CO2 capture and in-situ conversion method based on alkanol guanidine absorbent

Abstract

The invention discloses a CO2 capture and conversion method based on an alkanol guanidine absorbent. The method comprises the following steps: firstly capturing CO2 by using polyethylene glycol functionalized alkanol guanidine as an absorbent, further performing cycloaddition reaction with an epoxy compound by using the absorbent capturing CO2 as a CO2 raw material and a catalyst and adding PEG150 as a solvent and tetrabutylammonium iodide as a cocatalyst, and reacting at 100-140 DEG C under the conditions that the molar ratio of a substrate to the absorbent is 1: 1-1: 2, the molar ratio of the substrate to the cocatalyst is 1: 0.01-1: 0.2, and the reaction temperature is 100-140 DEG C, the yield of the corresponding cyclic carbonate can reach 50%-90% under the condition that the reaction temperature is 30-60 DEG C and the reaction pressure is 0-3 MPa. The absorbent provided by the invention has the advantages of simple preparation and large CO2 absorption capacity, the CO2 absorption product can react with epoxide in situ to prepare cyclic carbonate, and high energy consumption required by CO2 desorption and absorbent regeneration is avoided.

Description

Technical Field

[0001] This invention relates to the field of CO2 capture and conversion, and more particularly to a method for CO2 capture and in-situ conversion based on a novel guanidine alkanoate absorbent. Background Technology

[0002] With the massive burning of fossil fuels and deforestation, atmospheric CO2 emissions have increased rapidly over the past few decades. The intensifying greenhouse effect has led to abnormal global climate; if left unchecked, the Earth's temperature is projected to be 4°C higher than pre-industrial levels by the end of the 21st century, triggering a series of serious environmental problems. Given the impossibility of completely abandoning fossil fuels, carbon capture and storage (CCS) technology, as an indispensable part of carbon neutrality, is a key technological means and a safety net for achieving the temperature control targets of the Paris Agreement. Among these, carbon capture, as the crucial element in implementing CCS, has received widespread attention.

[0003] In recent decades, researchers have developed numerous carbon capture methods, such as solid adsorption, membrane separation, and chemical absorption. Among these, chemical absorption utilizes alkaline compounds, such as alkali metal carbonates, organic amines, and amino acid salts, to achieve high absorption capacity and selectivity by forming tight chemical bonds with CO2. It is considered the most promising technology for large-scale CO2 capture. Currently, the most commonly used chemical absorbents in industry are aqueous solutions of alkanolamines, represented by monoethanolamine. However, traditional alkanolamine aqueous solutions have drawbacks such as high regeneration energy, easy corrosion of equipment, and easy oxidative degradation ((a) Science, 2009, 325, 1652-1654. (b) Renewable Sustainable Energy Rev., 2022, 168, 112902). Therefore, the improvement of traditional amine absorbents and the development of alternatives have become research hotspots in the chemical absorption of CO2.

[0004] Non-aqueous absorbents utilize organic solvents or other methods with higher thermal stability to replace water. On one hand, the reduction in specific heat capacity and the increase in boiling point of the capture system significantly reduce latent and sensible heat losses during CO2 desorption. On the other hand, since the system is water-free, the corrosiveness of the captured products to equipment is greatly reduced. For example, using organic solvents with low specific heat capacity and high boiling points, such as ethylene glycol (J.CO2 Util., 2020, 35, 126-144), sulfolane, dimethyl sulfoxide (Chem.Eng.Sci., 2019, 202, 403-416), and N-methylpyrrolidone (Appl.Energy, 2020, 264, 114703), instead of water in traditional alkanolamine solution absorbents can effectively improve the recycling capacity of CO2 capture systems and reduce their regeneration energy consumption. However, the introduction of organic solvents as diluents increases capture costs, which is detrimental to large-scale industrial applications.

[0005] Introducing functional groups with different properties into organic amine molecules to enable their application in solvent-free CO2 capture processes, thereby avoiding the additional energy consumption caused by solvents during regeneration, is currently a research hotspot for reducing CO2 capture costs. For example, a polyethylene glycol solution of sodium amino acid salt with a sterically hindered substituent on the nitrogen atom can capture carbon dioxide in the form of carbamic acid, and the captured carbon dioxide can be completely desorbed at 60°C (Angew. Chem. Int. Ed., 2012, 51, 11306-11310). Silane-functionalized aliphatic amines can be used as single-component absorbents to capture CO2. The introduction of silane groups not only controls the increase in absorbent viscosity during absorption but also lowers the desorption temperature (ChemSusChem, 2014, 7, 299-307). Recently, a class of aminopyridine single-component absorbents was designed and synthesized by Koech et al. and applied to the process of reversible CO2 capture. This class of aminopyridines can improve the CO2 capture molar ratio to a certain extent by interacting weakly with in-situ generated carbamic acid through pyridine (ACS Sustainable Chem. Eng., 2019, 7, 7535-7542).

