Method and system for separating and purifying hydrogen in dry gas

Abstract

The invention relates to the field of petroleum refining, and discloses a method and a system for separating and purifying hydrogen in dry gas. The method comprises the following steps: (1) carrying out basic absorption on a dry gas raw material to obtain pretreated gas; (2) pressurizing the pretreated gas, then carrying out VOC membrane separation, and carrying out shallow cold oil absorption on the obtained permeation side gas to obtain C2 and above organic matter components; (3) performing one-stage or multi-stage hydrogen membrane separation on the retentate side gas obtained by VOC membrane separation to obtain crude hydrogen with the purity of more than 95% on the permeation side, and refluxing the retentate side gas to perform VOC membrane separation again; and (4) carrying out PSA (pressure swing adsorption) on the crude hydrogen to obtain high-purity hydrogen with the purity of 99.95% or above. According to the invention, a basic absorption technology, a plurality of membrane separation technologies, a shallow cold oil absorption technology and a PSA (Pressure Swing Adsorption) technology are ingeniously coupled, so that the purpose of purifying hydrogen can be achieved, and the effect of recovering organic matters can also be achieved to obtain high-purity hydrogen.

Description

Technical Field

[0001] The invention relates to the field of petroleum refining, and in particular to a method and system for separating and purifying hydrogen in dry gas. Background Art

[0002] Refinery dry gas mainly comes from the secondary processing of crude oil, such as catalytic cracking, delayed coking, continuous reforming and other devices. Refinery dry gas is rich in hydrogen, C1, C2, C3 and other light hydrocarbon resources. In traditional refineries, it is mainly used as supplementary fuel gas. It is impossible to efficiently utilize the components in the dry gas, resulting in a large amount of resource waste and environmental pollution. Many refineries have gradually begun to make rational use of dry gas, such as recovering important components such as ethane and ethylene through shallow cold oil absorption, and recovering hydrogen components through pressure swing adsorption, to achieve comprehensive utilization of resources.

[0003] At present, the main methods for purifying dry gas in my country's refineries are cryogenics, PSA pressure swing adsorption, shallow cold oil absorption, membrane separation, etc. However, none of them can meet the current requirements for obtaining high-purity hydrogen. The traditional dry gas purification hydrogen process mainly relies on cryogenic technology, which requires a large equipment scale and energy consumption requirements, and cannot meet high purity requirements. As an emerging technology, membrane separation is simple and convenient to operate, but it is easily inactivated by organic matter. Light hydrocarbons in natural gas need to be treated by shallow cold oil absorption before membrane separation operations can be performed. Therefore, it is urgent to improve the shallow cold oil absorption and hydrogen membrane separation processes to efficiently purify hydrogen. Summary of the invention

[0004] The purpose of the present 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 membrane in the prior art of purifying hydrogen from dry gas, and to provide a method and system for separating and purifying hydrogen from dry gas.

[0005] In order to achieve the above object, the first aspect of the present invention provides a method for separating and purifying hydrogen in dry gas, wherein the method comprises the following steps:

[0006] (1) subjecting the dry gas raw material to alkaline absorption to obtain pretreated gas;

[0007] (2) subjecting the pretreated gas to VOC membrane separation after pressurization, and subjecting the obtained permeate side gas to shallow cold oil absorption to obtain C2 and above organic components;

[0008] (3) subjecting the retentate side gas obtained by the VOC membrane separation to one or more stages of hydrogen membrane separation, obtaining crude hydrogen with a purity of more than 95% on the permeate side, and refluxing the retentate side gas to VOC membrane separation again;

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

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

[0011] An alkali absorption unit, a VOC membrane separation unit, a shallow cold oil absorption unit, a hydrogen membrane separation unit, and a PSA pressure swing adsorption unit. The dry gas feed gas is connected to the inlet of the alkali absorption unit, the outlet of the alkali absorption unit is connected to the inlet of the VOC membrane separation unit, the outlet of the VOC membrane separation unit is respectively connected to the inlets of the shallow cold 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 scheme, the present invention cleverly couples alkali 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 refinery dry gas hydrogen purification process, eliminating the need for cryogenic operation, significantly reducing the cost of equipment construction and operation;

[0014] (2) Through the combined action of VOC membrane separation and hydrogen membrane separation, the purpose of hydrogen purification can be achieved, and the role of organic matter recovery can also be achieved;

[0015] (3) The VOC membrane separation unit is cleverly set up, in which the gas on the retentate side undergoes subsequent purification operations with minimal pressure drop loss, thus achieving the purification effect while avoiding energy loss;

[0016] (4) By recirculating the gas with higher hydrogen concentration on the retentate side of the membrane unit, the hydrogen recovery rate can be significantly improved and the purity of the hydrogen product can be increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The present invention is a system flow chart for separating and purifying hydrogen in dry gas. DETAILED DESCRIPTION

[0018] 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.

