X is Xb, Y is Yd, and Zp is Z1;

or X is Xc, Y is Ya, and Zp is Z1;

or X is Xc, Y is Yb, and Zp is Z1;

or X is Xc, Y is Yc, and Zp is Z1;

or X is Xc, Y is Y4, and Zp is Z1;

or X is Xc, Y is Yd, and Zp is Z1;

or X is Xb, Y is Ya, and Zp is Z3;

or X is Xb, Y is Yb, and Zp is Z3;

or X is Xb, Y is Yd, and Zp is Z3;

or X is Xc, Y is Ya, and Zp is Z3;

or X is Xc, Y is Yb, and Zp is Z3;

or X is Xc, Y is Yd, and Zp is Z3.

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), more preferably 1: (1-9).

In the present invention, M and N satisfy 0.9. Gtoreq.N/(M + N). Gtoreq.0.3, preferably 0.7. Gtoreq.N/(M + N). Gtoreq.0.5.

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

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

In the present invention, the polycondensation reaction is carried out under an inert atmosphere. The inert atmosphere is preferably provided by nitrogen.

In the present invention, the first solvent may be selected from at least one of N, N-dimethylformamide, N-dimethylacetamide, dimethylsulfoxide, and N-methylpyrrolidone (NMP), and is preferably selected from N-methylpyrrolidone and/or N, N-dimethylformamide.

In the invention, the dosage of the first solvent is 1000-3000mL relative to 1mmol of diamine monomer.

In the present invention, the dianhydride monomer represented by formula (II) and the dianhydride monomer represented by formula (III) may be mixed to obtain a mixture in the following manner: mechanical stirring, shaking or sonication. Wherein, the mechanical stirring conditions may include: 20-40 ℃,2000-15000rpm,2-12h; the conditions of the ultrasound may include: 20-40 ℃ for 0.5-2.0h; conditions of the oscillation may include: 20-40 ℃,260-800rpm,12-36h.

In the present invention, the imidization treatment is performed in the following manner: adding a dehydrating agent and a catalyst into the material containing the amide acid obtained in the step (S1), and reacting for 12-24h at 170-200 ℃.

In the invention, the dehydrating agent is at least one selected from dichlorobenzene, toluene, acetic anhydride and xylene.

In the present invention, the catalyst is selected from pyridine and/or biquinoline.

In the present invention, the dehydrating solvent may be used in an amount of 2 to 15mol, preferably 3 to 8mol, based on 1mol of the diamine monomer.

In the present invention, the catalyst may be used in an amount of 2 to 15mol, preferably 3 to 8mol, relative to 1mol of the diamine monomer.

In the present invention, the method further comprises: before obtaining the polyimide copolymer, diluting the imidized material in the step (S2), and then contacting the diluted material with a precipitating agent to obtain the polyimide copolymer. Wherein, the precipitant may be a poor solvent for polyimide, and is selected from at least one of ethanol, acetone and water, and more preferably from at least two of ethanol, acetone and water. The total amount of the precipitant may be used in an amount of 10 to 50L, corresponding to 1mol of the diamine monomer. The solvent for dilution may be N-methylpyrrolidone. Preferably, the amount of the solvent for dilution may be 5 to 8L with respect to 1mol of the diamine monomer.

In the present invention, the mode of contacting the imidized material with the precipitant in the step (S2) is not particularly limited as long as the requirements of the present invention can be satisfied. This can be done, for example, in the following manner: and (3) adding the material (after dilution) subjected to imidization in the step (S2) into a precipitator to precipitate the polyimide, then leaching the precipitated polyimide with the precipitator (the leaching can be carried out for 3-5 times), and finally carrying out suction filtration and drying (at 70-150 ℃ for 24-48 h) to obtain the polyimide random copolymer.

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

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

(2) Extruding the inner core liquid and the casting solution at a temperature T, and curing to obtain a hollow fiber membrane precursor, wherein T is more than or equal to B2 and less than B1;

(3) And rolling and extracting the hollow fiber membrane precursor to obtain the polyimide-based hollow fiber membrane.

In the invention, in the 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%.

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

In the present invention, in order to facilitate formation of a dense layer of the hollow fiber membrane, the boiling point B1 of the poor solvent of the first polyimide is 5 to 200 ℃ higher, preferably 10 to 20 ℃ higher, than the boiling point B2 of the poor solvent of the second polyimide. In this case, the boiling point refers to an atmospheric boiling point unless otherwise specified.

In the present invention, the poor solvent of the first polyimide is at least one selected from the group consisting of saturated monohydric alcohols of C2 to C4, γ -butyrolactone, and water.

In the present invention, the poor solvent of the second polyimide is at least one selected from the group consisting of C3-C5 alkane, tetrahydrofuran, acetone and chloroform.

In the present invention, the good solvent for the polyimide is at least one selected from the group consisting of N-methylpyrrolidone, N-dimethylacetamide, and N, N-dimethylacetamide.

