Liquid phase process for the preparation of an epoxidation catalyst

Abstract

The application discloses an epoxidation catalyst and a liquid-phase preparation method. Titanium is grafted into the skeleton of a carrier SiO2 by adopting a liquid-phase static grafting method. The introduction of rare earth elements improves the stability of the carrier structure and active components, strengthens the directional grafting of titanium and the distribution of active sites, improves the activity and stability of the catalyst in olefin epoxidation, and avoids the corrosion of equipment and the poisoning of copper-based catalysts in the POSM process in the whole process without introducing chlorine elements.

Description

Technical Field

[0001] This invention relates to the field of epoxidation catalysts, and more specifically, to a liquid-phase preparation method for an epoxidation catalyst. Background Technology

[0002] Propylene oxide (PO) plays a crucial role in chemical synthesis, ranking third among propylene derivatives. It is primarily used in the production of polyether polyols and propylene glycol. Polyether polyols are essential raw materials for the synthesis of polyurethane and are widely used in industries such as insulation materials, furniture, elastomers, adhesives, and coatings. The number of downstream products derived from it is vast and its applications are extensive.

[0003] CN118302247A BASF disclosed an epoxidation catalyst and its preparation method. The catalyst is prepared by a one-step process involving mixing a silicon source and a titanium source, adding the mixture to an aqueous solution containing a structure-directing agent, and then subjecting the mixture to a series of steps including progressive heating and stirring, crystallization, washing, drying, and calcination. In propylene epoxidation, the H₂O₂ conversion rate is 69%, the PO selectivity is 22.1%, and the PO yield is 17.5%.

[0004] CN106964337B, published by Wanhua, discloses a method for preparing an epoxidation catalyst, the prepared epoxidation catalyst, and its applications. Titanium is loaded onto silica gel using chemical vapor deposition, followed by silanization and hydrolysis. Molybdenum is then loaded onto the titanium surface using a liquid-phase ion exchange composite method, achieving directional molybdenum loading. The epoxidation catalyst exhibits excellent molybdenum stability. This epoxidation catalyst is used for the oxidation of olefins to prepare corresponding epoxides, demonstrating high catalytic activity and selectivity. However, the large amount of hydrogen chloride generated during catalyst preparation via hydrolysis can severely corrode equipment, and the chlorine in the catalyst is difficult to completely remove, causing further corrosion. In POSM processes, this can poison subsequent copper-based catalysts.

[0005] Shell disclosed a method for preparing an epoxidation catalyst (CN108349918A). Titanium tetrachloride was loaded onto a dried support using vapor deposition, followed by calcination, hydrolysis, and silanization to obtain the catalyst. This catalyst exhibits a 54.8% EBHP conversion in the epoxidation of 1-octene and performs well in the epoxidation of propylene; however, the chlorine in the catalyst can easily corrode equipment.

[0006] CN104437450B, published by the Shanghai Institute, discloses a titanium-containing porous silica catalyst, its preparation method, and its applications. The catalyst is obtained through a one-step process in an inert atmosphere, involving the mixing and reaction of a silicon source, a titanium source, a pH adjuster, and a solvent. However, this method results in a large amount of titanium existing within the catalyst structure, preventing it from participating in the reaction and limiting the catalyst's lifetime.

[0007] CN104437636B, published by the Shanghai Institute, discloses a titanium-containing porous silica catalyst, its preparation method, and its applications. The catalyst, prepared by loading titanium tetrachloride onto a shaped support using a liquid-phase deposition method under heating, stirring, and reflux conditions, followed by hydrolysis and silanization, exhibits excellent activity and stability. However, the hydrogen chloride produced during the preparation process, as well as the chlorine in the catalyst, still pose a challenge in preventing equipment corrosion.

