A non-alkali CO 2 Method for preparing formic acid by hydrogenation

Abstract

The present invention relates to a method for preparing formic acid by hydrogenation of CO2 without alkali participation, wherein polymerized triphenylphosphine ruthenium trichloride is used as a catalyst and imidazole formate is used as a solvent, CO2 and H2 are reacted at a certain pressure and temperature to obtain formic acid, formate in the imidazole formate is used as a hydrogen bond acceptor and imidazole is used as a hydrogen bond donor to form multiple hydrogen bonds with the formic acid generated by the reaction, and the formation of hydrogen bonds thermodynamically compensates for the preparation of formic acid by hydrogenation of CO2, thereby promoting the reaction equilibrium to move toward formic acid. The polymerized triphenylphosphine ruthenium trichloride provided by the present invention exhibits good activity for preparing formic acid by hydrogenation of CO2 when imidazole formate is used as a solvent, and has a high catalyst turnover number TON.

Description

Technical Field

[0001] The present invention relates to the field of green chemical industry, and in particular to a CO 2 Method for preparing formic acid by hydrogenation. Background Art

[0002] Formic acid is an important organic chemical raw material, widely used in industries such as pesticides, leather, dyes, medicines and rubber. The main methods for producing formic acid currently in use or in the past include: sodium formate method, formamide method, butane liquid phase oxidation method and methyl formate hydrolysis method. Among them, methyl formate hydrolysis is the main process for producing formic acid, which includes the following two steps: (1) methanol and carbon monoxide carbonylation to synthesize methyl formate; (2) methyl formate hydrolysis to produce formic acid and methanol.

[0003] By CO 2 Direct preparation of formic acid by hydrogenation due to the use of CO 2 Compared with the above four formic acid production methods, CO 2 Hydrogenation to produce formic acid uses greenhouse gas CO 2 As raw material, the theoretical atomic economy is 100%, which is an ideal formic acid synthesis route. From a thermodynamic point of view, CO 2 The Gibbs free energy change (ΔG) of hydrogenation to formic acid is positive ( Figure 1 ). Without an external driving force, the equilibrium concentration of formic acid is very low. 2 In the research of hydrogenation to formic acid, organic or inorganic bases are generally used to react with formic acid in situ to form formate, which makes the reaction ΔG become negative to push the reaction equilibrium toward the product. 2 The following organic or inorganic bases are commonly used in the research on hydrogenation to formic acid: 1,8-diazabicycloundec-7-ene (J.Am.Chem.Soc.,2018,140,8082-8085; Nature Catal.,2018,1,743-747), triethylamine (Chem,2019,5,693-705; Nature Commun.,2017,8,1407; Angew.Chem.Int.Ed.,2020,59,20183-20191), superbase Vkd (J.Am.Chem.Soc.,2017,139,14244-14250), NaHCO 3 (ACS Catal., 2020, 10, 2108-2116; Angew. Chem. Int. Ed., 2017, 56, 15002-15005), KHCO 3(Angew. Chem. Int. Ed., 2019, 58, 722-726), NaOH (ACS Catal., 2020, 10, 6356-6366), KOH (ACS Catal., 2020, 10, 2990-2998), etc.

[0004] CO 2 Gibbs free energy change data of hydrogenation to formic acid and NH 3 Impact:

[0005]

[0006]

[0007] In this context, if we can find a way to propel CO without using bases, 2 The balanced conversion method of hydrogenation to formic acid will significantly enhance the industrialization potential of the corresponding process, and a small number of studies have explored this. For example, carbon dioxide hydrogenation can be carried out in the presence of dimethyl sulfoxide, but the overall reaction efficiency is still relatively low, and the corresponding catalyst conversion number TON is only 4200 at most (Nature Commun., 2014, 5, 4017; Angew. Chem. Int. Ed., 2016, 55, 8966-8969). How to significantly improve the CO2 conversion efficiency without the participation of alkali? 2 The catalyst turnover number (TON) of the hydrogenation reaction to produce formic acid is one of the important challenges faced by the industrial application of the corresponding process. Summary of the invention

[0008] The existing method of using organic or inorganic bases to react with formic acid to generate formate to promote CO 2 The method of hydrogenation formic acid equilibrium shift is different. The present invention provides a CO 2 A new method for producing formic acid by hydrogenation.

