Titanium-silicon catalysts for olefin epoxidation reactions and their preparation and use

Abstract

The application discloses a titanium-silicon catalyst for olefin epoxidation reaction, and a preparation method and application of the catalyst. The catalyst can control the mesoporous molecular sieve material and the Ti-rich outer surface of the molecular sieve, and the active substance for olefin epoxidation reaction can be as close to the active center as possible and has small diffusion resistance and high catalytic efficiency.

Description

Technical Field

[0001] The present invention relates to a titanium silicon catalyst for olefin epoxidation reaction (synthesizing non-fully crystalline all-silicon molecular sieve S-1 containing mesopores and then in-situ planting titanium on the mesopore surface), and its preparation and application. Background Art

[0002] With the rapid development of petrochemicals and fine chemicals, cyclic ethers containing a -CC- structure, known as epoxides, have become very important intermediates. Due to charge polarization and ring strain, epoxides are highly reactive and readily react with active hydrogen groups such as amines, carboxyls, hydroxyls, and amides. They are sensitive to acids and nucleophiles and can undergo ring-opening reactions with hydrogen halides and Grignard reagents, making them raw materials for the synthesis of halohydrins, 1,2-diols, and hydroxylamines. Ethylene oxide, propylene oxide, and aliphatic epoxides are the main epoxides currently synthesized. The mesoporous all-silica molecular sieve S-1, with its MFI topology, belongs to the pentasil titanium type. Heteroatoms are primarily present in an isolated, tetracoordinated form within the molecular sieve framework, which is the primary reason for the unique epoxidation ability of the TS-1 molecular sieve. Propylene oxide (PO), an important chemical product, is produced by the direct oxidation of propylene using TS-1 molecular sieve as a catalyst and H2O2 as an oxidant. This process is known as hydrogen peroxide oxidation (HPPO). Compared with traditional chlorohydrin and indirect oxidation processes, the HPPO process is an environmentally friendly and clean production process with great development prospects. Therefore, the TS-1 catalyst, as the core technology of this process, has attracted widespread attention.

[0003] However, since the epoxidation of propylene and hydrogen peroxide is a liquid-solid phase reaction, during the reaction process, the reacting molecules need to overcome diffusion resistance to approach the Ti active center of the molecular sieve catalyst. Due to the limitations of the TS-1's own topological structure, namely: the small pore size, the pores are easily clogged during the reaction, which not only hinders the diffusion of the substrate, but also limits the contact between the reactants and the active center of the catalyst, resulting in the decomposition of hydrogen peroxide and reducing the effective utilization rate of hydrogen peroxide. In addition, since the reaction releases a large amount of heat, if the heat cannot be removed in time, not only will the hydrogen peroxide decompose, but a large number of side reactions will also occur. Summary of the Invention

[0004] In order to at least partially solve the technical problems existing in the prior art, the present invention carries out surface titanium planting on the non-fully crystalline all-silicon molecular sieve S-1 containing mesopores, that is, heteroatom Ti is in situ placed on the surface of the all-silicon molecular sieve S-1 containing mesopores, which ultimately makes the catalytic active centers extremely easy to contact, which is very conducive to the rapid participation of the active sites in the reaction, thereby improving the conversion rate of the olefin epoxidation reaction.

[0005] As one aspect of the present invention, an embodiment of the present invention relates to a titanium silicon catalyst for olefin epoxidation reaction, wherein heteroatom Ti is in situ located on the surface of an all-silicon molecular sieve S-1 containing mesopores.

[0006] As another aspect of the present invention, embodiments of the present invention relate to a method for preparing the aforementioned titanium silicalite catalyst for olefin epoxidation reactions: synthesizing a non-fully crystalline, mesoporous, all-silica molecular sieve S-1, and then in situ implanting titanium on the mesoporous surfaces. The titanium silicalite molecular sieve obtained by this method, in which Ti is implanted on the outer surface of the mesoporous molecular sieve, solves the problem of low catalytic efficiency of existing TS-1 titanium silicalite molecular sieves in olefin epoxidation reactions.

[0007] In at least one specific embodiment, the in-situ implantation of titanium on the mesoporous surface in the above method involves mixing a mesoporous all-silica molecular sieve S-1 containing a template with TiO2 and placing the mixture in a solution of an organic amine at a certain concentration. This method allows the molecular sieve material to have mesopores while also enriching the outer surface of the molecular sieve with Ti. This allows the active species used in the olefin epoxidation reaction to be as close to the active centers as possible, with minimal diffusion resistance and high catalytic efficiency.

