A self-circulation reactor, an olefin epoxidation reaction method and application thereof

Abstract

The application provides a self-circulation reactor, an olefin epoxidation reaction method and application thereof, and belongs to the field of reactor design. The reactor comprises a reactor body which is composed of a feeding section, a reaction section, a gas-containing section and a gas-liquid separation section from bottom to top; and a downcomer which is in communication with the gas outlet and the liquid outlet of the gas-liquid separation section at the upper part and in communication with the feeding section at the lower part. In the application, the reaction material realizes self-circulation flow through the density difference between the downcomer and the reactor body in the self-circulation reactor. In this way, the flow speed of the material relative to the catalyst is increased, the mass transfer and heat transfer efficiency is improved, and the effect of the olefin epoxidation reaction is produced.

Description

Technical Field

[0001] This invention belongs to the field of reactor design, specifically relating to a self-circulating reactor and a method for olefin epoxidation reaction, and its applications. Background Technology

[0002] Selective oxidation of olefins using peroxides as oxidants is an important process in the production of epoxides. A typical example is the production of propylene oxide. Currently, the process of selectively oxidizing propylene to propylene oxide using oxidants such as hydrogen peroxide, tert-butyl hydroperoxide, ethylbenzene hydroperoxide (EBHP), and cumene hydroperoxide (CHP) has been widely industrialized. Moreover, due to its high efficiency and environmental friendliness, it has become the preferred option for the construction of propylene oxide industrial plants in recent years.

[0003] Taking EBHP and CHP as examples, these two types of peroxides have similar properties. Their reaction with propylene yields propylene oxide and 2-phenyl-1-ethanol (for EBHP) or 2-phenyl-2-propanol (for CHP). The reaction requires a catalyst, and the epoxidation catalysts that can be selected are homogeneous catalysts or heterogeneous catalysts. Typical heterogeneous catalysts include TS-1, Ti-MWW, Ti / HMS, etc.

[0004] Based on the current status of industrial plants and publicly available technical data, epoxidation processes using heterogeneous catalysts generally employ fixed-bed reactors in a liquid-solid configuration. Given the significant exothermic effect of the epoxidation reaction (approximately 200 kJ per mole), the consensus in the field is that the heat of reaction must be removed promptly to prevent excessively high reaction temperatures. This is crucial for selectivity, reaction efficiency, and process safety. For common peroxide systems, the suitable temperature for epoxidation reactions typically does not exceed 60–120 °C. In terms of reactor design, multi-stage inter-stage heat removal or tubular reactor heat removal schemes are commonly used. However, due to the temperature limitations, the removed heat of reaction is relatively low, limiting its utilization value.

[0005] A significant challenge in the design of epoxidation reactors is the need for prolonged residence time within the reactor to ensure complete conversion. This results in a relatively slow flow rate of the material relative to the catalyst, which limits mass and heat transfer, thus impacting reaction efficiency. While small reactors can employ designs like stirring to enhance flow and transfer, designing stirring mechanisms for large reactors is often challenging. Summary of the Invention

[0006] The purpose of this invention is to solve the problems existing in the prior art and provide a self-circulating reactor and a method for olefin epoxidation reaction and its application. This invention enhances the circulation flow of materials in the reactor, thereby ensuring that the materials have sufficient residence time for complete conversion while increasing their flow rate relative to the catalyst, improving mass and heat transfer efficiency, and thus producing an effect that is beneficial to the olefin epoxidation reaction.

[0007] This invention is achieved through the following technical solution:

[0008] In a first aspect, the present invention provides a self-circulating reactor for use in olefin epoxidation reactions;

[0009] The reactor includes:

[0010] The reactor body, from bottom to top, consists of a feeding section, a reaction section, a gas-containing section, and a gas-liquid separation section;

[0011] The downcomer is connected at the top to both the gas outlet and the liquid outlet of the gas-liquid separation section, and at the bottom to the feed section.

[0012] A further improvement of the present invention is that:

[0013] The feeding section includes a feeding section cylinder, the bottom of which is provided with a feeding port, which is connected to a metering pump via a pipeline; and / or

[0014] The feed section cylinder has a circulating material inlet on its side wall, which is connected to the lower part of the downcomer via a pipe.

[0015] A further improvement of the present invention is that:

[0016] The reaction section includes a reaction section cylinder and a catalyst disposed within the reaction section cylinder;

[0017] The catalyst is a heterogeneous catalyst.

