CN112871204A

CN112871204A - High-activity propylene gas-phase epoxidation catalyst and preparation method thereof

Info

Publication number: CN112871204A
Application number: CN202110069142.3A
Authority: CN
Inventors: 黄家辉; 贾玉华; 吕强; 龙化云
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2021-01-19
Filing date: 2021-01-19
Publication date: 2021-06-01

Abstract

本发明公开了一种高活性丙烯气相环氧化催化剂及其制备方法。催化剂的制备过程中添加了缺陷位助剂和S助剂，得到了富钛并具有大量适合Au负载的缺陷位，同时催化剂上的无定型物种被S稳定，得到了高活性的丙烯气相环氧化催化剂，大幅度提高了丙烯的转化率、PO的选择性以及氢效。The invention discloses a highly active propylene gas-phase epoxidation catalyst and a preparation method thereof. Defect site promoters and S promoters were added during the preparation of the catalyst to obtain titanium-rich and a large number of defect sites suitable for Au loading. At the same time, the amorphous species on the catalyst were stabilized by S, and a highly active propylene gas phase epoxy resin was obtained. The conversion of propylene, the selectivity of PO and the hydrogen efficiency are greatly improved.

Description

High-activity propylene gas-phase epoxidation catalyst and preparation method thereof

Technical Field

The invention belongs to the technical field of catalytic synthesis, and particularly relates to a preparation method of a propylene gas-phase epoxidation catalyst.

Background

At present, all production devices of liquid-phase HPPO process use methanol as solvent. However, the methanol solvent also contributes to the HPPO process. Firstly, methanol is easy to generate solvolysis side reaction with a propylene oxide product to generate byproducts such as high-boiling point propylene glycol monomethyl ether and the like. These by-products not only severely reduce propylene oxide selectivity, but also increase wastewaterThe difficulty of treatment. Secondly, the methanol solvent must be recycled, and complicated refining treatment (including hydrogenation, rectification and resin adsorption) is required before recycling, so that the HPPO process flow is complicated, and the investment and energy consumption are high. Worse still, the recycled methanol solvent still has over ten and even over twenty trace impurities (including fusel, aldehydes, ethers, esters and oxacycles) difficult to remove after complicated refining treatments. These trace impurities return to the reactor with the circulating methanol, accelerating the deactivation of the catalyst, severely shortening the life cycle and the life of the catalyst. Thus, propylene and H₂O₂HPPO processes for the production of PO by liquid phase epoxidation also have significant disadvantages.

For the above reasons, researchers at home and abroad have been unique to a propylene gas phase epoxidation process which does not involve organic solvents and can keep the advantage of green chemistry. One of the routes for the gas phase epoxidation of propylene in the presence of hydrogen with molecular oxygen as the oxidant is the propylene gas phase epoxidation route. H was first reported in 1998₂/O₂The study of the gas phase epoxidation reaction with propylene on a Au/Ti-HMS catalyst found. In the process, Au on the catalyst activates hydrogen and oxygen to firstly form hydrogen peroxide species, and then the hydrogen peroxide species is transferred to a Ti center to carry out epoxidation reaction with propylene, and the reaction can be realized only by the cooperation of Au-Ti active centers. Most of the current researches on propylene gas phase epoxidation catalysts still focus on taking Au as an active center and loading the Au on a titanium-containing molecular sieve. Research results show that in order to obtain high-activity Au species and epoxidized Ti centers as much as possible and better approach reactants, the titanium silicalite molecular sieve is modified after being synthesized, so that more active Ti sites are exposed and more defect sites for Au loading are generated, and amorphous Ti species can cause ineffective decomposition of hydrogen peroxide.

The prior art shows that the theoretical extreme value of the content of framework titanium in the titanium-silicon molecular sieve is 2.5 percent, namely the ratio of silicon to titanium is 40:1, and the result limits the quantity of Ti active sites of the TS-1 molecular sieve. Researchers have reduced the silicon-titanium ratio for the purpose of increasing the framework titanium, but at the same time have the problem of large amounts of amorphous titanium species.