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

[0020] (1) subjecting the dry gas raw material to alkaline absorption to obtain pretreated gas;

[0021] (2) subjecting the pretreated gas to VOC membrane separation after pressurization, and subjecting the obtained permeate side gas to shallow cold oil absorption to obtain C2 and above organic components;

[0022] (3) subjecting the retentate side gas obtained by the VOC membrane separation to one or more stages of hydrogen membrane separation, obtaining crude hydrogen with a purity of more than 95% on the permeate side, and refluxing the retentate side gas to VOC membrane separation again;

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

[0024] In the present invention, alkaline absorption technology, various 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 the role of recovering organic matter can also be achieved. The hydrogen purity reaches more than 99.95%, preferably more than 99.99%.

[0025] In some specific embodiments of the present invention, in step (1), during the alkaline absorption process, the absorption liquid used 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 pressure of the positive pressure side of the membrane separation of the VOC membrane separation is 200-2000 kPa, preferably 500-1000 kPa; the pressure of the membrane separation permeate side of the VOC membrane separation is lower than the pressure of the positive pressure side of the membrane separation of the VOC membrane separation. The above hydrogen separation method has the best separation effect when the pressure described in the present invention is 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 hydrogen separation method has the best separation effect when the pressure described in the present invention is met.

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

[0029] In some specific embodiments of the present invention, the membrane separation permeate side pressure of the hydrogen membrane separation is 20-4000 kPa, preferably 50-2000 kPa. The above hydrogen separation method has the best 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 hydrogen separation method has the best separation effect when it meets the adsorption pressure of the present invention.

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

[0032] An alkali absorption unit, a VOC membrane separation unit, a shallow cold oil absorption unit, a hydrogen membrane separation unit, and a PSA pressure swing adsorption unit. The dry gas feed gas is connected to the inlet of the alkali absorption unit, the outlet of the alkali absorption unit is connected to the inlet of the VOC membrane separation unit, the outlet of the VOC membrane separation unit is respectively connected to the inlets of the shallow cold 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 the present invention, the process of separating and purifying hydrogen in dry gas can be as follows: Figure 1 As shown in the description. First, the dry gas feed gas enters the alkaline absorption unit for dehydration, deacidification and other operations; then, the obtained pre-treated gas is pressurized and enters the VOC membrane separation unit. Through the high selectivity of the VOC separation membrane for organic matter, most of the C2 and above organic matter in the pre-treated gas passes through the separation membrane, and the permeate side gas can be further purified by the shallow cold oil recovery unit to recover the C2 and above organic matter components in the natural gas; the gas on the retentate side of the VOC separation membrane is pressurized and enters the hydrogen membrane separation unit for purification operation to obtain crude hydrogen with a purity of more than 95%, and the gas on the retentate side is refluxed to the VOC membrane separation unit; the crude hydrogen enters the PSA pressure swing adsorption unit to deeply purify the hydrogen to obtain high-purity hydrogen with a purity of more than 99.95%, preferably more than 99.99%.

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

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

[0036] In some specific embodiments of the present invention, in the VOC membrane separation unit, the VOC separation membrane may be a multi-layer composite membrane. The casting solution is coated on the 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 a flat membrane, a hollow fiber membrane or a tubular membrane.

[0038] In some specific embodiments of the present invention, the casting liquid 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 has higher separation performance for organic matter above C2, high flux and high selectivity. Compared with some traditional organic separation membranes, it has higher heat resistance, corrosion resistance and longer service life.

[0041] In some specific embodiments of the present invention, the C2 and above organic matter / methane separation coefficient of the VOC separation membrane is 30-50, the C2 and above organic matter / nitrogen separation coefficient is 80-150, and the C2 and above organic matter flux is 500-1000GPU. The VOC separation membrane used in the present invention is prepared by the above-mentioned base membrane material and casting liquid material to achieve the separation membrane parameters specified 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, and the purity of hydrogen separation can reach more than 99.95%, preferably more than 99.99%.

