Carbon dioxide absorbent based on piperazine derivatives, and preparation method and application thereof

Abstract

The application provides a kind of carbon dioxide absorbent based on piperazine derivative and preparation method and application, it is related to carbon dioxide capture technical field, the absorbent is piperazine derivative as main absorbent, including not less than 19% by mass fraction N-(2-hydroxyethyl) piperazine and / or N,N'-dihydroxyethyl piperazine, not more than 17% piperazine, not more than 1% N-hydroxyethyl-N'-hydroxyethoxyethyl piperazine, not less than 59% water.The application also provides a kind of preparation method of the absorbent.The absorbent provided by the application has good carbon dioxide absorption effect, low foaming, high cycle load and low regeneration energy consumption and other advantages.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of carbon dioxide capture, in particular to a carbon dioxide absorbent based on piperazine derivatives, and a preparation method and application thereof. BACKGROUND

[0002] With the increasing of CO2 emissions year by year, carbon capture and storage (CCS) is considered as an effective technology to reduce atmospheric CO2 levels, and is increasingly applied to industrial carbon capture. Among them, compared with other carbon capture technologies, post-combustion CO2 capture (PCC) based on amine method is easy to modify the existing power plant, can handle large flow gas, and can achieve efficient CO2 separation at low pressure, and is the most widely used capture method for reducing greenhouse gas emissions of thermal power plants, cement and iron plants.

[0003] In the prior art, solvent absorption carbon capture technology is the mainstream technology at present. Among them, ethanolamine (MEA) has become the main absorbent in the carbon dioxide absorbent due to its low cost and good absorption effect. However, ethanolamine has small absorption load, high saturated vapor pressure and is easy to degrade, which has obvious problems of aggravating equipment corrosion and causing solution foaming, which is not conducive to stable production. SUMMARY

[0004] The purpose of the present application is to provide a carbon dioxide absorbent based on piperazine derivatives, which has good carbon dioxide absorption effect, low foaming, high cycle load and low regeneration energy consumption and other advantages.

[0005] One of the purposes of the present application is to provide a preparation method of a carbon dioxide absorbent based on piperazine derivatives.

[0006] Another purpose of the present application is to provide an application of a carbon dioxide absorbent based on piperazine derivatives.

[0007] In the first aspect, in order to solve the above problems, the present application provides a carbon dioxide absorbent based on piperazine derivatives, taking piperazine derivatives as the main absorbent, including not less than 19% of N-(2-hydroxyethyl) piperazine and / or N,N'-dihydroxyethyl piperazine, not more than 17% of piperazine, not more than 1% of N-hydroxyethyl-N'-hydroxyethoxyethyl piperazine, and not less than 59% of water.

[0008] Further, in some embodiments of the present application, the carbon dioxide absorbent includes N-(2-hydroxyethyl) piperazine and N,N'-dihydroxyethyl piperazine, and the mass fraction of the N-(2-hydroxyethyl) piperazine and the N,N'-dihydroxyethyl piperazine in the carbon dioxide absorbent accounts for 19-35% of the total.

[0009] Further, in some embodiments of the present application, the carbon dioxide absorbent comprises the following components in mass fraction:

[0010] N-(2-hydroxyethyl)piperazine 15-35%

[0011] N,N'-dihydroxyethylpiperazine 0-6%

[0012] Piperazine 4-17%

[0013] N-hydroxyethyl-N'-hydroxyethoxyethylpiperazine 0-1%

[0014] Water 59-64%.

[0015] Further, in some embodiments of the present application, the carbon dioxide absorbent is directly prepared from piperazine and ethylene oxide.

[0016] In a second aspect, the present application further provides a preparation method of a carbon dioxide absorbent based on piperazine derivatives, comprising the following steps:

[0017] providing a piperazine aqueous solution and ethylene oxide;

[0018] contacting and reacting the piperazine aqueous solution and ethylene oxide, when the concentration of N-(2-hydroxyethyl)piperazine in the reaction system exceeds 15% in mass fraction, cooling and adding piperazine to make the concentration of piperazine in the reaction system 4-17% in mass fraction, and then continuing the reaction to obtain a carbon dioxide absorbent;

[0019] wherein the obtained carbon dioxide absorbent comprises not less than 19% of N-(2-hydroxyethyl)piperazine and / or N,N'-dihydroxyethylpiperazine, not more than 17% of piperazine, not more than 1% of N-hydroxyethyl-N'-hydroxyethoxyethylpiperazine, and not less than 59% of water in mass fraction.

[0020] Further, in some embodiments of the present application, when the piperazine is added, the amount of added piperazine is 23-33% of the content of piperazine in the initially added piperazine aqueous solution.

[0021] Further, in some embodiments of the present application, the cooling amplitude is 10-20°C.

[0022] Further, in some embodiments of the present application, contacting and reacting the piperazine aqueous solution and ethylene oxide specifically comprises the following steps:

[0023] placing the piperazine aqueous solution in a reaction container; and injecting ethylene oxide gas under the protection of gas at a pressure of 0.05-0.1 MPa and at a temperature of 40-55°C to contact and react the piperazine with the ethylene oxide.

[0024] Further, in some embodiments of the present application, the amount of ethylene oxide introduced per hour is 4-5% of the mass of piperazine in the aqueous piperazine solution initially added to the reaction vessel; the concentration of piperazine in the aqueous piperazine solution is 35-45% by mass.

[0025] In a third aspect, the present application also provides the use of the piperazine derivative-based carbon dioxide absorbent of the first aspect or the carbon dioxide absorbent prepared by the preparation method of the second aspect in the field of carbon dioxide capture.

[0026] The carbon dioxide concentration of the flue gas is 3-20%, and the carbon dioxide capture temperature is 35-45°C.