Disclosure of Invention

In order to make up the defects of the prior art, the catalyst for preparing propylene oxide by gas-phase epoxidation of propylene provided by the invention is an Au-loaded titanium silicalite molecular sieve, the chemical composition of the Au-loaded titanium silicalite molecular sieve is Au/TS-1, the content of each component in the catalyst is calculated according to the mass ratio, the titanium silicalite molecular sieve TS-1 accounts for 98-99.8%, and the content of Au accounts for 0.2-2%.

The invention is realized by the following technical scheme:

a catalyst for preparing propylene oxide by propylene gas phase epoxidation and a preparation method thereof are characterized in that: the preparation method of the catalyst specifically comprises the following steps:

(1) uniformly mixing a silicon source, a defect site auxiliary agent, a template agent and deionized water to obtain a silicon source hydrolysate A;

(2) uniformly mixing a titanium source and a complexing agent, dropwise adding the mixture into the silicon source hydrolysate A, and uniformly stirring to obtain a silicon-titanium hydrolysate B;

(3) heating the silicon-titanium hydrolysate B to remove alcohol, supplementing water and S auxiliary agent, and uniformly stirring to obtain silicon-titanium gel C;

(4) crystallizing the silicon-titanium gel C at the temperature of 150-210 ℃ for 20-120h to obtain a crystallized product, and filtering, separating, drying, washing and roasting to obtain a titanium-silicon molecular sieve TS-1;

(5) loading gold on the titanium silicalite TS-1 by an impregnation method to obtain the catalyst, namely powdery Au/TS-1;

further, the S auxiliary agent in the step (3) is one or a mixture of two of ammonium sulfite and ammonium bisulfite.

Preferably, the defect site assistant in step (1) is one or a mixture of soluble starch, sodium carboxymethyl cellulose, polyacrylamide and polyethyleneimine.

The titanium-silicon ratio of the titanium-silicon molecular sieve is 31-33, and the content of framework titanium is 3.0-3.2 wt%.

Further, the step (5) comprises the following steps: according to the mass ratio, the titanium-silicon molecular sieve TS-1 is 98-99.8%, the Au is 0.2-2%, 0.01mol/L chloroauric acid aqueous solution is taken, the pH value is adjusted to 7.0, TS-1 molecular sieve carrier is added, the pH value of the solution is kept to 7.0, and after stirring, suction filtration, washing, drying and hydrogen atmosphere roasting are carried out, so as to obtain the powdery catalyst Au/TS-1.

Further, the stirring temperature in the step (5) is preferably 60-70 ℃, the stirring time is preferably 1-2h, the drying temperature is preferably 60-90 ℃, the roasting temperature is preferably 350-400 ℃, and the roasting time is preferably 4-8 h.

Further, in the step (5), the titanium silicalite TS-1 accounts for 98.5-99.7%, and the Au accounts for 0.3-1.5%;

further, the composition of the substance molar ratio in the silicon-titanium gel C in the step (3) is SiO₂：TiO₂: template agent: defect site assistant: auxiliary agent: h₂O＝1：(0.033-0.05)：(0.25-0.4)：(0.002-0.008)：(0.001-0.01)：(25-30)。

More preferably, the molar ratio composition of the substances in the silicon-titanium gel C in the step (3) is SiO₂：TiO₂: template agent: defect site assistant: auxiliary agent: h₂O＝1：(0.04-0.05)：(0.3-0.4)：(0.003-0.008)：(0.002-0.01)：(25-30)。

Further, the drying temperature in the step (4) is preferably 80-120 ℃, and the roasting temperature is preferably 500-650 ℃.

Preferably, the silicon source in step (1) is one or a mixture of silica sol, tetraethyl orthosilicate and white carbon black.

Further, the template agent in the step (1) is tetrapropylammonium hydroxide (TPAOH).

