Bromine-mediated propane oxidative dehydrogenation propylene preparation system and method

Abstract

The invention relates to a system and a method for preparing propylene through bromine-mediated oxidative dehydrogenation of propane. According to the system and the method, propane and bromine recovered by a propane dehydrogenation device are used as raw materials, efficient conversion of the propane is realized through multi-step reaction and rectification processes including bromination reaction, hydrogenation reaction, dehydrogenation reaction and electrolytic reaction, and finally products of propylene and hydrogen are obtained. The invention solves the technical problems of low utilization efficiency of propane as fuel and low conversion rate in the process of converting propane into propylene at present; according to the invention, waste heat in a multi-step process is utilized to perform heat regeneration on the process, bromine produced in a propane dehydrogenation process is utilized to perform circular reaction with hydrogen, energy loss in the process is reduced, utilization efficiency of materials and energy is improved, propane is completely utilized, and flexible improvement of propylene production is realized at the same time.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical engineering, and particularly relates to a bromine-mediated propane oxidative dehydrogenation system and method for producing propylene. Background Art

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

[0003] In order to further enhance the advantages of the ODH process, researchers have begun to explore new oxidants. Among them, the halogen-mediated propane oxidative dehydrogenation process is a promising option. In many studies, the bromine-mediated oxidative dehydrogenation (Br-ODH) process has shown unique advantages: (1) The dehydrogenation reaction can be carried out under high-pressure conditions, avoiding the generation of carbon oxides and coke; (2) By introducing haloalkane intermediates, the energy consumption in the separation process of propane and propylene is reduced. Since bromine gas (Br2) has a higher selectivity for monohaloalkane than other halogen molecules, bromopropane can also be converted into propylene products under milder conditions. In summary, the bromine-mediated oxidative dehydrogenation process is expected to achieve higher propane equilibrium conversion and propylene selectivity under high-pressure conditions, thereby reducing costs and energy consumption.

[0004] However, the existing bromine-mediated propane oxidative dehydrogenation process still has some challenges. For example, there is still room for improvement in the selectivity of propylene, propane conversion rate, and hydrogen production rate, and the overall efficiency also needs to be improved. Therefore, in view of the existing technical problems, further optimization and upgrading are still required. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technology, the present invention provides a bromine-mediated propane oxidative dehydrogenation system and method for producing propylene. Through a multi-step dehydrogenation process to form propylene, and integrating a heat recovery system, the production efficiency of propylene can be significantly improved, the production cost can be reduced, and the environmental impact can be reduced.

[0006] To achieve the above objectives, the present invention is realized through the following technical solutions:

[0007] The present invention provides a bromine-mediated propane oxidative dehydrogenation system for producing propylene, which system 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 a bromination reaction of propane and bromine and conveying the generated compounds to the distillation separation unit; the compounds include 1-bromopropane, 2-bromopropane, hydrogen bromide and unreacted propane; the distillation separation unit is used for separating the compounds, conveying the separated hydrogen bromide and unreacted propane to the bromination reaction unit for reaction, conveying the separated 2-bromopropane to the hydrogenation reaction unit, and conveying the separated 1-bromopropane to the dehydrogenation reaction unit; the hydrogenation reaction unit is used for performing a hydrogenation reaction on 2-bromopropane and conveying the generated 1-bromopropane and hydrogen bromide to the distillation separation unit; the dehydrogenation reaction unit is used for performing a dehydrogenation reaction on 1-bromopropane and conveying the generated propylene, hydrogen bromide and incompletely reacted 1-bromopropane to the fourth distillation column; the fourth distillation column is used for separating hydrogen bromide and conveying it to the hydrogen bromide recovery unit, and conveying the remaining compounds to the fifth distillation column; the fifth distillation column is used for separating propylene and incompletely reacted 1-bromopropane, and conveying the incompletely reacted 1-bromopropane to the dehydrogenation reaction unit; the hydrogen bromide recovery unit is used for electrolytically regenerating bromine.

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

[0009] Further, a third heat exchanger is further 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 conveying the cooled products to the distillation separation unit.

