A coupling system for dehydrogenation of low-carbon alkanes and epoxidation of propylene to prepare propylene oxide

Abstract

The application provides a low-carbon alkane dehydrogenation and propylene epoxidation system for preparing propylene oxide, and belongs to the technical field of petroleum chemical industry, and solves the problem that the reaction catalyst is deactivated due to the fact that the rich methanol liquid is not subjected to hydrogenation treatment in the prior art. The system comprises, which are connected in sequence, a dehydrogenation reaction and compression device, a deethanizer, a C4-removing tower, a horizontal reactor, a deoxygenation tower, a propylene oxide pre-degassing tower, a methanol-removing tower, a propylene oxide purification tower and a hydrogenation reactor, the bottom of the horizontal reactor is connected with the propylene oxide pre-degassing tower, the bottom of the methanol-removing tower is connected with the hydrogenation reactor, and the hydrogenation reactor is connected with a methanol recovery unit which is communicated with the horizontal reactor. After the above equipment is processed, pure propylene oxide is obtained, the hydrogenation reactor is used to hydrogenate the last mixture, trace components which are difficult to separate in methanol are changed into water, ammonia and alcohol, and the enrichment of the trace components in the system is avoided to prevent the reaction catalyst from being deactivated.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of petrochemical industry, and particularly relates to a coupling system for dehydrogenation of low-carbon alkanes and epoxidation of propylene to prepare propylene oxide. BACKGROUND

[0002] Propylene oxide is the third largest propylene derivative after polypropylene and polyacrylonitrile. As one of the main downstream products of propylene, it can consume about 7% of propylene every year. At the same time, propylene oxide is an important intermediate chemical product, mainly used in the production of polyether polyols and propylene glycol. It is also the main raw material for polyurethane, surfactant, pesticide emulsifier, dimethyl carbonate, propylene carbonate, flame retardant, hydroxypropyl methyl cellulose, diethanol mono-isopropanol amine, etc. Among them, polyether polyol is the most important downstream product, and its main use is in automobiles, white household appliances and building materials dominated by coatings, etc.; another downstream product is dimethyl carbonate, with the continuous growth of domestic new energy vehicles, dimethyl carbonate is the main solvent for lithium battery electrolyte, therefore, the production of dimethyl carbonate has become a new growth point of propylene oxide.

[0003] The industrial production processes of propylene oxide mainly include direct oxidation method, co-oxidation method, chlorohydrination method and hydrogen peroxide direct oxidation method. The chlorohydrination method for producing propylene oxide is divided into lime process and electrolyte sodium hydroxide saponification process, and the chlorohydrination method has low production cost, mature technology, large operation flexibility and safe production; however, the biggest problem of the method is that the production process has great environmental pressure, and a large amount of chlorides and waste residues are generated, at present, the process is listed in the process of elimination or restriction in Europe and China. The co-oxidation method is divided into ethylbenzene co-oxidation method for coproduction of styrene and propylene oxide process, isobutane co-oxidation method for coproduction of tertiary butanol and propylene oxide process, etc. The advantage of co-oxidation is that the process is environmentally friendly and has less waste discharge, and the main disadvantage is that the process route is long and the investment is large, and since multiple products are produced, the market of the products is restricted, when the market price of one product is low, it is easy to cause enterprise loss. The hydrogen peroxide direct oxidation method solves the problems of environmental protection and multiple by-products of the chlorohydrination method and co-oxidation method, it uses hydrogen peroxide as the oxidant, propylene as the raw material and methanol as the solvent, and under the catalysis of titanium-silicon molecular sieve, the propylene epoxidation reaction is carried out. Although the profit rate of the method is not as good as that of the co-oxidation method, since the propylene raw material can use polymerization grade or chemical grade, or the volume fraction of propane is ≤5%, the raw material is easy to obtain, the reaction conditions are mild, the main product is unique, and the by-product is water, which is easy to handle, so it is the research direction of green production of propylene oxide.

[0004] The most important raw material for propylene oxide production is propylene. About 0.8 tons of propylene and 0.72 tons of hydrogen peroxide are needed to produce one ton of propylene oxide by the hydrogen peroxide direct oxidation method. Therefore, seeking a cheap source of propylene is a priority for the hydrogen peroxide direct oxidation method of propylene oxide. The representative production process of propylene is steam cracking, catalytic cracking, coal chemical method and propane dehydrogenation. The first process is to produce propylene by steam cracking of naphtha. This route is greatly affected by the price of crude oil. When the price of crude oil is high, the cost is high. The second process is a coal-based route. Bituminous coal is used as the raw material to produce synthesis gas through coal gasification technology. The synthesis gas is used to produce methanol, and the MTP conversion technology is used to produce propylene. This process has a long route, high investment and high carbon emission intensity. The production cost is subject to the price of coal. Under the background of double carbon in China, this process is subject to increasing restrictions. The third process is a propane dehydrogenation route. This route has a short industrial chain, low investment and low carbon emissions. It is an energy-saving and environmentally friendly technology. Propane dehydrogenation technology converts large amounts of low-cost low-carbon alkanes into high-value olefins in short supply. It has important research significance and economic value. With the import of a large amount of low-cost low-carbon alkanes, the economic advantage of the propylene production process by propane dehydrogenation technology is increasingly obvious.