[0018] A further improvement of the present invention is that:

[0019] The length L of the gas-containing section must satisfy L≥ΔP / (Δρ×g).

[0020] Where ΔP is the design pressure difference (unit: Pa), and Δρ is the density difference between the gas-containing section and the downcomer (unit: kg / m³). 3 g is the acceleration due to gravity (unit: m / s²). 2 ).

[0021] A further improvement of the present invention is that:

[0022] The gas-liquid separation section includes a gas-liquid two-phase separation component disposed at the top of the gas-containing section, and / or,

[0023] The gas outlet of the gas-liquid two-phase separation component is connected to a gas condenser via a pipeline, and the gas condenser is connected to the upper part of the downcomer; and / or,

[0024] The liquid outlet of the gas-liquid two-phase separation component is connected to an overflow port, and a liquid cooler is connected to the overflow port. The liquid cooler is then connected to the upper part of the downcomer through a pipe.

[0025] A further improvement of the present invention is that:

[0026] The downcomer is a straight tube with inlets at the top and upper sidewall. The gas condenser is connected to the top inlet of the downcomer via a pipe, and the liquid cooling pipe is connected to the sidewall inlet of the downcomer via a pipe; and / or,

[0027] The lower side wall of the downcomer is provided with a material outlet, which is connected to the circulating material inlet on the side wall of the feed section through a pipe.

[0028] A second aspect of the present invention provides a method for olefin epoxidation reaction, which uses the above-mentioned self-circulating reactor and specifically includes the following steps:

[0029] The reactants enter the feed section, rise through the reaction section for oxidation, and then pass through the gas-liquid separation section for separation. The separated gas is condensed by the gas condenser and enters the downcomer, while the separated liquid is cooled by the liquid cooler and enters the downcomer. The two mix in the downcomer and then enter the feed section to mix with the reactants and react again, thus achieving self-circulation.

[0030] A further improvement of the present invention is that:

[0031] The reactants contain low-boiling-point components. When the reactants come into contact with the catalyst in the reaction section and react, the reaction is exothermic and causes some of the low-boiling-point components to vaporize, forming a gas-liquid mixed phase. There is a certain density difference between the gas and the pure liquid phase in the downcomer. When the static pressure head provided by the density difference is sufficient to overcome the resistance, the material in the downcomer can return to the feed section, realizing the self-circulation of the material.

[0032] A further improvement of the present invention is that:

[0033] The reactants are a mixture of olefins and components including oxidants and solvents;

[0034] Preferably, the olefin is an olefin with a relatively low boiling point, the boiling point of which does not exceed 60°C or the lower limit of the reaction temperature, and preferably includes one or more of propylene, 1-butene, and isobutene;

[0035] Preferably, the oxidant is ethylbenzene hydrogen peroxide or cumene hydrogen peroxide;

[0036] Preferably, the solvent is ethylbenzene or cumene.

[0037] A further improvement of the present invention is that:

[0038] The reactants are a mixture of olefins, low-boiling-point components, and components including oxidants and solvents;

[0039] Preferably, the amount of the low-boiling-point component added accounts for 1% to 20% of the mass of the reactants, and its upper limit of boiling point does not exceed 60°C or the lower limit of reaction temperature; and / or,

[0040] The low-boiling-point components include small-molecule alkanes, ketones, and ethers, and are more preferably propane and butane.

[0041] A further improvement of the present invention is that:

[0042] The amount of olefins fed is greater than the amount of low-boiling-point olefins measured in the reaction.

[0043] Preferably, the olefins are fed at 4 to 10 times the reaction stoichiometry.

[0044] A third aspect of the invention provides the application of the above-described self-circulating reactor in olefin epoxidation reactions.

[0045] Compared with the prior art, the beneficial effects of the present invention are:

[0046] This invention relates to a self-circulating reactor where reactants circulate within the reactor due to density differences. This circulation increases the linear velocity of the material passing through the reaction section, enhancing mass and heat transfer efficiency and ensuring full utilization of the heat of reaction. The endothermic vaporization of low-boiling-point components facilitates rapid removal of the heat of reaction to prevent excessively high temperatures. These advantages are beneficial for certain reaction parameters, such as selectivity.

