Method and system for dehydrogenation of low-carbon alkane

Abstract

The present invention relates to the technical field of dehydrogenation of low-carbon alkanes, provides a method and system for dehydrogenation of a low-carbon alkane, and solves the problem in the prior art that the service life of catalysts and the yield of low-carbon olefins are affected by ununiform temperature distributions and temperature drops across catalyst beds. The method comprises: introducing a heated process gas and a low-carbon alkane into a reactor; the process gas and the low-carbon alkane making contact with and reacting with a dehydrogenation catalyst, a thermal coupling aid, inert alumina balls, and inert alumina ceramic balls in the reactor; and separating, by a separation system, a low-carbon olefin, a hydrogen-rich gas, a fuel gas, and C4 and C4+ from a reaction gas generated by the reaction, and introducing the unconverted low-carbon alkane back to the reactor for further reaction. The reactor is filled with the dehydrogenation catalyst, the thermal coupling aid, the inert alumina balls, and the inert alumina ceramic balls according to a certain volume ratio, thereby improving the temperature distribution across a fixed bed reactor catalyst bed, reducing the reaction and regeneration severity, and improving the product yield.

Description

A method and system for dehydrogenating light alkanes Technical Field

[0001] The present invention belongs to the technical field of light alkane dehydrogenation, and in particular to a method and system for light alkane dehydrogenation. Background Art

[0002] Light olefins are basic organic raw materials with high demand and wide applications in the petrochemical industry. For example, propylene is an important basic chemical raw material and is widely used in the production of chemical products such as polypropylene, isopropyl alcohol, isopropylbenzene, carbonyl alcohol, propylene oxide, acrylic acid, and acrylonitrile. Another important light olefin, butene, is also widely used. For example, mixed butenes are used to produce high-octane gasoline components, as well as products such as maleic anhydride and sec-butanol, heptene, polybutene, and acetic anhydride.

[0003] Currently, my country's demand for low-carbon olefin resources continues to grow. Propylene is primarily supplied by naphtha cracking to produce ethylene and byproducts from heavy oil catalytic cracking. Due to this growing demand, propylene supply has remained insufficient in recent years, with significant annual imports still required. Existing propylene sources are unable to fully meet demand. Propane dehydrogenation, olefin interconversion, olefin metathesis, and methanol-to-olefins are among the production processes that are expanding propylene sources. Propane dehydrogenation to produce propylene has garnered significant attention.

[0004] With the rapid growth of MTBE (methyl tertiary butyl ether) and alkylation plants, butene has also become insufficient. Dehydrogenation is a key production method, as the dehydrogenated olefins are used in a variety of chemical products, such as detergents, high-octane gasoline, pharmaceuticals, plastics, and synthetic rubber. One application of this method is the dehydrogenation of isobutane to produce isobutylene, which can be polymerized to provide tackifiers for adhesives, viscosity index additives for motor lubricants, impact and antioxidant additives for plastics, and components for oligomer gasoline. Therefore, the dehydrogenation of isobutane has also attracted attention.

[0005] my country has relatively abundant light hydrocarbon resources, including liquefied petroleum gas and condensate, which contain large quantities of low-carbon alkanes such as propane and butane. Effectively converting propane and butane directly into propylene and butene would fully utilize petroleum resources, alleviate the shortage of low-carbon olefins, particularly propylene and butene, and simultaneously produce high-value hydrogen. Therefore, the development of industrially applicable low-carbon alkane dehydrogenation processes is crucial.

[0006] In order to meet the practical application needs of the above-mentioned low-carbon olefins, domestic and foreign research and development institutions have developed a variety of alkane dehydrogenation processes for low-carbon alkanes such as propane and butane in the last century. Representative processes include ABB Lummus's Catofin process, UOP's Oleflex process, Phillips' Star process and Linde's PDH process.

[0007] Lummus' Catofin process is a major light alkane dehydrogenation process, a typical HOUDRY cyclic fixed-bed dehydrogenation process. It utilizes a relatively inexpensive Cr2O3 / Al2O3 chromium-based catalyst. Its core components are several fixed-bed reactors operating at a temperature of approximately 600°C. Under high temperature and low pressure, propane is dehydrogenated to propylene by the catalyst bed, absorbing significant heat. This process is accompanied by several side reactions, requiring catalyst regeneration every 15 minutes. This process boasts high propane conversion, good propylene selectivity, strong feedstock adaptability, and high plant availability. Consequently, it is gaining increasing attention, particularly in isobutane dehydrogenation, where it is gaining widespread adoption.

[0008] At present, during the dehydrogenation reaction of light alkanes, due to factors such as pressure drop differences caused by catalyst loading and material deviation caused by process piping, when light alkanes are dehydrogenated on the active sites of the catalyst surface, a strong endothermic process occurs, which makes the temperature distribution and temperature drop of the catalyst bed uneven, seriously affecting the service life of the catalyst and the product yield of light olefins. The process is still unsatisfactory in terms of process severity, stability, operability, and operating cycle, and needs further improvement and enhancement.

