Reactor, catalyst and application method for catalytic preparation of formic acid based on mea rich co2 solution

Abstract

The application discloses a kind of based on MEA rich CO2 solution catalytic formic acid reactor, catalyst and application method, belong to carbon capture and utilization technical field.The reactor is connected left desorption cavity and right reaction cavity by condensation reflux pipe, utilize boiling point difference and realize the efficient selective separation of CO2 and MEA / water, from the root, catalyst is deactivated and the problem of reaction medium interference by MEA poisoning.The application also designs the Ru-based catalyst with 1,3,5-triazine-7-phosphorus-7-phosphorus adamantane (PTA) as phosphine ligand, and its catalytic TON value is far superior to traditional phosphine ligand.The application realizes the independent temperature control and decoupling control of desorption and hydrogenation process, and the catalyst can be stably circulated more than 10 times, and the MEA capture liquid has no obvious degradation loss.The overall energy consumption is significantly lower than that of traditional process, the device cost is low, easy to industrial scale-up, and has important application value.

Description

Technical Field

[0001] This invention relates to the fields of carbon capture and utilization (CCU), catalytic conversion and chemical equipment technology, specifically to a reactor for the catalytic hydrogenation of MEA (monoethanolamine) CO2-rich solution to formic acid, and a highly efficient Ru-based catalyst adapted to the reactor with PTA (1,3,5-triaza-7-phosphaadamantane) as a ligand and its application method. Background Technology

[0002] With increasing global pressure to reduce CO2 emissions, carbon capture, utilization, and storage (CCUS) technologies have become crucial pathways to achieving carbon neutrality. Among various chemical absorption methods, MEA (monoethanolamine) solution has become the most widely used CO2 absorbent in industry due to its fast absorption rate and low cost. After absorbing CO2, MEA solution forms a CO2-rich MEA solution. Traditional processes require heating the CO2-rich MEA solution at high temperatures (>120°C) in a stripping tower to desorb and release high-purity CO2 for recovery. This process is energy-intensive, accounting for more than 60% of the total cost of carbon capture, severely restricting its techno-economic viability.

[0003] To overcome the energy consumption bottleneck, MEA-rich CO2 solutions can be directly subjected to catalytic hydrogenation conversion, achieving integrated "capture-conversion" and directly converting the captured CO2 into bulk chemicals such as formic acid or hydrogen carriers, thus eliminating the energy-intensive desorption and compression steps. However, existing technologies mostly use a single high-pressure reactor to directly mix the MEA-rich CO2 solution with the catalyst for the reaction, which has the following prominent problems: 1. Severe Deactivation of Catalyst and Collector: MEA, as an organic primary amine, has a strong coordination and poisoning effect on transition metal catalysts such as Ru and Ir. Under high temperature and pressure, the active sites of the catalyst are occupied by MEA, leading to nitridation deactivation. Simultaneously, direct contact between MEA and the catalyst also causes the degradation of the MEA collector. Experiments show that under the action of Ru-based catalytic systems, the MEA solution turns yellow after about one day and black after about seven days, indicating an irreversible degradation reaction. This not only reduces CO2 capture efficiency but also increases the cost of absorbent replenishment.

[0004] 2. Cross-interference of reaction media: The water in the MEA solution not only dilutes the effective reactant concentration, but also affects the structure and stability of catalytically active species, significantly reducing the space-time yield and selectivity of products such as formic acid.

[0005] 3. Lack of decoupling control between MEA desorption and CO2 hydrogenation processes: A single reactor cannot simultaneously meet the optimal thermodynamic and kinetic conditions for both processes, making it difficult to optimize reaction conditions.

