A cycloalkane dehydrogenation system
By employing high-pressure steam cascade heat exchange and circulating hydrogen in the cycloalkane dehydrogenation system, the shortcomings of the heating and heat exchange methods were solved, the lifespan of the catalyst and heat transfer medium was extended, the effective conversion of cyclohexane and methylcyclohexane was achieved, and the energy utilization efficiency and atom economy of the system were improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- CHINA CHEM TECH RES INST
- Filing Date
- 2025-07-22
- Publication Date
- 2026-06-30
AI Technical Summary
Existing cycloalkane dehydrogenation systems have room for improvement in terms of heating methods, heat exchange methods, and feeding methods, resulting in problems such as short catalyst life, large equipment footprint, and insufficient energy utilization.
High-pressure steam is used as a heat source to perform cascade heat exchange on the dehydrogenation feedstock, and recycled hydrogen is returned to the dehydrogenation reactor to extend the life of the heat transfer medium and catalyst, thereby optimizing the heating and heat exchange methods.
It improves catalyst life, reduces equipment investment and floor space, maximizes the use of high-pressure steam energy, avoids the problem of low catalyst life caused by excessively high reaction temperature, and achieves efficient conversion of cyclohexane and methylcyclohexane into benzene and hydrogen, thus improving atom economy.
Smart Images
Figure CN224422809U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to a cycloalkane dehydrogenation system and belongs to the field of cycloalkane dehydrogenation technology. Background Technology
[0002] Cyclohexane is primarily used in the industrial production of adipic acid and caprolactam, precursors for nylon. It is also commonly used as a solvent, paint remover, and raw material for other chemicals, finding wide applications in industrial coatings, adhesives, and organic synthesis. The hydration process for producing cyclohexanone generates approximately 20% cyclohexane as a byproduct. With the increasing capacity of the hydration process, the market will be unable to absorb the resulting cyclohexane production. To improve the efficient utilization of benzene, a cyclohexane dehydrogenation process is needed to directly convert the byproduct cyclohexane from the cyclohexanone unit into benzene and hydrogen. The benzene and hydrogen can then be recycled back to the cyclohexanone unit as feedstock, thus effectively utilizing the byproduct cyclohexane and improving atom economy.
[0003] Furthermore, methylcyclohexane (MCH) dehydrogenation technology is a key step in realizing organic liquid hydrogen storage (LOHC), and its development relies on the rapid advancement of the hydrogen energy industry and breakthroughs in storage and transportation technology bottlenecks. The MCH-toluene hydrogen storage system has advantages such as high hydrogen storage density (approximately 6.1% by mass), easy liquid transportation at room temperature and pressure, and the ability to utilize existing oil infrastructure, making it particularly suitable for medium- and long-distance transportation. To obtain the hydrogen stored in MCH, a methylcyclohexane dehydrogenation process is required to directly convert MCH into toluene and hydrogen. The hydrogen is then purified and used as a product. The toluene is recovered and transported to a hydrogenation unit, where it is converted back into MCH.
[0004] However, the heating, heat exchange, and feeding methods of existing cycloalkane dehydrogenation systems still need improvement. Utility Model Content
[0005] To address at least one of the aforementioned technical problems, the present invention aims to provide a cycloalkane dehydrogenation system. This system uses high-pressure steam as a heat source to perform staged heat exchange on the dehydrogenation feedstock and to heat the heat transfer medium. Simultaneously, it employs recycled hydrogen return to the dehydrogenation reactor, which extends the lifespan of the heat transfer medium, fully utilizes the energy of the high-pressure steam, and prolongs the catalyst lifespan.
[0006] To achieve the above objectives, this utility model provides a cycloalkane dehydrogenation system, which includes: a reaction feed heat exchanger, a steam condensate preheater, a reactor steam preheater, a reaction discharge cooler, a heat transfer medium steam heat exchanger, a dehydrogenation reactor, and a separator.
[0007] The reaction feed heat exchanger, the steam condensate preheater, the reactor steam preheater, and the feed inlet of the dehydrogenation reactor are connected in sequence.
[0008] The product outlet of the dehydrogenation reactor is sequentially connected to the reaction feed heat exchanger, the reaction discharge cooler, and the separator.
[0009] The reactor steam preheater is provided with a high-pressure steam inlet and a steam condensate outlet, and the steam condensate outlet of the reactor steam preheater is connected to the steam condensate preheater.
[0010] The separator is provided with a gas phase product outlet and a liquid phase product outlet. The gas phase product outlet of the separator is connected to a circulating hydrogen pipeline, which is used to return the circulating hydrogen to the dehydrogenation reactor.
[0011] The heat transfer medium steam heat exchanger is provided with a heat transfer medium inlet, a heat transfer medium outlet, a high-pressure steam inlet, and a steam condensate outlet. The heat transfer medium inlet and outlet of the heat transfer medium steam heat exchanger are circulatedly connected to the dehydrogenation reactor, and the steam condensate outlet of the heat transfer medium steam heat exchanger is connected to the steam condensate preheater.
[0012] According to a specific embodiment of the present invention, preferably, the dehydrogenation reactor comprises a tubular fixed-bed reactor. More preferably, the dehydrogenation reactor is a single-stage tubular fixed-bed reactor.
[0013] According to a specific embodiment of the present invention, preferably, a catalyst bed is provided in the tubes of the dehydrogenation reactor, and the length of the catalyst bed is 3 to 8 m.
[0014] According to a specific embodiment of the present invention, preferably, the catalyst bed is filled with a dehydrogenation catalyst, which includes a noble metal catalyst, preferably a platinum catalyst.
[0015] According to a specific embodiment of the present invention, preferably, the raw material inlet and product outlet of the dehydrogenation reactor are connected to the tube side of the dehydrogenation reactor.
[0016] According to a specific embodiment of this utility model, preferably, the heat transfer medium inlet and outlet of the heat transfer medium steam heat exchanger are circulatedly connected to the shell side of the dehydrogenation reactor for supplying heat to the dehydrogenation reactor using a heat transfer medium. More preferably, the heat transfer medium includes heat transfer oil.
[0017] According to a specific embodiment of the present invention, preferably, the circulating hydrogen pipeline is connected to the reaction feed heat exchanger and / or the steam condensate preheater.
[0018] According to a specific embodiment of this utility model, preferably, the reaction feed heat exchanger is provided with a dehydrogenation feed inlet, a dehydrogenation feed outlet, a dehydrogenation product inlet, and a dehydrogenation product outlet, for exchanging heat between the cycloalkane dehydrogenation feed or the mixed dehydrogenation feed of cycloalkane and circulating hydrogen and the dehydrogenation product; the dehydrogenation product inlet of the reaction feed heat exchanger is connected to the product outlet of the dehydrogenation reactor, and the dehydrogenation product outlet of the reaction feed heat exchanger is connected to the reaction discharge cooler.
[0019] According to a specific embodiment of this utility model, preferably, the steam condensate preheater is provided with a feed inlet, a discharge outlet, a steam condensate inlet, and a steam condensate outlet, for preheating the mixed dehydrogenation feedstock of cycloalkanes and circulating hydrogen using steam condensate from the reactor steam preheater and the heat transfer medium steam heat exchanger; the feed inlet of the steam condensate preheater is connected to the dehydrogenation feedstock outlet of the reaction feed heat exchanger, and the discharge outlet of the steam condensate preheater is connected to the reactor steam preheater.
