An intermittent fixed bed reaction process system

Abstract

The present application relates to a kind of intermittent fixed bed reaction process system, it is related to low carbon alkane dehydrogenation fixed bed reaction technical field, the intermittent fixed bed reaction process system includes variable-diameter low carbon alkane dehydrogenation reactor, the variable-diameter low carbon alkane dehydrogenation reactor is connected with nitrogen oxygen separator, feed heating furnace, natural gas combustion chamber and heat exchanger, the heat exchanger is connected with feed heating furnace and first cooler, the first cooler, compressor, second cooler and reaction product separation system are sequentially connected, the reaction stage of the variable-diameter low carbon alkane dehydrogenation reactor includes dehydrogenation reaction section, vacuum / purging section, catalyst regeneration section and vacuum / purging / reduction section.The present application solves the problem that existing low carbon alkane dehydrogenation reaction catalyst is prone to carbon deposition;Meanwhile, the low carbon alkane dehydrogenation conversion rate and low carbon alkane selectivity of catalyst are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of low-carbon alkane dehydrogenation fixed bed reaction, in particular to an intermittent fixed bed reaction process system. BACKGROUND

[0002] Fixed bed reaction is a common reaction process, catalyst is loaded in the reactor, and raw materials are converted into target products through the catalyst. For high-temperature organic process fixed bed reaction, coke formation inevitably occurs in the reaction process of organic raw materials, which requires the catalyst to be regenerated by calcination in an oxidizing atmosphere.

[0003] Low-carbon alkane dehydrogenation fixed bed reaction is a typical intermittent fixed bed reaction, the catalyst bed is purged by hydrogen, alkane dehydrogenation, alkane vacuum, catalyst regeneration, catalyst vapor purge, vacuum, and catalyst hydrogen reduction process. Among them, alkane dehydrogenation accounts for only 1 / 3 of the reaction process, and catalyst combustion regeneration accounts for 1 / 3 of the reaction time. The oxidizing atmosphere of the traditional catalyst regeneration process is a dilute oxygen gas after natural gas combustion, and the removal of coke in the catalyst is slow, and the regeneration process has high energy consumption. In addition, a large amount of high-temperature steam is required for the purging process, which will accelerate the deactivation of the catalyst and reduce the service life of the catalyst. SUMMARY

[0004] To solve the above problems, the present application provides an intermittent fixed bed reaction process system, which solves the problem of easy coke accumulation of the existing low-carbon alkane dehydrogenation reaction catalyst, and improves the low-carbon alkane dehydrogenation conversion rate and low-carbon alkane selectivity of the catalyst.

[0005] In a first aspect, the present application provides an intermittent fixed bed reaction process system, which comprises a variable-diameter low-carbon alkane dehydrogenation reactor, the variable-diameter low-carbon alkane dehydrogenation reactor is connected with a nitrogen-oxygen separator, a feed heating furnace, a natural gas combustion chamber and a heat exchanger, the heat exchanger is connected with the feed heating furnace and a first cooler, the first cooler, a compressor, a second cooler and a reaction product separation system are connected in sequence, the reaction stage of the variable-diameter low-carbon alkane dehydrogenation reactor comprises a dehydrogenation reaction section, a vacuum / purging section, a catalyst regeneration section and a vacuum / purging / reduction section, and the ratio of the diameter of the low-carbon alkane inlet to the diameter of the outlet of the variable-diameter low-carbon alkane dehydrogenation reactor is greater than 1.05.

[0006] Further, the ratio of the diameter of the low-carbon alkane inlet to the diameter of the outlet of the variable-diameter low-carbon alkane dehydrogenation reactor is greater than 1.1, preferably greater than 1.5, and more preferably 1.5-3.0.

[0007] Further, the ratio of the low carbon alkane inlet position pressure to the outlet position pressure of the variable-diameter low carbon alkane dehydrogenation reactor is greater than 1.2, preferably greater than 2.0, and more preferably 2.0-4.0.

[0008] Further, the nitrogen-oxygen separator comprises an oxygen production section for producing oxygen-rich gas by nitrogen absorption and a nitrogen production section for producing nitrogen-rich gas by pressure swing.

[0009] The oxygen-rich gas separated by the oxygen production section for producing oxygen-rich gas by nitrogen absorption is mixed with natural gas and then enters the natural gas combustion chamber to obtain high-temperature oxygen-rich gas, which is used as the catalyst regeneration section gas.

[0010] The nitrogen-rich gas separated by the nitrogen production section for producing nitrogen-rich gas by pressure swing is used as the purge gas.

[0011] Further, the variable-diameter low carbon alkane dehydrogenation reactor is an adiabatic fixed-bed reactor, which is a downward intermittent alkane dehydrogenation fixed-bed reactor or an upward intermittent alkane dehydrogenation fixed-bed reactor.

[0012] The top of the downward intermittent alkane dehydrogenation fixed-bed reactor is provided with a first low carbon alkane inlet, a first air / gas inlet, a first steam / hydrogen inlet and a reaction bed inlet.

[0013] The bottom of the downward intermittent alkane dehydrogenation fixed-bed reactor is provided with a first carbon-hydrogen compound outlet, a first combustion tail gas outlet and a reaction bed outlet.

[0014] The reaction bed inlet and the reaction bed outlet are sequentially provided with a first inert porcelain ball layer, a first dehydrogenation catalyst / inert alumina layer, a first dehydrogenation catalyst / heating aid layer, a second dehydrogenation catalyst / inert alumina layer, a first dehydrogenation catalyst layer and a second inert porcelain ball layer from the inlet to the outlet.

[0015] Inert packing layers are arranged between adjacent reaction beds.

