IL41739A - Process for the preparation of aromatic carboxylic acids - Google Patents

Description

t PROCESS FOR THE PREPARATION OF AROMATIC CARBOXYLIC ACIDS η·ρρκ¾ηκ m»V»opiaip mia'iirnpanV vVnn Norton S-71-2^ PROCESS-fOE—ARQMAgiO—CARBOXYLIC ACIDS Abstract of the Disclosure A process for making aromatic carboxylic acids from aromatic nitriles which comprises hydrolyzing an aqueous solution of. said nitriles without catalyst at 200° to 300°C in the presence of hydrolysis products of 'said nitrile, venting steam and ammonia vapors at about 200° to about '300°C under autogenous pressure and separating aromatic carboxylic acid from said solution.

It is known to prepare aromatic carboxylic acids by ammoxidation of alkyl substituted aromatic hydrocarbons to nitriles and hydrolyzing the nitriles to the desired acid. Howeverj in separating the acids after the hydrolysis step it is found that the acid products contain nitrogenous impurities. Since the carboxylic acids so made, particularly isophthalic and terephthalic acids, are used as polymer intermediates for synthetic polyester fibers, it is necessary that they be purified to remove the nitrogen containing products and this, of course, is a costly procedure.

It has now been found that if the nitrile hydrolysis is carried out in a particular manner, hereinafter described, the nitrogen content of the acid products is significantly reduced. Thus, in accord with the invention, an aromatic carboxylic acid of low nitrogen content is prepared from the corresponding nitrile by the non-catalytic hydrolysis of an aqueous solution of said nitrile at about 200° to about 300°C in the presence of hydrolysis products of said nitrile, venting steam and ammonia vapors at about 200°C to about 300°C, and separating aromatic carboxylic acid from said solution. The pressure of the system is not critical to the process and it will be understood that when the process is carried out under the above conditions an autogenous pressure. of about 200 to about 1500 psig will be generated.

However, the process is also operable under higher pressures (achieved with nitrogen or other inert gases, for example) or at lower pressures (achieved by employing a vacuum system). For obvious economic reasons, however, the autogenous pressure generated will be used.

The process of the invention is applicable 4*θ¾» the production of a wide variety of aromatic carboxylic acids. The aromatic nitrile starting material may be selected from any of directly to an aromatic ring compound] e.g., a benzene or naphtha lene ring. Examples of nitriles falling within this class include benzonitrile, phthalonitrile, terephthalonitrile, isophthalo-nltrile, the toluonitrlles, naphthonitriles and the like.

Preferred nitriles for use in the process are the phthalonitriles, particularly isophthalonitrile and terephthalonitrile.

The key requirement in the process of the invention is that the aqueous solution of aromatic nitrile undergoing hydrolysi contain nitrile hydrolysis intermediates and these are obtained from previous nitrile hydrolysis reaction solutions. It is to be understood that addition of nitrile hydrolysis products from sources other than the previous nitrile hydrolysis reaction solutions will also have a beneficial effect, but for convenience and economy, the recycle streams will be employed as indicated.

It is also to be understood that nitriles and/or other precursors of nitrile hydrolysis products may be added so as to quickly increase the concentration of such hydrolysis products in the recycle stream and reduce the number of recycles to achieve the desired purity of product. Thus, acetonitrile, benzonitrile, succinonitrile, the toluonitriles, and the like may be added if desired. It has now been found that the higher the concentration of these hydrolysis intermediates in the recycle streams, the less nitrogen is present in. the next recovered acid product.

These nitrile hydrolysis intermediates may be expressed in terms of carboxylic acid (COOH) hydrolysis equivalents and to obtain acid products which will have a significantly lowered nitrogen content, the hydrolysis medium will contain ®*¾®x:fc&x:2xjQ¾from about recycle carboxylic acid hydrolysis equivalents per equivalent of nitrile charged. These intermediates are introduced into. the s'ystem by recycling the filtrates from previous hydrolysis. In order to keep liquid volumes under control, the recycle filtrate may, of course, be concentrated by hydrolysis-. It is not known how these intermediates function to lower the nitrogen content in the aromatic acid products, but it has been determined that the mere presence of ammonium salts is ineffective for this purpose.

