A method for desorbing CO2-rich liquid and regenerating chemical absorbent by stepwise addition of acid and alkali without energy consumption

Abstract

The invention discloses a method for desorbing CO2 rich liquid and regenerating chemical absorbent by gradually adding acid and alkali without energy consumption. In the desorption process of CO2 rich liquid, the method first adds acid solution such as oxalic acid and citric acid, and realizes rapid and efficient release of CO2 from CO2 rich liquid through acid-base neutralization reaction; after CO2 desorption is completed, alkaline metal oxide or metal hydroxide is added to CO2 lean liquid to promote the protonated absorbent in CO2 lean liquid to undergo deprotonation reaction, complete absorbent regeneration, and at the same time, the metal oxide or metal hydroxide is converted into insoluble salt, and solid-liquid separation occurs with the absorbent solution. The method of the invention can retain the advantages of fast desorption rate, low desorption temperature and high desorption rate of the existing acid desorption CO2 technology; and after desorption is completed, the acid in the system can react chemically with the added alkali and be converted into insoluble salt, avoiding the weakening of the CO2 absorption capacity of the absorbent by the added acid and alkali, and meeting the recycling demand of the absorbent.

Description

Technical Field

[0001] The present invention belongs to CO 2 Capture field, specifically relates to a method for promoting absorbent CO2 without external heat source 2 Rich liquid completes CO 2 Methods for desorption and regeneration of the absorbent. Background Art

[0002] CO 2 Carbon capture is the primary link in carbon capture, utilization and storage (CCUS) technology. 2 Capturing and separating carbon dioxide from flue gas or air to a high concentration level for subsequent storage or utilization is the basis for the implementation of CCUS. At present, the relatively mature carbon capture technology is the chemical absorption method based on alkaline absorbents. The essence is to use alkaline absorbents to react with CO2 at a low temperature (40°C). 2 The reaction forms unstable salts and completes CO 2 Capture; then heat to 110-140°C to decompose the salt and release CO 2 , achieving CO 2 Enrichment and regeneration of alcohol amine. However, since more than 50% of the heat energy is consumed in the heating and evaporation of the solvent during the heating and desorption process, a large amount of heat energy is lost. Studies have shown that more than 50% of the heat energy is consumed in the heating and evaporation of the solvent water during the heating and desorption process, resulting in an energy consumption of up to 3.6-4.0 GJ / t CO for the desorption of alcohol amine. 2 , accounting for 70% of the capture energy consumption, resulting in a 2 The capture cost is 200-400 yuan, which greatly limits the large-scale promotion and application of chemical absorption method.

[0003] Obviously, reducing CO 2 Energy consumption of rich liquid desorption is the key point to build a low-energy, low-cost chemical absorption method. To this end, researchers proposed a new desorption method - acid desorption, which is to add CO to the absorbent. 2 Acid is added to the rich solution to break the absorbent and CO 2 chemical equilibrium, promoting the reaction toward CO 2 Since acid desorption does not require heat input, it avoids the inefficient thermal cycle in thermal desorption and reduces CO 2 Reduction of energy requirement of CO 2 desorption by adding acid into CO2 -loaded solvent.Energy Fuels 2010,24,213-219) Phthalic acid was added to 2 mol / L monoethanolamine (MEA) CO 2 In the rich solution, the results showed that CO 2 The desorption rate is higher than that of MEA CO without acid addition. 2 The rich solution increased by 4.5 times, and the desorption energy consumption decreased to 2.72MJ / mol CO 2 , which is only 1 / 5 of the energy consumption of thermal desorption, confirming that the acid desorption method can significantly reduce the CO 2 Energy consumption of desorption of rich solution. Du et al. (Du, M.; Feng, B.; An, H.; Liu, W.; Zhang, L. Effect of addition of weak acids on CO 2 desorption from rich aminesolvents. Korean J.Chem.Eng.2011,29,362-368.) in MEA, diethanolamine (DEA) and N-methyldiethanolamine (MDEA) CO 2 During the desorption of the rich solution, 0.3 g of adipic acid and CO were added. 2 The desorption rates increased by 336%, 217% and 154% respectively compared with the thermal desorption method, and the desorption energy consumption decreased by 51.7%, 55.9% and 43.8% respectively, which proved that the acid desorption method can be applied to different types of alcoholamine CO 2 Rich liquid.

