Method and system for separating and purifying hydrogen from dry gas

Abstract

This invention relates to the field of petroleum refining and discloses a method and system for separating and purifying hydrogen from dry gas. The method comprises the following steps: (1) subjecting the dry gas feedstock to alkaline absorption to obtain pretreated gas; (2) subjecting the pretreated gas to VOC membrane separation after pressurization, and subjecting the permeate gas to shallow cold oil absorption to obtain C2 and above organic components; (3) subjecting the permeate gas obtained from the VOC membrane separation to one or more stages of hydrogen membrane separation, obtaining crude hydrogen with a purity of 95% or higher on the permeate side, and refluxing the permeate gas for VOC membrane separation again; (4) subjecting the crude hydrogen to PSA pressure swing adsorption to obtain high-purity hydrogen with a purity of 99.95% or higher. This invention cleverly couples alkaline absorption technology, multiple membrane separation technologies, shallow cold oil absorption technology, and PSA pressure swing adsorption technology, which can both purify hydrogen and recover organic matter to obtain high-purity hydrogen.

Description

Technical Field

[0001] This invention relates to the field of petroleum refining, and specifically to a method and system for separating and purifying hydrogen from dry gas. Background Technology

[0002] Refinery dry gas primarily originates from the secondary processing of crude oil, such as catalytic cracking, delayed coking, and continuous reforming units. Rich in hydrogen, C1, C2, and C3 light hydrocarbons, refinery dry gas is traditionally used as supplementary fuel gas in refineries. This inefficient use of its components leads to significant resource waste and environmental pollution. Many refineries are gradually beginning to utilize dry gas more rationally, for example, by recovering important components like ethane and ethylene through shallow-cooled oil absorption and by recovering hydrogen components through pressure swing adsorption, thus achieving comprehensive resource utilization.

[0003] Currently, the main methods for purifying dry gas in Chinese refineries include cryogenic processes, pressure swing adsorption (PSA), shallow-cooled oil absorption, and membrane separation. However, none of these methods can meet the current requirements for obtaining high-purity hydrogen. Traditional dry gas purification processes mainly rely on cryogenic technology, which requires large-scale equipment and high energy consumption, and still fails to achieve the required high purity. Membrane separation, as an emerging technology, is simple and convenient to operate, but it is easily deactivated by organic matter. It requires the treatment of light hydrocarbons in natural gas through shallow-cooled oil absorption before membrane separation can proceed. Therefore, there is an urgent need to improve the shallow-cooled oil absorption and hydrogen membrane separation processes to efficiently purify hydrogen. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of high energy consumption, harsh operating conditions, complex equipment, poor hydrogen purification effect, and poor corrosion resistance of separation membranes in the existing technology for purifying hydrogen from dry gas, and to provide a method and system for separating and purifying hydrogen from dry gas.

[0005] To achieve the above objectives, a first aspect of the present invention provides a method for separating and purifying hydrogen from dry gas, wherein the method comprises the following steps:

[0006] (1) The dry gas raw material is subjected to alkaline absorption to obtain pretreated gas;

[0007] (2) The pretreated gas is pressurized and then subjected to VOC membrane separation, and the obtained permeate gas is absorbed by shallow cold oil to obtain organic components of C2 and above.

[0008] (3) The gas obtained from the VOC membrane separation is subjected to one or more stages of hydrogen membrane separation to obtain crude hydrogen with a purity of more than 95% on the permeate side, and the gas on the permeate side is refluxed and subjected to VOC membrane separation again.

[0009] (4) The crude hydrogen gas is subjected to PSA pressure swing adsorption to obtain high-purity hydrogen gas with a purity of over 99.95%.

[0010] A second aspect of the present invention provides a system for separating and purifying hydrogen from dry gas, wherein the system comprises:

[0011] The system includes an alkaline absorption unit, a VOC membrane separation unit, a shallow-cooled oil absorption unit, a hydrogen membrane separation unit, and a PSA pressure swing adsorption unit. The dry raw gas is connected to the inlet of the alkaline absorption unit, and the outlet of the alkaline absorption unit is connected to the inlet of the VOC membrane separation unit. The outlet of the VOC membrane separation unit is connected to the inlets of both the shallow-cooled oil absorption unit and the hydrogen membrane separation unit, and the outlet of the hydrogen membrane separation unit is connected to the inlet of the PSA pressure swing adsorption unit.

[0012] Through the above technical solution, this invention cleverly couples alkaline absorption technology, multiple membrane separation technologies, shallow cold oil absorption technology, and PSA pressure swing adsorption technology, and has the following advantages:

[0013] (1) Optimize the hydrogen purification process of dry gas in refineries, eliminating the need for cryogenic operation and significantly reducing the cost of plant construction and operation;

[0014] (2) Through the combined action of VOC membrane separation and hydrogen membrane separation, both the purpose of purifying hydrogen and the purpose of recovering organic matter can be achieved.