It has been' determined in the case of terephthalonitrile hydrolysis that the major intermediate hydrolysis products consist of -cyanobenzoic acid (as its ammonium salt), 4-cyanobenzamide, terephthalamide, and the ammonium salt of terephthalamic acid. Some terephthalic acid and its mono- and diammonium . salt is also in the recycle stream, but these materials do not contribute to the beneficial effects of the process of the invention. It is expected that with other nitrile hydrolysis reactants, corresponding hydrolysis products will be formed.

In order to illustrate the invention the following examples are given: General Procedure The reactants were charged into a 2 liter titanium pressure reactor and heated to 300°C at an autogenous pressure of 1200 pslg. The solution was held at these conditions for about 45 minutes to allow equilibration to occur among the hydrolysis intermediates, whereupon a vapor vent line was opened and the steam-ammonia vapor was condensed, collected, and titrated with standard hydrochloric acid solution. During the venting, distilled water was continuously added to the reactant solution by means of a pressure delivery system at l 00 psig so as to balance the quantity of distillate from the reactor and generate the acid in situ. After a suitable quantity of ammonia had been collected, the reactor was cooled to atmospheric pressure, opened, and the slurry of aromatic carboxylic acid rapidly filtered at 98-100 °C. A continuously operating process will utilize pressure filtration equipment at a steam pressure up to about 200. psig. The crystalline carboxylic acid was then rinsed with 500 ml. of boiling distilled water to remove the occluded filtrate solution, after which the carboxylic acid crystals were dried at 120 °C and their nitrogen content determined by combustion analysis.

The combined wash and reaction filtrates were concentrated and used as the reactant solution for the next recycle experiment .

Example 1 In the manner described above, isophthalor.itrile (128g, 1 mole) was added to diammonium isophthalate (200g, 1 mole) dissolved in 1 liter of distilled water. After equilibration of the solution at 300°C for 5 minutes, distillation at 300°C released 1.51 moles of free ammonia. Workup of the reactant slurry yielded isophthalic acid (138.1g, 0.83 moles) containing 3. l$ nitrogen as isophthalamic acid.

It is clear from this example, in view of the high nitrogen content of the aromatic acid product, that the presence of the diammonium salt of the acid was ineffective to give a product of low nitrogen content.

Example 2 In a manner identical to Example 1, isophthalonitrile (256g, 2 moles), as a slurry in 1 liter of deionized water, was charged into the 2 liter titanium reactor and distillation at 300°C released 2.02 moles of free ammonia. Product workup of the reactant slurry yielded isophthalic acid (l . g, 0.86 moles) containing 1.48$ nitrogen as isophthalamic acid.' It Is evident from this example that even the use of deionlzed water is not effective in permitting a low nitrogen product to be obtained.

Example 3 In the manner of the generalized description, a series of reaction filtrate recycle experiments on isophthalonitrile (iPN) hydrolysis was conducted whereby the reaction and wash filtrates from the previous experiment were used as the reactant solution for a fresh nitrile charge. The equilibration and distillation were done at 300°C. The following table indicates the decreasing nitrogen content of the iPA acid as the reach concentration of nitrile reaction intermediates a steady value. This steady concentration of reaction intermediates is apparent from the columns of data showing the COOH equivalents in the recycle stream divided by the nitrile equivalents in the feed. This value is multiplied by 100 and expressed on a percent basis. The results obtained are shown in Table I.

TABLE I Reactent Composition Moles of iPA Tdtal IPA iPN Aqueous Equivalents Equivalent Recycle (moles) Solution · in Recycle in Reacto A 2 1 1. distilled H20 0.00 2.00 B 2 filtrate from A 1.11 3.11 C 1 II " B 1.83 2.83 D 1 II " C 1.56 2.56 E 1 II " D 1.42 2.42 F 1 II " E 1.47 ; 2.47 ' G 1 II n F 1.48 2.48 H 1 II " G 1.51 2.5I I 1 II " H 1.52 2.52 J 1 It " I 1.58. 2.58 K 1 II " J l.59> 2.59 L 1 It " K 1.63 2.63 As can be seen from the above table the percent nitrogen in the acid product is reduced as the recycle runs progress.

These are a few inconsistencies (recycle C, E and I), but this is a reflection of experimental error and the unsteady-state nature of the reactant composition. However, it is quite clear that there is a definite trend toward significantly purer product as the recycle runs continue.

Example 4 In the manner of Example 3 a recycle experiment was conducted using as the original reactant solution 1 mole of isophthalonltrile and 1 mole of dlammonium isophthalate (DAiiA) at 300°C. The results obtained, are shown in Table II.