[0009] To achieve the above purpose, the technical solution provided by the present invention is:

[0010] A non-alkali CO 2 A method for preparing formic acid by hydrogenation, using polymerized triphenylphosphine ruthenium trichloride as a catalyst and imidazole formate as a solvent, 2 and H 2 The reaction is carried out under a certain pressure and temperature to obtain formic acid;

[0011] The preparation method of polymerized triphenylphosphine ruthenium trichloride is as follows: triphenylphosphine ruthenium trichloride, benzene, dimethoxymethane and 1,2-dichloroethane are mixed, anhydrous ferric chloride is added, heated to react under stirring, and then the temperature is raised to react to obtain a polymerized triphenylphosphine ruthenium trichloride catalyst; the synthetic reaction of polymerized triphenylphosphine ruthenium trichloride is:

[0012]

[0013] Imidazole carboxylate has the following structure:

[0014]

[0015] Among them, R 1 and R 2 It is a straight-chain or branched alkane having 1 to 10 carbon atoms; imidazole formic acid salts can be directly purchased from the market.

[0016] CO 2 When hydrogenating formic acid, the mass ratio of the catalyst polymeric triphenylphosphine ruthenium trichloride to the solvent imidazole formate is 0.00001:1-0.1:1; CO 2 The pressure is 0.2-10MPa; H 2 The pressure is 0.2-10MPa; the reaction temperature is 50-200℃.

[0017] Furthermore, the molar ratio of the reaction substances of triphenylphosphine ruthenium trichloride, benzene, dimethoxymethane and anhydrous ferric chloride is 1:1-10:1-30:1-30; 3-10 ml of 1,2-dichloroethane is used for every 1 mmol of triphenylphosphine ruthenium trichloride.

[0018] Furthermore, in the preparation of polymeric triphenylphosphine ruthenium trichloride, the mixture was heated to 50° C. with stirring for 5 hours, and then heated to 80° C. for 48 hours.

[0019] As a preferred solution, the mass ratio of the catalyst polymeric triphenylphosphine ruthenium trichloride to the solvent imidazole formate is 0.0001:1-0.05:1.

[0020] As a preferred solution, CO 2 The pressure is 1-6MPa; H 2 The pressure is 1-6MPa; the reaction temperature is 80-160℃.

[0021] CO 2 When hydrogenating formic acid, the reaction is stopped when the system pressure does not change within 30 minutes.

[0022] After the reaction is completed, the catalyst polymerized triphenylphosphine ruthenium trichloride is separated and used again for CO 2 Catalytic hydrogenation to produce formic acid.

[0023] After the reaction is completed and the catalyst is separated, formic acid is directly distilled from the resulting solution.

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

[0025] The present invention uses polymerized triphenylphosphine ruthenium trichloride as a catalyst and imidazole formate as a solvent. 2 -H 2 The reaction is carried out under pressure and temperature. The mechanism of the present invention to promote the shift of the reaction equilibrium is that the formate in the imidazole formate acts as a hydrogen bond acceptor and the imidazole acts as a hydrogen bond donor, which can form multiple hydrogen bonds with the formic acid generated by the reaction. The formation of these hydrogen bonds can thermodynamically promote the CO 2 Hydrogenation to produce formic acid is used to compensate, thereby pushing the reaction equilibrium toward formic acid. At the same time, the polymerized triphenylphosphine ruthenium trichloride provided by the present invention exhibits good CO 2 The activity of hydrogenation to produce formic acid, the catalyst turnover number TON can reach up to 23000. The following are the outstanding advantages of the present invention:

[0026] The present invention provides a method for carrying out CO 2 A new method for preparing formic acid by efficient hydrogenation. Compared with the conventional system using organic or inorganic bases, the present invention is more efficient in producing formic acid by hydrogenation. 2 The hydrogenation produces formic acid instead of formate, which fundamentally avoids the consumption of alkali and also saves the process of acidification of formate to prepare formic acid. It is a new green and economical way to synthesize formic acid.