[0015] (3) A VOC membrane separation membrane was cleverly designed, in which the gas on the permeate side was subjected to subsequent purification operations with minimal pressure drop loss, which can achieve the purification effect while avoiding energy loss.

[0016] (4) By recirculating the gas with a high hydrogen concentration on the permeate side of the membrane unit, the hydrogen recovery rate can be significantly improved and the purity of the hydrogen product can be increased. Attached Figure Description

[0017] Figure 1 This is a system flow diagram for separating and purifying hydrogen from dry gas. Detailed Implementation

[0018] The endpoints and any values ​​of the ranges disclosed herein 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 the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0019] The first aspect of this invention provides a method for separating and purifying hydrogen from dry gas, wherein the method comprises the following steps:

[0020] (1) The dry gas raw material is subjected to alkaline absorption to obtain pretreated gas;

[0021] (2) The pretreated gas is pressurized and then subjected to VOC membrane separation, and the obtained permeate gas is absorbed by shallow cold oil to obtain organic components of C2 and above.

[0022] (3) The gas obtained from the VOC membrane separation is subjected to one or more stages of hydrogen membrane separation to obtain crude hydrogen with a purity of more than 95% on the permeate side, and the gas on the permeate side is refluxed and subjected to VOC membrane separation again.

[0023] (4) The crude hydrogen gas is subjected to PSA pressure swing adsorption to obtain high-purity hydrogen gas with a purity of over 99.95%.

[0024] In this invention, alkaline absorption technology, multiple membrane separation technologies, shallow cold oil absorption technology, and PSA pressure swing adsorption technology are cleverly coupled. Through the combined action of VOC membrane separation and hydrogen membrane separation, the purpose of purifying hydrogen can be achieved, and organic matter can also be recovered. The hydrogen purity reaches 99.95% or more, preferably 99.99% or more.

[0025] In some specific embodiments of the present invention, in step (1), the absorbent used in the alkaline absorption process is selected from one or more of sodium hydroxide solution, sodium carbonate solution, and sodium bicarbonate solution, preferably sodium hydroxide solution.

[0026] In some specific embodiments of the present invention, in step (2), the positive pressure side of the VOC membrane separation is 200-2000 kPa, preferably 500-1000 kPa; the permeate side pressure of the VOC membrane separation is lower than the positive pressure side pressure of the VOC membrane separation. The above hydrogen separation method achieves optimal separation effect when the pressures described in the present invention are met.

[0027] In some specific embodiments of the present invention, the membrane separation permeate pressure of the VOC membrane separation is 20-1000 kPa, preferably 40-500 kPa. The above-mentioned hydrogen separation method achieves the optimal separation effect when the pressure described in the present invention is met.

[0028] In some specific embodiments of the present invention, the membrane separation positive pressure side pressure of the hydrogen membrane separation is 200-5000 kPa, preferably 500-3000 kPa, and the membrane separation permeation side pressure of the hydrogen membrane separation is lower than the membrane separation positive pressure side pressure of the helium membrane separation; the separation effect is optimal when the above hydrogen separation method meets the pressure described in the present invention.

[0029] In some specific embodiments of the present invention, the membrane separation permeate pressure of the hydrogen membrane separation is 20-4000 kPa, preferably 50-2000 kPa. The above-mentioned hydrogen separation method achieves optimal separation effect when the pressure described in the present invention is met.

[0030] In some specific embodiments of the present invention, the adsorption pressure of the PSA pressure swing adsorption is 0.5-10 MPa, preferably 2-10 MPa. The above-mentioned hydrogen separation method achieves the optimal separation effect when the adsorption pressure described in the present invention is met.

[0031] A second aspect of the present invention provides a system for separating and purifying hydrogen from dry gas, wherein the system comprises:

[0032] The system includes an alkaline absorption unit, a VOC membrane separation unit, a shallow-cooled oil absorption unit, a hydrogen membrane separation unit, and a PSA pressure swing adsorption unit. The dry feed gas is connected to the inlet of the alkaline absorption unit, and the outlet of the alkaline absorption unit is connected to the inlet of the VOC membrane separation unit. The outlet of the VOC membrane separation unit is connected to the inlets of both the shallow-cooled oil absorption unit and the hydrogen membrane separation unit. The outlet of the hydrogen membrane separation unit is connected to the inlet of the PSA pressure swing adsorption unit, and the outlet of the hydrogen membrane separation unit is also connected to the inlet of the VOC membrane separation unit.

[0033] In this invention, the process for separating and purifying hydrogen from dry gas can be as follows: Figure 1 The process is illustrated below. First, the dry raw gas enters the alkaline absorption unit for dehydration and deacidification. Then, the pretreated gas is pressurized and enters the VOC membrane separation unit. Due to the high selectivity of the VOC membrane for organic matter, most of the C2 and higher organic compounds in the pretreated gas permeate through the membrane. The permeate gas can be further purified and recovered from the natural gas using a shallow-cooled oil recovery unit. The gas on the permeate side of the VOC membrane is pressurized and enters the hydrogen membrane separation unit for purification, yielding crude hydrogen with a purity of over 95%. The permeate gas is then refluxed back to the VOC membrane separation unit. The crude hydrogen then enters the PSA pressure swing adsorption unit for deep purification, yielding high-purity hydrogen with a purity of over 99.95%, preferably over 99.99%.

