Preparation method for olefin epoxidation catalyst and applications thereof

Abstract

Disclosed in the present invention are a preparation method for an olefin epoxidation catalyst and applications thereof. The method comprises: loading an auxiliary metal salt onto a silica gel carrier, and carrying out a drying treatment to the silica gel carrier; loading a titanium salt (preferably TiCl.sub.4) onto the silica gel carrier by a chemical vapor deposition method; calcining to obtain a silica gel on which the auxiliary metal oxide and Ti species are loaded; obtaining an catalyst precursor (Ti-MeO—SiO.sub.2 composite oxide) by water vapor washing; loading alkyl silicate (preferably tetraethyl orthosilicate) onto the surface of the catalyst precursor by a chemical vapor deposition method and calcining the catalyst precursor to obtain a Ti-MeO—SiO.sub.2 composite oxide with the surface coated with a SiO.sub.2 layer; and carrying out a silylanization treatment to obtain the catalyst. The catalyst can be applied to a chemical process of propylene epoxidation to prepare propylene oxide, and has an average selectivity to PO up to 96.7%, the method of the present invention and the applications thereof have industrial application prospects.

Claims

1. A preparation method for an olefin epoxidation catalyst, which comprises the following steps: (1) loading an auxiliary metal salt onto a silica gel carrier to obtain an auxiliary metal salt modified silica gel carrier A; (2) carrying out a drying treatment for the A obtained in step (1); (3) carrying out a chemical vapor deposition for the dried A using a titanium salt vapor to obtain a silica gel B on which the auxiliary metal salt and the titanium salt, are loaded; (4) calcining the B obtained in step (3) to obtain a silica gel C on which the auxiliary metal salt and Ti species are loaded; (5) carrying out a water vapor washing for the C obtained in step (4) to obtain a Ti-MeO—SiO.sub.2 composite oxide; (6) carrying out a vapor deposition for the Ti-MeO—SiO.sub.2 composite oxide using an alkyl silicate vapor to obtain the Ti-MeO—SiO.sub.2 composite oxide D having a silicon-containing compound loaded on the surface of the composite oxide (7) calcining the D obtained in step (6) to obtain a Ti-MeO—SiO.sub.2 composite oxide having a SiO2 layer coated on the surface of the composite oxide, which is referred to as SiO2—Ti-MeO—SiO2; (8) carrying out a silylanization treatment for the SiO2—Ti-MeO—SiO2 obtained in step (7), wherein the auxiliary metal salt in the step (1) is selected from the group consisting of Ce(NO3).sub.3, Pr(NO.sub.3).sub.3, Tb(NO.sub.3).sub.3, La(NO.sub.3).sub.3, and combinations thereof.

2. The method according to claim 1, wherein in step (1) the auxiliary metal salt is added in an amount ranging from 0.6-2.4 wt % based on the mass of the silica gel carrier.

3. The method according to claim 1, wherein the silica gel carrier used in step (1) is a C-type silica gel.

4. The method according to claim 3, wherein the silica gel carrier used in step (1) has a spherical shape or is a block C-type silica gel.

5. The method according to claim 3, wherein the silica gel carrier used in step (1) is an irregular blocky C-type silica gel.

6. The method according to claim 3, wherein the silica gel carrier used in step (1) has a specific surface area of 100-350 m2/g, an average pore diameter of 8-11 nm, a pore volume of 0.7-1.2 ml/g, a Na2O impurity content of <100 ppm, a Fe2O3 impurity content of <500 ppm and a size of a spherical equivalent diameter of 0.5-2 mm.

7. The method according to claim 1, wherein in step (2), the drying temperature is 150-240° C. and drying time is 120 min-240 min.

8. The method according to claim 1, wherein based on the weight of the silica gel carrier used in step (1), in step (3), Ti is loaded on the silica gel carrier in an amount ranges from 0.1-5.0 wt %.

9. The method according to claim 8, wherein Ti is loaded on the silica gel carrier in an amount from 2.5-4.5 wt %.

10. The method according to claim 8, wherein the chemical vapor deposition of step (3) is carried out in a reaction tube, the dried A is charged in the reaction tube, an inert gas is used to introduce the titanium salt vapor into the reaction tube, the inert gas has a flow rate of 0.05-2.0 cm/s, the chemical vapor deposition temperature of the reaction is 150-300° C., and the chemical vapor deposition time is 120-240 min.