[0020] According to a specific embodiment of the present invention, preferably, the reactor steam preheater is provided with a feed inlet, a discharge outlet, a high-pressure steam inlet, and a steam condensate outlet, for preheating the mixed dehydrogenation feedstock of cycloalkanes and circulating hydrogen to the dehydrogenation reaction temperature using high-pressure steam; the feed inlet of the reactor steam preheater is connected to the discharge outlet of the steam condensate preheater, and the discharge outlet of the reactor steam preheater is connected to the feedstock inlet of the dehydrogenation reactor.
[0021] According to a specific embodiment of the present invention, preferably, the gaseous product outlet of the separator is connected to a compressor, and the compressor is connected to the product hydrogen pipeline and the circulating hydrogen pipeline, for pressurizing a portion of the gaseous product as circulating hydrogen and the other portion as product hydrogen.
[0022] According to a specific embodiment of this utility model, preferably, the cycloalkane dehydrogenation system further includes a liquid-phase product purification unit connected to the liquid-phase product outlet of the separator. More preferably, the liquid-phase product purification unit includes a distillation column, etc.
[0023] According to a specific embodiment of this utility model, preferably, the cycloalkane dehydrogenation system further includes a product hydrogen purification unit connected to the product hydrogen pipeline. More preferably, the product hydrogen purification unit includes a PSA (pressure swing adsorption) device and / or a membrane separation device, etc.
[0024] This utility model has at least the following beneficial effects:
[0025] This invention improves the heating, heat exchange, and feeding methods of a cycloalkane dehydrogenation system. High-pressure steam is used as a heat source to preheat the dehydrogenation feedstock and heat the heat transfer medium. The heat transfer medium then heats the dehydrogenation reactor, achieving indirect heating of the reaction from the steam heat source. Simultaneously, the condensate from the high-pressure steam preheats the dehydrogenation feedstock, and a portion of the hydrogen in the dehydrogenation products is returned to the dehydrogenation reactor as recycled hydrogen. Indirect heating of the dehydrogenation reaction with high-pressure steam reduces the reactor wall thickness, lowering equipment investment. Furthermore, heating the heat transfer medium with high-pressure steam results in a lower film temperature, avoiding the problems of excessively high film temperature and short lifespan associated with heating the heat transfer medium by a furnace, thus extending the lifespan of the heat transfer medium. Additionally, heating the heat transfer medium with high-pressure steam saves space in the equipment layout, minimizing the equipment footprint and avoiding the excessive footprint caused by a large distance between the furnace and the equipment, as well as the heat dissipation problems caused by excessively long heat transfer medium pipelines. This minimizes heat dissipation from the heat transfer medium equipment. Furthermore, by employing a cascade heat exchange system involving the reaction feed heat exchanger, steam condensate preheater, and reactor steam preheater, the energy of high-pressure steam is maximized, while reducing refrigerant consumption. Additionally, this invention allows for a lower dehydrogenation reaction temperature, avoiding the problem of shortened catalyst life caused by excessively high reaction temperatures and extending catalyst life. Moreover, by returning recycled hydrogen to the dehydrogenation reactor, the hydrogen partial pressure within the reactor is increased, preventing rapid coke formation and further enhancing catalyst life. Using the cyclohexane dehydrogenation process of this invention, the byproduct cyclohexane from the cyclohexanone unit can be directly converted into benzene and hydrogen, which are then recycled back to the cyclohexanone unit as feedstock, effectively utilizing the byproduct cyclohexane. Furthermore, using the methylcyclohexane dehydrogenation process of this invention, methylcyclohexane can be directly converted into toluene and hydrogen, obtaining product hydrogen, while the recovered toluene is sent to the hydrogenation unit for recycling toluene / MCH. Attached Figure Description
[0026] Figure 1 This is a schematic diagram of the structure of the cycloalkane dehydrogenation system in some specific embodiments of this utility model.
[0027] Figure 2 This is a schematic diagram of the structure of a cycloalkane dehydrogenation system in some other specific embodiments of this utility model.
[0028] Figure 3 This is a schematic diagram of the cycloalkane dehydrogenation system in Comparative Example 1.
[0029] Explanation of icon numbers:
[0030] 1-Reaction feed heat exchanger; 2-Steam condensate preheater; 3-Reactor steam preheater; 4-Reaction discharge cooler; 5-Heat transfer medium steam heat exchanger; 6-Dehydrogenation reactor; 7-Separating tank; 8-Circulating hydrogen pipeline; 9-Compressor; 10-Product hydrogen pipeline; 601-First stage reactor; 602-Second stage reactor. Detailed Implementation
[0031] To provide a clearer understanding of the technical features, objectives, and beneficial effects of this utility model, the following detailed description is provided, but it should not be construed as limiting the scope of implementation of this utility model.
[0032] It should be noted that, unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.
[0033] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.
[0034] It should be understood that the terms “comprising,” “including,” and / or “containing” as used herein specify the presence of the stated features, integers, steps, components, or combinations thereof, but do not exclude the presence or addition of one or more other features, integers, steps, components, or combinations thereof.
[0035] In the description of this utility model, it should be noted that the terms "upper", "lower", "top / bottom", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.
[0036] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed", "equipped with", "sleeved / connected", "connected", etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. For those skilled in the art, the specific meaning of the above terms in this utility model can be understood according to the specific circumstances.
[0037] This invention provides a cycloalkane dehydrogenation system, such as... Figure 1 and Figure 2As shown, it includes: a reaction feed heat exchanger 1, a steam condensate preheater 2, a reactor steam preheater 3, a reaction discharge cooler 4, a heat transfer medium steam heat exchanger 5, a dehydrogenation reactor 6, and a separator 7.
[0038] The reaction feed heat exchanger 1, the steam condensate preheater 2, the reactor steam preheater 3, and the raw material inlet of the dehydrogenation reactor 6 are connected in sequence.
[0039] The product outlet of the dehydrogenation reactor 6 is connected in sequence to the reaction feed heat exchanger 1, the reaction discharge cooler 4, and the separator 7.
[0040] The reactor steam preheater 3 is equipped with a high-pressure steam inlet and a steam condensate outlet, and the steam condensate outlet of the reactor steam preheater 3 is connected to the steam condensate preheater 2.
[0041] Separator 7 is equipped with a gas phase product outlet and a liquid phase product outlet. The gas phase product outlet of separator 7 is connected to a circulating hydrogen pipeline 8, which is used to return the circulating hydrogen to the dehydrogenation reactor 6.
[0042] The heat transfer medium steam heat exchanger 5 is provided with a heat transfer medium inlet, a heat transfer medium outlet, a high-pressure steam inlet, and a steam condensate outlet. The heat transfer medium inlet and outlet of the heat transfer medium steam heat exchanger 5 are circulated and connected to the dehydrogenation reactor 6, and the steam condensate outlet of the heat transfer medium steam heat exchanger 5 is connected to the steam condensate preheater 2.
[0043] In some embodiments, the dehydrogenation reactor 6 includes a tubular fixed-bed reactor. Preferably, the dehydrogenation reactor 6 is a single-stage tubular fixed-bed reactor. The present invention preferably uses a single-stage tubular fixed-bed reactor, which can reduce equipment investment and catalyst loading, and improve economic efficiency. Specifically, the dehydrogenation reactor 6 has a raw material inlet at the top and a product outlet at the bottom, and also has a heat transfer medium inlet and a heat transfer medium outlet.
[0044] In some embodiments, a catalyst bed is provided in the tube array of the dehydrogenation reactor 6, the length of which is 3 to 8 m. Preferably, the length of the catalyst bed is 4 to 7 m. By controlling the length of the catalyst bed within the above range, the pressure drop of the dehydrogenation reactor can be made appropriate, avoiding the problem of excessive pressure drop that is unfavorable to the dehydrogenation reaction, and thus achieving a higher conversion rate of the dehydrogenation reaction.
