Method for producing epoxypropane with low energy consumption by cumene method

Abstract

The invention discloses a method for producing epoxypropane with low energy consumption by a cumene method. Comprising the following steps: S1, carrying out a reaction on cumene and oxygen-containing gas in a gas-liquid bubbling bed reactor to obtain an oxidation solution with the concentration of cumene hydroperoxide being 30-70%, and removing impurities to obtain dried cumene hydroperoxide, S2, carrying out a reaction on the dried cumene hydroperoxide and propylene in a tubular fixed bed reactor to obtain an epoxide material, recovering excessive propylene from the epoxide material, and recovering the propylene from the epoxide material to obtain the cumene hydroperoxide. S3, carrying out hydrogenolysis reaction on the crude alpha, alpha-dimethyl benzyl alcohol and hydrogen, so as to convert the crude alpha, alpha-dimethyl benzyl alcohol into crude cumene; s4, heavy component removal, light component removal and alkali washing are conducted on the crude cumene, impurities in the crude cumene are removed, and then the crude cumene is returned to the step S1. According to the method, the oxidation depth of the cumene in the oxidation unit is increased, the circulation amount of the cumene is greatly reduced, the energy consumption of the device is greatly reduced, and the economical efficiency of the device is improved.

Description

Technical Field

[0001] The invention relates to the field of chemical engineering, in particular to an industrial technology for producing propylene oxide by a low-energy consumption cumene method. Background Art

[0002] Propylene oxide is an important organic chemical intermediate, mainly used in the production of polyether polyols, propylene glycol and propylene glycol ether. Its production and consumption are second only to polypropylene, making it the second largest derivative of propylene. At present, the industrial production method is gradually shifting from the chlorohydrin method to the oxidation method. The industrialized oxidation methods include the propylene oxide / styrene co-production method (POSM), the propylene oxide / MTBE method (POMTBE), the hydrogen peroxide method propylene oxide (HPPO) and the isopropylbenzene method propylene oxide (CHPPO).

[0003] The POSM and POMTBE methods can not only produce propylene oxide and styrene or MTBE at the same time, but also have good economic efficiency due to the added value of their co-products. However, the sales of a large number of co-products also bring great sales pressure to the production equipment. In contrast, the HPPO and CHPPO methods do not produce co-products, thus avoiding this problem. However, due to the lack of economic added value of co-products, the production costs of these two methods have always been high. Especially for HPPO, in addition to the high production cost, the safety issues of its equipment also pose a major challenge.

[0004] The process of producing propylene oxide (PO) by CHPPO was first disclosed in patent CS140743. The process includes the following steps:

[0005] (1) Cumene is oxidized by air to form cumene hydroperoxide (CHP);

[0006] (2) CHP and propylene are epoxidized to produce propylene oxide (PO) and α,α-dimethylbenzyl alcohol (DMBA);

[0007] (3) DMBA is subjected to hydrogenolysis or dehydration / hydrogenation reaction to generate cumene, and the reaction is returned to step (1).

[0008] Subsequently, in order to reduce the production cost of the CHPPO method PO production device, people conducted research from two aspects: one is to separate a part of the co-products for further processing to produce high value-added products. For example, patents CN104844493 and CN104876894 of Sinopec Shanghai Engineering Co., Ltd. proposed to react all or part of α,α-dimethylbenzyl alcohol with CHP to produce diisopropylbenzene peroxide (DCP) to increase the comprehensive benefits of the CHPPO device; the other aspect is to directly reduce the material consumption and production energy consumption of the CHPPO device.

[0009] Sinopec Shanghai Engineering Co., Ltd.'s patent CN104447629 discloses a method for producing steam as a by-product in the oxidation unit of a propylene oxide plant. This method adds a heat extractor in front of the circulating cooler of the oxidation unit to recover the heat of the oxidation liquid to generate steam, which is then used in the reboiler of the concentration tower, thereby saving steam consumption. Another patent of the company, CN104402843, introduces a new method for reducing the energy consumption of the oxidation unit of a propylene oxide plant. This method saves electricity by changing the power source of the circulating cooling system from a circulating pump to utilizing the density difference between the gas-liquid two-phase flow in the oxidation tower and the liquid phase flow in the circulating pipeline to achieve natural circulation.

[0010] Sumitomo Chemical's patent CN101233122 discloses a method for controlling the concentration of methyl hydroperoxide in the solution in the epoxidation step within the range of 1 to 20 ppm to reduce the energy consumption of refining propylene oxide.

[0011] Wuxi Zhigui's patent CN110483445 discloses a dehydration process of cumene hydroperoxide and cumene in a propylene oxide production device. The heat energy required for this process comes entirely from the heat released when the output material of the dehydration tower is cooled, effectively reducing the energy consumption of the device.

[0012] Sinopec reported a method for recovering propylene from epoxidation products with low energy consumption in patent CN105272939. This method reduces the energy consumption of propylene recovery by adding a flash tank. Another patent of the company, CN105272941, points out that the high-pressure propylene tower and the low-pressure propylene tower used for propylene recovery should be operated at a relatively low pressure, and 60-95% by weight of propylene in the epoxidation product is recovered from the top of the high-pressure propylene tower, and only a small amount of propylene is recovered from the low-pressure propylene tower. Since the low-pressure propylene recovery tower needs to use a coolant with a lower temperature, this patented technology can reduce energy consumption by up to 60% compared with the prior art.

[0013] Wanhua's patent invention authorization CN110437117 points out that while cumene is oxidized to produce CHP, CHP will further undergo a series of side reactions, resulting in a decrease in CHP selectivity. Therefore, the single-pass conversion rate of cumene in the industrial process is generally lower than 30wt%; Cao Gang pointed out in his monograph "Producing Phenol Acetone by Isopropylbenzene Method" P168-169 that the oxidation depth commonly used in current industrial plants is ~25%; while in the phenol acetone technologies of UOP and KBR, the cumene oxidation depth is 24wt% of the cumene hydroperoxide concentration (Zhong Zhaolong. Analysis and Comparison of Process Technologies of Phenol / Acetone Plants [J]. Anhui Chemical Industry. 2021, 47(2). 81-85). The oxidation section of the UOP phenol acetone process adopts a 4-stage oxidation reaction, and the CHP concentration of each stage increases step by step by 6wt%. The oxidation section of the KBR phenol acetone process adopts 6 towers in series, and the CHP concentration increases step by step by 4wt%. The final CHP concentration at the reactor outlet is 24%.

