Method for recovering carbon dioxide from field gas by membrane separation

Abstract

The application relates to the field of petroleum refining, and discloses a method for recovering carbon dioxide in oil displacement field gas through membrane separation, which comprises the following steps: (1) performing light oil absorption on the oil displacement field gas to obtain oil and a first mixed gas; (2) performing membrane separation on the first mixed gas to obtain a permeated gas and a retentate gas; and (3) optionally, performing gas-liquid separation on the retentate gas, returning a liquid phase part obtained in the step to the light oil absorption step in the step (1), and using a gas phase part as fuel gas; the method reduces the construction and operation costs of a device and makes up for the shortcomings of the membrane separation technology.

Description

Technical Field

[0001] This invention relates to the field of petroleum refining, specifically to a method for recovering carbon dioxide from oilfield gas using membrane separation. The method combines shallow cold oil absorption and membrane separation technology to recover carbon dioxide from semi-gas produced by carbon dioxide flooding. Background Technology

[0002] In recent years, the global warming and natural disasters caused by the massive emission of the greenhouse gas carbon dioxide have attracted widespread attention from various countries. Carbon dioxide enhanced oil recovery (CEOR) technology can not only improve crude oil recovery rates but also achieve carbon dioxide sequestration, making it an effective carbon emission control measure. By recovering and utilizing the high concentration of carbon dioxide in CEOR gas, the cost of CEOR can be reduced while avoiding secondary pollution. Therefore, research on carbon dioxide separation and purification technologies in CEOR gas is of great significance for resource utilization and environmental protection.

[0003] Currently, the main technologies for recovering carbon dioxide from oilfield gas include absorption, cryogenic distillation, and membrane separation. Due to the high concentration of carbon dioxide in oilfield gas and its frequent presence of sulfides, which significantly damage the absorbent, absorption methods are generally unsuitable due to high costs, low recovery rates, and demanding equipment requirements. Cryogenic distillation utilizes the boiling point differences of components in the feed gas to separate carbon dioxide through low-temperature condensation. This typically involves multiple compressions and cooling processes that induce a phase change, followed by distillation to separate the carbon dioxide. It is currently the primary carbon dioxide recovery technology. However, cryogenic distillation requires numerous compressors and cold boxes, resulting in high equipment and energy costs. Membrane separation, under pressure, selectively separates carbon dioxide from other gases based on the varying permeability of the membrane material to different gas components. Membrane separation offers advantages such as simple operation, long service life, and low energy consumption, but it suffers from disadvantages such as low separation efficiency and poor corrosion resistance.

[0004] Therefore, membrane separation, as a separation method with great potential, urgently needs to develop carbon dioxide separation membrane materials with high separation performance and corrosion resistance, which is of great strategic significance for the recovery and utilization of carbon dioxide in oilfield gas. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of low separation efficiency and poor corrosion resistance in the existing technology of membrane separation and recovery of carbon dioxide from oilfield gas, and to provide a method for membrane separation and recovery of carbon dioxide from oilfield gas.

[0006] To achieve the above objectives, the present invention provides a method for membrane separation and recovery of carbon dioxide from oilfield gas, wherein the method includes:

[0007] (1) The oilfield gas is subjected to shallow cooling oil absorption to obtain oil and the first mixed gas;

[0008] (2) The first mixed gas is separated by membrane separation to obtain permeate gas and permeate gas;

[0009] (3) Optionally, the gas on the permeate side is separated into liquid and liquid phases, and the liquid phase is returned to the shallow cold oil absorption step in step (1), while the gas phase is used as fuel gas.

[0010] Through the above technical solution, the present invention cleverly couples shallow cold oil absorption technology, carbon dioxide membrane separation technology, and optional gas-liquid separation and recovery technology, and can achieve at least the following beneficial effects:

[0011] (1) The process of recovering carbon dioxide from oilfield gas is optimized, eliminating the need for low-temperature distillation, which significantly reduces the construction and operating costs of the equipment.