[0009] Summary of the Invention

[0010] In response to the above problems, the object of the present invention is to provide a method and system for dehydrogenating light alkanes, by loading a dehydrogenation catalyst, a thermal coupling aid, an inert alumina ball and an inert alumina ceramic ball into the reactor in a volume ratio of 1:(0.1-0.2):(0.4-0.7):(0.4-0.6), thereby improving the temperature distribution of the catalyst bed in the fixed bed reactor, reducing the severity of the reaction and regeneration, and increasing the product yield.

[0011] The technical solution adopted in the present invention is as follows:

[0012] A method for dehydrogenating light alkanes comprises the following steps:

[0013] S1, the gas of light alkane, CO and / or CO2 process gas are heated at 200-500°C and then enter the reactor for reaction;

[0014] S2, low carbon alkane and process gas enter the reactor and contact with dehydrogenation catalyst, thermal coupling agent, inert alumina balls as heat storage body and inert alumina ceramic balls as support. The reaction temperature is 500-700℃, the reaction pressure is 50-200KPa(A), the reaction time is 5-30min, and the mass space velocity is 0.1-5h -1 The dehydrogenation reaction is carried out under the conditions of ; wherein the packing volume ratio of the dehydrogenation catalyst, the thermal coupling aid, the inert alumina balls as the heat storage body and the inert alumina ceramic balls as the support is 1:(0.1-0.2):(0.4-0.7):(0.4-0.6);

[0015] S3. The reaction gas produced by the reactor is separated into light olefins, hydrogen-rich gas, fuel gas, C4 and C4+ through a separation system, and the unconverted light alkanes are returned to the reactor.

[0016] Preferably, at least three reactors are provided, and dehydrogenation reaction, steam purging and catalyst regeneration are performed respectively; when the reactor performs catalyst regeneration, the catalyst bed needs to be heated first, then vacuumed and reduction reaction is performed; the time ratio of dehydrogenation reaction, steam purging, heating the catalyst bed and vacuuming / reduction reaction is 1:(0.2-0.4):(0.8-1.1):(0.2-0.4).

[0017] Preferably, the dehydrogenation catalyst comprises 18 mol% to 30 mol% of Cr2O3, 0.1 mol% to 3 mol% of CeO2, 0.1 mol% to 1 mol% of Cl and 67 mol% to 80 mol% of Al2O3, and the thermal coupling aid comprises 5 mol% to 30 mol% of CuO, 0.1 mol% to 3 mol% of CeO2, 10 mol% to 35 mol% of CaO, 0.1 mol% to 1 mol% of Cl and 50 mol% to 80 mol% of Al2O3.

[0018] A system for dehydrogenating low-carbon alkanes comprises a feed pipe, a heating furnace, a reactor and a separation system connected in sequence. The separation system is connected to the feed pipe through a pipeline. A catalyst bed is provided in the reactor, and the catalyst bed is filled with a dehydrogenation catalyst, a thermal coupling aid, inert alumina balls and inert alumina ceramic balls.

[0019] Preferably, a first heat exchanger, a condenser and a first compressor are sequentially arranged on the pipeline connecting the reactor and the separation system, and the feed pipe extends into the first heat exchanger.

[0020] Preferably, the separation system includes a flash separation tank connected to the reactor, the top of the flash separation tank is connected to a cold box through a pipeline, the top of the cold box is connected to a hydrogen-rich gas output pipe, the bottom of the cold box and the flash separation tank are connected to a deethanizer through a pipeline, the top of the deethanizer is connected to a fuel gas output pipe, the bottom of the deethanizer is connected to a separation tower through a pipeline, the top of the separation tower is connected to a heat pump compressor through a pipeline, the outlet of the heat pump compressor is connected to the separation tower through a pipeline, and the outlet of the heat pump compressor is also connected to a light olefin output pipe, the bottom of the separation tower is connected to a depropanizer through a pipeline, the bottom of the depropanizer is connected to C and C+ output pipes, and the top of the depropanizer is connected to a feed pipe through a pipeline.

[0021] Preferably, the deethanizer is connected to a first reboiler, and the pipeline connecting the reactor and the flash separation tank extends into the first reboiler.

[0022] Preferably, the heat pump compressor is a two-stage compression, and the outlet of the first stage is connected to the second reboiler, the outlet of the second stage is connected to the third reboiler, the cooling medium inlet and outlet of the second reboiler are connected to the separation tower, and the cooling medium inlet and outlet of the third reboiler are connected to the depropanizer.