[0034] In some specific embodiments of the present invention, the alkaline absorption unit is selected from packed towers, plate towers, spray towers, bubble towers or liquid column towers, and is preferably a packed tower.

[0035] In some specific embodiments of the present invention, the packing is selected from one or more of Raschig rings, Pall rings, stepped rings, and corrugated packing.

[0036] In some specific embodiments of the present invention, the VOC separation membrane in the VOC membrane separation unit can be a multilayer composite membrane. A casting solution is coated onto a base membrane to obtain a VOC separation membrane with high selectivity.

[0037] In some specific embodiments of the present invention, the VOC separation membrane is selected from one or more of flat sheet membranes, hollow fiber membranes, or tubular membranes.

[0038] In some specific embodiments of the present invention, the casting solution material of the VOC separation membrane is selected from polydimethylsiloxane and / or tetraethyl orthosilicate.

[0039] In some specific embodiments of the present invention, the base membrane material of the VOC separation membrane is selected from one or more of polypropylene, polyethylene, polyvinyl chloride, and polytetrafluoroethylene.

[0040] The VOC separation membrane prepared by this method exhibits high separation performance for organic compounds with C2 and above, with high throughput and high selectivity. Compared with some traditional organic separation membranes, it has higher heat resistance, corrosion resistance, and a longer service life.

[0041] In some specific embodiments of the present invention, the separation coefficient of the VOC separation membrane for C2 and above organic compounds / methane is 30-50, the separation coefficient for C2 and above organic compounds / nitrogen is 80-150, and the flux of C2 and above organic compounds is 500-1000 GPU. The VOC separation membrane used in the present invention is prepared by using the above-mentioned base membrane material and casting solution material, achieving the separation membrane parameters defined in the present invention. When the method or system composition of the present invention and the above-mentioned VOC separation method meet the VOC separation membrane performance parameters described in the present invention, the separation effect is optimal, enabling the purity of hydrogen separation to reach 99.95% or higher, preferably 99.99% or higher.

[0042] In this invention, by controlling the separation coefficient of C2 and above organic matter / methane to be 30-50, the separation coefficient of C2 and above organic matter / nitrogen to be 80-150, and the flux of C2 and above organic matter to be 500-1000 GPU, the purity of hydrogen separation can reach over 99.95%. At the same time, the C2 and above organic matter components in the dry gas are further purified and recovered by the shallow cold oil recovery unit, thus eliminating the influence of light hydrocarbons in natural gas on the performance of the hydrogen separation membrane.

[0043] In some specific embodiments of the present invention, the hydrogen membrane separation unit uses single-stage or multi-stage membrane separation technology to purify hydrogen gas, preferably two-stage or three-stage membrane separation technology.

[0044] In some specific embodiments of the present invention, the hydrogen separation membrane is selected from one or more of flat sheet membranes, hollow fiber membranes, or tubular membranes.

[0045] In some specific embodiments of the present invention, the hydrogen separation membrane is made of polybenzimidazole materials, and can be a hollow fiber hydrogen separation membrane made of polybenzimidazole materials.

[0046] In some specific embodiments of the present invention, the hydrogen / methane separation coefficient of the hydrogen separation membrane in the hydrogen membrane separation unit is 170-500, preferably 200-300.

[0047] In some specific embodiments of the present invention, the hydrogen flux is 8-30 GPUs, preferably 10-20 GPUs.

[0048] In this invention, the hydrogen separation membrane can be the hollow fiber polybenzimidazole separation membrane prepared in CN202211031910.7, the entire contents of which are incorporated herein by reference. The hydrogen separation membrane is prepared by dissolving polybenzimidazole in a monobasic acid to form a casting solution. The use of a monobasic acid allows the polymer to undergo protonation during dissolution, inhibiting the formation of hydrogen bonds between polymer molecules during film formation. This results in a more uniform free volume formed by the molecular stacking of the polymer, precisely controlled between the pre-separated gas molecules. A twin-screw extruder provides power, and a spinneret is used for extrusion molding. The extrusion process requires control of specific pressure and temperature. Heated gas is used as the core liquid, and high-temperature air is used to enhance mass transfer, achieving rapid solvent evaporation and hollow fiber membrane formation. Process control; multiple active guide rollers are used to traction the extruded hollow fiber membrane and stretch the membrane fibers; furthermore, the prepared polybenzimidazole membrane undergoes protonation with monobasic acid during the film formation process, inhibiting the formation of hydrogen bonds between polymer molecules, reducing the rigidity of the polymer, and enabling the polymer molecular chains to pack more tightly, thereby increasing the separation performance of small molecule gases such as H2 / CO2, H2 / N2, H2 / CH4, He / CO2, He / N2, and He / CH4. The prepared hollow fiber polybenzimidazole separation membrane has high selectivity and high permeation rate.

