Method for preparing high-purity hydrogen by distillation combined with membrane separation

Abstract

The present invention relates to the technical field of cracking gas separation, and discloses a method for preparing high-purity hydrogen by combining distillation with membrane separation. The method provided by the present invention comprises the following steps: (1) subjecting the raw gas to demethanization treatment in a demethanizer, obtaining a mixed gas containing methane and hydrogen at the top of the tower, and obtaining a product gas containing ethylene at the bottom of the tower; (2) subjecting the mixed gas containing methane and hydrogen to membrane separation. The method provided by the present invention can prepare crude hydrogen and high-purity hydrogen, thereby increasing the technical added value of the product; at the same time, it improves the quality of the gas entering the distillation, increases the yield of the methane-rich gas, and optimizes the methane-hydrogen separation process of the ethylene demethanizer. It has broad application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of cracking gas separation, and in particular to a method for preparing high-purity hydrogen by combining rectification with membrane separation. Background Art

[0002] Ethylene is one of the chemical products with the largest output and consumption in the world, and is known as the "mother of the petrochemical industry". Ethylene production capacity is one of the important indicators to measure the level of development of a country's petrochemical industry. my country's ethylene production capacity has long ranked second in the world, second only to the United States. The production of ethylene from petroleum mainly relies on cracking technology. As a result, a large number of by-products other than the target product are generated in the process, such as methane, hydrogen and other fuel gases, which require effective removal and recovery methods. In the process of purifying ethylene, a corresponding distillation demethanizer is set up to remove methane. Hydrogen removal mainly relies on cryogenic technology to separate hydrogen from other components, which can be set at the front or back end of the demethanizer. Since hydrogen consumes additional cooling capacity and affects the methane separation process, the hydrogen in the demethanized gas can be enriched and purified by combining an efficient membrane process before entering the cryogenic system, or the high-energy consumption cryogenic system can be replaced. Summary of the invention

[0003] In order to solve the technical problems of high energy consumption and poor separation effect in the prior art, the present invention provides a method for preparing high-purity hydrogen by combining distillation with membrane separation.

[0004] The present invention provides a method for preparing high-purity hydrogen by combining rectification with membrane separation, the method comprising the following steps:

[0005] (1) Demethanizing the raw gas in a demethanizer, obtaining a mixed gas containing methane and hydrogen at the top of the tower, and obtaining a product gas containing ethylene at the bottom of the tower;

[0006] (2) The mixed gas containing methane and hydrogen is subjected to membrane separation.

[0007] Compared with the prior art, the present invention has the following beneficial effects:

[0008] (1) The method provided by the present invention optimizes the methane-hydrogen separation process of the ethylene demethanizer, and can realize the expansion and capacity expansion of the ethylene plant without rebuilding or building a new cold box and demethanizer;

[0009] (2) The method provided by the present invention reduces the energy consumption of methane / hydrogen separation;

[0010] (3) The method provided by the present invention can prepare crude hydrogen, directly supply the catalytic hydrogenation process, and optimize the hydrogen balance of the refinery;

[0011] (4) The method provided by the present invention can produce high-purity hydrogen and increase the technical added value of the product. Hydrogen is concentrated under normal temperature and low pressure operating conditions, avoiding the extremely high requirements of cryogenic technology on equipment and energy consumption, making the hydrogen preparation process simple and economical;

[0012] (5) The method provided by the present invention improves the quality of the gas entering the separation device (distillation), thereby increasing the yield of methane-rich gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A schematic diagram of a process for preparing high-purity hydrogen by combining distillation with membrane separation according to a specific embodiment of the present invention;

[0014] Figure 2 This is a schematic diagram of the process of separating raw gas to produce high-purity hydrogen in Comparative Example 1.

[0015] Description of Reference Numerals

[0016] T1: demethanizer; MEM1-first polymer membrane separation unit; MEM2: second polymer membrane separation unit; MEM3: third polymer membrane separation unit; H1, H1', ​​H2', H3': heat exchangers; M1, M2: gas mixing devices; CP1: pressurizing device; 1-first separator; 2-second separator; S1: feed gas; S2: mixed gas containing methane and hydrogen; S3: product gas containing ethylene; S4: mixed gas containing methane and hydrogen after heat exchange; S5-mixed gas containing methane and hydrogen after heat exchange and compressed and heat exchanged second separator; S6-mixed gas containing methane and hydrogen after heat exchange and compressed and heat exchanged second separator; S7-mixed gas containing methane and hydrogen after heat exchange and compressed and heat exchanged second separator; S8-mixed gas containing methane and hydrogen after heat exchange and compressed and heat exchanged second separator; S9-mixed gas containing methane and hydrogen after heat exchange and compressed and heat exchanged second separator; S1-first separator; 2-second separator; S2-second separator; S3-second separator; S4-second separator; S5-second separator; S6-second separator; S7-second separator; S8-second separator; S9-second separator; S1-first separator; 2 ...1-first separator; 2-second separator; S2-second separator; S3-second separator; S4-second separator; S5-second separator; S6-second separator; Gas after hydrogen-rich mixture; S6-first methane-rich gas; S7-first hydrogen-rich gas; S8-second methane-rich gas; S9-high-purity hydrogen; S10-mixed gas of the first methane-rich gas and the second methane-rich gas; S11-third methane-rich gas; S12-second hydrogen-rich gas; S13-compressed second hydrogen-rich gas; S14-second hydrogen-rich gas after compression and heat exchange; S2'-mixed gas of methane and hydrogen; S3'-mixed gas of methane and hydrogen obtained by the first separation; S4'-mixed gas of methane and hydrogen obtained by the second separation; S5'-methane-rich product. DETAILED DESCRIPTION

[0017] 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.

