Propane dehydrogenation hot molten salt reaction system

Abstract

A propane dehydrogenation hot molten salt reaction system comprises a tubular reactor, a molten salt heating furnace, a hot molten salt tank and a cold molten salt tank, the hot molten salt tank is respectively connected with the tubular reactor, the molten salt heating furnace and the cold molten salt tank, and the cold molten salt tank is respectively connected with the molten salt heating furnace and the reactor. The cold molten salt tank is connected with the hot molten salt tank through the pipeline, so that the temperature of molten salt in the hot molten salt tank can be adjusted to the temperature required by the tubular reactor. Uniform temperature distribution of the catalyst bed layer of the tubular reactor can be realized, the phenomenon that the temperature of the catalyst bed layer is too high or too low is avoided, and then catalyst coking can be reduced. Correspondingly, the service life of the catalyst is prolonged. And the temperature distribution of the catalytic bed is uniform, so that the activity of the catalyst is maintained, and the yield of the product is further improved.

Description

Technical Field

[0001] This utility model relates to alkane dehydrogenation reaction systems, specifically, to a hot molten salt reaction system for propane dehydrogenation. Background Technology

[0002] Propylene is an important organic chemical raw material, widely used in the production of polypropylene, acrylonitrile, propylene oxide, and other chemical products. With the rapid growth in demand for downstream derivatives, the propylene market is developing rapidly. Propylene is traditionally produced through petroleum cracking and refinery catalytic cracking, but the economics of both methods are now limited. The rapid growth in propylene demand is also driving the development of propane dehydrogenation to propylene technology.

[0003] Traditional propane dehydrogenation processes require high temperatures to achieve high conversion rates, resulting in high energy consumption and carbon emissions. Secondly, due to inconsistent catalyst loading leading to pressure drop differences in the fixed bed or material flow deviation caused by imperfectly symmetrical piping, the temperature distribution and temperature drop in the fixed bed are generally not very uniform, severely impacting catalyst lifespan and propylene yield.

[0004] Currently, industrial-scale production utilizes processes such as the Catofin and Oleflex. The Catofin process employs multiple parallel reactors in intermittent sequential operation, while the continuous process utilizes a circulating reactor for reheat / regeneration. The Oleflex process uses a fully recyclable platinum alumina-based catalyst system, offering lower production costs, higher returns on investment, and minimal environmental impact. However, both the Catofin and Oleflex processes involve side reactions that occur simultaneously with the main reaction, resulting in the formation of hydrocarbons that deposit and coke on the catalyst, thus reducing catalyst activity. Chinese patent application CN11341092A discloses a tubular fixed-bed molten salt heater device that provides the heat required for the dehydrogenation reaction in multiple ways, including continuous heating and temperature control of the catalyst bed during the reaction process via heat exchange between molten salt and heat exchange tubes, and continuous heating of the catalyst bed during regeneration via heat exchange between molten salt and heat exchange tubes, as well as heating the catalyst bed with high-temperature hot air. Utility Model Content

[0005] On the one hand, this invention improves the catalyst coking problem in the propane dehydrogenation hot molten salt reaction system, extends the catalyst lifespan, and increases product yield.

[0006] On the other hand, the propane dehydrogenation hot molten salt reaction system of this invention can fully and rationally recover and utilize heat, thereby reducing energy consumption.

[0007] The present invention discloses a propane dehydrogenation hot molten salt reaction system comprising a tubular reactor, a molten salt heater, a hot molten salt tank, and a cold molten salt tank. The hot molten salt tank is connected to the tubular reactor, the molten salt heater, and the cold molten salt tank via pipelines, and the cold molten salt tank is connected to the molten salt heater and the reactor.