11. The method according to claim 1, wherein the calcination in step (4) is carried out in a N.sub.2 atmosphere, at a temperature ranging from 450-700° C. a time ranging from 30-240 min, and the flow rate of N.sub.2 is 0.05-2.0 cm/s.

12. The method according to claim 1, wherein the water vapor used for water vapor washing in step (5) has a temperature of 100-200° C.; based on the amount of the Ti element in the titanium salt vapor used in step (3), the molar ratio of the water vapor to Ti is 20-150:1, the water vapor washing time is 180-240 min.

13. The method according to claim 12, wherein the water vapor used for water vapor washing in step (5) has a temperature of 120-180° C., and based on the amount of the Ti element in the titanium salt vapor used in step (3), the molar ratio of the water vapor to Ti is 50-100:1.

14. The method according to claim 12, wherein the water vapor washing of step (5) is carried out in a reaction tube, water vapor is introduced into the reaction tube using an inert gas at a flow rate of 1-2.5 cm/s.

15. The method according to claim 1, wherein the alkyl silicate vapor used in step (6) is heated to a temperature of 166-200° C.; the vapor deposition of step (6) is carried out in a reaction tube, and the alkyl silicate vapor is introduced into the reaction tube using an inert gas; the flow rate of the inert gas in the reaction tube is 0.05-2.0 cm/s, the reaction temperature is 166-200° C., the deposition time is 120-180 min, and the weight ratio of alkyl silicate to the silica gel carrier used in step (1) is 0.5-1:1.

16. The method according to claim 1, wherein the calcination in step (7) is carried out in air atmosphere at a temperature of 500-700° C., with a calcination time of 30-120 min, and the flow rate of air is 0.5-1 cm/s.

17. The method according to claim 1, wherein the silylanization reagent used for the silylanization treatment in step (8) is hexamethyl disilylamine, based on the weight of the silica gel carrier used in step (1), hexamethyl disilylamine is used in an amount of 5 wt %-15 wt %; the temperature of hexamethyl disilylamine used in step (8) is 126-150° C.; the silylanization treatment is carried out in a reaction tube, the silylanization reagent is introduced into the reaction tube using an inert gas, the flow rate of the inert gas in the reaction tube is 0.5-1 cm/s, the silylanization temperature is 200-300° C., and the silylanization time is 60-180 min.

18. A method for catalyzing propylene epoxidation to prepare propylene oxide, comprising contacting a feed with the catalyst prepared by the method according to claim 1 and recovering the propylene oxide.

19. The method according to claim 18, wherein the contacting conditions for catalyzing propylene epoxidation to prepare propylene oxide are as follows: a reaction temperature of 40-120° C., a gauge pressure of 2-4.5 MPa, a molar ratio of propylene to ethylbenzene hydroperoxide of 3-10:1 and a mass space velocity of 1-5 h.sup.−1.

20. The method according to claim 1, wherein the titanium salt vapor is TiCl.sub.4 vapor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram showing the process flow of a catalyst preparation device.

(2) Description of the reference signs: 1 represents a alkyl silicate vaporization tank, 2 represents a TiCl.sub.4 vaporization tank, 3 represents a water and silylanization reagent vaporization tank; 4 represents an exhaust gas absorption tank; and 5 represents a reaction tube.

DETAILED DESCRIPTION

(3) In order to understand the present disclosure better, the present disclosure will be further illustrated below with reference to the embodiments, but the content of the present disclosure is not limited thereto.

(4) The Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) used in the examples of the present disclosure was produced by Agilent Technologies, model 720 ICP-OES;

(5) In the examples of the present disclosure, the content of PO (propylene oxide) in the reaction liquid and the exhaust gas absorption liquid was analyzed by gas chromatography, and the conversion rate of EBHP (ethylbenzene hydroperoxide) was analyzed by iodimetry. The conditions of chromatography are shown in Table 1.