[0018] The present invention provides a method for preparing high-purity hydrogen by combining rectification with membrane separation, the method comprising the following steps:

[0019] (1) Demethanizing the raw gas in a demethanizer, obtaining a mixed gas containing methane and hydrogen at the top of the tower, and obtaining a product gas containing ethylene at the bottom of the tower;

[0020] (2) The mixed gas containing methane and hydrogen is subjected to membrane separation.

[0021] In order to obtain better technical effects, preferably, the membrane separation method includes:

[0022] (2-1) subjecting the mixed gas containing methane and hydrogen to a first polymer membrane separation to obtain a first methane-rich gas and a first hydrogen-rich gas;

[0023] (2-2) subjecting the first hydrogen-rich gas to a second polymer membrane separation to obtain high-purity hydrogen gas and a second methane-rich gas;

[0024] (2-3) The first methane-rich gas and the second methane-rich gas are mixed and then subjected to a third polymer membrane separation to obtain a third methane-rich gas and a second hydrogen-rich gas; optionally, the second hydrogen-rich gas is returned to step (2-1) and subjected to the first polymer membrane separation together with the mixed gas containing methane and hydrogen. The first polymer membrane separation, the second polymer membrane separation and the third polymer membrane separation are carried out in a cross-flow separation manner. "Cross-flow" means that the flow direction of the gas to be separated is parallel to the membrane surface.

[0025] In the present invention, preferably, the second hydrogen-rich gas is compressed and heat-exchanged and then returned to step (2-1) to be separated by the first polymer membrane together with the mixed gas containing methane and hydrogen after heat exchange. There is no particular limitation on the conditions of compression and heat exchange, as long as they can meet the requirements of the present invention.

[0026] According to some embodiments of the present invention, the present invention does not impose any particular limitation on the type of raw gas, as long as high-purity hydrogen can be prepared according to the method of the present invention.

[0027] Preferably, the demethanizer is a distillation tower, and the distillation tower is a plate tower or a packed tower.

[0028] According to some embodiments of the present invention, the permeation pressure in the first polymer membrane separation process, the permeation pressure in the second polymer membrane separation process, and the permeation pressure in the third polymer membrane separation process are each independently 500 kPa-3500 kPa. Wherein, "permeation pressure" refers to the transmembrane pressure to which gas is subjected when passing through a membrane.

[0029] Preferably, the permeation pressure of the first polymer membrane separation is 500 kPa-3500 kPa;

[0030] Preferably, the permeation pressure of the second polymer membrane during separation is 500 kPa-2500 kPa;

[0031] Preferably, the permeation pressure during the separation process of the third polymer membrane is 500 kPa-2500 kPa.

[0032] According to some embodiments of the present invention, the membranes used for the first polymer membrane separation, the second polymer membrane separation and the third polymer membrane separation can each independently have a flux of 10-120 GPU for hydrogen, a flux of 0.1-3 GPU for methane and a flux of 0.1-2.5 GPU for ethylene. The unit of "GPU" is 10 -6 cm 3 (STP) / cm 2 ·s·cmHg.

[0033] In the present invention, before the first polymer membrane separation is performed, a step of heat exchanging the mixed gas containing methane and hydrogen obtained from the demethanizer to a temperature of -30°C to 20°C may be further included.

[0034] According to some embodiments of the present invention, the membranes used in the first polymer membrane separation, the second polymer membrane separation and the third polymer membrane separation are each independently selected from at least one of a hollow fiber membrane, a flat membrane and a tubular membrane.

[0035] According to some embodiments of the present invention, the materials of the polymer membranes used for the first polymer membrane separation, the second polymer membrane separation and the third polymer membrane separation are the same or different, and are independently selected from at least one of polysulfone, polyethersulfone, polyimide, polypropylene, polyethylene, synthetic resin, polyvinylidene fluoride, polytetrafluoroethylene, polyetheretherketone, polybenzimidazole, polydimethylsiloxane and metal organic framework materials.

[0036] In the present invention, the polymer membranes used for the first polymer membrane separation, the second polymer membrane separation and the third polymer membrane separation can be commercially available, or can be prepared by thermally induced phase separation, solution induced phase separation, melt stretching, interfacial polymerization, coating polymerization, in situ polymerization and the like.

[0037] According to some embodiments of the present invention, the polymer membranes used in the first polymer membrane separation, the second polymer membrane separation and the third polymer membrane separation are polyimide-based hollow fiber membranes.

[0038] 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%.

[0039] Preferably, the thickness of the dense layer is 100-500 nm, and the porosity of the hollow fiber membrane is 50-70%.