[0006] Besides organic amines, some guanidine and amidine organic base molecules are also used as the main body for modification in solvent-free, single-component CO2 capture conditions. For example, modifying aliphatic alcohols onto the organic base tetramethylguanidine yields an alkanoguanidine absorbent that can capture CO2 at nearly equivalent rates and can be regenerated at temperatures below 70°C (Green Chem. 2010, 12, 713-721). Solid hydroxylated amidines, obtained by combining short-chain alcohols with cyclic amidines, are difficult to use directly for CO2 capture due to their low gas-solid mass transfer efficiency. However, they can be loaded onto mesoporous silica by impregnation to increase their specific surface area, thereby improving capture efficiency (Chem. Commun., 2010, 46, 2507-2509). To address the issue of excessive viscosity in guanidine / alkanolamine absorbers after CO2 absorption, Koech et al. first synthesized a 1,3-dimethylimidazoline-2-imino guanidine absorber. This absorber reduces molecular order and intermolecular packing ability by introducing branching, resulting in a significantly lower viscosity after CO2 absorption compared to traditional straight-chain guanidine absorbers (RSCAdv., 2013, 3, 566-572). However, despite subsequent structural optimizations of this branched guanidine absorber ((a) J. Phys. Chem. Lett., 2016, 7, 1646-1652. (b) ChemSusChem, 2017, 10, 636-642), the actual absorption capacity of this type of absorber is only 35–44 mol%, far below the theoretical 100 mol%. Therefore, designing guanidine absorbers with both high fluidity and high absorption capacity is crucial for the development of guanidine absorbers.

[0007] While CCS technology holds great potential for reducing carbon emissions, its practicality is hampered by the energy-intensive desorption process, the high costs of compression and transportation, and the potential for gas leakage. Carbon Capture and Utilization (CCU), as a complement to CCS, aims to utilize CO2 as a sustainable C1 resource and, to some extent, replace traditional fossil fuels, thereby reducing human dependence on fossil fuels while achieving carbon reduction goals. CCU strategies advocate directly converting captured CO2 into valuable chemicals, opening up a new low-energy pathway for CO2 capture and utilization: on the one hand, it avoids the additional energy consumption during desorption by regenerating the absorbent through chemical reactions; on the other hand, the captured CO2 molecules undergo charge redistribution, essentially becoming activated CO2, thus facilitating conversion reactions under milder conditions.

[0008] Currently, carbon capture and conversion strategies mainly focus on the synthesis of oxazolidinones (Angew. Chem. Int. Ed., 2012, 51, 11306-11310), methyl formate (Inorg. Chem., 2014, 53, 9849-9854), methanol (J. Am. Chem. Soc., 2018, 140, 1580-1583), formic acid (Green Chem., 2016, 18, 5831-5838) or formate salts (J. Am. Chem. Soc., 2018, 140, 16873-16876), urea derivatives (Energy Environ. Sci., 2011, 4, 3971-3975), and cyclic carbonates ((a)ACS Sustainable). Chem. Eng., 2023, 11, 9613-9619.(b) Chem. Commun., 2016, 52, 7830-7833, etc. It is worth noting that existing methods for CO2 capture and in-situ conversion to prepare cyclic carbonates often use haloalcohols or propargyl alcohols as substrates, making it difficult to achieve 100% atom utilization. Although DJ Heldebrant et al. recently coupled CO2 capture with cycloaddition reactions using organic amines as absorbents and epoxides as substrates, the strong nucleophilicity of amines leads to unavoidable side reactions between the absorbent and substrate, severely affecting reaction selectivity (Energy Fuels. 2024, 38, 7959-7965). Therefore, it is necessary to design bifunctional reagents with both CO2 capture and catalytic effects to achieve CO2 capture and in-situ reaction with epoxides to prepare cyclic carbonates, achieving 100% atom utilization CO2 conversion. Summary of the Invention

[0009] To address the problem that commonly used amine-based CO2 trapping reagents are highly nucleophilic and prone to side reactions with epoxides, this invention designs and synthesizes an alkylguanidine-based absorbent containing alkylguanidine and polyethylene glycol groups. The alkylguanidine group is highly basic and weakly nucleophilic, avoiding side reactions with epoxides, but effectively abstracting protons from the hydroxyl groups of polyethylene glycol, promoting the reaction between alkylguanidine and CO2. Furthermore, the ether chain of polyethylene glycol increases the solubility of CO2 in the absorbent through intermolecular forces and enhances the absorbent's flowability and mass transfer efficiency through a "swelling effect." The absorbent captures CO2 through a synergistic combination of physical and chemical absorption, achieving an absorption capacity of up to and exceeding 100 mol%. Further addition of epoxides, solvents, and co-catalysts to the captured CO2 enables the direct conversion of the captured CO2 into cyclic carbonates.