[0045] In some embodiments, the catalyst bed is packed with a dehydrogenation catalyst, which includes a noble metal catalyst, preferably a platinum catalyst. More preferably, the dehydrogenation catalyst is a supported platinum catalyst, wherein the platinum content in the supported platinum catalyst is 0.5% to 5% by mass.
[0046] In some embodiments, the feed inlet and product outlet of the dehydrogenation reactor 6 are connected to the tube side of the dehydrogenation reactor 6.
[0047] In some embodiments, the heat transfer medium inlet and outlet of the heat transfer medium steam heat exchanger 5 are circulatedly connected to the shell side of the dehydrogenation reactor 6 for supplying heat to the dehydrogenation reactor 6 using a heat transfer medium. Specifically, the heat transfer medium inlet and outlet of the heat transfer medium steam heat exchanger 5 are circulatedly connected to the heat transfer medium outlet and inlet of the shell side of the dehydrogenation reactor 6. Preferably, the heat transfer medium includes heat transfer oil.
[0048] In some embodiments, the circulating hydrogen line 8 is connected to the reaction feed heat exchanger 1 and / or the steam condensate preheater 2. Specifically, as Figure 1 As shown, the circulating hydrogen pipeline 8 is connected to the reaction feed heat exchanger 1, used to mix the cycloalkanes and circulating hydrogen before they enter the reaction feed heat exchanger 1 to exchange heat with the dehydrogenation products. Alternatively, as... Figure 2 As shown, the circulating hydrogen pipeline 8 is connected to the steam condensate preheater 2. This allows the cycloalkanes to exchange heat with the dehydrogenation products in the reaction feed heat exchanger 1 before being mixed with circulating hydrogen and entering the steam condensate preheater 2 for preheating. By mixing and preheating the circulating hydrogen with the cycloalkanes through the circulating hydrogen pipeline 8 before entering the dehydrogenation reactor 6, the problem of potential side reactions that might occur if the preheated cycloalkanes directly enter the dehydrogenation reactor 6 in the absence of hydrogen can be avoided.
[0049] In some embodiments, the reaction feed heat exchanger 1 is provided with a dehydrogenation feed inlet, a dehydrogenation feed outlet, a dehydrogenation product inlet, and a dehydrogenation product outlet, for exchanging heat between the cycloalkane dehydrogenation feed or the mixed dehydrogenation feed of cycloalkane and circulating hydrogen and the dehydrogenation product; the dehydrogenation product inlet of the reaction feed heat exchanger 1 is connected to the product outlet of the dehydrogenation reactor 6, and the dehydrogenation product outlet of the reaction feed heat exchanger 1 is connected to the reaction discharge cooler 4.
[0050] In some embodiments, the steam condensate preheater 2 is provided with a feed inlet, a discharge outlet, a steam condensate inlet, and a steam condensate outlet, for preheating the mixed dehydrogenation feedstock of cycloalkanes and circulating hydrogen using steam condensate from the reactor steam preheater 3 and the heat transfer medium steam heat exchanger 5; the feed inlet of the steam condensate preheater 2 is connected to the dehydrogenation feedstock outlet of the reaction feed heat exchanger 1, and the discharge outlet of the steam condensate preheater 2 is connected to the reactor steam preheater 3.
[0051] In some embodiments, the reactor steam preheater 3 is provided with a feed inlet, a discharge outlet, a high-pressure steam inlet, and a steam condensate outlet, for preheating the mixed dehydrogenation feedstock of cycloalkanes and circulating hydrogen to the dehydrogenation reaction temperature using high-pressure steam; the feed inlet of the reactor steam preheater 3 is connected to the discharge outlet of the steam condensate preheater 2, and the discharge outlet of the reactor steam preheater 3 is connected to the feed inlet of the dehydrogenation reactor 6.
[0052] In some embodiments, the gaseous product outlet of the separator 7 is connected to the compressor 9, which is connected to the product hydrogen line 10 and the circulating hydrogen line 8, for pressurizing a portion of the gaseous product as circulating hydrogen and the other portion as product hydrogen.
[0053] In some embodiments, the cycloalkane dehydrogenation system further includes a liquid-phase product purification unit connected to the liquid-phase product outlet of the separator 7. Preferably, the liquid-phase product purification unit includes a distillation column, etc.
[0054] In some embodiments, the cycloalkane dehydrogenation system further includes a product hydrogen purification unit connected to the product hydrogen line 10. Preferably, the product hydrogen purification unit includes a PSA (pressure swing adsorption) device and / or a membrane separation device, etc.
[0055] In some embodiments, such as Figure 1 As shown, the method for dehydrogenating cycloalkanes using the cycloalkanes dehydrogenation system of this invention may include the following steps: cycloalkanes and circulating hydrogen supplied by the circulating hydrogen pipeline 8 are mixed to obtain a mixed dehydrogenation feedstock, which then enters the reaction feed heat exchanger 1 to exchange heat with the dehydrogenation products; subsequently, it enters the steam condensate preheater 2, where steam condensate from the reactor steam preheater 3 and the heat transfer medium steam heat exchanger 5 is used to preheat the mixed dehydrogenation feedstock; it then enters the reactor steam preheater 3 again, where high-pressure steam is used to preheat the mixed dehydrogenation feedstock to the dehydrogenation reaction temperature, generating steam condensate; finally, it enters the dehydrogenation reactor 6, where the dehydrogenation reaction takes place in the presence of a dehydrogenation catalyst and under the condition of heat transfer medium supply, yielding dehydrogenated products. Hydrogen products; the heat transfer medium comes from the heat transfer medium steam heat exchanger 5, which uses high-pressure steam to heat the heat transfer medium and generate steam condensate. The heat transfer medium, after being cooled in the dehydrogenation reactor 6, is recycled back to the heat transfer medium steam heat exchanger 5 for heating; the dehydrogenation products enter the reaction feed heat exchanger 1 to exchange heat with the mixed dehydrogenation raw materials; then they enter the reaction discharge cooler 4 for cooling; and then enter the separator 7 for gas-liquid separation to obtain gas phase products and liquid phase products; after being pressurized by the compressor 9, part of the gas phase products enters the circulating hydrogen pipeline 8 as circulating hydrogen, and the other part enters the product hydrogen pipeline 10 as product hydrogen, which leads to the product hydrogen purification unit; the liquid phase products are sent to the liquid phase product purification unit.
[0056] In other embodiments, such as Figure 2As shown, the method for dehydrogenating cycloalkanes using the cycloalkanes dehydrogenation system of this invention may include the following steps: cycloalkanes enter the reaction feed heat exchanger 1 to exchange heat with the dehydrogenation products; then they are mixed with circulating hydrogen transported by the circulating hydrogen pipeline 8 to obtain a mixed dehydrogenation feedstock, which enters the steam condensate preheater 2, where the mixed dehydrogenation feedstock is preheated using steam condensate from the reactor steam preheater 3 and the heat transfer medium steam heat exchanger 5; then it enters the reactor steam preheater 3 again, where the mixed dehydrogenation feedstock is preheated to the dehydrogenation reaction temperature using high-pressure steam, and steam condensate is generated; then it enters the dehydrogenation reactor 6, where the dehydrogenation reaction takes place in the presence of a dehydrogenation catalyst and under the condition of heat transfer medium supply, to obtain a dehydrogenated product. Hydrogen products; the heat transfer medium comes from the heat transfer medium steam heat exchanger 5, which uses high-pressure steam to heat the heat transfer medium and generate steam condensate. The heat transfer medium, after being cooled in the dehydrogenation reactor 6, is recycled back to the heat transfer medium steam heat exchanger 5 for heating; the dehydrogenation products enter the reaction feed heat exchanger 1 to exchange heat with cycloalkanes; then they enter the reaction discharge cooler 4 for cooling; and then enter the separator 7 for gas-liquid separation to obtain gaseous and liquid products; the gaseous products are pressurized by the compressor 9, and part of them enters the circulating hydrogen pipeline 8 as circulating hydrogen, while the other part enters the product hydrogen pipeline 10 as product hydrogen, which leads to the product hydrogen purification unit; the liquid products are sent to the liquid product purification unit.
