Zinc-aluminum composite oxide catalyst, its preparation method and application

Abstract

The application discloses a zinc-aluminum composite oxide catalyst and a preparation method and application thereof, and belongs to the technical field of catalytic materials and non-phosgene isocyanate preparation. The application solves the problems of high reaction temperature, low raw material concentration, many side reactions and insufficient catalyst stability in the process of preparing isocyanate by pyrolysis of carbamic acid ester. The zinc-aluminum composite oxide catalyst comprises a composite oxide of zinc and aluminum, and has a dual-phase heterogeneous structure of ZnO and ZnAl2O4 spinel. When the catalyst is applied to the preparation of 4-(4'-phenylaminomethylcarbamate) diphenyl methane isocyanate (MMI) and diphenyl methane diisocyanate (MDI) by vacuum thermal decomposition of diphenyl methane diamino methylcarbamate (MDC), the self-polymerization and condensation side reactions in the reaction process can be effectively inhibited by the synergistic effect of the ZnO phase and the spinel phase, the selectivity and yield of the target product are improved, and the catalyst has good mechanical stability and is easy to recycle and cyclically used.

Description

Technical Field

[0001] This invention belongs to the field of catalytic materials and non-phosgene isocyanate preparation technology, specifically relating to a zinc-aluminum composite oxide catalyst, its preparation method and application. Background Technology

[0002] Diphenylmethane diisocyanate (MDI) is a key monomer for the preparation of polyurethane materials. With increasingly stringent environmental regulations, the non-phosgene thermal decomposition route using diphenylmethane dicarboxylate (MDC) as a raw material has become an important research direction to replace the traditional phosgene method because it avoids the risks of phosgene's extreme toxicity and the corrosion problems caused by hydrogen chloride.

[0003] The MDC thermal decomposition to MDI route is a reversible endothermic reaction. Typically, methanol is first removed to generate the single-sided product 4-(4'-methyl phenylcarbamate)diphenylmethane isocyanate (MMI), which is then further decomposed to produce MDI. However, the MDC thermal decomposition reaction is an endothermic reaction constrained by thermodynamic equilibrium, usually requiring high temperatures. During this process, the isocyanate groups are highly susceptible to side reactions such as self-polymerization or condensation with carbamates, leading to increased coking and a decreased yield of the target product.

[0004] In the prior art, Koichi et al. in patent US4307029 used zinc chloride as a homogeneous catalyst. The yield of MDI obtained by decomposing MDC under normal pressure was only 46.1%. Moreover, the homogeneous system made it difficult to separate the catalyst from the reaction liquid, resulting in high recovery costs and equipment corrosion problems. Patent CN200510021147 discloses the use of zinc oxide powder as a catalyst, and the MDI yield in the examples can reach about 62%. However, this method is usually carried out at a high temperature (such as 240~280℃, and the upper limit of the claim is 300℃). Guan Xue et al. studied the ZnO / Zn composite catalyst, which increased the conversion rate to 99.2%, but the mass fraction of raw material MDC in the solvent was only 2.5%, resulting in low production efficiency (Guan Xue, Li Huiquan, Liu Haitao, et al. Study on the preparation of 4,4'-diphenylmethane diisocyanate by thermal decomposition of 4,4'-diphenylmethane dicarboxylate by ZnO / Zn composite catalyst [J]. Journal of Beijing University of Chemical Technology (Natural Science Edition) [J]. 2009, 36(4): 12-16.). Zhao et al. used zinc powder as a catalyst. Although the highest MDI yield was 87.3%, the process had problems such as low MDC concentration (2 wt%) and high reaction temperature (280 ℃). Moreover, the zinc content of their supported ZnCl2 / AC catalyst decreased from 11% to 5% before and after the reaction, indicating a clear loss of active components, resulting in a short catalyst life and inability to be recycled (Zhao XQ, Wang YJ, Wang SF, et al. Synthesis of MDI from DimethylCarbonate over Solid Catalysts[J].Industrial & Engineering ChemistryResearch, 2002, 41(21):5139-5144.). Summary of the Invention

[0005] To address the problems of high reaction temperature, low feed concentration, numerous side reactions, and insufficient catalyst stability in the pyrolysis of urethane to isocyanate in existing technologies, this invention provides a zinc-aluminum composite oxide catalyst, its preparation method, and its application. This invention employs a co-current co-precipitation method to prepare the zinc-aluminum composite oxide catalyst. This catalyst has a two-phase heterogeneous structure of ZnO and ZnAl₂O₄ spinel. Through the synergistic effect of the ZnO and spinel phases, suitable acid-base sites are provided, which not only facilitates the activation of carbonyl groups and the removal of alkoxy groups in urethane but also effectively inhibits the self-polymerization and condensation side reactions of isocyanate groups, thereby significantly improving the selectivity of the target product and the stability of the catalyst. This catalyst has a high specific surface area and good stability, is easy to separate, recover, and recycle, and can achieve efficient pyrolysis of diphenylmethane diurethane at high feed concentrations under mild conditions.

[0006] The technical solution adopted in this invention is as follows:

[0007] A zinc-aluminum composite oxide catalyst comprising a composite oxide of zinc and aluminum, and having a biphase heterostructure of ZnO and ZnAl2O4 spinel.

[0008] Preferably, the Zn / Al molar ratio is 1:1 to 5:1, and the specific surface area is 24 to 100 m². 2 / g.

[0009] Preferably, the Zn / Al molar ratio is 2:1 to 4:1, and the specific surface area is 35 to 75 m². 2 / g.

[0010] Preferably, the Zn / Al molar ratio is 3:1.

[0011] A method for preparing a zinc-aluminum composite oxide catalyst includes the following steps:

[0012] S1: Prepare a zinc-aluminum mixed salt solution;

[0013] S2: The zinc-aluminum mixed salt solution and the alkaline precipitant solution are co-precipitated in parallel flow, followed by crystallization treatment;

[0014] S3: After crystallization, the precursor is obtained by filtration, washing, and drying;

[0015] S4: The precursor is calcined to obtain a zinc-aluminum composite oxide catalyst.

[0016] Preferably, the alkaline precipitant is an alkaline compound that can provide hydroxide ions and / or carbonate ions.

[0017] Preferably, the alkaline precipitant is one or more of sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, potassium carbonate, potassium bicarbonate, ammonia, ammonium carbonate, and ammonium bicarbonate.

