Reactor for producing epoxypropane

Abstract

The utility model provides a reactor for producing epoxypropane, which is a tubular fixed bed reactor, a partition plate is arranged in a shell pass of the reactor, and the partition plate divides the shell pass into a first heat exchange section close to an inlet end of the reactor and a second heat exchange section close to an outlet end of the reactor; a newly input heat exchange medium performs countercurrent flow heat exchange in the first heat exchange section; and one part of the heat exchange medium output by the first heat exchange section is input into the second heat exchange section for parallel flow heat exchange. According to the reactor disclosed by the utility model, the epoxidation reaction of propylene and hydrogen peroxide is controlled within a proper reaction temperature range, and the temperature gradient of a bed layer is more uniform, so that better product selectivity is realized; the reactor used in the process is simple in structure, low in equipment investment and good in process economy.

Description

Technical Field

[0001] This utility model relates to the field of chemical synthesis technology, specifically to a reactor for producing propylene oxide. Background Technology

[0002] Propylene oxide, also known as propylene oxide or methyl ethylene oxide, is a very important organic compound raw material, and is the third largest propylene derivative after polypropylene and acrylonitrile. Propylene oxide has a wide range of industrial applications, its largest use being the synthesis of polyether polyols, which in turn manufacture polyurethane. In the United States and Western Europe, this application accounts for over 60% and 70% of the total, respectively. In addition, propylene oxide can be used to manufacture nonionic surfactants and products such as propylene alcohol, propylene glycol, alcohol ethers, propylene carbonate, polypropylene alcohol amine, propionaldehyde, synthetic glycerol, organic acids, synthetic resins, foamed plastics, plasticizers, emulsifiers, wetting agents, detergents, bactericides, and fumigants. Fine chemicals derived from propylene oxide are used in almost all industrial sectors and daily life.

[0003] Currently, the main production processes for propylene oxide include the chlorohydrin process, the co-oxidation process (PO / SM process, PO / TAB process), the cumene oxidation process (CHP process), and the direct oxidation process. Among these, the chlorohydrin process is corrosive to equipment and generates large amounts of wastewater and waste residue containing organochlorides, resulting in significant environmental pressure. Compared to the chlorohydrin process, the co-oxidation process reduces environmental pressure, but its process is lengthy, requires high investment, and has high co-product yields, making its economic benefits significantly constrained by co-products. The direct oxidation process involves the one-step reaction of propylene and hydrogen peroxide to obtain propylene oxide under the catalysis of a special molecular sieve catalyst. This process has mild reaction conditions, high product yield, no other co-products, minimal waste, and virtually no pollution, making it an environmentally friendly clean production process and representing the future direction of propylene oxide production technology.

[0004] In the direct epoxidation of propylene with hydrogen peroxide, the selectivity of the reaction products is closely related to temperature. The reaction temperature is typically controlled within the range of 30-60℃. The average temperature controlled in the reactor varies depending on the catalyst's operating cycle (from the initial stage of high activity to the final stage of low activity). However, regardless of the operating cycle, the overall temperature uniformity of the reactor significantly affects product selectivity. Excessive temperature gradients increase the proportion of side reactions between propylene oxide and solvents and water, thus impacting the economic efficiency of the plant.

[0005] Extensive research has been conducted both domestically and internationally on the impact of catalyst operating cycles on reaction temperature. For example, patent CN108430983A discloses an epoxidation reactor for propylene, which uses one inlet and multiple outlets to distribute the heat exchange medium, thereby reducing the temperature gradient. However, in this technical solution, the heat exchange medium and reactants flow in parallel. According to the principle of heat transfer, parallel flow is not conducive to heat transfer. Therefore, to achieve a better temperature gradient, this technical solution requires a large flow rate of heat exchange medium, increasing the overall energy consumption of the device. Patent CN109999728A discloses a method for controlling the temperature rise of the epoxidation reactor bed. This technical solution uses inert material mixing to pack the catalyst to improve heat transfer efficiency, but this complicates the packing scheme and affects the amount of catalyst packed for the same reactor volume, thus affecting the overall process capacity. Patent CN208824453U controls the reaction temperature by connecting multiple reactors in series and controlling the temperature of different heat exchange media in different reactors. However, this solution has a relatively complex system, high equipment investment, and is not conducive to industrial production. Utility Model Content

