A carbonylation synthesis catalyst for preparing dimethyl carbonate and a preparation method and use thereof

Abstract

The application discloses a carbonylation catalyst for preparing dimethyl carbonate, a preparation method and application thereof. The carbonylation catalyst is composed of a double-layer structure carrier and a platinum group metal active component. The carrier is composed of a mixed phase alumina material with a double-layer structure composite pore distribution including a central layer and an outer layer. The unique pore distribution of the carrier can improve the dispersion of the active component on the carrier and optimize the distribution state of the active component and the additive. The double-layer structure of the carrier can improve the heat resistance, hydrothermal resistance and corrosion resistance of the catalyst. Therefore, the catalyst has high activity, selectivity and space-time yield, stable reaction performance and can be operated for a long time.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of catalysts, and particularly relates to a carbonylation catalyst for producing dimethyl carbonate. BACKGROUND

[0002] Dimethyl carbonate (DMC) is a low-toxicity, environmentally friendly, and widely used chemical raw material. Due to the presence of functional groups such as carbonyl, methyl and methoxy in its molecular structure, DMC has good reactivity. As an important green new chemical raw material and intermediate, DMC meets the current concept of green and environmentally friendly chemical production and sustainable development. It has wide applications in the fields of gasoline additives, battery electrolyte, water treatment, polycarbonate, medicine, pesticide, perfume, synthetic lubricating oil, etc.

[0003] Currently, the main methods for synthesizing dimethyl carbonate in industry include ester exchange method, liquid phase oxidative carbonylation method, direct synthesis method of ester and carbon dioxide, and methanol gas phase oxidative carbonylation method. Among the above synthesis methods, the gas phase carbonylation method using carbon monoxide and methyl nitrite as raw materials to synthesize dimethyl carbonate is considered to be the most promising method. This process has the advantages of mild reaction conditions, environmental protection, no pollution, easy separation of catalyst, etc., and has attracted more and more attention. This process uses carbon monoxide and methyl nitrite as raw materials, and generates dimethyl carbonate through carbonylation under the action of a palladium-based noble metal catalyst.

[0004] US5426209A discloses a catalyst with activated carbon as a carrier, and the main active component is palladium chloride, and the auxiliary active component is copper chloride. The optimal space-time yield of DMC can reach 725 g / (L·h), but the catalyst can only be stable for about 8 hours. Although the service life of the catalyst can be greatly prolonged by using 50-1000 ppm methyl chloroformate as a chlorine supplement, the activity of the catalyst still decreases by 20-30% within 100 hours, and the service life of the catalyst needs to be improved.

[0005] Patent CN1736596A discloses a catalyst with palladium chloride as an active center. Although the catalyst has good DMC selectivity, its stability is poor, and the catalyst will be deactivated after a period of reaction, and the catalytic activity and selectivity will decrease seriously,

[0006] A carbonylation catalyst with high activity, high selectivity and high stability is the key to the process of preparing dimethyl carbonate by gas phase carbonylation. Some catalysts reported in the patents for preparing dimethyl carbonate by gas phase oxidative carbonylation of CO and methyl nitrite all have a common shortcoming, i.e., poor activity stability and short service life of the catalyst. SUMMARY

[0007] The present application aims to provide a carbonylation catalyst for preparing dimethyl carbonate and its preparation method and use. In view of the problem of the catalysts in the prior art that cannot maintain high activity for a long time and have poor stability, a catalyst for gas-phase carbonylation synthesis of dimethyl carbonate and its preparation method are provided, which uses a mixed-phase alumina carrier with a composite pore distribution, the unique pore distribution of the carrier can improve the dispersion of the active component on the carrier and optimize the distribution state of the active component and the adjuvant. The double-layer structure of the carrier can improve the heat resistance, hydrothermal resistance and corrosion resistance of the catalyst, so the catalyst has high activity, selectivity and space-time yield, and the reaction performance is stable and can run for a long time.