[0008] CN114616053A by LyondellTech discloses a titanate catalyst, a method for preparing the titanate catalyst, and a method for epoxidation. The catalyst, prepared by immersing a support in ethylene glycol or an aqueous solution containing bis(ammonium lactate) titanium dihydroxy(IV) using an equal-volume impregnation method, followed by calcination and silanization, exhibits a 95.7% molar selectivity for propylene oxide after 100 hours of operation in propylene epoxidation, indicating insufficient catalyst stability.

[0009] Therefore, existing preparation methods need to be improved to overcome the above problems. Summary of the Invention

[0010] The main objective of this invention is to provide a liquid-phase preparation method for epoxidation catalysts, which successfully prepares highly active and stable catalysts that are non-corrosive to equipment and harmless to subsequent copper-based catalysts.

[0011] To achieve the above objectives, in a first aspect, the present invention provides a liquid-phase preparation method for an epoxidation catalyst, comprising the following steps: S1. Dry the all-silicon carrier, and then impregnate the dried all-silicon carrier with an impregnation solution containing rare earth elements at room temperature for 12-24 hours. After that, filter and dry it in sequence, and then calcine it at 400~500℃ for 4-8 hours. S2. Prepare a titanium grafting solution by mixing the solvent, chlorine-free titanium source and pH adjuster in a preset ratio. After the materials in the titanium grafting solution are mixed evenly, put them into the reaction vessel. Then put the all-silicon carrier treated in step S1 into the reaction vessel and let it stand for 2-6 days. S3. The product obtained in step S2 is subjected to vacuum filtration, drying and calcination. S4. The product after calcination in step S3 is subjected to silanization treatment to obtain the catalyst.

[0012] Optionally, the all-silicone carrier in step S1 is one of HMS, SBA-15, MCM-41 and coarse-pore silicone.

[0013] Optionally, the rare earth element in step S1 is at least one of lanthanum, cerium, praseodymium, and neodymium.

[0014] Optionally, the concentration of the impregnation solution in step S1 is 0.50~5.00%, and the mass ratio of the impregnation solution to the silicon carrier is 2.00~5.00:1.

[0015] Optionally, the solvent in step S2 is one or a combination of several of the following: water, methanol, ethanol, n-propanol, isopropanol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol, and butanol.

[0016] Optionally, the titanium source in step S2 is one or a combination of several chlorine-free titanium compounds such as tetramethyl titanate, tetraethyl titanate, n-propyl titanate, isopropyl titanate, and tetrabutyl titanate.

[0017] Optionally, the pH adjuster in step S2 is one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.

[0018] Optionally, the molar ratio of each component in step S2 is solvent: silicon support: titanium source: pH adjuster = (5~25):1:(0.2~2.00):(0.1~1.50).

[0019] Optionally, the settling temperature in step S2 is 40-60℃.

[0020] Optionally, the roasting temperature in step S3 is 300-700℃.

[0021] Optionally, the all-silicon carrier described in step S1 is first dried at 120°C for 6 hours, and the impregnated all-silicon carrier is filtered and then dried at 100°C for 12 hours.

[0022] The liquid-phase preparation method of the epoxidation catalyst provided by this invention has the following advantages compared with the prior art: (1) Rare earth elements can enter the channels or cages of molecular sieves through ion exchange and interact strongly with silicon and oxygen atoms on the framework. This interaction significantly enhances the bond energy of the silicon-oxygen bond, improves the stability of the molecular sieve framework structure, and at the same time, can regulate the electronic structure of titanium atoms, effectively preventing the migration and aggregation of titanium atoms and improving the stability of the catalyst.

[0023] (2) The titanium-silicon catalyst synthesized by the liquid-phase static grafting method used in this patent does not contain chlorine in any of the raw materials. It does not corrode the equipment during the preparation process. The temperature is low during the titanium grafting process, which greatly reduces the requirements for the production equipment. The chlorine content of the catalyst is <0.1ppm. In the POSM process, it is friendly to copper-based catalysts and will not cause catalyst poisoning. It also avoids chlorine corrosion of the equipment.

