Natural gas selective desulfurization solvent system as well as preparation method and desulfurization method thereof

Abstract

The invention provides a natural gas selective desulfurization solvent system as well as a preparation method and a desulfurization method thereof. The natural gas selective desulfurization solvent system comprises a basic solvent, a bicyclic amine component and an isoamyl secondary amine component, the isoamyl secondary amine component has a structure shown as a formula I: # imgabs0 #, in the formula I, R1, R2 and R3 are independently selected from H, C1-C5 alkyl and derivatives thereof; the selective desulfurization solvent system for the natural gas can be used for deeply removing hydrogen sulfide and mercaptan from the natural gas, meanwhile, carbon dioxide in purified gas is reserved to the maximum extent, and the commercial gas rate and the acid gas concentration are increased.

Description

Technical Field

[0001] The present invention belongs to the technical field of natural gas desulfurization, and particularly relates to a natural gas selective desulfurization solvent system, a preparation method thereof, and a desulfurization method. Background Art

[0002] Most natural gas contains acidic components such as hydrogen sulfide, carbon dioxide, and organic sulfur (carbonyl sulfide, mercaptan, thioether). The concentration of organic sulfur in sulfur-containing natural gas is mostly below 1000 ppm. Compared with hydrogen sulfide and carbon dioxide, the concentration of organic sulfur is low, the partial pressure is low, and the mass transfer driving force is weak. At the same time, the acidity of organic sulfur is low, and it is difficult to react chemically with alkaline solvents. GB17820-2018 "Natural Gas" has made index requirements for natural gas entering the long-distance pipeline network, among which it is stipulated that the purified gas H2S ≤ 6 mg / m 3 , CO2 ≤ 3%, and total sulfur ≤ 20 mg / m 3 , and strict requirements are mainly made for hydrogen sulfide and total sulfur.

[0003] For the organic sulfur in the raw material gas, especially when the mercaptan content exceeds 500 mg / m 3 , the existing desulfurization technologies are difficult to meet the requirement of total sulfur ≤ 20 mg / m 3 . Moreover, when the existing solvents remove hydrogen sulfide and mercaptan, it is necessary to remove almost all of the carbon dioxide, resulting in problems such as low acid gas concentration in the sulfur recovery unit, high acid gas load of the solution, increased circulation volume, increased steam consumption, and increased operation energy consumption. Summary of the Invention

[0004] In order to solve the above problems, the purpose of the present invention is to provide a natural gas selective desulfurization solvent system, a preparation method thereof, and a desulfurization method. The natural gas selective desulfurization solvent system can be used for deep removal of hydrogen sulfide and mercaptan from natural gas, while maximizing the retention of carbon dioxide in the purified gas, improving the commercial gas rate and acid gas concentration.

[0005] To achieve the above purpose, the present invention provides a natural gas selective desulfurization solvent system, which comprises a basic solvent, a bicyclic amine component, and an isoamyl secondary amine component. The isoamyl secondary amine component has the structure shown in Formula I:

[0006]

[0007] In Formula I, R 1 , R 2 , R 3 are each independently selected from H, C1-C5 alkyl and its derivatives; the bicyclic amine component has the structure shown in Formula II or Formula III:

[0008] Both ends of the molecular structure of the isoamyl secondary amine component of the present invention have amino groups with active hydrogen atoms. The solvent has strong alkalinity and can chemically react with hydrogen sulfide and mercaptan to achieve a better removal effect and improve the removal depth. Under such alkaline conditions, a large amount of CO2 will also be removed by conventional solvents. However, the isoamyl group is present in the molecular structure of the isoamyl secondary amine of the present invention, and the isoamyl group is a steric hindrance group with extremely strong steric hindrance effect. Two isoamyl groups are introduced into the molecular structure of the isoamyl secondary amine of the present invention, which has a hindering effect on CO2 and can reduce the removal of CO2 under high alkaline conditions. Secondly, the isoamyl secondary amine contains a hydroxyl group and has high water solubility. The bicyclic amine component in the desulfurization solvent system helps to provide the H ions required for the nucleophilic substitution reaction. Under the strong alkaline conditions provided by the isoamyl secondary amine, the nitrogen atom in the -NH2 group of the bicyclic amine attacks the sulfur atom in the mercaptan, and a nucleophilic reaction occurs. The sulfur atom and the nitrogen atom form a thiourea group, which can achieve the deep removal of mercaptan.

[0009] According to a specific embodiment of the present invention, preferably, in formula I, R 1 , R 2 , R 3 are each independently selected from H, methyl, and ethyl.

[0010] According to a specific embodiment of the present invention, preferably, the base solvent includes water.

