US2588388A - Oxidation of alkyl-substituted cyclohexanes using aldehydeactivated catalysts - Google Patents

Description

Patented Mar. 11, 1952 OXIDATION OF ALKYL-SUBSTITUTED CYCLOHEXANES USING ALDEHYDE- ACTIVATED CATALYSTS David 0. Hull, Kingsport, Tenn., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application December 16, 1949, Serial N 0. 133,341 h 7 Claims.

This invention relates to the liquid phase catalytic oxidation of substituted cyclohexanes to obtain cyclic acids and ketones and more particularly to the oxidation, by means of aldehydeactivated metal catalysts, of alkyl-substituted cyclohexanes to form cyclic acids under conditions in which ring cleavage is avoided.

For many years in the carrying out of oxidations such as the conversion of various aliphatic alcohols to the corresponding acids it was necessary to employ a roundabout and indirect procedure involving a multiplicity of steps and complicated apparatus. For example, in the conversion of ethyl alcohol to acetic acid it was the practice first to oxidize the alcohol to acetaldehyde in one step and then, by a separate step, to oxidize the aldehyde to the acid. In later years a greatly improved and far more economical technique has been developed, whereby the alcohol may be converted directly, at relatively low temperature and pressure, into the corresponding acid without the necessity of a separate procedure for first obtaining the aldehyde. For example, in my United States Patents Nos. 2,287,- 803; 2,353,157; 2,353,158; 2,353,159; 2,353,160; 2,425,878; 2,425,879; 2,425,880; 2,425,881; 2,425,- 882, I have described an improved process wherein an alcohol, such as ethyl alcohol, may be converted directly to acetic acid by oxidizing the alcohol in the liquid phase by means of oxygen or an oxygen-containing gas in the presence of certain metal catalysts dissolved in an aliphatic acid and maintained in an active state through the agency of a continuous supply of aldehyde. This process has proved to be extremely elfective and economical for the production of aliphatic acids.

The catalytic oxidation of other organic compounds employing a somewhat similar technique, although operated, in general, under conditions which differ substantially from the low temperature processes described in my above-mentioned patents, has been applied to various aliphatic, alicyclic and aromatic ketones, including acetone, methyl ethyl ketone, cyclohexanone, methyl cyclohexanone and acetophenone to convert them to monobasic and dibasic acids such as acetic, propionic, adipic, methyl adipic and benzoic acids. Such a process is described in Flemming et a1. 2,005,183.

In Patent 2,223,493 Loder has described the liquid phase catalytic oxidation of cyclic saturated hydrocarbons such as cyclohexane, cyclopentane, cyclobutane and their substituted derivatives to obtain the corresponding aliphatic dibasic acids, such as adipic, glutaric and succinic. In Patent 2,223,494 Loder describes a similar process for converting cyclic saturated hydrocarbons to cyclic alcohols and ketones, while in Patent 2,265,948 he describes a process involv ing conversion of open chain aliphatic hydrocarbons to acids, ketones, esters and alcohols.

A further extension of the broad concept of oxidizing organic compounds in the liquid phase is described by Loder in Patent 2,245,528 in which reference is made to the oxidation of alkyl-substituted aromatic compounds such as ethyl benzene, toluene and the xylenes to the corresponding aromatic acids such as benzoic, toluic, phthalic and the like. A similar but more specific process is disclosed in the patent to Henke 2,276,774.

Reference to these patents will disclose that in no case have any of the various workers in this field conceived that the alkyl-substituted cyclohexanes could be converted to the corresponding cyclic acids or ketones without cleavage of the carbon ring. Furthermore, not only have none of these researchers recognized or applied the principle of aldehyde activation to such oxidations, but they also have operated under relatively high temperature conditions and obtained relatively low yields of theirrespective products.