Preferably, in the step (2), the titanium source is one or a mixture of more of tetraethyl orthotitanate, tetrabutyl orthotitanate, tetraisopropyl titanate, titanium trichloride and titanium tetrachloride, and more preferably tetrabutyl orthotitanate.

Further, in the step (2), the complexing agent is one of isopropanol, acetylacetone and ethanol.

The catalyst prepared by the invention can be applied to the preparation of propylene oxide by propylene gas phase epoxidation. The catalytic propylene gas phase epoxidation reaction is carried out at normal pressureThe reaction is carried out in a fixed bed reaction device. The reaction temperature is 140 ℃ and 200 ℃, and the reaction gas composition is C₃H₆/H₂/O₂/N₂1/1/1/7 (volume ratio), and the space velocity is 5000-^-1.g^-1 _catThe reaction tail gas is detected and analyzed by gas chromatography FID and TCD. The reaction was run for 10 hours each time, and the results of the reaction at 6 hours were compared.

The invention has the beneficial effects that:

the titanium silicalite TS-1 is synthesized in a system adopting tetrapropylammonium hydroxide, the particle size is 100-200nm, and the specific surface area is larger, so the synthesized TS-1 can provide more surfaces for Au loading.

The S additive is added into a synthesis system of the titanium silicalite TS-1, so that on one hand, the content of Ti in the titanium silicalite TS-1 is improved, and the number of epoxidized active centers is increased; on the other hand, the introduced sulfur group can form Ti-O-S bond with amorphous titanium species on the catalyst, so that the amorphous titanium species are passivated, thereby reducing H₂O₂The ineffective decomposition of the propylene is carried out, so that the conversion rate of the propylene and the hydrogen efficiency are improved;

the defect site auxiliary agent is added, so that a better environment can be provided for subsequent Au loading, and the loading of Au on the TS-1 molecular sieve with lower isoelectric point is facilitated, so that the loading rate and the stability of Au are improved; in addition, the sulfur group introduced into the auxiliary agent can also play a role in stabilizing the Au active center.

The defect site auxiliary agent and the S auxiliary agent are introduced in the preparation process of the titanium silicalite molecular sieve, so that the carrier suitable for subsequent Au loading is obtained, and the subsequent treatment process in other processes is avoided, thereby simplifying the preparation process of the catalyst, reducing the synthesis cost and being beneficial to the industrial application and popularization of the catalyst.

Detailed Description

Comparative example 1

Adding 46.2g of tetraethyl orthosilicate into a beaker, stirring, adding 44g of 25 wt% TPAOH aqueous solution and 38g of water, and hydrolyzing at 40 ℃ for 2 hours to obtain a silicon source hydrolysis mixture; dissolving 3.8g of tetrabutyl titanate in 18.7g of isopropanol, and then stirring for 30min to obtain a titanium source hydrolysis mixture; a titanium sourceMixing with hydrolytic mixture of silicon source, removing alcohol at 80 deg.C for 1.5 hr, adding 50.2g water, stirring for 30min, crystallizing the obtained transparent glue solution in a crystallization kettle, crystallizing at 170 deg.C for 36 hr, washing the crystallized product with 1M HCl aqueous solution (liquid-solid ratio of 50ml g/g)^-1) And roasting the mixture for 6 hours at 550 ℃ in air, and testing by XRF to obtain a TS-1 sample with a Si/Ti ratio of 50.5.

And (2) taking 20.8mL of chloroauric acid aqueous solution with the concentration of 0.01mol/L, adding 100mL of deionized water for dilution, adjusting the pH value to 7.0, adding 1g of the TS-1 molecular sieve carrier obtained above, keeping the pH value of the solution to be 7.0, stirring for 1h at 65 ℃, performing suction filtration and washing, drying for 10h at 80 ℃, and roasting for 4h at 400 ℃ in a hydrogen atmosphere to obtain 0.38% Au/TS-1-A.