In the present invention, in order to obtain a preferable effect, the present invention has a certain requirement on the amount ratio of the good solvent for polyimide, the poor solvent for first polyimide, and the poor solvent for second polyimide, and preferably, the weight ratio of the good solvent for polyimide, the poor solvent for first polyimide, and the poor solvent for second polyimide is 1: (0.1-0.5): (0.1-0.5), preferably 1: (0.15-0.3): (0.15-0.3).

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

In the invention, in step (1), the casting solution is prepared according to a method comprising the following steps: stirring polyimide, diluent and additive at 20-50 deg.C and 100-1200r/min for 12-48h, and removing impurities by vacuum defoaming and filtering (20-50 deg.C).

In the invention, the vacuum defoaming conditions comprise: the pressure is-0.1 MPa to-0.095 MPa, the temperature is 20-30 ℃, the rotating speed is 10-50r/min, and the time is 12-24h.

In the present invention, in step (2), the bore fluid includes a solvent a and a solvent B, wherein the solvent a is at least one selected from N-methylpyrrolidone, N-dimethylacetamide and N, N-dimethylacetamide, and the solvent B is at least one selected from C1-C4 saturated monohydric alcohols, γ -butyrolactone and water.

In the present invention, the solvent a accounts for 50 to 99wt%, preferably 60 to 95wt%, of the total weight of the core solution.

According to some embodiments of the invention, the extrusion is performed in a spinneret, wherein the extrusion temperature (temperature of the spinneret) is between 40 and 75 ℃, preferably between 60 and 70 ℃.

In the invention, the flow of the casting solution is 6-30mL/min in the extrusion process.

According to some embodiments of the invention, the flow rate of the bore fluid during extrusion is 2-10mL/min.

In the invention, before solidification, the hollow fiber obtained by extrusion passes through the air gap to promote the formation of the compact layer and better regulate and control the thickness of the compact layer.

In the invention, the height of the air gap is 5-30cm.

In the invention, the air gap is heated by adopting an annular sleeve, and the temperature is preferably controlled to be 70-150 ℃.

In the present invention, the solidification is carried out in a coagulation bath, and preferably, the bath used in the coagulation bath is solvent C and/or water, and the temperature of the coagulation bath is 40 to 70 ℃.

In the present invention, the solvent C is at least one selected from the group consisting of C1-C4 saturated monohydric alcohols, gamma-butyrolactone, and water.

In the invention, in the step (3), the winding speed is 0.5-2m/s.

In the present invention, the purpose of the extraction is to remove the diluent and additives from the hollow fiber membrane precursor.

In the invention, the extractant for extraction is at least one selected from water, C1-C4 saturated monohydric alcohol and C5-C7 alkane. The amount of the extractant used is not particularly limited, so long as the requirements of the present invention are satisfied.

In the present invention, the extraction conditions include: the temperature is 20-35 ℃ and the time is 3-48h. Wherein, the extraction time refers to the time for soaking the membrane filaments (hollow fiber membrane precursors).

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

In the invention, the method also comprises a drying step after the extraction.

In the present invention, the drying conditions include: the temperature is 20-35 ℃ and the time is 2-15h.

The adsorbent for pressure swing adsorption of the present invention is not particularly limited as long as the requirements of the present invention can be satisfied, and for example, the adsorbent for pressure swing adsorption may be selected from at least one of molecular sieves, activated carbons, and metal organic framework Materials (MOFs).

According to some embodiments of the invention, the pressure swing adsorption conditions may include: the pressure of pressure swing adsorption is 0.1-15MPa, preferably 2-4.5MPa; the space velocity of pressure swing adsorption is 10-550h ^-1 。

The invention provides a system for purifying helium from helium-rich gas, which 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 sequentially communicated;

preferably, a decarburization drying device is arranged between the chemical dehydrogenation unit and the cryogenic separation unit.

The present invention will be described in detail below by way of examples.

In the following preparation examples, all examples are commercially available without specific description; hollow spinnerets are commercially available from shanghai; the porosity of the hollow fiber membrane support layer is determined by mercury intrusion; the thickness of the dense layer was determined by scanning electron microscopy.

In the following examples, the test methods for the volume fraction of each gas: gas chromatography. In the examples, the first-stage membrane separation means performing a first membrane separation, the second-stage membrane separation means performing a second membrane separation (using a fresh membrane module) using the gas after the first-stage membrane separation as the inlet gas, and the third-stage membrane separation, the fourth-stage membrane separation and the fifth-stage membrane separation are similar to the first-stage membrane separation.

