Preparation method and application of copper-based catalyst for regulating and controlling dimethyl oxalate hydrogenation reaction product

Abstract

The invention belongs to the field of catalyst preparation and catalytic hydrogenation, and discloses a preparation method and application of a copper-based catalyst for regulating and controlling a dimethyl oxalate hydrogenation reaction product. A copper-based catalyst is a bulk phase catalyst, the catalyst is prepared by adopting a coprecipitation method, low-concentration acetylene treatment and hydrogen reduction steps, a catalyst precursor is synthesized under an ice-water bath condition, and the catalyst is obtained by performing low-concentration acetylene treatment and hydrogen reduction on the precursor. The preparation method adopted by the invention enables the catalyst preparation conditions to be milder and more efficient. In the aspect of application, the nickel hydroxide modified copper carbide catalyst is utilized to realize adjustable distribution of a dimethyl oxalate hydrogenation product, and the dimethyl oxalate can efficiently generate methyl glycolate or ethylene glycol under mild reaction conditions.

Description

Technical Field

[0001] The present invention belongs to the fields of catalyst preparation and catalytic hydrogenation, and relates to a preparation method and application of a copper-based catalyst for regulating the hydrogenation reaction products of dimethyl oxalate. Background Art

[0002] Methyl glycolate (MG), with the chemical formula C3H6O3, also known as methyl hydroxyacetate or methyl glycolate, is an important raw material for the production of biodegradable plastic polyglycolic acid. Methyl glycolate is hydrolyzed to glycolic acid, which is further polymerized to obtain polyglycolic acid (PGA). Since PGA can be completely degraded under natural conditions and only produces carbon dioxide and water, it is called an environmentally friendly plastic and is widely used in the fields of surgical sutures, transplantation scaffolds, and organ regeneration. Methyl glycolate is a colorless, transparent liquid with a special fragrance. It can not only dissolve in water but also be miscible with alcohols or ethers in any proportion. At the same time, methyl glycolate can also be used as a solvent for cellulose, resins, and rubbers. Its excellent solubility characteristics make it widely used in many fields such as chemical engineering, medicine, spices, and dyes.

[0003] The commonly used production process of methyl glycolate is the hydrolysis method of chloroacetic acid (The preparation of glycollicacid[J].Journal of the American Chemical Society,1917,39(1):109-112). The reaction conditions of this process are mild, but due to the presence of chloride ions, it has strong corrosion to equipment. Researchers have successively developed the formaldehyde carbonylation esterification method (Process for the production of ethylene glycol:US4087470A[P].1978-05-02), the coupling method of methyl formate and formaldehyde (Methylformate asanew buildingblockinC1chemistry[J].AppliedCatalysis,1990,57(1):1-30), etc. However, the above processes all face problems such as high equipment requirements and environmental pollution, which limit the industrialization process of methyl glycolate.

[0004] With the development of new coal chemical technologies, the technology of obtaining syngas from coal gasification, then coupling to obtain dimethyl oxalate, and further hydrogenation to obtain ethylene glycol has become increasingly mature. The hydrogenation of dimethyl oxalate to ethylene glycol is a series reaction. Dimethyl oxalate is first hydrogenated to methyl glycolate, and then further hydrogenated to ethylene glycol. Controlling the degree of the hydrogenation reaction to keep it in the preliminary hydrogenation stage is an important way to obtain a high yield of methyl glycolate. With the increasing demand for biodegradable plastics, the demand for methyl glycolate has also increased significantly. Based on the high demand for methyl glycolate, it is of great significance to design a catalyst with high activity and adjustable product distribution for the hydrogenation reaction of dimethyl oxalate.