[0024] (3) The catalyst preparation process used in this patent is environmentally friendly. In step (2), the grafting solution can be recycled after adding pH adjuster and titanium source, and in step (4), the silanization solution can be recycled after adding silane.

[0025] (4) Titanium in the catalyst exists in the form of tetracoordinated titanium, pentacoordinated titanium and hexacoordinated titanium, and there is no anatase form, which avoids the occurrence of side reactions and improves the selectivity of propylene oxide.

[0026] (5) The catalyst has a pore structure of 6-16 nm, which is suitable for various olefin epoxidation processes, including the epoxidation processes of various macrocyclic olefins. Attached Figure Description

[0027] Figure 1 The UV-Vis spectrum of the catalyst prepared in Example 1; Figure 2 The table shows the ICP and titanium, cerium, and chlorine content of the catalyst prepared in Example 1, as measured by a sulfur and chlorine analyzer. Detailed Implementation

[0028] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0029] It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of this invention can be combined with each other. The invention will now be described in detail with reference to the embodiments.

[0030] Example 1 Step (1): Dry the all-silicon MCM-41 molecular sieve at 120℃ for 6 hours, add 50g of 1.50% cerium nitrate impregnation solution to 20g of dried molecular sieve, let it stand at room temperature for 24 hours, filter, dry at 100℃ for 12 hours, and calcine at 400℃ for 8 hours.

[0031] Step (2): Add 230g of ethanol, 20g of the all-silicon MCM-41 carrier treated in step (1), 15g of tetraethyl titanate, and 39g of 25% tetraethylammonium hydroxide aqueous solution to the reaction vessel according to the ratio of solvent: all-silicon carrier: titanium source: pH adjuster (molar ratio) = 15:1:0.20:0.20, and let it stand at 50℃ for 6 days.

[0032] Step (3): Filter the catalyst from step (2), dry it in an oven at 100°C for 4 hours, and then calcine it in a muffle furnace at 400°C for 4 hours.

[0033] Step (4): Add 20g of the product from step (3), 16g of hexamethyldisilazane and 80g of ethylbenzene to the reactor according to the weight ratio of catalyst, silanizing agent and solvent = 1:0.8:4.0. Heat to 140℃ and reflux for 6 hours. After removing and recovering the solution, dry at 100℃ for 4 hours to obtain No. 1 epoxidation catalyst.

[0034] The UV-Vis spectrum of the catalyst prepared in this embodiment is as follows: Figure 1 As shown, Figure 2 The table shows the ICP and titanium, cerium, and chlorine content of the catalyst prepared in this embodiment, as measured by a sulfur and chlorine analyzer.

[0035] Example 2 Except for step (1) of Example 1, where the calcination time was changed from 400℃ for 8 hours to 500℃ for 6 hours, the other conditions were the same as in Example 1, and the No. 2 epoxidation catalyst was obtained.

[0036] Example 3 Except for replacing 50g of 1.50% cerium nitrate impregnation solution with 60g of 1.25% lanthanum nitrate impregnation solution in step (1) of Example 1, the other conditions are the same as in Example 1, and the No. 3 epoxidation catalyst is obtained.

[0037] Example 4 Except for replacing MCM-41 with SBA-15 in steps (1) and (2) of Example 1, the other conditions are the same as in Example 1, and the 4# epoxidation catalyst is obtained.

[0038] Example 5 Except for replacing MCM-41 with coarse-porous silica gel in steps (1) and (2) of Example 1, the other conditions are the same as in Example 1, and 5# epoxidation catalyst is obtained.

[0039] Example 6 Except for changing the standing treatment from 6 days to 4 days in step (2) of Example 1, the other conditions are the same as in Example 1, and 6# epoxidation catalyst is obtained.

[0040] Example 7 Except for changing the standing treatment from 6 days to 3 days in step (2) of Example 1, the other conditions are the same as in Example 1, and 7# epoxidation catalyst is obtained.