[0016] Further, the bottom of the upward intermittent alkane dehydrogenation fixed-bed reactor is provided with a second low carbon alkane inlet, a second air / gas inlet and a second steam / hydrogen inlet; the top of the upward intermittent alkane dehydrogenation fixed-bed reactor is provided with a second carbon-hydrogen compound outlet and a second combustion tail gas outlet; and the bottom and the top of the upward intermittent alkane dehydrogenation fixed-bed reactor are sequentially provided with a third inert porcelain ball layer, a third dehydrogenation catalyst / inert alumina layer, a second dehydrogenation catalyst / heating aid layer, a fourth dehydrogenation catalyst / inert alumina layer, a second dehydrogenation catalyst layer and a fourth inert porcelain ball layer from the bottom to the top.

[0017] Further, the reaction product separation system separates the material to obtain hydrogen, dry gas, low carbon olefins and recycled low carbon alkanes.

[0018] Further, the recycled low carbon alkane and the dry gas are returned to the feed for the cycle dehydrogenation.

[0019] Further, the purge tail gas discharged from the vacuum / purge section and the regeneration tail gas discharged from the catalyst regeneration section are both introduced into the preheating boiler.

[0020] In a second aspect, the application provides a method for low carbon alkane dehydrogenation reaction, which uses the intermittent fixed bed reaction process system of any one of the first aspect.

[0021] The above technical solution provided by the embodiments of the application has at least the following advantages compared with the prior art:

[0022] The application provides an intermittent fixed bed reaction process system. Oxygen and nitrogen are separated, the separated oxygen-rich air is reacted with methane to generate high-temperature oxygen-rich oxidation atmosphere, which is used to remove carbon deposition in the catalyst reaction, and the separated nitrogen is used to purge the reaction system. The oxygen and nitrogen separation system selects LiX molecular sieve, activated carbon, etc. Air enters the oxygen and nitrogen separation system, nitrogen is adsorbed in the adsorbent, and the outlet is normal-pressure oxygen-rich oxidation atmosphere. When the adsorbent is saturated with nitrogen adsorption, low pressure is generated. The low pressure can match the low pressure purge in the reaction process. After the low pressure purge is completed, the adsorbent can generate oxygen-rich oxidation atmosphere in the next round. The problem of easy carbon deposition of the catalyst is solved, and the low carbon alkane dehydrogenation conversion rate and low carbon alkane selectivity of the catalyst are improved. BRIEF DESCRIPTION OF DRAWINGS

[0023] The accompanying drawings, which are incorporated into and form part of the specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the application.

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, for those skilled in the art, other drawings can also be obtained without creative labor.

[0025] Figure 1 The intermittent alkane dehydrogenation downflow reaction fixed bed reaction process system flowchart provided by the embodiments of the application is shown in the figure.

[0026] Figure 2 The downflow intermittent alkane dehydrogenation fixed bed reactor side view provided by the embodiments of the application is shown in the figure.

[0027] Figure 3 The downflow intermittent alkane dehydrogenation fixed bed reactor top view provided by the embodiments of the application is shown in the figure.

[0028] Figure 4 An intermittent alkanes dehydrogenation upflow reaction fixed bed reaction process system flow schematic diagram provided for the embodiments of the present application;

[0029] Figure 5 An upflow intermittent alkanes dehydrogenation fixed bed reactor schematic diagram provided for the embodiments of the present application;

[0030] Figure 6 An intermittent alkanes dehydrogenation reaction fixed bed reaction process system flow schematic diagram without nitrogen oxygen separator provided for the comparative examples of the present application;

[0031] Figure 7 A reaction process change over time in the variable diameter low carbon alkanes dehydrogenation reactor provided for the embodiments of the present application as shown in the figure;

[0032] Figure 8 A time distribution diagram of the intermittent alkanes dehydrogenation fixed bed reactor provided for the comparative examples of the present application;