[0014] In general, the production consumption of the existing CHPPO technology is still relatively high, and the discussion on the depth of cumene oxidation is all based on the application of phenol-acetone units, and there is no discussion based on the application of cumene-based propylene oxide units (CHPPO). Therefore, it is necessary to develop a more efficient and energy-saving CHPPO process. Summary of the invention

[0015] The main purpose of the present application is to provide a method for producing propylene oxide with low energy consumption by using the cumene method, by appropriately increasing the single-pass conversion rate of cumene oxidation in step S1 to reduce the large-scale circulation of cumene, thereby significantly reducing the energy consumption of the CHPPO device.

[0016] In order to achieve the above objectives, in a first aspect, the present application provides a method for producing propylene oxide with low energy consumption by using a cumene process, comprising the following steps:

[0017] S1, an oxidation step, reacting cumene with an oxygen-containing gas in a gas-liquid bubbling bed reactor to obtain cumene hydroperoxide with a concentration of 30-70%, and after removing organic acid and water to remove impurities, obtaining dry cumene hydroperoxide;

[0018] S2, an epoxidation step, reacting dried cumene hydroperoxide with propylene in a tubular fixed bed reactor, recovering excess propylene from the epoxide material after the reaction, and then separating to obtain crude propylene oxide and crude α,α-dimethylbenzyl alcohol, and refining the crude propylene oxide to obtain a propylene oxide product;

[0019] S3, a hydrogenolysis step, converting crude α,α-dimethylbenzyl alcohol (DMBA) into crude cumene by hydrogenolysis reaction with hydrogen;

[0020] S4, refining cumene, removing heavy components, light components and alkali washing from crude cumene, removing impurities therein and using it as the cumene raw material in step S1;

[0021] The oxidation reaction heat, epoxidation reaction heat and hydrogenolysis reaction heat in steps S1-S3 are recovered, and the recovery rate of the reaction heat is ≥50%.

[0022] Optionally, in step S1, the oxidation reaction stage is 3 to 6, the oxidation reaction temperature is 90 to 130°C, and the temperature of at least one oxidation reaction is ≥120°C.

[0023] Optionally, each stage of the oxidation reactor is connected to a circulating heat recovery device, which includes a circulating pump, a first circulating cooler arranged in parallel for recovering oxidation reaction heat, and a second circulating cooler for controlling the oxidation reaction temperature.

[0024] Optionally, in step S2, the epoxidation reaction temperature of cumene hydroperoxide and propylene is 90-120° C., and the reaction pressure is 6-7 MPa.

[0025] Optionally, the shell-and-tube fixed bed reactor is connected to an epoxidation reaction heat recovery device, which includes a steam drum, and the heat exchange fluid outlet of the steam drum is connected to the shell side inlet of the shell-and-tube fixed bed reactor, and the shell side outlet of the shell-and-tube fixed bed reactor is connected to the heat exchange fluid inlet of the steam drum.

[0026] Optionally, the heat exchange fluid is water, and the epoxidation reaction heat recovery device further comprises a steam compressor connected to the top of the steam drum.

[0027] Optionally, the heat exchange fluid is propylene, and the epoxidation reaction heat recovery device also includes an expander connected to the top of the steam drum, and the exhaust gas flowing out of the gas outlet of the expander is condensed by circulating water and then connected to the steam drum through a pump.

[0028] Optionally, in step S3, hydrogen is used as a dispersed phase, and the flow direction in the hydrogenolysis reactor is bottom-in and top-out, the hydrogenolysis reaction temperature is 120-200° C., and the hydrogen / hydrocarbon ratio of the hydrogenolysis reaction is 3-30 mol.

[0029] Optionally, in step S3, the gas phase fluid at the top of the hydrogenolysis reactor is returned to the hydrogenolysis reactor after three-stage condensation, the first stage condensation temperature is 130-150°C, the second stage condensation temperature is 90-100°C, the third stage condensation temperature is 40-50°C, a part of the liquid phase material of the hydrogenolysis reactor is discharged, and the other part is returned to the hydrogenolysis reactor, and the return amount / discharge amount = 0.1-10.

[0030] Optionally, in step S4, a process of first removing heavy components, then removing light components, and finally alkali washing is adopted, and isopropylbenzene without α,α-dimethylbenzyl alcohol is separated at the top of the heavy removal tower, and 10-80% of isopropylbenzene is retained in the bottom of the tower, and the rest is α,α-dimethylbenzyl alcohol and heavier components. The crude isopropylbenzene containing light components separated from the top of the heavy removal tower enters the light removal tower, and ethylbenzene and other lighter components therein are separated. Crude ethylbenzene is obtained from the top of the light removal tower, and ethylbenzene by-product is obtained after refining; the material at the bottom of the heavy removal tower enters the alcohol recovery tower, and after removing components heavier than α,α-dimethylbenzyl alcohol, it returns to the hydrogenolysis reactor to continue the reaction. The isopropylbenzene obtained from the top of the light removal tower is washed with alkali to remove phenol therein and then returns to step S1, the bottom of the heavy removal tower is heated with 1.0-4.0MPa steam for reboiler heating, and the by-product of the top condenser is 0.3-2.0MPa steam.

[0031] The method for producing propylene oxide by a cumene method with low energy consumption provided by the present invention has the following beneficial effects compared with the prior art:

[0032] 1. During the oxidation reaction, the concentration of cumene hydroperoxide is controlled at 30-70%. By appropriately increasing the single-pass conversion rate of cumene oxidation in step S1 to reduce the large-scale circulation of cumene, the energy consumption of the CHPPO device is greatly reduced, breaking through the technical bottleneck that conventional technicians believe that the concentration of cumene hydroperoxide needs to be controlled within 30% in the oxidation step;

[0033] 2. When the temperature of the cumene oxidation reaction is increased and the reactor volume is reduced, higher-grade heat can be recovered from the cumene oxidation reaction, which is convenient for use by multiple other users of the CHPPO unit.

