A method for preparing monohydric alcohol by catalytic hydrogenation of a bio-based small molecule dihydric alcohol

Abstract

This invention discloses a method for the catalytic hydrogenation of bio-based small molecule diols to prepare monohydric alcohols. The method includes the following steps: placing an aqueous solution of a bio-based small molecule diol in a high-pressure reactor, adding an activated carbon-supported metal catalyst and a solid or liquid acid, then introducing hydrogen gas at a certain pressure, and stirring the reaction at a certain temperature for a period of time to obtain the monohydric alcohol; the small molecule diol is one of ethylene glycol, 1,2-propanediol, 1,4-butanediol, 1,2-pentanediol, 1,5-pentanediol, and 1,2-hexanediol; the activated carbon raw material is widely available, easy to prepare, and recyclable. The catalyst preparation process is simple, reusable, inexpensive, has high catalytic activity, and the reaction conditions are relatively mild, making it easy to promote.

Description

Technical fields:

[0001] This invention relates to a method for the catalytic hydrogenation of bio-based small molecule diols to prepare monohydric alcohols. Background technology:

[0002] Monohydric alcohols, which contain only one hydroxyl group (R-OH) in their molecule, are an important class of organic compounds. They can be used as organic solvents and fuels, and are also important platform compounds, widely used in modern industrial production and daily life. Currently, the main industrial production methods for monohydric alcohols include hydration, fermentation, and syngas production technology. However, hydration requires large amounts of concentrated sulfuric acid, and the sulfuric acid medium has a severe corrosive effect on equipment. Furthermore, product separation and purification are difficult, increasing production costs. Fermentation has a long production cycle, and the high cost of biological enzymes, along with the vulnerability of enzyme activity to recycling, makes it difficult to achieve sustainable production. Syngas production technology for monohydric alcohols is currently immature, with demanding reaction conditions and high equipment requirements, hindering large-scale implementation. In recent years, with the increasing consumption of fossil fuels, the deepening energy crisis, and multiple pressures from environmental issues, countries worldwide have accelerated the development and utilization of clean and renewable energy sources.

[0003] Biomass is a vast renewable carbon source on Earth, and its development and utilization have the dual significance of alleviating the energy crisis and protecting the environment. Small molecule diols (Diols) refer to alcohols with two hydroxyl groups (-OH), such as ethylene glycol, propylene glycol, and butanediol. Bio-based small molecule diols are important polyester monomers, widely used in food, pharmaceuticals, and fine chemicals. Bio-based small molecule diols are of great importance for sustainable social development and reducing carbon emissions. Lignocellulosic biomass is widely distributed in nature and has huge reserves. Through depolymerization, components such as cellulose and hemicellulose can be obtained, which can then be used to prepare small molecule diols via hydrogenolysis. These can be used as raw materials for the production of corresponding monohydric alcohols. Currently, the preparation technology for bio-based small molecule diols is becoming increasingly mature; therefore, developing methods for preparing monohydric alcohols from bio-based small molecule diols has significant implications and practical value.

[0004] Studies have shown that bio-based small molecule diols can be converted into aldehyde intermediates through catalytic dehydration, and then further hydrogenated to produce monohydric alcohols. However, due to the relatively stable nature of bio-based small molecule diols, they are difficult to directly convert and utilize, and there are currently few research reports on the preparation of monohydric alcohols from bio-based small molecule diols. Li et al. reported the use of Ru-WO3... xThe process of preparing ethanol from cellulose and ethylene glycol using / HZSM-5 catalyst (Green Chemistry, 2019.21(9):p.2234-2239) can achieve ethanol yields of 59% and 77.6%, respectively. However, the catalyst preparation is relatively complex, the reaction time is long, and the overall cost is high. Chu et al. reported a method for preparing ethanol from ethylene glycol using 1% Au-(20% Cu-2% Ni) / SiO2 catalyst (Chinese Journal of Catalysis, 2021.42(5):p.844-854). The ethanol yield of this method can reach 62.2%. However, the catalyst structure used in this method is relatively complex and difficult to prepare. In addition, the reaction temperature is high, which is not conducive to its widespread application. Schlaf et al. reported a method for preparing n-propanol from 1,2-propanediol (Adv.Synth.Catal.2009.351,789–800). However, the catalyst preparation process of this method is complex, the product is not easy to separate, and it is difficult to promote. Japanese scholars Amada and Liu et al. reported a method for preparing monohydric alcohols from 1,2-propanediol using a bimetallic supported catalyst (ChemSusChem 2010,3,728–736; ACS Sustainable Chem.Eng.2022,10,1220-1231), achieving yields of 66% and 19% for n-propanol and isopropanol, respectively. However, this reaction required a long reaction time and had low efficiency. Liu et al. studied the process of preparing n-butanol and isobutanol from 1,2-butanediol (ACS Catal.2022,12,15431-15450), achieving product selectivity of 78% and 64%, respectively. However, this reaction required high hydrogen pressure, long reaction time, and harsh conditions. Patent CN 102731247 A discloses a method for preparing n-propanol from bio-based small molecule diols. The method involves reacting 1,2-propanediol, a product of glycerol hydrogenolysis, with a catalyst supported on a transition metal element in a fixed-bed reactor via a high-temperature dehydration coupled with hydrogen transfer continuous reaction to prepare n-propanol. This method achieves a single-pass conversion of 86.01% and a n-propanol selectivity of 45.01% in the product. However, this method requires relatively high reaction temperatures and complex equipment, and the resulting product selectivity is low, which is not conducive to large-scale production. Beeck et al. reported a process for preparing monohydric alcohols from biomass derivatives 1,2-hexanediol and 2,5-hexanediol (Energy Environ. Sci., 2015, 8, 230–240). This method has a shorter reaction time, but the yield of the target product is less than 10%, resulting in low overall efficiency.Nakagawa et al. reported a method for preparing monohydric alcohols using biomass derivatives 1,2-pentanediol and 1,5-pentanediol (ACS Catal. 2013, 3, 2655-2668). This method has relatively mild reaction conditions, but requires a long reaction time and has low product selectivity (16%), making it unsuitable for widespread application.

