Bromine-mediated propane oxidative dehydrogenation to propylene system and method

Abstract

The present application relates to a kind of bromine-mediated propane oxidative dehydrogenation system and method for preparing propylene.The system and method use propane and the bromine recovered by propane dehydrogenation device as raw material, through multi-step reaction and rectification process, including bromination reaction, hydrogenation reaction, dehydrogenation reaction and electrolysis reaction, realize the efficient conversion of propane, finally obtain product propylene and hydrogen.The present application solves the technical problems of low utilization efficiency of propane as fuel and low conversion rate in the process of converting propane to propylene;The present application uses waste heat in multi-step process to recover heat, uses the bromine and hydrogen gas produced by propane dehydrogenation process to recycle reaction, reduces the energy loss in the process, improves the utilization efficiency of material and energy, realizes the flexible improvement of propylene production while fully utilizing propane.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of chemical industry, and particularly relates to a bromine-mediated propane oxidative dehydrogenation system and method for preparing propylene. BACKGROUND

[0002] Propylene is an important basic chemical raw material, which is widely used in the fields of plastics, synthetic fibers, etc. The traditional propane dehydrogenation process (PDH) has problems such as high energy consumption and many by-products. The electric energy consumption of PDH process for producing per kilogram of propylene is 6.3 to 9.0 kWh. In recent years, propane oxidative dehydrogenation (ODH) as a new type of propylene production process has attracted more and more attention due to its advantages such as wide raw material sources, low cost and environmental friendliness.

[0003] In order to further improve the advantages of ODH process, researchers have begun to explore new types of oxidizing agents, among which halogen-mediated propane oxidative dehydrogenation process is a potential choice. Among many studies, bromine-mediated oxidative dehydrogenation (Br-ODH) process shows unique advantages: (1) The dehydrogenation reaction can be carried out in a high-pressure environment, avoiding the generation of carbon oxides and coke; (2) By introducing halogenated propane intermediates, the energy consumption in the separation process of propane and propylene is reduced. Because bromine gas (Br2) has higher monohalogenated propane selectivity than other halogen molecules, bromopropane can also be converted into propylene product under milder conditions. In summary, bromine-mediated oxidative dehydrogenation process is expected to achieve higher propane equilibrium conversion and propylene selectivity under high-pressure conditions, thereby reducing cost and energy consumption.

[0004] However, the existing bromine-mediated propane oxidative dehydrogenation process still has some challenges, such as the selectivity of propylene, the conversion rate of propane and the hydrogen production rate still have room for improvement, and the overall efficiency needs to be improved. Therefore, in view of the problems of the prior art, further optimization and upgrading are still needed. SUMMARY

[0005] In view of the shortcomings of the prior art, the present application provides a bromine-mediated propane oxidative dehydrogenation system and method for preparing propylene, which forms propylene through a multi-step dehydrogenation process and integrates a heat recovery system to significantly improve the production efficiency of propylene, reduce production costs and reduce environmental impact.

[0006] To achieve the above purpose, the present application is realized by the following technical scheme:

[0007] The application provides a bromine-mediated propane oxidative dehydrogenation system for preparing propylene, which comprises a bromination reaction unit, a distillation separation unit, a hydrogenation reaction unit, a dehydrogenation reaction unit, a fourth distillation column, a fifth distillation column and a hydrogen bromide recovery unit; wherein the bromination reaction unit is used for providing propane with bromine for bromination reaction, and delivering the generated compounds to the distillation separation unit; the compounds include monobromopropane, dibromopropane, hydrogen bromide and unreacted propane; the distillation separation unit is used for separating the compounds, delivering the separated hydrogen bromide and unreacted propane to the bromination reaction unit for reaction, delivering the separated dibromopropane to the hydrogenation reaction unit, and delivering the separated monobromopropane to the dehydrogenation reaction unit; the hydrogenation reaction unit is used for hydrogenating the dibromopropane, and delivering the generated monobromopropane and hydrogen bromide to the distillation separation unit; the dehydrogenation reaction unit is used for dehydrogenating the monobromopropane, and delivering the generated propylene, hydrogen bromide and unreacted monobromopropane to the fourth distillation column; the fourth distillation column is used for separating the hydrogen bromide and delivering it to the hydrogen bromide recovery unit, and delivering the remaining compounds to the fifth distillation column; the fifth distillation column is used for separating the propylene and unreacted monobromopropane, and delivering the unreacted monobromopropane to the dehydrogenation reaction unit; and the hydrogen bromide recovery unit is used for electrolytic regeneration of bromine.

[0008] Further, the bromination reaction unit comprises a first pressure pump and a first heat exchanger connected in sequence, and a second pressure pump and a second heat exchanger connected in sequence, and the first heat exchanger and the second heat exchanger are connected to the bromination reactor; wherein the first pressure pump and the first heat exchanger are used for warming and pressurizing the propane; and the second pressure pump and the second heat exchanger are used for warming and pressurizing the bromine.

[0009] Further, a third heat exchanger is arranged between the bromination reactor and the distillation separation unit, and the third heat exchanger is used for cooling the compounds generated by the bromination reactor, and delivering the cooled products to the distillation separation unit.