[0049] In some specific embodiments of the present invention, in the hydrogen membrane separation unit, the hydrogen / methane separation coefficient of the hydrogen separation membrane is 170-500, preferably 200-300; the hydrogen flux is 8-30 GPU, preferably 10-20 GPU. In the present invention, when VOC membrane separation, hydrogen membrane separation, PSA pressure swing adsorption, and meeting the above-mentioned hydrogen separation membrane performance parameters (using the hollow fiber polybenzimidazole separation membrane prepared in CN202211031910.7), the separation effect of hydrogen in dry gas feedstock can be better achieved, and the purity of the separated hydrogen can reach 99.95% or more, preferably 99.99% or more.

[0050] In some specific embodiments of the present invention, the adsorbent in the PSA pressure swing adsorption unit is selected from one or more of activated carbon, activated alumina, molecular sieves, and MOFs materials.

[0051] The molecular sieve is selected from one or more of the following types: 3A molecular sieve, 4A molecular sieve, 5A molecular sieve, 10X molecular sieve, and 13X molecular sieve.

[0052] The MOFs material is selected from one or more of MIL-53, MIL-100, and MIL-101.

[0053] In this invention, VOC membrane separation and shallow-cooled oil absorption operations are cleverly designed to reduce the content of light hydrocarbons entering the helium separation membrane. This not only recovers organic matter but also eliminates the influence of light hydrocarbons in natural gas on the performance of the helium separation membrane. It also prevents the hydrogen separation membrane material from swelling with light hydrocarbons or even dissolving the membrane, which would otherwise reduce the membrane's separation performance. This invention achieves a coupling of alkaline absorption technology, VOC membrane separation technology, shallow-cooled oil absorption technology, hydrogen membrane separation technology, and PSA pressure swing adsorption technology.

[0054] The present invention will be described in detail below through embodiments.

[0055] Unless otherwise specified in the following examples and comparative examples, all conditions were performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available products.

[0056] In Examples 1-5 and Comparative Example 2 of the present invention, the VOC separation membrane used is a flat sheet membrane prepared using the polytetrafluoroethylene base membrane material and the casting solution material of polydimethylsiloxane and tetraethyl orthosilicate described in the present invention; in Examples 1-5 and Comparative Example 1 of the present invention, the hydrogen separation membrane used is the hollow fiber polybenzimidazole separation membrane prepared in CN202211031910.7.

[0057] Example 1

[0058] The dry gas from a certain refinery has the following approximate composition: hydrogen 25%, methane 46%, ethane 18%, ethylene 1%, C3 and above organic compounds 2.5%, carbon dioxide 1.5%, nitrogen 6% (all by volume), and trace amounts of sulfur dioxide. Using the technical solution of this invention, according to... Figure 1 The process shown describes the hydrogen purification operation of the dry gas from the refinery.

[0059] (1) The dry gas is first pressurized to 500 kPa and then enters the alkaline absorption tower. Sodium hydroxide solution is used as the absorbent to remove a large amount of acidic gases such as sulfur dioxide and carbon dioxide.

[0060] (2) The pretreated gas after alkaline washing enters the VOC membrane separation unit, with an operating pressure of 500 kPa. The VOC-rich gas on the permeate side after VOC membrane separation enters the shallow cold oil absorption unit, where organic components such as ethylene and ethane can be recovered after desorption. The hydrogen-rich gas on the permeate side enters the hydrogen membrane separation unit.

[0061] (3) The hydrogen membrane separation unit uses a two-stage membrane for purification, with operating pressures of 1MPa and 1MPa respectively. The gas on the permeate side of the first-stage membrane can be used as methane-rich fuel gas, and the gas on the permeate side of the second-stage membrane is returned to the inlet of the VOC membrane separation unit.

[0062] (4) The gas on the permeate side of the secondary membrane is relatively pure hydrogen, which enters the pressure swing adsorption unit for purification. Molecular sieves are selected as adsorbents, and the adsorption pressure is 2 MPa.

[0063] The main gas compositions of each step in hydrogen purification are shown in Table 1.

[0064] Table 1

[0065] Number\Composition% [H2] CH4 [C2H6] [C2H4] [C3+] CO2 [N2] intake 25 46 18 1 2.5 1.5 6 Absorber tower outlet 25.38 46.69 18.27 1.01 2.54 0.02 6.09 VOC membrane inlet 32.08 43.52 15.59 0.87 2.16 0.02 5.76 Shallow cold oil inlet 19.05 30.15 40.61 2.26 5.74 0.01 2.18 Hydrogen membrane inlet 37.38 48.96 5.41 0.3 0.7 0.02 7.23 Hydrogen membrane outlet 98.89 0.86 0.1 0.01 0.01 0 0.13 High-purity hydrogen 99.994 0.003 0 0 0 0 0.003

[0066] As can be seen from the table above, the process technology of this invention can combine alkaline absorption, VOC membrane separation, hydrogen membrane separation, shallow cold oil absorption, and pressure swing adsorption to obtain a high-purity hydrogen product with a purity of 99.994%, while simultaneously recovering organic components such as ethane and ethylene.