The present invention has for its principal object to provide a process for the economical and eflicient conversion of alkyl-substituted cyclohexanes to form cyclic acids and cyclic ketones. A further object is to provide a process whereby such compounds may be directly oxidized to the desired products without cleavage of the alicyclic ring and the resulting production of substantial amounts of open chain acids or other aliphatic compounds. A still further object is to provide a process whereby such oxidations may be carried out in a single step. Another object is to provide a process for the direct oxidation of the alkyl-substituted cyclohexanes to saturated cyclic acids and cyclic ketones in high yields at relatively low temperatures at either ordinary atmospheric or superatmospheric pressure conditions. Other objects will appear hereinafter.

These objects are accomplished by the following invention which, in its broader aspects, comprises firstpreparing an active catalyst solution by dissolving an appropriate metal, metal oxide or other suitable metal compound in an aliphatic acid, such as acetic acid, treating the solution with an oxygen-containing gas and simultaneously adding an aldehyde such as acetaldehyde,

thereby to bring the metal catalyst into a highly active state, and thereafter feeding the desired alkyl-substituted cyclohexane, together with an excess of oxygen, into the catalyst solution while maintaining the catalyst in the solution in an active state by continuously adding aldehyde. In accordance with the invention the solution is maintained under such conditions of temperature and pressure that the solution is maintained in the liquid phase and the cyclic compound in the solution is directly converted to the corresponding cyclic acid. For example, by maintaining a body of active catalyst solution in an appropriate vessel at a temperature within the range of C. and 90 C. and approximately atmospheric pressure and continuously adding methyl cyclohexane, acetaldehyde and oxygen or air to the solution, I obtain substantial yields of cyclohexanoic acid (hexahydrobenzoic acid).

In the following examples and description, I have set' forth several hfth'e preferred embodiments of my inventionjbutthey are included merely for purpos illustration and not as a limitation thereof,

The single figure oi the drawing represents one form of apparatus "may'rie employed for the practice of my inven Qther suitable forms of apparatus which"'rnay be employed for the carrying out of such aprc icess are illustrated in my abovementioned patents for example, Pat- I ents 2,287,803 and 2,353,157.

My invention will be more fully understood by a preliminary discussion of the preparation and the composition of my improved catalyst solutions and the general conditions under which my process is operated.

AS indicated, I employ what I have described as an aldehyde-activated metal catalyst solution. Sucha solution can appropriately be prepared, by dissolving a suitable catalyst metal or one of its aliphatic acid-soluble oxides, salts or other compound in an aliphatic 'acid such as acetic, propionic or butyric acid. While in accordance with my invention, I may employv almostrany metal which will produce metallic ions in solution, I

have found cobalt to be 'an especially valuable.

catalyst. In the same class with cobalt may be mentioned manganese; iron, nickel and, copper. Gther metals which may be, employed as, catalyst with substantially equa facility are lithium,

beryllium, sodium, potassium, rubidium, caseium, calciumfstrontium, barium, magnesium, zinc, aluminum, scandium, yttrium, lanthanum, neoytteibium, gallium, indium, thallium, cerium, ruthenium, rhodium, palladium, osmium, iridium, platinum, gold, tin, antimony, mercury, lead, chromium, .molybdenum, tungsten, uranium, tantalum, vanadium, columbium, niobium, ti-

tanium, thorium, neodymium, praseodymium, il-

linium, samarium, holmium, europium, erbium, gadolinium, thulium, terbium, dysprosium, and

luteciuin.

While in general I prefer to employ. a single metal as the catalyst and in, the form of one of its oxides, salts or other compound which is easily soluble in the aliphatic acid selected as the solvent medium, I may, if desired, employ a plurality of such metals. For example, while I prefer to employ a solution of cobaltous acetate. C0(C2H3 O2)2.4H2 O in glacial acetic acid, I may employ a plurality of metals in the form of their. acetates, propionates or butyrates, or in the form of oxideswhich form' thef'corresponding aliphatic acid salts in the acid'solution. Likewise, while Iprefer to use acetic acid alone as the solvent,

I may employ aliphatic acids such as acetic, propicnic, butyric and the like, either singly or in various combinations one with another.

