A method for synthesizing a titanium-silicon molecular sieve and applications thereof

Abstract

The application discloses synthesis and application of titanium silicalite molecular sieve. The titanium silicalite molecular sieve is synthesized by using a hydrothermal method, with silica sol as a silicon source, tetrabutyl titanate or titanium tetrachloride as a titanium source, tetrapropyl ammonium hydroxide as a template agent and an alkali source, and isopropyl alcohol and water as solvents. The tetrapropyl ammonium hydroxide is used to replace the template agent and the alkali source in a cheap synthesis process of the titanium silicalite molecular sieve, and small-grain titanium silicalite molecular sieve with a tablet crystal appearance is synthesized, the grain size of which is less than 200 nm, and the titanium silicalite molecular sieve has excellent catalytic performance when applied to an ammoximation reaction of cyclohexanone.

Description

Technical Field

[0001] This invention belongs to the field of molecular sieve material preparation, and relates to a method for synthesizing titanium-silicon molecular sieves and their application in the continuous reaction of cyclohexanone ammoniation. Background Technology

[0002] Titanium silicate molecular sieve TS-1 belongs to the orthorhombic crystal system and has the same MFI topology as ZSM-5 molecular sieve. The introduction of the transition metal titanium gives TS-1 unique catalytic oxidation properties. TS-1 is widely used in catalytic oxidation reactions such as olefin epoxidation, ketone oximeting, phenol and benzene hydroxylation, partial oxidation of alkanes, and alcohol oxidation.

[0003] Titanium silicate molecular sieves are typically synthesized via hydrothermal methods. Currently, hydrothermal synthesis systems are mainly divided into two categories: one uses tetraethyl orthosilicate as the silicon source and tetrapropylammonium hydroxide as the template agent, referred to as the classical hydrothermal method, which produces titanium silicate molecular sieves with spherical or ellipsoidal crystals; the other uses silica sol as the silicon source, tetrapropylammonium bromide as the template agent, and organic amines as the base source. Because the silicon source and template agent are less expensive than in the classical hydrothermal method, this is referred to as the low-cost hydrothermal method, and the resulting titanium silicate molecular sieves often have a "coffin lid" shape. It is evident that the morphologies of titanium silicate molecular sieves prepared by different synthesis methods and processes are completely different.

[0004] Patent CN105197956A discloses a method for synthesizing titanium-silicon molecular sieves using tetraalkyl silicate as an organosilicon source, tetraalkyl titanate as an organotitanium source, and tetrapropylammonium hydroxide as a template agent. The synthesized titanium-silicon molecular sieve has an ellipsoidal morphology resembling a "blackberry". In the reaction of preparing cyclohexanone oxime by ammonification of cyclohexanone, the selectivity and catalytic activity of the reaction product are significantly improved. Patent CN103641134B describes a method for preparing titanium-silicon molecular sieves with controllable crystal size. Tetrabutyl orthosilicate, tetrabutyl titanate, template agent, alkali source, inorganic ammonium salt, and molecular sieve mother liquor are mixed in a molar ratio of SiO2:TiO2:template agent:alkali source:inorganic ammonium salt:H2O of 1:0.01–0.04:0.2–0.6:0.1–3.0:0–0.3:20–60, and then crystallized. The titanium-silicon molecular sieve synthesized by this method has small crystal size, high crystallinity, high framework titanium content, and strong hydrophobicity, exhibiting high activity for selective oxidation reactions such as olefin epoxidation, aromatic hydrocarbon hydroxylation, and ketone ammoxidation. Patent CN109502601B describes a method for obtaining brick-shaped titanium-silicon molecular sieves by adding a free radical initiator during the synthesis process. The titanium-silicon molecular sieve prepared by this method is applied in the reaction of allyl alcohol epoxidation to prepare glycidyl.

[0005] It is evident that different silicon sources, template agents, and other methods and synthesis processes are used to synthesize titanium-silicon molecular sieves, resulting in significant differences in morphology, application areas, and catalytic performance. Summary of the Invention

[0006] This invention provides a method for synthesizing titanium-silicon molecular sieves and their application in the cyclohexanone ammonium oximation reaction. Using tetrapropylammonium hydroxide as both a template agent and a base source, and relatively inexpensive silica sol as the silicon source, a small-crystal titanium-silicon molecular sieve with a flattened tablet-like morphology was synthesized. The crystal size is less than 200 nm, and it exhibits excellent catalytic performance in the cyclohexanone ammonium oximation reaction.