Comparative example 2

Adding 46.2g of tetraethyl orthosilicate into a beaker, stirring, adding 44g of 25 wt% TPAOH aqueous solution and 38g of water, and hydrolyzing at 40 ℃ for 2 hours to obtain a silicon source hydrolysis mixture; dissolving 3.8g of tetrabutyl titanate in 18.7g of isopropanol, and then stirring for 30min to obtain a titanium source hydrolysis mixture; mixing a hydrolysis mixture of a titanium source and a silicon source, removing alcohol for 1.5h at 80 ℃, supplementing 50.2g of water and 0.045g of ammonium sulfite, stirring for 30min, filling the obtained transparent glue liquid into a crystallization kettle for crystallization, crystallizing for 36h at 170 ℃, washing and drying the obtained crystallized product, and then washing with 1M HCl aqueous solution (the liquid-solid ratio is 50ml g)^-1) And roasting the mixture for 6 hours at 550 ℃ in air, and testing by XRF to obtain a TS-1 sample with a Si/Ti ratio of 31.6.

The Au loading procedure of comparative example 1 was repeated to obtain a catalyst having 0.38% Au/TS-1-B.

Comparative example 3

Adding 0.2g of soluble starch and 38g of water into a beaker, stirring, then sequentially adding 44g of 25 wt% TPAOH aqueous solution and 46.2g of tetraethyl orthosilicate, and hydrolyzing for 3 hours at 40 ℃ to obtain a silicon source hydrolysis mixture; dissolving 3.8g of tetrabutyl titanate in 18.7g of isopropanol, and then stirring for 30min to obtain a titanium source hydrolysis mixture; mixing the hydrolyzed mixture of titanium source and silicon source, removing alcohol at 80 deg.C for 1.5 hr, adding 50.2g water, stirring for 30min, and filling the obtained transparent glue solution into crystalCrystallizing in a crystallization kettle at 170 deg.C for 36 hr, washing the crystallized product, oven drying, and washing with 1M HCl aqueous solution (liquid-solid ratio of 50ml g)^-1) And roasting the mixture for 6 hours at 550 ℃ in air, and testing by XRF to obtain a TS-1 sample with a Si/Ti ratio of 50.3.

The Au loading procedure of comparative example 1 was repeated to obtain a catalyst with 0.38% Au/TS-1-C.

Example 1

Mixing 45g of SiO₂Adding 30% silica sol into a jacketed three-neck flask, adding 0.05g of soluble starch, 44g of 25 wt% TPAOH aqueous solution and 38g of water, and hydrolyzing at 40 ℃ for 2h to obtain a silicon source hydrolysis mixture; dissolving 3.8g of tetrabutyl titanate in 18.7g of isopropanol, and then stirring for 30min to obtain a titanium source hydrolysis mixture; mixing titanium source and silicon source hydrolyzed mixture, removing alcohol at 80 deg.C for 1.5 hr, adding 50.2g water, stirring for 30min, crystallizing the obtained transparent glue solution in a crystallization kettle, crystallizing at 170 deg.C for 36 hr, washing the crystallized product with 1M HCl aqueous solution (liquid-solid ratio of 50ml g/g)^-1) And roasting the mixture for 6 hours at 550 ℃ in air, and testing by XRF to obtain a TS-1 sample with a Si/Ti ratio of 31.8. The Au loading procedure of comparative example 1 was repeated to obtain a catalyst having 0.38% Au/TS-1-D.

Example 2

Example 1 is repeated, the defect site assistant soluble starch in the TS-1 preparation process is replaced by sodium carboxymethylcellulose, polyacrylamide and polyethyleneimine, the amount of the component substances is kept unchanged, and after crystallization and drying, the solution is washed by 1M HCl aqueous solution (liquid-solid ratio is 50ml g)^-1) And roasting the mixture for 6 hours at 550 ℃ in air, and obtaining TS-1 samples with Si/Ti ratios of 31.7, 31.9 and 31.8 through XRF test.

The Au loading procedure of comparative example 1 was repeated to obtain catalysts of 0.38% Au/TS-1-E, 0.38% Au/TS-1-F, and 0.38% Au/TS-1-G.