[0067] Example 2

[0068] The dry gas from a certain refinery has the same gas composition as in Example 1. The technical solution of this invention is adopted, according to... Figure 1 The process shown describes the hydrogen purification operation of the dry gas from the refinery.

[0069] (1) The dry gas is first pressurized to 1MPa and then enters the alkaline absorption tower. Sodium carbonate solution is used as the absorbent to remove a large amount of acidic gases such as sulfur dioxide and carbon dioxide.

[0070] (2) The pretreated gas after alkaline washing enters the VOC membrane separation unit at an operating pressure of 1 MPa. The VOC-rich gas on the permeate side after VOC membrane separation enters the shallow cold oil absorption unit, where organic components such as ethylene and ethane can be recovered after desorption. The hydrogen-rich gas on the permeate side enters the hydrogen membrane separation unit.

[0071] (3) The hydrogen membrane separation unit uses a two-stage membrane for purification, with an operating pressure of 3 MPa. The gas on the permeate side of the first-stage membrane can be used as methane-rich fuel gas, and the gas on the permeate side of the second-stage membrane is returned to the inlet of the VOC membrane separation unit.

[0072] (4) The gas on the permeate side of the secondary membrane is relatively pure hydrogen, which enters the pressure swing adsorption unit for purification. Molecular sieves are selected as adsorbents, and the adsorption pressure is 2 MPa.

[0073] The main gas compositions of each step in hydrogen purification are shown in Table 2.

[0074] Table 2

[0075] Number\Composition% [H2] CH4 [C2H6] [C2H4] [C3+] CO2 [N2] intake 25 46 18 1 2.5 1.5 6 Absorber tower outlet 25.36 46.66 18.26 1.01 2.54 0.08 6.09 VOC membrane inlet 25.05 47.42 17.77 0.99 2.46 0.09 6.22 Shallow cold oil inlet 13.34 29.63 45.84 2.55 6.5 0.06 2.08 Hydrogen membrane inlet 30.59 55.84 4.48 0.25 0.56 0.1 8.18 Hydrogen membrane outlet 98.48 1.22 0.1 0.01 0.01 0 0.18 High-purity hydrogen 99.992 0.004 0 0 0 0 0.004

[0076] As can be seen from the table above, the process technology of this invention can combine alkaline absorption, VOC membrane separation, hydrogen membrane separation, shallow cold oil absorption, and pressure swing adsorption to obtain a high-purity hydrogen product with a purity of 99.992%, while also recovering organic components such as ethane and ethylene.

[0077] Example 3

[0078] The dry gas from a certain refinery has the same gas composition as in Example 1. The technical solution of this invention is adopted, according to... Figure 1 The process shown describes the hydrogen purification operation of the dry gas from the refinery.

[0079] (1) The dry gas is first pressurized to 2MPa and then enters the alkaline absorption tower. Sodium hydroxide solution is used as the absorbent to remove a large amount of acidic gases such as sulfur dioxide and carbon dioxide.

[0080] (2) The pretreated gas after alkaline washing enters the VOC membrane separation unit at an operating pressure of 2 MPa. The VOC-rich gas on the permeate side after VOC membrane separation enters the shallow cold oil absorption unit, where organic components such as ethylene and ethane can be recovered after desorption. The hydrogen-rich gas on the permeate side enters the hydrogen membrane separation unit.

[0081] (3) The hydrogen membrane separation unit uses a single-stage membrane for purification, with an operating pressure of 5 MPa. The hydrogen concentration in the permeate side gas is not high, so no reflux operation is performed, and it can be used as methane-rich fuel gas.

[0082] (4) The gas on the permeation side is relatively pure hydrogen, which enters the pressure swing adsorption unit for purification. Molecular sieves are selected as adsorbents, and the adsorption pressure is 2 MPa.

[0083] The main gas compositions of each step in hydrogen purification are shown in Table 3.

[0084] Table 3

[0085] Number\Composition% [H2] CH4 [C2H6] [C2H4] [C3+] CO2 <![CDATA[N2]]> intake 25 46 18 1 2.5 1.5 6 Absorber tower outlet 25.38 46.69 18.27 1.01 2.54 0.02 6.09 VOC membrane inlet 25.38 46.69 18.27 1.01 2.54 0.02 6.09 Shallow cold oil inlet 14.82 31.81 42.72 2.37 6.01 0.01 2.26 Hydrogen membrane inlet 32.32 56.49 2.18 0.12 0.25 0.03 8.61 Hydrogen membrane outlet 91.74 6.89 0.27 0.02 0.03 0 1.05 High-purity hydrogen 99.954 0.023 0.001 0 0 0 0.022

[0086] As can be seen from the table above, the process technology of this invention can combine alkaline absorption, VOC membrane separation, hydrogen membrane separation, shallow cold oil absorption, and pressure swing adsorption to obtain a high-purity hydrogen product with a purity of 99.954%, while simultaneously recovering organic components such as ethane and ethylene.

