A method for producing propylene oxide with low energy consumption by the cumene process

Abstract

The present invention discloses a method for producing propylene oxide with low energy consumption by the cumene method, which includes: S1 reacting cumene with an oxygen-containing gas in a gas-liquid bubble column reactor to obtain an oxidation liquid with a cumene hydroperoxide concentration of 30-70%, and obtaining dry cumene hydroperoxide after removing impurities; S2 reacting the dry cumene hydroperoxide with propylene in a shell-and-tube fixed-bed reactor, and first recovering the excessive propylene from the obtained epoxidation material, and then obtaining propylene oxide and crude α,α-dimethylbenzyl alcohol through separation and purification; S3 subjecting the crude α,α-dimethylbenzyl alcohol to a hydrogenolysis reaction with hydrogen to be converted into crude cumene; S4 subjecting the crude cumene to removal of heavy components, removal of light components and alkali washing, and returning it to step S1 after removing the impurities therein. By increasing the oxidation depth of cumene in the oxidation unit, the present invention greatly reduces the circulation amount of cumene and significantly reduces the energy consumption of the device, and improves the economy of the device.

Description

Technical Field

[0001] The present invention relates to the field of chemical engineering, and particularly to an industrial technology for producing propylene oxide by the cumene method with low energy consumption. Background Art

[0002] Propylene oxide is an important organic chemical intermediate, mainly used in the production of polyether polyols, propylene glycol, and propylene glycol ethers. Its production and consumption are second only to polypropylene, making it the second largest derivative of propylene. Currently, 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 for propylene oxide (HPPO), and the cumene method for propylene oxide (CHPPO).

[0003] The POSM method and the POMTBE method can not only produce propylene oxide and styrene or MTBE simultaneously, but also have better economics due to the value addition of their co-products. However, the sales of a large amount of co-products also bring greater sales pressure to the production unit. In contrast, the HPPO method and the CHPPO method do not produce co-products, thus avoiding this problem. However, due to the lack of economic value addition of co-products, the production costs of these two methods have been relatively high. Especially for HPPO, in addition to the high production cost, the safety problem of its unit also poses a major challenge.

[0004] The process for producing propylene oxide (PO) by the CHPPO method 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 reacts with propylene in epoxidation to form propylene oxide (PO) and α,α-dimethylbenzyl alcohol (DMBA);

[0007] (3) DMBA undergoes hydrogenolysis or dehydration / hydrogenation reaction to form cumene and is returned to step (1).

[0008] Subsequently, in order to reduce the production cost of the PO unit by the CHPPO method, research has been carried out 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. propose to react all or part of α,α-dimethylbenzyl alcohol with CHP to form dicumyl peroxide (DCP), increasing the comprehensive benefits of the CHPPO unit; the other aspect is to directly reduce the material consumption and production energy consumption of the CHPPO unit.

[0009] The patent CN104447629 of Sinopec Shanghai Engineering Co., Ltd. discloses a method for by - product steam production in the oxidation unit of a propylene oxide plant. This method adds a heat extraction device in front of the circulating cooler in the oxidation unit to recover the heat of the oxidation liquid to generate steam, and these steams are then used for the reboiler of the concentration tower, thus saving steam consumption. Another patent CN104402843 of this company introduces a new method for reducing the energy consumption of the oxidation unit in a propylene oxide plant. This method changes the power source of the circulating cooling system from a circulating pump to utilize 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, thereby saving electrical energy.

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

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

[0012] China Petroleum & Chemical Corporation reported a method for low - energy - consumption recovery of propylene from epoxidation products in the patent CN105272939. This method adds a flash tank to reduce the energy consumption of propylene recovery. Another patent CN105272941 of this company points out that the high - pressure propylene tower and the low - pressure propylene tower for propylene recovery should operate at a lower pressure. 60 - 95 wt% of the 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 requires a refrigerant at a lower temperature, compared with the prior art, this patented technology can reduce energy consumption by up to 60%.