[0018] Preferably, the alkaline precipitant is a mixture of sodium hydroxide and sodium carbonate in a molar ratio of (2~6):1.

[0019] Preferably, the total metal ion concentration in S1 is 0.01~2.0 mol / L, and the concentration of the alkaline precipitant solution in S2 is 0.02~3.0 mol / L.

[0020] Preferably, the zinc in S1 is derived from a water-soluble zinc salt, which is one or more of zinc nitrate, zinc acetate, zinc chloride, zinc sulfate, and zinc formate; the aluminum is derived from a water-soluble aluminum salt, which is one or more of aluminum nitrate, aluminum acetate, aluminum chloride, and aluminum sulfate.

[0021] Preferably, the flow rate of the zinc-aluminum mixed salt solution and the alkaline precipitant solution in S2 is 1–6 mL / min; the pH in S2 is controlled at 7–9, and the crystallization treatment is carried out at a temperature of 60–90 °C for 1–6 hours. Further preferably, the pH is 7.5–8.5.

[0022] As a preferred embodiment, S3 is dried at 80~120 ℃ for 2~8 hours, and S4 is calcined at 500~900 ℃ for 2~6 hours.

[0023] Preferably, the calcination temperature is 600–800 °C, most preferably 700 °C; the calcination time is 2–6 hours, more preferably 3–5 hours.

[0024] The application of a zinc-aluminum composite oxide catalyst, or a zinc-aluminum composite oxide catalyst prepared by the same method, in the catalytic thermal decomposition of diphenylmethane dicarboxylate to prepare isocyanate, wherein the mass fraction of diphenylmethane dicarboxylate in the reaction system is 5 wt% to 20 wt%, more preferably 8 wt% to 15 wt%, and most preferably 10 wt%; the mass fraction of the zinc-aluminum composite oxide catalyst in the reaction system is 0.05 wt% to 5 wt%, more preferably 0.1 wt% to 1 wt%, and most preferably 0.2 wt%; the absolute pressure of the reaction is 0.5 to 2.5 kPa, more preferably 0.8 to 1.5 kPa, and most preferably 1 kPa; the reaction temperature is 215 ℃ to 235 ℃, more preferably 225 to 232 ℃, and most preferably 230 ℃; and the reaction time is 30 to 70 min, more preferably 45 to 65 min, and most preferably 60 min.

[0025] Preferably, a zinc-aluminum composite oxide catalyst, diphenylmethane dicarboxylate, and an inert solvent are mixed and subjected to a thermal decomposition reaction under vacuum conditions to obtain diphenylmethane diisocyanate.

[0026] Preferably, the inert solvent is at least one selected from dibutyl sebacate, dioctyl sebacate, diisooctyl sebacate, chlorobenzene, o-dichlorobenzene, xylene, n-tetradecane, n-pentadecane, and n-hexadecane, with diisooctyl sebacate being the most preferred.

[0027] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0028] 1. The catalyst of this invention utilizes the synergistic effect of the dual-phase heterostructure of ZnO and ZnAl2O4 spinel to provide acid-base sites of moderate strength, effectively promoting the pyrolysis of urethane esters while suppressing side reactions. It can achieve efficient conversion at a relatively mild temperature (<235 ℃), effectively suppressing high-temperature self-polymerization side reactions, and exhibiting high MDI selectivity.

[0029] 2. The process of this invention has good adaptability to raw material concentration and can operate in the range of 5 to 20 wt% raw material concentration. Compared with common low concentration (<5 wt%) dilution systems, it is beneficial to improve the production efficiency of a single batch.

[0030] 3. The catalyst of this invention has good stability and can be recycled more than 5 times after simple washing and drying, maintaining good activity and making it suitable for industrial applications.

[0031] 4. The catalyst preparation method of the present invention has a simple process and controllable conditions, and is suitable for large-scale preparation. Attached Figure Description

[0032] Figure 1 The XRD pattern of the Zn3Al-700-A1B1 catalyst, the product of Example 1 of this invention;

[0033] Figure 2 The N2 adsorption-desorption isotherm of the Zn3Al-700-A1B1 catalyst produced in Example 1 of this invention;

[0034] Figure 3 This is a SEM image of the Zn3Al-700-A1B1 catalyst, the product of Example 1 of this invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0036] (I) Preparation of zinc-aluminum composite oxide catalysts

[0037] Example 1

[0038] A zinc-aluminum composite oxide catalyst, the preparation method of which includes the following steps:

[0039] S1: Keep the total metal ion concentration at 0.1 mol / L. Weigh Zn(NO3)2·6H2O and Al(NO3)3·9H2O according to the Zn / Al molar ratio of 3:1, and dissolve them in 100 mL of deionized water to prepare solution A1. Separately weigh 8.0 g NaOH and 5.3 g Na2CO3 and dissolve them in 100 mL of deionized water to prepare solution B1.

[0040] S2: At room temperature, add solutions A1 and B1 in parallel at a flow rate of 3 mL / min into a reactor containing 100 mL of deionized water, maintaining the pH at 7-8 and continuously stirring. After the addition is complete, raise the temperature to 80 ℃ for crystallization for 6 hours;

[0041] S3: Filter by suction, wash with deionized water and ethanol until neutral, and dry at 100 ℃ for 2-8 hours to obtain the precursor;

[0042] S4: The precursor was calcined in air at 700 °C for 4 hours to obtain the Zn3Al-700-A1B1 catalyst.

[0043] The characterization results of the Zn3Al-700-A1B1 catalyst are as follows: Figure 1-3 As shown, from Figure 1-3 It can be seen that: SEM morphology images show an interlaced nanosheet structure with fine surface particle modification; XRD patterns show ZnO diffraction peaks at 2θ=31.8° and ZnAl2O4 spinel characteristic peaks at 2θ=31.3°, forming a complete two-phase heterostructure; BET analysis shows a specific surface area of ​​54 m². 2 / g. Based on the ZnO / ZnAl2O4 dual-phase composition and the Zn / Al = 3:1 feed ratio, it can be inferred that the larger lamellar structures mainly constitute the ZnO main framework, while the ZnAl2O4 spinel phase is more likely to be uniformly attached or embedded on its surface in the form of fine dispersed particles, thus forming a tightly coupled dual-phase heterostructure.