[0006] In addition, existing technologies include a Chinese invention patent (CN114225668A) that discloses a carbon dioxide capture and hydrogenation formic acid production reactor, but it is a cylindrical tubular structure with a gas distributor at the bottom, which cannot effectively separate CO2 from the MEA (Mechanical Electrodesorption). Other technologies mostly use polymer membranes or inorganic membranes for CO2 separation, which suffers from problems such as expensive membrane materials, easy clogging, and short lifespan. Therefore, there is an urgent need to develop a novel reaction device that can spatially separate and functionally synergistically perform the two processes of CO2 desorption and catalytic hydrogenation, and to design a highly efficient and stable catalyst suitable for it. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a reactor, catalyst, and application method for the catalytic production of formic acid based on MEA-rich CO2 solution. The invention achieves highly efficient and selective separation of CO2 from MEA / water through a condenser reflux pipe, fundamentally solving the problems of catalyst poisoning and deactivation by MEA and interference from the reaction medium. Simultaneously, a highly efficient Ru-based catalyst system with PTA (1,3,5-triaza-7-phosphaadamantane) as a ligand is designed, significantly improving catalytic activity and cycle stability.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is: a reactor for the catalytic production of formic acid based on MEA rich CO2 solution, comprising a left chamber, a right chamber, a condenser reflux pipe, and a temperature control system.

[0009] The left chamber is a desorption chamber with an inlet and a outlet for loading MEA-rich CO2 solution. The left chamber is heated by a temperature control system to cause CO2 to desorb from the solution and enter the condenser reflux pipe.

[0010] The right chamber is a reaction chamber used to load a catalyst solution containing Ru precursor and phosphine ligand, serving as the site for CO2 hydrogenation reaction. It also contains a three-way mixing pipe, with its first port extending out of the right chamber for injecting H2 gas, and its second port connected to the interior of the right chamber.

[0011] The condenser reflux pipe is located between the left and right chambers. Its inlet and outlet are connected to the top of the left chamber and the third port of the three-way mixing pipe in the right chamber, respectively. A cooling jacket or condenser is provided externally to maintain a set temperature inside the condenser reflux pipe. The interior is filled with inert filler (such as glass beads or stainless steel wire mesh; both inert fillers effectively separate CO2 from MEA / water, resulting in extremely low MEA loss). Glass beads are less expensive, while stainless steel wire mesh offers better mechanical strength and heat transfer performance; the choice can be made based on actual industrial needs. Its working principle is as follows: CO2 gas, water vapor and MEA vapor desorbed by the MEA solution in the left chamber are mixed and rise into the condenser reflux tube; under the cooling effect of the current tube temperature, the water vapor and MEA vapor, due to their high boiling points (water 100℃, MEA about 170℃), are condensed into liquid under the cooling effect and flow back to the left chamber along the tube wall under the action of gravity; while CO2 gas does not condense at this temperature, it enters the three-way mixing tube through the condenser reflux tube and mixes with H2 gas before being injected into the catalyst solution to carry out the formic acid production reaction.

[0012] Both the left and right chambers are equipped with temperature control systems to regulate the temperature within the left and right chambers, thereby satisfying the optimal difference in conditions between desorption and hydrogenation.

[0013] Furthermore, an electrically controlled valve is installed at the second port of the three-way mixing pipe to control the opening and closing of the second port. By setting the electrically controlled valve, the required H2 gas and desorbed CO2 gas can be injected into the right chamber as needed.

[0014] Furthermore, a first pressure gauge is installed in the left chamber, and a second pressure gauge is installed in the right chamber. The pressure gauges allow for pressure monitoring of both chambers, ensuring the stable operation of desorption and hydrogenation to methanol.

[0015] The present invention also provides a catalyst adapted to the above-described reactor, comprising: Metal precursor: RuCl3, with Ru used in catalytic amounts. The preferred range for the amount of MEA rich in CO2 solution is 0.005~0.05 mmol Ru / 20 mL MEA solution.

[0016] Phosphine ligand: 1,3,5-triaza-7-phosphaadamantane (PTA); the molar ratio of the phosphine ligand to RuCl3 is (3~6):1.

[0017] Solvent: The reaction medium in the right chamber can be water or an organic solvent, preferably dimethyl sulfoxide (DMSO).

[0018] This invention also provides a method for preparing formic acid using the above-mentioned dual-cavity coupled reaction apparatus and catalyst system, specifically comprising the following steps: S1. Solution loading: Add a certain volume of 30% MEA CO2-rich solution to the left chamber; add a dimethyl sulfoxide solution containing RuCl3 and 1,3,5-triaza-7-phosphaadamantane to the right chamber. Seal the device and check for leaks.