[0047] This invention achieves material self-circulation through density difference, eliminating the need for mechanical power such as circulation pumps and stirring mechanisms. It also utilizes reaction heat, eliminating the need for gas bubbling or heating components. The equipment has a simple structure, low cost, and is easy to operate and maintain. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the structure of a reactor provided by the present invention;

[0049] Figure 2 This is a schematic diagram of the reactor used in Example 1.

[0050] In the diagram, 1. Reactor body, 11. Feed section, 12. Reaction section, 13. Gas-containing section, 14. Gas-liquid separation section, 2. Downcomer, 3. Metering pump, 4. Gas condenser, 5. Overflow port, 6. Liquid cooler, 7. First valve, 8. Second valve, 9. Shut-off valve. Detailed Implementation

[0051] The present invention will now be described in further detail with reference to the accompanying drawings:

[0052] In a first aspect, the present invention provides a self-circulating reactor for use in olefin epoxidation reactions, wherein the reactants achieve self-circulation flow within the self-circulating reactor through density differences.

[0053] like Figure 1 As shown, the reactor includes:

[0054] The reactor body 1 consists of a feeding section 11, a reaction section 12, a gas-containing section 13, and a gas-liquid separation section 14 from bottom to top;

[0055] The downcomer 2 is connected at the top to both the gas outlet and the liquid outlet of the gas-liquid separation section 14, and at the bottom to the feed section 11.

[0056] The reactants contain certain low-boiling-point components. The reactants enter the feed section 11 of the reactor body 1, rise through the reaction section 12 for oxidation, and then pass through the gas-liquid separation section 14. The gas flows out from the gas outlet of the gas-liquid separation section 14, is condensed, and then enters the downcomer 2. The liquid flows out from the liquid outlet of the gas-liquid separation section 14 and enters the downcomer 2. The two mix in the downcomer 2 and then enter the feed section 11 again, where they mix with the reactants (pure liquid phase) and then react again, thus achieving self-circulation.

[0057] Since the reactants contain certain low-boiling-point components, which are preferably raw materials within the system and significantly more abundant than the stoichiometric low-boiling-point olefins, when the reactants come into contact with the catalyst in the reaction section and react, the reaction is exothermic and causes some of the low-boiling-point components to vaporize, forming a gas-liquid mixed phase. This mixed phase has a certain density difference with the pure liquid phase in the downcomer, meaning that the density of the material in the downcomer is greater than the density of the material in the reactor body. Therefore, the pressure at the bottom of the downcomer is greater than the pressure at the bottom of the feed section. When the static pressure head provided by the density difference (pressure difference) is sufficient to overcome the resistance, the material in the downcomer can return to the feed section, realizing material self-circulation. While ensuring that the material has sufficient residence time for complete conversion, it increases its relative flow rate to the catalyst, improves mass and heat transfer efficiency, and thus produces an effect that is beneficial to the olefin epoxidation reaction.

[0058] In this invention, the density difference between the material in the downcomer 2 and the material in the reactor body 1 is used to drive the material to circulate within the reactor body 1. This circulation does not require mechanical power such as pumps or agitators, but uses the heat of reaction as the driving force, hence it is called thermal self-circulation.

[0059] In a preferred embodiment of the present invention, the feeding section 11 includes a feeding section cylinder with a feed inlet at the bottom. The feed inlet is connected to a metering pump 3 via a pipe. The reactants enter the feeding section cylinder sequentially through the metering pump 3, the pipe, and the feed inlet. The reactants are a mixture of olefins, oxidants, and solvents. It is recommended that the olefins be selected from those with relatively low boiling points, including but not limited to propylene, 1-butene, isobutene, and mixtures thereof. It is recommended that the oxidants and solvents be selected from peroxides with relatively high boiling points, such as ethylbenzene hydroperoxide and cumene hydroperoxide, and corresponding solvents such as ethylbenzene and cumene.

[0060] The side wall of the feed section cylinder is provided with a circulating material inlet. The circulating material inlet is connected to the lower part of the downcomer 2 through a pipe. The material in the downcomer 2 enters the feed section cylinder in sequence through the pipe and the circulating material inlet, and mixes with the reaction material entering from the feed inlet to achieve material self-circulation.

