Combined absorbent for removing acid gas and application thereof

Abstract

The application discloses a combined absorbent for removing acid gas and application, and belongs to the field of acid gas removal. The combined absorbent comprises a ring group substituted organic amine, a defoaming agent, a corrosion inhibitor, an oxygen scavenger, an organic solvent and a deionized water solvent. The application comprises the following steps: directly using the combined absorbent or using the combined absorbent after dilution with water to remove acid gas in raw material gas. The application of the combined absorbent is simple, low in cost and outstanding in synergistic effect, and especially obvious improvement is achieved in reducing energy consumption, reducing the circulation amount of the absorbent and corrosion of acid gas absorption and regeneration equipment.

Description

Technical Field

[0001] This invention relates to the field of acid gas absorption technology, specifically to a combined absorbent for removing acid gases and its application, wherein the acid gases include CO2, H2S and organic sulfides, and can be applied to the capture of carbon dioxide-like acid gases in natural gas, refinery gas and nitrogen fertilizer plant gas. Background Technology

[0002] Industrial natural gas typically contains high levels of acidic and harmful impurities such as H2S and CO2 during extraction, failing to meet national quality standards. National standard GB 17820-2018 classifies commercial natural gas into Class I and Class II natural gas, with the latter primarily used as residential fuel. To prevent corrosion during gathering, transmission, and distribution, and to ensure the safety and health of personnel and residents, the standard stipulates that the hydrogen sulfide content in Class I and Class II natural gas must not exceed 6 mg / m³. 3 20mg / m 3 The carbon dioxide content must not exceed 3% or 4%. Therefore, natural gas needs to undergo purification treatments such as desulfurization and decarbonization after extraction to prepare it into dry and clean natural gas for use.

[0003] To date, there are no fewer than a hundred desulfurization and decarbonization purification technologies for natural gas, with dozens of them being widely used. The amine-based desulfurization and decarbonization process is not only widely applied to natural gas but also frequently used in the purification of refinery gas and synthetic ammonia industrial gases, as well as in the production of downstream products from syngas. Although other desulfurization and decarbonization processes, such as physical solvent absorption, oxidation-reduction, and modified hot potassium alkali methods, are often employed under specific operating conditions, the amine-based process remains dominant for the purification of natural gas and refinery gas. Especially for natural gas purification units that require large-scale sulfur recovery through subsequent Claus units, the amine-based process can be considered the most effective.

[0004] Alkylamine liquid absorbents for desulfurization and decarbonization utilize chemically active alkyl alcoholamine organic compounds. Internationally, the first method to absorb and regenerate acidic gases through acid-base reactions was to use alkyl alcoholamine organic absorbents such as monoethanolamine (MEA), diethanolamine (DEA), diisopropanolamine (DIPA), and diethylene glycolamine (DGA). These organic absorbents are highly efficient at removing CO2 and H2S, but less efficient at selectively removing H2S and organic sulfur. Furthermore, they suffer from high energy consumption and operating costs for desulfurization and decarbonization, and significant degradation of the organic absorbents and corrosion of equipment. Since 1980, the N-methyl-diethanolamine (MDEA) purification technology has been developed. Due to its advantages of high selectivity, high acid load, low energy consumption, and low corrosivity, it has been widely used in the natural gas purification industry.

[0005] However, because MDEA is a tertiary amine and lacks free hydrogen atoms in its molecule, its reaction rate with CO2 is very slow. For applications requiring deep desulfurization and rapid removal of large quantities of CO2, conventional MDEA absorbents are unsuitable. Therefore, a new approach has emerged: adding a certain amount of highly active DEA, MEA (primary amine), or secondary amine to the tertiary amine MDEA as an activator. These organic alcohol amine activators utilize the rapid reaction of MEA or DEA with CO2 to form carbamates, thereby activating MDEA and acting as a catalyst. This overcomes the shortcomings of solvent-based desulfurization and decarbonization of MDEA, achieving better results. However, the stable carbamates formed by MEA or DEA reacting with CO2 in these absorbents accumulate during long-term regeneration, requiring significant heat for decomposition, leading to high regeneration energy consumption. Simultaneously, carbamates can cause equipment corrosion and scale formation. Furthermore, the presence of carbamates exacerbates the degradation reaction between the alcohol amine absorbent and CO2, resulting in increased absorbent loss, decreased deacidification performance, and increased corrosion of operating equipment.