[0057] In some embodiments, the dehydrogenation reaction is carried out at a temperature of 280–330°C and a pressure of 10–100 kPaG. Preferably, the dehydrogenation reaction is carried out at a temperature of 290–330°C and a pressure of 10–50 kPaG.
[0058] In some embodiments, the cycloalkane (i.e., cycloalkane dehydrogenation feedstock) includes cyclohexane and / or methylcyclohexane.
[0059] In some embodiments, the molar ratio of the recycled hydrogen to the cycloalkane (i.e., the cycloalkane dehydrogenation feedstock) is 0.1 to 3.
[0060] In some embodiments, in the dehydrogenation reactor 6, the mass hourly space velocity (HSV) of the cycloalkanes (i.e., the cycloalkanes dehydrogenation feedstock) is 0.1–2 h⁻¹. -1 .
[0061] In some embodiments, the mass content of methylcyclopentane in the cycloalkanes (i.e., cycloalkanes dehydrogenation feedstocks) is not higher than 50 ppm, preferably not higher than 30 ppm.
[0062] In some embodiments, the high-pressure steam (including the high-pressure steam used in the reactor steam preheater 3 and the high-pressure steam used in the heat transfer medium steam heat exchanger 5) has a temperature of 320–600°C and a pressure of 8–15 MPaG. Preferably, the high-pressure steam has a temperature of 400–550°C and a pressure of 10–13 MPaG.
[0063] Using the system of this invention, cycloalkanes are dehydrogenated to produce aromatics and hydrogen under certain reaction temperature (280~330℃), pressure (slight positive pressure 10~100kPaG) and dehydrogenation catalyst (such as supported Pt and other noble metal catalysts). For example, cyclohexane is directly converted into benzene and hydrogen, or methylcyclohexane is directly converted into toluene and hydrogen. Cycloalkanes dehydrogenation is a strongly endothermic reaction. This invention uses high-pressure steam as a heat source to preheat the dehydrogenation feedstock and simultaneously heat the heat transfer medium. The heat transfer medium then heats the dehydrogenation reactor 6, achieving indirect heating of the reaction from the steam heat source. Simultaneously, the condensate generated by the high-pressure steam preheats the dehydrogenation feedstock, and a portion of the hydrogen in the dehydrogenation products is returned to the dehydrogenation reactor 6 as recycled hydrogen. By utilizing high-pressure steam heating, a stepped heat exchange method, and a feeding method that mixes and preheats the recycled hydrogen with cycloalkanes before returning it to the dehydrogenation reactor 6, the lifespan of the heat transfer medium is extended, the equipment footprint is minimized, heat dissipation from the heat transfer medium equipment is minimized, the energy utilization of high-pressure steam is maximized, and the catalyst lifespan is extended.
[0064] The technical solution of this utility model is specifically illustrated by the following embodiments, but this utility model is not limited to these embodiments. Of course, various modifications can be made within the scope of the key points of this utility model.
[0065] Example 1
[0066] This embodiment provides a cycloalkane dehydrogenation system, such as Figure 1 As shown, it includes: a reaction feed heat exchanger 1, a steam condensate preheater 2, a reactor steam preheater 3, a reaction discharge cooler 4, a heat transfer medium steam heat exchanger 5, a dehydrogenation reactor 6, a separator 7, a circulating hydrogen pipeline 8, a compressor 9, and a product hydrogen pipeline 10.
[0067] The dehydrogenation reactor 6 is a single-section tubular fixed-bed reactor; the top of the dehydrogenation reactor 6 is provided with a raw material inlet and the bottom is provided with a product outlet; the upper part of the dehydrogenation reactor 6 is provided with a heat transfer medium inlet and the lower part is provided with a heat transfer medium outlet; the raw material inlet and product outlet of the dehydrogenation reactor 6 are connected to the tube side of the dehydrogenation reactor 6, and the heat transfer medium inlet and heat transfer medium outlet of the dehydrogenation reactor 6 are connected to the shell side of the dehydrogenation reactor 6.
[0068] The reaction feed heat exchanger 1 is equipped with a dehydrogenation feed inlet, a dehydrogenation feed outlet, a dehydrogenation product inlet, and a dehydrogenation product outlet. The circulating hydrogen pipeline 8 is connected to the dehydrogenation feed inlet of the reaction feed heat exchanger 1, and the dehydrogenation feed inlet is also connected to a cycloalkane conveying pipeline for heat exchange between the mixed dehydrogenation feed of cycloalkane and circulating hydrogen and the dehydrogenation product. The dehydrogenation product inlet of the reaction feed heat exchanger 1 is connected to the product outlet of the dehydrogenation reactor 6, and the dehydrogenation product outlet of the reaction feed heat exchanger 1 is connected to the reaction discharge cooler 4.
[0069] The steam condensate preheater 2 is equipped with a feed inlet, a discharge outlet, a steam condensate inlet, and a steam condensate outlet. It is used to preheat the mixed dehydrogenation feedstock of cycloalkanes and circulating hydrogen using steam condensate from the reactor steam preheater 3 and the heat transfer medium steam heat exchanger 5. The feed inlet of the steam condensate preheater 2 is connected to the dehydrogenation feedstock outlet of the reactor feed-discharge heat exchanger 1.
[0070] The reactor steam preheater 3 is equipped with a feed inlet, a discharge outlet, a high-pressure steam inlet, and a steam condensate outlet. It is used to preheat the mixed dehydrogenation feedstock of cycloalkanes and circulating hydrogen to the dehydrogenation reaction temperature using high-pressure steam. The feed inlet of the reactor steam preheater 3 is connected to the discharge outlet of the steam condensate preheater 2, the discharge outlet of the reactor steam preheater 3 is connected to the feed inlet of the dehydrogenation reactor 6, and the steam condensate outlet of the reactor steam preheater 3 is connected to the steam condensate inlet of the steam condensate preheater 2.
[0071] The reaction discharge cooler 4 is connected to the separator 7; the separator 7 is provided with a gaseous product outlet and a liquid product outlet. The gaseous product outlet of the separator 7 is connected to the compressor 9. The compressor 9 is connected to the product hydrogen pipeline 10 and the circulating hydrogen pipeline 8, which are used to pressurize a portion of the gaseous product as circulating hydrogen and the other portion as product hydrogen.
[0072] The heat transfer medium steam heat exchanger 5 is provided with a heat transfer medium inlet, a heat transfer medium outlet, a high-pressure steam inlet, and a steam condensate outlet. The heat transfer medium inlet and outlet of the heat transfer medium steam heat exchanger 5 are circulatedly connected to the heat transfer medium outlet and inlet of the dehydrogenation reactor 6, and are used to heat the dehydrogenation reactor 6 with heat transfer medium. The steam condensate outlet of the heat transfer medium steam heat exchanger 5 is connected to the steam condensate inlet of the steam condensate preheater 2.
[0073] The dehydrogenation reactor 6 has a catalyst bed in its tubes, filled with a dehydrogenation catalyst. The dehydrogenation catalyst is a supported platinum catalyst, with activated alumina as the support, and the platinum content in the supported platinum catalyst is 0.9% by mass. The heat transfer medium is heat transfer oil. The cycloalkane dehydrogenation system of this embodiment further includes a liquid-phase product purification unit connected to the liquid-phase product outlet of the separator 7, which includes a distillation column, etc. The cycloalkane dehydrogenation system of this embodiment further includes a product hydrogen purification unit connected to the product hydrogen pipeline 10, which includes a PSA (pressure swing adsorption) device and / or a membrane separation device, etc.