[0012] (2) By using shallow cold oil absorption operation, acidic gases and high-carbon organic matter in the oilfield gas are separated, thereby reducing the damage to the carbon dioxide separation membrane and making up for the shortcomings of membrane separation technology.

[0013] (3) In a preferred embodiment of the present invention, the absorbent is recovered by setting up a gas-liquid separation and recovery process, which significantly reduces the process cost. Detailed Implementation

[0014] 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.

[0015] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0016] This invention provides a method for membrane separation and recovery of carbon dioxide from oilfield gas, wherein the method includes:

[0017] (1) The oilfield gas is subjected to shallow cooling oil absorption to obtain oil and the first mixed gas;

[0018] (2) The first mixed gas is separated by membrane separation to obtain permeate gas and permeate gas;

[0019] (3) Optionally, the gas on the permeate side is separated into liquid and liquid phases, and the liquid phase is returned to the shallow cold oil absorption step in step (1), while the gas phase is used as fuel gas.

[0020] In this invention, the shallow cold oil absorption in step (1) can be carried out in an absorption tower, which is selected from packed towers, plate towers, spray towers, bubble towers or liquid column towers, preferably packed towers; the packing in the packed tower is one of Raschig rings, Pall rings, stepped rings or corrugated packing.

[0021] In this invention, the pressure of the gas phase feed tray of the absorption tower is 100-1000 kPa; the pressure of the liquid phase feed tray is 500-1000 kPa; and the temperature of the absorption tower is -20℃ to 10℃.

[0022] In this invention, the absorbent used in step (1) for absorbing shallow cold oil is selected from C3-C4 organic compounds; preferably, it is a C4 absorbent.

[0023] In this invention, the oil in step (1) is discharged from the bottom of the absorption tower; the first mixed gas is discharged from the top of the absorption tower.

[0024] In this invention, the membrane used for membrane separation in step (2) can be selected from at least one of flat sheet membranes, hollow fiber membranes, and tubular membranes; preferably, the material of the membrane is selected from at least one of polysulfone, polyethersulfone, polyamide, polypropylene, polyethylene, synthetic resin, polyvinylidene fluoride, polytetrafluoroethylene, polyether ether ketone, polybenzimidazole, polydimethylsiloxane, cellulose acetate, polycarbonate, polymethyl methacrylate, silica, zeolite molecular sieve, carbon molecular sieve, and metal-organic framework materials. To further improve the flux and selectivity of carbon dioxide separation membrane for carbon dioxide, preferably, the membrane is selected from a separation composite membrane or a separation membrane made of polyamide material comprising a support layer, a silicone rubber intermediate layer, and a polymer layer stacked sequentially; the crosslinked polymer constituting the polymer layer contains structural unit I from polyamine compounds, structural unit II from polyacrylamide compounds, and structural unit III from polyphenol compounds (see application number: 202311127284.6, which is incorporated herein by reference).

[0025] In this invention, in the membrane separation described in step (2), the carbon dioxide flux of the separation membrane used is 300-800 GPU, and the carbon dioxide / nitrogen separation coefficient is 40-80; more preferably 55-65.

[0026] In this invention, there are no special requirements for the membrane separation conditions. For example, the positive pressure side pressure of the membrane separation in step (2) can be 100-2000 kPa; preferably 300-1500 kPa; the permeate side pressure is lower than the osmotic side pressure, and the osmotic side pressure can also be negative.

[0027] In this invention, the positive pressure is the inlet pressure on the upstream side of the separation membrane.

[0028] In this invention, preferably, the method may further include: pressurizing the first mixed gas by a compressor before membrane separation, wherein the pressurized pressure is 100-2000 kPa.

[0029] In this invention, the membrane separation employs single-stage or multi-stage membrane separation technology; preferably, it involves 2-3 stages. During multi-stage membrane separation, the positive pressure of the separating membranes can be the same or different.

[0030] In this invention, the gas-liquid separation method in step (3) is condensation, and the condensation temperature is -20°C to 15°C; preferably -10°C to 10°C.