The following preparation examples are given to illustrate random polyimide copolymers

Preparation example 1

(1) Under the protection of nitrogen, 200mL of anhydrous N-methylpyrrolidone and m-phenylenediamine (10.81g, 0.1mmol) are sequentially added into a 1L three-necked bottle, and the mixture is stirred until the materials are completely dissolved; uniformly mixing 4, 4-diphenyl ether dianhydride (ODPA) (0.01 mmol) and 4,4' - (hexafluoroisopropylene) diphthalic anhydride (6 FDA) (0.09 mmol) under mechanical stirring, adding the system at 0 ℃, and carrying out polycondensation reaction for 12 hours to obtain a material containing polyimidic acid;

(2) Adding a mixture of acetic anhydride (0.36 mmol) and pyridine (0.36 mmol) into the polyimide acid material obtained in the step (1), and performing intramolecular dehydration at 200 ℃ for 24h to obtain a polyimide-containing material; then, 600mL of N-methylpyrrolidone (NMP) was added to the polyimide-containing material to dilute the material, and the above-mentioned diluted material was poured into a mixed solvent of water and ethanol (500ml ) with stirring to precipitate polyimide, followed by rinsing (3 times) with a mixed solution of water and ethanol (1500 mL. The infrared test shows that the polyimide random copolymer has a structure shown in a formula (I), wherein X is Xc, Y is Ya, and Z' are both Z1. In addition, no starting material could be detected in the liquid phase remaining after the polyimide had precipitated, indicating that all starting materials were involved in the reaction.

The following preparation examples are illustrative of the preparation of polyimide-based hollow fiber membranes

Preparation of example 1

(1) 20wt% of the polyimide random copolymer obtained in preparation example 1, 50wt% of NMP, 10wt% of ethanol (boiling point of 78 ℃), 10wt% of THF (boiling point of 68.28 ℃) and 10wt% of lithium nitrate are added into a kettle with a stirring device, heated to 50 ℃, stirred under the protection of nitrogen (rotating speed of 600 r/min) for 36 hours, stopped stirring, defoamed at 25 ℃,0.1 MPa and 30r/min for 24 hours, and filtered by a filter screen (aperture of 100 meshes) at 50 ℃ to obtain a casting solution;

(2) Respectively conveying the casting solution and the inner core solution (NMP: water =95wt%:5 wt%) to a hollow spinning nozzle by adopting a metering pump, extruding the inner core solution and the casting solution together through the spinning nozzle to obtain hollow fibers, passing the hollow fibers through an air gap of 10cm, and then placing the hollow fibers into water at 50 ℃ for curing to obtain a polyimide-based hollow fiber membrane precursor; wherein the spinneret temperature (extrusion temperature) is 75 ℃; the flow rates of the casting solution and the inner core solution entering the hollow spinning nozzle are respectively 6mL/min and 2mL/min;

(3) Winding the polyimide hollow fiber membrane precursor obtained in the step (2) by using a winding machine, and then sequentially extracting the polyimide hollow fiber membrane precursor in water, ethanol and n-hexane for two times, wherein the extraction time is 3 hours; and then placing the extracted hollow fiber membrane in a fume hood at room temperature, and naturally drying the hollow fiber membrane in the air for 12 hours to obtain the polyimide-based hollow fiber membrane. Wherein the winding speed is 1m/s.

The obtained hollow fiber membrane is characterized by mercury intrusion method, and the porosity is 80%. The thickness of the dense layer was 135nm.

The following examples are provided to illustrate the purification of helium using the method of the present invention

Example 1

In a helium-rich gas, the volume fraction of helium is 8.5%, and the composition of the 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, 9.5% by volume of oxygen and 0.1% by volume of water;

(1) The helium-rich gas is introduced (space velocity of 300 h) ^-1 ) Introducing a catalytic dehydrogenation separation unit to enable hydrogen and oxygen (pure oxygen is used as a combustion improver) to react to obtain gas subjected to catalytic dehydrogenation, wherein the adopted catalyst is Pt, and the temperature for the reaction of the hydrogen and the oxygen is 120 ℃;

(2) Directly feeding the gas after catalytic dehydrogenation into a chemical dehydrogenation reactor (the catalyst for chemical dehydrogenation is copper oxide) through a pipeline for chemical dehydrogenation reaction to obtain the gas after chemical dehydrogenation, wherein the temperature of the chemical dehydrogenation is 500 ℃, and the space velocity is 80h ^-1 ；

(3) Introducing the gas after chemical dehydrogenation into a decarburization drying device (adopting soda lime as the adsorbent), wherein the space velocity is 310h ^-1 Introducing the decarbonized and dried gas into a cryogenic separation unit, wherein the cryogenic separation temperature is-150 ℃, the pressure is 6MPa, the temperature is raised to-20 ℃, then introducing a polybenzimidazole hollow fiber membrane component (PBI membrane, china scientific and technology (Dalian) Co., ltd.) for primary, secondary and tertiary membrane separation operations (the pressure is 5 MPa), the gas after membrane separation is sent into a pressure swing adsorption unit (13 XAPG 4X 8 zeolite molecular sieve as an adsorbent, purchased from Shanghai Bo crystal molecular sieve Co., ltd.), the adsorption pressure is 5MPa, and the adsorption space velocity is 250h ^-1 And obtaining the ultra-pure helium gas. Wherein the volume fractions of the separated gas components of each stage are shown in Table 1.

TABLE 1

Example 2

In the produced gas of a certain gas field, the volume fraction of helium is 20%, and the compositions of other gases comprise: methane in a volume fraction of 18%, nitrogen in a volume fraction of 60%, hydrogen in a volume fraction of 1%, carbon dioxide in a volume fraction of 0.5% and oxygen in a volume fraction of 0.5%.

