A method for prolonging the service life of a titanium-silicate molecular sieve catalyst

Abstract

The present invention relates to a method for prolonging the service life of a titanium silicalite catalyst. In a fixed-bed reactor, when the activity of the titanium silicalite catalyst decreases, resulting in a hydrogen peroxide conversion rate lower than 95% or an epichlorohydrin yield lower than 90% based on the amount of hydrogen peroxide, a fixed-bed reactor filled with titanium silicalite is flushed with a tetrahydrofuran solution dissolved with a thermal initiator and a low-concentration organic oxidant, so that the catalyst restores its catalytic activity and its service life is prolonged. Among them, the thermal initiator is one or a mixture of several of benzoyl peroxide, methyl ethyl ketone peroxide and azobisisobutyronitrile, and the organic oxidant is one or a mixture of tert-butyl peroxide and tert-amyl peroxide. The present invention has the advantages of simple operation, no need to disassemble the reactor and the catalyst, can be completed online, low cost, mild conditions and high safety.

Description

Technical Field

[0001] The present invention relates to a method for prolonging the service life of a titanium silicalite catalyst in the fixed-bed reaction of synthesizing epichlorohydrin by hydrogen peroxide oxidation of allyl chloride, specifically a method for prolonging the service life of a titanium silicalite catalyst that can complete the operation online without disassembling the reactor and the catalyst in the fixed-bed reaction of synthesizing epichlorohydrin by hydrogen peroxide oxidation of allyl chloride. Background Art

[0002] Epichlorohydrin is an important organic chemical intermediate, which can be used in the production of epoxy resin, synthetic glycerol, chlorohydrin rubber and other derivatives, and has a wide range of uses. There are four production technologies for epichlorohydrin. Among them, the propylene high-temperature chlorination method mainly consists of three steps: preparing allyl chloride from propylene, synthesizing dichloropropanol, and saponifying to prepare epichlorohydrin. This process discharges a large amount of wastewater and waste residue in the saponification process, and it is difficult to treat the pollution. With the continuous promotion of the concept of sustainable development, this method may be gradually phased out. The allyl acetate method consists of four steps: preparing allyl acetate from propylene, hydrolyzing allyl acetate to prepare allyl alcohol, synthesizing dichloropropanol, and saponifying to prepare epichlorohydrin. This process has a long process flow, acetic acid in the reaction process will corrode the equipment, and a large amount of wastewater will also be produced in the saponification process. Currently, this process is basically not used in industrial production. The glycerol method uses glycerol and hydrogen chloride as raw materials, and synthesizes epichlorohydrin in two steps: glycerol chlorination and dichloropropanol saponification. The synthesis of epichlorohydrin by hydrogen peroxide oxidation of allyl chloride catalyzed by titanium silicalite omits the intermediate step of preparing dichloropropanol from allyl chloride, has less wastewater discharge, and also avoids the generation of calcium chloride waste residue in the saponification process. It is a green and clean synthesis process with high atom economy and has good application prospects.

[0003] However, when using TS-1 type titanium silicalite to catalyze the synthesis of epichlorohydrin by hydrogen peroxide oxidation of allyl chloride, since the average pore diameter of TS-1 is 0.55 nm, the catalytic performance is strongly affected by the substrate molecular size, solvent properties, crystal grain size and pore structure. In particular, epichlorohydrin is prone to ring opening to form by-products, which stay in the molecular sieve pores and block the pores, resulting in a gradual decrease in the catalyst activity and a decline in the service life. Therefore, it is necessary to take corresponding measures to treat the deactivated catalyst or take corresponding measures to prolong the service life of the catalyst. Lin Yi used solvent washing method, oxidation method and high-temperature calcination method to treat the deactivated catalyst in the process of synthesizing epichlorohydrin by hydrogen peroxide oxidation of allyl chloride, and investigated the influence of three different treatment methods on the catalyst activity. It was found that the activity of the deactivated catalyst was best restored by high-temperature calcination treatment. Zhang Yu et al. found that after the titanium silicalite was deactivated in the process of synthesizing epichlorohydrin by hydrogen peroxide oxidation of allyl chloride, the lost activity of the titanium silicalite could be basically restored by alcohol washing at 120 °C. The above methods have problems such as strict condition requirements, low catalyst activity recovery rate and high cost. Summary of the Invention

[0004] The present invention relates to a method for prolonging the service life of a titanium silicalite molecular sieve catalyst, and solves the problems of strict requirements for conditions for prolonging the service life of the titanium silicalite molecular sieve catalyst, low recovery rate of catalyst activity, and high cost in the synthesis of epichlorohydrin by the epoxidation of allyl chloride with hydrogen peroxide in a fixed-bed reactor.

[0005] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0006] A method for prolonging the service life of a titanium silicalite molecular sieve catalyst, comprising the following steps:

[0007] (1) In a fixed-bed reactor for the synthesis of epichlorohydrin by the epoxidation of allyl chloride with hydrogen peroxide, when the activity of the titanium silicalite molecular sieve catalyst decreases and the conversion rate of hydrogen peroxide is lower than 95% or the yield of epichlorohydrin in terms of the amount of substance of hydrogen peroxide is lower than 90%, stop inputting the reaction raw materials into the fixed-bed reactor filled with the titanium silicalite molecular sieve, and switch to inputting tetrahydrofuran into the fixed-bed reactor. Under the condition that the flow space velocity of tetrahydrofuran is 0.1 ml•min -1 •ml -1 , rinse for 20 minutes, and at the same time raise the reactor temperature to 50°C - 70°C;

[0008] (2) Under the condition of heat preservation, rinse the fixed-bed reactor filled with the titanium silicalite molecular sieve with a tetrahydrofuran solution dissolved with a thermal initiator and a low-concentration organic oxidant;

[0009] (3) Finally, input methanol into the reactor filled with the titanium silicalite molecular sieve. Under the condition that the flow space velocity of methanol is 0.1 ml·min -1 ·ml -1 , continue to rinse for 20 minutes, and cool down to the original catalytic reaction temperature. After the rinsing is completed, the catalyst restores its activity, and the reaction raw materials can be input into the reactor to continue the reaction.

