US3859343A - Method for oxidizing hydrocarbons - Google Patents

Abstract

A process for oxidizing polyalkyl monoaromatic hydrocarbons to the corresponding polycarboxylic monoaromatic acid by contacting them with an aqueous solution of ammonium dichromate at elevated temperatures. The product of the reaction is the ammonium salt of the corresponding polycarboxylic acid, which, upon acidification, yields the free organic polycarboxylic acid.

Description

United States Patent Benham et al. *Jan. 7, 1975 METHOD FOR OXIDIZING [58] Field of Search 260/524 M, 531 R; 23/56 HYDROCARBONS [75] Inventors: Alvin L. Benham, Clear Lake, Tex.; [561 References Cited Dennis E. Drayer, Littleton, Colo.; UNITED STATES PATENTS Harold D. McBride, Lincoln, Nebr. 3,560,559 2/1971 Benham et a] 260/524 [73] Asslgnee: g fi s Company Fmdlay Primary Examiner-Lorraine A. Weinberger Assistant Examiner-Richard D. Kelly Notice: The portion of the term of this Attorney, Agent, or FirmSughrue, Rothwell, Mion,

patent subsequent to Feb. 2, 1988, Zinn & Macpeak has been disclaimed. 22 Filed: Dec. 18, 1970 [57] A process for oxidizing polyalkyl monoaromatic hyi i PP NOJ 99,380 drocarbons to the corresponding polycarboxylic Related Application Data monoarornatic acid by contacting them with an aque- [63] C ti v t f S r NO 408 884 N 4 ous solution of ammonium dichromate at elevated 52 gz wg g gg 2 temperatures. The product of the reaction is the ammonium salt of the corresponding polycarboxylic acid, [52] U S Cl 260/524 M 260,518 R 260,523 A which, upon acidification, yields the free organic poly- D u--.- a a 260/531 R, 260/533 C, 260/558 R Int. Cl C07c 55/14, C07c 63/02 carboxylic acid.

18 Claims, 1 Drawing Figure PAIENTED JAN 7 S RECYCLED AMMONIUM DICHROMATE FEEDSTOCKW 1 OXIDATION CHROMIC oxmE REMOVAL ACIDIFY AMMONIUM SALT PRODUCT REGENERATION AMMONIA REMOVAL RECYCLED AMMONIUM- DICHROMATE TO OXIDATION INVENTORS ALVIN L. BENHAM DENNIS E. DRAYER HAROLD D. MCBRIDE M, Ki/5141c, 014,80 Z114 WQ K ATTORNEYS METHOD FOR OXlDlZlNG HYDROCARBONS This application is a continuation-in-part of U.S. application Ser. No. 408,884, filed Nov. 4, 1964, now U.S. Pat. No. 3,560,559.

The present invention relates to the oxidation of cyclic hydrocarbons and partially oxidized cyclic hydrocarbons by ammonium chromate or dichromate. More particularly, the invention relates to the oxidation of these compounds by reaction with aqueous ammonium chromate or dichromate.

Prior oxidation processes utilizing a chromium (VI) oxidant are economically unfeasible for commercial application because they result in the formation of large amounts of alkali metal halides or sulphates which are of low value. According to the present process, the production of large amounts of low value byproducts is avoided and the reduced chromium compound, Cr O is regenerated to the dichromate while producing the more economically attractive ammonium salts.

The following is a general description of the present process. An understanding of the major steps of the process and their inter-relation may be facilitated by reference to the accompanying flow diagram.

A feedstock containing cyclic hydrocarbons and/or partially oxidized cyclic hydrocarbons is contacted with an aqueous solution of ammonium dichromate at elevated temperatures to form various oxidation products. Depending upon the pH of the reaction media, the oxidation product formed will be either the ammonium salt of an organic carboxylic acid or an organic carboxylic acid amide.

The primary products formed by the present invention are carboxylic acids or carboxylic acid amides. At pH levels of about 7 or below, the predominant product is the ammonium salt of an organic carboxylic acid which can be acidified to form the free acid. When the pH of the reaction media is above about 7, high yields of carboxylic acid amides are formed.

