DE2040596C3 - Purification of trimellitic anhydride produced by oxidation of nitric acid - Google Patents

Description

a temperature lower than the melting point of TMSA, which has a very low solubility, the solubility in benzene decreases very suddenly at the melting point or at an even higher temperature to. Correspondingly crude TMSA, produced from amellitic acid, is dissolved by nitric acid oxidation was obtained in benzene at a temperature not lower than the melting point of the Trimellitic anhydride is, and cools the resulting solution to a temperature that is lower than the melting point of the anhydride, it can be achieved that only the TMSA crystallizes out in pure form, while the colored or coloring impurities Remain dissolved in the benzene. The present invention is based on this surprising in principle Fact established.

The above-mentioned important feature according to the invention is achieved by using a benzene, optionally blended with other organic solvents up to 20 percent by weight, as a recrystallization solution; medium used. If other aromatic hydrocarbons are used in place of benzene, for example alkylbenzenes such as toluene, xylene and ethylbenzene, the cleaning effect is very low and the crystallization rate is also low compared with benzene. If other aromatic solvents are used, the size of the crystals is very small, which also causes difficulties. Furthermore, the solubility of crude TMSA in such alkylbenzenes is less than the solubility in benzene, and even when the crude ■ \ nhydrid exceeds in such alkylbenzenes by heating to a Temperatun the chmel- the £ _f mnkt of the crude anhydride veifiüjsigt ¹ ^ ird. the liquefied anhydride often forms a second fugue.

At temperatures not below the melting point, crude TMSA is highly soluble in benzene, and a solution having an anhydride concentration in excess of 50% can be produced. The relationship between the solubility of the anhydride in benzene and the temperature is shown in the table! reproduced, off which can be seen that the important thing is to dissolve the crude TMSA in benzene at temperatures that are not are lower than the melting point of the anhydride. The melting point of the TMSA used is 167 ° C. For comparison, Table I also shows the relationships between temperature and solubility of TMSA in xylene, selected as a typical representative of other aromatic hydrocarbon solvents would.

Table I.

temperature Solubility in Benzo! solubility
in xylene ( ⁰ C) (g / 100 g benzene) (g, 100g xylene) 80 less than 0.2 2.0 100 less than 0.5 3.6 120 1.6 6.4 150 6.0 15th 180 more than 120 37 200 more than 120 65

The melting point of the crude TMSA will vary depending on the amounts of impurities present in the crude anhydride. It is ierinch from the fact that the melting point of crude trimellitic is never lower than 150 ⁰ C, whatever the content may be of impurities _t as big. At temperatures above the melting point of the crude trimellitic anhydride, its solubility in benzene continues to increase in proportion to the temperature. In the present invention, however, it is unnecessary to use excessively high temperatures. In the practice it is preferred to provide temperatures ίο up to 300 ⁰ C, particularly at 170, are in the range from the melting point of the crude trimellitic anhydride to 250 ⁰ C. In the present invention, therefore, it is necessary to keep the system under a pressure sufficient to keep the benzene in the liquid phase. The selected pressure depends on the temperature.

It is preferred. To use benzene in an amount sufficient to dissolve all of the anhydride, or in a larger amount. The amount of benzene which should be used, can easily liufdi preliminary tests be determined. It depends on the type of raw trimellitic anhydride and the temperature away. At temperatures within the aforementioned preferred range, the benzene will generally used in an amount 1 to 15 times based on the weight of the crude anhydride.

The method according to the invention shows various advantages. The solubility of the crude trimellitic anhydride in benzene is - as described above - at temperatures not lower than the melting point of crude anhydride are extremely high. The pure crystallization can therefore with smaller amounts of Benzene can be compared with the use of other solvents, and because the solubility wedge of the anhydride in benzene are very low at temperatures below the anhydride melting point, even if you use excess benzene, the amount of TMSA that remains dissolved in the benzene is tiny. For the amount of benzene used in the invention Method is used, on the other hand, there is no upper limit, but it is hardly necessary To use benzene in an amount more than 15 times, especially 20 times the amount of raw anhydride.

