Preparation method for propylene epoxidation catalyst, and application thereof

Abstract

A preparation method for a propylene epoxidation catalyst: pre-hydrolyzing a silicon source, adding a titanium source and reacting to form a sol, atomizing the sol and then spraying it into liquid ammonia for molding, implementing pore broadening, and performing drying, calcination, and silanization treatment to obtain a Ti—SiO.sub.2 composite oxide catalyst. The present catalyst can be used in the chemical process of preparing propylene oxide by epoxidation of propylene, the average propylene oxide selectivity being up to 97.5%, having prospects for industrial application.

Claims

1. A preparation method for a propylene epoxidation catalyst, comprising the following steps: (1) pre-hydrolysis of silicon source: dissolving a silicon ester in a lower alcohol, adding a hydrolysis catalyst and water to react to obtain liquid A; (2) sol formation: dissolving a titanium ester in a lower alcohol and adding the obtained system to liquid A; adding water or adding a mixed aqueous solution of NH.sub.4ReO.sub.4 and a zinc salt to react to obtain a sol; (3) atomizing the sol obtained in step (2) and spraying the atomized sol into liquid ammonia to obtain a catalyst precursor; (4) carrying out a pore broadening treatment to the catalyst precursor obtained in step (3); (5) drying and calcining the pore broadened catalyst precursor in step (4); (6) carrying out a silanization treatment to the product obtained in step (5).

2. The method according to claim 1, wherein the silicon ester in step (1) is selected from the group consisting of tetraethyl orthosilicate, tetramethyl orthosilicate, tetrapropyl orthosilicate and tetrabutyl orthosilicate and combinations thereof.

3. The method according to claim 1, wherein the hydrolysis catalyst in step (1) is one of acetic acid and formic acid or a mixture thereof.

4. The method according to claim 3, wherein, in step (1), the hydrolysis catalyst is added in an amount that is 0.8-1.5 wt % of the silicon ester; water is added in an amount that is the amount of water theoretically required to hydrolyze 30-80 wt % of the silicon ester; the reaction temperature in step (1) is 40-70° C., and the reaction time is 1-3 h.

5. The method according to claim 1, wherein the titanium ester used in step (2) is selected from the group consisting of tetramethyl titanate, tetraethyl titanate, tetrapropyl titanate, tetraisopropyl titanate, tetrabutyl titanate and tetraisobutyl titanate and combinations thereof.

6. The method according to claim 5, wherein, based on the weight of SiO.sub.2 corresponding to SiO.sub.2 from the complete hydrolysis of the raw silicon ester in step (1), the amount of Ti in the titanium ester used in step (2) is 2-5% of the weight of SiO.sub.2; in step (2), the concentration of the titanium ester in the lower alcohol is 30-50 wt %; the reaction time in step (2) is 1˜4 h.

7. The method according claim 1, wherein in step (2), the molar ratio of Re in the used NH.sub.4ReO.sub.4 to Ti in the used titanium ester is 0.01-0.05:1, and the molar ratio of Zn in the used zinc salt to Ti in the used titanium ester is 0.05-0.15:1.

8. The method according to claim 7, wherein in step (2), if water is added for the reaction to form a sol, water is added in an amount that is the amount of water required for theoretical complete hydrolysis of the unhydrolyzed silicone ester in step (1) and the titanium ester in step (2); in step (2), if the mixed aqueous solution of NH.sub.4ReO.sub.4 and a zinc salt is added for the reaction to form a sol, the amount of water contained in the mixed aqueous solution of NH.sub.4ReO.sub.4 and a zinc salt is the amount of water required for theoretical complete hydrolysis of the unhydrolyzed silicone ester in step (1) and the titanium ester in step (2).

9. The method according to claim 7, wherein a pore broadening agent used in step (4) for performing the pore broadening treatment is liquid ammonia.

10. The method according to claim 9, wherein the process conditions for the pore broadening treatment in step (4) include: the pore broadening temperature is 60-140° C., and the pore broadening time is 3-15 h.

11. The method according to claim 1, wherein in step (2), if water is added for the reaction to form a sol, water is added in an amount that is the amount of water required for theoretical complete hydrolysis of the unhydrolyzed silicone ester in step (1) and the titanium ester in step (2); in step (2), if the mixed aqueous solution of NH.sub.4ReO.sub.4 and a zinc salt is added for the reaction to form a sol, the amount of water contained in the mixed aqueous solution of NH.sub.4ReO.sub.4 and a zinc salt is the amount of water required for theoretical complete hydrolysis of the unhydrolyzed silicone ester in step (1) and the titanium ester in step (2).