[0006] To address the shortcomings of existing technologies, this utility model discloses a reactor for producing propylene oxide. This reactor can effectively reduce the temperature gradient in the epoxidation reaction of propylene and hydrogen peroxide, improve the uniformity of the reaction temperature distribution, and thus improve the selectivity of propylene oxide.

[0007] To achieve the above technical objectives, this utility model proposes a reactor for producing propylene oxide. The reactor is a tubular fixed-bed reactor. The reactor inlet is used to input a mixture containing propylene, an aqueous hydrogen peroxide solution, and a solvent, while the reactor outlet is used to output the reacted material. A baffle is installed within the shell side of the reactor, dividing the shell side into a first heat exchange section near the reactor inlet and a second heat exchange section near the reactor outlet. The first heat exchange section has a first heat exchange medium inlet near the baffle and a first heat exchange medium outlet near the reactor inlet, with newly input heat exchange medium undergoing countercurrent heat exchange within the first heat exchange section. The second heat exchange section has a second heat exchange medium inlet near the baffle and a second heat exchange medium outlet near the reactor outlet. A branch line connected to the cooler inlet is installed on the pipeline connected to the first heat exchange medium outlet, allowing a portion of the heat exchange medium output from the first heat exchange section to enter the second heat exchange section for cocurrent heat exchange.

[0008] Based on extensive exploratory experiments, the research team of this utility model discovered that the temperature gradient in the epoxidation reaction of propylene and hydrogen peroxide is directly related to the concentration of the reactant hydrogen peroxide, in addition to being affected by the catalyst's operating cycle. Specifically, since the epoxidation reaction of propylene and hydrogen peroxide is exothermic, the reaction rate directly affects the amount of heat released, with higher reaction rates resulting in greater heat release and lower reaction rates in turn. When a fixed-bed reactor is used, the concentration of hydrogen peroxide at the reactor inlet is relatively high, and its concentration gradually decreases as the reactants are transported to the reactor outlet. This results in a high heat release at the front of the reaction tube (near the inlet) and a lower heat release at the rear of the reaction tube (near the outlet). Therefore, in actual production, it is necessary to rapidly remove heat at the front of the reaction tube to prevent temperature rise and exacerbation of side reactions, and to continuously remove heat at the rear of the reaction tube while avoiding excessive heat removal that could lower the reaction temperature and affect the reaction process.

[0009] When using the aforementioned reactor for propylene oxide production, a first heat exchange section is installed in the shell side of the reaction tube at the high hydrogen peroxide concentration, where it exchanges heat countercurrently with the newly input heat exchange medium, thus achieving rapid and efficient heat transfer. A second heat exchange section is installed in the shell side of the reaction tube at the low hydrogen peroxide concentration, where it exchanges heat in parallel. The heat exchange medium used in the second heat exchange section is a portion of the heat exchange medium output from the first heat exchange section. Due to the reduced heat release in the low hydrogen peroxide concentration at the low end of the reaction tube, the coupling of the heat exchange media in the first and second heat exchange sections, combined with a more moderate parallel heat transfer efficiency, allows the use of some of the heat removed from the first heat exchange section. This helps maintain the temperature at both ends of the reaction tube within the optimal reaction temperature range, promoting a uniform reaction temperature distribution, weakening the reaction temperature gradient, enhancing the overall performance of the catalyst, and improving feed conversion rate and product selectivity. Furthermore, inputting a portion of the heat exchange medium output from the first heat exchange section into the second heat exchange section also saves on the overall circulation volume of the heat exchange medium, reducing process energy consumption.