During the oxidation reaction, the ammonium dichromate is reduced to Cr O which precipitates from the reaction mixture and is removed by conventional means. After being removed from the reaction zone, the Cr O is mixed with ammonium hydroxide and oxidized with oxygen to form ammonium chromate which can be converted to ammonium dichromate. The regeneration of Cr O is enhanced by conducting it in the presence of catalysts, such as copper sulphate or cobalt naphthenate. In a preferred embodiment, the Cr O is regenerated in the presence of a mixture of cupric sulphate and sodium sulphate. The copper ions, which detrimentally effect the oxidation reactions, are precipitated from the regeneration mixture by removing ammonia from the mixture after completion of the regeneration period. 7

Following the removal of the Cr O from the oxidation product, water and ammonia are flashed from-the hot reaction mixture. The oxidation product is then recovered. When the product is the ammonium salt of an organic carboxylic acid, it is reacted with a nonoxidizing strong acid to form the organic free acid and an ammonium salt of a strong acid.

The regeneration of Cr O to form ammonium chromate is more fully disclosed in application Ser. No. 373,879, filed June 9, 1964, now US. Pat. No. 3,393,972, and Ser. No. 402,958, filed Oct. 9, 1964,

now US. Pat. No. 3,369,86l, both assigned to the assigneeof this application.

The present invention has utility in the oxidation of a wide variety of hydrocarbons and partially oxygenated hydrocarbons. Examples of suitable feedstock materials include the xylenes, mesitylene, durene, propylbenzene, cymene, toluic acid, toluol, tolualdehyde, 2,6-dimethylnaphthalene, acenaphthene, acenaphthylene, l-methyl-4-isopropylnaphthalene, 1,4-dimethyl- 4-isopropylnaphthalene, 1,3-dimethylanthracene, 2,7-

dimethylanthracene, 1,7-dimethylphenanthrene, 1,6-diisopropylnaphthalene, 1,2,4- trimethylanthracene, 7-methyl- 1 -ethylphenanthrene,

1-methyl-4-isopropylanthracene, 1,3,6,8-tetram ethylanthracene, I 9,l0-diethylphenanthrene, cyclohexane, cyclopentane, cycloheptane, cyclohexanol, and cyclopentanol. Generally, any aromatic compound substituted with a lower alkyl group can be used as a feedstock. Mixtures of hydrocarbons can also be oxidized by this procedure. An example of such a mixture is cycle oil, a product of the catalytic refining of petroleum (Industrial and Engineering Chemistry, Vol. 38, pp. 136-( 1946) at page 137). Generally these products are a mixture of alkylnaphthalene, anthracene, etc.

The oxidation of the feedstock is generally accomplished by mixing the alkylaromatic or cycloaliphatic compound with an aqueous ammonium dichromate solution and heating. The reaction conditions may vary over fairly wide ranges. The oxidation temperatures which are utilized vary widely with the raw material. Thus, temperatures from about 200 to 325C are suitable temperatures for the preparation of the carboxylic acid amides, preferably carried out in the range of from to 325C. The pH of the oxidation reaction mixture can vary from about 1 to about 11, with a pH below about 7 being preferable for the preparation of high yields of organic carboxylic acid products. The ratio of dichromate equivalents to oxidizable carbon atoms which are useful in the process range from about 0.5 to l to in excess of 3 to l. A ratio in the range of from about 1.5:1 to 25:1 is preferred. High yields are obtained with relatively short reaction times on the order of about 15 minutes to 30 minutes. The reaction may be conducted at ambient pressures.

The oxidation reaction mixture is in two phases and the known techniques for increasing miscibility and surface area are generally applicable to the instant process. For example, surfactants can be added to the mixture to reduce the surface tension between the two phases and stirring or bubbling can be used to increase interfacial area.

After oxidation is substantially completed, ammonia and steam are removed from the reaction zone, preferably by flashing off these compounds. The precipitated chromic oxide is then removed, usually by filtration, or by other means, such as decantation. The ammonium salts of the organic acis in the reaction medium are then neutralized with a non-oxidizing strong acid, such as sulphuric acid, hydrochloric acid, hydrobromic acid, phosphoric acid, etc., to form the free organic acid which precipitates and is removed by filtration, decantation or similar well-known methods.

