Reactor and method for producing epoxypropane

Abstract

The invention provides a reactor and method for producing epoxypropane, the reactor is a tubular fixed bed reactor, a partition plate is arranged in a shell side of the reactor, and the partition plate divides the shell side 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 invention, 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] The invention relates to the technical field of chemical synthesis, and in particular to a reactor and a method for producing propylene oxide. Background Art

[0002] Propylene oxide, also known as propylene oxide and methyl ethylene oxide, is a very important organic compound raw material and the third largest propylene derivative after polypropylene and acrylonitrile. Propylene oxide has a wide range of applications in industry. Its largest application is the synthesis of polyether polyols, which in turn produce polyurethanes. In the United States and Western Europe, this application accounts for more than 60% and 70% respectively. In addition, propylene oxide can also be used to produce nonionic surfactants and propylene alcohol, propylene glycol, alcohol ethers, propylene carbonate, polypropanolamine, propionaldehyde, synthetic glycerin, organic acids, synthetic resins, foam plastics, plasticizers, emulsifiers, wetting agents, detergents, bactericides, fumigants, etc. Fine chemicals derived from propylene oxide are used in almost all industrial sectors and daily life.

[0003] At present, the main production processes of propylene oxide include chlorohydrin method, co-oxidation method (PO / SM method, PO / TAB method), cumene oxidation method (CHP method) and direct oxidation method. Among them, the chlorohydrin method is corrosive to equipment, and a large amount of wastewater and waste residue containing organic chlorides are produced during the production process, which puts great pressure on the environment. Compared with the chlorohydrin method, the co-oxidation method reduces the environmental pressure, but its process is long, the investment is high, the output of co-products is high, and the economic benefits are obviously restricted by the co-products. The direct oxidation method is a process in which propylene and hydrogen peroxide are reacted in one step under the catalytic action of a special molecular sieve catalyst to obtain propylene oxide. This process has mild reaction conditions, high product yield, no other co-products, less three wastes, and basically no pollution. It is an environmentally friendly clean production process, which represents the development direction of propylene oxide production technology.

[0004] In the production process of direct propylene epoxidation with hydrogen peroxide, the selectivity of the reaction product is closely related to the temperature. The reaction temperature is usually controlled within the range of 30-60°C. As the catalyst operation cycle (from the initial stage of high activity to the final stage of low activity) changes, the average temperature controlled by the reactor is different. However, no matter which operation cycle it is in, the overall temperature uniformity of the reactor has a great influence on the product selectivity. Excessive temperature gradient increases the proportion of side reactions between propylene oxide and solvents and water, affecting the economic benefits of the device.

[0005] Based on the influence of the catalyst operation cycle on the reaction temperature, a large number of studies have been carried out at home and abroad. 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 the reaction material flow in parallel. According to the heat transfer principle, the parallel flow is not conducive to heat transfer. Therefore, in order to achieve a better temperature gradient, this technical solution requires a larger heat exchange medium flow rate, which increases the overall device energy consumption. Patent CN109999728A discloses a method for controlling the temperature rise of the bed of an epoxidation reactor. This technical solution mixes inert materials with the catalyst to improve the heat transfer efficiency, but this complicates the loading scheme and affects the catalyst loading amount under the same reactor volume, thereby affecting the overall process capacity. Patent CN208824453U controls the reaction temperature by connecting multiple reactors in series and controlling different heat medium temperatures in different reactors, but this solution system is relatively complex, the equipment investment is high, and it is not conducive to industrial production. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention discloses a reactor and a method for producing propylene oxide, which can effectively reduce the temperature gradient of 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] In order to achieve the above technical objectives, on the one hand, the present invention proposes a reactor for producing propylene oxide, wherein the reactor is a shell-and-tube fixed bed reactor, the reactor inlet is used to input a mixed material containing propylene, an aqueous hydrogen peroxide solution and a solvent, and the reactor outlet is used to output the reacted material; wherein a partition is arranged in the shell side of the reactor, and the partition divides the shell side into a first heat exchange section near the inlet end of the reactor and a second heat exchange section near the outlet end of the reactor; the first heat exchange section is provided with a first heat exchange medium inlet near the partition and a first heat exchange medium outlet near the inlet end of the reactor, and the newly input heat exchange medium performs countercurrent heat exchange in the first heat exchange section; the second heat exchange section is provided with a second heat exchange medium inlet near the partition and a second heat exchange medium outlet near the outlet end of the reactor; a branch connected to the cooler inlet is arranged on the pipeline connected to the first heat exchange medium outlet, 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 flow heat exchange.