[0013] Wanhua's patented invention authorization CN110437117 points out that since cumene is oxidized to form CHP, CHP will further undergo a tandem side reaction, resulting in a decrease in the selectivity of CHP. Therefore, in the industrial process, the single-pass conversion rate of cumene is generally lower than 30 wt%. Cao Gang pointed out in the monograph "Production of Phenol and Acetone by Cumene Process" on pages 168-169 that the current oxidation depth of industrial plants is generally about 25%. In the phenol and acetone technologies of UOP and KBR, the oxidation depth of cumene is the cumene hydroperoxide concentration of 24 wt% (Zhong Zhaolong. Process Technology Analysis and Comparison of Phenol / Acetone Plant [J]. Anhui Chemical Industry. 2021, 47(2). 81-85). The oxidation section of the UOP phenol and acetone process uses a 4-stage oxidation reaction, and the CHP concentration in each stage is increased step by step by 6 wt%. The oxidation section of the KBR phenol and acetone process uses 6 towers in series, and the CHP concentration is increased step by step by 4 wt%. Finally, the CHP concentration at the outlet of the reactor is 24% in both cases.

[0014] Generally speaking, the production consumption of existing CHPPO technology is still relatively high. The discussion on the oxidation depth of cumene is also based on the application of phenol and acetone plants, and there is no discussion based on the application of the cumene process for propylene oxide plant (CHPPO). Therefore, it is necessary to develop a more efficient and energy-saving CHPPO process. Summary of the Invention

[0015] The main purpose of this application is to provide a method for producing propylene oxide with low energy consumption by the cumene process, by appropriately increasing the single-pass conversion rate of cumene oxidation in step S1 to reduce the large-scale recycling of cumene and significantly reduce the energy consumption of the CHPPO plant.

[0016] To achieve the above purpose, in the first aspect, this application provides a method for producing propylene oxide with low energy consumption by the cumene process, including the following steps:

[0017] S1. Oxidation step: React cumene with an oxygen-containing gas in a gas-liquid bubbling bed reactor to obtain cumene hydroperoxide with a concentration of 30-70%. After removing organic acids and water to remove impurities, dry cumene hydroperoxide is obtained.

[0018] S2. Epoxidation step: React dry cumene hydroperoxide with propylene in a shell-and-tube fixed-bed reactor. After the reaction, the epoxidation material is first recovered for the excessive propylene, and then separated to obtain crude propylene oxide and crude α,α-dimethylbenzyl alcohol. The crude propylene oxide is refined to obtain propylene oxide product.

[0019] S3. Hydrogenolysis step: React crude α,α-dimethylbenzyl alcohol (DMBA) with hydrogen to undergo a hydrogenolysis reaction to convert it into crude cumene.

[0020] S4. Cumene refining: The crude cumene is subjected to removal of heavy components, removal of light components, and caustic washing to remove impurities therein, and then used as the cumene raw material in step S1.

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

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

[0023] Optionally, each oxidation reactor is connected with a circulating heat recovery device, and the circulating heat recovery device includes a circulating pump, a first circulating cooler arranged in parallel for recovering the heat of oxidation reaction, 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 tubular fixed - bed reactor is connected with an epoxidation reaction heat recovery device, and the epoxidation reaction heat recovery device includes a steam drum. The heat - exchange fluid outlet of the steam drum is communicated with the shell - side inlet of the tubular fixed - bed reactor, and the shell - side outlet of the tubular fixed - bed reactor is communicated with 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 includes a steam compressor communicated with the top of the steam drum.

[0027] Optionally, the heat - exchange fluid is propylene, and the epoxidation reaction heat recovery device further includes an expander communicated with the top of the steam drum. The exhausted gas flowing out from 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 the dispersed phase, and its flow direction in the hydrogenolysis reactor is from bottom to top. 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 condensed in three stages and then returned to the hydrogenolysis reactor. 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. 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 caustic washing is adopted. The cumene without α,α-dimethylbenzyl alcohol is separated from the top of the heavy component removal column. 10-80% of the cumene is retained in the bottom of the column, and the rest are α,α-dimethylbenzyl alcohol and heavier components. The crude cumene containing light components separated from the top of the heavy component removal column enters the light component removal column, where ethylbenzene and other lighter components are separated out. The crude ethylbenzene is obtained from the top of the light component removal column and is refined to obtain ethylbenzene by-products. The material at the bottom of the heavy component removal column enters the alcohol recovery column. After removing components heavier than α,α-dimethylbenzyl alcohol, it returns to the hydrocracking reactor for continuous reaction. The cumene obtained from the top of the light component removal column is caustic washed to remove phenol therein and then returned to step S1. The bottom of the heavy component removal column is heated by a reboiler with 1.0-4.0 MPa steam, and the by-product of the top condenser is 0.3-2.0 MPa steam.