[0019] S2. Reaction conditions are established: The temperature of the left chamber is set to 90~100℃ and the temperature of the right chamber is set to 80~120℃ through the temperature control system; and the temperature in the condenser reflux tube is maintained at the set temperature, which is lower than the boiling point of water vapor and MEA vapor and higher than the liquefaction temperature of CO2 gas. H2 gas at a pressure of 3~5MPa is introduced into the right chamber through the three-way mixing tube.

[0020] S3, CO2 desorption-hydrogenation coupling reaction: The MEA solution in the left chamber is heated and desorbs CO2 gas. The mixed gas rises into the condenser reflux tube; water vapor and MEA vapor are condensed and refluxed back to the left chamber, while CO2 gas does not condense. It passes through the condenser reflux tube into the three-way mixing tube and mixes with H2 gas before entering the dimethyl sulfoxide solution to undergo a hydrogenation reaction to produce formic acid. The reaction lasts for 8 to 16 hours.

[0021] S4. Product Sampling and Analysis: After the reaction is complete, cool down and slowly depressurize. Take a sample from the sampling port of the right chamber and analyze the formic acid concentration using high-performance liquid chromatography or nuclear magnetic resonance spectroscopy to calculate TON. Take a sample from the left chamber to analyze the change in CO2 loading and MEA loss of the MEA solution.

[0022] S5. Dual-chamber material recovery and reuse: Metal precursors and phosphine ligands are separated from the solution in the right chamber by extraction, distillation, or column chromatography. After drying, they can be directly used in the next batch of reaction. The lean MEA solution in the left chamber can reabsorb CO2 for recycling.

[0023] Compared with the prior art, the present invention has the following advantages: 1. A qualitative breakthrough in catalyst cycle stability: Using a condensation reflux separation reactor and a correspondingly suitable catalyst, the TON (conversion number) value showed virtually no decline in ten cycles, averaging around 439. In contrast, in traditional single-reactor MEA direct contact reactions, the catalyst becomes significantly deactivated after only one use.

[0024] 2. Significantly enhanced catalytic activity and selectivity: Under optimal conditions, the TON value reaches as high as 465, far exceeding the levels reported in traditional single-reactor processes and existing literature. The use of 1,3,5-triaza-7-phosphaadamantane (PTA) as a phosphine ligand is key to achieving this high activity, as it exhibits extremely high selectivity for the formation of formic acid.

[0025] 3. The MEA trapping solution can be stably circulated over a long period of time: After ten cycles, the CO2 absorption of the MEA solution in the left chamber remains stable, avoiding the 5%~8% loss of MEA per cycle in the traditional system.

[0026] 4. Decoupled control achieves global energy saving and optimal efficiency: The desorption chamber and reaction chamber are independently temperature controlled, allowing each to operate under the most favorable thermodynamic and kinetic conditions. The overall energy consumption is significantly lower than that of the traditional high-temperature desorption + independent high-pressure hydrogenation route.

[0027] 5. Low device cost and easy industrial scale-up: Compared with separation schemes using polymer membranes or inorganic membranes, the condenser reflux tube used in this invention is a conventional chemical component with a simple structure and low cost. It does not require the import or customization of expensive membrane materials, which greatly reduces the manufacturing and maintenance costs of the device. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the overall structure of the reactor of the present invention.

[0029] Figure 2 This is a graph showing the relationship between the number of catalyst cycles and TON.

[0030] In the diagram: 1-Left chamber; 2-Right chamber; 3-Heat insulation plate; 4-Inlet; 5-First pressure gauge; 6-Second pressure gauge; 7-Heating jacket; 8-Condensation reflux pipe; 9-T-way mixing pipe; 10-Exhaust port; 11-MEA CO2-rich solution; 12-First temperature sensor; 13-Second temperature sensor; 14-Catalyst solution. Detailed Implementation

[0031] The present invention will be further described below.

[0032] The reactors used in the following embodiments are as follows: Figure 1 As shown, it includes a left chamber 1, a right chamber 2, a condenser reflux pipe 8, and a temperature control system; The left chamber 1 is a desorption chamber, equipped with an inlet 4 and a outlet, for loading MEA-rich CO2 solution; the left chamber 1 is heated by a temperature control system to cause CO2 to desorb from the solution and enter the condenser reflux pipe 8.

