US2851496A - Preparation of oxidation products of cyclohexane - Google Patents

Description

nited States PREPARATIGN OF GXIDATEUN PRODUCTS F CYCLOHEXANE Harry Louis Cates, Jr., .lohn Ulivcr Punderson, and Robert William Whcatcroft, Wilmington, Bet, and Alvin Barber Stiles, Charleston, W. Va., assignors to E. I. du Pont de Nemours and Company Wilniin ton Del. a corporation of Delaware g No Drawing. Application July 27, 1954 Serial No. 446,176

6 Claims. (Cl. 260-586) This invention relates to an improved process for preparing adipic acid and precursors thereof.

The art of oxidizing organic compounds in the liquid phase developed rapidly in recent years,

of oxidizing cyclohexane in the liquid phase hexanol and cyclohexanone. In the Loder process the preferred catalysts included cobalt naphthenate, and the preferred oxidation initiators included such materials as ket-ones, aldehydes, peroxides,

cyclohexane oxidized was less than When the quantity of cyclohexane oxidized was from about 5% to about 12%, the yield of cyclohexanol-cyclohexanone was about 65% to about 85%. It has more recently been reported '(Farkas et al., U. S. 2,410,- 642) that under conditions similar to those previously used, but in the absence of Loders catalysts, quantitative yields of oxidation products 2,497,349) that the hydroperoxide which is formed under conditions similar to those previously used for oxidation of cyclohexane can be converted to cyclohexanol by the action of reducing agents such as ferrous salts.

The thermal decomposition of pure or relatively concentrated cyclohexyl hydroperoxide yields cyclohexanone as a main product, while the chemical reduction of cyclohexyl hydroperoxide yields primarily cyclohexanol. If the oxidized product is to be used for making adipic acid by further air oxidation, it is highly desirable to produce cyclohexanone, since the yield of adipic acid jhy air oxidation of cyclohexanone is much higher than by over, it has also been disclosed (Farkas et al., U. S.

atent 235L496 Patented Sept. 9, 1958 sition of cyclohexyl hydroperoxide so as to produce a high proportion of ketone to alcohol. It is, however, highly desirable in that process to effect a reaction between cyclohexyl hydroperoxide and cyclohexane, for such a reaction gives rise stoichiometrically to two mols of cyclohexanol, instead of only one mol of cyclohexanol or cyclohexanone otherwise obtainable from cyclohexyl hydroperoxide. One of the advantages of the present invention is that it provides a hydroperoxide decomposition step wherein, if desired, somewhat more than one mol of adipic acid precursors is formed from each mol of cyclohexyl hydroperoxide which decomposes. It is to peroxides, in addition to cyclohexyl hydroperoxide, are generally present at least to some extent in the mixtures in question, and that these other peroxides also can undergo decomposition.

It is an object of this invention to provide an improved process for the oxidation of naphthenic hydrocarbons such as cyclohexane. Another object of the invention is to expedite and control the decomposition of the naphthenic hydroperoxide which is produced as one of the primary oxidation products, in the oxidation of naphthenes so as to produce an improved yield of desirable dibasic acid precursors. A further object is to control this decomposition of peroxides formed by cyclohexane oxidation without introducing any reducing agent or other reactant from an external source. Still another object is to control this decomposition of peroxides so as, if desired, to form cyclohexanone Without simultaneously forming cyclohexanol. Other objects of the invention will appear hereinafter.

The present invention provides a process wherein naphthenic hydroperoxides are produced by liquid phase oxidation of naphthenes with a gas containing molecular oxygen, following which these hydroperoxides are destroyed in a separate step, without adding a reducing agent or other reactant prior to separation of the oxidized naphthenes (comprising monoketonaphthene and monohydroxynaphthene) from the oxidation mixture. The destruction of the hydroperoxide is achieved by including in the overall process, after from 1 to 12% or more of the naphthene molecules have been oxidized, a controlled decomposition of peroxides on a bed of solid catalyst in the absence of any reducing agent or oxygen. Thus the present invention includes the step of controlling the thermal decomposition of peroxide, prior to distillation of the reaction products, by carrying out this decomposition in a separate step using a bed of solid catalyst, rather than effecting the peroxide decomposition incidentally,

during distillation of the partial oxidation products, as in the prior art process.

The process of this invention is of considerable value in connection with processes wherein crude mixed oxidation products are converted by later oxidation (e. g., with nitric acid) to dibasic acids, and especially where the material subjected to nitric acid oxidation is a volatile fraction, free from relatively non-steam volatile products. The economic advantages of the latter type of process for oxidation of cyclohexane are explained in further detail in U. S. patent application of Goldbeck and Johnson, 8. N. 390,634, filed November 6, 1953, now Patent No. 2,703,331. To obtain the maximum yield of steamvolatile adipic acid precursors, While producing the minimum amount of impurity to be removed in relatively expensive recrystallization processes, a peroxide decomposition step is especially helpful, and there are advantages in performing such a step without introducing added quantities of soluble catalyst or reducing agent.

