Method for Catalytically Hydrogenating Oxalates

Abstract

The invention discloses a method for catalytically hydrogenating oxalates. In the method, an oxalate and hydrogen gas are contacted with a nanotube assembled hollow sphere catalyst, to produce a product comprising glycolate or glycol. The predominant chemical components of the catalyst include copper and silica, in which the copper is in an amount of 5 to 60% by weight of the catalyst, and the silica is in an amount of 40-95% by weight of the catalyst. The catalyst has a specific surface area of 450-500 m.sup.2/g, an average pore volume of 0.5-1 cm.sup.3/g, and an average pore diameter of 5-6 nm. The catalyst is in a structure of assembling nanotubes on hollow spheres, wherein the hollow spheres have a diameter of 50-450 nm, and a wall thickness of 10-20 nm, and the nanotubes, vertically arranged on the surfaces of the hollow spheres, have a diameter of 3-5 nm, and a length of 40-300 nm. Even in the case of a low H.sub.2/DMO feeding ratio, the method of the invention still can exhibit an excellent activity of hydrogenating oxalates and an excellent selectivity to ethylene glycol, and reduce circulation quantity of hydrogen gas, thereby to save power costs and apparatus costs, and it can flexibility adjust the selectivity of ethylene glycol and glycolate. Thus, the method has high industry prospects and application values.

Claims

1. A method for catalytically hydrogenating an oxalate, characterized in that: the oxalate and hydrogen gas are contacted with a nanotube assembled hollow sphere catalyst, to produce a product comprising glycolate or ethylene glycol, wherein the predominant chemical components of the catalyst include copper and silica, in which the copper is in an amount of 5 to 60% by weight of the catalyst, and the silica is in an amount of 40-95% by weight of the catalyst; the catalyst has a specific surface area of 450-500 m.sup.2g, an average pore volume of 0.5-1 cm.sup.3/g, and an average pore diameter of 5-6 nm; the catalyst is in a structure of assembling nanotubes on hollow spheres, in which the hollow spheres have a diameter of 50-450 nm and a wall thickness of 10-20 nm, and the nanotubes, vertically arrange on the surfaces of the hollow spheres, have a diameter of 3-5 nm and a length of 40-300 nm.

2. The method according to claim 1, characterized in that the nanotube assembled hollow sphere catalyst comprising nanotubes with a length of 40-65 nm, preferably 40-60 nm, is used so that the selectivity of the glycolate in the product can reach 84%-100%.

3. The method according to claim 1, characterized in that the nanotube assembled hollow sphere catalyst comprising nanotubes having a length of 60-300 nm, preferably 110-300 nm, is used so that the selectivity of the ethylene glycol in the product can reach 85-98%.

4. The method according to claim 3, characterized in that under the conditions of the molar ratio of hydrogen gas to oxalate of 20, the reaction temperature of from 160 to 220 C., the reaction pressure of from 1.5 to 3 MPa, and the liquid weight hourly space velocity of from 0.5 to 5H.sup.1, the yield of ethylene glycol is higher than 95%.

5. The method according to claim 1, characterized in that the copper is in an amount 10-40% by weight of the catalyst, and the silica is in an amount of 60-90% by weight of the catalyst.

6. The method according to claim 1, characterized in that the catalyst has a specific surface area of 460-470 m.sup.2/g, an average pore volume of 0.7-0.8 cm.sup.3/g, and an average pore diameter of 5.1-5.5 nm.

7. The method according to claim 1, characterized in that the hollow spheres have a diameter of 200-350 nm, and a wall thickness of 10-15 nm.

8. The method according to claim 1, characterized in that the nanotubes have a diameter of 3.5-4 nm, and a length of 180-230 nm.

Description

ILLUSTRATIONS TO THE DRAWINGS

[0029] FIG. 1 shows the transmission electron micrographs of the nanotube assembled hollow sphere catalysts used in the present invention, wherein A and B are the transmission electron micrographs of the catalysts before they are reduced by H.sub.2, and C and D are transmission electron micrographs of the catalysts themselves.