[0010] Further, the titanium silicalite molecular sieve catalyst is a TS-1 type titanium silicalite molecular sieve catalyst.

[0011] Further, the thermal initiator is one or a mixture of several of benzoyl peroxide, methyl ethyl ketone peroxide, and azobisisobutyronitrile. The mass fraction concentration of the thermal initiator in the tetrahydrofuran solution is 0.1% - 0.5%, and the preferred mass fraction concentration is 0.2% - 0.4%.

[0012] Further, the organic oxidant is one or a mixture of tert-butyl peroxide and tert-amyl peroxide. The mass fraction concentration of the organic oxidant in the tetrahydrofuran solution is 1% - 3%, and the preferred mass fraction concentration is 1.5% - 2.5%.

[0013] Further, the reactor temperature of the fixed-bed reactor is 50°C to 70°C.

[0014] Further, calculated based on the catalyst per unit volume (ml), the flow space velocity of the tetrahydrofuran solution dissolved with a thermal initiator and a low-concentration organic oxidant flowing through the catalyst bed is 0.01 to 0.03 ml·min -1 ·ml -1 , and the preferred flow space velocity is 0.015 to 0.025 ml·min -1 ·ml -1 .

[0015] Further, the flushing time is 1 hour to 3 hours, and the preferred flushing time is 1.5 hours to 2.5 hours.

[0016] Advantages of the present invention

[0017] In the present invention, under heating conditions and in the presence of an initiator, organic peroxides generate free radicals, which react with the carbon deposits in the titanium silicalite catalyst, oxidize and degrade the carbon deposits, reduce the adhesion to the titanium silicalite catalyst in the fixed bed, and disperse into the tetrahydrofuran solution and flow out therewith, so that the catalyst restores its catalytic activity and extends its service life. The present invention has the advantages of simple operation, no need to unload the catalyst, can be completed online, low cost, mild conditions, high safety, etc. Specific embodiments

[0018] Next, in combination with the embodiments of the present invention, the technical solutions in these embodiments will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. Example 1

[0019] Methanol, allyl chloride, and 50% aqueous hydrogen peroxide solution were input into a fixed-bed reactor filled with TS-1 type titanium silicalite catalyst under the conditions of methanol:allyl chloride:hydrogen peroxide = 10:2:1 (molar ratio), volume space velocity of 0.025 ml·min -1 ·ml -1 , and reaction temperature of 30°C, so that the TS-1 type titanium silicalite catalyst catalyzed the oxidation of allyl chloride by hydrogen peroxide to produce epichlorohydrin. As the reaction continued, when the catalyst activity decreased and the hydrogen peroxide conversion rate was 94.6%, the epichlorohydrin yield based on the amount of substance of hydrogen peroxide was 91.5%. The input of reaction raw materials into the reactor was stopped, and the input was switched to tetrahydrofuran into the reactor filled with titanium silicalite. The flow space velocity of tetrahydrofuran was 0.1 ml·min -1·ml -1 Flush for 20 minutes under the condition of -1 , while raising the reactor temperature to 70 °C, and then input a tetrahydrofuran solution dissolved with benzoyl peroxide and tert-butyl peroxide to flush the reactor filled with titanium silicalite molecular sieve under the condition of heat preservation. The mass fraction concentration of benzoyl peroxide in the tetrahydrofuran solution is 0.3%, and the mass fraction concentration of tert-butyl peroxide in the tetrahydrofuran solution is 2%; calculated by the catalyst per unit volume (ml), the flow space velocity of the tetrahydrofuran solution is 0.02 ml·min -1 ·ml -1 Flush for 2 hours. Then, input methanol into the reactor filled with titanium silicalite molecular sieve, and continue to flush for 20 minutes under the condition that the flow space velocity of methanol is 0.1 ml·min -1 ·ml -1 and cool down to the original catalytic reaction temperature. After flushing is completed, the catalyst resumes its activity. Input the reaction raw materials into the reactor under the same conditions and continue the reaction of hydrogen peroxide oxidizing allyl chloride to produce epichlorohydrin. The conversion rate of hydrogen peroxide is 99.8%, and the yield of epichlorohydrin calculated by the amount of substance of hydrogen peroxide is 98.2%. The reaction with a hydrogen peroxide conversion rate higher than 95% and an epichlorohydrin yield calculated by the amount of substance of hydrogen peroxide higher than 90% can be maintained for 1200 hours Example 2

