DE1009625B - Process for the production of partial oxidation products of cyclohexane - Google Patents

Description

Process for the production of Teiloxidationspro products of cyclohexane The invention relates to the oxidation of cyclohexane or cyclohexane-containing petroleum fractions with gaseous oxygen.

It is known that the oxidation of cyclohexane to partial oxidation products an important step in the production of polyamide intermediates, e.g. B. adipic acid, represents. The process of oxidation of cyclohexane in the liquid phase too Cyclohexanol and cyclohexanone with only low conversion while achieving high yields a few years ago in U.S. Patents 2,223,493, 2,223,494 and 2,321,551. In general, this procedure resulted in the implementation on a laboratory scale, cyclohexanol-cyclohexanone yields of about 85 to 95 0 / g when the percentage of oxidized cyclohexane molecules is less than 5 5 ° / o. When the percentage of cyclohexane molecules oxidized is about 5 to was about 12ovo, the yield of cyclohexanol - cyclohexanone was about 65 bis 85 o / o. In practice, you can work at any given degree of implementation, if one accepts a decrease in the yield in order to make such a process possible which can be carried out continuously for many months or years without Interruptions are required to remove accumulated by-products.

The invention now relates to a method that is technically feasible is and at which the yield of products convertible into adipic acid of the Degree of conversion of the cyclohexane completely within a wide conversion range is independent.

The invention is based on a prior art that one Method corresponds to which cyclohexane in several reaction vessels in liquid Phase with gaseous oxygen at a temperature of 75 to 200 ° and below a pressure of 3.5 to 35 at in the presence of a catalytically effective amount of a hydrocarbon-soluble cobalt compound up to a conversion of 5 to 20% oxidized and the water formed by the oxidation to the extent of its formation the oxidation mixture is separated.

The invention consists in that at least part of the oxidation mixture before the end of the oxidation extracted with water in the meantime, after the end The oxidation mixture obtained from the oxidation reaction mixes with water, the layers separates and the oxidation products of the cyclohexane after the removal of the cyclohexane wins in the usual way by fractional distillation. The well-known method to remove water, namely by opening the oxidation vessel or where appropriate the oxidation vessels with a reflux condenser and a device for extraction the water layer from the condensate coming from the condenser is provided extremely suitable in the method according to the invention.

In another embodiment of the invention, only one Oxidation vessel operated, while a side stream withdrawn therefrom, continuously extracted with water and then returned to the oxidation vessel. The water layer can then be sent to a collecting vessel and the distillate can be put into circulation to be led back.

Such a side stream can, if necessary, rapidly increase to 50 to 1000 be cooled, a second liquid phase separating out. The distance the latter has a favorable influence on the yield at a relatively high one Degree of implementation within the permissible range.

The oxidation can also be in successive stages and the water extraction take place between the individual stages of oxidation. The continuous water separation during the oxidation is advantageously carried out by azeotropic distillation. In general the yield of cyclohexanol and cyclohexanone in this is on a large scale procedures carried out between 65 and 85o on the crowd of the cyclohexane consumed, and the total yield of partial oxidation products, which yield adipic acid on further oxidation is much higher than that Yield of cyclohexanol-cyclohexanone. In addition, the yield of precursors of the adipic acid, regardless of the degree of conversion within the stated range.

The process according to the invention can also be used in the absence a catalyst can be carried out. However, it has been found that you can do something higher yields of cyclohexanol and cyclohexanone achieved if at least one small amount of catalyst is used. However, the amount of the catalyst can be be extremely small. It is enough z. B. only 0.1 part cobalt per million parts reaction mixture, wherein the cobalt is in the form of a hydrocarbon soluble salt. Other Catalysts, which in place of cobalt in amounts of about 0.1 to 1000 and preferably About 0.5 to 50 parts per million parts can be used, among others Hydrocarbon-soluble compounds of copper, cerium, vanadium, chromium or manganese. The hydrocarbon-soluble cobalt compounds, however, give the best results.

The method according to the invention can be used in any facility, z. B. in tubular reaction vessels, reaction towers or with a stirring device provided autoclaves are carried out.