[0033] 1 is a fresh low-carbon alkane feed pipeline; 2 is a feed heating furnace; 3 is a variable-diameter low-carbon alkane dehydrogenation reactor; 3-1 is a dehydrogenation reaction section; 3-2 is a vacuum / purging section; 3-3 is a catalyst regeneration section; 3-4 is a vacuum / purging / reducing section; 3-5 is a first low-carbon alkane inlet; 3-6 is a first air / gas inlet; 3-7 is a first steam / hydrogen inlet; 3-8 is a reaction bed inlet; 3-9 is a first hydrocarbon outlet; 3-10 is a first combustion tail gas outlet; 3-11 is a reaction bed outlet; 3-12 is an inert packing layer; 3-13 is a first inert porcelain ball layer; 3-14 is a first dehydrogenation catalyst / inert alumina layer; 3-15 is a first dehydrogenation catalyst / heat generating aid layer; 3-16 is a second dehydrogenation catalyst / inert alumina layer; 3-17 is a first dehydrogenation catalyst layer; 3-18 is a second inert porcelain ball layer; 3-19 is a second low-carbon alkane inlet; 3-20 is a second air / gas inlet; 3-21 is a second steam / hydrogen inlet; 3-22 is a second hydrocarbon outlet; 3-23 is a second combustion tail gas outlet; 3-24 is a third inert porcelain ball layer; 3-25 is a third dehydrogenation catalyst / inert alumina layer; 3-26 is a second dehydrogenation catalyst / heat generating aid layer; 3-27 is a fourth dehydrogenation catalyst / inert alumina layer; 3-28 is a second dehydrogenation catalyst layer; 3-29 is a fourth inert porcelain ball layer; 4 is a heat exchanger; 5 is a first cooler; 6 is a compressor; 7 is a second cooler; 8 is a reaction product separation system; 9 is a first hydrogen pipeline; 10 is a dry gas pipeline; 11 is a low-carbon alkene pipeline; 12 is a circulating low-carbon alkane pipeline; 13 is a first air feed pipeline; 14 is a nitrogen / oxygen separator; 14-1 is a variable-pressure nitrogen removal to produce nitrogen-rich gas section; 14-2 is a nitrogen absorption to produce oxygen-rich gas section; 15 is a nitrogen-rich gas pipeline; 16 is a second hydrogen pipeline; 17 is an oxygen-rich gas pipeline; 18 is a natural gas pipeline; 19 is a combustion chamber; 20 is a purge tail gas pipeline; 21 is a preheating boiler; 22 is a steam pipeline; 23 is a third hydrogen pipeline; 24 is a second air feed pipeline. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0035] Unless otherwise specifically indicated, all the various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0036] In a first aspect, the application provides an intermittent fixed bed reaction process system, which comprises a variable-diameter low-carbon alkane dehydrogenation reactor 3, which is connected with a nitrogen-oxygen separator 14, a feed heating furnace 2, a natural gas combustion chamber 19 and a heat exchanger 4, the heat exchanger 4 is connected with the feed heating furnace 2 and a first cooler 5, the first cooler 5, a compressor 6, a second cooler 7 and a reaction product separation system 8 are connected in sequence, and the reaction stages of the variable-diameter low-carbon alkane dehydrogenation reactor 3 include a dehydrogenation reaction section 3-1, a vacuum / purging section 3-2, a catalyst regeneration section 3-3 and a vacuum / purging / reduction section 3-4; the nitrogen-oxygen separator 14 comprises an oxygen-enriched gas production oxygen production by nitrogen adsorption section 14-2 and a nitrogen-enriched gas production by pressure swing nitrogen removal section 14-1; the oxygen-enriched gas separated from the oxygen production by nitrogen adsorption section 14-2 is mixed with natural gas and then enters the natural gas combustion chamber 19 to obtain high-temperature oxygen-enriched gas, which is used as the gas of the catalyst regeneration section 3-3; the nitrogen-enriched gas separated from the nitrogen-enriched gas production by pressure swing nitrogen removal section 14-1 is used as a purge gas, and the ratio of the diameter of the low-carbon alkane inlet to the diameter of the outlet of the variable-diameter low-carbon alkane dehydrogenation reactor is greater than 1.05.

[0037] The application provides an intermittent fixed bed reaction process system, which separates oxygen and nitrogen, and uses the separated oxygen-enriched air to react with methane to generate high-temperature oxygen-enriched oxidizing atmosphere for removing carbon deposition in the catalyst reaction, and uses the separated nitrogen for purging the reaction system. The oxygen-nitrogen separation system selects LiX molecular sieve, activated carbon and the like, air enters the oxygen-nitrogen separation system, nitrogen is adsorbed in the adsorbent, the outlet is normal-pressure oxygen-enriched oxidizing atmosphere, the adsorbent is saturated with nitrogen adsorption, and low pressure is generated, which can be matched with low-pressure purging in the reaction process. After the low-pressure purging is completed, the adsorbent can generate oxygen-enriched oxidizing atmosphere in the next round, thereby solving the problem of easy carbon deposition of the catalyst and improving the low-carbon alkane dehydrogenation conversion rate and low-carbon alkane selectivity of the catalyst.

[0038] In some specific embodiments, the ratio of the diameter of the low-carbon alkane inlet to the diameter of the outlet of the variable-diameter low-carbon alkane dehydrogenation reactor is greater than 1.1, preferably greater than 1.5, and more preferably 1.5-3.0.

[0039] In some specific embodiments, the ratio of the pressure at the low-carbon alkane inlet position to the pressure at the outlet position of the variable-diameter low-carbon alkane dehydrogenation reactor is greater than 1.2, preferably greater than 2.0, and more preferably 2.0-4.0.

[0040] The variable-diameter reactor designed in the application naturally makes the outlet pressure lower than the inlet pressure based on the Bernoulli equation and the Venturi effect, thereby promoting the conversion rate and the selectivity of olefins. The low-carbon alkane dehydrogenation is a reaction with increasing volume, and low pressure promotes the dehydrogenation reaction of low-carbon alkanes.

[0041] In some embodiments, the variable-diameter low-carbon alkane dehydrogenation reactor 3 is an adiabatic fixed-bed reactor, which is a down-flow intermittent alkane dehydrogenation fixed-bed reactor or an up-flow intermittent alkane dehydrogenation fixed-bed reactor.

[0042] The top of the down-flow intermittent alkane dehydrogenation fixed-bed reactor is provided with a first low-carbon alkane inlet 3-5, a first air / gas inlet 3-6, a first steam / hydrogen inlet 3-7, and a reaction bed inlet 3-8.

[0043] The bottom of the down-flow intermittent alkane dehydrogenation fixed-bed reactor is provided with a first hydrocarbon outlet 3-9, a first combustion tail gas outlet 3-10, and a reaction bed outlet 3-11.

[0044] Between the reaction bed inlet 3-8 and the reaction bed outlet 3-11, there are sequentially provided, from the inlet to the outlet, a first inert porcelain ball layer 3-13, a first dehydrogenation catalyst / inert alumina layer 3-14, a first dehydrogenation catalyst / heat generating aid layer 3-15, a second dehydrogenation catalyst / inert alumina layer 3-16, a first dehydrogenation catalyst layer 3-17, and a second inert porcelain ball layer 3-18.

[0045] An inert packing layer 3-12 is provided between adjacent reaction beds.