[0061] In a preferred embodiment of the present invention, the reaction section 12 includes a reaction section cylinder and a catalyst disposed within the reaction section cylinder. The catalyst is a heterogeneous catalyst. The reactant material entering from the feed inlet of the feed section 11 and the material entering from the downcomer 2 of the feed section 11 are mixed in the feed section 11 and then pass through the reaction section 12 from bottom to top, where they undergo an oxidation reaction under catalysis. This reaction releases heat and causes some of the low-boiling-point components in the material to vaporize, ensuring that the material in the downcomer 2 and the material in the reactor body 1 always have a certain density difference. This allows the material to always achieve self-circulation, ensuring that the material has sufficient residence time for complete conversion while increasing its relative flow rate to the catalyst, improving mass and heat transfer efficiency, thereby producing an effect that is beneficial to the olefin epoxidation reaction.

[0062] A portion of the low-boiling-point components, after vaporization, pass through a gas-containing section as a gas-liquid mixture. This gas-containing section should be of sufficient length to accumulate a sufficient pressure differential to drive the circulating flow.

[0063] The lengths of the feed section 11 and the reaction section 12 have virtually no impact on the circulation flow. The length L of the gas-containing section 13 must satisfy L≥ΔP / (Δρ×g), where ΔP is the designed pressure difference (unit: Pa), and Δρ is the density difference between the gas-containing section and the downcomer (unit: kg / m³). 3 g is the acceleration due to gravity (unit: m / s²). 2 ).

[0064] In a preferred embodiment of the present invention, the gas-liquid separation section 14 includes a gas-liquid two-phase separation component disposed at the top of the gas-containing section. The gas outlet of the gas-liquid two-phase separation component is connected to a gas condenser 4 via a pipe, and the gas condenser 4 is connected to the upper part of the downcomer 2. The liquid outlet of the gas-liquid two-phase separation component is connected to an overflow port 5, and a liquid cooler 6 is connected to the overflow port 5. The liquid cooler 6 is also connected to the upper part of the downcomer 2 via a pipe. After the separated gas enters the gas condenser 4, it is completely cooled into condensate before entering the downcomer 2. The non-condensable gas is vented (while the pressure inside the system can be maintained through the back pressure valve of the non-condensable gas). The separated liquid overflows through the overflow port 5, is cooled by the liquid cooler 6, and then enters the downcomer 2. The purpose of liquid cooling is to prevent overheating and re-vaporization of the condensed gas.

[0065] The liquid outlet of the liquid cooler 6 is also connected to a discharge pipe, allowing some of the overflowing liquid to be collected as reaction products as needed. The collection rate is equal to the feed rate, but is usually significantly lower than the circulation flow rate.

[0066] Both gas condensers and liquid coolers are existing technology products, and their function is sufficient to achieve a cooling effect.

[0067] In a preferred embodiment of the present invention, the downcomer 2 is a straight tube with inlets at the top and upper sidewall. The gas condenser 4 is connected to the top inlet of the downcomer 2 through a pipe, and the liquid cooling pipe 6 is connected to the sidewall inlet of the downcomer 2 through a pipe. The lower sidewall of the downcomer 2 has a material outlet, which is connected to the circulating material inlet on the sidewall of the feeding section 11 through a pipe.

[0068] This invention relates to a self-circulating reactor where reactants circulate within the reactor due to density differences. This circulation increases the linear velocity of the material passing through the reaction section, enhancing mass and heat transfer efficiency and ensuring full utilization of the heat of reaction. The endothermic vaporization of low-boiling-point components facilitates rapid removal of the heat of reaction to prevent excessively high temperatures. These advantages are beneficial for certain reaction parameters, such as selectivity.

[0069] This invention achieves material self-circulation through density difference, eliminating the need for mechanical power such as circulation pumps and stirring mechanisms. It also utilizes reaction heat, eliminating the need for gas bubbling or heating components. The equipment has a simple structure, low cost, and is easy to operate and maintain.

[0070] A second aspect of the present invention provides a method for olefin epoxidation reaction, which uses the above-mentioned self-circulating reactor and specifically includes the following steps:

[0071] The reactants enter the feed section 11, rise through the reaction section 12 for oxidation, and then pass through the gas-liquid separation section 14 for separation. The separated gas is condensed by the gas condenser 4 and enters the downcomer 2. The separated liquid is cooled by the liquid cooler 6 and enters the downcomer 2. The two are mixed in the downcomer 2 and then enter the feed section 11 to mix with the reactants and then react again, thus achieving self-circulation.