[0005] The commonly used catalyst for the hydrogenation of dimethyl oxalate to methyl glycolate is an Ag-based catalyst. The Ag / SiO2 catalyst prepared by Yin et al. using the sol-gel method has a MG selectivity as high as 92% at a 15 wt.% Ag loading (Highactivityandselectivity of Ag / SiO2 catalystfor hydrogenation of dimethyloxalate[J].ChemicalCommunications,2010,46(24):4348-4350.). Due to the high cost of precious metals and the difficulty of recovery during use, large-scale industrial production has not been carried out for the reaction of Ag-catalyzed hydrogenation of dimethyl oxalate to methyl glycolate. Cu-based catalysts are often used in the hydrogenation of dimethyl oxalate because of their good C=O / C-O bond cleavage activity. However, due to thermodynamic limitations, over-hydrogenation to ethylene glycol occurs in the hydrogenation of dimethyl oxalate (Cu / SiO2 catalystsprepared by the ammonia-evaporation method:Texture,structure,and catalyticperformance in hydrogenation of dimethyl oxalate to ethylene glycol,Journalof Catalysis,2008,257(1):172-180.). Many researchers have regulated the reaction of Cu-based catalysts for the hydrogenation of dimethyl oxalate to produce methyl glycolate, but most of them achieved this by controlling reaction conditions such as increasing the reaction space velocity and decreasing the reaction temperature, and the yield of methyl glycolate obtained was generally lower than 80% (Synergetic effect of Cu andpentacoordinate Al3+sites:direct synthesis of ethyl ethoxyacetate viahydrogenation of diethyl oxalate[J].Catalysis Communications,2017,89(8):106-110.). Based on this, it is of great significance to regulate the Cu-based catalyst to make the hydrogenation reaction of dimethyl oxalate stay in the initial hydrogenation stage. This can not only avoid using expensive precious metals but also modulate the product distribution of the hydrogenation of dimethyl oxalate by only modifying the Cu-based catalyst, achieving high yields of ethylene glycol and methyl glycolate respectively.

[0006] In order to selectively regulate the product distribution of the hydrogenation of dimethyl oxalate, nickel hydroxide is introduced during the preparation of the copper carbide catalyst for modification, obtaining a catalyst containing components of C, Cu, copper carbide and nickel hydroxide. In the hydrogenation reaction of dimethyl oxalate, a high methyl glycolate yield is achieved. Compared with the traditional methyl glycolate production process, the reaction conditions are milder, the catalyst preparation is simple, and the reaction cost is low. The copper carbide catalyst without the introduction of nickel hydroxide shows a high ethylene glycol yield in the hydrogenation reaction of dimethyl oxalate, realizing the selective regulation of the product distribution of the hydrogenation reaction of dimethyl oxalate. Summary of the Invention

[0007] The present invention provides a copper-based catalyst for regulating the products of the hydrogenation of dimethyl oxalate, its preparation method and application. The synthesis process of the catalyst precursor is simple and convenient, the conditions in the precursor pretreatment stage are mild, the prepared catalyst has high reaction activity for the hydrogenation reaction of dimethyl oxalate, and changing the addition amount of nickel hydroxide can regulate the product distribution of the hydrogenation of dimethyl oxalate.

[0008] The technical solution of the present invention:

[0009] A preparation method of a copper-based catalyst for regulating the products of the hydrogenation of dimethyl oxalate, the steps are as follows:

[0010] S1. Prepare a nitrate solution with a concentration of 0.1 mol / L and stir for 30 min under an ice-water bath condition;

[0011] S2. Prepare a NaOH solution with a concentration of 2 mol / L, add it to the nitrate solution prepared in step S1, and continue to stir for 30 min under an ice-water bath condition; wherein, the volume ratio of the nitrate solution to the NaOH solution is 4:1;

[0012] S3. After the reaction is completed, filter the filtrate and wash the filter cake until it is neutral, and dry it overnight at room temperature in a vacuum drying oven to obtain a blue catalyst precursor;

[0013] S4. Place the catalyst precursor in a quartz tube reactor for pretreatment; in an atmosphere containing low-concentration acetylene, raise the temperature of the catalyst precursor from room temperature to 100-200 °C and treat it for 2 h, then cool it to room temperature;

[0014] S5. In an atmosphere of hydrogen being introduced, raise the temperature of the sample obtained in step S4 from room temperature to 100-300 °C and reduce it for 3 h to obtain a copper-based catalyst.

[0015] In step S1, the nitrate is a mixed nitrate of copper nitrate trihydrate and nickel nitrate hexahydrate, and the molar ratio range of copper nitrate trihydrate to nickel nitrate hexahydrate is 9:1-6:4.

[0016] In the atmosphere containing low-concentration acetylene in step S4, the atmosphere concentration is 0.5 vol% C2H2 and 99.5 vol% Ar.

[0017] In the atmosphere containing low-concentration acetylene in step S4, the flow rate is 30 mL / min.

[0018] In step S5, the hydrogen flow rate is 10 mL / min.

[0019] In steps S4 and S5, the heating rate is 3 °C / min.