In general, it may be desirable, although it is not absolutely necessary, to employ an oxidation catalyst in the oxidation of the naphthenic hydrocarbons hereinabove described. A suitable temperature is 50 to 200 C., preferably 140 to 175 C. and at a pressure of 50 to 750 lbs. per sq. in. If a catalyst is employed the quantity thereof should be relatively small, e. g., an amount of cobalt containing or chromium-containing catalyst corresponding to l to 5000 parts per million of Co or Cr may be present, but higher quantities generally are not required.

Temperatures in the naphthene hydroperoxide decomposition step are suitably to 300 C., preferably 50 to 175 C.

In a specific embodiment the invention can be practiced by oxidizing cyclohexane with an oxygen-containing gas, such as air, under the temperature and pressure conditions defined hereinabove, continuing the oxidation until from 1 to 12% of the cyelohexane molecules have been oxidized, whereby an oxidation product containing cyclohexanol. cyclohexanone and cyclohexyl hydroperoxide is obtained, and heating the resulting mixture, in the presence of a bed of solid peroxide decomposition catalyst, in the absence of added reactant at a temperature within the range of 100 to 300 C. preferably 125 to 200 C. until disappearance of the said hydroperoxide takes place, and thereupon distilling the resulting mixture for recovery of unreacted cyclohexane and also for recovery of cyclohexanol and cyclohexanone or mixtures thereof. If desired, the cyclohexanol and cyclohexanone need not be separated from the relatively small amounts of other oxidation products which are present in the distillation residues. A convenient method for utilizing the oxidation products and hydroperoxide decomposition products thus obtained is to convert them to adipic acid by the nitric acid method disclosed in the Hamblet et al. patents U. S. 2,439,513, 2,557,281 and 2,557,282.

.he form or shape of the reaction vessels employed in practicing the invention, in both the oxidation andhydroperoxide decomposition steps, is of relatively minor consequence, suitable types being tubular converters, upright towers, packed columns, vessels equipped with devices for producing agitation or rapid flow, aerosol sprays. etc. The process may be carried out in a continuous or batchwise manner. The same reaction vessel may be employed in both the oxidation and hydroperoxide decomposition steps, but it is usually more convenient to use separate vessels for these distinctly different steps of the process.

In the continuous reaction systems, viscous or turbulent flow may be used. The vessels may be made of or lined with inert materials such as stainless steel, aluminum, tantalum, noble metals, ceramics, etc. The vessels should of course be sufficiently strong to withstand the prevailing pressures, which in both the oxidation step and in the hydroperoxide decomposition step should be sufficiently high to maintain the naphthene largely in the liquid phase, and from atmospheric pressure to about 1000 lbs. per sq. in. gauge or higher. The preferred pressure in the oxidation step is about 50 to 750 lbs. per sq. in. In the peroxide decomposition step the pressure is not particularly critical, although it is desirable to employ pressures high enough to permit the naphthene to remain largely in the liquid phase at the prevailing temperature.

At least a part of the unreacted naphthene may be recovered from the oxidizer efiiuent prior to performing the peroxide ecomposition step, if desired, but this is not a preferred practice. The hydroperoxide should not be concentrated in the extent that only a relatively small amount of diluent naphthene remains, however, because lit concentrated naphthene hydroperoxide can undergo a spontaneous reaction which is almost explosive in its violence.

In the oxidation step the gas containing molecular oxygen may be air, pure oxygen, oxygen-enriched air, air containing relatively inert gaseous diluents and the like.

In the oxidation step the reaction time, i. e. the time during which the oxygen-containing gas is in contact with the oxidizable naphthene, should preferably be controlled. that the conversion (i. e. the percentage of molecules oxidized to all products) is within the range of about 1% to 12%. Usually the percentage of peroxide formed increases very rapidly with time until a maximum is reached, after which the peroxide content of the oxidation mixture decreases rapidly. For most effective results from the standpoint of the incremental increase in yield, it is desirable to remove the oxidation mixture from the oxidation zone, e. g. by physically transferring it to the hydroperoxide decomposition vessel, when the proportion of hydroperoxide in the oxidized product is close to the maximum. This occurs when the total conversion is quite low, a most preferred range of conversion being from 3 to 9%. The mechanical'losscs are, of course, kept at the lowest practicable minimum. Generally, the quantity of residual oxidation catalyst dissolved in the hydrocarbon phase at the end of the oxidation step is even smaller than was present initially in the oxidation step.