[0023] Preferably, the reactor includes a shell, the top of the shell is connected to a hot air inlet pipe, the hot air inlet pipe is connected to a low-carbon alkane inlet pipe and other gas inlet pipes, the bottom of the shell is connected to a hot air outlet pipe and a hydrocarbon product outlet pipe, the hot air outlet pipe and the hydrocarbon product outlet pipe are both connected to an evacuation pipe, and valves are provided in the hot air inlet pipe, the low-carbon alkane inlet pipe, the other gas inlet pipes, the evacuation pipe, the hot air outlet pipe and the hydrocarbon product outlet pipe.

[0024] Preferably, the hot air inlet pipe is connected to an air heating furnace through a pipe, the air heating furnace is connected to a second heat exchanger, the second heat exchanger is connected to a gasifier, the hot air outlet pipe is connected to a third heat exchanger, the third heat exchanger is connected to a waste heat boiler, and the pipe connecting the third heat exchanger and the waste heat boiler extends into the second heat exchanger.

[0025] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0026] By loading a dehydrogenation catalyst, a thermal coupling aid, an inert alumina ball and an inert alumina ceramic ball into the reactor in a volume ratio of 1:(0.1-0.2):(0.4-0.7):(0.4-0.6), the temperature distribution of the catalyst bed of the fixed bed reactor is improved, the reaction and regeneration severity are reduced, and the product yield is increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0028] FIG1 is a schematic diagram of a process according to an embodiment of the present invention;

[0029] FIG2 is a schematic diagram of a reactor regeneration state according to an embodiment of the present invention;

[0030] FIG3 is a schematic diagram of the structure of a reactor provided in an embodiment of the present invention.

[0031] Description of the drawings: 1-heating furnace; 2-fifth heat exchanger; 3-reactor; 4-fourth heat exchanger; 5-first heat exchanger; 6-condenser; 7-first compressor; 8-second compressor; 9-flash separation tank; 10-cold box; 11-deethanizer; 12-first reboiler; 13-heat pump compressor; 14-second reboiler; 15-third reboiler; 16-separation tower; 17-depropanizer; 18-feed pipe; 19-hydrogen-rich gas output pipe; 20-fuel gas output pipe; 21-C4 and C4+ Output pipe; 22-low-carbon olefin output pipe; 23-second heat exchanger; 24-air heating furnace; 25-third heat exchanger; 26-waste heat boiler; 27-gasifier; 301-hot air inlet pipe; 302-low-carbon alkane inlet pipe; 303-guide plate; 304-other gas inlet pipe; 305-three-point thermocouple; 306-catalyst bed; 307-refractory brick bottom plate; 308-arch support part; 309-evacuation pipe; 310-hot air outlet pipe; 311-hydrocarbon product outlet pipe; 312-housing. DETAILED DESCRIPTION

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0033] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0034] In the description of the present invention, it should be noted that if the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside" and the like appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the accompanying drawings, or is the orientation or position relationship in which the product of the application is usually placed when in use. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0035] The present invention will be described in detail below with reference to FIG1 to FIG3 .

[0036] Example

[0037] A method for dehydrogenating light alkanes comprises the following steps:

[0038] S1, the gas of light alkane, CO and / or CO2 process gas are heated at 200-500°C and then enter the reactor 3 for reaction, preferably at a heating temperature of 300-450°C; the ratio of CO and CO2 in the process gas to the light alkane raw material is 1-20 mol%, preferably 1.5-5 mol%; the light alkane is preferably one or more of propane, isobutane and n-butane;

[0039] S2, low carbon alkane and process gas enter the reactor 3 and contact with the dehydrogenation catalyst, thermal coupling agent, inert alumina balls as heat storage body and inert alumina ceramic balls as support. The reaction temperature is 500-700℃, the reaction pressure is 50-200KPa(A), the reaction time is 5-30min, and the mass space velocity is 0.1-5h -1 The dehydrogenation reaction is carried out under the conditions of 540-650 ° C, the reaction pressure is 70-150 KPa (A), the reaction time is 10-20 min, the mass space velocity is 0.3-2 h -1 The volume ratio of the dehydrogenation catalyst, the thermal coupling agent, the inert alumina balls as the heat storage body, and the inert alumina ceramic balls as the support is 1:(0.1-0.2):(0.4-0.7):(0.4-0.6), and the preferred volume ratio is 1:(0.15-0.18):(0.5-0.6):(0.45-0.55);

[0040] The reaction gas produced in S3 and reactor 3 is separated into light olefins, hydrogen-rich gas, fuel gas, C4 and C4+ through a separation system, and the unconverted light alkanes are returned to reactor 3.