[0030] FIG. 2 shows the transmission electron micrographs of the catalyst precursors synthesized in different hydrothermal treatment time periods, wherein the hydrothermal treatment time periods are shown as follows: A: 5 h, B: 10 h, C: 15 h, D: 20 h, E: 25 h, F: 30 h; a scale: 100 nm.

[0031] FIG. 3 shows transmission electron micrographs of the reduced catalysts obtained after reductions of the catalyst precursors shown in FIG. 2 with hydrogen gas, wherein the hydrothermal treatment time periods are shown as follows: A: 5 h, B: 10 h, C: 15 h, D: 20 h, E: 25 h, F: 30 h; a scale: 20 nm.

[0032] FIG. 4 is a statistical diagram of the diameters of the nanotubes of the nanotube assembled hollow sphere catalysts used in the invention.

[0033] FIG. 5 is a data diagram of the lifetime of the catalysts for preparation of ethylene glycol by hydrogenating dimethyl oxalate.

[0034] FIG. 6 is a diagram showing the performance evaluations to the catalyst of the invention and an existing catalyst in different hydrogen gas/dimethyl oxalate molar ratios, wherein the existing catalyst is Cu/SiO.sub.2 catalyst as prepared by an ammonia-evaporation method, which currently has a good activity in the hydrogenation reaction of oxalates to produce ethylene glycol, see Gong J, et al. J. Am. Chem. Soc., 134, 13922-13925 (2012) and Chen J, et al. J. Catal., 257, 172-180 (2008).

[0035] FIG. 7 is a diagram showing the performance evaluations to the catalyst of the invention and an existing catalyst in different hydrogen gas/diethyl oxalate molar ratios, wherein the existing catalyst is the existing catalyst as used in FIG. 6.

[0036] FIG. 8 is a diagram showing the performance evaluations to the catalyst of the invention and an existing catalyst in different hydrogen gas/dibutyl oxalate molar ratios, wherein the existing catalyst is the existing catalyst as used in FIG. 6.

[0037] FIG. 9 is an X-ray diffraction (XRD) pattern of the nanotube assembled hollow sphere catalyst used in the invention.

BEST MODES FOR CARRYING OUT THE INVENTION

[0038] The present invention will be further described in detail by combining the drawings and the specific examples. It should be noted that the following examples are only illustrative, but not limited, and the invention cannot be limited by the following examples. Raw materials as used in the following examples and in the comparative examples each are commercially available, and the used alkaline agents (ammonia-water solution, ammonium chloride and sodium hydroxide) each are in a form of aqueous solution.

Example 1

Preparation of Ultrapure Silica Spheres

[0039] 80 g of tetraethyl orthosilicate were weighted and dissolved in 200 ml of ethanol while stirring, to obtain a clear solution A; 132 mL of ammonia-water solution were taken to uniformly mix with 98 mL of deionized water and 86 mL of ethanol, to obtain a clear solution B; at 40 C., the two solutions A and B were mixed and stirred for 5 hour, to obtain a solution of ultrapure silica spheres with uniform surfaces that have homogenous particle sizes.

Preparation of Catalyst Precursors

[0040] 18 g of trihydrated copper nitrate were weighed and, with 80 mL of ammonia-water solution, dissolved in 200 mL of deionized water, and they were mixed uniformly while stirring to obtain a clear solution. Thereafter, the solution of ultrapure silica spheres was dropwise added to the clear solution (1 drop per second) and stirred at 60 C. for 1 h, to obtain a uniformly dispersed solution. The solution, being placed in a closed container, was hydrothermally treated at 150 C. for 30 h, and after solids were separated therefrom, they were vacuum dried at 80 C. for 6 h and calcined at 500 C. for 6 h, to obtain the catalyst.