[0027] The present application provides a piperazine derivative-based carbon dioxide absorbent, which uses piperazine derivatives as the main absorbent and controls the ratio of N-(2-hydroxyethyl) piperazine, N,N'-dihydroxyethyl piperazine, N-hydroxyethyl-N'-hydroxyethoxyethyl piperazine, and piperazine to form a specific absorbent system that does not require the addition of other auxiliary absorbents. The absorbent system has good operational stability, avoids salt precipitation after absorption, does not crystallize under all operating conditions, has a CO2 removal efficiency of ≥90%, has a high cycle load, greatly reduces the regeneration energy consumption, and reduces the regeneration energy consumption of 30% ethanolamine by 38%.

[0028] The present application also provides a preparation method of a piperazine derivative-based carbon dioxide absorbent, which directly reacts piperazine and ethylene oxide as raw materials without the need for compounding various piperazine derivatives and piperazine, thereby omitting the separate synthesis and purification processes of various piperazine derivatives required for the formation of an absorbent by compounding high-purity piperazine derivatives. The method only needs to be prepared once to obtain the required absorbent, thereby reducing production costs and cycle time, and the process is simple and economical, which greatly reduces the capture cost of carbon dioxide by absorption and promotes the commercial application of piperazine derivative-based carbon dioxide absorbents. DETAILED DESCRIPTION

[0029] The technical solutions of the present application will be described below in conjunction with the embodiments. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application.

[0030] The disclosure below provides many different embodiments or examples for implementing different structures of the application. For the sake of brevity and clarity, descriptions of all possible combinations are not provided in the disclosure. Of course, it is contemplated that the application can be practiced with many other system configurations, including those in addition to the examples mentioned above. It is intended to include all possible combinations of the conditions disclosed and / or enabled in the present disclosure.

[0031] The application of piperazine and its derivatives in CO2 capture has a long history. Patent CN1057018C discloses that a piperazine compound or derivative aqueous solution is contacted with combustion exhaust gas at atmospheric pressure to remove CO2 in the exhaust gas. Piperazine, 2-methylpiperazine, 2,3-dimethylpiperazine, etc. are used as absorbent components to capture CO2. However, with the application of piperazine and its derivatives, researchers have found that piperazine and its derivatives have defects as carbon dioxide capture absorbents. It is difficult to form a single product during synthesis, purification is difficult, the cost is high, additional energy is required for dissolution, and it is difficult to be widely used. Therefore, piperazine and its derivatives gradually evolved into auxiliary absorbents or additives of carbon dioxide absorbents, and carbon dioxide absorbents based on alkali metal carbonates with ethanolamine (MEA) as the main absorbent became the mainstream. For example, CN102762293B discloses a carbon dioxide absorbent based on alkali metal carbonate with a piperazine steric hindered cyclic amine as an additive, and CN117046266A studies an alcohol amine carbon dioxide absorbent with N,N'-dihydroxyethylpiperazine and piperazine as an activator. In addition, the applicant has found that the effects of piperazine and its derivatives as carbon dioxide absorbents are not completely the same, and some piperazine derivatives can even have adverse effects. Therefore, based on this problem, the applicant proposes a carbon dioxide absorbent that can be prepared and has good carbon dioxide absorption effect, low foaming, high cycle load, and low regeneration energy consumption. The carbon dioxide absorbent uses a specific piperazine derivative as the main absorbent, and controls the content of piperazine derivatives that are not conducive to long-term stable use of the absorbent and regeneration, so that the formed absorbent not only has good carbon dioxide absorption effect, but also has small foaming tendency, is not easy to crystallize, is conducive to long-term stable use, and has small regeneration energy consumption, which is conducive to widespread use.

[0032] Specifically, the carbon dioxide absorbent based on piperazine derivatives provided by the present application comprises: not less than 19% of N-(2-hydroxyethyl)piperazine and / or N,N'-dihydroxyethylpiperazine, not more than 17% of piperazine, not more than 1% of N-hydroxyethyl-N'-hydroxyethoxyethylpiperazine, and not less than 59% of water.

[0033] In the present application, N-(2-hydroxyethyl)piperazine and / or N,N'-dihydroxyethylpiperazine are used as the main absorbent of the absorbent, piperazine is also used as one of the absorbents, and the content of piperazine and the content of N-hydroxyethyl-N'-hydroxyethoxyethylpiperazine are controlled to be not higher than 1%, based on the formula of the absorbent, the problem of crystallization precipitation, salt precipitation after absorbing carbon dioxide, and the tendency of foaming are avoided, and the decarbonization rate is good and the energy consumption of regeneration is low.

[0034] [N-(2-hydroxyethyl)piperazine and N,N'-dihydroxyethylpiperazine]

[0035] The carbon dioxide absorbent provided by the present application comprises N-(2-hydroxyethyl)piperazine and / or N,N'-dihydroxyethylpiperazine, and the total mass fraction of the N-(2-hydroxyethyl)piperazine and the N,N'-dihydroxyethylpiperazine in the carbon dioxide absorbent is 19-35%. For example, in some embodiments of the present application, the total mass fraction of the N-(2-hydroxyethyl)piperazine and the N,N'-dihydroxyethylpiperazine in the carbon dioxide absorbent can be 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, or 35%, and all ranges and sub-ranges between the above-mentioned values. It should be understood that in the embodiments, any of the above-mentioned ranges can be combined with any other range.

[0036] Preferably, the carbon dioxide absorbent provided by the present application comprises N-(2-hydroxyethyl)piperazine and N,N'-dihydroxyethylpiperazine. The applicant found that N,N'-dihydroxyethylpiperazine has a large carbon dioxide absorption capacity, but the absorption rate is low, and if N-(2-hydroxyethyl)piperazine is introduced on this basis and the ratio of N-(2-hydroxyethyl)piperazine to N,N'-dihydroxyethylpiperazine is controlled, a synergistic effect can be produced, so that the absorbent has both absorption rate and absorption load.