[0042] In the present invention, by using the VOC separation membrane of the present invention, by controlling the C2 and above organic matter / methane separation coefficient of the VOC separation membrane to be 30-50, the C2 and above organic matter / nitrogen separation coefficient to be 80-150, and the C2 and above organic matter flux to be 500-1000GPU, the purity of hydrogen separation can reach more than 99.95%, and 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, thereby 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, in the hydrogen membrane separation unit, one-stage or multi-stage membrane separation technology is used to purify the 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 a flat membrane, a hollow fiber membrane or a tubular membrane.

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

[0046] 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.

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

[0048] In the present invention, the hydrogen separation membrane can be the hollow fiber polybenzimidazole separation membrane prepared in CN202211031910.7, and the full text of the patent is introduced into this article. The hydrogen separation membrane is prepared by dissolving polybenzimidazole in a monobasic acid to form a casting liquid. The use of a monobasic acid can cause the polymer to be protonated during the dissolution process, and the formation of hydrogen bonds between polymer molecules is inhibited during the film formation process, so that the free volume formed by the molecular accumulation of the polymer is more uniform and just regulated between the pre-separated gas molecules; a twin-screw extruder is used to provide power, and a spinneret is used for extrusion molding. The extrusion process requires control of a certain pressure and temperature; heated gas is used as the core liquid, and high-temperature air is used to enhance mass transfer, so as to achieve rapid volatilization of the solvent and hollow fiber membrane formation. Process control; multiple active guide wheels are used to pull the extruded hollow fiber membrane and stretch the membrane filaments; further, the prepared polybenzimidazole membrane is protonated with the monobasic acid during the membrane formation process, which inhibits the formation of hydrogen bonds between polymer molecules, reduces the rigidity of the polymer, and enables the polymer molecular chains to be more densely stacked, 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 8-30GPU, preferably 10-20GPU. In the present invention, when VOC membrane separation, hydrogen membrane separation, PSA pressure swing adsorption and the above-mentioned hydrogen separation membrane performance parameters are combined (using the hollow fiber polybenzimidazole separation membrane prepared in CN202211031910.7), the separation effect of hydrogen in the dry gas raw material can be better achieved, and the purity of hydrogen separation can reach more than 99.95%, preferably more than 99.99%.

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

[0051] Wherein, the molecular sieve is one or more selected from 3A molecular sieve, 4A molecular sieve, 5A molecular sieve, 10X molecular sieve and 13X molecular sieve.

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

[0053] In the present invention, VOC membrane separation and shallow cold oil absorption operations are cleverly arranged to reduce the light hydrocarbon content of the gas entering the helium separation membrane, thereby recovering organic matter and eliminating the influence of light hydrocarbons in natural gas on the performance of the helium separation membrane, preventing the hydrogen separation membrane material from swelling with light hydrocarbons and even dissolving the separation membrane, which would lead to a decrease in the separation performance of the membrane, thereby achieving the coupling of alkaline absorption technology, VOC membrane separation technology, shallow cold oil absorption technology, hydrogen membrane separation technology, and PSA pressure swing adsorption technology.

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

[0055] In the following examples and comparative examples, if no specific conditions are specified, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used, if no manufacturer is specified, are all conventional products that can be obtained through commercial channels.

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

[0057] Example 1

[0058] The gas composition of a refinery dry gas is roughly as follows: 25% hydrogen, 46% methane, 18% ethane, 1% ethylene, 2.5% C3 and above organic matter, 1.5% carbon dioxide, 6% nitrogen (all the above are volume fractions), and a trace amount of sulfur dioxide. Figure 1 The process shown is to carry out hydrogen purification operation on the refinery dry gas.

[0059] (1) The dry gas is first pressurized to 500 kPa before entering the alkaline absorption tower, where 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 pre-treated gas after alkali 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, and the hydrogen-rich gas on the retentate 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 1 MPa and 1 MPa respectively. The gas on the retentate side of the first membrane can be used as methane-rich fuel gas, and the gas on the retentate side of the second membrane is refluxed 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 sieve is selected as the adsorbent, and the adsorption pressure is 2 MPa.