In a preferred cyclic process, the Cr O is regenerated to form ammonium dichromate. The chromic oxide is transferred to a regenerator, usually a pressure resistant vessel or autoclave, in which it is reacted with oxygen and aqueous ammonia. Generally the chromic oxide is preferably mixed with aqueous ammonia, most of which is derived from the ammonia removal step which may be conducted as part of the process. The aqueous ammonia solution may contain from about 4% to 80% by weight of ammonia, about being preferred, and the mole ratio of ammonia to chromic oxide should be from about 2 to 160. Oxygen, in the form of pure oxygen, oxygen enriched air, air, and oxygennitrogen mixtures, is then added to the autoclave containing this mixture to provide an'oxygen partial pressure of from about to in excess of 500 psi and preferably about 200 psi. The reaction mixture is then heated for at least about 15 minutes at a temperature of from 140 to 225C and preferably about 180C. The reaction is conducted in the presence of copper sulphate and sodium sulphate. In this manner, about 90% of the spent Cr(l11), in the form of Cr O may be converted into Cr(Vl) in the form of ammonium chromate.

After the regeneration of chromic oxide is completed, ammonia is removed from the reaction vessel. Preferably, ammonia and steam are flashed from the reaction vessel. Additional heating at from about 150 to 250C can be used to flash off excess ammonia, thereby reducing the pH of the reaction mixture and precipitating copper ions as the insoluble hydroxide. Ammonium dichromate is formed from ammonium chromate as the ammonia is removed. The flashed ammonia is then recycled to the chromic oxide regeneration vessel.

Having described the invention in general and in terms of a preferred cyclical mode of operation, it is believed that the following detailed examples of preferred procedures will assist towards a better understanding of the process.

The invention will also be better understood by reference to the flow diagram of the process which is set forth in the single FIGURE of the accompanying drawmg.

EXAMPLE 1 A mixture of 154 ml of distilled water, 50.7 g (0.201 mole) of reagent ammonium dichromate having an initial pH of 3.65 and 9.13 ml (0.074 mole) of p-xylene were placed in a 300 ml rocking autoclave and heated to 225C. The mixture was allowed to react for a period of 60 minutes with continuous rocking of the autocla've.

The reaction products of the p-xylene oxidation were then filtered and acidified with hydrochloric acid to a pH of about 1 toprecipitate the aromatic acids. A 97.8% conversion of the p-xylene was obtained and a total mixed acid yield of 86.5% was recovered. Upon analysis, it was found that about two-thirds of the mixed acids were terephthalic acid and most of the balance was terephthalamic acid. Base hydrolysis of the mixed acids produced over 99% pure terephthalic acid and ammonia gas. I

The acidification ofthe oxidation products with hydrochloric acid also produced ammonium chloride. This salt was recovered by filtration, purified by recrystallization, and then stored. In large scale commercial process, the by-product ammonium chloride can be sold, thus renderingthe process more attractive than prior methods in which sodium chloride is produced.

EXAMPLE 2 Following the procedure of Example 1, a mixture of 154 ml of water. 50.7 g (0.201 mole) of ammonium dichromate and 15.62 gms (0.10 mole)' 2,6-dimethylnaphthalene was added to a 300 ml rocking autoclave. The reaction was conducted during continuous rocking of the autoclave at 225C for 1 hour. After flashing off excess ammonia, the oxidation reaction filtrate was acidified with hydrochloric acid to a pH of approximately 1 to precipitate naphthalene-2,6-dicarboxy1ic acid. The yield was 38.8%.

Following the procedure of Example 1, a number of oxidations were conducted using a variety of feedstock materials and varying some of the reaction conditions to determine the effect such changes may have on yield.

' The oxidation of o-xylene with aqueous (N-H Cr O was conducted following the procedure of Example 1.

In each case, 0.201 mole of (NH Cr O and 0.123 mole of o-xy1ene was reacted in 154 ml of H 0 for 60 minutes, with an initial pH of about 3.5. The ammonium dichromate solution was free from residual cupric sulphate. The results of a series of such runs at varying temperatures appear in Table 1.

From the data of Table 1, it is evident that the major product of the oxidation of o-xylene with ammonium dichromate is o-toluic acid. Relatively minor amounts of o-toluamide and phthalic acid are also produced. The yield of o-toluic acid tends to increase at more elevated temperatures with the highest yield being obtained at 275C. The yield computed from the results of the experiments reported in Table 1 and Table 2 is based on the mole percent of aromatic acid or amide produced per mole of o-xylene charged.

Another series of runs was conducted under exactly the same conditions as were-employed in the reactions reported in Table 1, but the aqueous ammonium dichromate solution contained 6.8 grams of residual cupric sulphate'catalyst. The results of this series of reactions are reported in Table 2.