Online Reduction of Catalyst and Evaluations on Catalytic Effects

[0041] In the invention, a gas phase hydrogenation reaction of dimethyl oxalate was conducted in a fixed bed reactor. The catalyst that has been calcined was tableted and sieved to prepare particles having a size of from 40 to 60 meshes. 0.58 g of the catalyst were weighed and placed in an isothermal reactor while a 10% H.sub.2/N.sub.2 atmosphere was charged to conduct the reduction reaction at 300 C. for 4 h, and after the online reduction, the catalyst as used in the invention was obtained. After the reduction, the temperature was decreased to the reaction temperature at 190 C. Dimethyl oxalate was gasified and charged into the reactor by being mixed with hydrogen gas, and the reaction was conducted in a hydrogen to ester ratio of 20 and a weight space velocity of dimethyl oxalate (DMO) of 3 h.sup.1 at the pressure of 3 MPa. The product was analyzed by utilizing gas chromatography to determine the components of dimethyl oxalate (DMO), ethylene glycol (EG), methyl glycolate (MG) and ethanol (EtOH), and obtain the conversion of dimethyl oxalate and the selectivity of each product. The evaluation results of the obtained catalyst are shown in Table 1.

[0042] The catalyst of the invention (i.e. the product after the online reduction) was also characterized by XRD. From the X-ray diffraction (XRD) pattern of the catalyst of the invention as shown in FIG. 9, it can be seen that there is a broad diffraction peak at 2=22, the peak being a characteristic diffraction peak of amorphous SiO.sub.2, and this shows that the silicon is present in the form of silica. The characteristic diffraction peak at 2=37.0 is the diffraction peak (JCPDS 34-1354) of Cu.sub.2O (111), while the characteristic diffraction peaks at 2=43.3, 2=50.6 and 2=74.1 are the diffraction peaks (JCPDS 65-9743) of the metal copper (Cu). These peaks each are weak and broad, which shows that Cu and Cu.sub.2O are highly dispersed in the reduced catalyst, and the catalyst exhibits a good activity.

Comparative Example 1

Preparation of Ultrapure Silica Spheres

[0043] The method for preparation of ultrapure silica spheres is the same as that of Example 1.

Preparation of Catalyst Precursor

[0044] 13 g of dehydrated copper chloride were weighed and, with 80 mL of ammonia-water solution, dissolved in 200 mL of deionized water, and they were mixed uniformly while stirring to obtain a clear solution. Thereafter, the solution of ultrapure silica spheres was dropwise added to the clear solution (1 drop per second) and stirred at 60 C. for 1 h, to obtain a uniformly dispersed solution. The solution, being placed in a closed container, was hydrothermally treated at 150 C. for 30 h, and after solids were separated therefrom, they were vacuum dried at 80 C. for 6 h and calcined at 500 C. for 6 h, to obtain the catalyst.

Evaluations of Catalyst

[0045] The method of evaluating the catalyst is the same as that in Example 1, and the results are shown in Table 1.

Comparative Example 2

Preparation of Ultrapure Silica Spheres

[0046] The method for preparation of ultrapure silica spheres is the same as that of Example 1.

Preparation of Catalyst

[0047] 22 g of trihydrated copper acetate were weighed and, with 80 mL of ammonia-water solution, dissolved in 200 mL of deionized water, and they were mixed uniformly while stirring to obtain a clear solution. Thereafter, the solution of ultrapure silica spheres was dropwise added to the clear solution (1 drop per second) and stirred at 60 C. for 1 h. to obtain a uniformly dispersed solution. The solution, being placed in a closed container, was hydrothermally treated at 150 C. for 30 h, and after solids were separated therefrom, they were vacuum dried at 80 C. for 6 h and calcined at 500 C. for 6 h, to obtain the catalyst.

Evaluation of Catalyst

[0048] The method of evaluating the catalyst is the same as that in Example 1, and the results are shown in Table 1.

Comparative Example 3

Preparation of Ultrapure Silica Spheres

[0049] The method for preparation of ultrapure silica spheres is the same as that of Example 1.