[0074] like Figure 1 As shown, the method for dehydrogenating cycloalkanes using the cycloalkanes dehydrogenation system of this embodiment may include the following steps: cycloalkanes and circulating hydrogen supplied by the circulating hydrogen pipeline 8 are mixed to obtain a mixed dehydrogenation feedstock, which enters the reaction feed-in / outfeed heat exchanger 1 to exchange heat with the dehydrogenation products; then it enters the steam condensate preheater 2, where steam condensate from the reactor steam preheater 3 and the heat transfer medium steam heat exchanger 5 is used to preheat the mixed dehydrogenation feedstock; then it enters the reactor steam preheater 3 again, where high-pressure steam is used to preheat the mixed dehydrogenation feedstock to the dehydrogenation reaction temperature, and steam condensate is generated; finally, it enters the dehydrogenation reactor 6, where the dehydrogenation reaction is carried out in the presence of a dehydrogenation catalyst and under the condition of heat transfer medium supply, to obtain dehydrogenated products. The heat transfer medium comes from the heat transfer medium steam heat exchanger 5, which uses high-pressure steam to heat the heat transfer medium and generate steam condensate. The heat transfer medium, after being cooled in the dehydrogenation reactor 6, is recycled back to the heat transfer medium steam heat exchanger 5 for heating. The dehydrogenation product enters the reaction feed heat exchanger 1 to exchange heat with the mixed dehydrogenation raw materials. Then it enters the reaction discharge cooler 4 for cooling. Then it enters the separator 7 for gas-liquid separation to obtain gas phase product and liquid phase product. After being pressurized by the compressor 9, part of the gas phase product enters the circulating hydrogen pipeline 8 as circulating hydrogen, and the other part enters the product hydrogen pipeline 10 as product hydrogen. The product hydrogen pipeline 10 leads to the product hydrogen purification unit. The liquid phase product is sent to the liquid phase product purification unit.
[0075] The method for dehydrogenating cyclohexane using the cycloalkane dehydrogenation system of this embodiment can specifically include the following processes:
[0076] The feedstock, mainly cyclohexane (99.975 wt% cyclohexane, 0.02 wt% benzene, and 50 ppm methylcyclopentane), is mixed with recycled hydrogen and then sent to the reaction feed heat exchanger 1 to exchange heat with the dehydrogenation products to 200°C. It is then preheated to 260°C in the steam condensate preheater 2, and further preheated to 320°C in the reactor steam preheater 3 before being fed into the dehydrogenation reactor 6. The mass hourly space velocity (HSV) of cyclohexane in this reactor is 0.5 h⁻¹. -1 .
[0077] The shell-side heat transfer medium in dehydrogenation reactor 6 has an inlet temperature of 325℃ and an outlet temperature of 320℃. The heat transfer oil used is hydrogenated terphenyl. The feed inlet pressure is 35 kPaG, the molar ratio of hydrogen to cyclohexane in the mixed dehydrogenation feed is 0.63, and the dehydrogenation product outlet temperature is 318℃. The catalyst bed length is 6 m, the equivalent diameter of the catalyst particles is 0.002 m, and the fluid density of the mixed dehydrogenation feed is 0.48 kg / m³. 3 The dynamic viscosity of the mixed dehydrogenation feedstock is 1.76 × 10⁻⁶. -5 The apparent flow rate of the mixed dehydrogenation feedstock is 0.9 m / s, the porosity of the catalyst bed is 0.5, and the pressure drop of the dehydrogenation reactor 6 is 15 kPa.
[0078] The dehydrogenation product is heated to 81°C by the reaction feed heat exchanger 1, then cooled to 12°C by the reaction discharge cooler 4, and then enters the separator 7. The gaseous product separated by the separator 7 is pressurized by the compressor 9, and part of it is used as circulating hydrogen and part as product hydrogen. The liquid product separated by the separator is then purified.
[0079] The reactor steam preheater 3 uses 500℃, 13MPaG steam to heat the dehydrogenation feedstock, and the resulting steam condensate is sent to the steam condensate preheater 2 for further heating. The heat transfer medium steam heat exchanger 5 uses 500℃, 13MPaG steam to heat the heat transfer oil, and the resulting steam condensate is mixed with the steam condensate from the reactor steam preheater 3 before being sent to the steam condensate preheater 2 for further heating. The outlet temperature of the steam condensate preheater 2 is 316℃.
[0080] Using the above process for dehydrogenation, the cyclohexane conversion rate is 95.3%, the benzene selectivity is 99.7%, the catalyst single-pass life is 2.5 years, and the heat transfer oil life is 10 years.
[0081] Furthermore, the method for dehydrogenating methylcyclohexane using the cycloalkane dehydrogenation system of this embodiment can specifically include the following processes:
[0082] The feedstock, mainly methylcyclohexane (methylcyclohexane concentration 99.975 wt%, toluene concentration 0.02 wt%, methylcyclopentane concentration 50 ppm), is mixed with recycled hydrogen and then sent to the reaction feed heat exchanger 1 to exchange heat with the dehydrogenation products to 200°C. It is then preheated to 260°C in the steam condensate preheater 2, and further preheated to 320°C in the reactor steam preheater 3 before being fed into the dehydrogenation reactor 6. The mass hourly space velocity (HSV) of methylcyclohexane in this reactor is 0.7 h⁻¹. -1 .
[0083] The shell-side heat transfer medium in dehydrogenation reactor 6 has an inlet temperature of 325℃ and an outlet temperature of 320℃. The heat transfer oil used is hydrogenated terphenyl. The feed inlet pressure of dehydrogenation reactor 6 is 50 kPaG, the molar ratio of hydrogen to methylcyclohexane in the mixed dehydrogenation feed is 0.54, and the outlet temperature of the dehydrogenation product is 318℃. The catalyst bed length is 5 m, the equivalent diameter of the catalyst particles is 0.002 m, and the fluid density of the mixed dehydrogenation feed is 0.64 kg / m³. 3 The dynamic viscosity of the mixed dehydrogenation feedstock is 1.66 × 10⁻⁶. -5 The apparent flow rate of the mixed dehydrogenation feedstock is 1 m / s, the porosity of the catalyst bed is 0.5, and the pressure drop of dehydrogenation reactor 6 is 17 kPa.
[0084] The dehydrogenation product is heated to 73°C by the reaction feed heat exchanger 1, then cooled to 12°C by the reaction discharge cooler 4, and then enters the separator 7. The gaseous product separated by the separator 7 is pressurized by the compressor 9, and part of it is used as circulating hydrogen and part as product hydrogen. The liquid product separated by the separator is then purified.
[0085] The reactor steam preheater 3 uses 500℃, 13MPaG steam to heat the dehydrogenation feedstock, and the resulting steam condensate is sent to the steam condensate preheater 2 for further heating. The heat transfer medium steam heat exchanger 5 uses 500℃, 13MPaG steam to heat the heat transfer oil, and the resulting steam condensate is mixed with the steam condensate from the reactor steam preheater 3 before being sent to the steam condensate preheater 2 for further heating. The outlet temperature of the steam condensate preheater 2 is 313℃.
[0086] Using the above process for dehydrogenation, the conversion rate of methylcyclohexane is 96.3%, the selectivity of toluene is 99.7%, the catalyst single-pass life is 2.5 years, and the heat transfer oil life is 10 years.