[0037] For example, the mass fraction of N-(2-hydroxyethyl)piperazine in the carbon dioxide absorbent provided by the present application is 15-35% (not including 35%), and the mass fraction of N,N'-dihydroxyethylpiperazine is 0-6% (not including 0%).

[0038] Exemplarily, in some embodiments of the present application, the content of N-(2-hydroxyethyl)piperazine in the absorbent can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34% or 34.5% and all ranges and sub-ranges between the above-mentioned values in terms of mass fraction. It should be understood that in the embodiments, any of the above-mentioned ranges can be combined with any other range. The content of N,N'-dihydroxyethylpiperazine in the absorbent can be 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0% or 5.5% and all ranges and sub-ranges between the above-mentioned values in terms of mass fraction. It should be understood that in the embodiments, any of the above-mentioned ranges can be combined with any other range. However, it should be noted that in some preferred embodiments, when the absorbent simultaneously includes N-(2-hydroxyethyl)piperazine and N,N'-dihydroxyethylpiperazine, the total amount of the two needs to be controlled in the range of 19-35%.

[0039] [piperazine]

[0040] Piperazine is a commonly used carbon dioxide absorption activator, which can effectively improve the carbon dioxide absorption rate of the aqueous solution of piperazine derivatives. However, when the residual amount of piperazine is too much, the rich solution after absorbing CO2 may form salt and precipitate, and the absorbent is easy to crystallize. The applicant found that when the mass fraction of piperazine is controlled within 17%, not only can the carbon dioxide absorption rate be effectively improved, but also the non-crystallization effect under full working condition can be achieved. Therefore, in the present application, the content of piperazine in the absorbent is not higher than 17% in terms of mass fraction, preferably 4% to 17%, and more preferably 8% to 17%. Exemplarily, in some embodiments of the present application, the content of piperazine in the absorbent can be 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16% or 17% and all ranges and sub-ranges between the above-mentioned values. It should be understood that in the embodiments, any of the above-mentioned ranges can be combined with any other range.

[0041] [N-hydroxyethyl-N'-hydroxyethoxyethylpiperazine]

[0042] Applicants found that although N-hydroxyethyl-N'-hydroxyethoxyethyl piperazine is also one of the derivatives of piperazine, its presence in the absorbent does not significantly improve the absorption rate or absorption load, etc. On the contrary, the excessive N-hydroxyethyl-N'-hydroxyethoxyethyl piperazine present can cause the absorbent to foam significantly. Applicants found that on the basis of the above component control, the content of N-hydroxyethyl-N'-hydroxyethoxyethyl piperazine is controlled to be ≤1%, which can reduce the foaming ability of the absorbent. Preferably, the mass fraction of N-hydroxyethyl-N'-hydroxyethoxyethyl piperazine in the absorbent is controlled to be within 0.5%.

[0043] [water]

[0044] The solvent in the absorbent in the present application is water, wherein the water can be added in the form of raw material solvent during the raw material addition process, water generated during the raw material reaction process, and additional water. The mass fraction of the solvent water is controlled to be within the range of not less than 59%, which can provide the absorbent with activation function and low viscosity. Preferably, the mass fraction of the solvent water is 59% to 64%. Exemplarily, in some embodiments of the present application, the content of water in the absorbent can be: 59%, 60%, 61%, 62%, 63% or 64%, and all ranges and sub-ranges between the above-mentioned values. It should be understood that in the embodiments, any of the above-mentioned ranges can be combined with any other range.

[0045] [other]

[0046] The absorbent provided by the present application can also contain a certain amount of other impurities, such as residual ethylene oxide during the raw material reaction process. When the other impurities are residual ethylene oxide, the amount of ethylene oxide is not more than 1% in mass fraction, preferably not more than 0.8%. In addition, the above-mentioned carbon dioxide absorbent provided by the present application can also be directly prepared from piperazine and ethylene oxide as raw materials, without the need to obtain N-(2-hydroxyethyl) piperazine, N,N'-dihydroxyethyl piperazine, and piperazine by separate preparation and purification, which reduces the energy consumption for reagent purification and dissolution compared to the current compounding preparation, and greatly reduces the cost of the absorbent.

[0047] For this purpose, the present application also provides a preparation method of the above-mentioned carbon dioxide absorbent, which specifically comprises the following steps:

[0048] providing a piperazine aqueous solution and ethylene oxide;

[0049] contacting and reacting the piperazine aqueous solution and ethylene oxide, when the concentration of N-(2-hydroxyethyl) piperazine in the reaction system exceeds 15% in mass fraction, cooling and adding piperazine to make the concentration of piperazine in the reaction system be 4 to 17% in mass fraction, and then continuously reacting to obtain the carbon dioxide absorbent.

[0050] It should be noted that the concentration of the piperazine aqueous solution initially added into the container for contacting reaction of piperazine and ethylene oxide is 35-45% by mass fraction, and it is not suitable to be higher or lower, and higher or lower piperazine aqueous solution concentration can easily lead to the difficulty of achieving the required concentration of each component in the product obtained.

[0051] The container for contacting reaction of piperazine and ethylene oxide is filled with protective gas such as nitrogen before the reaction of the reaction system, so as to discharge oxygen, and the partial pressure of the protective gas is maintained at 0.05-0.1 MPa during the reaction of the reaction system.