[0040] Preferably, the hollow fiber membrane is made of polyimide random copolymer.

[0041] According to some embodiments of the present invention, the polyimide random copolymer has a structure shown in formula (I):

[0042]

[0043] In formula (I), m and n are each independently an integer of 10-2000;

[0044] X has a structure represented by any one of formula (X1) to formula (X3);

[0045]

[0046] In formula (X1) to formula (X3), R 1 , R 2 , R 3 , R 4 , R 5 and R 6 Each is independently H, C1-C4 alkyl, C6-C10 aryl, amino, hydroxyl or carboxyl;

[0047] Y has a structure represented by any one of formula (Y1) to formula (Y5);

[0048]

[0049] 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;

[0050] Z and Z' each independently have a structure represented by formula (Z1) or formula (Z2);

[0051]

[0052] In formula (Z2), Ra and Rb are each independently H, C1-C4 alkyl or C1-C4 halogenated alkyl.

[0053] Preferably, m and n are each independently an integer of 50-1000.

[0054] Preferably, 0.9≥n / (m+n)≥0.3, preferably, 0.7≥n / (m+n)≥0.5.

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

[0056]

[0057] In the present invention, Y has one of the following structures,

[0058]

[0059] In the present invention, Z and Z' both have the structure shown by Z1 or Z3,

[0060]

[0061] Preferably, X is Xa, Y is Ya, and Z and Z' are both Z1;

[0062] Alternatively, X is Xa, Y is Yb, and Z and Z' are both Z1;

[0063] Or, X is Xa, Y is Yd, and Z and Z' are both Z1;

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

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

[0066] Or, X is Xb, Y is Yd, and Z and Z' are both Z1;

[0067] Or, X is Xc, Y is Ya, and Z and Z' are both Z1;

[0068] Alternatively, X is Xc, Y is Yb, and Z and Z' are both Z1;

[0069] Or, X is Xc, Y is Yc, and Z and Z' are both Z1;

[0070] Alternatively, X is Xc, Y is Y4, and Z and Z' are both Z1;

[0071] Or, X is Xc, Y is Yd, and Z and Z' are both Z1;

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

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

[0074] Or, X is Xb, Y is Yd, and Z and Z' are both Z3;

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

[0076] Or, X is Xc, Y is Yb, and Z and Z' are both Z3;

[0077] Alternatively, X is Xc, Y is Yd, and Z and Z' are both Z3.

[0078] 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".

[0079] In the present invention, based on firstly carrying out polycondensation reaction of dianhydride monomer (dianhydride shown in formula (II) and dianhydride shown in formula (III)) and diamine monomer to obtain polyamic acid, then imidization (intramolecular dehydration) is carried out to polyamic acid, dianhydride monomer and diamine monomer can be carried out polycondensation reaction to obtain polyamic acid by one-pot method, or dianhydride monomer (i.e. dianhydride shown in formula (II) and dianhydride shown in formula (III)) can be mixed uniformly before carrying out polycondensation reaction with diamine monomer. However, in order to better control the reaction, it is preferred to react in the latter mode. Therefore, the present invention also provides a method for preparing polyimide random copolymer, and the method comprises the following steps:

[0080] (S1) in the presence of a first solvent, mixing a mixture of a dianhydride monomer represented by formula (II) and a dianhydride monomer represented by formula (III) with a diamine monomer to carry out a polycondensation reaction to obtain a material containing polyamic acid,

[0081]

[0082] (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;

[0083] In formula (II) and formula (III), X and Y have the same meanings as described above.

[0084] 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),

[0085]

[0086] In formula (Z2), Ra and Rb are each independently H, C1-C4 alkyl or C1-C4 halogenated alkyl.

[0087] Preferably, X is Xa, Y is Ya, and Zp is Z1;

[0088] Alternatively, X is Xa, Y is Yb, and Zp is Z1;

[0089] Or, X is Xa, Y is Yd, and Zp is Z1;

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

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

[0092] Or, X is Xb, Y is Yd, and Zp is Z1;

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

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

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

[0096] Or, X is Xc, Y is Y4, and Zp is Z1;

[0097] Or, X is Xc, Y is Yd, and Zp is Z1;

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

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

[0100] Or, X is Xb, Y is Yd, and Zp is Z3;

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

[0102] Or, X is Xc, Y is Yb, and Zp is Z3;

[0103] Alternatively, X is Xc, Y is Yd, and Zp is Z3.

[0104] 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).

[0105] In the present invention, M and N satisfy 0.9≥N / (M+N)≥0.3, preferably, 0.7≥N / (M+N)≥0.5.

[0106] 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).

[0107] 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.

[0108] In the present invention, the polycondensation reaction is carried out under an inert atmosphere, which is preferably provided by nitrogen.

[0109] 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.

[0110] In the present invention, the usage of the first solvent is 1000-3000 mL relative to 1 mmol of the diamine monomer.

