Method for preparing methyl glycolate by catalyzing oxidative esterification of ethylene glycol with palladium-based nano-alloy catalyst

Abstract

The invention discloses a method for preparing methyl glycolate by catalyzing ethylene glycol oxidative esterification with a palladium-based nano-alloy catalyst, and belongs to the technical field of catalysis. According to the palladium-based nano-alloy catalyst, precious metal palladium serves as a main active component, an oxide or a composite oxide serves as a carrier, at least one of bismuth, lead, cobalt, copper, zinc, nickel, iron, aluminum, manganese, magnesium and other elements is added to serve as an auxiliary to modulate the catalyst, and the palladium-based nano-alloy catalyst is prepared through an impregnation method, a deposition-precipitation method or a coprecipitation method. The reaction activity and the product selectivity are obviously improved in the reaction of catalyzing the oxidation esterification of ethylene glycol to prepare methyl glycolate, the efficient conversion from ethylene glycol to methyl glycolate is realized, and the method has a very wide industrial application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysis, and in particular relates to a method for preparing methyl glycolate by oxidative esterification of ethylene glycol catalyzed by a palladium-based nano alloy catalyst. Background Art

[0002] Methyl glycolate (HOCH2COOCH3) has the chemical properties of both alcohol and ester because it has α-H, hydroxyl and ester functional groups. It can undergo chemical reactions such as carbonylation, amination, hydrolysis, hydrogenation and oxidative dehydrogenation. It is widely used in various fields such as chemical industry, pesticides, medicine, feed and dyes. In addition, methyl glycolate is also an excellent solvent for cellulose, resin, rubber, etc.

[0003] The methods for synthesizing methyl glycolate mainly include: addition of formaldehyde to hydrocyanic acid, addition of methylal to formaldehyde free radicals, carbonylation and esterification of formaldehyde, and coupling reaction of methyl formate and formaldehyde, etc. These processes have been gradually eliminated due to the disadvantages of high raw material prices, serious corrosion in the production process, and difficulty in separating the products.

[0004] Qin Xiaoxia et al. used Au / ZnO to selectively oxidize ethylene glycol to synthesize methyl glycolate. The results showed that the Au / ZnO catalyst with a gold loading mass fraction of 5% had the best catalytic performance in the oxidative esterification of ethylene glycol to synthesize methyl glycolate (The 8th National Industrial Catalysis Technology and Application Annual Conference, 2011, conference paper). Although gold-based catalysts show excellent activity, the price of gold is relatively high. In order to reduce costs, palladium catalysts may be a better choice. However, compared with gold catalysts under the same reaction conditions, the selectivity of palladium-based catalysts for catalyzing methyl glycolate is lower. Therefore, improving palladium-based catalysts and then improving the activity and selectivity of palladium-based catalysts for catalyzing methyl glycolate has become a technical problem that needs to be solved urgently. Summary of the invention

[0005] In order to solve the problems in the background technology, the purpose of the present invention is to provide a method for preparing methyl glycolate by oxidative esterification of ethylene glycol using a palladium-based nano alloy catalyst. The present invention prepares a supported palladium catalyst by loading palladium nanoparticles onto an oxide or composite oxide carrier by an impregnation method or a deposition precipitation method, and introduces doping of elements such as bismuth, lead, cobalt, copper, zinc, nickel, iron, aluminum, manganese, and magnesium (catalyst modification mechanism: by introducing doping of elements such as bismuth, lead, cobalt, copper, zinc, nickel, iron, aluminum, manganese, and magnesium, alloys or intermetallic compounds are formed with palladium, and the coordination environment of palladium is adjusted, thereby the electronic properties of palladium are modulated, the adsorption strength of palladium on organic reactants and the CC bond dissociation ability are weakened, the generation of by-products is reduced, and the conversion rate of the reactant ethylene glycol and the selectivity for the product are improved). After reduction, the catalyst is used in the reaction of preparing methyl glycolate by oxidative esterification of ethylene glycol, which significantly improves the activity and product selectivity of the oxidative esterification of ethylene glycol.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing methyl glycolate by oxidative esterification of ethylene glycol catalyzed by a palladium-based nano alloy catalyst, comprising the following steps:

[0008] (1) impregnating a soluble salt of a modified metal onto an oxide or composite oxide support, allowing the mixture to stand at room temperature for 10 to 24 hours, drying the mixture, and calcining the mixture in an air atmosphere at 400 to 700° C. to obtain a modified oxide or composite oxide support; then impregnating an equal volume of a palladium salt solution onto the surface of the modified oxide or composite oxide support; or mixing the palladium salt aqueous solution with the modified oxide or composite oxide support, adding an alkali solution to adjust the pH to 8 to 13, allowing the mixture to stand at room temperature for 2 to 24 hours, drying the mixture, and calcining the mixture in an air atmosphere at 400 to 700° C., and finally reducing the mixture in a hydrogen atmosphere at 150 to 500° C. to obtain a catalyst;