[0072] The reactants contain certain low-boiling-point components, which are preferably raw materials within the system and significantly exceed the stoichiometric amount of low-boiling-point olefins. When the reactants come into contact with the catalyst in the reaction section and react, the reaction is exothermic and causes some of the low-boiling-point components to vaporize, forming a gas-liquid mixture. This mixture has a certain density difference with the pure liquid phase in the downcomer, meaning the density of the material in the downcomer is greater than the density of the material in the reactor body. Therefore, the pressure at the bottom of the downcomer is greater than the pressure at the bottom of the feed section. When the static pressure head provided by the density difference (pressure difference) is sufficient to overcome the resistance, the material in the downcomer can return to the feed section, achieving material self-circulation. This ensures that the material has sufficient residence time for complete conversion while increasing its relative flow rate to the catalyst, improving mass and heat transfer efficiency, thereby producing an effect beneficial to the olefin epoxidation reaction.

[0073] The reaction conditions for olefin epoxidation of the present invention, such as reaction temperature, pressure, time, and catalyst, can all adopt the reaction conditions and catalysts of existing olefin epoxidation processes in the prior art. For example, in the present invention, the olefin epoxidation reaction is carried out at 60-120°C and 1.0-6.0 MPa, and the feed rate is usually based on the space velocity of the oxidant, i.e., the mass of oxidant processed per unit mass of catalyst per hour, which is 0.2-2.0 kg / (kg·h).

[0074] The catalyst is preferably a heterogeneous catalyst, more preferably a Ti-HMS catalyst (such as the catalyst disclosed in patent CN104437636A).

[0075] Preferably, the reactants are a mixture of olefins and components including oxidants and solvents. The olefins are preferably selected from those with relatively low boiling points, including but not limited to propylene, 1-butene, isobutene, and mixtures thereof. The oxidants and solvents can be those commonly used in olefin epoxidation reactions in the prior art. It is recommended to select peroxides with relatively high boiling points, such as ethylbenzene hydroperoxide and cumene hydroperoxide, and corresponding solvents such as ethylbenzene and cumene.

[0076] A lower boiling point is relative to the oxidizing agent and solvent. For example, the atmospheric boiling points of CHP and cumene are above 150°C, so propylene (-47.7°C) and 1-butene (-6.3°C) would be more suitable. Because epoxidation, especially epoxidation using ethylbenzene or cumene peroxide, typically occurs in the range of 60°C to 120°C, the upper limit of the olefin's boiling point should not exceed 60°C or the lower limit of the reaction temperature; otherwise, vaporization will be hindered.

[0077] Preferably, the reactants are a mixture of high-boiling-point olefins, low-boiling-point components, and components including oxidants and solvents. The amount of low-boiling-point components added accounts for 1% to 20% of the mass of the reactants. Too little may result in low vaporization and failure to provide a density gradient, while too much will reduce the reactor's processing capacity. The upper limit of the boiling point of the low-boiling-point components should not exceed 60°C or the lower limit of the reaction temperature.

[0078] For low-boiling-point components, it is advisable to add components that are inert to the epoxidation reaction and have low boiling points to the system, including but not limited to small-molecule alkanes, ketones, and ethers, such as adding propane or butane to the propylene-CHP system. However, a more preferred approach is to directly utilize the low-boiling-point olefins in the system, serving both as epoxidation reactants and as vaporization components.

[0079] To avoid affecting the reaction efficiency, a sufficient amount of olefins required for the reaction must be retained in the system. In fact, in current industrial practice, to ensure complete conversion of peroxides, olefins are often added at 4 to 10 times the stoichiometric ratio. Taking propylene and CHP as an example, the stoichiometric ratio is 1:1, but the propylene is often added at more than 4 times the stoichiometric ratio. This means that even after complete conversion of CHP, there will still be 3 or more parts of propylene that have not reacted and can be vaporized. As for the solvent, it refers to the cumene that is inevitably carried in CHP, which does not participate in the reaction or stoichiometry.

[0080] The vaporization of low-boiling-point components requires the absorption of heat. This invention proposes to utilize the heat of reaction released during the epoxidation reaction to achieve the vaporization of low-boiling-point components. The advantages of doing so are: enhanced heat removal and cooling effect, which helps maintain the epoxidation reaction at a safe and suitable temperature; full utilization of the heat of reaction, converting the low-temperature heat source into the driving force for circulating flow; and elimination of heat exchange internal components, reducing equipment costs and flow resistance.