12. The method according to claim 11, wherein a pore broadening agent used in step (4) for performing the pore broadening treatment is liquid ammonia.

13. The method according to claim 12, wherein the process conditions for the pore broadening treatment in step (4) include: the pore broadening temperature is 60-140° C., and the pore broadening time is 3-15 h.

14. The method according to claim 1, wherein an atomizer is used in the step (3) to atomize the sol, and the sol sprayed by the atomizer has an average particle diameter that is from 100 to 850 μm.

15. The method according to claim 14, wherein the sol sprayed by the atomizer has an average particle diameter that is from 400 to 580 μm.

16. The method according to claim 1, wherein a pore broadening agent used in step (4) for performing the pore broadening treatment is liquid ammonia.

17. The method according to claim 16, wherein the process conditions for the pore broadening treatment in step (4) include: the pore broadening temperature is 60-140° C., and the pore broadening time is 3-15 h.

18. The method according to claim 1, wherein in the step (5), the drying temperature is 80-120° C.; the calcination temperature is 450-600° C.

19. The method according to claim 1, wherein a silanization agent used in the silanization treatment in step (6) is hexamethyldisilazane; based on the weight of SiO.sub.2 corresponding to the SiO.sub.2 from complete hydrolysis of the raw silicon ester in step (1), the amount of the hexamethyldisilazane used is 5-15 wt %.

20. The method according to claim 19, wherein the temperature of hexamethyldisilazane used for the silanization treatment is 126-150° C., the temperature of the silanization treatment is 200-300° C., and the time of the silanization treatment is 60-180 min.

21. The method according to claim 1, wherein the lower alcohol in step (1) and step (2) is selected from C1-C3 alcohols.

22. A method for preparing propylene oxide, comprising contacting under epoxidation conditions a feedstock with the catalyst prepared by the method according to claim 1 to produce a product comprising said propylene oxide.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an XRD pattern of the catalyst of Example 1;

(2) FIG. 2 is an XRD pattern of the catalyst of Example 2;

(3) FIG. 3 is an XRD pattern of the catalyst of Example 3;

(4) FIG. 4 is an XRD pattern of the catalyst of Example 4;

(5) FIG. 5 is an XRD pattern of the catalyst of Comparative Example 2.

EMBODIMENT

(6) In order to better understand the present invention, the content of the present invention is further clarified below with reference to the examples, but the content of the present invention is not limited to the following examples.

(7) The method for measuring the specific surface area and the pore structure in the examples of the present invention is the BET method (N.sub.2 physical adsorption method), the model number of the instrument is ASP2020, produced by Micromeritics Instruments Corporation, USA.

(8) The strength tester in the examples of the present invention is KC-3 digital display particle strength tester, produced by Analytical Instrument Factory of Jiangyan.

(9) In the examples of the present invention, the content of PO in the reaction liquid and the exhaust gas absorption liquid was analyzed by gas chromatography, and the conversion rate of CHP was analyzed by iodimetry. The conditions of chromatography are shown in Table 1.

(10) TABLE-US-00001 TABLE 1 Conditions for chromatographic operation 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 25 mL/min (N.sub.2) Heater 270° C. Column box 250° C. Heating procedure Initial temperature: 50° C. Heating program: 50° C.-100° C. 15° C./min maintaining for 0 min 100° C.-250° C. 20° C./min maintaining for 2 min Split ratio of injection 30:1 port Temperature of FID 270° C. detector

(11) 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.
Concentration of PO in liquid phase=(0.6985×(A.sub.PO/A.sub.DT)−0.0046)×0.01×dilution ratio;
Content of PO in liquid phase=concentration of PO in liquid phase×weight of sample in liquid phase;
Concentration of PO in gas phase=(2.162×(A.sub.PO/A.sub.toluene)+0.0002)×weight of toluene;
Content of PO in gas phase=concentration of PO in gas phase×total amount of absorption liquid/amount of sample in gas phase;
Total production amount of PO=content of PO in gas phase+content of PO in liquid phase;
Selectivity to PO=total production amount of PO/amount of PO theoretically produced from propylene oxidized by CHP×100%;

(12) The conversion rate of CHP was titrated by iodimetry and measured by a titrator.
Conversion rate of CHP=(initial value of CHP−residual amount of CHP)/initial value of CHP.
Residual amount of CHP=(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.

(13) The silicon ester used in the examples is tetraethyl orthosilicate, and the titanium ester is tetrabutyl titanate.