[0010] Further, the distillation separation unit comprises a first distillation column connected to the third heat exchanger, and the first distillation column is further connected with a second distillation column and a third distillation column; wherein the first distillation column is used for rectifying and separating the cooled products, and the separated hydrogen bromide and propane at the top of the column are delivered to the second distillation column, and the separated monobromopropane and dibromopropane at the bottom of the column are delivered to the third distillation column; the second distillation column is used for separating the hydrogen bromide at the top of the column and delivering it to the hydrogen bromide recovery unit, and separating the propane at the bottom of the column and delivering it to the first heat exchanger for preheating and then re-entering the bromination reactor for reaction; and the third distillation column is used for separating the monobromopropane at the top of the column and delivering it to the dehydrogenation reaction unit, and separating the dibromopropane at the bottom of the column and delivering it to the hydrogenation reaction unit.

[0011] Further, the hydrogenation reaction unit comprises a third pressure pump, a fourth heat exchanger, a hydrogenation reactor and a fifth heat exchanger connected in sequence, and the third pressure pump is connected with the third distillation tower.

[0012] Further, the dehydrogenation reaction unit comprises a fourth pressure pump, a sixth heat exchanger, a dehydrogenation reactor and a seventh heat exchanger connected in sequence, and the fourth pressure pump is connected with the third distillation tower.

[0013] Further, the hydrogen bromide recovery unit comprises a eighth heat exchanger and an electrolytic cell connected in sequence; wherein the eighth heat exchanger is used for mixing and preheating the hydrogen bromide separated from the fourth distillation tower and the second distillation tower; and the electrolytic cell is used for electrolysis reaction of the hydrogen bromide.

[0014] The application also provides a method for preparing propylene by bromine-mediated oxidative dehydrogenation of propane, which is applied to the system for preparing propylene by bromine-mediated oxidative dehydrogenation of propane as described above; the method comprises: feeding propane into a first pressure pump for pressurization, and then preheating the propane to a predetermined temperature by a first heat exchanger; feeding bromine recycled from the process of oxidative dehydrogenation of propane into a second pressure pump for pressurization, and then preheating the bromine to a predetermined temperature by a second heat exchanger; mixing the propane and the bromine, and then feeding the mixture into a bromination reactor for bromination reaction; feeding the reaction product into a third heat exchanger for cooling; feeding the cooled product into a first distillation column for rectification and separation; separating hydrogen bromide and propane from the top of the first distillation column, and separating monobromopropane and dibromopropane from the bottom of the first distillation column; feeding the product from the top of the first distillation column into a second distillation column for rectification and separation; separating hydrogen bromide from the top of the second distillation column for subsequent reaction, and feeding propane from the bottom of the second distillation column into the first heat exchanger for preheating, and then re-feeding the propane into the bromination reactor for reaction; feeding the product from the bottom of the first distillation column into a third distillation column for rectification and separation; separating monobromopropane from the top of the third distillation column for subsequent reaction, and separating dibromopropane from the bottom of the third distillation column; feeding the dibromopropane separated from the bottom of the third distillation column into a third pressure pump for pressurization, and then mixing the dibromopropane with hydrogen at a ratio of 1:1, preheating the mixture to a specified temperature by a fourth heat exchanger, preheating the mixture by the fourth heat exchanger, and then feeding the mixture into a hydrogenation reactor for hydrogenation reaction; feeding the reaction product into a fifth heat exchanger for cooling, and then re-feeding the product into the first distillation column for rectification and separation; feeding monobromopropane separated from the top of the third distillation column into a fourth pressure pump for pressurization, feeding the monobromopropane into a sixth heat exchanger for preheating, and then feeding the monobromopropane into a dehydrogenation reactor for reaction; feeding the reaction product into a seventh heat exchanger for cooling, feeding the cooled product into a fourth distillation column for rectification and separation; feeding the product from the bottom of the fourth distillation column into a fifth distillation column, and separating unreacted monobromopropane from the bottom of the fifth distillation column for re-feeding into the fifth heat exchanger for preheating, and then for dehydrogenation reaction; separating propylene with high purity from the bottom of the fifth distillation column; mixing hydrogen bromide separated from the top of the fourth distillation column with hydrogen bromide separated from the top of the second distillation column, and feeding the mixture into an eighth heat exchanger for preheating, and then feeding the mixture into an electrolytic cell for electrolysis reaction; separating the electrolysis reaction product, cooling the separated product, and then re-feeding the cooled product into the system to realize the circulation of the whole process. One of the methods is a multi-stage separation method for separating the required materials to form monobromopropane stream, dibromopropane stream, hydrogen bromide stream and recycled propane stream; separating monobromopropane / propylene / hydrogen bromide stream to form propylene stream, hydrogen bromide stream and recycled monobromopropane stream; and separating hydrogen and bromine by distillation.

[0015] Further, in the bromination reaction, the reaction temperature is greater than or equal to 200 DEG C and less than or equal to 450 DEG C, the molar ratio of bromine to propane is 1:0.95-1:1.1, the pressure is 1-30 bar, and the conversion rate of propane and the selectivity of monobromopropane are greater than 80%; optionally, in the hydrogenation reaction, the reaction temperature is 350 DEG C, the hydrogen source is a by-product generated by propane oxidative dehydrogenation, and the catalyst used is Pd, Pt, Ni or Cu; optionally, in the dehydrogenation reaction, the reaction temperature is 400 DEG C, and the catalyst used is selected from one or more of silica-based catalysts, titanium dioxide and zirconium dioxide.