[0008] Based on a large number of exploratory experiments, the research and development team of the present invention found that the reason for the temperature gradient in the epoxidation reaction of propylene and hydrogen peroxide is not only affected by the catalyst operation cycle, but also directly related to the concentration of the raw material hydrogen peroxide. Specifically, since the epoxidation reaction of propylene and hydrogen peroxide is an exothermic reaction, the speed of the reaction rate directly affects the size of the reaction heat release, which is manifested as a large reaction heat release when the reaction rate is high and a small reaction heat release when the reaction rate is low; when a fixed bed reactor is used for the reaction, the concentration of the raw material hydrogen peroxide at the inlet end of the reactor is high and its concentration gradually decreases as the reaction material is transported to the outlet end of the reactor, resulting in a high reaction heat release in the front section of the reaction tube (near the inlet end) and a low reaction heat release in the rear section of the reaction tube (near the outlet end). Therefore, in the actual production process, it is necessary to quickly remove heat in the front section of the reaction tube to prevent the temperature from rising and causing the side reaction to intensify, and to continue to remove heat in the rear section of the reaction while avoiding excessive heat removal to cause the reaction temperature to be too low and affect the reaction process.

[0009] When the above reactor is used for propylene oxide production, a first heat exchange section for countercurrent heat exchange with a newly input heat exchange medium is set in the shell side of the front section of the reaction tube with a higher hydrogen peroxide concentration, so as to quickly and efficiently remove heat; a second heat exchange section for parallel heat exchange is set in the shell side of the rear section of the reaction tube with a lower hydrogen peroxide concentration, and the heat exchange medium used in the second heat exchange section is a part of the heat exchange medium output from the first heat exchange section. Since the rear section of the reaction tube is affected by the lower hydrogen peroxide concentration and the reaction exotherm is less, by coupling the heat exchange medium of the first heat exchange section and the second heat exchange section and combining the parallel heat exchange with a more moderate heat transfer efficiency, part of the heat withdrawn from the first heat exchange section can be used to facilitate the temperature of the rear section of the reaction tube and the temperature of the front section to be kept within the optimal reaction temperature range, thereby promoting uniform distribution of reaction temperature and weakening reaction temperature gradient, promoting the overall performance of the catalyst, and improving raw material conversion rate and product selectivity. In addition, inputting part of the heat exchange medium output from the first heat exchange section into the second heat exchange section also saves the circulation amount of the overall heat exchange medium and reduces process energy consumption.

[0010] Based on the above technical solution, the research and development team of the present invention explored and optimized the location of the partition. Optionally, the technical solution of the present invention can be used to set the partition in the direction of reaction material delivery, near the hot spot of the reaction tube. The hot spot refers to the point with the highest temperature in the reaction tube in the conventional heat extraction design.

[0011] In an optional example of the present invention, the partition may be located at 10%-60% of the length of the reaction tube, taking the inlet of the reaction tube as the starting point, so that the first heat exchange section surrounds the area of ​​the reaction tube with the largest heat release, and quickly removes heat through countercurrent contact with the newly input heat exchange medium at a lower temperature. In some optional embodiments of the present invention, the partition may be located at 10%-35% of the length of the reaction tube, taking the inlet of the reaction tube as the starting point, to achieve better heat removal efficiency.

[0012] In an optional example of the present invention, a first heat exchange medium inlet for inputting new circulating medium into the first heat exchange section can be optionally provided between the partition and the hot spot of the reaction tube, thereby facilitating heat exchange between the new input heat exchange medium at a lower temperature and the point with the highest temperature in the reaction tube, thereby improving heat exchange efficiency.

[0013] Based on the above technical solution, the feeding method of the reaction material is top-in and bottom-out or bottom-in and top-out. In some optional embodiments of the present invention, the feeding method of the reaction material is preferably top-in and bottom-out, which can more effectively push and mix the materials in the reactor and make the reaction proceed more evenly and rapidly.