(1) The gas field is mined (the airspeed is 800 h) ^-1 ) Introducing a catalytic dehydrogenation separation unit to enable hydrogen and oxygen (pure oxygen is used as a combustion improver) to react to obtain gas subjected to catalytic dehydrogenation, wherein the adopted catalyst is Pd, and the temperature for the reaction of the hydrogen and the oxygen is 106 ℃;

(2) Directly feeding the gas after catalytic dehydrogenation into a chemical dehydrogenation reactor (the catalyst for chemical dehydrogenation is copper oxide) through a pipeline for chemical dehydrogenation reaction to obtain the gas after chemical dehydrogenation, wherein the temperature of the chemical dehydrogenation is 350 ℃, and the space velocity is 400h ^-1 ；

(3) Introducing the gas after chemical dehydrogenation into a decarburization drying device (adopting soda lime as adsorbent), wherein the space velocity is 750h ^-1 Introducing the decarbonized and dried gas into a cryogenic separation unit, wherein the cryogenic separation temperature is-140 ℃, the pressure is 6MPa, the temperature is raised to-20 ℃, then introducing a hollow fiber membrane component (PBI membrane, chinese energy materials science and technology (Dalian) Co., ltd.) adopting polybenzimidazole for primary, secondary, tertiary, quaternary and quinary membrane separation operations (the pressure is 11 MPa), conveying the gas subjected to membrane separation into a pressure swing adsorption unit (13 XAPG 4X 8 zeolite molecular sieve as an adsorbent, purchased from Shanghai Bo crystal molecular sieve Co., ltd.), the pressure swing adsorption pressure is 10MPa, and the pressure swing adsorption space velocity is 300h ^-1 And obtaining the ultra-pure helium gas. Wherein the volume fractions of the separated gas components of each stage are shown in Table 2.

TABLE 2

Example 3

In the gas of flash vapor (BOG) of the lng plant, the volume fraction of helium is 15.73%, and the composition of the other gases includes: 19.9% by volume of methane, 57.7% by volume of nitrogen, 6.66% by volume of hydrogen and 0.01% by volume of carbon dioxide;

(1) The gas (space velocity of 290 h) of the flash steam (BOG) of the natural gas station is introduced ^-1 ) Introducing a catalytic dehydrogenation separation unit to enable hydrogen and oxygen (pure oxygen is used as a combustion improver) to react to obtain gas subjected to catalytic dehydrogenation, wherein the adopted catalyst is Au, and the temperature for the reaction of the hydrogen and the oxygen is 74 ℃;

(2) Directly feeding the gas after catalytic dehydrogenation into a chemical dehydrogenation reactor (the catalyst for chemical dehydrogenation is copper oxide) through a pipeline for chemical dehydrogenation reaction to obtain the gas after chemical dehydrogenation, wherein the temperature of the chemical dehydrogenation is 600 ℃, and the space velocity is 360h ^-1

(3) Introducing the gas after chemical dehydrogenation into a decarburization drying device (adopting potassium hydroxide as the adsorbent) at an airspeed of 200h ^-1 The decarbonized and dried gas is introduced into a cryogenic separation unit, wherein the cryogenic separation temperature is-135 ℃, the pressure is 0.5MPa, the temperature is raised to 20 ℃, the gas is introduced into the polyimide-based hollow fiber membrane component prepared by the preparation example 1 to carry out primary, secondary and tertiary membrane separation operations (the pressure is 2 MPa), the gas after the membrane separation is sent into a pressure swing adsorption unit (13 XAPG 4X 8 zeolite molecular sieve is taken as an adsorbent and purchased from Shanghai Bo crystal molecular sieve Co., ltd.), the pressure swing adsorption pressure is 1MPa, and the pressure swing adsorption space velocity is 10h ^-1 And obtaining the ultra-pure helium gas. Wherein the volume fractions of the separated gas components of each stage are shown in Table 3.

TABLE 3

Example 4

After pretreatment (multi-stage flash evaporation) of natural gas produced in a certain gas field, the volume fraction of helium in flash evaporation gas is 19.7%, and the composition of other gases comprises: 15.9% by volume of methane, 53.7% by volume of nitrogen, 10.65% by volume of hydrogen and 0.05% by volume of carbon dioxide.

(1) The flash steam (space velocity of 10 h) ^-1 ) Introducing a catalytic dehydrogenation separation unit to enable hydrogen and oxygen (pure oxygen is used as a combustion improver) to react to obtain gas subjected to catalytic dehydrogenation, wherein the adopted catalyst is Pd, and the temperature for the reaction of the hydrogen and the oxygen is 83 ℃;

(2) Directly feeding the gas after catalytic dehydrogenation into a chemical dehydrogenation reactor (the catalyst for chemical dehydrogenation is chromium oxide) through a pipeline for chemical dehydrogenation reaction to obtain the gas after chemical dehydrogenation, wherein the temperature of the chemical dehydrogenation is 800 ℃, and the space velocity is 286h ^-1 ；