[0087] Example 4

[0088] The dry gas from a certain refinery has the same gas composition as in Example 1. The technical solution of this invention is adopted, according to... Figure 1 The process shown describes the hydrogen purification operation of the dry gas from the refinery.

[0089] (1) The dry gas is first pressurized to 200 kPa and then enters the alkaline absorption tower. Sodium hydroxide solution is used as the absorbent to remove a large amount of acidic gases such as sulfur dioxide and carbon dioxide.

[0090] (2) The pretreated gas after alkaline washing enters the VOC membrane separation unit, with an operating pressure of 300 kPa. The VOC-rich gas on the permeate side after VOC membrane separation enters the shallow cold oil absorption unit, where organic components such as ethylene and ethane can be recovered after desorption. The hydrogen-rich gas on the permeate side enters the hydrogen membrane separation unit.

[0091] (3) The hydrogen membrane separation unit uses a two-stage membrane for purification, with an operating pressure of 300 kPa. The gas on the permeate side of the first-stage membrane can be used as methane-rich fuel gas, and the gas on the permeate side of the second-stage membrane is returned to the inlet of the VOC membrane separation unit.

[0092] (4) The gas on the permeation side is relatively pure hydrogen, which enters the pressure swing adsorption unit for purification. Molecular sieves are selected as adsorbents, and the adsorption pressure is 2 MPa.

[0093] The main gas compositions of each step in hydrogen purification are shown in Table 4.

[0094] Table 4

[0095] Number\Composition% <![CDATA[H2]]> <![CDATA[CH4]]> <![CDATA[C2H6]]> <![CDATA[C2H4]]> <![CDATA[C3+]]> <![CDATA[CO2]]> <![CDATA[N2]]> intake 25 46 18 1 2.5 1.5 6 Absorber tower outlet 25.38 46.69 18.27 1.01 2.54 0.02 6.09 VOC membrane inlet 26.46 47.19 16.62 0.92 2.31 0.02 6.48 Shallow cold oil inlet 21.54 42.66 26.81 1.49 3.73 0.02 3.75 Hydrogen membrane inlet 33.5 53.64 2.07 0.12 0.27 0.02 10.38 Hydrogen membrane outlet 90.95 7.3 0.28 0.02 0.04 0 1.41 High-purity hydrogen 99.944 0.024 0.001 0 0 0 0.031

[0096] As shown in the table above, the process technology of this invention, combining alkaline absorption, VOC membrane separation, hydrogen membrane separation, shallow-cooled oil absorption, and pressure swing adsorption, can produce high-purity hydrogen with a purity of 99.954%, while simultaneously recovering organic components such as ethane and ethylene. However, it can be seen that the concentrations of hydrogen and methane at the shallow-cooled oil inlet are relatively high, while the concentrations of the target product ethylene and ethane are lower than in Examples 1-3, thus making the shallow-cooled oil absorption operation more difficult. Furthermore, the yield of the target product hydrogen is also lower compared to Examples 1-3.

[0097] Example 5

[0098] The dry gas from a certain refinery has the same gas composition as in Example 1. The technical solution of this invention is adopted, according to... Figure 1 The process shown describes the hydrogen purification operation of the dry gas from the refinery.

[0099] (1) The dry gas is first pressurized to 500 kPa and then enters the alkaline absorption tower. Sodium hydroxide solution is used as the absorbent to remove a large amount of acidic gases such as sulfur dioxide and carbon dioxide.

[0100] (2) The pretreated gas after alkaline washing enters the VOC membrane separation unit, with an operating pressure of 500 kPa. The VOC-rich gas on the permeate side after VOC membrane separation enters the shallow cold oil absorption unit, where organic components such as ethylene and ethane can be recovered after desorption. The hydrogen-rich gas on the permeate side enters the hydrogen membrane separation unit.

[0101] (3) The hydrogen membrane separation unit uses a two-stage membrane for purification, with operating pressures of 1MPa, 1MPa and 2MPa respectively. The gas on the permeate side of the first-stage membrane can be used as methane-rich fuel gas, and the gas on the permeate side of the second-stage and third-stage membranes is returned to the inlet of the VOC membrane separation unit.

[0102] (4) The gas on the permeate side of the third-stage membrane is relatively pure hydrogen, which enters the pressure swing adsorption unit for purification. MOFs material is selected as the adsorbent, and the adsorption pressure is 5MPa.

[0103] The main gas compositions of each step in hydrogen purification are shown in Table 5.