[0009] Alternatively, the palladium salt solution and the soluble salt of the modified metal are directly impregnated into the oxide or composite oxide, left to stand at room temperature for 10 to 24 hours, dried, calcined in an air atmosphere at 400 to 700° C., and finally reduced in a hydrogen atmosphere at 150 to 500° C. to obtain a catalyst;

[0010] (2) The catalyst obtained in step (1) is loaded into a high-pressure reactor, and a mixed solution of alkaline substances, ethylene glycol and methanol is added to react in an oxygen-containing atmosphere at a reaction pressure of 0.5-5 MPa and a reaction temperature of 80-200° C. Ethylene glycol is oxidatively esterified to obtain methyl glycolate.

[0011] Based on the above technical solution, further, the modified metal described in step (1) is one or a combination of more than two of bismuth, lead, cobalt, copper, zinc, nickel, iron, aluminum, manganese, and magnesium, and the loading of the modified metal is 0.1-2wt%, preferably 0.5-1.5wt%.

[0012] Based on the above technical solution, further, the loading amount of palladium metal in step (1) is 0.1-5wt%, preferably 0.5-1.5wt%.

[0013] Based on the above technical solution, further, the palladium salt described in step (1) is one of palladium sulfate, nitrate, oxalate, chloride, acetate and phosphate.

[0014] Based on the above technical solution, further, the soluble salt of the modified metal described in step (1) is sulfate, nitrate, oxalate, chloride, acetate or phosphate of the corresponding metal.

[0015] Based on the above technical scheme, further, the oxide described in step (1) is one of Al2O3, MgO, SiO2, CaO, ZnO, TiO2, and ZrO2, and the composite oxide is a mixture of two of Al2O3, MgO, SiO2, CaO, ZnO, TiO2, and ZrO2, and the mass ratio of the two oxides is 10:1-1:10.

[0016] Based on the above technical solution, further, the solute of the alkali solution described in step (1) is one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, ammonia water, and urea.

[0017] Based on the above technical solution, further, the drying described in step (1) is carried out at 100-140°C, the roasting temperature is 400-600°C, the roasting time is 2-6h, the reduction temperature is 300-500°C, and the reduction time is 1-5h.

[0018] Based on the above technical solution, further, in step (2), the reaction pressure is 1-3 MPa, the reaction temperature is 100-130° C., and the reaction time is 0.5-24 h.

[0019] Based on the above technical solution, further, the alkaline substance described in step (2) is sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, and the concentration of the alkaline substance is 0.0001-0.1 g / mL.

[0020] Based on the above technical solution, further, in step (2), the molar ratio of methanol to ethylene glycol is 0.1-50:1, preferably 5-50:1; the amount of catalyst added is 0.1-20wt% of the total amount of methanol and ethylene glycol, preferably 1-10wt%.

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

[0022] In order to reduce the catalyst cost and improve the selectivity of methyl glycolate, the present invention loads relatively cheap palladium nanoparticles onto an oxide or composite oxide carrier, and adjusts the activity of the catalyst and the selectivity of the product by adding a second element such as bismuth, lead, cobalt, copper, zinc, nickel, iron, aluminum, manganese, and magnesium, thereby achieving an activity close to that of gold salt at 120-150° C., which is more conducive to application in industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention, the drawings related to the embodiments are briefly introduced below.

[0024] Figure 1 This is a TEM electron microscope image of the palladium-bismuth nanoalloy catalyst of Example 1;

[0025] Figure 2 The SEM image and element distribution diagram of the palladium-bismuth nanoalloy catalyst of Example 1; DETAILED DESCRIPTION

[0026] The present invention is described in detail below through specific examples, but these examples do not limit the contents of the present invention.

[0027] The reaction products were analyzed online by gas chromatography:

[0028] The conversion rate of ethylene glycol is calculated as follows:

[0029] Conv(ethylene glycol)%=[1-(amount of unreacted ethylene glycol / amount of supplied ethylene glycol)]×100%

[0030] The selectivity of methyl glycolate is calculated as follows:

[0031] S (methyl glycolate)%=[the amount of substance of methyl glycolate produced / (the amount of substance of ethylene glycol supplied-the amount of substance of unreacted ethylene glycol)]×100%.