[0008] The present application provides a carbonylation catalyst for preparing dimethyl carbonate, which comprises a spherical carrier with a composite pore distribution composed of a mixed-phase alumina and a platinum group metal active component; the carrier is composed of an alumina material with a double-layer structure composite pore distribution of a central layer and an outer layer, the thickness of the central layer is 0.01d-0.3d, wherein d is the diameter of the spherical carrier; the spherical carrier has a mesopore-macropore composite pore distribution, which comprises: 10-40% of the total pore volume is composed of pores with a pore diameter of <15nm, 20-75% of the total pore volume is composed of pores with a pore diameter of 15-50nm, and 10-40% of the total pore volume is composed of pores with a pore diameter of >50nm.

[0009] Preferably, the diameter d of the spherical carrier is 2.8-8mm, the thickness of the central layer of the carrier is 0.01d-0.3d, more preferably the thickness of the central layer of the carrier is 0.05d-0.3d.

[0010] Preferably, the specific surface area of the spherical carrier is 40-150m 2 / g, and the total pore volume is 0.2-1.2mL / g.

[0011] The present application provides a preparation method of the carbonylation catalyst for preparing dimethyl carbonate, which comprises the following steps:

[0012] 1) mixing a carrier precursor raw material W1, a mineralizer and ethanol, adding an aluminum sol, granulating, drying and calcining to obtain a carrier precursor A1;

[0013] 2) mixing a carrier precursor raw material W2, the carrier precursor A1, an aluminum sol, a physical pore expander and a binder, drying and low-temperature calcining to obtain a carrier precursor A2;

[0014] 3) immersing the carrier precursor A2 in an ammonium chloride solution, drying and then performing secondary calcination under water vapor conditions to obtain a catalyst carrier;

[0015] 4) The platinum group metal component, the co-catalyst component and the solvent are mixed to prepare an impregnation solution, the catalyst carrier is soaked in the impregnation solution, and then dried and calcined to obtain the catalyst.

[0016] Preferably, the carrier precursor raw material W1 in step 1) is one or more of aluminum hydroxide, pseudo-boehmite and boehmite.

[0017] Preferably, the mineralizer in step 1) is one of fluoride salt, silicofluoride salt, sulfate salt and phosphate salt. Specifically, the fluoride salt includes NH4F, CaF2, NaF, BaF2, AlF3 and MgF2, the silicofluoride salt includes Na2SiF6, MgSiF6 and CaSiF6, the sulfate salt includes barium sulfate and iron sulfate, and the phosphate salt includes Ca3(PO4)2 and FePO4. More preferably, the mineralizer is CaF2 and / or NaF.

[0018] Preferably, the solid content of the aluminum sol in step 1) is 15-20% and the pH value is 2-7, calculated based on Al2O3.

[0019] Preferably, the granulation in step 1) adopts the methods of rolling ball forming and oil column forming. Preferably, in step 1), the mass ratio of the precursor raw material W1, the mineralizer, ethanol and the aluminum sol is 2.2-2.5:0.02-0.03:2.2-2.5:1.

[0020] Preferably, the carrier precursor raw material W2 in step 2) is one or more of aluminum hydroxide, pseudo-boehmite and boehmite.

[0021] Preferably, the binder in step 2) is one or more of the aqueous solutions of nitric acid, phosphoric acid, oxalic acid, acetic acid and citric acid, and the concentration of the solution is 1wt%-5wt%.

[0022] Preferably, the solid content of the aluminum sol in step 2) is 15-20% and the pH value is 2-7, calculated based on Al2O3.

[0023] Preferably, the physical pore-expanding agent in step 2) is one or more of urea, activated carbon, wood chips, carbon black, propylene glycol, glycerol, triethylene glycol, polyethylene glycol, polyethylene oxide, methyl cellulose, polyacrylamide and starch, and the mass of the physical pore-expanding agent is 3-10% of the mass of the carrier precursor W2.

[0024] Preferably, in step 2), the calcination temperature is 500-600℃ and the calcination time is 4-6h.

[0025] Preferably, in step 2), the mass ratio of the carrier precursor raw material W2, the carrier precursor A1, the aluminum sol, the physical pore-expanding agent and the binder is 7-10:1-1.5:1.2-2:1:0.3-1.

[0026] Preferably, the impregnation of the aqueous ammonium chloride solution in step 3) is carried out by equal volume impregnation, preferably using an aqueous ammonium chloride solution having a concentration of 2-10 wt%.