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

[0032] 1. When performing 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 circulation of cumene, the purpose of significantly reducing the energy consumption of the CHPPO device is achieved, 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 increasing the temperature of the cumene oxidation reaction and reducing the reactor volume, higher-grade heat can be recovered from the cumene oxidation reaction, which is convenient for other multiple users of the CHPPO device.

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

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

[0036] 5. In step S4, a process of first removing heavy components and then removing light components is adopted. The heavy component removal tower adopts a heat integration scheme. The reboiler at the bottom of the tower is heated by steam at 1.0 - 4.0 MPa, and the top condenser by-product steam is at 0.3 - 2.0 MPa, which can directly recover heat for use by other heating users. This makes the operation of removing heavy components of cumene basically consume no latent heat of steam because the heat of the steam injected at the bottom of the tower is recovered at the top. In addition, compared with the process of first removing light components and then removing heavy components, the by-product steam of the heavy component removal tower can be used for the light component removal tower, which is more advantageous in terms of device operation and energy configuration. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The drawings forming a part of this application are used to provide a further understanding of this application, making other features, objectives, and advantages of this application more obvious. The schematic embodiments and their descriptions of this application are used to explain this application and do not constitute an improper limitation of this application. In the drawings:

[0038] Figure 1 is a schematic flow diagram of the present invention (Example 1);

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

[0040] Figure 3 is a schematic diagram of heat recovery of the epoxidation reaction (Example 2). DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] In order to enable those skilled in the art to better understand the solution of this application, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of this application.

[0042] It should be noted that the terms "first", "second", etc. in the specification, claims, and above-mentioned drawings of this application are used to distinguish similar objects and do not necessarily describe a specific order or sequence. It should be understood that such used data can be interchanged under appropriate circumstances for the embodiments of this application described here. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units does not necessarily limit to those clearly listed steps or units, but may include other steps or units not clearly listed or inherent to these processes, methods, products, or devices.

[0043] In this application, the orientation or positional relationship indicated by terms such as "upper", "lower", "left", "right", "front", "rear", "top", "bottom", "inner", "outer", "middle", "vertical", "horizontal", "lateral", "longitudinal", etc. is based on the orientation or positional relationship shown in the drawings. These terms are mainly used to better describe this application and its embodiments, and are not used to limit that the indicated devices, elements or components must have a specific orientation, or be constructed and operated in a specific orientation.

[0044] Moreover, in addition to being able to represent the orientation or positional relationship, some of the above terms may also be used to represent other meanings. For example, the term "upper" may also be used to represent a certain attachment relationship 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 meaning of the term "plurality" should be two or more.

[0046] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The following will refer to the drawings and combine with embodiments to detail this application.

[0047] A method for low-energy consumption production of propylene oxide by the cumene method, comprising the following steps:

[0048] S1. Oxidation step: React cumene with an oxygen-containing gas in a gas-liquid bubble column reactor to obtain cumene hydroperoxide with a concentration of 30-70%. After removing organic acids and water to remove impurities, dry cumene hydroperoxide is obtained;

[0049] S2. Epoxidation step: React dry cumene hydroperoxide with propylene in a shell-and-tube fixed-bed reactor. After the reaction, the epoxidation material is first recovered of the excessive propylene, and then separated to obtain crude propylene oxide and crude α,α-dimethylbenzyl alcohol. The crude propylene oxide is refined to obtain a propylene oxide product;

[0050] S3. Hydrogenolysis step: React crude α,α-dimethylbenzyl alcohol (DMBA) with hydrogen to be converted into crude cumene;

[0051] S4. Cumene refining: The crude cumene is subjected to removal of heavy components, removal of light components and caustic washing to remove the impurities therein and used as the cumene raw material in step S1;

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

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

[0054] Preferably, in step S1, the oxidation reaction order is 3 - 6, the oxidation reaction temperature is 90 - 130 °C, and the temperature of at least one stage of the oxidation reaction ≥ 120 °C. After the oxidation reaction, the concentration of cumene hydroperoxide is concentrated, and the increase in the concentration of cumene hydroperoxide after concentration is not more than 20%, preferably not more than 10%.