(3) Introducing the gas after chemical dehydrogenation into a decarburization drying link (adopting sodium hydroxide as a drying agent), wherein the space velocity is 600h ^-1 And introducing the decarbonized and dried gas into a cryogenic separation unit, wherein the cryogenic separation temperature is-120 ℃, the pressure is 0.35MPa, the temperature is increased to 25 ℃, and then a hollow fiber membrane component made of polysulfone (Cuimeia,

) Performing primary and secondary membrane separation (pressure is 6 MPa), feeding the membrane-separated gas into pressure swing adsorption unit (13 XAPG 4X 8 zeolite molecular sieve as adsorbent, from Shanghai Bo crystal molecular sieve Co., ltd.), with adsorption pressure of 2MPa and pressure swing adsorption space velocity of 20h ^-1 And obtaining the ultra-pure helium gas. The volume fractions of the separated gas components in each stage are shown in Table 4.

TABLE 4

Example 5

In a helium-rich gas, the volume fraction of helium is 17%, and the composition of the 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;

(1) The helium-rich gas is introduced (space velocity of 1000 h) ^-1 ) Introducing a catalytic dehydrogenation separation unit to enable hydrogen and oxygen (pure oxygen is used as a combustion improver) to react to obtain gas subjected to catalytic dehydrogenation, wherein the adopted catalyst is Pt, and the reaction temperature of the hydrogen and the oxygen is 59 ℃;

(2) Directly feeding the gas after catalytic dehydrogenation into a chemical dehydrogenation reactor (the catalyst for chemical dehydrogenation is copper oxide) through a pipeline for chemical dehydrogenation reaction to obtain the gas after chemical dehydrogenation, wherein the temperature of the chemical dehydrogenation is 300 ℃, and the space velocity is 150h ^-1 ；

(3) Cooling the gas after chemical dehydrogenation, pressurizing to 10MPa, and introducing into a decarburization drying link (adopting soda lime as a drying agent) at an airspeed of 710h ^-1 Introducing the decarbonized and dried gas into a cryogenic separation unit, wherein the temperature of cryogenic separation is-115 ℃, the pressure is 10MPa, the temperature is raised to-20 ℃, then introducing a polysulfone hollow fiber membrane component (Permaya, PRISM O R) to perform primary, secondary and tertiary membrane separation operations (the pressure is 10 MPa), the gas subjected to membrane separation is sent into a pressure swing adsorption unit (adopting coconut shell activated carbon as an adsorbent, purchased from Tianjin green scene environmental protection science and technology Limited), the pressure swing adsorption pressure is 2MPa, and the pressure swing adsorption airspeed is 83h ^-1 And obtaining the ultra-pure helium gas. The volume fractions of the separated gas components in each stage are shown in Table 5.

TABLE 5

Example 6

In natural gas multistage flash steam (BOG) produced in a certain gas field, the volume fraction of helium is 10%, and the compositions of other gases comprise: 45 volume percent methane, 40 volume percent nitrogen, 2.5 volume percent hydrogen, 0.5 volume percent carbon dioxide, and 2 volume percent oxygen;

(1) The gas field is mined (space velocity is 410 h) ^-1 ) Introducing a catalytic dehydrogenation separation unit to enable hydrogen and oxygen (pure oxygen is used as a combustion improver) to react to obtain gas subjected to catalytic dehydrogenation, wherein the adopted catalyst is Au, and the temperature for the reaction of the hydrogen and the oxygen is 115 ℃;

(2) Directly feeding the gas after catalytic dehydrogenation into a chemical dehydrogenation reactor (the catalyst for chemical dehydrogenation is ferric oxide) through a pipeline for chemical dehydrogenation reaction to obtain the gas after chemical dehydrogenation, wherein the temperature of the chemical dehydrogenation is 930 ℃, and the space velocity is 50h ^-1 ；

(3) Cooling and pressurizing the gas after chemical dehydrogenation to 1MPa, introducing soda lime in a decarburization drying link as a drying agent), and keeping the space velocity at 300h ^-1 Introducing the decarbonized and dried gas into a cryogenic separation unit, wherein the cryogenic separation temperature is-120 ℃, the pressure is 7MPa, the temperature is raised to-20 ℃, then introducing a polysulfone hollow fiber membrane assembly (PRISM O R) to perform primary and secondary membrane separation operation (the pressure is 5 MPa), conveying the gas subjected to membrane separation into a pressure swing adsorption unit (13 XAPG 4X 8 zeolite molecular sieve is used as an adsorbent and purchased from Shanghai Bo crystal molecular sieve Co., ltd.), the pressure swing adsorption pressure is 5MPa, and the pressure swing adsorption airspeed is 10MPa ^-1 Ultra pure helium gas was obtained. The volume fractions of the separated gas components in each stage are shown in Table 6.