[0087] Example 2
[0088] This embodiment provides a cycloalkane dehydrogenation system, such as Figure 2 As shown, it includes: a reaction feed heat exchanger 1, a steam condensate preheater 2, a reactor steam preheater 3, a reaction discharge cooler 4, a heat transfer medium steam heat exchanger 5, a dehydrogenation reactor 6, a separator 7, a circulating hydrogen pipeline 8, a compressor 9, and a product hydrogen pipeline 10.
[0089] The dehydrogenation reactor 6 is a single-section tubular fixed-bed reactor; the top of the dehydrogenation reactor 6 is provided with a raw material inlet and the bottom is provided with a product outlet; the upper part of the dehydrogenation reactor 6 is provided with a heat transfer medium inlet and the lower part is provided with a heat transfer medium outlet; the raw material inlet and product outlet of the dehydrogenation reactor 6 are connected to the tube side of the dehydrogenation reactor 6, and the heat transfer medium inlet and heat transfer medium outlet of the dehydrogenation reactor 6 are connected to the shell side of the dehydrogenation reactor 6.
[0090] The reaction feed heat exchanger 1 is equipped with a dehydrogenation feed inlet, a dehydrogenation feed outlet, a dehydrogenation product inlet, and a dehydrogenation product outlet. The dehydrogenation feed inlet is connected to a cycloalkane conveying pipeline for heat exchange between the cycloalkane dehydrogenation feed and the dehydrogenation product. The dehydrogenation product inlet of the reaction feed heat exchanger 1 is connected to the product outlet of the dehydrogenation reactor 6, and the dehydrogenation product outlet of the reaction feed heat exchanger 1 is connected to the reaction discharge cooler 4.
[0091] The steam condensate preheater 2 is equipped with a feed inlet, a discharge outlet, a steam condensate inlet, and a steam condensate outlet. The feed inlet of the steam condensate preheater 2 is connected to the dehydrogenation feed outlet of the reaction feed heat exchanger 1 and the circulating hydrogen pipeline 8. It is used to preheat the mixed dehydrogenation feed of cycloalkanes and circulating hydrogen using steam condensate from the reactor steam preheater 3 and the heat transfer medium steam heat exchanger 5.
[0092] The reactor steam preheater 3 is equipped with a feed inlet, a discharge outlet, a high-pressure steam inlet, and a steam condensate outlet. It is used to preheat the mixed dehydrogenation feedstock of cycloalkanes and circulating hydrogen to the dehydrogenation reaction temperature using high-pressure steam. The feed inlet of the reactor steam preheater 3 is connected to the discharge outlet of the steam condensate preheater 2, the discharge outlet of the reactor steam preheater 3 is connected to the feed inlet of the dehydrogenation reactor 6, and the steam condensate outlet of the reactor steam preheater 3 is connected to the steam condensate inlet of the steam condensate preheater 2.
[0093] The reaction discharge cooler 4 is connected to the separator 7; the separator 7 is provided with a gaseous product outlet and a liquid product outlet. The gaseous product outlet of the separator 7 is connected to the compressor 9. The compressor 9 is connected to the product hydrogen pipeline 10 and the circulating hydrogen pipeline 8, which are used to pressurize a portion of the gaseous product as circulating hydrogen and the other portion as product hydrogen.
[0094] The heat transfer medium steam heat exchanger 5 is provided with a heat transfer medium inlet, a heat transfer medium outlet, a high-pressure steam inlet, and a steam condensate outlet. The heat transfer medium inlet and outlet of the heat transfer medium steam heat exchanger 5 are circulatedly connected to the heat transfer medium outlet and inlet of the dehydrogenation reactor 6, and are used to heat the dehydrogenation reactor 6 with heat transfer medium. The steam condensate outlet of the heat transfer medium steam heat exchanger 5 is connected to the steam condensate inlet of the steam condensate preheater 2.
[0095] The dehydrogenation reactor 6 is equipped with a catalyst bed in its tubes, and the catalyst bed is filled with dehydrogenation catalyst. The heat transfer medium is heat transfer oil. The cycloalkane dehydrogenation system of this embodiment further includes a liquid-phase product purification unit connected to the liquid-phase product outlet of the separator 7, which includes a distillation column, etc. The cycloalkane dehydrogenation system of this embodiment further includes a product hydrogen purification unit connected to the product hydrogen pipeline 10, which includes a PSA (Pressure Swing Adsorption) device and / or a membrane separation device, etc.
[0096] like Figure 2 As shown, the method for dehydrogenating cycloalkanes using the cycloalkanes dehydrogenation system of this embodiment may include the following steps: cycloalkanes enter the reaction feed heat exchanger 1 and exchange heat with the dehydrogenation products; then they are mixed with circulating hydrogen transported by the circulating hydrogen pipeline 8 to obtain a mixed dehydrogenation feedstock, which enters the steam condensate preheater 2, where steam condensate from the reactor steam preheater 3 and the heat transfer medium steam heat exchanger 5 is used to preheat the mixed dehydrogenation feedstock; then it enters the reactor steam preheater 3 again, where high-pressure steam is used to preheat the mixed dehydrogenation feedstock to the dehydrogenation reaction temperature, and steam condensate is generated; then it enters the dehydrogenation reactor 6, where a dehydrogenation reaction is carried out in the presence of a dehydrogenation catalyst and under the condition of heat transfer medium supply, to obtain dehydrogenated... The products are as follows: The heat transfer medium comes from the heat transfer medium steam heat exchanger 5, which uses high-pressure steam to heat the heat transfer medium and generate steam condensate. The heat transfer medium, after being cooled in the dehydrogenation reactor 6, is recycled back to the heat transfer medium steam heat exchanger 5 for heating. The dehydrogenation products enter the reaction feed heat exchanger 1 to exchange heat with cycloalkanes. Then they enter the reaction discharge cooler 4 for cooling. Then they enter the separator 7 for gas-liquid separation to obtain gaseous products and liquid products. After being pressurized by the compressor 9, part of the gaseous products enters the circulating hydrogen pipeline 8 as circulating hydrogen, and the other part enters the product hydrogen pipeline 10 as product hydrogen. The product hydrogen pipeline 10 leads to the product hydrogen purification unit. The liquid products are sent to the liquid product purification unit.
[0097] The method for dehydrogenating cyclohexane using the cycloalkane dehydrogenation system of this embodiment can specifically include the following processes:
[0098] The feedstock, mainly cyclohexane (cyclohexane concentration 99.977 wt%, benzene concentration 0.02 wt%, methylcyclopentane concentration 30 ppm), is fed into the reaction feed heat exchanger 1 to exchange heat with the dehydrogenation products to 200°C. After mixing with circulating hydrogen, it is preheated to 260°C in the steam condensate preheater 2, and then preheated to 326°C in the reactor steam preheater 3. Finally, it is fed into the dehydrogenation reactor 6, where the dehydrogenation catalyst is a supported platinum catalyst with activated alumina as the support. The platinum content in the supported platinum catalyst is 1.2% by mass, and the mass hourly space velocity (WHSV) of cyclohexane is 0.5 h⁻¹. -1 .
[0099] The shell-side heat transfer medium in dehydrogenation reactor 6 has an inlet temperature of 330℃ and an outlet temperature of 325℃. The heat transfer oil used is hydrogenated terphenyl. The feed inlet pressure is 30 kPaG, the molar ratio of hydrogen to cyclohexane in the mixed dehydrogenation feed is 0.69, and the dehydrogenation product outlet temperature is 323℃. The catalyst bed length is 6 m, the equivalent diameter of the catalyst particles is 0.002 m, and the fluid density of the mixed dehydrogenation feed is 0.45 kg / m³. 3The dynamic viscosity of the mixed dehydrogenation feedstock is 1.78 × 10⁻⁶. -5 The apparent flow rate of the mixed dehydrogenation feedstock is 0.9 m / s, the porosity of the catalyst bed is 0.5, and the pressure drop of the dehydrogenation reactor 6 is 15 kPa.