[0007] To achieve the above objectives and effects, the following plan is adopted:

[0008] A method for synthesizing titanium-silicon molecular sieves is disclosed, using silica sol as the silicon source, one of tetrabutyl titanate and titanium tetrachloride as the titanium source, a quaternary ammonium base as both a template agent and a base source, and isopropanol and water as solvents. The titanium-silicon molecular sieves are synthesized via a hydrothermal method. The specific synthesis steps are as follows:

[0009] (1) Mix silica sol, deionized water and tetrapropylammonium hydroxide, and stir to obtain mixture A;

[0010] (2) Mix one of tetrabutyl titanate and titanium tetrachloride with isopropanol to obtain mixture B;

[0011] (3) Add mixture B dropwise to mixture A, controlling the dropwise addition time to be 1.0~2.0h, to obtain mixture C;

[0012] (4) Mix the remaining deionized water and 25% tetrapropylammonium hydroxide solution, add them to mixture C, and stir for 1-2 hours to obtain mixture D;

[0013] (5) The mixture D was placed in a stainless steel high-pressure reactor and crystallized at 100°C for 12-24 hours. Then the temperature was raised to 170°C and crystallized for 48-72 hours. The mixture was cooled, filtered, washed, dried at 80-100°C, and calcined at 500-600°C to obtain titanium silicon molecular sieve TS-1.

[0014] Furthermore, in the synthesis method described above, the mass ratio of each substance in mixture D is silicon dioxide: titanium dioxide: tetrapropylammonium hydroxide: isopropanol: water = 1 : 0.015~0.035 : 0.5~0.9 : 0.2~0.45 : 6.0~10.

[0015] Furthermore, in the synthesis method described above, the amount of deionized water used in step (1) is 1 to 1.5 times the amount of deionized water used in step (3).

[0016] Furthermore, in the synthesis method described above, the amount of tetrapropylammonium hydroxide used in step (1) is 1 to 1.5 times that used in step (3).

[0017] Furthermore, in the synthesis method described above, the silica sol uses a silica sol with a silicon oxide content of 30%, and the tetrapropylammonium hydroxide uses a tetrapropylammonium hydroxide solution with a mass fraction of 25%.

[0018] This invention provides a titanium-silicon molecular sieve synthesized by the method described above.

[0019] This invention provides the application of the above-mentioned titanium-silicon molecular sieve in the cyclohexanone amination reaction.

[0020] Furthermore, in the above technical solution, the cyclohexanone amination reaction occurs in a continuous reaction apparatus.

[0021] The beneficial effects of this invention are as follows: This invention provides a method for synthesizing titanium-silicon molecular sieves. In this method, tetrapropylammonium hydroxide is combined with silica sol, with tetrapropylammonium hydroxide serving as both a template agent and an alkali source. The mixture is added to the reaction system in two separate steps to obtain a flat, tablet-shaped, small-crystal titanium-silicon molecular sieve. This molecular sieve can efficiently catalyze the cyclohexanone ammoniation reaction, while simultaneously reducing the color of the cyclohexanone ammoniation reaction product, thereby improving the color of the downstream product caprolactam. Attached Figure Description

[0022] Figure 1 The XRD pattern of CAT-1 titanium silicate molecular sieve is shown.

[0023] Figure 2 and Figure 3 SEM image of titanium silicate molecular sieve CAT-1;

[0024] Figure 4 The XRD pattern of titanium silicate molecular sieve D-1 is shown.

[0025] Figure 5 SEM image of titanium silicate molecular sieve D-1. Detailed Implementation

[0026] The following embodiments will further illustrate the present invention, but do not limit the scope of the invention.

[0027] The purity of the materials used in the examples is not less than 99%.

[0028] The flat, tablet-like crystalline titanium-silicon molecular sieve synthesized in this invention is used in the continuous reaction of cyclohexanone ammonium oximeation. For the specific implementation process and equipment, please refer to patent document CN 205562489 U.

[0029] The catalyst was characterized by XRD analysis using an X-ray diffraction analyzer (Panaco, X'Pert3 Powder).

[0030] Catalyst characterization was performed using a scanning electron microscope (Hitachi, SU5000).

[0031] The color of the cyclohexanone amination reaction material was measured by a UV-Vis spectrophotometer (Shimadzu, UV1800). Example 1

[0032] Mix 100g of silica sol (silica content of 30%, the same below), 61g of deionized water, and 42g of tetrapropylammonium hydroxide aqueous solution (mass fraction of 25%, the same below), and stir to obtain mixture A;

[0033] Mix 3.6g of tetrabutyl titanate with 10.8g of isopropanol to obtain mixture B;

[0034] Mixture B was added dropwise to mixture A over a total time of 1.5 hours to obtain mixture C.