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

[0064] Table 1

[0065] No.\Composition% <![CDATA[H2]]> <![CDATA[CH4]]> <![CDATA[C2H6]]> <![CDATA[C2H4]]> <![CDATA[C3+]]> <![CDATA[CO2]]> <![CDATA[N2]]> Air Intake 25 46 18 1 2.5 1.5 6 Absorption 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 above table, through the process technology of the present invention, a high-purity hydrogen product with a purity of 99.994% can be obtained by combining alkaline absorption, VOC membrane separation, hydrogen membrane separation, shallow cold oil absorption, and pressure swing adsorption processes, and organic components such as ethane and ethylene can be recovered at the same time.

[0067] Example 2

[0068] The dry gas of a refinery has the same gas composition as that of Example 1. The technical solution of the present invention is adopted according to Figure 1 The process shown is to carry out hydrogen purification operation on the refinery dry gas.

[0069] (1) The dry gas is first pressurized to 1 MPa before entering the alkaline absorption tower, where 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 pre-treated gas after alkali washing enters the VOC membrane separation unit with 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, and the hydrogen-rich gas on the retentate side enters the hydrogen membrane separation unit.

[0071] (3) The hydrogen membrane separation unit uses a two-stage membrane for purification, and the operating pressure is 3MPa and 3MPa. The gas on the retentate side of the first membrane can be used as methane-rich fuel gas, and the gas on the retentate side of the second membrane flows back 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 sieve is selected as the adsorbent, and the adsorption pressure is 2 MPa.

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

[0074] Table 2

[0075] No.\Composition% <![CDATA[H2]]> <![CDATA[CH4]]> <![CDATA[C2H6]]> <![CDATA[C2H4]]> <![CDATA[C3+]]> <![CDATA[CO2]]> <![CDATA[N2]]> Air Intake 25 46 18 1 2.5 1.5 6 Absorption 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 above table, through the process technology of the present invention, a high-purity hydrogen product with a purity of 99.992% can be obtained by combining alkaline absorption, VOC membrane separation, hydrogen membrane separation, shallow cold oil absorption, and pressure swing adsorption processes, and organic components such as ethane and ethylene can be recovered at the same time.

[0077] Example 3

[0078] The dry gas of a refinery has the same gas composition as that of Example 1. The technical solution of the present invention is adopted according to Figure 1 The process shown is to carry out hydrogen purification operation on the refinery dry gas.

[0079] (1) The dry gas is first pressurized to 2MPa before entering the alkaline absorption tower, where 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 pre-treated gas after alkali washing enters the VOC membrane separation unit with an operating pressure of 2MPa. 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, and the hydrogen-rich gas on the retentate side enters the hydrogen membrane separation unit.

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

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

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

[0084] Table 3

[0085] No.\Composition% <![CDATA[H2]]> <![CDATA[CH4]]> <![CDATA[C2H6]]> <![CDATA[C2H4]]> <![CDATA[C3+]]> <![CDATA[CO2]]> <![CDATA[N2]]> Air Intake 25 46 18 1 2.5 1.5 6 Absorption 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 above table, through the process technology of the present invention, a high-purity hydrogen product with a purity of 99.954% can be obtained by combining alkaline absorption, VOC membrane separation, hydrogen membrane separation, shallow cold oil absorption, and pressure swing adsorption processes, and organic components such as ethane and ethylene can be recovered at the same time.

[0087] Example 4

[0088] The dry gas of a refinery has the same gas composition as that of Example 1. The technical solution of the present invention is adopted according to Figure 1 The process shown is to carry out hydrogen purification operation on the refinery dry gas.

[0089] (1) The dry gas is first pressurized to 200 kPa before entering the alkaline absorption tower, where 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 pre-treated gas after alkali 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, and the hydrogen-rich gas on the retentate side enters the hydrogen membrane separation unit.