[0044] Example 2

[0045] A zinc-aluminum composite oxide catalyst, the preparation method of which includes the following steps:

[0046] S1: Maintain the total metal ion concentration at 0.1 mol / L. Weigh Zn(CH3COO)2·2H2O and Al(NO3)3·9H2O according to the Zn / Al molar ratio of 3:1, and dissolve them in 100 mL of deionized water to prepare solution A2. Separately weigh 8.0 g NaOH and 5.3 g Na2CO3 and dissolve them in 100 mL of deionized water to prepare solution B1.

[0047] S2: At room temperature, add solutions A2 and B1 in parallel at a flow rate of 3 mL / min into a reactor containing 100 mL of deionized water, maintaining the pH at 7-8 and stirring continuously. After the addition is complete, raise the temperature to 80 ℃ for crystallization for 6 hours;

[0048] S3: Filter by suction, wash with deionized water and ethanol until neutral, and dry at 100 ℃ for 2-8 hours to obtain the precursor;

[0049] S4: The precursor was calcined in air at 700 °C for 4 hours to obtain a Zn3Al-700-A2B1 catalyst with a specific surface area of ​​100 m². 2 / g.

[0050] Example 3

[0051] A zinc-aluminum composite oxide catalyst, the preparation method of which includes the following steps:

[0052] S1: Keep the total metal ion concentration at 0.1 mol / L. Weigh Zn(CH3COO)2·2H2O and AlCl3 according to the Zn / Al molar ratio of 3:1, and dissolve them in 100 mL of deionized water to prepare solution A3. Separately weigh 8.0 g NaOH and 5.3 g Na2CO3 and dissolve them in 100 mL of deionized water to prepare solution B1.

[0053] S2: At room temperature, add solutions A3 and B1 in parallel at a flow rate of 3 mL / min into a reactor containing 100 mL of deionized water, maintaining the pH at 7-8 and continuously stirring. After the addition is complete, raise the temperature to 80 ℃ for crystallization for 6 hours;

[0054] S3: Filter by suction, wash with deionized water and ethanol until neutral, and dry at 100 ℃ for 2-8 hours to obtain the precursor;

[0055] S4: The precursor was calcined in air at 700 °C for 4 hours to obtain a Zn3Al-700-A3B1 catalyst with a specific surface area of ​​64 m². 2 / g.

[0056] Example 4

[0057] A zinc-aluminum composite oxide catalyst, the preparation method of which includes the following steps:

[0058] S1: Keep the total metal ion concentration at 0.1 mol / L. Weigh Zn(NO3)2·6H2O and Al(NO3)3·9H2O according to the Zn / Al molar ratio of 3:1, and dissolve them in 100 mL of deionized water to prepare solution A1. Separately weigh 11.2 g KOH and 5.3 g Na2CO3 and dissolve them in 100 mL of deionized water to prepare solution B2.

[0059] S2: At room temperature, add solutions A1 and B2 in parallel at a flow rate of 3 mL / min into a reactor containing 100 mL of deionized water, maintaining the pH at 7-8 and continuously stirring. After the addition is complete, raise the temperature to 80 ℃ for crystallization for 6 hours;

[0060] S3: Filter by suction, wash with deionized water and ethanol until neutral, and dry at 100 ℃ for 2-8 hours to obtain the precursor;

[0061] S4: The precursor was calcined in air at 700 °C for 4 hours to obtain a Zn3Al-700-A1B2 catalyst with a specific surface area of ​​59 m². 2 / g.

[0062] Example 5

[0063] A zinc-aluminum composite oxide catalyst, the preparation method of which includes the following steps:

[0064] S1: Keep the total metal ion concentration at 0.1 mol / L. Weigh Zn(NO3)2·6H2O and Al(NO3)3·9H2O according to the Zn / Al molar ratio of 3:1, and dissolve them in 100 mL of deionized water to prepare solution A1. Separately weigh 8.0 g NaOH and 4.8 g (NH4)2CO3 and dissolve them in 100 mL of deionized water to prepare solution B3.

[0065] S2: At room temperature, add solutions A1 and B3 in parallel at a flow rate of 3 mL / min into a reactor containing 100 mL of deionized water, maintaining the pH at 7-8 and continuously stirring. After the addition is complete, raise the temperature to 80 ℃ for crystallization for 6 hours;

[0066] S3: Filter by suction, wash with deionized water and ethanol until neutral, and dry at 100 ℃ for 2-8 hours to obtain the precursor;

[0067] S4: The precursor was calcined in air at 700 °C for 4 hours to obtain a Zn3Al-700-A1B3 catalyst with a specific surface area of ​​82 m². 2 / g.

[0068] Example 6

[0069] A zinc-aluminum composite oxide catalyst, the preparation method of which includes the following steps:

[0070] S1: Keep the total metal ion concentration at 0.1 mol / L. Weigh Zn(NO3)2·6H2O and Al(NO3)3·9H2O according to the Zn / Al molar ratio of 5:1, and dissolve them in 100 mL of deionized water to prepare solution A1. Separately weigh 8.0 g NaOH and 5.3 g Na2CO3 and dissolve them in 100 mL of deionized water to prepare solution B1.

[0071] S2: At room temperature, add solutions A1 and B1 in parallel at a flow rate of 3 mL / min into a reactor containing 100 mL of deionized water, maintaining the pH at 7-8 and continuously stirring. After the addition is complete, raise the temperature to 80 ℃ for crystallization for 6 hours;

[0072] S3: Filter by suction, wash with deionized water and ethanol until neutral, and dry at 100 ℃ for 2-8 hours to obtain the precursor;

[0073] S4: The precursor was calcined in air at 700 °C for 4 hours to obtain a Zn5Al-700-A1B1 catalyst with a specific surface area of ​​37 m². 2 / g.

[0074] Example 7

[0075] A zinc-aluminum composite oxide catalyst, the preparation method of which includes the following steps:

[0076] S1: Keep the total metal ion concentration at 0.1 mol / L. Weigh Zn(NO3)2·6H2O and Al(NO3)3·9H2O according to the Zn / Al molar ratio of 1:1, and dissolve them in 100 mL of deionized water to prepare solution A1. Separately weigh 8.0 g NaOH and 5.3 g Na2CO3 and dissolve them in 100 mL of deionized water to prepare solution B1.

[0077] S2: At room temperature, add solutions A1 and B1 in parallel at a flow rate of 3 mL / min into a reactor containing 100 mL of deionized water, maintaining the pH at 7-8 and continuously stirring. After the addition is complete, raise the temperature to 80 ℃ for crystallization for 6 hours;

[0078] S3: Filter by suction, wash with deionized water and ethanol until neutral, and dry at 100 ℃ for 2-8 hours to obtain the precursor;

[0079] S4: The precursor was calcined in air at 700 °C for 4 hours to obtain a Zn1Al-700-A1B1 catalyst with a specific surface area of ​​45 m². 2 / g.

