A high-activity titanium silicon molecular sieve microsphere catalyst, preparation method and application thereof

Abstract

A high-activity titanium silicon molecular sieve microsphere catalyst, a preparation method and its application belong to the field of catalyst technology. Tetraethyl silicate, tetrapropylammonium hydroxide, deionized water and titanium silicon molecular sieve raw powder are used as raw materials to prepare a slurry containing titanium silicon molecular sieve, and titanium silicon molecular sieve microspheres are obtained after granulation; the slurry is evenly mixed with tetrabutylammonium hydroxide solution under water bath conditions to obtain modified titanium silicon molecular sieve microspheres; argon gas is then introduced into the reactor of the fluidized bed device to fluidize the modified titanium silicon molecular sieve microspheres, and the vaporized titanium tetrachloride is diluted and enters the reactor to react with the modified titanium silicon molecular sieve microspheres to obtain a high-activity titanium silicon molecular sieve microsphere catalyst. The present invention uses tetrabutylammonium hydroxide solution to locally etch the surface of the titanium silicon molecular sieve microspheres, increase the defect sites on the surface of the molecular sieve microspheres, promote the chemical bonding between titanium and the molecular sieve microspheres, and increase the content of tetracoordinated titanium on the catalyst, which can be used in propylene epoxidation reactions.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts, and specifically relates to a high-activity titanium silicon molecular sieve microsphere catalyst, a preparation method and application thereof, in particular to application in propylene epoxidation reaction. Background Art

[0002] In the 1970s, Eni of Italy first disclosed the synthesis of a titanium-doped molecular sieve (titanium silicate molecular sieve) with a microporous MFI topological structure. Subsequently, researchers found that the molecular sieve showed excellent catalytic performance in the propylene epoxidation to propylene oxide reaction. After a large number of experimental studies and in-situ characterization techniques, it was found that the mechanism of titanium silicate molecular sieve catalyzing propylene epoxidation is roughly as follows: the titanium active sites (tetracoordinated titanium) on the molecular sieve react with hydrogen peroxide to form a five-membered ring titanium peroxide, which then reacts with propylene to form propylene oxide (Yi Zuo, Min Liu, Ting Zhang, RSC Adv., 2015, 5, 17897~17904). The more titanium active sites (tetracoordinated titanium) in the molecular sieve, the more favorable it is for the synthesis of propylene oxide.

[0003] The traditional propylene epoxidation process uses a fixed bed reactor. Since the reaction generates a large amount of heat, hot spots are easily generated on the catalyst, which leads to increased carbon deposition and rapid deactivation. Slurry bed and fluidized bed reactors can effectively remove hot spots and increase the yield of propylene oxide, and have gradually become the research focus of scientific and technological personnel. Slurry bed and fluidized bed reactors usually use microspherical titanium silicon molecular sieves prepared by spray molding as catalysts.

[0004] Patent CN103212435B discloses a method for preparing a titanium silicate molecular sieve microsphere catalyst. The method uses a mixed solution of an organic base and a silica sol as a binder, mixes it with a titanium silicate molecular sieve, and then sprays the mixture to obtain a titanium silicate molecular sieve microsphere catalyst.

[0005] Patent CN104368382A discloses a method for preparing a titanium silicate molecular sieve microsphere catalyst, wherein a mixed solution of tetraethyl silicate and an organic base is used as a binder, which is mixed with the titanium silicate molecular sieve and then formed by a spray dryer to obtain a microsphere titanium silicate molecular sieve catalyst.

