A device and method for dynamic oil-water separation of benzene partial hydrogenation to cyclohexene

Abstract

The application discloses a device for dynamically separating oil and water and partially hydrogenating benzene into cyclohexene and a method thereof. The device comprises a reaction unit and a catalyst recovery unit connected in sequence. The reaction unit is composed of multiple series-connected reaction kettles. The catalyst recovery unit comprises a water washing tank, a flash tank, an evaporation kettle, an evaporation water tank and a condenser. After benzene, hydrogen and zinc sulfate aqueous solution containing catalysts pass through the multiple series-connected reaction kettles, oil and water are separated in the water washing tank, the oil phase is sent out of the system after water washing, the water phase flows out from the bottom of the water washing tank, part of the water phase is returned to the reaction kettle, and the other part is sequentially introduced into the flash tank and the evaporation kettle and then returned to the reaction kettle. The cyclohexene preparation method based on the device can greatly reduce the consumption of catalysts and zinc sulfate.

Description

Technical Field

[0001] This invention relates to a method for preparing cyclohexene, specifically to an apparatus and method for producing cyclohexene by dynamic oil-water separation and partial hydrogenation of benzene, belonging to the field of petrochemical technology development. Background Technology

[0002] Cyclohexene is an important organic chemical raw material, widely used in the production of pharmaceuticals, pesticides, dyes, detergents, feed additives, polyesters, and polyamide products. Traditional methods for producing cyclohexene include cyclohexanol dehydration, dehydrohalogenation of halocyclohexane, and dehydrogenation of cyclohexane. Due to the use of relatively expensive cyclohexanol and halocyclohexane as raw materials, cyclohexene produced by these methods can only be used in the production of a few high-value-added fine chemical products such as L-lysine and cyclohexene oxide. Benzene is abundant and inexpensive; therefore, the partial hydrogenation of benzene to produce cyclohexene is the preferred method in modern industrial production.

[0003] In the 1990s, Asahi Kasei Corporation of Japan pioneered the industrial-scale production of cyclohexene through partial hydrogenation of benzene. Using ruthenium as a catalyst and zinc sulfate aqueous solution as a circulating phase, benzene and hydrogen underwent a partial hydrogenation reaction in a reactor to obtain cyclohexene. Shenma Group was the first domestic company to introduce this technology, and Shijiazhuang Coking Group also adopted Asahi Kasei's process in the early 21st century. With the deepening of domestic research, numerous patents have been filed regarding catalysts and reaction apparatus for cyclohexene production.

[0004] Invention patent CN1696087A discloses an apparatus for producing cyclohexene by hydrogenating benzene. The design of the oil-water phase separator is complex, which increases the difficulty of manufacturing. In addition, in order to ensure the uniform distribution of catalyst in the aqueous phase during operation, a short residence time is designed, which leads to oil-water phase difference, catalyst entrainment in the oil phase, and increased catalyst consumption. Conversely, in order to ensure the oil-water phase separation effect, the residence time must be increased, which will lead to catalyst deposition and uneven distribution.

[0005] Invention patent CN101850225B discloses a tubular reactor and a membrane recovery catalyst system. Although the tubular reactor has a simple structure, it has limitations in the four-phase mass transfer reaction of benzene partial hydrogenation, which is not conducive to improving the conversion rate. In addition, the membrane is difficult to operate and maintain in multiphase filtration.

[0006] Invention patent CN102241558B discloses a reaction device and process for selective hydrogenation of benzene to prepare cyclohexene. This invention mainly emphasizes the external static mixing of materials benzene, hydrogen, and circulating water phase. Since it is difficult to simply mix and maintain uniformity of the four phases of gas-liquid-liquid-solid, the effect is not obvious. In addition, the catalyst in the aqueous phase will be unevenly distributed in the settling tank, resulting in changes in the catalyst concentration.

[0007] Invention patent CN115259992B discloses a continuous production method for selective hydrogenation of benzene to cyclohexene. This invention involves benzene hydrogenation reaction, oil-water phase separation and catalyst regeneration, but it does not solve the problems of catalyst and zinc sulfate loss and system water balance in the production unit.