[0034] 3. The epoxidation reaction temperature of cumene hydroperoxide and propylene in step S2 is 90-120° C., and the recovery of the epoxidation reaction heat can significantly reduce energy consumption;

[0035] 4. In step S3, a direct hydrogenation scheme is adopted, and a high hydrogen-to-hydrocarbon ratio of 3 to 30 is adopted, so that the water generated by the reaction can enter the gas phase and be quickly removed from the reactor, thereby preventing the rapid deactivation of the catalyst caused by excessive liquid water, avoiding the problem of too short catalyst life during direct hydrogenolysis, and also avoiding the increase in energy consumption when the dehydration-then-hydrogenation method is adopted. In addition, the step condensation of the circulating hydrogen flowing out of the reactor can recover a large amount of hydrogenolysis reaction heat. Finally, the return amount / discharge amount of the hydrogenolysis reaction material = 0.1 to 10, which can improve the conversion rate of α, α-dimethylbenzyl alcohol and reduce the energy consumption of isopropylbenzene refining;

[0036] 5. In step S4, the process of first removing heavy components and then removing light components is adopted. The heavy-removing tower adopts a thermal coupling scheme. The tower bottom uses 1.0-4.0MPa steam to heat the reboiler. The tower top condenser produces 0.3-2.0MPa steam as a byproduct, which can directly recover heat for other heating users. This makes the heavy component removal operation of cumene basically without consuming steam latent heat, because the steam heat injected into the tower bottom is recovered at the top of the tower. In addition, compared with the process of first removing light components and then removing heavy components, the steam produced by the heavy-removing tower can be used in the light-removing tower, which is more advantageous in terms of device operation and energy configuration. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The drawings constituting a part of this application are used to provide a further understanding of this application, so that other features, purposes and advantages of this application become more obvious. The schematic embodiment drawings and their descriptions of this application are used to explain this application and do not constitute an improper limitation on this application. In the drawings:

[0038] Figure 1 Schematic diagram of the process of the present invention (Example 1);

[0039] Figure 2 This is a schematic diagram of heat recovery from oxidation reaction;

[0040] Figure 3 Schematic diagram of heat recovery from epoxidation reaction (Example 2). DETAILED DESCRIPTION

[0041] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present application.

[0042] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0043] In the present application, the terms "upper", "lower", "left", "right", "front", "back", "top", "bottom", "inner", "outer", "middle", "vertical", "horizontal", "lateral", "longitudinal" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings. These terms are mainly used to better describe the present application and its embodiments, and are not used to limit the indicated devices, elements or components to have a specific orientation, or to be constructed and operated in a specific orientation.

[0044] In addition, some of the above terms may be used to express other meanings in addition to indicating orientation or positional relationship. For example, the term "on" may also be used to express a certain dependency or connection relationship in some cases. For those of ordinary skill in the art, the specific meanings of these terms in this application can be understood according to specific circumstances.

[0045] In addition, the term "plurality" shall mean two or more.

[0046] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0047] A method for producing propylene oxide with low energy consumption using a cumene process comprises the following steps:

[0048] S1, an oxidation step, reacting cumene with an oxygen-containing gas in a gas-liquid bubbling bed reactor to obtain cumene hydroperoxide with a concentration of 30-70%, and after removing organic acid and water to remove impurities, obtaining dry cumene hydroperoxide;

[0049] S2, an epoxidation step, reacting dried cumene hydroperoxide with propylene in a tubular fixed bed reactor, recovering excess propylene from the epoxide material after the reaction, and then separating to obtain crude propylene oxide and crude α,α-dimethylbenzyl alcohol, and refining the crude propylene oxide to obtain a propylene oxide product;

[0050] S3, a hydrogenolysis step, converting crude α,α-dimethylbenzyl alcohol (DMBA) into crude cumene by hydrogenolysis reaction with hydrogen;

[0051] S4, refining cumene, removing heavy components, light components and alkali washing from crude cumene, removing impurities therein and using it as the cumene raw material in step S1;

[0052] The oxidation reaction heat, epoxidation reaction heat and hydrogenolysis reaction heat in steps S1-S3 are recovered, and the recovery rate of the reaction heat is ≥50%.

[0053] The oxidation step S1 refers to the oxidation of cumene to obtain cumene hydroperoxide, which is usually obtained by reacting air with liquid cumene. The reaction temperature of liquid phase oxidation of cumene is generally 50-150°C, and the reaction pressure is mostly between 0.01 and 1 MPa. The oxygen source can be air or a mixed gas containing oxygen. The oxidation reaction of cumene is a free radical reaction, and generally no catalyst is required. However, in order to control the acid content in the reactor as much as possible, some alkaline substances can also be added. There are many kinds of these alkaline additives, mainly alkali metals and amines, such as NaOH, Na2CO3, NH4OH, and organic amines. The oxidizing liquid flowing out from the oxidation reaction will contain a small amount of impurities such as organic acid and water, which need to be removed. The commonly used method is to perform alkali washing and water washing on the oxidizing liquid, and the process of removing water is usually carried out simultaneously with the process of concentrating the oxidizing liquid. This is because cumene and water are azeotropic. Therefore, during the concentration process of the oxidizing liquid, water and a part of cumene will be evaporated to the top of the tower, and the cumene hydroperoxide in the bottom of the tower will be concentrated to obtain dry and relatively high concentration cumene hydroperoxide.

[0054] Preferably, in step S1, the oxidation reaction stage is 3 to 6, the oxidation reaction temperature is 90 to 130° C., and the temperature of at least one oxidation reaction is ≥120° C. After the oxidation reaction, the concentration of cumene hydroperoxide is concentrated, and the concentration of cumene hydroperoxide after concentration is increased by no more than 20%, preferably no more than 10%.