[0008] This invention relates to a propane dehydrogenation hot molten salt reaction system. By connecting a cold molten salt tank and a hot molten salt tank via pipelines, the temperature of the molten salt in the hot molten salt tank can be adjusted to the required temperature of the tubular reactor. This ensures uniform temperature distribution in the catalyst bed of the tubular reactor, preventing excessively high or low temperatures and thus reducing catalyst coking. Consequently, the catalyst lifespan is extended. The uniform temperature distribution of the catalytic bed maintains catalyst activity, thereby improving product yield. Attached Figure Description

[0009] Figure 1 A schematic diagram of the hot molten salt reaction system for propane dehydrogenation. Detailed Implementation

[0010] The propane dehydrogenation hot molten salt reaction system of this application is described in further detail below. This does not limit the scope of protection of this application, which is defined by the claims. Certain specific details disclosed provide a comprehensive understanding of the various disclosed embodiments. However, those skilled in the art will recognize that embodiments can be implemented using other materials, etc., without employing one or more of these specific details.

[0011] Unless the context otherwise requires, the terms “comprising” and “including” in the specification and claims shall be understood as open-ended and inclusive, meaning “including, but not limited to”.

[0012] The terms "implementation," "an implementation," "another implementation," or "certain implementations" used in this specification refer to specific features, structures, or characteristics described in relation to the implementation, which are included in at least one implementation. Therefore, "implementation," "an implementation," "another implementation," or "certain implementations" do not necessarily all refer to the same implementation. Furthermore, specific features, structures, or characteristics can be combined in any way within one or more implementations. Each feature disclosed in this specification can be replaced by any alternative feature that provides the same, equivalent, or similar purpose. Therefore, unless otherwise specified, the disclosed features are merely general examples of equivalent or similar features.

[0013] This invention relates to a shell-and-tube reactor, a fixed-bed reactor composed of numerous very fine reaction tubes, each containing a catalyst. Its structure is similar to a shell-and-tube heat exchanger, consisting of a tube bundle, a shell, and end caps. Flue gas or high-temperature steam is used outside the tubes to provide the heat required for the reaction and maintain the reaction temperature.

[0014] The hot molten salt container of this utility model refers to a container for hot molten salt that has been heated to a high temperature, while the cold molten salt container refers to a container for hot molten salt that has been heated to a lower temperature.

[0015] The present invention discloses a propane dehydrogenation hot molten salt reaction system comprising a tubular reactor, a molten salt heater, a hot molten salt tank, and a cold molten salt tank, wherein the hot molten salt tank is connected to the tubular reactor, the molten salt heater, and the cold molten salt tank, and the cold molten salt tank is connected to the molten salt heater and the reactor, respectively.

[0016] In some embodiments, the shell-side inlet of the tubular reactor is connected to a hot molten salt tank, and the shell-side outlet of the tubular reactor is connected to a cold molten salt tank.

[0017] During the reaction, molten salt in the cold molten salt tank is transported to a molten salt heater for heating. The heated molten salt is then transferred to a hot molten salt tank, where it enters the tube reactor from the shell-side inlet to heat the materials inside, facilitating heat exchange. After heat exchange, the hot molten salt in the tube reactor is discharged from the shell-side outlet back into the cold molten salt tank. The cold molten salt in the cold molten salt tank then continues the same cycle. This invention connects the cold molten salt tank and the hot molten salt tank, allowing for real-time adjustment of the ratio of cold molten salt to hot molten salt and the temperature of the molten salt to meet the heat requirements of the tube reactor during the reaction.

[0018] Optionally, in the vertical direction, the shell-side inlet of the tubular reactor is higher than the shell-side outlet.

[0019] In some embodiments, a first temperature sensor is installed in the upper and lower parts of the tubular reactor, and a second temperature sensor is installed at the outlet of the hot molten salt tank. A regulating valve is installed on the pipeline connecting the cold molten salt tank and the hot molten salt tank. The first temperature sensor, the second temperature sensor, and the regulating valve are electrically connected to the control unit of the reaction system.