The best results are achieved if the oxidation vessel used is an autoclave provided with a stirring device or if the process is continuous carried out with a number of such stirred autoclaves arranged in series will. If necessary, several such rows can be arranged in parallel. So can e.g. B. nine autoclaves can be arranged three times three autoclaves. Everyone the autoclave should be equipped with a means for removing water (Condenser with water drainage option). When the removal of water is azeotropic by means of a condenser arranged behind each autoclave in the path of the escaping gases (which is usually under the same pressure as the oxidation vessel), so can the hydrocarbon which is azeotropically distilled off and condensed together with the water separated in a decanter and in one of the oxidation vessels or in one Hydrocarbon recovery flasks are passed. The reaction mixture can continuously pass through the autoclave, with the withdrawn from the first autoclave Liquid is passed into the second, etc. The withdrawn from the last autoclave In preferred embodiments, liquid is passed to a fractionation column, to recover the unreacted hydrocarbon. If necessary, can this can be rapidly cooled to 50 to 1000, with a second acid containing liquid phase forms. The hydrocarbon layer can go directly into the circuit returned or distilled beforehand. If petroleum-derived, benzene and cyclohexane containing other impurities is used, it is best Method for working up the reaction products is described in US Pat. No. 2,557 281 described. According to this method, at a temperature up to 69 "or slightly higher either directly fractionated or steam distilled and then the one containing benzene azeotropic distillate by re-distilling the hydrocarbon layer separated. This azeotropic distillate boils for the most part at one temperature close to the boiling point of cyclohexane just below 810 and completely between 40 and 810.

The main fraction of cyclohexane, which of course has a smaller percentage contains benzene as an oxidation mixture, is returned to the oxidation vessel. The gas that eventually escapes is usually a high-boiling hydrocarbon washed or to recover further amounts of cyclohexane through a low temperature condenser directed. A noticeable increase in the yield of cyclohexanol and cyclohexanone (which several percent with a conversion of about 15Q / o) is then obtained when the recovered cyclohexane from the decanter and / or from the Main still to recover hydrocarbon in the first oxidation vessel and not returned to the second or third or one of the following oxidation vessels will. The reason for this is that it results in a lower concentration obtained on primary oxidation products in the first oxidation vessels, d. H., the average concentration in the row of oxidation vessels is reduced, if the mixture is at the beginning of the series and not at the end of the same with the one in the Recirculated hydrocarbon is diluted. Because of this, will all of the recovered cyclohexane is expediently returned to the first oxidation vessel.

A very economical process for processing the in'dem drain The so-called "Wet KA" process is the reaction products contained in the oxidation vessel.

According to this process, the oxidizable charge, which in the nitric acid oxidation vessel for the production of adipic acid is introduced, an old distillate obtained by pouring water down the drain from a working in the liquid phase cyclohexane oxidation vessel, whereupon one sprayed Separated hydrocarbon and aqueous phases from the mixture obtained, with Steam distillable oil was removed from this aqueous phase, the oil of the hydrocarbon phase added essentially all of the hydrocarbon from the resulting mixture withdrew and the residue obtained was distilled with steam until it was exhausted, thereby serving as oxidizable loading for the nitric acid oxidation vessel suitable oil was obtained.

Although it is essential that that formed in the oxidation reaction Water is removed from the oxidation mixture to the extent that it is formed, it is as stated above, nevertheless expedient that in the mixture after leaving the oxidation vessel contains water. The reason for this is that adipic acid and other solids crystallize out when the oxidation mixture cools. It is therefore advisable to add to the oxidation mixture after it has left the oxidation vessel, however, before the recovery of the hydrocarbon water too, to a precipitate of adipic acid to prevent. The presence of water is also present during the recovery of the hydrocarbon is advantageous, as there is elimination of water from cyclohexanol and cyclohexanone to compounds such as cyclohexylidenecyclohexanone, cyclohexyl ethers and cyclohexyl esters.

Fig. 1 of the drawing shows a flow diagram of an embodiment of the Invention. Here, cyclohexane is transferred from the storage container 1 into an oxidation container 2, which can be an autoclave equipped with a stirrer. The one from this Liquid withdrawn from the oxidation tank is extracted in the tank 3 with water. The extracted hydrocarbon phase is in the second oxidation tank 4, then to a second water extraction 5 and from there into a third oxidation tank 6 headed. Each oxidation tank is provided with capacitors 7, 8 and 9 (e.g. B. a reflux condenser and a decanter or separating funnel, whereby a Recirculation of hydrocarbons and removal of water is made possible). Air is blown into each oxidation tank until the total conversion is as desired Degree of z. B. has reached 12 ° / o. The rate of oxidation is in everyone Oxidation tanks (which are all the same size) are the same. In each of the extraction containers water is introduced and the aqueous phase is removed from the extraction vessels combined with the liquid withdrawn from the last oxidation tank. Likewise this is combined, if necessary, from the capacitors 7, 8 and / or 9 obtained water.

All of the oxidation products in the vessel 10 can be treated further directly by placing both layers in a distillation apparatus for recovery of cyclohexane pumps. Preferably, however, the aqueous phase can be removed in 11 and in 12 for recovery distilled separately from oil which can be distilled with steam. The latter can be combined with the hydrocarbon phase in the product obtained in the vessel 10 and distilled in vessel 13 to recover cyclohexane. This will returned to the reservoir 1. The residue 14, which is all higher than Cyclohexane contains boiling substances, is to be converted into adipic acid by nitric acid oxidation ready. A remarkable observation of both thboretic and practical Interest is that the addition of considerable amounts of cyclohexanol and Cyclohexanone to the starting cyclohexane feed did not result in a yield decrease of the same order of magnitude as one would with a correspondingly increased turnover obtained from cyclohexane to cyclohexanol and cyclohexanone. From this observation can inferred that probably one or more formed during oxidation other constituents of the oxidized mixture the yield of precursors of adipic acid affect unfavorably. Through the intermittent water extraction according to the invention these components are removed from the reaction mixture during the oxidation reaction removed.