[0055] Preferably, if Figure 2 As shown, in step S1, the reaction heat of the oxidation reaction is removed by an external circulating cooler, and two circulating coolers are provided in parallel, one for recovering the oxidation reaction heat and producing low-pressure steam or hot water as a by-product, and the other for controlling the temperature of the oxidation reaction by cooling with circulating cooling water.

[0056] Principle description: Since the current industrial process of cumene oxidation reaction is basically applied to phenol-acetone production equipment, the post-treatment of cumene hydroperoxide generated by cumene oxidation is to produce phenol and acetone through acid decomposition. Therefore, in order to maximize the selectivity of cumene hydroperoxide and reduce the generation of by-product dimethylbenzyl alcohol (DMBA), the single-pass conversion rate of cumene oxidation in the current industrial process is generally lower than 30wt%, and usually 24-25% is the optimal. Different from this, for the application field of the present invention, in the epoxidation reaction of step b, cumene hydroperoxide is used as an oxidant to undergo epoxidation reaction with propylene, propylene is oxidized to propylene oxide, and the oxidant cumene hydroperoxide is reduced to α,α-dimethylbenzyl alcohol, which is the main by-product of the cumene oxidation reaction. This shows that strict control of α,α-dimethylbenzyl alcohol, the main by-product of cumene oxidation in step a, does not bring significant advantages, because a small increase in the production of α,α-dimethylbenzyl alcohol, a by-product of cumene oxidation in step a, does not significantly affect the content of α,α-dimethylbenzyl alcohol (DMBA) in the liquid phase after epoxidation, and also does not affect the load and hydrogen consumption of the hydrogenolysis unit. Furthermore, the amount of α,α-dimethylbenzyl alcohol (DMBA) generated in step a is very small relative to the amount of α,α-dimethylbenzyl alcohol (DMBA) generated by reduction of cumene hydroperoxide (CHP) in step b. Since the selectivity of cumene hydroperoxide in step a is generally >90%, the amount of α,α-dimethylbenzyl alcohol (DMBA) generated in step a affects the total circulation amount of DMBA by <5-10%. Therefore, the single-pass conversion rate of cumene oxidation in step a can be appropriately increased to reduce the large-scale circulation of cumene, thereby greatly reducing the energy consumption of the CHPPO unit. At the same time, the single-pass conversion rate of the cumene oxidation step in step a cannot be increased indefinitely. Although an excessively high single-pass conversion rate can reduce the overall large circulation of cumene, an excessively high concentration of cumene hydroperoxide material will increase the risk of decomposition. In addition to the increase in the main by-product α, α-dimethylbenzyl alcohol (DMBA), the content of other by-products acetophenone and organic acids will also increase, which in turn increases the material consumption of the device. Therefore, considering the energy consumption and material consumption factors comprehensively, for the CHPPO production device, the appropriate concentration of cumene hydroperoxide in the oxidation liquid flowing out of the cumene oxidation reactor is 30-70%.

[0057] Through the above analysis of α,α-dimethylbenzyl alcohol (DMBA), a by-product of the cumene oxidation reaction in the CHPPO unit, in step a of the present invention, the temperature of the cumene oxidation reaction can be appropriately increased, and while reducing the volume of the reactor, higher-grade heat can be recovered from the cumene oxidation reaction, which is convenient for use by multiple other users, and is not limited to the use of the concentration tower reboiler described in patent CN104447629.

[0058] Compared with the method described in patent CN104447629, the present invention starts from the overall energy consumption reduction of the CHPPO device, improves the single-pass conversion rate of cumene oxidation, reduces the large circulation ratio of cumene, and greatly reduces the energy consumption of the device. This also increases the concentration of cumene hydroperoxide in the oxidation liquid flowing out of the oxidation reactor, so the degree and necessity of concentration are greatly weakened. In other words, the heat required for the concentration of cumene hydroperoxide is much less than the reaction heat of the cumene oxidation reaction. If the cumene oxidation reaction heat is directly recovered according to the method described in patent CN104447629 and used for the concentration operation of cumene hydroperoxide, it is inappropriate, which will cause a large amount of low-pressure steam to be vented and energy waste. At the same time, the present invention further explains the advantages and feasibility of increasing the temperature of the cumene oxidation reaction to 125-130°C, and the recovery of the cumene oxidation reaction heat of the present invention is not directly used for the consumption of the concentration tower, but is used to generate low-pressure steam to enter the steam pipe network, which is conducive to the steam cascade utilization of the entire CHPPO device, with lower energy consumption and more convenient use of recovered heat.

[0059] In the present invention, the temperature of the cumene oxidation reaction is 90-130°C, and the operating temperature of at least one oxidation reactor is ≥120°C. Figure 2 As shown, the heat transfer mode of the oxidation reactor adopts external circulation heat transfer, and each reactor is provided with 2 circulating coolers for heat transfer, one of which is used to recover steam or hot water to reduce the energy consumption of the device, and the other is cooled by circulating water to control the oxidation reaction temperature and ensure the safety of the oxidation reaction. During actual operation, the two circulating coolers operate at the same time, but the flow rates entering the circulating coolers are different. While recovering as much oxidation reaction heat as possible, if the temperature of the oxidation reactor has an increasing trend, more materials are sent to the circulating water cooler, and more cold is input into the oxidation reactor to ensure that the temperature in the reactor is stable. Compared with the two coolers described in patent CN104447629, the present invention can avoid rapid scaling on the circulating water side of the cooler located after the heat collector when the series arrangement is performed. In order to ensure that there is sufficient cooling capacity when the temperature of the cumene oxidation reaction rises, the heat exchange area of ​​the circulating water cooler is designed to be larger when designing the circulating cooler of cumene. In the series design, the normal heat transfer load of the circulating water cooler placed after the process is very small, and only a small amount of circulating water is needed to complete the process operation, but a small amount of circulating water will cause the circulating water flow rate to be too low, and the heat exchanger is very easy to scale. The two circulating coolers of the present invention are arranged in parallel, and the temperature of the oxidation reactor is adjusted by adjusting the ratio of the process materials entering the two coolers, which can ensure the recovery of the oxidation reactor and the safety of the oxidation reaction operation, and also prevent the problem of the circulating water structure.