[0005] The propane dehydrogenation production of propylene device is divided into fixed bed, moving bed and fluidized bed three process routes. Limited by the dehydrogenation catalyst, the single pass conversion rate of propane in the reactor is only between 35% and 45%. Therefore, there are about 35 mol% of propane and 26 mol% of propylene in the gas out of the propane dehydrogenation reactor. In order to make the propane fully convert and obtain pure polymerization agent or chemical grade propylene, a large and energy-consuming propane propylene separation tower needs to be set up.

[0006] Currently, the existing technology for hydrogen peroxide oxidation production of propylene oxide all uses polymerization grade or chemical grade propylene as raw material, and there is no use of refinery grade propylene or even lower concentration propylene as raw material for hydrogen peroxide epoxidation reaction. There is no deep coupling of heat and flow between the propane dehydrogenation device and the hydrogen peroxide oxidation process for producing propylene oxide. In the traditional propylene oxide product rectification system, the methanol-rich liquid after purification of propylene oxide is not subjected to hydrogenation treatment, resulting in the presence of trace amounts of acetaldehyde, acetal, hydrogen peroxide, hydrazine hydrate and other impurities in the recycled methanol to the reaction unit. Long-term accumulation causes the deactivation of the reaction catalyst. SUMMARY

[0007] In order to solve the above problems, the present application aims to provide a low carbon alkane dehydrogenation and propylene epoxidation system for preparing propylene oxide, propane raw gas enters the dehydrogenation reaction and compression device for reaction, the light components such as methane and ethane in the product are separated from the deethanizer, the separated light hydrocarbon components are removed from the C4 and C4+ components in the circulating propane by the de-C4 tower, the excessive C4 and C4+ are prevented from enriching in the horizontal reactor, after the reaction of the horizontal reactor, the product enters the deoxygenation tower to remove the oxygen generated by the self-decomposition of hydrogen peroxide in the horizontal reactor, the product enters the propylene oxide pre-degassing tower for preliminary rectification, then the methanol is removed by the methanol removal tower, the propylene oxide purification tower is used for extraction rectification to separate the propylene oxide and other mixtures, the methanol and other mixtures enter the hydrogenation reactor, the trace components which are difficult to separate in methanol are changed into water, ammonia, alcohol and the like by the hydrogenation reactor, the trace components are prevented from enriching in the system to cause the deactivation of the reaction catalyst, and finally the methanol is recovered by the methanol recovery unit.

[0008] The technical scheme adopted by the present application is as follows:

[0009] The low carbon alkane dehydrogenation and propylene epoxidation system for preparing propylene oxide comprises a dehydrogenation reaction and compression device, the dehydrogenation reaction and compression device is connected with a deethanizer, the bottom of the deethanizer is connected with a de-C4 tower through a pipeline, the top of the de-C4 tower is connected with a horizontal reactor through a pipeline, the bottom of the horizontal reactor is connected with a deoxygenation tower through a pipeline, the bottom of the deoxygenation tower is connected with a propylene oxide pre-degassing tower through a pipeline, the bottom of the propylene oxide pre-degassing tower is connected with a methanol removal tower through a pipeline, the top of the methanol removal tower is connected with a propylene oxide purification tower through a pipeline, the bottom of the propylene oxide purification tower is connected with a hydrogenation reactor through a pipeline, the bottom of the horizontal reactor is connected with the propylene oxide pre-degassing tower through a pipeline, the bottom of the methanol removal tower is connected with the hydrogenation reactor through a pipeline, and the hydrogenation reactor is connected with a methanol recovery unit which is in communication with the horizontal reactor.

[0010] Preferably, the horizontal reactor comprises a horizontally arranged shell, a reaction tube bundle is arranged in the shell, the two ends of the reaction tube bundle are respectively communicated with a mixing chamber and a layered chamber, the mixing chamber is connected with an epoxidation reaction feed inlet, a tower kettle circulation gas outlet and a tower kettle liquid inlet are arranged on the shell and located between the mixing chamber and the layered chamber, the layered chamber is provided with a reaction heavy component phase outlet and a reaction light component phase outlet, the reaction heavy component phase outlet is communicated with the bottom of the deoxygenation tower, and the reaction light component phase outlet is communicated with the propylene oxide pre-degassing tower.

[0011] Preferably, a partition plate connected with the bottom and the side wall of the layered chamber is arranged in the layered chamber, a chamber between the partition plate and the reaction tube bundle is communicated with the reaction heavy component phase outlet, and the reaction light component phase outlet is located on an end face of the layered chamber away from the reaction tube bundle.

[0012] Preferably, a liquid collecting bag is arranged at the bottom of the shell.

[0013] Preferably, a grid is arranged in the mixing chamber.

[0014] Preferably, the coupling system further comprises a propylene refining tower in communication with the top of the propylene oxide pre-degassing tower, the bottom of the propylene refining tower is connected with the tower bottom liquid inlet, the dehydrogenation reaction and compression device through a pipeline, the top of the propylene refining tower is connected with the epoxidation reaction feed inlet through a pipeline, a first condenser is arranged on the top pipeline of the propylene refining tower, the first condenser is connected with the propylene refining tower through a pipeline, and the tower bottom circulating gas outlet is connected with the propylene refining tower.

[0015] Preferably, the bottom of the propylene refining tower is connected with a first reboiler through a pipeline, and the first reboiler is connected with the propylene refining tower through another pipeline.