[0010] Further, the distillation separation unit includes a first distillation column connected to the third heat exchanger, and the first distillation column is further respectively connected to a second distillation column and a third distillation column; wherein, the first distillation column is used for rectifying and separating the cooled products, the hydrogen bromide and propane separated from the top of the column are conveyed to the second distillation column, and the 1-bromopropane and 2-bromopropane separated from the bottom of the column are conveyed to the third distillation column; the second distillation column is used for separating hydrogen bromide from the top of the column and conveying it to the hydrogen bromide recovery unit, and separating propane from the bottom of the column and sending it into the first heat exchanger for preheating and then re-entering the bromination reactor for reaction; the third distillation column is used for separating 1-bromopropane from the top of the column and conveying it to the dehydrogenation reaction unit, and separating 2-bromopropane from the bottom of the column and conveying it to the hydrogenation reaction unit.

[0011] Further, the hydrogenation reaction unit includes 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 to the third distillation column.

[0012] Further, the dehydrogenation reaction unit includes 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 to the third distillation column.

[0013] Further, the hydrogen bromide recovery unit includes an 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 column and the second distillation column; the electrolytic cell is used for electrolytic reaction of the hydrogen bromide.

[0014] The present invention also provides a method for bromine-mediated oxidative dehydrogenation of propane to propylene, which is applied to the bromine-mediated oxidative dehydrogenation of propane to propylene system as described above; the method includes: feeding propane into a first pressure pump for pressurization, and then preheating it to a predetermined temperature through a first heat exchanger. Bromine recycled from the propane oxidative dehydrogenation process is fed into a second pressure pump for pressurization, and then preheated to a predetermined temperature through a second heat exchanger; after propane and bromine are mixed, they enter a bromination reactor for bromination reaction, and the reaction product enters a third heat exchanger for cooling; the cooled product enters a first distillation column for rectification separation. Hydrogen bromide and propane are separated from the top of the first distillation column, and 1-bromopropane and 2-bromopropane are separated from the bottom; the product from the top of the first distillation column enters a second distillation column for rectification separation. Hydrogen bromide is separated from the top of the second distillation column to participate in subsequent reactions, and propane is separated from the bottom and enters the first heat exchanger for preheating and then re-enters the bromination reactor for reaction; the product from the bottom of the first distillation column enters a third distillation column for rectification separation. 1-bromopropane is separated from the top of the third distillation column to participate in subsequent reactions, and 2-bromopropane is separated from the bottom; the 2-bromopropane separated from the bottom of the third distillation column enters a third pressure pump for pressurization, and then is mixed with hydrogen in a 1:1 ratio and enters a fourth heat exchanger for preheating to a specified temperature. After preheating, it enters a hydrogenation reactor for hydrogenation reaction, and the reaction product enters a fifth heat exchanger for cooling, and then re-enters the first distillation column for rectification separation; 1-bromopropane separated from the top of the third distillation column enters a fourth pressure pump for pressurization, enters a sixth heat exchanger for preheating, and then enters a dehydrogenation reactor for reaction; the reaction product enters a seventh heat exchanger for cooling, and the cooled product enters a fourth distillation column for rectification separation; the product from the bottom of the fourth distillation column enters a fifth distillation column, and unreacted 1-bromopropane is separated from the bottom product and re-enters the fifth heat exchanger for preheating and then dehydrogenation reaction; a propylene with higher purity is separated from the bottom product of the fifth distillation column; hydrogen bromide separated from the top of the fourth distillation column is mixed with hydrogen bromide separated from the top of the second distillation column and enters an eighth heat exchanger for preheating, and then enters an electrolytic cell for electrolytic reaction; after the electrolytic reaction product is separated, it is cooled and re-enters the system to realize the circulation of the whole process. One of the methods is to separate the required materials by a multi-stage separation method, separating the 1-bromopropane / 2-bromopropane / hydrogen bromide / propane stream to form a 1-bromopropane stream, a 2-bromopropane stream, a hydrogen bromide stream and a recycled propane stream; separating the 1-bromopropane / propylene / hydrogen bromide stream to form a propylene stream, a hydrogen bromide stream and a recycled 1-bromopropane stream; the step of separating hydrogen and bromine is achieved by distillation.

[0015] Further, 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 to 1:1.1, the pressure is 1 to 30 bar, and the conversion rate of propane and the selectivity of 1-bromopropane are greater than 80%; optionally, in the hydrogenation reaction, the reaction temperature is 350°C, the source of hydrogen is the by-product generated from the oxidative dehydrogenation of propane, and the catalysts used are Pd, Pt, Ni or Cu; optionally, in the dehydrogenation reaction, the reaction temperature is 400°C, and the catalysts used are selected from one or more of silica-based catalysts, titanium dioxide, and zirconium dioxide.