[0033] The right chamber 2 is a reaction chamber used to load a catalyst solution containing Ru precursor and phosphine ligand, serving as the site for CO2 hydrogenation reaction. It also contains a three-way mixing pipe 9. The first port of the three-way mixing pipe 9 extends out of the right chamber 2 for injecting H2 gas, and the second port communicates with the interior of the right chamber 2, equipped with an electrically controlled valve to control its opening and closing. By using the electrically controlled valve, the required amount of H2 gas and desorbed CO2 gas can be injected into the right chamber 2 as needed. The left chamber 1 and right chamber 2 are separated by a heat insulation plate 3 to reduce the mutual temperature influence between the two chambers. An exhaust port 10 is located at the upper end of the right chamber 2 to discharge residual CO2 and H2 gas after the reaction is complete.

[0034] The condenser reflux pipe 8 is located between the left chamber 1 and the right chamber 2. Its inlet and outlet are connected to the top of the left chamber 1 and the third port of the three-way mixing pipe 9 in the right chamber 2, respectively. It is externally equipped with a cooling jacket or condenser to maintain a set temperature inside the condenser reflux pipe 8, and is filled with inert filler (such as glass beads or stainless steel wire mesh). Its working principle is as follows: CO2 gas, water vapor, and MEA vapor desorbed from the MEA solution in the left chamber are mixed and rise into the condenser reflux pipe 8. Cooled by the current temperature inside the pipe, the water vapor and MEA vapor, due to their higher boiling points (water 100℃, MEA approximately 170℃), are condensed into liquid and flow back to the left chamber along the pipe wall under gravity. Meanwhile, the CO2 gas does not condense at this temperature and enters the three-way mixing pipe 9 through the condenser reflux pipe 8, mixes with H2 gas, and is then injected into the catalyst solution for the formic acid production reaction.

[0035] Both the left chamber 1 and the right chamber 2 are equipped with temperature control systems to regulate the temperature within each chamber, ensuring optimal conditions for desorption and hydrogenation. These systems include a heating jacket 7, a first temperature sensor 12, and a second temperature sensor 13. The heating jacket 7 is installed around both chambers 1 and 2, allowing for independent heating of each chamber. The first temperature sensor 12 is installed in the left chamber 1, and the second temperature sensor 13 is installed in the right chamber 2, monitoring the temperature of their respective chambers. The left chamber 1 is equipped with a first pressure gauge 5, and the right chamber 2 is equipped with a second pressure gauge 6. The placement of these pressure gauges allows for pressure monitoring of both chambers, ensuring stable desorption and hydrogenation for methanol production.

[0036] Example 1: Screening of phosphine ligands in catalysts To verify the superiority of 1,3,5-triaza-7-phosphaadamantane (PTA) as a phosphine ligand, a ligand screening experiment was conducted in a high-pressure batch reactor to simulate the environment of the right chamber of the reactor of this invention (i.e., under pure conditions without MEA).

[0037] Experimental procedure: 0.01 mmol RuCl3 was dissolved in 20 mL of dimethyl sulfoxide with different phosphine ligands (P / L molar ratio = 3 / 1). The mixture was then purged with CO2 and H2 to a total pressure of 4 MPa and reacted at 100 °C for 12 hours. The TON values ​​obtained with different phosphine ligands are shown in Table 1. Table 1 Comparison of catalytic activities of different phosphine ligands Experimental results show that the catalytic activity of PTA ligand is far superior to that of other tertiary phosphine and phosphonium ligands, demonstrating significant technical advantages. In particular, PTA exhibits a TON content that is twice that of the traditional water-soluble ligand TPPTS and more than five times that of the commonly used ligand PPh3, showcasing its unique catalytic performance.

