Method and device for improving oxidation yield of cyclohexanol and cyclohexanone prepared by cyclohexane oxidation

Abstract

The invention discloses a method and a device for improving the oxidation yield of cyclohexanol and cyclohexanone prepared by cyclohexane oxidation, and the method comprises the following steps: under the condition of no catalysis, cyclohexane is oxidized by molecular oxygen in an oxidation reactor formed by connecting a series of full-backmixing oxidation reaction kettles in series to generate an oxidation liquid taking cyclohexyl hydroperoxide as a main product; according to the series of full-back-mixing oxidation reaction kettles connected in series, the volumes of all the full-back-mixing oxidation reaction kettles are different, and the full-back-mixing oxidation reaction kettles are sequentially arranged from large to small according to the sizes of the volumes. The invention also comprises a cyclohexane oxidation device for implementing the method. According to the method, the yield of the cyclohexane oxidation process can be increased to the maximum extent, the oxidation side reaction is reduced, and the energy consumption is reduced.

Description

Technical Field

[0001] The present invention relates to a method and apparatus for preparing cyclohexanol and cyclohexanone by cyclohexane oxidation, and more particularly to a method for increasing the oxidation yields of cyclohexanol and cyclohexanone in cyclohexane oxidation and a cyclohexane oxidation apparatus for implementing the method. Background Art

[0002] Cyclohexanol and cyclohexanone are important raw materials for the production of caprolactam and adipic acid, and further for the production of nylon 6 and nylon 66.

[0003] The cyclohexane oxidation method is currently a main method for producing cyclohexanol and cyclohexanone. Generally, cyclohexane is oxidized with a gas containing molecular oxygen at a high temperature to partially form an oxidation mixture of cyclohexyl hydroperoxide, cyclohexanol and cyclohexanone, and then the target products cyclohexanol and cyclohexanone are obtained through processes such as decomposition and cyclohexane recovery. The gas containing molecular oxygen can use air, lean oxygen, rich oxygen or even pure oxygen. However, cyclohexane and a gas with an oxygen content exceeding 8-9% will form an explosive mixture under high temperature and high pressure, seriously affecting production safety; in addition, it has been proven that using different oxygen partial pressures to control the oxidation reaction rate is not as direct and rapid as using the reaction temperature adjustment. Therefore, the vast majority of cyclohexane oxidation apparatuses still use the cheaper direct air oxidation.

[0004] The mechanism of cyclohexane oxidation is generally considered to be a free radical chain reaction mechanism. Before the 1970s, transition metal catalysts were added during the oxidation process to increase the free radical concentration and improve the oxidation reaction rate, and the reaction temperature was 150°C - 160°C. However, most of the oxidized cyclohexyl hydroperoxide is catalytically decomposed into cyclohexanol and cyclohexanone by the transition metal catalyst at this temperature, and cyclohexanol and cyclohexanone are more easily oxidized to form organic acids and esters than cyclohexane under the same conditions, resulting in a low yield of the catalytic oxidation process.

[0005] After the 1980s, Rhodia Company in France proposed a cyclohexane non-catalytic lean oxygen oxidation process, and DSM Company in the Netherlands developed a cyclohexane non-catalytic air oxidation process. Since the reaction conditions of air oxidation are milder, the vast majority of the later-built cyclohexane oxidation apparatuses have adopted the cyclohexane non-catalytic air oxidation process, and its reaction temperature is between 165°C and 175°C.

[0006] The reaction mechanism of cyclohexane non-catalytic oxidation is basically the same as that of catalytic oxidation. The only difference is that no catalyst is added, and the free radicals generated by the chain reaction during the oxidation of cyclohexane are used to catalyze the reaction. Therefore, the cyclohexane non-catalytic oxidation process requires a relatively high oxidation temperature at the initial stage to maintain an appropriate reaction rate and ensure that the oxygen content in the oxidation tail gas is within a safe range (generally 2-3%). Since there are no transition metal ion catalysts in the oxidation reaction system, the decomposition rate of cyclohexyl hydroperoxide generated by oxidation decreases significantly, much less cyclohexanol and cyclohexanone are produced, and the deep oxidation of alcohols and ketones also decreases. Therefore, a higher oxidation yield can be obtained.