[0081] Before the reaction, the materials need to remain in a liquid phase to ensure sufficient contact between the reactants (olefins and peroxides) and the catalyst, thereby guaranteeing the reaction effect. The bubbly phase forms after passing through the catalyst. This effectively requires the reactor to operate near its bubble point. Before the reaction, the material temperature is low, below the bubble point of the mixture of olefins, peroxides, and solvents, and therefore in a liquid state. After the reaction, the material temperature is above the bubble point of the mixture, thus the low-boiling-point components vaporize. Of course, for the temperature before and after the reaction to cross the bubble point, the reactor also needs to operate at a suitable pressure. If the pressure is too low, the material cannot remain liquid before the reaction; if the pressure is too high, the post-reaction temperature rise will still be insufficient to vaporize the low-boiling-point components. The appropriate pressure should depend on the actual composition of the material, requiring the bubble point temperature to be precisely between the pre-reaction and post-reaction temperatures. Specific bubble point temperature calculations are publicly known in the field and will not be elaborated here.

[0082]

Example 1

[0083] Example 1 uses the self-circulating reactor of the present invention to carry out olefin epoxidation reaction. The reaction system is propylene-CHP-isocumene. The products obtained by the epoxidation reaction are propylene oxide and α,α-dimethylbenzyl alcohol.

[0084] The structure of the self-circulating reactor is shown in the attached figure. Figure 2 As shown, the reactor consists of two straight pipes with an inner diameter of 66 mm and a length of 1600 mm arranged side by side. An upward bend is connected to the top side of the reactor body (left straight pipe) as an overflow port. The overflow pipe is connected to the upper part of the downcomer (right straight pipe) after passing through a section of air-cooling coil. A second valve 8 is installed on the pipe connecting the air-cooling coil and the downcomer. There is also a 20 mm inner diameter pipeline connecting the lower part of the two pipes. A shut-off valve 9 is installed on the connecting pipeline, which can cut off the circulation and switch the reactor to a single-pass operation state.

[0085] The lower part of the reactor body is filled with about 600g of catalyst. The Ti-HMS catalyst used in the experiment was prepared according to Example 2 of patent CN104437636A. The catalyst section is loosely stacked with a height of about 450mm. It is supported by grids at both the top and bottom. A straight pipe section of about 800mm is reserved at the top of the catalyst section as a gas-containing section.

[0086] The length of the gas-containing section is designed based on the following calculations: According to the material composition, it is estimated that at 2.2 MPa, when the reaction temperature increases to 80℃, the propylene gasification rate is approximately 1 / 2. Before separating the gas phase, the material density in the gas-containing section is approximately 400 kg / m³. 3 The density of the liquid phase in the downcomer after gas phase separation is approximately 680 kg / m³. 3 That is, the density difference Δρ = 280 kg / m³ 3To achieve smoother circulation, the design pressure difference ΔP = 2 kPa is used. Therefore, the design length of the gas-containing section is L = 800 mm ≥ ΔP / (Δρ×g) = 2000 / (280×10) = 714 mm.

[0087] The feed section cylinder has a diameter of 66mm and a length of 350mm; the reaction section cylinder has a diameter of 66mm and a length of 450mm; the gas-containing section cylinder has a diameter of 66mm and a length of 750mm (with a 50mm height space above the overflow port for phase separation). The top of the left-side pipe is the gas phase outlet, which is connected to a water-cooled heat exchanger as a propylene condenser. A first valve 7 is installed on the pipe connecting the gas phase outlet and the water-cooled heat exchanger. The condensate returns to the upper part of the right-side pipe, and the non-condensable gas is released through the back pressure valve. The pressure inside the reactor body can be effectively controlled through this back pressure valve.

[0088] A feed inlet is located at the bottom of the left-side tube, through which a metering pump introduces the reactants, a mixture of propylene, CHP, and cumene. After preheating, the feed mixes with the circulating material at the bottom of the left-side tube and then flows upward through the catalyst bed (i.e., the reaction section).

[0089] After separation, the liquid overflows through the air-cooling coil and is then branched off as a discharge port, where the reaction liquid product is also pumped out by a metering pump. The flow rates of the discharge pump and the feed pump are approximately equal to maintain a stable liquid level within the reactor.

[0090] The reactants used in the experiment were a mixture of 480 g / h CHP, 560 g / h IPB, and 530 g / h propylene. The feed was preheated to 60°C, and the reaction pressure was controlled at 2.2 MPaG.