[0100] The dehydrogenation product is heated to 104°C by the reaction feed heat exchanger 1, and then cooled to 12°C by the reaction discharge cooler 4. It then enters the separator 7. The gaseous product separated by the separator 7 is pressurized by the compressor 9, and part of it is used as circulating hydrogen and part of it is used as product hydrogen. The liquid product separated by the separator is then purified.
[0101] The reactor steam preheater 3 uses 460℃, 14MPaG steam to heat the dehydrogenation feedstock, and the resulting steam condensate is sent to the steam condensate preheater 2 for further heating. The heat transfer medium steam heat exchanger 5 uses 460℃, 14MPaG steam to heat the heat transfer oil, and the resulting steam condensate is mixed with the steam condensate from the reactor steam preheater 3 before being sent to the steam condensate preheater 2 for further heating. The outlet temperature of the steam condensate preheater 2 is 320℃.
[0102] Using the above process for dehydrogenation, the cyclohexane conversion rate is 96.4%, the benzene selectivity is 99.6%, the catalyst single-pass life is 2.6 years, and the heat transfer oil life is 10 years.
[0103] Furthermore, the method for dehydrogenating methylcyclohexane using the cycloalkane dehydrogenation system of this embodiment can specifically include the following processes:
[0104] The feedstock, mainly methylcyclohexane (methylcyclohexane concentration 99.947 wt%, toluene concentration 0.05 wt%, methylcyclopentane concentration 30 ppm), is fed into the reaction feed heat exchanger 1 to exchange heat with the dehydrogenation products to 220°C. After mixing with circulating hydrogen, it is preheated to 260°C in the steam condensate preheater 2, and then preheated to 322°C in the reactor steam preheater 3. Finally, it is fed into the dehydrogenation reactor 6, where the dehydrogenation catalyst is a supported platinum catalyst with activated alumina as the support. The platinum content in the supported platinum catalyst is 0.9%, and the mass hourly space velocity (WHSV) of methylcyclohexane is 0.8 h⁻¹. -1 .
[0105] The shell-side heat transfer medium in dehydrogenation reactor 6 has an inlet temperature of 320℃ and an outlet temperature of 315℃. The heat transfer oil used is hydrogenated terphenyl. The feed inlet pressure is 50 kPaG, the molar ratio of hydrogen to methylcyclohexane in the mixed dehydrogenation feed is 0.46, and the dehydrogenation product outlet temperature is 313℃. The catalyst bed length is 5 m, the equivalent diameter of the catalyst particles is 0.002 m, and the fluid density of the mixed dehydrogenation feed is 0.66 kg / m³. 3 The dynamic viscosity of the mixed dehydrogenation feedstock is 1.64 × 10⁻⁶.-5 The apparent flow rate of the mixed dehydrogenation feedstock is 1 m / s, the porosity of the catalyst bed is 0.5, and the pressure drop of the dehydrogenation reactor 6 is 18 kPa.
[0106] The dehydrogenation product is heated to 71°C by the reaction feed heat exchanger 1, and then cooled to 12°C by the reaction discharge cooler 4. It then enters the separator 7. The gaseous product separated by the separator 7 is pressurized by the compressor 9, and part of it is used as circulating hydrogen and part as product hydrogen. The liquid product separated by the separator is then purified.
[0107] The reactor steam preheater 3 uses 500℃, 12MPaG steam to heat the dehydrogenation feedstock, and the resulting steam condensate is sent to the steam condensate preheater 2 for further heating. The heat transfer medium steam heat exchanger 5 uses 500℃, 12MPaG steam to heat the heat transfer oil, and the resulting steam condensate is mixed with the steam condensate from the reactor steam preheater 3 before being sent to the steam condensate preheater 2 for further heating. The outlet temperature of the steam condensate preheater 2 is 309℃.
[0108] Using the above process for dehydrogenation, the conversion rate of methylcyclohexane is 95.2%, the selectivity of toluene is 99.8%, the catalyst single-pass life is 2.6 years, and the heat transfer oil life is 10 years.
[0109] Comparative Example 1
[0110] This comparative example is basically the same as Example 1, except that: Figure 3 As shown, this comparative example adds a dehydrogenation reactor, that is, this comparative example uses two dehydrogenation reactors in series. The mixed dehydrogenation feedstock enters the first stage reactor 601 and the second stage reactor 602 in sequence for reaction. The heat transfer oil is heated by the heat transfer medium steam heat exchanger 5 and first goes to the second stage reactor 602 for heating, and then goes to the first stage reactor 601 for heating.
[0111] The method for dehydrogenating cyclohexane using the cycloalkane dehydrogenation system of this comparative example can specifically include the following processes:
[0112] The feedstock, mainly cyclohexane (99.975 wt% cyclohexane, 0.02 wt% benzene, and 50 ppm methylcyclopentane), is mixed with recycled hydrogen and then sent to the reaction feed heat exchanger 1 to exchange heat with the dehydrogenation products to 200°C. It is then preheated to 260°C in the steam condensate preheater 2, and further preheated to 320°C in the reactor steam preheater 3. Finally, it is fed into two reactors connected in series, a first-stage reactor 601 and a second-stage reactor 602. The dehydrogenation catalyst is a supported platinum catalyst with activated alumina as the support. The platinum content in the supported platinum catalyst is 0.9% by mass. The cyclohexane mass hourly space velocity (HSV) in the first-stage reactor 601 is 0.5 h⁻¹. -1 The mass hourly space velocity (HSV) of cyclohexane in the second-stage reactor 602 is 0.2 h⁻¹.-1 .
[0113] The inlet temperature of the shell-side heat transfer medium in the second-stage reactor 602 is 325℃, and the outlet temperature of the shell-side heat transfer medium in the first-stage reactor 601 is 320℃. Hydrogenated terphenyl is used as the heat transfer oil. The feed inlet pressure of the first-stage reactor 601 is 35 kPaG, and the molar ratio of hydrogen to cyclohexane in the mixed dehydrogenation feed is 0.68. The outlet temperature of the dehydrogenation product in the second-stage reactor 602 is 318℃. The catalyst bed length of the first-stage reactor 601 is 6 m, the equivalent diameter of the catalyst particles is 0.002 m, and the fluid density of the mixed dehydrogenation feed is 0.48 kg / m³. 3 The dynamic viscosity of the mixed dehydrogenation feedstock is 1.76 × 10⁻⁶. -5 The apparent flow rate of the mixed dehydrogenation feedstock is 0.9 m / s, the porosity of the catalyst bed is 0.5, and the pressure drop of the first-stage reactor 601 is 15 kPa. The catalyst bed length of the second-stage reactor 602 is 3 m, the equivalent diameter of the catalyst particles is 0.002 m, and the fluid density of the mixed dehydrogenation feedstock is 0.48 kg / m³. 3 The dynamic viscosity of the mixed dehydrogenation feedstock is 1.76 × 10⁻⁶. -5 The apparent flow rate of the mixed dehydrogenation feedstock is 1 m / s, the porosity of the catalyst bed is 0.5, and the pressure drop of the two-stage reactor 602 is 9 kPa. The total pressure drop of the two reactors is 24 kPa.
[0114] The dehydrogenation product is heated to 84°C by the reaction feed heat exchanger 1, then cooled to 12°C by the reaction discharge cooler 4, and then enters the separator 7. The gaseous product separated by the separator 7 is pressurized by the compressor 9, and part of it is used as circulating hydrogen and part as product hydrogen. The liquid product separated by the separator is then purified.