[0008] Utility model patent CN202860529U discloses a reaction device for the partial hydrogenation of benzene to produce cyclohexene. The feature of this utility model is that an upper and lower guide tube is added to the reaction vessel, and a phase separation zone is generated in the upper part of the reaction vessel, which enables the catalyst to circulate internally. The disadvantage is that the oil-water ratio of the reaction vessel is difficult to control, and the selectivity of cyclohexene production decreases. Summary of the Invention

[0009] To address the problems existing in the prior art, the first objective of this invention is to provide a dynamic oil-water separation apparatus for the partial hydrogenation of benzene to cyclohexene. This apparatus improves the cyclohexene yield by controlling the mass transfer process of cyclohexene on the catalyst surface and in the solution, especially by increasing the stirring intensity to enhance mass transfer while avoiding excessively high catalyst activity, and by controlling the flow pattern in the reactor and reducing backmixing in a plug flow reaction mode. The benzene conversion rate in a single reactor is controlled below 30%, thereby achieving a total conversion rate >49% and a total cyclohexene selectivity >80%.

[0010] The second objective of this invention is to provide a method for the dynamic oil-water separation and partial hydrogenation of benzene to produce cyclohexene. This method is based on the above-mentioned apparatus. The oil phase of the reactants is washed with water in a water washing tank to recover the catalyst and zinc sulfate entrained in the oil phase, thereby reducing the consumption of catalyst and zinc sulfate. Then, a portion of the aqueous phase is subjected to flash evaporation and evaporation operations. Excess water in the system can be discharged through an evaporation condensate tank, maintaining the stability of the phase-reactance vessel interface and the water balance of the system.

[0011] To address the aforementioned technical issues, this invention provides an apparatus for the dynamic oil-water separation and partial hydrogenation of benzene to produce cyclohexene, comprising: a reaction unit and a catalyst recovery unit connected in sequence.

[0012] As a preferred embodiment, the reaction unit is a multi-stage series reactor, with a liquid phase feed distributor (5), a gas phase feed distributor (6), and a water phase inlet containing catalyst at the bottom of the reactor.

[0013] As a preferred embodiment, the catalyst recovery unit includes a water washing tank (4), a flash tank (16), an evaporator (17), an evaporation water tank (21), and a condenser (20).

[0014] As a preferred embodiment, the washing tank is equipped with an inlet material guide tube (10), an outlet overflow weir (11), and a washing distributor (12).

[0015] As a preferred embodiment, the multi-stage reactor consists of 2 to 4 reactors connected in series.

[0016] As a preferred embodiment, the reactor wall is also provided with 4 to 6 baffles, the lower part adopts propulsion stirring, and the middle and upper parts adopt radial flow stirring.

[0017] As a preferred embodiment, the oil phase water washing distributor in the water washing tank is located 50-500 mm below the overflow weir inside the vessel.

[0018] This invention also provides a method for the dynamic oil-water separation of benzene partial hydrogenation to produce cyclohexene, implemented by any of the above-described apparatus. The process is as follows: benzene and a circulating aqueous phase containing a catalyst enter from the bottom of a first reactor, and after passing through multiple reactor stages, enter a phase separation reactor for oil-water separation. The oil phase obtained from the oil-water separation is sprayed and washed by a water washing distributor and then discharged by an overflow weir. After the aqueous phase is separated from the catalyst and the oil phase, a portion is recycled back into the first reactor, and the remainder is sent to a flash tank, then to an evaporation tank for boiling treatment, and then returned to the first reactor. The oil phase generated by evaporation and condensation is sent to the outside, and the generated aqueous phase is sent to an evaporation water tank.