[0010] Based on the above technical solution, the research and development team of this utility model explored and optimized the position of the partition. Optionally, the technical solution of this utility model can be configured such that the partition is placed behind the hot spot of the reaction tube in the direction of reaction material conveying. The hot spot refers to the point with the highest temperature inside the reaction tube in a conventional heat extraction design.

[0011] In one optional embodiment of this invention, the baffle is optionally located at 10%-60% of the length of the reaction tube, taking the inlet of the reaction tube as the starting point. This allows the first heat exchange section to surround the area of ​​the reaction tube with the greatest heat release, and enables rapid countercurrent contact heat removal through the newly input heat exchange medium at a lower temperature. In some optional embodiments of this invention, the baffle is optionally located at 10%-35% of the length of the reaction tube, achieving even better heat removal efficiency.

[0012] In an optional embodiment of this utility model, a first heat exchange medium inlet for introducing new circulating medium into the first heat exchange section can be provided between the partition and the hot spot of the reaction tube, thereby facilitating heat exchange between the new heat exchange medium with a lower temperature and the point with the highest temperature in the reaction tube, and improving heat exchange efficiency.

[0013] Based on the above technical solution, the feeding method of the reactant is either top-in, bottom-out or bottom-in, top-out. In some optional embodiments of this utility model, the feeding method of the reactant is preferably top-in, bottom-out, which can more effectively push and mix the materials in the reactor, making the reaction more uniform and rapid.

[0014] Based on the above technical solution, the reactor may be equipped with multiple temperature monitoring devices, thereby enabling the observation of reaction temperatures in different regions of the reaction tube. This facilitates the adjustment of heat exchange capacity by regulating the input temperature and flow rate of the heat exchange medium, promoting a suitable reaction temperature range within the reaction tube and improving reaction selectivity. Optionally, the temperature monitoring device may be a temperature sensor or a thermometer.

[0015] Based on the above technical solution, multiple baffles can be optionally arranged in the shell side of the reactor. The baffles promote full contact and heat exchange between the heat transfer medium and the reaction tube, thereby improving the heat exchange efficiency. Furthermore, the baffles can be either arc-shaped baffles or disk-annular baffles.

[0016] On the other hand, this utility model proposes a method for producing propylene oxide. The method is carried out in the reactor for producing propylene oxide. After a mixture containing propylene, an aqueous hydrogen peroxide solution and a solvent is fed into the inlet of the reactor, an epoxidation reaction is carried out in the reaction tube under the action of a catalyst to produce propylene oxide. The reacted material is output from the outlet of the reactor.

[0017] Furthermore, the research and development team of this utility model explored and optimized the amount of heat exchange medium input to the second heat exchange section. Optionally, the mass of the heat exchange medium input to the second heat exchange section accounts for 10%-70% of the total mass of the heat exchange medium input to the first heat exchange section. Based on experimental data, the research and development team found that the front section of the reaction tube concentrates most of the heat release of the process. Therefore, a large amount of heat needs to be removed in the first heat exchange section to maintain the front section of the reaction tube at a suitable reaction temperature, causing a certain degree of temperature change in the heat exchange medium output from the first heat exchange section. In order to achieve the purpose of removing heat from the rear section of the reaction tube and maintaining a suitable temperature, only 10%-70% of the mass of the heat exchange medium used in the first heat exchange section needs to be input to the second heat exchange section to achieve better heat exchange effect. In the actual process, the flow rate of the heat exchange medium input to the second heat exchange section can be adjusted within the above control range according to the actual temperature control needs. In some optional examples of this utility model, the mass of the heat exchange medium input to the second heat exchange section accounts for 15%-50% of the total mass of the heat exchange medium input to the first heat exchange section. Inputting the heat exchange medium within this flow range for parallel flow heat exchange can effectively remove the heat release from the downstream section of the reaction tube and keep the reaction temperature within a suitable range, preventing the reaction process from being affected by excessively rapid cooling.