[0006] Stericly hindered amines, such as CB, possess a high Taft coefficient and exhibit higher selectivity for H2S absorption and greater carbon absorption capacity than MDEA, along with lower regeneration energy consumption. In particular, as a secondary amine, its amino nitrogen atom is bonded to a hydrogen atom and a large nonlinear carbon chain group, which generates a steric hindrance effect, giving the amino group of CB higher activity and selectivity. Furthermore, the intermediate product carbamate formed by combining with CO2 is extremely unstable and rapidly converts to HCO3-. - Due to the high reactivity of amines and the instability of carbamates, sterically hindered amines can absorb CO2 at a ratio of 1 mol / mol amine, with a reaction rate higher than tertiary amines such as MDEA, and a larger carbon capacity. Simultaneously, the regeneration conditions are mild, and carbamate accumulation is low, overcoming various problems caused by the stability of carbamates. CB has a large acid gas load and low regeneration energy consumption (approximately 70% of MDEA's energy consumption), thus showing good application prospects. However, existing sterically hindered amines suffer from limited sources, poor selectivity, and generally limited steric hindrance effects, and are constrained by cost, failing to meet production needs. Summary of the Invention

[0007] In view of the shortcomings of the existing technology, the present invention provides a combined absorbent for removing acidic gases and its application.

[0008] This invention discloses a combined absorbent for removing acidic gases, comprising: a cyclic-substituted organic amine, an antifoaming agent, a corrosion inhibitor, an oxygen scavenger, an organic solvent, and a deionized water solvent.

[0009] As a further improvement to the present invention, by weight percentage

[0010] The content of the cyclic-substituted organic amine is 20-79%;

[0011] The content of the defoamer is 0.01-2%;

[0012] The content of the corrosion inhibitor is 0.01-2%;

[0013] The content of the oxygen scavenger is 0.01-2%;

[0014] The content of the organic solvent is 10-30%;

[0015] The content of the deionized water solvent is 10-30%.

[0016] As a further improvement of the present invention, the cyclic-substituted organic amine is selected from one of the following general structural formulas, or a mixture of two or more in any proportion:

[0017]

[0018] in,

[0019] R1 is selected from one of cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, methyl-substituted cyclopropyl, methyl-substituted cyclobutyl, methyl-substituted cyclopentyl, and methyl-substituted cyclohexyl;

[0020] R2 is selected from one of the following: epoxyethyl, epoxypropyl, epoxybutyl, epoxypentyl, methyl-substituted epoxyethyl, methyl-substituted epoxypropyl, methyl-substituted epoxybutyl, methyl-substituted epoxypentyl, hydroxy-substituted cyclopropyl, hydroxy-substituted cyclobutyl, hydroxy-substituted cyclopentyl, and hydroxy-substituted cyclohexyl.

[0021] As a further improvement to the present invention, the structure of R1 is as follows:

[0022]

[0023] in,

[0024] A can be H or methyl, and at least one A in the cyclic group is methyl.

[0025] As a further improvement to the present invention, the structure of R2 is as follows:

[0026]

[0027] in,

[0028] A is H or methyl, and at least one A in the cyclic group is methyl; B is H or hydroxyl, and at least one B in the cyclic group is hydroxyl.

[0029] As a further improvement of the present invention

[0030] The defoamer is selected from one or a mixture of two of the following in any proportion: polysiloxane, fluorinated polysiloxane, polyether-modified polysiloxane, and polyoxyethylene ether.

[0031] The corrosion inhibitor is selected from one or more of the following: organic imidazoline, inorganic nitrite, tungstate, molybdate, and vanadate, in any proportion;

[0032] The oxygen scavenger is selected from one or a mixture of two of sodium sulfite and sodium thiosulfate in any proportion.

