Absorbent for treating carbon dioxide in flue gas as well as preparation method and application of absorbent

Abstract

The invention provides an absorbent for treating carbon dioxide in flue gas as well as a preparation method and application thereof, and belongs to the technical field of carbon dioxide capture and separation. The absorbent provided by the invention comprises triethylenetetramine, a phase splitting accelerant and water, the triethylene tetramine accounts for 30 parts by mass, the phase splitting accelerant accounts for 0-60 parts by mass, and the water accounts for 10-70 parts by mass. The obtained phase change absorbent has the three core advantages of being high in absorption capacity, low in operation cost and good in stability; meanwhile, due to the introduction of the alcohol solvent, the viscosity of the system is reduced, the pumping and mass transfer performance is improved, and the operation problem that the viscosity is sharply increased under the high load of TETA is solved; by selecting high-boiling-point alcohol, the volatilization loss of amine and alcohol can be effectively controlled, and the industrial applicability of the absorbent is further improved.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide capture and separation technology, and in particular to an absorbent for treating carbon dioxide in flue gas, its preparation method and application. Background Technology

[0002] Faced with the severe environmental pollution caused by large amounts of acidic gases such as CO2, H2S, and SO2 emitted from industrial processes and vehicle exhaust, acidic gas separation technology has become one of the key means of pollution control. Among the various existing separation methods, chemical absorption is a mature and widely used technology, especially the process using ethanolamine (MEA) as the absorbent, which occupies an important position in industry. However, the MEA method has revealed problems such as low absorption load, severe equipment corrosion, easy degradation of amine liquid, and high regeneration energy consumption during operation, which restricts its further promotion. In particular, in the carbon dioxide (CO2) capture process, taking a typical MEA process as an example, its thermal desorption energy consumption is about 3.7 GJ / tCO2, of which about 40-60% of the energy consumption is used for water heating and evaporation processes, that is, the latent heat of water vaporization and the sensible heat of temperature rise constitute the main part of the regeneration energy consumption. In the context of addressing global climate change and promoting carbon emission reduction, carbon dioxide capture and storage (CCS) technology is regarded as a key path to control greenhouse gases, and reducing separation energy consumption has become the core challenge to improve the economic feasibility of this technology. Therefore, developing novel absorbents to reduce ineffective heat consumption and optimizing process systems has become an important research direction, aiming to achieve the goal of efficient and low-energy separation of acidic gases.

[0003] The phase change absorbent obtained in patent CN110960956A exhibits a significant increase in viscosity of the liquid phase after absorbing CO2. This not only reduces the mass transfer coefficient of CO2 in the liquid phase, leading to a slower absorption rate, but may also require increasing the size of the absorption tower or reducing the throughput, thereby increasing equipment investment and operating costs. The high viscosity also brings problems such as difficulties in solution transportation and increased power consumption.

[0004] The CO2 absorption load of the phase change absorbent obtained in patent CN119139879A is still relatively low, making it difficult to meet the high treatment efficiency requirements of industrial capture. Furthermore, the amine blend system obtained in patent CN114011207A has an excessively large proportion of the enriched phase volume under high loads, limiting the degree of CO2 enrichment and affecting the overall absorption and regeneration efficiency. While the phase separation in patent CN120037770A is rapid and thorough, some liquid-liquid phase change absorbents require a very long settling time (up to 12 hours) to achieve complete phase separation. This results in bulky equipment (such as phase separators), prolonged residence time, and a significant increase in floor space and investment costs.

[0005] The system in patent CN112892160A exhibits low regeneration efficiency (below 30%) and insufficient desorption load (<0.50 mol / mol). This means the absorbent cannot effectively release CO2 during regeneration, resulting in low recycling efficiency and directly impacting the overall economic efficiency of the process. Although phase change strategies aim to reduce energy consumption, their energy-saving advantages are weakened if desorption performance is poor. In long-term absorption-regeneration cycles, especially in aerobic flue gas environments, the organic amine absorbent in patent CN108686484A is prone to oxidative and thermal degradation, leading to deactivation of the active ingredient, solution discoloration, and the generation of corrosive substances. This not only reduces absorption performance but also increases solvent replenishment costs and system maintenance burden.