(14) When the catalyst is evaluated in the following examples and comparative examples, the process conditions for catalyzing the epoxidation of propylene to produce propylene oxide are as follows: the oxidant is cumyl hydroperoxide (CHP), and the reaction tube is a fixed-bed reactor with an inner diameter of 24 mm, the loading amount of the catalyst is 10 g; the molar ratio of propylene to CHP is 7:1, the mass space velocity is 3.5 hr.sup.−1; the initial reaction temperature is 50° C., and the reaction temperature is gradually increased according to the CHP conversion rate (CHP conversion rate is guaranteed to be >99%).

EXAMPLES

Example 1

(15) 208 g of tetraethyl orthosilicate was dissolved in 792 g of isopropanol, then 1.67 g of formic acid was added as a hydrolysis catalyst, 10.8 g of deionized water was added dropwise, and the reaction was carried out at 50° C. for 1 h, the obtained liquid was denoted as liquid A;

(16) 8.5 g of tetrabutyl titanate was weighed and dissolved in 19.8 g of isopropanol, the obtained solution was added dropwise to liquid A, stirred evenly and the obtained liquid was denoted as liquid B; 0.067 g of NH.sub.4ReO.sub.4 and 0.17 g of ZnCl.sub.2 were weighed and dissolved in 25.2 g of deionized water, the obtained solution was added dropwise to liquid B, stirred evenly and the obtained liquid was denoted as liquid C. The liquid C was reacted for 4 h to form a sol;

(17) The sol was sprayed into liquid ammonia using a centrifugal atomizer for molding, a catalyst precursor was obtained;

(18) Then, the catalyst precursor was subjected to a pore broadening treatment at 80° C. for 15 h (with liquid ammonia as the pore broadening agent).

(19) The pore broadened catalyst precursor was dried in an oven at 80° C. for 2 h, and calcined in a muffle furnace at 550° C. for 3 h.

(20) The calcined sample was subjected to a gas-phase silanization treatment: 3 g of hexamethyldisilazane was added to the vaporization tank, the heating temperature of the vaporization tank was 130° C., the hexamethyldisilazane vapor was brought into the reaction tube with N.sub.2 to react with the calcined sample, the linear velocity of N.sub.2 in the reaction tube was 1 cm/s, the silanization temperature was 200° C. and the silanization time was 180 min; the obtained catalyst was denoted as TS-A1.

(21) The specific surface area of the TS-A1 catalyst was 278.9 m.sup.2/g, the pore volume was 0.93 ml/g, the average pore diameter was 9.7 nm, determined by the BET method; the average strength was 26.2 N/particle. XRD characterization of the TS-A1 catalyst (see FIG. 1) did not obtain any diffraction peaks of Ti species (TiO.sub.2 or other Ti-containing compounds), the results can reflect a good dispersion of Ti species from one aspect. The TS-A1 was evaluated and continuously operated for 480 hours, the reaction temperature was increased from the initial 50° C. to 65° C., samples were taken for gas chromatography analysis, the CHP conversion rate was >99.9%, and the selectivity to PO was up to 96.8% with an average of 96.1%.

Example 2

(22) 249.6 g of tetraethyl orthosilicate was dissolved in 750.4 g of isopropanol, then 2.5 g of formic acid was added as a hydrolysis catalyst, 21.6 g of deionized water was added dropwise, and the reaction was carried out at 60° C. for 90 min, the obtained liquid was denoted as liquid A;

(23) 17.85 g of tetrabutyl titanate was weighed and dissolved in 26.78 g of isopropanol, the obtained solution was added dropwise to liquid A, stirred evenly and the obtained liquid was denoted as liquid B; 0.422 g of NH.sub.4ReO.sub.4 and 0.714 g of ZnCl.sub.2 were weighed and dissolved in 21.6 g of deionized water, the obtained solution was added dropwise to liquid B, stirred evenly and the obtained liquid was denoted as liquid C. The liquid C was reacted for 2 h to form a sol;

(24) The sol was sprayed into liquid ammonia using a centrifugal atomizer for molding, a catalyst precursor was obtained;

(25) Then, the catalyst precursor was subjected to a pore broadening treatment at 120° C. for 6 h (with liquid ammonia as the pore broadening agent).

(26) The pore broadened catalyst precursor was dried in an oven at 100° C. for 3 h, and calcined in a muffle furnace at 450° C. for 5 h.

(27) The calcined sample was subjected to a gas-phase silanization treatment: 7.2 g of hexamethyldisilazane was added to the vaporization tank, the heating temperature of the vaporization tank was 140° C., the hexamethyldisilazane vapor was brought into the reaction tube with N.sub.2 to react with the calcined sample, the linear velocity of N.sub.2 in the reaction tube was 0.5 cm/s, the silanization temperature was 250° C. and the silanization time was 120 min; the obtained catalyst was denoted as TS-A2.