[0111] In the present invention, the dianhydride monomer represented by formula (II) and the dianhydride monomer represented by formula (III) can be mixed to obtain a mixture by the following methods: mechanical stirring, shaking or ultrasound. The mechanical stirring conditions may include: 20-40°C, 2000-15000rpm, 2-12h; the ultrasound conditions may include: 20-40°C, 0.5-2.0h; the shaking conditions may include: 20-40°C, 260-800rpm, 12-36h.

[0112] 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.

[0113] In the present invention, the dehydrating agent is selected from at least one of dichlorobenzene, toluene, acetic anhydride and xylene.

[0114] In the present invention, the catalyst is selected from pyridine and / or diquinoline.

[0115] 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.

[0116] 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.

[0117] In the present invention, the method further comprises: before obtaining the polyimide copolymer, the material after the imidization treatment in step (S2) is diluted and contacted with a precipitant to obtain the polyimide copolymer. Wherein, the precipitant can be a poor solvent for polyimide, selected from at least one of ethanol, acetone and water, and more preferably selected from at least two of ethanol, acetone and water. Equivalent to 1 mol of diamine monomer, the total amount of the precipitant can be 10-50L. Wherein, the solvent for dilution can be N-methylpyrrolidone. Preferably, relative to 1 mol of diamine monomer, the amount of the solvent for dilution can be 5-8L.

[0118] In the present invention, there is no particular limitation on the manner in which the imidization-treated material in step (S2) is contacted with the precipitant, as long as the requirements of the present invention are met. For example, the following manner may be used: the imidization-treated material in step (S2) (after dilution) is added to the precipitant to precipitate the polyimide, and then the precipitated polyimide is eluted with the precipitant (the elution may be 3-5 times), and finally filtered and dried (70-150° C., 24-48 hours) to obtain a polyimide random copolymer.

[0119] In the present invention, the polyimide-based hollow fiber membrane is prepared according to a method comprising the following steps:

[0120] (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;

[0121] (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;

[0122] (3) The hollow fiber membrane precursor is rolled up and extracted to obtain the polyimide-based hollow fiber membrane.

[0123] 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%.

[0124] 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%.

[0125] 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.

[0126] 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.

[0127] In the present invention, the poor solvent for the second polyimide is at least one selected from C3-C5 alkanes, tetrahydrofuran, acetone and chloroform.

[0128] 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.

[0129] 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).

[0130] In the present invention, the additive may be a lithium salt, preferably selected from lithium nitrate and / or lithium chloride.

[0131] 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).

[0132] 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.

[0133] In the present invention, in step (2), the inner core liquid includes solvent A and solvent B, wherein the solvent A is selected from at least one of N-methylpyrrolidone, N,N-dimethylacetamide and N,N-dimethylacetamide, and the solvent B is selected from at least one of a saturated monohydric alcohol of C1-C4, γ-butyrolactone and water.

[0134] In the present invention, the solvent A accounts for 50-99wt%, preferably 60-95wt%, of the total weight of the inner core liquid.

[0135] According to some embodiments of the present invention, the extrusion is carried out in a spinneret, wherein the extrusion temperature (temperature of the spinneret) is 40-75°C, preferably 60-70°C.

[0136] In the present invention, during the extrusion process, the flow rate of the casting solution is 6-30 mL / min.

[0137] According to some embodiments of the present invention, during the extrusion process, the flow rate of the core liquid is 2-10 mL / min.

[0138] 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.

[0139] In the present invention, the height of the air gap is 5-30 cm.

[0140] In the present invention, the air gap is heated by an annular sleeve, and the temperature is preferably controlled to be 70-150°C.

[0141] 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.

[0142] In the present invention, the solvent C is selected from at least one of a C1-C4 saturated monohydric alcohol, γ-butyrolactone and water.

[0143] In the present invention, in step (3), the winding rate is 0.5-2 m / s.

[0144] In the present invention, the purpose of the extraction is to remove the diluent and additives in the hollow fiber membrane precursor.

[0145] 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.

[0146] 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.

[0147] 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.

[0148] In the present invention, the extraction further includes a drying step.

[0149] In the present invention, the drying conditions include: temperature of 20-35° C. and time of 2-15 h.

[0150] According to a preferred embodiment, the present invention also provides a system for preparing high-purity hydrogen by combining a membrane separation post-dehydrogenation process with rectification, the system comprising: a demethanizer, a first polymer membrane separation unit, a second polymer membrane separation unit and a third polymer membrane separation unit, wherein:

[0151] The demethanizer is used to demethanize the raw gas, obtain a mixed gas containing methane and hydrogen at the top of the tower, and obtain a product gas containing ethylene at the bottom of the tower;

[0152] The first polymer membrane separation unit is connected to the demethanizer, and is used to perform a first polymer membrane separation on the mixed gas containing methane and hydrogen from the demethanizer to obtain a first methane-rich gas and a first hydrogen-rich gas;

[0153] The second polymer membrane separation unit is used to perform a second polymer membrane separation on the first hydrogen-rich gas from the first polymer membrane separation unit to obtain high-purity hydrogen gas and a second methane-rich gas;

[0154] The third polymer membrane separation unit is used to perform a third polymer membrane separation on the first methane-rich gas from the first polymer separation unit and the second methane-rich gas from the second polymer membrane separation unit to obtain a third methane-rich gas and a second hydrogen-rich gas.

