A method for preparing an acid by catalytic dehydrogenation of an alcohol

Abstract

The present invention relates to the technical field of chemical synthesis, and particularly relates to a method for preparing an acid by catalytic dehydrogenation of an alcohol. The method for preparing an acid by catalytic dehydrogenation of an alcohol according to the present invention comprises the following steps: mixing a primary alcohol, a catalyst, and a base, and carrying out a catalytic reaction under an inert atmosphere to obtain the acid; the catalyst is carbon-coated copper nanoparticles. The present invention uses carbon-coated copper nanoparticles (Cu@C) as the catalyst, and utilizes the coating of C on the Cu nanoparticles to avoid the aggregation and growth of the Cu nanoparticles during the reaction process, so that the Cu@C catalyst can be recycled multiple times and has better stability. The method for preparing an acid by catalytic dehydrogenation of an alcohol disclosed by the present invention has the advantages of high alcohol conversion rate, high acid selectivity, short reaction time, and excellent catalyst stability, and the method for preparing an acid by catalytic dehydrogenation of an alcohol has good industrial application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical synthesis, and particularly relates to a method for catalytic dehydrogenation of alcohol to prepare acid. Background Art

[0002] Glycolic acid, lactic acid and 3-hydroxypropionic acid are fine chemicals with high added value, and are widely used in fields such as food, chemical industry, cosmetics, medicine and agriculture. They can also be used as monomers to synthesize biodegradable plastics, such as polyglycolic acid, polylactic acid and poly-3-hydroxypropionic acid. At present, fermentation method is mainly used in industry to produce glycolic acid, lactic acid and 3-hydroxypropionic acid; however, this method has problems such as high cost, low yield and difficult separation and purification of products. Therefore, developing new chemical methods to prepare glycolic acid, lactic acid and 3-hydroxypropionic acid remains a hot issue.

[0003] Glycerol is a by-product in the process of biodiesel preparation. For every 10 tons of biodiesel produced, 1 ton of glycerol will be generated. With the rapid development of the biodiesel industry, there is an oversupply of glycerol by-products, and how to convert glycerol into high-value-added chemicals has received wide attention. Glycerol can be converted into ethylene glycol, 1,2-propanediol and 1,3-propanetriol through hydrocracking reaction, and cellulose and sugar can also be converted into ethylene glycol, 1,2-propanediol and glycerol. Therefore, ethylene glycol, 1,2-propanediol and glycerol can be widely obtained from biomass resources. In addition, alcohol can be converted into the corresponding acid through catalytic dehydrogenation. For example, ethylene glycol can be converted into glycolic acid, 1,2-propanediol and glycerol can be converted into lactic acid, and 1,3-propanediol can be converted into 3-hydroxypropionic acid. Thus, glycerol can ultimately be converted into glycolic acid, lactic acid and 3-hydroxypropionic acid, which not only provides a new idea for the preparation of glycolic acid, lactic acid and 3-hydroxypropionic acid, but also realizes the high-value utilization of glycerol by-products.

[0004] At present, most of the heterogeneous catalytic reactions for preparing acid by catalytic dehydrogenation of alcohol are carried out under high-temperature aqueous phase conditions. For example, glycerol undergoes aqueous phase catalytic dehydrogenation reaction under the action of a Cu-based heterogeneous catalyst to prepare lactic acid. However, under high-temperature aqueous phase reaction conditions, Cu nanoparticles in the Cu-based heterogeneous catalyst are prone to aggregation, resulting in catalyst deactivation and poor catalyst stability. Although the prior art discloses that the Cu-Cu 2 O@NC catalyst can catalyze the dehydrogenation of glycerol to prepare lactic acid, the preparation of the Cu-Cu 2 O@NC catalyst takes a long time, and nitrogen element needs to be incorporated. The cost is high, the preparation process is complex, and it is only applied to the reaction of catalytic dehydrogenation of glycerol to prepare lactic acid.