[0018] It should be noted that the control of the mass ratio of the heat exchange medium in the first heat exchange section and the second heat exchange section can be achieved in the actual process by setting a flow regulating valve on the pipeline connecting the outlet of the first heat exchange medium in the first heat exchange section and the inlet of the second heat exchange medium in the second heat exchange section. Those skilled in the art can also choose other devices or operating methods that can achieve the same purpose as needed, which does not limit the scope of protection of this utility model.

[0019] Furthermore, the research and development team of this utility model explored and optimized the temperature control methods for the input of the first heat exchange section and the second heat exchange section. In an optional embodiment of this utility model, another portion of the heat exchange medium output from the first heat exchange section (the portion not input to the second heat exchange section) is combined with the heat exchange medium output from the second heat exchange section, cooled by a cooler, and then input as a new heat exchange medium into the first heat exchange section. In actual process, the heat exchange medium can be adjusted to a suitable temperature by adjusting the heat exchange area, refrigerant temperature, and other technical features of the cooler.

[0020] Optionally, the reactor is equipped with a temperature monitoring device to adjust the temperature and / or flow rate of the newly input heat exchange medium by monitoring the temperature of the reaction tube within the first heat exchange section. This invention adjusts the temperature of the heat exchange medium input to the first heat exchange section based on the temperature of different reaction sections of the reaction tube, especially the temperature at the front of the reaction tube, which can at least meet the temperature control requirements of the following operating conditions: ① In the initial stage of the reaction or when the catalyst activity decreases, by controlling the temperature and flow rate of the newly input heat exchange medium, the temperature of the newly input heat exchange medium fed into the reactor is kept within a suitable temperature range, thereby increasing the reaction temperature within the reaction tube and further improving the overall hydrogen peroxide conversion rate in the reaction; ② During the reaction process, especially in the rapid reaction conditions at the front of the reaction tube, by controlling the flow rate of the input heat exchange medium, the temperature within the reaction tube is kept within a suitable temperature range, preventing a continuous rise in temperature that could lead to an aggravation of side reactions. In some optional examples of this invention, it is preferable to adjust the temperature of the newly input heat exchange medium by monitoring the temperature of the reaction tube within the first heat exchange section, which helps to control the total amount of heat exchange medium input to the reactor, reduce the heat exchange medium circulation volume, and improve process operability.

[0021] It should be noted that this utility model does not limit the specific structure of the cooler or the specific operation mode of heat exchange. Any device and operation mode that can reduce the temperature of the heat exchange medium output from the shell side of the reactor is acceptable. For example, by adjusting the circulation rate of the refrigerant in the cooler, the fan frequency of the air cooler, the chilled water volume of the chilled water heat exchanger, etc., those skilled in the art can choose according to their needs.

[0022] Furthermore, the temperature and / or flow rate of the heat exchange medium input to the second heat exchange section are adjusted by monitoring the temperature of the reaction tube within the second heat exchange section. This invention adjusts the temperature of the heat exchange medium input to the second heat exchange section based on the temperature of different reaction sections of the reaction tube, especially the temperature of the downstream section of the reaction tube, which can at least meet the temperature control requirements of the following operating conditions: ③ At the initial stage of the reaction or when the catalyst activity decreases, by inputting a heat exchange medium with a certain temperature output from the first heat exchange section into the second heat exchange section, the temperature at the downstream end of the reaction tube is increased to promote the reaction and improve the selectivity of propylene oxide; ④ During the reaction, by controlling the temperature or flow rate of the heat exchange medium in conjunction with co-current heat exchange, the heat of reaction in the downstream section of the reaction tube is continuously removed, promoting the complete conversion of the raw materials. In some optional examples of this invention, it is preferable to adjust the flow rate of the heat exchange medium input to the second heat exchange section by monitoring the temperature of the reaction tube within the second heat exchange section, thereby improving the recycling rate of the heat exchange medium and reducing process energy consumption.

