A method for separating hydrogen and methane
By connecting multiple hollow carbon molecular sieve membrane systems in series and using pressurization and cooling, the problem of separating low-concentration hydrogen and methane mixtures was solved, achieving high recovery rate and low-cost transportation of high-purity hydrogen.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA PETROLEUM & CHEMICAL CORP
- Filing Date
- 2024-11-27
- Publication Date
- 2026-05-29
AI Technical Summary
Existing technologies struggle to efficiently separate low-concentration hydrogen and methane mixtures, and conventional membrane systems are insufficient to meet the demand for high-purity hydrogen with low recovery rates.
A multi-stage hollow carbon molecular sieve membrane system is adopted, which uses series-connected hollow carbon molecular sieve membranes for multi-stage membrane separation, combined with pressurization and cooling treatment, to achieve efficient separation of hydrogen and methane.
This improved the purity and recovery rate of hydrogen, meeting the demand for high-purity hydrogen and reducing hydrogen transportation costs.
Smart Images
Figure CN122098201A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of gas separation technology, and more specifically to a method for separating hydrogen and methane. Background Technology
[0002] Hydrogen (H2) has long been considered a "future-ready fuel." Along with electricity, H2 can serve as a universal energy carrier, directly applicable to portable devices and stationary power plants. The future hydrogen economy has garnered significant attention over the past decade. Furthermore, as a "green" energy source, hydrogen can greatly reduce its environmental impact.
[0003] However, due to its low density, flammability, explosiveness, and hydrogen embrittlement / corrosion, the storage and transportation of H2 faces high costs and difficulties. Transporting pure H2 via pipeline is quite challenging. On the other hand, the construction of CH4 pipelines is relatively mature, and the significant difference in molecular size between H2 and CH4 facilitates their separation to some extent. Therefore, the possibility of mixing H2 into existing natural gas pipelines is being considered to achieve efficient and inexpensive H2 storage and transportation. This necessitates the construction of a highly efficient H2 / CH4 membrane separation system to meet the downstream demand for high-purity H2 from pipeline transportation.
[0004] Currently, there are three main methods for hydrogen extraction from natural gas: cryogenic separation, selective adsorption, and membrane separation. While cryogenic separation can yield high-purity hydrogen and a considerable recovery rate, the compression and cooling processes are energy-intensive. Selective adsorption can be used to prepare ultra-high-purity hydrogen, achieving a purity of up to 99.9999%, but it requires high-quality feed gas, necessitating the removal of impurities such as CO2, H2S, and H2O, with a hydrogen content generally exceeding 95%. Furthermore, this method involves significant equipment investment, high energy consumption, and complex operation. Membrane separation, driven by a pressure difference across a membrane, utilizes the different permeability properties of various components in natural gas within the membrane material. Hydrogen typically has a high permeability coefficient, thus achieving hydrogen separation. As a next-generation separation technology, membrane separation technology shows great promise in natural gas hydrogen extraction due to its non-phase-change process, low energy consumption, small equipment footprint, and low investment.
[0005] Due to the low H2 concentration in the H2 mixed pipeline gas, conventional single-cycle two-stage membrane systems are insufficient to meet the requirements for high H2 purity and high recovery rates. For 60 mol% H2 mixtures from biofermentation processes, a single-cycle two-stage membrane system may be suitable for producing high-purity H2 and ensuring high H2 recovery rates. However, for feeds with low H2 concentrations, a large amount of H2 in the primary membrane retrieval gas is directly discarded, resulting in low H2 recovery rates. Summary of the Invention
[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for separating hydrogen and methane.
[0007] The present invention provides a method for separating hydrogen and methane, comprising: separating a mixture of hydrogen and methane by passing it through a hollow carbon molecular sieve membrane.
[0008] Hollow carbon molecular sieve membranes exhibit excellent gas separation performance. Furthermore, the precursor polymer membranes for preparing self-supporting hollow carbon molecular sieve membranes with hollow fiber structures are typically fabricated using dry-wet spinning technology, a simple process that enables automated mass production, thus providing feasibility for large-scale membrane material production. In addition, self-supporting hollow fiber membranes have high packing density, and their membrane module encapsulation technology, already widely used in polymer hollow fiber membranes and relatively mature, can also be applied to hollow carbon molecular sieve membranes with hollow fiber structures.
[0009] In some embodiments, the pore size of the hollow carbon molecular sieve membrane is 0.3-0.9 nm, for example, 0.3 nm, 0.4 nm, 0.5 nm, 0.6 nm, 0.7 nm, 0.8 nm, 0.9 nm or any value between them.
[0010] In some embodiments, the hollow carbon molecular sieve membrane has a bimodal distribution with pore sizes of 0.35±0.05 nm and 0.5±0.05 nm.
[0011] In some embodiments, the hollow carbon molecular sieve membrane has a bimodal distribution with pore sizes of 0.35 nm and 0.5 nm.
[0012] In some embodiments, the hollow carbon molecular sieve membrane has a thickness of 20-30 μm, for example, 20 μm, 22 μm, 24 μm, 26 μm, 28 μm, 30 μm or any value between them.