(28) The specific surface area of the TS-A2 catalyst was 248.4 m.sup.2/g, the pore volume was 1.04 ml/g, the average pore diameter was 11 nm, determined by the BET method; the average strength was 27.1 N/particle. XRD characterization of the TS-A2 catalyst (see FIG. 2) did not obtain any diffraction peaks of Ti species (TiO.sub.2 or other Ti-containing compounds), the results can reflect a good dispersion of Ti species from one aspect.

(29) The TS-A2 was evaluated and continuously operated for 1000 hours, the reaction temperature was increased from the initial 50° C. to 80° C., samples were taken for gas chromatography analysis, the CHP conversion rate was >99.9%, and the selectivity to PO was up to 97.8% with an average of 97.5%.

Example 3

(30) 291.2 g of tetraethyl orthosilicate was dissolved in 707.8 g of isopropanol, then 4.36 g of acetic acid was added as a hydrolysis catalyst, 50.4 g of deionized water was added dropwise, and the reaction was carried out at 70° C. for 140 min, the obtained liquid was denoted as liquid A;

(31) 29.75 g of tetrabutyl titanate was weighed and dissolved in 29.75 g of isopropanol, the obtained solution was added dropwise to liquid A, stirred evenly and the obtained liquid was denoted as liquid B; 1.172 g of NH.sub.4ReO.sub.4 and 1.785 g of ZnCl.sub.2 were weighed and dissolved in 10.08 g of deionized water, the obtained solution was added dropwise to liquid B, stirred evenly and the obtained liquid was denoted as liquid C. The liquid C was reacted for 1 h to form a sol;

(32) The sol was sprayed into liquid ammonia using a centrifugal atomizer for molding, a catalyst precursor was obtained;

(33) Then, the catalyst precursor was subjected to a pore broadening treatment at 140° C. for 3 h (with liquid ammonia as the pore broadening agent).

(34) The pore broadened catalyst precursor was dried in an oven at 120° C. for 5 h, and calcined in a muffle furnace at 600° C. for 2 h.

(35) The calcined sample was subjected to a gas-phase silanization treatment: 12.6 g of hexamethyldisilazane was added to the vaporization tank, the heating temperature of the vaporization tank was 150° C., the hexamethyldisilazane vapor was brought into the reaction tube with N.sub.2 to react with the calcined sample, the linear velocity of N.sub.2 in the reaction tube was 0.6 cm/s, the silanization time was 100 min and the silanization temperature was 300° C.; the obtained catalyst was denoted as TS-A3.

(36) The specific surface area of the TS-A3 catalyst was 208.6 m.sup.2/g, the pore volume was 1.2 ml/g, the average pore diameter was 12.8 nm, determined by the BET method; the average strength was 26.0 N/particle. XRD characterization of the TS-A3 catalyst (see FIG. 3) did not obtain any diffraction peaks of Ti species (TiO.sub.2 or other Ti-containing compounds), the results can reflect a good dispersion of Ti species from one aspect.

(37) The TS-A3 was evaluated and continuously operated for 800 hours, the reaction temperature was increased from the initial 50° C. to 90° C., samples were taken for gas chromatography analysis, the CHP conversion rate was >99.9%, and the selectivity to PO was up to 97.2% with an average of 96.9%.

Example 4

(38) 249.6 g of tetraethyl orthosilicate was dissolved in 750.4 g of isopropanol, then 2.5 g of formic acid was added as a hydrolysis catalyst, 21.6 g of deionized water was added dropwise, and the reaction was carried out at 60° C. for 90 min, the obtained liquid was denoted as liquid A;

(39) 17.85 g of tetrabutyl titanate was weighed and dissolved in 26.78 g of isopropanol, the obtained solution was added dropwise to liquid A, stirred evenly and the obtained liquid was denoted as liquid B; 21.6 g of deionized water was added dropwise to liquid B. The liquid B was reacted for 3 h to form a sol;

(40) The sol was sprayed into liquid ammonia using a centrifugal atomizer for molding, a catalyst precursor was obtained;

(41) Then, the catalyst precursor was subjected to a pore broadening treatment at 120° C. for 6 h (with liquid ammonia as the pore broadening agent).

(42) The pore broadened catalyst precursor was dried in an oven at 100° C. for 3 h, and calcined in a muffle furnace at 450° C. for 5 h.

(43) The calcined sample was subjected to a gas-phase silanization treatment: 7.2 g of hexamethyldisilazane was added to the vaporization tank, the heating temperature of the vaporization tank was 140° C., the hexamethyldisilazane vapor was brought into the reaction tube with N.sub.2 to react with the calcined sample, the linear velocity of N.sub.2 in the reaction tube was 0.5 cm/s, the silanization temperature was 250° C. and the silanization time was 120 min; the obtained catalyst was denoted as TS-A4.