[0020] Mix and input methanol, allyl chloride, and 50% aqueous hydrogen peroxide solution into a fixed-bed reactor filled with TS-1 type titanium silicalite molecular sieve catalyst under the conditions of methanol∶allyl chloride∶hydrogen peroxide = 10∶2∶1 (molar ratio), volume space velocity of 0.025 ml·min -1 ·ml -1 and reaction temperature of 30 °C, so that the TS-1 type titanium silicalite molecular sieve catalyst catalyzes the oxidation of allyl chloride by hydrogen peroxide to produce epichlorohydrin. As the reaction continues, when the catalyst activity decreases and the yield of epichlorohydrin calculated by the amount of substance of hydrogen peroxide is 89.0%, the conversion rate of hydrogen peroxide is 93.8%. Stop inputting the reaction raw materials into the reactor and switch to inputting tetrahydrofuran into the reactor filled with titanium silicalite molecular sieve. Flush for 20 minutes under the condition that the flow space velocity of tetrahydrofuran is 0.1 ml·min -1 ·ml -1 while raising the reactor temperature to 50 °C, and then input a tetrahydrofuran solution dissolved with methyl ethyl ketone peroxide and tert-butyl peroxide to flush the reactor filled with titanium silicalite molecular sieve under the condition of heat preservation. The mass fraction concentration of methyl ethyl ketone peroxide in the tetrahydrofuran solution is 0.3%, and the mass fraction concentration of tert-butyl peroxide in the tetrahydrofuran solution is 2%. Calculated by the catalyst per unit volume (ml), the flow space velocity of the tetrahydrofuran solution is 0.03 ml·min -1 ·ml -1, the flushing time is 1 hour. Then, methanol is introduced into the reactor filled with titanium silicalite molecular sieve. Under the condition that the liquid hourly space velocity of methanol is 0.1 ml·min -1 ·ml -1 , continue to flush for 20 minutes and cool down to the original catalytic reaction temperature. After the flushing is completed, the catalyst resumes its activity. Under the same conditions, introduce the reaction raw materials into the reactor and continue the reaction of hydrogen peroxide epoxidation of allyl chloride to produce epichlorohydrin. The conversion rate of hydrogen peroxide is 99.6%, and the yield of epichlorohydrin based on the amount of substance of hydrogen peroxide is 97.8%. The reaction with a hydrogen peroxide conversion rate higher than 95% and an epichlorohydrin yield based on the amount of substance of hydrogen peroxide higher than 90% can be maintained for 1224 hours. Example 3

[0021] Mix and introduce methanol, allyl chloride, and 50% aqueous hydrogen peroxide solution into a fixed-bed reactor filled with TS-1 type titanium silicalite molecular sieve catalyst under the conditions of methanol:allyl chloride:hydrogen peroxide = 10:2:1 (molar ratio), liquid hourly space velocity of 0.025 ml·min -1 ·ml -1 , and reaction temperature of 30 °C, so that the TS-1 type titanium silicalite molecular sieve catalyst catalyzes the epoxidation of allyl chloride with hydrogen peroxide to produce epichlorohydrin. As the reaction continues, when the catalyst activity decreases and the conversion rate of hydrogen peroxide is 94.0%, the yield of epichlorohydrin based on the amount of substance of hydrogen peroxide is 88.6%. Stop introducing the reaction raw materials into the reactor and switch to introducing tetrahydrofuran into the reactor filled with titanium silicalite molecular sieve. Under the condition that the liquid hourly space velocity of tetrahydrofuran is 0.1 ml·min -1 ·ml -1 , flush for 20 minutes, and at the same time raise the reactor temperature to 60 °C. Then, under the condition of heat preservation, introduce a tetrahydrofuran solution dissolved with azobisisobutyronitrile and tert-amyl peroxide to flush the reactor filled with titanium silicalite molecular sieve. In the tetrahydrofuran solution, the mass fraction concentration of azobisisobutyronitrile is 0.1%, and the concentration of tert-amyl peroxide is 2.5%. Calculated based on the catalyst per unit volume (ml), the liquid hourly space velocity of the tetrahydrofuran solution is 0.015 ml·min -1 ·ml -1 , and the flushing time is 2 hours. Then, introduce methanol into the reactor filled with titanium silicalite molecular sieve. Under the condition that the liquid hourly space velocity of methanol is 0.1 ml·min -1 ·ml -1Continue to rinse for 20 minutes under the conditions and cool down to the original catalytic reaction temperature. After rinsing is completed, the catalyst resumes its activity. Input the reaction raw materials into the reactor under the same conditions and continue the reaction of hydrogen peroxide oxidizing allyl chloride to produce epichlorohydrin. The conversion rate of hydrogen peroxide is 99.5%, and the yield of epichlorohydrin based on the amount of substance of hydrogen peroxide is 97.6%. The reaction with a hydrogen peroxide conversion rate higher than 95% and an epichlorohydrin yield based on the amount of substance of hydrogen peroxide higher than 90% can be maintained for 1080 hours. Example 4

[0022] Input methanol, allyl chloride, and 50% aqueous hydrogen peroxide solution into a fixed-bed reactor filled with TS-1 type titanium silicate molecular sieve catalyst under the conditions of methanol:allyl chloride:hydrogen peroxide = 10:2:1 (molar ratio) and a space velocity of 0.025 ml·min -1 ·ml -1 、at a reaction temperature of 30 °C, and make the TS-1 type titanium silicate molecular sieve catalyst catalyze the oxidation of allyl chloride by hydrogen peroxide to produce epichlorohydrin. As the reaction proceeds continuously, when the activity of the catalyst decreases and the conversion rate of hydrogen peroxide is 94.3%, the yield of epichlorohydrin based on the amount of substance of hydrogen peroxide is 89.2%. Stop inputting the reaction raw materials into the reactor and switch to inputting tetrahydrofuran into the reactor filled with titanium silicate molecular sieve. Rinse for 20 minutes under the condition that the flow space velocity of tetrahydrofuran is 0.1 ml·min -1 ·ml -1 Meanwhile, raise the reactor temperature to 60 °C, and then input a tetrahydrofuran solution dissolved with azobisisobutyronitrile and tert-butyl peroxide to rinse the reactor filled with titanium silicate molecular sieve under the condition of heat preservation. In the tetrahydrofuran solution, the mass fraction concentration of azobisisobutyronitrile is 0.5%, and the mass fraction concentration of tert-butyl peroxide is 2%. Calculated based on the catalyst per unit volume (ml), the flow space velocity of the tetrahydrofuran solution is 0.015 ml·min -1 ·ml -1 , and the rinsing time is 2 hours. Then, input methanol into the reactor filled with titanium silicate molecular sieve and continue to rinse for 20 minutes under the condition that the flow space velocity of methanol is 0.1 ml·min -1 ·ml -1 and cool down to the original catalytic reaction temperature. After rinsing is completed, the catalyst resumes its activity. Input the reaction raw materials into the reactor under the same conditions and continue the reaction of hydrogen peroxide oxidizing allyl chloride to produce epichlorohydrin. The conversion rate of hydrogen peroxide is 99.2%, and the yield of epichlorohydrin based on the amount of substance of hydrogen peroxide is 97.2%. The reaction with a hydrogen peroxide conversion rate higher than 95% and an epichlorohydrin yield based on the amount of substance of hydrogen peroxide higher than 90% can be maintained for 1060 hours. Example 5