[0038] Example 2: Optimization of catalyst dosage Using the same reaction conditions as in Example 1, with the ligand fixed at 1,3,5-triaza-7-phosphaadamantane (PTA), and varying the amount of RuCl3, the results are shown in Table 2: Table 2 Effect of Ru dosage on catalytic activity Experiments showed that when the Ru dosage was 0.005 mmol, the TON reached a maximum of 156, but at this point the catalyst concentration was too low and difficult to recover and recycle. Considering both activity and practical economy, the optimal RuCl3 dosage was determined to be 0.01 mmol.

[0039] Example 3: Optimization of the molar ratio of phosphine ligand to RuCl3 With RuCl3 fixed at 0.01 mmol and 1,3,5-triaza-7-phosphaadamantane (PTA) as the ligand, and other conditions the same as in Example 1, the effect of the molar ratio of phosphine ligand to RuCl3 on TON was investigated. The results are shown in Table 3. Table 3 Effect of molar ratio on catalytic activity The results showed that the TON peak value of 169 was achieved when the molar ratio of phosphine ligand to RuCl3 was 4. Too few ligands could not effectively stabilize the Ru active center; too many ligands would occupy the active sites of the catalyst, both of which were detrimental to catalytic activity. Therefore, the optimal molar ratio was determined to be 4 / 1.

[0040] Example 4: Optimization of reaction temperature With RuCl3 fixed at 0.01 mmol, 1,3,5-triaza-7-phosphaadamantane (PTA) as the ligand, and the molar ratio of phosphine ligand to RuCl3 at 4 / 1, and other conditions the same as in Example 1, the effect of reaction temperature was investigated, and the results are shown in Table 4: Table 4 Effect of reaction temperature on catalytic activity The results showed that 100℃ was the optimal reaction temperature. At temperatures too low, the reaction kinetics were slow; at temperatures too high, the thermodynamic equilibrium of CO2 hydrogenation to formic acid shifted towards the reverse reaction, and side reactions may have been initiated, leading to decreased reactivity.

[0041] Example 5: Verification of Cyclic Stability in the Reactor The reactor of this invention uses a condenser reflux pipe with a water-cooled jacket (6 mm inner diameter, 150 mm length, and 3 mm glass beads as packing material). The left chamber is loaded with 20 mL of 30% MEA-rich CO2 solution, and the right chamber is loaded with 20 mL of a dimethyl sulfoxide solution containing 0.01 mmol RuCl3 and 0.04 mmol PTA. The right chamber is pressurized with 4 MPa H2 gas and maintained at that pressure. Both the left and right chambers are heated to 100°C. After 12 hours of reaction, samples are taken to determine TON. The catalyst is separated from the reaction solution in the right chamber by vacuum distillation, dried, and used in the next cycle. This process is repeated 10 times. The results are shown in Table 5. Figure 2 As shown: Table 5 Catalyst cycling stability data in a dual-chamber reactor Experimental data clearly demonstrate that, thanks to the effective interception and isolation of MEA vapor and water by the condenser reflux tube, and the unique high stability of 1,3,5-triaza-7-phosphaadamantane (PTA) as a ligand, the catalyst exhibits virtually no performance degradation after ten cycles, with an average TON stabilizing at around 439. Testing showed that the CO2 absorption capacity of the MEA solution in the left chamber remained stable after ten CO2 adsorption-desorption cycles, without any degradation loss. This fully demonstrates the advantages of the device and the adapted catalyst in terms of long-term stability.

[0042] Example 6: Comparison of different solvent systems Using the same reactor and catalyst ratio as in Example 5, dimethyl sulfoxide, water, and methanol were used as the reaction solvents in the right chamber, with other conditions remaining unchanged. The results are shown in Table 6: Table 6. Effect of solvent type on catalytic activity Experimental results show that dimethyl sulfoxide exhibits the highest catalytic activity when used as a solvent. This is because dimethyl sulfoxide has good solubility for CO2 and excellent compatibility with the specific Ru-PTA catalyst of this invention. Water, as a green solvent, also exhibits certain catalytic activity and can be used in scenarios with high environmental protection requirements.