As mentioned above, in the present invention, as a solvent for recrystallization not only benzene alone can be used, but also solvent mixtures of benzene with less than 20 percent by weight, e.g. B. an organic acid, a ketone. an ether or an aromatic one Hydrocarbon other than benzene. As such, secondary solvents can called acetic acid. Propionic acid, acetone, methyl ethyl ketone, butyraldehyde, benzaldehyde, ethyl ether. Toluene and xylene. When using such mixed solvents it is sometimes possible to use milder conditions than when using benzene alone. However, the best results are obtained in general, if you only use benzene. What was described above for benzene, also applies to the mixed solvents.

The method according to the invention is advantageously carried out in the absence of molecular oxygen carried out using an anhydrous solvent under anhydrous conditions.

The first stage of the process of the invention is that the crude TMSA in benzene or a mixed solvent containing benzene

dissolves, heated under pressure to temperatures that put. Said trimellitic anhydride as an additive

are not lower than the melting point of the raw material for synthetic resins or as raw material for

hydrids, and stir until all of the anhydride has been used, so the coloring properties are

komme.'i has dissolved in the solvent. It is closely related to craftsmanship of the products

preferred that the crude trimellitic anhydride, the ο the color of the trimellitic anhydride, if anything

treated by the process according to the invention is heated together in triethylene glycol. To the-

is, no iron or other metallic impurities - accordingly, the purified according to the invention

contains. Therefore, the production and ent-trimellitic anhydride together with triethylene

Soaking the trimellitic acid in corrosion-resistant glycol heated, and the evaluation of the product

gene devices are carried out. io is determined on the basis of the coloring (TEG color)

In the second stage of the power according to the invention, which is observed on heating. The anhydride is continued by cooling the hot one, the product is also characterized by the melting benzene solution at temperatures that are lower than point and the acid number,
the melting point of the crude anhydride, preferably As described above, the melting point depends on the temperature lower than 100 ⁰ C, crystallized out. The crude TMSA depends on the amount and nature of the contaminants. In the present invention, the crystallization purifications contained therein can depend. If trition is carried out by rapid killing processes, then it is used for the manufacture of soft earths. The crystallization temperature can be used by carpenters for vinyl chloride resins, so a temperature or lower than room temperature, with anhydride with a relatively high purity and a for example 10 "C. However, since trimellite melting point above 165 ° C is required. The Säbre number acid anhydride in benzene at temperatures that are little of pure TMSA -Tigefahr 876. Although those are lower than the melting point of the anhydride, the acid number of purified TMSA varies somewhat and is hardly soluble, the application is a * .; · relatively high around the purity and the degree of dehydration Auskristallisationstemperatur, such as 100 C advantageous, ablu..igi, the acid value of the anhydride must, so that when repeating the benzene as Umkristallisa- 25 in this ^e; can be used nem wide range, tionslösungsmittcl used so that the repeated n. amount to at least 870.

Warming can be done more easily. How the invention is illustrated by the following examples

known, benzene solidifies at 5.5 ° C. Explained accordingly. In the examples, the value was > TEG-

the benzene solution should not be at temperatures, the color «determined by adding 4 g of a sample of TMSA

lie near the benchmark of benzene, heated up together with 28 ml of triethyiengiykol,

be cooled. In the present invention, dO minutes in a nitrogen atmosphere under normal

if desired, part of the solvent was kept at 260C before painting LVuck, the resulting solvent

evaporated during crystallization. The crystals. solution cooled to room temperature and the color

which mainly consist of pure TMSA, this solution is provided with an APHA standard (Hazen

compared to that of the mother liquor using the known solid 35 scale, platinum-cobalt color). The »TEG-

Liquid separation processes such as filtration, centric color »is therefore an APHA color. Triethylene glycol,

fuging or decanting, separated. that is used to determine the »TFG color«

If, as previously described, alkylben- is used, it must be so pure that, if the ethylene glycol

zole, wj »" toluene, xylene, ethylbenzene or pseudo alone is heated under the same conditions,

cumene instead of benzene, the impurities will have a TEG color value of less than 50,

conditions that are to be removed by alkylbenzene in general, it is required that trimellitic acid

with a ratio less than about 'j _t the distribution anhydride in the preparation of plasticizers

Conversion ratio that is used by the use of or resins, a TEG color value

Benzene reached, distributed. Furthermore, the solubility is less than 300, preferably less than

of trimellitic anhydride in such alkylbenzenes !! 45 200 is.