[0016] Preferably, the methanol recovery unit comprises a medium-pressure methanol tower in communication with the top of the hydrogenation reactor, the bottom of the medium-pressure methanol tower is connected with the low-pressure methanol tower through a pipeline, and the top of the low-pressure methanol tower and the medium-pressure methanol tower is connected with the epoxidation reaction feed inlet through a pipeline.

[0017] Preferably, a second condenser is arranged on the top pipeline of the low-pressure methanol tower, and the second condenser is connected with the low-pressure methanol tower through another pipeline.

[0018] Preferably, the low-pressure methanol tower is connected with a second reboiler, the top pipeline of the medium-pressure methanol tower is connected with the medium channel of the second reboiler, and the medium-pressure methanol tower is further connected with the medium channel of the second reboiler through another pipeline.

[0019] As described above, by adopting the technical scheme, the application has the following beneficial effects:

[0020] The propane raw material gas enters the dehydrogenation reaction and compression device for reaction, the methane, ethane and other light components in the product are separated out from the de-ethane tower, the separated light hydrocarbon components are removed from the C4 and C4+ components in the circulating propane in the de-C4 tower, the excessive C4 and C4+ are prevented from being enriched in the horizontal reactor, after the reaction of the horizontal reactor, the product enters the de-oxygen tower to remove the oxygen generated by the self-decomposition of the hydrogen peroxide in the horizontal reactor, the product enters the propylene oxide pre-degassing tower for preliminary rectification, the methanol is removed by the de-methanol tower, the propylene oxide is separated from other mixtures by the propylene oxide purification tower, the methanol and other mixtures enter the hydrogenation reactor, the trace components which are difficult to separate in the methanol are changed into water, ammonia, alcohol and the like by the hydrogenation reactor, the trace components are prevented from being enriched in the system to cause the deactivation of the reaction catalyst, and finally the methanol is recovered by the methanol recovery unit. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be regarded as a limitation to the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0022] Figure 1 The flow schematic diagram provided for the embodiments of the present application;

[0023] Figure 2 The horizontal reactor structure schematic diagram provided for the embodiments of the present application.

[0024] BRIEF DESCRIPTION OF DRAWINGS: 1 - C4 removal column; 2 - dehydrogenation reaction and compression device; 3 - ethane removal column; 4 - horizontal reactor; 401 - mixing chamber; 402 - epoxidation reaction feed port; 403 - column still circulating gas outlet; 404 - liquid collection package; 405 - column still liquid inlet; 406 - layered chamber; 407 - partition; 408 - reaction heavy component phase outlet; 409 - reaction light component phase outlet; 410 - reaction tube bundle; 411 - grid; 5 - deoxygenation column; 6 - propylene oxide pre-removal column; 7 - propylene refining column; 8 - first reboiler; 9 - first condenser; 10 - methanol removal column; 11 - propylene oxide purification column; 12 - hydrogenation reactor; 13 - medium-pressure methanol column; 14 - low-pressure methanol column; 15 - second condenser; 16 - second reboiler; 17 - C4 and C4+ stream; 18 - hydrogen-rich tail gas; 19 - ethane-rich tail gas; 20 - propane raw gas; 21 - refinery-grade propylene stream; 22 - column still first discharge liquid; 23 - column bottom circulating gas; 24 - reaction heavy component phase; 25 - reaction light component phase; 26 - oxygen-containing waste gas; 27 - gas stripping nitrogen; 28 - propylene oxide-rich liquid; 29 - propane propylene stream; 30 - propane-rich stream; 31 - column still second discharge liquid; 32 - circulating propylene stream; 33 - methanol removal column discharge liquid; 34 - propylene oxide purification column discharge liquid; 35 - propylene oxide-rich stream; 36 - propylene oxide product; 37 - water and hydrazine hydrate; 38 - medium-pressure methanol column top hot steam; 39 - medium-pressure methanol column circulating methanol; 40 - low-pressure methanol column circulating methanol; 41 - waste water; 42 - hydrogen peroxide solution. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the following will combine the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are some of the embodiments of the present application, but not all the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0026] The following detailed description of embodiments of the application provided in the accompanying drawings is not intended to limit the scope of the application as claimed, but merely represents selected embodiments of the application. Based upon the embodiments of the application, all other embodiments obtained by persons of ordinary skill in the art without creative effort, fall within the scope of the application.

[0027] In the description of the application, it should be noted that if the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship commonly placed when the product of the application is used, and are only for the convenience of describing the application and simplifying the description, and therefore cannot be understood as indicating or implying that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the application.

[0028] The following will be described in detail Figure 1 and Figure 2 The application will be described in detail.