[0016] Further, the first distillation column, the second distillation column, the third distillation column, the fourth distillation column and the fifth distillation column are all packed columns or plate columns and have a multi-stage column structure; optionally, the first heat exchanger, the second heat exchanger, the third heat exchanger, the fourth heat exchanger, the fifth heat exchanger, the sixth heat exchanger, the seventh heat exchanger and the eighth heat exchanger are all multi-stage heat exchangers. Through the multi-stage heat exchange network, the heat at the outlet of each reactor is recovered, and the heat is used to preheat the feed of the reactor, so that the energy is used in stages, wherein the heat exchange network comprises at least one heat exchanger and a column reboiler and a condenser.

[0017] Compared with the prior art, the present application has the following beneficial effects:

[0018] The present application is used for efficiently producing propylene and hydrogen. The single-pass conversion rate of propylene can be greater than 80%, the selectivity of propylene can be greater than 95%, the recovery rate of bromine is greater than 98%, the reaction conditions, the catalyst and the bromine recovery method are optimized, the energy recovery measures are integrated, the loss of bromine and the production cost are significantly reduced, the energy consumption is significantly reduced compared with the prior art, the amount of waste emissions is greatly reduced, and the environmental impact is significantly reduced. The process system is more stable, efficient and safe. BRIEF DESCRIPTION OF DRAWINGS

[0019] One or more embodiments are illustrated by way of example in the accompanying drawings that are not intended to be limiting of the embodiments so far as they may depart from the prior art. Unless otherwise indicated, the drawings in the accompanying drawings are not to scale.

[0020] Figure 1 A schematic diagram of a bromine-mediated propane oxidative dehydrogenation system provided by an embodiment of the present application;

[0021] Figure 2 An energy flow diagram of bromine-mediated propane oxidative dehydrogenation provided by an embodiment of the present application;

[0022] Figure 3A A graph showing the change of propane conversion rate with temperature and pressure when the ratio of bromine to propane is 1 in Embodiment 1 of the present application;

[0023] Figure 3BThis is a graph showing the propane conversion rate as a function of temperature and bromine to propane ratio under a pressure of 30 bar, as provided in Example 1 of this invention.

[0024] Figure 4A This is a graph showing the change in monobromopropane selectivity with temperature and pressure when the bromine to propane ratio is 1, as provided in Example 2 of the present invention.

[0025] Figure 4B This is a graph showing the change in monobromopropane selectivity with temperature and bromine to propane ratio under a pressure of 30 bar, as provided in Example 2 of this invention.

[0026] Figure 5A This is a graph showing the change in propylene selectivity with temperature and pressure when the bromine to propane ratio is 1, as provided in Example 3 of this invention.

[0027] Figure 5B This is a graph showing the propylene selectivity as a function of temperature and bromine to propane ratio under a pressure of 30 bar, as provided in Example 3 of this invention.

[0028] Figure 1 In the middle: 1. Bromination reaction unit, 1-1. First pressure pump, 1-2. Second pressure pump, 1-3. First heat exchanger, 1-4. Second heat exchanger, 1-5. Bromination reactor;

[0029] 2. Third heat exchanger;

[0030] 3. Distillation and separation unit, 3-1, First distillation column, 3-2, Second distillation column, 3-3, Third distillation column;

[0031] 4. Hydrogenation reaction unit; 4-1. Fifth heat exchanger; 4-2. Hydrogenation reactor; 4-3. Fourth heat exchanger; 4-4. Third pressure pump;

[0032] 5. Dehydrogenation reaction unit; 5-1. Fourth pressure pump; 5-2. Sixth heat exchanger; 5-3. Dehydrogenation reactor; 5-4. Seventh heat exchanger;

[0033] 6. Fourth distillation column;

[0034] 7. Fifth distillation column;

[0035] 8. Hydrogen bromide recovery unit; 8-1. Eighth heat exchanger; 8-2. Electrolytic cell. Detailed Implementation

[0036] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0037] This invention provides a bromine-mediated propane oxidative dehydrogenation system for propylene production, such as...Figure 1 The system is shown in the figure. The system comprises: a bromination reaction unit 1, a distillation separation unit 3, a hydrogenation reaction unit 4, a dehydrogenation reaction unit 5, a fourth distillation column 6, a fifth distillation column 7 and a hydrogen bromide recovery unit 8.

[0038] The bromination reaction unit 1 is used to provide propane and bromine for bromination reaction, and deliver the generated compounds to the distillation separation unit 3; the compounds include monobromopropane, dibromopropane, hydrogen bromide and unreacted propane. The distillation separation unit 3 is used to separate the compounds, and deliver the separated hydrogen bromide and unreacted propane to the bromination reaction unit 1 for reaction, deliver the separated dibromopropane to the hydrogenation reaction unit 4, and deliver the separated monobromopropane to the dehydrogenation reaction unit 5. The hydrogenation reaction unit 4 is used to perform hydrogenation reaction on the dibromopropane, and deliver the generated monobromopropane and hydrogen bromide to the distillation separation unit 3. The dehydrogenation reaction unit 5 is used to perform dehydrogenation reaction on the monobromopropane, and deliver the generated propylene, hydrogen bromide and unreacted monobromopropane to the fourth distillation column 6. The fourth distillation column 6 is used to separate the hydrogen bromide and deliver it to the hydrogen bromide recovery unit 8, and deliver the remaining compounds to the fifth distillation column 7. The fifth distillation column 7 is used to separate the propylene and unreacted monobromopropane, and deliver the unreacted monobromopropane to the dehydrogenation reaction unit 5. The hydrogen bromide recovery unit 8 is used to electrolytically regenerate bromine.