[0006] The titanium silicate molecular sieve microspheres prepared by the above spray molding are mainly composed of titanium silicate molecular sieve wrapped with a silicon oxide film. This method will cause some titanium active sites (tetracoordinated titanium) to be covered by the silicon oxide film and unable to play a role in the reaction. The titanium active sites (tetracoordinated titanium) are the main catalytic sites of titanium silicate molecular sieves. Therefore, the titanium active sites (tetracoordinated titanium) on the molecular sieve microspheres obtained by conventional spray drying are less exposed, which is not conducive to the complete epoxidation conversion of propylene in slurry bed and fluidized bed reactors. Summary of the invention

[0007] The purpose of the present invention is to provide a high-activity titanium silicalite molecular sieve microsphere catalyst, a preparation method and its application in propylene epoxidation reaction. The present invention improves the content of titanium active sites (tetracoordinated titanium) in titanium silicalite molecular sieve microspheres, thereby improving the activity of titanium silicalite molecular sieve microsphere catalysts in propylene liquid phase epoxidation, and further promotes the industrialization process of molecular sieve microsphere catalysts in propylene liquid phase epoxidation fluidized bed reaction process.

[0008] The method for preparing a high-activity titanium silicon molecular sieve microsphere catalyst of the present invention comprises the following steps:

[0009] (1) Tetraethyl silicate, tetrapropylammonium hydroxide and deionized water were mixed for 4-6 hours, and then titanium silicate raw powder was added and mixed evenly, wherein the mass ratio of tetraethyl silicate, tetrapropylammonium hydroxide, deionized water and titanium silicate raw powder was 1:0.4-0.6:1.4-2.0:0.8-1.2, and a slurry containing titanium silicate was obtained; the granulation was carried out by spray drying, and then washed with water, centrifuged and dried (100-120 °C) to obtain titanium silicate microspheres;

[0010] (2) The titanium silicalite microspheres obtained in step (1) are mixed evenly with an aqueous solution of tetrabutylammonium hydroxide at a solid-liquid mass ratio of 1:25-30 in a water bath, and then washed with water, centrifuged, dried (90-110°C), and calcined at 500-560°C to obtain modified titanium silicalite microspheres; wherein the concentration of the aqueous solution of tetrabutylammonium hydroxide is in the range of 0.01-0.06 mol / L;

[0011] (3) The modified titanium silicate microspheres obtained in step (2) are loaded into a reactor of a fluidized bed device, argon gas at 30-50 mL / min is introduced to fluidize the modified titanium silicate microspheres, the reactor temperature is raised to 520-560°C and kept constant for 0.5-2.0 h, and then the reactor temperature is lowered to 360-450°C; the titanium tetrachloride solution is added to the vaporizer through a metering pump, and the vaporized titanium tetrachloride is diluted with argon gas at 80-120 mL / min and then enters the reactor of the fluidized bed device to react with the modified titanium silicate microspheres; finally, the metering pump is closed, and argon gas is introduced to purge and cool the modified titanium silicate microspheres after reacting with titanium tetrachloride, thereby obtaining the high-activity titanium silicate microsphere catalyst.

[0012] Furthermore, in step (1), the feed inlet temperature of the spray dryer is 280-300°C, the discharge port temperature is 100-120°C, and the atomizer speed of the spray dryer is 8,000-10,000 rpm;

[0013] Furthermore, in step (2), the water bath temperature is 35-45°C and the mixing time is 2-4 h;

[0014] Furthermore, in step (3), the feed rate of the titanium tetrachloride solution is 0.1-0.5 mL / min, and the temperature of the vaporizer is 250-300 °C;

[0015] Furthermore, in step (3), the volume fraction of gaseous titanium tetrachloride after argon dilution is 15% to 35%, and the mass ratio of titanium tetrachloride solution to modified titanium silicalite microspheres is 0.05 to 0.15:1; these conditions affect the titanium active content and chemical coordination properties of titanium on the final catalyst, and thus have a great influence on the activity of the catalyst;

[0016] Furthermore, in step (3), the titanium tetrachloride gas and the modified titanium silicate molecular sieve microspheres are reacted for 2 to 8 minutes.

[0017] The preparation technology of titanium silicon molecular sieve raw powder refers to patent US4,410,501, which is a technology that technicians in this field are familiar with. The particle size of the molecular sieve is about 200 nm.