[0019] The partial hydrogenation of benzene to cyclohexene is a four-phase reaction system involving gas, oil, water, and solid. Mass transfer of cyclohexene on the catalyst surface and in the solution is the key control point determining the cyclohexene yield. If the reaction rate is too fast or the cyclohexene detaches from the catalyst surface too slowly, the formation of cyclohexene will be reduced. Therefore, measures such as reducing catalyst activity, increasing stirring intensity to enhance mass transfer, and reducing backmixing in a plug flow reaction mode are methods to improve the cyclohexene yield. Using a plug flow reaction mode with multiple reactors in series and multiple layers of stirring in each reactor can control the benzene conversion rate in each reactor to below 25%, thereby obtaining a total benzene conversion rate of more than 49% and a total cyclohexene selectivity of more than 80%.

[0020] As a preferred embodiment, the catalyst in the aqueous phase is a composition comprising ruthenium, zirconium, zinc, and their compounds.

[0021] As a preferred embodiment, the pH of the aqueous phase is 4 to 6.5.

[0022] As a preferred embodiment, the reaction conditions in the reactor are: temperature of 120-150℃, pressure of 3.0-6.0MPa, and water-oil phase mass ratio of 1.5-5.

[0023] As a preferred embodiment, the oil-to-water mass ratio in the spray washing is 50-200.

[0024] As a preferred embodiment, the aqueous phase fed into the catalyst recovery unit is 1-5% of the total aqueous phase mass.

[0025] As a preferred embodiment, the conditions of the evaporator are: temperature of 100-150°C and pressure equal to the saturated vapor pressure of water vapor at the corresponding temperature.

[0026] Compared with the prior art, the beneficial technical effects of the technical solution of the present invention are as follows:

[0027] 1) The apparatus provided by the present invention first controls the mass transfer process of cyclohexene on the catalyst surface and in the solution, especially avoiding excessively high catalyst activity while increasing the stirring intensity to enhance mass transfer. By controlling the flow mode in the reactor and reducing backmixing in the plug flow reaction mode, the yield of cyclohexene is improved. The benzene conversion rate in a single reactor is controlled below 25%, thereby achieving a total conversion rate >49% and a total cyclohexene selectivity >80%.

[0028] 2) The method provided by the present invention is based on the above-mentioned device. The reaction material is washed with water in a water washing tank to recover the catalyst and zinc sulfate entrained in the oil phase, thereby reducing the consumption of catalyst and zinc sulfate auxiliary agent. Then, a portion of the aqueous phase is subjected to flash evaporation and evaporation operations. Excess water in the system can be discharged through the evaporation condensate bag, thereby maintaining the stability of the phase-reactor interface and the water balance of the system. Attached Figure Description

[0029] Figure 1 The flowchart of the reaction apparatus for the partial hydrogenation of benzene to prepare cyclohexene provided by the present invention is shown below.

[0030] Among them, 1-first reaction vessel; 2-second reaction vessel; 3-third reaction vessel; 4-washing tank; 5-liquid phase feed distributor; 6-gas phase feed distributor; 7-stirring blade; 8-heat exchange coil; 9-reaction vessel overflow weir; 10-inlet material guide tube; 11-outlet overflow weir; 12-washing distributor; 13-circulating pump; 14-gas phase balance pipe; 15-motor; 16-flash tank; 17-evaporator; 18-stirring blade; 19-steam heating coil; 20-condenser; 21-water tank; 22-diaphragm metering pump. Detailed Implementation

[0031] The present invention will be described in detail below with reference to the accompanying drawings and embodiments, but the embodiments do not constitute a limitation on the present invention.

[0032] Example 1

[0033] This embodiment provides a dynamic oil-water separation and partial hydrogenation reaction apparatus for the preparation of cyclohexene from benzene, the flow chart of which is shown below. Figure 1 As shown: The device includes a reaction unit, an oil-water separation unit, and a catalyst regeneration unit.

[0034] The reaction unit consists of three-stage reactors 1 / 2 / 3 connected in series. Heat exchange coils 8 and agitators 7 are installed inside reactors 1 / 2 / 3, with the heat exchange coils 8 and agitators 7 axially spaced apart. These are connected to temperature control points within reactors 1 / 2 / 3 to regulate the reaction temperature, driven by a motor 15 located at the top of reactors 1 / 2 / 3. A gas phase feed distributor 6 and a liquid phase feed distributor 5 are located at the bottom of reactor 1, and a gas phase feed distributor 6 is located at the bottom of reactor 2 / 3. An overflow weir 9 is also installed within reactors 1 / 2 / 3.