[0023] Furthermore, the temperature of the newly input heat exchange medium is 20-45℃. In the actual process, the temperature of the heat exchange medium at this temperature is about 5-20℃ lower than the temperature of the front section of the reaction tube surrounded by the first heat exchange section. Through the countercurrent heat exchange between the first heat exchange section and the reaction tube, the heat released from the front section of the reaction tube can be quickly removed to prevent the temperature from getting too high and improve product selectivity.

[0024] Furthermore, the temperature of the heat exchange medium input to the second heat exchange section is 23-50℃. In actual processes, the temperature of the heat exchange medium under this temperature condition is about 5-15℃ lower than the temperature of the downstream section of the reaction tube surrounded by the second heat exchange section. By exchanging heat in parallel with the reaction tube within this temperature range, the heat released from the downstream section of the reaction tube can be removed more evenly, so as to maintain a suitable reaction temperature and promote the full progress of the reaction.

[0025] Furthermore, the mass concentration of the hydrogen peroxide aqueous solution is 30%-80%, preferably 45%-70%. Optimizing the concentration of the hydrogen peroxide aqueous solution is beneficial for controlling the overall reaction process and facilitating the control of the reaction system temperature.

[0026] Furthermore, the feed mass ratio of the solvent, propylene, and the hydrogen peroxide aqueous solution can be selected as (2-6):(1-4):1, preferably (3-5):(1.5-3):1. Optimizing the ratio of reactants is beneficial to controlling reaction efficiency and reducing the occurrence of side reactions.

[0027] Furthermore, the temperature of the epoxidation reaction can be selected as 30-55℃, and the reaction pressure can be selected as 2.0-2.9MPa.

[0028] Furthermore, the catalyst is a titanium-silicon molecular sieve.

[0029] Furthermore, the solvent is methanol.

[0030] Furthermore, in the actual process, those skilled in the art can select a suitable heat exchange medium as needed. For example, the heat exchange medium can be water, chilled water (ethylene glycol aqueous solution, calcium chloride aqueous solution, etc.), methanol, ethanol or other optional heat exchange media, with water being preferred.

[0031] Compared with the prior art, the beneficial effects of this utility model are as follows: by dividing the shell side of the fixed-bed tubular reactor into a first heat exchange section near the raw material inlet and a second heat exchange section near the outlet of the reacted material, and by using a newly input heat exchange medium for countercurrent heat exchange in the first heat exchange section and a portion of the heat exchange medium output from the first heat exchange section for cocurrent heat exchange in the second heat exchange section, the bed temperature of the fixed-bed reactor used for the propylene and hydrogen peroxide epoxidation reaction is controlled within a suitable range, and the bed temperature gradient is more uniform, thereby achieving better product selectivity; the reactor structure used in the process is simple, the equipment investment is low, and the process economy is good. Attached Figure Description

[0032] The accompanying drawings, which form part of this application, are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an undue limitation of the present invention. In the drawings:

[0033] Figure 1 This invention illustrates a structural diagram of a fixed-bed tubular reactor used in this invention.

[0034] Figure 2 This diagram shows another structural diagram of the fixed-bed tubular reactor used in this invention;

[0035] Figure 3 Temperature monitoring graphs for Example 1, Comparative Example 1, and Comparative Example 2 are shown.

[0036] The above figures include the following reference numerals:

[0037] 11-Reactor inlet, 12-Reactor outlet, 2-Baffle, 31-First heat exchange medium inlet, 32-First heat exchange medium outlet, 41-Second heat exchange medium inlet, 42-Second heat exchange medium outlet, 5-Baffle plate, 6-Cooler. Detailed Implementation

[0038] To facilitate understanding of this utility model, a more comprehensive description of it will be provided below, along with preferred embodiments. However, it should be understood that these embodiments are merely for more detailed explanation and should not be construed as limiting the utility model in any way, i.e., not limiting the scope of protection of this utility model.

[0039] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which this invention pertains. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.