Preparation of Catalyst

[0050] 19 g of copper sulfate pentahydrate were weighed and, with 80 mL of ammonia-water solution, dissolved in 200 mL of deionized water, and they were mixed uniformly while stirring to obtain a clear solution. Thereafter, the solution of ultrapure silica spheres was dropwise added to the clear solution (1 drop per second) and stirred at 60 C. for 1 h, to obtain a uniformly dispersed solution. The solution, being placed in a closed container, was hydrothermally treated at 150 C. for 30 h, and after solids were separated therefrom, they were vacuum dried at 80 C. for 6 h and calcined at 500 C. for 6 h, to obtain the catalyst.

Evaluation of Catalyst

[0051] The method of evaluating the catalyst is the same as that in Example 1, and the results are shown in Table 1.

Comparative Example 4

Preparation of Ultrapure Silica Spheres

[0052] The method for preparation of ultrapure silica spheres is the same as that of Example 1.

Preparation of Catalyst

[0053] 18 g of copper nitrate trihydrate were weighed and, with 80 mL of ammonia-water solution, dissolved in 200 mL of deionized water, and they were mixed uniformly while stirring to obtain a clear solution. Thereafter, the solution of ultrapure silica spheres was rapidly added (in a spout form) to the clear solution and stirred at 60 C. for 1 h, to obtain a uniformly dispersed solution. The solution, being placed in a closed container, was hydrothermally treated at 150 C. for 30 h, and after solids were separated therefrom, they were vacuum dried at 80 C. for 6 h and calcined at 500 C. for 6 h, to obtain the catalyst.

Evaluation of Catalyst

[0054] The method of evaluating the catalyst is the same as that in Example 1, and the results are shown in Table 1. It can be seen that when the copper nitrate is used as the copper salt precursor and the solution of ultrapure silica spheres was dropwise added (1 drop per second), the conversion of dimethyl oxalate (DMO) can reach 100% and the selectivity of ethylene glycol (FG) is 98%. The evaluation on the stability of Example 1 is shown in FIG. 5, and it can be seen that the catalysts of the invention exhibit excellent stability.

TABLE-US-00001 TABLE 1 Evaluattons on Catalysts Prepared by using Different Methods and Precursors Copper Salt Method for Adding Cu DMO EG Precursors Silica spheres conent/% Conversion/% Selective/% Example 1 Copper nitrate Adding dropwise 20 100 98 Comparative Copper chloride Adding dropwise 20 87 75 Example 1 Comparative Copper acetate Adding dropwise 20 100 86 Example 2 Comparative Copper sulfate Adding dropwise 20 95 78 Example 3 Comparative Copper nitrate Adding rapidly 20 82 70 Example 4

Examples 2-5

[0055] The preparation method of the catalysts and the evaluation conditions thereof are the same as those in Example 1. By varying the amount of the added trihydrated copper nitrate, the catalysts with different copper loading quantities (S wt %, 10 wt %, 30 wt %, 40 wt %) were respectively obtained. The evaluation results are shown in Table 2, and it can be seen that when the Cu loading is greater than 20 wt %, the selectivity of ethylene glycol is higher than 90%.

TABLE-US-00002 TABLE 2 Performance Evaluations on Catalysts with Different Loading Quantities Cu Loading DMO EG Quantity wt % Conversion/% Selectivity/%) Example 1 20 100 98 Example 2 5 95 80 Example 3 10 98 85 Example 4 30 100 96 Example 5 40 100 92

Examples 6-10

[0056] The preparation method of the catalysts and the evaluation conditions thereof are the same as those in Example 1. By varying the hydrothermal treatment time, hollow sphere catalysts assembled with nanotubes having different lengths were respectively obtained, and the lengths of the nanotubes were determined by TEM (see FIG. 2 and FIG. 3), and the diameters of the nanotubes were shown in FIG. 4. The evaluation results of the catalysts are shown in Table 3, and it can be seen that when the length of the nanotubes in the catalysts is lower than 65 nm, the predominant product is methyl glycolate, and when the length of the nanotubes in the catalysts is greater than 110 nm, the predominant product is ethylene glycol.