TABLE II Reactant Composition Moles of iPA -Total i&A* 1PN Aqueous Equivalents Equivalent ycle (moles) Solution in Reacto A 1 1 mole DAipA in 1.00 2.00 1 1. d'ist. H20 B 1 filtrate from A 1"'.15 2.15 C 1 filtrate from B 1.05 2.05 D 1 filtrate from C 0.99 1.99 E 1 filtrate from.D 0;9 1.94 This experiment illustrates that even with a large amount of the dlammonium salt present, the recycle technique of the invention is effective in reducing the nitrogen content of the acid produced.

Exam le 5 In the manner of the general description recycle experiments were conducted using Ό.5 mole charges of isophthalo-nitrile at an- equilibration temperature of 290°C for 40-50 minutes and a distillation temperature of 290°C initial to 260°C final. The results obtained are shown in Table III.

TABLE III Reactant Composition Moles of iPA Total XPA. iPN Aqueous Equivalents Equivalent Recycle (moles) Solution : . in Recycle in Reacto A 0.5 1 1. H20 0.00 0.5 B 0 , 5 filtrate from A 0.17 0.67 C 0 ,5 filtrate from B 0.20 0.70 D 0.5 filtrate from C 0.21 0.71 E 0.5 filtrate from D 0.25 0.75 F 0.5 filtrate from E 0.29 0.79 Example 6 In the manner of the generalized experiment, a mixture of isophthalonitrile (0.5 moles), acetonitrile (0.2 moles) and water (70 moles) was reacted at 290°C for one hour and distilled the ammonia at 290°C. The following data were obtained (Table IV) TABLE IV Reactant Composition Moles of iPA Total iPA...

IPN Aqueous Equivalents Equivalents Recycle (moles) Solution in Recycle in Reactor A- 0.5 0.2 moles aceto- 0.00 0.50 nitrile 70 moles H20 B 0.5 iltrate from A 0.11 0.6l C 0.5 filtrate from B 0.23 0.73 D 0.5 filtrate from C 0.31 0.8l In the above experiment, acetonitrile was added since it is a precursor to acetamide and ammonium acetate. As can be seen from the results, the percent nitrogen in the isophthalic acid product is extremely low after the second recycle (Recycle C and D). Thus, the beneficial effects of nitrile hydrolysis products is again clearly evident.

Example 7 In the manner of the general description, recycle experiments were conducted using an initial charge of isophthalo-nitrile (0.5 moles) in water (50* moles) containing dipotassium isophthalate (0.5 moles). In experiments A and B, only a small portion of the available ammonia was vented so as to develop a concentrated solution of hydrolysis intermediates for recycle in C through F. The equilibration was for one hour at 300°C for each run and distillation was at 295°C to 300°C. The results obtained. are shown in Table V.

TABLE V Reactant Composition Moles of iPA Total iPA Aqueous Equivalents Equivalents :ycle (moles) Solution in Recycle in Reacto A ' 0.5 0.5 Dipotassium 0.00 0.5 isophthalate 50 moles of H20 B 0.5 filtrate from A 0.23 0.73 C 0.5 filtrate from B 0.48. O.98 D 0.5 ' . filtrate from C oAl 0.91 E 0.5 filtrate from D 0.34 0.84 F 0.5 filtrate from E 0.32 Ο.82 I \ i ( Example 8 In the manner of the general description, recycle experiments to prepare terephthalic acid (TPA) were conducted using an initial charge of 1.0 mole of terephthalonitrile (TPN) in 55 moles of water containing 1.0 mole of diammonium terephthalate (DAT). The mixture for each experiment was equilibrated at 300°C for 50 minutes ..ancLdistillation was at 295-305°C. The results obtained are shown in Table VI. ycle A 1.0 1 1 . (1 mole DAT) 4.00 B 1.0 1 1 . (0.59 mole TPA eq . ) 3.18 C 1.5 o.4o tl 3.80 D 1. . 0.33 it it 3.66 E 1.5 0.35 3.70 t it F 1.5 „ n 0. 4 tl i 4.08 G 1.5 0.59 4.18 The unsteady state nature of the system in experiments A and B are reflected in the discontinuity. In experiments C through G the reactor conditions were sufficiently stabilized so as to yield the characteristic decreasing nitrogen valu,es.