[0040] This invention proposes a reactor for producing propylene oxide, such as... Figure 1 As shown, the reactor is a tubular fixed-bed reactor. The reactor inlet 11 is used to input a mixture containing propylene, hydrogen peroxide aqueous solution, and solvent, and the reactor outlet 12 is used to output the reacted material. A baffle 2 is installed in the shell side of the reactor, dividing the shell side into a first heat exchange section near the reactor inlet and a second heat exchange section near the reactor outlet. The first heat exchange section has a first heat exchange medium inlet 31 near the baffle 2 and a first heat exchange medium outlet 32 ​​near the reactor inlet 11, where newly input heat exchange medium undergoes countercurrent heat exchange. The second heat exchange section has a second heat exchange medium inlet 41 near the baffle 2 and a second heat exchange medium outlet 42 near the reactor outlet. A branch line connected to the inlet 41 of the cooler 6 is installed on the pipeline connected to the first heat exchange medium outlet 32, allowing a portion of the heat exchange medium output from the first heat exchange section to enter the second heat exchange section for cocurrent heat exchange.

[0041] Optionally, the baffle 2 of the reactor for producing propylene oxide is located at 10%-60% of the length of the reaction tube, preferably at 10%-35% of the length of the reaction tube, with the inlet of the reaction tube in the reactor as the starting point.

[0042] Optionally, the feed method of the reactants is either top-in, bottom-out or bottom-in, top-out, preferably top-in, bottom-out. Figure 1 The reactor used in this invention for producing propylene oxide has a top-in, bottom-out feeding method. Figure 2 The feed method of the reactor used in this invention for producing propylene oxide is bottom inlet and top outlet.

[0043] It should be noted that those skilled in the art can, as needed, combine the heat exchange medium output from the second heat exchange medium outlet 42 with another portion (the heat exchange medium input to the second heat exchange inlet) output from the first heat exchange medium outlet 32, and then cool it to a suitable temperature through the cooler 6 before inputting it into the first heat exchange medium inlet 31 for heat exchange and heat removal. Those skilled in the art can, as needed, install devices or equipment such as circulating pumps or compressors on the pipeline for transporting liquid materials, without limiting the scope of protection of this utility model.

[0044] Optionally, multiple baffles 5 are provided in the shell side of the reactor; the baffles 5 can be bow-shaped baffles or disk-annular baffles.

[0045] Example 1

[0046] A method for producing propylene oxide, the method employing Figure 1The reactor shown has reactants fed into it through reactor inlet 11 at the top and reacting with a catalyst inside the reaction tube to produce propylene oxide. The reactants are then discharged through reactor outlet 12 at the bottom. The shell side of the reactor is divided into two parts by a partition 2. Newly introduced heat exchange medium enters the first heat exchange section through a first heat exchange medium inlet 31 near the partition 2 and exits through a first heat exchange medium outlet 32 ​​near the inlet end of the reaction tube. A portion of the heat exchange medium discharged from the first heat exchange medium outlet 32 ​​enters the second heat exchange section through a second heat exchange medium inlet 41 near the partition 2 and exits through a second heat exchange medium outlet 42 near the outlet end of the reaction tube.

[0047] In this embodiment, the tubular fixed-bed reactor has a 16m long reaction tube, with baffle 2 positioned 4m from the inlet of the reaction tube. Inert balls are packed within 0.5m of the inlet side and 0.5m of the outlet side of the reaction tube, with titanium-silicon molecular sieve catalyst packed between the inert balls at both ends. A mixture of methanol, propylene, and a 50% (w / w) aqueous solution of hydrogen peroxide (mass ratio 4:2:1) is introduced into the fixed-bed reactor. The hydrogen peroxide feed space velocity is 0.15 h / h. The reactor pressure is controlled at 3.0 MPaG to allow the propylene to undergo an epoxidation reaction with the hydrogen peroxide. Before the reaction begins, the required amount of cooling water is introduced into the first cooling medium inlet at a temperature of 30°C. Subsequently, 30% of the cooling water from the first cooling medium outlet is introduced into the second cooling medium inlet. After the reaction begins, the temperature of the cooling water output from the first heat exchange section is measured to be 33°C.