[0018] The centrifugal spray dryer and fluidized bed apparatus are well-known and used instruments in the art, wherein the reactor of the fluidized bed apparatus is a stainless steel tube with an inner diameter of 20 mm, a length of 280 mm and a wall thickness of 2 mm.

[0019] The high-activity titanium silicon molecular sieve microsphere catalyst of the present invention is prepared by the above method.

[0020] The high-activity titanium silicon molecular sieve microsphere catalyst of the present invention can be used in propylene epoxidation reaction. The catalyst performance is evaluated by using a high-pressure reactor commonly used in the art, the reactor volume is 300 mL, and the material is 316 L.

[0021] The catalyst performance evaluation process is as follows: 32 mL of methanol and 4 mL of hydrogen peroxide (mass fraction of 35 wt%) are weighed and loaded into a high-pressure reactor, and then 0.2 g of the high-activity titanium silicon molecular sieve microsphere catalyst prepared by the present invention is added and mixed evenly; first, argon is introduced to remove the air in the reactor, and then propylene is introduced instead, and the pressure in the reactor is adjusted to 0.4 MPa; then the reaction is carried out in a 43°C water bath for 1 h. After the reaction, the concentration of hydrogen peroxide is determined by an automatic potentiometric titrator, and the selectivity of the liquid product is determined by a gas chromatograph (the liquid product will have a signal peak in the gas spectrometer, and the molar amount of the liquid product can be obtained by comparing the signal peak of the liquid product with the signal peak of the standard sample in the chromatogram, which can then be used to calculate the selectivity of the product). Automatic potentiometric titrators and gas chromatographs are well-known and commonly used instruments.

[0022] Beneficial effects of the present invention:

[0023] (1) The present invention uses a tetrabutylammonium hydroxide aqueous solution to locally etch the surface of the titanium silicon molecular sieve microspheres, thereby increasing the defect sites on the surface of the molecular sieve microspheres and promoting the chemical bonding between titanium and the molecular sieve microspheres;

[0024] (2) Under certain conditions, the gaseous titanium tetrachloride diluted with argon undergoes chemical bonding with the surface of the molecular sieve microspheres, replenishing the content of titanium active sites (tetracoordinated titanium) on the surface of the titanium silicate molecular sieve microspheres, further enhancing the activity of the titanium silicate molecular sieve microsphere catalyst in the propylene epoxidation reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 : Flow chart of the titanium supplementation process of the high-activity titanium silicon molecular sieve microsphere catalyst based on the fluidized bed device described in the present invention. DETAILED DESCRIPTION

[0026] The present invention is further described below through specific examples and comparative examples, but the protection scope of the present invention is not limited to the scope of the examples.

[0027] The chemical reagents used in the embodiments and comparative examples are all common drugs on the market, the gases used are all high-purity gases sold by gas companies on the market, and the water used is deionized water made in the laboratory.

[0028] Comparative Example 1: This comparative example illustrates the preparation method of a conventional titanium silicon molecular sieve microsphere catalyst. 15g of silica sol (30wt% solid content, the solid component is mainly silicon dioxide), 7.5g of tetrapropylammonium hydroxide and 26g of deionized water were mixed for 5h, and then 16g of titanium silicon molecular sieve raw powder was added and mixed evenly, wherein the mass ratio of silica sol, tetrapropylammonium hydroxide, deionized water and titanium silicon molecular sieve raw powder was 1:0.5:1.73:1.06, and a slurry containing titanium silicon molecular sieve was obtained; the feed inlet temperature was 300℃, the discharge port temperature was 120℃, and the atomizer speed was 10,000 rpm, and the formed sample was washed, centrifuged, dried, and calcined at 550℃ to obtain titanium silicon molecular sieve microsphere particles (the product mass was about 13.5g, and a small number of broken particles passed through the cyclone separator of the spray drying device into the waste bag), marked as catalyst A.