[0004] However, the acid desorption method has two obvious drawbacks: (1) the residual acid is difficult to remove from CO 2 The removal of the lean solution causes part of the absorbent to be in a protonated state and unable to complete regeneration, thus weakening the CO 2 absorption capacity, making it difficult to recycle the capture system; (2) due to the non-recyclability of acid, CO 2 The capture cycle consumes a large amount of acid, and the cost of acid also restricts the large-scale application of acid desorption. 2 Desorption principle and technology to achieve low energy consumption, recyclable and low-cost CO 2 Capture. Summary of the invention

[0005] The purpose of the present invention is to provide a method for desorbing CO without energy consumption by gradually adding an acid-base desorbent, so as to solve the bottleneck problem that the acid solution cannot be recovered after desorption, so that the absorbent is in a protonated state, which makes it difficult to regenerate the absorbent and cannot be recycled. 2 A method for enriching and regenerating a chemical absorbent.

[0006] This method is used in CO 2 During the desorption process of the rich solution, oxalic acid, citric acid and other acids are first added to complete the CO 2 Desorption; when desorption is completed, in CO 2 Add alkaline metal oxides or metal hydroxides to the lean solution to react with CO 2 The protonated absorbent in the lean solution undergoes an acid-base neutralization reaction, which prompts the absorbent to complete regeneration, and at the same time, the metal oxide or metal hydroxide is converted into an insoluble salt. This method can retain the existing acid desorption technology CO 2 The desorption rate is fast, the desorption temperature is low, and the desorption rate is high. After the desorption is completed, the acid in the system can react chemically with the added alkali to transform into an insoluble salt, thus avoiding the CO2 absorption of the added acid on the absorbent. 2 The absorption capacity is negatively affected, meeting the need for recycling of absorbents.

[0007] In order to achieve the above-mentioned object of the invention, the technical solution of the present invention is as follows:

[0008] Step 1: Use pre-prepared CO 2 The absorbent solution absorbs CO 2 , forming CO 2 Rich liquid (CO 2 high loading solution).

[0009] Step 2: Dissolve the acid in water to form an acid solution, and add the acid solution to the CO 2 Desorption of CO in rich solution 2 , or add the acid directly to the CO 2 Desorption of CO in rich solution 2 The acid is capable of 2 A large number of hydrogen ions are dissociated in the rich liquid and absorbed by CO 2 The resulting product is an acid that reacts rapidly, and after desorption is completed, CO is obtained. 2 Lean solution (CO 2 low-load solution).

[0010] Step 3: Add alkali to the CO obtained in step 2 2 In the lean liquid, stirring, neutralizing the added acid and protonating the absorbent, the regeneration of the absorbent is completed, and the absorbent is recycled for the convenience of recycling. The base is a base that can react with the acid and its conjugate base to generate insoluble matter.

[0011] In the above method, further, the CO 2The absorbent is prepared from a chemical absorbent and a solvent thereof, wherein the solvent is water, an organic solvent or a mixture of an organic solvent and water; the chemical absorbent includes but is not limited to at least one of monoethanolamine, diethanolamine, N-methyldiethanolamine, 2-amino-2-methyl-1-propanol, ethylenediamine, triethylamine, piperazine, ammonia water and potassium carbonate; the organic solvent includes but is not limited to at least one of methanol, ethanol, acetone and acetonitrile.

[0012] In the above method, further, the acid includes but is not limited to at least one of sulfuric acid, acetic acid, oxalic acid, citric acid, malic acid, lactic acid, and industrial waste acid; the industrial waste acid can be at least one of oxalic acid waste liquid, sulfuric acid waste liquid, and hydrofluoric acid waste liquid.

[0013] In the above method, further, the alkali is at least one of alkaline metal oxides, metal hydroxides, and alkaline solid wastes, and the alkaline solid wastes are fly ash (the active ingredient is CaO), carbide slag (the active ingredient is Ca(OH) 2 ) at least one of; the metal hydroxide is preferably Ca(OH) 2 , NaOH, KOH, Mg(OH) 2 、Ba(OH) 2 、Sr(OH) 2 At least one of; the metal oxide is preferably CaO, MgO, Na 2 O, BaO, CrO, MnO, etc.