[0010] This invention is achieved through the following technical solution:

[0011] A method for CO2 capture and in-situ conversion based on guanidine alkanol absorbents includes the following steps:

[0012] 1) The guanidine alkanol absorbent is loaded into a glass liner tube and sealed with a rubber stopper. Then, two needles, one long and one short, are inserted into the test tube through the rubber stopper. The long needle is connected to a gas cylinder and used to blow in CO2. The flow rate of the blown-in gas is adjusted and measured by a rotor flow meter. The short needle is suspended above the liquid surface as a gas outlet to balance the gas pressure inside and outside the test tube.

[0013] 2) Use a CO2 gas stream to purge the upper part of the liquid surface to replace the air in the tube, then insert the needle below the liquid surface and bubble the guanidine absorbent at a certain temperature. Control the gas flow rate so that the absorbent is not blown out. Measure the amount of CO2 absorbed by weighing.

[0014] 3) When the CO2 absorption no longer increases, add a certain amount of epoxide, co-catalyst tetrabutylammonium iodide and solvent triethylene glycol to the liner, and put the glass liner into the reactor, fill it with CO2 at a certain pressure, seal it and react at a certain temperature and pressure.

[0015] 4) After the reaction is complete, cool the reactor in an ice-water bath, slowly open the gas valve to release the unreacted CO2 and epoxides, and use the tail gas absorption tube containing N,N-dimethylformamide to absorb the organic matter in the tail gas.

[0016] 5) After opening the vessel, clean the vessel lid and walls with a small amount of DMF and combine it with the DMF solution in the tail gas absorption tube. Add biphenyl as an internal standard, take a sample, dilute it, and use gas chromatography-mass spectrometry to identify the product. Then, use gas chromatography to determine the yield of cyclic carbonates.

[0017] Preferably, the guanidine alkanoate absorbent is obtained by reacting 2-chloro-1,3-dimethylimidazoline chloride with amino-functionalized polyethylene glycol of different chain lengths, and its structure is as follows:

[0018]

[0019] Preferably, the guanidine alkanoate absorbent captures CO2 at a temperature of 25–40°C and the partial pressure of CO2 is 0.15–1 bar.

[0020] Preferably, in the conversion reaction, the substrate is an epoxy compound, the molar ratio of which to the absorbent is 1:1 to 1:2, the molar ratio of which to tetrabutylammonium iodide is 1:0.01 to 1:0.2, the amount of solvent added is 0 to 2 mL / mmol of epoxy substrate, the reaction temperature is 100 to 140 °C, the pressure of additional CO2 introduced during the reaction is 0 to 3 MPa, and the reaction time is 6 to 12 h.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The alkylguanidine absorbent in this invention has the advantages of simple preparation and large CO2 absorption capacity. Further reaction of the CO2 absorption product with epoxy compounds can not only avoid the energy-intensive CO2 desorption step, but also effectively activate CO2 and epoxy compounds, promoting the reaction. This invention realizes the integration of CO2 capture and conversion, showing broad prospects for industrial application. Detailed Implementation

[0023] This invention provides a method for CO2 capture and in-situ conversion based on guanidine alkanol absorbents, specifically comprising the following steps:

[0024] 1) Preparation of CO2 absorbent: Alkylguanidine with the following structure was obtained by reacting 2-chloro-1,3-dimethylimidazoline chloride with amino-functionalized polyethylene glycol of different chain lengths:

[0025]

[0026] 2) CO2 capture: Alkylguanidine is placed in a glass liner tube and sealed with a rubber stopper. Two needles, one long and one short, are then inserted into the tube through the rubber stopper. The long needle is connected to a gas cylinder for introducing CO2, and the gas flow rate is controlled and measured using a rotor flow meter. The short needle is suspended above the liquid surface, serving as the gas outlet to balance the pressure inside and outside the tube. A CO2 gas stream is used to purge the air from the liquid surface, and then the needles are inserted below the liquid surface. While maintaining the temperature of the capturing reagent at 25℃~40℃, air bubbles are introduced to capture CO2. The gas flow rate should be such that the capturing reagent is not blown out (the partial pressure of CO2 in the gas stream is 0.15~1 bar). The mass of the glass liner tube is monitored; when the total weight no longer changes, CO2 absorption has reached equilibrium.