[0048] In this embodiment, the temperature of the reaction tube is measured using a set of multi-point thermometers spaced 0.5m apart, installed at the center of the reaction tube (the first measuring point is located 0.7m from the inlet of the reaction tube). After the reaction reaches steady state, the temperature distribution inside the reaction tube is measured and recorded. The temperature monitoring results are as follows: Figure 3 As shown in the figure, the maximum temperature difference inside the reaction tube is 0.9℃.

[0049] After the reaction in this embodiment is completed, the mass concentrations of hydrogen peroxide and propylene oxide in the reaction product are determined by analysis and testing, thereby calculating the hydrogen peroxide conversion rate and the selectivity of the propylene oxide product.

[0050] The calculation process is as follows:

[0051]

[0052] After testing and calculation, the total hydrogen peroxide conversion rate in this embodiment is 99.2%, and the propylene oxide selectivity is 98.3%.

[0053] Comparative Example 1

[0054] A method for preparing propylene oxide is disclosed. The tubular fixed-bed reactor used in this method has a reaction tube with a length of 16m. The type and loading method of the catalyst in the reactor, as well as the ratio of reactants and the control of reaction pressure are the same as in Example 1. The difference is that the shell side of the reactor used in this comparative example is not equipped with a baffle. During the process, the required amount of cooling water is introduced into the cooling medium inlet near the reactor inlet end, and all cooling medium is led out from the cooling medium outlet near the reactor outlet end. That is, the cooling medium and the reactants are in parallel flow.

[0055] This comparative example uses a set of multi-point thermometers spaced 0.5m apart, installed at the center of the reaction tube (the first measuring point is located 0.7m from the inlet of the reaction tube). After the reaction reaches steady state, the temperature distribution inside the reaction tube is measured and recorded. The temperature monitoring results are as follows: Figure 3 As shown, the maximum temperature difference inside the reaction tube is 10℃.

[0056] Furthermore, after testing and calculation, the hydrogen peroxide conversion rate in this comparative example was 99.1%, and the propylene oxide selectivity was 97.1%.

[0057] Comparative Example 2

[0058] A method for preparing propylene oxide is disclosed. The tubular fixed-bed reactor used in this method has a reaction tube with a length of 16m. The type and loading method of the catalyst in the reactor, as well as the ratio of reactants and the control of reaction pressure are the same as in Example 1. The difference is that the shell side of the reactor used in this comparative example is not equipped with a baffle. During the process, the required amount of cooling water is introduced into the cooling medium inlet near the reactor outlet, and all cooling medium is led out from the cooling medium outlet near the reactor inlet. That is, the cooling medium and the reactants are in countercurrent contact for heat exchange.

[0059] The temperature of the reaction tube was measured using a set of multi-point thermometers spaced 0.5m apart, installed at the center of the tube (the first measuring point was located 0.7m from the inlet). After the reaction reached steady state, the temperature distribution inside the reaction tube was measured and recorded. The temperature monitoring results are as follows: Figure 3 As shown, the maximum temperature difference inside the reaction tube is 14℃.

[0060] After testing and calculation, the hydrogen peroxide conversion rate in this comparative example was 98.7%, and the propylene oxide selectivity was 97.5%.

[0061] Example 2

[0062] A method for producing propylene oxide, wherein the structure of the tubular fixed-bed reactor used in the method is as follows: Figure 2As shown, the reactants are fed from bottom to top. Specifically, the reactants are input through reactor inlet 11 at the bottom of the reactor, react with the catalyst inside the reaction tube to produce propylene oxide, and the reacted material is output from reactor outlet 12 at the top of the reactor. The shell side of the reactor is divided into two parts by a partition 2. Newly input heat exchange medium enters the first heat exchange section through the first heat exchange medium inlet 31 near the partition 2 and exits through the first heat exchange medium outlet 32 ​​near the inlet end of the reaction tube. A portion of the heat exchange medium output from the first heat exchange medium outlet 32 ​​enters the second heat exchange section through the second heat exchange medium inlet 41 near the partition 2 and exits through the second heat exchange medium outlet 42 near the outlet end of the reaction tube.