[0035] Mix 61g of deionized water and 42g of tetrapropylammonium hydroxide aqueous solution, add to mixture C, and stir for 1 hour to obtain mixture D;

[0036] Mixture D was placed in a stainless steel high-pressure reactor and crystallized at 100℃ for 18 hours. The temperature was then raised to 170℃ and crystallized for 48 hours. The mixture was cooled, filtered, washed, dried at 100℃, and calcined at 500℃ for 5 hours to obtain titanium silicon molecular sieve TS-1, denoted as CAT-1.

[0037] The XRD pattern and SEM image of the titanium silicate molecular sieve CAT-1 are attached. Figure 1 and attached Figure 2 . Example 2

[0038] Mix 100g of silica sol, 38.8g of deionized water, and 30g of tetrapropylammonium hydroxide aqueous solution, and stir to obtain mixture A;

[0039] Mix 2.3g of tetrabutyl titanate with 7.0g of isopropanol to obtain mixture B;

[0040] Mixture B was added dropwise to mixture A over a total time of 1.0 h to obtain mixture C;

[0041] Mix 38.7g of deionized water and 30g of tetrapropylammonium hydroxide aqueous solution, add them to mixture C, and stir for 1 hour to obtain mixture D;

[0042] Mixture D was placed in a stainless steel high-pressure reactor and crystallized at 100℃ for 18 hours. The temperature was then raised to 170℃ and crystallized for 48 hours. The mixture was cooled, filtered, washed, dried at 100℃, and calcined at 500℃ for 5 hours to obtain titanium-silicon molecular sieve TS-1, denoted as CAT-2. Example 3

[0043] Mix 100g of silica sol, 64g of deionized water, and 48g of tetrapropylammonium hydroxide aqueous solution, and stir to obtain mixture A;

[0044] Mix 4.5g of tetrabutyl titanate with 13.5g of isopropanol to obtain mixture B;

[0045] Mixture B was added dropwise to mixture A over a total time of 2.0 hours to obtain mixture C.

[0046] Mix 64g of deionized water and 48g of tetrapropylammonium hydroxide aqueous solution, add to mixture C, and stir for 1 hour to obtain mixture D;

[0047] Mixture D was placed in a stainless steel high-pressure reactor and crystallized at 100°C for 18 hours. The temperature was then raised to 170°C and crystallized for 48 hours. The mixture was cooled, filtered, washed, dried at 100°C, and calcined at 500°C for 5 hours to obtain titanium-silicon molecular sieve TS-1, denoted as CAT-3. Example 4

[0048] Mix 100g of silica sol, 73.2g of deionized water, and 50.4g of tetrapropylammonium hydroxide aqueous solution (mass fraction of 25%, the same below), and stir to obtain mixture A;

[0049] Mix 3.6g of tetrabutyl titanate with 10.8g of isopropanol to obtain mixture B;

[0050] Mixture B was added dropwise to mixture A over a total time of 1.5 hours to obtain mixture C.

[0051] Mix 48.8g of deionized water and 33.6g of tetrapropylammonium hydroxide aqueous solution, add to mixture C, and stir for 1 hour to obtain mixture D;

[0052] Mixture D was placed in a stainless steel high-pressure reactor and crystallized at 100℃ for 18 hours. The temperature was then raised to 170℃ and crystallized for 48 hours. The mixture was cooled, filtered, washed, dried at 100℃, and calcined at 500℃ for 5 hours to obtain titanium-silicon molecular sieve TS-1, denoted as CAT-4. Example 5

[0053] Mix 100g of silica sol, 61g of deionized water, and 42g of tetrapropylammonium hydroxide aqueous solution, and stir to obtain mixture A;

[0054] Mix 3.6g of tetrabutyl titanate with 10.8g of isopropanol to obtain mixture B;

[0055] Mixture B was added dropwise to mixture A over a total time of 1.5 hours to obtain mixture C.

[0056] Mix 61g of deionized water and 42g of tetrapropylammonium hydroxide aqueous solution, add to mixture C, and stir for 1 hour to obtain mixture D;

[0057] Mixture D was placed in a stainless steel high-pressure reactor and crystallized at 100℃ for 24 hours. The temperature was then raised to 170℃ and crystallized for 72 hours. The mixture was cooled, filtered, washed, dried at 100℃, and calcined at 500℃ for 5 hours to obtain titanium-silicon molecular sieve TS-1, denoted as CAT-5. Example 6

[0058] Mix 100g of silica sol, 61g of deionized water, and 42g of tetrapropylammonium hydroxide aqueous solution, and stir to obtain mixture A;

[0059] Mix 2.0 g of titanium tetrachloride with 10.8 g of isopropanol to obtain mixture B;

[0060] Mixture B was added dropwise to mixture A over a total time of 1.5 hours to obtain mixture C.