TABLE 6

/>

Example 7

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

(1) The helium-rich gas is introduced (space velocity of 600 h) ^-1 ) Introducing a catalytic dehydrogenation separation unit to enable hydrogen and oxygen (pure oxygen is used as a combustion improver) to react to obtain gas subjected to catalytic dehydrogenation, wherein the adopted catalyst is Rh, and the temperature for the reaction of the hydrogen and the oxygen is 260 ℃;

(2) Directly feeding the gas after catalytic dehydrogenation into a chemical dehydrogenation reactor (the catalyst for chemical dehydrogenation is copper oxide) through a pipeline for chemical dehydrogenation reaction to obtain the gas after chemical dehydrogenation, wherein the temperature of the chemical dehydrogenation is 660 ℃, and the space velocity is 360h ^-1 ；

(3) Pressurizing the gas after chemical dehydrogenation to 6MPa, introducing into a decarburization drying link (soda lime is used as a drying agent), and keeping the airspeed at 200h ^-1 Introducing the decarbonized and dried gas into a cryogenic separation unit, wherein the cryogenic separation temperature is-220 ℃, the pressure is 8MPa, the temperature is raised to-20 ℃, then introducing a hollow fiber membrane component (Chinese energy materials science and technology (Dalian) limited, PBI membrane) adopting polybenzimidazole to perform primary membrane separation operation (the pressure is 15 MPa), and the gas subjected to membrane separation is sent into a pressure swing adsorption unit (Tianjin green scene environmental protection science and technology limited, coconut shell activated carbon), the pressure swing adsorption pressure is 12MPa, and the pressure swing adsorption airspeed is 200h ^-1 And obtaining the ultra-pure helium gas. The volume fractions of the separated gas components in each stage are shown in Table 7.

TABLE 7

Example 8

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

(1) The flash steam (space velocity of 20 h) ^-1 ) Introducing a catalytic dehydrogenation separation unit to enable hydrogen and oxygen (pure oxygen is used as a combustion improver) to react to obtain gas subjected to catalytic dehydrogenation, wherein the adopted catalyst is Pd, and the temperature for the reaction of the hydrogen and the oxygen is 110 ℃;

(2) Directly feeding the gas after catalytic dehydrogenation into a chemical dehydrogenation reactor (the catalyst for chemical dehydrogenation is copper oxide) through a pipeline for chemical dehydrogenation reaction to obtain the gas after chemical dehydrogenation, wherein the temperature of the chemical dehydrogenation is 520 ℃, and the space velocity is 146h ^-1 ；

(3) Cooling the gas after chemical dehydrogenation, pressurizing to 8MPa, and introducing into a decarburization drying link (adopting the drying agent which is potassium hydroxide) at an airspeed of 350h ^-1 Introducing the decarbonized and dried gas into a cryogenic separation unit, wherein the cryogenic separation temperature is-145 ℃, the pressure is 6MPa, the temperature is raised to-20 ℃, then introducing the polyimide hollow fiber membrane component prepared in the preparation example 1 to perform primary and secondary membrane separation operations (the pressure is 12 MPa), conveying the gas subjected to membrane separation into a pressure swing adsorption unit (adopting a 13XAPG 4X 8 zeolite molecular sieve as an adsorbent and purchased from Shanghai Bo crystal molecular sieve Co., ltd.), the pressure swing adsorption pressure is 5.5MPa, and the pressure swing adsorption airspeed is 60h ^-1 And obtaining the ultra-pure helium gas. The volume fractions of the separated gas components of each stage are shown in Table 8.

TABLE 8

Example 9

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

(1) The gas field is mined (the space velocity is 400 h) ^-1 ) Introducing a catalytic dehydrogenation separation unit to enable hydrogen and oxygen (pure oxygen is used as a combustion improver) to react to obtain gas subjected to catalytic dehydrogenation, wherein the adopted catalyst is Pt, and the temperature for the reaction of the hydrogen and the oxygen is 99 ℃;

(2) Directly feeding the gas after catalytic dehydrogenation into a chemical dehydrogenation reactor (the catalyst for chemical dehydrogenation is copper oxide) through a pipeline for chemical dehydrogenation reaction to obtain the gas after chemical dehydrogenation, wherein the temperature of the chemical dehydrogenation is 550 ℃, and the space velocity is 130h ^-1 ；

(3) Introducing the gas after chemical dehydrogenation into a decarburization drying device (soda lime as a drying agent), wherein the space velocity is 800h ^-1 Introducing the decarbonized and dried gas into a cryogenic separation unit, wherein the cryogenic separation temperature is-220 ℃, the pressure is 10MPa, the temperature is raised to-20 ℃, then introducing the polyimide-based hollow fiber membrane component prepared in the preparation example 1 to perform primary, secondary and tertiary membrane separation operations (the pressure is 15 MPa), conveying the gas subjected to membrane separation into a pressure swing adsorption unit (adopting coconut shell activated carbon as an adsorbent and purchased from Tianjin green scene environmental protection science and technology Co., ltd.), the pressure swing adsorption pressure is 14MPa, and the adsorption airspeed is 110h ^-1 To obtain the ultra-pure helium gas. The volume fractions of the separated gas components in each stage are shown in Table 9.