[0006] In patent CN114011207A, solid-liquid phase change or liquid-solid phase change absorbents produce solid precipitates after absorbing CO2. These solid products have poor flowability and easily clog pipes, pumps, valves, heat exchangers, and other equipment, posing a serious threat to continuous and stable industrial plants and limiting their application in conventional processes. Some absorbent formulations designed to achieve good phase separation performance are complex, and patent CN105536434A uses expensive or difficult-to-synthesize components (such as amines or ionic liquids with special structures), increasing initial investment and raw material costs, which is not conducive to large-scale industrial promotion.

[0007] In summary, various phase change absorbents have broken through the limitations of traditional absorbents, providing new pathways to reduce the energy consumption of chemical absorption regeneration. However, problems such as high viscosity of the rich phase, low absorption load, and poor regeneration effect still exist.

[0008] Therefore, developing an absorbent for treating carbon dioxide in flue gas, and its preparation method, that combines high absorption capacity, rapid phase separation characteristics, low viscosity, high regeneration efficiency, and excellent long-term chemical stability, while being compatible with existing industrial equipment and free from the risk of solid phase blockage, to form a low-energy carbon capture technology solution, has significant practical significance and application value. Summary of the Invention

[0009] The purpose of this invention is to provide an absorbent for treating carbon dioxide in flue gas, its preparation method and application, so as to solve the problems of low carbon dioxide capture efficiency, insignificant phase change, difficulty in absorbent regeneration and stability in the prior art.

[0010] To achieve the above-mentioned objectives, the present invention provides the following technical solution: The present invention provides an absorbent for treating carbon dioxide in flue gas, the absorbent comprising triethylenetetramine, a phase separation promoter and water; The triethylenetetramine is present in a mass fraction of 30 parts, the phase separation promoter is present in a mass fraction of 0-60 parts, and the water is present in a mass fraction of 10-70 parts.

[0011] Preferably, the phase separation promoter includes one or more of n-propanol, n-butanol, and n-pentanol.

[0012] Preferably, the total mass fraction of each component of the absorbent is 100 parts.

[0013] This invention also provides a method for preparing an absorbent for treating carbon dioxide in flue gas, the method comprising: The absorbent is obtained by mixing triethylenetetramine, a phase separation promoter, and water.

[0014] Preferably, the mixing is ultrasonic mixing, the ultrasonic mixing power is 100~150W, the ultrasonic mixing time is 3~8min, and the ultrasonic mixing temperature is 20~30℃.

[0015] This invention also provides an application of an absorbent for treating carbon dioxide in flue gas in the capture of low-concentration carbon dioxide in flue gas, wherein the capture steps are as follows: 1) The mixed gas is passed into the absorbent to carry out the absorption reaction, resulting in an upper liquid phase and a lower liquid phase; 2) Desorb the lower liquid phase to obtain carbon dioxide and the remaining liquid. The remaining liquid is mixed with the upper liquid phase and recycled.

[0016] Preferably, in step 1), the volume fraction of carbon dioxide in the mixed gas is 14-16%; The absorption reaction temperature is 30~60℃, and the absorption reaction pressure is 1~1.1 standard atmospheres.

[0017] Preferably, in step 2), the desorption temperature is 110~130℃ and the desorption time is 30~60min.