[0060] Regarding step S2, it is an epoxidation process, in which the cumene hydroperoxide solution obtained in step S1 is used as an oxidant, propylene is oxidized to produce propylene oxide, and cumene hydroperoxide is reduced to α,α-dimethylbenzyl alcohol. This reaction requires the participation of a catalyst, usually a Ti / Si-based solid catalyst, and the reaction is carried out in a liquid phase environment, propylene / cumene hydroperoxide = 5-15 mol / mol, the reaction temperature is 50-150°C, the reaction pressure is 3-10 MPa, and the reaction conversion rate of cumene hydroperoxide is generally >99%.

[0061] The epoxidation reaction is an exothermic reaction. The heat released by the epoxidation reaction of each mole of CHP and propylene is 188.393 kJ. Therefore, it is very important to remove the heat of the epoxidation reaction in time, otherwise it will cause over-temperature decomposition or even a temperature runaway accident. The method of removing the heat of the epoxidation reaction can be to use a multi-stage adiabatic fixed bed reactor in series, and set up interstage circulating water to remove the heat of the reaction. There is also a method of using a shell-and-tube isothermal reactor to directly remove the heat medium from the shell side. See patent CN112174914. One of the advantages of the present invention is to recover the heat of the reaction released by the epoxidation reaction and utilize it, thereby reducing the production energy consumption of the CHPPO device. The heat of the epoxidation reaction can be recovered by using the shell-and-tube isothermal reactor disclosed in patent CN107855078B. The catalyst is placed in the reaction tube, and a heat transfer medium is used outside the tube to remove the heat of the epoxidation reaction. Common heat transfer media include water, methanol, thermal oil, etc. Since the main raw material of the CHPPO device is propylene, propylene can also be used as a heat transfer medium for the epoxidation reaction, which is easier to obtain than traditional heat transfer media.

[0062] After the epoxidation reaction is completed, the excess propylene in the epoxidation liquid is first recovered. In order to reduce the energy consumption of propylene recovery, the energy-saving method of recycling propylene recovery disclosed in patent CN112479800 can be adopted. The recovered epoxidation liquid enters the distillation tower, and crude propylene oxide is obtained at the top of the tower after separation, which is sent to the propylene oxide refining area to obtain the propylene oxide product after refining; and the mixed liquid phase of crude α,α-dimethylbenzyl alcohol (DMBA) and isopropylbenzene is obtained in the bottom of the tower and sent to the hydrogenolysis unit.

[0063] Preferably, the epoxidation reaction of cumene hydroperoxide and propylene adopts a shell-and-tube reactor, the reaction temperature is 90-120°C, the reaction pressure is 6-7MPa, and the recovery of the epoxidation reaction heat can significantly reduce energy consumption. In the present invention, when a shell-and-tube isothermal reactor is used, the epoxidation reaction heat can be directly recovered in the reactor shell side. When the shell side heat transfer medium is water, 47-150kPaA steam can be directly generated in the shell side, and pressurized to 0.3MPa by a subsequent steam compressor and enter the steam network for use. When propane is used as the heat transfer medium, high-pressure propane gas can be generated on the shell side, which can be used for expander power generation and recovery of epoxidation reaction heat. Compared with the method for recovering reaction heat under 120-250°C and gas phase epoxidation reaction conditions described in patent CN112174914, the present invention is characterized in that the liquid phase epoxidation reaction of cumene hydroperoxide and propylene can also be directly recovered by using water as an introduction when operating at a temperature of <120°C.

[0064] When recovering heat, water is used as the heat transfer medium, the shell side operating temperature is 80-110°C, the operating pressure is 47-150 kPaA, liquid water enters the inlet of the shell side of the epoxidation shell-and-tube reactor, the gas-liquid mixed flow flows out from the outlet of the shell side, enters the steam drum, the saturated liquid water therein is separated and circulated into the shell side of the reactor, and the water vapor flows out from the top of the steam drum, enters the steam compressor to be pressurized to 0.3 MPa, and can be directly used as heating steam; alternatively, propane is used as the heat transfer medium, the shell side operating temperature is 80-95°C, the operating pressure is 3.0-4.0 MPa, liquid propane enters the inlet of the shell side of the epoxidation shell-and-tube reactor, the gas-liquid mixed flow flows out from the outlet of the shell side, enters the steam drum, after the liquid propane therein is separated, the gaseous propane flows out from the top of the steam drum and enters the expander to generate electricity, and the exhaust gas after power generation is condensed by circulating water and pumped into the steam drum for continued circulation, which is described in detail in the following by way of specific embodiments.

[0065] Step S3 is a hydrogenolysis process, in which the epoxidation co-product α,α-dimethylbenzyl alcohol obtained in step S2 is hydrogenolyzed to obtain crude isopropylbenzene. According to the reaction steps, α,α-dimethylbenzyl alcohol can be first dehydrated to produce a-methylstyrene, and then hydrogenated to produce isopropylbenzene; or α,α-dimethylbenzyl alcohol can be directly hydrogenolyzed to produce isopropylbenzene. Compared with the method of first dehydrating and then hydrogenating, although water is generated during the hydrogenolysis of α,α-dimethylbenzyl alcohol, the active components of the hydrogenolysis catalyst are easily lost and deactivated, but the direct hydrogenolysis method is simple, the process is shorter, and the energy consumption is lower. Commonly used active components of hydrogenolysis catalysts are Ru, Rh, Pd, Pt, Ag, Ir, Fe, Cu, Co and Ni, and the carriers are activated carbon and SiO2, TiO2, ZrO2, Al2O3, etc. The hydrogenolysis reaction pressure is generally 0.5-0.8MPa, and the reaction temperature is generally 50-300℃. The hydrogenolysis reactor adopts an adiabatic fixed bed reactor or a tubular fixed bed reactor. The flow direction of the material in the reactor can be from top to bottom, with hydrogen as the continuous phase, or from bottom to top, with hydrogen as the dispersed phase. After the hydrogen enters the reactor and reacts with α,α-dimethylbenzyl alcohol, the excess hydrogen carries out the water and part of the isopropylbenzene generated by the reaction and flows out of the reactor. After condensation, it enters the circulating hydrogen compressor and is compressed and circulated back to the reactor again.