[0039] Propane and bromine react in the bromination reactor to generate bromopropane and hydrogen bromide, and the reaction equation is:

[0040] C3H8 + Br2 → C3H7Br + HBr

[0041] C3H7Br + Br2 → C3H6Br2 + HBr

[0042] In the embodiment of the present application, the reaction is only heat-induced, and is not catalyzed, and the reaction occurs when the temperature is higher than 200°C. When the temperature is higher than 450°C, the bromination reaction can generate other by-products and unacceptable coke, thereby reducing the conversion rate of propane.

[0043] In the embodiment, since the bromination reaction is an exothermic reaction, the temperature needs to be controlled within the desired range. The generated heat can also be used elsewhere.

[0044] In the embodiment, the propane and bromine mixture with a temperature greater than or equal to 200°C is introduced into the bromination reactor, and the reaction can be performed in a shell-and-tube reactor, and steam is generated on the shell side to limit the temperature within the desired range.

[0045] The excess molar ratio of propane can increase the selectivity of monobromopropane, and the excessive reaction pressure can increase the reaction conversion rate and reduce the occurrence of side reactions, and the bromination reaction pressure close to the required pressure for subsequent separation can improve the efficiency of the process.

[0046] The products from the bromination reaction are all vapors, mainly consisting of hydrogen bromide, monobromopropane, dibromopropane and unreacted propane, part of which is connected to the distillation separation section, which includes multiple distillation columns, such as Figure 1 As shown in the section, three distillation columns are included to achieve the basic separation of hydrogen bromide, monobromopropane, dibromopropane and unreacted propane.

[0047] It should be noted that the bromination reaction unit 1 includes a first pressure pump 1-1 and a first heat exchanger 1-3 connected in series, a second pressure pump 1-2 and a second heat exchanger 1-4 connected in series, and the first heat exchanger 1-3 and the second heat exchanger 1-4 are connected to the bromination reactor 1-5; wherein the first pressure pump 1-1 and the first heat exchanger 1-3 are used to warm and pressurize the propane; the second pressure pump 1-2 and the second heat exchanger 1-4 are used to warm and pressurize the bromine.

[0048] A third heat exchanger 2 is further provided between the bromination reactor 1-5 and the distillation separation unit 3, which is used to cool the compounds produced by the bromination reactor 1-5 and deliver the cooled products to the distillation separation unit 3.

[0049] The distillation separation unit 3 includes a first distillation column 3-1 connected to the third heat exchanger 2, and the first distillation column 3-1 is further connected to a second distillation column 3-2 and a third distillation column 3-3; wherein the first distillation column 3-1 is used to distill and separate the cooled products, the hydrogen bromide separated at the top is delivered to the second distillation column 3-2, and the monobromopropane and dibromopropane separated at the bottom are delivered to the third distillation column 3-3; the second distillation column 3-2 is used to separate hydrogen bromide at the top and deliver it to the hydrogen bromide recovery unit 8, and the propane separated at the bottom is preheated in the first heat exchanger 1-3 and then reenters the bromination reactor 1-5 for reaction; the third distillation column 3-3 is used to separate monobromopropane at the top and deliver it to the dehydrogenation reaction unit 5, and the dibromopropane separated at the bottom is delivered to the hydrogenation reaction unit 4.

[0050] The hydrogenation reaction unit 4 includes a third pressure pump 4-4, a fourth heat exchanger 4-3, a hydrogenation reactor 4-2 and a fifth heat exchanger 4-1 connected in series, and the third pressure pump 4-4 is connected to the third distillation column 3-3.

[0051] The dehydrogenation reaction unit 5 includes a fourth pressure pump 5-1, a sixth heat exchanger 5-2, a dehydrogenation reactor 5-3 and a seventh heat exchanger 5-4 connected in series, and the fourth pressure pump 5-1 is connected to the third distillation column 3-3.

[0052] The hydrogen bromide recovery unit 8 comprises an eighth heat exchanger 8-1 and an electrolytic cell 8-2 connected in sequence; wherein the eighth heat exchanger 8-1 is used for mixing and preheating the hydrogen bromide separated from the fourth distillation column 6 and the second distillation column 3-2; the electrolytic cell 8-2 is used for electrolysis reaction of the hydrogen bromide.

[0053] The first distillation column 3-1 separates a recirculated propane stream and a hydrogen bromide stream, and the second distillation column 3-2 separates a hydrogen bromide stream. The hydrogen bromide stream is used for subsequent reactions, and the recirculated propane stream reenters the bromination reactor for reaction. The third distillation column 3-3 separates a monobromopropane stream.