[0005] Therefore, it is necessary to develop new methods to achieve efficient catalytic dehydrogenation of alcohol to prepare acid. Summary of the Invention

[0006] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. For this purpose, the present invention provides a method for preparing acids by catalytic dehydrogenation of alcohols, with relatively high conversion rates of raw material alcohols and selectivities of product acids.

[0007] The present invention provides a method for preparing acids by catalytic dehydrogenation of alcohols, comprising the following steps:

[0008] Mix a primary alcohol, a catalyst, and a base, and conduct a catalytic reaction under an inert atmosphere to obtain the acid; the catalyst is carbon-coated copper nanoparticles.

[0009] Compared with the prior art, the present invention has at least the following beneficial effects:

[0010] 1. The present invention uses carbon-coated copper nanoparticles (Cu@C) as the catalyst, and the coating of C on the Cu nanoparticles is used to avoid the aggregation and growth of Cu nanoparticles during the reaction, so that the Cu@C catalyst can be recycled multiple times and has better stability.

[0011] 2. The method for preparing acids by catalytic dehydrogenation of alcohols disclosed in the present invention has the advantages of high alcohol conversion rate, high acid selectivity, short reaction time, and excellent catalyst stability, and has good industrial application prospects.

[0012] Preferably, the temperature of the catalytic reaction is 180-260°C, more preferably 200-240°C; the time of the catalytic reaction is 40-200 min, more preferably 60-150 min.

[0013] Preferably, the inert atmosphere includes at least one of nitrogen, helium, and argon. The air in the reaction system is replaced with an inert gas multiple times (5-7 times), and then an inert gas is charged into the reaction system to obtain an inert atmosphere reaction system.

[0014] Preferably, the pressure of the catalytic reaction is 0.1-2.0 MPa, more preferably 1.0-2.0 MPa.

[0015] Preferably, the particle size of the carbon-coated copper nanoparticles (Cu@C) is 30-155 nm, more preferably 50-100 nm, and further preferably 70-90 nm.

[0016] Preferably, the mass fraction of Cu in the Cu@C catalyst is 50-80 wt%, more preferably 75 wt%.

[0017] Preferably, the mass ratio of the catalyst to the primary alcohol is 0.05-0.6:1, more preferably 0.08-0.4:1.

[0018] Preferably, the molar ratio of the primary alcohol to the base is 1:1-1.5, more preferably 1:1.1-1.3.

[0019] Preferably, the primary alcohol participates in the reaction in the form of an aqueous solution of the primary alcohol, and the mass fraction of the aqueous solution of the primary alcohol is 2 to 25 wt%, more preferably 5 to 20 wt%.

[0020] Preferably, the addition amount of the catalyst is 0.2 to 5% of the mass of the aqueous solution of the primary alcohol, more preferably 0.5 to 2%.

[0021] Preferably, the primary alcohol includes at least one of ethylene glycol, 1,2 - propanediol, 1,3 - propanediol, and glycerol. The Cu@C catalyst of the present invention can not only catalyze the dehydrogenation of glycerol to prepare lactic acid, but also catalyze the dehydrogenation of ethylene glycol, 1,2 - propanediol, and 1,3 - propanediol to obtain glycolic acid, lactic acid, and 3 - hydroxypropionic acid respectively, with a wider range of use.

[0022] Preferably, the acid includes at least one of glycolic acid, lactic acid, and 3 - hydroxypropionic acid.

[0023] Preferably, the base includes at least one of alkali metal hydroxides and alkaline earth metal hydroxides, and more preferably the base includes at least one of sodium hydroxide and potassium hydroxide.

[0024] Preferably, the preparation method of the Cu@C catalyst of the present invention includes the following steps:

[0025] (1) Mix a copper salt, 1,3,5 - benzenetricarboxylic acid, and a solvent, and carry out a solvothermal reaction to obtain a copper - organic framework precursor CuBTC;

[0026] (2) Calcinate the copper - organic framework precursor under a reducing gas to obtain the carbon - coated copper nanoparticles.