(6) TABLE-US-00001 TABLE 1 Operating conditions of Chromatography Chromatographic column Agilent 19091N-133 (30 m × 250 μm × 0.25 μm) Flow rate of H.sub.2 35 mL/min Flow rate of air 350 mL/min Flow rate of makeup gas (N.sub.2) 25 mL/min Heater 270° C. Column box 250° C. Heating procedure Initial temperature: 50° C. Heating program: 50-100° C., 15° C./min, maintaining for 0 min, 100-250° C., 20° C./min, maintaining for 2 min Split ratio of injection port 30:1 Temperature of FID detector 270° C.

(7) The content of PO was determined by internal standard method. The liquid phase concentration was determined using DMF as the solvent and DT (dioxane) as the internal standard substance. The internal standard curve of PO and DT was determined to be y=0.6985x−0.0046, R.sup.2=0.999; the concentration of PO in gas phase absorption liquid was determined using toluene as the internal standard substance, the internal standard curve of PO and toluene was determined to be y=2.161x+0.0002, R.sup.2=0.999.

(8) Concentration of PO in liquid phase=(0.6985×(A.sub.PO/A.sub.DT)−0.0046)×0.01×dilution ratio, A represents the peak area, the same below;

(9) Content of PO in liquid phase=concentration of PO in liquid phase×mass of sample in liquid phase;

(10) Concentration of PO in gas phase=(2.162×(A.sub.PO/A.sub.toluene)+0.0002)×mass of toluene;

(11) Content of PO in gas phase=concentration of PO in gas phase×total amount of absorption liquid/amount of sample in gas phase;

(12) Total production amount of PO=content of PO in gas phase+content of PO in liquid phase;

(13) Selectivity to PO=total production amount of PO/amount of PO theoretically produced from propylene oxidized by EBHP (ethylbenzene hydroperoxide)×100%.

(14) The conversion rate of EBHP was titrated by iodimetry and measured by a titrator.

(15) Conversion rate of EBHP=(initial value of EBHP−residual amount of EBHP)/initial value of EBHP.

(16) Residual amount of EBHP=(titration end point−blank)×C.sub.Na.sub.2.sub.S.sub.2.sub.O.sub.3×0.001×0.5×142×total amount of liquid sample/sample amount for titration, wherein C.sub.Na.sub.2.sub.S.sub.2.sub.O.sub.3 is the concentration of sodium thiosulfate.

(17) The silica gel carrier used in the examples or the comparative examples is an irregular blocky C-type silica gel carrier, which is provided by Qingdao GuiChuang Fine Chemical Co., Ltd., and has a silica gel particle size (spherical equivalent diameter) of 0.6-1.1 mm, a specific surface area of 256 m.sup.2/g, an average pore diameter of 9.2 nm, a pore volume of 0.94 ml/g, a water absorption rate of 1.12 g water/g of silica gel (saturated water absorption), a Na.sub.2O impurity content of 89 ppm and a Fe.sub.2O.sub.3 impurity content of 327 ppm.

(18) The process conditions for propylene epoxidation to produce propylene oxide in the examples and comparative examples are as follows: the oxidant is ethylbenzene hydroperoxide (EBHP), the reaction tube is a fixed bed reactor with an inner diameter of 24 mm, and the catalyst is loaded in an amount of 10 g; the molar ratio of propylene to EBHP is 5:1, the mass space velocity is 4 h.sup.−1; the initial reaction temperature is 50° C., and the reaction temperature is gradually increased according to the conversion rate of EBHP (the conversion rate of EBHP was guaranteed to be >99%).

Example 1

(19) 0.36 g of Ce(NO.sub.3).sub.3 was weighed and dissolved in 33.6 g of distilled water, sprayed onto 30 g of silica gel carrier, to settle for 2 hours and then dried at 80° C. The product obtained in this step was called auxiliary metal salt modified silica gel carrier A (or referred to as product A or A for short).

(20) As shown in FIG. 1, the silica gel carrier on which Ce(NO.sub.3).sub.3 was loaded (i.e., product A) was charged into reaction tube 5 and dried at 180° C. for 120 min in N.sub.2 atmosphere, and the linear velocity of N.sub.2 in reaction tube 5 was 1.2 cm/s. Dried A was obtained in this step.