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

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

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

[0094] Table 4

[0095] No.\Composition% <![CDATA[H2]]> <![CDATA[CH4]]> <![CDATA[C2H6]]> <![CDATA[C2H4]]> <![CDATA[C3+]]> <![CDATA[CO2]]> <![CDATA[N2]]> Air Intake 25 46 18 1 2.5 1.5 6 Absorption 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] According to the above table, it can be seen that through the process technology of the present invention, a high-purity hydrogen product with a purity of 99.954% can be obtained by combining alkali absorption, VOC membrane separation, hydrogen membrane separation, shallow cold oil absorption, and pressure swing adsorption processes, and organic components such as ethane and ethylene can be recovered at the same time. However, it can be seen that the concentrations of hydrogen and methane at the shallow cold oil inlet are relatively high, and the concentrations of the target products ethylene and ethane are not as good as those in Examples 1-3, so the shallow cold oil absorption operation is more difficult. At the same time, the yield of the target product hydrogen is also reduced compared with Examples 1-3.

[0097] Example 5

[0098] The dry gas of a refinery has the same gas composition as that of Example 1. The technical solution of the present invention is adopted according to Figure 1 The process shown is to carry out hydrogen purification operation on the refinery dry gas.

[0099] (1) The dry gas is first pressurized to 500 kPa before entering the alkaline absorption tower, where 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 pre-treated gas after alkali 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, and the hydrogen-rich gas on the retentate side enters the hydrogen membrane separation unit.

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

[0102] (4) The gas on the permeate side of the tertiary 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 5 MPa.

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

[0104] Table 5

[0105] No.\Composition% <![CDATA[H2]]> <![CDATA[CH4]]> <![CDATA[C2H6]]> <![CDATA[C2H4]]> <![CDATA[C3+]]> <![CDATA[CO2]]> <![CDATA[N2]]> Air Intake 25 46 18 1 2.5 1.5 6 Absorption 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 above table, through the process technology of the present invention, a high-purity hydrogen product with a purity of 99.996% can be obtained by combining alkaline absorption, VOC membrane separation, hydrogen membrane separation, shallow cold oil absorption, and pressure swing adsorption processes, and organic components such as ethane and ethylene can be recovered at the same time.

[0107] Comparative Example 1

[0108] The dry gas of a refinery has the same gas composition as that of Example 1.

[0109] (1) The dry gas is first pressurized to 500 kPa before entering the alkaline absorption tower, where 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 alkali washing enters the hydrogen membrane separation unit, which uses a two-stage membrane for purification, and the operating pressures are 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 sieve is selected as the adsorbent, and the adsorption pressure is 2 MPa.

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

[0113] Table 6

[0114] No.\Composition% <![CDATA[H2]]> <![CDATA[CH4]]> <![CDATA[C2H6]]> <![CDATA[C2H4]]> <![CDATA[C3+]]> <![CDATA[CO2]]> <![CDATA[N2]]> Air Intake 25 46 18 1 2.5 1.5 6 Absorption 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] According to the above table, it can be seen that through the process technology without VOC membrane separation, 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, but by-products such as ethylene and ethane cannot be obtained. At the same time, due to the low inlet hydrogen concentration of the hydrogen membrane separation unit, the hydrogen recovery rate is also lower than that of Example 1.

[0116] Comparative Example 2

[0117] The dry gas of a refinery has the same gas composition as that of Example 1.

[0118] (1) The dry gas is first pressurized to 500 kPa before entering the alkaline absorption tower, where 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 pre-treated gas after alkali 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, and the hydrogen-rich gas on the retentate side enters the pressure swing adsorption unit.

[0120] (3) The hydrogen-rich gas on the retentate side enters the pressure swing adsorption unit for purification, and molecular sieve is selected as the adsorbent with an adsorption pressure of 2 MPa.

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

[0122] Table 7

[0123]

[0124]

[0125] According to the above table, it can be seen that through process technology without hydrogen membrane separation, by-products such as ethylene and ethane, as well as hydrogen products with a purity of 98.904% can be obtained through a combination of alkaline absorption, VOC membrane separation, shallow cold oil absorption, and pressure swing adsorption processes. However, it is impossible to reach the high-purity hydrogen level and the product value has decreased.

[0126] 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 separating and purifying hydrogen in dry gas, characterized in that: The steps of this method are: (1) subjecting the dry gas raw material to alkaline absorption to obtain pretreated gas; (2) subjecting the pretreated gas to VOC membrane separation after pressurization, and subjecting the obtained permeate side gas to shallow cold oil absorption to obtain C2 and above organic components; (3) subjecting the retentate side gas obtained by the VOC membrane separation to one or more stages of hydrogen membrane separation, obtaining crude hydrogen with a purity of more than 95% on the permeate side, and refluxing the retentate side gas to VOC membrane separation again; (4) The crude hydrogen is subjected to PSA pressure swing adsorption to obtain high-purity hydrogen with a purity of more than 99.95%.