cyclohexyl hydroperoxide is itself convertible to adipic acid by nitric acid oxidation. In fact, the nitric acid oxidation of cyclohexyl hydroperoxide yields adipic acid in high yields under the conditions disclosed in U. S. Patents 2,439,513 and 2,557,282 for oxidation of primary oxidation products of cyclohexane, the quantity of adipic acid produced being nearly 1.0 mol per mol of hydroperoxide. Accordingly, in the manufacture of adipic acid by the processes of the above-cited patents the distillation residue obtained by recovery of cyclohexane from the total crude oxidation products when subjected to further nitric acid oxidation will produce, in addition to the adipic acid formed from other components of the residue one mol of adipic acid per mol of cyclohexyl hydroperoxide. If, however, a peroxide decomposition step is interposed, and is carried out under such conditions of temperature, catalyst composition and concentration, pressure, etc. that the peroxide decomposes in part by the following mechanism 051113 CgHnOOH 20011 011 (oyclohexane) (cyclohexylhydroperoxide) (cyclohexanol) it is apparent that during the said nitric acid oxidation step, every mol of cyclohexyl hydroperoxide reacting in this manner will be converted, during the subsequent nitric acid oxidation, to two mols of adipic acid, rather than one. The conversion to adipic acid is thus increased without sacrifice in yield.

One of the important facets of this invention is the discovery of the conditions required for converting the hydroperoxide (with cyclohexane) to more than one mol of adipic acid precursors, instead of only one. In copending U. S. patent application of R. W. Wheatcroft and W. Warner S. N. 429,366, filed May 12, 1954, it is disclosed that cobalt catalysts, such as cobalt naphthenate, are effective for this bimolecular production of the precursor. To effect the bimolecular reaction, the amount of, this catalyst in many instances need not be any greater than is present in the effluent from commercial cyclohexane oxidizers. The situation is, however, complicated somewhat by the further discovery that cyclohexanone is also a catalyst for cyclohexyl hydroperoxide disappearance in cyclohexane solutions at elevated temperatures. Acids are also catalysts for this decomposition. Oxygen, on the other hand, has no such accelerating effect. The complete mathematical analysis of these variables is not essential to an understanding of the present invention, it

peroxide-containing fraction thereof, is conducted through a bed of solid catalyst, hereinafter described, at about 0, under sufiicient pressure to maintain a liquid phase, until the hydroperoxide content has drop- The cobalt concentration in the peroxide decomposition vessel, in the process of this invention, is not enhanced by further addition of cobalt naphthenate, as in the Punderson application, S. N. 279,239, filed March 28, 1952.

The solid of salts such as like.

While the decomposition can be made to occur thermally, without any added catalyst, this is a process which requires a sizeable hold-up tank, since the non-catalytic process is comparatively slow even at elevated temperatures and is present invention is that it speeds making it almost instantaneous, thus eliminating from the process any need for a large hold-up tank; moreover, the invention accomplishes this desirable result without introducing into fire system any new contaminants.

A series of experiments was performed in which numerous solid catalysts were compared to determine their effect upon decomposition of cyclohexyl hydroperoxide in cyclohexane oxidizer efiluent. The efiduent used in these tests was taken from the third oxidizer in a battery of three air-oxidizers wherein cyclohexane was converted to primary oxidation products at 147 to 160 C. as described in U. S. 2,557,281. The contact time in these tests was somewhat less than one minute, and the temperature was maintained at 125 to 135 C.

Table I.Peroxide decomposition in crude cyclohexane oxidation products of low peroxide content, on fixed bed catalysts (conversion to cyclohexanol-l-cyclohexanone, 5.8 to 6.6%)

Peroxide (09.10. as cyclohexyl up the decomposition,

Catalyst hydroperoxlde) percent conversion Control 0. 6 1 l 0. 2 0. 0. 2 3 Contr 0. 4 Ruthenium on activated a1 0.0 4 Control 0.3 Iron molybdate on activated alumina 0. 1

The foregoing table records data which show that each of the fixed bed catalysts catalytically decomposed the' increase in total number of mols of adipic acid pre- Two of the most valuable catalysts in the practice of M083, the

produced only crude product.

taining the granular catalyst. at a rate corresponding to the specified contact time until a steady state was reached, whereupon the material flowing into, and out of, the cartridge was sampled and analyzed.