[0091] Comparative Example 1

[0092] Using the reactor from Example 1, the first valve 7, the second valve 8, and the shut-off valve 9 were closed, switching to a single-pass liquid-phase fixed-bed reaction. Since gas-phase back pressure was no longer used, the discharge pump was stopped, the pump bypass was opened, and the pressure inside the reactor was controlled by the liquid-phase back pressure valve at the outlet. In Comparative Example 1, the catalyst type and dosage, and feed conditions were consistent with Example 1, and the reaction pressure was controlled at 5.0 MPaG, confirming a pure liquid-phase reaction at this pressure.

[0093] Since the reaction temperatures of Example 1 and Comparative Example 1 cannot be kept consistent, the preheating temperature will be adjusted to maintain the conversion rate of CHP in the reaction product at the same level for easy comparison. The reaction effect will be judged by analyzing the characteristic components such as phenol and acetophenone in the product. The more of these byproduct components there are, the worse the reaction control effect is.

[0094] In Table 1, the conversion rate of CHP was obtained by iodometric titration, while the contents of marker components such as phenol and acetophenone were determined by liquid chromatography. Before analysis, the effluent undergoes depressurization to remove some olefins; therefore, propylene is not included in the component content baseline.

[0095] Table 1

[0096] Preheating temperature 60℃ 53℃ CHP conversion rate 60.7％ 61.9％ Phenol content of the product 0.0685wt% 0.1130wt% Acetophenone content of the product 0.3055wt% 0.3565wt%

[0097]

Example 2

[0098] For the high-boiling-point olefin cyclohexene (boiling point 85.6℃ at normal pressure), butane (boiling point 0.5℃ at normal pressure) is blended in.

[0099] The reactor used was the same as in Example 1, but the experimental conditions were changed, specifically:

[0100] The catalyst loading was reduced to 300g, the catalyst section height was reduced to 230mm, and the gas-containing section height was increased to 1000mm.

[0101] The reactants were changed to a mixture of 240 g / h CHP, 280 g / h IPB, 520 g / h cyclohexene, and 100 g / h butane. The feed was preheated to 60°C, and the reaction pressure was controlled at 0.3 MPaG.

[0102] Comparative Example 2

[0103] Using the reactor described in Example 2, the first valve 7, the second valve 8, and the shut-off valve 9 are closed, switching to a single-pass liquid-phase fixed-bed reaction mode. Since gas-phase back pressure is no longer used, the discharge pump is stopped, the pump bypass is opened, and the pressure inside the reactor is controlled by the liquid-phase back pressure valve at the outlet.

[0104] The feed composition was the same as in Example 2, consisting of a mixture of 240 g / h CHP, 280 g / h IPB, 520 g / h cyclohexene, and 100 g / h butane. The feed was preheated to 60°C.

[0105] The reaction pressure was controlled at 4.0 MPaG, which is higher than the critical pressure of butane, and it has been confirmed that the reaction is a pure liquid phase reaction at this pressure.

[0106] By appropriately adjusting the preheating temperature, the conversion rate of CHP in the reaction product can be maintained at the same level as in Example 2. Similarly, the reaction effect is judged by analyzing the characteristic components such as phenol and acetophenone in the product.

[0107] In Table 2, the conversion rate of CHP was obtained by iodometric titration, while the contents of marker components such as phenol and acetophenone were obtained by liquid chromatography analysis.

[0108] Table 2

[0109] Preheating temperature 60℃ 57℃ CHP conversion rate 67.5％ 67.3％ Phenol content of the product 0.0325wt% 0.0745wt% Acetophenone content of the product 0.1620wt% 0.1850wt%

[0110] The results showed that the content of byproduct components in both examples was significantly lower than that in the comparative example, indicating that the self-circulating reactor of the present invention is indeed beneficial to improving the selectivity of the epoxidation reaction.

[0111] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0112] In the description of this invention, unless otherwise stated, the terms "upper," "lower," "left," "right," "inner," "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0113] The above technical solution is only one embodiment of the present invention. For those skilled in the art, based on the principles disclosed in the present invention, it is easy to make various types of improvements or modifications, and not limited to the technical solutions described in the specific embodiments of the present invention. Therefore, the foregoing description is only a preferred option and is not restrictive.