[0027] Preferably, in step 3), the secondary calcination temperature is 600-800°C and the calcination time is 4-6 h.

[0028] Preferably, in step 4), the platinum group metal element comprises at least Pd. The loading of the platinum group metal element is 0.1-2 wt% based on the total weight of the catalyst, more preferably 0.5-2 wt%.

[0029] Preferably, in step 4), the promoter component is one or more of K, Cu, Co or Ni. The loading of the promoter component element is 0.1-2 wt% based on the total weight of the catalyst, more preferably 0.5-2 wt%.

[0030] Preferably, in step 4), the solvent is one selected from the group consisting of aqueous ammonia, hydrochloric acid and aqueous sodium chloride, more preferably the solvent is one of aqueous ammonia and aqueous hydrochloric acid, preferably the concentration of the aqueous solution is 5-10 wt%.

[0031] Preferably, in step 4), the mass ratio of the impregnation solution to the carrier is 0.5-3:1.

[0032] The catalyst of the present application can be used in the process for producing dimethyl carbonate by gas phase carbonylation reaction.

[0033] A method for preparing dimethyl carbonate by gas phase carbonylation reaction, comprising the following steps: reacting methyl nitrite and carbon monoxide in the presence of the carbonylation synthesis catalyst of the present application to prepare dimethyl carbonate.

[0034] Preferably, in the method for preparing dimethyl carbonate of the present application, the reaction temperature is 80-130°C.

[0035] Preferably, in the method for preparing dimethyl carbonate of the present application, the reaction pressure is 0-1.0 Mpa.

[0036] Preferably, in the method for preparing dimethyl carbonate of the present application, the space velocity is 500 h -1 -20000 h -1 .

[0037] Compared with the prior art, the present application has the following beneficial effects:

[0038] (1) The carrier of the present application adopts a double-layer structure, the center layer material of which is alumina treated at high temperature, having excellent heat resistance, hydrothermal resistance and corrosion resistance, which can ensure the stability of the catalyst structure during long-term operation, and excellent heat conductivity can also avoid the aggregation of active components caused by local high temperature. The outer layer of the carrier is a mixed phase alumina material, which has a high specific surface area and is beneficial to improve the interaction force between the active components, the additives and the carrier.

[0039] (2) The carrier of the present application is modified by ammonium chloride solution. Ammonia, water vapor and hydrogen chloride gas generated by the decomposition of ammonium chloride under heating can play a role of punching, improving the connectivity of the carrier pores. The secondary calcination can ensure that the generated large pores are more uniform, and the generated ammonia and hydrogen chloride gas can react with alumina grains to change the grain size and packing morphology, thereby improving the pore structure of the alumina material and increasing the content of large pores of the carrier.

[0040] (3) The carrier material of the present application has a composite pore distribution, and large pores are beneficial to the contact between raw materials and active components of the catalyst, avoiding the decomposition and other side reactions of raw materials. Mesopores ensure a certain specific surface area and active site center of the catalyst, and the surface active components are aggregated and grown. DETAILED DESCRIPTION

[0041] The present application will be further described below in conjunction with examples. However, the present application is not limited to the listed examples, and any other known changes within the scope of the claimed rights of the present application should also be included. The analysis methods and analysis devices involved in the examples are described as follows.

[0042] The content of organic compound substances (including dimethyl carbonate, methanol, methyl nitrite, dimethyl oxalate, etc.) in raw materials and products is analyzed by using a gas chromatograph 8090 manufactured by Agilent Technology, equipped with a HP-VOC capillary column manufactured by Agilent Technology.

[0043] The pore structure of the catalyst is characterized by a physical adsorption instrument for full pore analysis. An X-ray diffractometer (Bruker Company) with copper radiation (30 kV, 10 mA) is used to obtain XRD patterns at 10 to 80° (step: 0.05°, measurement time per step: 1 s). Then, based on the XRD analysis data, the structure is analyzed by Rietveld refinement to calculate the content ratio (wt%) of different crystalline aluminas.

[0044] Example 1

[0045] Catalyst preparation:

[0046] (1) 50 g of nanometer boehmite, 0.5 g of ammonium fluoride and 45 g of anhydrous ethanol were mixed and ball milled for 18 hours, and 20 g of the mixture was added to 20 g of deionized water to form a slurry.