[0043] 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. A reactor for the catalytic production of formic acid based on MEA-rich CO2 solution, characterized in that, Includes left chamber, right chamber, condenser reflux pipe, and temperature control system; The left chamber is a desorption chamber used to load MEA-rich CO2 solution; The right chamber is a reaction chamber used to load a catalyst solution containing Ru precursor and phosphine ligand. It is also equipped with a three-way mixing tube. The first port of the three-way mixing tube extends out of the right chamber and is used to inject H2 gas through the port. The second port is connected to the inside of the right chamber. The condensation reflux pipe is located between the left and right chambers. Its inlet and outlet are connected to the top of the left chamber and the third port of the three-way mixing pipe in the right chamber, respectively. It is equipped with a cooling jacket or condenser to maintain the set temperature inside the condensation reflux pipe, and is filled with inert packing. When the CO2 gas, water vapor and MEA vapor generated by the thermal desorption of the MEA-rich CO2 solution in the left chamber enter the condensation reflux pipe, the water vapor and MEA vapor condense into liquid under the cooling effect of the current pipe temperature and flow back to the left chamber under gravity. At the same time, the CO2 gas enters the three-way mixing pipe through the condensation reflux pipe and mixes with the H2 gas before being injected into the catalyst solution for the formic acid production reaction. Both the left and right chambers are equipped with temperature control systems to regulate the temperature within the left and right chambers.

2. The reactor according to claim 1, characterized in that, The inert filler inside the condensation reflux pipe is glass beads or stainless steel wire mesh, with a particle size of 2~5mm.

3. The reactor according to claim 1, characterized in that, An electrically controlled valve is installed at the second port of the three-way mixing pipe to control the opening and closing of the second port.

4. The reactor according to claim 1, characterized in that, The left chamber is equipped with a first pressure gauge, and the right chamber is equipped with a second pressure gauge.

5. A catalyst adapted to the reactor according to any one of claims 1 to 4, characterized in that, include: Metal precursor: RuCl3; Phosphine ligand: 1,3,5-triaza-7-phosphaadamantane; Solvent: Dimethyl sulfoxide.

6. The catalyst according to claim 5, characterized in that, The amount of RuCl3 used is 0.005~0.05 mmol Ru / 20 mL MEA CO2-rich solution; the molar ratio of the phosphine ligand to RuCl3 is (3~6):

1.

7. A method for preparing formic acid using the reactor of claim 1 and the catalyst of claim 5, characterized in that, Includes the following steps: S1, Solution loading: Add 30% MEA CO2-rich solution to the left chamber; add a dimethyl sulfoxide solution containing RuCl3 and 1,3,5-triaza-7-phosphaadamantane to the right chamber; S2. Reaction conditions: Set the temperature of the left chamber to 90~100℃ and the temperature of the right chamber to 80~120℃ through the temperature control system; and maintain the temperature in the condenser reflux tube at the set temperature. Then, fill the right chamber with H2 gas at a pressure of 3~5MPa through the three-way mixing tube. S3, CO2 desorption-hydrogenation coupling reaction: The MEA solution in the left chamber is heated and desorbs CO2 gas. The mixed gas enters the condenser reflux tube. Water vapor and MEA vapor are condensed and refluxed back to the left chamber. CO2 gas enters the three-way mixing tube through the condenser reflux tube and mixes with H2 gas before entering the dimethyl sulfoxide solution to undergo a hydrogenation reaction to produce formic acid. The reaction lasts for 8-16 hours. S4. Product sampling and analysis and material recovery.

8. The method for preparing formic acid according to claim 7, characterized in that, In step S1, the amount of RuCl3 used is 0.01 mmol, and the amount of 1,3,5-triaza-7-phosphaadamantane used is 0.04 mmol; the temperature of the right chamber is 100℃, and the pressure of H2 gas is 4 MPa.

9. The method for preparing formic acid according to claim 7, characterized in that, In step S2, the set temperature in the condenser reflux pipe is lower than the boiling point of water vapor and MEA vapor, but higher than the liquefaction temperature of CO2 gas.

10. The method for preparing formic acid according to claim 7, characterized in that, In step S4, after the reaction is completed, the metal precursor and phosphine ligand are separated from the solution in the right chamber by extraction, distillation or column chromatography, dried and used for the next batch of reaction; the MEA lean solution in the left chamber reabsorbs CO2 for recycling.

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