[0008] In at least one specific embodiment, in the above method, the template is provided by one of tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetrapropylammonium chloride, and any mixture thereof; the organic amine is provided by one of TPAOH solution, TEAOH solution, TMAOH solution, n-butylamine solution, ethylenediamine solution, and any mixture thereof.

[0009] In at least one specific embodiment, the method for preparing the titanium silicon catalyst for olefin epoxidation comprises the following steps:

[0010] Step 1: Preparation of non-fully crystalline all-silicon molecular sieve S-1 containing mesopores

[0011] (1) Preparation of gel

[0012] A silicon source, a template, an alkali source, and activated carbon fibers are uniformly mixed, and seed crystals are added under stirring to form a uniform gel. The gel mixture has the following molar composition: R / SiO2 = 0.01-0.2, Na2O / SiO2 = 0.02-0.25, H2O / SiO2 = 10-50, seed crystal / SiO2 = 0-20 wt%, X / SiO2 = 0.5-5 wt%, R being an organic template and X being activated carbon fibers.

[0013] The silicon source is one of tetraethyl orthosilicate, silica sol, white carbon black, solid silica gel, and any mixture thereof; the activated carbon fiber is one of viscose-based activated carbon fiber, phenolic-based activated carbon fiber, polyacrylonitrile-based activated carbon fiber, asphalt-based activated carbon fiber, polyvinylidene chloride, polyimide fiber, polystyrene fiber, polyvinyl alcohol fiber, lignin fiber, and any mixture thereof; the alkali is one of sodium hydroxide, potassium hydroxide, ammonia, and any mixture thereof;

[0014] (2) Gel crystallization

[0015] The prepared gel is hydrothermally crystallized under suitable conditions, and the crystallized solid is filtered, washed, and dried to obtain a template-containing mesoporous all-silica molecular sieve S-1.

[0016] The crystallization conditions are a crystallization temperature of 80-200°C and a crystallization time of 1-80 hours. Crystallization can be performed statically, but stirring is recommended to achieve uniform particle size in the crystallized product. Stirring is preferably performed to achieve uniform mixing, and can be continuous or intermittent.

[0017] Step 2: Preparation of Ti-rich all-silicon molecular sieve S-1 containing mesopores on the outer surface of the molecular sieve

[0018] Under stirring, the dried, non-fully crystalline, mesoporous all-silicon molecular sieve S-1, a titanium source, and an organic amine are uniformly mixed and placed in a kettle for crystallization under certain conditions. After crystallization, the solid product is separated, washed, dried, and calcined to obtain a special titanium-rich titanium-silicon molecular sieve on the outer surface of the molecular sieve.

[0019] The titanium source is provided by one of titanium dioxide, titanium tetrachloride and tetrabutyl titanate or any mixture thereof.

[0020] The crystallization conditions are a temperature of 25 to 200° C. and a reaction time of 1 to 100 hours. The reaction is carried out under stirring, which can be continuous or intermittent.

[0021] As another aspect of the present invention, an embodiment relates to the use of the above-mentioned titanium silicon catalyst in the epoxidation reaction of olefins.

[0022] Compared with the prior art, the present invention has at least the following beneficial effects:

[0023] Whether the existing TS-1 is obtained by traditional synthesis methods or post-processing, most of the Ti that is directly related to the catalytic activity is distributed in the pores of the crystal skeleton, and the reaction molecules need to diffuse into the pores of the molecular sieve catalyst. However, for olefin molecules, due to the size of the molecules, they need to overcome the diffusion resistance to enter the molecular sieve pores close to the catalytic active center, resulting in low reaction efficiency. In the experiment, a surface titanium planting method was performed on the non-fully crystalline all-silicon molecular sieve S-1 containing mesopores, that is, heteroatom Ti was placed in situ on the surface of the all-silicon S-1 containing mesopores, which ultimately made the Ti in the catalytic active center very conducive to the rapid participation of the active site in the reaction. It not only has a terminal titanium hydroxyl group with high catalytic activity, but also enables olefins and hydrogen peroxide to quickly contact and react. This greatly improves the effective utilization rate of hydrogen peroxide while making the catalyst have a good catalytic reaction effect for olefin epoxidation reactions. DETAILED DESCRIPTION

[0024] The following is a detailed description of the embodiments of the present invention: This embodiment is implemented based on the technical solution of the present invention, and a detailed implementation method and process are given. However, the scope of protection of the present invention is not limited to the following embodiments. The process parameters for which specific conditions are not specified in the following embodiments are generally based on conventional conditions.