Example 9 · In the manner of the general description, recycle experiments were conducted using an initial charge of 1.5 moles of terephthalonitrile in 55 moles of water containing 1.0 mole of diammonium terephthalate . The recycle mixtures were equilibrated for 30 minutes at 300 °C prior to distillation at 300°C. The results obtained are shown in Table VII.

Aqueous Solution Total COOH TPN of TPA Equivalents Equivalents Recycle (moles) From Recycle in Reactor A 1.5 1 1. H20 (1 mole DAT) 5-00 B 1.5 1 1. H20 (0.69 TPA eq.) 4.38 c 1.5 " " " 0.63 " " 4.26 D 1.5 " " " 0.69 " " 4.38 E 1.5 " " " 0.69 " " 4.38 P 1.5 " " " 0.75 " " 4. 0 G 1.5 11 " " 0.88 " " 4.76 Example 10 In the manner of the general description, recycle experiments were conducted using an initial charge of 0.5 moles 2, 6-dicyanonaphthalene (2,6-DCYN) in 55 moles of water containing 0.5 moles of diammonium 2, 6-naphthalenedicarboxylate (DA-2.6-NDCA) . The recycle mixtures were equilibrated for 30 minutes at 300°C and distilled at 250°C. The results obtained are shown in Table VIII'.

Aqueous Solution Total COOH 2,6-DCYN of TPA Equivalents Equivalents Di Recycle ( moles) Prom Recycle in Reactor ( A 0.5 1 1. (0.5 mole DA-2,6-NDCA) 2.00 B 0.5 " " 0.25 " " 1.50 C 0.5 " " 0.30 11 " 1.60 D 0.5 " " 0.28 " " 1.56 . E 0.5 " " 0.24 " " 1.48 F 0. " " 0.25 " " 1.50 G 0.5 " " 0.24 " 1.48 •

Claims (11)

Appln. 1 39 2 C L AI M S f

1. Δ process for making atomatio carboxylic acids from aromatic nitrlles comprising the non-catalytic hydrolysis to equilibrium of ah aqueous solution of said nitrilee at 200° to 300°C in the presence of soluble recycled hydrolysis products of said nitrile separated from admixture with precipitated aromatic acids obtained in the process, the hydrolysis medium containing from about 0. 5 to about 2.0 recycle carboxylic acid hydrolysis equivalents per mole of nitrile, venting steam and ammonia vapors at about 200° to about 300°C and at autogenous pressure, the amount of ammonia vented being more than 5 $ of that formed from said nitrile, cooling to preoi-pitate free aromatic carboxylic acid, separating said solid acid from the solution of soluble products and recycling said aqueous solution to a subsequent hydrolysis.

2. » The process of claim 1 inhere the nitrile hydrolyzed is phthalonitrlle.

3. The process of claim 1 where the nitrile hydrolyzed is ioophthalonitrile. k.

4. The process of claim 1 where the nltrlle hydrolyzed is terephthalonltrile.

5. The process of claim 1 where the nitrile hydrolyzed Is 2·6-dlcyanonaphthalene.

6. The process of claim 1 where a nitrile other than that hydrolyzed is added to the reaction.

7. The process of claim 6 where the nitrile added is aoetonitrile . mononuclear

8. A process for making/aromatic carboxylic acids from y Appln. 41739 /2 phthaionit iles comprising the non-catalytic hydrolysis to equilibrium of an aqueous solution of said nitriles at 200° to 300°C in the presenoe of soluble recycled hydrolysis products of said nitriles separated from admixture with precipitated aromatic aoids obtained in the process, the hydrolysis medium containing from about 0 *6 to about 1.2 reoyclo oarboxylio acid hydrolysis equivalents per mole of o nitrile, venting steam and ammonia vapors at about 200 to about 300°C and at autogenous pressure, the amount of ammonia vented being between about 75$ and 95$ of that formed from said nitrile, cooling to precipitate aromatic carboxylic acid separating said solid acid from the solution of soluble products and recycling said aqueous solution to a subsequent hydrolysis .

9. · The process of claim 8 where the nitrile is lsoph-thalonitrile and the reoyole carboxylic acid hydrolysis equivalents per mole of nitrile is from about 0.6 to about 1.

10. The process of claim 8 where the nitrile is tereph-thanlonitrile and the recylole carboxylic acid hydrolysis equivalents per mole of nitrile is about 1.

11. The procoSB of claim 8 where acetonitrile is added to the system. Tel-Aviv, March 7 , 1973.