[0031] In this invention, the condensation in step (3) can be carried out using various condensers commonly found in the art. For example, the condenser can be at least one of water, methanol, ethanol, ethylene glycol and sodium chloride solution.

[0032] In this invention, the method is applicable to recovering carbon dioxide from carbon dioxide-containing oilfield gas. The composition of the oilfield gas is preferably: 50-80 vol% carbon dioxide, and other gas components are not limited. For example, the composition of the oilfield gas can be: 50-80 vol% carbon dioxide, 1-5 vol% nitrogen, 10-20 vol% methane, 2-6 vol% C2, 1-3 vol% C3, 2-5 vol% C4, 1-7 vol% C5 and above, and 0.1-1 vol% sulfur dioxide.

[0033] In a preferred embodiment of the present invention, the separation membrane is selected from a separation composite membrane comprising a support layer, a silicone rubber intermediate layer and a polymer layer stacked sequentially, or a separation membrane made of polyamide material; the separation coefficient of carbon dioxide / nitrogen of the separation membrane is 55-65; the pressure on the positive pressure side of the membrane separation is 300-1500 kPa; the membrane separation adopts 2-3 stage membrane separation technology; using the above preferred embodiment, the purity of CO2 separated from the oilfield gas is above 99%, and the CO2 recovery rate is above 75%.

[0034] The present invention will be described in detail below through examples. Unless otherwise specified in the following examples and comparative examples, conditions were performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available products.

[0035] In the following preparation examples, embodiments, and comparative examples,

[0036] The weight-average molecular weight of the support layer material can be determined by the GPC method.

[0037] The porosity of the support layer is measured by scanning electron microscopy and obtained by dividing the pore area within the field of view by the total surface area.

[0038] The method for testing the average pore diameter of the support layer is as follows: measure the diameter of all visible pores in the field of view using a scanning electron microscope and calculate the average value;

[0039] The method for testing the viscosity of silicone rubber at 25°C is as follows: measurement is performed using a rotor viscometer;

[0040] The method for testing the degree of crosslinking of the crosslinked polymer in the separation composite membrane C1 is as follows: calculation by XPS and infrared spectroscopy;

[0041] The average pore size of the polymer layer was tested according to the standard GB / T42269-2022 "Separation Membrane Pore Size Test Method Gas Permeation Method";

[0042] IsoparG, purchased from Aladdin Reagents;

[0043] Polysulfone (20 wt%), purchased from Solvay;

[0044] Polydimethylsiloxane, acquired by Adamas-Beta;

[0045] 5,5',6,6'-Tetrahydroxy-3,3,3',3'-Tetramethylspirobisindane and diethylene glycol di(3-aminopropyl) ether were acquired by TCI.

[0046] Triethylamine and pyromellitic acid chloride were acquired by Anaiji Chemical.

[0047] Sodium hydroxide was purchased from Sinopharm Reagent.

[0048] Gas composition analysis methods use a gas analyzer to test gas concentration.

[0049] Preparation Example

[0050] (1) Add 200g of polysulfone, 680g of dimethylacetamide, 60g of polyvinylpyrrolidone, and 60g of polyethylene glycol, heat to 70°C for 24 hours, prepare support layer A1, and then wash with water for 48 hours.

[0051] The material of the support layer A1 has a weight-average molecular weight of 3500 Da, a porosity of 59%, and an average pore size of 21 nm.

[0052] (2) Use the casting method on the above 400cm 28 mL of 1 wt% polydimethylsiloxane solution was coated on the support layer A1. The thickness of the doctor blade was 100 μm. The coating and curing temperature was 30 °C and the coating and curing time was 12 h. After curing, an intermediate layer was formed, and the composite film B1 was obtained.

[0053] The silicone rubber in the intermediate layer of composite film B1 has a viscosity of 820 cP at 25°C.