Example 3

Example 1 was repeated, the amounts of the tetraethyl orthosilicate used in the preparation of TS-1 were replaced with the amounts of the constituent substances tetramethyl orthosilicate, tetrapropyl orthosilicate, tetrabutyl orthosilicate, and the like, the crystallization was followed by drying with 1M HCl aqueous solution (liquid-solid ratio 50ml g)^-1) And roasting the mixture for 6 hours at 550 ℃ in air, and testing by XRF to obtain TS-1 samples with Si/Ti ratios of 32.1, 31.9 and 32.0.

The Au loading procedure of comparative example 1 was repeated to obtain catalysts of 0.38% Au/TS-1-H, 0.38% Au/TS-1-I, and 0.38% Au/TS-1-J.

Example 4

Example 1 was repeated, tetrabutyl titanate in the preparation of TS-1 was replaced with tetramethyl titanate, tetraethyl titanate and tetrapropyl titanate, the amounts of the component substances were kept constant, and after crystallization, drying and washing with 1M aqueous HCl (liquid-solid ratio: 50ml g/g)^-1) And roasting the mixture for 6 hours at 550 ℃ in air, and obtaining TS-1 samples with Si/Ti ratios of 31.7, 32.0 and 32.1 through XRF test.

The Au loading procedure of comparative example 1 was repeated to obtain catalysts of 0.38% Au/TS-1-K, 0.38% Au/TS-1-L, and 0.38% Au/TS-1-M.

Example 5

Example 1 was repeated, the complexing agent in the preparation of TS-1 was replaced by isopropanol and ethanol, the amounts of the component substances were kept constant, after crystallization, drying and washing with 1M aqueous HCl (liquid-solid ratio 50ml g)^-1) And roasting the mixture for 6 hours at 550 ℃ in air, and testing by XRF to obtain TS-1 samples with Si/Ti ratios of 31.9 and 31.7.

The Au loading procedure of comparative example 1 was repeated to obtain a catalyst of 0.38% Au/TS-1-N, 0.38% Au/TS-1-O.

Example 6

Example 1 was repeated, the S adjuvant was replaced by ammonium bisulfite in the preparation of TS-1, the amounts of the component substances were kept constant, and after crystallization, drying and washing with 1M aqueous HCl (liquid-solid ratio 50ml g)^-1) And roasting the mixture for 6 hours at 550 ℃ in air, and testing by XRF to obtain a TS-1 sample with a Si/Ti ratio of 31.8.

The Au loading procedure of comparative example 1 was repeated to obtain a catalyst of 0.38% Au/TS-1-P.

Example 7

The catalytic propylene gas phase epoxidation reaction is carried out in a fixed bed reactor at normal pressure. The reaction temperature is 160 ℃, and the reaction gasThe composition of the body is C₃H₆/H₂/O₂/N₂1/1/1/7 (volume ratio), and the space velocity is 7000mL^-1.g^-1 _catAnd the reaction tail gas is detected and analyzed by gas chromatography FID and TCD. The reaction was run for 10 hours each time, and the results of the reaction at 6 hours were compared.

The results are shown in Table 1. Wherein, the hydrogen efficiency means the effective utilization rate of hydrogen, and the calculation mode is the amount of PO generated substance/H₂The amount of converted material of (a) 100%.

TABLE 1 propylene vapor phase epoxidation performance data for Au/TS-1 samples

As can be seen from the results in the table, due to the addition of the defect site auxiliary agent and the S auxiliary agent, the activity of the catalyst is greatly improved, so that the conversion rate, the selectivity and the hydrogen efficiency of propylene are greatly improved; is an effect which cannot be achieved by adding the defect site assistant or the S assistant alone.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be able to cover the technical solutions and the inventive concepts of the present invention within the technical scope of the present invention.