[0013] In some embodiments, the diameter of the hollow carbon molecular sieve membrane is 160-230 μm, for example, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm, 210 μm, 220 μm, 230 μm or any value between them.
[0014] In some embodiments, the carbon source for preparing the hollow carbon molecular sieve membrane is microcrystalline cellulose or cellulose acetate.
[0015] In some embodiments, the carbon source for preparing the hollow carbon molecular sieve membrane is microcrystalline cellulose.
[0016] The inventors of this application have discovered that, compared to cellulose acetate, using microcrystalline cellulose as the carbon source results in hollow carbon molecular sieve membranes with higher H2 / CH4 selectivity.
[0017] In some embodiments, the membrane separation is performed using multi-stage hollow carbon molecular sieve membranes.
[0018] In some embodiments, the multi-stage hollow carbon molecular sieve membrane has 2-5 stages.
[0019] In some embodiments, the multi-stage hollow carbon molecular sieve membrane is three-stage.
[0020] In some embodiments, at least two stages of the multi-stage hollow carbon molecular sieve membrane are connected in series.
[0021] In some embodiments, at least one of the multi-stage hollow carbon molecular sieve membranes has an H2 flux exceeding 900 barrer at 1.5 MPaG and 60°C.
[0022] In some embodiments, at least one of the multi-stage hollow carbon molecular sieve membranes has an H2 flux of 900-1500 barrer, for example, 920 barrer, 940 barrer, 960 barrer, 980 barrer, 1000 barrer, 1200 barrer, 1400 barrer or any value between them.
[0023] In some embodiments, at 1.5 MPaG and 60°C, at least one hollow carbon molecular sieve membrane has an H2 flux of 900-1500 barrer.
[0024] In some embodiments, at 1.5 MPaG and 60°C, at least one hollow carbon molecular sieve membrane exhibits an H2 / CH4 selectivity exceeding 2000.
[0025] In some embodiments, at 1.5 MPaG and 60°C, at least one hollow carbon molecular sieve membrane has an H2 / CH4 selectivity of 2500-3500, for example, 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, 3400 or any value between them.
[0026] At 1.5 MPaG and 20 °C, the H2 / CH4 selectivity of the multi-stage hollow carbon molecular sieve membrane exceeds 500.
[0027] In some embodiments, the separation method includes:
[0028] 1) A mixture of hydrogen and methane is passed through a first hollow carbon molecular sieve membrane for first membrane separation to obtain a first permeate gas and a first permeate gas;
[0029] (2) The first residual gas is separated by a second hollow carbon molecular sieve membrane to obtain a second residual gas and a second permeate gas; the second permeate gas is refluxed and mixed with the mixed gas and then separated by a first hollow carbon molecular sieve membrane.
[0030] (3) The first permeate gas is separated by a third hollow carbon molecular sieve membrane to obtain a third residual gas and a third permeate gas; the third residual gas is refluxed and mixed with the mixed gas and then separated by a first hollow carbon molecular sieve membrane.
[0031] This invention employs a multi-stage circulating three-stage membrane system for the purification of H2 in mixed natural gas with low H2 concentration. It retains two concentration levels while sending the trapped gas from the first-stage membrane module to the second-stage membrane, and then recovers the second-stage permeate gas, thus ensuring the purity of the H2 product and improving the H2 recovery rate.
[0032] In some embodiments, the third permeation gas is hydrogen.
[0033] In some embodiments, the purity of the hydrogen gas is 99.5 mol% or higher.
[0034] This invention employs a first hollow carbon molecular sieve membrane with high H2 flux for initial hydrogen purification. The permeate gas is pressurized by a compressor and cooled by a heat exchanger, then passed through a second hollow carbon molecular sieve membrane with high H2 / CH4 selectivity to obtain methane-rich material on the permeate side, which can be used for high-purity methane production. The permeate gas is refluxed to the feed of the first hollow carbon molecular sieve membrane for recycling, reducing hydrogen loss and improving hydrogen recovery rate. The permeate gas from the first hollow carbon molecular sieve membrane is pressurized by a compressor and cooled by a heat exchanger before passing through a third hollow carbon molecular sieve membrane. The permeate side contains a certain amount of hydrogen, which is recycled to the feed of the first hollow carbon molecular sieve membrane and mixed with the feed gas for further hydrogen purification, yielding hydrogen with a purity exceeding 99.5 mol%. High-purity hydrogen product is obtained on the permeate side. This invention achieves high hydrogen recovery rate purification through the optimized coupling of three-stage hollow carbon molecular sieve membrane processes, thus meeting the required standards.
[0035] In some embodiments, the pressure of the first membrane separation, the second membrane separation, or the third membrane separation is each independently 1-2 MPa, for example 1 MPa, 1.2 MPa, 1.4 MPa, 1.6 MPa, 1.8 MPa, 2 MPa, or any value between them.
[0036] In some embodiments, the pressure of the first membrane separation, the second membrane separation, or the third membrane separation is 1.5 MPa.
[0037] In some embodiments, the temperature of the first membrane separation, the second membrane separation, or the third membrane separation is each independently 50-70°C, for example 50°C, 53°C, 56°C, 59°C, 62°C, 65°C, 68°C, or any value between them.