[0027] The preparation method of the Cu@C catalyst of the present invention is simple, does not require doping with other elements (such as nitrogen), has low cost, wide material sources, and can be mass - produced industrially.

[0028] Preferably, the temperature of the solvothermal reaction in step (1) is 60 to 100 °C, more preferably 80 to 90 °C, and further preferably about 85 °C.

[0029] Preferably, the time of the solvothermal reaction in step (1) is 6 to 10 h, more preferably 6 to 8 h, and further preferably about 8 h.

[0030] Preferably, the process of mixing the copper salt, 1,3,5 - benzenetricarboxylic acid, and the solvent in step (1) is specifically to add the 1,3,5 - benzenetricarboxylic acid solution to the copper salt solution and stir for 10 to 30 min, more preferably stir for about 10 min.

[0031] Preferably, the mass ratio of the copper salt to 1,3,5-benzenetricarboxylic acid is 1-3:1, more preferably around 2:1.

[0032] Preferably, the mass-to-volume ratio of 1,3,5-benzenetricarboxylic acid to the solvent in the 1,3,5-benzenetricarboxylic acid solution is 1 g: 20-40 mL, more preferably 1 g: 30 mL.

[0033] Preferably, the solvent of the 1,3,5-benzenetricarboxylic acid solution includes at least one of alcohol solvents and amine solvents, and the more preferred solvents include at least one of ethanol and N,N-dimethylformamide.

[0034] Preferably, the mass-to-volume ratio of the copper salt to the solvent in the copper salt solution is 1 g: 5-10 mL; more preferably 1 g: 7-8 mL.

[0035] Preferably, the copper salt includes at least one of copper nitrate and copper sulfate.

[0036] Preferably, the solvent of the copper salt solution includes water.

[0037] Preferably, the calcination temperature in step (2) is 300-600 °C, more preferably 400-600 °C; the calcination time is 1-4 h, more preferably 2-3 h.

[0038] Preferably, the reducing gas in step (2) includes at least one of hydrogen, carbon monoxide, sulfur monoxide, methane, and ammonia. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The present invention will be further described below in conjunction with the drawings and embodiments, wherein:

[0040] Figure 1 is the XRD characterization diagram of the catalyst Cu@C-400 prepared in Example 1 of the present invention;

[0041] Figure 2 is the (a) TEM characterization diagram and (b) particle size distribution diagram of the catalyst Cu@C-400 prepared in Example 1 of the present invention;

[0042] Figure 3 is the catalyst Cu-Cu 2 O@NC-400 prepared in Comparative Example 1 of the present invention (a) TEM characterization diagram and (b) particle size distribution diagram;

[0043] Figure 4 is the XRD characterization diagram of the catalyst Cu@C-400 after being recycled 5 times in Example 6 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0044] The concept of the present invention and the technical effects produced will be clearly and completely described below in conjunction with embodiments to fully understand the purpose, features, and effects of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative efforts all fall within the scope of protection of the present invention.

[0045] Example 1

[0046] In this example, a Cu@C catalyst was prepared. The specific process is as follows:

[0047] (1) Synthesis of CuBTC:

[0048] (I) Preparation of solution A: Add 1.0 g of 1,3,5-benzenetricarboxylic acid, 15 mL of ethanol, and 15 mL of N,N-dimethylformamide to a 100 mL beaker in sequence, and stir until the solid dissolves.

[0049] (II) Preparation of solution B: Add 2.0 g of copper nitrate and 15 mL of water to another 100 mL beaker in sequence, and stir until the solid dissolves.

[0050] (III) Under stirring, add solution A to solution B, and then continue stirring for 10 min.

[0051] (IV) Transfer the above mixed solution to a hydrothermal reaction kettle and react at 85 °C for 8 h.

[0052] (V) Finally, obtain the copper-organic framework precursor CuBTC through centrifugal filtration, washing, and vacuum drying.

[0053] (2) Preparation of the catalyst Cu@C: Under H 2 atmosphere, calcine CuBTC at 400 °C for 2 h to obtain the catalyst Cu@C-400.