[0007] How to further improve the oxidation yield of cyclohexane in the non-catalytic oxidation process has always been a topic of interest to industry insiders. From the process of cyclohexane oxidation, this is a classic irreversible series reaction:

[0008]

[0009] Cyclohexyl hydroperoxide, cyclohexanol, and cyclohexanone are the target products, while acids and esters are by-products. According to classical reaction kinetics calculations, assuming that the reaction orders of the above reactions are all 1.0,

[0010] r 1 =k 1 C 烷 p 氧 =k 1 C 烷0 (1-X)p 氧 ...(1)

[0011] r 2 =k 2 C 过 =k 2 C 烷0 X...(2)

[0012] r 3 =k 3 k 2 C 过 p 氧 =k 3 k 2 C 烷0 Xp 氧 ...(3)

[0013]

[0014] Among them, r 1 is the main reaction, r 2 is the decomposition reaction of the product peroxide, r 3 is the side reaction, k 1 , k 2 , k3 is the reaction rate constant corresponding to each reaction, C 烷0 is the initial concentration of cyclohexane, C 烷 is the concentration of cyclohexane, p 氧 is the partial pressure of oxygen in the oxidation reactor, C 过 is the concentration of the product peroxide, and X is the conversion rate of cyclohexane.

[0015] From Equation (3), it can be found that the lower the concentration C 过 of the product peroxide, the fewer the side reactions r 3 . Then, from the perspective of the form of the oxidation reactor selected, the ideal plug flow reactor is the most suitable reactor for the cyclohexane oxidation process because the product concentration gradually increases in it, while the product concentration in the completely backmixed reactor is single and equal to the concentration at the final outlet, which will result in a lower reaction yield. However, the cyclohexane oxidation process also involves the mixing and mass transfer process of air and cyclohexane. Therefore, in actual situations, the oxidation reactor is composed of several completely backmixed oxidation reaction vessels connected in series, and the more reaction vessels are connected in series, the closer it is to a plug flow reactor. However, too many series-connected reaction vessels will cause trouble in engineering design. The more reaction vessels are connected in series, the more investment is required and the greater the possible leakage risk. Therefore, most current cyclohexane oxidation plants are designed with 5 - 6 oxidation reaction vessels connected in series, and the volumes of each oxidation reaction vessel are approximately the same.

[0016] From Equation (4), it is most obvious that in order to obtain a higher selectivity α, the lower the value of the cyclohexane conversion rate X is, the better. However, a low cyclohexane conversion rate means that more energy needs to be spent to recover the unreacted cyclohexane. Therefore, based on the prices of cyclohexane and steam energy, there will be a balance here. Generally, the cyclohexane conversion rate is designed between 3 - 4% to obtain the most economically optimized selectivity.

[0017] In addition, from Equation (4), it can be found that by changing the values of k 1 , k 2 and k 3 , the overall selectivity of the oxidation can also be improved.

[0018] Xiao Zhaosheng proposed in CN200310113778.5 that 0.05 - 1 ppm of diphosphonic acid ester (HEDP ester) is continuously added to the oxidation feed to make it a passivator for the metal walls of the oxidation reactor and trace metal ions entrained in the material, reducing the decomposition of cyclohexyl hydroperoxide in the oxidation reactor, that is, significantly reducing k 2 , thereby increasing the oxidation yield. However, the addition of diphosphonic acid ester will also simultaneously reduce the initiation rate of the cyclohexane chain reaction, resulting in an increase in the starting temperature of the oxidation reaction.