[0080] Example 8

[0081] A zinc-aluminum composite oxide catalyst, the preparation method of which includes the following steps:

[0082] S1: Keep the total metal ion concentration at 0.1 mol / L. Weigh Zn(NO3)2·6H2O and Al(NO3)3·9H2O according to the Zn / Al molar ratio of 3:1, and dissolve them in 100 mL of deionized water to prepare solution A1. Separately weigh 8.0 g NaOH and 5.3 g Na2CO3 and dissolve them in 100 mL of deionized water to prepare solution B1.

[0083] S2: At room temperature, add solutions A1 and B1 in parallel at a flow rate of 3 mL / min into a reactor containing 100 mL of deionized water, maintaining the pH at 7-8 and continuously stirring. After the addition is complete, raise the temperature to 80 ℃ for crystallization for 6 hours;

[0084] S3: Filter by suction, wash with deionized water and ethanol until neutral, and dry at 100 ℃ for 2-8 hours to obtain the precursor;

[0085] S4: The precursor was calcined in air at 500 °C for 4 hours to obtain a Zn3Al-500-A1B1 catalyst with a specific surface area of ​​76 m². 2 / g.

[0086] Example 9

[0087] A zinc-aluminum composite oxide catalyst, the preparation method of which includes the following steps:

[0088] S1: Keep the total metal ion concentration at 0.1 mol / L. Weigh Zn(NO3)2·6H2O and Al(NO3)3·9H2O according to the Zn / Al molar ratio of 3:1, and dissolve them in 100 mL of deionized water to prepare solution A1. Separately weigh 8.0 g NaOH and 5.3 g Na2CO3 and dissolve them in 100 mL of deionized water to prepare solution B1.

[0089] S2: At room temperature, add solutions A1 and B1 in parallel at a flow rate of 3 mL / min into a reactor containing 100 mL of deionized water, maintaining the pH at 7-8 and continuously stirring. After the addition is complete, raise the temperature to 80 ℃ for crystallization for 6 hours;

[0090] S3: Filter by suction, wash with deionized water and ethanol until neutral, and dry at 100 ℃ for 2-8 hours to obtain the precursor;

[0091] S4: The precursor was calcined in air at 900 °C for 4 hours to obtain a Zn3Al-900-A1B1 catalyst with a specific surface area of ​​24 m². 2 / g.

[0092] Comparative Example 1

[0093] A zinc-aluminum composite oxide catalyst, the preparation method of which includes the following steps:

[0094] S1: Keep the total metal ion concentration at 0.1 mol / L. Weigh out Al(NO3)3·9H2O and dissolve it in 100 mL of deionized water to prepare solution A4 (without adding zinc salt). Weigh out 8.0 g NaOH and 5.3 g Na2CO3 and dissolve them in 100 mL of deionized water to prepare solution B1.

[0095] S2: At room temperature, add solutions A4 and B1 in parallel at a flow rate of 3 mL / min into a reactor containing 100 mL of deionized water, maintaining the pH at 7-8 and stirring continuously. After the addition is complete, raise the temperature to 80 ℃ for crystallization for 6 hours;

[0096] S3: Filter by suction, wash with deionized water and ethanol until neutral, and dry at 100 ℃ for 2-8 hours to obtain the precursor;

[0097] S4: The precursor was calcined in air at 700 °C for 4 hours to obtain Al2O. 3- 700-A4B1 catalyst.

[0098] Comparative Example 2

[0099] A zinc-aluminum composite oxide catalyst, the preparation method of which includes the following steps:

[0100] S1: Keep the total metal ion concentration at 0.1 mol / L. Weigh out Zn(NO3)2·6H2O and dissolve it in 100 mL of deionized water to prepare solution A5 (without adding aluminum salt). Weigh out 8.0 g NaOH and 5.3 g Na2CO3 and dissolve them in 100 mL of deionized water to prepare solution B1.

[0101] S2: At room temperature, add solutions A4 and B1 in parallel at a flow rate of 3 mL / min into a reactor containing 100 mL of deionized water, maintaining the pH at 7-8 and stirring continuously. After the addition is complete, raise the temperature to 80 ℃ for crystallization for 6 hours;

[0102] S3: Filter by suction, wash with deionized water and ethanol until neutral, and dry at 100 ℃ for 2-8 hours to obtain the precursor;

[0103] S4: The precursor was calcined in air at 700 °C for 4 hours to obtain the ZnO-700-A5B1 catalyst.

[0104] Comparative Example 3

[0105] The Al2O prepared in Comparative Example 1 3- After drying, the 700-A4B1 catalyst and the comparative example 2ZnO-700-A5B1 catalyst were weighed at a Zn / Al molar ratio of 3:1, placed in a mortar and ground and mixed thoroughly for 30 min to obtain a physically mixed catalyst, denoted as Zn3Al-mix.

[0106] The parameter changes in Examples 1-9 and Comparative Examples 1-3 are shown in Table 1:

[0107] Table 1

[0108]

[0109] (II) Application of zinc-aluminum composite oxide catalyst in the catalytic thermal decomposition of diphenylmethane dicarboxylate to prepare isocyanate

[0110] Example 10

[0111] The application of zinc-aluminum composite oxide catalysts in the catalytic thermal decomposition of diphenylmethane dicarboxylate to prepare isocyanate is as follows:

[0112] Add 10 g MDC (10 wt% of the total mass of the reaction system), 0.02 g of Zn3Al-700-A1B1 catalyst prepared in Example 1 (0.2 wt% of the mass of MDC), and 90 g of diisooctyl sebacate (DOS) solvent to a 250 mL three-necked flask. Stir and heat to 170 °C to dissolve the MDC. Then replace the high-temperature salt bath and adjust the absolute pressure to 1 kPa. After the internal temperature reaches 230 °C, start the reaction for 60 min. After the reaction is completed, separate the catalyst from the reaction solution.