[0011] According to a specific embodiment of the present invention, preferably, calculated based on the mass of the natural gas selective desulfurization solvent system being 100%, the composition of the natural gas selective desulfurization solvent system includes 20% - 50% of the isoamyl secondary amine component, 5% - 10% of the bicyclic amine component, and the balance is the base solvent.

[0012] According to a specific embodiment of the present invention, preferably, the composition of the natural gas selective desulfurization solvent system further includes an ether component.

[0013] According to a specific embodiment of the present invention, preferably, the ether component includes diethylene glycol ethyl ether and / or triethylene glycol ethyl ether.

[0014] The ether component plays a dual role in the desulfurization solvent system. On the one hand, the ether solvent has a greater solubility for organic sulfur than water and plays a role in dissolving organic sulfur. On the other hand, both water and ether are neutral solvents. The autoprotolysis constant and dielectric constant of the solvent itself determine the ease of dissociation of compounds in it. A large dielectric constant can weaken the attraction between opposite charges and contribute to the dissociation of compounds in the solvent. Water autoprotolysis constant: K 自 = [OH - [H + = 10 -14 mol·L -2, the dielectric constant is 78.39. The dielectric constant of ether solvents < 10, which is much smaller than that of water. Therefore, amine compounds are prone to dissociation in water and not prone to dissociation in ether compounds. In the present invention, an ether solvent is added to isopentyl secondary amine, which reduces the dissociation of isopentyl secondary amine to a certain extent, thereby reducing the concentration of ammonium ions in the solution. Compared with carbon dioxide, hydrogen sulfide is more acidic and more likely to react with amines. When the concentration of ammonium ions in the solution decreases, the reaction with H2S will be guaranteed first, and then the reaction with CO2 will occur. Therefore, the concentration of ammonium ions decreases and the removal rate of CO2 by the solvent decreases. After the ether compound is added to the solvent system, it not only improves the removal rate of organic sulfur, but also improves the selectivity and reduces the removal rate of CO2 under the synergistic effect with isopentyl secondary amine, achieving unexpected effects.

[0015] According to a specific embodiment of the present invention, preferably, calculated based on the mass of the natural gas selective desulfurization solvent system being 100%, the composition of the natural gas selective desulfurization solvent system includes 20%-50% of isopentyl secondary amine components, 5%-10% of bicyclic amine components, 10%-40% of ether components, and the balance is the base solvent.

[0016] The present invention also provides a preparation method of the above natural gas selective desulfurization solvent system, which includes the following steps: mixing each component at 20-30 °C for 10-40 min at 30-50 r / min.

[0017] The present invention also provides a natural gas selective desulfurization method, which uses the above natural gas selective desulfurization solvent system.

[0018] According to a specific embodiment of the present invention, preferably, the mercaptan content of the desulfurized feed gas ≥ 500 mg / m 3 .

[0019] The present invention has the following beneficial effects:

[0020] (1) The isopentyl secondary amine in the natural gas selective desulfurization solvent system of the present invention has a strong steric hindrance effect on CO2, which can improve the removal effect of hydrogen sulfide; it contains two secondary amine groups, providing active H atoms, and the solvent has strong alkalinity, and can react chemically with hydrogen sulfide and mercaptans to achieve the purpose of deep removal of hydrogen sulfide and organic sulfur;

[0021] (2) The bicyclic amine in the natural gas selective desulfurization solvent system of the present invention, with the help of the H ions provided by isopentyl secondary amine, the nitrogen atom in the -NH2 group attacks the sulfur atom in mercaptan to undergo a nucleophilic reaction to form a thioureido group, thereby further increasing the removal depth of mercaptan;

[0022] (3) The ether compound in the natural gas selective desulfurization solvent system of the present invention, on the one hand, improves the solubility of the solvent in organic sulfur, and on the other hand, reduces the concentration of ammonium ions ionized from isoamyl secondary amine, thereby reducing the absorption of CO2, which helps to retain CO2 in the purified gas;

[0023] (4) The natural gas selective desulfurization solvent system of the present invention can selectively remove hydrogen sulfide and mercaptan in the raw material gas, and minimize the absorption of carbon dioxide. It is applicable to the gas quality with mercaptan as the main component in the raw material gas, especially when the mercaptan content is as high as 500 mg / m 3 or more. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a process flow chart of the desulfurization effect evaluation device.

[0025] Figure 2 It is the NMR spectrum of isoamyl secondary amine. DETAILED DESCRIPTION OF THE INVENTION

[0026] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solutions of the present invention are described in detail below, but it should not be construed as a limitation on the scope of implementation of the present invention.