[0033] As a further improvement of the present invention, the organic solvent is selected from one or a mixture of two or more of the following in any proportion: sulfolane, piperazine, ethylene glycol, ethylene glycol dimethyl ether, ethylene glycol monomethyl ether, ethylene glycol diethyl ether, and ethylene glycol monoethyl ether.

[0034] This invention also discloses an application of a combined absorbent, comprising: using the combined absorbent directly or after dilution with water to remove acidic gases from a feed gas; wherein,

[0035] The feed gas includes one or more of natural gas, refinery gas, liquefied petroleum gas and fertilizer plant synthesis gas, and the acid gas includes one or more of hydrogen sulfide, carbon dioxide and organic sulfides. The mass concentration of the combined absorbent after dilution with water is 40-60%.

[0036] As a further improvement of the present invention, the combined absorbent and the raw gas are subjected to desulfurization and decarbonization treatment under conditions of 20-70°C and 0.1-10 MPa; wherein,

[0037] The mass ratio of the combined absorbent to the organic sulfides in the feed gas is 100:(0.1-1);

[0038] The volume ratio of the combined absorbent to hydrogen sulfide in the feed gas is 100:(0.1-40);

[0039] The volume ratio of the combined absorbent to carbon dioxide in the feed gas is 100:(0.1-80).

[0040] As a further improvement of the present invention, it also includes: regenerating the combined absorbent that has absorbed acidic gas, and using the regenerated combined absorbent again to remove acidic gas from the raw material gas; wherein the regeneration pressure is 0.1 to 0.4 MPa and the regeneration temperature is 90 to 130°C.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] The cyclic-substituted organic amine in this invention's combined absorbent possesses advantages similar to sterically hindered amines (CB). The cyclic-substituted secondary organic amine retains an H atom, thus exhibiting the high reactivity of an amino group. The carbamate formed by its reaction with acidic gases is unstable, and its high reactivity ensures rapid reaction with acidic gases such as hydrogen sulfide and carbon dioxide, as well as with organic sulfur impurities in the gas. Simultaneously, when the feed gas has a high sulfur-to-carbon ratio, it can preferentially and deeply desulfurize, demonstrating higher selectivity. Furthermore, the electron-donating nature of the carbon ring in the cyclic substituent group ensures the strong basic activity of the organic amine. The steric hindrance effect of the cyclic substituent makes the intermediate carbamate unstable; that is, the intermediate is easily formed and easily removed, preventing the accumulation of stable salts during operation and solving the problems of scaling, corrosion, and absorbent degradation. At the same time, the high acid gas load reduces the absorbent circulation volume, further lowering operating and maintenance costs and equipment construction expenses. Attached Figure Description

[0043] Figure 1 This is a structural diagram of a device for natural gas desulfurization and decarbonization using a combined absorbent disclosed in this invention.

[0044] In the picture:

[0045] 1. Absorption tower; 2. Regeneration tower; 3. Cooler; 4. Heat exchanger; 5. Pump; 6. Condenser; 7. Boiler. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] The present invention will now be described in further detail with reference to the accompanying drawings:

[0048] This invention provides a combined absorbent for removing acidic gases, comprising: a cyclic-substituted organic amine, an antifoaming agent, a corrosion inhibitor, an oxygen scavenger, an organic solvent, and a deionized water solvent.

[0049] Specifically:

[0050] By weight percentage, the combination absorbent includes:

[0051] The content of cyclic-substituted organic amines is 20-79%;

[0052] The content of defoamer is 0.01-2%;

[0053] The content of corrosion inhibitor is 0.01-2%;

[0054] The content of the oxygen scavenger is 0.01-2%;

[0055] The content of organic solvent is 10-30%;

[0056] The content of deionized water solvent is 10-30%.