[0029] Embodiments

[0030] Example 1

[0031] A low-carbon alkane dehydrogenation and propylene epoxidation system for preparing propylene oxide, comprising a dehydrogenation reaction and compression device 2, the dehydrogenation reaction and compression device 2 is connected with a deethanizer 3, the bottom of the deethanizer 3 is connected with a de-C4 tower 1 through a pipeline, the top of the de-C4 tower 1 is connected with a horizontal reactor 4 through a pipeline, the bottom of the horizontal reactor 4 is connected with a deoxygenation tower 5 through a pipeline, the bottom of the deoxygenation tower 5 is connected with a propylene oxide pre-degassing tower 6 through a pipeline, the bottom of the propylene oxide pre-degassing tower 6 is connected with a de-methanol tower 10 through a pipeline, the top of the de-methanol tower 10 is connected with a propylene oxide purification tower 11 through a pipeline, the bottom of the propylene oxide purification tower 11 is connected with a hydrogenation reactor 12 through a pipeline, the bottom of the horizontal reactor 4 is connected with the propylene oxide pre-degassing tower 6 through a pipeline, the bottom of the de-methanol tower 10 is connected with the hydrogenation reactor 12 through a pipeline, and the hydrogenation reactor 12 is connected with a methanol recovery unit in communication with the horizontal reactor 4.

[0032] The catalyst used in the dehydrogenation reaction and compression device 2 is a low-carbon alkane chromium dehydrogenation catalyst containing a spinel structure. The mass fraction of the components in the chromium dehydrogenation catalyst dry base total mass is as follows: chromium oxide 17%; first additive 4%, second additive 3%, third additive 8%, fixed bed carrier 68%. The dehydrogenation reaction operating temperature is 590℃, the operating pressure is 0.02Mpa(G), and the bed space velocity is 0.65h-1. Under these conditions, the catalyst has good selectivity and conversion rate, and the single-pass conversion rate reaches 46%, and the propylene selectivity reaches 89.5%.

[0033] like Figure 1 As shown, a propane feed gas 20 with a gas flow rate of 44.8 t / h is mixed with a propane-rich stream 30 (the propane concentration of the mixed propane feed gas and propane-rich gas is 96.5 mol%) and enters the dehydrogenation reaction and compression unit 2 for reaction. The outlet gas of the dehydrogenation reaction and compression unit 2 contains approximately 26 mol% propylene, approximately 35 mol% propane, approximately 29 mol% hydrogen, and the remainder is water, carbon monoxide, C4, C4+, etc. Using known compression and cryogenic separation technologies, a hydrogen-rich tail gas 18 can be separated. The hydrogen content of the hydrogen-rich tail gas 18 is 87.5 mol%, and the remainder is carbon monoxide, carbon dioxide, methane, and a small amount of ethane. The product gas and product liquid after cryogenic separation are residual ethane, propane, propylene, ethane, C4, C4+, etc.

[0034] The product liquid then enters the deethanizer 3 to separate ethane. The top of the deethanizer 3 produces an ethane-rich tail gas 19, primarily composed of 35 mol% hydrogen, 22 mol% methane, and 27 mol% ethane. The bottoms stream consists of propane, propylene, and C4 / C4+ hydrocarbons. Deethanizer 3 operates at a pressure of 0.7 MPa and utilizes a tray-type tower. Due to the significant mass difference between the ethane component at the top and the heavy components at the bottom, a variable-diameter tower structure with a thin top and thick bottom is employed to conserve investment and reduce energy consumption. The bottoms liquid from the deethanizer 3 is pressurized and transferred to the C4 removal tower 1, where the propane and propylene products are separated from C4 and higher hydrocarbons. The bottoms of the C4 removal tower 1 produce a C4 and C4+ stream 17, primarily composed of isobutane, isobutylene, n-butane, butadiene, benzene, and toluene. The C4 and C4+ stream 17 is transported to the outside as product at a rate of approximately 1.6 t / h. The overhead product is a refinery-grade propylene stream 21, comprising approximately 44 mol% propylene and 56 mol% propane. The C4 removal tower 1 operates at a pressure of 0.6 MPa and utilizes a plate-type tower. Due to the significant quality difference between the overhead propane and propylene components and the C4 and C4+ heavy components at the bottom, a tapered tower structure with a coarse top and a finer bottom is employed to conserve investment and reduce energy consumption.

[0035] The total flow of the refinery grade propylene stream 21 is 2130 kmol / h, of which 42.25 mol% is propylene and the rest is propane, which is equivalent to 900 kmol / h of propylene and 1230 kmol / h of propane. The refinery grade propylene stream 21, the hydrogen peroxide solution 42, the recycled methanol from the medium pressure methanol recovery unit 39, the recycled methanol from the low pressure methanol recovery unit 40 and the recycled propylene stream 32 are mixed and then fed into the horizontal reactor 4, which is provided with a titanium silicate molecular sieve catalyst having a molar ratio of titanium to silicon of 0.025:1, a pore size of 1 nm, a specific surface area of 500 m2 / g, a total pore volume of 0.5 cm3 / g and a particle size of 200 nm. The feed to the horizontal reactor 4 is in liquid phase; the molar ratio of propylene to hydrogen peroxide is 2:1 to 5:1, and more preferably 3:1 to 5:1. The molar ratio of propylene to propane is 0.6:1 to 1.5, and more preferably 0.77:1. The molar ratio of methanol to hydrogen peroxide is 1:1 to 8:1, and more preferably 5:1 to 6:1. When the molar ratio of propylene to hydrogen peroxide is 4:1 and the molar ratio of methanol to hydrogen peroxide is 5:1, the flow of the mixture of the refinery grade propylene stream 21, the recycled propylene stream 32, the recycled methanol from the medium pressure methanol recovery unit 39, the recycled methanol from the low pressure methanol recovery unit 40 and the hydrogen peroxide solution 42 is as follows: 930 kmol / h of hydrogen peroxide, 930 kmol / h of water, 1230 kmol / h of propane, 4650 kmol / h of methanol and 3720 kmol / h of propylene. The recycle ratio of propylene is 3.1, the single pass conversion of hydrogen peroxide is 97% and the selectivity of propylene oxide is 95%.