[0014] Based on the above technical solution, the reactor can be optionally provided with a temperature monitoring device, and the number of the temperature detection devices is multiple, so that the reaction temperature of different regions of the reaction tube can be observed, and the heat exchange amount can be adjusted by adjusting the input temperature and flow rate of the heat exchange medium, so as to promote the reaction tube to be in a suitable reaction temperature range and improve the reaction selectivity. Optionally, the temperature monitoring device can be selected as a temperature sensor or a thermometer.

[0015] Based on the above technical solution, a plurality of baffles can be optionally arranged in the shell side of the reactor, and the baffles can promote the heat exchange between the heat exchange medium and the reaction tube to fully contact and exchange heat, thereby improving the heat exchange efficiency. Furthermore, the baffles can be selected as arched baffles or disc-ring baffles.

[0016] On the other hand, the present invention provides a method for producing propylene oxide, which is carried out in the above-mentioned reactor for producing propylene oxide. After a mixture of propylene, aqueous hydrogen peroxide solution and a solvent is input into the inlet of the reactor, an epoxidation reaction is carried out in a reaction tube under the action of a catalyst to generate propylene oxide, and the reacted material is output from the outlet of the reactor.

[0017] Furthermore, the research and development team of the present invention 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 amount 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, so that the temperature of the heat exchange medium output by the first heat exchange section changes to a certain extent; in order to achieve the purpose of removing heat from the rear section of the reaction tube and maintaining a suitable temperature, it is only necessary to input 10%-70% of the mass of the heat exchange medium used in the first heat exchange section into the second heat exchange section to achieve a 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 the present invention, the mass of the heat exchange medium input to the second heat exchange section accounts for 15%-50% of the total amount of the heat exchange medium input to the first heat exchange section. The heat exchange medium input within this flow range is used for parallel flow heat exchange, which can effectively withdraw the heat released from the rear section of the reaction tube and maintain the reaction temperature within a suitable range, thereby preventing the reaction process from being affected by excessive cooling.

[0018] It should be noted that the regulation of the mass ratio of the heat exchange medium input to 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 first heat exchange medium outlet of the first heat exchange section and the second heat exchange medium inlet of 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, and the scope of protection of the present invention is not limited thereby.

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

[0020] Optionally, the reactor is provided with a temperature monitoring device, and the temperature and / or flow rate of the newly input heat exchange medium is adjusted by monitoring the temperature of the reaction tube within the range of the first heat exchange section. The present invention adjusts the temperature of the heat exchange medium input to the first heat exchange section according to the temperature of different reaction sections of the reaction tube, especially the temperature of the front section of the reaction tube, and can at least meet the temperature control requirements of the following working conditions: ① In the initial stage of the reaction or when the catalyst reaction 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 sent to the reactor is within a suitable temperature range, thereby increasing the reaction temperature in the reaction tube and further improving the hydrogen peroxide conversion rate in the overall reaction; ② During the reaction process, especially in the fast reaction condition of the front section of the reaction tube, by controlling the flow rate of the input heat exchange medium thermometer, the temperature in the reaction tube is kept within a suitable temperature range to prevent the temperature from continuously rising and causing the side reaction to intensify. In some optional examples of the present invention, it is preferred to adjust the temperature of the newly input heat exchange medium by monitoring the temperature of the reaction tube within the range of the first heat exchange section, so as to help control the total amount of heat exchange medium input to the reactor, reduce the circulation amount of heat exchange medium, and improve the process operability.