[0027] The following evaluation methods for removing hydrogen sulfide, carbon dioxide and mercaptan: The process flow of the desulfurization effect evaluation device is as Figure 1As shown in the figure, natural gas, H2S, CO2 and organic sulfur are mixed in a mixing tank and then pressurized by a compressor to the pressure required for the test; the purified gas coming out of the top of the absorption tower is separated by a separator and then measured by a gas meter; the rich liquid coming out of the bottom of the absorption tower enters the regeneration tower for regeneration after flashing in a rich liquid flash tank and preheating in a preheating tank, and the regenerated lean liquid is pumped into the absorption tower for recycling by a pump. By sampling, the components of the raw gas and the purified gas are analyzed by chromatography. The purified natural gas with a pressure of 6 MPa and a temperature of 20 °C is mixed with gases such as H2S, CO2, and organic sulfur from the gas storage cylinder in the raw gas mixing tank, and then enters the raw gas preheating tank. After the raw gas is compressed to the experimental pressure by a natural gas compressor, it enters the bottom of the absorption tower. The natural gas flows upward. The flow rate of the raw gas is 400 L / h and it contacts the desulfurization solution flowing from top to bottom. The desulfurization solution enters the absorption tower from a packing height of 1.0 m. The temperature of the lean liquid is 40 °C and the circulation rate is 2.0 L / h. H2S, CO2, and organic sulfur are removed therefrom. The lean liquid enters the absorption tower from the lean liquid inlet. The purified natural gas that has removed all H2S and part of CO2 flows out of the top of the tower, is separated from the carried liquid droplets by a purified gas separator, and then enters the natural gas pressure regulating device. After the pressure is reduced, it returns to the intake system. The rich liquid flowing out of the bottom of the absorption tower is depressurized to 0.5 - 0.6 MPa by a liquid level regulating valve and then enters the flash tank. Part of the dissolved natural gas flashes out of the rich liquid in the flash tank. The rich liquid exits the flash tank and enters the rich liquid preheating tank to be heated to 90 °C, and then enters the upper part of the regeneration tower. The rich liquid flows from top to bottom and contacts the steam rising from bottom to top in a countercurrent manner, and H2S, CO2, and organic sulfur are desorbed therefrom. The heat required for regeneration is provided by an electric heating wire at the bottom of the regeneration tower. The temperature of the regenerated lean liquid is 120 - 140 °C, which is led out from the bottom of the regeneration tower, exchanges heat with fresh water in a lean liquid cooler, and the temperature drops to 40 °C and then flows into the lean liquid buffer tank. After being pressurized by a circulation pump, it enters the lean liquid preheating tank for preheating, and then is pumped into the upper part of the absorption tower to complete the circulation of the entire solution. The acid gas is condensed and cooled to 40 °C at the top of the regeneration tower, enters the acid gas separator, and a small amount of acid water is separated. The acid gas exits the acid gas separator and is transported to the burning system for burning and then discharged into the atmosphere.

[0028] Isoamyl secondary amine (C 14 H 32 ON2) Preparation method: The molar ratio of 1,4-dichloro-2-butanol to 2-aminopentane is 1:3. The reaction is carried out in a reaction kettle. The reaction temperature is 140 - 200 °C, the reaction time is 2 - 4 h, the reaction solvent is ethanol, and the molar ratio of ethanol to 1,4-dichloro-2-butanol is 1.5:1. After the reaction is completed, an aqueous sodium hydroxide solution is added, and the reflux reaction is carried out at a temperature of 70 - 90 °C for 4 - 6 h. The molar ratio of sodium hydroxide to 1,4-dichloro-2-butanol is 2.5:1. After the reflux reaction is completed, filtration is carried out under normal pressure, the filtrate is collected, and then vacuum distillation is carried out to collect the fraction to obtain the target product. The yield of the target product is about 65%, and the NMR spectrum of the product is as shown in Figure 2 shown. Other isoamyl secondary amines are synthesized by referring to this method.

[0029] Example 1

[0030] This example provides a natural gas selective desulfurization solvent system. By mass percentage, the solvent system of this example includes the following components: isoamyl secondary amine C 14 H 32 ON2 50% (R1, R2, and R3 are all H), 1-azabicyclo[2.2.1]-3-heptanamine (cas: 773056-73-8) 10%, deionized water 40%. The preparation process of the desulfurization solvent system is as follows: Mix each component at 25°C for 20 min at 40 r / min. The effects of the solvent system on removing hydrogen sulfide, carbon dioxide, and mercaptan are shown in Table 1 below.