[0023] Methanol, allyl chloride, and 50% aqueous hydrogen peroxide solution were mixed and fed into a fixed-bed reactor filled with TS-1 type titanium silicate molecular sieve catalyst under the conditions of methanol∶allyl chloride∶hydrogen peroxide = 10∶2∶1 (molar ratio), a volume space velocity of 0.025 ml·min⁻¹·ml⁻¹, and a reaction temperature of 30 °C, so that the TS-1 type titanium silicate molecular sieve catalyst catalyzed the oxidation of allyl chloride by hydrogen peroxide to produce epichlorohydrin. As the reaction continued, when the catalyst activity decreased and the hydrogen peroxide conversion rate was 94.4%, the epichlorohydrin yield based on the amount of substance of hydrogen peroxide was 89.8%. The input of reaction raw materials into the reactor was stopped, and the input was switched to tetrahydrofuran into the reactor filled with titanium silicate molecular sieve. Under the condition that the flow space velocity of tetrahydrofuran was 0.1 ml·min -1 ·ml -1 , and it was rinsed for 20 minutes. At the same time, the reactor temperature was raised to 65 °C, and then a tetrahydrofuran solution dissolved with benzoyl peroxide and tert-amyl peroxide was input to rinse the reactor filled with titanium silicate molecular sieve under the condition of heat preservation. The mass fraction concentration of benzoyl peroxide in the tetrahydrofuran solution was 0.5%, and the mass fraction concentration of tert-amyl peroxide in the tetrahydrofuran solution was 1%; calculated based on the catalyst per unit volume (ml), the flow space velocity of the tetrahydrofuran solution was 0.01 ml·min -1 ·ml -1 , and the rinsing time was 3 hours. Then, methanol was input into the reactor filled with titanium silicate molecular sieve. Under the condition that the flow space velocity of methanol was 0.1 ml·min -1 ·ml -1 , and it was continuously rinsed for 20 minutes and cooled to the original catalytic reaction temperature. After rinsing, the catalyst regained its activity, and the reaction raw materials were input into the reactor under the same conditions, and the reaction of oxidizing allyl chloride by hydrogen peroxide to produce epichlorohydrin was continued. The hydrogen peroxide conversion rate was 99.7%, and the epichlorohydrin yield based on the amount of substance of hydrogen peroxide was 98.0%. The reaction with a hydrogen peroxide conversion rate higher than 95% and an epichlorohydrin yield based on the amount of substance of hydrogen peroxide higher than 90% could be maintained for 1080 hours. Example 6

[0024] Methanol, allyl chloride, and 50% aqueous hydrogen peroxide solution were under the conditions of methanol∶allyl chloride∶hydrogen peroxide = 10∶2∶1 (molar ratio), and a volume space velocity of 0.025 ml·min -1 ·ml -1, under the condition that the reaction temperature is 30 °C, the mixture is fed into a fixed-bed reactor filled with TS-1 titanium silicalite molecular sieve catalyst, and the TS-1 titanium silicalite molecular sieve catalyst is used to catalyze the oxidation of allyl chloride with hydrogen peroxide to produce epichlorohydrin. As the reaction continues, when the catalyst activity decreases and the conversion rate of hydrogen peroxide is 94.7%, the yield of epichlorohydrin based on the amount of hydrogen peroxide is 90.0%. Stop feeding the reaction raw materials into the reactor and switch to feeding tetrahydrofuran into the reactor filled with titanium silicalite molecular sieve. Under the condition that the space velocity of tetrahydrofuran is 0.1 ml·min -1 ·ml -1 , rinse for 20 minutes while raising the reactor temperature to 65 °C, and then feed a tetrahydrofuran solution containing methyl ethyl ketone peroxide and tert-amyl peroxide dissolved therein to rinse the reactor filled with titanium silicalite molecular sieve under the condition of heat preservation. The mass fraction concentration of methyl ethyl ketone peroxide in the tetrahydrofuran solution is 0.5%, and the mass fraction concentration of tert-amyl peroxide in the tetrahydrofuran solution is 3%; calculated based on the catalyst per unit volume (ml), the space velocity of the tetrahydrofuran solution is 0.015 ml·min-1·ml-1, and the rinsing time is 2 hours. Then, feed methanol into the reactor filled with titanium silicalite molecular sieve. Under the condition that the space velocity of methanol is 0.1 ml·min -1 ·ml -1 , continue to rinse for 20 minutes and cool down to the original catalytic reaction temperature. After rinsing, the catalyst recovers its activity, and the reaction raw materials are fed into the reactor under the same conditions, and the reaction of oxidizing allyl chloride with hydrogen peroxide to produce epichlorohydrin continues. The conversion rate of hydrogen peroxide is 99.4%, and the yield of epichlorohydrin based on the amount of hydrogen peroxide is 97.5%. The reaction with a hydrogen peroxide conversion rate higher than 95% and an epichlorohydrin yield based on the amount of hydrogen peroxide higher than 90% can be maintained for 1150 hours. Example 7