[0054] Referring to Figure 1 , the dibromopropane recirculation stream is subjected to hydrogenation reaction with hydrogen in the presence of heat and catalyst, and the reaction equation is as follows:

[0055]

[0056] In an embodiment of the present application, under the condition of 350°C, 30 bar, and 1% Pd / Al2O3 catalyst, the conversion rate of dibromopropane is greater than 85%, and the molar ratio of hydrogen to dibromopropane is 1, so as to maximize the conversion rate of dibromopropane.

[0057] The source of hydrogen is the byproduct of the propane oxidative dehydrogenation process.

[0058] Further referring to Figure 1 , the monobromopropane stream is supplied to a dehydrogenation reactor to form propylene and hydrogen bromide, and the reaction equation is as follows:

[0059]

[0060] In an embodiment of the present application, the reaction is uncatalyzed, but under catalyzed conditions, the dehydrogenation reaction can be very slow, requiring a long residence time or a higher temperature in order to achieve a suitable conversion rate. Based on the higher reaction rate, a silica-based catalyst is preferred for the catalytic reaction, which shows that at a temperature of 400°C, the conversion rate of monobromopropane is greater than 97%, and the selectivity of propylene is greater than 99%. In an embodiment, the reaction pressure is carried out at a pressure higher than atmospheric pressure, and based on the pressure required for subsequent separation, the pressure is selected to be 20 bar, so as to improve the separation efficiency of the intermediate product.

[0061] The dehydrogenation reactor produces a stream containing propylene, hydrogen bromide, and unconverted monobromopropane, and the stream is introduced into a distillation section for separation. The unconverted monobromopropane stream separated is re-introduced into the dehydrogenation reactor for reaction. The distillation section simultaneously separates high-purity propylene and hydrogen bromide.

[0062] The two streams of hydrogen bromide are mixed and then electrolyzed in an electrolyzer at 300°C and 20 bar, with the hydrogen bromide being converted entirely to hydrogen and bromine. The energy required for the decomposition of hydrogen bromide is estimated based on the Gibbs free energy of thermodynamics, as follows:

[0063] ΔG = n · F · ΔE

[0064] n represents the number of moles of electrons required per mole of product. F represents the Faraday constant, and ΔE is the theoretical electrode potential.

[0065] The process uses renewable electricity and electrolyzers that are widely commercially available.

[0066] In the process flow, heat generated in the high-temperature reaction and separation processes is recovered and utilized, thereby reducing the consumption of external energy and lowering operating costs. The heat recovery process includes heat exchangers as well as column reboilers and condensers.

[0067] Figure 2 The process of energy flow in the oxidative dehydrogenation of propane is shown.

[0068] The present application also provides a method for preparing propylene by bromine-mediated oxidative dehydrogenation of propane, which comprises:

[0069] Propane is fed into a first pressure pump 1-1 for pressurization, and then preheated to a predetermined temperature by a first heat exchanger 1-3. Bromine recycled from the oxidative dehydrogenation of propane is fed into a second pressure pump 1-2 for pressurization, and then preheated to a predetermined temperature by a second heat exchanger 1-4;

[0070] The mixture of propane and bromine is fed into a bromination reactor 1-5 for bromination reaction, and the reaction product is cooled by a third heat exchanger 2;

[0071] The cooled product is fed into a first distillation column 3-1 for rectification and separation. Hydrogen bromide and propane are separated from the top of the first distillation column 3-1, and monobromopropane and dibromopropane are separated from the bottom;

[0072] The top product of the first distillation column 3-1 is fed into a second distillation column 3-2 for rectification and separation. Hydrogen bromide is separated from the top of the second distillation column 3-2 for subsequent reaction, and propane is separated from the bottom and preheated by the first heat exchanger before being re-fed into the bromination reactor for reaction;

[0073] The bottom product of the first distillation column 3-1 is fed into a third distillation column 3-3 for rectification and separation. Monobromopropane is separated from the top of the third distillation column 3-3 for subsequent reaction, and dibromopropane is separated from the bottom;

[0074] The dibromopropane separated from the third distillation column 3-3 is pressurized by the third pressure pump 4-4, mixed with hydrogen at a ratio of 1:1, preheated to a specified temperature in the fourth heat exchanger 4-3, and then enters the hydrogenation reactor 4-2 for hydrogenation reaction. The reaction product is cooled in the fifth heat exchanger 4-1, and then reenters the first distillation column 3-1 for rectification and separation;

[0075] Monobromopropane is separated from the top of the third distillation column 3-3, pressurized by the fourth pressure pump 5-1, preheated in the sixth heat exchanger 5-2, and then enters the dehydrogenation reactor 5-3 for reaction.

[0076] The reaction product is cooled in the seventh heat exchanger 5-4, and then enters the fourth distillation column 6 for rectification and separation.

[0077] The bottom product of the fourth distillation column 6 enters the fifth distillation column 7, and the unreacted monobromopropane is separated from the bottom product and reenters the sixth heat exchanger 5-2 for preheating before dehydrogenation reaction.

[0078] The bottom product of the fifth distillation column 7 separates high-purity propylene.

[0079] Hydrogen bromide separated from the top of the fourth distillation column 6 is mixed with hydrogen bromide separated from the top of the second distillation column 3-2, preheated in the eighth heat exchanger 8-1, and then enters the electrolytic cell 8-2 for electrolysis reaction.

