CS257112B1 - The method of absorption of organic compounds from off-gases of the cyclohexane oxidation process - Google Patents

Abstract

The purpose of the solution is to reduce the energy consumption of the cyclohexanone production process by cyclohexane oxidation and to increase the efficiency of absorption of organic compounds from the off-gases of the cyclohexane oxidation process and the subsequent processing of the oxidation mixture. The above purpose is achieved by using as an absorption medium and/or as its component in the process of absorption of organic compounds from the off-gases of cyclohexane oxidation and processing of the oxidation mixture a dehydrated mixture of mainly cyclohexanol and cyclohexanone, containing 40 to 80 wt. % cyclohexanol, 20 to 50 wt. % cyclohexanone, up to 3 wt. % organic compounds formed in the process of cyclohexane oxidation and processing of the oxidation mixture with a boiling point higher than the boiling point of cyclohexanol, up to 5 wt. % organic compounds with a boiling point lower than the boiling point of cyclohexanone and up to 0.3 wt. % water. The amount of absorption medium at the inlet to the absorption is 0.003 to 1 kg/1 kg of cyclohexanone, with at least 5% by weight of this amount being continuously withdrawn for cyclohexane regeneration carried out on the rectification column producing the absorbent, which ensures the following rules:

Description

257112

SUMMARY OF THE INVENTION The present invention relates to a process for absorbing organic compounds from degassing processes of cyclohexane oxidation and treating the resulting oxidation mixture.

Oxidation of cyclohexane with air is generally used for the production of cyclohexanone. Most often, it is carried out in the liquid phase at elevated pressure, at temperatures of 150-170 ° C and under catalytic delivery of transition metals such as cobalt, chromium, nickel and the like.

In addition to cyclohexanone and cyclohexanol, which are the desired products, a number of undesirable products are also formed by the oxidation of cyclohexane by the deeper oxidation associated with the destruction of the cyclohexane ring and subsequent oxidation of its products. Thus, aliphatic alcohols, carbon dioxide, carbon monoxide, mono- and di-carboxylic acids, hydroxy- and ketocarboxylic acids, water, aldehydes but also esters, especially cyclohexyl esters of the corresponding carboxylic acids, are formed.

In the oxidation of cyclohexane, it is necessary to carry out the reaction so as to achieve as high a selectivity as possible for cyclohexanone and cyclohexanol, but at still acceptable energy costs. it is known that, in reducing conversion, the selectivity of stupa and vice versa, it is necessary to conduct the process under the conditions of the lowest material and energy costs.

The process selectivity is also influenced by the pressure construction of the oxidation reactor or reactor. Any change in these influences is particularly challenging in nature, the most in terms of machine-technological equipment, this is related to some other accompanying phenomena, such as the supply of heat to the reactor from the outside (the so-called cut-off value when the presses are lowered) and the like.

As is clear from the data of MS. No. 162,623 is very important for achieving the high degree of selectivity of the cyclohexane oxidation process, the concentration of cyclohexanol and cyclohexanone in cyclohexane entering the reactor. The scales of these data up to 50% cyclohexanone and 25% cyclohexanol are oxidized to the undesired compounds by the reactors.

Said patent application discloses a method for concentrating cyclohexanol and cyclohexanone from the reactor degasses by pre-condensation of cyclohexane which is recycled to the oxidation reactor with a minimum concentration of cyclohexanol and cyclohexanone. In degasses from the cyclohexane oxidation process before being discharged to the atmosphere, a reduction in the content of cyclohexane, but also of residual cyclohexanol and cyclohexanone, is unavoidable to the lowest possible value. This is important not only from the point of view of the economy of the process, but also from the point of view of reducing the environmental emissions of organic compounds.

Most often, the process of reducing the concentration of organic compounds in the off-gases not only from the oxidation process, but also from the subsequent treatment of the oxidation mixture, in particular by the rectification of cyclohexane, is carried out by absorption in gray-type absorption columns, e.g. approximately the same pressure as in the process which produces the off-gas, while, together with a substantial reduction in temperature, has a favorable effect on the cyclohexane condensation and adsorption process.

Glycol rings are used for heat removal from absorption columns and the temperature of degassing is about 0 ° C.

The maximum use of these parameters to achieve the highest possible absorption system is given by the possibility of existing machinery and equipment, respectively. their change often requires disproportionate energy costs, the effect achieved.

Therefore, it is first of all an effort to exhaust the possibilities of improving the efficiency of the absorption process in a modest manner. From this viewpoint, the medium (absorption) used for its regeneration has proven to be very interesting, whereby cyclohexane is recycled to the oxidation process. In the prior art, rectified cyclohexanone of high purity, up to 99.9% by weight, is used as the absorbent. Its use, but also the method of regeneration, has a number of technical and economic disadvantages. It is an absorbent that unnecessarily energy-consumingly prepares for the purpose of use, resulting in raw materials. Due to the repeated thermal stress of the relatively small amount of absorbent resulting from the regeneration, so-called heavy compounds are formed, clogging up the absorption system and deteriorating its effectiveness, which adversely affects the amount of organic compounds in the water. The exchange of the adsorbent is fed once, after the parameter properties have been reached, when this measure is necessary. The overwhelming part of the aforementioned disadvantages can be overcome by using the method of the present invention.