(21) Chemical vapor deposition of TiCl.sub.4: 2.98 g of TiCl.sub.4 was added to TiCl.sub.4 vaporization tank 2 which was then heated at a temperature of 137° C., TiCl.sub.4 vapor was introduced into reaction tube 5 using N.sub.2 to react with the silica gel, the linear velocity of N.sub.2 in reaction tube 5 was 0.5 cm/s, the deposition time was 120 min (the reaction temperature of this step was the same as the drying temperature in the previous step, which was 180° C.); the product obtained in this step was called auxiliary metal salt and TiCl.sub.4 loaded silica gel B (referred to as silica gel B or B for short).

(22) Calcination: the temperature was raised to 500° C. at a heating rate of 2° C./min, the linear velocity of N.sub.2 in reaction tube 5 was 1 cm/s, and the silica gel B was calcined for 120 min; the product obtained in this step was called auxiliary metal oxide and Ti species loaded silica gel C (or referred to as C for short).

(23) Water washing: 14.1 g of distilled water was added to water and silylanization reagent vaporization tank 3 which was then heated at a temperature of 120° C., water vapor was introduced into reaction tube 5 using N.sub.2 for water washing the obtained silica gel C, the linear velocity of N.sub.2 in the reaction tube was 1 cm/s and the water washing time was 180 min; the product obtained by water vapor washing was referred to as a Ti-MeO—SiO.sub.2 composite oxide.

(24) Chemical vapor deposition of alkyl silicate: 15 g of tetraethyl orthosilicate was added to alkyl silicate vaporization tank 1 which was then heated at a temperature of 166° C., tetraethyl orthosilicate vapor was introduced into the reaction tube using N.sub.2 to react with the silica gel, the linear velocity of N.sub.2 in the reaction tube was 0.5 cm/s, and the deposition time was 120 min (the reaction temperature of this step was the same as the temperature at which the alkyl silicate vaporization tank was heated, which was 166° C.); the product obtained in this step was called a Ti-MeO—SiO.sub.2 composite oxide D having a silicon-containing compound loaded on the surface of the composite oxide (or referred to as product D);

(25) Calcination: the temperature was raised to 500° C. at a heating rate of 3° C./min, the linear velocity of air in the reaction tube was 0.5 cm/s, and the product D was calcined for 120 min; a product having a SiO.sub.2 layer coated on the surface was obtained by calcination, the product was called a Ti-MeO—SiO.sub.2 composite oxide having a SiO.sub.2 layer coated on the surface, or is referred to as SiO.sub.2—Ti-MeO—SiO.sub.2.

(26) Silylanization treatment: 4.5 g of hexamethyl disilylamine was added to water and silylanization reagent vaporization tank 3 which was then heated at a temperature of 130° C., the hexamethyl disilylamine vapor was introduced into the reaction tube using N.sub.2 to react with the silica gel (the silica gel refers to the product obtained by calcination, SiO.sub.2—Ti-MeO—SiO.sub.2), the linear velocity of N.sub.2 in the reaction tube was 1 cm/s, the silylanization temperature was 200° C., and the silylanization time was 180 min; the obtained catalyst is referred to as TS-C1.

(27) Exhaust gas absorption tank 4 was used for absorbing TiCl.sub.4 that was not loaded on the carrier and HCl gas generated during the calcination and water washing procedure.

(28) The TS-C1 was evaluated. The catalyst was used for propylene epoxidation to produce propylene oxide, operated continuously for 1000 hr, the reaction temperature was raised from the initial 50° C. to 80° C., and sampled for gas chromatography analysis. The EBHP conversion rate was >99.9%, the highest selectivity to PO reached 96.4%, the average selectivity reached 95.2%. The product was collected for ICP-OES analysis and no catalyst component Ti was found.

Example 2

(29) 0.48 g of Pr(NO.sub.3).sub.3 was weighed and dissolved in 33.6 g of distilled water, sprayed onto 30 g of silica gel carrier, allowed to settle for 2 hours and then dried at 80° C.

(30) As shown in FIG. 1, the silica gel carrier on which Pr(NO.sub.3).sub.3 was loaded was charged into a reaction tube and dried at 200° C. for 180 min in N.sub.2 atmosphere, and the linear velocity of N.sub.2 in the reaction tube was 1.6 cm/s.