TABLE 9

/>

From the data, the hydrogen and a small amount of methane micromolecular combustible gas which are difficult to separate from helium in the mixed gas can be converted into CO through the catalytic oxidation and chemical dehydrogenation two-stage dehydrogenation process ₂ And water, the volume fraction of hydrogen is greatly reduced, and CO is cooled and decarbonized and dried (compression drying for adsorption and water removal), and ₂ and the volume fraction of water is greatly reduced, and then the helium gas is enabled to be subjected to deep coolingThe volume fraction of the nitrogen and the methane is greatly improved, part of the nitrogen and the methane are removed, the gas subjected to cryogenic separation is further subjected to membrane separation, then the nitrogen, the oxygen, the methane and the carbon dioxide are gradually separated from the helium, the volume fraction of the helium can be improved to 99.99%, and finally, the volume fraction of the helium can reach 99.999% after pressure swing adsorption by a molecular sieve.

The polymer film of the preferred embodiment used in the present invention can obtain better effects, and can be specifically referred to the content described in (application No. 202110864549.5).

The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.

Claims (12)

1. A method for purifying helium from a helium-rich gas, the method comprising the steps of:

(1) Contacting the helium-rich gas with oxygen to enable hydrogen in the helium-rich gas to react with the oxygen to obtain gas subjected to catalytic dehydrogenation;

(2) In the presence of metal oxide, carrying out chemical dehydrogenation on the gas subjected to catalytic dehydrogenation to obtain a gas subjected to chemical dehydrogenation;

(3) And carrying out cryogenic separation, membrane separation and pressure swing adsorption on the gas subjected to chemical dehydrogenation in sequence to obtain the ultrapure helium.

2. The method of claim 1, wherein the helium-rich gas is selected from at least one of natural gas, shale gas, and liquefied natural gas flash vapor (BOG).

3. The method according to claim 1 or 2, wherein the catalyst used for the reaction of hydrogen with oxygen in step (1) is a noble metal catalyst selected from at least one of Pt, pd, rh, ru and Au;

and/or, the contacting conditions include: the temperature is 30-300 ℃, preferably 50-120 ℃; the airspeed of the feed gas is 1-10000h ^-1 Preferably 10-1000h ^-1 。

4. The process of claim 1 or 2, wherein in step (2), the conditions of the chemical dehydrogenation comprise: the temperature of the chemical dehydrogenation is 100 ℃ to 1000 ℃, and the space velocity of the 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;

preferably, decarburization drying is further included between the chemical dehydrogenation and the cryogenic separation, and the adsorbent is at least one of potassium hydroxide, sodium hydroxide and soda lime;

preferably, the space velocity of the decarburization drying is 200-800h ^-1 。

5. The process according to claim 1 or 2, wherein the conditions of cryogenic separation comprise: the temperature is-220 ℃ to-100 ℃, and the pressure is 0.1MPa to 10MPa.

6. The method according to claim 1 or 2, wherein the membrane used in the membrane separation is selected from at least one of a hollow fiber membrane, a flat sheet membrane, and a tubular membrane;

preferably, the membrane used in the membrane separation is made of at least one material selected from 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, and more preferably polyimide;

and/or, the membrane separation adopts a one-stage or multi-stage separation mode;

and/or, the conditions of the membrane separation comprise: before membrane separation, the pressure of the gas obtained by cryogenic separation is controlled to be 0.1-15MPa, and the temperature of the gas is controlled to be-20-100 ℃.

7. The method according to claim 6, wherein the membrane used in the membrane separation is a polyimide-based hollow fiber membrane;

preferably, the polyimide-based hollow fiber membrane comprises a supporting layer and a dense layer attached to the outer surface of the supporting layer, the thickness of the dense layer is less than 1000nm, and the porosity of the hollow fiber membrane is 40-80%;

preferably, the thickness of the dense layer is 100-500nm, and the porosity of the hollow fiber membrane is 50-70%;

preferably, the material of the hollow fiber membrane is polyimide random copolymer.

8. The method of claim 7, wherein the polyimide random copolymer has a structure according to formula (I):

in the formula (I), m and n are each independently an integer of 10 to 2000;

x has a structure represented by any one of formula (X1) to formula (X3);

in the formula (X1) -formula (X3), R ¹ 、R ² 、R ³ 、R ⁴ 、R ⁵ And R ⁶ Each independently is H, C1-C4 alkyl, C6-C10 aryl, amino, hydroxyl or carboxyl;

y has a structure represented by any one of the formulae (Y1) to (Y5);

in the formula (Y1) -formula (Y5), R ⁷ 、R ⁸ 、R ⁹ 、R ¹⁰ 、R ¹¹ 、R ¹² 、R ¹³ 、R ¹⁴ 、R ¹⁵ And R ¹⁶ Each independently is 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);

in the formula (Z2), ra and Rb are each independently H, C1-C4 alkyl or C1-C4 haloalkyl;

preferably, m and n are each independently an integer from 50 to 1000;

preferably, 0.9. Gtoreq.n/(m + n). Gtoreq.0.3, preferably 0.7. Gtoreq.n/(m + n). Gtoreq.0.5.