[0054] (3) Interfacial polymerization reaction was carried out at 25°C: 0.4 g of trimesoyl chloride was added to 99.6 g of Isopar G solution, and 35 mL of the prepared oil phase solution was added to the above 400 cm... 2 Composite membrane B1 was immersed in 35 mL of oil phase solution for 3 min. In the presence of 0.05 g of triethylamine, 0.1 g of 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethylspirobisindane and 0.1 g of diethylene glycol di(3-aminopropyl) ether were added to 99.75 g of water, and the pH was adjusted to 12 with sodium hydroxide. Composite membrane B1, after being immersed in the oil phase, was immersed in 35 mL of aqueous solution for 5 min. After the interfacial polymerization reaction was completed, the residual solvent was thoroughly washed with water to form a polymer layer containing crosslinked polymers (structural unit I from diethylene glycol di(3-aminopropyl) ether, structural unit II from trimesoyl chloride, and structural unit III from 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethylspirobisindane), thus obtaining separation composite membrane C1. Total reflectance infrared absorption spectroscopy analysis showed that there were linking groups a and b in the crosslinked polymer.

[0055] Among them, the degree of crosslinking of the crosslinked polymer in the separation composite membrane C1 is 55.3%;

[0056] The average pore size of the polymer layer is 0.37 nm.

[0057] Example 1

[0058] The composition of the gas from a certain oilfield undergoing carbon dioxide flooding is approximately: 65 vol% carbon dioxide, 1 vol% nitrogen, 19 vol% methane, 4.5 vol% C2, 2.5 vol% C3, 3.9 vol% C4, 4 vol% C5 and above, and 0.1 vol% sulfur dioxide. The present invention is used to recover carbon dioxide from this oilfield gas.

[0059] The oilfield gas first enters an absorption tower for shallow-cooled oil absorption. The absorption tower is a packed tower, using Raschig rings as packing material and n-butane as the absorbent. The inlet pressure of the absorption tower is 100 kPa, the absorbent feed pressure is 500 kPa, and the temperature of the packed tower is 0°C. Oil is obtained at the bottom outlet of the absorption tower, and the first mixed gas is obtained at the top outlet.

[0060] The first mixed gas is pressurized to 1000 kPa by a compressor and then enters the carbon dioxide membrane separation step for separation. The separation membrane used is the C1 composite membrane prepared in the preparation example, which has a carbon dioxide / nitrogen separation coefficient of 65. A secondary membrane is used for purification, with positive pressures of 500 kPa and 500 kPa respectively. The gas on the permeate side of the membrane is carbon dioxide, and the gas on the residual side is mixed to obtain the second mixed gas. The second mixed gas is condensed using a water-ethylene glycol mixture (60 vol% water, 40 vol% ethylene glycol) as the condenser at 0°C. After condensation, it enters a two-phase separator. The liquid phase, mainly composed of C4, is refluxed to the inlet of the shallow-cooled oil absorption unit, while the gas phase is used as fuel gas.

[0061] The main gas compositions of each step in carbon dioxide recovery are shown in Table 1.

[0062] Table 1 Gas Composition at Each Stage

[0063]

[0064]

[0065] As can be seen from the table above, the preferred process technology of this invention, using the preferred separation membrane, yields a carbon dioxide product with a purity of 99.8%, and the carbon dioxide recovery rate reaches 77%.

[0066] Example 2

[0067] Carbon dioxide is recovered according to the method of Example 1, except that the separation membrane is a hollow fiber membrane made of polyamide, and the separation coefficient of carbon dioxide / nitrogen is 55.

[0068] The main gas compositions of each step in carbon dioxide recovery are shown in Table 2.

[0069] Table 2 Gas Composition at Each Stage

[0070]

[0071] As can be seen from the table above, the process technology of this invention yields a carbon dioxide product with a purity of 99.2%, and the carbon dioxide recovery rate reaches 75%.

[0072] Example 3

[0073] Carbon dioxide is recovered according to the method of Example 2, except that the carbon dioxide membrane separation step is performed with primary membrane purification at a positive pressure of 1500 kPa.