[0038] In some embodiments, the temperature for the first membrane separation, the second membrane separation, or the third membrane separation is 60°C.
[0039] In some embodiments, the H2 flux of the first hollow carbon molecular sieve membrane exceeds 900 barrer at 1.5 MPaG and 60°C.
[0040] In some embodiments, at 1.5 MPaG and 60°C, the H2 flux of the first hollow carbon molecular sieve membrane is 900-1500 barrer, for example, 920 barrer, 940 barrer, 960 barrer, 980 barrer, 1000 barrer, 1200 barrer, 1400 barrer or any value between them.
[0041] In some embodiments, at 1.5 MPaG and 60°C, the H2 / CH4 selectivity of the first hollow carbon molecular sieve membrane is 400-600, for example, 400, 430, 460, 490, 520, 550, 580 or any value between them.
[0042] In some embodiments, at 1.5 MPaG and 60°C, the H2 / CH4 selectivity of the second and third hollow carbon molecular sieve membranes exceeds 2000.
[0043] In some embodiments, at 1.5 MPaG and 60°C, the H2 / CH4 selectivity of the second and third hollow carbon molecular sieve membranes is 2500-3500, for example, 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, and 3400.
[0044] In some embodiments, at 1.5 MPaG and 60°C, the H2 flux of the second and third hollow carbon molecular sieve membranes is 600-700 barrer, for example, 600 barrer, 620 barrer, 640 barrer, 660 barrer, 680 barrer or any value between them.
[0045] In some embodiments, the membrane area of the first hollow carbon molecular sieve membrane is 300,000-400,000 m². 2 Preferably 310,000-3,300,000m2 .
[0046] In some embodiments, the membrane area of the second hollow carbon molecular sieve membrane is 400-2000 m². 2 Preferably 400-1700m 2 .
[0047] In some embodiments, the membrane area of the third hollow carbon molecular sieve membrane is 15,000-40,000 m². 2 .
[0048] In some embodiments, the hydrogen content in the first permeate is 1-3 mol%; for example, 1 mol%, 1.4 mol%, 1.8 mol%, 2.2 mol%, 2.6 mol%, 3 mol%, or any value between them.
[0049] In some embodiments, the hydrogen content in the first permeate gas is 70-80 mol%; for example, 70 mol%, 73 mol%, 76 mol%, 79 mol%, or any value between them.
[0050] In some embodiments, the second permeate gas is methane with a purity of 98.5-99.5 mol% or any value therebetween.
[0051] In some embodiments, the hydrogen content in the second permeate is 0.5-1.5 mol%; for example, 0.5 mol%, 0.7 mol%, 0.9 mol%, 1.1 mol%, 1.3 mol%, 1.5 mol%, or any value between them.
[0052] In some embodiments, the hydrogen content in the second permeate gas is 95-98 mol%; for example, 95 mol%, 95.5 mol%, 96 mol%, 96.5 mol%, 97 mol%, 97.5 mol%, 98 mol% or any value between them.
[0053] In some embodiments, the hydrogen content in the third permeate gas is 3-4 mol%, 3 mol%, 3.2 mol%, 3.4 mol%, 3.6 mol%, 3.8 mol%, 4 mol%, or any value between them.
[0054] In some implementations, a pressurization and cooling process is performed before the second and third membrane separations.
[0055] In some embodiments, the pressurization is performed in a compressor. The compressor is used to pressurize the gas to the feed concentration, and its power consumption depends primarily on the gas flow rate and the required compression ratio.
[0056] In some implementations, the compressor is a single-stage or multi-stage compressor connected in series.
[0057] In some implementations, the cooling is performed in a heat exchanger.
[0058] In some implementations, the heat exchanger is a single-stage or multi-stage heat exchanger connected in series.
[0059] In some embodiments, the hydrogen content in the hydrogen and methane mixture is ≤10 mol%, for example, 1 mol%, 2 mol%, 3 mol%, 4 mol%, 5 mol%, 6 mol%, 7 mol%, 8 mol%, 9 mol%, 10 mol%, or any value between them.
[0060] In some embodiments, the hydrogen content in the hydrogen and methane mixture is 5-10 mol%.
[0061] In some embodiments, the pressure of the hydrogen and methane mixture prior to membrane separation is 0.1-2.5 MPaG, for example 0.1 MPaG, 0.5 MPaG, 1 MPaG, 1.5 MPaG, 2 MPaG, 2.5 MPaG, or any value between them.
[0062] In some embodiments, the method for preparing the hollow carbon molecular sieve membrane includes the following steps:
[0063] S1, a carbon source, ionic liquid and organic solvent are mixed to obtain a spinning solution; the spinning solution is then used to make a hollow fiber membrane by a dry-wet spinning method;
[0064] S2, heating and carbonizing the hollow fiber membrane.
[0065] In some embodiments, the carbon source is selected from microcrystalline cellulose or cellulose acetate.
[0066] In some embodiments, the carbon source is microcrystalline cellulose.
[0067] In some embodiments, the ionic liquid is one or more of 1-allyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium chloride, and 1-ethyl-3-methylimidazolium acetate.
