The method of separation of cyclohexane

 

The invention relates to a method of separation of cyclohexane from the reaction mixture for the synthesis of cyclohexanone and cyclohexanol and may find application in the chemical industry for preparation of caprolactam. According to the invention the selection lead by rectification series of two distillation columns. From the top of the first column divert gases, water and part of the unreacted cyclohexane, from the cube partially enriched fraction of the reaction products. From the top of the second column, assign the second main part of cyclohexane, and the cube of the column is a concentrated fraction of the reaction products at a temperature of 75 to 120C. the Proposed method allows to lower the boiling point in the cube of the second column and to reduce the amount of vapor when Parke concentrated product. Because maintaining a low concentration of reaction products in the cube reduces the loss of cyclohexanone in Cuba the first column and are soft conditions for the allocation of fractions of the reaction products with a minimum loss of cyclohexanone and minimal contamination of the mixture of impurities, it is difficult detachable from cyclohexanone and cyclohexanol. 3 Il., table 2.

The invention relates to a method videomicroscopy industry for preparation of caprolactam and adipic acid.

A known method of separation of cyclohexane by distillation under a pressure close to atmospheric, in the same column, in accordance with which the oxidation product is served in a distillation column, where emit the bulk of cyclohexane at a temperature of 130-150In Cuba, bringing its residual content in the bottom product to 3-10%. [Production of cyclohexanol and adipic acid by oxidation of cyclohexane / edited by M. S. Furman, A. M. Goldman. - M.: Chemistry, 1967, S. 103].

The disadvantage of this method is loss of cyclohexanone under the influence in Cuba columns high temperature, and the formation of impurities that degrade the quality indicators of cyclohexanone and the final product - caprolactam.

The closest technical solution is an improved method of extraction of cyclohexane by distillation in a single column at a temperature in the cube 120And the concentration of cyclohexane in the bottom liquid 12-21 wt.%, used in bench studies of the process of separation of the reaction mixture [Proceedings of GIAP. - M., 1959, S. 376].

The disadvantage of this method is that it entails gas emissions. In the process tmiti from cyclohexane and then sent to disposal. To do this, on top of the column support excess pressure of 0.17-0.27 MPa. And in order to get the columns in the cube residual concentration of cyclohexane 12-21 wt.%, you must have a temperature in the cube column 130-140With that leads to increased losses of cyclohexanone and deterioration of product quality.

The basis of the invention the task is to provide an improved method of separation of cyclohexane from the reaction mixture for the synthesis of cyclohexanone and cyclohexanol by reducing thermal treatment fluid containing the greatest concentration of cyclohexanone, which will allow to reduce losses of cyclohexanone, to improve its quality and to increase the quality of caprolactam.

The problem is solved in that in the method of separation of cyclohexane from the reaction mixture for the synthesis of cyclohexanone and cyclohexanol by rectification according to the claimed method, the process is carried out in two distillation columns, where the top of the first column divert gases, water and part of the unreacted cyclohexane, from the cube partially enriched fraction of the reaction products from the top of the second column, assign the second main part of cyclohexane and from Cuba columns kontsentrirovannymi allocation method cyclohexane, what due process in two columns, selection in the first column strip and parts of cyclohexane when diluted fractions of the reaction products in the cube column and a second column selection remaining main part of the cyclohexane in a concentrated fraction of the reaction products in the cube of the column and a temperature of 75 to 120To achieve the reduction heat treatment of the reaction products in cubes columns than reduce loss of cyclohexanone, the formation of trace contaminants and improve the quality of products. In the prototype of all pairs emerging from exhaustive of the column in a stabilizing part, are created in the cube columns in the area with the highest concentration of cyclohexanone (at a concentration of cyclohexane in a mixture of 25-30%). In the present method most or all pairs are formed under mild conditions: the first column in the cube at small concentrations of the reaction products and the high concentration of low-boiling component - cyclohexane, and the second column at relatively low temperatures 75-120C. Temperature 75With the cube of the second column support by reducing the pressure in the unit. Lower temperature to maintain impractical because it greatly decreases the temperature at the top to the greater surface condensers. Temperature 120Can be achieved by increasing the concentration in the bottom liquid of the reaction products (cyclohexanone and cyclohexanol). Further increase in temperature is impractical because begins appreciable formation of high-boiling impurities.

In Fig.1 shows a diagram of the method on the prototype, and Fig.2 and 3 diagram of the proposed method of allocation of cyclohexane.