[0025] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0026] Comparative Example 1

[0027] TS-1 was synthesized by the classical method (USP4410501). 250 ml of deionized water was added to 84 g of ethyl orthosilicate and 14.7 g of tetrapropylammonium hydroxide, and stirred for 20 minutes to obtain a raw silicon solution. Tetrabutyl titanate and isopropyl alcohol were mixed in a mass ratio of 1:0.6 and stirred for 15 minutes to obtain a raw titanium solution. 15.7 ml of the prepared raw titanium solution was added to the raw silicon solution and stirred for 30 minutes to obtain a uniform gel. The obtained gel was transferred to a stainless steel reactor and crystallized at autogenous pressure and 170°C for 120 hours. After filtration, washing to neutrality, drying at 110°C, and calcining at 540°C for 6 hours, the classical TS-1 molecular sieve (denoted as TS-1) was obtained.

[0028] Comparative Example 2

[0029] The TS-1 sample was post-modified to improve the catalytic activity. The treatment process was as follows: TS-1 was placed in a hydrothermal synthesis reactor with polytetrafluoroethylene, a certain concentration of tetrapropylammonium hydroxide treatment solution was added, and it was treated at 180 degrees autogenous pressure for 36 hours. After filtering, washing to neutrality, drying at 110°C, and calcining at 540°C for 6 hours, a modified TS-1 molecular sieve (denoted as TS1-P) was obtained.

[0030] Example 1

[0031] first step:

[0032] Under vigorous stirring, 200 g of tetraethyl orthosilicate and 50 g of water were mixed uniformly. 50 g of TPAOH (25% wt) and 5 g of NaOH were then added and mixed uniformly. 1.68 g of seed crystals and 2 g of viscose-based activated carbon fiber were then added to form a uniform gel. The gel mixture had the following molar composition: Na₂O / SiO₂ = 0.2, R / SiO₂ = 0.2, H₂O / SiO₂ = 11.5, seed crystals / SiO₂ = 3 wt%, and X / SiO₂ = 3.3 wt%. The resulting gel was placed in a polytetrafluoroethylene-lined autoclave and crystallized at 170°C for 12 hours. The mixture was then cooled to room temperature, filtered, washed, dried, and calcined. X-ray powder diffraction analysis revealed a relative crystallinity of 35% for the fully silica mesoporous zeolite (denoted as NS-1).

[0033] Step 2:

[0034] Under vigorous stirring, 10g of dried NS-1 powder, 1g of tetrabutyl titanate, and 50g of a 25% wt TPAOH solution were mixed uniformly and placed in a polytetrafluoroethylene-lined autoclave. The mixture was crystallized at 170°C for approximately 48 hours, cooled to room temperature, filtered, washed, dried, and calcined. X-ray powder diffraction determined that the relative crystallinity of the all-silica molecular sieve S-1, which contained mesopores and Ti-rich outer surfaces, was 95%.

[0035] Example 2

[0036] Example 1 was repeated, except that the tetraethyl orthosilicate in the first step was replaced with silica sol. X-ray powder diffraction analysis revealed a relative crystallinity of 45% for the all-silica mesoporous zeolite. The resulting all-silica molecular sieve S-1, containing mesopores and Ti-rich outer surfaces, had a relative crystallinity of 95% (denoted as NS-2).

[0037] Example 3

[0038] Example 1 was repeated, except that the sodium hydroxide in the first step was replaced with potassium hydroxide. X-ray powder diffraction analysis revealed a relative crystallinity of 55% for the all-silica mesoporous zeolite. The resulting all-silica molecular sieve S-1, containing mesopores and Ti-rich outer surfaces, had a relative crystallinity of 96% (denoted as NS-3).

[0039] Example 4

[0040] Example 1 was repeated, except that the sodium hydroxide in the second step of Example 1 was replaced with aqueous ammonia. The final obtained molecular sieve S-1, which had a Ti-rich outer surface and contained mesopores and a relative crystallinity of 98%, was obtained (denoted as NS-4).

[0041] Example 5

[0042] Example 1 was repeated, except that the TPAOH concentration in the third step was changed to 20 wt %. The final obtained molecular sieve S-1 with Ti-rich outer surface and mesopores had a relative crystallinity of 95% (denoted as NS-5).

[0043] Example 6

[0044] Example 1 was repeated, except that the amount of TPAOH in the third step was changed to 70 g. The final obtained molecular sieve S-1 with Ti-rich outer surface and mesopores had a relative crystallinity of 97% (denoted as NS-6).