9. The method of claim 8, wherein X has one of the structures shown below,

and/or, Y has one of the structures shown below,

and/or, Z and Z' both have the structure shown by Z1 or Z3,

preferably, X is Xa, Y is Ya, and Z' are both Z1;

or X is Xa, Y is Yb, and Z' are both Z1;

or X is Xa, Y is Yd, and Z' are both Z1;

or X is Xb, Y is Ya, and Z' are both Z1;

or X is Xb, Y is Yb, and Z' are both Z1;

or X is Xb, Y is Yd, and Z' are both Z1;

or X is Xc, Y is Ya, and Z' are both Z1;

or X is Xc, Y is Yb, and Z' are both Z1;

or X is Xc, Y is Yc, and Z' are both Z1;

or, X is Xc, Y is Y4, and Z' are both Z1;

or X is Xc, Y is Yd, and Z' are both Z1;

or X is Xb, Y is Ya, and Z' are both Z3;

or X is Xb, Y is Yb, and Z' are both Z3;

or X is Xb, Y is Yd, and Z' are both Z3;

or X is Xc, Y is Ya, and Z' are both Z3;

or X is Xc, Y is Yb, and Z' are both Z3;

alternatively, X is Xc, Y is Yd, and Z' are both Z3.

10. The method of any one of claims 7-9, wherein the polyimide-based hollow fiber membrane is prepared according to a method comprising:

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

(2) Extruding the inner core liquid and the casting solution at a temperature T, and curing to obtain a hollow fiber membrane precursor, wherein T is more than or equal to B2 and less than B1;

(3) Rolling and extracting the hollow fiber membrane precursor to obtain the polyimide-based hollow fiber membrane;

preferably, in the 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%;

preferably, 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%, based on the total weight of the casting solution;

preferably, the boiling point B1 of the poor solvent of the first polyimide is 5 to 200 ℃, preferably 10 to 20 ℃ higher than the boiling point B2 of the poor solvent of the second polyimide;

preferably, the poor solvent of the first polyimide is selected from at least one of saturated monohydric alcohols of C2-C4, gamma-butyrolactone and water;

preferably, the poor solvent of the second polyimide is selected from at least one of C3-C5 alkane, tetrahydrofuran, acetone and chloroform;

preferably, the good solvent of the polyimide is selected from at least one of N-methylpyrrolidone, N-dimethylacetamide and N, N-dimethylacetamide;

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);

preferably, the additive is a lithium salt, preferably selected from lithium nitrate and/or lithium chloride;

preferably, the casting solution is prepared according to a method comprising the following steps: stirring polyimide, diluent and additive at 20-50 deg.C and 100-1200r/min for 12-48h, and removing impurities by vacuum defoaming and filtering (20-50 deg.C);

preferably, the vacuum defoaming conditions include: the pressure is-0.1 MPa to-0.095 MPa, the temperature is 20-30 ℃, the rotating speed is 10-50r/min, and the time is 12-24h;

preferably, in the step (2), the bore fluid comprises a solvent A and a solvent B, wherein the solvent A is selected from at least one of N-methylpyrrolidone, N-dimethylacetamide and N, N-dimethylacetamide, and the solvent B is selected from at least one of C1-C4 saturated monohydric alcohol, gamma-butyrolactone and water;

preferably, the solvent A accounts for 50-99wt%, preferably 60-95% of the total weight of the inner core solution;

preferably, the extrusion is carried out in a spinneret, wherein the temperature of the extrusion is 40-75 ℃, preferably 60-70 ℃;

preferably, in the extrusion process, the flow rate of the casting solution is 6-30mL/min;

preferably, during the extrusion process, the flow rate of the inner core liquid is 2-10mL/min;

preferably, the extruded hollow fibers are passed through an air gap before curing;

preferably, the height of the air gap is 5-30cm;

preferably, the air gap is heated by adopting an annular sleeve, and the temperature is preferably controlled to be 70-150 ℃;

preferably, the solidification is carried out in a coagulating bath, preferably, the coagulating bath uses a bath solution of solvent C and/or water, and the temperature of the coagulating bath is 40-70 ℃;

preferably, the solvent C is selected from at least one of C1-C4 saturated monohydric alcohol, gamma-butyrolactone and water;

preferably, in the step (3), the rolling speed is 0.5-2m/s;

preferably, the extractant for extraction is selected from at least one of water, saturated monohydric alcohol of C1-C4 and alkane of C5-C7;

preferably, the conditions of the extraction include: the temperature is 20-35 ℃, and the time is 3-48h;

preferably, the extraction is followed by a drying step;

preferably, the drying conditions include: the temperature is 20-35 ℃ and the time is 2-15h.

11. The process of claim 1 or 2, wherein the adsorbent for pressure swing adsorption is selected from at least one of molecular sieves, activated carbon, and metal organic framework materials;

preferably, the pressure swing adsorption conditions include: the pressure of pressure swing adsorption is 0.1-15MPa, preferably 2-4.5MPa; the space velocity of pressure swing adsorption is 10-500h ^-1 。

12. A system for purifying helium from helium-rich gas is characterized by comprising 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 sequentially communicated;

preferably, a decarburization drying device is arranged between the chemical dehydrogenation unit and the cryogenic separation unit.