[0025] Mix and feed methanol, allyl chloride, and 50% aqueous hydrogen peroxide solution into a fixed-bed reactor filled with TS-1 titanium silicalite molecular sieve catalyst under the conditions of methanol∶allyl chloride∶hydrogen peroxide = 10∶2∶1 (molar ratio) and a space velocity of 0.025 ml·min -1 ·ml -1 , under the condition that the reaction temperature is 30 °C, and the TS-1 titanium silicalite molecular sieve catalyst is used to catalyze the oxidation of allyl chloride with hydrogen peroxide to produce epichlorohydrin. As the reaction continues, when the catalyst activity decreases and the conversion rate of hydrogen peroxide is 94.3%, the yield of epichlorohydrin based on the amount of hydrogen peroxide is 89.2%. Stop feeding the reaction raw materials into the reactor and switch to feeding tetrahydrofuran into the reactor filled with titanium silicalite molecular sieve. Under the condition that the space velocity of tetrahydrofuran is 0.1 ml·min -1 ·ml -1Flush for 20 minutes under the condition that the reactor temperature is raised to 60 °C, and then input a tetrahydrofuran solution dissolved with benzoyl peroxide, azobisisobutyronitrile and tert-butyl peroxide to flush the reactor filled with titanium silicalite molecular sieve under the condition of heat preservation. In the tetrahydrofuran solution, the mass fraction concentration of benzoyl peroxide is 0.1%, the mass fraction concentration of azobisisobutyronitrile is 0.1%, and the mass fraction concentration of tert-butyl peroxide is 3%. Calculated by the catalyst per unit volume (ml), the flow space velocity of the tetrahydrofuran solution is 0.015 ml·min -1 ·ml -1 , and the flushing time is 2 hours. Then, input methanol into the reactor filled with titanium silicalite molecular sieve, and continue to flush for 20 minutes under the condition that the flow space velocity of methanol is 0.1 ml·min -1 ·ml -1 , and cool down to the original catalytic reaction temperature. After the flushing is completed, the catalyst resumes its activity. Input the reaction raw materials into the reactor under the same conditions, and continue the reaction of hydrogen peroxide oxidizing allyl chloride to produce epichlorohydrin. The conversion rate of hydrogen peroxide is 99.2%, and the yield of epichlorohydrin calculated by the amount of substance of hydrogen peroxide is 97.2%. The reaction with a hydrogen peroxide conversion rate higher than 95% and an epichlorohydrin yield calculated by the amount of substance of hydrogen peroxide higher than 90% can be maintained for 1026 hours. Example 8

[0026] Mix and input methanol, allyl chloride, and 50% aqueous hydrogen peroxide solution into a fixed-bed reactor filled with TS-1 type titanium silicalite molecular sieve catalyst under the conditions of methanol∶allyl chloride∶hydrogen peroxide = 10∶2∶1 (molar ratio), a volume space velocity of 0.025 ml·min -1 ·ml -1 , and a reaction temperature of 30 °C, so that the TS-1 type titanium silicalite molecular sieve catalyst catalyzes the oxidation of allyl chloride by hydrogen peroxide to produce epichlorohydrin. As the reaction continues, when the catalyst activity decreases and the yield of epichlorohydrin calculated by the amount of substance of hydrogen peroxide is 89.0%, the conversion rate of hydrogen peroxide is 93.8%. Stop inputting the reaction raw materials into the reactor and switch to inputting tetrahydrofuran into the reactor filled with titanium silicalite molecular sieve. The flow space velocity of tetrahydrofuran is 0.1 ml·min -1 ·ml -1Flush for 20 minutes under the condition that the reactor temperature is raised to 50 °C, and then input a tetrahydrofuran solution dissolved with methyl ethyl ketone peroxide, tert-butyl peroxide and tert-amyl peroxide to flush the reactor filled with titanium silicalite molecular sieve under the condition of heat preservation. The mass fraction concentration of methyl ethyl ketone peroxide in the tetrahydrofuran solution is 0.5%, the mass fraction concentration of tert-butyl peroxide in the tetrahydrofuran solution is 1%, and the mass fraction concentration of tert-amyl peroxide in the tetrahydrofuran solution is 1%. Calculated based on the catalyst per unit volume (ml), the flow space velocity of the tetrahydrofuran solution is 0.02 ml·min -1 ·ml -1 , and the flushing time is 3 hours. Then, input methanol into the reactor filled with titanium silicalite molecular sieve. Under the condition that the flow space velocity of methanol is 0.1 ml·min -1 ·ml -1 , continue to flush for 20 minutes and cool down to the original catalytic reaction temperature. After the flushing is completed, the catalyst resumes its activity. Input the reaction raw materials into the reactor under the same conditions and continue the reaction of hydrogen peroxide oxidizing allyl chloride to produce epichlorohydrin. The conversion rate of hydrogen peroxide is 99.6%, and the yield of epichlorohydrin calculated based on the amount of substance of hydrogen peroxide is 97.8%. The reaction with a hydrogen peroxide conversion rate higher than 95% and an epichlorohydrin yield higher than 90% calculated based on the amount of substance of hydrogen peroxide can continue for 1007 hours. Comparative Example 1