[0020] By detecting the temperature changes of the reactants before and after the reaction within the tubes of the tubular reactor using temperature sensors, the heat required for a certain stage of the reactor can be determined, and thus the required temperature of the molten salt can be obtained. The temperature of the molten salt in the molten salt tank can be adjusted to the desired temperature by controlling the regulating valve. Therefore, this invention achieves uniform temperature distribution in the reactor catalyst bed by adjusting the temperature of the molten salt in the molten salt tank, reducing coking on the catalyst surface or tube walls, improving catalyst lifespan, and ultimately increasing product yield.

[0021] In some embodiments, the tube side inlet of the tubular reactor is located at the top of the reactor, and the tube side outlet is located at the bottom of the reactor. The tube side is filled with catalyst. Propane feedstock enters the tube side through the tube side inlet to undergo catalytic dehydrogenation, and the resulting mixture is discharged through the tube side outlet.

[0022] The catalyst is any catalyst disclosed in the prior art that can be used to catalyze the dehydrogenation of propane.

[0023] Optionally, a third temperature sensor may be installed inside the pipe connected to the upper part of the tubular reactor for conveying raw materials; the third temperature sensor is electrically connected to the control unit of the reaction system.

[0024] By sensing the temperatures at different locations using the first, second, and third temperature sensors, the control unit can more precisely control the temperature of the catalyst bed in the reactor, resulting in a smaller temperature difference during the reaction process and a more uniform temperature distribution in the catalyst bed, thereby further improving the efficiency of propane dehydrogenation.

[0025] In existing propane dehydrogenation systems heated by molten salt, intermittent operation is typically employed. Intermittent operation of the propane dehydrogenation process is unstable, prone to coking, and the catalyst is easily deactivated by coking, requiring multiple tubular reactors to alternate the reaction. For example, after a period of reaction in the tubular reactor, the catalyst becomes deactivated by coking, necessitating stopping the reaction and introducing fuel combustion to regenerate the catalyst. In actual production, one tubular reactor performs the propane dehydrogenation reaction while another regenerates the catalyst. This invention's propane dehydrogenation system, by controlling the temperature distribution and temperature difference of the catalyst bed through molten salt temperature regulation, enables a single tubular reactor heating the molten salt system for continuous operation, one-step reaction, reduced reactor numbers, and lower equipment investment.

[0026] In some embodiments, a first heat exchanger is installed in the pipeline through which fuel is introduced into the molten salt heater, and the pipeline connecting the shell-side outlet of the tubular reactor to the cold molten salt tank passes through the first heat exchanger.

[0027] Within the first heat exchanger, the molten salt discharged from the shell side of the tubular reactor exchanges heat with the fuel, preheating it. The preheated fuel entering the molten salt furnace improves its ignition rate and combustion stability, thereby increasing the efficiency of heating the molten heat. Therefore, the reaction system of this invention improves fuel utilization by utilizing the heat from the molten salt discharged from the tubular reactor to preheat the fuel.

[0028] In some embodiments, a second heat exchanger is installed in the pipeline through which the raw material propane is introduced into the tubular reactor, and the pipeline through which the mixture after reaction is discharged from the shell-side outlet of the tubular reactor passes through the second heat exchanger.

[0029] In the second heat exchanger, the raw material propane exchanges heat with the reaction mixture to recover the heat from the reaction mixture.

[0030] A preferred embodiment of a propane dehydrogenation hot molten salt reaction system includes: a tubular reactor, a molten salt heater, a hot molten salt tank, and a cold molten salt tank; wherein,

[0031] The first pipeline for conveying raw materials is connected to the tube-side inlet at the top of the tubular reactor, and the second pipeline for conveying the reacted mixture is connected to the tube-side outlet at the top of the tubular reactor. The first and second pipelines are respectively connected to the second heat exchanger.