It is readily apparent from the data of Table 2 that the presence of a substantial amount of residual copper ions in the oxidant solution sharply reduces the yield of Table 4 Cone. Reaction p-Xylene Run p-Xylene H O NH OH Temp. Percent Percent yield No. ml ml ml (C) Conversion Acids p-Toluamide valuable aromatic acids. regardless of variation in temperature. This demonstrates the importance of the copper ion removal step before the recirculation of the regenerated oxidant solution. a

A number of oxidation reactions were also conducted utilizing p-xylene as the alkyl aromatic compound. Still following the general procedure of Example 1, 0.201 mole of (NH Cr O was reacted with varying amounts of p-xylene in 154 ml of H 0. The reactions were conducted at a temperature of 225C for 60 minutes. The initial pH of each reaction mixture was adjusted to 3.65. The yields are computed as the mole percent of organic acid or amide produced per mole of hydrocarbon charged to the autoclave. Conversion is the mole percent of a given reaction component converted to other products and includes any unrecovered portion of the component. The results of these runs are reported in Table 3.

The data contained in Table 3 indicates that substantial yields of terephthalic acid may be obtained by the oxidation of p-xylene with ammonium dichromate. It also shows that higher yields are obtained at higher mole ratios of (NH Cr O to p-xylene. A commensurate decrease in the yield of secondary products is experienced as the (NH.,) Cr O to p-xylene ratio is increased.

dium contained 6.8 g of cupric sulphate. The results of these reactions are set forth in Table 4. The percent yield of acids below includes terephthalic plus terephthalamic acids.

The data of Table 4 indicate that higher yields of mixed terephthalic and terephthalamic acids are obtained at more elevated temperatures, the maximum yield being obtained at a reaction temperature of 225C. However, the results are relatively poor when compared with the yields obtained from the reactions reported in Table 3 where an ammonium dichromate oxidant solution substantially free from copper ions is employed. This again demonstrates the importance of the removal of copper ions from the oxidant solution.

A feedstock of 2,6-dimethylnaphthalene was also subjected to oxidation by aqueous ammonium dichro mate in another series of reactions conducted according to the general procedure of Example 1. The reaction was conducted with 50.7 g (0.201 mole) (NH Cr O and varying amounts of 2,6-dimethylnaphthalene in 154 ml of water. The initial pH of each reaction media was 3.65. In addition to varying the amount of the alkyl aromatic reactant, the reaction times and temperatures were also varied from one run to another. The different conditionscmployed in each reaction and the results obtained appear in Table 5.

Table 3 (NH,),Cr,O Percent Yield Ru pXylene Percent p-Xylene Terephthalic Terephthalamic No (ml) Millimole Conversion Mole Ratio Acid Acid p-Toluamide Table 5 2,6-Dimethylnaphthalene Reaction Reaction Naphthalene-2,6- Run Percent Temperature Time Dicarboxylic Acid No. grams mole Conversion (C) Hours Percent Yield Another series ofreactions was conducted to determine the effect of 1) reaction temperature variations and (2) the presence of copper ions, as cupric sulphate, on the oxidation of p-xylene with ammonium dichromate. The same general procedure was employed as in the preceding oxidations. The amount of reactants was the same in each run, 50.7 g (0.201 mole) of (NHJ Cr O and 9.13 ml ofp-xylene. The reaction me- As shown in Table 5, substantial amounts of naphthalene2,6-dicarboxylic acid are produced according to this process. The yield of the acid tends to be higher at more elevated reaction temperatures as may be seen by comparing Run Nos. 5-1 and 5-2, 5-4 and 5-5, 5-3 and 5-5. A comparison of the results of Run Nos. 5-2 and 5-5 also indicates that a higher acid yield is obtained at higher mole ratios of (NHJ Cr O to 2,6-dimethylnaphthalene. Some improvement in yield at longer reaction times is also evident from a comparison of Run Nos. -2 and 5-7. 5

A further study of the effect of reaction time on the oxidation of 2,6-dimethylnaphthalene was made in a series of reactions in which only the time was varied. In these runs, 50.7 g (0.201 mole) of (NH,,) Cr O and 15.62 g (0.10 mole) of 2,6-dimethylnaphthalene in 154 ml H O were reacted at 215C. The results are set forth The data of Table 6 demonstrate that the yield of the dicarboxylic acid increases with increase in the reaction time up to about 6 hours. A corresponding increase in 2,6-dicarboxylic acid selectivity is also experienced as the time is increased progressively from 1 to 6 hours in Run Nos. 6-1 through 6-4. However, between 6 and 8 hours reaction time, a decrease in yield and selectivityis noted, due perhaps to some degradation or recombination of the products. In this context, selectivity refers to the fraction of converted 2,6-dimethylnaphthalene'that is oxidized to naphthalene 2,6- dicarboxylic acid.