[0005] In summary, the hydrogenation of bio-based small molecule diols to prepare monohydric alcohols is a feasible process route. However, most current methods are complex and require harsh reaction conditions, hindering the industrial-scale preparation of monohydric alcohols from bio-based small molecule diols. Therefore, developing low-cost, high-efficiency methods for preparing monohydric alcohols is urgently needed. Summary of the Invention:

[0006] The purpose of this invention is to provide a method for the catalytic hydrogenation of bio-based small molecule diols to prepare monohydric alcohols.

[0007] This invention is achieved through the following technical solutions:

[0008] A method for catalytic hydrogenation of a bio-based small molecule diol to prepare a monohydric alcohol, comprising the following steps: placing an aqueous solution of a bio-based small molecule diol in a high-pressure reactor, adding an activated carbon-supported metal catalyst and a solid or liquid acid, then introducing hydrogen gas at a certain pressure, and stirring the reaction at a certain temperature for a period of time to obtain a monohydric alcohol; wherein the small molecule diol is one of ethylene glycol, 1,2-propanediol, 1,4-butanediol, 1,2-pentanediol, 1,5-pentanediol, and 1,2-hexanediol, and the monohydric alcohol... The active carbon is selected from one of the following: ethanol, n-propanol, isopropanol, n-butanol, n-pentanol, and n-hexanol; the metal in the activated carbon-supported metal salt is one of Ru, Pd, Pt, Ir, Ni, Co, and Rh, with a metal loading of 1-5%; the solid acid is any one of phosphotungstic acid, silicotungstic acid, phosphomolybdic acid, zirconium oxide, and tungsten oxide; the liquid acid is any one of sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid; the hydrogen pressure is 1-6 MPa, the reaction temperature is 150-220℃, and the reaction time is 0.5-30 h.

[0009] The preparation method of the activated carbon supported metal catalyst is as follows: First, the activated carbon is washed with 1M nitric acid solution for 8 hours, then washed with water until neutral, and dried at 100°C to obtain the activated carbon support. Then, the prepared metal salt solution is uniformly impregnated on the surface of the activated carbon in a certain proportion, and then reduced with hydrogen to obtain the desired activated carbon supported catalyst.

[0010] Preferably, the concentration of the bio-based small molecule diol is 10-60 g / L, the mass ratio of the metal catalyst to the solid / liquid acid is 1:10-1:2, more preferably 1:5-1:2, and the mass ratio of the total amount of the metal catalyst and the solid / liquid acid to the bio-based small molecule diol is 1:10-4:1, more preferably 1:10-2:1.

[0011] Preferably, the hydrogen pressure is 3-6 MPa, the reaction temperature is 180-220℃, and the reaction time is 0.5-12 h.

[0012] The beneficial effects of this invention are as follows: the activated carbon raw material is widely available, easy to prepare, and recyclable. The catalyst preparation process is simple, reusable, inexpensive, has high catalytic activity, and operates under relatively mild reaction conditions, making it easy to promote. Attached image description:

[0013] Figure 1 This is a schematic diagram of the catalytic conversion pathway of diols;

[0014] Figure 2 This is the HPLC chromatogram of the ethylene glycol reaction product in Example 1;

[0015] Figure 3 The GC spectrum of the 1,2-propanediol reaction product in Example 19 is shown.

[0016] Figure 4 The GC spectrum of the 1,4-butanediol reaction product in Example 27 is shown.

[0017] Figure 5 The GC spectrum of the 1,2-pentanediol reaction product in Example 34 is shown.