[0032] Comparative Example 1: Preparation of 1% Pd / Al2O3

[0033] 0.2 mL of chloropalladic acid aqueous solution was dripped onto the Al2O3 carrier dropwise to make the palladium loading on the carrier 1%. After impregnation, it was left to stand at room temperature for 12 hours, then dried at 120°C for 2 hours, finally calcined at 500°C in air atmosphere for 2 hours, and finally reduced at 400°C in hydrogen atmosphere for 2 hours to obtain the catalyst 1% Pd / Al2O3.

[0034] Comparative Example 2: Preparation of 1% Au / Al2O3

[0035] Take 0.1 mL of chloroauric acid aqueous solution, dissolve it in 150 mL of water, add alumina carrier, disperse evenly, adjust the solution pH to 8 with sodium carbonate and maintain for 2 hours, filter, wash and dry, and calcine at 350°C for 2 hours in an air atmosphere to obtain a catalyst 1% Au / Al2O3.

[0036] Reaction evaluation of the catalyst of Comparative Examples 1-2 The selective oxidation reaction of ethylene glycol was carried out in a high-pressure reactor, taking 0.5 g of the catalyst prepared in Comparative Example 1 or Comparative Example 2, 0.01 g of sodium carbonate, 10 mL of a mixed solution of ethylene glycol in methanol, the molar ratio of methanol to ethylene glycol = 10:1, and the air pressure was filled to 3 MPa, the reaction temperature was 120°C, and the reaction time was 1 h. The results of ethylene glycol conversion and methyl glycolate selectivity are shown in Table 1.

[0037] Table 1. Catalytic activity of the catalysts of Comparative Examples 1-2 in ethylene glycol oxidation reaction

[0038]

[0039] Example 1: Preparation of oxide-supported palladium catalyst 1% Pd-1% Bi / Al2O3 by impregnation method

[0040] Catalyst preparation: 0.2 mL of 20% bismuth nitrate aqueous solution was dripped onto the alumina carrier drop by drop, stirred evenly, and allowed to stand at room temperature for 12 hours, then dried at 120°C for 2 hours, and finally calcined at 600°C in air atmosphere for 3 hours to obtain 1% Bi / Al2O3. 0.2 mL of a certain concentration of chloropalladic acid aqueous solution was dripped onto the Bi / Al2O3 carrier drop by drop to ensure that the mass ratio of palladium to bismuth was 1:1, allowed to stand at room temperature for 12 hours, then dried at 120°C for 2 hours, calcined at 500°C in air atmosphere for 2 hours, and finally reduced at 400°C in hydrogen atmosphere for 2 hours to obtain the catalyst 1% Pd-1% Bi / Al2O3.

[0041] Embodiment 2:

[0042] Referring to the method of Example 1, a catalyst 1% Pd-1% Zn / Al2O3 was obtained.

[0043] Embodiment 3:

[0044] Referring to the method of Example 1, a catalyst 1% Pd-1% Pb / Al2O3 was obtained.

[0045] Embodiment 4:

[0046] Referring to the method of Example 1, a catalyst 1% Pd-1% Co / Al2O3 was obtained.

[0047] Embodiment 5:

[0048] Referring to the method of Example 1, a catalyst 1% Pd-1% Ni / Al2O3 was obtained.

[0049] Reaction evaluation of the catalyst of Examples 1-5 The selective oxidation reaction of ethylene glycol was carried out in a high-pressure reactor, taking 0.5 g of catalyst, 0.01 g of sodium carbonate, 10 mL of a mixed solution of ethylene glycol and methanol, with a methanol / ethylene glycol molar ratio of 10:1, and the air pressure was filled to 3 MPa, the reaction temperature was 120°C, and the reaction time was 1 h. The results of ethylene glycol conversion and methyl glycolate selectivity are shown in Table 2.

[0050] Table 2. Activity of different catalysts prepared by impregnation method in oxidative esterification of ethylene glycol

[0051]

[0052] Compared with Comparative Example 1, the selectivity of methyl glycolate in Examples 1-5 is significantly improved, and is comparable to the selectivity of the gold catalyst in Comparative Example 2.