[0036] The horizontal reactor 4 is used in the present application to replace the vertical reactor in the prior art, and the cooling medium of the vertical reactor is chilled water or circulating water, which consumes extra energy for refrigeration. The horizontal reactor is used in the present application, and the heat released in the epoxidation reaction can be used as the heat source for evaporation of the tower kettle of the subsequent propylene refining tower 7, while the energy consumption for refrigeration is reduced. The reaction conditions of the horizontal reactor 4 are as follows: the bed temperature is 40-60°C, and more preferably 45-50°C, and the reaction temperature is preferably 50°C in the present application; the reaction pressure is 1.8-4.0 MPa, and more preferably 2.0-2.5 MPa; the liquid hourly space velocity of the catalyst is 5-15 h-1, and more preferably 7-10 h-1. The superficial velocity of the reactant stream through the bed is preferably 0.002-0.02 m / s.

[0037] As Figure 2As shown, the horizontal reactor 4 comprises a horizontally arranged shell, in which a reaction tube bundle 410 is arranged, two ends of the reaction tube bundle 410 are communicated with a mixing chamber 401 and a layered chamber 406 respectively, the mixing chamber 401 is connected with an epoxidation reaction feed port 402, the shell is provided with a tower kettle circulating gas outlet 403 and a tower kettle liquid inlet 405 between the mixing chamber 401 and the layered chamber 406, the layered chamber 406 is provided with a reaction heavy component phase outlet 408 and a reaction light component phase outlet 409, the reaction heavy component phase outlet 408 is communicated with the bottom of the deoxidation tower 5, and the reaction light component phase outlet 409 is communicated with the propylene oxide pre-deoxidation tower 6. The mixing chamber 401 and the layered chamber 406 are connected with the shell by flexible tube plates, so as to separate the chambers. The outer diameter of the reaction tube bundle 410 can be selected from φ40mm to φ100mm, and is preferably φ50mm; the length of the tube bundle ranges from 8000mm to 12000mm, and is preferably from 9000mm to 10000mm. In order to improve the heat transfer efficiency between the tube and the shell, the reaction tube bundle 410 is preferably a corrugated tube bundle. Such heat exchange tube can strengthen the flow rate of the fluid in the tube, so that the fluid forms turbulent flow and has good thermal stress, has good flexibility, the tube bundle can freely expand, and can eliminate stress by its own thermal expansion, and can be suitable for a larger temperature difference between the inside and outside of the tube.

[0038] The mixed feed of methanol, propane, propylene and hydrogen peroxide first enters the mixing chamber 401, and after mixing, enters the reaction tube bundle 410, in which the titanium silicalite molecular sieve catalyst is loaded. Under the action of the titanium silicalite molecular sieve catalyst, propylene and hydrogen peroxide generate the main product propylene oxide and other reaction products (propane, unreacted propylene, trace hydrogen peroxide, water, propylene oxide and trace components such as ketones and acids). The reaction products then flow into the layered chamber 406, and the heavy component phase 24 (rich in methanol and water) and the light component phase 25 (rich in propane, propylene and propylene oxide) are separated and transported by the layered chamber 406.

[0039] The layered chamber 406 is provided with a partition plate 407 connected with the bottom and side wall of the layered chamber 406, the chamber between the partition plate 407 and the reaction tube bundle 410 is communicated with a reaction heavy component phase outlet 408, and a reaction light component phase outlet 409 is located on the end face of the layered chamber 406 away from the reaction tube bundle 410. The partition plate 407 is arranged to block the heavy component phase 24 on the left side of the partition plate 407, and the light component phase 25 enters the right side of the partition plate 407. The light component phase 25 is separated again by once settling, and is discharged from the reaction light component phase outlet 409. The less heavy component phase 24 is collected at the bottom of the right side of the partition plate 407 after two times of separation, and the separation efficiency is greatly increased. The heavy component phase 24 is discharged from the reaction heavy component phase outlet 408. The bottom of the shell is provided with a liquid collecting package 404 for collecting possible water, methanol and other heavy components in the liquid phase on the shell side. Since the mixed feed contains polar and non-polar substances, the feed is layered, and therefore, a grid 411 is arranged in the mixing chamber 401 to facilitate uniform mixing of the feed streams. The grid 411 is arranged in the form of an arc-shaped grid or a circular grid, and in the present application, the arc-shaped grid is adopted.

[0040] The coupling system further comprises a propylene rectification tower 7 communicated with the top of the propylene oxide pre-decomposition tower 6, the bottom of the propylene rectification tower 7 is communicated with the tower bottom liquid inlet 405, the dehydrogenation reaction and compression device 2 through a pipeline, the top of the propylene rectification tower 7 is communicated with the epoxidation reaction feed inlet 402 through a pipeline, the top pipeline of the propylene rectification tower 7 is provided with a first condenser 9, the first condenser 9 is connected with the propylene rectification tower 7 through a pipeline, and the tower bottom circulating gas outlet 403 is communicated with the propylene rectification tower 7. The tower bottom liquid inlet 405 and the tower bottom circulating gas outlet 403 are both provided with two, which can ensure that the shell side feed temperature is consistent, the distribution is consistent, the static pressure difference of the inlet and outlet is consistent, so that the problems of uneven flow and pressure imbalance do not occur in the device operation. The first condenser 9 is a total condenser, and the reflux ratio of the rectification section is controlled to be 10-25, preferably 18-21.