[0052] The feeding rate of the ethylene oxide gas is controlled at 4-5% of the mass of piperazine in the initial piperazine solution per hour, which is beneficial to control the heat release of the system reaction, so that the temperature of the reaction system can be easily and stably controlled at 40-55°C, and the gas pressure in the reaction container can also be easily controlled within the range of 0.05-0.1 MPa of the partial pressure of the protective gas.

[0053] When the concentration of N-(2-hydroxyethyl)piperazine in the reaction system exceeds 15% by mass fraction after the contacting and reaction of the piperazine aqueous solution and ethylene oxide, the reaction system is cooled by 10-20°C, so that the temperature of the reaction system is within the range of 30-40°C or close to this range, and then piperazine is added to the reaction system. The added piperazine can be added in the form of an initial piperazine aqueous solution with the same concentration, or in the form of a piperazine aqueous solution with a higher concentration or pure piperazine. The amount of piperazine added is 23-33% of the mass of piperazine in the initial piperazine aqueous solution. Taking 100 g of piperazine in the initial piperazine aqueous solution as an example, the mass of piperazine in the added piperazine system is 23-33 g.

[0054] After the addition of piperazine, the ethylene oxide gas is continuously fed, and the reaction is continued until the obtained carbon dioxide absorbent contains not less than 19% of N-(2-hydroxyethyl)piperazine and / or N,N'-dihydroxyethylpiperazine by mass fraction, not more than 17% of piperazine, not more than 1% of N-hydroxyethyl-N'-hydroxyethoxyethylpiperazine, and not less than 59% of water.

[0055] During the process, the rate of ethylene oxide gas can remain unchanged, or can be appropriately adjusted in the range of 4-5% of the mass of piperazine in the initial aqueous piperazine solution. When the components in the reaction system approach the desired component content of the carbon dioxide absorbent described above, the introduction of ethylene oxide can be stopped in advance, and the residual ethylene oxide in the reaction system continues to react, thereby reducing the content of ethylene oxide in the product. In some specific embodiments, the aqueous piperazine solution and ethylene oxide are contacted and reacted until the concentration of N-(2-hydroxyethyl)piperazine in the reaction system exceeds 15% by mass, and the reaction time at this stage is usually 6-8 h, and after the addition of piperazine, the reaction time to obtain the product is usually 5-7 h; the ethylene oxide can be stopped 1-3 h before the end of the reaction, i.e., the ethylene oxide is introduced for 11-13 h, and the introduction of ethylene oxide gas can be stopped, and the reaction can be continued for 1-3 h after the introduction of ethylene oxide is stopped, thereby obtaining the carbon dioxide absorbent of the present application.

[0056] It should be noted that after the addition of piperazine, the reaction temperature is also controlled in the range of 10-20°C lower than the reaction temperature of the initial aqueous piperazine solution with ethylene oxide, so as to reduce the side reactions of ethylene oxide and hydroxyethylpiperazine and slow down the generation of dihydroxyethylpiperazine, so that the content of each component in the obtained carbon dioxide absorbent is controlled in the desired range.

[0057] In a third aspect, the present application also provides the use of the carbon dioxide absorbent based on piperazine derivatives of the first aspect or the carbon dioxide absorbent based on piperazine derivatives prepared by the preparation method of the second aspect in the field of carbon dioxide capture.

[0058] When the carbon dioxide absorbent is applied in the field of carbon dioxide capture, the application process is the prior art, for example: the absorbent provided by the present application is contacted with the gas to be treated in a countercurrent manner in a packed tower at a certain temperature, and then flows out from the bottom of the tower into a lean- rich liquid heat exchanger, and then the rich liquid after absorbing CO2 enters a desorption tower for regeneration, and then returns to the absorption tower after desorption, and the cycle is repeated.

[0059] Preferably, the carbon dioxide capture process conditions are as follows: the CO2 concentration of the flue gas is 3-20%, the rest is nitrogen or air, the absorption temperature is 35-45°C, the desorption temperature is 105-115°C, and the liquid-gas ratio is 3.0-6.0 L / Nm 3 .

[0060] In order to facilitate those skilled in the art to better understand the innovative points of the present application, the technical solutions of the present application are further described in detail below in combination with embodiments. The embodiments of the present application described in detail below are exemplary and are used to explain the present application, and cannot be understood as a limitation of the present application.

[0061] Example 1

[0062] A solution was prepared by mixing 200 g hexa-8-azapiperazine and 350 g deionized water, and then the solution was transferred into a reactor. The air in the reactor was replaced with N2, and then the pressure was maintained at 0.05 MPa. The temperature of the reactor was controlled at 40 °C by using a thermostat, and the stirring was started. 8 g of ethylene oxide was introduced into the reactor per hour, and the temperature of the reactor was controlled at 40 °C during the introduction. After 6 h of the introduction of ethylene oxide, the temperature of the reactor was decreased to 30 °C, and 66 g of hexa-8-azapiperazine was added. The introduction of ethylene oxide was stopped after 11 h, and the temperature of the reactor was maintained at 30 °C for 2 h. The carbon dioxide absorbent was obtained. The product was analyzed by moisture test and GC, and the results were as follows: hydroxyethylpiperazine 15.52%, dihydroxyethylpiperazine 4.19%, piperazine 16.20%; moisture content 63.12%, unreacted ethylene oxide 0.18%, and heavy component (N-hydroxyethyl-N'-hydroxyethoxyethylpiperazine) 0.79%.