[0016] Further, the first distillation tower, the second distillation tower, the third distillation tower, the fourth distillation tower, and the fifth distillation tower are all packed towers or plate towers and have a multi-stage tower 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 to achieve the cascaded utilization of energy. Among them, the heat exchange network includes at least one heat exchanger, as well as a tower reboiler and a condenser.

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

[0018] It is used for the efficient production of propylene and hydrogen. The single-pass conversion rate of propylene can reach more than 80%, and the selectivity of propylene can reach more than 95%; the recovery rate of bromine is as high as more than 98%. This process optimizes the reaction conditions, catalysts, bromine recovery methods, and integrates energy recovery measures, significantly reducing the loss of bromine and production costs, and significantly reducing the energy consumption compared with the existing process; the waste emissions are greatly reduced, and the environmental impact is significantly reduced; this process system is more stable, efficient, and safe. Description of the Drawings

[0019] One or more embodiments are exemplarily illustrated by the pictures in the corresponding drawings. These exemplary illustrations do not limit the embodiments unless otherwise stated. The figures in the drawings do not constitute a proportional limitation.

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

[0021] Figure 2 It is the energy flow chart of bromine-mediated propane oxidative dehydrogenation described in the embodiment of the present invention;

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

[0023] Figure 3BThis is a graph showing the variation of propane conversion rate with temperature and bromine-to-propane ratio under the condition of 30 bar pressure provided in Example 1 of the present invention;

[0024] Figure 4A This is a graph showing the variation of the selectivity of 1-bromopropane with temperature and pressure when the bromine-to-propane ratio is 1 provided in Example 2 of the present invention;

[0025] Figure 4B This is a graph showing the variation of the selectivity of 1-bromopropane with temperature and bromine-to-propane ratio under the condition of 30 bar pressure provided in Example 2 of the present invention;

[0026] Figure 5A This is a graph showing the variation of the selectivity of propylene with temperature and pressure when the bromine-to-propane ratio is 1 provided in Example 3 of the present invention;

[0027] Figure 5B This is a graph showing the variation of the selectivity of propylene with temperature and bromine-to-propane ratio under the condition of 30 bar pressure provided in Example 3 of the present invention.

[0028] Figure 1 In the figure: 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 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 mode

[0036] The following further describes in detail the implementation mode of the present invention in conjunction with the drawings and embodiments. The following embodiments are used to illustrate the present invention, but cannot be used to limit the scope of the present invention.

[0037] The present invention provides a bromine-mediated propane oxidative dehydrogenation to propylene system, asFigure 1 As shown. 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.

[0038] Among them, the bromination reaction unit 1 is used to provide propane and bromine for bromination reaction, and convey the generated compounds to the distillation separation unit 3; the compounds include 1-bromopropane, 2-bromopropane, hydrogen bromide, and unreacted propane. The distillation separation unit 3 is used to separate the compounds, and convey the separated hydrogen bromide and unreacted propane to the bromination reaction unit 1 for reaction, convey the separated 2-bromopropane to the hydrogenation reaction unit 4, and convey the separated 1-bromopropane to the dehydrogenation reaction unit 5. The hydrogenation reaction unit 4 is used to carry out hydrogenation reaction on 2-bromopropane, and convey the generated 1-bromopropane and hydrogen bromide to the distillation separation unit 3. The dehydrogenation reaction unit 5 is used to carry out dehydrogenation reaction on 1-bromopropane, and convey the generated propylene, hydrogen bromide, and incompletely reacted 1-bromopropane to the fourth distillation column 6. The fourth distillation column 6 is used to separate out hydrogen bromide and convey it to the hydrogen bromide recovery unit 8, and convey the remaining compounds to the fifth distillation column 7. The fifth distillation column 7 is used to separate out propylene and incompletely reacted 1-bromopropane, and convey the incompletely reacted 1-bromopropane to the dehydrogenation reaction unit 5. The hydrogen bromide recovery unit 8 is used to electrolytically regenerate bromine.

[0039] Propane and bromine react in a bromination reactor to produce bromopropane and hydrogen bromide. The reaction equation is:

[0040] C 3 H 8 +Br 2 →C 3 H 7 Br + HBr

[0041] C 3 H 7 Br + Br 2 →C 3 H 6 Br 2 + HBr

[0042] In an embodiment of the present invention, this reaction is only thermally induced and uncatalyzed. The reaction occurs when the temperature is higher than 200 °C. When the temperature is higher than 450 °C, other by-products and unacceptable coke may be produced in the bromination reaction, thereby reducing the propane conversion rate.