[0047] (20% solid content, pH = 7) was added and mixed, and then ball-molded, dried at 80°C for 12 h, and calcined at 1100°C to obtain a carrier precursor Al;

[0048] (2) 500 g nanometer boehmite, 50 g carrier precursor Al, 100 g aluminum sol (20% solid content, pH = 7), 50 g citric acid solution (5% mass fraction) binder, and 15 g urea were mixed and ball-molded, dried at 80°C for 12 h, and calcined at 600°C for 5 h to obtain a carrier precursor A2;

[0049]

[0050] (3) 500 g carrier precursor A2 was impregnated with 120 g ammonium chloride solution (10% mass fraction), dried at 80°C for 12 h, and calcined at 700°C for 5 h under water vapor to obtain a catalyst carrier B1;

[0051] (4) 6.9 g PdCl2, 13.4 g CuCl2·2H2O, and 5% ammonia water were mixed to prepare an impregnation solution, 500 g catalyst carrier was soaked in the impregnation solution, and equal-volume impregnation was performed at room temperature, and dried at 80°C for 12 h, and calcined at 200°C for 2 h to obtain a catalyst C1.

[0052]

[0053] The prepared catalyst carrier B1 had an average particle size of 5 mm, a center layer thickness of 1.4 mm, a specific surface area of 103 m 2 / g, and a total pore volume of 0.43 mL / g. Of the total pore volume, the pore volume of pores with a pore diameter < 15 nm accounted for 40%, the pore volume of pores with a pore diameter of 15-50 nm accounted for 48%, and the pore volume of pores with a pore diameter > 50 nm accounted for 12%.

[0054] Catalyst evaluation: The catalyst prepared above was evaluated in a fixed-bed reactor under the following conditions: catalyst loading of 20 mL, pressure of 0.6 MPaG, reaction temperature of 110°C, and WHSV of 4000 h -1 After the carbonyl synthesis reaction, the reaction product was cooled at 5°C for gas-liquid separation, and the composition of the gas and liquid phases was analyzed to calculate the catalyst space-time yield and DMC selectivity. The space-time yield of the C1 catalyst was 600 g / L*h -1 , and the selectivity of DMC was 97.8%. The space-time yield of the catalyst after 500 h of operation was 598 g / L*h -1 , and the selectivity of DMC was 97.7%.

[0055] Example 2

[0056] Catalyst preparation:​​

[0057] (1) Mix 48g of boehmite, 0.4g of aluminum fluoride and 50g of anhydrous ethanol and ball mill for 18 hours.

[0058] 20g of aluminum sol (20% solids content, pH=5) was added, mixed, and then ball-formed at 80℃.

[0059] The substrate was dried for 12 hours and then calcined at 1100℃ to obtain the carrier precursor A1.

[0060] (2) Mix 350g of boehmite, 50g of carrier precursor A1, and 60g of aluminum sol (solid content 20%).

[0061] pH=5), 50g nitric acid solution (3% by mass) binder, and 35g polyethylene glycol are mixed and rolled into balls, dried at 80℃ for 12h, and calcined at 550℃ for 5h to obtain carrier precursor A2;

[0062] (3) 200g of carrier precursor A2 was impregnated with 100g of ammonium chloride solution (mass fraction of 6%), dried at 100℃ for 4h, and calcined at 600℃ for 4h under steam conditions to obtain catalyst carrier B2.

[0063] (4) Prepare an impregnation solution by mixing 6.1g PdCl2, 9.7g CoCl2, and 5% hydrochloric acid aqueous solution.

[0064] 350g of catalyst support was immersed in the impregnation solution and impregnated at room temperature with an equal volume of solution at 80℃.

[0065] Catalyst C2 was obtained by drying for 12 hours and calcining at 200℃ for 2 hours.

[0066] The prepared catalyst support B2 has an average particle size of 4.5 mm, a central layer thickness of 0.8 mm, and a specific surface area of ​​98 m². 2 / g, with a total pore volume of 0.54mL / g. Among them, pores with a diameter <15nm account for 32% of the total pore volume, pores with a diameter of 15-50nm account for 59% of the total pore volume, and pores with a diameter >50nm account for 9% of the total pore volume.