[0020] A method for catalytic hydrogenation of dimethyl oxalate using the above copper-based catalyst: After pressing the copper-based catalyst into 20-40 mesh, it is loaded into a stainless steel reaction tube with an inner diameter of 10 mm. Under an atmosphere of hydrogen flow rate of 70 mL / min, at 100-300 °C and 2.5 MPa, it is pre-reduced for 2 h. Then, the reactor temperature is adjusted to 160-220 °C, the hydrogen pressure is 0.5-2.5 MPa, and the liquid hourly space velocity is 1-10 h -1 , the hydrogen to ester ratio is 80. After pumping a methanol solution of 10 wt.% dimethyl oxalate into the reaction tube using a high-pressure liquid pump, the reaction starts. After waiting for the reaction system to stabilize, the effluent is collected from the liquid collector below the reaction tube and analyzed in a gas chromatograph.

[0021] Advantages of the present invention: Introducing nickel hydroxide modified copper carbide catalyst realizes the adjustable distribution of hydrogenation products of dimethyl oxalate. The copper carbide catalyst has excellent hydrogen dissociation ability and can efficiently catalyze the hydrogenation of dimethyl oxalate to produce ethylene glycol. After introducing nickel hydroxide, the number of active phases of copper carbide is reduced, and the hydrogenation activity is decreased. At the same time, there is an interaction between nickel and copper, and electron transfer occurs between Cu and Ni species, which is beneficial to the rapid desorption of the primary hydrogenation product methyl glycolate in the hydrogenation reaction of dimethyl oxalate and avoids deep hydrogenation. In terms of application, the present invention uses nickel hydroxide modified copper carbide catalyst to realize the adjustable distribution of hydrogenation products of dimethyl oxalate, and realizes the efficient production of methyl glycolate or ethylene glycol from dimethyl oxalate under mild reaction conditions. Description of the Drawings

[0022] Figure 1 It is the XRD pattern of the catalyst in Example 6.

[0023] Figure 2 It is the TEM pattern of the catalyst in Example 6. Detailed Embodiments

[0024] The following further illustrates the detailed embodiments of the present invention in combination with the drawings and technical solutions.

[0025] Example 1

[0026] Weigh a total of 0.02 mol with a molar ratio of 8 / 2, that is, 2.42 g and 1.16 g of Cu(NO3)2·3H2O and Ni(NO3)2·6H2O respectively. Dissolve them in 200 mL of deionized water, stir for 30 min under an ice-water bath condition to obtain Solution A. Dissolve 4 g of NaOH in 50 mL of deionized water, drop it into Solution A, and continue to stir for 30 min under the ice-water bath condition. After waiting for the reaction to complete, filter the filtrate by suction filtration, wash the filter cake with deionized water until it is neutral, and dry it overnight at room temperature in a vacuum drying oven to obtain a blue catalyst precursor. Weigh 0.2 g of the catalyst precursor, load it into the inner lining of a quartz tube, heat it from room temperature to 140 °C at a heating rate of 3 °C / min in an atmosphere containing a low concentration of acetylene (0.5% C2H2 / -99.5% Ar) for 2 h, cool it down, then introduce hydrogen, and heat it from room temperature to 170 °C at the same heating rate in a hydrogen atmosphere for 3 h to obtain the target catalyst.

[0027] Evaluate the reaction activity of the catalyst using a fixed-bed reactor. Weigh 0.2 g of the catalyst and load it into the fixed-bed reactor. Under an atmosphere with a hydrogen flow rate of 70 mL / min, at 170 °C and 2.5 MPa, pre-reduce it for 2 h. After reduction, adjust the reaction temperature to 200 °C, the system pressure is 2.5 MPa, and the liquid hourly space velocity is 1 h -1 , use a high-pressure liquid pump to pump the dimethyl oxalate / methanol solution (10 wt%.) into the reaction tube to start the reaction. After waiting for the reaction system to stabilize, collect the effluent and analyze and detect the reaction products by gas chromatography.

[0028] Example 2

[0029] Replace the molar ratio of 8 / 2 in Example 1, that is, 2.42 g and 1.16 g respectively, with a molar ratio of 9 / 1, that is, 4.35 g and 0.58 g respectively. The remaining reaction conditions are the same as in Example 1.

[0030] Example 3

[0031] Replace the molar ratio of 8 / 2 in Example 1, that is, 2.42 g and 1.16 g respectively, with a molar ratio of 7 / 3, that is, 3.38 g and 1.74 g respectively. The remaining reaction conditions are the same as in Example 1. Replace the treatment at 120 °C for 2 h with the treatment at 160 °C for 2 h. The remaining reaction conditions are the same as in Example 1.