[0046] In some embodiments, the bottom of the up-flow intermittent alkane dehydrogenation fixed-bed reactor is provided with a second low-carbon alkane inlet 3-19, a second air / gas inlet 3-20, and a second steam / hydrogen inlet 3-21; the top of the up-flow intermittent alkane dehydrogenation fixed-bed reactor is provided with a second hydrocarbon outlet 3-22 and a second combustion tail gas outlet 3-23; and between the bottom and the top of the up-flow intermittent alkane dehydrogenation fixed-bed reactor, there are sequentially provided, from the bottom to the top, a third inert porcelain ball layer 3-24, a third dehydrogenation catalyst / inert alumina layer 3-25, a second dehydrogenation catalyst / heat generating aid layer 3-26, a fourth dehydrogenation catalyst / inert alumina layer 3-27, a second dehydrogenation catalyst layer 3-28, and a fourth inert porcelain ball layer 3-29.

[0047] In some embodiments, the reaction product separation system 8 separates the obtained materials including hydrogen, dry gas, low-carbon olefins, and recycled low-carbon alkanes.

[0048] In some embodiments, the recycled low-carbon alkanes and the dry gas are returned to the feed for recycling dehydrogenation.

[0049] In some embodiments, the vacuum / purge section 3-2 and the catalyst regeneration section 3-3 both discharge purge tail gas into a purge tail gas pipeline 20, and the purge tail gas enters a preheating boiler 21.

[0050] Specifically, when a down-flow intermittent fixed-bed reactor for dehydrogenation of alkanes is used, as shown in Figure 1 , Figure 2 and Figure 3 , the intermittent fixed-bed reactor process system for down-flow dehydrogenation of alkanes provided in the embodiments of the present application comprises 4-16 variable-diameter low-carbon alkane dehydrogenation reactors 3, which sequentially perform dehydrogenation reaction section 3-1, vacuum / purging section 3-2, catalyst regeneration section 3-3, and vacuum / purging / reduction section 3-4, heat exchanger 4 for reaction feed and reaction product, feed heating furnace 2, first cooler 5 for reaction product, compressor 6, second cooler 7, reaction product separation system 8, 1-8 nitrogen-oxygen separators 14, which are always maintained in variable-pressure nitrogen production section 14-1 and nitrogen absorption oxygen production section 14-2, and the produced oxygen-rich gas is combusted with natural gas to rapidly raise the feed gas and remove the carbon deposited on the catalyst in the reactor; the produced nitrogen-rich gas is used for purging the device through nitrogen-rich gas pipeline 15 to avoid the safety problem caused by the contact between the reducing gas and the oxidizing gas in the reactor. The reaction product separation system 8 is a conventional low-carbon alkane dehydrogenation separation system, and the propane dehydrogenation reaction product separation process includes deethanizer, propane-propylene separation column, PSA hydrogen separation column, etc., and the product separation can obtain hydrogen, propylene product, propane, and dry gas containing methane, ethane, ethylene, nitrogen, etc., and the propane is returned to the feed for cyclic dehydrogenation; the isobutane dehydrogenation reaction product separation process includes deethanizer, propane-propylene separation column, butane-butene separation column, PSA hydrogen separation column, etc., and the product separation can obtain hydrogen, isobutene product, isobutane, and dry gas containing methane, ethane, ethylene, nitrogen, etc., and the isobutane is returned to the feed for cyclic dehydrogenation. The specific process is as follows:

[0051] Fresh low-carbon alkanes pass through heat exchanger 4 to exchange heat with the reaction product gas, and then pass through feed heating furnace 2 to be heated to 500-630°C, and then enter variable-diameter low-carbon alkane dehydrogenation reactor 3 for dehydrogenation reaction. Each variable-diameter low-carbon alkane dehydrogenation reactor 3 performs dehydrogenation reaction section 3-1, vacuum / purging section 3-2, catalyst regeneration section 3-3, and vacuum / purging / reduction section 3-4, and the reaction process of each reactor is staggered, and the reaction process in variable-diameter low-carbon alkane dehydrogenation reactor 3 changes with time as shown in Figure 7As shown, the product gas of the dehydrogenation reaction section 3-1 passes through the heat exchanger 4, exchanges heat with the feed, is cooled by the first cooler 5, and then passes through the compressor 6 and the second cooler 7, and enters the reaction product separation system 8. The separated hydrogen gas enters the subsequent section through the first hydrogen gas pipeline 9, and can be used for catalyst reduction and external sales. The separated dry gas can be used for combustion to provide heat through the dry gas pipeline 10. The separated low-carbon olefins (main target product) can be collected through the low-carbon olefin pipeline 11. The separated low-carbon alkanes are mixed with fresh low-carbon alkanes through the recycled low-carbon alkane pipeline 12 and then recycled for dehydrogenation reaction.

[0052] The dehydrogenation process produces a large amount of carbon on the catalyst, which needs to be regenerated. Before regeneration, the combustible gas in the catalyst needs to be removed, i.e., enters the variable-diameter low-carbon alkane dehydrogenation reactor 3 vacuum / purging section 3-2. First, the vacuum system is used to reduce the pressure of the variable-diameter low-carbon alkane dehydrogenation reactor 3 to below 0.1 atm, and the low-carbon alkanes in the variable-diameter low-carbon alkane dehydrogenation reactor 3 are removed and sent to the subsequent section through the heat exchanger 4. Then, nitrogen-rich gas is used for purging to replace the residual gas in the reactor. The purging gas enters the preheating boiler 21. The process and the subsequent nitrogen-rich gas are obtained by separating the air from the first air feed pipeline 13 through the nitrogen-oxygen separator 14.