[0055] Preferably, as Figure 2 shown, in step S1, the reaction heat of the oxidation reaction is removed by an external circulating cooler, and there are 2 circulating coolers, which are arranged in parallel. One is used to recover the oxidation reaction heat and by-product low-pressure steam or hot water, and the other is used to control the temperature of the oxidation reaction and is cooled by circulating cooling water.

[0056] Principle description: Since the current industrial process of cumene oxidation is basically applied to phenol and acetone production plants, the post-treatment of cumene hydroperoxide produced 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 formation of by-product dimethylbenzyl alcohol (DMBA), the single-pass conversion rate of cumene oxidation in the current industrial process is generally less than 30 wt%, and usually 24-25% is optimal. In contrast, for the application field of the present invention, in the epoxidation reaction of step b, cumene hydroperoxide is used as an oxidant to react with propylene in an epoxidation reaction, and propylene is oxidized to propylene oxide, while the oxidant cumene hydroperoxide is reduced to α,α-dimethylbenzyl alcohol, which is exactly the main by-product of the cumene oxidation reaction. This shows that strict control of the main by-product α,α-dimethylbenzyl alcohol in the cumene oxidation in step a does not bring significant advantages, because a small increase in the production amount of α,α-dimethylbenzyl alcohol, the by-product of cumene oxidation in step a, will not significantly affect the content of α,α-dimethylbenzyl alcohol (DMBA) in the liquid phase after epoxidation, nor will it affect the load and hydrogen consumption of the hydrogenolysis unit. Further, the amount of α,α-dimethylbenzyl alcohol (DMBA) generated in step a is very small compared to the amount of α,α-dimethylbenzyl alcohol (DMBA) reduced from 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 has an impact on the total DMBA recycle amount of <5-10%. Therefore, the single-pass conversion rate of cumene oxidation in step a can be appropriately increased to reduce the large recycle of cumene, significantly reducing the energy consumption of the CHPPO plant. At the same time, the single-pass conversion rate of the cumene oxidation step in step a cannot be increased without limit. Although a too high single-pass conversion rate can reduce the overall large recycle of cumene, a cumene hydroperoxide material with too high a concentration will increase the decomposition risk. In addition to the increase in the main by-product α,α-dimethylbenzyl alcohol (DMBA), the contents of other by-products such as acetophenone and organic acids will also increase, which in turn increases the material consumption of the plant. Therefore, considering the factors of energy consumption and material consumption comprehensively, for the CHPPO production plant, 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 the by-product α,α-dimethylbenzyl alcohol (DMBA) in the cumene oxidation reaction of the CHPPO plant, in step a of the present invention, the temperature of the cumene oxidation reaction can be appropriately increased. While reducing the reactor volume, higher-grade heat can be recovered from the cumene oxidation reaction, which is convenient for use by multiple other users, not limited to the reboiler of the concentration tower described in Patent CN104447629.

[0058] Compared with the method described in Patent CN104447629, the present invention starts from reducing the overall energy consumption of the CHPPO device, improves the single-pass conversion rate of cumene oxidation, reduces the large circulation ratio of cumene, and significantly 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, thus significantly weakening the degree and necessity of concentration. That is to say, the heat required for concentrating cumene hydroperoxide is much less than the reaction heat of cumene oxidation reaction. If the reaction heat of cumene oxidation is directly recovered and used for the concentration operation of cumene hydroperoxide according to the method described in Patent CN104447629, it is inappropriate and will cause a large amount of low-pressure steam to be vented and energy wasted. At the same time, the present invention more specifically explains the advantages and feasibility of increasing the temperature of cumene oxidation reaction to 125-130°C. And the recovery of the reaction heat of cumene oxidation in the present invention is not directly used for the consumption of the concentration tower, but is used to generate low-pressure steam and enter the steam network, which is conducive to the steam cascade utilization of the entire CHPPO device, with lower energy consumption and more convenient use of the recovered heat.