[0027] Mix and input methanol, allyl chloride, and 50% aqueous hydrogen peroxide solution into a fixed-bed reactor filled with TS-1 type titanium silicalite molecular sieve catalyst under the conditions of methanol∶allyl chloride∶hydrogen peroxide = 10∶2∶1 (molar ratio), a volume space velocity of 0.025 ml·min -1 ·ml -1 , and a reaction temperature of 30 °C, so that the TS-1 type titanium silicalite molecular sieve catalyst catalyzes the oxidation of allyl chloride by hydrogen peroxide to produce epichlorohydrin. As the reaction continues, when the catalyst activity decreases and the hydrogen peroxide conversion rate is 94.5%, the yield of epichlorohydrin calculated based on the amount of substance of hydrogen peroxide is 89.0%. Without any change, input the reaction raw materials into the reactor under the same conditions and continue the reaction of hydrogen peroxide oxidizing allyl chloride to produce epichlorohydrin. After 24 hours, the hydrogen peroxide conversion rate continues to decrease by 78.6%, and the yield of epichlorohydrin calculated based on the amount of substance of hydrogen peroxide continues to decrease to 72.2%, and the catalyst is significantly further deactivated.

[0028] It can be seen from Comparative Example 1 that when the hydrogen peroxide conversion rate is lower than 95% or the epichlorohydrin yield calculated based on the amount of substance of hydrogen peroxide is lower than 90%, if the TS-1 type titanium silicalite molecular sieve catalyst is not treated in time, it will seriously affect the catalytic activity of the TS-1 type titanium silicalite molecular sieve catalyst and reduce its service life. Comparative Example 2

[0029] Methanol, allyl chloride, and 50% aqueous hydrogen peroxide solution were mixed at a molar ratio of methanol:allyl chloride:hydrogen peroxide = 10:2:1 and a volumetric space velocity of 0.025 ml·min -1 ·ml -1 and fed into a fixed-bed reactor filled with TS-1 titanium silicalite molecular sieve catalyst at a reaction temperature of 30 °C, enabling the TS-1 titanium silicalite molecular sieve catalyst to catalyze the oxidation of allyl chloride by hydrogen peroxide to produce epichlorohydrin. As the reaction continued, when the catalyst activity decreased and the hydrogen peroxide conversion was 94.9%, the epichlorohydrin yield based on the amount of hydrogen peroxide was 90.5%. The input of reaction raw materials into the reactor was stopped, and methanol was switched to be fed into the reactor filled with titanium silicalite molecular sieve. The reactor was flushed for 20 minutes at a flow space velocity of methanol of 0.1 ml·min -1 ·ml -1 under the condition, and at the same time, the reactor temperature was raised to 75 °C, and then methanol was used to continue flushing for 5 hours at a space velocity of 0.1 ml·min-1·ml-1 under the condition of heat preservation, and the temperature was lowered to the original catalytic reaction temperature. After the flushing was completed, the reaction raw materials were fed into the reactor under the same conditions, and the reaction of oxidizing allyl chloride by hydrogen peroxide to produce epichlorohydrin was continued. The hydrogen peroxide conversion was 96.5%, and the epichlorohydrin yield based on the amount of hydrogen peroxide was 92.6%. After 72 hours, the hydrogen peroxide conversion was 93.6%, and the epichlorohydrin yield based on the amount of hydrogen peroxide was 87.3%. It can be seen that the reaction with a hydrogen peroxide conversion higher than 95% and an epichlorohydrin yield higher than 90% based on the amount of hydrogen peroxide could not be maintained for more than 72 hours.

[0030] It can be seen from Comparative Example 2 that if pure methanol is used as the washing liquid to treat the TS-1 titanium silicalite molecular sieve catalyst, the recovery rate of catalytic activity is not high, and the continuous reaction time after recovery is only 72 h, which is much less than more than 1000 hours of the present invention. Comparative Example 3

[0031] Methanol, allyl chloride, and 50% aqueous hydrogen peroxide solution were mixed at a molar ratio of methanol:allyl chloride:hydrogen peroxide = 10:2:1 and a volumetric space velocity of 0.025 ml·min -1 ·ml -1, under the condition that the reaction temperature is 30°C, the reactants are fed into a fixed-bed reactor filled with TS-1 titanium silicalite molecular sieve catalyst in a mixed manner, and the TS-1 titanium silicalite molecular sieve catalyst catalyzes the oxidation of allyl chloride by hydrogen peroxide to produce epichlorohydrin. As the reaction proceeds, when the catalyst activity decreases and the conversion rate of hydrogen peroxide is 94.8%, the yield of epichlorohydrin based on the amount of substance of hydrogen peroxide is 91.6%. Stop feeding the reaction raw materials into the reactor and switch to feeding tetrahydrofuran into the reactor filled with titanium silicalite molecular sieve. Under the condition that the space velocity of tetrahydrofuran is 0.1 ml·min -1 ·ml -1 , rinse for 20 minutes while raising the reactor temperature to 70°C, and then continue to feed tetrahydrofuran at a space velocity of 0.1 ml·min -1 ·ml -1 to rinse the reactor filled with titanium silicalite molecular sieve. Calculated based on the catalyst per unit volume (ml), the space velocity of the tetrahydrofuran solution is 0.008 ml·min -1 ·ml -1 , and the rinsing time is 3 hours. Then, feed methanol into the reactor filled with titanium silicalite molecular sieve, and the space velocity of methanol is 0.1 ml·min -1 ·ml -1 and continue to rinse for 20 minutes, and then cool down to the original catalytic reaction temperature. After the rinsing is completed, feed the reaction raw materials into the reactor under the same conditions, and continue the reaction of oxidizing allyl chloride by hydrogen peroxide to produce epichlorohydrin. The conversion rate of hydrogen peroxide is 97.0%, and the yield of epichlorohydrin based on the amount of substance of hydrogen peroxide is 94.5%. After 96 hours, the conversion rate of hydrogen peroxide is 92.7%, and the yield of epichlorohydrin based on the amount of substance of hydrogen peroxide is 88.1%. It can be seen that the reaction with a hydrogen peroxide conversion rate higher than 95% and an epichlorohydrin yield based on the amount of substance of hydrogen peroxide higher than 90% can only be maintained for less than 96 hours.