[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 an embodiment, a propane and bromine mixture at a temperature greater than or equal to 200 °C is introduced into a bromination reactor. This reaction can be carried out in a shell-and-tube reactor, where steam is generated on the shell side to limit the temperature within the desired range.

[0045] An excess molar ratio of propane can increase the selectivity of 1-bromopropane. An excessively high reaction pressure can increase the reaction conversion rate and reduce the occurrence of side reactions. When the bromination reaction pressure is close to the pressure required for subsequent separation, the efficiency of the process can be improved.

[0046] The products from the bromination reaction are all in vapor form. The products mainly consist of hydrogen bromide, 1-bromopropane, 2-bromopropane, and unreacted propane. Part of them is connected to the distillation separation section, which includes multiple distillation towers, such as Figure 1 As shown, this section contains three distillation towers to achieve the basic separation of hydrogen bromide, 1-bromopropane, 2-bromopropane, and unreacted propane.

[0047] It should be noted that the bromination reaction unit 1 includes a connected first pressure pump 1-1 and a first heat exchanger 1-3, a connected second pressure pump 1-2 and a second heat exchanger 1-4. Both the first heat exchanger 1-3 and the second heat exchanger 1-4 are connected to the bromination reactor 1-5. Among them, 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 bromine.

[0048] 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 compounds generated by the bromination reactor 1-5 and transport the cooled products to the distillation separation unit 3.

[0049] The distillation separation unit 3 includes a first distillation tower 3-1 connected to the third heat exchanger 2. The first distillation tower 3-1 is also respectively connected to a second distillation tower 3-2 and a third distillation tower 3-3. Among them, the first distillation tower 3-1 is used for rectifying and separating the cooled products. The hydrogen bromide and propane separated from the top of the tower are transported to the second distillation tower 3-2, and the 1-bromopropane and 2-bromopropane separated from the bottom of the tower are transported to the third distillation tower 3-3. The second distillation tower 3-2 is used to separate hydrogen bromide from the top of the tower and transport it to the hydrogen bromide recovery unit 8, and the propane separated from the bottom of the tower enters the first heat exchanger 1-3 for preheating and then re-enters the bromination reactor 1-5 for reaction. The third distillation tower 3-3 is used to separate 1-bromopropane from the top of the tower and transport it to the dehydrogenation reaction unit 5, and the 2-bromopropane separated from the bottom of the tower is transported 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 sequence. The third pressure pump 4-4 is connected to the third distillation tower 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 that are connected in sequence. The fourth pressure pump 5-1 is connected to the third distillation column 3-3.

[0052] The hydrogen bromide recovery unit 8 includes an eighth heat exchanger 8-1 and an electrolytic cell 8-2 that are connected in sequence; among them, 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 perform an electrolysis reaction on the hydrogen bromide.

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

[0054] Reference Figure 1 , in the presence of heat and a catalyst, the dibromopropane recycle stream undergoes a hydrogenation reaction with hydrogen, and the reaction equation is:

[0055]

[0056] In an embodiment of the present invention, at 350 °C, 30 bar, and 1% Pd / Al 2 O 3 catalyst conditions, the conversion rate of dibromopropane is greater than 85%, and the molar ratio of hydrogen to dibromopropane is 1 to maximize the conversion rate of dibromopropane.

[0057] The source of hydrogen is a by-product of the propane oxidative dehydrogenation process.

[0058] Further reference Figure 1 , the 1-bromopropane stream is supplied to the dehydrogenation reactor to form propylene and hydrogen bromide, and the reaction equation is:

[0059]

[0060] In an embodiment of the present invention, this reaction is uncatalyzed, but under catalyzed conditions, the dehydrogenation reaction may be very slow and require a longer residence time or a higher temperature to achieve a suitable conversion rate. Based on the higher reaction rate, a catalytic reaction with a silica-based catalyst is preferably used, showing that at a temperature of 400 °C, the conversion rate of 1-bromopropane is greater than 97% and the propylene selectivity is greater than 99%. In the implemented scheme, the reaction pressure is carried out under a pressure higher than atmospheric pressure. Based on the pressure required for subsequent separation, the pressure is selected as 20 bar to improve the separation efficiency of the intermediate product.