(44) The specific surface area of the TS-A4 catalyst was 248.2 m.sup.2/g, the pore volume was 1.04 ml/g, the average pore diameter was 11 nm, determined by the BET method; the average strength was 26.6 N/particle. XRD characterization of the TS-A4 catalyst (see FIG. 4) did not obtain any diffraction peaks of Ti species (TiO.sub.2 or other Ti-containing compounds), the results can reflect a good dispersion of Ti species from one aspect.

(45) The TS-A4 was evaluated and continuously operated for 600 hours, the reaction temperature was increased from the initial 60° C. to 90° C., samples were taken for gas chromatography analysis, the CHP conversion rate was >99.9%, and the selectivity to PO was up to 93.8% with an average of 92.7%.

Comparative Example 1

(46) 249.6 g of tetraethyl orthosilicate was dissolved in 750.4 g of isopropanol, then 2.5 g of formic acid was added as a hydrolysis catalyst, 21.6 g of deionized water was added dropwise, and the reaction was carried out at 60° C. for 90 min, the obtained liquid was denoted as liquid A;

(47) 17.85 g of tetrabutyl titanate was weighed and dissolved in 26.78 g of isopropanol, the obtained solution was added dropwise to liquid A, stirred evenly and the obtained liquid was denoted as liquid B; 21.6 g of deionized water was added dropwise to liquid B, stirred evenly and the obtained liquid was denoted as liquid C. The liquid C was reacted for 1 h to form a sol;

(48) The sol was aged for 12 h to form a gel.

(49) The gel was then dried in an oven at 100° C. for 3 h, crushed, sieved for particles of 0.4-1.2 mm, and calcined in a muffle furnace at 450° C. for 5 h.

(50) The calcined sample was subjected to a gas-phase silanization treatment: 7.2 g of hexamethyldisilazane was added to the vaporization tank, the heating temperature of the vaporization tank was 140° C., the hexamethyldisilazane vapor was brought into the reaction tube with N.sub.2 to react with the calcined sample, the linear velocity of N.sub.2 in the reaction tube was 0.5 cm/s, the silanization temperature was 250° C. and the silanization time was 120 min; the obtained catalyst was denoted as TS-A5.

(51) The specific surface area of the TS-A5 catalyst was 17.6 m.sup.2/g, the pore volume was 12.3 ml/g, the average pore diameter was 1.2 nm, determined by the BET method; the average strength of a single particle was 14.2 N/particle.

(52) The TS-A5 was evaluated and continuously operated for 10 hours, the reaction temperature was 80° C., samples were taken for gas chromatography analysis, the CHP conversion rate was >99.9%, and the selectivity to PO was 7.4%.

Comparative Example 2

(53) Refer to patent CN1894030 for catalyst preparation:

(54) 30 g of silica gel carrier was weighed and loaded into a reaction tube, dried under N.sub.2 atmosphere at 240° C. for 240 min, and the linear velocity of N.sub.2 in the reaction tube was 2 cm/s; 4.17 g of TiCl.sub.4 was added to the TiCl.sub.4 vaporization tank, which was heated at a temperature of 145° C., the TiCl.sub.4 vapor was brought into the reaction tube with 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 200 min; 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 calcined for 200 min; 33.5 g of distilled water was added to the water and silanization reagent vaporization tank, which was heated at a temperature of 160° C., the water vapor was brought into the reaction tube with N.sub.2 for washing, the linear velocity of N.sub.2 in the reaction tube was 2 cm/s, and the washing time was 200 min; 2.4 g of hexamethyldisilazane was added to the water and silanization reagent vaporization tank, which was heated at a temperature of 140° C., the hexamethyldisilazane vapor was brought into the reaction tube with 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 silanization temperature was 250° C., and the silanization time was 120 min; the obtained catalyst was denoted as TS-A6.

(55) X-ray characterization of the TS-A6 catalyst (see FIG. 5) obtained the diffraction peaks of TiO.sub.2 (sharp diffraction peaks in FIG. 5), indicating that the Ti—SiO.sub.2 catalyst prepared by the vapor deposition method has poor dispersion of Ti species, the Ti species thereof are easy to aggregate and free titanium dioxide was produced. The TS-A6 was evaluated and continuously operated for 200 hours, the reaction temperature was increased from the initial 50° C. to 90° C., samples were taken for gas chromatography analysis, the CHP conversion rate was >99.9%, and the selectivity to PO was up to 92.8% with an average of 91.7%.