It is significant to point out that an improvement of 0.4% in cyclohexanol content is of major magnitude in this low conversion process, amounting to an increase of about 7% in the production capacity of the plant. In

composition step is especially The invention is further illustrated by means of the following example:

Example.Cyclohexane was oxidized with air at 169 C. under 160 lbs. per sq. in. pressure with 1 p. p. m. cobalt (added as naphthenate) catalyst, until the peroxide content of the reaction mixture reached 1% by weight (peroxide calculated as cyclohexyl hydroperoxide). The total conversion at this point was 4%. The resulting mixture was conducted over a powdered reduced sintered cobalt oxide (C00) catalyst at C. at a contact time of 15 minutes. The peroxide content of the mixture decreased as set forth in the following table,

decomposed peroxide molecules (calc. as cyclohexyl hydroperoxide). The cyclohexanol/cyclohexanone mol ratio for the increased quantity of cyclohexanoI-cyclohexanone is also given The experiment Table lI.-Dec0mp0sition of peroxides in crude cyclohexane oxidation product with various fixed bed catalysts at 70 C. and 15 minute contact time Peroxide Catalyst Dccom- Percent K/A posed, KA 1 Ratio Percent M Cobalt oxide (000) -90 104 2. 9 Vanadium Oxide on Alumina 60-65 114 2. 6 Molybdenum Sulfide 50-70 infinity Platinum on Carbon. 60-85 109 1.35 Cobalt oxide on charcoal 75 103 1. 3

1 KA signifies cyclohexanone-cyclohexanol.

perature in the catalysts, a detectable quantity of peroxide remains after about 15 minutes time. At 100 C., the reaction takes less than a minute, and at higher temperatures the reaction is even more rapid. Generally it is not necessary or advantageous to use a temperature in excess of the cyclohexane oxidation temperature, which preferably need not exceed 175 C., although, when very low cyclohexane oxidation temperatures are used, a higher temperoxide decomposition step is feasible. Temperatures above the critical temperature of the oxidation product (mostly cyclohexane) are not employed.

One of the advantages of the process of this invention is that it permits control over the peroxide content of the partial oxidation products prior to distillation of these products, while at the same time increasing the rate of production of adipic acid precursors, especially those which are recoverable in the.cyclohexanol-cyclohexanone steam distillate, without the necessity for introducing any additional catalyst at the decomposition step. Where the decomposition step is omitted, the peroxide does not decompose appreciably during rapid distillation of cyclohexane (unless the quantity of catalyst is large), and

hence the decomposition occurs either during distillation of the ketone and alcohol, or

not at all. Where steam distillation is employed for recovery of volatile precursors of adipic acid, it is highly advantageous to interpose the herein disclosed peroxide decomposition step prior to the steam distillation step.

We claim:

1. In a process for liquid phase oxidation of cyclohexane with molecular oxygen, the steps which comprise effecting said oxidation at a temperature of from to 200 C. under a pressure of S0 to 750 lbs. per sq. in, heating at least a part of the resulting mixture at a temperature of 30 to 300 C. in the presence of a granular peroxide-decomposition catalyst of the class consisting of group VIII metals, molybdenum sulfide, iron molybdate-on-alumina, vanadium oxide-on-alumina, and cobalt oxide of the formula C00, until the cyclohexyl hydroperoxide content thereof has been reduced, and thereafter recovering steam-volatile partial oxidation products of cyclohexane from the resulting mixture by distillation.

2. Process of claim 1 wherein the oxidation of cyclohexane is carried out at a temperature of to C.

3. Process of claim 1 wherein the decomposition of peroxide is effected at 50 to 175 C.

4. Process of claim 3 wherein the said catalyst is CoO.

5. Process of claim 3 wherein the said catalyst is M08 and the decomposition produces cyclohexanone without simultaneously producing cyclohexanol.

6. Process of claim 3 wherein the said catalyst is ruthenium-on-alumina.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. IN A PROCESS FOR LIQUID PHASE OXIDATION OF CYCLOHEXANE WITH MOLECULAR OXYGEN, THE STEPS WHICH COMPRISE EFFECTING SAID OXIDATION AT A TEMPERATURE OF FROM 50* TO 200*C. UNDER A PRESSURE OF 50 TO 750 LBS. PER SQ. IN., HEATING AT LEAST A PART OF THE RESULTING MIXTURE AT A TEMPERATURE OF 30* TO 300*C. IN THE PRESENCE OF A GRANULAR PEROXIDE-DECOMPOSITION CATALYST OF THE CLASS CONSISTING OF GROUP VIII METALS, MOLYBENUM SULFIDE, IRON MOLYBDATE-ON-ALUMINA, VANADIUM OXIDE-ON-ALUMA, AND COBALT OXIDE OF THE FORMULA COO, UNTIL THE CYCLOHEXYL HYDROPEROXIDE CONTENT THEREOF HAS BEEN REDUCED, AND THEREAFTER RECOVERING STEAM-VOLATILE PARTIAL OXIDATION PRODUCTS OF CYCLOHEXANE FROM THE RESULTING MIXTURE BY DISTILLATION.