[0074] The main gas compositions of each step in carbon dioxide recovery are shown in Table 3.

[0075] Table 3 Gas Composition at Each Stage

[0076]

[0077] As can be seen from the table above, the process technology of this invention yields a carbon dioxide product with a purity of 96.04%, and the carbon dioxide recovery rate reaches 71%.

[0078] Example 4

[0079] Carbon dioxide is recovered according to the method in Example 2, except that the carbon dioxide membrane separation step involves purification through a three-stage membrane with positive pressures of 500 kPa, 300 kPa, and 300 kPa respectively. The gas on the permeate side of the membrane is the carbon dioxide product, and the gas on the residual side is mixed to obtain a second mixed gas, which is then condensed. Water is used as the condensate, and the condensation temperature is 10°C.

[0080] The main gas compositions of each step in carbon dioxide recovery are shown in Table 4.

[0081] Table 4 Gas Composition at Each Stage

[0082]

[0083]

[0084] As can be seen from the table above, the process technology of this invention yields a carbon dioxide product with a purity of 99.75% and a carbon dioxide recovery rate of 85%.

[0085] Example 5

[0086] Carbon dioxide is recovered according to the method of Example 2, except that: the inlet pressure of the absorption tower is 500 kPa and the feed pressure of the absorbent is 800 kPa; the carbon dioxide membrane separation step is purified by two-stage membranes with positive pressures of 1000 kPa and 500 kPa respectively; and water is used as the condenser in the condensation step, with a condensation temperature of -10°C.

[0087] The main gas compositions of each step in carbon dioxide recovery are shown in Table 5.

[0088] Table 5 Gas Composition at Each Stage

[0089]

[0090] As can be seen from the table above, the process technology of this invention yields a carbon dioxide product with a purity of 99.04%, and the carbon dioxide recovery rate reaches 79%.

[0091] Example 6

[0092] Carbon dioxide is recovered according to the method of Example 2, except that: in the carbon dioxide membrane separation step, purification is carried out through two-stage membranes with positive pressures of 200 kPa and 200 kPa respectively; in the condensation step, water is used as the condenser and the condensation temperature is -10°C.

[0093] The main gas compositions of each step in carbon dioxide recovery are shown in Table 6.

[0094] Table 6 Gas Composition at Each Stage

[0095]

[0096] As shown in the table above, the process technology of this invention yields a carbon dioxide product with a purity of 90.86% and a carbon dioxide recovery rate of 68%. The data also shows that the products obtained in Examples 1-5 have higher carbon dioxide purity and recovery rates, and require less carbon dioxide separation membrane. Therefore, it is evident that using the preferred separation membrane with positive pressure for carbon dioxide separation in this invention results in superior separation performance.

[0097] Example 7

[0098] Carbon dioxide is recovered according to the method of Example 2, except that: in the carbon dioxide membrane separation step, the separation membrane is a polydimethylsiloxane hollow fiber membrane, and the separation coefficient of carbon dioxide / nitrogen is 31.

[0099] The main gas compositions of each step in carbon dioxide recovery are shown in Table 7.

[0100] Table 7 Gas Composition at Each Stage

[0101]

[0102]

[0103] As shown in the table above, the process technology of this invention yields a carbon dioxide product with a purity of 78.37%, and a carbon dioxide recovery rate of 64%. The data also demonstrates that the products obtained in Examples 1-6 have higher carbon dioxide purity and recovery rates, and require less carbon dioxide separation membrane. Therefore, it is evident that using the preferred separation membrane of this invention for carbon dioxide separation results in superior separation performance.

[0104] Example 8

[0105] Carbon dioxide is recovered according to the method of Example 2, except that a condensation step is not performed.

[0106] The main gas compositions of each step in carbon dioxide recovery are shown in Table 8.