[0027] 3) In-situ conversion for CO2 capture: After CO2 absorption reaches equilibrium, the substrate epoxide, co-catalyst tetrabutylammonium iodide, and solvent triethylene glycol (PEG150) are added to the liner. The molar ratio of substrate to guanidine is 1:1 to 1:2, and the molar ratio of substrate to tetrabutylammonium iodide is 1:0.01 to 1:0.2. The amount of solvent added is 0 to 3 mL / mmol of epoxide substrate. The glass liner is placed in the reactor, and an additional 0 to 3 MPa is introduced. CO2 was stirred at 100–140 °C for 6–12 h. After the reaction was completed, the reactor was cooled in an ice-water bath. The unreacted CO2 was released by slowly opening the gas valve, and the compounds in the tail gas were absorbed using a tail gas absorption tube containing N,N-dimethylformamide (DMF). After opening the reactor, the reactor lid and walls were cleaned with a small amount of DMF. Biphenyl was added as an internal standard. The solutions in the tail gas tube and the reactor were combined, and samples were taken, diluted, and the products were qualitatively analyzed by gas chromatography-mass spectrometry (GC-MS). The yield of the products was determined by GC-MS.

[0028] The present invention will be further described in detail with reference to specific embodiments. The following embodiments are only used to illustrate the present invention and are not intended to limit the present invention.

[0029] Example 1

[0030] A method for capturing CO2 and converting it in situ into propylene carbonate based on guanidine alkanol absorbents includes the following steps:

[0031] 1) Synthesis of CO2 trapping reagent: Under ice bath conditions, 2.10 g (20 mmol) of diethylene glycolamine and 4.05 g (40.0 mmol) of triethylamine were dissolved in 20.0 mL of dichloromethane. Then, a solution of 3.38 g (20.0 mmol) of 2-chloro-1,3-dimethylimidazoline chloride in 20.0 mL of dichloromethane was added dropwise. The mixture was refluxed at 50 °C for 48 h. The resulting system was extracted three times with 30 wt.% KOH solution. The separated organic phase was dried with anhydrous magnesium sulfate, filtered, and the solvent was removed by rotary evaporation. 2.95 g (14.5 mmol) of a yellow solid was obtained by vacuum distillation, with a yield of 73%. This yellow solid was 2-(2-((1,3-dimethylimidazoline-2-imino)ethoxy)ethane-1-ol, denoted as Monogly-DMI, with a melting point of 61.3–62.5 °C.

[0032] 2) CO2 capture: 0.61 g (3 mmol) Monogly-DMI was placed in a glass-lined tube and sealed with a rubber stopper. A CO2 gas stream was used to purge the upper part of the absorbent, displacing the air inside the tube. Then, at 25°C, the gas flow rate was controlled at 0.1 L / min, and the yellow solid gradually liquefied. The apparatus was weighed and recorded at regular intervals until the mass no longer changed. By calculating the mass difference before and after absorption, the absorption capacity of the absorbent Digly-DMI was found to be 70 mol%.

[0033] 3) Conversion of CO2 capture product: The absorption device was removed, and 116.2 mg (2.0 mmol) of propylene oxide, 3 mL of triethylene glycol, and 73.88 mg (0.2 mmol) of tetrabutylammonium iodide were added to the liner to make the molar ratio of substrate to guanidine 1:1.5 and the molar ratio of substrate to tetrabutylammonium iodide 1:0.1. The liner was placed in a 25 mL reactor, and CO2 was introduced at 3 MPa. The reaction was carried out at 120 °C for 12 h. After the reaction was completed, the reactor was cooled in an ice-water bath, and the unreacted CO2 was slowly released by opening the gas valve. The compounds carried by the CO2 gas stream were absorbed using a tail gas absorption tube containing DMF. After opening the reactor, the reactor lid and walls were cleaned with a small amount of DMF, and biphenyl was added as an internal standard. The solutions in the tail gas tube and the reactor were combined, and samples were taken, diluted, and qualitatively analyzed by gas chromatography-mass spectrometry (GC-MS). The yield of propylene carbonate was found to be 88% in the GC-MS.

[0034] Example 2

[0035] A method for capturing CO2 and converting it in situ into propylene carbonate based on guanidine alkanol absorbents includes the following steps:

[0036] 1) Synthesis of CO2 trapping reagent: Under ice bath conditions, 2.98 g (20 mmol) of triethylene glycolamine and 4.05 g (40 mmol) of triethylamine were dissolved in 20 mL of dichloromethane. Then, a 20 mL solution of dichloromethane containing 3.38 g (20 mmol) of 2-chloro-1,3-dimethylimidazoline chloride was added dropwise. The mixture was refluxed at 50 °C for 48 h. The resulting system was extracted three times with 30 wt.% KOH solution. Anhydrous magnesium sulfate was added to the separated organic phase for drying, followed by filtration and rotary evaporation to remove the solvent. 2.95 g (14.5 mmol) of a yellow liquid was obtained by vacuum distillation, with a yield of 73%. This yellow liquid was 2-(2-(2-((1,3-dimethylimidazoline-2-yl)amino)ethoxy)ethoxy)ethane-1-ol, denoted as Digly-DMI.