[0063] Example 2

[0064] A solution was prepared by mixing 240 g hexa-8-azapiperazine and 310 g deionized water, and then the solution was transferred into a reactor. The air in the reactor was replaced with N2, and then the pressure was maintained at 0.05 MPa. The temperature of the reactor was controlled at 45 °C by using a thermostat, and the stirring was started. 9 g of ethylene oxide was introduced into the reactor per hour, and the temperature of the reactor was controlled at 45 °C during the introduction. After 7 h of the introduction of ethylene oxide, the temperature of the reactor was decreased to 35 °C, and 55 g of hexa-8-azapiperazine was added. The introduction of ethylene oxide was stopped after 13 h, and the temperature of the reactor was maintained at 35 °C for 1 h. The carbon dioxide absorbent was obtained. The product was analyzed by moisture test and GC, and the results were as follows: hydroxyethylpiperazine 25.67%, dihydroxyethylpiperazine 2.21%, piperazine 11.11%; moisture content 59.90%, unreacted ethylene oxide 0.15%, and heavy component (N-hydroxyethyl-N'-hydroxyethoxyethylpiperazine) 0.96%.

[0065] Example 3

[0066] Mix 240 g hexobezpiazine and 310 g deionized water to form a solution, and then transfer the solution into a reactor. Replace the air in the reactor with N2, and then maintain the pressure at 0.1 MPa. Open a thermostat to control the temperature of the reactor at 55 ℃, and then start stirring. Introduce 10 g of ethylene oxide into the reactor per hour. During the introduction, the temperature of the reactor is controlled at 55 ℃. After 7 h of the introduction, reduce the temperature of the reactor to 40 ℃, and then add 66 g of hexobezpiazine. Stop the introduction of ethylene oxide after 12 h of the introduction. Continue the reaction for 3 h at 40 ℃. The carbon dioxide absorbent is obtained. The product is subjected to moisture test and GC analysis, and the composition and content are as follows: 34.11% of hydroxyethylpiperazine, 0.78% of dihydroxyethylpiperazine, 4.52% of piperazine, 59.56% of moisture, 0.12% of unreacted ethylene oxide, and 0.91% of heavy components (N-hydroxyethyl-N'-hydroxyethoxyethylpiperazine).

[0067] Example 4

[0068] Mix 200 g hexobezpiazine and 350 g deionized water to form a solution, and then transfer the solution into a reactor. Replace the air in the reactor with N2, and then maintain the pressure at 0.05 MPa. Open a thermostat to control the temperature of the reactor at 50 ℃, and then start stirring. Introduce 8 g of ethylene oxide into the reactor per hour. During the introduction, the temperature of the reactor is controlled at 50 ℃. After 6 h of the introduction, reduce the temperature of the reactor to 30 ℃, and then add 55 g of hexobezpiazine. Stop the introduction of ethylene oxide after 11 h of the introduction. Continue the reaction for 1 h at 30 ℃. The carbon dioxide absorbent is obtained. The product is subjected to moisture test and GC analysis, and the composition and content are as follows: 19.36% of hydroxyethylpiperazine, 1.65% of dihydroxyethylpiperazine, 13.36% of piperazine, 65.37% of moisture, 0.07% of unreacted ethylene oxide, and 0.19% of heavy components (N-hydroxyethyl-N'-hydroxyethoxyethylpiperazine).

[0069] Example 5

[0070] Mix 220 g hexa-piperazine and 330 g deionized water to form a solution, and then transfer the solution into a reactor. Replace the air in the reactor with N2, and then maintain the pressure at 0.1 MPa. Open a thermostat device to control the temperature of the reactor at 45 °C, and then start stirring. Introduce 9 g of ethylene oxide per hour. During the reaction, the temperature of the reactor is controlled at 45 °C. After 8 h of reaction, decrease the temperature of the reactor to 35 °C, and then add 55 g of hexa-piperazine. Stop the introduction of ethylene oxide after 13 h. Continue the reaction for 2 h at 35 °C. The carbon dioxide absorbent is obtained. The product is analyzed by moisture test and GC. The composition and content are as follows: hydroxyethylpiperazine 25.44%, dihydroxyethylpiperazine 5.42%, piperazine 8.23%; moisture content 59.97%, unreacted ethylene oxide 0.21%, and heavy component (N-hydroxyethyl-N'-hydroxyethoxyethylpiperazine) 0.73%.

[0071] Example 6

[0072] Mix 220 g hexa-piperazine and 330 g deionized water to form a solution, and then transfer the solution into a reactor. Replace the air in the reactor with N2, and then maintain the pressure at 0.1 MPa. Open a thermostat device to control the temperature of the reactor at 45 °C, and then start stirring. Introduce 9 g of ethylene oxide per hour. During the reaction, the temperature of the reactor is controlled at 45 °C. After 6 h of reaction, decrease the temperature of the reactor to 35 °C, and then add 55 g of hexa-piperazine. Stop the introduction of ethylene oxide after 13 h. Continue the reaction for 2 h at 35 °C. The carbon dioxide absorbent is obtained. The product is analyzed by moisture test and GC. The composition and content are as follows: hydroxyethylpiperazine 28.48%, dihydroxyethylpiperazine 2.08%, piperazine 8.37%; moisture content 59.91%, unreacted ethylene oxide 0.52%, and heavy component (N-hydroxyethyl-N'-hydroxyethoxyethylpiperazine) 0.64%.

[0073] Example 7

[0074] The 240 g hexa-8-piperazine and 310 g deionized water were mixed to form a solution, which was then transferred into a reactor. The air in the reactor was replaced by N2, and the pressure was maintained at 0.1 MPa. The temperature of the reactor was controlled at 55 °C by a thermostat, and the stirring was started. 10 g of ethylene oxide was introduced into the reactor every hour. The temperature of the reactor was maintained at 55 °C during the reaction. After 7 h of reaction, the temperature of the reactor was decreased to 35 °C. 66 g of hexa-8-piperazine was added into the reactor. The reaction was stopped after 12 h of reaction. The temperature of the reactor was maintained at 40 °C for another 3 h. The carbon dioxide absorbent was obtained. The product was analyzed by moisture test and GC. The composition and content of the product were as follows: hydroxyethylpiperazine 34.22%, dihydroxyethylpiperazine 0.75%, piperazine 4.51%; moisture content 59.48%, unreacted ethylene oxide 0.21%, and heavy component (N-hydroxyethyl-N'-hydroxyethoxyethylpiperazine) 0.83%.