[0057] in,

[0058] The cyclic-substituted organic amines of this invention are selected from one of the following general structural formulas, or a mixture of two or more in any proportion:

[0059]

[0060] in,

[0061] R1 is selected from one of cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, methyl-substituted cyclopropyl, methyl-substituted cyclobutyl, methyl-substituted cyclopentyl, and methyl-substituted cyclohexyl; the structure of R1 is:

[0062]

[0063] in,

[0064] A can be H or methyl, and at least one A in the cyclic group is methyl.

[0065] R2 is selected from one of the following: epoxyethyl, epoxypropyl, epoxybutyl, epoxypentyl, methyl-substituted epoxyethyl, methyl-substituted epoxypropyl, methyl-substituted epoxybutyl, methyl-substituted epoxypentyl, hydroxy-substituted cyclopropyl, hydroxy-substituted cyclobutyl, hydroxy-substituted cyclopentyl, and hydroxy-substituted cyclohexyl. The structure of R2 is as follows:

[0066]

[0067] in,

[0068] A is H or methyl, and at least one A in the cyclic group is methyl; B is H or hydroxyl, and at least one B in the cyclic group is hydroxyl.

[0069] The defoamer of this invention is selected from one or a mixture of two of polysiloxanes, fluorinated polysiloxanes, polyether-modified polysiloxanes, and polyoxyethylene ethers in any proportion; the corrosion inhibitor is selected from one or a mixture of two or more of organic imidazoline compounds, inorganic nitrites, tungstates, molybdates, and vanadates in any proportion; and the oxygen scavenger is selected from one or a mixture of two of sodium sulfite and sodium thiosulfate in any proportion.

[0070] The organic solvent of the present invention is selected from one or a mixture of two or more of sulfolane, piperazine, ethylene glycol, ethylene glycol dimethyl ether, ethylene glycol monomethyl ether, ethylene glycol diethyl ether, and ethylene glycol monoethyl ether in any proportion.

[0071] This invention also provides an application of a combination absorbent, which is used in... Figure 1 In the device, the combined absorbent is used directly or diluted with water to remove acidic gases from the feed gas; the combined absorbent that has absorbed acidic gases is regenerated, and the regenerated combined absorbent is used again to remove acidic gases from the feed gas.

[0072] Specifically:

[0073] like Figure 1 As shown, the combined absorbent device for natural gas desulfurization and decarbonization includes: absorber 1, regeneration tower 2, cooler 3, heat exchanger 4, pump 5, condenser 6, and reboiler 7. The connection relationships of absorber 1, regeneration tower 2, cooler 3, heat exchanger 4, pump 5, condenser 6, and reboiler 7 are as follows: Figure 1 As shown; taking purified natural gas as an example, the purification process is as follows: the prepared raw gas (5% CO2, 5% H2S, 1% organic sulfur, 89% CH4) enters the bottom of the absorption tower 1 and comes into countercurrent contact with the fresh absorbent and lean amine absorbent mixture entering from the top of the tower. The acid components CO2, H2S, and organic sulfur in the gas are absorbed. The purified gas exits from the top of the tower and enters the gas-liquid separator, where it is further dehydrated to obtain clean natural gas. The rich amine absorbent that has absorbed the acid components is drawn from the bottom of the absorption tower 1 to the top of the regeneration tower 2, where it is regenerated by countercurrent contact with rising steam. The regenerated lean amine absorbent is cooled and then sent to the top of the absorption tower 1 for circulation absorption. The gas exiting from the top of the regeneration tower enters the next process or is used to recover sulfur.

[0074] in,

[0075] The absorption temperature of the absorption tower is 20–70℃ and the absorption pressure is 0.1–10MPa; the regeneration pressure of the regeneration tower is 0.1–0.4MPa and the regeneration temperature is 90–130℃.

[0076] The mass concentration of the combined absorbent after dilution with water is 40-60%, the mass ratio of the combined absorbent to the organic sulfides in the feed gas is 100:(0.1-1), the volume ratio of the combined absorbent to the hydrogen sulfide in the feed gas is 100:(0.1-40), and the volume ratio of the combined absorbent to the carbon dioxide in the feed gas is 100:(0.1-80).