[0032] The outlet of the molten salt heater is connected to the first inlet of the hot molten salt tank; the inlet of the molten salt heater is connected to the first outlet of the cold molten salt tank; the outlet of the hot molten salt tank is connected to the shell-side inlet of the tubular reactor; the shell-side outlet of the tubular reactor is connected to the inlet of the cold molten salt tank; the second outlet of the cold molten salt tank is connected to the second inlet of the hot molten salt tank; a third pipe connecting the shell-side outlet of the tubular reactor to the inlet of the cold molten salt tank and a fourth pipe supplying fuel to the molten salt heater are respectively connected to the first heat exchanger; and

[0033] A first temperature sensor is installed in the upper and lower parts of the tubular reactor, a second temperature sensor is installed at the outlet of the hot molten salt tank, and a third temperature sensor is installed in the pipeline connected to the upper part of the tubular reactor for conveying raw materials. A first regulating valve and a second regulating valve are respectively installed on the second pipeline and the fifth pipeline for connecting the second outlet of the cold molten salt tank and the second inlet of the hot molten salt tank. The first temperature sensor, the second temperature sensor, the third temperature sensor, the first regulating valve, and the second regulating valve are electrically connected to the control unit.

[0034] In a preferred embodiment, a first temperature sensor is installed at the inlet and outlet of the tube side of the tubular reactor and inside the reaction tube.

[0035] The components of this invention are connected by pipes.

[0036] The regulating valve and sensor used in this invention are commonly used equipment in the chemical industry.

[0037] Molten salt heating furnaces can utilize various energy sources such as solar thermal, photovoltaic, off-peak electricity, and industrial waste heat to heat molten salt.

[0038] In some embodiments, in the propane dehydrogenation hot molten salt reaction system, the temperature at the top of the reaction tubes of the tubular reactor is 575°C to 625°C, and the reaction pressure is 0.05 MPa.

[0039] In the propane dehydrogenation hot molten salt reaction system, the bottom temperature of the tubular reactor is controlled within the range of 578℃ to 598℃.

[0040] The structure of the propane dehydrogenation hot molten salt reaction system of this utility model will be further described in detail below with reference to the accompanying drawings.

[0041] As attached Figure 1 As shown, a propane dehydrogenation hot molten salt reaction system includes: a tubular reactor 3, a molten salt heating furnace 12, a hot molten salt tank 1, and a cold molten salt tank 2.

[0042] Molten salt circulation pipeline: The outlet of the molten salt heater 12 is connected to the first inlet of the hot molten salt tank 1, and the inlet of the molten salt heater 12 is connected to the first outlet of the cold molten salt tank 2. The outlet of the hot molten salt tank 1 is connected to the shell-side inlet of the tubular reactor 3. The shell-side outlet of the tubular reactor 3 is connected to the inlet of the cold molten salt tank 2. A pump is installed on the connecting pipeline between these two components to drive the molten salt to flow in the circulation pipeline. The second outlet of the cold molten salt tank 2 is connected to the second inlet of the hot molten salt tank 1. A third pipeline connecting the shell-side outlet of the tubular reactor 3 to the inlet of the cold molten salt tank 2 and a fourth pipeline supplying fuel to the molten salt heater are respectively connected to the first heat exchanger 4. In the first heat exchanger (also called the fuel preheater), the molten salt discharged from the tubular reactor 3 exchanges heat with the fuel to preheat the fuel.

[0043] The feedstock delivery pipelines are as follows: The first pipeline for transporting propane is connected to the tube-side inlet at the top of the tubular reactor 3, and the second pipeline for transporting the reacted mixture is connected to the tube-side outlet at the bottom of the tubular reactor 3. Both the first and second pipelines are connected to the second heat exchanger 5. Inside the second heat exchanger 5, fresh propane exchanges heat with the reaction products, recovering the heat carried away by the products, i.e., heat reuse, thus reducing energy consumption.

[0044] The control circuit of the reaction system includes: first temperature sensors (8, 9) installed at the upper and lower parts of the tubular reactor 3, specifically at the inlet and outlet of the tube side, to measure the temperature changes of the reactants before and after the reaction; a second temperature sensor 6 installed at the outlet of the hot molten salt tank; and a third temperature sensor 7 installed in the pipeline connected to the upper part of the tubular reactor for conveying raw materials to measure the temperature of the raw materials entering the reactor. A first regulating valve 10 is installed on the fifth pipeline connecting the second outlet of the cold molten salt tank 2 to the second inlet of the hot molten salt tank 1, and a second regulating valve 11 is installed on the second pipeline discharging the products propylene and hydrogen. The first, second, and third temperature sensors, the first regulating valve, and the second regulating valve are all electrically connected to the control unit 13.