A feedstock of m-xylenewas also oxidized with aqueous (NH Cr O In these reactions, 50.7 g (0.201 mole) (NH Cr and 9.13 ml (0.074 mole) m-xylene in 1 54 ml H O were reacted for 60 minutes. The results appear in Table 7.

Table 7 case, 50.7 g (0.201 mole) (NH Cr O was reacted with the feedstock in 154 ml H O for 60 minutes. The results of these reactions are set forth in Table 8. In this data, weight percent yield is weight of product/weight of starting material X 100.

Table 8 Org. Temper- Con- Run Start. ature version No. Material (C) Products Percent mole yield mixed durene acids including mellitic acid 8-2 0.050 225 11.78 wt. 87.2

mole yield mixed durene acids including Py mellitic acid 8-3 15.5 ml 215 12.5 wt.

, LCCO yield mixed extract acids 8-4 0.1 mole 215 18.0% adipic cycloacid hexanol As mentioned before, when the pH of the reaction media is in excess of about 7, substantially increased yields of carboxylic acid amides can be produced. This embodiment of our invention will be better understood by resorting to the following examples and tables.

EXAMPLE 3 300 ml rocking bomb was charged with 9.13 ml pxylene, 50.7 g ammonium dichromate, 100 ml concentrated ammonium hydroxide (30% NH and 54 ml distilled water. The pH of the aqueous phase before reaction was 10.42. The reaction mixture was then heated at 225C for 60 minutes, after which the pH of the aqueous phase was 10.75. The aqueous effluent remaining after the completion of the oxidation reaction Reaction m-Xylene lsophthalic isophthalamic Run Temp. Percent m-Toluamide Acid Acid No. (C) Conversion Percent Yield Percent Yield Percent Yield The data in Table 7 show that a substantial yield of isophthalic acid is obtained by the oxidation of mxylene according to this process. A significant yield of isophthalamic acid is also produced. The variation in temperature from 215C to 235C does not produce a .great increase in diacid yield, but a large yield of isophthalamic' acid was secured at 235C.

Mixed xylenes m-, 25% o-'and 25% p-xylene) were also subjected to ammonium dichromate oxidation and substantial amounts of mixed acids were produced.

A number of other feedstocks were oxidized according to the present process with good results. In each addition of ammonia or sulphuric acid from runto run.

Otherwise, the same amounts of reactants and the same reaction condition was employed. The results appear in Table 9. The results of Example 3 are also included in the Table for purposes of comparison.

Table 9 p-Toluamide- Tcrephthalamic Terephthalic pXy1ene Run lnitial Final Percent Acid Acid Percent No. pH pH Yield Percent Yield Percent Yield Conversion Table 9 p-Toluamide Terephthalamic Terephthalic p-Xylene Run lnitial Final Percent Acid Acid Percent No. pH pH Yield Percent Yield Percent Yield Conversion From the data in Table 9, it is evident that a sharply increased yield of terephthalamic acid and p-toluamide is obtained at pH levels above about 7. At lower pH levels, Run Nos. 9-1 through 9-4, aromatic acid production is favored.

1n the present data, yield is the mole percent of product per mole of alkyl aromatic charged. Conversion is the percent of a given reaction component converted to other products including any unaccounted for portion of the reaction component Reactions were also conducted according to the procedure of Example 3 using o-xylene as the feedstock. In each case, 9.32 ml of o-xylene was mixed with 50.7 g of ammonium dichromate in 154 ml of water. The initial pH of the reaction mixture was adjusted to the desired level by the addition of 10% H 50 or 58% NH OH to the reaction mixture. The reaction was carried out at 225C for 60 minutes. The results of the runs appear in Table 10.

Table 10 oToluic Phthalic Run Initial Final Acid o-Toluamide Acid No pH pH Percent Percent Percent The data of Table 10 clearly show that more than twice as much o-toluamide is produced by reaction at a pH above 7, than is formed at lower relatively acidic pH levels.

EXAMPLE 4 EXAMPLE 5 Example 4 was repeated, but the initial pH of the reaction mixture was adjusted to 6.9. A yield of 6.6% of mixed amides was obtained.