[0032] Example 4

[0033] Replace the molar ratio of 8 / 2 in Example 1, that is, 2.42 g and 1.16 g respectively, with a molar ratio of 6 / 4, that is, 2.90 g and 2.32 g respectively. The remaining reaction conditions are the same as in Example 1.

[0034] Example 5

[0035] Replace the treatment at 140°C for 2 h in Example 1 with treatment at 120°C for 2 h. The remaining reaction conditions are the same as in Example 1.

[0036] Example 6

[0037] Replace the treatment at 140°C for 2 h in Example 1 with treatment at 160°C for 2 h. The remaining reaction conditions are the same as in Example 1.

[0038] Example 7

[0039] Replace the treatment at 140°C for 2 h in Example 1 with treatment at 180°C for 2 h. The remaining reaction conditions are the same as in Example 1.

[0040] Example 8

[0041] Replace the treatment at 140°C for 2 h and reduction at 170°C for 3 h in Example 1 with treatment at 160°C for 2 h and reduction at 150°C for 3 h. The remaining reaction conditions are the same as in Example 1.

[0042] Example 9

[0043] Replace the treatment at 140°C for 2 h and reduction at 170°C for 3 h in Example 1 with treatment at 160°C for 2 h and reduction at 190°C for 3 h. The remaining reaction conditions are the same as in Example 1.

[0044] Example 10

[0045] Replace the treatment at 140°C for 2 h and reduction at 170°C for 3 h in Example 1 with treatment at 160°C for 2 h and reduction at 210°C for 3 h. The remaining reaction conditions are the same as in Example 1.

[0046] Comparative Example 1

[0047] Weigh 0.02 mol (4.83 g) of Cu(NO3)2·3H2O and dissolve it in 200 mL of deionized water. Stir for 30 min under an ice-water bath to obtain Solution A. Dissolve 4 g of NaOH in 50 mL of deionized water and add it dropwise to Solution A. Continue to stir for 30 min under an ice-water bath. After the reaction is complete, filter the filtrate by suction filtration, wash the filter cake with deionized water until it is neutral, and dry it overnight at room temperature in a vacuum drying oven to obtain the catalyst precursor. Weigh 0.2 g of the catalyst precursor, load it into the inner lining of a quartz tube, heat it from room temperature to 160°C at a heating rate of 3°C / min in an atmosphere containing a low concentration of acetylene (0.5% C2H2 / -99.5% Ar) for 2 h, cool it down, then introduce hydrogen, and heat it from room temperature to 170°C at the same heating rate in a hydrogen atmosphere for 3 h to obtain the target catalyst.

[0048] The reaction activity of the catalyst was evaluated using a fixed-bed reactor. 0.2 g of the catalyst was weighed and loaded into the fixed-bed reactor. Under an atmosphere of a hydrogen flow rate of 70 mL / min, it was pre-reduced at 170 °C and 2.5 MPa for 2 h. After reduction, the reaction temperature was adjusted to 200 °C, the system pressure was 2.5 MPa, and the liquid hourly space velocity was 1 h -1 , and a dimethyl oxalate / methanol solution (10 wt%) was pumped into the reaction tube using a high-pressure liquid pump to start the reaction. After waiting for the reaction system to stabilize, the effluent was collected, and the reaction products were analyzed and detected by gas chromatography.

[0049] Comparative Example 2

[0050] 4.83 g of Cu(NO3)2·3H2O in Comparative Example 1 was replaced with 5.82 g of Ni(NO3)2·6H2O, and the remaining reaction conditions were the same as those in Comparative Example 1.

[0051] The gas chromatography data in Examples 1-10 and Comparative Examples 1-2 were analyzed, and the results are shown in Table 1:

[0052] Table 1. Comparison of the hydrogenation reaction performance of dimethyl oxalate in Examples and Comparative Examples

[0053]

[0054] As can be seen from Table 1, in Examples 1-4, when the Cu / Ni molar ratio was 8 / 2, the highest yield of methyl glycolate was obtained from the hydrogenation of dimethyl oxalate. As the proportion of Ni species increased, the hydrogenation activity of dimethyl oxalate gradually decreased, and the selectivity of methyl glycolate gradually increased, indicating that the Cu species was the main active phase species and the Ni species affected the product distribution. When the amount of Cu species decreased, the reaction activity decreased, and the reaction more often stayed at the stage of forming the preliminary hydrogenation product methyl glycolate. Since the reaction conversion rate and the selectivity of methyl glycolate were negatively correlated, the selectivity yield was selected as the evaluation index for the reaction performance of the hydrogenation of dimethyl oxalate to methyl glycolate.