[0053] After the vacuum / purging section 3-2, the variable-diameter low-carbon alkane dehydrogenation reactor 3 enters the catalyst regeneration section 3-3. The gas in the catalyst regeneration section 3-3 is high-temperature oxygen-rich gas. The high-temperature oxygen-rich gas is obtained by mixing the oxygen-rich gas separated from the air from the first air feed pipeline 13 through the nitrogen-oxygen separator 14 with natural gas from the natural gas pipeline 18, combusting in the combustion chamber 19, and obtaining high-temperature oxygen-rich gas. The main components of the high-temperature oxygen-rich gas are oxygen, carbon dioxide, nitrogen, and a small amount of methane. The high-temperature oxygen-rich gas reacts with the carbon in the catalyst to generate CO2. The regenerated gas enters the preheating boiler 21 to remove the carbon in the catalyst, restore the activity of the catalyst, and provide heat for the reaction system.

[0054] After the catalyst regeneration section 3-3, the vacuum system is first used to reduce the pressure of the reactor to below 0.1 atm, and the oxygen-rich gas in the variable-diameter low-carbon alkane dehydrogenation reactor 3 is removed. The regenerated gas enters the preheating boiler 21. Then, nitrogen-rich gas is used for purging to replace the residual oxygen in the variable-diameter low-carbon alkane dehydrogenation reactor 3 and enters the preheating boiler 21. The regenerated gas enters the preheating boiler 21. Hydrogen from the second hydrogen gas pipeline 16 is used to pretreat the catalyst, reducing the high-valence active metal in the catalyst to a low-valence metal. The gas passes through the heat exchanger 4 to reach the subsequent section. As described above, one cycle of catalytic reaction is completed.

[0055] In addition, when an upflow intermittent alkane dehydrogenation fixed bed reactor is used, as shown in FIG. 2, the product gas of the dehydrogenation reaction section 3-1 passes through the heat exchanger 4, exchanges heat with the feed, is cooled by the first cooler 5, and then passes through the compressor 6 and the second cooler 7, and enters the reaction product separation system 8. The separated hydrogen gas enters the subsequent section through the first hydrogen gas pipeline 9, and can be used for catalyst reduction and external sales. The separated dry gas can be used for combustion to provide heat through the dry gas pipeline 10. The separated low-carbon olefins (main target product) can be collected through the low-carbon olefin pipeline 11. The separated low-carbon alkanes are mixed with fresh low-carbon alkanes through the recycled low-carbon alkane pipeline 12 and then recycled for dehydrogenation reaction.Figure 4 , Figure 5 As shown in the embodiment of this application, the intermittent alkane dehydrogenation upward reaction fixed bed reaction process system is similar to the intermittent alkane dehydrogenation downward reaction fixed bed reaction process system, except that the material flow direction is different due to the use of an upward intermittent alkane dehydrogenation fixed bed reactor.

[0056] Secondly, this application provides a method for the dehydrogenation reaction of low-carbon alkane, wherein the method employs the intermittent fixed-bed reaction process system described in any one of the first aspects.

[0057] The method for dehydrogenation of low-carbon alkanes provided by this invention has a high conversion rate and high selectivity for low-carbon alkanes in the catalyst.

[0058] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0059] Example 1

[0060] This example provides a downflow intermittent fixed-bed reaction process system, such as... Figures 1-3 As shown, the specific reaction process is as follows:

[0061] Fresh low-carbon alkanes pass through the fresh low-carbon alkane feed pipe 1 and heat exchanger 4, where they exchange heat with the reaction product gas. After passing through the feed heater 2, they are heated to 500–630°C and then enter the variable-diameter low-carbon alkane dehydrogenation reactor 3 for dehydrogenation. Each variable-diameter low-carbon alkane dehydrogenation reactor 3 consists of a dehydrogenation reaction section 3-1, a vacuum / purging section 3-2, a catalyst regeneration section 3-3, and a vacuum / purging / reduction section 3-4. The reaction processes in each reactor are staggered. The reaction process in the variable-diameter low-carbon alkane dehydrogenation reactor 3 changes over time as follows: Figure 7 As shown, the product gas from the dehydrogenation reaction section 3-1 passes through heat exchanger 4, exchanges heat with the feed, and then passes through first cooler 5 for cooling. After passing through compressor 6 and second cooler 7, it enters reaction product separation system 8. The separated hydrogen enters the subsequent process section through first hydrogen pipeline 9, which can be used for catalyst reduction and external sales. The separated dry gas can be used for combustion to provide heat through dry gas pipeline 10. The separated low-carbon olefins (the main target product) can be collected through low-carbon olefin pipeline 11. The separated low-carbon alkanes are mixed with fresh low-carbon alkanes through circulating low-carbon alkanes pipeline 12 and then subjected to a circulating dehydrogenation reaction.

[0062] The dehydrogenation process produces a large amount of carbon on the catalyst, which needs to be regenerated. Before regeneration, combustible gas in the catalyst needs to be removed, i.e. entering the variable-diameter low-carbon alkane dehydrogenation reactor 3 vacuum / purging section 3-2. First, the variable-diameter low-carbon alkane dehydrogenation reactor 3 is subjected to a vacuum system to reduce the pressure to below 0.1 atm, and the low-carbon alkane in the variable-diameter low-carbon alkane dehydrogenation reactor 3 is removed and reaches the subsequent section through the heat exchanger 4. Then, nitrogen-rich gas is used for purging to replace the residual gas in the reactor, and the purging gas enters the preheating boiler 21. The process and the subsequent nitrogen-rich gas are obtained by separating the air from the first air feed pipe 13 through the nitrogen-oxygen separator 14.