[0059] In the present invention, the temperature of cumene oxidation reaction is 90-130°C, and the operating temperature of at least one oxidation reactor is ≥120°C. As Figure 2 shown, the heat removal method of the oxidation reactor adopts external circulation heat removal. Each reactor is equipped with 2 circulating coolers for heat removal. One of them is used to recover steam or hot water to reduce the energy consumption of the device, and the other uses circulating water for cooling to control the temperature of the oxidation reaction and ensure the safety of the oxidation reaction. During actual operation, the two circulating coolers operate simultaneously, 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 shows an upward trend, more materials will be sent into the circulating water cooler to input more cold energy into the oxidation reactor to ensure the temperature stability in the reactor. Compared with the series setting of 2 coolers described in Patent CN104447629, the present invention can avoid the rapid fouling of the circulating water side of the cooler located behind the heat extractor during series setting. In order to ensure sufficient cooling capacity when the temperature of cumene oxidation reaction increases, the heat transfer area of the circulating water cooler will be designed larger when designing the circulating cooler of cumene. However, during series design, the normal heat removal load of the circulating water cooler located behind the process is very small, and only a small amount of circulating water is required to complete the process operation. But the 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 process materials entering the two coolers, which can ensure the recovery of the oxidation reactor, the operation safety of the oxidation reaction, and at the same time prevent the problem of circulating water fouling.

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

[0061] The epoxidation reaction is an exothermic reaction, and the heat released by the epoxidation reaction of each mole of CHP with propylene is 188.393 kJ. Therefore, it is very important to remove the reaction heat of the epoxidation reaction in a timely manner, otherwise it will cause over-temperature decomposition and even runaway temperature accidents. The method of removing the epoxidation reaction heat can be to use a series of multi-stage adiabatic fixed-bed reactors in series and set up inter-stage circulating water to remove the reaction heat, or a shell-and-tube isothermal reactor can be used to directly remove the heat transfer medium on the shell side to remove the heat of the reactor. For details, please refer to Patent CN112174914. One of the advantages of the present invention is to recover and utilize the reaction heat released by the epoxidation reaction, reducing the production energy consumption of the CHPPO plant. The reaction 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 the heat transfer medium is used outside the tube to remove the reaction heat of the epoxidation reaction. Common heat transfer media include water, methanol, heat transfer oil, etc. Since the main raw material of the CHPPO plant is propylene, propylene can also be used as the heat transfer medium for the epoxidation reaction, which is more easily available compared to traditional heat transfer media.

[0062] After the epoxidation reaction is completed, the excess propylene in the epoxidation liquid is first recovered. To reduce the energy consumption of propylene recovery, the method of energy-saving recycling of propylene recovery disclosed in Patent CN112479800 can be used. After the recovery, the epoxidation liquid enters the distillation column. After separation, crude propylene oxide is obtained at the top of the column and sent to the propylene oxide refining area. After refining, propylene oxide products are obtained; while a mixed liquid phase of crude α,α-dimethylbenzyl alcohol (DMBA) and cumene is obtained at the bottom of the column and sent to the hydrogenolysis unit.

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

[0064] When recovering heat, using water as the heat transfer medium, the operating temperature on the shell side is 80-110 °C, and the operating pressure is 47-150 kPaA. Liquid water enters the inlet on the shell side of the epoxidation shell-and-tube reactor, and the gas-liquid mixed flow flows out from the outlet on the shell side and enters the steam drum. The saturated liquid water is separated and recycled into the shell side of the reactor, while the water vapor flows out from the top of the steam drum and is pressurized to 0.3 MPa by a steam compressor and can be directly used as heating steam; or, using propane as the heat transfer medium, the operating temperature on the shell side is 80-95 °C, and the operating pressure is 3.0-4.0 MPa. Liquid propane enters the inlet on the shell side of the epoxidation shell-and-tube reactor, and the gas-liquid mixed flow flows out from the outlet on the shell side and enters the steam drum. After separating the liquid propane, the gaseous propane flows out from the top of the steam drum and enters the expander for power generation. The exhausted gas after power generation is condensed by circulating water and then pumped into the steam drum for continuous circulation. The following will be introduced in detail by way of specific examples.