[0037] 2) CO2 capture: 0.73 g (3 mmol) of Digly-DMI was placed in a glass-lined tube and sealed with a rubber stopper. A CO2 gas stream was used through a long needle to purge the upper part of the liquid surface, displacing the air inside the tube. Then, at 30°C, the gas was continuously bubbled at a flow rate of 0.15 L / min. The apparatus was weighed and recorded at regular intervals until the mass no longer changed. By calculating the mass difference before and after absorption, the absorption capacity of the absorbent Digly-DMI was found to be 100 mol%.

[0038] 3) Conversion of CO2 capture products: The absorption device was removed, and 174.3 mg (3.0 mmol) of propylene oxide, 3 mL of triethylene glycol, and 11.1 mg (0.03 mmol) of tetrabutylammonium iodide were added to the liner to make the molar ratio of substrate to guanidine 1:1 and the molar ratio of substrate to tetrabutylammonium iodide 1:0.01. The liner was placed in a 25 mL reactor, which was charged with 3 MPa of CO2 and reacted at 100 °C for 12 h. After the reaction, the reactor was cooled in an ice-water bath, and the unreacted CO2 was slowly released by opening the gas valve. The compounds carried by the CO2 gas stream were absorbed using a tail gas absorption tube containing DMF. After opening the reactor, the reactor lid and walls were cleaned with a small amount of DMF, and biphenyl was added as an internal standard. The solutions in the tail gas tube and the reactor were combined, and samples were taken, diluted, and qualitatively analyzed by gas chromatography-mass spectrometry (GC-MS). The yield of propylene carbonate was determined to be 70% by GC-MS.

[0039] Example 3

[0040] A method for capturing CO2 and converting it in situ into propylene carbonate based on guanidine alkanol absorbents includes the following steps:

[0041] 1) Synthesis of CO2 trapping reagent: Under ice bath conditions, 2.98 g (20 mmol) of triethylene glycolamine and 4.05 g (40 mmol) of triethylamine were dissolved in 20 mL of dichloromethane. Then, a 20 mL solution of dichloromethane containing 3.38 g (20 mmol) of 2-chloro-1,3-dimethylimidazoline chloride was added dropwise. The mixture was refluxed at 50 °C for 48 h. The resulting system was extracted three times with 30 wt.% KOH solution. The separated organic phase was dried over anhydrous magnesium sulfate, filtered, and the solvent was removed by rotary evaporation. 2.95 g (14.5 mmol) of a yellow liquid was obtained by vacuum distillation, with a yield of 76%. This yellow liquid was 2-(2-(2-((1,3-dimethylimidazoline-2-yl)amino)ethoxy)ethoxy)ethane-1-ol, denoted as Digly-DMI.

[0042] 2) CO2 capture: 0.73 g (3 mmol) of Digly-DMI was placed in a glass-lined tube and sealed with a rubber stopper. A CO2 gas stream was used through a long needle to purge the upper part of the liquid surface, displacing the air inside the tube. Then, at 25°C, the gas was continuously bubbled at a flow rate of 0.18 L / min. The apparatus was weighed and recorded at regular intervals until the mass no longer changed. By calculating the mass difference before and after absorption, the absorption capacity of the absorbent Digly-DMI was found to be 101 mol%.

[0043] 3) Conversion of CO2 capture product: The absorption device was removed, and 174.2 mg (3.0 mmol) of propylene oxide, 3 mL of triethylene glycol, and 111.6 mg (0.03 mmol) of tetrabutylammonium iodide were added to the liner to make the molar ratio of substrate to guanidine 1:1 and the molar ratio of substrate to tetrabutylammonium iodide 1:0.1. The liner was placed in a 25 mL reactor, which was charged with 2 MPa of CO2 and reacted at 100 °C for 10 h. After the reaction, the reactor was cooled in an ice-water bath, and the tail gas was slowly released by opening the gas valve. The compounds in the tail gas were absorbed using a tail gas absorption tube containing DMF. After opening the reactor, the reactor lid and walls were cleaned with a small amount of DMF, and biphenyl was added as an internal standard. The solutions in the tail gas tube and the reactor were combined, and samples were taken, diluted, and qualitatively analyzed by gas chromatography-mass spectrometry (GC-MS). The yield of propylene carbonate was determined to be 79% by GC-MS.