EXAMPLE 6 Example 4 was repeated, but the initial pH of the reaction mixture was adjusted to 9.8. A yield of 7.9% of mixed amides was obtained.

The results of Examples 4, 5 and 6 also demonstrate that conducting the oxidation of alkylaromatic compounds at a pH about 7 or higher results in a substantial increase in amide yield over that obtained by reacting at relatively acid pH levels.

lt will be understood that various changes in the de tails of the process may be made by those skilled in the art without departing from the spirit of our invention. It is our invention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

l. A method for oxidizing a polyalkyl monoaromatic hydrocarbon feedstock to the corresponding polycarboxylic monoaromatic acid comprising:

a. reacting the feedstock with aqueous ammonium dichromate in an equivalent ratio of from about 0.511 to about 3:1 of said ammonium dichromate to oxidizable carbon atoms of said polyalkyl monoaromatic hydrocarbon and at a temperature of from C to 325C to produce chromic oxide and the ammonium salt of said polycarboxylic monoaromatic acid,

. reacting the chromic oxide with oxygen in aqueous ammonia to produce aqueous ammonium chromate, i c. removing ammonia from said aqueous ammonium chromate to form aqueous ammonium dichromate, recycling the aqueous ammonium dichromate for the oxidation of additional feedstock, and d. acidifying the ammonium salt of said polycarboxylic monoaromatic acid to preciptate the acid therefrom.

2. The method of claim 1 wherein said feedstock is a polymethyl substituted monoaromatic hydrocarbon.

3. The method of claim 2 wherein said feedstock comprises a member selected from the group consisting of mesitylene and durene.

4. The method of claim 3 wherein said feedstock comprises mesitylene and the corresponding polycarboxylic monoaromatic acid is trimesic acid.

5. The method of claim 3 wherein said feedstock comprises durene and the corresponding polycarboxylic monoaromatic acid is pyromellitic acid.

6. The method of claim 1 wherein said chromic oxide is separated from the ammonium salt of the said polycarboxylic monoaromatic acid prior to reaction with oxygen, and further wherein said ammonium salt of said polycarboxylic monoaromatic acid is precipitated by acidifying the ammonia free aqueous phase remaining after the reaction of the feedstock with the ammonium dichromate.

7. The method of claim 1 wherein said polyalky monoaromatic hydrocarbon feedstock comprises a member selected from the group consisting of mesitylene which is oxidized to trimesic acid and durene which is oxidized to pyromellitic acid wherein said feedstock is reacted with said aqueous ammonium dichromate to produce an aqueous phase in which is dissolved the ammonium salt of the product acid of the feedstock and to produce a chromic acid precipitate, and further wherein ammonia is removed from said aqueous ammonium chromate by heating said aqueous ammonium chromate to form aqueous ammonium dichromate and ammonia.

8. The method of claim 1 further comprising recovering ammonia generated during the process of recycling it as aqueous ammonia for reaction with said chromic oxide and oxygen to produce aqueous ammonium chromate.

phate.

9. The method of claim I wherein said chromic oxide, oxygen and aqueous ammonia are reacted in the presence of a cupric sulphate catalyst and sodium sulphate.

10. A method for oxidizing a polymethyl monoaromatic hydrocarbon feedstock to the corresponding polycarboxylic monoaromatic acid comprising:

a. reacting the feedstock with aqueous ammonium dichromate in an equivalent ratio of from about 0.511 to about 3:1 of said ammonium dichromate to oxidizable carbon atoms of said polymethyl monoaromatic hydrocarbon and at a temperature of from 160C to 325C to produce a chromic oxide precipitate and an aqueous phase containing the ammonium salt of said monoaromatic acid,

b. separating said chromic oxide and said aqueous phase,

0. catalytically reacting the chromic oxide with oxygen in aqueous ammonia to produce aqueous ammonium chromate,

d..removing ammonia from said aqueous ammonium chromate by heating said aqueous ammonium chromate to form aqueous ammonium dichromate,

e. recycling the aqueous ammonium dichromate for the oxidation of additional feedstock, and

f. acidifying the'aqueous phase containing the ammonium salt of said monoaromatic acid to precipitate the acid therefrom.

11. The method of claim wherein said feedstock comprises mesitylene and the corresponding polycarboxylic monoaromatic acid is trimesic acid.