[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, a part of the liquid-phase material flowing out of the hydrocracking reactor is returned to the hydrocracking reactor for continuous reaction, and the return amount / discharge amount = 0.1 - 10, so as to improve the single-pass conversion rate of the hydrocracking reaction. The total conversion rate of α,α-dimethylbenzyl alcohol in the hydrocracking reaction zone > 90%, more preferably > 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 the cumene refining process. The cumene refining process is to refine 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 hydrocracking contains, in addition to a large amount of cumene, α,α-dimethylbenzyl alcohol, ethylbenzene, butylbenzene, phenol, acetophenone, propanol, isopropanol, 1,2-propanediol, methanol, acetone, H2, water, dimethyldiphenylbutane, tar, etc., the main impurities can be removed by distillation. Through the light component removal column, light components such as ethylbenzene, propanol, isopropanol, methanol, acetone, H2, water, etc. are removed; through the heavy component removal column, heavy components such as α,α-dimethylbenzyl alcohol, butylbenzene, acetophenone, propylene glycol, dimethyldiphenylbutane, tar, etc. are removed; finally, the cumene is washed with alkali to remove the phenol therein, and the recycled cumene meeting the requirements of step a) is obtained. At the same time, it is also possible to first remove the heavy components,

[0073] then remove the light components, and then wash with alkali to remove phenol. This process, as well as the process of first removing the light components, then removing the heavy components, and finally removing the phenol, can all achieve cumene refining. The alkali washing can use organic amines such as NaOH, Na2CO3, ethanolamine, etc. 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 washing with alkali is adopted.

[0075] Using the process of first removing the heavy components and then removing the light components, the heavy component removal column adopts a heat integration scheme. The reboiler at the bottom of the column is heated by steam at 1.0 - 4.0 MPa, and the top condenser by-product is steam at 0.3 - 2.0 MPa, which can directly recover heat for use by other heating users. This makes the operation of removing heavy components of cumene basically consume no steam latent heat, because the heat of the steam injected at the bottom of the column is recovered at the top. In addition, compared with the process of first removing the light components and then removing the heavy components, the steam by-produced by the heavy component removal column can be used for the light component removal column, which is more beneficial in terms of device operation and energy configuration.

[0076] The cumene separated from the top of the heavy component removal column is free of α,α-dimethylbenzyl alcohol. 10-80% of the cumene is retained at the bottom of the column, and the rest is α,α-dimethylbenzyl alcohol and heavier components. The crude cumene containing light components separated from the top of the heavy component removal column enters the light component removal column, where ethylbenzene and other lighter components are separated out. The crude ethylbenzene obtained from the top of the light component removal column is refined to obtain the by-product ethylbenzene; the material at the bottom of the heavy component removal column enters the alcohol recovery column. After removing components heavier than α,α-dimethylbenzyl alcohol, it returns to the hydrocracking reactor for further reaction. The cumene obtained from the top of the light component removal column is washed with alkali to remove phenol therein and then returned to step S1.

[0077] Example 1:

[0078] According to the method described in this specification, taking a 100,000-ton / year CHPPO plant as an example, the oxidation step, epoxidation step, hydrocracking step, and cumene refining step are implemented. Refer to Figure 1 。

[0079] In the oxidation process, liquid-phase cumene enters the oxidation reactor and contacts the air entering the bottom of the oxidation reactor to react to form a reaction mixture of cumene hydroperoxide. The oxidation reactor is in a 3-stage series connection, and the reaction temperature decreases step by step, being 125 °C, 112 °C, and 98 °C respectively. Each reactor is equipped with a circulation pump and 2 parallel circulation coolers to remove the heat of the oxidation reaction. One of the 2 circulation coolers is used for steam generation, and the other is cooled with circulating water for the adjustment of 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 passing through 3 oxidation reactors, the concentration of cumene hydroperoxide in the liquid phase at the outlet of the 3rd reactor is approximately 48%, the concentration of α,α-dimethylbenzyl alcohol is approximately 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 one can be directly steamed, and the steam produced by the second and third ones needs to be pressurized by a steam compressor. The total exotherm of the oxidation reaction is 5902 kW, and a total of 5.2 t / h (about 3240 kW) of steam at 160 kPaa and 113 °C is produced as a by-product. The oxidation heat recovery rate is approximately 55%.