[0104] Table 5

[0105] Number\Composition% <![CDATA[H2]]> <![CDATA[CH4]]> <![CDATA[C2H6]]> <![CDATA[C2H4]]> <![CDATA[C3+]]> <![CDATA[CO2]]> <![CDATA[N2]]> intake 25 46 18 1 2.5 1.5 6 Absorber tower outlet 25.38 46.69 18.27 1.01 2.54 0.02 6.09 VOC membrane inlet 32.07 43.52 15.6 0.87 2.16 0.02 5.76 Shallow cold oil inlet 19.05 30.15 40.61 2.26 5.74 0.01 2.18 Hydrogen membrane inlet 37.37 48.97 5.41 0.3 0.7 0.02 7.23 Hydrogen membrane outlet 99.18 0.64 0.07 0 0.01 0 0.1 High-purity hydrogen 99.996 0.002 0 0 0 0 0.002

[0106] As can be seen from the table above, the process technology of this invention can combine alkaline absorption, VOC membrane separation, hydrogen membrane separation, shallow cold oil absorption, and pressure swing adsorption to obtain a high-purity hydrogen product with a purity of 99.996%, while also recovering organic components such as ethane and ethylene.

[0107] Comparative Example 1

[0108] The dry gas from a certain refinery has the same gas composition as in Example 1.

[0109] (1) The dry gas is first pressurized to 500 kPa and then enters the alkaline absorption tower. Sodium carbonate solution is used as the absorbent to remove a large amount of acidic gases such as sulfur dioxide and carbon dioxide.

[0110] (2) The pretreated gas after alkaline washing enters the hydrogen membrane separation unit. The hydrogen membrane separation unit uses a two-stage membrane for purification, with operating pressures of 1 MPa and 1 MPa respectively.

[0111] (3) The gas on the permeate side of the secondary membrane is relatively pure hydrogen, which enters the pressure swing adsorption unit for purification. Molecular sieves are selected as adsorbents, and the adsorption pressure is 2 MPa.

[0112] The main gas compositions of each step in hydrogen purification are shown in Table 6.

[0113] Table 6

[0114] Number\Composition% <![CDATA[H2]]> <![CDATA[CH4]]> <![CDATA[C2H6]]> <![CDATA[C2H4]]> <![CDATA[C3+]]> <![CDATA[CO2]]> <![CDATA[N2]]> intake 25 46 18 1 2.5 1.5 6 Absorber tower outlet 25.38 46.69 18.27 1.01 2.54 0.02 6.09 Hydrogen membrane inlet 24.8 47.05 18.41 1.02 2.56 0.02 6.14 Hydrogen membrane outlet 89.25 6.72 2.63 0.15 0.37 0 0.88 High-purity hydrogen 99.947 0.023 0.009 0 0.001 0 0.02

[0115] As shown in the table above, a high-purity hydrogen product with a purity of 99.947% can be obtained by combining alkaline absorption, hydrogen membrane separation, and pressure swing adsorption processes without VOC membrane separation. However, byproducts such as ethylene and ethane cannot be obtained. Furthermore, due to the lower inlet hydrogen concentration in the hydrogen membrane separation unit, the hydrogen recovery rate is also lower than in Example 1.

[0116] Comparative Example 2

[0117] The dry gas from a certain refinery has the same gas composition as in Example 1.

[0118] (1) The dry gas is first pressurized to 500 kPa and then enters the alkaline absorption tower. Sodium hydroxide solution is used as the absorbent to remove a large amount of acidic gases such as sulfur dioxide and carbon dioxide.

[0119] (2) The pretreated gas after alkaline washing enters the VOC membrane separation unit at an operating pressure of 500 kPa. The VOC-rich gas on the permeate side after VOC membrane separation enters the shallow cold oil absorption unit, where organic components such as ethylene and ethane can be recovered after desorption. The hydrogen-rich gas on the permeate side enters the pressure swing adsorption unit.

[0120] (3) The hydrogen-rich gas on the permeate side enters the pressure swing adsorption unit for purification. Molecular sieves are selected as adsorbents, and the adsorption pressure is 2 MPa.

[0121] The main gas compositions of each step in hydrogen purification are shown in Table 7.

[0122] Table 7

[0123]

[0124]

[0125] As can be seen from the table above, without hydrogen membrane separation technology, by combining alkaline absorption, VOC membrane separation, shallow cold oil absorption, and pressure swing adsorption processes, byproducts such as ethylene and ethane, as well as hydrogen products with a purity of 98.904%, can be obtained. However, this cannot reach the level of high-purity hydrogen, and the product value is reduced.

[0126] 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 and purifying hydrogen from dry gas, characterized in that, The steps of this method are as follows: (1) The dry gas raw material is subjected to alkaline absorption to obtain pretreated gas; (2) The pretreated gas is pressurized and then subjected to VOC membrane separation, and the obtained permeate gas is absorbed by shallow cold oil to obtain C2 and above organic components; (3) The gas on the permeate side obtained by the VOC membrane separation is subjected to one or more stages of hydrogen membrane separation to obtain crude hydrogen with a purity of more than 95% on the permeate side, and the gas on the permeate side is refluxed and subjected to VOC membrane separation again. (4) The crude hydrogen gas is subjected to PSA pressure swing adsorption to obtain high-purity hydrogen gas with a purity of over 99.95%; Wherein, the positive pressure side of the VOC membrane separation is 200-2000 kPa; the permeate side pressure of the VOC membrane separation is lower than the positive pressure side pressure of the VOC membrane separation; and the permeate side pressure of the VOC membrane separation is 20-1000 kPa.