[0113] The reaction mixture was analyzed using high-performance liquid chromatography (HPLC). MDC conversion, MDI selectivity, MMI and total MDI selectivity, and yield were calculated using the following formulas (other examples and comparative examples were also calculated using the following formulas):

[0114]

[0115]

[0116]

[0117] m f The amount of reaction solution weighed when indicating the derivative product; ω j Indicates the components in the sample j mass fraction (components) j (For MDC, MMI, MDI); M j This represents the molar mass of component j; m 0 This indicates the amount of MDC added during the reaction; P 0 Indicates the purity of MDC; C MDC This indicates the conversion rate of MDC; S j Indicates the selectivity of component j; Y j Indicates components j Yield;

[0118] Liquid chromatography analysis showed that the MDC conversion rate was 98.62%, the MDI selectivity was 73.35%, and the total selectivity of MMI and MDI was 95.62%.

[0119] The Zn3Al-700-A1B1 catalyst prepared in Example 1 was used to carry out the MDC thermal decomposition reaction under the conditions described in Example 10. After the reaction was completed, the reaction system was cooled to room temperature, and the catalyst was recovered by centrifugation or filtration. The recovered catalyst was first washed with an organic solvent to remove surface-adsorbed organic matter (preferably ethyl acetate and / or toluene), then washed with deionized water until neutral, and subsequently dried at 100°C to constant weight to obtain a reusable catalyst. The dried catalyst was directly used in the next reaction.

[0120] Under the same conditions as the first reaction in Example 10, including MDC concentration, catalyst dosage, reaction temperature, absolute pressure, and reaction time, the reaction was repeated 5 times. Cycle number 0 represents fresh catalyst, and 1-4 represent 1-4 cycles (a total of 5 evaluations). The MDC conversion, MDI selectivity, and MMI and total MDI selectivity were measured for each reaction. The results are shown in Table 2 below:

[0121] Table 2

[0122]

[0123] Example 11

[0124] The application of zinc-aluminum composite oxide catalysts in the catalytic thermal decomposition of diphenylmethane dicarboxylate to prepare isocyanate is as follows:

[0125] Add 10 g MDC (10 wt% of the total mass of the reaction system), 0.02 g of Zn3Al-700-A2B1 catalyst prepared in Example 2 (0.2 wt% of the mass of MDC), and 90 g of diisooctyl sebacate (DOS) solvent to a 250 mL three-necked flask. Stir and heat to 170 °C to dissolve the MDC. Then replace the high-temperature salt bath and adjust the absolute pressure to 1 kPa. After the internal temperature reaches 230 °C, start the reaction for 60 min. After the reaction is completed, separate the catalyst from the reaction solution.

[0126] Liquid chromatography analysis showed that the MDC conversion rate was 98.26%, the MDI selectivity was 72.52%, and the total selectivity of MMI and MDI was 93.69%.

[0127] Example 12

[0128] The application of zinc-aluminum composite oxide catalysts in the catalytic thermal decomposition of diphenylmethane dicarboxylate to prepare isocyanate is as follows:

[0129] Add 10 g MDC (10 wt% of the total mass of the reaction system), 0.02 g of Zn3Al-700-A3B1 catalyst prepared in Example 3 (0.2 wt% of the mass of MDC), and 90 g of diisooctyl sebacate (DOS) solvent to a 250 mL three-necked flask. Stir and heat to 170 °C to dissolve the MDC. Then replace the high-temperature salt bath and adjust the absolute pressure to 1 kPa. After the internal temperature reaches 230 °C, start the reaction for 60 min. After the reaction is completed, separate the catalyst from the reaction solution.

[0130] Liquid chromatography analysis showed that the MDC conversion rate was 97.56%, the MDI selectivity was 69.22%, and the total selectivity of MMI and MDI was 92.45%.

[0131] Example 13

[0132] The application of zinc-aluminum composite oxide catalysts in the catalytic thermal decomposition of diphenylmethane dicarboxylate to prepare isocyanate is as follows:

[0133] Add 10 g MDC (10 wt% of the total mass of the reaction system), 0.02 g of Zn3Al-700-A1B2 catalyst prepared in Example 4 (0.2 wt% of the mass of MDC), and 90 g of diisooctyl sebacate (DOS) solvent to a 250 mL three-necked flask. Stir and heat to 170 °C to dissolve the MDC. Then replace the high-temperature salt bath and adjust the absolute pressure to 1 kPa. After the internal temperature reaches 230 °C, start the reaction for 60 min. After the reaction is completed, separate the catalyst from the reaction solution.

[0134] Liquid chromatography analysis showed that the MDC conversion rate was 96.46%, the MDI selectivity was 69.11%, and the total selectivity of MMI and MDI was 91.89%.

[0135] Example 14

[0136] The application of zinc-aluminum composite oxide catalysts in the catalytic thermal decomposition of diphenylmethane dicarboxylate to prepare isocyanate is as follows:

[0137] Add 10 g MDC (10 wt% of the total mass of the reaction system), 0.02 g of Zn3Al-700-A1B3 catalyst prepared in Example 5 (0.2 wt% of the mass of MDC), and 90 g of diisooctyl sebacate (DOS) solvent to a 250 mL three-necked flask. Stir and heat to 170 °C to dissolve the MDC. Then replace the high-temperature salt bath and adjust the absolute pressure to 1 kPa. After the internal temperature reaches 230 °C, start the reaction for 60 min. After the reaction is completed, separate the catalyst from the reaction solution.

[0138] Liquid chromatography analysis showed that the MDC conversion rate was 97.42%, the MDI selectivity was 68.44%, and the total selectivity of MMI and MDI was 94.58%.

[0139] Example 15

[0140] The application of zinc-aluminum composite oxide catalysts in the catalytic thermal decomposition of diphenylmethane dicarboxylate to prepare isocyanate is as follows:

[0141] Add 10 g MDC (10 wt% of the total mass of the reaction system), 0.02 g of Zn5Al-700-A1B1 catalyst prepared in Example 6 (0.2 wt% of the mass of MDC), and 90 g of diisooctyl sebacate (DOS) solvent to a 250 mL three-necked flask. Stir and heat to 170 °C to dissolve the MDC. Then replace the high-temperature salt bath and adjust the absolute pressure to 1 kPa. After the internal temperature reaches 230 °C, start the reaction for 60 min. After the reaction is completed, separate the catalyst from the reaction solution.

[0142] Liquid chromatography analysis showed that the MDC conversion rate was 97.12%, the MDI selectivity was 65.48%, and the total selectivity of MMI and MDI was 92.56%.