[0068] In some embodiments, the organic solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, tetrahydrofuran, chloroform, dimethyl sulfoxide, and N-methylpyrrolidone.
[0069] In some embodiments, in step S1, the carbon source content in the spinning solution is 10-14 wt%; for example, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt% or any value between them.
[0070] In some embodiments, in step S1, the mass ratio of the ionic liquid to the organic solvent in the spinning solution is 1:(2-4); for example, 1:2, 1:2.5, 1:3, 1:3.5, 1:4 or any value between them.
[0071] In some embodiments, in step S2, the carbonization temperature is 550-750°C, for example, 550°C, 570°C, 590°C, 610°C, 630°C, 650°C, 670°C, 690°C, 710°C, 730°C or any value between them.
[0072] In some implementations, the carbonization time in step S2 is 6-8 hours, for example, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours or any value between them.
[0073] This invention utilizes multi-stage hollow carbon molecular sieve membranes to separate a mixture of hydrogen and natural gas (methane) to obtain hydrogen with a high molar concentration, meeting the requirements of subsequent hydrogen end-processing. When hydrogen is stored and transported via natural gas pipelines, this invention allows for hydrogen purification at the end of the process, thereby solving the problems of high hydrogen transportation costs and difficulties.
[0074] Furthermore, this invention utilizes a hollow carbon molecular sieve membrane with high H2 flux and a hollow carbon molecular sieve membrane with high selectivity to purify the H2 / CH4 mixture through two-stage reflux, obtaining hydrogen gas with a purity of over 99.5 mol% at a recovery rate of over 10%. Attached Figure Description
[0075] Figure 1 This is a schematic diagram of a separation system according to one embodiment of the present invention;
[0076] Figure 2 The diagram shows the separation performance of the hollow carbon molecular sieve membranes obtained in Preparation Example 1 and Preparation Example 2 of this invention at high temperatures.
[0077] Figure label:
[0078] M-1, First membrane separation unit; M-2, Second membrane separation unit; M-3, Third membrane separation unit; K-1, First compressor; K-2, Second compressor; K-3, Third compressor; E-1, First heat exchanger; E-2, Second heat exchanger; E-3, Third heat exchanger; E-4, Fourth heat exchanger. Detailed Implementation
[0079] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments and accompanying drawings. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention in any way.
[0080] Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art. Unless otherwise specified, the reagents used in the following embodiments are conventional biochemical reagents; the raw materials, instruments, and equipment used in the following embodiments can all be obtained commercially or by existing methods; unless otherwise specified, the reagent dosages are those used in routine experimental operations; unless otherwise specified, the experimental methods are conventional methods.
[0081] This invention uses a Nova Nano SEM 450 to perform scanning electron microscopy (SEM) to obtain surface and cross-sectional images of hollow carbon molecular sieve membranes, thereby obtaining the diameter and thickness of the hollow carbon molecular sieve membranes.
[0082] This invention utilizes a BELSORP max II (MicrotracBEL, Japan) to conduct gas adsorption experiments on hollow carbon molecular sieve membranes at 298 K using CO2 as a probe gas. A nonlocal density functional theory (NLDFT) model applied to the physical adsorption of CO2 is then used to analyze the pore size distribution.
[0083] In this invention, "upper bound" refers to the upper limit of properties. In 1991, Robeson proposed a property limit for polymers, which he described as the upper bound, suggesting that the relationship between gas permeability and selectivity is inversely related. This upper bound was updated in 2008 and 2015, namely the 2008 upper bound and the 2015 upper bound.
[0084] Preparation Example 1
[0085] 12 wt% microcrystalline cellulose was added to a mixture of ionic liquid EmimAc (1-ethyl-3-methylimidazolium acetate) and DMSO, with a mass ratio of DMSO to EmimAc of 3:1. The solution was stirred at 400 rpm for 20 hours in an oil bath at 60°C to prepare a spinning solution. Cellulose-based hollow precursor membranes were prepared using a wet-dry spinning process. The outer layer of the double-layered spinneret was the spinning solution, and the inner layer was ultrapure water. The spinning solution from the spinneret needed to pass through a 50 mm air gap before entering a gelation tank and a washing tank (both controlled at 25±2°C) to finally prepare the hollow precursor membrane. The specific spinning conditions were a feed flow rate of 3.5 mL / min, a core liquid flow rate of 2.5 mL / min, and a winding speed of 8.5 m / min. After drying the prepared precursor membrane in air for 24 hours, it was placed in a tube furnace and carbonized at a rate of 60 mL / min under a flowing argon atmosphere. The carbonization temperature was increased from room temperature to 120°C at a rate of 5°C / min, held at 120°C for 2 hours, then increased to 340°C at a rate of 10°C / min and held steady for 1 hour. Finally, the temperature was further increased to 700°C at a rate of 5°C / min and held for 2 hours. After carbonization, a hollow carbon molecular sieve membrane (CMS-1) at 700°C was obtained, which was stored and sealed for further characterization tests.