[0032] It can be seen from Comparative Example 3 that if tetrahydrofuran alone is used as the washing liquid to treat the TS-1 titanium silicalite molecular sieve catalyst, the recovery rate of catalytic activity is not high, and the continuous reaction time after recovery is only 96 h, which is much less than more than 1000 hours of the present invention. Comparative Example 4

[0033] Mix methanol, allyl chloride, and 50% aqueous hydrogen peroxide solution at a molar ratio of methanol:allyl chloride:hydrogen peroxide = 10:2:1, and the volume space velocity is 0.025 ml·min -1 ·ml -1、At a reaction temperature of 30 °C, the reaction mixture is fed into a fixed-bed reactor filled with TS-1 titanium silicate molecular sieve catalyst, and the TS-1 titanium silicate molecular sieve catalyst catalyzes the oxidation of allyl chloride with hydrogen peroxide to produce epichlorohydrin. As the reaction proceeds, when the catalyst activity decreases and the conversion rate of hydrogen peroxide based on the amount of substance of hydrogen peroxide is 94.4% and the yield of epichlorohydrin is 89.5%, the input of reaction raw materials into the reactor is stopped, and the input is switched to tetrahydrofuran into the reactor filled with titanium silicate molecular sieve. Under the condition that the flow space velocity of tetrahydrofuran is 0.1 ml•min -1 •ml -1 , it is rinsed for 20 minutes, and at the same time the reactor temperature is raised to 60 °C. Then, under the condition of heat preservation, a tetrahydrofuran solution dissolved with tert-butyl hydroperoxide is fed into the reactor filled with titanium silicate molecular sieve for rinsing. In the tetrahydrofuran solution, the mass fraction concentration of tert-butyl hydroperoxide is 3%. Calculated based on the catalyst per unit volume (ml), the flow space velocity of the tetrahydrofuran solution is 0.015 ml•min -1 •ml -1 , and the rinsing time is 3 hours. Then, methanol is fed into the reactor filled with titanium silicate molecular sieve. Under the condition that the flow space velocity of methanol is 0.1 ml•min -1 •ml -1 , it is continuously rinsed for 20 minutes and cooled to the original catalytic reaction temperature. After rinsing is completed, the reaction raw materials are fed into the reactor under the same conditions, and the reaction of oxidizing allyl chloride with hydrogen peroxide to produce epichlorohydrin continues. The conversion rate of hydrogen peroxide is 96.1%, and the yield of epichlorohydrin based on the amount of substance of hydrogen peroxide is 90.8%. After 96 hours, the conversion rate of hydrogen peroxide is 91.5%, and the yield of epichlorohydrin based on the amount of substance of hydrogen peroxide is 86.2%. It can be seen that the reaction with a hydrogen peroxide conversion rate higher than 95% and an epichlorohydrin yield higher than 90% based on the amount of substance of hydrogen peroxide continues for less than 96 hours.

[0034] It can be seen from Comparative Example 4 that if a tetrahydrofuran solution only dissolved with tert-butyl hydroperoxide is used as the washing liquid to treat the catalytic activity recovery rate of the TS-1 titanium silicate molecular sieve catalyst is not high, and the continuous reaction time after recovery is only 96 h, which is much less than more than 1000 hours of the present invention. Comparative Example 5

[0035] Methanol, allyl chloride, and 50% aqueous hydrogen peroxide solution are used at a molar ratio of methanol:allyl chloride:hydrogen peroxide = 10:2:1, and the volume space velocity is 0.025 ml·min -1 ·ml -1, under the condition that the reaction temperature is 30°C, the reactants are fed into a fixed-bed reactor filled with TS-1 titanium silicalite molecular sieve catalyst in a mixed manner, and the TS-1 titanium silicalite molecular sieve catalyst catalyzes the oxidation of allyl chloride by hydrogen peroxide to produce epichlorohydrin. As the reaction proceeds, when the catalyst activity decreases and the conversion rate of hydrogen peroxide is 94.6%, the yield of epichlorohydrin based on the amount of substance of hydrogen peroxide is 90.2%. Then, the input of reaction raw materials into the reactor is stopped, and the feeding is switched to tetrahydrofuran into the reactor filled with titanium silicalite molecular sieve. Under the condition that the liquid hourly space velocity of tetrahydrofuran is 0.1 ml·min -1 ·ml -1 , the reactor is flushed for 20 minutes, and at the same time, the reactor temperature is raised to 60°C. Then, under the condition of heat preservation, a tetrahydrofuran solution dissolved with benzoyl peroxide and azodiisobutyronitrile is fed into the reactor filled with titanium silicalite molecular sieve for flushing. In the tetrahydrofuran solution, the mass fraction concentration of benzoyl peroxide is 0.1%, and the mass fraction concentration of azodiisobutyronitrile is 0.1%. Calculated based on the catalyst per unit volume (ml), the liquid hourly space velocity of the tetrahydrofuran solution is 0.015 ml·min -1 ·ml -1 , and the flushing time is 3 hours. Then, methanol is fed into the reactor filled with titanium silicalite molecular sieve. Under the condition that the liquid hourly space velocity of methanol is 0.1 ml·min -1 ·ml -1 , the reactor is continuously flushed for 20 minutes and cooled to the original catalytic reaction temperature. After the flushing is completed, the reaction raw materials are fed into the reactor under the same conditions, and the reaction of oxidizing allyl chloride by hydrogen peroxide to produce epichlorohydrin is continued. The conversion rate of hydrogen peroxide is 96.6%, and the yield of epichlorohydrin based on the amount of substance of hydrogen peroxide is 93.8%. After 96 hours, the conversion rate of hydrogen peroxide is 92.5%, and the yield of epichlorohydrin based on the amount of substance of hydrogen peroxide is 88.3%. It can be seen that the reaction with the hydrogen peroxide conversion rate higher than 95% and the epichlorohydrin yield based on the amount of substance of hydrogen peroxide higher than 90% can only be maintained for less than 96 hours.