[0063] After the vacuum / purging section 3-2, the variable-diameter low-carbon alkane dehydrogenation reactor 3 enters the catalyst regeneration section 3-3. The gas in the catalyst regeneration section 3-3 is high-temperature oxygen-rich gas. The high-temperature oxygen-rich gas is obtained by mixing the oxygen-rich gas separated from the air from the first air feed pipe 13 through the nitrogen-oxygen separator 14 and the natural gas from the natural gas pipe, and is combusted in the combustion chamber 19 to obtain the high-temperature oxygen-rich gas. The main components of the high-temperature oxygen-rich gas are oxygen, carbon dioxide, nitrogen and a small amount of methane. The high-temperature oxygen-rich gas reacts with the carbon in the catalyst to generate CO2. The regenerated gas enters the preheating boiler 21 to remove the carbon in the catalyst, restore the activity of the catalyst, and provide heat for the reaction system.

[0064] After the catalyst regeneration section 3-3, the reactor is first subjected to a vacuum system to reduce the pressure to below 0.1 atm, and the oxygen-rich gas in the variable-diameter low-carbon alkane dehydrogenation reactor 3 is removed. The regenerated gas enters the preheating boiler 21, and then nitrogen-rich gas is used for purging to replace the residual oxygen in the variable-diameter low-carbon alkane dehydrogenation reactor 3 and enters the preheating boiler 21. The regenerated gas enters the preheating boiler 21, and then hydrogen is used for pretreatment of the catalyst to reduce the high-valence active metal in the catalyst to low-valence metal. The gas reaches the subsequent section through the heat exchanger 4. As described above, one cycle of catalytic reaction is completed. The nitrogen content in the nitrogen-rich gas is more than 98%, the oxygen content in the oxygen-rich gas is more than 50%, and the ratio of the diameter of the low-carbon alkane inlet to the diameter of the outlet of the variable-diameter low-carbon alkane dehydrogenation reactor is 1.5-3.0.

[0065] Example 2

[0066] This example provides an upflow intermittent fixed bed reaction process system, as shown in Figure 4 , Figure 5 The difference between this example and Example 1 is that an upflow intermittent alkane dehydrogenation fixed bed reactor is used, so the flow direction of the material is different. The specific flow of the reaction is as follows:

[0067] The low carbon alkane is heated to 500-630°C by heat exchanger and heating furnace after exchanging heat with the reaction product gas, and then enters the reactor system for dehydrogenation reaction. The reaction process of each reactor is staggered, and the reaction process in the reactor changes with time as shown in the figure Figure 7 The product gas of the dehydrogenation reaction section exchanges heat with the feed through the heat exchanger, and then is cooled by the cooler, and then enters the product separation system through the compressor and the cooler. The separated hydrogen can be used for catalyst reduction and external sales. The separated dry gas is used for combustion to provide heat. The separated low carbon alkene is the main target product of the system. The separated low carbon alkane is mixed with the low carbon alkane and then recycled for dehydrogenation reaction.

[0068] The dehydrogenation process produces a large amount of carbon on the catalyst, which needs to be regenerated. Before regeneration, the combustible gas in the catalyst needs to be removed, i.e. entering the vacuum / purging section of the reactor. First, the vacuum system is used to reduce the pressure in the reactor to below 0.1 atm, and the low carbon alkane in the reactor is removed through the heat exchanger 4 to the subsequent section. Then, nitrogen-rich gas is used for purging to replace the residual gas in the reactor, and the purging gas enters the waste heat boiler. The process and the subsequent nitrogen-rich gas are obtained by separating air through a nitrogen-oxygen separation system.

[0069] After vacuum / purging, the reactor enters the regeneration section. The regeneration section gas is high-temperature oxygen-rich gas. The high-temperature oxygen-rich gas is obtained by mixing oxygen-rich gas obtained from air through a nitrogen-oxygen separation system and natural gas, and is obtained by burning in a combustion chamber. Its main components are oxygen, carbon dioxide, nitrogen and a small amount of methane. The high-temperature oxygen-rich gas reacts with the carbon in the catalyst to generate CO2. The regenerated gas enters the waste heat boiler to remove the carbon in the catalyst, restore the catalyst activity, and provide heat for the reaction system.

[0070] After regeneration, the reactor pressure is first reduced to below 0.1 atm by the vacuum system, and the oxygen-rich gas in the reactor is removed. The regenerated gas enters the waste heat boiler. Then, nitrogen-rich gas is used for purging to replace the residual oxygen in the reactor and enters the waste heat boiler. The regenerated gas is then pretreated with hydrogen to reduce the high-valence active metal in the catalyst to low-valence metal. The gas passes through the heat exchanger to the subsequent section. As described above, one cycle of catalytic reaction is completed.

[0071] Comparative Example 1

[0072] This example provides a conventional intermittent alkane dehydrogenation reaction fixed bed reaction process system without a nitrogen-oxygen separator 14, as shown in Figure 6The difference between the embodiment 1 and the comparative example is only that the nitrogen oxygen separator 14 is removed; the vacuum / sweeping section 3-2 of the variable-diameter low-carbon alkane dehydrogenation reactor 3 is swept by water vapor introduced through the water vapor pipeline 22, the vacuum / sweeping / reducing section 3-4 is supplied with hydrogen through the third hydrogen pipeline 23, and the gas in the catalyst regeneration section 3-3 is high-temperature air obtained by mixing air introduced through the second air feeding pipeline 24 with natural gas in the combustion chamber 19. Figure 8 The time distribution of the intermittent alkane dehydrogenation fixed-bed reactor in the comparative example is shown in Table 2.