[0086] Preparation Example 2
[0087] 12 wt% microcrystalline cellulose was added to a mixture of ionic liquid EmimAc (1-ethyl-3-methylimidazolium acetate) and DMSO, with a DMSO to ionic liquid mass ratio of 3:1. The solution was stirred at 400 rpm for 20 hours in an oil bath at 60°C to prepare a spinning solution. Cellulose-based hollow precursor membranes were prepared using a wet-dry spinning process. The outer layer of the double-layered spinneret was the spinning solution, and the inner layer was ultrapure water. The spinning solution from the spinneret needed to pass through a 50 mm air gap before entering a gelation tank and a washing tank (both controlled at 25±2°C) to finally prepare the hollow precursor membrane. The specific spinning conditions were a feed flow rate of 3.5 mL / min, a core liquid flow rate of 2.5 mL / min, and a winding speed of 8.5 m / min. After drying the prepared precursor membrane in air for 24 hours, it was placed in a tube furnace and carbonized at a rate of 60 mL / min under a flowing argon atmosphere. The carbonization temperature was increased from room temperature to 120°C at a rate of 5°C / min, held at 120°C for 2 hours, then increased to 340°C at a rate of 10°C / min and held steady for 1 hour. Finally, the temperature was further increased to 600°C at a rate of 5°C / min and held for 2 hours. After carbonization, a hollow carbon molecular sieve membrane (CMS-2) at 600°C was obtained, which was stored and sealed for further characterization tests.
[0088] Testing revealed that CMS-1 and CMS-2 exhibited a bimodal distribution with pore sizes of 0.35 nm and 0.5 nm, a diameter of 196 μm, and a film thickness of 20-30 μm.
[0089] Preparation Example 3
[0090] First, weigh 300g of dimethyl sulfoxide, then add 40.91g of microcrystalline cellulose in three portions, shaking well each time. Next, add 13.64g of cellulose acetate in three portions, shaking well each time. Then add 100g of 1-ethyl-3-methylimidazolium acetate. Place the mixture in a mixer and heat to 60℃, stirring mechanically at 30r / min for 24h. A cellulose-based hollow precursor membrane was prepared using a wet-dry spinning process. The outer layer of the double-layered spinneret was the spinning solution, and the inner layer was ultrapure water. The spinning solution from the needle needed to pass through a 50mm air gap before entering a gelation tank and a washing tank (both controlled at 25±2℃) to finally prepare the hollow precursor membrane. The parameters set were: casting solution temperature 25℃, core solution temperature and coagulation bath temperature 25℃, casting solution flow rate 3.5mL / min, core solution flow rate 2.5mL / min, and drawing and winding rates 8m / min. The prepared precursor membrane was dried in air for 24 hours and then placed in a tube furnace for carbonization at a rate of 60 mL / min under a flowing argon atmosphere. The carbonization temperature was increased from room temperature to 120 °C at a rate of 5 °C / min, held at 120 °C for 2 hours, then increased to 340 °C at a rate of 10 °C / min and held for 1 hour. Finally, the temperature was further increased to 600 °C at a rate of 5 °C / min and held for 2 hours. After carbonization, a hollow carbon molecular sieve membrane (CMS-3) was obtained at 600 °C, which was stored and sealed for further characterization tests.
[0091] The high-temperature performance of the prepared CMS-1 and CMS-2 at 1.5 MPaG is as follows: Figure 2 As shown. By Figure 2It can be seen that as the temperature increases from 20℃ to 100℃, the H2 flux of the high-selectivity hollow carbon molecular sieve membrane CMS-1 increases from 247.25 barrer to 997.13 barrer, while the H2 / CH4 selectivity decreases from 4414.72 to 2035.08. Conversely, the H2 flux of the high-flux hollow carbon molecular sieve membrane CMS-2 increases from 500.21 barrer to 1485.21 barrer, while the H2 / CH4 selectivity decreases from 660.54 to 375.14. With increasing temperature, the H2 flux of both membranes (CMS-1 and CMS-2) increases, while the H2 / CH4 selectivity decreases, but their performance significantly exceeds the 2015 upper bound. This demonstrates that the high-flux hollow carbon molecular sieve membrane CMS-2 and the high-selectivity hollow carbon molecular sieve membrane CMS-1 have significant application value for the selective separation of H2 / CH4 under high temperature and high pressure. Meanwhile, at 1.5 MPaG and 60°C, the high-selectivity hollow carbon molecular sieve membrane CMS-1 exhibited an H2 flux of 652.26 barrer and an H2 / CH4 selectivity of 3082.23, while the high-flux hollow carbon molecular sieve membrane CMS-2 showed an H2 flux of 980.17 barrer and an H2 / CH4 selectivity of 503.12. These conditions will be used as an example in the separation process of the three-stage hollow carbon molecular sieve membranes in this embodiment of the invention. The prepared CMS-3 showed an H2 flux of 1475.8 barrer and an H2 / CH4 selectivity of 487.1 at 20°C and 1.5 MPaG. The H2 / CH4 selectivity of CMS-3 at 20°C and 1.5 MPaG was significantly lower than that of CMS-1 and CMS-2. It is evident that the addition of cellulose acetate during the preparation process results in CMS-3 having a significantly lower separation capacity for hydrogen and methane compared to CMS-1 and CMS-2. Therefore, this invention selects CMS-1 and CMS-2 as membrane separation units.