[0035] The catalyst recovery unit consists of a washing tank 4, a flash tank 16, and an evaporator 17. The washing tank 4 is equipped with an inlet material guide tube 10 and an oil phase outlet overflow weir 11. A water washing distributor 12 is located below the overflow weir 11. The bottom of the washing tank 4 has an outlet for the aqueous phase containing the catalyst. Part of the aqueous phase is returned to the reactor 1 via a catalyst circulation pump 13, and the other part is sent to the flash tank 16. Reactors 1 / 2 / 3 are connected to the upper part of the washing tank 4 via a gas phase balance pipe 14. The top of the flash tank 16 discharges material to the outside, and the bottom discharges material to the evaporator 17. The evaporator 17 has a steam heating coil 19 on its wall and a steam outlet at the top connected to a condenser 20. The condensate is sent to a water tank 21. Part of the material in the water tank 21 is sent outside, and part is returned to the evaporator 17. The lower part of the evaporator 17 has a liquid outlet, and the material is transported to the reactor by a diaphragm metering pump 22.

[0036] In the reaction unit, the aqueous phase is zinc sulfate with a pH of 4.5–6.0, the catalyst is Ru-Zn / ZrO2, the reaction temperature is controlled at 130–145℃ by the heat exchange coil of the reactor, and the reaction pressure is controlled at 3.5–5.5 MPa by adjusting the amount of hydrogen entering the reactor; benzene is added from the first reactor, and hydrogen is added from the three reactors respectively, with a hydrogen-to-oil ratio of 1–2 and a water-to-oil ratio of 1.5–5.

[0037] The water washing tank of the catalyst recovery unit has a water washing distributor 50-500 mm away from the bottom of the overflow weir inside the vessel, and the mass ratio of oil to washing water is 80-150.

[0038] The feed rate of the aqueous phase in the flash tank of the catalyst recovery unit is 2-4% of the total aqueous phase mass. The flash-evaporated material enters the evaporator, where the evaporation temperature is 100-150℃ and the pressure is the saturated vapor pressure of water. The external discharge of the condensate water tank is equivalent to the washing water volume of the washing tank.

[0039] The results showed that the conversion rate of benzene was 50%, the selectivity of cyclohexene was 80%, the zinc sulfate content in the oil phase of the phase separation vessel was less than 50 ppm, the phase separation vessel interface was stable, and the water balance was normal. The catalyst activity index before regeneration was 100 g benzene / g ruthenium / h, and the catalyst activity index after regeneration was 120 g benzene / g ruthenium / h. The catalyst consumption index was 1.5 g ruthenium / t cyclohexene.

[0040] Comparative Example 1

[0041] As in Example 1, the reaction unit uses two reactors connected in series. The sum of the effective volumes of the reactors is the same as in Example 1. Under the same conditions of total feed rate, reaction temperature, pressure, and water-oil ratio, the results show that the conversion rate of benzene is 50%, the selectivity of cyclohexene is 72%, and the catalyst consumption index increases to 2.3 g ruthenium / t cyclohexene.

[0042] Comparative Example 2

[0043] As in Example 1, the catalyst recovery unit water washing tank was not used for oil phase washing. Under the same operating conditions, the results showed that the zinc sulfate content in the oil phase of the phase separation vessel increased to 500 ppm; the catalyst consumption index increased to 2.0 g ruthenium / t cyclohexene.

[0044] Comparative Example 3

[0045] As in Example 1, with the reaction temperature of the reaction unit increased to 150°C and other operating conditions remaining the same, the results showed that the catalyst activity index increased to 130 g benzene / g ruthenium / h and the catalyst consumption index increased to 2.5 g ruthenium / t cyclohexene.