[0075] Example 8

[0076] The 240 g hexa-8-piperazine and 310 g deionized water were mixed to form a solution, which was then transferred into a reactor. The air in the reactor was replaced by N2, and the pressure was maintained at 0.1 MPa. The temperature of the reactor was controlled at 55 °C by a thermostat, and the stirring was started. 10 g of ethylene oxide was introduced into the reactor every hour. The temperature of the reactor was maintained at 55 °C during the reaction. After 7 h of reaction, the temperature of the reactor was decreased to 35 °C. 66 g of hexa-8-piperazine was added into the reactor. The reaction was stopped after 12 h of reaction. The temperature of the reactor was maintained at 40 °C for another 3 h. The carbon dioxide absorbent was obtained. The product was analyzed by moisture test and GC. The composition and content of the product were as follows: hydroxyethylpiperazine 34.22%, dihydroxyethylpiperazine 0.75%, piperazine 4.51%; moisture content 59.48%, unreacted ethylene oxide 0.21%, and heavy component (N-hydroxyethyl-N'-hydroxyethoxyethylpiperazine) 0.83%.

[0077] Example 9

[0078] The absorbent obtained in Example 1 was used as the raw material. The composition of the absorbent was as follows: hydroxyethylpiperazine 15.52%, dihydroxyethylpiperazine 4.19%, piperazine 16.20%; moisture content 63.12%, unreacted ethylene oxide 0.18%, and heavy component (N-hydroxyethyl-N'-hydroxyethoxyethylpiperazine) 0.79%. The raw material was placed in a beaker, and stirred at 25 °C and 300 rpm for 30 min to form a homogeneous solution.

[0079] Comparative Example 1

[0080] A solution of 200 g hexa-piperazine and 350 g deionized water was prepared and transferred into a reactor. The air in the reactor was replaced with N2, and the pressure was maintained at 0.05 MPa. The temperature of the reactor was controlled at 25 °C or room temperature by opening a thermostat device. The stirring was started, and 8 g of ethylene oxide was introduced into the reactor per hour. The temperature of the reactor was controlled at 25 °C or room temperature during the introduction of ethylene oxide. After 6 h of introduction of ethylene oxide, 66 g of hexa-piperazine was added. The introduction of ethylene oxide was stopped after 11 h. The temperature of the reactor was maintained at 25 °C for 2 h to continue the reaction. The carbon dioxide absorbent was obtained. The product was analyzed by moisture test and GC. The composition and content were as follows: hydroxyethylpiperazine 13.54%, dihydroxyethylpiperazine 5.21%, piperazine 18.17%; moisture content 60.61%, unreacted ethylene oxide 1.34%, and heavy component (N-hydroxyethyl-N'-hydroxyethoxyethylpiperazine) 1.13%.

[0081] Comparative Example 2

[0082] A solution of 200 g hexa-piperazine and 350 g deionized water was prepared and transferred into a reactor. The air in the reactor was replaced with N2, and the pressure was maintained at 0.05 MPa. The temperature of the reactor was controlled at 40 °C by opening a thermostat device. The stirring was started, and 8 g of ethylene oxide was introduced into the reactor per hour. The temperature of the reactor was controlled at 40 °C during the introduction of ethylene oxide. After 6 h of introduction of ethylene oxide, 66 g of hexa-piperazine was added. The introduction of ethylene oxide was stopped after 11 h. The temperature of the reactor was maintained at 40 °C for 2 h to continue the reaction. The carbon dioxide absorbent was obtained. The product was analyzed by moisture test and GC. The composition and content were as follows: hydroxyethylpiperazine 11.39%, dihydroxyethylpiperazine 7.24%, piperazine 16.79%; moisture content 63.69%, unreacted ethylene oxide 0.21%, and heavy component (N-hydroxyethyl-N'-hydroxyethoxyethylpiperazine) 0.68%.

[0083] Comparative Example 3

[0084] A solution of 200 g hexa-piperazine and 350 g deionized water was prepared and transferred into a reactor. The air in the reactor was replaced with N2, and the pressure was maintained at 0.05 MPa. The temperature of the reactor was controlled at 40 °C by opening a thermostat device. The stirring was started, and 8 g of ethylene oxide was introduced into the reactor per hour. The temperature of the reactor was controlled at 40 °C during the introduction of ethylene oxide. After 6 h of introduction of ethylene oxide, 66 g of hexa-piperazine was added. The introduction of ethylene oxide was stopped after 11 h. The temperature of the reactor was maintained at 40 °C for 2 h to continue the reaction. The carbon dioxide absorbent was obtained. The product was analyzed by moisture test and GC. The composition and content were as follows: hydroxyethylpiperazine 11.39%, dihydroxyethylpiperazine 7.24%, piperazine 16.79%; moisture content 63.69%, unreacted ethylene oxide 0.21%, and heavy component (N-hydroxyethyl-N'-hydroxyethoxyethylpiperazine) 0.68%.

[0085] Comparative Example 4

[0086] 30wt% ethanolamine and 70wt% water were weighed into a container and mixed into a homogeneous solution at 25°C with stirring at 300rpm for 30min, to give a conventional commercial (30wt% MEA) carbon dioxide absorbent.