[0021] It should be noted that the present invention does not limit the specific structure of the cooler or the specific heat exchange operation mode. Any device and operation mode that can reduce the temperature of the heat exchange medium output from the shell side of the reactor can be used. For example, by adjusting the circulation amount of the refrigerant in the cooler, the fan frequency of the air cooler, the chilled water amount of the chilled water heat exchanger, etc., technicians in this field 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 is adjusted by monitoring the temperature of the reaction tube within the second heat exchange section. The present invention adjusts the temperature of the heat exchange medium input to the second heat exchange section according to the temperature of different reaction sections of the reaction tube, especially the temperature of the rear section of the reaction tube, and can at least meet the temperature control requirements of the following working conditions: ③ At the beginning of the reaction or when the catalyst reaction activity decreases, the heat exchange medium with a certain temperature output from the first heat exchange section is input into the second heat exchange section, thereby increasing the temperature at the rear end of the reaction tube to promote the reaction and improve the selectivity of propylene oxide; ④ During the reaction, the reaction heat of the rear section of the reaction tube is continuously removed by controlling the temperature or flow rate of the heat exchange medium in combination with parallel flow heat exchange, thereby promoting the complete conversion of the raw materials. In some optional examples of the present invention, it is preferred 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 the process energy consumption.

[0023] Furthermore, the temperature of the newly input heat exchange medium is 20-45°C. In the actual process, the heat exchange medium at this temperature is about 5-20°C lower than the temperature of the front section of the reaction tube surrounded by the first heat exchange section. Through the countercurrent contact heat exchange between the first heat exchange section and the reaction tube, the heat release of the front section of the reaction tube can be quickly withdrawn to prevent the temperature from being too high, thereby improving product selectivity.

[0024] Furthermore, the temperature of the heat exchange medium input into the second heat exchange section is 23-50°C. In the actual process, the heat exchange medium under this temperature condition is about 5-15°C lower than the temperature of the rear section of the reaction tube surrounded by the second heat exchange section. Through the co-current contact heat exchange between the heat exchange medium and the reaction tube within this temperature range, the heat released in the rear section of the reaction tube can be withdrawn more evenly to maintain a suitable reaction temperature and promote the full progress of the reaction.

[0025] Furthermore, the mass concentration of the aqueous hydrogen peroxide solution is 30%-80%, preferably 45%-70%. By optimizing the concentration of the aqueous hydrogen peroxide solution, it is beneficial to control the overall reaction process and facilitate the control of the temperature of the reaction system.

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

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

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

[0029] Furthermore, the solvent is methanol.

[0030] Furthermore, in the actual process, technicians in this field can select a suitable heat exchange medium as needed. For example, the heat exchange medium can be selected from water, methanol, ethanol or other optional heat exchange media, preferably water, such as process water, chilled water (ethylene glycol aqueous solution, calcium chloride aqueous solution, etc.).

[0031] Compared with the prior art, the present invention has the following beneficial effects: by dividing the shell side of the fixed bed tubular reactor into a first heat exchange section close to the raw material inlet and a second heat exchange section close to the outlet end of the reacted material, and using the newly input heat exchange medium in the first heat exchange section for countercurrent heat exchange, and using a part of the heat exchange medium output from the first heat exchange section to be input into the second heat exchange section for parallel flow heat exchange, the bed temperature of the fixed bed reactor for the epoxidation reaction of propylene and hydrogen peroxide is controlled within a suitable range, and the gradient of the bed temperature is more uniform, thereby achieving better product selectivity; the reactor used in the process has a simple structure, low equipment investment, and good process economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0033] Figure 1 A structural diagram of a fixed bed tubular reactor used in the present invention is shown;

[0034] Figure 2 Another structural diagram of the fixed bed tubular reactor used in the present invention is shown;

[0035] Figure 3 The temperature monitoring diagrams of Example 1, Comparative Example 1 and Comparative Example 2 are shown.

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

[0037] 11 - reactor inlet, 12 - reactor outlet, 2 - partition, 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, 6 - cooler. DETAILED DESCRIPTION

[0038] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively below, and preferred embodiments of the present invention are given. However, it should be understood that these embodiments are only used for more detailed description and should not be understood as limiting the present invention in any form, i.e., not intended to limit the scope of protection of the present invention.

[0039] Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. The test reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods, unless otherwise specified, are all conventional methods.

[0040] The present invention provides a reactor for producing propylene oxide, such as Figure 1As shown, the reactor is a tube-in-tube fixed bed reactor, the reactor inlet 11 is used to input a mixed material containing propylene, aqueous hydrogen peroxide solution and a solvent, and the reactor outlet 12 is used to output the reacted material; wherein, a partition 2 is arranged in the shell side of the reactor, and the partition 2 divides the shell side into a first heat exchange section near the reactor inlet end and a second heat exchange section near the reactor outlet end; 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 11, and the newly input heat exchange medium is countercurrently heat exchanged 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 connected to the inlet 41 of the cooler 6 is arranged on the pipeline connected to the first heat exchange medium outlet 32, 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 flow heat exchange.