[0014] When acetic acid, oxalic acid, citric acid, malic acid, or lactic acid is selected and a metal hydroxide is selected as the base, the reaction process in the above method is as follows:

[0015] Absorbent captures CO 2 :2R 1 R 2 NH+CO 2 +H 2 O→R 1 R 2 NH·H + +R 1 R 2 NCOO -

[0016] Acid desorption of CO 2 : R 1 R 2 NCOO - +RCOOH→R 1 R 2 NH·H + +RCOO - +CO 2 ↑

[0017] Alkali neutralization regeneration: R 1 R 2 NH·H + +BOH→R 1 R 2 NH+RCOO - ·B + ↓+H 2 O

[0018] Where R 1 R 2 NH to CO 2 The chemical absorbent in the capture solution, RCOOH is the acid and BOH is the base.

[0019] In the above method, further, the molar ratio of the chemical absorbent, the acid and the alkali is 1: (0.25-1): (0.5-2) in sequence. When the acid selected is a waste acid, the amount of the waste acid is calculated according to the molar ratio and the mass content of the effective acid (referring to the acid that meets the above technical solution of the present invention) in the waste acid, wherein the amount of oxalic acid waste liquid is calculated according to the mass content of oxalic acid of 5%, the amount of sulfuric acid waste liquid is calculated according to the mass content of sulfuric acid of 5%, and the amount of hydrofluoric acid waste liquid is calculated according to the mass content of hydrofluoric acid of 5%; when the alkali selected is fly ash or carbide slag, the amount of fly ash or carbide slag is calculated according to the molar ratio and the mass content of the effective alkali in the fly ash.

[0020] In a preferred embodiment, the molar ratio of the chemical absorbent, the acid and the base is 1:0.5:1.

[0021] The present invention also provides a combined use of an acid and a base in carbon capture, utilization and storage (CCUS). The acid is capable of 2 A large number of hydrogen ions are dissociated in the rich liquid and react with CO 2 The absorption product is an acid that reacts rapidly, and the base is a base that can react with the acid and its conjugate base to form an insoluble substance.

[0022] Furthermore, in the above application, the acid is at least one of sulfuric acid, acetic acid, oxalic acid, citric acid, malic acid, lactic acid, oxalic acid waste liquid, sulfuric acid waste liquid, and hydrofluoric acid waste liquid; the alkali is at least one of alkaline metal oxides, metal hydroxides, and alkaline solid wastes; the alkaline solid waste is at least one of fly ash and carbide slag; and further, the alkali is preferably Ca(OH) 2 , NaOH, KOH, Mg(OH) 2 、Ba(OH) 2 、Sr(OH) 2 At least one of .

[0023] Furthermore, the above application is more specifically as a CO 2 The capture solution absorbs CO2 After forming CO 2 Desorption of rich liquid and CO 2 The chemical absorbent in the capture solution is regenerated.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. Compared with the traditional thermal desorption method, the CO 2 The temperature of the rich liquid can be kept at room temperature during desorption, without the need for additional heat energy, which significantly reduces the CO 2 The capture energy consumption, more importantly, this method can regenerate the chemical absorbent and achieve recycling.

[0026] 2. The present invention opens up a new method for the utilization of waste acid and waste alkali by combining with CO 2 The desorption process is coupled, which not only effectively realizes the resource utilization of waste acid and waste alkali, but also makes CO 2 The rich liquid desorption process does not require additional heat energy, which significantly reduces CO 2 The capture energy consumption, more importantly, this method can regenerate the chemical absorbent and achieve recycling.

[0027] 3. The insoluble salt generated by the reaction of alkali and acid in the present invention is a chemical with high economic value, such as oxalic acid and Ca(OH) 2 After completing CO 2 After the rich liquid is desorbed, calcium oxalate is produced, which has great economic value and market demand, and can effectively improve the economic benefits of this technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a process flow diagram of the method of the embodiment of the invention.