[0155] In the present invention, a pressurizing device, a heat exchanging device and a gas mixing device are provided between the third polymer membrane separation unit and the first polymer membrane separation unit; a gas mixing device is also provided between the second polymer membrane separation unit and the third polymer membrane separation unit.

[0156] Wherein, a heat exchange device is arranged between the demethanizer and the first polymer membrane separation unit.

[0157] The present invention will be described in detail below through examples.

[0158] The following embodiments will be combined with Figure 1The method for preparing high-purity hydrogen by membrane separation combined with distillation of the present invention is described. Unless otherwise specified, the specific operations of the process are as described above. The first polymer membrane separation, the second polymer membrane separation and the third polymer membrane separation are performed by cross-flow separation.

[0159] In the following examples, the volume fraction of each gas is measured by gas chromatography.

[0160] 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.

[0161] The following preparation examples are used to illustrate the polyimide random copolymer

[0162] Preparation Example 1

[0163] (1) Under nitrogen protection, 200 mL of anhydrous N-methylpyrrolidone and m-phenylenediamine (10.81 g, 0.1 mmol) were added to a 1 L three-necked flask in sequence, and stirred until the materials were completely dissolved; 4,4-diphenyl ether dianhydride (ODPA) (0.01 mmol) and 4,4'-(hexafluoroisopropylene) diphthalic anhydride (6FDA) (0.09 mmol) were mixed under mechanical stirring, and then added to the above system at 0°C, and polycondensation reaction was carried out for 12 hours to obtain a material containing polyimide acid;

[0164] (2) Add a mixture of acetic anhydride (0.36 mmol) and pyridine (0.36 mmol) to the polyimide acid material obtained in step (1), and perform intramolecular dehydration at 200°C for 24 hours to obtain a material containing polyimide; then add 600 mL of N-methylpyrrolidone (NMP) to the polyimide-containing material for dilution, and pour the diluted material into a mixed solvent of water and ethanol (500 mL: 500 mL) under stirring to precipitate polyimide to obtain polyimide, and then rinse with a mixed solution of water and ethanol (1500 mL: 1500 mL) (3 times), and obtain a polyimide random copolymer after suction filtration and drying. Infrared testing shows that the polyimide random copolymer has a structure shown in formula (I), wherein X is Xc, Y is Ya, and Z and Z' are both Z1. In addition, no raw materials can be detected in the remaining liquid phase after the polyimide is precipitated, indicating that all raw materials participate in the reaction.

[0165] The following preparation examples are used to illustrate the preparation of polyimide-based hollow fiber membranes.

[0166] Preparation Example 1

[0167] (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, and speed 30 r / min for 24 hours, and then filter through a filter screen (pore size 100 mesh) at 50° C. to obtain a casting solution;

[0168] (2) using a metering pump to deliver the casting liquid and the inner core liquid (NMP: water = 95wt%: 5wt%) to the hollow spinneret, respectively, the inner core liquid and the casting liquid are extruded through the spinneret together to obtain a hollow fiber, the hollow fiber is passed through an air gap of 10 cm, and then placed in 50°C water for solidification to obtain a polyimide-based hollow fiber membrane precursor; wherein the spinneret temperature (extrusion temperature) is 75°C; the flow rates of the casting liquid and the inner core liquid entering the hollow spinneret are 6mL / min and 2mL / min, respectively;

[0169] (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.

[0170] 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.

[0171] Example 1

[0172] (1) Demethanizing the raw gas S1 in a demethanizer to obtain a mixed gas S2 containing methane and hydrogen at the top of the tower, and obtaining a product gas S3 containing ethylene at the bottom of the tower;

[0173] (2-1) exchanging heat of the mixed gas S2 containing methane and hydrogen to -20°C to obtain S4, and mixing S4 with S14 to obtain S5, and then passing S5 into a first polymer membrane separation unit for first polymer separation to obtain a first methane-rich gas S6 and a first hydrogen-rich gas S7; wherein the permeation pressure during the first polymer membrane separation process is 2000 kPa;

[0174] (2-2) sending the first hydrogen-rich gas S7 to a second polymer membrane separation unit for second polymer membrane separation to obtain high-purity hydrogen gas S9 and second methane-rich gas S8; wherein the permeation pressure of the membrane in the second polymer membrane separation is 500 kPa;

[0175] (2-3) The first methane-rich gas S6 and the second methane-rich gas S8 are mixed to obtain S10, and S10 is sent to a third polymer membrane separation unit for third polymer membrane separation to obtain a third methane-rich gas S11 (methane-rich product gas) and a second hydrogen-rich gas S12; wherein the permeation pressure of the membrane in the third polymer membrane separation is 500 kPa;

[0176] wherein S12 is compressed to obtain S13, and S13 is heat exchanged to obtain S14 which is returned to step (2-1) to be separated by the first polymer membrane together with the mixed gas S4 containing methane and hydrogen after heat exchange;

[0177] Among them, the membranes used in the first polymer membrane separation, the second polymer membrane separation and the third polymer membrane separation are the same, all of which are polyimide hollow fiber membranes prepared in the above-mentioned Preparation Example 1. The hollow fiber membrane has a hydrogen flux of 100GPU, a methane flux of about 3GPU, and an ethylene flux of about 2.5GPU.