[0018] Figure 6 The GC spectrum of the 1,2-hexanediol reaction product in Example 42 is shown.

[0019] Figure 7 The XRD characterization results of the Pd / C catalyst in Example 1 are shown below.

[0020] Figure 8 The results are TEM characterizations of the tungsten oxide catalyst in Example 58. Detailed implementation method:

[0021] The following is a further description of the invention, but not a limitation thereof.

[0022] Example 1:

[0023] 1 gram of activated carbon was washed with 1M nitric acid solution for 8 hours, then washed with water until neutral, and dried at 100°C to obtain an activated carbon support. 1% PdCl3 (w / w) metal chloride solution was then mixed with activated carbon at a ratio of 5:1 (w / w) and uniformly impregnated onto the surface of the activated carbon. Subsequently, it was reduced with hydrogen at 500°C under normal pressure for 2 hours to obtain a 5% Pd / C catalyst.

[0024] 20 mL of a 10 g / L ethylene glycol solution was placed in a high-pressure reactor, along with 0.2 g of the prepared 5% Pd / C catalyst and 0.6 g of phosphotungstic acid. The reactor was then purged with hydrogen three times, followed by the introduction of 6 MPa hydrogen gas. The reaction was carried out at 220 °C and 800 rpm with stirring for 2 h. The product was analyzed by HPLC, and the ethanol yield was 80.6%.

[0025] Examples 2-8:

[0026] Referring to Example 1, the difference lies in the ratio of the supported catalyst to the solid acid and the reaction time. Specific examples are shown in Table 1.

[0027] Table 1:

[0028] Example Metal catalyst to solid acid ratio Reaction time (h) Ethanol yield (%) 2 1:5 5 71.9 3 1:5 10 61.2 4 1:4 12 63.3 5 1:3 10 65.8 6 1:2.5 6 70.6 7 1:2.5 8 72.3 8 1:2.5 12 78.5

[0029] Examples 9-18:

[0030] Referring to Example 1, the differences lie in the amount of catalyst, the mass ratio of bio-based small molecule diols, the reaction time, and the hydrogen pressure. Specific examples are shown in Table 2.

[0031] Table 2:

[0032] Example Catalyst to substrate ratio Reaction time (h) Hydrogen pressure (MPa) Ethanol yield (%) 9 1:10 10 6 39.5 10 1:8 10 5 40.3 11 1:8 12 5 44.6 12 1:6 10 5 45.2 13 1:5 10 4 50.1 14 1:4 8 5 52.6 15 1:2 10 3 61.8 16 1:1 2 5 75.6 17 2:1 1 6 85.6 18 2:1 0.5 6 82.5

[0033] Example 19:

[0034] Take 20 mL of 1,2-propanediol solution with a concentration of 10 g / L, place it in a high-pressure reactor, add 0.2 g of the prepared 5% Pt / C catalyst and 0.4 g of phosphoric acid, then introduce 3 MPa of hydrogen gas, and react for 3 h at 220 °C and 800 rpm with stirring. The yield of n-propanol is 88.5%.

[0035] Examples 20-26:

[0036] Referring to Example 19, the difference lies in the reaction time and hydrogen pressure. Specific examples are shown in Table 3.

[0037] Table 3:

[0038]

[0039]

[0040] Example 27:

[0041] The catalyst was prepared according to Example 1, except that the metal salt was 1% IrCl3 (w / w), and a 5% Ir / C catalyst was finally obtained.

[0042] Take 20 mL of 1,4-butanediol solution with a concentration of 10 g / L, place it in a high-pressure reactor, add 0.1 g of the prepared 5% Ir / C catalyst and 0.2 g of hydrochloric acid, then introduce 3 MPa of hydrogen gas, and react for 6 h at 220 °C and 800 rpm with stirring. The yield of n-butanol is 86.02%.

[0043] Examples 28-33:

[0044] Refer to Example 27, the difference being the reaction time and hydrogen pressure. Specific examples are shown in Table 4.

[0045] Table 4:

[0046]

[0047]

[0048] Example 34:

[0049] The catalyst was prepared according to Example 1, except that the metal salt was 1% Co(NO3)2 (w / w), and a 5% Co / C catalyst was finally obtained.

[0050] Take 20 mL of 1,2-pentanediol solution with a concentration of 10 g / L, place it in a high-pressure reactor, add 0.02 g of the prepared 5% Co / C catalyst and 0.05 g of sulfuric acid, then introduce 3 MPa of hydrogen gas, and react for 6 h at 200 °C and 800 rpm with stirring. The yield of n-pentanediol is 72.5%.

[0051] Examples 35-41:

[0052] Refer to Example 34, the difference being the reaction time and hydrogen pressure. Specific examples are shown in Table 5.