[0143] Example 16

[0144] The application of zinc-aluminum composite oxide catalysts in the catalytic thermal decomposition of diphenylmethane dicarboxylate to prepare isocyanate is as follows:

[0145] Add 10 g MDC (10 wt% of the total mass of the reaction system), 0.02 g of Zn1Al-700-A1B1 catalyst prepared in Example 7 (0.2 wt% of the mass of MDC), and 90 g of diisooctyl sebacate (DOS) solvent to a 250 mL three-necked flask. Stir and heat to 170 °C to dissolve the MDC. Then replace the high-temperature salt bath and adjust the absolute pressure to 1 kPa. After the internal temperature reaches 230 °C, start the reaction for 60 min. After the reaction is completed, separate the catalyst from the reaction solution.

[0146] Liquid chromatography analysis showed that the MDC conversion rate was 93.57%, the MDI selectivity was 55.62%, and the total selectivity of MMI and MDI was 92.67%.

[0147] Example 17

[0148] The application of zinc-aluminum composite oxide catalysts in the catalytic thermal decomposition of diphenylmethane dicarboxylate to prepare isocyanate is as follows:

[0149] Add 10 g MDC (10 wt% of the total mass of the reaction system), 0.02 g of Zn3Al-500-A1B1 catalyst prepared in Example 8 (0.2 wt% of the mass of MDC), and 90 g of diisooctyl sebacate (DOS) solvent to a 250 mL three-necked flask. Stir and heat to 170 °C to dissolve the MDC. Then replace the high-temperature salt bath and adjust the absolute pressure to 1 kPa. After the internal temperature reaches 230 °C, start the reaction for 60 min. After the reaction is completed, separate the catalyst from the reaction solution.

[0150] Liquid chromatography analysis showed that the MDC conversion rate was 96.78%, the MDI selectivity was 62.55%, and the total selectivity of MMI and MDI was 90.15%.

[0151] Example 18

[0152] The application of zinc-aluminum composite oxide catalysts in the catalytic thermal decomposition of diphenylmethane dicarboxylate to prepare isocyanate is as follows:

[0153] Add 10 g MDC (10 wt% of the total mass of the reaction system), 0.02 g of Zn3Al-900-A1B1 catalyst prepared in Example 9 (0.2 wt% of the mass of MDC), and 90 g of diisooctyl sebacate (DOS) solvent to a 250 mL three-necked flask. Stir and heat to 170 °C to dissolve the MDC. Then replace the high-temperature salt bath and adjust the absolute pressure to 1 kPa. After the internal temperature reaches 230 °C, start the reaction for 60 min. After the reaction is completed, separate the catalyst from the reaction solution.

[0154] Liquid chromatography analysis showed that the MDC conversion rate was 97.41%, the MDI selectivity was 64.23%, and the total selectivity of MMI and MDI was 91.33%.

[0155] Example 19

[0156] The application of zinc-aluminum composite oxide catalysts in the catalytic thermal decomposition of diphenylmethane dicarboxylate to prepare isocyanate is as follows:

[0157] Add 10 g MDC (10 wt% of the total mass of the reaction system), 0.02 g of Zn3Al-700-A1B1 catalyst prepared in Example 1 (0.2 wt% of the mass of MDC), and 90 g of diisooctyl sebacate (DOS) solvent to a 250 mL three-necked flask. Stir and heat to 170 °C to dissolve the MDC. Then replace the high-temperature salt bath and adjust the absolute pressure to 1 kPa. After the internal temperature reaches 215 °C, start the reaction for 60 min. After the reaction is completed, separate the catalyst from the reaction solution.

[0158] Liquid chromatography analysis showed that the MDC conversion rate was 72.79%, the MDI selectivity was 21.64%, and the total selectivity of MMI and MDI was 98.77%.

[0159] Example 20

[0160] The application of zinc-aluminum composite oxide catalysts in the catalytic thermal decomposition of diphenylmethane dicarboxylate to prepare isocyanate is as follows:

[0161] Add 10 g MDC (10 wt% of the total mass of the reaction system), 0.02 g of Zn3Al-700-A1B1 catalyst prepared in Example 1 (0.2 wt% of the mass of MDC), and 90 g of diisooctyl sebacate (DOS) solvent to a 250 mL three-necked flask. Stir and heat to 170 °C to dissolve the MDC. Then replace the high-temperature salt bath and adjust the absolute pressure to 1 kPa. After the internal temperature reaches 235 °C, start the reaction for 60 min. After the reaction is completed, separate the catalyst from the reaction solution.

[0162] Liquid chromatography analysis showed that the MDC conversion rate was 99.09%, the MDI selectivity was 69.30%, and the total selectivity of MMI and MDI was 85.31%.

[0163] Example 21

[0164] The application of zinc-aluminum composite oxide catalysts in the catalytic thermal decomposition of diphenylmethane dicarboxylate to prepare isocyanate is as follows:

[0165] Add 10 g MDC (10 wt% of the total mass of the reaction system), 0.02 g of Zn3Al-700-A1B1 catalyst prepared in Example 1 (0.2 wt% of the mass of MDC), and 90 g of diisooctyl sebacate (DOS) solvent to a 250 mL three-necked flask. Stir and heat to 170 °C to dissolve the MDC. Then replace the high-temperature salt bath and adjust the absolute pressure to 1 kPa. After the internal temperature reaches 230 °C, start the reaction for 30 min. After the reaction is completed, separate the catalyst from the reaction solution.

[0166] Liquid chromatography analysis showed that the MDC conversion rate was 95.75%, the MDI selectivity was 58.34%, and the total selectivity of MMI and MDI was 97.68%.

[0167] Example 22

[0168] The application of zinc-aluminum composite oxide catalysts in the catalytic thermal decomposition of diphenylmethane dicarboxylate to prepare isocyanate is as follows:

[0169] Add 10 g MDC (10 wt% of the total mass of the reaction system), 0.02 g of Zn3Al-700-A1B1 catalyst prepared in Example 1 (0.2 wt% of the mass of MDC), and 90 g of diisooctyl sebacate (DOS) solvent to a 250 mL three-necked flask. Stir and heat to 170 °C to dissolve the MDC. Then replace the high-temperature salt bath and adjust the absolute pressure to 1 kPa. After the internal temperature reaches 230 °C, start the reaction for 70 min. After the reaction is completed, separate the catalyst from the reaction solution.

[0170] Liquid chromatography analysis showed that the MDC conversion rate was 99.03%, the MDI selectivity was 69.27%, and the total selectivity of MMI and MDI was 88.21%.