[0080] The electrolysis reaction product is separated, cooled, and then reenters the system to realize the entire process cycle. One method is to separate the required materials by multi-stage separation to form a monobromopropane stream, a dibromopropane stream, a hydrogen bromide stream, and a recycled propane stream; separate monobromopropane / propylene / hydrogen bromide stream to form propylene stream, hydrogen bromide stream, and recycled monobromopropane stream; and separate hydrogen and bromine by distillation.

[0081] In the bromination reaction, the reaction temperature is greater than or equal to 200°C and less than or equal to 450°C, the molar ratio of bromine to propane is 1:0.95-1:1.1, the pressure is 1-30 bar, and the propane conversion rate and monobromopropane selectivity are greater than 80%; optionally, in the hydrogenation reaction, the reaction temperature is 350°C, the hydrogen source is the byproduct produced by propane oxidative dehydrogenation, the catalyst used is Pd, Pt, Ni, or Cu; optionally, in the dehydrogenation reaction, the reaction temperature is 400°C, and the catalyst used is selected from one or more of silica-based catalyst, titanium dioxide, and zirconium dioxide.

[0082] The first distillation column 3-1, the second distillation column 3-2, the third distillation column 3-3, the fourth distillation column 6 and the fifth distillation column 7 are all packed columns or plate columns, and have a multi-stage column structure; optionally, the first heat exchanger 1-3, the second heat exchanger 1-4, the third heat exchanger 2, the fourth heat exchanger 4-3, the fifth heat exchanger 4-1, the sixth heat exchanger 5-2, the seventh heat exchanger 5-4 and the eighth heat exchanger 8-1 are all multi-stage heat exchangers. Through the multi-stage heat exchange network, the heat at the outlets of the reactors is recovered, and the heat is used to preheat the feeds of the reactors, so that the energy is used in stages, wherein the heat exchange network comprises at least one heat exchanger and a column reboiler and a condenser.

[0083] Example 1

[0084] The bromination reactor in the bromine-mediated propane oxidative dehydrogenation process was simulated based on the RGibbs model in Aspen Plus V11, the simulation temperature was 200℃, 250℃, 300℃, 350℃, the pressure was from 0.1bar to 30bar, and the molar ratio of bromine to propane was 0.25, 0.5, 0.75, 1, 1.25, 1.5, and the temperature was 200℃, 250℃, 300℃, 350℃, respectively. The propane conversion rate changed with the change of the design condition, and the results are shown in Figure 3A Fig. 3B, which shows that the propane conversion rate continuously increases as the pressure increases from 0bar to 30bar; on the contrary, as the temperature increases, the propane conversion rate gradually decreases; analysis of the propane conversion rate at different bromine to propane ratios under a fixed pressure of 30bar shows that the propane conversion rate gradually increases as the molar ratio of bromine to propane increases at a temperature of 200℃ to 350℃.

[0085] Example 2

[0086] The bromination reactor in the bromine-mediated propane oxidative dehydrogenation process was simulated based on the RGibbs model in Aspen Plus V11, the simulation temperature was 200℃, 250℃, 300℃, 350℃, the pressure was from 0.1bar to 30bar, and the molar ratio of bromine to propane was 0.25, 0.5, 0.75, 1, 1.25, 1.5, and the temperature was 200℃, 250℃, 300℃, 350℃, respectively. The propane conversion rate changed with the change of the design condition, and the results are shown in Figure 4A Fig. 4B, which shows that a lower reaction temperature will slow down the reaction rate, which is conducive to the generation of monobromopropane and inhibits the generation of subsequent dibromopropane, and a higher pressure will accelerate the reaction; and as the molar ratio increases, the selectivity of monobromopropane decreases.

[0087] Example 3

[0088] Based on the RGibbs model in Aspen Plus V11, the bromination reactor in the bromine-mediated propane oxidative dehydrogenation process was simulated. The simulation temperature was 200℃, 250℃, 300℃, and 350℃, respectively, the pressure was from 0.1bar to 30bar, and the molar ratio of bromine to propane was 0.25, 0.5, 0.75, 1, 1.25, and 1.5, respectively. The temperature was 200℃, 250℃, 300℃, and 350℃, respectively. The selectivity of propylene produced in the entire process changed with the change of the operating condition in the bromination reaction. The results are shown in FIGS. 5A and 5B, which show that, similar to the trend of the selectivity of monobromopropane, the increase of temperature will reduce the selectivity of propylene; and at 30bar pressure, the selectivity of propylene increases steadily with the increase of the ratio of bromine to propane. Figure 5A

[0089] Example 4

[0090] Based on Aspen Plus, a single-pass bromine-mediated propane oxidative dehydrogenation non-recuperation process was established. The evaluation results of the system under the conditions of bromination reaction temperature and pressure of 300℃ and 30Bar are shown in Table 1.

[0091] Table 1, system performance of Example 4

[0092] Propane oxidative dehydrogenation system performance ％ Single pass propylene selectivity 53.37 Hydrogen production rate 76.68 System efficiency 5.68

[0093] Comparative Example 1

[0094] Based on Aspen Plus, a single-pass bromine-mediated propane oxidative dehydrogenation recuperation process was established. The evaluation results of the system under the conditions of bromination reaction temperature and pressure of 300℃ and 30Bar are shown in Table 2.