As to the matter of concentration, I may dissolve the catalyst metal in the acid to produce solutions containing anywhere from 0.1% to 8% of the metal, although, in general, I prefer to keep within the range of 5% to 8%. Likewise, although I prefer to dissolve the catalyst in anhydrous acid, a more dilute acid may be employed. In general, I have found that, in use, more satisfactory. yields of product are obtained if the acid concentration of the catalyst solution is at all times maintained at approximately Once the catalyst solution has been prepared as above described and charged into a suitable reaction vessel, it is brought into a highly active or activated condition by simultaneously feeding in an aliphatic aldehyde, such as acetaldehyde, and oxygen or anoxygencontaining gas at such a rate and at such atemperature as to cause the catalyst to become and remain active, a condition usually initially indicated by change in color of the original solution. The oxyn f d is late to provide a slight excess r oxygen over and above that required for the oxidation reaction, such excess being indicated by the presence of a few per cent of oxygen in the gaseous eflluents from the process. It will, of course, be understood that such matters as feed rates of aldehyde and oxygen, temperature and the like, in general, have to be determined for each particular catalyst and with reference to the compound to be oxidized. In the case of a cobalt catalyst in acetic acid, the original solution, which is pink, changes to green upon activation, indicating that the cobalt ions have changed from a lower to a higher state of valence, that is, from the cobaltous to the cobaltic stateand that the solution is in the desired catalytically active condition. While air is the most economical source of oxygen, I may employ any suitable oxygen-contain: ing gas such as pure oxygen, ozone, or mixtures of such gases with inert gaseous diluents. Likes wise, although I prefer to use acetaldehyde, I may employ other aliphatic aldehydes suchaspropionaldehyde, butyraldehyde and the like, all or which aldehydes may be employedsingly or. in various combinations. one with another. In, gen eral, the aldehyde feed will be so regulatedas to maintain 1% to 5% of the aldehyde in the reaction liquid. I

While in some cases the catalyst solution will become active merely upon introduction of the aldehyde and blowing with air or oxygen at ordi nary atmospheric temperatures, it may be necessary to heat the solution moderately, say, to a temperature in the vicinity of 50-60 C. in order, to initiate catalyst activity.

As to the matter of temperature, I may oxidize alkyl-substituted cyclohexanes in accordancewith my invention at a temperature within the range of 5 C. to 150 0., although I prefer to operate in the vicinity of 80 C. to C. In general, high temperatures, that is, temperatures in excess of the boiling point of the solvent or product, are to be avoided in the interest offpre-j eluding degradation of reactants or products, or losses by evaporation, polymerization or like phenomena. In view of the fact thatthe oxida-, tion reactions here involved are exothermic in character, it is usually necessary continuously to cool the reaction medium in order to keepthe temperature within the desired limits, to prevent J excessive loss of reactants by evaporation and to preclude the possibility of the reaction becoming too greatly accelerated. On the other hand, under certain circumstances it may be necessary actually to supply heat, as, for example, in the case of first starting the process, in order to initiate catalyst, activity.

As to pressure, while I prefer to operate at atmospheric pressure, I may operate at pressures below atmospheric or as high as 2 to 10 atmospheres or more. pheric in general permit operation at higher temperatures. It will of course be understood that thetemperature and pressure will vary according to the requirements of the particular material undergoing oxidation, the rate of feed of the several reactants and with other variables, the control of which is within the skill of the trained chemist or chemical engineer.

It will, of course, be understood that in oxidizing alkyl-substituted cyclic hexanes in accordance with my invention the oxygen supplied by continuous introduction of air or other oxygen-containing gas, as explained above, is the fundamental source of oxygen for the oxidation reaction. The chief reaction product will be one or more of the cyclohexanoic acids or homologous or related acids. For example, methyl cyclohexane yields cyclohexanoic acid, ethyl cyclohexane gives methyl cyclohexyl ketone and cyclohexanoic acid, 1,4 dimethyl cyclohexane converts to hexahydroterphthalic acid, and so on, together with the production of small amounts of carbon dioxide, formic acid and other degradation products.

My invention will now be more clearly understood by reference to a practical operation which may be conveniently carried out in an apparatus such as that illustrated in the single figure of the drawing.