(31) Chemical vapor deposition of TiCl.sub.4: 3.57 g of TiCl.sub.4 was added to a TiCl.sub.4 vaporization tank which was then heated at a temperature of 140° C., TiCl.sub.4 vapor was introduced into the reaction tube using N.sub.2 to react with the silica gel, the linear velocity of N.sub.2 in the reaction tube was 0.7 cm/s, the deposition time was 180 min (the reaction temperature of this step was the same as the drying temperature in the previous step, which was 200° C.);

(32) Calcination: the temperature was raised to 550° C. at a heating rate of 2° C./min, the linear velocity of N.sub.2 in the reaction tube was 1.5 cm/s, the calcination lasted for 180 min;

(33) Water washing: 26.7 g of distilled water was added to a water and silylanization reagent vaporization tank which was then heated at a temperature of 140° C., water vapor was introduced into the reaction tube using N.sub.2 for water washing, the linear velocity of N.sub.2 in the reaction tube was 1.5 cm/s and the water washing time was 180 min;

(34) Chemical vapor deposition of alkyl silicate: 21 g of tetraethyl orthosilicate was added to a alkyl silicate vaporization tank which was then heated at a temperature of 170° C., tetraethyl orthosilicate vapor was introduced into the reaction tube using N.sub.2 to react with the silica gel, the linear velocity of N.sub.2 in the reaction tube was 0.8 cm/s, and the deposition time was 150 min (the reaction temperature of this step was the same as the temperature at which the alkyl silicate vaporization tank was heated, which was 170° C.);

(35) Calcination: the temperature was raised to 550° C. at a heating rate of 3° C./min, the linear velocity of air in the reaction tube was 0.7 cm/s, the calcination lasted for 60 min;

(36) Silylanization treatment: 3 g of hexamethyl disilylamine was added to a water and silylanization reagent vaporization tank which was then heated at a temperature of 135° C., hexamethyl disilylamine vapor was introduced into the reaction tube using N.sub.2 to react with the silica gel, the linear velocity of N.sub.2 in the reaction tube was 0.7 cm/s, the silylanization temperature was 200° C., and the silylanization time was 150 min; the obtained catalyst was referred to as TS-C2.

(37) The TS-C2 was evaluated. The catalyst was used for propylene epoxidation to produce propylene oxide, operated continuously for 1550 hr, the reaction temperature was raised from the initial 50° C. to 85° C., and sampled for gas chromatography analysis. The EBHP conversion rate was >99.9%, the highest selectivity to PO reached 96.7%, the average selectivity reached 95.1%. The product was collected for ICP-OES analysis and no catalyst component Ti was found.

Example 3

(38) 0.6 g of Tb(NO.sub.3).sub.3 was weighed and dissolved in 33.6 g of distilled water, sprayed onto 30 g of silica gel carrier, allowed to settle for 2 hours and then dried at 80° C.

(39) As shown in FIG. 1, the silica gel carrier on which Tb(NO.sub.3).sub.3 was loaded was charged into a reaction tube and dried at 240° C. for 240 min in N.sub.2 atmosphere, and the linear velocity of N.sub.2 in the reaction tube was 2 cm/s.

(40) Chemical vapor deposition of TiCl.sub.4: 4.17 g of TiCl.sub.4 was added to a TiCl.sub.4 vaporization tank which was then heated at a temperature of 145° C., TiCl.sub.4 vapor was introduced into the reaction tube using N.sub.2 to react with the silica gel, the linear velocity of N.sub.2 in the reaction tube was 0.8 cm/s, the deposition time was 200 min (the reaction temperature of this step was the same as the drying temperature in the previous step, which was 240° C.);

(41) Calcination: the temperature was raised to 600° C. at a heating rate of 2° C./min, the linear velocity of N.sub.2 in the reaction tube was 2 cm/s, the calcination lasted for 200 min;

(42) Water washing: 33.5 g of distilled water was added to a water and silylanization reagent vaporization tank which was then heated at a temperature of 160° C., water vapor was introduced into the reaction tube using N.sub.2 for water washing, the linear velocity of N.sub.2 in the reaction tube was 2 cm/s and the water washing time was 200 min;

(43) Chemical vapor deposition of alkyl silicate: 27 g of tetraethyl orthosilicate was added to a alkyl silicate vaporization tank which was then heated at a temperature of 180° C., tetraethyl orthosilicate vapor was introduced into the reaction tube using N.sub.2 to react with the silica gel, the linear velocity of N.sub.2 in the reaction tube was 0.9 cm/s, and the deposition time was 180 min (the reaction temperature of this step was the same as the temperature at which the alkyl silicate vaporization tank was heated, which was 180° C.);