This is z. B. through experiments with a total turnover of 10 up to 120 / o were carried out, explains which after a third and after two thirds of the total conversion, the reaction mixture is cooled and extracted with water will.

In a number of such attempts it has been found that between the first two stages by such a water extraction (weight ratio of Cyclohexane to water = 10: 1) 70 to 75% of the acids, 20 to 40% of the esters, 2 up to 3% of the cyclohexanone, 4 to 50% of the cyclohexanol and 4% of the peroxide compounds removed. Both with and without added catalyst the repeated result Oxidation of the upper ones extracted with water Layer yields of adipic acid precursors, which were about 100 / o higher than they were without water extraction at the same degree of conversion could be achieved. The yield of cyclohexanol and peroxide was greatest elevated.

In the previously known methods, the decanting took place The water layer formed on the reflux condensers is also a partial removal of a volatile monobasic acid, which is a by-product. This is going through the data given below, obtained in a series of comparative tests shown, the distribution of the oxidation products in the air oxidation of cyclohexane in the liquid phase was that given in Table 1 below. The values also show the advantage of intermittent water extraction.

The temperature in these tests was 152 to 154 °. The amount of the cobalt naphthenate catalyst used corresponded to one part cobalt per million Parts of reaction mixture. The air supply rate was controlled so that an exhaust gas containing 0.5% oxygen was obtained in the desired reaction.

Table 1 Distribution of cyclohexane oxidation products 1. 2. One-step procedure Three-stage extra Water- extraction Reflux condensate Gross conversion,% ....... 10.4 9.5 Yield of cyclohexanone 31.0 31.2 Yield of cyclohexanol 36.0 30.0 Yield of peroxide ...... 6.9 3.7 Yield of adipic acid ... 6.5 6.0 80.4 70.9 The loss of adipic acid precursors by water extraction of the condensate is surprisingly low. However, a surprisingly large part of the monobasic acids is removed in the process. This was demonstrated by carrying out a one-step process in which all of the condensate was removed and an equal amount of cyclohexane contained in the condensate was continuously added to the oxidation mixture. The decanter was used in the usual manner, and the amounts of various products withdrawn from the decanter in the aqueous phase were measured.

The results were as follows: Table 2 Oxidation products withdrawn from the oxidation mixture in the aqueous phase obtained in the decanter % of the total Compound 'generated quantity distant Oxidation product Cyclohexanone .............. 0.13 Cyclohexanol .............. 0.27 Peroxide ................... 0.80 % of the total Compound generated crowd distant Oxidation product Monobasic acids C5 ....................... 0.69 C3 ....................... 1.12 C2 ....................... 11.0 C1 ....................... 37.7 Dibasic acids Adipic acid .............. 0.28 Glutaric acid .............. 0.51 Succinic acid ........... 2.12 As can be seen, hardly any precursors of adipic acid are removed from the condensate, but formic acid and acetic acid are largely removed from the condensate.

Example cyclohexane was mixed with air in the liquid phase under the The reaction conditions given in Table 3 ("1st stage") are oxidized. The oxidation vessel was equipped with a reflux condenser and a decanter or separation vessel for removal from Water to the extent of its formation during the oxidation reaction. To this »1. Stage «the mixture was cooled to room temperature and with about 1/10 of its volume of water is extracted, the latter being extracted from the decanter contained separated water. The analyzes given show the amounts of the the products obtained from the aqueous and hydrocarbon phases.

However, these products were not segregated as such, as the eventually mixture obtained by distilling off cyclohexane and water from the end products of oxidation products as such for the production of adipic acid by oxidation with nitric acid was suitable. As can be seen from the table, the "1. Stage «obtained upper layer as a charge for the oxidation vessel of the »2. Stage "and in the same way in the" 2. Stage «preserved upper layer as a charge for the oxidation vessel of the »3. Stadiums «is used. The quantities of the products formed are shown in Table 3. For comparison purposes Similar operations, but carried out without intermittent water extraction. The results are recorded in Table 3.