[0041] The reactor 3 is provided with at least three units, and dehydrogenation reaction, steam purging and catalyst regeneration are respectively performed; when the reactor 3 performs catalyst regeneration, it is necessary to first heat the catalyst bed (by introducing hot air at 560-730°C and 0.01-1MPa(A) for heating, preferably hot air at 600-700°C and 0.05-0.5MPa(A)), then evacuate and perform reduction reaction, and hydrogen-rich gas can be used for reduction. The time for heating the catalyst bed and evacuating / reduction reaction is 10-70 minutes each time, and the preferred time is 20-35 minutes; the time ratio of dehydrogenation reaction, steam purging, heating the catalyst bed and evacuating / reduction reaction is 1:(0.2-0.4):(0.8-1.1):(0.2-0.4), and the preferred time ratio is 1:(0.25-0.35):(0.9-1.05):(0.25-0.35).

[0042] The dehydrogenation catalyst comprises 18-30 mol% Cr2O3, 0.1-3 mol% CeO2, 0.1-1 mol% Cl, and 67-80 mol% Al2O3. The thermal coupling agent comprises 5-30 mol% CuO, 0.1-3 mol% CeO2, 10-35 mol% CaO, 0.1-1 mol% Cl, and 50-80 mol% Al2O3. The inert alumina balls serving as the heat storage element and the inert alumina ceramic balls serving as the support element have an Al2O3 content of ≥99.5 mol%, a heat capacity of 0.2-0.35 cal / g°C, preferably 0.25-0.32 cal / g°C, and a maximum operating temperature of ≥1400°C. This ensures stability under harsh operating conditions by effectively accumulating heat. The Cl is present in the form of sodium chloride or calcium chloride.

[0043] Because the dehydrogenation catalyst uses a Cr-based catalyst, the reduction reaction can be omitted during a single reaction-regeneration cycle, thereby saving a large amount of hydrogen-rich fuel. In this case, the time ratio of the dehydrogenation reaction, steam purge, and hot air heating of the catalyst bed is 1:(0.1-0.2):(0.4-0.6).

[0044] A system for dehydrogenating light alkanes, as shown in FIG1 , comprises a feed pipe 18, a heating furnace 1, a reactor 3, and a separation system, which are connected in sequence. The separation system is connected to the feed pipe 18 via a pipeline. The reactor 3 is provided with a catalyst bed 306, which is loaded with a dehydrogenation catalyst, a thermal coupling agent, inert alumina balls, and inert alumina ceramic balls. The feed pipe 18 introduces light alkanes into the heating furnace 1 for heating, and then passes them into the reactor 3 where they mix with process gas and come into contact with the dehydrogenation catalyst, thermal coupling agent, inert alumina balls, and inert alumina ceramic balls to undergo a dehydrogenation reaction. The separation system separates the reaction gas to produce light olefins, hydrogen-rich gas, fuel gas, and C4 and C4+. Some unreacted light alkanes are transported to the reactor 3 to continue the reaction.

[0045] The pipeline connecting the reactor 3 and the separation system is sequentially equipped with a first heat exchanger 5, a condenser 6, and a first compressor 7. A feed pipe 18 extends into the first heat exchanger 5. The first heat exchanger 5 preheats the light alkanes in the feed pipe 18, allowing the heat of the reaction gas to be reused and reducing the workload of the heating furnace 1. After the reaction gas passes through the first heat exchanger 5, it is cooled again by the condenser 6, reducing the workload of the separation system and preventing the service life of the first compressor 7 from being shortened due to high temperatures. Because the dehydrogenation reaction operates at a slightly positive pressure, the first compressor 7 can reduce a stage of compression, reducing its energy consumption.

[0046] The pipeline connecting reactor 3 to the separation system is also equipped with a fourth heat exchanger 4, located between reactor 3 and first heat exchanger 5. This fourth heat exchanger 4 utilizes the temperature of the reaction gas to produce steam, recovering some of the heat. Reactor 3 is connected to a fifth heat exchanger 2, which heats the process gas.

[0047] The separation system includes a flash separation tank 9 connected to the reactor 3, the top of the flash separation tank 9 is connected to a cold box 10 through a pipeline, the top of the cold box 10 is connected to a hydrogen-rich gas output pipe 19, the bottom of the cold box 10 and the flash separation tank 9 are connected to a deethanizer 11 through a pipeline, the top of the deethanizer 11 is connected to a fuel gas output pipe 20, the bottom of the deethanizer 11 is connected to a separation tower 16 through a pipeline, the top of the separation tower 16 is connected to a heat pump compressor 13 through a pipeline, the outlet of the heat pump compressor 13 is connected to the separation tower 16 through a pipeline, and the outlet of the heat pump compressor 13 is also connected to a light olefin output pipe 22, the bottom of the separation tower 16 is connected to a depropanizer 17 through a pipeline, the bottom of the depropanizer 17 is connected to a C4 and C4+ output pipe 21, and the top of the depropanizer 17 is connected to a feed pipe 18 through a pipeline.