[0087] Comparative Example 5

[0088] 40wt% dihydroxyethylpiperazine, 6wt% hydroxyethylpiperazine, 2wt% piperazine, 2wt% N-hydroxyethyl-N'-hydroxyethoxyethylpiperazine and 50wt% water were weighed into a container and mixed into a homogeneous solution at 25°C with stirring at 300rpm for 30min.

[0089] Comparative Example 6

[0090] 40wt% dihydroxyethylpiperazine and 60wt% water were weighed into a container and mixed into a homogeneous solution at 25°C with stirring at 300rpm for 30min.

[0091] Comparative Example 7

[0092] 20wt% piperazine, 15wt% hydroxyethylpiperazine, 2wt% dihydroxyethylpiperazine, 3wt% N-hydroxyethyl-N'-hydroxyethoxyethylpiperazine and 60wt% water were weighed into a container and mixed into a homogeneous solution at 25°C with stirring at 300rpm for 30min.

[0093] Comparative Example 8

[0094] 18wt% piperazine, 18wt% hydroxyethylpiperazine, 2wt% dihydroxyethylpiperazine, 2wt% N-hydroxyethyl-N'-hydroxyethoxyethylpiperazine and 60wt% water were weighed into a container and mixed into a homogeneous solution at 25°C with stirring at 300rpm for 30min.

[0095] Comparative Example 9

[0096] A solution was prepared by mixing 200 g hexa-piperazine and 350 g deionized water uniformly, and then was moved into a reaction kettle. After the air in the reaction kettle was replaced by N2, N2 was kept at a pressure of 0.05 MPa. The temperature of the reaction kettle was controlled at 40 DEG C by opening a thermostat device, and stirring was started. 16 g of ethylene oxide was introduced per hour, and the temperature of the reaction kettle was controlled at 40 DEG C during the period. After 6 h of introduction of ethylene oxide, the temperature of the reaction kettle was decreased to 30 DEG C, 66 g of hexa-piperazine was added, and the introduction of ethylene oxide was stopped after 11 h. The temperature was maintained at 30 DEG C for 2 h of continuous reaction, and then the carbon dioxide absorbent was obtained. The product was subjected to moisture testing and GC analysis, and the composition and content were as follows: hydroxyethylpiperazine 5.33%, dihydroxyethylpiperazine 28.86%, piperazine 1.23%; the moisture content was 63.23%, the unreacted ethylene oxide was 0.46%, and the heavy component (N-hydroxyethyl-N'-hydroxyethoxyethylpiperazine) was 0.89%.

[0097] Comparative Example 10

[0098] A solution was prepared by mixing 200 g hexa-piperazine and 350 g deionized water uniformly, and then was moved into a reaction kettle. After the air in the reaction kettle was replaced by N2, N2 was kept at a pressure of 0.05 MPa. The temperature of the reaction kettle was controlled at 40 DEG C by opening a thermostat device, and stirring was started. 16 g of ethylene oxide was introduced per hour, and the temperature of the reaction kettle was controlled at 40 DEG C during the period. After 6 h of introduction of ethylene oxide, the temperature of the reaction kettle was decreased to 30 DEG C, 66 g of hexa-piperazine was added, and the introduction of ethylene oxide was stopped after 11 h. The temperature was maintained at 30 DEG C for 2 h of continuous reaction, and then the carbon dioxide absorbent was obtained. The product was subjected to moisture testing and GC analysis, and the composition and content were as follows: hydroxyethylpiperazine 5.33%, dihydroxyethylpiperazine 28.86%, piperazine 1.23%; the moisture content was 63.23%, the unreacted ethylene oxide was 0.46%, and the heavy component (N-hydroxyethyl-N'-hydroxyethoxyethylpiperazine) was 0.89%.

[0099] Test

[0100] The absorbents prepared in Examples 1-9 and Comparative Examples 1-10 above were subjected to CO2 absorption performance test, foaming trend test and regeneration energy consumption test. The specific test methods are as follows:

[0101] (1) CO2 absorption performance test

[0102] The CO2 absorption performance was tested according to the national standard "GB / T 36767-2018 Purification performance evaluation method of alcohol amine method desulfurization and decarbonization agent"; the liquid-gas ratio was controlled in the range of 3.0-6.0, the air produced by an oil-free air compressor was used to dilute CO2, and a 2kw electric heater was used to supply heat to the desorption tower to desorb carbon dioxide.

[0103] Test specific method: The carbon dioxide absorbent prepared by the present application and 30wt% ethanolamine (commercial absorbent) were respectively introduced from the top of the absorption tower, the absorbent flowed out from the bottom after flowing through the packing layer, was introduced into the lean-rich liquid heat exchanger by the rich liquid pump, and then entered the regeneration tower for desorption. The regeneration tower was connected with an electric heater at the bottom, the required heat energy was provided by electric energy, the absorbent flowed out from the bottom, entered the lean-rich liquid heat exchanger, and then returned to the absorption tower by the lean liquid pump, so as to circulate. Each absorbent was tested for 72h, and the average regeneration energy consumption was calculated; the simulated flue gas was introduced from the bottom, the composition of the simulated flue gas was controlled by a mass flow meter, the CO2 concentration of the simulated flue gas was 15%, the flue gas flow was 1Nm 3 / h, and the flow of the lean and rich liquid pumps was adjusted to 50.0~100mL / min according to the liquid-gas ratio;

[0104] Detection parameters: the absorption temperature was set to 40±5℃, the desorption temperature was 110±5℃, the liquid-gas ratio was 3.0~6.0 L / m 3 , the composition of the flue gas was tested by a flue gas analyzer, the manufacturer was Germany Kane, and the model was testo 350. The test results are shown in Table 1.