[0029] Comparative Example 2: This comparative example illustrates the preparation method of a conventional titanium silicon molecular sieve microsphere catalyst. 17.4g of tetraethyl silicate, 8.5g of tetrapropylammonium hydroxide, and 27g of deionized water were mixed for 5h, and then 16g of titanium silicon molecular sieve raw powder was added and mixed evenly, wherein the mass ratio of tetraethyl silicate, tetrapropylammonium hydroxide, deionized water, and titanium silicon molecular sieve raw powder was 1:0.48:1.55:0.91, and a slurry containing titanium silicon molecular sieve was obtained; the slurry was sprayed and formed by a centrifugal spray dryer under the conditions of a feed inlet temperature of 280°C, a discharge outlet temperature of 110°C, and an atomizer speed of 8,000 rpm, and the formed sample was washed, centrifuged, dried, and calcined at 550°C to obtain titanium silicon molecular sieve microsphere particles (product mass is about 14.5g), which are marked as catalyst B. Example 1

[0030] This example illustrates a method for preparing a highly active titanium silicon molecular sieve microsphere catalyst. 17.4g of tetraethyl silicate, 8.5g of tetrapropylammonium hydroxide, and 25g of deionized water were mixed for 5h, and then 16g of titanium silicon molecular sieve raw powder was added and mixed evenly, wherein the mass ratio of tetraethyl silicate, tetrapropylammonium hydroxide, deionized water, and titanium silicon molecular sieve raw powder was 1:0.48:1.55:0.91, and a slurry containing titanium silicon molecular sieve was obtained; a centrifugal spray dryer was used for spray molding, the feed inlet temperature was 300℃, the discharge port temperature was 120℃, and the atomizer speed was 10,000 rpm. The molded sample was washed, centrifuged, and dried to obtain titanium silicon molecular sieve microspheres (the product mass was about 13.5g). Take 10g of titanium silicalite microspheres and 250g of tetrabutylammonium hydroxide aqueous solution (concentration of 0.03mol / L) and mix them in a 40℃ water bath for 4h. The solid-liquid mass ratio of titanium silicalite microspheres to tetrabutylammonium hydroxide aqueous solution is 1:25. Then, wash with water, centrifuge, dry, and calcine at 520℃ to obtain modified titanium silicalite microspheres (product mass is about 9.2g).

[0031] like Figure 1The figure shows the titanium supplementation process flow chart of high-activity titanium silicalite microsphere catalyst based on fluidized bed device. 8g of modified titanium silicalite microspheres were loaded into the reactor of fluidized bed device, 30mL / min argon was introduced to fluidize the catalyst, the reactor temperature was raised to 550℃ and kept constant for 1h, and then the reactor temperature was lowered to 420℃. Subsequently, the titanium tetrachloride solution (pure solution, concentration of 99.9%) was added to the vaporizer (the temperature of the vaporizer was 280°C) at a rate of 0.3 mL / min through a metering pump. The vaporized titanium tetrachloride was diluted with argon (the flow rate was adjusted to 100 mL / min) and then entered the reactor to react with the molecular sieve microsphere catalyst (the volume fraction of gaseous titanium tetrachloride after argon dilution was 25%, and the mass ratio of titanium tetrachloride solution to modified titanium silicon molecular sieve microspheres was 0.10:1). After 3 minutes, the metering pump was turned off; finally, argon was introduced to purge and cool the modified titanium silicon molecular sieve microspheres after the reaction with titanium tetrachloride to obtain a high-activity titanium silicon molecular sieve microsphere catalyst sample, marked as catalyst C (the product mass was about 7.6 g), and the tail gas generated during the reaction was recovered and treated. Two one-way valves are set on the pipeline between the vaporizer and the reactor, one for controlling the one-way flow of vaporized titanium tetrachloride to the reactor, and the other for controlling the one-way flow of argon to the reactor. Example 2