[0053] Example 6: Preparation of palladium-based catalyst 1% Pd-1% Bi / Al2O3-D by deposition precipitation method

[0054] Catalyst preparation: 0.2 mL of 20% bismuth nitrate aqueous solution was dripped onto the alumina carrier drop by drop, stirred evenly, and allowed to stand at room temperature for 12 hours, then dried at 120°C for 2 hours, and finally calcined at 600°C in an air atmosphere for 3 hours to obtain a bismuth-modified Al2O3 carrier. 0.2 mL of chloropalladic acid aqueous solution was dissolved in 150 mL of water, and the bismuth-modified Al2O3 carrier was dispersed in the above solution. At 60°C, the pH of the solution was adjusted to 10 using sodium carbonate and maintained for 4 hours. Subsequently, the solution was filtered, washed, dried at 120°C, calcined at 500°C in an air atmosphere for 2 hours, and finally reduced at 400°C in a hydrogen atmosphere for 2 hours to obtain the catalyst 1% Pd-1% Bi / Al2O3-D.

[0055] Example 7

[0056] Referring to the method of Example 6, a catalyst 1% Pd-1% Zn / Al2O3-D was obtained.

[0057] Example 8

[0058] Referring to the method of Example 6, a catalyst 1% Pd-1% Pb / Al2O3-D was obtained.

[0059] Example 9

[0060] Referring to the method of Example 6, a catalyst 1% Pd-1% Co / Al2O3-D was obtained.

[0061] Example 10

[0062] Referring to the method of Example 6, a catalyst 1% Pd-1% Ni / Al2O3-D was obtained.

[0063] Catalyst reaction evaluation of Examples 6-10 The selective oxidation reaction of ethylene glycol was carried out in a high-pressure reactor, with 0.5 g of catalyst, 0.01 g of sodium carbonate, 10 mL of a mixed solution of ethylene glycol in methanol, a methanol / ethylene glycol molar ratio of 10:1, and air pressure of 3 MPa, a reaction temperature of 120°C, and a reaction time of 1 h. The results of ethylene glycol conversion and methyl glycolate selectivity are shown in Table 3.

[0064] Table 3. Activities of different catalysts prepared by coprecipitation in the oxidative esterification of ethylene glycol

[0065]

[0066] Example 11: Preparation of catalyst 1% Pd-1% Bi / Al2O3-C by coprecipitation method

[0067] Catalyst preparation: 0.5 g of bismuth nitrate and 0.2 ml of 1 mol / L chloropalladic acid aqueous solution were dissolved in 150 mL of water, and the Al2O3 carrier was dispersed in the above solution. At 70°C, the pH of the solution was adjusted to 11 using sodium carbonate and maintained for 4 hours. Subsequently, the solution was filtered, washed, dried at 120°C, calcined at 550°C in an air atmosphere for 2 hours, and finally reduced at 400°C in a hydrogen atmosphere for 2 hours to obtain the catalyst 1% Pd-1% Bi / Al2O3-C.

[0068] Example 12

[0069] Referring to the method of Example 11, a catalyst 1% Pd-1% Zn / Al2O3-C was obtained.

[0070] Example 13

[0071] Referring to the method of Example 11, a catalyst 1% Pd-1% Pb / Al2O3-C was obtained.

[0072] Embodiment 14

[0073] Referring to the method of Example 11, a catalyst 1% Pd-1% Co / Al2O3-C was obtained.

[0074] Embodiment 15

[0075] Referring to the method of Example 11, a catalyst 1% Pd-1% Ni / Al2O3-C was obtained.

[0076] Catalyst reaction evaluation of Examples 11-15 The selective oxidation reaction of ethylene glycol was carried out in a high-pressure reactor, with 0.5 g of catalyst, 0.01 g of sodium carbonate, 10 mL of a mixed solution of ethylene glycol in methanol, a methanol / ethylene glycol molar ratio of 10:1, and air pressure of 3 MPa, a reaction temperature of 120°C, and a reaction time of 1 h. The results of ethylene glycol conversion and methyl glycolate selectivity are shown in Table 4.

[0077] Table 4. Activities of different catalysts prepared by the deposition precipitation method in the oxidative esterification of ethylene glycol

[0078]

[0079] Example 16

[0080] A composite oxide-supported palladium-based catalyst was prepared by the preparation method of Reference Example 11, wherein the oxides Al2O3 and SiO2 were mixed in a mass ratio of 1:1 to replace the single Al2O3 carrier, and a catalyst 1% Pd-1% Bi / Al2O3-SiO2-D was prepared.

[0081] Embodiment 17

[0082] Referring to the method of Example 16, the type of loaded metal and different carriers were changed to obtain the catalyst 1% Pd-1% Pb / MgO-SiO2-D.

[0083] Embodiment 18

[0084] Referring to the method of Example 16, the type of loaded metal and different carriers were changed to obtain the catalyst 1% Pd-1% Co / Al2O3-MgO-D.

[0085] Embodiment 19

[0086] Referring to the method of Example 16, the type of loaded metal and different carriers were changed to obtain the catalyst 1% Pd-1% Ni / CaO-ZnO-D.