[0048] The flash separation tank 9 separates the reaction gas, and the top gas of the flash separation tank 9 is condensed through the cold box 10, and the hydrogen-rich gas is output from the hydrogen-rich gas output pipe 19. The condensate produced by the condensation is transported together with the bottom liquid of the flash separation tank 9 to the deethanizer 11 for further separation; the top gas of the deethanizer 11 is fuel gas and is merged into the fuel gas output pipe 20 for output, and the bottom liquid of the deethanizer 11 enters the separation tower 16. The top gas of the separation tower 16 is compressed and transported by the heat pump compressor 13. The top gas is divided into two streams, one of which is used as the reflux of the separation tower 16, and the other is output as a light olefin product through the light olefin output pipe 22. The bottom liquid of the separation tower 16 enters the depropanizer 17 for further separation. The bottom liquid of the depropanizer 17 is C4 and C4+ and is output to the outside through the C4 and C4+ output pipes 21. The top gas of the depropanizer 17 is light alkanes, which are returned to the feed pipe 18 through a pipeline.

[0049] Cold box 10 is connected to a refrigerant circulation pipeline, in which a second compressor 8 is installed to circulate the refrigerant. The refrigerant is a mixed refrigerant composed of methane, ethane, ethylene, and propylene. The refrigerant temperature after compression and throttling can reach -90°C. This refrigeration method simplifies the process of setting up the compressor, reduces the investment in the refrigeration system, improves the refrigeration efficiency, and reduces the power consumption of the refrigeration.

[0050] The deethanizer 11 is connected to a first reboiler 12, and the pipeline connecting the reactor 3 and the flash separation tank 9 extends into the first reboiler 12. The first reboiler 12 recovers the heat of the reaction gas, heating the bottom liquid of the deethanizer 11 while further cooling the reaction gas.

[0051] Heat pump compressor 13 is a two-stage compressor. The outlet of the first stage is connected to a second reboiler 14, and the outlet of the second stage is connected to a third reboiler 15. The cooling medium inlet and outlet of second reboiler 14 are connected to separation tower 16, and the cooling medium inlet and outlet of third reboiler 15 are connected to depropanizer 17. Second reboiler 14 initially cools the overhead gas and uses the heat to heat the bottom liquid of separation tower 16. Third reboiler 15 cools the overhead gas again and uses the heat to heat the bottom liquid of depropanizer 17.

[0052] As shown in Figure 3, the reactor 3 includes an outer shell 312, the top of the outer shell 312 is connected to a hot air inlet pipe 301, the hot air inlet pipe 301 is connected to a light alkane inlet pipe 302 and an other gas inlet pipe 304, the bottom of the outer shell 312 is connected to a hot air outlet pipe 310 and a hydrocarbon product outlet pipe 311, the hot air outlet pipe 310 and the hydrocarbon product outlet pipe 311 are both connected to an evacuation pipe 309, and valves are provided in the hot air inlet pipe 301, the light alkane inlet pipe 302, the other gas inlet pipe 304, the evacuation pipe 309, the hot air outlet pipe 310 and the hydrocarbon product outlet pipe 311.

[0053] Multiple other gas inlet pipes 304 are provided for conveying steam, process gas, and reducing gas. At least three reactors 3 are provided, with some reactors 3 in a reaction state, some in a steam purge state, and others in a regeneration state. This cycle ensures that there are always reactors 3 available for reaction, ensuring continuous production. When the reactor 3 is reacting, the light alkane inlet pipe 302, the other gas inlet pipe 304 for conveying process gas, and the hydrocarbon product outlet pipe 311 are opened, and other pipes are closed; when the reactor 3 is steam purging, the other gas inlet pipe 304 for conveying steam and the hydrocarbon product outlet pipe 311 are opened, and other pipes are closed, and steam is purged from top to bottom through the catalyst bed 306, and the residual hydrocarbons are discharged from the hydrocarbon product outlet pipe 311; when the reactor 3 is regenerating, the hot air inlet pipe 301 and the hot air outlet pipe 310 are opened, and other pipes are closed, and high-temperature hot air passes through the catalyst bed 306 from top to bottom to regenerate the catalyst and the auxiliary agent, and accumulates heat in the dehydrogenation catalyst, thermal coupling auxiliary agent, inert alumina balls and inert alumina ceramic balls in the catalyst bed 306, thereby raising the bed temperature, and the waste hot air is discharged from the hot air outlet pipe 310 at the bottom of the reaction. After heating is completed, the hot air inlet pipe 301 and the hot air outlet pipe 310 are closed again. The evacuation pipe 309 is opened to evacuate the gas. After the evacuation is completed, the other gas inlet pipe 304 for conveying the reducing gas is opened to reduce the dehydrogenation catalyst and the thermal coupling auxiliary agent, and the waste gas is discharged from the evacuation pipe 309.