2. The method according to claim 1, characterized in that: In step (1), during the alkaline absorption process, the absorption liquid used is selected from one or more of sodium hydroxide solution, sodium carbonate solution, and sodium bicarbonate solution, preferably sodium hydroxide solution; Preferably, in step (2), the pressure on the positive pressure side of the membrane separation of the VOC membrane separation is 200-2000 kPa, preferably 500-1000 kPa; the pressure on the membrane separation permeate side of the VOC membrane separation is lower than the pressure on the positive pressure side of the membrane separation of the VOC membrane separation; Preferably, the membrane separation permeate side pressure of the VOC membrane separation is 20-1000 kPa, preferably 40-500 kPa.

3. The method according to claim 1 or 2, characterized in that: The pressure of the membrane separation positive pressure side of the hydrogen membrane separation is 200-5000 kPa, preferably 500-3000 kPa, and the pressure of the membrane separation permeate side of the hydrogen membrane separation is lower than the pressure of the membrane separation positive pressure side of the helium membrane separation; Preferably, the membrane separation permeate side pressure of the hydrogen membrane separation is 20-4000 kPa, preferably 50-2000 kPa.

4. The method according to any one of claims 1 to 3, characterized in that: The adsorption pressure of the PSA pressure swing adsorption is 0.5-10 MPa, preferably 2-10 MPa.

5. A system for separating and purifying hydrogen from dry gas, characterized in that: The system includes: An alkali absorption unit, a VOC membrane separation unit, a shallow cold oil absorption unit, a hydrogen membrane separation unit, and a PSA pressure swing adsorption unit. The dry gas feed gas is connected to the inlet of the alkali absorption unit, the outlet of the alkali absorption unit is connected to the inlet of the VOC membrane separation unit, the outlet of the VOC membrane separation unit is respectively connected to the inlets of the shallow cold 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.

6. The system according to claim 5 or 6, characterized in that: In the alkaline absorption unit, the absorption tower is selected from a packed tower, a plate tower, a spray tower, a bubble tower or a liquid column tower, preferably a packed tower; Preferably, the filler is selected from one or more of Raschig rings, Pall rings, step rings and corrugated fillers.

7. The system according to claim 5 or 6, characterized in that: In the VOC membrane separation unit, the VOC separation membrane is a multi-layer composite membrane; Preferably, the VOC separation membrane is selected from one or more of a flat membrane, a hollow fiber membrane or a tubular membrane; Preferably, the casting liquid material of the VOC separation membrane is selected from polydimethylsiloxane and / or tetraethyl orthosilicate; Preferably, the base membrane material of the VOC separation membrane is selected from one or more of polypropylene, polyethylene, polyvinyl chloride, and polytetrafluoroethylene; Preferably, the C2 and above organic matter / methane separation coefficient of the VOC separation membrane is 30-50, the C2 and above organic matter / nitrogen separation coefficient is 80-150, and the C2 and above organic matter flux is 500-1000 GPU.

8. The system according to any one of claims 5 to 7, characterized in that: In the hydrogen membrane separation unit, the hydrogen gas is purified by using one-stage or multi-stage membrane separation technology, preferably two-stage or three-stage membrane separation technology; Preferably, the hydrogen separation membrane is selected from one or more of a flat membrane, a hollow fiber membrane or a tubular membrane; Preferably, the material of the hydrogen separation membrane is selected from polybenzimidazole materials.

9. The system according to any one of claims 5 to 8, characterized in that: In the hydrogen membrane separation unit, the hydrogen / methane separation coefficient of the hydrogen separation membrane is 170-500, preferably 200-300; Preferably, the hydrogen flux is 8-30 GPU, preferably 10-20 GPU.

10. The system according to any one of claims 5 to 9, characterized in that: In the PSA pressure swing adsorption unit, the adsorbent is selected from one or more of activated carbon, activated alumina, molecular sieve, and MOFs materials; Wherein, the molecular sieve is one or more selected from 3A molecular sieve, 4A molecular sieve, 5A molecular sieve, 10X molecular sieve, and 13X molecular sieve; Wherein, the MOFs material is selected from one or more of MIL-53, MIL-100, and MIL-101.

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