[0041] The bottom of the propylene rectification tower 7 discharges the tower bottom first discharge liquid 22, the tower bottom first discharge liquid 22 enters the horizontal reactor 4 to be heat-absorbed from the tower bottom liquid inlet 405, and the tower bottom first discharge liquid 22 is partially gasified, so that the density of the upper part of the shell is lower than that of the lower part, thereby driving the whole thermosyphon to proceed through the density difference, realizing automatic absorption of the tower bottom first discharge liquid 22, and reducing the use of pumps. The temperature of the tower bottom first discharge liquid 22 (propane-rich liquid) is 30-50°C, and the preferred temperature is 40°C. The tower bottom circulating gas 23 is discharged from the tower bottom circulating gas outlet 403 and enters the stripping section of the propylene rectification tower 7 to provide the required steam for the stripping section. The propane-rich stream 30 is sent to the dehydrogenation reaction and compression device 2 and mixed with the propane raw material gas 20. Part of the condensate at the top returns to the tower as reflux liquid, and part of the condensate at the top returns to the horizontal reactor 4 as a circulating propylene stream 32 and reacts with hydrogen peroxide.

[0042] The bottom of the propylene refining tower 7 is connected with a first reboiler 8 through a pipeline, and the first reboiler 8 is further communicated with the propylene refining tower 7 through another pipeline. The second tower bottom discharge 31 passes through the first reboiler 8 and then returns to the propylene refining tower 7. The first reboiler 8 is in a standby state, which prevents the heat generated by the horizontal reactor from being insufficient to meet the demand of the propylene refining tower 7 when the load fluctuates. The hot water inlet temperature of the first reboiler 8 is about 80°C.

[0043] The reaction heavy component phase 24 is transported to the deoxygenation tower 5 to remove the oxygen generated by the self-decomposition of hydrogen peroxide in the horizontal reactor 4, so as to ensure the purity of the subsequent purification unit and prevent the enrichment of oxygen in the system. The bottom of the deoxygenation tower 5 is provided with stripping nitrogen 27, which is used to reduce the oxygen partial pressure and ensure that the oxygen in the rich liquid phase is stripped clean. The deoxygenation tower 5 is operated at low pressure, which facilitates the resolution of oxygen, and the operating pressure is selected to be 0.5 MPa. The oxygen-containing waste gas 26 is discharged from the top of the deoxygenation tower 5 and enters the tail gas treatment device for treatment. The tower bottom of the deoxygenation tower 5 discharges the rich epoxy propane liquid 28, which is mixed with the light component phase 25 (mainly containing water, hydrogen peroxide, propylene, propane, methanol, propylene glycol, epoxy propane, etc.) and then enters the middle part of the epoxy propane pre-decomposition tower 6 for simple rectification. The operating pressure of the epoxy propane pre-decomposition tower 6 is 0.5-1.0 MPa, preferably 0.6-0.8 MPa. In this application, 0.7 MPa is selected. The top of the epoxy propane pre-decomposition tower 6 discharges the propane propylene stream 29, and the tower bottom of the epoxy propane pre-decomposition tower 6 is the polar substance such as water, hydrogen peroxide, methanol and epoxy propane, which is then sent to the next unit. The propane propylene stream 29 is sent to the propylene refining tower 7 to separate propane and propylene, which cancels the energy-consuming propane propylene separation tower of the propane dehydrogenation device, and realizes the energy coupling of the heat generated by the epoxidation reaction of the horizontal reactor 4 and the heat required by the propylene refining tower 7.

[0044] The rich epoxy propane, methanol and water solution in the epoxy propane pre-decomposition tower 6 enters the demethanolization tower 10, the top of which discharges the rich epoxy propane stream 35, and the tower bottom of which discharges the demethanolization tower discharge liquid 33 (mainly containing water and methanol). The operating pressure of the demethanolization tower 10 is 0.1-0.3 MPa. The rich epoxy propane stream 35 enters the epoxy propane purification tower 11, in which water and hydrazine hydrate 37 are added to purify the epoxy propane. The top of the epoxy propane purification tower 11 discharges the epoxy propane product 36, and the bottom of the epoxy propane purification tower 11 discharges the epoxy propane purification tower discharge liquid 34, which is mixed with the demethanolization tower discharge liquid 33 and then enters the hydrogenation reactor 12. The hydrogenation reactor 12 converts the trace components that are difficult to separate in methanol into water, ammonia and alcohol, etc., so as to avoid the enrichment of trace components in the system.