The essence of the method consists in the following. The reaction mixture 1 (Fig.2) after throttling the flow coming from the site of synthesis, refer to the first column 3 under a pressure of 0.11-0.35 MPa at the top of the column, in which the mixture allocate thread 5 dissolved gases, a portion of unreacted cyclohexane (stream 7) and impurities of water flow 7A, and the remaining reaction products with a large residual content of unreacted cyclohexane is removed from the cube column flow 8 (at a temperature of 105-131(C) which is sent in the following column 12, the pressure at the top of the column 0.04 to 0.11 MPa, in which through the top of the column allocate the remainder to retrieve cyclohexane stream 17, and a concentrated fraction of the reaction products is removed from the cube thread 13 at temperative from acids at low temperature.

Proof of the proposed allocation method of cyclohexane are the following examples.

Example 1 (comparative).

The reaction mixture for the synthesis of cyclohexanone and cyclohexanol with a temperature of 150-155C and a pressure of 1.5-1.7 MPa drossellied to a pressure of about 0.2 MPa and liquid-vapor mixture of 1 (Fig.1) at a temperature of 95-110With together with product recycle 2 served in the distillation column 3, working under pressure above ~0,17-0,25 MPa. Vapors leaving the top of the column are condensed in the condenser 4, neskondensirovannyh gases leaving the condenser flow 5; the distillate is formed partially returned to the column in the form of phlegmy 6; however, the main part 7 of distillate sent to the site of synthesis. The vapor stream leaving the top of the column is formed from the obtained in the evaporator vapor 9 10 and vapor power supply 11. 43000 kg/h of vapor 11 is formed under mild conditions from the liquid phase flow power 1, consisting mainly of cyclohexane (~94 wt.%), at a temperature of 95-110And 134774 kg/h of vapor 10 is formed in the hard conditions of the cubic product containing ~29.2% of cyclohexanone, to 32.7% of cyclohexanol, 8.1% of Na-organic salts and high-boiling primes the e converted into other compounds of 0.5% cyclohexanone and impurities are formed, inseparable from cyclohexanone at subsequent stages. Quantities and compositions of the streams are shown in tables 1 and 2.

Example 2.

The reaction mixture 1 (Fig.2) in the form of a vapor-liquid mixture with a temperature of 128Together with the stream recycling 2 is fed to the rectification column 3. A couple from the top of the column with a temperature of 125To enter the heat exchanger-condenser 4, nscontainerframe gases output stream 5, part of distillate 6 return to the column in the form of phlegmy, the second part of distillate 7 is removed from the unit for reuse at the site of synthesis, the stream 7A bring water fraction. From the cube columns display the diluted fraction of the reaction products 8. Vapor phase ascending the height of the column 3, consists of vapors that come with meals and educated in Cuba in the evaporator 9 column 3. With power came G1=23301 kg/h of vapor. In the evaporator 9 is formed G2=73179 kg/h of vapor. Pair both in food and in the evaporator 9, are formed under mild conditions (evaporated from the mixture containing the reaction products of only 5-10%, the rest - cyclohexane). The amount of degradable cyclohexane in a cube column is not more than 0.06% obtained by synthesis. To separate the greater part of the remaining cyclohexane stream 8 from the s condense in the heat exchanger 15, part 16 of distillate used as phlegmy, part 17 is removed from the unit at the site of synthesis. In Cuba, the column 12 is formed steam stream 18 in number G4=77489 kg/h in the relatively mild temperature conditions (at low temperature ~100With against 125-135 mAC). Moreover, the amount of the concentrated fractions of the reaction product vapor of cyclohexane decreases in 134774/77489=1,74 times in comparison with example 1. Therefore, the amount of degradable cyclohexanone drops to ~0,1%. The pressure at the top of the column 3 0,325 MPa, the temperature in Cuba 131C.

Power 8 column 12 is a vapor-liquid emulsion with a temperature of ~86C. the Amount of vapour G3=21949 kg/h Values and compositions of the streams are shown in tables 1,2.

Example 3.

The original mixture of 1 (Fig.2) in the form of vapor-liquid emulsion with a temperature of 102Together with the product of the recycling enters the distillation column 3 under a pressure of 0.17 MPa at the top of the column. A couple from the top of the column with a temperature of 98To enter the heat exchanger-condenser 4, where the distillate is partially returned to the column in the form of phlegmy 6, the m 5. Flow 7 allocate a smaller portion of current cyclohexane.