The numeral I designates an oxidation unit which may consist of a plurality of flanged stainless steel tubes of six-inch inside diameter and approximately ten feet long, or any other convenient size or proportions, superimposed one on top of the other and bolted together, the main sections being represented by numerals 2, 3, 4 and 5. Each section is provided with a suitable cooling means which may take the form of an in-' ternal centrally disposed stainless steel coil, such as coil 6 of section 5, of one-half inch or other appropriate inside diameter, each coil being supplied with cooling medium, such as water through inlet 1 and emerging therefrom through outlet 8. Each section is also supplied with a thermometer, as shown, inserted through the wall of each section by means of a thermometer well (not shown) The lowermost section of the oxidation unit consists of a tubular stainless steel member 9 of the same inside diameter as the upper sections of the unit, flanged at the top and closed at the bottom. To section 9 is connected inlet conduit, l0, flow of liquid through which is controlled by valve H. Connected into conduit I is valved aldehyde feed conduit l 2 and another valved conduit l3 for supplying the material to be oxidized to the oxidation unit. While the valves in these feed lines may be so operated as to provide a regulated or metered flow of materials to the unit, a, somewhat more convenient method is to provide rotameters or other metering device's 'for this purpose.

Section 9 has tapped into its lower closed end another inlet conduit l4 into which is connected air inlet conduit l5, flow of air or other oxygen Use of pressures above atmos-- means for draining the unit when not in use or between successive runs.

A perforated difiusion plate is inserted and bolted in place between the lower flange of section 2 and the flanged top of bottom section 9 to provide a means of evenly distributing the liquidgaseous mixture which enters the bottom of the unit.

The topmost portion of the oxidation unit may conveniently comprise three sections, l8, l9 and 20, each of which is flanged and bolted together as previously described. A distributor plate, which may include a bubble cup and downcomer, is positioned between the upper flange of section 5 and the lower flange of section I8. To sections l8 and I9 there is connected a high-pressure sight glass 2| for indicating the level of liquid in the upper part of the unit.

The upper closed end of section 2B is provided with an outlet conduit 22 adapted to conduct vapors and gas evolved from the top of the unit to cyclone separator 23 where any entrained liquid is separated from the mixture and conveyed back into the upper part of the oxidation unit at section I8 through conduit 24, the latter being so formed at its end as to provide a liquid seal in proximity to its junction with section I8.

Cyclone separator 23 is also provided with an outlet conduit 25 which conveys gaseous and vaporous materials to water-cooled condenser 26 of appropriate size and design, cooling medium for which is supplied through inlet 21 and emerges through outlet 28. Condenser 26 i also connected through conduit 29 and sight glass 30 to product receiver 3|, the latter also being provided with a sight glass 32 for indicating the level therein.' The product receiver is also equipped with valved conduit 33 for withdrawing product therefrom as desired.

Vapors not condensed in condenser 25 may find their way in the direction indicated by the arrows, through conduits 3t, 35, and 36 into the bottom of scrubber 31 which may take the form of a stainless steel tube of appropriate diameter packed with a liquid distributing material such as berl saddles or Raschig rings. Scrubber 31 is provided near its upper closed end with conduit 38 through which water is supplied, passing in countercurrent to the vapor-gas stream ascending in 3'! and thereby dissolving out any portions of products or reactants which may have escaped entrapment in separator 23 or condenser 25.

The lower end of scrubber at is connected, through conduit se' to receiver 3!. The scrubber receiver may be drained, when necessary, through valve 33" to a recovery system.

Scrubber 31 is also provided at its upper end with a gas outlet conduit 37 and pressure con-' trol valve 39. The gas then escapes through pressure control valve 39 to the atmosphere.

In order to recover the acid made from the oxidation of the alkyl-substituted cyclohexanes, the catalyst solution is withdrawn from the oxidation unit at a slow rate through conduit 39, valves 40 or 4| to jacketed crystallizers 4d or 45. Cooling medium isturned into the jackets of the crystallizers and the mixture is cooled to around 5 C. While crystallization is being carried out in one crystallizer, the other is being filled. When thecrystallization is complete valve 44 C51- 45{ opened and the material is allowed to pass into filter 46 or to a centrifuge. The solid acid is removed from the filter or centrifuge and further purified. The filtrate, containing most of catalyst passes through conduit 49 to receiver 50 or From here it is pumped continuously by means of pump 53 to the oxidation unit.