[0066] Preferably, the hydrogenolysis reactor is an adiabatic fixed bed reactor, and hydrogen is used as the dispersed phase, and the flow direction in the reactor is bottom-in and top-out.

[0067] Preferably, the hydrogenolysis reaction temperature is 120-200° C., more preferably 150-200° C., which is conducive to recovering the heat of the hydrogenation reaction while not causing the activity attenuation of the hydrogenation catalyst under high temperature conditions.

[0068] Preferably, a direct hydrogenation scheme is adopted, and a high hydrogen-to-hydrocarbon ratio of 3 to 30 is used, so that the water generated by the reaction can enter the gas phase and be quickly removed from the reactor, preventing excessive liquid water from causing rapid deactivation of the catalyst, avoiding the problem of too short catalyst life during direct hydrogenolysis, and also avoiding the increase in energy consumption when using the method of first dehydrating and then hydrogenating.

[0069] Preferably, the condensation of the circulating hydrogen adopts 2 to 5 stages of condensation to recover as much heat of the hydrogenolysis reaction as possible. In a preferred embodiment of the present invention, 3 stages of condensation are adopted, the first stage is condensed to 130 to 150°C, and the heat at a higher temperature in the circulating hydrogen is used to produce 0.06 to 0.3 MPa of steam as a by-product, and the circulating hydrogen is condensed to 90 to 100°C every 2 stages, and the heat at a medium temperature in the circulating hydrogen is used to produce 85 to 95°C hot water as a by-product, and finally the circulating hydrogen is cooled to 40 to 50°C, and the water in the circulating hydrogen is removed as much as possible to avoid excessive circulation of water in the hydrogenolysis reaction. The cascade condensation of the circulating hydrogen flowing out of the reactor can recover a large amount of heat of the hydrogenolysis reaction.

[0070] Preferably, part of the liquid phase material flowing out of the hydrogenolysis reactor is returned to the hydrogenolysis reactor for further reaction, and the return amount / discharge amount=0.1-10, so as to improve the single-pass conversion rate of the hydrogenolysis reaction, and the total conversion rate of α,α-dimethylbenzyl alcohol in the hydrogenolysis reaction zone is greater than 90%, more preferably greater than 95%, which can effectively improve the conversion rate of α,α-dimethylbenzyl alcohol and reduce the energy consumption of cumene refining.

[0071] Step S4 is a cumene refining process. The cumene refining process is to purify the crude cumene obtained in step S3 to meet the feed requirements of the cumene oxidation process in step S1.

[0072] Since the crude cumene after hydrogenolysis contains, in addition to a large amount of cumene, α,α-dimethylbenzyl alcohol, ethylbenzene, butylbenzene, phenol, acetophenone, propanol, isopropanol, 1,2-propylene glycol, methanol, acetone, H2, water, dimethyldiphenylbutane, tar, etc., the main impurities can be removed by distillation. After passing through a light component removal tower, light components such as ethylbenzene, propanol, isopropanol, methanol, acetone, H2, and water are removed; after passing through a heavy component removal tower, heavy components such as α,α-dimethylbenzyl alcohol, butylbenzene, acetophenone, propylene glycol, dimethyldiphenylbutane, tar are removed; finally, cumene is washed with alkali to remove phenol, and the recycled cumene that meets the requirements of step a) is obtained. At the same time, the heavy components can also be removed first.

[0073] The process of removing light components and then removing phenol by alkali washing can achieve the purification of cumene, as can the process of first removing light components, then removing heavy components and finally removing phenol. Alkali washing can use organic amines such as NaOH, Na2CO3, and ethanolamine as neutralizing agents, and the alkali washing equipment can use stirring tanks, static mixers, extraction towers, etc.

[0074] Preferably, the process of first removing the heavy components, then removing the light components and finally alkali washing is adopted.

[0075] The process of first removing heavy components and then removing light components is adopted. The de-heavy tower adopts a thermal coupling scheme. The tower bottom uses 1.0-4.0MPa steam to heat the reboiler. The top condenser produces 0.3-2.0MPa steam by-product, which can directly recover heat for other heating users. This makes the operation of removing heavy components of isopropylbenzene basically without consuming steam latent heat, because the steam heat injected into the tower bottom is recovered at the top of the tower. In addition, compared with the process of first removing light components and then removing heavy components, the steam produced by the de-heavy tower can be used in the de-light tower, which is more advantageous in terms of device operation and energy configuration.

[0076] The top of the de-heavy tower is separated to obtain isopropylbenzene without α,α-dimethylbenzyl alcohol, and the bottom of the tower retains 10-80% of isopropylbenzene, and the rest is α,α-dimethylbenzyl alcohol and heavier components. The crude isopropylbenzene containing light components separated from the top of the de-heavy tower enters the light-removal tower to separate ethylbenzene and other lighter components, and crude ethylbenzene is obtained from the top of the light-removal tower, and ethylbenzene by-product is obtained after refining; the material at the bottom of the de-heavy tower enters the alcohol recovery tower, removes components heavier than α,α-dimethylbenzyl alcohol, and then returns to the hydrogenolysis reactor to continue the reaction. The isopropylbenzene obtained from the top of the light-removal tower is washed with alkali to remove phenol and then returned to step S1.

[0077] Embodiment 1:

[0078] According to the method described in this specification, taking a 100,000 ton / year CHPPO unit as an example, an oxidation step, an epoxidation step, a hydrogenolysis step, and an isopropylbenzene refining step are implemented. Figure 1 .