[0032] This embodiment illustrates a method for preparing a high-titanium titanium silicon molecular sieve microsphere catalyst. Take 17.4g of tetraethyl silicate, 9.5g of tetrapropylammonium hydroxide, and 34g of deionized water and mix them evenly, then add 19.5g of titanium silicon molecular sieve raw powder and mix them, wherein the mass ratio of tetraethyl silicate, tetrapropylammonium hydroxide, deionized water and titanium silicon molecular sieve raw powder is 1:0.55:1.95:1.10, and obtain a slurry containing titanium silicon molecular sieve; then use a centrifugal spray dryer to spray the slurry under the conditions of a feed inlet temperature of 280°C, a discharge port temperature of 100°C, and an atomizer speed of 8,000 rpm, and the molded sample is washed with water, centrifuged, and dried to obtain titanium silicon molecular sieve microspheres (the product mass is about 16.5g, and a small number of broken particles pass through the cyclone separator of the spray drying device and enter the waste bag). Then, 10 g of titanium silicalite microspheres were mixed with 300 g of tetrabutylammonium hydroxide aqueous solution (concentration of 0.06 mol / L) in a 35°C water bath for 2 h, and the solid-liquid mass ratio of the titanium silicalite microspheres to the tetrabutylammonium hydroxide aqueous solution was 1:30. The mixture was then washed with water, centrifuged, dried, and calcined at 550°C to obtain modified titanium silicalite microsphere particles (product mass of about 9.3 g).

[0033] Then, 9g of modified titanium silicon molecular sieve microspheres were loaded into the reactor of the fluidized bed device, and argon was introduced to fluidize the catalyst. The reactor was heated to 550℃ and kept at a constant temperature for 1h, and then the reactor temperature was reduced to 380℃. Subsequently, titanium tetrachloride solution (pure solution, concentration of 99.9%) was added to the vaporizer (the temperature of the vaporizer was 300℃) at a rate of 0.1mL / min through a metering pump. The vaporized titanium tetrachloride was diluted with argon (the flow rate was adjusted to 90mL / min) and then entered the reactor to react with the molecular sieve microsphere catalyst (the volume fraction of gaseous titanium tetrachloride after argon dilution was 18%, and the mass ratio of titanium tetrachloride solution to modified titanium silicon molecular sieve microspheres was 0.07:1). After 6min of interaction, the metering pump was turned off; finally, argon was introduced to purge and cool the modified titanium silicon molecular sieve microspheres after the reaction with titanium tetrachloride, and a high-activity titanium silicon molecular sieve microsphere catalyst sample was obtained, which was marked as catalyst D (the product mass was about 8.9g).

[0034] ICP-AES was used to test the titanium content in the catalysts in the comparative examples and the embodiments, and FI-IR was used to test the infrared absorption peaks of the catalysts in the comparative examples and the embodiments, wherein 960 cm -1 and 800cm -1 The ratio of the absorption peak intensities at 960 / I 800 ) reflects the content of tetracoordinated titanium in the catalyst (Chinese Journal of Catalysis, Teng Xue, Huaping Liu, Yimeng Wang, 36 (2015) 1928–1935), the results are shown in Table 1:

[0035] Table 1: Titanium content data of catalysts in comparative examples and examples

[0036] sample Ti content in catalyst (wt%) <![CDATA[I 960 / I 800 ]]> Catalyst A 1.09 0.65 Catalyst B 1.12 0.63 Catalyst C 1.32 0.82 Catalyst D 1.35 0.81

[0037] From the ICP-AES characterization results, it can be obtained that the titanium content on the titanium silicate molecular sieve microspheres in the embodiment is increased compared with the control example. From the FT-IR characterization results, it can be obtained that the active titanium content on the titanium silicate molecular sieve microspheres in the embodiment is greatly improved, indicating that the tetracoordinate titanium content of the titanium silicate molecular sieve microspheres can be increased by the method in the embodiment.