[0054] Figure 1 is the XRD characterization pattern of the catalyst Cu@C-400. Figure 1 In, the diffraction peaks at the positions of 43.3°, 50.4°, and 74.1° are attributed to Cu. The above results indicate that the active component on the prepared catalyst is Cu nanoparticles.

[0055] Example 2

[0056] In this example, the Cu@C-400 catalyst prepared in Example 1 was used to catalyze the dehydrogenation of ethylene glycol to prepare glycolic acid. The specific process is as follows:

[0057] Add 40 g of a 5 wt% aqueous ethylene glycol solution to a 100 mL high-temperature and high-pressure reactor, then add the Cu@C-400 catalyst (the addition amount is 2% of the mass of the aqueous ethylene glycol solution), and then add NaOH (the molar ratio of ethylene glycol to NaOH is 1:1.1). Finally, seal the reactor and use N 2 Replace the air in the reactor 5 times, and then fill it with N 2 until the pressure in the reactor reaches 1 MPa, heat to 200 °C, and react for 100 min. After the reaction is completed, take samples for gas-phase and liquid-phase analysis to determine the conversion rate of ethylene glycol and the selectivity of glycolic acid. After testing, the conversion rate of ethylene glycol is 92%, and the selectivity of glycolic acid is 82%.

[0058] Example 3

[0059] In this example, the Cu@C-400 catalyst prepared in Example 1 was used to catalyze the dehydrogenation of 1,2-propanediol to prepare lactic acid. The specific process is as follows:

[0060] Add 50 g of a 10 wt% aqueous 1,2-propanediol solution to a 100 mL high-temperature and high-pressure reactor, then add the Cu@C-400 catalyst (the addition amount is 1.2% of the mass of the aqueous 1,2-propanediol solution), and then add KOH (the molar ratio of 1,2-propanediol to KOH is 1:1.1). Finally, seal the reactor and use N 2 Replace the air in the reactor 5 times, and then fill it with N 2 until the pressure in the reactor reaches 1 MPa, heat to 220 °C, and react for 80 min. After the reaction is completed, take samples for gas-phase and liquid-phase analysis to determine the conversion rate of 1,2-propanediol and the selectivity of lactic acid. After testing, the conversion rate of 1,2-propanediol is 95%, and the selectivity of lactic acid is 85%.

[0061] Example 4

[0062] In this example, the Cu@C-400 catalyst prepared in Example 1 was used to catalyze the dehydrogenation of 1,3-propanediol to prepare lactic acid. The specific process is as follows:

[0063] Add 40 g of a 20 wt% aqueous 1,3-propanediol solution to a 100 mL high-temperature and high-pressure reactor, then add the Cu@C-400 catalyst (the addition amount is 2% of the mass of the aqueous 1,3-propanediol solution), and then add NaOH (the molar ratio of 1,3-propanediol to NaOH is 1:1.3). Finally, seal the reactor and use N 2 Replace the air in the reactor 5 times, and then fill it with N 2Until the pressure in the reactor reaches 1 MPa, heat to 240 °C and react for 150 min. After the reaction is completed, take samples for gas-phase and liquid-phase analysis to determine the conversion rate of 1,3-propanediol and the selectivity of 3-hydroxypropionic acid. After testing, the conversion rate of 1,3-propanediol is 96%, and the selectivity of 3-hydroxypropionic acid is 82%.

[0064] Example 5

[0065] In this example, the Cu@C-400 catalyst prepared in Example 1 was used to catalyze the dehydrogenation of glycerol to prepare lactic acid. The specific process was as follows:

[0066] Add 40 g of 12 wt% aqueous glycerol solution to a 100 mL high-temperature and high-pressure reactor, then add the Cu@C-400 catalyst (the addition amount is 1% of the mass of the aqueous glycerol solution), and then add NaOH (the molar ratio of glycerol to NaOH is 1:1.1). Finally, seal the reactor and use N 2 Replace the air in the reactor 5 times, and then fill it with N 2 Until the pressure in the reactor reaches 1 MPa, heat to 220 °C and react for 60 min. After the reaction is completed, take samples for gas-phase and liquid-phase analysis to determine the conversion rate of glycerol and the selectivity of lactic acid. After testing, the conversion rate of glycerol is 90%, and the selectivity of lactic acid is 81%.