[0046] Comparative Example 4

[0047] As in Example 1, with the reaction temperature of the reaction unit reduced to 120°C and other operating conditions remaining the same, the results showed that the catalyst activity index decreased to 30 g benzene / g ruthenium / h, while the catalyst consumption index increased to 2.0 g ruthenium / t cyclohexene.

[0048] Comparative Example 5

[0049] As in Example 1, with the pH of the aqueous phase in the reaction unit adjusted to 6.5 and other operating conditions remaining the same, the results showed that the catalyst activity index decreased to 60 g benzene / g ruthenium / h, while the catalyst consumption index increased to 1.8 g ruthenium / t cyclohexene.

[0050] Comparative Example 6

[0051] As in Example 1, with the pH of the aqueous phase in the reaction unit adjusted to 4.0 and other operating conditions remaining the same, the results showed that the catalyst activity index increased to 120 g benzene / g ruthenium / h, the benzene conversion rate was 50%, the cyclohexene selectivity was 68%, and the catalyst consumption index increased to 2.0 g ruthenium / t cyclohexene.

Claims

1. An apparatus for the dynamic oil-water separation and partial hydrogenation of benzene to produce cyclohexene, characterized in that, include: A reaction unit and a catalyst recovery unit are connected in sequence; the reaction unit consists of multiple series-connected reactors. The catalyst recovery unit includes a water washing tank (4), a flash tank (16), an evaporator (17), an evaporation water tank (21), and a condenser (20).

2. The apparatus for dynamic oil-water separation and partial hydrogenation of benzene to cyclohexene according to claim 1, characterized in that: The reaction unit is a multi-stage series reactor, with a liquid phase feed distributor (5), a gas phase feed distributor (6), and a water phase inlet containing catalyst at the bottom of the reactor.

3. The apparatus for dynamic oil-water separation and partial hydrogenation of benzene to cyclohexene according to claim 1, characterized in that: The washing tank is equipped with an inlet material guide tube (10), an oil phase outlet overflow weir (11), and a washing distributor (12).

4. The apparatus for dynamic oil-water separation and partial hydrogenation of benzene to cyclohexene according to claim 1, characterized in that: The multi-stage reactor consists of 2 to 4 reactors connected in series.

5. The apparatus for dynamic oil-water separation and partial hydrogenation of benzene to cyclohexene according to claim 4, characterized in that: The water washing distributor inside the water washing tank is located 50-500 mm below the overflow weir at the oil phase outlet.

6. A method for the dynamic oil-water separation and partial hydrogenation of benzene to produce cyclohexene, characterized in that: The process is carried out by the apparatus according to any one of claims 1 to 4, and is as follows: benzene and a circulating aqueous phase including the catalyst enter from the bottom of the first reactor, and after passing through multiple reactors in sequence, they enter the water washing tank for oil-water separation; the oil phase obtained from the oil-water separation is sprayed and washed by the water washing distributor and then sent out by the overflow weir; after the aqueous phase and the catalyst are separated from the oil phase, a portion is recycled back into the first reactor, and the remainder is sent to the flash tank, then sent to the evaporation tank for boiling treatment and then returned to the first reactor; the oil phase generated by evaporation and condensation is sent to the outside, and the generated aqueous phase is sent to the evaporation water tank.

7. The method for producing cyclohexene by partial hydrogenation of benzene in dynamic oil-water separation according to claim 6, characterized in that: The catalyst in the aqueous phase is a composition containing ruthenium, zirconium, zinc and their compounds; the pH of the aqueous phase is 4 to 6.

5.

8. The method for producing cyclohexene by partial hydrogenation of benzene in dynamic oil-water separation according to claim 6, characterized in that: The reaction conditions in the reactor are: temperature 120-150℃, pressure 3.0-6.0MPa, and water-oil phase mass ratio 1.5-5; the oil-water mass ratio in the spray washing is 50-200; and the water phase sent to the regeneration unit is 1-5% of the total water phase mass.

9. The method for producing cyclohexene by partial hydrogenation of benzene from dynamic oil-water separation according to claim 6, wherein the conditions of the evaporator are: temperature of 100–150°C and pressure equal to the saturated vapor pressure of water at the corresponding temperature.

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