[0029] Figure 2 Oxalic acid desorbs MEA CO 2 CO2-rich liquid 2 Release rate (solid line in the figure) and CO 2 The desorption rate (dashed line in the figure) changes with time.

[0030] Figure 3 It is oxalate-Ca(OH) 2 Desorption regeneration MEA CO 2 MEA during the rich solution process 1 H NMR comparison spectra.

[0031] Figure 4 is Ca(OH) 2 Neutralization of oxalic acid MEA CO 2 XRD spectrum of the precipitate after barren solution regeneration.

[0032] Figure 5 Oxalic acid-NaOH desorption regeneration MEA CO 2 MEA during the rich solution process 1 H NMR comparison spectra.

[0033] Figure 6 Oxalic acid desorbs MEA CO 2 CO2-rich liquid 2 Release rate and CO 2 Desorption rate variation trend over time.

[0034] Figure 7 NaOH neutralizes oxalic acid MEA CO 2 XRD spectrum of the precipitate after barren solution regeneration.

[0035] Figure 8 Citric acid desorbs MEA CO 2 CO2-rich liquid 2 Release rate (solid line in the figure) and CO 2 The desorption rate (dashed line in the figure) changes with time.

[0036] Fig. 9 It is citric acid-Ca(OH) 2 Desorption regeneration MEA CO 2 Solution Process MEA 1 H NMR comparison spectra.

[0037] Fig.10 is Ca(OH) 2 Neutralized citric acid MEA CO 2 XRD spectrum of the precipitate after barren solution regeneration.

[0038] Fig.11 Waste acid desorption MEA CO 2 CO2-rich liquid 2 Release rate (solid line in the figure) and CO 2 The desorption rate (dashed line in the figure) changes with time. DETAILED DESCRIPTION

[0039] The present invention is further described below by way of examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Those skilled in the art may make some non-essential improvements and adjustments to the present invention according to the above-mentioned invention content and implement the invention specifically, which still falls within the scope of protection of the invention.

[0040] Example 1

[0041] (1) Oxalic acid desorption of CO 2 Rich liquid

[0042] like Figure 1 As shown, simulated flue gas (15 vol.% CO 2 / 75vol.%N 2 ), and obtain CO 2 MEA CO with a loading of 0.48 mol / mol 2 Rich solution. Add oxalic acid to MEA CO according to the molar ratio of MEA: oxalic acid = 1:0.5 2 Rich liquid, stirred at 25℃ to make it fully react and release CO 2 , using infrared flue gas analyzer to monitor CO in exhaust gas 2 Concentration and flow rate, calculate CO 2 Desorption rate and desorption ratio (CO 2 Desorption and CO 2 The results showed that oxalate CO 2 The desorption rate is about 78% ( Figure 2 After the reaction, the pH of MEA CO was measured by a pH meter. 2 The pH value of the barren solution is about 3.5. 1 HNMR characterization confirmed that the MEA in the solution was in a protonated state ( Figure 3 ).

[0043] (2) Ca(OH) 2 Neutralization and regeneration of alcohol amine

[0044] According to the molar ratio MEA:Ca(OH) 2 =1:0.5, Ca(OH) 2 Join MEA CO 2 The barren solution was stirred at 25°C for 2 h, allowed to settle, and the solid precipitate and supernatant were collected by filtration and characterized. Figure 4 As shown, the main component of the precipitate is CaC 2 O 4 ·H 2 O and CaC 2 O 4 ·2H 2 O, indicating Ca(OH) 2 The oxalate was successfully displaced from the solution. The pH value of the supernatant was 10.40. 1 H NMR spectra confirmed that MEA in the supernatant had recovered from the protonated state to the initial structure ( Figure 3 ), meet CO 2 Requirements for recycling of capture.

[0045] Example 2

[0046] The operation process of this embodiment is basically the same as that of embodiment 1, except that the solvent of MEA is replaced by ethanol from water and the alkali is replaced by NaOH.