[0095] Table 2, system performance of Comparative Example 1

[0096]

[0097]

[0098] It is shown that the energy efficiency is improved after increasing the heat exchange network. Compared with the non-recuperation process, the efficiency of the recuperation process is increased by about 5% under different temperature and pressure conditions, and by about 4% under different molar ratio conditions. This analysis shows that the energy efficiency can be significantly improved by using heat recovery technology.

[0099] It should be noted that the propane conversion rate is:

[0100]

[0101] wherein is the propane conversion rate, and F is the molar flow. The subscripts i and o represent the input and output, respectively.

[0102] ​propyl bromide selectivity is:

[0103]

[0104] wherein is the propyl bromide selectivity.

[0105] propylene selectivity is:

[0106]

[0107] wherein is the propylene selectivity.

[0108] hydrogen production rate is:

[0109]

[0110] wherein η hy is the hydrogen production rate, is the actual hydrogen production, is the theoretical hydrogen production.

[0111] system efficiency is:

[0112]

[0113] wherein η is the system efficiency, Q is the enthalpy, E HBr is the amount of electricity consumed by the hydrogen bromide electrolysis.

[0114] The above merely describes the preferred embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art, according to the technical solution and the inventive concept of the present application, makes equivalent replacement or change within the technical range disclosed by the present application, should be covered within the protection scope of the present application.

Claims

1. A bromine-mediated propane oxidative dehydrogenation system for propylene production, characterized in that, The system includes: a bromination reaction unit (1), a distillation separation unit (3), a hydrogenation reaction unit (4), a dehydrogenation reaction unit (5), a fourth distillation column (6), a fifth distillation column (7), and a hydrogen bromide recovery unit (8); The bromination reaction unit (1) is used to provide propane and bromine for bromination reaction and to transport the resulting compound to the distillation separation unit (3); the compound includes monobromopropane, dibromopropane, hydrogen bromide and unreacted propane; The distillation separation unit (3) is used to separate the compound and to transport the separated hydrogen bromide and unreacted propane to the bromination reaction unit (1) for reaction, to transport the separated dibromopropane to the hydrogenation reaction unit (4), and to transport the separated monobromopropane to the dehydrogenation reaction unit (5). The hydrogenation reaction unit (4) is used to hydrogenate dibromopropane and transport the resulting monobromopropane and hydrogen bromide to the distillation separation unit (3); The dehydrogenation reaction unit (5) is used to dehydrogenate monobromopropane and to transport the generated propylene, hydrogen bromide and unreacted monobromopropane to the fourth distillation column (6). The fourth distillation column (6) is used to separate hydrogen bromide and transport it to the hydrogen bromide recovery unit (8), and to transport the remaining compounds to the fifth distillation column (7); The fifth distillation column (7) is used to separate propylene and unreacted monobromopropane, and to transport the unreacted monobromopropane to the dehydrogenation reaction unit (5); The hydrogen bromide recovery unit (8) is used for electrolytic regeneration of bromine.

2. The bromine-mediated propane oxidative dehydrogenation to propylene system according to claim 1, characterized in that, The bromination reaction unit (1) includes a first pressure pump (1-1) and a first heat exchanger (1-3) connected together, a second pressure pump (1-2) and a second heat exchanger (1-4) connected together, and the first heat exchanger (1-3) and the second heat exchanger (1-4) are both connected to the bromination reactor (1-5). The first pressure pump (1-1) and the first heat exchanger (1-3) are used to heat and pressurize propane. The second pressure pump (1-2) and the second heat exchanger (1-4) are used to heat and pressurize the bromine.

3. The bromine-mediated propane oxidative dehydrogenation to propylene system according to claim 2, characterized in that, A third heat exchanger (2) is also provided between the bromination reactor (1-5) and the distillation separation unit (3). The third heat exchanger (2) is used to cool the compound produced by the bromination reactor (1-5) and transport the cooled product to the distillation separation unit (3).

4. The bromine-mediated propane oxidative dehydrogenation to propylene system according to claim 3, characterized in that, The distillation separation unit (3) includes a first distillation column (3-1) connected to the third heat exchanger (2), and the first distillation column (3-1) is also connected to a second distillation column (3-2) and a third distillation column (3-3); The first distillation column (3-1) is used to perform distillation separation on the cooled product. The hydrogen bromide and propane separated at the top of the column are sent to the second distillation column (3-2), and the monobromopropane and dibromopropane separated at the bottom of the column are sent to the third distillation column (3-3). The second distillation column (3-2) is used to separate hydrogen bromide at the top of the column and send it to the hydrogen bromide recovery unit (8). Propane separated at the bottom of the column enters the first heat exchanger (1-3) for preheating and then re-enters the bromination reactor (1-5) for reaction. The third distillation column (3-3) is used to separate monobromopropane at the top of the column and send it to the dehydrogenation reaction unit (5), and to separate dibromopropane at the bottom of the column and send it to the hydrogenation reaction unit (4).

5. The bromine-mediated propane oxidative dehydrogenation to propylene system according to claim 4, characterized in that, The hydrogenation reaction unit (4) includes a third pressure pump (4-4), a fourth heat exchanger (4-3), a hydrogenation reactor (4-2), and a fifth heat exchanger (4-1) connected in sequence. The third pressure pump (4-4) is connected to the third distillation column (3-3).