[0063] In this embodiment, the tubular fixed-bed reactor has a 16m long reaction tube, with baffle 2 positioned 5m from the inlet (lower end) of the reaction tube. Inert spheres are packed within 0.5m of the inlet side and 0.5m of the outlet side of the reaction tube, with titanium-silicon molecular sieve catalyst packed between the inert spheres at both ends. A mixture of methanol, propylene, and a 50% (w / w) aqueous solution of hydrogen peroxide (mass ratio 5:2:1) is introduced into the fixed-bed reactor. The hydrogen peroxide feed space velocity is 0.15 h / h. The reactor pressure is controlled at 2.8 MPaG to allow the propylene to undergo an epoxidation reaction with the hydrogen peroxide. Before the reaction begins, the required amount of cooling water is introduced into the first cooling medium inlet at a temperature of 30°C. Subsequently, 27% of the first cooling medium outlet cooling water is introduced into the second cooling medium inlet. After the reaction begins, the temperature of the cooling water output from the first heat exchange section is measured to be 33.5°C.

[0064] Based on temperature gradient measurements, the bed temperature gradient in this embodiment is 0.8℃. Analysis and calculations of the products show that the hydrogen peroxide conversion rate is 99.3% and the propylene oxide selectivity is 98.1% in this embodiment.

[0065] It should be noted that the above description is a further detailed explanation of the present invention in conjunction with specific embodiments, and should not be construed as limiting the specific implementation of the present invention to these descriptions. For those skilled in the art, several simple improvements can be made without departing from the concept of the present invention, and all such improvements should be considered to fall within the scope of protection of the present invention.

Claims

1. A reactor for producing propylene oxide, characterized in that, The reactor is a tubular fixed-bed reactor. The reactor inlet (11) is used to input a mixture containing propylene, hydrogen peroxide aqueous solution and solvent, and the reactor outlet (12) is used to output the reacted material. The reactor is provided with a baffle (2) in the shell side, which divides the shell side into a first heat exchange section near the reactor inlet and a second heat exchange section near the reactor outlet. The first heat exchange section is provided with a first heat exchange medium inlet (31) near the partition (2) and a first heat exchange medium outlet (32) near the reactor inlet end. The newly input heat exchange medium undergoes countercurrent heat exchange in the first heat exchange section. The second heat exchange section is provided with a second heat exchange medium inlet (41) near the partition (2) and a second heat exchange medium outlet (42) near the reactor outlet end; a branch is provided on the pipeline connected to the first heat exchange medium outlet (32) and connected to the second heat exchange medium inlet (41), so that a part of the heat exchange medium output from the first heat exchange section is input into the second heat exchange section for parallel heat exchange.

2. The reactor for producing propylene oxide according to claim 1, characterized in that, The baffle (2) is located at 10%-60% of the length of the reaction tube, starting from the inlet of the reaction tube in the reactor.

3. The reactor for producing propylene oxide according to claim 2, characterized in that, The baffle (2) is located at 10%-35% of the length of the reaction tube, starting from the inlet of the reaction tube in the reactor.

4. The reactor for producing propylene oxide according to claim 1, characterized in that, The feed method for the reactants is either top-in, bottom-out or bottom-in, top-out.

5. The reactor for producing propylene oxide according to claim 4, characterized in that, The feed method for the reactants is top-in, bottom-out.

6. The reactor for producing propylene oxide according to claim 1, characterized in that, Multiple baffles (5) are provided in the shell side of the reactor.

7. The reactor for producing propylene oxide according to claim 1, characterized in that, The baffle (5) is an arc-shaped baffle or a disk-ring baffle.

8. The reactor for producing propylene oxide according to claim 1, characterized in that, The reactor is equipped with a temperature monitoring device.

9. The reactor for producing propylene oxide according to claim 8, characterized in that, The temperature monitoring device is a multi-point thermometer.

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