(44) Calcination: the temperature was raised to 600° C. at a heating rate of 3° C./min, the linear velocity of air in the reaction tube was 0.8 cm/s, the calcination lasted for 60 min;

(45) Silylanization treatment: 2.4 g of hexamethyl disilylamine was added to a water and silylanization reagent vaporization tank which was then heated at a temperature of 140° C., hexamethyl disilylamine vapor was introduced into the reaction tube using N.sub.2 to react with the silica gel, the linear velocity of N.sub.2 in the reaction tube was 0.5 cm/s, the silylanization temperature was 250° C., and the silylanization time was 120 min; the obtained catalyst was referred to as TS-T3.

(46) The TS-T3 was evaluated. The catalyst was used for propylene epoxidation to produce propylene oxide, operated continuously for 1800 hr, the reaction temperature was raised from the initial 50° C. to 90° C., and sampled for gas chromatography analysis. The EBHP conversion rate was >99.9%, the highest selectivity to PO reached 97.8%, the average selectivity reached 96.7%. The product was collected for ICP-OES analysis and no catalyst component Ti was found.

Example 4

(47) 0.72 g of La(NO.sub.3).sub.3 was weighed and dissolved in 33.6 g of distilled water, sprayed onto 30 g of silica gel carrier, allowed to settle for 2 hours and then dried at 80° C.

(48) As shown in FIG. 1, the silica gel carrier on which La(NO.sub.3).sub.3 was loaded was charged into a reaction tube and dried at 220° C. for 120 min in N.sub.2 atmosphere, and the linear velocity of N.sub.2 in the reaction tube was 2.5 cm/s.

(49) Chemical vapor deposition of TiCl.sub.4: 5.36 g of TiCl.sub.4 was added to a TiCl.sub.4 vaporization tank which was then heated at a temperature of 150° C., TiCl.sub.4 vapor was introduced into the reaction tube using N.sub.2 to react with the silica gel, the linear velocity of N.sub.2 in the reaction tube was 1.35 cm/s, the deposition time was 240 min (the reaction temperature of this step was the same as the drying temperature in the previous step, which was 220° C.);

(50) Calcination: the temperature was raised to 550° C. at a heating rate of 2° C./min, the linear velocity of N.sub.2 in the reaction tube was 2.5 cm/s, and the calcination lasted for 240 min;

(51) Water washing: 50.7 g of distilled water was added to a water and silylanization reagent vaporization tank which was then heated at a temperature of 180° C., water vapor was introduced into the reaction tube using N.sub.2 for water washing, the linear velocity of N.sub.2 in the reaction tube was 2.5 cm/s and the water washing time was 240 min;

(52) Chemical vapor deposition of alkyl silicate: 30 g of tetraethyl orthosilicate was added to a alkyl silicate vaporization tank which was then heated at a temperature of 200° C., the tetraethyl orthosilicate vapor was introduced into the reaction tube using N.sub.2 to react with the silica gel, the linear velocity of N.sub.2 in the reaction tube was 1 cm/s, and the deposition time was 180 min (the reaction temperature of this step was the same as the temperature at which the alkyl silicate vaporization tank was heated, which was 200° C.);

(53) Calcination: the temperature was raised to 700° C. at a heating rate of 3° C./min, the linear velocity of air in the reaction tube was 1 cm/s, the calcination lasted for 30 min;

(54) Silylanization treatment: 1.8 g of hexamethyl disilylamine was added to a water and silylanization reagent vaporization tank which was then heated at a temperature of 150° C., hexamethyl disilylamine vapor was introduced into the reaction tube using N.sub.2 to react with the silica gel, the linear velocity of N.sub.2 in the reaction tube was 0.6 cm/s, the silylanization time was 150 min; the silylanization temperature was 300° C., the obtained catalyst was referred to as TS-L4.

(55) The TS-L4 was evaluated. The catalyst was used for propylene epoxidation to produce propylene oxide, operated continuously for 1200 hr, the reaction temperature was raised from the initial 50° C. to 75° C., and sampled for gas chromatography analysis. The EBHP conversion rate was >99.9%, the highest selectivity to PO reached 96.8%, the average selectivity reached 95.6%. The product was collected for ICP-OES analysis and no catalyst component Ti was found.