[0041] Optionally, taking the inlet of the reaction tube in the reactor as the starting point, the partition 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.

[0042] Optionally, the reaction materials are fed in a top-in and bottom-out manner or a bottom-in and top-out manner, preferably a top-in and bottom-out manner. Figure 1 The feeding method of the reactor for producing propylene oxide of the present invention is shown as top-in and bottom-out. Figure 2 The feeding method of the reactor for producing propylene oxide of the present invention is shown as bottom-in and top-out.

[0043] It should be noted that those skilled in the art can combine the heat exchange medium output from the second heat exchange medium outlet 42 and the other part of the heat exchange medium output from the first heat exchange medium outlet 32 ​​(the heat exchange medium input to the second heat exchange inlet) as needed, and then cool it to a suitable temperature through the cooler 6 and then input it into the first heat exchange medium inlet 31 for heat exchange and heat removal. Those skilled in the art can set a circulating pump or a compressor or other device or equipment to promote the flow of materials on the pipeline for liquid-phase material transportation as needed, and the protection scope of the present invention is not limited thereby.

[0044] Optionally, a plurality of baffles 5 are arranged in the shell side of the reactor; the baffles 5 may be arcuate baffles or disc-ring baffles.

[0045] Example 1

[0046] A method for producing propylene oxide, the method using Figure 1In the reactor shown, the reaction materials are inputted from the reactor inlet 11 at the upper part of the reactor, reacted to generate propylene oxide under the catalysis of the catalyst in the reaction tube, and the reacted materials are outputted from the reactor outlet 12 at the lower part of the reactor. The shell side of the reactor is divided into two parts by the partition 2, and the newly input heat exchange medium is inputted into the first heat exchange section from the first heat exchange medium inlet 31 near the partition 2, and outputted from the first heat exchange medium outlet 32 ​​near the inlet end of the reaction tube; a part of the heat exchange medium outputted from the first heat exchange medium outlet 32 ​​is inputted into the second heat exchange section from the second heat exchange medium inlet 41 near the partition 2, and outputted from the second heat exchange medium outlet 42 near the outlet end of the reaction tube.

[0047] In the specific process of this embodiment, the tube-in-tube fixed bed reactor has a reaction tube of 16m in length, and the partition 2 is set at 4m from the inlet of the reaction tube. The reaction tube is filled with inert balls within 0.5m near the inlet side and inert balls within 0.5m near the outlet side, and titanium silicon molecular sieve catalyst is filled between the inert balls at both ends. A mixed solution of methanol, propylene, and an aqueous solution of 50% mass concentration of hydrogen peroxide in a mass ratio of 4:2:1 is introduced into the fixed bed reactor, and the hydrogen peroxide feed space velocity of the catalyst is 0.15 / h; the reactor pressure is controlled at 3.0MPaG, so that propylene and hydrogen peroxide undergo epoxidation reaction, and the required amount of cooling water is introduced into the first cooling medium inlet before starting the reaction, and the temperature of the newly input cooling water is 30℃, and then 30% of the first cooling medium outlet cooling water is introduced into the second cooling medium inlet. After the reaction starts, the temperature of the cooling water output from the first heat exchange section is measured to be 33℃.

[0048] In this embodiment, the temperature of the reaction tube is measured by a group of multi-point thermometers installed at the center of the reaction tube with an interval of 0.5m (the first measuring point is located at 0.7m from the entrance of the reaction tube). After the reaction reaches a steady state, the temperature distribution inside the reaction tube is measured and recorded. The temperature monitoring results are shown in FIG. Figure 3 As shown, it can be seen that the maximum temperature difference in the reaction tube is 0.9°C.

[0049] After the reaction in this embodiment is completed, the mass concentration of hydrogen peroxide and the mass concentration of propylene oxide in the reaction discharge are determined by analytical testing, so as to calculate 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 of this embodiment is 99.2%, and the propylene oxide selectivity is 98.3%.