[0178] The gas composition of each flow is shown in Table 1.

[0179] Table 1

[0180] No.\composition mol% hydrogen Methane Ethylene S2 32.0 65.0 3.0 S4 32.0 65.0 3.0 S5 65.9 32.6 1.5 S6 54.0 44.0 2.0 S7 86.6 12.9 0.5 S8 81.8 17.5 0.7 S9 99.4 0.6 0 S10 62.3 36.1 1.6 S11 8.5 87.5 4.0 S12 86.8 12.7 0.5 S13 86.8 12.7 0.5 S14 86.8 12.7 0.5

[0181] Example 2

[0182] (1) Demethanizing the raw gas S1 in a demethanizer to obtain a mixed gas S2 containing methane and hydrogen at the top of the tower, and obtaining a product gas S3 containing ethylene at the bottom of the tower;

[0183] (2-1) exchanging heat of the mixed gas S2 containing methane and hydrogen to -20°C to obtain S4, and mixing S4 with S14 to obtain S5, and then passing S5 into a first polymer membrane separation unit for first polymer separation to obtain a first methane-rich gas S6 and a first hydrogen-rich gas S7; wherein, during the first polymer membrane separation process, the permeation pressure is 2000 kPa;

[0184] (2-2) sending the first hydrogen-rich gas S7 to a second polymer membrane separation unit for second polymer membrane separation to obtain high-purity hydrogen gas S9 and second methane-rich gas S8; wherein the permeation pressure of the membrane in the second polymer membrane separation is 3500 kPa;

[0185] (2-3) mixing the first methane-rich gas S6 and the second methane-rich gas S8 to obtain S10, and sending S10 to a third polymer membrane separation unit for third polymer membrane separation to obtain a third methane-rich gas S11 and a second hydrogen-rich gas S12; wherein the permeation pressure of the membrane in the third polymer membrane separation is 1000 kPa;

[0186] wherein S12 is compressed to obtain S13, and S13 is heat exchanged to obtain S14 which is returned to step (2-1) to be separated by the first polymer membrane together with the mixed gas S4 containing methane and hydrogen after heat exchange;

[0187] Among them, the membranes used in the first polymer membrane separation, the second polymer membrane separation and the third polymer membrane separation are the same, all of which are polyimide hollow fiber membranes prepared in the above-mentioned Preparation Example 1. The hollow fiber membrane has a hydrogen flux of 100GPU, a methane flux of about 3GPU, and an ethylene flux of about 2.5GPU.

[0188] The gas composition of each flow is shown in Table 2.

[0189] Table 2

[0190] No.\composition mol% hydrogen Methane Ethylene S2 34.0 65.7 0.3 S4 34.0 65.7 0.3 S5 61.4 38.4 0.2 S6 53.1 46.7 0.2 S7 83.7 16.2 0.6 S8 64.0 35.9 0.1 S9 99.0 1.0 0 S10 54.6 45.2 0.2 S11 7.4 92.2 0.4 S12 91.7 8.3 0 S13 91.7 8.3 0 S14 91.7 8.3 0

[0191] Example 3

[0192] (1) Demethanizing the raw gas S1 in a demethanizer to obtain a mixed gas S2 containing methane and hydrogen at the top of the tower, and obtaining a product gas S3 containing ethylene at the bottom of the tower;

[0193] (2-1) exchanging heat of the mixed gas S2 containing methane and hydrogen to 0°C to obtain S4, and mixing S4 with S14 to obtain S5, and then passing S5 into a first polymer membrane separation unit for first polymer separation to obtain a first methane-rich gas S6 and a first hydrogen-rich gas S7; wherein the permeation pressure during the first polymer membrane separation process is 1500 kPa;

[0194] (2-2) sending the first hydrogen-rich gas S7 to a second polymer membrane separation unit for second polymer membrane separation to obtain high-purity hydrogen gas S9 and second methane-rich gas S8; wherein the permeation pressure of the membrane in the second polymer membrane separation is 600 kPa;

[0195] (2-3) mixing the first methane-rich gas S6 and the second methane-rich gas S8 to obtain S10, and sending S10 to a third polymer membrane separation unit for third polymer membrane separation to obtain a third methane-rich gas S11 and a second hydrogen-rich gas S12; wherein the permeation pressure of the membrane in the third polymer membrane separation is 2500 kPa;

[0196] wherein S12 is compressed to obtain S13, and S13 is heat exchanged to obtain S14 which is returned to step (2-1) to be separated by the first polymer membrane together with the mixed gas S4 containing methane and hydrogen after heat exchange;

[0197] Among them, the membranes used in the first polymer membrane separation, the second polymer membrane separation and the third polymer membrane separation are the same, and the material is a polybenzimidazole hollow fiber membrane component (China Science Energy Materials Technology (Dalian) Co., Ltd., PBI membrane). The membrane has a hydrogen flux of 50GPU, a methane flux of about 2.5GPU, and an ethylene flux of about 2GPU.