[0067] Example 6

[0068] In this example, the Cu@C-400 catalyst prepared in Example 1 was used to catalyze the dehydrogenation of glycerol to prepare lactic acid multiple times. The specific process was as follows:

[0069] Add 40 g of 10 wt% aqueous glycerol solution to a 100 mL high-temperature and high-pressure reactor, then add the Cu@C-400 catalyst (the addition amount is 1.5% of the mass of the aqueous glycerol solution), and then add KOH (the molar ratio of glycerol to KOH is 1:1.2). Finally, seal the reactor and use N 2 Replace the air in the reactor 5 times, and then fill it with N 2 Until the pressure in the reactor reaches 1 MPa, heat to 220 °C and react for 90 min. After the reaction is completed, take samples for gas-phase and liquid-phase analysis to determine the conversion rate of glycerol and the selectivity of lactic acid.

[0070] The steps for recycling the Cu@C-400 catalyst in this example are as follows:

[0071] Centrifuge and separate the Cu@C-400 catalyst from the reaction mixture at the end of the reaction, wash it 4 times with water, and directly use it for the next reaction. The reaction conditions are the same as those for the method of catalytic dehydrogenation of glycerol to prepare lactic acid in this example above. The catalyst was recycled 6 times, and Table 2 shows the test results of the recycling performance of the Cu@C-400 catalyst.

[0072] Comparative Example 1

[0073] In this comparative example, a Cu-Cu 2 O@NC catalyst was prepared. The specific process was as follows:

[0074] (1) Synthesis of Cu 2 (BDC) 2 (BPY): 0.72 g of copper nitrate, 0.23 g of 4,4'-bipyridine, 0.50 g of terephthalic acid, 30 mL of methanol and 30 mL of DMF were successively added to a 100 mL beaker, and then stirred at room temperature for 1 h. The above mixed solution was transferred to a hydrothermal reaction kettle and reacted at 120 °C for 48 h. Finally, the copper-organic framework precursor Cu 2 (BDC) 2 (BPY) was obtained through centrifugation, filtration, washing and vacuum drying.

[0075] (2) Preparation of Cu-Cu 2 O@NC: Under N 2 atmosphere, Cu 2 (BDC) 2 (BPY) was calcined at 400 °C for 2 h respectively to obtain the catalyst Cu-Cu 2 O@NC-400.

[0076] Figure 3 is the TEM characterization diagram and particle size distribution diagram of the catalyst Cu-Cu 2 O@NC-400. The particle size distribution range of Cu nanoparticles in the catalyst Cu-Cu 2 O@NC-400 is relatively narrow, and the average particle size is relatively small (24 nm).

[0077] Comparative Example 2

[0078] This comparative example lists the recycling performance of Cu-based catalysts in the published literature.

[0079] Table 3 Recycling times of Cu-based catalysts in the reaction of catalytic dehydrogenation of glycerol to prepare lactic acid in the published literature.

[0080]

[0081] Test Example

[0082] In this test example, the performance of the catalysts and acids prepared in the examples and comparative examples was tested. Among them:

[0083] The conversion rate of alcohol was calculated based on the quantitative results of gas chromatography of alcohol. The quantitative results of acid were calculated based on the test results of high performance liquid chromatography of the product;

[0084] The calculation formula for the conversion rate is as follows: (the mass of alcohol before the reaction - the mass of alcohol after the reaction) / (the mass of alcohol before the reaction) × 100%.

[0085] The selectivity is calculated based on the conservation of C atoms, and the calculation formula is as follows: (the molar amount of acid) × (the number of carbon atoms in the acid molecular formula) / ((the molar amount of alcohol reacted) × (the number of carbon atoms in the alcohol molecular formula)) × 100%.