[0067] The catalyst evaluation procedure was the same as in Example 1, and the space-time yield of the C2 catalyst was 760 g / L*h. -1 The selectivity of DMC was 97.9%, and the space-time yield of the catalyst after 500 hours of operation was 750 g / L*h. -1 The selectivity of DMC was 98.0%.

[0068] Example 3

[0069] Catalyst preparation:

[0070] (1) 44 g pseudo-boehmite, 0.5 g sodium fluoride and 44 g absolute ethanol were mixed and ball-milled for 24 hours, 20 g (solid content 20%, pH = 6) aluminum sol was added thereto, and after mixing, the mixture was ball-molded, dried at 80°C for 12 hours, and calcined at 1100°C to obtain a support precursor Al;

[0071] (2) 450 g pseudo-boehmite, 50 g of the support precursor Al, 60 g of aluminum sol (solid content 20%, pH = 6), 50 g of a nitric acid solution (mass fraction 3%) binder, and 25 g of polyethylene glycol were mixed and ball-molded, dried at 80°C for 12 hours, and calcined at 550°C for 5 hours to obtain a support precursor A2;

[0072] (3) 300 g of the support precursor A2 was impregnated with 100 g of an ammonium chloride solution (mass fraction 2%), dried at 100°C for 4 hours, and calcined at 800°C for 4 hours under water vapor to obtain a catalyst support B3;

[0073] (4) 8.7 g of PdCl2, 9.8 g of CoCl2, and 10% hydrochloric acid aqueous solution were mixed to prepare an impregnation solution, 350 g of the catalyst support was soaked in the impregnation solution, and equal-volume impregnation was performed at room temperature, dried at 80°C for 12 hours, and calcined at 200°C for 2 hours to obtain a catalyst C3.

[0074] The catalyst support B3 thus prepared had an average particle size of 4.3 mm, a center layer thickness of 0.22 mm, a specific surface area of 143 m 2 / g, and a total pore volume of 0.66 mL / g. Of the total pore volume, the pore volume of pores having a diameter of < 15 nm was 33%, the pore volume of pores having a diameter of 15-50 nm was 57%, and the pore volume of pores having a diameter of > 50 nm was 10%.

[0075] Catalyst evaluation: The catalyst thus prepared was evaluated in a fixed bed reactor under the following conditions: catalyst loading 20 mL, pressure 0.4 MPaG, reaction temperature 120°C, and WHSV 6000 h -1 -1. After the oxo reaction, the reaction product was cooled at 5°C to separate gas and liquid, and the composition of the gas and liquid was analyzed to calculate the catalyst space-time yield and DMC selectivity. The space-time yield of the C3 catalyst was 890 g / L*h -1 , and the selectivity of DMC was 97.9%. The space-time yield of the catalyst operated for 500 h was 887 g / L*h -1 , and the selectivity of DMC was 97.7%.

[0076] Comparative Example 1

[0077] The catalyst was prepared as described in Example 1, except that step 3) was not carried out, to obtain catalyst carrier B4 and catalyst C4. Under the same catalyst evaluation conditions, the space-time yield of C4 catalyst was 500 g / L*h-1, the selectivity of DMC was 96.9%, and the space-time yield of the catalyst after 500 h of operation was 450 g / L*h -1 , the selectivity of DMC was 96.0%.

[0078] The prepared catalyst carrier B4 had an average particle size of 5 mm, was a single-layer structure, a specific surface area of 103 m 2 / g, and a total pore volume of 0.43 mL / g. Of the total pore volume, the pore volume of pores with a pore diameter of <15 nm accounted for 81%, the pore volume of pores with a pore diameter of 15-50 nm accounted for 14%, and the pore volume of pores with a pore diameter of >50 nm accounted for 5%.

[0079] Comparative Example 2

[0080] The catalyst carrier B5 was prepared using a mixture of different crystalline phase alumina powders (5% by mass of α-alumina powder, 20% by mass of θ-alumina powder, and 75% by mass of γ-alumina powder), to obtain catalyst C5. Under the same catalyst evaluation conditions, the space-time yield of C5 catalyst was 320 g / L*h -1 , the selectivity of DMC was 95.5%, and the space-time yield of the catalyst after 500 h of operation was 150 g / L*h -1 , the selectivity of DMC was 91.0%.