Table 3 Intermittent water extraction during the oxidation of cyclohexane Comparative tests in the liquid phase, but without 2nd stage 3rd stage intermittent water extraction 1st stage Upper Layer Upper Layer Loading 1 2 3 Cyclohexane from the from the 1st stage 2nd stage cyclohexane cyclohexane cyclohexane Catalyst ............... Co- none none Co- Co- Co- Naphthenate added added naphthenate naphthenate nephthenate Concentration of the cata- lysators .................. 1 part each about 1 part each about 1 part each 1 part each 1 part each 1 part each Million million million million million million Temperature, ° C ............ 154 154 154 147 to 153 153 153 to 155 Pressure, kg / cm2 ............. 9.28 9.28 9.28 9.28 9.28 9.28 Liquid residence time, Minutes, 14.8 14.7 14.9 15 15 15 Air supply per loading unit (1), 1 / minute ...... 2.63 2.63 2.63 2.63 5.26 7.89 O2 in the escaping gas, Mole percent ................. 0.9 0.7 0.7 0.9 0.7 0.7 Net gross net gross Sales,% .................. 3.82 3.63 7.33 3.18 10.4 3.8 7.6 11.4 % Yield of: Cyclohexanone ................ 23.4 27.2 25.2 44.8 31.0 28.5 29.2 29.2 Cyclohexanol ............... 40.5 41.3 40.9 24.6 36.0 43.7 33.6 29.0 Peroxide (calculated as Cy- clohexyl hydroperoxide) .... 10.3 7.2 8.8 2.4 6.9 19.7 3.5 2.0 Adipic acid ............. 6.1 5.5 5.8 8.3 6.5 6.0 7.5 9.7 Carbon oxides ............. 1.9 2.7 2.3 3.7 2.8 2.2 2.9 3.3 Other acids ........... 7.0 8.1 5.4 8.9 4.9 6.1 7.0 8.0 Sum of cyclohexanone, Cyclohexanol, peroxide and Adipic acid ............. 80.3 81.2 80.7 80.1 80.4 87.9 73.8 1 69.9 The conversion to adipic acid precursors achieved in the above example is shown graphically in FIG. The curves show that an intermittent extraction of water achieves a constant yield of precursors which are suitable for oxidation to adipic acid with increasing conversion. Similar results are obtained when extracting a side stream instead of the multi-stage extraction process.

In Fig. 2, curves A and C give those in the previous example achieved results again.

Curve B shows those according to the previously known method among similar ones Conditions obtained results, but with the cyclohexane from the reflux condensers each of the three oxidation vessels connected in series into the first oxidation vessel and not returned to that from which the condensate originates will.

From the above data it can be seen that according to the invention Process Yields of precursors of adipic acid of more than 80 01G at higher Conversions are available than previously obtained to achieve such high yields could become. The precursors of adipic acid include both those above specifically mentioned as well as lactones, cyclohexyl esters and others, in relatively smaller Amount of compounds formed.

In certain circumstances the relative amounts may change, however, such minor changes are beneficial to those obtained in accordance with the invention Results do not interfere.

The extraction can be carried out at any suitable temperature will. Essentially the same results were obtained when using the extraction performed at room temperature, 70 and 1400 (under pressure).

While the water extraction according to the invention has a constant yield with increasing conversion, it is noteworthy that a regulation of the acid concentration no effective process in the oxidation mixture with aqueous sodium hydroxide to increase the yield. Rather, the acidity in the oxidation vessel becomes increased instead of decreased by adding alkali.

Furthermore, the formation of other monobasic acids should be suppressed, when monobasic acids are intentionally used up to the amount usually generated in the oxidation mixture are introduced. In fact, it has been observed that one noticeable improvement in the overall yield is achieved when the amount of added monobasic acid is kept low (26 / o). The water extraction process thus keeps the monobasic acid content at a low, optimal value. One complete development removal by alkali is therefore, compared with water extraction, not advantageous, in fact even disadvantageous in certain respects. A periodic one Water extraction lowers the acidity to a level which for one continuous operation with high yield is suitable.

The process can be carried out continuously or batchwise are, however, of course, the advantages of the invention in the continuous Procedures are most notable.

Claims (1)

PATENT CLAIM Process for the production of partial oxidation products of cyclohexane, such as cyclohexanol and cyclohexanone, with one cyclohexane in several Reaction vessels in the liquid phase with gaseous oxygen at one temperature from 75 to 2000 and under a pressure of 3.5 to 35 atm in the presence of a catalytic effective amount of a hydrocarbon-soluble cobalt compound to a conversion from 5 to 200 / o is oxidized and the water formed by the oxidation to the same extent Separation of formation from the oxidation mixture, characterized in that at least a part of the oxidation mixture before the end of the oxidation in the meantime extracted with water, the oxidation mixture obtained after the oxidation reaction mixes with water, separates the layers and the oxidation products of cyclohexane after separating off the cyclohexane in the customary manner by fractional distillation wins. ~~~~~~~ Publications taken into consideration: German Patent Specifications No. 860 491, 859 465, 854 505; U.S. Patent Nos. 2,557,281, 2,565,087.