The oxidation unit is operated at such a temperature that the acid produced is boiled ofi through conduit 22, through separator 23 and condenser 26 to receiver 3|, as it is made.

The operation of the apparatus when used to carry out the process of my invention will be apparent on inspection. in starting, oxidation unit 4 is filled somewhat less than full with catalyst solution, which may conventiently take the form of a 3% solution of cobaltous acetate in glacial acetic acid. Air valve I6 is opened slightly and aldehyde feed is put on the unit by opening the valve in feed line I2. It will, of course, be understood that a suitable cooling medium such as water is supplied to the several coils of the unit and that the thermometers are in place in the respective thermometer wells for taking readings of the temperature of the solution.

If the catalyst solution does not become active, as indicated by change in color from pink to green, after the elapse of several hours, it may be necessary to supply steam to the coils instead of cooling medium, thus to raise the temperature to approximately 60 C. When the catalyst has become active, it is generally desirable to add more cobalt acetate to bring the concentration up to approximately 6%. The amount of catalyst dissolved in the original solution will vary, not only with the particular catalyst selected, but also with the temperature and various other conditions. Sufiice it to say that a few percent of the material is generally sur'hcient for effective operation.

Once the catalst has been activated, the material to be oxidized is introduced into the oxidation unit through conduit I3 and the aldehyde and air feeds are adjusted so as to provide the proper proportion of each material to perform their respective functions. In general, the rate of aldehyde introduction will be controlled so as to maintain the catalyst at all times in an active condition, while the rate of oxygen feed will be so regulated as to provide a slight excess of oxygen over and above that actually required for oxidation of the material being converted, as indicated by a few percent of free oxygen in the ef fluents from the process.

Assuming the material to be oxidized, and aldehyde and air or oxygen, are being continuously fed, oxidation product will be continuously removed from the unit through conduit 22 and conduit 39. A certain amount of gaseous and liquid material also passes out of the device along with the product, the liquid portions being separated from the aseous or vaporous portions in cyclone separator 23 and eventually returned to the zone of oxidation through conduit 2 3.

The major portion of the condensable vapors, consisting mainly of the products of oxidation, are condensed in condenser 26 and find their way into product receiver 3| from which they are continuously removed at such a volume rate as to maintain the proper liquid level in the oxidation unit. The uncondensable gases and vapors are conveyed through conduits 3t, 35 and 36 into water scrubber 31, passing upwardly in countercurrent to a stream of water. Any vaporized materials which have escaped condensation in condenser 26 are thus dissolved in the water and pass to receiver 3 I.

The product of the process may be removed from the system and conveyed to any desired concentrating or purifying steps for conversion into the desired concentrated acid or other product. Likewise, the acid or other materials which have been scrubbed out of the vapor-gas stream passing through scrubber 31 may be removed from scrub receiver 3! through valved conduit 33 and treated in any appropriate manner for recovery of the dissolved materials.

As'to the matter of temperature, I may conveniently carry out oxidations in accordance with my process, when operated at atmospheric pressure, within the range of -5 C. to C. Since the reactions involved are exothermic, it is generally necessary continuously to supply a cooling medium to the coils of the oxidation unit in order to maintain the temperature within the indicated limits. However, in some cases, as for ex.- ample, in oxidizing materials of high boiling points, or in accelerating the oxidation reaction, it may be desired to employ higher temperatures than those indicated. When such higher temperatures are employed, pressures in excess of atmospheric will be desirable in order to prevent boiling away, either of the acetic or other aliphatic acid catalyst solvent or of the product of the reaction itself. When employing apparatus such as described herein for the carrying out of oxidation reactions at higher temperatures, say in the range of C. to 150 C., it will be understood that valve 38' will be closed and provision made for maintaining the desired pressure in the system. Pressure operation will of course require that reactants and scrubbing media be in.- troduced under a pressure sufficient to compensate or balance the pressure existing in the system. While the pressure may under such circumstances vary over a wide range, depending on the temperature it is desired to maintain in the oxidation Zone and on various other factors, in general pressures ranging from atmospheric to 10 atmospheres are satisfactory.