[0115] The reactor steam preheater 3 uses 500℃, 13MPaG steam to heat the dehydrogenation feedstock, and the resulting steam condensate goes to the steam condensate preheater 2 for further heating. The heat transfer medium steam heat exchanger 5 uses 500℃, 13MPaG steam to heat the heat transfer oil. The heat transfer oil first heats the second-stage reactor 602, and then heats the first-stage reactor 601. The resulting steam condensate is mixed with the steam condensate from the reactor steam preheater 3 and then goes to the steam condensate preheater 2 for further heating. The outlet temperature of the steam condensate preheater 2 is 316℃.
[0116] Using the above process for dehydrogenation, the cyclohexane conversion rate is 95.8%, the benzene selectivity is 99.7%, the catalyst single-pass life is 2.5 years, and the heat transfer oil life is 10 years. However, compared to Example 1, this comparative example adds a reactor, increasing equipment investment and catalyst loading, increasing reactor cost by 50%, and reducing economic efficiency.
[0117] As can be seen from the above embodiments and comparative examples, the embodiments of this utility model improve the heating method, heat exchange method, and feeding method of the cycloalkane dehydrogenation system. High-pressure steam is used as a heat source to preheat the dehydrogenation feedstock and heat the heat transfer medium. The heat transfer medium then heats the dehydrogenation reactor, realizing indirect heating of the reaction by the steam heat source. At the same time, the steam condensate generated by the high-pressure steam condensation preheats the dehydrogenation feedstock. Moreover, part of the hydrogen in the dehydrogenation product is returned to the dehydrogenation reactor as recycled hydrogen. By utilizing the high-pressure steam heating method, the stepped heat exchange method, and the feeding method of mixing and preheating the recycled hydrogen with cycloalkane before returning it to the dehydrogenation reactor, the life of the heat transfer medium is extended, the equipment footprint is minimized, the heat dissipation of the heat transfer medium equipment is minimized, the energy utilization of high-pressure steam is maximized, the catalyst life is extended, the economy is improved, and the dehydrogenation reaction has a high conversion rate and selectivity.
[0118] The above description is only a preferred embodiment of the present utility model and is not intended to limit the scope of the substantive technical content of the present utility model. The substantive technical content of the present utility model is broadly defined within the scope of the claims. Any technical entity or method completed by others that is completely identical to or an equivalent modification of the claims is considered to be covered within the scope of the claims.
Claims
1. A naphthene dehydrogenation system, characterized by, include: Reactor feed heat exchanger, steam condensate preheater, reactor steam preheater, reaction discharge cooler, heat transfer medium steam heat exchanger, dehydrogenation reactor and separator; The reaction feed heat exchanger, the steam condensate preheater, the reactor steam preheater, and the feed inlet of the dehydrogenation reactor are connected in sequence. The product outlet of the dehydrogenation reactor is sequentially connected to the reaction feed heat exchanger, the reaction discharge cooler, and the separator. The reactor steam preheater is provided with a high-pressure steam inlet and a steam condensate outlet, and the steam condensate outlet of the reactor steam preheater is connected to the steam condensate preheater. The separator is provided with a gas phase product outlet and a liquid phase product outlet. The gas phase product outlet of the separator is connected to a circulating hydrogen pipeline, which is used to return the circulating hydrogen to the dehydrogenation reactor. The heat transfer medium steam heat exchanger is provided with a heat transfer medium inlet, a heat transfer medium outlet, a high-pressure steam inlet, and a steam condensate outlet. The heat transfer medium inlet and outlet of the heat transfer medium steam heat exchanger are circulatedly connected to the dehydrogenation reactor, and the steam condensate outlet of the heat transfer medium steam heat exchanger is connected to the steam condensate preheater.
2. The cycloalkane dehydrogenation system of claim 1, wherein, The dehydrogenation reactor includes a tubular fixed-bed reactor; And / or, the dehydrogenation reactor is a single-section tubular fixed-bed reactor.
3. The cycloalkane dehydrogenation system according to claim 1, characterized in that, The dehydrogenation reactor is equipped with a catalyst bed in its tubes, and the length of the catalyst bed is 3 to 8 m.
4. The cycloalkane dehydrogenation system according to claim 3, characterized in that, The catalyst bed is filled with a dehydrogenation catalyst, which includes a noble metal catalyst.
5. The cycloalkane dehydrogenation system according to claim 2, characterized in that, The feed inlet and product outlet of the dehydrogenation reactor are connected to the tube side of the dehydrogenation reactor. And / or, the heat transfer medium inlet and outlet of the heat transfer medium steam heat exchanger are circulatedly connected to the shell side of the dehydrogenation reactor for supplying heat to the dehydrogenation reactor using the heat transfer medium.
6. The cycloalkane dehydrogenation system according to claim 1, characterized in that, The circulating hydrogen pipeline is connected to the reaction feed heat exchanger and / or the steam condensate preheater.
7. The cycloalkane dehydrogenation system according to claim 1, characterized in that, The reaction feed heat exchanger is equipped with a dehydrogenation feed inlet, a dehydrogenation feed outlet, a dehydrogenation product inlet, and a dehydrogenation product outlet. It is used to exchange heat between the cycloalkane dehydrogenation feed or a mixed dehydrogenation feed of cycloalkane and circulating hydrogen and the dehydrogenation product. The dehydrogenation product inlet of the reaction feed heat exchanger is connected to the product outlet of the dehydrogenation reactor, and the dehydrogenation product outlet of the reaction feed heat exchanger is connected to the reaction discharge cooler.
8. The cycloalkane dehydrogenation system according to claim 7, characterized in that, The steam condensate preheater is provided with a feed inlet, a discharge outlet, a steam condensate inlet, and a steam condensate outlet, and is used to preheat the mixed dehydrogenation feedstock of cycloalkanes and circulating hydrogen using steam condensate from the reactor steam preheater and the heat transfer medium steam heat exchanger; the feed inlet of the steam condensate preheater is connected to the dehydrogenation feedstock outlet of the reactor feed-discharge heat exchanger, and the discharge outlet of the steam condensate preheater is connected to the reactor steam preheater.
9. The cycloalkane dehydrogenation system according to claim 8, characterized in that, The reactor steam preheater is equipped with a feed inlet, a discharge outlet, a high-pressure steam inlet, and a steam condensate outlet, and is used to preheat the mixed dehydrogenation feedstock of cycloalkanes and circulating hydrogen to the dehydrogenation reaction temperature using high-pressure steam; the feed inlet of the reactor steam preheater is connected to the discharge outlet of the steam condensate preheater, and the discharge outlet of the reactor steam preheater is connected to the feedstock inlet of the dehydrogenation reactor.
10. The cycloalkane dehydrogenation system according to claim 1, characterized in that, The gaseous product outlet of the separator is connected to a compressor, which is connected to the product hydrogen pipeline and the circulating hydrogen pipeline. The compressor is used to pressurize a portion of the gaseous product and use it as circulating hydrogen, while using the other portion as product hydrogen.
11. The cycloalkane dehydrogenation system according to claim 1, characterized in that, The cycloalkane dehydrogenation system further includes a liquid-phase product purification unit connected to the liquid-phase product outlet of the separator; the liquid-phase product purification unit includes a distillation column.
12. The cycloalkane dehydrogenation system according to claim 10, characterized in that, The cycloalkane dehydrogenation system further includes a product hydrogen purification unit connected to the product hydrogen pipeline; the product hydrogen purification unit includes a PSA device and / or a membrane separation device.