12. The method of claim 10 wherein said feedstock comprises durene and the corresponding polycarboxylic monoaromatic acid is pyromellitic acid.

13. The method of claim 10 further comprising recovering ammonia generated during the process and recycling it as aqueous ammonia for reaction with said chromic oxide and oxygento produce said aqueous ammonium chromate.

14. The method of claim 10 wherein said chromic oxide, oxygen and aqueous ammonia are reacted in the presence of a cupric sulphate catalyst and sodium sullS..The method for oxidizing a polymethyl monoaromatic hydrocarbon to produce the corresponding polycarboxylic monoaromatic acid comprising:

mixing said hydrocarbon with aqueous ammonium dichromate, the equivalent ratio of said ammonium dichromate to oxidizable carbon atoms in said hydrocarbon being in the range of from 0.5 to 3, heating said hydrocarbon and aqueous ammonium dichromate in an oxidation reactor at a temperature offrom 200C to 325C for at least 15 minutes to produce an aqueous phase containing the dissolved ammonium salt of said acid and to precipitate chromic oxide, separating said chromic oxide and said aqueous phase, mixing said chromic oxide with aqueous ammonia, the mole ratio of said ammonia to said chromic oxide being in the range of from 2 to 160, heating the mixture of chromic oxide and aqueous ammonia in an autoclave in the presence of a cupric sulphate catalyst and sodium sulphate to a temperature in the range of from l40to 225C, under an oxygen partial pressure of from 20 to 500 :psi, to produce aqueous ammonium chromate containing some dissolved cupric sulphate, heating said aqueous ammonium chromate to form aqueous ammonium dichromate and ammonia and to precipitate hydrated cupric oxide, recycling said aqueous ammonium dichromate to said oxidation reactor for the oxidation of additional hydrocarbon, and I acidifying said aqueous phase containing the dissolved ammonium salt of said acid to precipitate said acid. 16. the method of claim 15 wherein said hydrocarbon is mesitylene and said acid is trimesic acid.. 17. The method of claim 15 wherein said hydrocarbon is durene and said acid is pyromellitic acid.

18. The method of claim 15 further comprising recovering ammonia generated during the process and recycling it to said autoclave.

Claims (18)

1. A METHOD FOR OXIDIZING A POLYALKY MONOARCONTIC HYDROCARBON FEEDSTOCK TO THE CORRESPONDING POLYCARBOXYLIC MONOAROMATIC ACID COMPRISING: A. REACTING THE FEEDSTOCK WITH AQUEOUS AMMONIUM DICHROMATE IN AN EQUIVALENT RATIO FO FROM ABOUT 0.5:1 TO ABOUT 3:1 OF SAID AMMONIUM DICHROMATE TO OXIDIZABLE CARBON ATOMS OF SAID POLYALKYL MONOAROMATIC HYDROCARBON AND AT A TEMPERATURE OF FROM 160*C TO 325*C TO PRODUCE CHROMIC OXIDE AND THE AMMONIUM SALT OF SAID POLYCARBOXYLIC MONOAROMATIC ACID, B. REACTING THE CHROMIC OXIDE WITH OXYGEN IN AQUEOUS AMMONIA TO PRODUCE AQUEOUS AMMONIUM CHROMATE, C. REMOVING AMMONIA FROM SAID AQUEOUS AMMONIUM CHROMATE TO FORM AQUEOUS AMMONIUM DICHROMATE, RECYCLING THE AQUEOUS AMMONIUM DICHROMATE FOR THE OXIDATION OF ADDITIONAL FEEDSTOCK, AND D. ACIDIFYING THE AMMONIUM SALT OF SAID POLYCARBOXYLIC MONOAROMATIC ACID TO PRECIPITATE THE ACID THEREFROM.

2. The method of claim 1 wherein said feedstock is a polymethyl substituted monoaromatic hydrocarbon.

3. The method of claim 2 wherein said feedstock comprises a member selected from the group consisting of mesitylene and durene.

4. The method of claim 3 wherein said feedstock comprises mesitylene and the corresponding polycarboxylic monoaromatic acid is trimesic acid.

5. The method of claim 3 wherein said feedstock comprises durene and the corresponding polycarboxylic monoaromatic acid is pyromellitic acid.

6. The method of claim 1 wherein said chromic oxide is separated from the ammonium salt of the said polycarboxylic monoaromatic acid prior to reaction with oxygen, and further wherein said ammonium salt of said polycarboxyLic monoaromatic acid is precipitated by acidifying the ammonia free aqueous phase remaining after the reaction of the feedstock with the ammonium dichromate.