Comparative Example 1

(56) 0.6 g of Tb(NO.sub.3).sub.3 was weighed and dissolved in 33.6 g of distilled water, sprayed onto 30 g of silica gel carrier, allowed to settle for 2 hours and then dried at 80° C.

(57) The silica gel carrier on which Tb(NO.sub.3).sub.3 was loaded was charged into the reaction tube and dried at 240° C. for 240 min in N.sub.2 atmosphere, and the linear velocity of N.sub.2 in the reaction tube was 2 cm/s.

(58) Chemical vapor deposition of TiCl.sub.4: 4.17 g of TiCl.sub.4 was added to a TiCl.sub.4 vaporization tank which was then heated at a temperature of 145° C., TiCl.sub.4 vapor was introduced into the reaction tube using N.sub.2 to react with the silica gel, the linear velocity of N.sub.2 in the reaction tube was 0.8 cm/s, the deposition time was 200 min (the reaction temperature of this step was the same as the drying temperature in the previous step, which was 240° C.);

(59) Calcination: the temperature was raised to 600° C. at a heating rate of 2° C./min, the linear velocity of N.sub.2 in the reaction tube was 2 cm/s, and calcination lasted for 200 min;

(60) Water washing: 33.5 g of distilled water was added to a water and silylanization reagent vaporization tank which was then heated at a temperature of 160° C., water vapor was introduced into the reaction tube using N.sub.2 for water washing, the linear velocity of N.sub.2 in the reaction tube was 2 cm/s and the water washing time was 200 min;

(61) Silylanization treatment: 2.4 g of hexamethyl disilylamine was added to a water and silylanization reagent vaporization tank which was then heated at a temperature of 140° C., the hexamethyl disilylamine vapor was introduced into the reaction tube using N.sub.2 to react with the silica gel, the linear velocity of N.sub.2 in the reaction tube was 0.5 cm/s, the silylanization temperature was 250° C., and the silylanization time was 120 min; the obtained catalyst was referred to as TS-B4.

(62) The TS-B4 was evaluated. The catalyst was used for propylene epoxidation to produce propylene oxide, operated continuously for 750 hr, the reaction temperature was raised from the initial 50° C. to 80° C., and sampled for gas chromatography analysis. The EBHP conversion rate was >99.9%, the highest selectivity to PO reached 97.5%, the average selectivity reached 95.7%. The product was collected for ICP-OES analysis, the content of the catalyst component Ti in the product was about 313 ppm; the Ti content in the fresh catalyst was about 3.42%, the Ti content in the catalyst after evaluation was about 2.61%, and the loss rate reached 23.7%.

Comparative Example 2

(63) 30 g of silica gel carrier was weighed and charged into the reaction tube and dried at 240° C. for 240 min in N.sub.2 atmosphere, and the linear velocity of N.sub.2 in the reaction tube was 2 cm/s.

(64) Chemical vapor deposition of TiCl.sub.4: 4.17 g of TiCl.sub.4 was added to a TiCl.sub.4 vaporization tank which was then heated at a temperature of 145° C., the TiCl.sub.4 vapor was introduced into the reaction tube using N.sub.2 to react with the silica gel, the linear velocity of N.sub.2 in the reaction tube was 0.8 cm/s, the deposition time was 200 min (the reaction temperature of this step was the same as the drying temperature in the previous step, which was 240° C.);

(65) Calcination: the temperature was raised to 600° C. at a heating rate of 2° C./min, the linear velocity of N.sub.2 in the reaction tube was 2 cm/s, the calcination lasted for 200 min;

(66) Water washing: 33.5 g of distilled water was added to a water and silylanization reagent vaporization tank which was then heated at a temperature of 160° C., the water vapor was introduced into the reaction tube using N.sub.2 for water washing, the linear velocity of N.sub.2 in the reaction tube was 2 cm/s and the water washing time was 200 min;

(67) Chemical vapor deposition of alkyl silicate: 27 g of tetraethyl orthosilicate was added to a alkyl silicate vaporization tank which was then heated at a temperature of 180° C., tetraethyl orthosilicate vapor was introduced into the reaction tube using N.sub.2 to react with the silica gel, the linear velocity of N.sub.2 in the reaction tube was 0.9 cm/s, and the deposition time was 180 min (the reaction temperature of this step was the same as the temperature at which the alkyl silicate vaporization tank was heated, which was 180° C.);