[0045] The methanol recovery unit comprises a medium-pressure methanol column 13 connected to the top of the hydrogenation reactor 12, the bottom of the medium-pressure methanol column 13 is connected to a low-pressure methanol column 14 through a pipeline, and the top of the low-pressure methanol column 14 and the medium-pressure methanol column 13 are connected to the epoxidation reaction feed port 402 through a pipeline. The operating pressure of the medium-pressure methanol column 13 is 0.6-0.8 MPa, and the gas phase temperature at the top of the column is 120-128℃. The operating pressure of the medium-pressure methanol column 13 is 0.8 MPa, and the gas phase temperature at the top of the column is 128℃. The liquid phase outlet of the hydrogenation reactor 12 is connected to the feed port of the medium-pressure methanol column 13, and the mixed liquid after hydrogenation enters the medium-pressure methanol column 13 for preliminary fractionation. The medium-pressure methanol column 13 discharges medium-pressure methanol overhead hot steam 38 at the top. The column still liquid (containing methanol, water, propylene glycol, etc.) of the medium-pressure methanol column 13 is transported to the low-pressure methanol column 14, and the operating pressure of the low-pressure methanol column 14 is 0.15-0.25 MPa, and the operating temperature of the column is 105-110℃. A second condenser 15 is arranged on the top pipeline of the low-pressure methanol column 14, and the second condenser 15 is connected to the low-pressure methanol column 14 through another pipeline. The low-pressure methanol column 14 discharges low-pressure methanol circulating methanol 40, which is condensed by the second condenser 15, part of which is returned to the low-pressure methanol column 14, and the other part is transported to the horizontal reactor 4 for reaction. The column still liquid of the low-pressure methanol column 14 is discharged as waste water 41 (mainly water, propylene glycol, etc.) and sent to a downstream processing unit.

[0046] The low-pressure methanol column 14 is connected to a second reboiler 16, the top pipeline of the medium-pressure methanol column 13 is connected to the medium passage of the second reboiler 16, and the medium-pressure methanol column 13 is also connected to the medium passage of the second reboiler 16 through another pipeline. The high-temperature steam in the medium-pressure methanol column 13 is introduced into the second reboiler 16 to heat the low-temperature water solution in the column still of the low-pressure methanol column 14, so that the water solution is partially vaporized, thereby providing heat for the low-pressure methanol column 14. The medium-pressure methanol overhead hot steam 38 is changed into liquid medium-pressure methanol circulating methanol 39 after heat exchange, part of the medium-pressure methanol circulating methanol 39 is transported to the horizontal reactor 4 for reaction, and the other part is returned to the medium-pressure methanol column 13. The second reboiler 16 is arranged, which saves the use of a condenser for the medium-pressure methanol column 13, and saves the consumption of heating steam for the low-pressure methanol column 14.

[0047] Example 2:

[0048] In this embodiment, the same capacity as that of Example 1 (propane dehydrogenation device propylene production is 300,000 tons / year, propylene oxide production is 400,000 tons / year). The total mass fraction of the dry base of the chromium-based dehydrogenation catalyst is as follows: chromium oxide 14%; first aid 3%, second aid 3%, third aid 7%, fixed bed carrier 72%. Under this condition, it is found that the single-pass conversion rate and selectivity of the catalyst are reduced, the single-pass conversion rate of the catalyst is 43%, and the propylene selectivity is 88%. The rest of the de-ethane and de-C4 steps are the same as those of Example 1, at this time, after a series of treatments, the mixed raw material flow rate entering the horizontal reactor 4 is as follows: hydrogen peroxide 930 kmol / h, water 930 kmol / h, propane 1190 kmol / h, methanol 4650 kmol / h, propylene 3680 kmol / h. Subsequently, in the epoxidation reaction stage, titanium silicalite is used, the reaction temperature is selected to be 40°C; the reaction pressure is 2.4 MPa, and the rest of the conditions are the same as those of Example 1. It is found that the change of the reaction conditions leads to the decrease of the conversion rate of hydrogen peroxide and the decrease of the selectivity of propylene oxide. The single-pass conversion rate of hydrogen peroxide is 96%, and the selectivity of propylene oxide is 94%.

[0049] Comparative Example:

[0050] In the comparative example, a propane propylene separation tower is used to make the propylene reach 99%, 1% of the chemical grade purity, and then the polymerization grade propylene enters the epoxidation unit reaction. Compared with Example 1, the propane dehydrogenation catalyst and the epoxidation catalyst used in the comparative example are consistent. It is found that the comparative example adds the product separation tower of the energy consumer of the propane dehydrogenation unit, and also adds the refrigeration consumption of the epoxidation reactor. Except for the propylene oxide pre-depot tower 6 and the propylene rectification tower 7, the other unit operations are basically the same. The comparison of the main equipment energy consumption of the comparative example, Example 1 and Example 2 is shown in Table 1.

[0051] Table 1 Comparison of main equipment energy consumption of comparative example, Example 1 and Example 2

[0052] Item Example 1 Example 2 Comparative Example Dehydrogenation unit propane propylene column Not provided Not provided Provided Dehydrogenation unit propane propylene column bottom temperature, °C -- -- 38 Dehydrogenation unit propane propylene column reflux ratio -- -- 18 Dehydrogenation unit propane propylene column reboiler duty, MW -- -- 68 Epoxidation unit propylene oxide pre-depot tower Provided Provided Provided Epoxidation unit propylene purification column Provided Provided Provided Propylene oxide pre-depot tower reboiler duty, MW 38 40 24 Propylene purification column additional reboiler duty, MW 53 55 12 Summary of core energy consumers 91 95 104 Energy consumption ratio compared to Example 1 100％ 104％ 114％

[0053] In summary, the process energy consumption of Example 1 is the lowest, which is the optimal process.