[0053] Comparative Example 1

[0054] A method for preparing propylene oxide, wherein a tubular fixed bed reactor used in the preparation method has a reaction tube with a length of 16 m, the type and filling method of the catalyst in the reactor, the ratio of the reaction materials, and the control of the reaction pressure are the same as those in Example 1, except that no baffle is provided on the shell side of the reactor used in this comparative example, and during the process, a required amount of cooling water is introduced into a cooling medium inlet near the reactor inlet end, and all cooling medium is led out from a cooling medium outlet near the reactor outlet end, that is, the cooling medium and the reaction materials are parallel flow.

[0055] In this comparative example, the temperature of the reaction tube is measured by a set of multi-point thermometers installed at the center of the reaction tube with an interval of 0.5m (the first measuring point is located at 0.7m from the entrance of the reaction tube). After the reaction reaches a steady state, the temperature distribution inside the reaction tube is measured and recorded. The temperature monitoring results are shown in Figure 2. Figure 3 As shown, it can be seen that the maximum temperature difference in the reaction tube is 10°C.

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

[0057] Comparative Example 2

[0058] A method for preparing propylene oxide, wherein a tubular fixed bed reactor used in the preparation method has a reaction tube with a length of 16 m, the type and filling method of the catalyst in the reactor, the ratio of the reaction materials, and the control of the reaction pressure are the same as those in Example 1, except that no baffle is provided on the shell side of the reactor used in this comparative example, and during the process, a required amount of cooling water is introduced into a cooling medium inlet near the reactor outlet end, and all cooling medium is led out from a cooling medium outlet near the reactor inlet end, that is, the cooling medium and the reaction materials are in countercurrent contact heat exchange.

[0059] The temperature of the reaction tube is measured by a set of multi-point thermometers installed at the center of the reaction tube with an interval of 0.5m (the first measurement point is located at 0.7m from the entrance of the reaction tube). After the reaction reaches a steady state, the temperature distribution inside the reaction tube is measured and recorded. The temperature monitoring results are as follows: Figure 3 As shown, it can be seen that the maximum temperature difference in the reaction tube is 14°C.

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

[0061] Example 2

[0062] A method for producing propylene oxide, the structure of the tube-in-tube fixed bed reactor used in the method is as follows Figure 2As shown, the feeding method of the reaction materials is bottom-in and top-out. Specifically, the reaction materials are input from the reactor inlet 11 at the lower part of the reactor, react to generate propylene oxide under the catalysis of the catalyst in the reaction tube, and the reacted materials are output from the reactor outlet 12 at the upper part of the reactor. Among them, the shell side of the reactor is divided into two parts by the partition 2, and the newly input heat exchange medium is input into the first heat exchange section from the first heat exchange medium inlet 31 close to the partition 2, and is output from the first heat exchange medium outlet 32 ​​close to the inlet end of the reaction tube; a part of the heat exchange medium output from the first heat exchange medium outlet 32 ​​is input into the second heat exchange section from the second heat exchange medium inlet 41 close to the partition 2, and is output from the second heat exchange medium outlet 42 close to the outlet end of the reaction tube.

[0063] In the specific process of this embodiment, the tubular fixed bed reactor has a reaction tube of 16m in length, and the partition 2 is set at 5m from the inlet (i.e., the lower end) of the reaction tube. The reaction tube is filled with inert balls within 0.5m near the inlet side, and inert balls within 0.5m near the outlet side, and titanium silicon molecular sieve catalyst is filled between the inert balls at both ends. A mixed solution of methanol, propylene, and an aqueous solution of 50% mass concentration of hydrogen peroxide in a mass ratio of 5:2:1 is introduced into the fixed bed reactor, and the hydrogen peroxide feed space velocity of the catalyst is 0.15 / h; the reactor pressure is controlled at 2.8MPaG, so that propylene and hydrogen peroxide undergo epoxidation reaction, and the required amount of cooling water is introduced into the first cooling medium inlet before starting the reaction, and the temperature of the newly input cooling water is 30℃, and then 27% of the first cooling medium outlet cooling water is introduced into the second cooling medium inlet. After the reaction starts, the temperature of the cooling water output from the first heat exchange section is measured to be 33.5℃.