[0041] Example 8 Except for the solvent being changed to isopropanol and the titanium source being changed to isopropyl titanate in step (2) of Example 1, the other conditions were the same as in Example 1, and 8# epoxidation catalyst was obtained.

[0042] Comparative Example 1 Step (1): Dry the all-silicon MCM-41 molecular sieve at 120℃ for 6 hours.

[0043] Step (2): Add 230g of ethanol, 20g of the all-silicon MCM-41 carrier treated in step (1), 15g of tetraethyl titanate, and 39g of 25% tetraethylammonium hydroxide aqueous solution to the reactor according to the ratio of solvent: all-silicon carrier: titanium source: pH adjuster (molar ratio) = 15:1:0.20:0.20. Heat and reflux at 80℃ for 6 days.

[0044] Step (3): Filter the catalyst from step (2), dry it in an oven at 100°C for 4 hours, and then calcine it in a muffle furnace at 400°C for 4 hours.

[0045] Step (4): Add 20g of the product from step (3), 16g of hexamethyldisilazane and 80g of ethylbenzene to the reactor according to the weight ratio of catalyst, silanizing agent and solvent = 1:0.8:4.0. Heat to 140℃ and reflux for 6 hours. After removing and recovering the solution, dry at 100℃ for 4 hours. The synthesized epoxidation catalyst is named BJ-1.

[0046] Comparative Example 2 Except for the temperature being changed to 100°C in step (2) of Comparative Example 1, the other conditions are the same as in Example 1, and the synthesized epoxidation catalyst is designated as BJ-2.

[0047] Comparative Example 3 Except for step (3) of Comparative Example 1, where 400℃ is changed to 550℃, the other conditions are the same as in Example 1, and the synthesized epoxidation catalyst is designated as BJ-3.

[0048] Comparative Example 4 Except for step (3) of Comparative Example 1, where 400℃ is changed to 700℃, the other conditions are the same as in Example 1, and the synthesized epoxidation catalyst is designated as BJ-4.

[0049] Comparative Example 5 Except for replacing tetraethyl titanate with an equimolar amount of titanium tetrachloride, replacing ethanol with an equimolar amount of ethylbenzene, removing the pH adjuster, and changing the heating temperature to 100°C in step (2) of Comparative Example 1, the other conditions are the same as in Example 1, and the synthesized epoxidation catalyst is designated as BJ-5.

[0050] The epoxidation reaction of ethylbenzene hydrogen peroxide and propylene was carried out using the catalysts prepared in Examples 1-7 and Comparative Examples 1-5. 2.00 g of catalyst was loaded into a fixed-bed reactor, and propylene was mixed with approximately 20% EBHP and then passed through the catalyst bed for reaction. Under the conditions of a reaction pressure of 4.5 MPa, a reaction temperature of 100 °C, an EBHP space velocity of 1.5, and a propylene to EBHP molar ratio of 10, the EBHP conversion, propylene oxide selectivity, and α-phenylethanol selectivity during the 1500-hour epoxidation reaction are shown in Tables 1 and 2.