[0077] Experiment 1

[0078] With a constant absorbent solution circulation volume, at the same absorption and regeneration temperatures, and after running for the same amount of time, the operational performance of different absorbents was analyzed and checked, as shown in Table 1.

[0079] Table 1: Desulfurization, decarbonization, and organic sulfur removal effects of different absorbents

[0080]

[0081]

[0082] The specific formulation of the combined absorbent 1 in Example 1 is as follows: 30% cyclopropylepoxyethyl secondary amine; 0.1% polysiloxane; 0.1% organic imidazoline; 0.1% sodium sulfite; 30% sulfolane; and the remainder is deionized water.

[0083] The specific formulation of the combined absorbent 2 in Example 2 is as follows: cyclopropyl c 35%; polysiloxane 0.1%; organic imidazoline 0.1%; sodium sulfite 0.1%; sulfolane 30%; the remainder is deionized water.

[0084] The specific formulation of the combined absorbent 3 in Example 3 is as follows: 35% cyclopropylmethyl-substituted glycidyl secondary amine; 0.1% polysiloxane; 0.1% organic imidazoline; 0.1% sodium sulfite; 25% piperazine; and the remainder is deionized water.

[0085] The specific formulation of the combined absorbent 4 in Example 4 is as follows: 40% cyclopropylmethyl-substituted glycidyl secondary amine; 0.1% polysiloxane; 0.1% molybdate; 0.1% sodium sulfite; 30% ethylene glycol dimethyl ether; and the remainder is deionized water.

[0086] The specific formulation of the combined absorbent 5 in Example 5 is as follows: 40% methyl-substituted cyclobutylepoxyethyl secondary amine; 0.1% polysiloxane; 0.1% molybdate; 0.1% sodium sulfite; 35% piperazine; and the remainder is deionized water.

[0087] The specific formulation of the combined absorbent 6 in Example 6 is as follows: 30% methyl-substituted cyclobutyl epoxide ethyl secondary amine; 0.1% polysiloxane; 0.1% molybdate; 0.1% sodium sulfite; 40% ethylene glycol monoethyl ether; the remainder is deionized water.

[0088] The specific formulation of the combined absorbent 7 in Example 7 is as follows: 40% cyclopropylepoxyethyl secondary amine; 0.1% polysiloxane; 0.1% organic imidazoline; 0.1% sodium sulfite; 40% sulfolane; and the remainder is deionized water.

[0089] The results show that the combined absorbent of the present invention has better deacidification performance than the traditional MDEA absorbent and sterically hindered amine CB absorbent.

[0090] Experiment 2:

[0091] This experiment evaluates the corrosion of equipment by combined absorbents. L265 steel sheets were used. After degreasing, polishing, drying, and constant weight, the steel sheets were weighed and immersed in an amine absorbent solution at 100℃. A mixed gas (2% CO2, 6% H2S, 92% CH4) was bubbled into the solution at a certain rate for 48 hours. Afterward, the L265 steel sheets were removed, corrosion products on the surface were removed, and the sheets were dried and weighed. The weight loss of the sheets was measured. The corrosion of carbon steel by solutions with different compositions is shown in Table 2.

[0092] Table 2 Comparison of corrosion rates

[0093] Solution composition MDEA 50% CB50% Combined absorbent 3 Corrosion rate, mm / a 0.065 0.059 0.047

[0094] The data in Table 2 show that the corrosivity is reduced when using the combined absorbent of the present invention.

[0095] Experiment 3:

[0096] This experiment evaluated the accumulation of stable salts after 760 hours of operation under the conditions of using a combined absorbent. The accumulation of stable salts in solutions with different compositions is shown in Table 3.

[0097] Table 3 Comparison of the accumulation of stable salts

[0098] Solution composition MDEA 50% CB50% Combined absorbent 3 Combined absorbent 2 Stable salt, % 0.8 0.4 0.3 0.2

[0099] The data in Table 3 show that the stability of salt accumulation is greatly improved when using the combined absorbent of the present invention.