[0044] Example 4

[0045] A method for capturing CO2 and converting it in situ into propylene carbonate based on guanidine alkanol absorbents includes the following steps:

[0046] 1) Synthesis of CO2 trapping reagent: Under ice bath conditions, 2.98 g (20 mmol) of diethylene glycolamine and 4.05 g (40 mmol) of triethylamine were dissolved in 20 mL of dichloromethane. Then, a 20 mL solution of dichloromethane containing 3.38 g (20 mmol) of 2-chloro-1,3-dimethylimidazoline chloride was added dropwise. The mixture was refluxed at 50 °C for 48 h. The resulting system was extracted three times with 30 wt.% KOH solution. The separated organic phase was dried over anhydrous magnesium sulfate, filtered, and the solvent was removed by rotary evaporation. 2.95 g (14.5 mmol) of a yellow liquid was obtained by vacuum distillation, with a yield of 73%. This yellow liquid was 2-(2-(2-((1,3-dimethylimidazoline-2-yl)amino)ethoxy)ethoxy)ethane-1-ol, denoted as Digly-DMI.

[0047] 2) CO2 capture: 0.73 g (3 mmol) of Digly-DMI was placed in a glass-lined tube and sealed with a rubber stopper. A mixed gas flow with a CO2:N2 volume fraction of 15%:85% was used to purge the upper part of the liquid surface through a long needle to displace the air inside the tube. Then, at a temperature of 25°C, the gas was continuously bubbled at a flow rate of 0.1 L / min. The apparatus was weighed and recorded at regular intervals until the mass no longer changed. The absorption capacity of the absorbent Digly-DMI was calculated to be 71 mol% by calculating the mass difference before and after absorption.

[0048] 3) Conversion of CO2 capture product: Remove the absorption device and add 87.2 mg (1.5 mmol) propylene oxide, 3 mL triethylene glycol, and 110.8 mg (0.3 mmol) tetrabutylammonium iodide to the liner, making the molar ratio of substrate to guanidine 1:2 and the molar ratio of substrate to tetrabutylammonium iodide 1:0.2. Place the liner into a 25 mL reactor, charge with 1 MPa CO2, and react at 140 °C for 6 h. After the reaction, cool the reactor in an ice-water bath, slowly open the gas valve to release the tail gas, and absorb the compounds in the tail gas using a tail gas absorption tube containing DMF. After opening the reactor, clean the reactor lid and walls with a small amount of DMF, add biphenyl as an internal standard, combine the solutions in the tail gas tube and the reactor, take samples, dilute, and qualitatively analyze the product using gas chromatography-mass spectrometry (GC-MS). The yield of propylene carbonate was determined to be 90% by gas chromatography.

[0049] Example 5

[0050] A method for capturing CO2 and converting it in situ into propylene carbonate based on guanidine alkanol absorbents includes the following steps:

[0051] 1) Synthesis of CO2 trapping reagent: Under ice bath conditions, 2.98 g (20 mmol) of triethylene glycolamine and 4.05 g (40 mmol) of triethylamine were dissolved in 20 mL of dichloromethane. Then, a 20 mL solution of dichloromethane containing 3.38 g (20 mmol) of 2-chloro-1,3-dimethylimidazoline chloride was added dropwise. The mixture was refluxed at 50 °C for 48 h. The resulting system was extracted three times with 30 wt.% KOH solution. Anhydrous magnesium sulfate was added to the separated organic phase for drying, followed by filtration and rotary evaporation to remove the solvent. 2.95 g (14.5 mmol) of a yellow liquid was obtained by vacuum distillation, with a yield of 73%. This yellow liquid was 2-(2-(2-((1,3-dimethylimidazoline-2-yl)amino)ethoxy)ethoxy)ethane-1-ol, denoted as Digly-DMI.

[0052] 2) CO2 capture: 0.73 g (3 mmol) of Digly-DMI was placed in a glass-lined tube and sealed with a rubber stopper. A CO2 gas stream was used through a long needle to purge the upper part of the liquid surface, displacing the air inside the tube. Then, at 40°C, the gas was continuously bubbled at a flow rate of 0.1 L / min. The apparatus was weighed and recorded at regular intervals until the mass no longer changed. The absorption capacity of the absorbent Digly-DMI was calculated to be 68 mol% by calculating the mass difference before and after absorption.