[0036] It can be seen from Comparative Example 5 that if a tetrahydrofuran solution only dissolved with benzoyl peroxide and azodiisobutyronitrile is used as the washing liquid to treat the catalytic activity recovery rate of the TS-1 titanium silicalite molecular sieve catalyst is not high, and the continuous reaction time after recovery is only 96 h, which is much less than more than 1000 hours of the present invention.

[0037] It can be seen from Comparative Examples 2-5 that if methanol, tetrahydrofuran, a tetrahydrofuran solution only dissolved with tert-butyl peroxide, or a tetrahydrofuran solution only dissolved with benzoyl peroxide and azodiisobutyronitrile is used alone as the solvent to wash the titanium silicalite molecular sieve, the activity recovery rate is very low, the continuous reaction time after washing is very short, and it is far lower than the continuous reaction time of the method of the present invention.

[0038] Although embodiments of the present invention have been described above, modifications and substitutions made by those skilled in the art without departing from the principles and spirit of the present invention fall within the scope of the present invention claimed.

Claims

1. A method for prolonging the service life of a titanium-silicate molecular sieve catalyst, characterized in that, Comprising the following steps: (1) In a fixed-bed reactor for synthesizing epichlorohydrin by hydrogen peroxide oxidation of allyl chloride, when the activity of the titanium silicalite catalyst decreases, resulting in a hydrogen peroxide conversion rate lower than 95% or an epichlorohydrin yield lower than 90% based on the amount of hydrogen peroxide, stop inputting the reaction raw materials into the fixed-bed reactor filled with titanium silicalite, and switch to inputting tetrahydrofuran into the fixed-bed reactor. Flush for 20 minutes under the condition that the flow space velocity of tetrahydrofuran is 0.1 ml·min -1 ·ml -1 , and at the same time raise the reactor temperature to 50°C - 70°C; (2) Flushing a fixed-bed reactor filled with titanium silicalite molecular sieve with a tetrahydrofuran solution dissolved with a thermal initiator and an organic oxidant under the condition of heat preservation; (3) Finally, methanol is introduced into the reactor filled with titanium silicalite molecular sieve. Under the condition that the flow space velocity of methanol is 0.1 ml·min -1 ·ml -1 , continue to rinse for 20 minutes and cool down to the original catalytic reaction temperature. After the rinsing is completed, the catalyst resumes its activity, and the reaction raw materials can be introduced into the reactor to continue the reaction; The titanium silicalite molecular sieve catalyst is a TS-1 type titanium silicalite molecular sieve catalyst; The thermal initiator is one or a mixture of several of benzoyl peroxide, methyl ethyl ketone peroxide and azobisisobutyronitrile, and the mass fraction concentration of the thermal initiator in the tetrahydrofuran solution is 0.1% - 0.5%; The organic oxidant is one or a mixture of tert-butyl peroxide and tert-amyl peroxide, and the mass fraction concentration of the organic oxidant in the tetrahydrofuran solution is 1% - 3%.

2. A method for prolonging the service life of a titanium-silicate molecular sieve catalyst according to claim 1, characterized in that: The mass fraction concentration of the thermal initiator in the tetrahydrofuran solution is 0.2% - 0.4%.

3. A method for prolonging the service life of a titanium silicate molecular sieve catalyst according to claim 1, characterized in that: The mass fraction concentration of the organic oxidant in the tetrahydrofuran solution is 1.5% - 2.5%.

4. A method for extending the service life of a titanium silicate molecular sieve catalyst according to claim 1, characterized in that: The reactor temperature of the fixed-bed reactor is 50°C - 70°C.

5. A method for prolonging the service life of a titanium-silicate molecular sieve catalyst according to claim 1, characterized in that: Calculated based on per unit volume (ml) of the catalyst, the flow space velocity of the tetrahydrofuran solution dissolved with a thermal initiator and a low-concentration organic oxidant flowing through the catalyst bed is 0.01 - 0.03 ml·min -1 ·ml -1 .

6. A method for prolonging the service life of a titanium-silicate molecular sieve catalyst according to claim 5, characterized in that: The flow space velocity is 0.015 - 0.025 ml·min -1 ·ml -1 .

7. A method for prolonging the service life of a titanium-silicate molecular sieve catalyst according to claim 1, characterized in that: The flushing time is 1 hour - 3 hours.

8. A method for prolonging the service life of a titanium-silicate molecular sieve catalyst according to claim 7, characterized in that: The flushing time is 1.5 hours - 2.5 hours.