[0019] The current common practice is to gradually decrease the reaction temperature of each series-connected oxidation reactor in the order from front to back. Since the cyclohexane oxidation is a chain radical reaction, the reaction rate increases faster and faster as the radical content in the system increases. That is, a certain k can be maintained by continuously decreasing the oxidation reaction temperature. 1 , while at the same time k 2 and k 3 values decrease as the oxidation reaction temperature of the reactor decreases, thus ultimately obtaining a relatively high oxidation selectivity. However, since cyclohexane oxidation is an exothermic reaction, especially the heat release of side reactions is more obvious. How to more economically and effectively decrease the reaction temperature of each series-connected oxidation reactor one by one becomes the key. Most of the existing devices achieve this by adjusting the distribution of the air addition amount, gradually increasing the air inlet amount of each series-connected oxidation reactor, and using the inert gas in the air that does not react to vaporize and carry out cyclohexane out of the oxidation reactor. Thus, the heat in the reactor is removed by the vaporization heat of this part of cyclohexane to achieve the purpose of cooling. However, the different air inlet amounts of each oxidation reactor violate the original design intention of approaching a plug flow reactor and have a negative impact on the overall oxidation selectivity. There are also devices that use adding cyclohexane with a lower temperature to cool in the subsequent reactor, but this method will increase the amount of recycled cyclohexane and the energy consumption required for recovering cyclohexane. Other methods such as using external circulation cooling or individually controlling the pressure of each reactor can also achieve the purpose of controlling the reaction temperature of each series-connected oxidation kettle one by one, but their investment amount and safety risk are relatively too high. Summary of the Invention

[0020] The technical problem to be solved by the present invention is to overcome the above-mentioned defects existing in the prior art and provide a method for improving the oxidation yields of cyclohexanol and cyclohexanone in the oxidation of cyclohexane, which is simple to operate, has high efficiency and low energy consumption, and a cyclohexane oxidation device for implementing this method.

[0021] The technical solution adopted by the present invention to solve its technical problem is a method for improving the oxidation yields of cyclohexanol and cyclohexanone in the oxidation of cyclohexane. Under non-catalytic conditions, cyclohexane is oxidized by molecular oxygen in an oxidation reactor composed of a series of fully back-mixed oxidation reactors connected in series to generate an oxidation liquid with cyclohexyl hydroperoxide as the main product; for the series of serially connected fully back-mixed oxidation reactors, the volumes of each fully back-mixed oxidation reactor are all different and are arranged in descending order according to the volume size.

[0022] Furthermore, the number of the series of serially connected fully back-mixed oxidation reactors is 3 - 7.

[0023] Furthermore, the gas containing molecular oxygen introduced into each completely back-mixed oxidation reactor is oxygen-rich gas, air or oxygen-deficient gas, but the relative volume flow rate converted to pure oxygen is the same, so as to ensure the same oxidation conversion rate of each completely back-mixed oxidation reactor, and the oxygen content in the tail gas meets the safety range of 2-2.5%.

[0024] Furthermore, the oxidation reaction temperature of each completely back-mixed oxidation reactor is in the range of 175-160°C, and the oxidation reaction temperatures of each completely back-mixed oxidation reactor are sorted from high to low in sequence.

[0025] Furthermore, the oxidation reaction pressure of each completely back-mixed oxidation reactor is 1.15-1.35 MpaG.

[0026] Furthermore, the molar conversion rate of cyclohexane is controlled within 2.5-4.5%.

[0027] Furthermore, the molar conversion rate of cyclohexane is controlled within 3-4%.

[0028] Furthermore, the oxygen content of the gas entering the completely back-mixed oxidation reactor sorted later decreases continuously, and the amount of inert gas increases continuously. The oxidation reaction temperature of each completely back-mixed oxidation reactor is adjusted by increasing the amount of inert gas.

[0029] Furthermore, the inert gas is compressed oxidation reaction tail gas.