[0053] 3) Conversion of CO2-captured products: The absorption device was then removed, and 116.2 mg (2.0 mmol) of propylene oxide and 73.88 mg (0.2 mmol) of tetrabutylammonium iodide were added to the liner without any solvent, making the molar ratio of substrate to guanidine 1:1.5 and the molar ratio of substrate to tetrabutylammonium iodide 1:0.1. The liner was placed in a 25 mL reactor, which was then charged with 1 MPa of CO2 and reacted at 120 °C for 6 h. After the reaction, the reactor was cooled in an ice-water bath, and the tail gas was slowly released by opening the gas valve. The compounds in the tail gas were absorbed using a tail gas absorption tube containing DMF. After opening the reactor, the reactor lid and walls were cleaned with a small amount of DMF, and biphenyl was added as an internal standard. The solutions in the tail gas tube and the reactor were combined, and samples were taken, diluted, and qualitatively analyzed by gas chromatography-mass spectrometry (GC-MS). The yield of propylene carbonate was determined to be 74% by GC-MS.

[0054] Example 6

[0055] A method for capturing CO2 and converting it in situ into propylene carbonate based on guanidine alkanol absorbents includes the following steps:

[0056] 1) Synthesis of CO2 trapping reagent: Under ice bath conditions, 3.86 g (20 mmol) of aminotetraethylene glycol and 4.05 g (40 mmol) of triethylamine were dissolved in 20 mL of dichloromethane. Then, a 20 mL dichloromethane solution containing 3.38 g (20 mmol) of 2-chloro-1,3-dimethylimidazoline chloride was added dropwise. The mixture was refluxed at 50 °C for 72 h. The resulting system was extracted three times with 30 wt.% KOH solution. Anhydrous magnesium sulfate was added to the organic phase for drying, followed by filtration and rotary evaporation to remove the solvent. Column chromatography (CH2Cl2:CH3OH = 5:1) yielded 3.47 g (12 mmol) of a pale yellow liquid, with a yield of 60%. This pale yellow liquid was 2-(2-(2-(2-((1,3-dimethylimidazoline-2-yl)amino)ethoxy)ethoxy)ethoxy)ethane-1-ol, denoted as Trigly-DMI.

[0057] 2) CO2 capture: 0.86 g (3 mmol) of Trigly-DMI was placed in a glass-lined tube and sealed with a rubber stopper. A CO2 gas stream was used through a long needle to purge the upper part of the liquid surface, displacing the air inside the tube. Then, at 25°C, the gas was continuously bubbled at a flow rate of 0.1 L / min. The apparatus was weighed and recorded at regular intervals until the mass no longer changed. By calculating the mass difference before and after absorption, the absorption capacity of the absorbent Digly-DMI was found to be 107 mol%.

[0058] 3) Conversion of CO2 capture product: The absorption device was then removed, and 116.2 mg (2.0 mmol) of propylene oxide, 3 mL of triethylene glycol, and 73.88 mg (0.2 mmol) of tetrabutylammonium iodide were added to the liner to achieve a substrate-to-alkanoguanidine molar ratio of 1:1.5 and a substrate-to-tetrabutylammonium iodide molar ratio of 1:0.1. The liner was placed in a 25 mL reactor and reacted at 120 °C for 6 h. After the reaction, the reactor was cooled in an ice-water bath, and the tail gas was slowly released by opening the gas valve. The compounds in the tail gas were absorbed using a tail gas absorption tube containing DMF. After opening the reactor, the reactor lid and walls were cleaned with a small amount of DMF, and biphenyl was added as an internal standard. The solutions in the tail gas tube and the reactor were combined, and samples were taken, diluted, and qualitatively analyzed by gas chromatography-mass spectrometry (GC-MS). The yield of propylene carbonate was determined to be 58% by GC-MS.

[0059] Example 7

[0060] A method for CO2 capture and in-situ conversion based on guanidine alkanol absorbents, comprising the following steps:

[0061] 1) Synthesis of CO2 trapping reagent: Under ice bath conditions, 2.98 g (20 mmol) of triethylene glycolamine and 4.05 g (40 mmol) of triethylamine were dissolved in 20 mL of dichloromethane. Then, a 20 mL solution of dichloromethane containing 3.38 g (20 mmol) of 2-chloro-1,3-dimethylimidazoline chloride was added dropwise. The mixture was refluxed at 50 °C for 48 h. The resulting system was extracted three times with 30 wt.% KOH solution. Anhydrous magnesium sulfate was added to the separated organic phase for drying, followed by filtration and rotary evaporation to remove the solvent. 2.95 g (14.5 mmol) of a yellow liquid was obtained by vacuum distillation, with a yield of 73%. This yellow liquid was 2-(2-(2-((1,3-dimethylimidazoline-2-yl)amino)ethoxy)ethoxy)ethane-1-ol, denoted as Digly-DMI.