[0051] Table 1 Table 2 Comparative analysis of Tables 1 and 2 shows that the catalyst prepared using the technical solution of this invention still achieves an EBHP conversion rate >99% and a PO selectivity >99% after 1500 hours of operation. This indicates that the combination of rare earth Ce / La modification, chlorine-free titanate as the titanium source, mild liquid-phase static grafting, mesoporous structure, and silanization post-treatment constructs stable, highly dispersed titanium active centers without side reaction sites. Rare earth elements enter the molecular sieve framework, strengthening the Si–O framework and improving the stability of the support structure. Simultaneously, the rare earth element modification generates relatively dispersed defect sites on the support, improving the dispersibility of the active component titanium. Furthermore, the electronic structure of titanium can be controlled during catalyst use, preventing titanium migration, aggregation, and loss. In addition, the entire process is chlorine-free, with no HCl corrosion of production equipment, and the catalyst itself is chlorine-free, which is beneficial for copper in the POSM process. The catalyst is catalyst-friendly, eliminating safety hazards caused by chlorine corrosion. Furthermore, the use of a mild and uniform liquid-phase static grafting method ensures long-term stability of the organic base during prolonged use at 50°C, while avoiding titanium clusters caused by excessively high temperatures. Under the action of the organic base, titanium is highly dispersed, forming tetra- / penta- / hexa-coordinated active titanium, free of anatase TiO2. Anatase is a major culprit in side reactions, capable of decomposing propylene oxide and rapidly reducing selectivity and lifespan. The catalyst also features wide pores, preventing carbon buildup and clogging, which facilitates the adsorption and desorption of large EBHP molecules. Finally, the silanization treatment transforms hydrophilic silanol groups into hydrophobic silanyl groups, improving catalyst hydrophobicity, reducing surface acidity, and preventing catalyst deactivation caused by polar substances adsorbing onto silanol groups and covering titanium active sites.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A liquid-phase preparation method for an epoxidation catalyst, characterized in that: Includes the following steps: S1. Dry the all-silicon carrier, and then impregnate the dried all-silicon carrier with an impregnation solution containing rare earth elements at room temperature for 12-24 hours. After that, filter and dry it in sequence, and then calcine it at 400~500℃ for 4-8 hours. S2. Prepare a titanium grafting solution by mixing the solvent, chlorine-free titanium source and pH adjuster in a preset ratio. After the materials in the titanium grafting solution are mixed evenly, put them into the reaction vessel. Then put the all-silicon carrier treated in step S1 into the reaction vessel and let it stand for 2-6 days. S3. The product obtained in step S2 is subjected to vacuum filtration, drying and calcination. S4. The product after calcination in step S3 is subjected to silanization treatment to obtain the catalyst.

2. The liquid-phase preparation method of an epoxidation catalyst as described in claim 1, characterized in that: The all-silicone carrier in step S1 is one of HMS, SBA-15, MCM-41 and coarse-porous silicone.

3. The liquid-phase preparation method of an epoxidation catalyst as described in claim 1, characterized in that: The rare earth element mentioned in step S1 is at least one of lanthanum, cerium, praseodymium, and neodymium.

4. The liquid-phase preparation method of an epoxidation catalyst as described in claim 1, characterized in that: The concentration of the impregnation solution in step S1 is 0.50~5.00%, and the mass ratio of the impregnation solution to the silicon carrier is 2.00~5.00:

1.

5. The liquid-phase preparation method of an epoxidation catalyst as described in claim 1, characterized in that: The solvent in step S2 is one or a combination of several of the following: water, methanol, ethanol, n-propanol, isopropanol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol, and butanol.

6. The liquid-phase preparation method of an epoxidation catalyst as described in claim 1, characterized in that: The titanium source in step S2 is one or a combination of tetramethyl titanate, tetraethyl titanate, tetrapropyl titanate, tetraisopropyl titanate, and tetrabutyl titanate.

7. The liquid-phase preparation method of an epoxidation catalyst as described in claim 1, characterized in that: The pH adjuster in step S2 is one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.

8. The liquid-phase preparation method of an epoxidation catalyst as described in claim 1, characterized in that: The molar ratio of each component in step S2 is solvent: silicon support: titanium source: pH adjuster = (5~25):1:(0.2~2.00):(0.1~1.50).

9. The liquid-phase preparation method of an epoxidation catalyst as described in claim 1, characterized in that: The settling temperature in step S2 is 40-60℃.

10. The liquid-phase preparation method of an epoxidation catalyst according to claim 1, characterized in that: The roasting temperature in step S3 is 300-700℃.

11. The liquid-phase preparation method of an epoxidation catalyst as described in claim 1, characterized in that: The all-silicon carrier described in step S1 is first dried at 120°C for 6 hours, and the impregnated all-silicon carrier is filtered and then dried at 100°C for 12 hours.

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