[0171] Example 23

[0172] The application of zinc-aluminum composite oxide catalysts in the catalytic thermal decomposition of diphenylmethane dicarboxylate to prepare isocyanate is as follows:

[0173] Add 10 g MDC (10 wt% of the total mass of the reaction system), 0.005 g of Zn3Al-700-A1B1 catalyst prepared in Example 1 (0.05 wt% of the mass of MDC), and 90 g of diisooctyl sebacate (DOS) solvent to a 250 mL three-necked flask. Stir and heat to 170 °C to dissolve the MDC. Then replace the high-temperature salt bath and adjust the absolute pressure to 1 kPa. After the internal temperature reaches 230 °C, start the reaction for 60 min. After the reaction is completed, separate the catalyst from the reaction solution.

[0174] Liquid chromatography analysis showed that the MDC conversion rate was 91.85%, the MDI selectivity was 48.78%, and the total selectivity of MMI and MDI was 86.64%.

[0175] Example 24

[0176] The application of zinc-aluminum composite oxide catalysts in the catalytic thermal decomposition of diphenylmethane dicarboxylate to prepare isocyanate is as follows:

[0177] Add 10 g MDC (10 wt% of the total mass of the reaction system), 0.5 g of Zn3Al-700-A1B1 catalyst prepared in Example 1 (5 wt% of the mass of MDC), and 90 g of diisooctyl sebacate (DOS) solvent to a 250 mL three-necked flask. Stir and heat to 170 °C to dissolve the MDC. Then replace the high-temperature salt bath and adjust the absolute pressure to 1 kPa. After the internal temperature reaches 230 °C, start the reaction for 60 min. After the reaction is completed, separate the catalyst from the reaction solution.

[0178] Liquid chromatography analysis showed that the MDC conversion rate was 99.64%, the MDI selectivity was 68.53%, and the total selectivity of MMI and MDI was 85.31%.

[0179] Example 25

[0180] The application of zinc-aluminum composite oxide catalysts in the catalytic thermal decomposition of diphenylmethane dicarboxylate to prepare isocyanate is as follows:

[0181] Add 10 g MDC (10 wt% of the total mass of the reaction system), 0.02 g of Zn3Al-700-A1B1 catalyst prepared in Example 1 (0.2 wt% of the mass of MDC), and 90 g of diisooctyl sebacate (DOS) solvent to a 250 mL three-necked flask. Stir and heat to 170 °C to dissolve the MDC. Then replace the high-temperature salt bath and adjust the absolute pressure to 0.5 kPa. After the internal temperature reaches 230 °C, start the reaction for 60 min. After the reaction is completed, separate the catalyst from the reaction solution.

[0182] Liquid chromatography analysis showed that the MDC conversion rate was 98.82%, the MDI selectivity was 71.69%, and the total selectivity of MMI and MDI was 85.92%.

[0183] Example 26

[0184] The application of zinc-aluminum composite oxide catalysts in the catalytic thermal decomposition of diphenylmethane dicarboxylate to prepare isocyanate is as follows:

[0185] Add 10 g MDC (10 wt% of the total mass of the reaction system), 0.02 g of Zn3Al-700-A1B1 catalyst prepared in Example 1 (0.2 wt% of the mass of MDC), and 90 g of diisooctyl sebacate (DOS) solvent to a 250 mL three-necked flask. Stir and heat to 170 °C to dissolve the MDC. Then replace the high-temperature salt bath and adjust the absolute pressure to 2.5 kPa. After the internal temperature reaches 230 °C, start the reaction for 60 min. After the reaction is completed, separate the catalyst from the reaction solution.

[0186] Liquid chromatography analysis showed that the MDC conversion rate was 95.78%, the MDI selectivity was 52.02%, and the total selectivity of MMI and MDI was 88.32%.

[0187] Example 27

[0188] The application of zinc-aluminum composite oxide catalysts in the catalytic thermal decomposition of diphenylmethane dicarboxylate to prepare isocyanate is as follows:

[0189] Add 5 g MDC (5 wt% of the total mass of the reaction system), 0.01 g of Zn3Al-700-A1B1 catalyst prepared in Example 1 (0.2 wt% of the mass of MDC), and 95 g of diisooctyl sebacate (DOS) solvent to a 250 mL three-necked flask. Stir and heat to 170 °C to dissolve the MDC. Then replace the high-temperature salt bath and adjust the absolute pressure to 1 kPa. After the internal temperature reaches 230 °C, start the reaction for 60 min. After the reaction is completed, separate the catalyst from the reaction solution.

[0190] Liquid chromatography analysis showed that the MDC conversion rate was 99.70%, the MDI selectivity was 87.62%, and the total selectivity of MMI and MDI was 98.02%.

[0191] Example 28

[0192] The application of zinc-aluminum composite oxide catalysts in the catalytic thermal decomposition of diphenylmethane dicarboxylate to prepare isocyanate is as follows:

[0193] Add 20 g MDC (20 wt% of the total mass of the reaction system), 0.04 g of Zn3Al-700-A1B1 catalyst prepared in Example 1 (0.2 wt% of the mass of MDC), and 80 g of diisooctyl sebacate (DOS) solvent to a 250 mL three-necked flask. Stir and heat to 170 °C to dissolve the MDC. Then replace the high-temperature salt bath and adjust the absolute pressure to 1 kPa. After the internal temperature reaches 230 °C, start the reaction for 60 min. After the reaction is completed, separate the catalyst from the reaction solution.

[0194] Liquid chromatography analysis showed that the MDC conversion rate was 97.35%, the MDI selectivity was 59.68%, and the total selectivity of MMI and MDI was 85.13%.

[0195] Comparative Example 4

[0196] Add 10 g MDC (10 wt% of the total mass of the reaction system), 0.02 g of Al2O3-700-A4B1 catalyst prepared in Comparative Example 1 (0.2 wt% of the mass of MDC), and 90 g of diisooctyl sebacate (DOS) solvent to a 250 mL three-necked flask. Stir and heat to 170 °C to dissolve the MDC. Then replace the high-temperature salt bath and adjust the absolute pressure to 1 kPa. After the internal temperature reaches 230 °C, start the reaction for 60 min. After the reaction is completed, separate the catalyst from the reaction solution.

[0197] Liquid chromatography analysis showed that the MDC conversion rate was 94.85%, the MDI selectivity was 48.69%, and the total selectivity of MMI and MDI was 83.04%.