[0073] Test examples

[0074] The process systems in the embodiment 1, the embodiment 2 and the comparative example 1 were evaluated by using propane as the dehydrogenation raw material. The catalysts were loaded into the reaction tube for reaction. Compared with the catalysts in the comparative example, the low-carbon alkane dehydrogenation conversion rate of the catalysts in the embodiments of the present application was high, and the low-carbon alkane selectivity was high. The propane dehydrogenation catalyst, the heat generating aid, the heat storage ball and the heat storage ball in the embodiments were all from Runhe Catalyst Co., Ltd. The propane dehydrogenation catalyst contained 2.5% additive, 21% chromium oxide and the rest was alumina, with a specific surface area greater than 90 m2 / g, a crushing strength greater than 100 N and a bulk density of 0.9-1.2 g / ml. The heat generating aid contained 10% copper oxide and the rest was calcium aluminate spinel, with a specific surface area less than 10 m2 / g, a crushing strength greater than 100 N and a bulk density of 1.0-1.3 g / ml. The heat storage body and the supporting alumina ball were both inert alumina, with a bulk density of the heat storage body greater than 2.0 g / ml and a bulk density of the supporting alumina ball greater than 1.7 g / ml. Specifically, test example 1 was that propane was used as the dehydrogenation raw material, and the down-flow intermittent fixed-bed reaction process system provided by the embodiment 1 was used as the reaction system. Test example 2 was that propane was used as the dehydrogenation raw material, and the down-flow intermittent fixed-bed reaction process system provided by the embodiment 1 was used as the reaction system. Test example 3 was that propane was used as the dehydrogenation raw material, and the up-flow intermittent fixed-bed reaction process system provided by the embodiment 1 was used as the reaction system. Comparative test example 1 was that propane was used as the dehydrogenation raw material, and the conventional intermittent alkane dehydrogenation reaction fixed-bed reaction process system provided by the comparative example 1 without the nitrogen oxygen separator 14 was used as the reaction system. Test example 4 was that isobutane was used as the dehydrogenation raw material, and the down-flow intermittent fixed-bed reaction process system provided by the embodiment 1 was used as the reaction system. Test example 5 was that isobutane was used as the dehydrogenation raw material, and the down-flow intermittent fixed-bed reaction process system provided by the embodiment 1 was used as the reaction system. Test example 6 was that isobutane was used as the dehydrogenation raw material, and the up-flow intermittent fixed-bed reaction process system provided by the embodiment 1 was used as the reaction system. Comparative test example 2 was that isobutane was used as the dehydrogenation raw material, and the conventional intermittent alkane dehydrogenation reaction fixed-bed reaction process system provided by the comparative example 1 without the nitrogen oxygen separator 14 was used as the reaction system.

[0075] 1. The feedstock composition for the dehydrogenation of propane is shown in Table 1.

[0076] Table 1

[0077] Item Composition / m% Propane 99.9 Nitrogen 0.1

[0078] 2. The process conditions and performance for the dehydrogenation of propane are shown in Table 2.

[0079] Table 2

[0080]

[0081]

[0082] The LHSV is in the range of 0.5-3, the inlet pressure of the dehydrogenation catalyst bed is 1-0.4 atm, the outlet pressure of the catalyst bed is 0.8-0.01 atm, the inlet temperature of the hydrocarbon feed is 500-650°C, and the inlet temperature of the regeneration gas is 550-650°C.

[0083] The process system in Example 1 and Comparative Example 1 was evaluated using isobutane as the dehydrogenation feedstock. The catalyst was loaded into a reaction tube and reacted. The catalyst in the present application has a high conversion rate of low carbon alkanes and a high selectivity of low carbon alkanes compared to the catalyst in the comparative example.

[0084] 1. The feedstock composition for the dehydrogenation of isobutane is shown in Table 3.

[0085] Table 3

[0086] Item Composition / m% Isobutane 99.9 Nitrogen 0.1

[0087] 2. The process conditions and performance for the dehydrogenation of isobutane are shown in Table 4.

[0088] Table 4

[0089]

[0090]

[0091] The LHSV is in the range of 0.5-3, the inlet pressure of the dehydrogenation catalyst bed is 1-0.4 atm, the outlet pressure of the catalyst bed is 0.8-0.01 atm, the inlet temperature of the hydrocarbon feed is 500-620°C, and the inlet temperature of the regeneration gas is 550-650°C.

[0092] The unit energy consumption for the dehydrogenation of low carbon alkanes in the above test examples is shown in Table 5.

[0093] Table 5

[0094] Dehydrogenation section time / total reaction cycle time Reactor energy consumption, kg of marker oil / ton of propylene Example 1-1 50％ 78% Base 1 Example 1-2 50％ 78% Base 1 Example 1-3 50％ 78% Base 1 Example 1-4 50％ 78% Base 2 Example 1-5 50％ 78% Base 2 Example 1-6 50％ 78% Base 2 Comparative Example 1-1 37.5％ Base 1 Comparative Example 1-2 37.5％ Base 2 Comparative Example 1-2

[0095] In summary, the present application provides an intermittent fixed bed reaction process system, by using oxygen and nitrogen separation, the oxygen and nitrogen in the feed air are separated, the oxygen is used for catalyst regeneration combustion, and the nitrogen is used for device purging. And establish a gas shunting system to realize the reasonable distribution of separated nitrogen and oxygen. Realize the reduction of the overall energy consumption of the device, and improve the service life of the catalyst. The design of large inlet bed cross-sectional area and small outlet bed cross-sectional area makes the flow rate of the reaction outlet higher than that of the inlet, and the pressure of the reaction outlet lower than that of the inlet, which is beneficial to the dehydrogenation of alkanes to the positive reaction direction.