[0030] Furthermore, the inert gas is nitrogen or oxygen-deficient air.

[0031] The cyclohexane oxidation device for implementing the method for improving the oxidation yield of cyclohexanol and cyclohexanone in the present invention includes an oxidation reactor composed of a series of completely back-mixed oxidation reactors connected in series. The volumes of each completely back-mixed oxidation reactor are different and are arranged in descending order according to the volume size.

[0032] The present invention has the following positive effects: (1) The oxidation reactor of the present invention is composed of a series of completely back-mixed oxidation reactors with different volumes, which are arranged in series in descending order according to the volume size. This design form not only ensures the mass transfer and mixing requirements of the reactants but also meets the high yield requirements of a plug flow reactor. The oxidation yield of cyclohexane to cyclohexanol and cyclohexanone can be increased to more than 91.6%, which is about 4% higher than the best value of the existing operating device; (2) Since the present invention adjusts the oxidation reaction temperature of each oxidation reactor by using the high-pressure oxidation reaction compressed tail gas in the system, the required compressor power is very small and will not significantly increase the power consumption, which is beneficial to energy conservation; (3) The present invention does not need to introduce external inert gas, which will not affect the absorption load of the oxidation reaction tail gas and will not cause more refrigerant consumption. Description of the Drawings

[0033] Figure 1This is a schematic diagram of the process flow and device structure for a method of improving the oxidation yields of cyclohexane to cyclohexanol and cyclohexanone in the present invention.

[0034] In the figure: 01 - 1# oxidation reactor, 02 - 2# oxidation reactor, 03 - 3# oxidation reactor, 04 - 4# oxidation reactor, 05 - 5# oxidation reactor, 06 - 6# oxidation reactor, 07 - tail gas compressor;

[0035] 010 - cyclohexane input pipe of 1# oxidation reactor, 011 - tail gas pipe of 1# oxidation reactor, 012 - air pipe of 1# oxidation reactor, 013 - total oxidation reaction tail gas pipe, 014 - air main pipe, 020 - cyclohexane overflow pipe of 2# oxidation reactor, 021 - tail gas pipe of 2# oxidation reactor, 022 - air pipe of 2# oxidation reactor, 030 - cyclohexane overflow pipe of 3# oxidation reactor, 031 - tail gas pipe of 3# oxidation reactor, 032 - air pipe of 3# oxidation reactor, 040 - cyclohexane overflow pipe of 4# oxidation reactor, 041 - tail gas pipe of 4# oxidation reactor, 042 - air pipe of 4# oxidation reactor, 043 - compressed tail gas pipe of 4# oxidation reactor, 050 - cyclohexane overflow pipe of 5# oxidation reactor, 051 - tail gas pipe of 5# oxidation reactor, 052 - air pipe of 5# oxidation reactor, 053 - compressed tail gas pipe of 5# oxidation reactor, 060 - cyclohexane overflow pipe of 6# oxidation reactor, 061 - tail gas pipe of 6# oxidation reactor, 062 - air pipe of 6# oxidation reactor, 063 - compressed tail gas pipe of 6# oxidation reactor, 064 - oxidation liquid pipe, 070 - high - pressure tail gas pipe. Detailed implementation mode

[0036] The following further describes a method for improving the oxidation yields of cyclohexane to cyclohexanol and cyclohexanone in the present invention and the device for implementing this method with reference to the embodiments and the drawings.