Claims

1. A self-circulating reactor, characterized in that, The reactor includes: The reactor body consists of a feeding section, a reaction section, a gas-containing section, and a gas-liquid separation section from bottom to top. The reaction section includes a reaction section cylinder and a catalyst disposed inside the reaction section cylinder. The length L of the gas-containing section must satisfy L≥ΔP / (Δρ×g), where ΔP is the designed pressure difference, Δρ is the density difference between the gas-containing section and the downcomer, and g is the acceleration due to gravity. The downcomer is a straight tube, with its upper part connected to both the gas outlet and the liquid outlet of the gas-liquid separation section, and its lower part connected to the feed section. The gas-liquid separation section includes a gas-liquid two-phase separation component installed at the top of the gas-containing section. The gas outlet of the gas-liquid two-phase separation component is connected to a gas condenser via a pipe. The gas condenser is connected to the upper part of the downcomer. The reactor utilizes the exothermic reaction to vaporize the low-boiling-point components in the reactants, creating a density difference between the reactor body and the downcomer, thereby driving the reactants to circulate within the reactor.

2. The self-circulating reactor according to claim 1, characterized in that, The feeding section includes a feeding section cylinder, and the bottom of the feeding section cylinder is provided with a feeding port, which is connected to a metering pump through a pipeline; The feed section cylinder has a circulating material inlet on its side wall, which is connected to the lower part of the downcomer via a pipe.

3. The self-circulating reactor according to claim 1, characterized in that, The catalyst is a heterogeneous catalyst.

4. The self-circulating reactor according to any one of claims 1 to 3, characterized in that, The liquid outlet of the gas-liquid two-phase separation component is connected to an overflow port, and a liquid cooler is connected to the overflow port. The liquid cooler is then connected to the upper part of the downcomer through a pipe.

5. The self-circulating reactor according to claim 4, characterized in that, The downcomer has inlets at the top and upper sidewall. The gas condenser is connected to the top inlet of the downcomer through a pipe, and the liquid cooler is connected to the sidewall inlet of the downcomer through a pipe.

6. The self-circulating reactor according to claim 5, characterized in that, The lower side wall of the downcomer is provided with a material outlet, which is connected to the circulating material inlet on the side wall of the feed section through a pipe.

7. A method for olefin epoxidation reaction, carried out using the self-circulating reactor according to any one of claims 4 to 6, the method specifically comprising the following steps: The reactants enter the feed section, rise through the reaction section for oxidation, and then pass through the gas-liquid separation section for separation. The separated gas is condensed by the gas condenser and enters the downcomer, while the separated liquid is cooled by the liquid cooler and enters the downcomer. The two mix in the downcomer and then enter the feed section to mix with the reactants and react again, thus achieving self-circulation.

8. The olefin epoxidation reaction method according to claim 7, characterized in that, The reactants contain low-boiling-point components. When the reactants come into contact with the catalyst in the reaction section and react, the reaction is exothermic and causes some of the low-boiling-point components to vaporize, forming a gas-liquid mixed phase. This mixed phase has a density difference with the pure liquid phase in the downcomer, which drives the reactants to circulate within the reactor.

9. The olefin epoxidation reaction method according to claim 8, characterized in that, The reactants are a mixture of olefins and components including oxidants and solvents; The olefin is an olefin with a relatively low boiling point, with the boiling point not exceeding 60°C or the lower limit of the reaction temperature, including one or more of propylene, 1-butene, and isobutene. The oxidant is ethylbenzene hydrogen peroxide or cumene hydrogen peroxide; The solvent is ethylbenzene or cumene.

10. The olefin epoxidation reaction method according to claim 8, characterized in that, The reactants are a mixture of olefins, low-boiling-point components, and components including oxidants and solvents; The amount of low-boiling-point components added accounts for 1% to 20% of the mass of the reactants, and their upper limit of boiling point does not exceed 60℃ or the lower limit of reaction temperature. Low-boiling-point components include small molecules of alkanes, ketones, or ethers.

11. The olefin epoxidation reaction method according to claim 10, characterized in that, The low-boiling-point component is propane or butane.

12. The olefin epoxidation reaction method according to claim 9 or 10, characterized in that, The amount of olefin fed is greater than its reaction stoichiometry.

13. The olefin epoxidation reaction method according to claim 12, characterized in that, Olefins are fed at 4 to 10 times the reaction stoichiometry.

14. The application of the self-circulating reactor according to any one of claims 1 to 6 in the olefin epoxidation reaction.

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