[0096] Various embodiments of the present application can exist in the form of a range; it should be understood that the description in the form of a range is only for the convenience and brevity, and should not be understood as a hard limit on the scope of the present application; therefore, it should be considered that the range described has been specifically disclosed all possible sub-ranges and single values within the range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. In addition, whenever a numerical range is indicated in this document, it refers to any cited number (fraction or integer) within the indicated range.

[0097] In the present application, the orientation words such as "upper" and "lower" are specific to the drawing direction in the drawings. In addition, in the description of the present application, the terms "include", "contain" and the like mean "include but not limited to". In this document, relational terms such as "first" and "second" and the like are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that these entities or operations have any such actual relationship or order. In this document, "and / or" describes the relationship between the associated objects, which means that there can be three relationships, for example, A and / or B can represent the existence of A alone, the existence of A and B together, and the existence of B alone. Where A and B can be singular or plural. In this document, "one or more" means one or more, and "multiple" means two or more. "At least one", "at least one of the following" or the like means any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can mean a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple.

[0098] The foregoing detailed description of the application has been presented for purposes of illustration and description. Various modifications and changes can be made to these embodiments without departing from the spirit and scope of the application. It is intended that the scope of the application should not be limited by the particular representative embodiments described above. Rather, the general scope of the application is to be determined by the appended claims and their equivalents.

Claims

1. An intermittent fixed-bed reaction system, characterized in that, The intermittent fixed-bed reaction system includes a variable-diameter low-carbon alkane dehydrogenation reactor, which is connected to a nitrogen-oxygen separator, a feed heater, a natural gas combustion chamber, and a heat exchanger. The heat exchanger is connected to the feed heater and a first cooler. The first cooler, a compressor, a second cooler, and a reaction product separation system are connected in sequence. The reaction stages of the variable-diameter low-carbon alkane dehydrogenation reactor include a dehydrogenation reaction section, a vacuum / purge section, a catalyst regeneration section, and a vacuum / purge / reduction section. The ratio of the diameter of the low-carbon alkane inlet to the diameter of the outlet of the variable-diameter low-carbon alkane dehydrogenation reactor is greater than 1.

05. The nitrogen-oxygen separator includes a nitrogen absorption and oxygen production section for producing oxygen-enriched gas and a pressure swing denitrification section for producing nitrogen-enriched gas. The oxygen-enriched gas separated from the nitrogen absorption and oxygen production section is mixed with natural gas and then enters the natural gas combustion chamber to obtain high-temperature oxygen-enriched gas, which is used as the gas in the catalyst regeneration section. The nitrogen-rich gas separated in the pressure swing denitrification process is used as the purging gas.

2. The intermittent fixed-bed reaction system according to claim 1, characterized in that, The ratio of the pressure at the low-carbon alkane inlet to the pressure at the outlet of the variable-diameter low-carbon alkane dehydrogenation reactor is greater than 1.

2.

3. The intermittent fixed-bed reaction system according to claim 1 or 2, characterized in that, The variable-diameter low-carbon alkane dehydrogenation reactor is an adiabatic fixed-bed reactor, which can be either a downward intermittent alkane dehydrogenation fixed-bed reactor or an upward intermittent alkane dehydrogenation fixed-bed reactor. The top of the downflow intermittent alkane dehydrogenation fixed-bed reactor is provided with a first low-carbon alkane inlet, a first air / fuel gas inlet, a first steam / hydrogen gas inlet, and a reaction bed inlet; The bottom of the downflow intermittent alkane dehydrogenation fixed-bed reactor is provided with a first hydrocarbon outlet, a first combustion exhaust gas outlet, and a reaction bed outlet. Between the inlet and outlet of the reaction bed, from inlet to outlet, there are sequentially arranged a first inert ceramic ball layer, a first dehydrogenation catalyst / inert alumina layer, a first dehydrogenation catalyst / heat-generating agent layer, a second dehydrogenation catalyst / inert alumina layer, a first dehydrogenation catalyst layer, and a second inert ceramic ball layer; inert filling layers are provided at the top and bottom of the bed.

4. The intermittent fixed-bed reaction system according to claim 3, characterized in that, The bottom of the upward intermittent alkane dehydrogenation fixed-bed reactor is provided with a second low-carbon alkane inlet, a second air / fuel gas inlet, and a second steam / hydrogen inlet; the top of the upward intermittent alkane dehydrogenation fixed-bed reactor is provided with a second hydrocarbon outlet and a second combustion exhaust gas outlet; between the bottom and top of the upward intermittent alkane dehydrogenation fixed-bed reactor, from bottom to top, are arranged a third inert ceramic ball layer, a third dehydrogenation catalyst / inert alumina layer, a second dehydrogenation catalyst / heat-generating aid layer, a fourth dehydrogenation catalyst / inert alumina layer, a second dehydrogenation catalyst layer, and a fourth inert ceramic ball layer.

5. The intermittent fixed-bed reaction system according to claim 3, characterized in that, The reaction product separation system separates materials including hydrogen, dry gas, low-carbon olefins and recycled low-carbon alkanes, and the recycled low-carbon alkanes and the dry gas are returned to the feed for cyclic dehydrogenation.

6. The intermittent fixed-bed reaction system according to claim 3, characterized in that, The purging exhaust gas discharged from the vacuum / purging section and the regeneration exhaust gas discharged from the catalyst regeneration section both enter the preheating boiler.

7. A method for dehydrogenation reaction of low-carbon alkanes, characterized in that, The method employs the intermittent fixed-bed reaction system as described in any one of claims 1 to 6.

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