[0055] Examples 1, 5, 6, and 7 showed that the treatment temperature of the low-concentration acetylene atmosphere had an impact on the catalytic performance of the catalyst. Among them, when the treatment temperature was 160 °C, the catalyst catalyzed the hydrogenation reaction of dimethyl oxalate, and the highest yield of methyl glycolate was obtained.

[0056] Examples 6, 8, 9, and 10 showed that the hydrogen reduction temperature had an impact on the catalytic performance of the catalyst. Among them, when the hydrogen reduction temperature was 170 °C, the catalyst catalyzed the hydrogenation reaction of dimethyl oxalate, and the highest yield of methyl glycolate was obtained.

[0057] Comparing Example 6 with Comparative Example 1, it can be seen that for the hydrogenation reaction of dimethyl oxalate catalyzed by the copper carbide catalyst without the introduction of nickel hydroxide, the main reaction product is ethylene glycol. After the introduction of nickel hydroxide, the product distribution of the reaction is modulated, and methyl glycolate with a high yield is obtained. This shows that nickel hydroxide reduces the number of Cu active species, decreases the hydrogenation activity of the reaction, and there is an electron transfer between Cu and Ni, enabling the methyl glycolate, the first-step hydrogenation product, to desorb rapidly after formation and avoiding over-hydrogenation to ethylene glycol.

[0058] Comparing Example 6 with Comparative Example 2, it can be seen that when there is no Cu species present, the catalyst has basically no activity in the hydrogenation of dimethyl oxalate, indicating that the Cu species is the main hydrogenation active phase.

[0059] The above embodiments are the preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Without departing from the essence of the present invention, any improvements or modifications made by those skilled in the art to the above description shall fall within the protection scope of the appended claims of the present invention.

Claims

1. A method for preparing a copper-based catalyst for regulating the product of dimethyl oxalate hydrogenation reaction, characterized in that: Here are the steps: S1. Prepare a nitrate solution with a concentration of 0.1 mol / L and stir in an ice-water bath for 30 min; S2. Prepare a 2 mol / L NaOH solution, add it to the nitrate solution prepared in step S1, and continue stirring for 30 min in an ice water bath; wherein the volume ratio of the nitrate solution to the NaOH solution is 4:1; S3. After the reaction is completed, the filtrate is filtered and the filter cake is washed to neutrality, and dried in a vacuum drying oven at room temperature overnight to obtain a blue catalyst precursor; S4. The catalyst precursor is placed in a quartz tube reactor for pretreatment; in an atmosphere containing a low concentration of acetylene, the catalyst precursor is heated from room temperature to 100-200 ° C for 2h and cooled to room temperature; S5. In an atmosphere of hydrogen, the sample obtained in step S4 is reduced from room temperature to 100-300° C. for 3 h to obtain a copper-based catalyst.

2. The preparation method according to claim 1, characterized in that: In step S1, the nitrate is a mixed nitrate of copper nitrate trihydrate and nickel nitrate hexahydrate, wherein the molar ratio of copper nitrate trihydrate to nickel nitrate hexahydrate is in the range of 9:1-6:

4.

3. The preparation method according to claim 1, characterized in that: In step S4, the atmosphere containing low-concentration acetylene has an atmosphere concentration of 0.5 vol% C2H2 and 99.5 vol% Ar.

4. The preparation method according to claim 1, characterized in that: In step S4, the flow rate in the atmosphere containing low-concentration acetylene is 30 mL / min.

5. The preparation method according to claim 1, characterized in that: In step S5, the hydrogen flow rate is 10 mL / min.

6. The preparation method according to claim 1, characterized in that: The heating rate in steps S4 and S5 is 3°C / min.

7. A method for hydrogenating dimethyl oxalate using a copper-based catalyst obtained by the preparation method according to any one of claims 1 to 6, characterized in that: The copper-based catalyst was pressed into 20-40 mesh and loaded into a stainless steel reaction tube with an inner diameter of 10 mm. It was pre-reduced for 2 h at 100-300 ° C and 2.5 MPa in a hydrogen flow atmosphere of 70 mL / min. The temperature was then adjusted to 160-220 ° C, the hydrogen pressure was 0.5-2.5 MPa, and the liquid hourly space velocity was 1-10 h. -1 , the hydrogen-ester ratio is 80, and a 10wt.% methanol solution of dimethyl oxalate is pumped into the reaction tube to start the reaction.

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