TABLE-US-00003 TABLE 3 Performance Evaluations on Catalysts with Different Nanotube Lengths Hydrothermal Treatment Nanotube DMO MG EG Time/h Length/nm Conversion/% Selectivity/%) Selectivity/%) Example 1 30 232 100 2 98 Exampie 6 5 63 92 84 15 Example 7 10 70 95 47 53 Example 8 15 92 100 27 72 Example 9 20 119 100 12 87 Example 10 25 180 100 5 94

Examples 11-14

[0057] The evaluated catalyst is the same as the catalyst in Example 1, and by varying the reaction temperature in the reaction conditions and maintaining the other conditions unchanged, examples 11-14 were obtained. The evaluation results of the catalyst are shown in Table 4, and it can be seen that when the reaction temperature is from 190 to 200 C., the selectivity of ethylene glycol obtained by the catalyst reaches 95% or above.

TABLE-US-00004 TABLE 4 Performance Evaluations on Catalysts at Different Reaction Temperatures Reaction DMO MG EG EtOH Temperature/ C. Conversion/% Selectivity/% Selectivity/% Selectivity/% Example 1 190 100 2 98 0 Example 11 180 81 63 37 0 Example 12 185 98 17 83 0 Example 13 200 100 0 95 5 Example 14 205 100 0 92 8

Comparative Example 5

[0058] 8 g of copper nitrate trihydrate were weighed and added with deionized water to dissolve them while stirring, and thereafter, a suitable amount of 28% ammonia-water solution was slowly added to formulate a copper ammonia solution while a certain amount of deionized water was supplemented. Then, the copper ammonia solution was added with 77 g of a 30% silica sol solution and aged for 4 hours while continuously stirring. The temperature was increased to 80 C. to remove the ammonia in the solution until the pH1-6-7. By filtration, solid materials were separated, and they were dried under vacuum at 80 C. for 6 h and calcined at 500 C. for 6 h, to obtain a catalyst. The catalyst is an existing catalyst that has been reported in the prior art documents (Gong J, et al. Synthesis of Ethanol via Synthesis on Cu/SiO.sub.2 Catalysts with balanced Cu.sup.0-Cu.sup.+ sites, Journal of the American Chemical Society 134, 13922-13925(2012); Chen L, et al. Cu/SiO.sub.2 Catalysts Prepared by the Ammonia-evaluation Method, Texture, Structure and Catalysis Performance in Hydrogenation of Dimethyl oxide to Ethylene Glycol, Journal of Catalysis 257, 172-180 (2008)). The catalyst is a conventional supported catalyst in which active sites of metal species are uniformly dispersed on internal and external surfaces of porous carriers.

[0059] Directed to the catalyst of the invention used in Example 1 and the existing catalyst in Comparative Example 5, in different hydrogen to ester ratios, the reaction of hydrogenating dimethyl oxalate, diethyl oxalate and dibutyl oxalate to prepare ethylene glycol was evaluated with the other conditions identical to those in Example 1. The results are shown in FIG. 6 to FIG. 8, it can be seen that for the hydrogenation of dimethyl oxalate, using the nanotube assembled hollow sphere catalyst of the invention can achieve a hydrogen to ester ratio in the raw material as low as 20 while assuring the yield of ethylene glycol to be higher than 95%, and as for the reactions of hydrogenating diethyl oxalate and dibutyl oxalate, the hydrogen to ester ratio in the raw material may be as low as 30. This demonstrates that the method of the invention can achieve unexpected technical effects.

[0060] The above contents has made illustrative depictions to the invention. It should be noted that any simple variations, modifications or other equivalent substitutions made by a person skilled in the art without paying any creative efforts fall into the protection scope of the invention.