[0018] The beneficial effects of this invention are: The phase change absorbent obtained by this invention has three core advantages: strong absorption capacity, low operating cost, and good stability. At the same time, the introduction of alcohol solvent reduces the viscosity of the system, improves pumping and mass transfer performance, and solves the problem of viscosity surge under high TETA load. By selecting high-boiling-point alcohol, the volatilization loss of amine and alcohol can also be effectively controlled, further improving the industrial applicability of the absorbent. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0020] Figure 1 The diagram shows the phase separation of the absorbent obtained in Example 4 after absorbing CO2. Figure 2 The graph shows the absorption performance test results of the absorbents obtained in Examples 1-7; Figure 3 This is a graph showing the trend of absorption load change over time for the absorbents obtained in Examples 1-7 and Comparative Example 1; Figure 4 The graph shows the CO2 absorption performance of the absorbent obtained in Example 4 at different absorption temperatures. Figure 5 The graph shows the desorption performance test results of the absorbent obtained in Example 4; Figure 6 This is a comparison graph showing the desorption performance of the absorbents obtained in Example 1, Example 4, and Comparative Example 1 at a desorption temperature of 120°C. Figure 7 This is a graph showing the regeneration efficiency of the absorbent obtained in Example 4 after multiple cycles. Detailed Implementation

[0021] The present invention provides an absorbent for treating carbon dioxide in flue gas, the absorbent comprising triethylenetetramine and water; The triethylenetetramine is present in a mass fraction of 30 parts, the phase separation promoter is present in a mass fraction of 0-60 parts, and the water is present in a mass fraction of 10-70 parts.

[0022] In this invention, the structural formula of the triethylenetetramine is as follows: .

[0023] In this invention, the mass fraction of the phase separation promoter is preferably 10-50 parts, more preferably 20-40 parts, and even more preferably 30-35 parts, and the mass fraction of the water is preferably 15-60 parts, more preferably 20-50 parts, and even more preferably 30-40 parts.

[0024] In this invention, the phase separation promoter preferably includes one or more of n-propanol, n-butanol, and n-pentanol.

[0025] In this invention, the mass fraction of each component of the absorbent is preferably 100 parts.

[0026] This invention also provides a method for preparing an absorbent for treating carbon dioxide in flue gas, the method comprising: The absorbent is obtained by mixing triethylenetetramine, a phase separation promoter, and water.

[0027] In this invention, the mixing is preferably ultrasonic mixing, the ultrasonic mixing power is preferably 100~150W, more preferably 110~140W, and even more preferably 120~130W, the ultrasonic mixing time is preferably 3~8min, more preferably 4~7min, and even more preferably 5~6min, and the ultrasonic mixing temperature is preferably 20~30℃, more preferably 22~28℃, and even more preferably 24~26℃.

[0028] In this invention, the ultrasonic mixing enables the absorbent to be mixed more uniformly, making the absorbent a more homogeneous absorbent liquid before absorption.

[0029] In this invention, the phase change absorbent is a homogeneous solution before absorbing carbon dioxide, specifically a homogeneous transparent liquid solution. After being saturated with carbon dioxide, it decomposes into a two-phase liquid-liquid phase change system, with carbon dioxide concentrated in the aqueous phase.

[0030] This invention also provides an application of an absorbent for treating carbon dioxide in flue gas in the capture of low-concentration carbon dioxide in flue gas, wherein the capture steps are as follows: 1) The mixed gas is passed into the absorbent to carry out the absorption reaction, resulting in an upper liquid phase and a lower liquid phase; 2) Desorb the lower liquid phase to obtain carbon dioxide and the remaining liquid. The remaining liquid is mixed with the upper liquid phase and recycled.

[0031] In this invention, in step 1), the volume fraction of carbon dioxide in the mixed gas is preferably 14-16%, more preferably 14.5-15.5%, and even more preferably 15-15.2%. The preferred temperature for the absorption reaction is 30-60°C, more preferably 35-55°C, and even more preferably 40-50°C. The preferred pressure for the absorption reaction is 1-1.1 atmospheres, more preferably 1.02-1.08 atmospheres, and even more preferably 1.05-1.06 atmospheres.

[0032] In this invention, the signal for the end of the absorption reaction is: when the exhaust gas concentration reaches 95% or more of the intake gas concentration and remains so for more than 10 minutes.

[0033] In this invention, in step 2), the desorption temperature is preferably 110~130℃, more preferably 115~125℃, and even more preferably 118~120℃, and the desorption time is preferably 30~60min, more preferably 35~55min, and even more preferably 40~50min.