[0198] The gas composition of each flow is shown in Table 3.

[0199] Table 3

[0200] No.\composition mol% hydrogen Methane Ethylene S2 25.8 52.0 22.2 S4 25.8 52.0 22.2 S5 84.3 14.2 4.5 S6 68.2 22.4 9.4 S7 95.6 3.3 1.1 S8 95.4 3.5 1.2 S9 99.8 0.2 0 S10 83.8 11.5 4.7 S11 7.9 64.5 27.6 S12 95.8 3.2 1.0 S13 95.8 3.2 1.0 S14 95.8 3.2 1.0

[0201] Example 4

[0202] (1) Demethanizing the raw gas S1 in a demethanizer to obtain a mixed gas S2 containing methane and hydrogen at the top of the tower, and obtaining a product gas S3 containing ethylene at the bottom of the tower;

[0203] (2-1) exchanging heat of the mixed gas S2 containing methane and hydrogen to 0°C to obtain S4, and mixing S4 with S14 to obtain S5, and then passing S5 into a first polymer membrane separation unit for first polymer separation to obtain a first methane-rich gas S6 and a first hydrogen-rich gas S7; wherein the permeation pressure of the membrane in the first polymer membrane separation is 500 kPa;

[0204] (2-2) sending the first hydrogen-rich gas S7 to a second polymer membrane separation unit for second polymer membrane separation to obtain high-purity hydrogen gas S9 and second methane-rich gas S8; wherein the permeation pressure of the membrane in the second polymer membrane separation is 900 kPa;

[0205] (2-3) The first methane-rich gas S6 and the second methane-rich gas S8 are mixed to obtain S10, and S10 is sent to a third polymer membrane separation unit for third polymer membrane separation to obtain a third methane-rich gas S11 and a second hydrogen-rich gas S12; wherein the permeation pressure of the membrane in the third polymer membrane separation is 1100 kPa;

[0206] wherein S12 is compressed to obtain S13, and S13 is heat exchanged to obtain S14 which is returned to step (2-1) to be separated by the first polymer membrane together with the mixed gas S4 containing methane and hydrogen after heat exchange;

[0207] The membranes used in the first polymer membrane separation, the second polymer membrane separation and the third polymer membrane separation are the same, which are hollow fiber membrane components made of polysulfone (Permea, ), the hollow fiber membrane has a hydrogen flux of 20 GPU, a methane flux of about 0.15 GPU, and an ethylene flux of about 0.1 GPU.

[0208] The gas composition of each flow is shown in Table 4.

[0209] Table 4

[0210]

[0211]

[0212] Example 5

[0213] (1) Demethanizing the raw gas S1 in a demethanizer to obtain a mixed gas S2 containing methane and hydrogen at the top of the tower, and obtaining a product gas S3 containing ethylene at the bottom of the tower;

[0214] (2-1) exchanging heat of the mixed gas S2 containing methane and hydrogen to 0°C to obtain S4, and mixing S4 with S14 to obtain S5, and then passing S5 into a first polymer membrane separation unit for first polymer separation to obtain a first methane-rich gas S6 and a first hydrogen-rich gas S7; wherein the permeation pressure during the first polymer membrane separation process is 3500 kPa;

[0215] (2-2) sending the first hydrogen-rich gas S7 to a second polymer membrane separation unit for second polymer membrane separation to obtain high-purity hydrogen gas S9 and second methane-rich gas S8; wherein the permeation pressure of the membrane in the second polymer membrane separation is 700 kPa;

[0216] (2-3) mixing the first methane-rich gas S6 and the second methane-rich gas S8 to obtain S10, and sending S10 to a third polymer membrane separation unit for third polymer membrane separation to obtain a third methane-rich gas S11 and a second hydrogen-rich gas S12; wherein the permeation pressure of the membrane in the third polymer membrane separation is 500 kPa;

[0217] wherein S12 is compressed to obtain S13, and S13 is heat exchanged to obtain S14 which is returned to step (2-1) to be separated by the first polymer membrane together with the mixed gas S4 containing methane and hydrogen after heat exchange;

[0218] Among them, the membranes used in the first polymer membrane separation, the second polymer membrane separation and the third polymer membrane separation are the same, all of which are polyimide hollow fiber membranes prepared in the above-mentioned Preparation Example 1. The hollow fiber membrane has a hydrogen flux of 100GPU, a methane flux of about 3GPU, and an ethylene flux of about 2.5GPU.

[0219] Among them, the composition of the gas of each logistics is shown in Table 5.

[0220] Table 5

[0221]

[0222]

[0223] Example 6

[0224] The method of Example 1 is followed, except that the third polymer membrane is not provided. The numbers of the various streams are shown in Table 6.