[0045] The above catalyst was used in the propylene / hydrogen peroxide reaction. The evaluation conditions are shown in Table 1, and the results are shown in Table 2.

[0046] Table 1

[0047] Reaction temperature Reaction pressure <![CDATA[H2O2 concentration]]> <![CDATA[H2O2 space velocity]]> <![CDATA[Propylene / H2O2 ratio]]> 40℃ 3mpa 3mol / L <![CDATA[0.17h -1 ]]> 5

[0048] Table 2

[0049]

[0050] Evaluation data indicates that the catalytic activity of TS-1 synthesized by the classical method is relatively poor. While alkaline treatment (TS1-P) can improve the catalyst's catalytic activity, its hydrogen peroxide conversion rate and effective utilization rate remain unsatisfactory. The series of catalysts synthesized using this patent further enhances catalytic activity, achieving an activation temperature of 35°C. At a reaction temperature of 40°C, the selectivity of propylene oxide to propylene can reach 99.6%, and the effective utilization rate of hydrogen peroxide can reach 98.5%.

[0051] The above are only preferred embodiments of the present invention, and do not limit the protection scope of the present invention. Various modifications or applications made according to the above embodiments are within the protection scope of this technical solution.

[0052] Although specific embodiments of the present invention have been described in detail, it will be understood by those skilled in the art that various modifications and substitutions may be made to those details in light of all the teachings disclosed herein, and such modifications are within the scope of the present invention. The full scope of the present invention is given by the appended claims and any equivalents thereof.

Claims

1. A method for preparing a titanium silicon catalyst for olefin epoxidation, characterized in that: Synthesize non-fully crystalline all-silicon molecular sieve S-1 containing mesopores, and then in situ implant titanium on the mesopore surface; In-situ titanium planting on the mesoporous surface means: mixing the all-silicon molecular sieve S-1 containing the template with TiO2 and placing it in a certain concentration of organic amine solution; The method comprises the following steps: Step 1: Preparation of non-fully crystalline mesoporous all-silica molecular sieve S-1 (1) Preparation of gel The silicon source, template, alkali source and activated carbon fiber are mixed uniformly, and seed crystals are added under stirring to form a uniform gel; The gel mixture has the following molar composition: R / SiO2=0.01-0.2, Na2O / SiO2=0.02-0.25, H2O / SiO2=10-50, the mass ratio of the seed crystal to SiO2 is greater than 0 and not more than 20wt%, X / SiO2=0.5-5wt%, R is an organic template, and X is activated carbon fiber; (2) Gel crystallization The prepared gel is hydrothermally crystallized under suitable conditions, and the crystallized solid is filtered, washed, and dried to obtain a mesoporous all-silica molecular sieve S-1 containing a template; Step 2: Preparation of Ti-rich mesoporous all-silicon molecular sieve S-1 on the outer surface of the molecular sieve Under stirring, the dried non-fully crystalline mesoporous all-silicon molecular sieve S-1, titanium source and organic amine are uniformly mixed and crystallized under certain conditions.

2. The method according to claim 1, characterized in that The template agent is provided by one of tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetrapropylammonium chloride and any mixture thereof; the organic amine is provided by one of TPAOH solution, TEAOH solution, TMAOH solution, n-butylamine solution, ethylenediamine solution and any mixture thereof.

3. The method according to claim 1, wherein In step (1), the silicon source is one of tetraethyl orthosilicate, silica sol, white carbon black, solid silica gel and any mixture thereof; the activated carbon fiber is one of viscose-based activated carbon fiber, phenolic-based activated carbon fiber, polyacrylonitrile-based activated carbon fiber, asphalt-based activated carbon fiber, polyvinylidene chloride, polyimide fiber, polystyrene fiber, polyvinyl alcohol fiber, lignin fiber and any mixture thereof; the alkali is provided by one of sodium hydroxide, potassium hydroxide, ammonia water and any mixture thereof.

4. The method according to claim 1, wherein In step (2), the crystallization conditions are: crystallization temperature 80-200°C; crystallization time 1-80 hours.

5. The method according to claim 1, wherein In the second step, the titanium source is provided by one of titanium dioxide, titanium tetrachloride and tetrabutyl titanate, or any mixture thereof.

6. The method according to claim 1, wherein In the second step, the crystallization conditions are a temperature of 25 to 200° C. and a reaction time of 1 to 100 hours.

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