[0081] The prepared catalyst carrier B5 had an average particle size of 4.5 mm, was a single-layer structure, a specific surface area of 128 m 2 / g, and a total pore volume of 0.30 mL / g. Of the total pore volume, the pore volume of pores with a pore diameter of <15 nm accounted for 78%, the pore volume of pores with a pore diameter of 15-50 nm accounted for 19%, and the pore volume of pores with a pore diameter of >50 nm accounted for 3%.

Claims

1. A carbonylation catalyst for the production of dimethyl carbonate, characterized by, The catalyst comprises a spherical carrier with a composite pore distribution of a mixed phase alumina composition and a platinum group metal active component; the carrier is composed of an alumina material with a double-layer structure composite pore distribution of a central layer and an outer layer, the thickness of the central layer is 0.01d-0.3d, wherein d is the diameter of the spherical carrier; the spherical carrier has a mesopore-macropore composite pore distribution, comprising: a pore volume of pores with a diameter of <15nm accounting for 10-40% of the total pore volume, a pore volume of pores with a diameter of 15-50nm accounting for 20-75% of the total pore volume, and a pore volume of pores with a diameter of >50nm accounting for 10-40% of the total pore volume.

2. The catalyst of claim 1, wherein The diameter d of the spherical carrier is 2.8-8mm, and the thickness of the central layer of the carrier is 0.05d-0.3d.

3. The catalyst of claim 1, wherein The specific surface area of the spherical support is between 40 and 150 m 2 / g, and the total pore volume is between 0.2 and 1.2 mL / g.

4. A preparation method of the carbonyl synthesis catalyst for dimethyl carbonate according to claim 1, comprising the following steps: 1) mixing a carrier precursor raw material W1 with a mineralizer and ethanol, adding an aluminum sol, granulating, drying, and calcining to obtain a carrier precursor A1; 2) mixing the carrier precursor raw material W2, the carrier precursor A1, an aluminum sol, a physical pore expander, and a binder, drying, and low-temperature calcining to obtain a carrier precursor A2; 3) impregnating the carrier precursor A2 with an ammonium chloride solution, drying, and then performing secondary calcination under water vapor conditions to obtain a catalyst carrier; 4) mixing a platinum group metal component, an auxiliary active component, and a solvent to prepare an impregnation solution, soaking the catalyst carrier in the impregnation solution, drying, and calcining to obtain the catalyst.

5. The method of claim 4, wherein, The carrier precursor raw material W1 in step 1) and the carrier precursor raw material W2 in step 2) are one or more of aluminum hydroxide, pseudo-boehmite, and boehmite.

6. The method of claim 4, wherein, The mineralizer in step 1) is one of a fluoride salt, a silicofluoride salt, a sulfate salt, and a phosphate salt.

7. The method of claim 6, wherein, The fluoride salt includes one or more of NH4F, CaF2, NaF, BaF2, AlF3, and MgF2, the silicofluoride salt includes one or more of Na2SiF6, MgSiF6, and CaSiF6, the sulfate salt includes one or more of barium sulfate and iron sulfate, and the phosphate salt includes one or more of Ca3(PO4)2 and FePO4.

8. The method of claim 4, wherein, The platinum group metal element in step 4) at least includes Pd, and the loading amount of the platinum group metal element is 0.1wt%-2wt% based on the total weight of the catalyst.

9. The method of claim 8, wherein, The loading amount of the platinum group metal element is 0.5wt%-2wt%.

10. The method of claim 4, wherein, In step 4), the auxiliary active component is one or more of K, Cu, Co, and Ni, and the loading amount of the auxiliary active component element is 0.1wt%-2wt% based on the total weight of the catalyst.

11. The method of claim 10, wherein, The loading amount of the auxiliary active component element is 0.5wt%-2wt%.

12. Use of the catalyst according to any one of claims 1-3 or the catalyst prepared by the method according to any one of claims 4-11 for preparing dimethyl carbonate by reacting methyl nitrite and carbon monoxide.