[0054] A deflector 303 is also installed within the housing 312 and is located directly below the hot air inlet pipe 301. An air drying device is installed within the hot air inlet pipe 301 to dry the hot air, heating and drying the air only when needed. The reactor 3 is also equipped with a three-point thermocouple 305 for monitoring the temperature of the catalyst bed 306. A refractory brick baseplate 307 is installed at the bottom of the catalyst bed 306, beneath which an arched support 308 is located.

[0055] The shell 312 is made of carbon steel, and the inner wall of the shell 312 is lined with refractory material. The reactor 3 does not need to be repaired for at least 10 years, ensuring continuous production. The reactor 3 also adopts external insulation, which has a good insulation effect.

[0056] As shown in Figure 2, during the regeneration heating phase of reactor 3, hot air inlet pipe 301 is connected to air heating furnace 24 via a pipe. Air heating furnace 24 is connected to second heat exchanger 23, which is connected to vaporizer 27. Hot air outlet pipe 310 is connected to third heat exchanger 25, which is connected to waste heat boiler 26. The pipe connecting third heat exchanger 25 and waste heat boiler 26 extends into second heat exchanger 23. After being vaporized in vaporizer 27, air is mixed with fuel gas and enters second heat exchanger 23 for heating. It then enters air heating furnace 24 for further heating, generating hot air. This hot air heats reactor 3. The third heat exchanger 25 then recovers heat from the used hot air, which then serves as a heat source for second heat exchanger 23 for further heat recovery. Waste heat boiler 26 recovers the final heat before discharging it as exhaust gas.

[0057] While maintaining the total heat constant, the present application reduces the maximum bed temperature and the probability of catalyst deactivation at the top of the bed, minimizes the temperature drop within a reaction cycle, and can improve selectivity while ensuring the conversion rate remains unchanged. Therefore, the present application synergistically improves the stability of the alkane dehydrogenation reaction process and the product yield of light olefins, extends the service life of the catalyst, and is conducive to the long-term operation of the dehydrogenation process.

[0058] Experiment 1:

[0059] A 3 mm strip dehydrogenation catalyst with a composition of 23 mol% Cr2O3, 1 mol% CeO2, 1 mol% Cl and 75 mol% Al2O3 was prepared, with a surface area of ​​95 m 2 / g, bulk density 1.05g / ml, crushing strength 65N / mm. A 3mm strip thermal coupling agent with a composition of 15mol% CuO, 3mol% CeO2, 17mol% CaO and 65mol% Al2O3 was prepared, with a surface area of ​​35m 2 / g, bulk density is 1.1g / ml, and crushing strength is 40N / mm.

[0060] The above-prepared 3mm strip dehydrogenation catalyst, 3mm strip thermal coupling aid, 5mm inert alumina balls (Al2O3≥99.5mol%, heat capacity 0.3cal / g℃, melting temperature ≥1700℃) as heat storage bodies, and 8mm inert alumina ceramic balls (Al2O3≥99.5mol%, heat capacity 0.3cal / g℃, operating temperature ≥1400℃) as supports are filled into the catalyst bed 306 in a volume ratio of 1:0.15:0.5:0.5.

[0061] Eight reactors 3 are used and are sequentially put into operation at 3-minute intervals. At any given moment, three reactors 3 are in the dehydrogenation process, three reactors 3 are in the regeneration and heating process, and two reactors are in the steam purge or vacuum / reduction process. A single cycle lasts approximately 25 to 30 minutes, including 10 to 15 minutes for dehydrogenation, approximately 3 minutes for steam purge, approximately 9 minutes for regeneration and reheating the catalyst bed, and approximately 3 minutes for vacuum and reduction.

[0062] Industrial-grade propane was used as the reaction raw material. The raw material properties of industrial-grade propane are shown in Table 1.

[0063] Table 1 Raw material properties of industrial-grade propane

[0064] As the process gas CO and CO 2 , industrial CO and CO 2 gases separated from waste heat gas in this application are used.

[0065] The dehydrogenation reaction and regeneration operating conditions of industrial-grade propane are shown in Table 2.

[0066] Table 2 Dehydrogenation reaction and regeneration operating conditions

[0067] Comparative Example 1:

[0068] The typical HOUDRY cycle fixed bed dehydrogenation process in the background art was used, and the reaction raw materials were consistent with those in Experiment 1, and a commercially available Cr / Al2O3 industrial dehydrogenation catalyst was used.

[0069] Comparative Example 2:

[0070] The typical HOUDRY cycle fixed bed dehydrogenation process in the background art was used, and the reaction raw materials were consistent with the reaction raw materials of Experiment 1, using commercially available Cr / Al2O3 industrial dehydrogenation catalyst and commercially available Cu / Al2O3 commercial industrial heating material.