[0061] The dehydrogenation reactor produces propylene, hydrogen bromide, and unreacted 1-bromopropane. The product stream enters the distillation section for separation. The unreacted 1-bromopropane stream separated is recycled back to the dehydrogenation reactor for further reaction. The distillation section simultaneously separates high-purity propylene and hydrogen bromide.

[0062] Two hydrogen bromide streams are mixed and then electrolyzed in an electrolytic cell at 300 °C and 20 bar. All hydrogen bromide is converted into hydrogen and bromine. The energy required for the decomposition of hydrogen bromide is estimated according to the thermodynamic Gibbs free energy 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 electrolytic cells with wide commercial feasibility.

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

[0067] Figure 2 It shows the process of energy flow in the oxidative dehydrogenation of propane.

[0068] The present invention also provides a method for bromine-mediated oxidative dehydrogenation of propane to propylene, which includes:

[0069] Propane is pressurized by a first pressure pump 1-1 and then preheated to a predetermined temperature through a first heat exchanger 1-3. Bromine recycled from the propane oxidative dehydrogenation process is pressurized by a second pressure pump 1-2 and then preheated to a predetermined temperature through a second heat exchanger 1-4;

[0070] Propane and bromine are mixed and then enter a bromination reactor 1-5 for bromination reaction. The reaction product enters a third heat exchanger 2 for cooling;

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

[0072] The product from the top of the first distillation column 3-1 enters a second distillation column 3-2 for rectification separation. Hydrogen bromide separated from the top of the second distillation column 3-2 participates in subsequent reactions, and propane separated from the bottom is preheated in the first heat exchanger and then recycled back to the bromination reactor for reaction;

[0073] The product from the bottom of the first distillation column 3-1 enters a third distillation column 3-3 for rectification separation. 1-bromopropane separated from the top of the third distillation column 3-3 participates in subsequent reactions, and dibromopropane is separated from the bottom;

[0074] The dibromopropane separated from the bottom of the third distillation column 3-3 enters the third pressure pump 4-4 for pressurization, and then enters the fourth heat exchanger 4-3 for preheating to a specified temperature after being mixed with hydrogen in a 1:1 ratio. After preheating, it enters the hydrogenation reactor 4-2 for hydrogenation reaction. The reaction products enter the fifth heat exchanger 4-1 for cooling, and then re-enter the first distillation column 3-1 for rectification separation;

[0075] The 1-bromopropane separated from the top of the third distillation column 3-3 enters the fourth pressure pump 5-1 for pressurization, enters the sixth heat exchanger 5-2 for preheating, and then enters the dehydrogenation reactor 5-3 for reaction;

[0076] The reaction products enter the seventh heat exchanger 5-4 for cooling, and the cooled products enter the fourth distillation column 6 for rectification separation;

[0077] The bottom product of the fourth distillation column 6 enters the fifth distillation column 7, and the unreacted 1-bromopropane separated from the bottom product re-enters the sixth heat exchanger 5-2 for preheating and then undergoes dehydrogenation reaction;

[0078] The bottom product of the fifth distillation column 7 separates out propylene with a relatively high purity;

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

[0080] After the separation of the electrolytic reaction products, they are cooled and re-entered into the system to realize the circulation of the whole process. One method is to separate the required materials by a multi-stage separation method, separating the 1-bromopropane / 2-bromopropane / hydrogen bromide / propane stream to form a 1-bromopropane stream, a 2-bromopropane stream, a hydrogen bromide stream, and a recycled propane stream; separating the 1-bromopropane / propylene / hydrogen bromide stream to form a propylene stream, a hydrogen bromide stream, and a recycled 1-bromopropane stream; the step of separating hydrogen and bromine is achieved 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 to 1:1.1, the pressure is 1 to 30 bar, and the propane conversion rate and the selectivity of 1-bromopropane are greater than 80%; optionally, in the hydrogenation reaction, the reaction temperature is 350 °C, the source of hydrogen is the by-product generated by the oxidative dehydrogenation of propane, and the catalysts used are Pd, Pt, Ni, or Cu; optionally, in the dehydrogenation reaction, the reaction temperature is 400 °C, and the catalysts used are selected from one or more of silica-based catalysts, titanium dioxide, and zirconium dioxide.