[0027] The present invention provides a method for efficiently catalyzing CO 2 The polymerized triphenylphosphine ruthenium trichloride catalyst for hydrogenation to formic acid has a maximum catalyst conversion number of only 4200 in the existing reaction system without alkali participation (Nature Commun., 2014, 5, 4017; Angew. Chem. Int. Ed., 2016, 55, 8966-8969). The catalyst conversion number of the present invention is as high as 23000, and the formic acid synthesis efficiency is greatly improved;

[0028] The catalyst used in the present invention can be directly filtered and separated after the reaction, and the obtained filtrate can be recycled together with the catalyst after formic acid is evaporated, which significantly reduces the process cost;

[0029] Since the present invention does not involve the participation of water in the reaction and separation process, the method provided by the present invention is easy to obtain anhydrous formic acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 : Infrared spectrum of the catalyst synthesized in Example 1.

[0031] Figure 2 : X-ray photoelectron spectrum of the catalyst synthesized in Example 1.

[0032] Figure 3: A partial enlarged view of the 450-500 eV portion of the X-ray photoelectron spectrum of the catalyst synthesized in Example 1.

[0033] Figure 4 : The hydrogen nuclear magnetic resonance spectrum of formic acid distilled out of Example 36. DETAILED DESCRIPTION

[0034] The above contents of the present invention are further described in detail below in the form of embodiments, but this should not be understood as the scope of the above subject matter of the present invention being limited to the following embodiments, and all technologies realized based on the above contents of the present invention belong to the scope of the present invention.

[0035] The experimental methods used in the following examples are all conventional methods unless otherwise specified, and the reagents, methods and equipment used are all conventional reagents, methods and equipment in the technical field unless otherwise specified.

[0036] Embodiment 1:

[0037] Preparation of polymerized triphenylphosphine-ruthenium trichloride catalyst: 10mmol triphenylphosphine-ruthenium trichloride, 40mmol benzene, 120mmol dimethoxymethane, 40ml 1,2-dichloroethane were mixed, and then 120mmol anhydrous ferric chloride was added, and the mixture was heated to 50°C for 5h under stirring, and then heated to 80°C for 48h. After the reaction, the mixture was filtered, and the solid was washed with 300ml methanol. The sample was dried to obtain 5.5g of polymerized triphenylphosphine-ruthenium trichloride (catalyst A).

[0038] Embodiment 2-4:

[0039] The catalyst was prepared under different conditions, and the rest was the same as in Example 1. The preparation conditions are shown in Table 1:

[0040] Table 1. Catalyst preparation under different conditions

[0041]

[0042] Embodiment 5:

[0043] CO 2 Hydrogenation to produce formic acid: In a 100 ml stainless steel autoclave, add 20.0 g 1-butyl-3-methylimidazolium formate, 0.02 g catalyst A, and introduce 3 MPa CO 2 and 3MPa H 2 , and the temperature was raised to 100°C for reaction. When the system pressure did not change within 30 minutes, the reaction was stopped. Samples were taken for nuclear magnetic resonance hydrogen spectrum analysis, with isopropanol as the internal standard, and the results showed that the catalyst turnover number TON was 17500.

[0044] Embodiment 6-14

[0045] Different imidazole formate salts were used to 2 The hydrogenation reaction was carried out in the same manner as in Example 5. The results are shown in Table 2:

[0046] Table 2. CO analysis using different imidazole formate salts 2 Hydrogenation reaction results

[0047]

[0048]

[0049] Examples 16-18

[0050] Using different catalysts for CO 2 The hydrogenation reaction was carried out in the same manner as in Example 5. The results are shown in Table 3:

[0051] Table 3. CO removal using different catalysts 2 Hydrogenation reaction results

[0052] Example catalyst Catalyst amount TON Example 16 Catalyst B 0.02g 15100 Embodiment 17 Catalyst C 0.02g 16700 Embodiment 18 Catalyst D 0.02g 17600

[0053] Examples 19-35

[0054] Using different reaction conditions to carry out CO 2 The hydrogenation reaction was the same as in Example 5, and the results are shown in Table 4:

[0055] Table 4. CO reaction under different reaction conditions 2 Hydrogenation reaction results

[0056]

[0057]

[0058] Embodiment 36

[0059] In a 100 ml stainless steel autoclave, 20.0 g 1-butyl-3-methylimidazolium formate and 0.02 g catalyst A were added, and 3 MPa CO 2 and 3MPa H 2 , raise the temperature to 100°C for reaction. When the system pressure does not change within 30 minutes, stop the reaction. Filter while hot, and the filter cake is the recovered catalyst A. Distill the filtrate under reduced pressure at 100°C to remove formic acid, and the bottom liquid obtained is the recovered 1-butyl-3-methylimidazole formate.

[0060] In a 100 ml stainless steel autoclave, add the recovered 1-butyl-3-methylimidazole formate and the recovered catalyst A, and introduce 3 MPa CO 2 and 3MPa H 2, and the temperature was raised to 100°C for reaction. When the system pressure did not change within 30 minutes, the reaction was stopped. Samples were taken for nuclear magnetic resonance hydrogen spectrum analysis, with isopropanol as the internal standard, and the results showed that the catalyst turnover number TON was 19300.

[0061] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any technician familiar with the profession, without departing from the scope of the technical solution of the present invention, according to the technical essence of the present invention, any simple modification, equivalent replacement and improvement made to the above embodiment still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing formic acid by hydrogenation of CO2 without alkali participation, characterized in that: Using polymerized triphenylphosphine ruthenium trichloride as a catalyst and imidazole formate as a solvent, CO2 and H2 are reacted at a certain pressure and temperature to obtain formic acid; The preparation method of polymerized triphenylphosphine ruthenium trichloride is as follows: triphenylphosphine ruthenium trichloride, benzene, dimethoxymethane and 1,2-dichloroethane are mixed, anhydrous ferric chloride is added, the mixture is heated to react under stirring, and the mixture is heated to react again to obtain a polymerized triphenylphosphine ruthenium trichloride catalyst; Imidazole carboxylate has the following structure: Wherein, R1 and R2 are straight or branched alkanes having 1 to 10 carbon atoms; When CO2 is hydrogenated to produce formic acid, the mass ratio of the catalyst polymerized triphenylphosphine ruthenium trichloride to the solvent imidazole formate is 0.00001:1-0.1:1; the CO2 pressure is 0.2-10MPa; the H2 pressure is 0.2-10MPa; the reaction temperature is 50-200°C; the molar ratio of the reaction substances of triphenylphosphine ruthenium trichloride, benzene, dimethoxymethane, and anhydrous ferric chloride is 1:1-10:1-30:1-30; 3-10ml 1,2-dichloroethane is used for every 1mmol of triphenylphosphine ruthenium trichloride; in the preparation of polymerized triphenylphosphine ruthenium trichloride, the mixture is heated to 50°C for reaction for 5h under stirring, and then the temperature is raised to 80°C for reaction for 48h.

2. The method for preparing formic acid by hydrogenation of CO2 without alkali participation according to claim 1, characterized in that: The mass ratio of the catalyst polymerized triphenylphosphine ruthenium trichloride to the solvent imidazole formate is 0.0001:1-0.05:

1.

3. The method for preparing formic acid by hydrogenation of CO2 without alkali participation according to claim 1, characterized in that: The CO2 pressure is 1-6MPa; the H2 pressure is 1-6MPa; the reaction temperature is 80-160℃.

4. The method for preparing formic acid by hydrogenation of CO2 without alkali participation according to claim 1, characterized in that: When CO2 is hydrogenated to produce formic acid, the reaction is stopped when the system pressure does not change within 30 minutes.

5. The method for preparing formic acid by hydrogenation of CO2 without alkali participation according to claim 1, characterized in that: After the reaction is completed, the catalyst polymerized triphenylphosphine ruthenium trichloride is separated and used again for catalytic hydrogenation of CO2 to produce formic acid.

6. The method for preparing formic acid by hydrogenation of CO2 without alkali participation according to claim 1, characterized in that: After the reaction is completed and the catalyst is separated, formic acid is directly distilled from the resulting solution.

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