[0053] Table 5:

[0054]

[0055]

[0056] Example 42:

[0057] The catalyst was prepared according to Example 1, except that the metal salt was 1% RhCl3 (w / w), and a 5% Rh / C catalyst was finally obtained.

[0058] Take 20 mL of 1,2-hexanediol solution with a concentration of 10 g / L, place it in a high-pressure reactor, add 0.01 g of the prepared 5% Rh / C catalyst and 0.02 g of silicotungstic acid, then introduce 3 MPa of hydrogen gas, and react for 2 h at 180 °C and 800 rpm with stirring. The yield of n-hexanol is 60.5%.

[0059] Examples 43-49:

[0060] Refer to Example 42, the difference being the reaction time and hydrogen pressure. Specific examples are shown in Table 6.

[0061] Table 6:

[0062] Example Reaction time (h) Hydrogen pressure (MPa) Hexanol yield (%) 43 12 5 50.2 44 10 3 52.3 45 8 3 56.1 46 5 4 62.5 47 2 6 58.6 48 1 5 43.3 49 0.5 5 39.6

[0063] Example 50:

[0064] Take 20 mL of a 10 g / L mixed solution of ethylene glycol, 1,2-propanediol, 1,4-butanediol, 1,2-pentanediol, and 1,2-hexanediol, in which the mass percentages of different diols are equal, place it in a high-pressure reactor, add 0.02 g of the prepared 5% Pd / C catalyst and 0.05 g of phosphotungstic acid, then introduce 3 MPa of hydrogen gas, and react at 200 °C and 800 rpm for 6 h, with a monohydric alcohol yield of 72.5%.

[0065] Examples 51-58:

[0066] Referring to Example 50, the difference lies in the type of acid used, the reaction time, and the hydrogen pressure. Specific examples are shown in Table 7.

[0067] Table 7:

[0068] Example solid / liquid acid Reaction time (h) Hydrogen pressure (MPa) Monohydric alcohol yield (%) 51 Phosphoric acid 12 5 82.6 52 hydrochloric acid 10 5 83.5 53 Nitric acid 8 6 80.2 54 sulfuric acid 5 6 75.6 55 Silicotungstic acid 3 4 68.1 56 Phosphomolybdic acid 8 5 65.4 57 Zirconia 12 6 58.9 58 Tungsten oxide 10 5 61.7

Claims

1. A method for the catalytic hydrogenation of bio-based small molecule diols to prepare monohydric alcohols, characterized in that, The method includes the following steps: placing a bio-based small molecule diol aqueous solution in a high-pressure reactor, adding an activated carbon-supported metal catalyst and a solid or liquid acid, then introducing hydrogen gas at a certain pressure, and stirring the reaction at a certain temperature for a period of time to obtain a monohydric alcohol; the small molecule diol is one of ethylene glycol, 1,2-propanediol, 1,4-butanediol, 1,2-pentanediol, 1,5-pentanediol, and 1,2-hexanediol, and the monohydric alcohol is one of ethanol, n-propanol, n-butanol, n-pentanol, and n-hexanol; the metal in the activated carbon-supported metal catalyst is one of Ru, Pd, Pt, Ir, Ni, Co, and Rh, and the metal loading is 1-5%; the solid acid is any one of phosphotungstic acid, silicotungstic acid, phosphomolybdic acid, zirconium oxide, and tungsten oxide; the liquid acid is any one of sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid; the hydrogen pressure is 1-6 MPa, the reaction temperature is 150-220℃, and the reaction time is 0.5-30 h.

2. The method according to claim 1, characterized in that, The preparation method of the activated carbon supported metal catalyst is as follows: First, the activated carbon is washed with 1M nitric acid solution for 8 hours, then washed with water until neutral, and dried at 100°C to obtain the activated carbon support. Then, the prepared metal salt solution is uniformly impregnated on the surface of the activated carbon, and then reduced with hydrogen to obtain the desired activated carbon supported metal catalyst.

3. The method according to claim 1, characterized in that, The concentration of the bio-based small molecule diol is 10-60 g / L, and the mass ratio of the activated carbon-supported metal catalyst to the solid acid / liquid acid is 1:10-1:

2.

4. The method according to claim 1, characterized in that, The mass ratio of activated carbon-supported metal catalyst to solid acid / liquid acid is 1:5-1:

2.

5. The method according to claim 1, characterized in that, The total amount of activated carbon-supported metal catalyst and solid acid / liquid acid, and the mass ratio of bio-based small molecule diol, are 1:10-4:

1.

6. The method according to claim 1, characterized in that, The total amount of activated carbon-supported metal catalyst and solid acid / liquid acid, and the mass ratio of bio-based small molecule diol, are 1:10-2:

1.

7. The method according to claim 1, characterized in that, The hydrogen pressure is 3-6 MPa, the reaction temperature is 180-220℃, and the reaction time is 0.5-12 h.

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