[0092] Example 1
[0093] The feed pressure, flow rate, and concentration in this embodiment are as follows: pressure is 1.5 MPaG, and flow rate is 18 × 10⁻⁶. 4 Nm 3 / h, temperature is 60℃, hydrogen content is 10mol%, methane content is 90mol%. In this embodiment, the permeate gas pressure of the first membrane separation unit M-1, the second membrane separation unit M-2, and the third membrane separation unit M-3 is 0.1 MPaG. In this embodiment, the membrane modules used in the first membrane separation unit M-1, the second membrane separation unit M-2, and the third membrane separation unit M-3 are membrane modules composed of hollow carbon molecular sieve membranes. In this embodiment, the permeation performance of the hollow carbon molecular sieve membrane is as follows: the first membrane separation unit M-1 uses a hollow carbon molecular sieve membrane CMS-2: H2 flux 980.17 barrer, CH4 flux 1.96 barrer, H2 / CH4 selectivity 503.12; the second membrane separation unit M-2 and the third membrane separation unit M-3 use hollow carbon molecular sieve membranes of CMS-1, with an H2 flux of 652.26 barrer, a CH4 flux of 0.22 barrer, and an H2 / CH4 selectivity of 3082.23. Where 1 barrer = 3.3819 × 10⁻⁶. - 10 mol m -1 s -1 Pa -1 .
[0094] like Figure 1 As shown, the natural gas feedstock f-1 containing the aforementioned hydrogen content, mixed with the second permeate gas from the second membrane separation unit M-2 and the third residual gas from the third membrane separation unit M-3 as circulating gas, becomes f-2, which enters the first membrane separation unit M-1. To ensure the required concentration and hydrogen recovery rate, the first membrane separation unit M-1 purifies the hydrogen to 70 mol%. The first residual gas f-4 from the first membrane separation unit M-1, still containing a certain amount of hydrogen, is pressurized to 1.5 MPaG by the second compressor K-2 and cooled to 60°C by the second heat exchanger E-2 before entering the second membrane separation unit M-2. The permeate gas from the second membrane separation unit M-2... The second permeate gas f-6 from the permeate analyzer is pressurized to 1.5 MPaG by the third compressor K-3 and cooled to 60°C by the third heat exchanger E-3 before being returned to the feed gas and mixed with f-1 for recycling. The second permeate gas f-5 from the residual gas analyzer is discharged as a natural gas-rich product for further use. The first permeate gas f-3 from the first membrane separation unit M-1 is used as a low-pressure hydrogen-rich gas stream. It is pressurized by the first compressor K-1 and cooled to 1.5 MPaG and 60°C by the first heat exchanger E-1 before entering the third membrane separation unit M-3. The third permeate gas f-7 from the third membrane separation unit M-3 is cooled by the fourth heat exchanger E-4 and mixed with the feed gas f-1 for recycling before entering the first membrane separation unit M-1. The third permeate gas f-8 from the third membrane separation unit M-3 is used as a high-purity hydrogen product or further processed.
[0095] In this implementation case, the hydrogen content in the first permeate f-4 after passing through the first membrane separation unit M-1 is 1.05 mol%, and the hydrogen content in the first permeate f-3 is 70.9 mol%. The membrane area of the first hollow carbon molecular sieve membrane in the first membrane separation unit M-1 is 319099.75 m². 2 .
[0096] In this implementation case, the hydrogen content in the second permeate f-5 after passing through the second membrane separation unit M-2 is 0.94 mol%, with a recovery rate of 90%. The hydrogen content in the second permeate f-6 after passing through the second membrane separation unit M-2 is 97.67 mol%, and the membrane area of the second hollow carbon molecular sieve membrane in the second membrane separation unit M-2 is 1693.48 m². 2 The second compressor K-2 on the feed side has a power of 63.56KW, and the third compressor K-3 on the discharge side has a power of 4.37KW.
[0097] In this implementation case, the hydrogen content in the third permeate f-7 after passing through the third membrane separation unit M-3 was 3.48 mol%, and the hydrogen permeate outlet concentration reached 99.5 mol%. The membrane area of the third hollow carbon molecular sieve membrane in the third membrane separation unit M-3 was 38970.44 m². 2 The first compressor on the feed side, K-1, has a power of 526.6KW.
[0098] After rough purification by the first membrane separation unit M-1, the first permeate gas f-4 on the permeate side and the first permeate gas f-3 on the permeate side enter the second membrane separation unit M-2 and the third membrane separation unit M-3 respectively, achieving a hydrogen recovery rate of 91% and an outlet hydrogen concentration of 99.5 mol%, as shown in Table 1.