[0047] The simulated flue gas was introduced into 50 g of 30% MEA ethanol solution to obtain CO 2 MEA CO with a loading of 0.48 mol / mol 2 Add oxalic acid to MEA CO according to the molar ratio of MEA: oxalic acid = 1:1 2 Rich liquid, stirred at 25℃ to make it fully react and release CO 2 , using infrared flue gas analyzer to monitor CO in exhaust gas 2 Concentration and flow rate, calculate CO 2 The desorption rate and desorption ratio show that oxalate CO 2 The desorption rate is about 50% ( Figure 5 After the reaction, the pH of MEA CO was measured by a pH meter. 2 The pH value of the barren solution is about 6.23. 1 H NMR characterization confirmed that the MEA in the solution was in a protonated state ( Figure 6 ).

[0048] According to the molar ratio of MEA:NaOH = 1:1, NaOH was added to MEA CO 2 The lean solution was stirred at 25°C for 4 hours, allowed to settle, and the solid precipitate and supernatant were collected by filtration, and the structures of the two were characterized. XRD test confirmed that the main component of the precipitate was Na 2 C 2 O 4 ( Figure 7 ), indicating that NaOH has successfully removed oxalate from MEA CO 2 The pH value of the supernatant is 10.10. 1 The HNMR spectrum confirmed that the MEA in the supernatant had recovered from the protonated state to the initial structure ( Figure 6 ), meet CO 2 Requirements for recycling of capture.

[0049] Example 3

[0050] (1) CO desorption by citric acid 2 Rich liquid

[0051] The operation process of this embodiment is basically the same as that of embodiment 1, except that the acid is replaced from oxalic acid to citric acid.

[0052] Simulated flue gas was introduced into 50 g of 30% MEA aqueous solution to obtain CO 2 MEA CO with a loading of 0.51 mol / mol 2Rich solution. Add citric acid to MEA CO according to the molar ratio of MEA: citric acid = 1:0.333. 2 Rich liquid, stirred at 25℃ to make it fully react and release CO 2 , using infrared flue gas analyzer to monitor CO in exhaust gas 2 Concentration and flow rate, calculate CO 2 The desorption rate and desorption ratio show that the CO 2 The desorption rate is about 71% ( Figure 8 After the reaction is completed, the pH value of MEA CO is measured. 2 The pH value of the barren solution is about 4.45. 1 H NMR characterization confirmed that the MEA in the solution was in a protonated state ( Fig. 9 ).

[0053] (2) Ca(OH) 2 Neutralization and regeneration of alcohol amine

[0054] According to the molar ratio MEA:Ca(OH) 2 =1:1, Ca(OH) 2 Join MEA CO 2 The lean solution was stirred at 25℃ for 2-4h, allowed to settle, and the solid precipitate and supernatant were collected by filtration, and the structures of the two were characterized. XRD test confirmed that the main component of the precipitate was C 12 H 10 Ca 3 O 14 ( Fig.10 ), indicating that Ca(OH) 2 The citric acid was successfully displaced from the solution and precipitated. The pH value of the supernatant was 11.10, indicating that the MEA in the solution had been successfully deprotonated and converted to the initial alkaline structure. 1 H NMR characterization confirmed that MEA in the supernatant had recovered from the protonated state to the initial structure ( Fig. 9 ), meet CO 2 Requirements for recycling of capture.

[0055] Example 4

[0056] (1) Waste acid desorption of CO 2 Rich liquid

[0057] The operation process of this embodiment is basically the same as that of embodiment 1, except that the acid is replaced from oxalic acid to oxalic acid waste liquid with 5% oxalic acid waste acid content and sulfuric acid waste liquid with 5% sulfuric acid content for testing.

[0058] The above two waste acids were added to MEACO according to the molar ratio of MEA: acid (the amount of effective acid in the waste acid) = 1:2. 2Rich liquid, stirred at 25℃ to make it fully react and release CO 2 , using infrared flue gas analyzer to monitor CO in exhaust gas 2 Concentration and flow rate, calculate CO 2 The desorption rate and desorption ratio show that the CO 2 The desorption rate is about 20% ( Fig.11 ), CO of sulfuric acid wastewater 2 The desorption rate is about 93% ( Fig.11 After the reaction was completed, the oxalic acid waste liquid MEA CO was measured by pH. 2 Barren liquid, sulfuric acid waste liquid MEA CO 2 Lean liquid MEA CO 2 The pH values ​​of the lean solution were 4.09 and 1.20, respectively, indicating that the MEA was in a protonated state.