[0045] The above propane dehydrogenation reaction system operates as follows: (1) Fresh propane is introduced as a feedstock to the top of the tubular reactor 3 and undergoes a dehydrogenation reaction with the catalyst in the reactor to obtain propylene and hydrogen. The reactants exchange heat with the feedstock and recover residual heat.

[0046] (2) The upper end of the molten salt heater 12 is connected to the hot molten salt tank 1, and the lower end of the molten salt heater 12 is connected to the cold molten salt tank 2. The molten salt heater heats the molten salt, and the high-temperature molten salt is introduced into the hot molten salt tank 1. The hot molten salt tank 1 is connected to the shell-side inlet of the tubular reactor 3. The high-temperature molten salt in the hot molten salt tank 1 provides the reaction heat required by the tubular reactor 3. The high-temperature molten salt flows through the tubular reactor 3 for heat exchange, and the temperature decreases. It is discharged from the shell-side outlet at the lower end of the tubular reactor 3. The outlet of the tubular reactor 3 is connected to the molten salt pump, which introduces the low-temperature molten salt into the fuel preheater (first heat exchanger), and then through the cold molten salt tank 2. The low-temperature molten salt in the cold molten salt tank 2 is led to the molten salt heater 12 for circulation.

[0047] (3) In the temperature control system, temperature sensors are installed at the tube reactor 3, the raw material inlet of the tube reactor 3, and the hot molten salt tank 1, respectively. After processing by the control unit 13, the control result is output and the execution signal is sent to the regulating valve of the pipeline connecting the cold and hot molten salt tanks and the regulating valve of the product outlet pipeline to regulate the flow rate and thus control the temperature of the catalyst bed in the reactor.

[0048] The following example uses the attached Figure 1 The reaction system shown performs a propane dehydrogenation reaction to produce propylene. Commercially available catalysts were used in all examples.

[0049] Example 1

[0050] Under the conditions of 600℃ and 0.05MPa in a tubular reactor, propane is converted to propylene with a propylene selectivity of approximately 85.6% and a single-pass conversion rate of approximately 45% for propane.

[0051] Example 2

[0052] At a temperature of 650°C and a reaction pressure of 0.05 MPa in the tubular reactor, the reactor temperature exceeded the set range. The temperature sensor transmitted a signal, and the control unit initiated regulation. Upon detecting that the hot molten salt tank temperature was too high, the regulating valve connecting the hot and cold molten salt tanks was opened to direct the low-temperature molten salt to the hot molten salt tank until the temperature in the hot molten salt tank dropped to the set range. The regulating valve then closed. Subsequently, the reactor temperature dropped to 598°C, with a propylene selectivity of approximately 85.3% and a single-pass propane conversion of approximately 44%.

[0053] Example 3

[0054] At a temperature of 550°C and a reaction pressure of 0.05 MPa in the tubular reactor, the reactor temperature fell below the set range. The temperature sensor transmitted a signal, and the control unit initiated adjustments. Detecting the low temperature at the top of the reactor, fuel was added, and the molten salt heater continued heating until the temperature in the hot molten salt tank rose to the set range. Subsequently, the reactor temperature rose to 578°C, with a propylene selectivity of approximately 85.1% and a single-pass propane conversion of approximately 44%.

[0055] The above description is only a preferred embodiment of the present utility model and is not intended to limit the scope of the substantive technical content of the present utility model. The substantive technical content of the present utility model is broadly defined within the scope of the claims. Any technical entity or method completed by others that is completely identical to or an equivalent modification of the claims is considered to be covered within the scope of the claims.