[0031] Table 1 Desulfurization effect of Example 1

[0032]

[0033] Example 2

[0034] This example provides a natural gas selective desulfurization solvent system. By mass percentage, the solvent system of this example includes the following components: isoamyl secondary amine C 14 H 32 ON2 50% (R1, R2, and R3 are all H), 1-azabicyclo[2.2.1]-3-heptanamine 10%, triethylene glycol ethyl ether 20%, deionized water 20%. The preparation process of the desulfurization solvent system is as follows: Mix each component at 25°C for 20 min at 40 r / min. The effects of the solvent system on removing hydrogen sulfide, carbon dioxide, and mercaptan are shown in Table 2 below.

[0035] Table 2 Desulfurization effect of Example 2

[0036]

[0037]

[0038] Example 3

[0039] This example provides a natural gas selective desulfurization solvent system. By mass percentage, the solvent system of this example includes the following components: isoamyl secondary amine C 16 H 36 ON2 50% (in this structure, R1 and R3 are CH3, and R2 is H), 1-azabicyclo[2.2.1]-3-heptanamine 10%, triethylene glycol ethyl ether 20%, deionized water 20%. The preparation process of the desulfurization solvent system is as follows: Mix each component at 25°C for 20 min at 40 r / min. The effects of the solvent system on removing hydrogen sulfide, carbon dioxide, and mercaptan are shown in Table 3 below.

[0040] Table 3 Desulfurization effect of Example 3

[0041]

[0042] Comparative Example 1

[0043] The Sulfinol-X solution developed by Shell is specifically used for the removal of organic sulfur. According to the solution ratio of Sulfinol-X, by mass percentage, the solvent system of the comparative example includes the following components: 40% MDEA, 7% piperazine, 30% sulfolane, and 23% deionized water. The effects of this solvent system on the removal of hydrogen sulfide, carbon dioxide, and mercaptan were evaluated as shown in Table 4 below.

[0044] Table 4 Desulfurization effect of Comparative Example 1

[0045]

[0046] Comparative Example 2

[0047] This comparative example provides a natural gas selective desulfurization solvent system. By mass percentage, the solvent system of this comparative example includes the following components: isoamyl secondary amine C 14 H 32 ON2 50% (R1, R2, and R3 are all H), and 50% deionized water. The preparation process of the desulfurization solvent system is as follows: Mix each component at 25°C for 20 minutes at 40 r / min. The effects of this solvent system on the removal of hydrogen sulfide, carbon dioxide, and mercaptan were evaluated as shown in Table 5 below.

[0048] Table 5 Desulfurization effect of Comparative Example 2

[0049]

[0050] As can be seen from the above, the natural gas selective desulfurization solvent system of the present invention can selectively remove hydrogen sulfide and mercaptan in the raw gas and minimize the absorption of carbon dioxide.

Claims

1. A natural gas selective desulfurization solvent system, whose composition includes a basic solvent, a bicyclic amine component and an isoamyl secondary amine component, and the isoamyl secondary amine component has the structure shown in Formula I: In Formula I, R 1 , R 2 , R 3 are each independently selected from H, C1-C5 alkyl and its derivatives; The bicyclic amine component has the structure shown in Formula II or Formula III:

2. The natural gas selective desulfurization solvent system according to claim 1, wherein In formula I, R 1 , R 2 , R 3 are each independently selected from H, methyl, and ethyl.

3. The natural gas selective desulfurization solvent system according to claim 1, wherein, The basic solvent includes water.

4. The natural gas selective desulfurization solvent system according to claim 1, wherein, Calculated based on the mass of the natural gas selective desulfurization solvent system being 100%, the composition of the natural gas selective desulfurization solvent system includes 20%-50% of the isoamyl secondary amine component, 5%-10% of the bicyclic amine component, and the balance is the basic solvent.

5. The natural gas selective desulfurization solvent system according to claim 1, wherein The composition of the natural gas selective desulfurization solvent system further includes an ether component.

6. The natural gas selective desulfurization solvent system according to claim 5, wherein, The ether component includes diethylene glycol ethyl ether and / or triethylene glycol ethyl ether.

7. The natural gas selective desulfurization solvent system according to claim 5, wherein, Calculated based on the mass of the natural gas selective desulfurization solvent system being 100%, the composition of the natural gas selective desulfurization solvent system includes 20%-50% of the isoamyl secondary amine component, 5%-10% of the bicyclic amine component, 10%-40% of the ether component, and the balance is the basic solvent.

8. A method for preparing the natural gas selective desulfurization solvent system according to any one of claims 1-7, comprising the following steps: Mix each component at 30 - 50 r / min at 20 - 30 °C for 10 - 40 min.

9. A natural gas selective desulfurization method, which is carried out using the natural gas selective desulfurization solvent system according to any one of claims 1 - 7.

10. The natural gas selective desulfurization method according to claim 9, wherein, The mercaptan content of the desulfurized raw gas ≥ 500 mg / m 3 .

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