[0107] Table 8 Gas Composition at Each Stage

[0108]

[0109] As shown in the table above, Example 8 yielded a carbon dioxide product with a purity of 99.2%, achieving a carbon dioxide recovery rate of 75%, the same as Example 2. However, because Example 2 employed a preferred scheme for the condensation recovery unit, C4 shallow cooling oil was recovered, reducing the cost of replenishing the absorbent in the shallow cooling oil absorption tower by approximately 50% compared to this example, thus further lowering the process cost.

[0110] Comparative Example 1

[0111] Carbon dioxide is recovered according to the method in Example 2, except that shallow cooling oil absorption is not performed for oilfield gas recovery. Since there is no need for shallow cooling oil recovery, a condensation recovery unit is not set up. Instead, carbon dioxide is directly purified through a three-stage membrane separation step, with positive pressures of 1000 kPa, 500 kPa, and 500 kPa, respectively.

[0112] The main gas compositions of each step in carbon dioxide recovery are shown in Table 9.

[0113] Table 9 Gas Composition at Each Stage

[0114]

[0115] As shown in the table above, Comparative Example 1 yielded a carbon dioxide product with a purity of 75.9% and a carbon dioxide recovery rate of 33%. The product obtained in Comparative Example 1 had very low carbon dioxide purity and recovery rate, and the primary membrane was severely damaged, exhibiting significant swelling. This is because the lack of pretreatment of C6 and higher organic compounds resulted in damage to the carbon dioxide separation membrane, thus significantly impacting the separation effect. This demonstrates that the shallow-cooled oil absorption unit plays a crucial role in the process technology of this invention.

[0116] 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 membrane separation and recovery of carbon dioxide from oilfield gas, characterized in that, The method includes: (1) The oilfield gas is subjected to shallow cooling oil absorption to obtain oil and the first mixed gas; (2) The first mixed gas is separated by membrane separation to obtain permeate gas and residual gas; (3) Separate the gas on the permeate side into liquid and liquid phases. The liquid phase is returned to the shallow cold oil absorption step in step (1), and the gas phase is used as fuel gas. The absorbent used in the shallow cold oil absorption is selected from C3-C4 organic compounds; the shallow cold oil absorption is carried out in an absorption tower; the pressure of the gas phase feed tray of the absorption tower is 100-1000 kPa; the pressure of the liquid phase feed tray of the absorption tower is 500-1000 kPa; and the temperature of the absorption tower is -20℃ to 10℃. The separation membrane used for membrane separation is selected from a separation composite membrane comprising a support layer, a silicone rubber intermediate layer and a polymer layer stacked sequentially; the crosslinked polymer constituting the polymer layer comprises structural unit I from a polyamine compound, structural unit II from a polyacrylamide compound and structural unit III from a polyphenol compound; The crosslinked polymer further comprises the general formula The connecting group a shown connects structural unit I and structural unit II, with the general formula [missing information]. The connecting group b shown connects the structural unit II and the structural unit III; in step (2), the separation membrane used in the membrane separation has a carbon dioxide flux of 300-800 GPU and a carbon dioxide / nitrogen separation coefficient of 40-80. The carbon dioxide content in the oilfield gas is 50-80 vol.

2. The method according to claim 1, wherein, In step (1), the absorption tower is selected from packed tower, plate tower, spray tower, bubble tower or liquid column tower.

3. The method according to claim 2, wherein, The absorption tower is a packed tower.

4. The method according to any one of claims 1-3, wherein, In step (1), the absorbent used for the shallow cold oil absorption is a C4 absorbent.

5. The method according to claim 1, wherein, In step (2), the pressure on the positive pressure side of the membrane separation is 100-2000 kPa.

6. The method according to claim 5, wherein, In step (2), the pressure on the positive pressure side of the membrane separation is 300-1500 kPa.

7. The method according to claim 5, wherein, In step (2), the permeate side pressure of the membrane separation is lower than the positive pressure side pressure.

8. The method according to claim 1, wherein, In step (3), the gas-liquid separation method is condensation, and the condensation temperature is -20℃ to 15℃.

9. The method according to claim 1, wherein, In step (3), the gas-liquid separation method is condensation, and the condensation temperature is -10℃ to 10℃.

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