[0071] Table 3 shows the comparison of the propane dehydrogenation reaction operation conditions at the initial and final stages of the catalyst life of Experiment 1, Comparative Example 1, and Comparative Example 2, where the initial and final stages of operation are defined as catalyst life ≮ 3 years.

[0072] Table 3 Comparison of propane dehydrogenation reaction operation conditions at the beginning and end of catalyst life

[0073] Compared with the operation of a typical HOUDRY cyclic fixed-bed dehydrogenation process, and compared with the operation of a HOUDRY cyclic fixed-bed dehydrogenation process combined with existing heating materials, the present application has better propane single-pass conversion rate and propylene selectivity, and achieves better implementation effect of the propane dehydrogenation reaction.

[0074] Experiment 2:

[0075] The same reaction conditions as in Experiment 1 were used, except that the raw materials were replaced with a mixture of propane and isobutane. The properties of the mixture of propane and isobutane are shown in Table 4.

[0076] Table 4 Properties of propane and isobutane mixed raw materials

[0077] The dehydrogenation reaction and regeneration operating conditions of the mixed feed of propane and isobutane are shown in Table 5.

[0078] Table 5 Dehydrogenation reaction and regeneration operating conditions of mixed feedstock of propane and isobutane

[0079] Comparative Example 3:

[0080] The same process as in Comparative Example 1 was adopted, except that the industrial-grade propane raw material in Comparative Example 1 was replaced with a mixed raw material of propane and isobutane.

[0081] Comparative Example 4:

[0082] The same process as in Comparative Example 2 was adopted, except that the industrial-grade propane raw material in Comparative Example 2 was replaced with a mixed raw material of propane and isobutane.

[0083] The comparison of the propane dehydrogenation reaction operation conditions at the initial and final stages of the catalyst life of Experiment 2, Comparative Example 3, and Comparative Example 4 is shown in Table 6, where the initial and final stages of operation are defined as catalyst life ≮ 3 years.

[0084] Table 6 Comparison of the operation status of propane and isobutane mixed dehydrogenation reaction at the beginning and end of catalyst life

[0085] Compared with the operation of a typical HOUDRY cyclic fixed-bed dehydrogenation process, and compared with the operation of a HOUDRY cyclic fixed-bed dehydrogenation process combined with existing heating materials, in the dehydrogenation reaction of a mixed industrial feedstock of propane and isobutane, the present application has better propane + isobutane conversion rate and selectivity, and achieves better implementation results. This shows that the present application can also achieve good implementation results for mixed low-carbon alkane feedstocks with more complex compositions and relatively more complex conversion processes, demonstrating good raw material and process adaptability.

[0086] The comparison of catalyst bed temperature and other operating conditions, as well as the comparison of process consumption data are shown in Table 7.

[0087] Table 7 Comparison of working conditions and process consumption

[0088] The present application effectively reduces the temperature difference and severity within the catalyst bed, making the temperature distribution more uniform.

[0089] Experiment 3:

[0090] On the basis of Experiment 1, the reaction section was kept unchanged, the heat pump compressor 13 and the heat reflux of the depropanizer 17 were added, the compression stage of the first compressor 7 was reduced by slightly positive pressure operation, and the regeneration reduction stage was eliminated. The process consumption comparison between Experiment 1 and Experiment 3 is shown in Table 8.

[0091] Table 8 Process consumption comparison

[0092] By increasing the heat pump compressor 13, heat reflux of the depropanizer 17, slightly positive pressure operation to reduce the compression stages of the first compressor 7 and eliminating the reduction stage of regeneration, the process energy consumption and material consumption can be reduced.

[0093] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for dehydrogenating light alkanes, characterized in that: The following steps are involved: S1, low carbon alkane gas, CO and / or CO2 process gas are heated to 200-500°C and then enter the reactor (3) for reaction; S2, low carbon alkane and process gas enter the reactor (3) and contact with the dehydrogenation catalyst, thermal coupling agent, inert alumina balls as heat storage body and inert alumina ceramic balls as support, at a reaction temperature of 500-700°C, a reaction pressure of 50-200 KPa (A), a reaction time of 5-30 min, and a mass space velocity of 0.1-5 h -1 The dehydrogenation reaction is carried out under the conditions of ; wherein the packing volume ratio of the dehydrogenation catalyst, the thermal coupling aid, the inert alumina balls as the heat storage body and the inert alumina ceramic balls as the support is 1:(0.1-0.2):(0.4-0.7):(0.4-0.6); S3. The reaction gas produced by the reactor (3) is separated into light olefins, hydrogen-rich gas, fuel gas, C4 and C4+ through a separation system, and the unconverted light alkanes are returned to the reactor (3).