2. The method according to claim 1, characterized in that, In step (1), the absorbent used in the alkaline absorption process is selected from one or more of sodium hydroxide solution, sodium carbonate solution, and sodium bicarbonate solution; And / or, in step (2), the positive pressure side pressure of the VOC membrane separation is 500-1000 kPa; And / or, the membrane separation permeate pressure of the VOC membrane separation is 40-500 kPa.

3. The method according to claim 2, characterized in that, In step (1), the sodium hydroxide solution is used as the absorption liquid in the alkaline absorption process.

4. The method according to any one of claims 1-3, characterized in that, The positive pressure side pressure of the hydrogen membrane separation is 200-5000 kPa, and the permeate side pressure of the hydrogen membrane separation is lower than the positive pressure side pressure of the hydrogen membrane separation. And / or, the membrane separation permeate side pressure of the hydrogen membrane separation is 20-4000 kPa.

5. The method according to claim 4, characterized in that, The positive pressure side pressure of the hydrogen membrane separation is 500-3000 kPa; And / or, the membrane separation permeate side pressure of the hydrogen membrane separation is 50-2000 kPa.

6. The method according to any one of claims 1-3, characterized in that, The adsorption pressure of the PSA pressure swing adsorption is 0.5-10 MPa.

7. The method according to claim 6, characterized in that, The adsorption pressure of the PSA pressure swing adsorption is 2-10 MPa.

8. A system for separating and purifying hydrogen from dry gas according to any one of claims 1-7, characterized in that, The system includes: The system includes an alkaline absorption unit, a VOC membrane separation unit, a shallow-cooled oil absorption unit, a hydrogen membrane separation unit, and a PSA pressure swing adsorption unit. The dry raw gas is connected to the inlet of the alkaline absorption unit, and the outlet of the alkaline absorption unit is connected to the inlet of the VOC membrane separation unit. The outlet of the VOC membrane separation unit is connected to the inlets of both the shallow-cooled oil absorption unit and the hydrogen membrane separation unit, and the outlet of the hydrogen membrane separation unit is connected to the inlet of the PSA pressure swing adsorption unit.

9. The system according to claim 8, characterized in that, In the alkaline absorption unit, the absorption tower is selected from packed tower, plate tower, spray tower, bubble tower or liquid column tower.

10. The system according to claim 9, characterized in that, In the alkaline absorption unit, the absorption tower is a packed tower.

11. The system according to claim 10, characterized in that, The packing material is selected from one or more of Raschig rings, Pall rings, stepped rings, and corrugated packing.

12. The system according to any one of claims 8-11, characterized in that, In the VOC membrane separation unit, the VOC separation membrane is a multilayer composite membrane; And / or, the VOC separation membrane is selected from one or more of flat sheet membranes, hollow fiber membranes, or tubular membranes; And / or, the casting solution material of the VOC separation membrane is selected from polydimethylsiloxane and / or tetraethyl orthosilicate; And / or, the base membrane material of the VOC separation membrane is selected from one or more of polypropylene, polyethylene, polyvinyl chloride, and polytetrafluoroethylene; And / or, the separation coefficient of the VOC separation membrane for C2 and above organic matter / methane is 30-50, the separation coefficient of C2 and above organic matter / nitrogen is 80-150, and the flux of C2 and above organic matter is 500-1000 GPU.

13. The system according to any one of claims 8-11, characterized in that, In the hydrogen membrane separation unit, hydrogen gas is purified using single-stage or multi-stage membrane separation technology; And / or, the hydrogen separation membrane is selected from one or more of flat sheet membranes, hollow fiber membranes, or tubular membranes; And / or, the material of the hydrogen separation membrane is selected from polybenzimidazole materials.

14. The system according to claim 13, characterized in that, The hydrogen membrane separation unit employs two- or three-stage membrane separation technology to purify the hydrogen gas.

15. The system according to any one of claims 8-11, characterized in that, In the hydrogen membrane separation unit, the hydrogen / methane separation coefficient of the hydrogen separation membrane is 170-500; And / or, the hydrogen flux is 8-30 GPUs.

16. The system according to claim 15, characterized in that, In the hydrogen membrane separation unit, the hydrogen / methane separation coefficient of the hydrogen separation membrane is 200-300; And / or, the hydrogen flux is 10-20 GPUs.

17. The system according to any one of claims 8-11, characterized in that, In the PSA pressure swing adsorption unit, the adsorbent is selected from one or more of activated carbon, activated alumina, molecular sieves, and MOF materials; The molecular sieve is selected from one or more of the following types: 3A molecular sieve, 4A molecular sieve, 5A molecular sieve, 10X molecular sieve, and 13X molecular sieve. The MOFs material is selected from one or more of MIL-53, MIL-100, and MIL-101.

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