[0038] The catalytic performance of the catalysts in the comparative example and the example was evaluated by propylene epoxidation reaction. The results are shown in Table 2:

[0039] Table 2: Catalytic performance evaluation data of catalysts in comparative examples and examples

[0040] sample <![CDATA[H2O2 conversion rate (%)]]> Propylene oxide selectivity (%) Catalyst A 48 87.2 Catalyst B 56 86.3 Catalyst C 68 86.2 Catalyst D 67 86.9

[0041] It can be seen from the experimental data that compared with the traditional titanium silicalite microspheres in the comparative example, the titanium silicalite microspheres prepared by the preparation method of the present invention have significantly improved H2O2 conversion in the propylene epoxidation reaction, while the propylene oxide selectivity is not affected.

[0042] The above results show that the active titanium content of the titanium silicate molecular sieve microspheres can be increased by the method described in the examples, thereby achieving an improvement in the catalytic performance of the titanium silicate molecular sieve microspheres.

[0043] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a high-activity titanium silicon molecular sieve microsphere catalyst, characterized in that: The steps of the preparation method are as follows, (1) Tetraethyl silicate, tetrapropylammonium hydroxide and deionized water were mixed for 4-6 hours, and then titanium silicate raw powder was added and mixed evenly, wherein the mass ratio of tetraethyl silicate, tetrapropylammonium hydroxide, deionized water and titanium silicate raw powder was 1:0.4-0.6:1.4-2.0:0.8-1.2, and a slurry containing titanium silicate was obtained; the granulation was carried out by spray drying, and then washed, centrifuged and dried to obtain titanium silicate microspheres; the feed inlet temperature of the spray dryer was 280-300 °C, the discharge port temperature was 100-120 °C, and the atomizer speed of the spray dryer was 8,000-10,000 rpm; (2) The titanium silicalite microspheres obtained in step (1) are mixed evenly with a tetrabutylammonium hydroxide aqueous solution at a solid-liquid mass ratio of 1:25-30 in a water bath, and then washed with water, centrifuged, dried, and calcined at 500-560°C to obtain modified titanium silicalite microspheres; the water bath temperature is 35-45°C, the mixing time is 2-4 h; the concentration range of the tetrabutylammonium hydroxide aqueous solution is 0.01-0.06 mol / L; (3) The modified titanium silicate microspheres obtained in step (2) are loaded into a reactor of a fluidized bed device, and 30-50 mL / min argon gas is introduced to fluidize the modified titanium silicate microspheres. The reactor is heated to 520-560 °C and kept at a constant temperature for 0.5-2.0 h, and then the reactor temperature is reduced to 360-450 °C; the titanium tetrachloride solution is added to the vaporizer through a metering pump, and the vaporized titanium tetrachloride is diluted with 80-120 mL / min argon gas and then enters the reactor of the fluidized bed device to react with the modified titanium silicate microspheres; finally, the metering pump is closed, and argon gas is introduced to purge and cool the modified titanium silicate microspheres after reacting with titanium tetrachloride, thereby obtaining the high-activity titanium silicate microsphere catalyst; the feed rate of the titanium tetrachloride solution is 0.1-0.5 mL / min, and the temperature of the vaporizer is 250-300 ℃; the action time of titanium tetrachloride gas and molecular sieve is 2~8min; the volume fraction of gaseous titanium tetrachloride after argon dilution is 15%~35%, and the mass ratio of titanium tetrachloride solution to modified titanium silicalite molecular sieve microspheres is 0.05~0.15:

1.

2. A highly active titanium silicon molecular sieve microsphere catalyst, characterized in that: The preparation method is as claimed in claim 1.

3. Use of the high-activity titanium silicon molecular sieve microsphere catalyst according to claim 2 in propylene epoxidation reaction.

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