[0099] Example 2
[0100] Using the hydrogen-containing natural gas feedstock provided by this invention, with the following feed pressure, flow rate, and concentration as an example: pressure is 1.5 MPaG, flow rate is 18 × 10⁻⁶ m³ / s. 4 Nm 3 The temperature is 60°C, the hydrogen content is 10 mol%, and the methane content is 90 mol%. The membrane components in the first, second, and third membrane separation units are the same as in Example 1. In this example, the membrane area of the first hollow carbon molecular sieve membrane in the first membrane separation unit M-1 is 321642.32 m². 2 The membrane area of the second hollow carbon molecular sieve membrane in the second membrane separation unit M-2 is 1693.49 m². 2 In the third membrane separation unit M-3, the membrane area of the third hollow carbon molecular sieve membrane is 15559.19 m². 2The first compressor, K-1, has a power of 533.75 kW, the second compressor, K-2, has a power of 63.56 kW, and the third compressor, K-3, has a power of 4.06 kW. The final hydrogen recovery rate is 90%, and the outlet hydrogen concentration is 99.9 mol%.
[0101] Example 3
[0102] Using the hydrogen-containing natural gas feedstock provided by this invention, with the following feed pressure, flow rate, and concentration as an example: pressure is 1.5 MPaG, flow rate is 18 × 10⁻⁶ m³ / s. 4 Nm 3 The temperature was 60°C, the hydrogen content was 7.5 mol%, and the methane content was 92.5 mol%. The membrane modules in the first, second, and third membrane separation units were the same as in Example 1. In this embodiment, the membrane area of the first hollow carbon molecular sieve membrane in the first membrane separation unit M-1 was 319783.29 m². 2 The membrane area of the second hollow carbon molecular sieve membrane in the second membrane separation unit M-2 is 408.58 m². 2 The membrane area of the third hollow carbon molecular sieve membrane in the third membrane separation unit M-3 is 22197.67 m². 2 The first compressor K-1 has a power of 436.95 kW, the second compressor K-2 has a power of 65.40 kW, and the third compressor K-3 has a power of 16.55 kW. The final hydrogen recovery rate is 92%, and the outlet hydrogen concentration is 99.6 mol%, as shown in Table 1.
[0103] Example 4
[0104] Unlike Example 1, the hydrogen content in the mixed gas is 5 mol%.
[0105] Using the hydrogen-containing natural gas feedstock provided by this invention, with the following feed pressure, flow rate, and concentration as an example: pressure is 1.5 MPaG, flow rate is 18 × 10⁻⁶ m³ / s. 4 Nm 3 The temperature was 60°C, the hydrogen content was 5 mol%, and the methane content was 95 mol%. The membrane modules in the first, second, and third membrane separation units were the same as in Example 1. In this embodiment, the membrane area of the first hollow carbon molecular sieve membrane in the first membrane separation unit M-1 was 587403.98 m². 2 The membrane area of the second hollow carbon molecular sieve membrane in the second membrane separation unit M-2 is 212.39 m². 2 The hollow carbon molecular sieve membrane in the third membrane separation unit M-3 has a membrane area of 20080.12 m². 2The first compressor K-1 has a power of 539.14 kW, the second compressor K-2 has a power of 66.55 kW, and the third compressor K-3 has a power of 1.31 kW. The final hydrogen recovery rate is 91%, and the outlet hydrogen concentration is 99.5 mol%, as shown in Table 1.
[0106] Comparative Example 1
[0107] Unlike Example 1, the hydrogen content in the mixed gas was 5 mol%, and a polymer hollow fiber membrane (prepared according to the synthesis method of PIM-1-500 in the literature He, S.; Jiang, X.; Li, S.; Ran, F.; Long, J.; Shao, L., Intermediate thermal manipulation of polymers of intrinsic microporous (PIMs) membranes for gas separations. AIChE Journal 2020, 66(10)) was used as the separation membrane material of the membrane separation unit. Its H2 flux was 509 barrer, CH4 flux was 4.5 barrer, and its pore distribution was mainly at 0.35 nm and 0.5 nm. The difference was that this membrane had more micropores than CMS-1 and CMS-2. Other feed conditions remained the same. In this comparative example, while maintaining a final hydrogen recovery rate of 90%, the outlet hydrogen concentration was 80.5 mol%, as shown in Table 1.
[0108] Table 1
[0109]
[0110]
[0111] As shown in Table 1, the hollow carbon molecular sieve membrane of the present invention can increase the outlet hydrogen concentration.
[0112] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.
Claims
1. A method for separating hydrogen and methane, comprising: A mixture of hydrogen and methane is separated by passing it through a hollow carbon molecular sieve membrane. Preferably, the hollow carbon molecular sieve membrane has a pore size of 0.3-0.9 nm, a bimodal distribution of pore sizes of 0.35±0.05 nm and 0.5±0.05 nm, and / or the membrane thickness is 20-30 μm; and / or the diameter is 160-230 μm. The carbon source for preparing the hollow carbon molecular sieve membrane is microcrystalline cellulose or cellulose acetate, preferably microcrystalline cellulose.
2. The separation method according to claim 1, characterized in that, The membrane separation is achieved through a multi-stage hollow carbon molecular sieve membrane. Preferably, the multi-stage hollow carbon molecular sieve membrane has 2-5 stages; Preferably, the multi-stage hollow carbon molecular sieve membrane has 3 stages; Preferably, in the multi-stage hollow carbon molecular sieve membrane, at least two stages of hollow carbon molecular sieve membranes are connected in series.