Steam flow rising along the column height, is formed in two places: ~45587 kg/h supplied from the raw material with a temperature of 102And ~29824 kg/h of vapor is formed in a cube column at a temperature of 105C. Both the steam flow are formed under mild conditions from dilute solutions of reaction products of (6,0-7 wt.%). The expected loss of cyclohexanone is 0.07 per cent.

For further separation of unreacted cyclohexane cubic liquid column 3 of the thread 8 are directed to the following column 12, operating at reduced pressure (0,04 MPa at the top of the column) and at low temperatures (75With the bottom of the column). Steam flow columns are formed in two places: G3=~20239 kg/h included with the original product with a temperature of ~66With, and G4=83708 kg/h is formed in a cube at a temperature of 75C. the Softness of the situation of education in vapor phase from a more concentrated solution of the reaction products (~60%) is a low temperature in the cube column. The expected number of lost cyclohexanone if this is 0.04%. The number of the resulting vapor is Ah 1 and 2.

Example 4.

The original mixture of 1 (Fig.3) from node washing acids after preheat served in the distillation column 2, the pressure at the top of the column of 0.13 MPa. A couple from the top of the column with a temperature of 89To enter the condenser 4, the distillate is collected in a collection of distillate 4A, and then deduce from it the thread 6 on the irrigation of the column, flow 7 as part of the recoil cyclohexane sent to the head of process flow 7A output exfoliated water. Steam flow rising along the column height, is formed in a cube column under mild conditions: a high concentration of cyclohexane; low concentration of the reaction products and the relatively low boiling point (104C). Cubic liquid columns 2 thread 8 serves in the next column for further separation of unreacted cyclohexane. The pressure at the top of the column 9 atmospheric temperatures above 81With below 120C. a Pair of 10, leaving the top of column 9, condense in the condenser 11, a part of distillate flow 12 return to the top of the column part 13, which is extracted with cyclohexane, returned to the synthesis loop. From the cube column 9 output comparator is Ola.

The amount of vapor generated in the cube the first column under mild conditions (t=104C, the concentration of cyclohexane is 90.2 wt.%) located at 108 t/h, the number of decaying cyclohexanone in the process of heat treatment is at a level of 0.07% of the cyclohexanone in the mixture. In Cuba, the second column is formed 73900 kg/h of vapor at a temperature of 120C. It 134774:73900=1.82 times less than in the prototype. The expected amount of degradable cyclohexanone is at a level of 0.20%. Quantities and compositions of the streams are presented in tables 1 and 2.

From the material balances of the examples (table 1) shows that in each example the amount of degradable cyclohexanone in products related to the line "Esters, resin acids", are different. In the example, compare the growth in the number of these substances (the difference between the thread 8 and 1) is 9 kg/h In the second example (the difference between threads 13 and 1) 2.9 kg/h In the third example (the difference between the content in the threads 13 and 1) is 1.95 kg/h In the fourth example (the difference between the content in the threads 14 and 1) 4.9 kg/h Of table 2 shows that in example 1 (comparative) 9 kg/h of impurities is formed in the column at a temperature of 131With a boiling mixture, �tp://img.russianpatents.com/chr/176.gif">(Example 2) of the diluted solution of the reaction products (up to 7.61%) and subsequent oparka under 100With Stripping fewer vapors (77489 kg/h) quantity of generated impurities is reduced to 2.9 kg/h With a further reduction of the temperature in the cube (example 3) the first column to 104And in Cuba the second column up to 75With the formation of impurities is reduced to 1,95 kg/hour, a temperature Increase by the cube of the second column (example 4), 120With the residue from the concentrated mixture (83% of the reaction products) vapor in the number 79900 kg/h (less than in the prototype) increase the formation of by-products to 4.9 kg/h Is less than in the prototype.

The implementation of desorption and full release of dissolved gases from the mixture in the first column makes it possible to lower the boiling point in the cube of the second column, and conducting two-stage selection process cyclohexane allows you to reduce the amount of vapour in Parke concentrated product. Because maintaining a low concentration of reaction products in the cube reduces the loss of cyclohexanone in Cuba the first column. The result is a soft conditions for the allocation of fractions of the reaction products with minimal is cyclohexanol.

Claims

The method of separation of cyclohexane from the reaction mixture for the synthesis of cyclohexanone and cyclohexanol by distillation, characterized in that the process is conducted as a series of two distillation columns, where the top of the first column divert gases, water and part neproreagirovavshikh cyclohexane, from the cube partially enriched fraction of the reaction products from the top of the second column, assign the second main part of cyclohexane, and the cube of the column is a concentrated fraction of the reaction products at a temperature of 75 to 120C.

 

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