The invention solves the absorption of organic compounds, from the degasses of the cyclohexane oxidation process, which takes place in the liquid phase as well as from the degassing of the oxidation mixture, consisting of the unreacted cyclohexane recycled by the oxidation, acidic and alkaline hydrolysis of the esters a pressure of 0.2 to 1.5 MPa and a temperature of 120 to 200 ° C, with simultaneous removal of the cyclohexanol and cyclohexane-water vapor and removal of the mixture.

Under these conditions, a mixture of 40-80 wt. % cyclohexaanol, 20 to 56 wt. cyclohexanone to 5% by weight of the organic compounds formed in the cyclohexane oxidation process and to the oxidation mixture having a boiling point lower than

Claims (3)

257112 the boiling point of cyclohexanone, up to 3% by weight of organic compounds with a boiling point higher than the boiling point of cyclohexanol and up to 0.3% by weight of water, is in the amount of 0.003 to 1 kg / kg of cyclohexanone produced into the degassing absorption process as ab adsorptively the medium and / or its component. In order to increase the efficiency of the absorption system, the absorption medium is continuously absorbed by regenerating at least 5% by weight of the amount used, most preferably by varying the total amount of absorbent on the rectifying column producing the medium, thereby reducing the regeneration medium recovery potential and providing a recovery device. , for other purposes. The process of the present invention has the most technical and economic advantages: using a mixture of high cyclohexanol content, which has a lower vapor pressure than cyclohexanone, reduces the loss of absorption media, reduces the material and energy efficiency of the cyclohexanone production process, resulting from the change The reduction in the amount of exhaled cyclohexane also has a beneficial impact on the environment. The clogging with so-called heavy compounds is removed, which also affects the beneficial absorption efficiency. EXAMPLE 1 (Comparative) Degassing from the process of cyclohexane oxidation at 0.95 MPa and 155-163 degrees Celsius, containing 90% by weight of the process according to the invention. %, 2.5 wt. % cyclohexane, 3.55% by weight of oxygen, 1.75% by wt. carbon dioxide, 2.1. wt. of the uhoinate oxide and the remainder being water, formic acid and acetic acid, is introduced into the tray column at a temperature of 15 ° C and a pressure of 0.9 MPa. 15 "C, at a slight overpressure, consisting of: 68.9% by weight of nitrogen, 24.2% by weight of cyclohexane 2.7% by weight of oxygen, 1.3% by weight of carbon dioxide, 1.6% by weight of carbon, The weight ratio of the degassing rate of the oxidation and treatment of the oxidation mixture is from 25 to 26. Rectified cyclohexanone, as absorbent, is supplied to both absorbent systems in an amount of 0.25 kg / kg of cyclohexanone produced. the absorbent through the off-gas to the atmosphere is 0.004 kg of cyclohexanone (tons of cyclohexanone produced, the cyclohexane content of the off-gas decreases to 3.2% by weight of inlet amount, at a degassing temperature of 0 DEG C. from The re-generation column, n and wherein the cyclohexane is rectified, thereby providing the desired qualitative parameters of the absorbent. The sorption circuit does not change, only the losses incurred. EXAMPLE 2 Under analogous conditions to Example 1, oxidation and work-up oxidation mixtures are fed to an exhaust gas absorption system, containing 70 wt. % cyclohexanol, 28 wt. cyclohexanone, 1.5% by weight of organic compounds with a boiling point lower than that of cyclohexanone, 0.4. wt. % of compounds having a boiling point higher than cyclohexanol and 0.1 wt. water. The absorbent flux to the atmosphere at 0 ° C is reduced by 20% by weight, the energy efficiency of cyclohexanone production is reduced to 0.26 GJ / t of cyclohexanone produced, with 20% by weight being reduced. the absorbance used is recycled to the rectification column producing the absorption mixture, which is continually altered and the residue is regenerated analogously to Example 1. A process for absorbing organic compounds from off-gases from a liquid phase oxidation process of cyclohexane by airborne oxygen and from degassing of an oxidation mixture consisting of recrystallization of unreacted cyclohexane recycled to an oxidation process, acid of alkaline ester hydrolysis at pressure 0.2 to 1.5 MPa and a temperature of 120 to 200 ° C, while distilling off the cyclohexanol and cyclohexanone with water vapor and a dewatered mixture, characterized in that dehydrated ynAsez is used as the absorbent medium and / or as a component thereof in the absorption process. a mixture predominantly cyclohexanol and cyclohexanone. 2. Process according to claim 1, characterized in that 0.003 to 1 kg of absorbent / 1 kg of cyclohexanone produced, which contains 40 to 80% by weight, are metered into the absorption process. % cyclohexanol, 20-50% cyclohexanone, up to 5% wt. % of the organic compounds formed in the oxidation process of cyclohexane and the treatment of the oxidizing mixture, with a boiling point lower than that of cyclohexanone, up to 3% by weight. % of organic compounds with a boiling point higher than that of cyclohexanol and up to 0.3% by weight. water. 2 E 7 11 2 7 8 3. The spasob of clauses 1 and 2, characterized in that at least 5 wt. from the metered amount of absorbent medium to the absorption process, preferably its entire amount is led to regeneration of the cyclohexane-rectification column producing the adsorbent medium. Severografia, n. P. Plant 7, Most Price 2,40 Kcs