[0082] Among them, 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, having 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 outlet of each reactor is recovered and used to preheat the feed of the reactor, realizing the cascaded utilization of energy. Among them, the heat exchange network includes at least one heat exchanger, as well as a tower reboiler and a condenser.

[0083] Example 1:

[0084] Based on the RGibbs model in Aspen Plus V11, the bromination reactor in the bromine-mediated propane oxidative dehydrogenation process was simulated. The simulation temperatures were 200°C, 250°C, 300°C, and 350°C, the pressure ranged from 0.1 bar to 30 bar, and the molar ratios of bromine to propane were 0.25, 0.5, 0.75, 1, 1.25, and 1.5, respectively, at temperatures of 200°C, 250°C, 300°C, and 350°C. The conversion rate of propane changed with the change of the design conditions, and the results were as Figure 3A , shown in Figure 3B, indicating that the conversion rate of propane continuously increased as the pressure increased from 0 bar to 30 bar; on the contrary, as the temperature increased, the conversion rate of propane gradually decreased; analyzing the conversion rate of propane at different bromine-to-propane ratios under a fixed pressure of 30 bar showed that at temperatures from 200°C to 350°C, the conversion rate of propane gradually increased as the molar ratio of bromine to propane increased.

[0085] Example 2:

[0086] Based on the RGibbs model in Aspen Plus V11, the bromination reactor in the bromine-mediated propane oxidative dehydrogenation process was simulated. The simulation temperatures were 200°C, 250°C, 300°C, and 350°C, the pressure ranged from 0.1 bar to 30 bar, and the molar ratios of bromine to propane were 0.25, 0.5, 0.75, 1, 1.25, and 1.5, respectively, at temperatures of 200°C, 250°C, 300°C, and 350°C. The selectivity of 1-bromopropane changed with the change of the design conditions, and the results were as Figure 4A , shown in Figure 4B, indicating that a lower reaction temperature would slow down the reaction rate, be beneficial to the formation of 1-bromopropane and inhibit the subsequent formation of 2-bromopropane, while a higher pressure would accelerate the reaction; and as the molar ratio increased, the selectivity of 1-bromopropane decreased.

[0087] Example 3:

[0088] The bromination reactor in the bromine-mediated propane oxidative dehydrogenation process was simulated based on the RGibbs model in Aspen Plus V11. The simulation temperatures were 200 °C, 250 °C, 300 °C, and 350 °C respectively, the pressure ranged from 0.1 bar to 30 bar, and the molar ratios of bromine to propane were 0.25, 0.5, 0.75, 1, 1.25, and 1.5 respectively. At the temperatures of 200 °C, 250 °C, 300 °C, and 350 °C, the selectivity of propylene produced in the entire process by the bromination reaction changed with the operating conditions. The results are as Figure 5A , shown in Figure 5B, indicating a similar trend to the selectivity of 1-bromopropane, where an increase in temperature would decrease the propylene selectivity; while at a pressure of 30 bar, the propylene selectivity increased steadily with the increase in the ratio of bromine to propane.

[0089] Example 4:

[0090] A single-pass bromine-mediated propane oxidative dehydrogenation non-regenerative process was established based on Aspen Plus. The evaluation results of the system under the conditions of a bromination reaction temperature of 300 °C and a pressure of 30 bar are shown in Table 1.

[0091] Table 1. System performance of Example 4

[0092] Performance of propane oxidative dehydrogenation system ％ Single-pass propylene selectivity 53.37 Hydrogen production rate 76.68 System efficiency 5.68

[0093] Comparative Example 1

[0094] A single-pass bromine-mediated propane oxidative dehydrogenation regenerative process was established based on Aspen Plus. The evaluation results of the system under the conditions of a bromination reaction temperature of 300 °C and a pressure of 30 bar are shown in Table 2.

[0095] Table 2. System performance of Comparative Example 1

[0096]

[0097]

[0098] It shows the improvement of energy efficiency after adding a heat exchange network. Compared with the non-regenerative process, the efficiency of the regenerative process increased by about 5% under different temperature and pressure conditions and by about 4% under different molar ratio conditions. This analysis indicates that the energy efficiency can be significantly improved by adopting heat recovery technology.

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

[0100]

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

[0102] The selectivity of 1-bromopropane is:

[0103]

[0104] where is the selectivity of 1-bromopropane.

[0105] The selectivity of propylene is:

[0106]

[0107] where is the selectivity of propylene.