[0034] In this invention, the phase change absorbent is a homogeneous solution before absorbing CO2, and after absorbing CO2 to saturation, it separates into upper and lower liquid phases, with CO2 enriched in the lower liquid phase.

[0035] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0036] Example 1

[0037] Weigh 6g of triethylenetetramine and 14g of water, and ultrasonically mix them at 120W power for 5 minutes at 25℃ to obtain 20g of absorbent, which is recorded as "3:0:7".

[0038] Example 2

[0039] Weigh out 6g of triethylenetetramine, 2g of n-butanol and 12g of water, and ultrasonically mix them at 25℃ with a power of 120W for 5 minutes to obtain 20g of phase change absorbent, which is denoted as "3:1:6".

[0040] Example 3

[0041] Weigh out 6g of triethylenetetramine, 4g of n-butanol and 10g of water, and ultrasonically mix them at 25℃ with a power of 120W for 5 minutes to obtain 20g of phase change absorbent, denoted as "3:2:5".

[0042] Example 4

[0043] Weigh out 6g of triethylenetetramine, 6g of n-butanol and 8g of water, and ultrasonically mix them at 120W power for 5 minutes at 25℃ to obtain 20g of phase change absorbent, denoted as "3:3:4".

[0044] Example 5

[0045] Weigh out 6g of triethylenetetramine, 8g of n-butanol and 6g of water, and ultrasonically mix them at 25℃ with a power of 120W for 5 minutes to obtain 20g of phase change absorbent, denoted as "3:5:3".

[0046] Example 6

[0047] Weigh out 6g of triethylenetetramine, 10g of n-butanol and 4g of water, and ultrasonically mix them at 25℃ with a power of 120W for 5 minutes to obtain 20g of phase change absorbent, denoted as "3:6:2".

[0048] Example 7

[0049] Weigh out 6g of triethylenetetramine, 12g of n-butanol and 2g of water, and ultrasonically mix them at 25℃ with a power of 120W for 5 minutes to obtain 20g of phase change absorbent, which is denoted as "3:7:1".

[0050] Comparative Example 1

[0051] Ethanolamine and water were mixed evenly at a mass ratio of 3:7, and the total mass was controlled at 20g to obtain ethanolamine absorbent, denoted as "MEA".

[0052] The absorbents obtained in Examples 1-7 and Comparative Example 1 were subjected to the following performance tests: Absorption performance test: The absorbents obtained in Examples 1-7 and Comparative Example 1 were subjected to the following steps respectively: The bubbling reactor containing the absorbent was placed in a 40°C water bath. After maintaining the temperature, the absorption test began. A mixed gas with a CO2 volume fraction of 15% was introduced into the bubbling reactor, and the flow rate of the mixed gas was controlled at 100 mL / min using a mass flow controller. The CO2 content of the exhaust gas after the absorption reaction was measured using an infrared CO2 analyzer. The bubbling reactor was connected to a computer, and data was recorded every 1 minute. When the exhaust gas concentration reached 95% or more of the inlet gas concentration and remained at that level for more than 10 minutes, the absorbent was considered saturated. After absorption saturation, the phase separation of the absorbent could be observed by allowing it to stand.

[0053] Viscosity testing method: The viscometer used for viscosity measurement is equipped with four types of rotors, with a measuring range of 1~1×10⁻⁶. 5 mPa·s, during the test, the solution to be tested is kept at a constant temperature of 40℃ in a water bath, and the solution is measured by selecting an appropriate rotor and speed.

[0054] The change in absorption rate over time can be calculated. Based on the relationship between CO2 absorption rate and time, the absorption rate can be integrated to obtain the CO2 absorption load of the absorbent. The saturated absorbent is then subjected to two-phase separation. The CO2 loading in the lean phase (upper liquid phase) and rich phase (lower liquid phase) is determined using sulfuric acid titration (a 0.1 mol / L dilute sulfuric acid solution is used to titrate the absorbed liquid phase to determine its carbon dioxide content, thus obtaining the corresponding absorption load).