[0087] Embodiment 20

[0088] Referring to the method of Example 16, the type of loaded metal and different carriers were changed to obtain the catalyst 1% Pd-1% Bi / SiO2-MgO-D.

[0089] Catalyst reaction evaluation of Examples 16-20 The selective oxidation reaction of ethylene glycol was carried out in a high-pressure reactor, with 0.5 g of catalyst, 0.01 g of sodium carbonate, 10 mL of a mixed solution of ethylene glycol in methanol, a methanol / ethylene glycol molar ratio of 10:1, and air pressure of 3 MPa, a reaction temperature of 150° C., and a reaction time of 1 h. The results of ethylene glycol conversion and methyl glycolate selectivity are shown in Table 5.

[0090] Table 5. Activity of catalysts supported by different composite oxides prepared by coprecipitation in oxidative esterification of ethylene glycol

[0091]

Claims

1. A method for preparing methyl glycolate by oxidative esterification of ethylene glycol using a palladium-based nano-alloy catalyst, characterized in that: The steps include: (1) impregnating a soluble salt of a modified metal onto an oxide or composite oxide support, allowing the mixture to stand at room temperature for 10 to 24 hours, drying the mixture, and calcining the mixture in an air atmosphere at 400 to 700° C. to obtain a modified oxide or composite oxide support; then impregnating an equal volume of a palladium salt solution onto the surface of the modified oxide or composite oxide support; or mixing the palladium salt aqueous solution with the modified oxide or composite oxide support, adding an alkali solution to adjust the pH to 8 to 13, allowing the mixture to stand at room temperature for 2 to 24 hours, drying the mixture, and calcining the mixture in an air atmosphere at 400 to 700° C., and finally reducing the mixture in a hydrogen atmosphere at 150 to 500° C. to obtain a catalyst; Alternatively, the palladium salt solution and the soluble salt of the modified metal are directly impregnated into the oxide or composite oxide, left to stand at room temperature for 10 to 24 hours, dried, calcined in an air atmosphere at 400 to 700° C., and finally reduced in a hydrogen atmosphere at 150 to 500° C. to obtain a catalyst; (2) The catalyst obtained in step (1) is loaded into a high-pressure reactor, and a mixed solution of alkaline substances, ethylene glycol and methanol is added to react in an oxygen-containing atmosphere at a reaction pressure of 0.5-5 MPa and a reaction temperature of 80-200° C. Ethylene glycol is oxidatively esterified to obtain methyl glycolate.

2. The method according to claim 1, characterized in that The modified metal described in step (1) is one or a combination of two or more of bismuth, lead, cobalt, copper, zinc, nickel, iron, aluminum, manganese, and magnesium, and the loading of the modified metal is 0.1-2wt%, preferably 0.5-1.5wt%.

3. The method according to claim 1, characterized in that The loading amount of palladium metal in step (1) is 0.1-5wt%, preferably 0.5-1.5wt%.

4. The method according to claim 1, characterized in that The palladium salt described in step (1) is one of palladium sulfate, nitrate, oxalate, chloride, acetate and phosphate; the soluble salt of the modified metal is the sulfate, nitrate, oxalate, chloride, acetate and phosphate of the corresponding metal.

5. The method according to claim 1, characterized in that The oxide described in step (1) is one of Al2O3, MgO, SiO2, CaO, ZnO, TiO2, and ZrO2, and the composite oxide is a mixture of two of Al2O3, MgO, SiO2, CaO, ZnO, TiO2, and ZrO2, and the mass ratio of the two oxides is 10:1-1:

10.

6. The method according to claim 1, characterized in that The solute of the alkali solution described in step (1) is one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, ammonia water and urea.

7. The method according to claim 1, characterized in that The drying described in step (1) is carried out at 100-140° C., the roasting temperature is 400-600° C., the roasting time is 2-6 hours, the reduction temperature is 300-500° C., and the reduction time is 1-5 hours.

8. The method according to claim 1, characterized in that: In step (2), the reaction pressure is 1-3 MPa, the reaction temperature is 100-130° C., and the reaction time is 0.5-24 h.

9. The method according to claim 1, characterized in that: The alkaline substance described in step (2) is sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, and the concentration of the alkaline substance is 0.0001-0.1 g / mL.

10. The method according to claim 1, characterized in that In step (2), the molar ratio of methanol to ethylene glycol is 0.1-50:1, preferably 5-50:1; the amount of catalyst added is 0.1-20wt% of the total amount of methanol and ethylene glycol, preferably 1-10wt%.

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