(68) Calcination: the temperature was raised to 600° C. at a heating rate of 3° C./min, the linear velocity of air in the reaction tube was 0.8 cm/s, the calcination lasted for 60 min;

(69) Silylanization treatment: 2.4 g of hexamethyl disilylamine was added to a water and silylanization reagent vaporization tank which was then heated at a temperature of 140° C., hexamethyl disilylamine vapor was introduced into the reaction tube using N.sub.2 to react with the silica gel, the linear velocity of N.sub.2 in the reaction tube was 0.5 cm/s, the silylanization temperature was 250° C., and the silylanization time was 120 min; the obtained catalyst was referred to as TS-01.

(70) The TS-01 was evaluated. The catalyst was used for propylene epoxidation to produce propylene oxide, operated continuously for 1500 hr, the reaction temperature was raised from the initial 50° C. to 100° C., and sampled for gas chromatography analysis. The EBHP conversion rate was >99.9%, the highest selectivity to PO reached 94.6%, the average selectivity reached 92.1%. The product was collected for ICP-OES analysis and no catalyst component Ti was found.

Comparative Example 3

(71) 30 g of silica gel carrier was weighed and charged into the reaction tube and dried at 240° C. for 240 min in N.sub.2 atmosphere, and the linear velocity of N.sub.2 in the reaction tube was 2 cm/s.

(72) Chemical vapor deposition of TiCl.sub.4: 4.17 g of TiCl.sub.4 was added to a TiCl.sub.4 vaporization tank which was then heated to a temperature of 145° C., TiCl.sub.4 vapor was introduced into the reaction tube using N.sub.2 to react with the silica gel, the linear velocity of N.sub.2 in the reaction tube was 0.8 cm/s, the deposition time was 200 min (the reaction temperature was the same as the drying temperature in the previous step, which was 200° C.);

(73) Calcination: the temperature was raised to 600° C. at a heating rate of 2° C./min, the linear velocity of N.sub.2 in the reaction tube was 2 cm/s, and the calcination lasted for 200 min;

(74) Water washing: 33.5 g of distilled water was added to a water and silylanization reagent vaporization tank which was then heated at a temperature of 160° C., the water vapor was introduced into the reaction tube using N.sub.2 for water washing, the linear velocity of N.sub.2 in the reaction tube was 2 cm/s and the water washing time was 200 min;

(75) Calcination: the temperature was raised to 600° C. at a heating rate of 3° C./min, the linear velocity of air in the reaction tube was 0.8 cm/s, the calcination lasted for 60 min;

(76) Silylanization treatment: 2.4 g of hexamethyl disilylamine was added to a water and silylanization reagent vaporization tank which was then heated at a temperature of 140° C., hexamethyl disilylamine vapor was introduced into the reaction tube using N.sub.2 to react with the silica gel, the linear velocity of N.sub.2 in the reaction tube was 0.5 cm/s, the silylanization temperature was 250° C., and the silylanization time was 120 min; the obtained catalyst was referred to as TS-02.

(77) The TS-02 was evaluated. The catalyst was used for propylene epoxidation to produce propylene oxide, operated continuously for 620 hr, the reaction temperature was raised from the initial 50° C. to 95° C., and sampled for gas chromatography analysis. The EBHP conversion rate was >99.9%, the highest selectivity to PO reached 93.6%, the average selectivity reached 91.1%; the Ti content in the fresh catalyst was about 3.45%, the product was collected for ICP-OES analysis, the Ti content in the catalyst after evaluation was about 2.56%, and the loss rate reached 25.8%.

(78) The experimental results of the examples and the comparative examples show that the catalysts prepared by the preparation methods of the present disclosure had good catalyst stabilities during use, the activities and selectivities of the catalysts did not change significantly during the observation time, and the activities were stable; Ti element was not found in the product of each example, indicating that the active component in the catalyst was not lost. It can be seen that the catalysts prepared by the preparation methods of the present disclosure can reduce the loss of the Ti active centers during use, the catalyst activities were stable, the service lives of the catalysts were improved; and the catalysts had high selectivities to PO.