3. The separation method according to claim 2, characterized in that, In the multi-stage hollow carbon molecular sieve membranes, at 1.5 MPaG and 60°C, at least one hollow carbon molecular sieve membrane has an H2 flux exceeding 900 barrer, preferably 900-1500 barrer; and / or In the multi-stage hollow carbon molecular sieve membranes, at 1.5 MPaG and 60°C, at least one hollow carbon molecular sieve membrane exhibits an H2 / CH4 selectivity exceeding 2000, preferably 2500-3500; and / or At 1.5 MPaG and 20 °C, the H2 / CH4 selectivity of the multi-stage hollow carbon molecular sieve membrane exceeds 500.
4. The separation method according to any one of claims 1-3, characterized in that, The separation method includes: (1) A mixture of hydrogen and methane is passed through a first hollow carbon molecular sieve membrane for first membrane separation to obtain first residual gas and first permeate gas; (2) The first residual gas is separated by a second hollow carbon molecular sieve membrane to obtain a second residual gas and a second permeate gas; the second permeate gas is refluxed and mixed with the mixed gas and then separated by a first hollow carbon molecular sieve membrane. (3) The first permeate gas is separated by a third hollow carbon molecular sieve membrane to obtain a third residual gas and a third permeate gas; the third residual gas is refluxed and mixed with the mixed gas and then separated by a first hollow carbon molecular sieve membrane. Preferably, the third permeate gas is hydrogen; preferably, the purity of the hydrogen in the third permeate gas is 99.5 mol% or higher; and / or The pressure of the first membrane separation, the second membrane separation, or the third membrane separation is independently 1-2 MPa, and / or The temperatures for the first membrane separation, the second membrane separation, or the third membrane separation are each independently 50-70°C; and / or At 1.5 MPaG and 60°C, the H2 flux of the first hollow carbon molecular sieve membrane exceeds 900 barrer, preferably 900-1500 barrer; and / or At 1.5 MPaG and 60 °C, the H2 / CH4 selectivity of the first hollow carbon molecular sieve membrane is 400-600. At 1.5 MPaG and 60 °C, the H2 / CH4 selectivity of the second hollow carbon molecular sieve membrane and / or the third hollow carbon molecular sieve membrane exceeds 2000, preferably 2500-3500; and / or At 1.5 MPaG and 60 °C, the H2 flux of the second hollow carbon molecular sieve membrane and / or the third hollow carbon molecular sieve membrane is 600-700 barrer; and / or The membrane area of the first hollow carbon molecular sieve membrane is 300,000-400,000 m². 2 Preferably 310,000-3,300,000m 2 ; and / or The membrane area of the second hollow carbon molecular sieve membrane is 400-2000 m². 2 Preferably 400-1700m 2 ; and / or The membrane area of the third hollow carbon molecular sieve membrane is 15,000-40,000 m². 2 .
5. The separation method according to claim 4, characterized in that, The hydrogen content in the first permeate gas is 1-3 mol%; and / or The hydrogen content in the first permeate gas is 70-80 mol%; and / or The second permeate gas is methane, wherein the purity of the methane is 98.5-99.5 mol%; and / or The hydrogen content in the second permeate is 0.5-1.5 mol%; and / or The hydrogen content in the second permeate gas is 95-98 mol%; and / or The hydrogen content in the third residual gas is 3-4 mol%.
6. The separation method according to claim 4, characterized in that, Before the second and third membrane separation processes, a pressurization and cooling process is performed. Preferably, the pressurization occurs in a compressor; preferably, the compressor is a single-stage or multi-stage compressor connected in series; and / or Cooling is carried out in a heat exchanger, preferably a single-stage or multi-stage heat exchanger connected in series.
7. The separation method according to any one of claims 1-6, characterized in that, The hydrogen content in the hydrogen and methane mixture is ≤10 mol%, preferably 5-10 mol%; and / or The pressure of the hydrogen and methane mixture prior to membrane separation is 0.1-2.5 MPaG, and / or The temperature of the hydrogen and methane mixture before membrane separation is 20-100°C.
8. The separation method according to any one of claims 1-7, characterized in that, The method for preparing the hollow carbon molecular sieve membrane includes the following steps: S1, a carbon source, ionic liquid and organic solvent are mixed to obtain a spinning solution; the spinning solution is then used to make a hollow fiber membrane by a dry-wet spinning method; S2, heating and carbonizing the hollow fiber membrane; Preferably, the carbon source is selected from microcrystalline cellulose or cellulose acetate, with microcrystalline cellulose being more preferred.
9. The separation method according to claim 8, characterized in that, The ionic liquid is one or more of 1-allyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium chloride, and 1-ethyl-3-methylimidazolium acetate; The organic solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, tetrahydrofuran, chloroform, dimethyl sulfoxide, and N-methylpyrrolidone.
10. The separation method according to claim 8 or 9, characterized in that, In step S1, the carbon source content in the spinning solution is 10-14 wt%; the mass ratio of the ionic liquid to the organic solvent is 1:(2-4). Preferably, in step S2, the carbonization temperature is 550-750℃ and the carbonization time is 6-8h.