[0064] After measuring the temperature gradient, the bed temperature gradient in this embodiment is 0.8° C. After analyzing and calculating the product, the hydrogen peroxide conversion rate in this embodiment is 99.3%, and the propylene oxide selectivity is 98.1%.

[0065] It should be noted that the above contents are further detailed descriptions of the present invention in combination with specific implementation methods, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple improvements can be made without departing from the concept of the present invention, which should be regarded as falling 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, aqueous hydrogen peroxide solution and a solvent, and the reactor outlet (12) is used to output the reacted material; Wherein, a partition (2) is arranged in the shell side of the reactor, and the partition (2) divides the shell side into a first heat exchange section near the inlet end of the reactor and a second heat exchange section near the outlet end of the reactor; The first heat exchange section is provided with a first heat exchange medium inlet (31) close to the partition (2) and a first heat exchange medium outlet (32) close to the reactor inlet end, and the newly input heat exchange medium performs countercurrent heat exchange in the first heat exchange section; The second heat exchange section is provided with a second heat exchange medium inlet (41) close to the partition (2) and a second heat exchange medium outlet (42) close to the reactor outlet end; a branch connected to the second heat exchange medium inlet (41) is provided on the pipeline connected to the first heat exchange medium outlet (32), 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 flow heat exchange.

2. The reactor for producing propylene oxide according to claim 1, characterized in that Taking the inlet of the reaction tube in the reactor as the starting point, the partition (2) is located at 10%-60% of the length of the reaction tube, preferably at 10%-35% of the length of the reaction tube.

3. The reactor for producing propylene oxide according to claim 1, characterized in that The reaction materials are fed in a manner of top-in and bottom-out or bottom-in and top-out, preferably top-in and bottom-out.

4. The reactor for producing propylene oxide according to claim 1, characterized in that A plurality of baffles (5) are arranged in the shell side of the reactor; Preferably, the baffle (5) is a bow-shaped baffle or a disc-ring baffle.

5. A method for producing propylene oxide, characterized in that The method is carried out in a reactor as claimed in any one of claims 1 to 4, wherein a mixture of propylene, aqueous hydrogen peroxide solution and a solvent is input into the inlet of the reactor, and an epoxidation reaction is carried out in a reaction tube under the action of a catalyst to generate propylene oxide, and the reacted material is output from the outlet of the reactor.

6. The method for producing propylene oxide according to claim 5, characterized in that The mass of the heat exchange medium input into the second heat exchange section accounts for 10%-70%, preferably 15%-50% of the mass of the heat exchange medium input into the first heat exchange section.

7. The method for producing propylene oxide according to claim 5, characterized in that The reactor is provided with a temperature monitoring device, and the temperature and / or flow rate of the newly input heat exchange medium is adjusted by monitoring the temperature of the reaction tube within the first heat exchange section. Preferably, the temperature of the newly input heat exchange medium is adjusted by monitoring the temperature of the reaction tube within the first heat exchange section.

8. The method for producing propylene oxide according to claim 7, characterized in that The temperature and / or flow rate of the heat exchange medium input to the second heat exchange section is adjusted by monitoring the temperature of the reaction tube within the second heat exchange section. Preferably, the flow rate of the heat exchange medium input to the second heat exchange section is adjusted by monitoring the temperature of the reaction tube within the second heat exchange section.

9. The method for producing propylene oxide according to claim 7 or 8, characterized in that The temperature of the newly input heat exchange medium is 20-45℃; And / or, the temperature of the heat exchange medium input into the second heat exchange stage is 23-50°C.

10. The method for producing propylene oxide according to claim 1, characterized in that The mass concentration of the aqueous hydrogen peroxide solution is 30%-80%, preferably 45%-70%; Preferably, the feed mass ratio of the solvent, propylene and the aqueous hydrogen peroxide solution is (2-6): (1-4): 1, preferably (3-5): (1.5-3): 1; And / or, the epoxidation reaction temperature is 30-55°C and the reaction pressure is 2.0-2.9MPa; And / or, the catalyst is titanium silicon molecular sieve; And / or, the solvent is methanol; And / or, the heat exchange medium includes water, methanol, ethanol, preferably water.

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