[0079] In the oxidation process, liquid cumene enters the oxidation reactor and contacts the air entering the bottom of the oxidation reactor to react and generate a reaction mixture of cumene hydroperoxide. The oxidation reactor is connected in series in three stages, and the reaction temperature is gradually reduced to 125°C, 112°C, and 98°C, respectively. Each reactor is equipped with a circulating pump and two parallel circulating coolers to remove the heat of the oxidation reaction. One of the two circulating coolers is used to generate steam, and the other is cooled with circulating water for regulating the reaction temperature and emergency cooling. This can not only recover the reaction heat of the oxidation reaction, but also ensure the effective control of the reaction temperature. After three oxidation reactors, the concentration of cumene hydroperoxide in the liquid phase at the outlet of the third-stage reactor is about 48%, the concentration of α,α-dimethylbenzyl alcohol is about 5%, and the concentration of acetophenone is ~1%. The heat of the oxidation reaction is recovered, and steam is produced as a by-product. The first reactor can be directly steamed, and the steam produced by the second and third reactors needs to be pressurized by a steam compressor. The total heat release of the oxidation reaction is 5902kW, and a total by-product is 5.2t / h (about 3240kW) of steam at 160kPaa and 113°C, with an oxidation heat recovery rate of about 55%.

[0080] In the epoxidation process, the reaction liquid containing cumene hydroperoxide obtained in the oxidation step is mixed with liquid propylene and then fed into the epoxidation reactor. The epoxidation reactor is a shell-and-tube isothermal reactor with a Ti-based solid catalyst in the tube. The reaction temperature is 110°C and the reaction pressure is 5.2MPag. The feed passes through the epoxidation catalyst bed, propylene is oxidized to propylene oxide, and the cumene hydroperoxide as an oxidant is reduced to α,α-dimethylbenzyl alcohol. At the same time, trace by-products such as phenol, acetone, acetophenone, and organic acids are also generated. The shell side of the epoxidation shell-and-tube reactor uses water to transfer heat. The reaction heat of the epoxidation reaction in the tube vaporizes the water part on the shell side into a water-vapor mixture, which enters the drum and separates the water vapor. The liquid water returns from the bottom of the drum and enters the epoxidation reactor. Since the density of the water phase is greater than the density of the water / vapor mixture on the shell side of the reactor, a thermal siphon cycle can be formed, and no additional circulation pump is required, saving power consumption. The steam pressure flowing out of the drum outlet is 120kPaa, which is not enough to be directly sent to other heat users. Therefore, this steam is pressurized to 160kPaa by the compressor and sent to other users of the CHPPO device. For this embodiment, the heat of epoxidation reaction is 6731KW, and about 11.0 tons of steam with a pressure of 160kPaa and a temperature of 113°C are produced per hour. Since the epoxidation reaction is not 100% carried out in the shell-and-tube reactor, the recovery rate of the heat of epoxidation reaction is 90-95%. Since the CHPPO device includes distillation towers such as PO refining and CHP concentration, it is not necessary or cannot be operated at too high a temperature, so the steam produced by epoxidation can be used, which significantly reduces energy consumption. The mixture after the epoxidation reaction contains excess propylene that has not been completely reacted, propylene oxide and α, α-dimethylbenzyl alcohol generated by the reaction, and cumene brought in by oxidation step a. First, propylene is recovered from the epoxidation liquid, and then propylene oxide is roughly separated from the mixture. After refining, the propylene oxide product can be obtained. The final remaining material is a mixture rich in α,α-dimethylbenzyl alcohol and isopropylbenzene.

[0081] In the hydrogenolysis process, a Cu-based hydrogenolysis catalyst is used to directly hydrogenolyze the residual mixture rich in α,α-dimethylbenzyl alcohol and cumene obtained in the epoxidation process, and α,α-dimethylbenzyl alcohol is converted into cumene to obtain crude cumene. After the crude cumene passes through the heavy tower and the light tower to remove α,α-dimethylbenzyl alcohol and ethylbenzene, the phenol is removed by alkali washing to obtain refined circulating cumene, which is returned to the peroxidation process. The liquid material flows into the hydrogenolysis reactor from the bottom liquid phase, and the circulating hydrogen bubbles from the bottom of the hydrogenolysis reactor, passes through the catalyst bed and is discharged from the top of the reactor. The discharged hydrogen has a temperature of 160-190°C, is first cooled to 130°C to produce 160kPaa low-pressure steam, and then continues to cool to 90°C to recover hot water. Finally, after condensing to 40-50°C, it enters the circulating hydrogen compression and pressurization, and is mixed with new hydrogen and then returned to the hydrogenolysis reactor. The hydrogenolysis liquid phase at 160-190°C passes through a circulation pump, and the circulating part is cooled to 150°C before returning to the hydrogenolysis reactor, and the discharged part is directly sent to the separation process without cooling. In order to ensure a high conversion rate of the hydrogenolysis reaction and reduce the separation energy consumption of the hydrogenolysis liquid, the circulation ratio of the hydrogenolysis reaction liquid (circulating liquid / discharged liquid) is 4. For this embodiment, the heat of the hydrogenolysis reaction is 5609KW, and about 2.2 tons of steam and about 274 tons of hot water are produced as byproducts per hour, and the recovery rate of the hydrogenolysis heat is about 85%.

[0082] In the cumene refining process, the crude cumene after hydrogenolysis is removed from the heavy components such as dimethylbenzyl alcohol in the de-heavy distillation tower. The operating pressure at the top of the de-heavy tower is 135kPaa, and the tower bottom reboiler is heated by 1.0MPag steam, with a usage of ~17.5t / h. The de-heavy tower top condenser produces 14.1t / h of 0.3MPag steam. The de-heavy cumene enters the light component removal tower to remove the light components, and then returns to the oxidation reactor to continue the reaction after alkaline washing to remove phenol.

[0083] In this embodiment, the single-pass conversion rate of cumene in the oxidation reactor is 50%, and the concentration of the oxidizing liquid obtained is 48%. Compared with the conventional 24% cumene hydroperoxide oxidizing liquid, the circulation amount of cumene is reduced by about 50%, which greatly reduces the energy consumption of the epoxidation process, hydrogenolysis process and cumene refining process in which a large amount of circulating cumene is involved, except for the PO refining and by-product ethylbenzene refining processes. Since the circulation amount of cumene in these three processes is reduced by about 50%, the energy consumption of these three steps is also reduced by about 50%.