[0080] In the epoxidation process, the reaction liquid containing cumene hydroperoxide obtained from the oxidation step is mixed with liquid-phase propylene and then fed into an epoxidation reactor. The epoxidation reactor is a shell-and-tube isothermal reactor. Inside the tubes is a Ti-based solid catalyst. The reaction temperature is 110 °C and the reaction pressure is 5.2 MPag. The feed passes through the epoxidation catalyst bed, where propylene is oxidized to propylene oxide, and cumene hydroperoxide as the 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 is cooled by water. The heat of the epoxidation reaction inside the tubes partially vaporizes the water on the shell side into a water-vapor mixture, which enters the steam drum. The water vapor is separated, and the liquid water returns from the bottom of the steam drum back into the epoxidation reactor. Since the density of the water phase is greater than that of the water / vapor mixture on the shell side of the reactor, a thermosyphon circulation can be formed without the need for an additional circulation pump, saving power consumption. The water vapor flowing out of the steam drum has a pressure of 120 kPaa, which is not sufficient to be directly supplied to other heat users. Therefore, this water vapor is pressurized to 160 kPaa by a compressor and then supplied to other users of the CHPPO plant. For this embodiment, the epoxidation reaction heat is 6731 KW, and approximately 11.0 tons of steam with a pressure of 160 kPaa and a temperature of 113 °C will be by-produced per hour. Since the epoxidation reaction does not proceed 100% in the shell-and-tube reactor, the recovery rate of the epoxidation reaction heat is 90 - 95%. Since the CHPPO plant includes distillation towers such as PO refining and CHP concentration and cannot or does not need to operate at too high a temperature, the steam by-produced from epoxidation can just be utilized, significantly reducing energy consumption. The mixture after the epoxidation reaction contains unreacted excess propylene, propylene oxide and α,α-dimethylbenzyl alcohol generated by the reaction, and cumene brought in from the oxidation step a. First, the propylene in the epoxidation liquid is recovered, then propylene oxide is roughly separated from the mixture, and the propylene oxide product can be obtained after refining. Finally, the remaining material is a mixture rich in α,α-dimethylbenzyl alcohol and cumene.

[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. α,α-Dimethylbenzyl alcohol is converted into cumene to obtain crude cumene. After the crude cumene passes through a heavy component removal tower and a light component removal tower to remove α,α-dimethylbenzyl alcohol and ethylbenzene therein, phenol is removed by caustic washing to obtain refined recycled cumene, which is returned to the peroxidation process. The liquid material flows into the hydrogenolysis reactor from the bottom in the liquid phase, and the recycled hydrogen bubbles from the bottom of the hydrogenolysis reactor, passes through the catalyst bed layer, and is discharged from the top of the reactor. The temperature of the discharged hydrogen is 160 - 190°C. It is first cooled to 130°C to produce low-pressure steam of 160 kPaa as a by-product, then further cooled to 90°C to recover hot water, and finally condensed to 40 - 50°C and then enters the recycled hydrogen compressor for pressurization. After mixing with fresh hydrogen, it is returned to the hydrogenolysis reactor. The hydrogenolysis liquid phase at 160 - 190°C passes through a recycle pump. Part of the recycle passes through cooling to 150°C and then returns to the hydrogenolysis reactor, and the part discharged externally directly goes 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 recycle ratio (recycle liquid / discharged liquid) of the hydrogenolysis reaction liquid is 4. For this embodiment, the hydrogenolysis reaction heat is 5609 KW, and about 2.2 tons of steam and about 274 tons of hot water will be produced as by-products per hour, and the recovery rate of the hydrogenolysis heat is about 85%.

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

[0083] In this embodiment, the single-pass conversion rate of cumene in the oxidation reactor is 50%, and the concentration of the oxidation liquid of cumene hydroperoxide obtained is 48%. Compared with the traditional oxidation liquid of cumene hydroperoxide with a concentration of 24%, the recycle amount of cumene is reduced by about 50%. This significantly reduces the energy consumption of the epoxidation process, hydrogenolysis process, and cumene refining process in which a large amount of recycled cumene participates, except for the PO refining and by-product ethylbenzene refining processes. Since the recycle 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] Example Two:

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

[0086] The reaction temperature on the tube side of the epoxidation reactor is 110°C. Propane is used as the heat transfer medium on the shell side. The operating pressure of the liquid-phase propane flowing out from the bottom of the steam drum is 4.0 MPag, and the saturation temperature is ~95°C. It enters the bottom of the shell side, vaporizes after absorbing the heat of the epoxidation reaction in the tube, and flows out from the upper part of the reactor shell side and enters the steam drum. After the liquid-phase propane is separated in the steam drum, 414 t / h of the gas-phase propane enters the expander to drive the expander to generate electricity ~2704 kw. The pressure of the gas-phase propane is reduced to 1.5 MPag, cooled to 40°C by circulating water, and then returned to the steam drum after being pressurized by the pump for continuous circulation.