[0086] Table 1 Raw material conversion rate and product selectivity prepared in the examples of the present invention

[0087] Example 2 Example 3 Example 4 Example 5 Conversion rate of raw material (alcohols) / % 92 95 96 90 Selectivity of product (acids) / % 82 85 82 81

[0088] Table 2 Test results of the recycling performance of the catalyst Cu@C-400 in Example 6 of the present invention

[0089]

[0090]

[0091] As can be seen from Table 1, the Cu@C-400 catalyst prepared by the present invention can efficiently catalyze the dehydrogenation of alcohols to prepare acids. The alcohol conversion rate in the reaction is 90 - 96%, and the acid selectivity is 81 - 85%. From Table 2 and Figure 4 it can be seen that the Cu@C-400 catalyst can be recycled multiple times. The conversion rate of glycerol in the 5th recycling is 89%, and the lactic acid selectivity is 72%, showing good recycling stability. As shown in Table 3, the Cu-based catalysts in the published literature have fewer recycling times in the reaction of catalytic dehydrogenation of glycerol to prepare lactic acid, and cannot meet the requirements of industrial catalytic dehydrogenation of alcohols to prepare acids.

[0092] From Figure 2 and Figure 3 it can be seen that the average particle size of the catalyst Cu@C-400 prepared by the present invention is 84.2 nm, which is uniformly dispersed and has no agglomeration phenomenon; in Comparative Example 1, 4,4'-bipyridine is used as the nitrogen source on the basis of Example 1, and nitrogen is further doped in the catalyst. Although the average particle size of the catalyst Cu@NC-400 is smaller, with an average particle size of 24 nm and a narrower particle size distribution, it needs to add 4,4'-bipyridine, resulting in a higher preparation cost and a more complex preparation process of the catalyst precursor; the preparation temperature is higher, the time is longer, and the energy consumption is greater. Moreover, even though the catalyst Cu@C-400 of the present invention has a wider particle size range and a larger average particle size, it still has better catalytic performance and stability, and can not only catalyze the dehydrogenation of glycerol to obtain lactic acid, but also catalyze the dehydrogenation of ethylene glycol, 1,2-propanediol, and 1,3-propanediol to obtain glycolic acid, lactic acid, and 3-hydroxypropionic acid respectively, with a wider range of uses.

[0093] The embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention within the scope of knowledge possessed by those of ordinary skill in the relevant art. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

Claims

1. A method for preparing an acid by catalytic dehydrogenation of an alcohol, characterized in that, it comprises the following steps: mixing a primary alcohol, a catalyst, and a base, and carrying out a catalytic reaction under an inert atmosphere to obtain the acid; the catalyst is carbon-coated copper nanoparticles; the primary alcohol includes at least one of ethylene glycol, 1,2-propanediol, 1,3-propanediol, and glycerol; the preparation method of the carbon-coated copper nanoparticle catalyst comprises the following steps: (1) Mixing a copper salt, 1,3,5-benzenetricarboxylic acid, and a solvent, and carrying out a solvothermal reaction to obtain a copper organic framework precursor CuBTC; (2) Calcining the copper organic framework precursor under a reducing gas to obtain the carbon-coated copper nanoparticles; the temperature of the solvothermal reaction in step (1) is 80-90 °C.

2. The method according to claim 1, characterized in that, the particle size of the carbon-coated copper nanoparticles is 30-155 nm.

3. The method according to claim 1, characterized in that, the mass ratio of the catalyst to the primary alcohol is 0.05-0.6:

1.

4. The method according to claim 1, characterized in that, the molar ratio of the primary alcohol to the base is 1:1-1.

5.

5. The method according to claim 1, characterized in that, the temperature of the catalytic reaction is 180-260 °C.

6. The method according to claim 1, characterized in that, the base includes at least one of alkali metal hydroxides and alkaline earth metal hydroxides.

7. The method according to claim 1, characterized in that, the mass ratio of the copper salt to 1,3,5-benzenetricarboxylic acid is 1-3:1.

Images