[0100] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A combined absorbent for removing acidic gases, characterized in that, Acidic gases include CO2, H2S, and organic sulfides; the combined absorbent includes: cyclic substituted organic amines, defoamers, corrosion inhibitors, oxygen scavengers, organic solvents, and deionized water solvents; The cyclic-substituted organic amine is selected from one of the following general structural formulas, or a mixture of two or more in any proportion: in, R1 is selected from one of cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, methyl-substituted cyclopropyl, methyl-substituted cyclobutyl, methyl-substituted cyclopentyl, and methyl-substituted cyclohexyl; R2 is selected from one of the following: epoxyethyl, epoxypropyl, epoxybutyl, epoxypentyl, methyl-substituted epoxyethyl, methyl-substituted epoxypropyl, methyl-substituted epoxybutyl, methyl-substituted epoxypentyl, hydroxy-substituted cyclopropyl, hydroxy-substituted cyclobutyl, hydroxy-substituted cyclopentyl, and hydroxy-substituted cyclohexyl.

2. The combined absorbent as described in claim 1, characterized in that, By weight percentage The content of the cyclic-substituted organic amine is 20-79%; The content of the defoamer is 0.01-2%; The content of the corrosion inhibitor is 0.01-2%; The content of the oxygen scavenger is 0.01-2%; The content of the organic solvent is 10-30%; The content of the deionized water solvent is 10-30%.

3. The combined absorbent as described in claim 1 or 2, characterized in that, The structure of R1 is as follows: R1 in, A can be H or methyl, and at least one A in the cyclic group is methyl.

4. The combined absorbent as described in claim 1 or 2, characterized in that, The structure of R2 is as follows: R2 in, A is H or methyl, and at least one A in the cyclic group is methyl; B is H or hydroxyl, and at least one B in the cyclic group is hydroxyl.

5. The combined absorbent as described in claim 1 or 2, characterized in that, The defoamer is selected from one or a mixture of two of the following in any proportion: polysiloxane, fluorinated polysiloxane, polyether-modified polysiloxane, and polyoxyethylene ether. The corrosion inhibitor is selected from one or more of the following: organic imidazoline, inorganic nitrite, tungstate, molybdate, and vanadate, in any proportion; The oxygen scavenger is selected from one or a mixture of two of sodium sulfite and sodium thiosulfate in any proportion.

6. The combined absorbent as described in claim 1 or 2, characterized in that, The organic solvent is selected from one or a mixture of two or more of the following in any proportion: sulfolane, piperazine, ethylene glycol, ethylene glycol dimethyl ether, ethylene glycol monomethyl ether, ethylene glycol diethyl ether, and ethylene glycol monoethyl ether.

7. The application of a combined absorbent as described in any one of claims 1 to 6, characterized in that, include: The combined absorbent is used directly or diluted with water to remove acidic gases from the feed gas; wherein... The feed gas includes one or more of natural gas, refinery gas, liquefied petroleum gas and fertilizer plant synthesis gas, and the acid gas includes one or more of hydrogen sulfide, carbon dioxide and organic sulfides. The mass concentration of the combined absorbent after dilution with water is 40-60%.

8. The application of the combined absorbent as described in claim 7, characterized in that, The combined absorbent and the feed gas are subjected to desulfurization and decarbonization treatment under conditions of 20–70°C and 0.1–10 MPa; wherein, The mass ratio of the combined absorbent to the organic sulfides in the feed gas is 100:(0.1-1); The volume ratio of the combined absorbent to hydrogen sulfide in the feed gas is 100:(0.1-40); The volume ratio of the combined absorbent to carbon dioxide in the feed gas is 100:(0.1-80).

9. The application of the combined absorbent as described in claim 7, characterized in that, Also includes: The combined absorbent that has absorbed acidic gases is regenerated, and the regenerated combined absorbent is used again to remove acidic gases from the feed gas; wherein the regeneration pressure is 0.1 to 0.4 MPa and the regeneration temperature is 90 to 130°C.

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