[0087] The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A method for producing propylene oxide with low energy consumption by the cumene method, characterized in that: It includes the following steps: S1. Oxidation step: React cumene with an oxygen-containing gas in a gas-liquid bubble column reactor to obtain cumene hydroperoxide with a concentration of 30-70%. After removing organic acids and water to remove impurities, dry cumene hydroperoxide is obtained; S2. Epoxidation step: React the dry cumene hydroperoxide with propylene in a shell-and-tube fixed bed reactor. After the reaction, the epoxidation material first recovers the excessive propylene, and then through separation, crude propylene oxide and crude α,α-dimethylbenzyl alcohol are obtained. The crude propylene oxide is refined to obtain propylene oxide products; S3. Hydrolysis step: React the crude α,α-dimethylbenzyl alcohol (DMBA) with hydrogen to be converted into crude cumene. The gas-phase fluid at the top of the hydrolysis reactor returns to the hydrolysis 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. Part of the liquid-phase material of the hydrolysis reactor is discharged, and the other part returns to the hydrolysis reactor. The return amount / discharge amount = 0.1-10; S4. Cumene refining: The crude cumene is subjected to removal of heavy components, removal of light components, and caustic washing to remove the impurities therein and then used as the cumene raw material in step S1; Recover the oxidation reaction heat, epoxidation reaction heat, and hydrolysis reaction heat in steps S1-S3, and the recovery rate of the reaction heat ≥ 50%.

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

3. The method for producing propylene oxide with low energy consumption by the cumene method according to claim 2, characterized in that: Each stage of the oxidation reactor is connected with a circulating heat recovery device. The circulating heat recovery device includes a circulating pump, a first circulating cooler arranged in parallel for recovering the 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 the cumene method according to 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 the cumene method according to claim 1, characterized in that: The shell-and-tube fixed bed reactor is connected with an epoxidation reaction heat recovery device. The epoxidation reaction heat recovery device includes a steam drum. The heat exchange fluid outlet of the steam drum is communicated with 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 communicated with the heat exchange fluid inlet of the steam drum.

6. The method for low - energy - consumption production of propylene oxide by the cumene method according to claim 5, characterized in that: The heat exchange fluid is water, and the epoxidation reaction heat recovery device further includes a steam compressor communicated with the top of the steam drum.

7. The method for producing propylene oxide with low energy consumption by the cumene method according to claim 5, characterized in that: The heat exchange fluid is propylene, and the epoxidation reaction heat recovery device further includes an expander communicated with the top of the steam drum. The exhausted gas flowing out from 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 the cumene method according to claim 1, characterized in that: In step S3, hydrogen is used as the dispersed phase, and its flow direction in the hydrolysis reactor is from bottom to top. The hydrolysis reaction temperature is 120-200 °C, and the hydrogen / hydrocarbon ratio of the hydrolysis reaction is 3-30 mol.

9. The method for producing propylene oxide with low energy consumption by the cumene method according to claim 1, wherein: In step S4, a process of first removing heavy components, then removing light components, and finally performing caustic washing is adopted. The cumene without α,α-dimethylbenzyl alcohol is separated from the top of the heavy component removal tower. 10 - 80% of the cumene is retained at the bottom of the tower, and the rest are α,α-dimethylbenzyl alcohol and heavier components. The crude cumene containing light components separated from the top of the heavy component removal tower enters the light component removal tower, where ethylbenzene and other lighter components are separated out. The crude ethylbenzene is obtained from the top of the light component removal tower and is refined to obtain ethylbenzene by-product; the material at the bottom of the heavy component removal tower enters the alcohol recovery tower. After removing components heavier than α,α-dimethylbenzyl alcohol, it returns to the hydrogenolysis reactor for continuous reaction. The cumene obtained from the top of the light component removal tower is washed with caustic to remove phenol therein and then returns to step S1. The bottom of the heavy component removal tower is heated by 1.0 - 4.0 MPa steam in the reboiler, and the by-product of the top condenser is 0.3 - 2.0 MPa steam.

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