[0062] 2) CO2 capture: 0.73 g (3.0 mmol) of Digly-DMI was placed in a glass-lined tube and sealed with a rubber stopper. The air in the tube was displaced by a CO2 gas stream through a long needle. Then, at a temperature of 25 °C, the gas was continuously bubbled at a flow rate of 0.05 L / min. The device was weighed and recorded at regular intervals until the mass no longer changed. The absorption capacity of the absorbent Digly-DMI was calculated to be 10¹ mol by calculating the mass difference before and after absorption.

[0063] 3) Conversion of CO2 capture products: The absorption device was removed, and 87.2 mg (1.5 mmol) of propylene oxide, 3 mL of triethylene glycol, and 27.7 mg (0.075 mmol) of tetrabutylammonium iodide were added to the liner to make the molar ratio of propylene oxide to guanidine 1:2 and the molar ratio of propylene oxide to tetrabutylammonium iodide 1:0.05. The liner was placed in a 25 mL reactor and reacted at 120 °C for 6 h. After the reaction, the reactor was cooled in an ice-water bath, and the tail gas was slowly released by opening the gas valve. The compounds in the tail gas were absorbed using a tail gas absorption tube containing DMF. After opening the reactor, the reactor lid and walls were cleaned with a small amount of DMF, and biphenyl was added as an internal standard. The solutions in the tail gas tube and the reactor were combined, and a sample was diluted and analyzed by gas chromatography. The yield of propylene carbonate was 52%.

[0064] Example 8

[0065] A method for capturing CO2 and converting it in situ into cyclic carbonates containing different substituents based on guanidine alkanoates is described. The specific experimental procedures and quantitative methods are the same as in Example 5. Epoxides containing different substituents are selected to react with activated CO2, and the results are shown in Table 1.

[0066] Table 1. In-situ catalytic conversion of CO2 to synthesize cyclic carbonates with different substituents.

[0067]

[0068] The foregoing has described several embodiments of the present invention in detail, but these are merely preferred embodiments and should not be construed as limiting the scope of the invention. All equivalent variations and improvements made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A method for CO2 capture and in-situ conversion based on guanidine alkanol absorbents, characterized in that: Includes the following steps: 1) The guanidine alkanol absorbent is loaded into a glass liner tube and sealed with a rubber stopper. Then, two needles, one long and one short, are inserted into the test tube through the rubber stopper. The long needle is connected to a gas cylinder and used to blow in CO2. The flow rate of the blown-in gas is adjusted and measured by a rotor flow meter. The short needle is suspended above the liquid surface as a gas outlet to balance the gas pressure inside and outside the test tube. 2) Use a CO2 gas stream to purge the upper part of the liquid surface to replace the air in the tube, then insert the needle below the liquid surface and bubble the guanidine absorbent at a certain temperature. Control the gas flow rate so that the absorbent is not blown out. Measure the amount of CO2 absorbed by weighing. 3) When the CO2 absorption no longer increases, add a certain amount of epoxide, co-catalyst tetrabutylammonium iodide and solvent triethylene glycol to the liner, and put the glass liner into the reactor, fill it with CO2 at a certain pressure, seal it and react at a certain temperature and pressure. 4) After the reaction is complete, cool the reactor in an ice-water bath, slowly open the gas valve to release the unreacted CO2 and epoxides, and use the tail gas absorption tube containing N,N-dimethylformamide to absorb the organic matter in the tail gas. 5) After opening the vessel, clean the vessel lid and walls with a small amount of DMF and combine it with the DMF solution in the tail gas absorption tube. Add biphenyl as an internal standard, take a sample, dilute it, and use gas chromatography-mass spectrometry to identify the product. Then, use gas chromatography to determine the yield of cyclic carbonates.

2. The method for CO2 capture and in-situ conversion based on alkanoguanidine absorbents according to claim 1, characterized in that: The guanidine alkanoate absorbent was obtained by reacting 2-chloro-1,3-dimethylimidazoline chloride with amino-functionalized polyethylene glycol of different chain lengths, and its structure is as follows:

3. A method for CO2 capture and in-situ conversion based on alkanoguanidine absorbents according to claim 1 or 2, characterized in that: The guanidine-based absorbent captures CO2 at a temperature of 25–40°C and a partial pressure of CO2 of 0.15–1 bar.

4. A method for CO2 capture and in-situ conversion based on alkanoguanidine absorbents according to claim 1 or 2, characterized in that: In the conversion reaction, the substrate is an epoxy compound, with a molar ratio of 1:1 to 1:2 to the absorbent and a molar ratio of 1:0.01 to 1:0.2 to tetrabutylammonium iodide. The amount of solvent added is 0 to 2 mL / mmol of epoxy substrate. The reaction temperature is 100 to 140 °C. The pressure of additional CO2 introduced during the reaction is 0 to 3 MPa. The reaction time is 6 to 12 h.

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