My invention will be more fully understood by reference to a number of specific examples illustrating typical conversions carried out in accordance therewith.

EXAMPLE I Oxidation of methyl cyclo errane to cyclohexs anoic acid The oxidation unit was filled approximately /3 full with a catalyst solution which comprised about 3% cobalt acetate in glacial acetic acid. Air was turned on and acetaldehyde feed was started. The initial temperature was 30? C. and after two hours the temperature rose rapidly to 60 C. at which time cooling water was added to maintain the temperature at (SO-70 C. Morelcobalt acetate was added to bring the content up from 3 to 6%. After severalhours operation with the additional cobalt acetate added, the catalyst solution was sufficiently active to start full operation.

The feed was adjusted at such a rate so that 20 mol per cent methyl cyclohexane and 80 mol per cent acetaldehyde was being fed. The temperature was controlled at 70-80 C. at atmospheric pressure. The feed was continuousat the rate of 29 units of methyl cyclohexane per hour and 53' units of acetaldehyde per hour. At the end of ten hours operation it was found that units of cyclohexanoic acid were made, representlng a 35% conversion per pass. The ultimate yield based on methyl cyclohexane was 91%. The cyclohexanoic acid was removed from the system continuously by withdrawing the catalyst solution, containing the dissolved cyclohexanoic acid, into a cooled tank. The solution was cooled to about (3., and a good portion of the cyclohexanoic acid crystallized out. The crystals were then filtered out or centrifuged and purified. The filtrate, which contained most of the catalyst was then returned to the oxidation unit. The filtrate also contained unconverted methyl cyclohexane in an amount corresponding to 65% unconverted methyl cyclohexane.

EXAMPLE II Oxidation of ethyl cyclohexane to cyclohexanoz'c acid and methyl cyclo eccyl Icetone A catalyst was prepared in a similar manner as described in Example I. In this case ethyl cyclohexane and acetaldehyde were fed continuously to the oxidation unit in the ratio of 20 mol per cent to 80 mol per cent. The temperature was maintained at 70-80 C. and the pressure atmospheric. After feeding a total of 370 units of ethyl cyclohexane and 580 units of acetaldehyde', it was found that 127 units of cyclohexanoic acid was made and small amounts of methyl cyclohexyl ketone representing a conversion of ethyl cyclohexane to cyclohexanoic acid of 30% per pass and of ethyl cyclohexane to methyl cyclohexyl ketone of approximately 3%. The ultimate yield based on ethyl cyclohexane was 89%. The recovery of the acid and the recycling of the catalyst was carried out in the same manner as described in Example I.

EXAMPLE III Om'dation of 1,4 dimethyl cyclohexane to hexahydroterphthalic acid After preparing an active catalyst as in Example I, 1,4 dimethyl cyclohexane was fed to the cyclohexane and 89 mol per cent acetaldehyde or a total of 168 units of 1,4 dimethyl cyclohexane and 530 units of acetaldehyde over a 10 hour period. After completing the run,

acid was made, representing a conversion of 25% of 1,4 dimethyl cyclohexane to the acid per pass.

An ultimate yield of 90.5% was obtained based on the 1,4 dimethyl cyclohexane fed. The recovery of the acid and the recycling of the catalyst was done as described in Examples I and 11.