[0059] (2) Ca(OH) 2 Neutralization and regeneration of alcohol amine

[0060] According to the molar ratio MEA:Ca(OH) 2 =1:1, Ca(OH) 2 Add oxalic acid waste liquid MEA CO 2 Barren liquid, sulfuric acid waste liquid MEA CO 2 The lean solution was stirred at 25 °C for 4 h, allowed to settle, and the solid precipitate and supernatant were collected by filtration. The pH values ​​of the supernatant were 9.40 and 12.30, respectively, indicating that the MEA in the solution had been successfully deprotonated and transformed into the initial alkaline structure, satisfying the CO 2 Requirements for recycling of capture.

Claims

1. A method for desorbing CO2-rich liquid and regenerating chemical absorbent by stepwise addition of acid and alkali without energy consumption, characterized in that: The following steps are involved: Step 1: Use a pre-prepared CO2 absorbent solution to absorb CO2 to form a CO2-rich solution; the CO2 absorbent solution is prepared from a chemical absorbent and its solvent, the solvent is water, an organic solvent or a mixture of an organic solvent and water, and the chemical absorbent is monoethanolamine, diethanolamine, N - at least one of methyldiethanolamine, 2-amino-2-methyl-1-propanol, ethylenediamine, triethylamine, piperazine, ammonia water and potassium carbonate; the organic solvent is at least one of methanol, ethanol, acetone and acetonitrile; Step 2: dissolving an acid in water to form an acid solution, adding the acid solution to the CO2 rich solution of step 1 at room temperature to desorb CO2, or directly adding the acid to the CO2 rich solution of step 1 to desorb CO2, wherein the acid is an acid that can dissociate a large number of hydrogen ions in the CO2 rich solution and react with the product obtained after absorbing CO2, and a CO2 lean solution is obtained after the desorption is completed; the acid is at least one of sulfuric acid, acetic acid, oxalic acid, citric acid, malic acid, lactic acid, and industrial waste acid; the industrial waste acid is at least one of oxalic acid waste liquid, sulfuric acid waste liquid, and hydrofluoric acid waste liquid; Step three: adding alkali to the CO2-lean solution obtained in step two, stirring, neutralizing the added acid and the protonated absorbent, and completing the regeneration of the absorbent, wherein the alkali is a alkali that can react with the acid and its conjugate base to form an insoluble substance; the alkali is at least one of alkaline metal oxides, alkaline metal hydroxides, and alkaline solid wastes, and the alkaline solid waste is at least one of fly ash and carbide slag.

2. The method according to claim 1, characterized in that: The metal hydroxide is at least one of Ca(OH)2, NaOH, KOH, Mg(OH)2, Ba(OH)2, and Sr(OH)2; the metal oxide is at least one of CaO, MgO, Na2O, BaO, CrO, and MnO.

3. The method according to claim 1, characterized in that: The molar ratio of the chemical absorbent, acid and alkali is 1:(0.25-1):(0.5-2) respectively.

4. Combined use of acid and alkali in carbon capture, utilization and storage, characterized in that: In the method of claim 1, the acid is an acid that can dissociate a large amount of hydrogen ions in the CO2 rich solution and react rapidly with the CO2 absorption product, and the base is a base that can react with the acid and its conjugate base to form an insoluble substance.

5. The application according to claim 4, characterized in that: The acid is at least one of sulfuric acid, acetic acid, oxalic acid, citric acid, malic acid and lactic acid; the base is an alkaline metal oxide or metal hydroxide; the metal hydroxide is at least one of Ca(OH)2, NaOH, KOH, Mg(OH)2, Ba(OH)2, Sr(OH)2; the metal oxide is at least one of CaO, MgO, Na2O, BaO, CrO and MnO.

6. The use according to claim 5, characterized in that: The application is to desorb the CO2 rich solution formed after the CO2 capture solution absorbs CO2 and to regenerate the chemical absorbent in the CO2 capture solution.

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