7. The method of claim 1 wherein said polyalky monoaromatic hydrocarbon feedstock comprises a member selected from the group consisting of mesitylene which is oxidized to trimesic acid and durene which is oxidized to pyromellitic acid wherein said feedstock is reacted with said aqueous ammonium dichromate to produce an aqueous phase in which is dissolved the ammonium salt of the product acid of the feedstock and to produce a chromic acid precipitate, and further wherein ammonia is removed from said aqueous ammonium chromate by heating said aqueous ammonium chromate to form aqueous ammonium dichromate and ammonia.

8. The method of claim 1 further comprising recovering ammonia generated during the process of recycling it as aqueous ammonia for reaction with said chromic oxide and oxygen to produce aqueous ammonium chromate.

9. The method of claim 1 wherein said chromic oxide, oxygen and aqueous ammonia are reacted in the presence of a cupric sulphate catalyst and sodium sulphate.

10. A method for oxidizing a polymethyl monoaromatic hydrocarbon feedstock to the corresponding polycarboxylic monoaromatic acid comprising: a. reacting the feedstock with aqueous ammonium dichromate in an equivalent ratio of from about 0.5:1 to about 3:1 of said ammonium dichromate to oxidizable carbon atoms of said polymethyl monoaromatic hydrocarbon and at a temperature of from 160*C to 325*C to produce a chromic oxide precipitate and an aqueous phase containing the ammonium salt of said monoaromatic acid, b. separating said chromic oxide and said aqueous phase, c. catalytically reacting the chromic oxide with oxygen in aqueous ammonia to produce aqueous ammonium chromate, d. removing ammonia from said aqueous ammonium chromate by heating said aqueous ammonium chromate to form aqueous ammonium dichromate, e. recycling the aqueous ammonium dichromate for the oxidation of additional feedstock, and f. acidifying the aqueous phase containing the ammonium salt of said monoaromatic acid to precipitate the acid therefrom.

11. The method of claim 10 wherein said feedstock comprises mesitylene and the corresponding polycarboxylic monoaromatic acid is trimesic acid.

12. The method of claim 10 wherein said feedstock comprises durene and the corresponding polycarboxylic monoaromatic acid is pyromellitic acid.

13. The method of claim 10 further comprising recovering ammonia generated during the process and recycling it as aqueous ammonia for reaction with said chromic oxide and oxygen to produce said aqueous ammonium chromate.

14. The method of claim 10 wherein said chromic oxide, oxygen and aqueous ammonia are reacted in the presence of a cupric sulphate catalyst and sodium sulphate.

15. The method for oxidizing a polymethyl monoaromatic hydrocarbon to produce the corresponding polycarboxylic monoaromatic acid comprising: mixing said hydrocarbon with aqueous ammonium dichromate, the equivalent ratio of said ammonium dichromate to oxidizable carbon atoms in said hydrocarbon being in the range of from 0.5 to 3, heating said hydrocarbon and aqueous ammonium dichromate in an oxidation reactor at a temperature of from 200*C to 325*C for at least 15 minutes to produce an aqueous phase containing the dissolved ammonium salt of said acid and to precipitate chromic oxide, separating said chromic oxide and said aqueous phase, mixing said chromic oxide with aqueous ammonia, the mole ratio of said ammonia to said chromic oxide being in the range of from 2 to 160, heating the mixture of chromic oxide and aqueous ammonia in an autoclave in the presence of a cupric sulphate catalyst and sodium sulphate to a temperature in the range of from 140*to 225*C, under an oxygen partial pressuRe of from 20 to 500 psi, to produce aqueous ammonium chromate containing some dissolved cupric sulphate, heating said aqueous ammonium chromate to form aqueous ammonium dichromate and ammonia and to precipitate hydrated cupric oxide, recycling said aqueous ammonium dichromate to said oxidation reactor for the oxidation of additional hydrocarbon, and acidifying said aqueous phase containing the dissolved ammonium salt of said acid to precipitate said acid.

16. the method of claim 15 wherein said hydrocarbon is mesitylene and said acid is trimesic acid.

17. The method of claim 15 wherein said hydrocarbon is durene and said acid is pyromellitic acid.

18. The method of claim 15 further comprising recovering ammonia generated during the process and recycling it to said autoclave.

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