Claims

1. a preparation method for the catalyst of propylene gas phase epoxidation reaction, is characterized in that, described method comprises the following steps:

(1) uniformly mixing silicon source, defect site assistant, template agent and deionized water to obtain silicon source hydrolyzate A;

(2) after the titanium source and the complexing agent are evenly mixed, add dropwise to the silicon source hydrolyzate A, and stir to obtain the silicon-titanium hydrolyzate B;

(3) the silicon-titanium hydrolyzate B is heated up and alcohol-removing treatment is carried out, and after adding water and S auxiliary agent, stirring is uniform to obtain silicon-titanium gel C;

(4) Crystallizing the silica-titanium gel C at 150-210° C. for 20-120 hours to obtain a crystallized product, which is filtered, separated, dried, washed and calcined to obtain the titanium-silicon molecular sieve TS-1;

(5) supporting gold on the titanium-silicon molecular sieve TS-1 by impregnation method to obtain the catalyst, namely powdery Au/TS-1;

The defect site auxiliary agent is one or a mixture of soluble starch, sodium carboxymethyl cellulose, polyacrylamide and polyethyleneimine;

The S auxiliary agent is one or a mixture of ammonium sulfite and ammonium bisulfite.

2. preparation method according to claim 1, is characterized in that,

The titanium-silicon ratio of the titanium-silicon molecular sieve is 31-33, and the content of framework titanium is 3.0-3.2 wt%;

In the step (3), the molar ratio of materials in the silicon-titanium gel C is composed of SiO ₂ : TiO ₂ : template agent: defect site assistant: S assistant: H ₂ O=1: (0.033-0.05): ( 0.25-0.4): (0.0002-0.008): (0.001-0.01): (25-30);

In step (4), the drying temperature is 80-120°C, and the roasting temperature is 500-650°C.

3 . The preparation method according to claim 2 , wherein the molar ratio of materials in the silicon-titanium gel C described in step (3) is composed of SiO ₂ : TiO ₂ : template agent: defect site assistant: assistant Agent: _H2O =1:(0.04-0.05):(0.3-0.4):(0.003-0.008):(0.002-0.01):(25-30).

4. preparation method according to claim 1 is characterized in that, step (5) comprises the following steps:

According to the mass ratio, titanium-silicon molecular sieve TS-1 is 98%-99.8%, Au is 0.2%-2%, take chloroauric acid aqueous solution, adjust the pH value to 7.0, add TS-1 molecular sieve carrier, keep the solution pH The value is 7.0, and after stirring, suction filtration, washing, drying, and calcination in a hydrogen atmosphere are performed to obtain a powdery catalyst Au/TS-1;

In step (5), the stirring temperature is 60-70°C, the stirring time is 1-2h, the drying temperature is 60-90°C, the roasting temperature is 350-400°C, and the roasting time is 4-8h.

5 . The preparation method according to claim 4 , wherein the titanium-silicon molecular sieve TS-1 is 98.5-99.7%, and the Au is 0.3-1.5%. 6 .

6. preparation method according to claim 1 is characterized in that, in step (1), described silicon source is tetraethylorthosilicate, tetramethylorthosilicate, tetrapropylorthosilicate and orthosilicic acid One or more mixtures of tetrabutyl esters; the template agent is tetrapropylammonium hydroxide.

7. preparation method according to claim 1, is characterized in that, in step (2), described titanium source is tetraethyl orthotitanate, tetrabutyl orthotitanate, tetraisopropyl titanate, trichloride One or more mixtures of titanium oxide and titanium tetrachloride, preferably tetrabutyl orthotitanate; the complexing agent is one of isopropanol, acetylacetone, and ethanol.

8. A catalyst prepared by the method of any one of claims 1 to 7.

9. the application of the described catalyst of claim 8 in propylene gas phase epoxidation to prepare propylene oxide.

10 . The application according to claim 9 , wherein the reaction is carried out in a fixed-bed reaction device at atmospheric pressure, the reaction temperature is 140-200° C., and the reaction gas composition is C ₃ H ₆ /H ₂ /O ₂ . /N ₂ =1/1/1/7 (volume ratio), the space velocity is 5000-10000 mL mL·h ⁻¹ ·g ⁻¹ _cat .