2. The method for dehydrogenating light alkanes according to claim 1, characterized in that: The reactor (3) is provided with at least three units, and performs dehydrogenation reaction, steam purging and catalyst regeneration respectively; when the reactor (3) performs catalyst regeneration, it is necessary to first heat the catalyst bed, then evacuate and perform reduction reaction; the time ratio of dehydrogenation reaction, steam purging, heating the catalyst bed and evacuating / reduction reaction is 1:(0.2-0.4):(0.8-1.1):(0.2-0.4).

3. The method for dehydrogenating light alkanes according to claim 1, characterized in that: The dehydrogenation catalyst includes 18 mol% to 30 mol% of Cr2O3, 0.1 mol% to 3 mol% of CeO2, 0.1 mol% to 1 mol% of Cl and 67 mol% to 80 mol% of Al2O3, and the thermal coupling aid includes 5 mol% to 30 mol% of CuO, 0.1 mol% to 3 mol% of CeO2, 10 mol% to 35 mol% of CaO, 0.1 mol% to 1 mol% of Cl and 50 mol% to 80 mol% of Al2O3.

4. A system for dehydrogenating light alkanes, comprising a feed pipe (18), a heating furnace (1), a reactor (3) and a separation system connected in sequence, characterized in that: The separation system is connected to the feed pipe (18) through a pipeline. A catalyst bed (306) is arranged in the reactor (3). The catalyst bed (306) is filled with a dehydrogenation catalyst, a thermal coupling aid, inert alumina balls and inert alumina ceramic balls.

5. A system for dehydrogenating light alkanes according to claim 4, characterized in that: A first heat exchanger (5), a condenser (6) and a first compressor (7) are sequentially arranged on the pipeline connecting the reactor (3) and the separation system, and a feed pipe (18) extends into the first heat exchanger (5).

6. A system for dehydrogenating light alkanes according to claim 4, characterized in that: The separation system comprises a flash separation tank (9) connected to the reactor (3); the top of the flash separation tank (9) is connected to a cold box (10) via a pipeline; the top of the cold box (10) is connected to a hydrogen-rich gas output pipe (19); the bottoms of the cold box (10) and the flash separation tank (9) are connected to a deethanizer (11) via a pipeline; the top of the deethanizer (11) is connected to a fuel gas output pipe (20); the bottom of the deethanizer (11) is connected to a separation tower (16) via a pipeline; The top of the separation tower (16) is connected to a heat pump compressor (13) via a pipeline, the outlet of the heat pump compressor (13) is communicated with the separation tower (16) via a pipeline, and the outlet of the heat pump compressor (13) is also connected to a low-carbon olefin output pipe (22), the bottom of the separation tower (16) is connected to a depropanizer (17) via a pipeline, the bottom of the depropanizer (17) is connected to a C4 and C4+ output pipe (21), and the top of the depropanizer (17) is connected to a feed pipe (18) via a pipeline.

7. A system for dehydrogenating light alkanes according to claim 6, characterized in that: The deethanizer (11) is connected to a first reboiler (12), and a pipeline connecting the reactor (3) and the flash separation tank (9) extends into the first reboiler (12).

8. A system for dehydrogenating light alkanes according to claim 6, characterized in that: The heat pump compressor (13) is a two-stage compression device, and the outlet of the first stage is connected to the second reboiler (14), and the outlet of the second stage is connected to the third reboiler (15). The cooling medium inlet and outlet of the second reboiler (14) are connected to the separation tower (16), and the cooling medium inlet and outlet of the third reboiler (15) are connected to the depropanizer (17).

9. A system for dehydrogenating light alkanes according to claim 6, characterized in that: The reactor (3) comprises a shell (312), the top of the shell (312) is connected to a hot air inlet pipe (301), the hot air inlet pipe (301) is connected to a low carbon alkane inlet pipe (302) and other gas inlet pipes (304), the bottom of the shell (312) is connected to a hot air outlet pipe (310) and a hydrocarbon product outlet pipe (311), the hot air outlet pipe (310) and the hydrocarbon product outlet pipe (311) are both connected to an evacuation pipe (309), and valves are provided in the hot air inlet pipe (301), the low carbon alkane inlet pipe (302), other gas inlet pipes (304), the evacuation pipe (309), the hot air outlet pipe (310) and the hydrocarbon product outlet pipe (311).

10. A system for dehydrogenating light alkanes according to claim 9, characterized in that: The hot air inlet pipe (301) is connected to an air heating furnace (24) through a pipeline, the air heating furnace (24) is connected to a second heat exchanger (23), the second heat exchanger (23) is connected to a gasifier (27), the hot air outlet pipe (310) is connected to a third heat exchanger (25), the third heat exchanger (25) is connected to a waste heat boiler (26), and the pipeline connecting the third heat exchanger (25) and the waste heat boiler (26) extends into the second heat exchanger (23).

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