Claims

1. A propane dehydrogenation hot molten salt reaction system, comprising: The system comprises a tubular reactor, a molten salt heater, a hot molten salt tank, and a cold molten salt tank, wherein the hot molten salt tank is connected to the tubular reactor, the molten salt heater, and the cold molten salt tank, respectively, and the cold molten salt tank is connected to the molten salt heater and the tubular reactor, respectively.

2. The propane dehydrogenation hot molten salt reaction system according to claim 1, characterized in that, The shell-side inlet of the tubular reactor is connected to a hot molten salt tank, and the shell-side outlet of the tubular reactor is connected to a cold molten salt tank.

3. The propane dehydrogenation hot molten salt reaction system according to claim 2, characterized in that, In the vertical direction, the shell-side inlet of the tubular reactor is higher than the shell-side outlet.

4. The propane dehydrogenation hot molten salt reaction system according to any one of claims 1-3, characterized in that, A first temperature sensor is installed in the upper and lower parts of the tubular reactor, and a second temperature sensor is installed at the outlet of the hot molten salt tank. A regulating valve is installed on the pipeline connecting the cold molten salt tank and the hot molten salt tank. The first temperature sensor, the second temperature sensor, and the regulating valve are electrically connected to the control unit of the reaction system.

5. The propane dehydrogenation hot molten salt reaction system according to any one of claims 1-3, characterized in that, The tube side inlet of the tubular reactor is located at the top of the reactor, and the tube side outlet is located at the bottom of the reactor. The tube side is filled with catalyst.

6. The propane dehydrogenation hot molten salt reaction system according to claim 5, characterized in that, A third temperature sensor is installed inside the pipeline used to transport raw materials, which is connected to the upper part of the tubular reactor. The third temperature sensor is electrically connected to the control unit of the reaction system.

7. The propane dehydrogenation hot molten salt reaction system according to any one of claims 1-3, characterized in that, A first heat exchanger is installed in the pipeline that supplies fuel to the molten salt heater. The pipeline connecting the shell-side outlet of the tubular reactor to the cold molten salt tank passes through the first heat exchanger.

8. The propane dehydrogenation hot molten salt reaction system according to any one of claims 1-3, characterized in that, A second heat exchanger is installed in the pipeline that feeds the propane feedstock into the tubular reactor, and the pipeline that discharges the reaction mixture from the shell-side outlet of the tubular reactor passes through the second heat exchanger.

9. The propane dehydrogenation hot molten salt reaction system according to any one of claims 1-3, characterized in that, The first pipeline for conveying raw materials is connected to the tube-side inlet at the top of the tubular reactor, and the second pipeline for conveying the reacted mixture is connected to the tube-side outlet at the top of the tubular reactor. The first and second pipelines are respectively connected to the second heat exchanger. The outlet of the molten salt heater is connected to the first inlet of the hot molten salt tank; the inlet of the molten salt heater is connected to the first outlet of the cold molten salt tank; the outlet of the hot molten salt tank is connected to the shell-side inlet of the tubular reactor; the shell-side outlet of the tubular reactor is connected to the inlet of the cold molten salt tank; the second outlet of the cold molten salt tank is connected to the second inlet of the hot molten salt tank; a third pipe connecting the shell-side outlet of the tubular reactor to the inlet of the cold molten salt tank and a fourth pipe supplying fuel to the molten salt heater are respectively connected to the first heat exchanger; and A first temperature sensor is installed in the upper and lower parts of the tubular reactor, a second temperature sensor is installed at the outlet of the hot molten salt tank, and a third temperature sensor is installed in the pipeline connected to the upper part of the tubular reactor for conveying raw materials. A first regulating valve and a second regulating valve are respectively installed on the second pipeline and the fifth pipeline for connecting the second outlet of the cold molten salt tank and the second inlet of the hot molten salt tank. The first temperature sensor, the second temperature sensor, the third temperature sensor, the first regulating valve, and the second regulating valve are electrically connected to the control unit.

10. The propane dehydrogenation hot molten salt reaction system according to claim 9, characterized in that, A first temperature sensor is installed at the inlet and outlet of the tube side of the tubular reactor and inside the reaction tube.

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