[0055] The phase separation diagram of the absorbent obtained in Example 4 after absorbing CO2 is shown below. Figure 1 As shown. By Figure 1 As can be seen, the absorbent obtained in Example 4 has a rich phase volume ratio of 62.5% after absorption. Furthermore, as the proportion of n-butanol increases, the viscosity of the rich phase increases, and the volume of the lower CO2 rich phase gradually decreases, as shown in Table 1. Moreover, by utilizing the phase separation characteristics of the absorbent in absorbing CO2, the regeneration volume of the absorbent can be reduced, thereby achieving the goal of reducing regeneration energy consumption.

[0056] Table 1. Test results of the absorption performance of the absorbents obtained in Examples 1-7

[0057] The absorption performance test results of the absorbents obtained in Examples 1-7 are shown in the figure below. Figure 2As shown. By Figure 2 It can be seen that the absorption rate decreases with increasing absorption time, while the absorption load first increases and then gradually levels off with increasing absorption time. This is because the absorption gradually becomes saturated. The absorption loads of Examples 1 to 7 can all be maintained above 1 mol / mol, which is higher than the CO2 load of 0.51 mol / mol of the traditional MEA absorbent.

[0058] The absorption load of the absorbents obtained in Examples 1-7 and Comparative Example 1 varies with time as shown in the graph. Figure 3 As shown. By Figure 3 It can be seen that the absorption load of the phase change absorbents obtained in Examples 1-7 is much higher than that of the absorbent obtained in Comparative Example 1. After the absorption is completed, the absorption load of the absorbent obtained in Comparative Example 1 is 0.51 mol / mol. Compared with Example 1, the addition of the phase separation agent n-butanol in Examples 2-7 did not affect the absorption performance of the original amine, indicating that the absorbent obtained in this invention has good CO2 absorption performance.

[0059] The CO2 absorption performance of the absorbent obtained in Example 4 was tested at different absorption temperatures: The specific steps are the same as those for absorption performance testing, the only difference being that the temperature of the constant temperature water bath is controlled at 30℃, 40℃, 50℃ and 60℃ respectively during the absorption process.

[0060] The CO2 absorption performance of the absorbent obtained in Example 4 at different absorption temperatures is shown in the figure below. Figure 4 As shown. By Figure 4 It can be seen that the absorption load is the highest at an absorption temperature of 40℃, reaching 1.327 mol / mol.

[0061] The desorption properties of the absorbents obtained in Example 4 and Comparative Example 1 were tested: The absorbents obtained in Example 4 and Comparative Example 1 were used to capture CO2, using the same methods as those used for the absorption performance test. After capture, the resulting CO2-rich phase layers were desorbed at different temperatures (100~120℃) for 30~60 min. The CO2 desorption performance of the absorbents at different desorption temperatures and times was measured, and the test results are as follows: Figure 5 As shown.

[0062] The desorption performance test results of the absorbent obtained in Example 4 are shown in the figure below. Figure 5 As shown. By Figure 5 It can be seen that the CO2-rich phase of the absorbent obtained in Example 4 can achieve good CO2 desorption at 100~120℃, and the CO2 desorption load increases with the increase of desorption temperature.

[0063] The desorption performance of the absorbents obtained in Examples 1, 4, and 1, at a desorption temperature of 120°C is compared in the following figure. Figure 6 As shown. By Figure 6 It can be seen that when the desorption temperature is 120℃ and the desorption time is 40min, the desorption rate is 69.8% and the desorption load is 1.153mol / kg. Under the same desorption temperature and desorption time, the desorption load of the absorbent obtained in Comparative Example 1 is 0.65mol / kg and the desorption rate is 61.1%, indicating that the absorbent obtained in Example 4 has good regeneration performance and is beneficial for industrial application.