6. The bromine-mediated propane oxidative dehydrogenation to propylene system according to claim 5, characterized in that, The dehydrogenation reaction unit (5) includes a fourth pressure pump (5-1), a sixth heat exchanger (5-2), a dehydrogenation reactor (5-3), and a seventh heat exchanger (5-4) connected in sequence. The fourth pressure pump (5-1) is connected to the third distillation column (3-3).

7. The bromine-mediated propane oxidative dehydrogenation to propylene system according to claim 6, characterized in that, The hydrogen bromide recovery unit (8) includes an eighth heat exchanger (8-1) and an electrolytic cell (8-2) connected in sequence; The eighth heat exchanger (8-1) is used to mix and preheat the hydrogen bromide separated from the fourth distillation column (6) and the second distillation column (3-2); The electrolytic cell (8-2) is used to electrolyze hydrogen bromide.

8. A bromine-mediated oxidative dehydrogenation method for producing propylene from propane, characterized in that, This method is applied to a bromine-mediated propane oxidative dehydrogenation system for propylene production as described in any one of claims 1 to 7; the method comprises: Propane is pressurized by the first pressure pump (1-1) and then preheated to the predetermined temperature by the first heat exchanger (1-3). Bromine circulating from the propane oxidation and dehydrogenation process is pressurized by the second pressure pump (1-2) and then preheated to the predetermined temperature by the second heat exchanger (1-4). Propane and bromine are mixed and then fed into the bromination reactor (1-5) for bromination reaction. The reaction product is cooled in the third heat exchanger (2). The cooled product enters the first distillation column (3-1) for rectification and separation. Hydrogen bromide and propane are separated at the top of the first distillation column (3-1), and monobromopropane and dibromopropane are separated at the bottom. The top product of the first distillation column (3-1) enters the second distillation column (3-2) for rectification and separation. Hydrogen bromide is separated from the top of the second distillation column (3-2) to participate in subsequent reactions, and propane is separated from the bottom of the column. After being preheated in the first heat exchanger, it re-enters the bromination reactor for reaction. The bottom product of the first distillation column (3-1) enters the third distillation column (3-3) for rectification and separation. The top of the third distillation column (3-3) separates monobromopropane to participate in subsequent reactions, and the bottom of the column separates dibromopropane. The dibromopropane separated at the bottom of the third distillation column (3-3) is pressurized by the third pressure pump (4-4), then mixed with hydrogen at a 1:1 ratio and preheated to the specified temperature in the fourth heat exchanger (4-3). After preheating, it enters the hydrogenation reactor (4-2) for hydrogenation reaction. The reaction product enters the fifth heat exchanger (4-1) for cooling, and then re-enters the first distillation column (3-1) for rectification and separation. The top of the third distillation column (3-3) separates monobromopropane, which is then pressurized by the fourth pressure pump (5-1), preheated by the sixth heat exchanger (5-2), and then reacted in the dehydrogenation reactor (5-3). The reaction product enters the seventh heat exchanger (5-4) for cooling, and the cooled product enters the fourth distillation column (6) for rectification and separation; The bottom product of the fourth distillation column (6) enters the fifth distillation column (7). The unreacted monobromopropane is separated from the bottom product and re-enters the fifth heat exchanger (4-1) for preheating and dehydrogenation reaction. The bottom product of the fifth distillation column (7) separates propylene with higher purity; Hydrogen bromide separated from the top of the fourth distillation column (6) is mixed with hydrogen bromide separated from the top of the second distillation column (3-2) and enters the eighth heat exchanger (8-1) for preheating, and then enters the electrolytic cell (8-2) for electrolysis reaction; After the electrolytic reaction products are separated and cooled, they are reintroduced into the system, thus completing the entire process cycle.

9. The method for bromine-mediated oxidative dehydrogenation of propane to propylene according to claim 8, characterized in that, In the bromination reaction, the reaction temperature is greater than or equal to 200℃ and less than or equal to 450℃, the molar ratio of bromine to propane is 1:0.95 to 1:1.1, the pressure is 1 to 30 bar, and the propane conversion rate and monobromopropane selectivity are greater than 80%. Optionally, in the hydrogenation reaction, the reaction temperature is 350°C, the hydrogen source is a byproduct of propane oxidative dehydrogenation, and the catalyst used is Pd, Pt, Ni, or Cu. Optionally, in the dehydrogenation reaction, the reaction temperature is 400°C, and the catalyst used is selected from one or more of silica-based catalysts, titanium dioxide, and zirconium dioxide.

10. The method for bromine-mediated oxidative dehydrogenation of propane to propylene according to claim 8, characterized in that, The first distillation column (3-1), the second distillation column (3-2), the third distillation column (3-3), the fourth distillation column (6) and the fifth distillation column (7) are all packed columns or plate columns with multi-stage column structures; Optionally, the first heat exchanger (1-3), the second heat exchanger (1-4), the third heat exchanger (2), the fourth heat exchanger (4-3), the fifth heat exchanger (4-1), the sixth heat exchanger (5-2), the seventh heat exchanger (5-4), and the eighth heat exchanger (8-1) are all multi-stage heat exchangers.

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