[0105] (2) Foaming tendency test

[0106] The foaming tendency of the absorbent was tested by the standard “SY / T 6538-2016 Formulated Selective Desulfurization Solvent”. The foaming height and defoaming time of the fresh absorbent before absorption-regeneration cycle and the absorbent after 72h cycle were tested, and the foaming performance of the absorbent was examined.

[0107] From Table 1, it can be seen that the carbon dioxide absorbent formed by the specific component piperazine derivative provided in the present application has high absorption load, decarburization rate, low foaming tendency and low regeneration energy consumption. The absorption load can reach more than 0.39 mol / mol, in some preferred embodiments, it can reach more than 0.4 mol / mol, while the decarburization rate can reach more than 90%, in some preferred embodiments, it can reach more than 97%, while the bubble height can be controlled within 0.4 cm, the regeneration energy consumption is reduced to within 3.65 MJ / kg, in some preferred embodiments, the regeneration energy consumption is even reduced to within 2.49 MJ / kg. The carbon dioxide absorbent obtained from Comparative Example 1, Comparative Example 7, Comparative Example 8 and Comparative Example 10 has too high piperazine content (more than 17%) and too high N-hydroxyethyl-N'-hydroxyethoxyethyl piperazine content (more than 1%), and has obvious foaming, higher bubble height, lower decarburization rate and higher regeneration energy consumption compared with Examples 1-9. In addition, the carbon dioxide absorbent obtained from Comparative Example 3 has too high N-hydroxyethyl-N'-hydroxyethoxyethyl piperazine content (more than 1%), has high bubble height, long foam collapse time, low decarburization rate and high regeneration energy consumption compared with Examples 1-9. In the absorbent formed by compounding, from Comparative Example 4, it can be seen that the carbon dioxide absorbent formed based on the piperazine derivative provided in the present application has higher absorption load and decarburization rate and lower regeneration energy consumption compared with the carbon dioxide absorbent using ethanolamine as the main absorbent. From Comparative Example 6, it can be seen that if a single piperazine derivative, dihydroxyethyl piperazine, is used as the main absorbent, the decarburization rate of the obtained absorbent is lower. In addition, from Comparative Examples 5 and 9, it can be seen that when dihydroxyethyl piperazine is used as the main absorbent, the absorption effect is poor, and the CO2 load is low, so the regeneration energy consumption is not tested. It can be seen that in the specific formula carbon dioxide absorbent provided in the present application, although other components such as piperazine have certain defects, controlling the content of the components in the formula can achieve certain synergistic effect and optimize the performance of the absorbent. This can also be seen from the comparison between Example 9 and Comparative Example 7.

[0108] Table 1

[0109]

[0110] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and not to limit them. Although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing examples, or make equivalent substitutions for part or all of the technical features; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A carbon dioxide absorbent based on a piperazine derivative, characterized in that, The carbon dioxide absorbent comprises the following components by mass fraction: N-(2-hydroxyethyl)piperazine 15~35% N,N'-dihydroxyethylpiperazine 0.5~6% Piperazine 4~17% N-hydroxyethyl-N'-hydroxyethoxyethylpiperazine 0~1% Water 59%~64%; The carbon dioxide absorbent comprises N-(2-hydroxyethyl)piperazine and N,N'-dihydroxyethylpiperazine, and the mass fraction of the N-(2-hydroxyethyl)piperazine and the N,N'-dihydroxyethylpiperazine in the carbon dioxide absorbent accounts for 19~35% of the total; the carbon dioxide absorbent has no other auxiliary absorbent components of non-piperazine or piperazine derivatives.

2. The carbon dioxide absorbent based on a piperazine derivative according to claim 1, characterized in that, The carbon dioxide absorbent is directly prepared from piperazine and ethylene oxide.

3. The method for producing a carbon dioxide absorbent based on a piperazine derivative according to claim 1 or 2, characterized by, The method comprises the following steps: providing a piperazine aqueous solution and ethylene oxide; contacting and reacting the piperazine aqueous solution and the ethylene oxide, when the concentration of N-(2-hydroxyethyl)piperazine in the reaction system exceeds 15% by mass fraction, cooling and supplementing piperazine to make the concentration of piperazine in the reaction system 4~17% by mass fraction, and then continuously reacting to obtain the carbon dioxide absorbent.

4. The method for producing a carbon dioxide absorbent based on a piperazine derivative according to claim 3, characterized by, When the piperazine is supplemented, the supplementing amount of the piperazine is 23%~33% of the content of the piperazine in the initially added piperazine aqueous solution.

5. The method for producing a carbon dioxide absorbent based on a piperazine derivative according to claim 3, characterized by, The cooling range is 10~20℃.

6. The method for producing a carbon dioxide absorbent based on a piperazine derivative according to any one of claims 3 to 5, characterized by, The contacting and reacting of the piperazine aqueous solution and the ethylene oxide specifically comprises the following steps: placing the piperazine aqueous solution in a reaction container; and injecting ethylene oxide gas under the protection of a gas at 40~55℃ and a pressure of 0.05~0.1 MPa to make the piperazine contact and react with the ethylene oxide.

7. The method for producing a carbon dioxide absorbent based on a piperazine derivative according to any one of claims 3 to 5, characterized by, The hourly input amount of the ethylene oxide is 4~5% of the mass of the piperazine in the piperazine aqueous solution initially added into the reaction container; and the concentration of the piperazine in the piperazine aqueous solution is 35%~45% by mass fraction.

8. The application of the carbon dioxide absorbent based on piperazine derivatives in the field of carbon dioxide capture, which is prepared by the method for preparing the carbon dioxide absorbent based on piperazine derivatives in any one of claims 1~2 or any one of claims 3~7, wherein and is applied to flue gas with a carbon dioxide concentration of 3~20% and a carbon dioxide capture temperature of 35~45℃.

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