[0084] Embodiment 2:

[0085] See also Figure 2 The reaction heat of epoxidation is recovered by propane and used for power generation, and the remaining steps are the same as those in Example 1.

[0086] The reaction temperature on the tube side of the epoxidation reactor is 110°C, and the heat transfer medium on the shell side is propane. The operating pressure of the liquid propane flowing out from the bottom of the drum is 4.0MPag, and the saturation temperature is ~95°C. It enters the bottom of the shell side, absorbs the heat of the epoxidation reaction in the tube, and then vaporizes, flows out from the upper part of the shell side of the reactor, and enters the drum. After the liquid propane is separated from the drum, 414t / h of gaseous propane enters the expander, driving the expander to generate ~2704kw. The pressure of the gaseous propane is reduced to 1.5Mpag. After being cooled to 40°C by circulating water, it is pressurized by the pump and returned to the drum to continue the cycle.

[0087] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for producing propylene oxide with low energy consumption by using cumene, characterized in that: The following steps are involved: S1, an oxidation step, reacting cumene with an oxygen-containing gas in a gas-liquid bubbling bed reactor to obtain cumene hydroperoxide with a concentration of 30-70%, and after removing organic acid and water to remove impurities, obtaining dry cumene hydroperoxide; S2, an epoxidation step, reacting dried cumene hydroperoxide with propylene in a tubular fixed bed reactor, recovering excess propylene from the epoxide material after the reaction, and then separating to obtain crude propylene oxide and crude α,α-dimethylbenzyl alcohol, and refining the crude propylene oxide to obtain a propylene oxide product; S3, a hydrogenolysis step, converting crude α,α-dimethylbenzyl alcohol (DMBA) into crude cumene by hydrogenolysis reaction with hydrogen; S4, refining cumene, removing heavy components, light components and alkali washing from crude cumene, removing impurities therein and using it as the cumene raw material in step S1; The oxidation reaction heat, epoxidation reaction heat and hydrogenolysis reaction heat in steps S1-S3 are recovered, and the recovery rate of the reaction heat is ≥50%.

2. The method for producing propylene oxide with low energy consumption by using cumene as claimed in claim 1, characterized in that: In step S1, the oxidation reaction stage is 3 to 6, and the oxidation reaction temperature is 90 to 130°C.

3. A method for producing propylene oxide with low energy consumption by using cumene as claimed in claim 2, characterized in that: Each stage of the oxidation reactor is connected to a circulating heat recovery device, which includes a circulating pump, a first circulating cooler arranged in parallel for recovering oxidation reaction heat, and a second circulating cooler for controlling the oxidation reaction temperature.

4. The method for producing propylene oxide with low energy consumption by using cumene as claimed in claim 1, characterized in that: In step S2, the epoxidation reaction temperature of cumene hydroperoxide and propylene is 90-120° C., and the reaction pressure is 6-7 MPa.

5. The method for producing propylene oxide with low energy consumption by using cumene as claimed in claim 1, characterized in that: The shell-and-tube fixed bed reactor is connected to an epoxidation reaction heat recovery device, which includes a steam drum, a heat exchange fluid outlet of the steam drum is connected to a shell-side inlet of the shell-and-tube fixed bed reactor, and a shell-side outlet of the shell-and-tube fixed bed reactor is connected to a heat exchange fluid inlet of the steam drum.

6. The method for producing propylene oxide with low energy consumption by using cumene as claimed in claim 5, characterized in that: The heat exchange fluid is water, and the epoxidation reaction heat recovery device also includes a steam compressor connected to the top of the steam drum.

7. The method for producing propylene oxide with low energy consumption by using cumene as claimed in claim 5, characterized in that: The heat exchange fluid is propylene, and the epoxidation reaction heat recovery device also includes an expander connected to the top of the steam drum. The exhaust gas flowing out of the gas outlet of the expander is condensed by circulating water and then connected to the steam drum through a pump.

8. The method for producing propylene oxide with low energy consumption by using cumene as claimed in claim 1, characterized in that: In step S3, hydrogen is used as a dispersed phase, and the flow direction in the hydrogenolysis reactor is bottom-in and top-out. The hydrogenolysis reaction temperature is 120-200° C., and the hydrogen / hydrocarbon ratio of the hydrogenolysis reaction is 3-30 mol.

9. The method for producing propylene oxide with low energy consumption by using cumene as claimed in claim 1, characterized in that: In step S3, the gas phase fluid at the top of the hydrogenolysis reactor is returned to the hydrogenolysis reactor after three-stage condensation, the first stage condensation temperature is 130-150° C., the second stage condensation temperature is 90-100° C., and the third stage condensation temperature is 40-50° C., a part of the liquid phase material of the hydrogenolysis reactor is discharged, and the other part is returned to the hydrogenolysis reactor, and the return amount / discharge amount=0.1-10.

10. The method for producing propylene oxide with low energy consumption by using cumene as claimed in claim 1, characterized in that: In step S4, a process of first removing heavy components, then removing light components, and finally alkali washing is adopted. The top of the heavy removal tower is separated to obtain cumene without α,α-dimethylbenzyl alcohol, and 10-80% of cumene is retained in the bottom of the tower, and the rest is α,α-dimethylbenzyl alcohol and heavier components. The crude cumene containing light components separated from the top of the heavy removal tower enters the light removal tower to separate ethylbenzene and other lighter components therein, and crude ethylbenzene is obtained from the top of the light removal tower, and ethylbenzene by-product is obtained after refining; the material at the bottom of the heavy removal tower enters the alcohol recovery tower, and after removing components heavier than α,α-dimethylbenzyl alcohol, it returns to the hydrogenolysis reactor to continue the reaction. The cumene obtained from the top of the light removal tower is washed with alkali to remove phenol therein and then returns to step S1. The bottom of the heavy removal tower is heated by 1.0-4.0MPa steam for reboiler heating, and the by-product of the top condenser is 0.3-2.0MPa steam.

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