[0225] Table 6

[0226] No.\composition mol% hydrogen Methane Ethylene S2 32.0 65.0 3.0 S4 32.0 65.0 3.0 S5 32.0 65.0 3.0 S6 26.8 69.9 3.3 S7 45.7 52.1 2.2 S8 20.0 76.7 3.3 S9 93.3 6.5 0.2 S10 25.4 71.3 3.3 S11 25.4 71.3 3.3 S12 / / / S13 / / / S14 / / /

[0227] Comparative Example 1

[0228] according to Figure 2 The process flow is used to purify hydrogen, wherein the process is a traditional demethanizer post-dehydrogenation process, including a distillation tower T1 and two separation towers 1-2, and heat exchangers H1'-H3' are set between the distillation tower T1 and the first separator 1 and the second separator 2 for a multi-stage cooling and gradual separation process. The top gas S2' of the distillation tower T1 contains a large amount of methane and hydrogen. Through cooling and separation, the top of the first separation tower 1 contains a large amount of methane and a small amount of hydrogen. A small amount of methane is condensed and discharged from the bottom of the tower for collection and heat exchange. After the second cooling and separation, the top of the second separation tower 2 is recovered with relatively pure hydrogen, and most of the bottom of the tower is used for methane recovery and heat exchange. The numbers of the various logistics are shown in Table 7.

[0229] Table 7

[0230] No.\composition mol% hydrogen Methane Ethylene S2’ 32.0 65.0 3.0 S3’ 32.9 64.7 2.4 S4’ 72.1 27.8 0.1 S5’ 3.2 92.7 4.1

[0231] It can be seen from the above examples and comparative examples that the method of the present invention can be used to separate hydrogen and methane, two small molecules that are difficult to separate from ethylene in the feed gas, through the membrane separation process, and the selective separation of the membrane can be effectively separated, and the hydrogen concentration can reach 99.95%. It can be seen from comparative example 1 that the hydrogen concentration in the dehydrogenation output material S8 is lower than the hydrogen output concentration of membrane method S12 and S9, and the hydrogen has a very good purification and recovery effect, and the membrane method S11 methane also has a good purification effect; it can be seen from the results of Example 6 without the third polymer membrane that compared with Example 1, the hydrogen purification effect in S9 and the methane purification effect in S11 are both reduced.

[0232] 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).

[0233] 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 preparing high-purity hydrogen by distillation combined with membrane separation, It is characterized in that The method comprises the following steps: (1) The raw gas is demethanized in a demethanizer, and a mixed gas containing methane and hydrogen is obtained at the top of the tower, and a product gas containing ethylene is obtained at the bottom of the tower; (2) subjecting the mixed gas containing methane and hydrogen to membrane separation; Wherein, the membrane separation method includes: (2-1) subjecting the mixed gas containing methane and hydrogen to a first polymer membrane separation to obtain a first methane-rich gas and a first hydrogen-rich gas; (2-2) subjecting the first hydrogen-rich gas to a second polymer membrane separation to obtain high-purity hydrogen gas and a second methane-rich gas; (2-3) mixing the first methane-rich gas and the second methane-rich gas and performing a third polymer membrane separation to obtain a third methane-rich gas and a second hydrogen-rich gas; optionally, returning the second hydrogen-rich gas to step (2-1) and performing the first polymer membrane separation together with the mixed gas containing methane and hydrogen; Wherein, the polymer membranes used in the first polymer membrane separation, the second polymer membrane separation and the third polymer membrane separation are polyimide-based hollow fiber membranes; the material of the hollow fiber membranes is polyimide random copolymer; Wherein, 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 demethanizer is a distillation tower.

3. The method according to claim 1, in, The permeation pressure during the first polymer membrane separation, the permeation pressure during the second polymer membrane separation, and the permeation pressure during the third polymer membrane separation are each independently 500 kPa-3500 kPa; and / or, the permeation pressure of the first polymer membrane separation is 500 kPa-3500 kPa; and / or, the permeation pressure of the second polymer membrane during separation is 500 kPa-2500 kPa; And / or, the permeation pressure during the separation process of the third polymer membrane is 500 kPa-2500 kPa.

4. The method according to claim 1, in, The membranes used in the first polymer membrane separation, the second polymer membrane separation and the third polymer membrane separation each independently have a flux of 10-120 GPU for hydrogen, a flux of 0.1-3 GPU for methane and a flux of 0.1-2.5 GPU for ethylene.

5. 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%.

6. The method according to claim 5, in, The thickness of the dense layer is 100-500 nm, and the porosity of the hollow fiber membrane is 50-70%.

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

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

3.

9. The method according to claim 8, in, 0.7≥n / (m+n)≥0.

5.

10. The method according to any one of claims 7 to 9, 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, 、 。 11. The method according to claim 10, 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.

12. The method according to any one of claims 5 to 9 and 11, 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.

13. The method according to claim 12, 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, prior to solidification, passing the extruded hollow fibers through an air gap; and / or, the solidification is carried out in a coagulation bath; And / or, in step (3), the winding speed is 0.5-2 m / s; And / or, the extractant used for extraction is at least one selected from water, a C1-C4 saturated monohydric alcohol and a 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.

14. The method according to claim 13, 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 at a controlled temperature of 70-150°C; And / or, the bath liquid used in the coagulation bath is solvent C and / or water, and the temperature of the coagulation bath is 40-70°C; And / or, the drying conditions include: temperature of 20-35° C. and time of 2-15 h.

15. The method according to claim 14, 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.

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