[0037] Refer to Figure 1, the cyclohexane oxidation device used in the examples of the method for improving the oxidation yields of cyclohexanol and cyclohexanone in the present invention, wherein the oxidation reactor is composed of 6 oxidation reaction vessels connected in series through corresponding cyclohexane overflow pipes: The 1# oxidation reaction vessel 01 provided with a cyclohexane input pipe 010 is connected to the 2# oxidation reaction vessel 02 through the 2# oxidation reaction vessel cyclohexane overflow pipe 020, the 2# oxidation reaction vessel 02 is connected to the 3# oxidation reaction vessel 03 through the 3# oxidation reaction vessel cyclohexane overflow pipe 030, the 3# oxidation reaction vessel 03 is connected to the 4# oxidation reaction vessel 04 through the 4# oxidation reaction vessel cyclohexane overflow pipe 040, the 4# oxidation reaction vessel 04 is connected to the 5# oxidation reaction vessel 05 through the 5# oxidation reaction vessel cyclohexane overflow pipe 050, and the 5# oxidation reaction vessel 05 is connected to the 6# oxidation reaction vessel 06 through the 6# oxidation reaction vessel cyclohexane overflow pipe 060; The 1# oxidation reaction vessel 01 is also connected with a 1# oxidation reaction vessel tail gas pipe 011 and a 1# oxidation reaction vessel air pipe 012; The 2# oxidation reaction vessel 02 is also connected with a 2# oxidation reaction vessel tail gas pipe 021 and a 1# oxidation reaction vessel air pipe 022; The 3# oxidation reaction vessel 03 is also connected with a 3# oxidation reaction vessel tail gas pipe 031 and a 3# oxidation reaction vessel air pipe 032; The 4# oxidation reaction vessel 04 is also connected with a 4# oxidation reaction vessel tail gas pipe 041, a 4# oxidation reaction vessel air pipe 042 and a 4# oxidation reaction vessel compressed tail gas pipe 043; The 5# oxidation reaction vessel 05 is also connected with a 5# oxidation reaction vessel tail gas pipe 051, a 5# oxidation reaction vessel air pipe 052 and a 5# oxidation reaction vessel compressed tail gas pipe 053; The 6# oxidation reaction vessel 06 is connected with a 6# oxidation reaction vessel tail gas pipe 061, a 6# oxidation reaction vessel air pipe 062 and a 6# oxidation reaction vessel compressed tail gas pipe 063, and at the same time, an oxidation liquid delivery pipe 064 is also provided for delivering the oxidation liquid to subsequent processes; The air main pipe 014 is respectively connected to the air pipes 012, 022, 032, 042, 052, 062 of the 1st - 6th oxidation reaction vessels; The tail gas pipes 011, 021, 031, 041, 051, 061 of the 1st - 6th oxidation reaction vessels are all connected to the total oxidation tail gas pipe 013; The high - pressure tail gas pipe 070 is connected to the tail gas compressor 071 and is connected to the 4th - 6th oxidation reaction vessel compressed tail gas pipes 043, 053, 063; The volumes of the 1# oxidation reaction vessel 01, 2# oxidation reaction vessel 02, 3# oxidation reaction vessel 03, 4# oxidation reaction vessel 04, 5# oxidation reaction vessel 05, 6# oxidation reaction vessel 06 are 150m 3 , 130m 3 , 100m 3 , 90m 3 , 80m 3 , 70m 3It should be noted that the specific size of the volume of the oxidation reactor is only applicable to the cyclohexane oxidation unit with an annual output of 110,000 tons. Those skilled in the art know that if the scale of the production unit changes, the volume of the oxidation reactor will also change.

[0038] Refer to Figure 1 , the device used in the example of the method for improving the oxidation yields of cyclohexanol and cyclohexanone by cyclohexane oxidation in the present invention is a set of cyclohexane oxidation unit with an annual output of 110,000 tons. The specific implementation operation process is as follows:

[0039] After the start-up is stable, adjust the cyclohexane flow rate in the cyclohexane delivery pipe 010 of the 1# oxidation reactor to 550 t / h and enter the 1# oxidation reactor 01, and then pass through the cyclohexane overflow pipes 020 of the 2# oxidation reactor, 030 of the 3# oxidation reactor, 040 of the 4# oxidation reactor, 050 of the 5# oxidation reactor, 050 of the 6# oxidation reactor and the cyclohexane 060 of the 6# oxidation reactor and other overflow pipelines, and enter the 2# oxidation reactor 02, 3# oxidation reactor 03, 4# oxidation reactor 04, 5# oxidation reactor 05, 6# oxidation reactor 06 in sequence; the flow rate of the air main pipe 014 is 18,600 Nm 3 / h; the volumes of the 6 series-connected oxidation reactors: 1# oxidation reactor 01, 2# oxidation reactor 02, 3# oxidation reactor 03, 4# oxidation reactor 04, 5# oxidation reactor 05, 6# oxidation reactor 06 are 150 m 3 , 130 m 3 , 100 m 3 , 90 m 3 , 80 m 3 , 70 m 3 ; the air flow rates into the 1# oxidation reactor, 2# oxidation reactor, 3# oxidation reactor, 4# oxidation reactor, 5# oxidation reactor and 6# oxidation reactor are all 3,100 Nm 3 / h, the oxygen contents of the tail gases of the 1# oxidation reactor, 2# oxidation reactor, 3# oxidation reactor, 4# oxidation reactor, 5# oxidation reactor, 6# oxidation reactor and the total oxidation tail gas are all 2 - 2.5%, the oxidation pressure is controlled at 1.2 MPaG by the pressure in the total oxidation reaction tail gas pipe 013, and about 130 t / h of vaporized cyclohexane is carried away by the tail gas in the total oxidation reaction tail gas pipe 013; the total tail gas flow rate of the high-pressure tail gas pipe 070 from which cyclohexane has been removed is 1,500 Nm 3 / h. After being pressurized to above 1.3 MpaG by the tail gas compressor 07, it enters the 4# oxidation reactor 04, 5# oxidation reactor 05, and 6# oxidation reactor 06 respectively. The tail gas flow rates in the compressed tail gas pipes 043 of the 4# oxidation reactor, 053 of the 5# oxidation reactor, and 063 of the 6# oxidation reactor are 300 Nm 3 / h, 500 Nm 3 / h, 700 Nm 3 / h respectively. The oxidation reaction temperatures of the 1# oxidation reactor 01, 2# oxidation reactor 02, 3# oxidation reactor 03, 4# oxidation reactor 04, 5# oxidation reactor 05, and 6# oxidation reactor 06 are controlled at 172 °C, 169 °C, 167 °C, 165 °C, 163 °C, and 162 °C respectively. After the system is stable, the total amount of the oxidation liquid flowing out from the outlet oxidation liquid pipe 064 of the 6# oxidation reactor 06 is about 425 t / h, containing 0.67% wt of cyclohexanone, 0.33% wt of cyclohexanol, 0.24% wt of acid, 0.16% wt of ester, 0.04% wt of light and heavy components, and 3.20% wt of peroxide. It is calculated that the molar conversion rate of cyclohexane is 3.50%, and the molar yield of useful products is 91.6%.

[0040] Comparative Example

[0041] An existing production line of a cyclohexane oxidation device with an annual output of 110,000 tons that reduces the reaction temperature by gradually increasing the ventilation volume of the oxidation reactor operates as follows:

[0042] After the start-up is stable, the cyclohexane flow rate is adjusted to 550 t / h, and the total air flow rate is 18,800 Nm 3 / h. The volumes of the 1-6# oxidation reactors are 86 m 3 , 86 m 3 , 86 m 3 , 86 m 3 , 86 m 3 , 110 m 3 respectively. The ventilation volumes of the 1-6# oxidation reactors are 1800 Nm 3 / h, 2400 Nm 3 / h, 2700 Nm 3 / h, 3100 Nm 3 / h, 3400 Nm 3 / h, 5400 Nm 3 / h, pressure control at 1.2 MPaG, tail gas content 2 - 2.5%; the temperatures of the 1st - 6th oxidation reactors are 172°C, 170°C, 168°C, 166°C, 165°C, and 165°C respectively. After the system is stable, the oxidation liquid at 430 t / h contains cyclohexanone 0.65% wt, cyclohexanol 0.32% wt, acid 0.3% wt, ester 0.26% wt, light and heavy components 0.07% wt, and peroxide 3.09% wt. It is calculated that the molar conversion rate of cyclohexane is 3.53%, and the molar yield of useful products is 87.8%.