[0061] Mix 61g of deionized water and 42g of tetrapropylammonium hydroxide aqueous solution, add to mixture C, and stir for 1 hour to obtain mixture D;

[0062] Mixture D was placed in a stainless steel high-pressure reactor and crystallized at 100℃ for 18 hours. The temperature was then raised to 170℃ and crystallized for 48 hours. The mixture was cooled, filtered, washed, dried at 100℃, and calcined at 500℃ for 5 hours to obtain titanium-silicon molecular sieve TS-1, denoted as CAT-6. Comparative Example 1

[0063] Mix 100g silica sol, 100g deionized water, and 26g ethanolamine, and stir to obtain mixture A;

[0064] Mix 3.6g of tetrabutyl titanate with 10.8g of isopropanol to obtain mixture B;

[0065] Mixture B was added dropwise to mixture A over a total time of 1.5 hours to obtain mixture C.

[0066] Mix 100g of deionized water and 27.5g of tetrapropylammonium bromide aqueous solution, add to mixture C, and stir for 1 hour to obtain mixture D;

[0067] Mixture D was placed in a stainless steel high-pressure reactor and crystallized at 100℃ for 18 hours. The temperature was then raised to 170℃ and crystallized for 48 hours. The mixture was cooled, filtered, washed, dried at 100℃, and calcined at 500℃ for 5 hours to obtain titanium silicon molecular sieve TS-1, denoted as D-1.

[0068] The XRD pattern and SEM image of titanium silicate molecular sieve D-1 are attached. Figure 4 and attached Figure 5 . Comparative Example 2

[0069] Mix 100g silica sol, 61g deionized water, and 58.8g tetrapropylammonium hydroxide aqueous solution (mass fraction of 25%, the same below), and stir to obtain mixture A;

[0070] Mix 3.6g of tetrabutyl titanate with 10.8g of isopropanol to obtain mixture B;

[0071] Mixture B was added dropwise to mixture A over a total time of 1.5 hours to obtain mixture C.

[0072] Mix 61g of deionized water and 25.2g of tetrapropylammonium hydroxide aqueous solution, add to mixture C, and stir for 1 hour to obtain mixture D;

[0073] Mixture D was placed in a stainless steel high-pressure reactor and crystallized at 100°C for 18 hours. The temperature was then raised to 170°C and crystallized for 48 hours. The mixture was cooled, filtered, washed, dried at 100°C, and calcined at 500°C for 5 hours to obtain titanium-silicon molecular sieve TS-1, denoted as D-2.

[0074] Application examples

[0075] For the specific implementation process and equipment, please refer to patent CN 205562489 U. The ratio of each reactant and the apparatus are the same as those in Example 1 of this patent. Samples were taken for analysis after the reaction had been running for 6 hours. The reaction results of the catalysts prepared in Examples 1-6 and Comparative Examples 1-2 of this invention in the cyclohexanone amination reaction are shown in the table below.

[0076] Table 1. Catalytic performance evaluation results of each sample catalyst

[0077] .

Claims

1. A method for synthesizing titanium-silicon molecular sieves, characterized in that, The specific synthesis steps are as follows: (1) Mix silica sol, deionized water and tetrapropylammonium hydroxide, and stir to obtain mixture A; (2) Mix one of tetrabutyl titanate and titanium tetrachloride with isopropanol to obtain mixture B; (3) Add mixture B dropwise to mixture A, controlling the dropwise addition time to be 1.0-2.0 h, to obtain mixture C; (4) Mix deionized water and tetrapropylammonium hydroxide, add to mixture C, and stir for 1-2 hours to obtain mixture D; (5) The mixture D was loaded into a stainless steel high-pressure reactor and crystallized at 100°C for 12-24 hours. The temperature was then raised to 170°C and crystallized for 48-72 hours. The product was filtered, washed, dried and calcined to obtain the titanium silicon molecular sieve TS-1. In mixture D, silicon and titanium are considered as oxides, and the mass ratio of each substance is silicon oxide: titanium oxide: tetrapropylammonium hydroxide: isopropanol: water = 1:0.015~0.035:0.5~0.9:0.2~0.45:6.0~10; The amount of deionized water used in step (1) is 1 to 1.5 times the amount of deionized water used in step (4); The amount of tetrapropylammonium hydroxide used in step (1) is 1 to 1.5 times that used in step (4).

2. The synthesis method according to claim 1, characterized in that, The drying temperature is 80-100℃, and the calcination temperature is 500-600℃.

3. A titanium-silicon molecular sieve synthesized by the method described in claim 1 or 2.

4. The application of the titanium-silicon molecular sieve of claim 3 in the cyclohexanone ammoniation reaction.

5. The application according to claim 4, characterized in that, The cyclohexanone amination reaction occurs in a continuous reaction unit.

Images