What I claim is:

1. A process for the direct and the substantially continuous oxidation of methyl cyclohexane to cyclohexanoic acid wherein a predetermined number of units of the methyl cyclohexane per hour are subjected to the substantially continuous oxidation process which comprises preparing a cobalt acetate catalyst solution in acetic acid by incorporating approximately 3% cobalt acetate in glacial acetic acid, activating this catalyst solution by passing air and acetaldehyde therethrough at a temperature between 30-60 0., adding further cobalt acetate to the catalyst solution to bring the content of the cobalt up to approximately 6%, continuing the treatment of the catalyst solution with air and acetaldehyde for several hours until the catalyst solution is activated, then passing into the activated catalyst solution the methyl cycleoxidation unit along with acetaldehyde. The ratio of feed was 11 mol per cent 1,4 dimethyl analysis showed that 64.5 units of hexahydro terphthalic hexane wherein a predetermined number of units thereof per hour are substantially continuously oxidized to cyclohexanoic acid which comprises preparing an acetic acid catalyst solution by incorporating a metal ion in glacial acetic acid, activating this catalyst solution by passing air and acetaldehyde therethrough at a temperature between 30-60" (3., adding further metal ion to the catalyst solution, continuing the treatment of the catalyst solution with air and acetaldehyde for several hours until the catalyst solu tion is fully activated, then passing into the activated catalyst solution the methyl cyclohexane to be oxidized, additional acetaldehyde for maintaining the activity of the catalyst and gaseous oxidizing medium, the process being characterized in that the units per hour of acetaldehyde substantially continuously fed to the process are substantially in excess of the units per hour of cyclohexane substantially continuously fed,

-maintaining the process under a temperature lyst solution by incorporating a metal ion in a lower aliphatic acid, activating this catalyst solution by passing air and acetaldehyde therethrough at a temperature between 30-60" C., adding further metal ion to the catalyst solution, continuing the treatmentof the catalyst solution with air and aldehyde for several hours until the catalyst solution is activated, then passing into the activated catalyst solution the ethyl cyclohexane to be oxidized, additional aldehyde for maintaining the activity of the catalyst and gaseousoxidizing medium, the process being characterized in that the units per hour of aldehyde fed substantially continuously to the process are substantially in excess of the units per hour ofthe ethyl cyclohexane continuously fed, maintaining the process under a temperature between -5 and C. and at a pressure such that a substantial portion of catalyst solution is maintained in liquid phase, thereafter recovering the aforesaid products produced.

4. A process for the direct oxidation of 1,4 dimethyl cyclohexane to hexahydroterphthalic acid which comprises preparing a catalyst solution,

hour of aldehyde fed to the process are substantially in excess of the units per hour of the 1,4 dimethyl cyclohexane continuously fed, maintaining the process under a temperature between -5 and 90 C. and at a pressure such that the solution is maintained in liquid phase, and thereafter recovering the hexahydroterphthalic acid produced. 1

5. A process for the direct oxidation of alkylsubstituted cyclohexanes from the group consisting of methyl cyclohexane, ethyl cyclohexane and dimethyl cyclohexane by procedure including substantially continuously oxidizing a predetermined number of units per hour of the substituted cyclohexanes to a cyclic carboxylic acid which comprises preparing an activated catalyst solution, then substantially continuously passing through this activated catalyst solution the substituted cyclohexane to be oxidized and also substantially, simultaneously and continuously passing through the activated catalyst solution, additional amounts of a lower aliphatic aldehyde and gaseous oxidizing medium, the units of the aldehyde passed through the activated catalyst solution substantially exceeding the units of the substituted cyclohexane per hour passed through the solution, maintaining the catalyst solution during the process at a temperature within the range of -5 C. and 90 C. and a pressure such that the substantial part of the catalyst solution remains in the liquid phase and recovering the cyclo carboxylic acid produced.

6. A process for the direct oxidation of alkylsubstituted cyclohexanes from the group consisting of r ethyl cyclohexane, ethyl cyclohexane and dimethvl cyclohexane by procedure including substantially continuously oxidizing a predetermined number of units per hour of the substituted cyclohexanes to a cyclic carboxylic acid which comprises preparing an activated catalyst solution, by substantially continuously treating the catalyst solution for several hours with a gaseous medium comprised of air and lower aliphatic aldeh de whereby the catalyst solution is activated, then substantially continuously passcyclic carboxylic acid produced by substantially continuously withdrawing from the oxidation process catalyst liquid containing the acid, subjecting the Withdrawn liquid to a crystallization treatment whereby crystals in the withdrawn catalyst liquid are formed, separating the cyclic acid crystals from the liquid, returning the catalyst liquid to the oxidation process and prior to the introduction of the catalyst liquid into the oxidation process incorporating a content of lower aliphatic acid therein.