[0064] Regeneration efficiency test: The upper and lower phases of the phase change absorbent prepared in Example 4 were separated. The rich phase layer was desorbed in an oil bath at 120°C and magnetically stirred to obtain the regenerated solvent after desorption. This solvent was mixed with the poor phase layer, and the CO2 loading test was repeated using the method described in the absorbent absorption performance test above. The absorption / desorption performance was measured for 5 cycles. The regeneration efficiency was calculated as (nth absorption load - n-1th absorption load). The test results are as follows: Figure 7 As shown.

[0065] The regeneration efficiency of the absorbent obtained in Example 4 after multiple cycles is shown in the figure below. Figure 7 As shown, the CO2 cycling load of the phase change absorbent prepared in Example 4 decreased to 50% with increasing absorption-desorption cycles, indicating a reduction in absorption load. This is mainly because multiple absorption-desorption cycles generate more difficult-to-decompose absorption products, and some solvent cannot be condensed in time during desorption, resulting in volatilization loss and degradation of organic amines. The cycling capacity was 31.3% higher than that of the absorbent obtained in Comparative Example 1, the regeneration volume was reduced by 31%, and the desorption efficiency for each desorption cycle was over 88%. This indicates that the absorbent obtained in Example 4 has good stability, excellent desorption performance, and stable regenerability.

[0066] As can be seen from the above embodiments, the present invention provides an absorbent for treating carbon dioxide in flue gas, its preparation method, and its application. The absorbent obtained by the present invention mainly consists of TETA, a phase separation promoter, and water. TETA, due to the presence of more active sites in its molecular structure, ensures that the absorbent has a high absorption capacity and superior desorption performance. The phase separation promoter and the product are immiscible due to their polarity differences, resulting in a liquid-liquid phase transition, thereby reducing the volume of the regeneration solution and lowering regeneration energy consumption.

[0067] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An absorbent for treating carbon dioxide in flue gas, characterized in that, The absorbent comprises triethylenetetramine, a phase separation promoter, and water; The triethylenetetramine is present in a mass fraction of 30 parts, the phase separation promoter is present in a mass fraction of 0-60 parts, and the water is present in a mass fraction of 10-70 parts.

2. The absorbent for treating carbon dioxide in flue gas according to claim 1, characterized in that, The phase separation promoter includes one or more of n-propanol, n-butanol, and n-pentanol.

3. An absorbent for treating carbon dioxide in flue gas according to claim 1 or 2, characterized in that, The total mass fraction of each component of the absorbent is 100 parts.

4. A method for preparing an absorbent for treating carbon dioxide in flue gas according to any one of claims 1 to 3, characterized in that, The preparation method is as follows: The absorbent is obtained by mixing triethylenetetramine, a phase separation promoter, and water.

5. The method for preparing an absorbent for treating carbon dioxide in flue gas according to claim 4, characterized in that, The mixing is ultrasonic mixing, with a power of 100~150W, a mixing time of 3~8min, and a mixing temperature of 20~30℃.

6. The application of the absorbent for treating carbon dioxide in flue gas according to any one of claims 1 to 3 in the capture and concentration of low-concentration carbon dioxide in flue gas, characterized in that, The capture steps are as follows: 1) The mixed gas is passed into the absorbent to carry out the absorption reaction, resulting in an upper liquid phase and a lower liquid phase; 2) Desorb the lower liquid phase to obtain carbon dioxide and the remaining liquid. The remaining liquid is mixed with the upper liquid phase and recycled.

7. The application of the absorbent for treating carbon dioxide in flue gas according to claim 6 in the capture and concentration of low-concentration carbon dioxide in flue gas, characterized in that, In step 1), the volume fraction of carbon dioxide in the mixed gas is 14-16%. The absorption reaction temperature is 30~60℃, and the absorption reaction pressure is 1~1.1 standard atmospheres.

8. The application of the absorbent for treating carbon dioxide in flue gas according to claim 6 in the capture and concentration of low-concentration carbon dioxide in flue gas, characterized in that, In step 2), the desorption temperature is 110~130℃ and the desorption time is 30~60min.

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