[0198] Comparative Example 5

[0199] Add 10 g MDC (10 wt% of the total mass of the reaction system), 0.02 g of ZnO-700-A5B1 catalyst prepared in Comparative Example 2 (0.2 wt% of the mass of MDC), and 90 g of diisooctyl sebacate (DOS) solvent to a 250 mL three-necked flask. Stir and heat to 170 °C to dissolve the MDC. Then replace the high-temperature salt bath and adjust the absolute pressure to 1 kPa. After the internal temperature reaches 230 °C, start the reaction for 60 min. After the reaction is completed, separate the catalyst from the reaction solution.

[0200] Liquid chromatography analysis showed that the MDC conversion rate was 92.16%, the MDI selectivity was 38.94%, and the total selectivity of MMI and MDI was 81.13%.

[0201] Comparative Example 6

[0202] Add 10 g MDC (10 wt% of the total mass of the reaction system), 0.02 g Zn3Al-mix prepared in Comparative Example 3 (0.2 wt% of the mass of MDC), and 90 g diisooctyl sebacate (DOS) solvent to a 250 mL three-necked flask. Stir and heat to 170 °C to dissolve the MDC. Then replace the high-temperature salt bath and adjust the absolute pressure to 1 kPa. After the internal temperature reaches 230 °C, start the reaction for 60 min. After the reaction is completed, separate the catalyst from the reaction solution.

[0203] Liquid chromatography analysis showed that the MDC conversion rate was 94.95%, the MDI selectivity was 51.31%, and the total selectivity of MMI and MDI was 84.08%.

[0204] The parameter changes in Examples 10-28 and Comparative Examples 4-6 are shown in Table 3:

[0205] Table 3

[0206]

[0207] Table 4 shows the MDC conversion rate, MDI selectivity, and total MMI+MDI selectivity data for Examples 10-28 and Comparative Examples 4-6:

[0208] Table 4

[0209]

[0210] As can be seen from Examples 1-28 and Comparative Examples 1-6 above, the zinc-aluminum composite oxide catalyst of the present invention achieves both activity and stability that are difficult to achieve with a single metal oxide system by forming a ZnO / ZnAl2O4 spinel biphase heterostructure. Compared with single alumina (Comparative Example 4, total selectivity 83.04%) or zinc oxide (Comparative Example 5, total selectivity 81.13%), the zinc-aluminum composite oxide catalyst utilizes the biphase synergistic effect of ZnO and ZnAl2O4 spinel to improve the conversion rate and total selectivity of the reaction, and makes a significant contribution to suppressing side reactions and improving the effective yield of isocyanates. Among them, Example 10 achieved a total selectivity of 95.62% for MMI and MDI under mild conditions (230 °C) and high feed concentration (10 wt%). In addition, the catalyst of the present invention has good reusability: its activity remains good after five consecutive cycles, and it can be regenerated by simple solvent washing, reducing the loss of metal active components and lowering the catalyst regeneration cost in industrial applications, thus showing good industrialization potential.

[0211] The embodiments described above merely illustrate specific implementation methods of this application, and while the descriptions are detailed and specific, they should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the technical solution of this application, and these modifications and improvements all fall within the scope of protection of this application.

Claims

1. A zinc-aluminum composite oxide catalyst, characterized in that: It is a composite oxide containing zinc and aluminum, and has a two-phase heterostructure of ZnO and ZnAl2O4 spinel.

2. The zinc-aluminum composite oxide catalyst according to claim 1, characterized in that: The Zn / Al molar ratio is 1:1 to 5:1, and the specific surface area is 24 to 100 m². 2 / g.

3. The zinc-aluminum composite oxide catalyst according to claim 2, characterized in that: The Zn / Al molar ratio is 2:1 to 4:1, and the specific surface area is 35 to 75 m². 2 / g.

4. A method for preparing the zinc-aluminum composite oxide catalyst according to claims 1-3, characterized in that: Includes the following steps: S1: Prepare a zinc-aluminum mixed salt solution; S2: The zinc-aluminum mixed salt solution and the alkaline precipitant solution are co-precipitated in parallel flow, followed by crystallization treatment; S3: After crystallization, the precursor is obtained by filtration, washing, and drying; S4: The precursor is calcined to obtain a zinc-aluminum composite oxide catalyst.

5. The method for preparing a zinc-aluminum composite oxide catalyst according to claim 4, characterized in that: The alkaline precipitant is an alkaline compound that can provide hydroxide ions and / or carbonate ions.

6. The method for preparing a zinc-aluminum composite oxide catalyst according to claim 4, characterized in that: The total metal ion concentration in S1 is 0.01~2.0 mol / L, and the concentration of the alkaline precipitant solution in S2 is 0.02~3.0 mol / L.

7. The method for preparing a zinc-aluminum composite oxide catalyst according to claim 4, characterized in that: In S1, zinc is derived from water-soluble zinc salts, which are one or more of zinc nitrate, zinc acetate, zinc chloride, zinc sulfate, and zinc formate; aluminum is derived from water-soluble aluminum salts, which are one or more of aluminum nitrate, aluminum acetate, aluminum chloride, and aluminum sulfate.

8. The method for preparing a zinc-aluminum composite oxide catalyst according to claim 4, characterized in that: The flow rate of the zinc-aluminum mixed salt solution and the alkaline precipitant solution in S2 is 1–6 mL / min; the pH in S2 is controlled at 7–9, and the crystallization treatment is carried out at a temperature of 60–90 °C for 1–6 hours.

9. The method for preparing a zinc-aluminum composite oxide catalyst according to claim 4, characterized in that: S3 is dried at 80-120 ℃ for 2-8 hours, and S4 is calcined at 500-900 ℃ for 2-6 hours.

10. The application of a zinc-aluminum composite oxide catalyst as described in any one of claims 1-3, or a zinc-aluminum composite oxide catalyst prepared by the method described in any one of claims 4-9, in the catalytic thermal decomposition of diphenylmethane dicarboxylate to prepare isocyanate, characterized in that: The mass fraction of diphenylmethane dicarboxylate in the reaction system is 5 wt%~20 wt%, the mass fraction of zinc-aluminum composite oxide catalyst in the reaction system is 0.05 wt%~5 wt%, the absolute pressure of the reaction is 0.5~2.5 kPa, the reaction temperature is 215 ℃~235 ℃, and the reaction time is 30~70 min.

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