[0108] The hydrogen production rate is:

[0109]

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

[0111] The system efficiency is:

[0112]

[0113] where η is the system efficiency, Q is the enthalpy, and E HBr is the electricity consumed in the electrolysis of hydrogen bromide.

[0114] As mentioned above, the above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A bromine-mediated propane oxidative dehydrogenation system for producing propylene, characterized in that: 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 tower (6), a fifth distillation tower (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 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 transport the separated hydrogen bromide and unreacted propane to the bromination reaction unit (1) for reaction, transport the separated dibromopropane to the hydrogenation reaction unit (4), and transport the separated monobromopropane to the dehydrogenation reaction unit (5); The hydrogenation reaction unit (4) is used to carry out a hydrogenation reaction on dibromopropane, and to transport the generated monobromopropane and hydrogen bromide to the distillation separation unit (3); The dehydrogenation reaction unit (5) is used to carry out a dehydrogenation reaction on monobromopropane, and to transport the generated propylene, hydrogen bromide and incompletely reacted monobromopropane to the fourth distillation tower (6); The fourth distillation tower (6) is used to separate hydrogen bromide and transport it to the hydrogen bromide recovery unit (8), and transport the remaining compounds to the fifth distillation tower (7); The fifth distillation tower (7) is used to separate propylene and incompletely reacted monobromopropane, and transport the incompletely reacted monobromopropane to the dehydrogenation reaction unit (5); The hydrogen bromide recovery unit (8) is used to regenerate bromine by electrolysis.

2. The bromine-mediated propane oxidative dehydrogenation to propylene system according to claim 1, characterized in that: The bromination reaction unit (1) comprises a first pressure pump (1-1) and a first heat exchanger (1-3) connected to each other, a second pressure pump (1-2) and a second heat exchanger (1-4) connected to each other, and the first heat exchanger (1-3) and the second heat exchanger (1-4) are both connected to a bromination reactor (1-5); Wherein, 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 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), and the third heat exchanger (2) is used to cool the compounds produced by the bromination reactor (1-5) and transport the cooled products 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) comprises a first distillation tower (3-1) connected to the third heat exchanger (2), and the first distillation tower (3-1) is also connected to a second distillation tower (3-2) and a third distillation tower (3-3) respectively; The first distillation tower (3-1) is used to perform distillation separation on the cooled product, the hydrogen bromide and propane separated at the top of the tower are transported to the second distillation tower (3-2), and the monobromopropane and dibromopropane separated at the bottom of the tower are transported to the third distillation tower (3-3); The second distillation tower (3-2) is used to separate hydrogen bromide at the top of the tower and transport it to the hydrogen bromide recovery unit (8), and separate propane at the bottom of the tower and enter the first heat exchanger (1-3) for preheating before re-entering the bromination reactor (1-5) for reaction; The third distillation tower (3-3) is used to separate monobromopropane at the top of the tower and transport it to the dehydrogenation reaction unit (5), and to separate dibromopropane at the bottom of the tower and transport 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) comprises a third pressure pump (4-4), a fourth heat exchanger (4-3), a hydrogenation reactor (4-2) and a fifth heat exchanger (4-1) which are connected in sequence, and the third pressure pump (4-4) is connected to a third distillation tower (3-3).

6. The bromine-mediated propane oxidative dehydrogenation to propylene system according to claim 5, characterized in that: The dehydrogenation reaction unit (5) comprises a fourth pressure pump (5-1), a sixth heat exchanger (5-2), a dehydrogenation reactor (5-3) and a seventh heat exchanger (5-4) which are connected in sequence, and the fourth pressure pump (5-1) is connected to the third distillation tower (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) 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 to mix and preheat the hydrogen bromide separated by the fourth distillation tower (6) and the second distillation tower (3-2); The electrolytic cell (8-2) is used for electrolyzing hydrogen bromide.

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

9. The method for preparing propylene by bromine-mediated oxidative dehydrogenation of propane according to claim 8, characterized in that: 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 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 source of hydrogen is a byproduct produced by 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 a silica-based catalyst, titanium dioxide, and zirconium dioxide.

10. The method for preparing propylene by bromine-mediated oxidative dehydrogenation of propane according to claim 8, characterized in that: The first distillation tower (3-1), the second distillation tower (3-2), the third distillation tower (3-3), the fourth distillation tower (6) and the fifth distillation tower (7) are all packed towers or plate towers, and have a multi-stage tower 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.

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