[0043] Each of the oxidation reactors described above is a fully back - mixed oxidation reactor.

Claims

1. A method for improving the oxidation yield of cyclohexane to prepare cyclohexanol and cyclohexanone, wherein cyclohexane is oxidized by molecular oxygen in an oxidation reactor composed of a series of fully back-mixed oxidation reactors connected in series under non-catalytic conditions to generate an oxidation liquid with cyclohexyl hydroperoxide as the main product; characterized in that: The series of fully back-mixed oxidation reactors connected in series have different volumes of each fully back-mixed oxidation reactor, and are arranged in order from large to small according to the volume.

2. A method for improving the oxidation yield of cyclohexane to prepare cyclohexanol and cyclohexanone according to claim 1, characterized in that: The number of the series of fully back-mixed oxidation reactors connected in series is 3-7.

3. A method for improving the oxidation yield of cyclohexane to prepare cyclohexanol and cyclohexanone according to claim 1 or 2, characterized in that: The molecular oxygen-containing gas introduced into each full back-mixed oxidation reactor is oxygen-rich gas, air or oxygen-depleted gas, but the relative volume flow rate converted into pure oxygen is consistent to ensure the same oxidation conversion rate of each full back-mixed oxidation reactor, and the oxygen content in the tail gas meets the safety range of 2-2.5%.

4. A method for improving the oxidation yield of cyclohexane to prepare cyclohexanol and cyclohexanone according to any one of claims 1 to 3, characterized in that: The oxidation reaction temperature of each full back-mixed oxidation reactor is in the range of 175-160°C, and the oxidation reaction temperature of each full back-mixed oxidation reactor is arranged in order from high to low.

5. A method for improving the oxidation yield of cyclohexane to prepare cyclohexanol and cyclohexanone according to any one of claims 1 to 4, characterized in that: The oxidation reaction pressure of each full backmixing oxidation reactor is 1.15-1.35MpaG.

6. A method for improving the oxidation yield of cyclohexane to prepare cyclohexanol and cyclohexanone according to any one of claims 1 to 5, characterized in that: After passing through all the fully back-mixed oxidation reactors, the molar conversion rate of cyclohexane is controlled at 2.5-4.5%.

7. A method for improving the oxidation yield of cyclohexane to prepare cyclohexanol and cyclohexanone according to claim 6, characterized in that: The molar conversion rate of the cyclohexane is controlled at 3.0-4.0%.

8. A method for improving the oxidation yield of cyclohexane to prepare cyclohexanol and cyclohexanone according to any one of claims 1 to 7, characterized in that: The oxygen content of the inlet gas of the fully back-mixed oxidation reactor arranged later is continuously reduced, and the amount of inert gas is continuously increased. The oxidation reaction temperature of each fully back-mixed oxidation reactor is adjusted by increasing the amount of inert gas.

9. A method for improving the oxidation yield of cyclohexane to prepare cyclohexanol and cyclohexanone according to claim 8, characterized in that: The inert gas is nitrogen, oxygen-depleted air or compressed oxidation reaction tail gas.

10. A cyclohexane oxidation device for implementing the method for improving the oxidation yield of cyclohexane to prepare cyclohexanol and cyclohexanone according to any one of claims 1 to 9, comprising an oxidation reactor composed of a series of fully back-mixed oxidation reactors connected in series, characterized in that: The volumes of the full back-mixed oxidation reactors are different and are arranged in order from large to small according to the volume.

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