'7, A process for the direct oxidation of alkylsubstituted cyclohexanes from the group consisting of methyl cyclohexane, ethyl cyclohexane and dimethyl cyclohexane by procedure including substantially continuously oxidizing a predetermined number of units per hour of the cyclohexanes to a cyclic carboxylic acid which comprises preparing an activated catalyst solution by substantially continuously for several hours treating cobalt acetate in acetic acid with a gaseous medium whereby the catalyst solution is activated, said gaseous medium comprised of a lower aliphatic aldehyde and air, then substantially continuously passing through this activated catalyst solution the substituted cyclohexane to be oxidized and also substantially, simultaneously and continuously passing through the activated catalyst solution additional amounts of a lower aliphatic aldehyde and gaseous oxidizing medium, the units of the aldehyde passed through the activated catalyst solution exceeding the units of the substituted cyclohexane per hour passed through the solution, maintaining the catalyst solution during the process at a temper-- ature within the range of -5 and 90 C. and a pressure such that the substantial part of the catalyst solution remains in the liquid pha e and recovering the cyclic acid produced by substantially continuously withdrawing from the oxidation process catalyst liquid containing the acid, subjecting the withdrawn liquid to a crystallization treatment whereby crystals in the withdrawn catalyst liquid are formed. separating the cyclic acid crystals from the liquid and returning the catalyst liquid to the oxidation process.

DAVID C. HULL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,223,493 Loder Dec. 3, 1940 2,245,528 Loder June 10, 1941 2,276,774 Henke Mar. 17, 1942 2,302,463 Palmer et al Nov. 17, 1942

Claims (1)

1. A PROCESS FOR THE DIRECT AND THE SUBSTANTIALLY CONTINUOUS OXIDATION OF METHYL CYCLOHEXANE TO CYCLOHANOIC ACID WHEREIN A PREDETERMINED NUMBER OF UNITS OF THE METHYL CYCLOHEXANE PER HOUR ARE SUBJECTED TO THE SUBSTANTIALLY CONTINUOUS OXIDATION PROCESS WHICH COMPRISES PREPARING A COBALT ACETATE CATALYST SOLUTION IN ACETIC ACID BY INCORPORATING APPROXIMATELY 3% COBALT ACETATE IN GLACIAL ACETIC ACID, ACTIVATING THIS CATALYST SOLUTION BY PASSING AIR AND ACETALDEHYDE THERETHROUGH AT A TEMPERATURE BETWEEN 30-60* C., ADDING FURTHER COBALT ACETATE TO THE CATALYST SOLUTION TO BRING THE CONTENT OF THE COBALT UP TO APPROXIMATELY 6%, CONTINUING THE TREATMENT OF THE CATALYST SOLUTION WITH AIR AND ACETALDEHYDE FOR SEVERAL HOURS UNTIL THE CATALYST SOLUTION IS ACTIVATED, THEN PASSING INTO THE ACTIVATED CATALYST SOLUTION THE METHYL CYCLOHEXANE TO BE OXIDIZED, ADDITIONAL ACETALDEHYDE FOR MAINTAINING THE ACTIVITY OF THE CATALYST AND GASEOUS OXIDIZING MEDIUM, THE PROCESS BEING CHARACTERIZED IN THAT THE UNITS PER HOURS OF ACETALDEHYDE FED TO THE CONTINUOUS OXIDATION PROCESS ARE SUBSTANTIALLY IN EXCESS OF THE UNITS PER HOUR METHYL CYCLOHEXANE CONTINUOUSLY FED, MAINTAINING THE PROCESS UNDER A TEMPERATURE BETWEEN -5* AND 90* C. AND AT A PRESSURE SUCH THAT A SUBSTANTIAL PART OF THE SOLUTION IS MAINTAINED IN LIQUID PHASE, THEREAFTER RECOVERING THE CYCLOHEDXANOIC ACID PRODUCED.

Images