[0054] The above is only a preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A coupled system for the dehydrogenation of light alkanes and the epoxidation of propylene to produce propylene oxide, characterized in that: The device comprises a dehydrogenation reaction and compression device (2), the dehydrogenation reaction and compression device (2) is connected with a deethanizer (3), the bottom of the deethanizer (3) is connected with a C4-removal column (1) through a pipeline, the top of the C4-removal column (1) is connected with a horizontal reactor (4) through a pipeline, the bottom of the horizontal reactor (4) is connected with a deoxygenation column (5) through a pipeline, the bottom of the deoxygenation column (5) is connected with a propylene oxide pre-removal column (6) through a pipeline, the bottom of the propylene oxide pre-removal column (6) is connected with a methanol-removal column (10) through a pipeline, the top of the methanol-removal column (10) is connected with a propylene oxide purification column (11) through a pipeline, the bottom of the propylene oxide purification column (11) is connected with a hydrogenation reactor (12) through a pipeline, the bottom of the horizontal reactor (4) is connected with the propylene oxide pre-removal column (6) through a pipeline, the bottom of the methanol-removal column (10) is connected with the hydrogenation reactor (12) through a pipeline, the hydrogenation reactor (12) is connected with a methanol recovery unit which is communicated with the horizontal reactor (4); the horizontal reactor (4) comprises a horizontally arranged shell, a reaction tube bundle (410) is arranged in the shell, the two ends of the reaction tube bundle (410) are respectively communicated with a mixing chamber (401) and a layered chamber (406), the mixing chamber (401) is connected with an epoxidation reaction feed inlet (402), a tower kettle circulating gas outlet (403) and a tower kettle liquid inlet (405) are arranged on the shell and located between the mixing chamber (401) and the layered chamber (406), the layered chamber (406) is provided with a reaction heavy component phase outlet (408) and a reaction light component phase outlet (409), the reaction heavy component phase outlet (408) is communicated with the bottom of the deoxygenation column (5), and the reaction light component phase outlet (409) is communicated with the propylene oxide pre-removal column (6).

2. The system for coupling dehydrogenation of low carbon alkane and epoxidation of propylene to prepare propylene oxide according to claim 1, characterized in that, A baffle (407) is arranged in the layered chamber (406) and connected with the bottom and the side wall of the layered chamber (406), the chamber between the baffle (407) and the reaction tube bundle (410) is communicated with the reaction heavy component phase outlet (408), and the reaction light component phase outlet (409) is located on the end face of the layered chamber (406) which is away from the reaction tube bundle (410).

3. The system for coupling dehydrogenation of low carbon alkane and epoxidation of propylene to prepare propylene oxide according to claim 1, characterized in that, A liquid collecting package (404) is arranged at the bottom of the shell.

4. The system for coupling dehydrogenation of low carbon alkane and epoxidation of propylene to prepare propylene oxide according to claim 1, characterized in that, A grid (411) is arranged in the mixing chamber (401).

5. The system for coupling dehydrogenation of low carbon alkane and epoxidation of propylene to prepare propylene oxide according to claim 1, characterized in that, The coupling system further comprises a propylene rectification column (7) which is communicated with the top of the propylene oxide pre-removal column (6), the bottom of the propylene rectification column (7) is communicated with the tower kettle liquid inlet (405) and the dehydrogenation reaction and compression device (2) through a pipeline, the top of the propylene rectification column (7) is communicated with the epoxidation reaction feed inlet (402) through a pipeline, a first condenser (9) is arranged on the top pipeline of the propylene rectification column (7), the first condenser (9) is connected with the propylene rectification column (7) through a pipeline, and the tower kettle circulating gas outlet (403) is communicated with the propylene rectification column (7).

6. The system for coupling dehydrogenation of low carbon alkane and epoxidation of propylene to prepare propylene oxide according to claim 5, characterized in that, The bottom of the propylene rectification column (7) is connected with a first reboiler (8) through a pipeline, and the first reboiler (8) is further communicated with the propylene rectification column (7) through another pipeline.

7. The system for coupling dehydrogenation of low carbon alkane and epoxidation of propylene to prepare propylene oxide according to claim 1, characterized in that, The methanol recovery unit comprises a medium-pressure methanol column (13) communicated with the top of the hydrogenation reactor (12), the bottom of the medium-pressure methanol column (13) is connected with a low-pressure methanol column (14) through a pipeline, and the top of the low-pressure methanol column (14) and the medium-pressure methanol column (13) are communicated with the epoxidation reaction feed port (402) through a pipeline.

8. The system for coupling dehydrogenation of low carbon alkane and epoxidation of propylene to prepare propylene oxide according to claim 7, characterized in that, A second condenser (15) is arranged on the top pipeline of the low-pressure methanol column (14), and the second condenser (15) is communicated with the low-pressure methanol column (14) through another pipeline.

9. The system for coupling dehydrogenation of low carbon alkane and epoxidation of propylene to prepare propylene oxide according to claim 7, characterized in that, The low-pressure methanol column (14) is connected with a second reboiler (16), the top pipeline of the medium-pressure methanol column (13) is communicated with the medium channel of the second reboiler (16), and the medium-pressure methanol column (13) is also communicated with the medium channel of the second reboiler (16) through another pipeline.

Images