relatively low at high temperatures and relatively low at low temperatures

relatively high temperatures; there is no critical TMSA and an essentially anhydrous solution

the point at which the solubility in the medium had filled, flushed with nitrogen and then

kylbenzene suddenly changed. Accordingly, the post is heated to dissolve the TMSA.
Amount of crude trimellitic anhydride by 50

a unit amount can be treated, very small, example 1
compared with benzene, and the recovery rate of the crude trimellitic anhydride In an autoclave equipped with a stirrer is low. Compared to the well-known recrystalline it was equipped. gives 100 g Trimellilhsäureanhydrid sationsvcrfahren, wherein the low carbonyl 55 technical grade and solves this at 180 ⁰ C in the compounds, such as acetone and methyl ethyl ketone, II solvents indicated in Table comparable. The TMSA used as a result of the process according to the invention achieved an output. Atcrial was by oxy higher effect in the separation of colored data from pseudocumene at 25O "C and 70 Ajmo or coloring impurities, and the cleaned spheres with 20% nitric acid and dehydration Trimelitic anhydride is recovered in high yields from the trimellitic acid formed; a crystallized preheating to 23O "C is obtained. The TMSA has a larger particle size duct. The invention thus shows a TEG color value of 300, a melting point compared to the known method of 163 ° C. and an acid number of 862. One of them is making great technical progress. remarkable amount of unconverted tri-

The nature of the purified trimellitic acid is not found in the crude anhydride.

anhydrides are generally made by chemical anahandcn.

lysis, acid numbers, melting point and coloration of the The solution is then abEster at room temperature., which were made from this product, chilled, whereby the trimellitic acid canhvdricl

installed. The results are given in Table 11.

Table Il

solvent
Alles

benzene
Xylene
acetone
acetic acid

I I mcrystallized lcs

Applied | Trimellitic anhydride
Amount of enamel

400
400
100
400

150

250
270
265

167
i 65
! 64
164

From the results shown in Table II it can be seen that the crfmdungsgemiilic process using ben / ol as solvent for the recrystallization around 1 rimellitic anhydride gives excellent results. If benzene is used as the solvent in the above experiment, 98.5 g of purified trimyclic acid anhydride with an acid content of 870 are obtained.

V e r g I c i c h s b c i s ρ i c 1

Trimyllithic anhydride. that by l.urtnx
if l'seudocumene was prepared in acetic acid using a cobalt acetate-mancanacetate-official nonium bromide catalyst, it is heated for 1.5 hours. Ir. 100 g of the crude trimyllithic acid anhydride formed in this way and 100 g Hcn / ol are added to the autoclave, and the mixture is stirred for 30 mils at ISO C. The contents of the autoclave are then cooled to room temperature so that the trimyllithic acid anhydride crystallizes out. The results of testing the crude TMSA and that crystallized from the Bcn / .ollusune are given in Table III.

Table III

Trimelli ι lisäu rcanln i
sample

High
product

Melting point (C)
Co and Mn content

in the rehearsal

TEG color type

160

1,500 ppm
over 500

Crystallized
product

160

1,500 ppm
over 500

From the results shown in Table III it can be seen dall if raw TMSA. obtained from pseudocumene by air oxidation. from benzo! The Oxydalionskalysator is recrystallized and the tarry by-products cannot be separated.

Example 2

Into an autoclave equipped with a stirrer was. 100 g of the crude TMSA as used in Example 1 are added. and a solvent mixture from 750 g of benzene and 10 g of acetone and heated to 185 ° C. for 30 minutes. The resulting solution is cooled to room temperature, 95 g of the crystallized TMSA being recovered. The results are given in Table IV.

Table IV

Trirr.jllilh-
acid anhydride Acid / ahl Enamel
Point
(C) TEG-
color roll
cleaned 862
872 163
167 300
130

B c i s ρ i e I 3

In an autoclave equipped with a stirrer, KX) g of the crude TMSA are added. as used in Example I. and a dissolution, _s mixture of 780 g of benzene and 20 g Essigsäureanliydrid and heated for 30 minutes at 175 "C. The resulting solution is cooled to room temperature, 96 g TMSA be obtained in crystalline form. The results are given in Table V.

Table V

Trimellitic anhydride

raw
cleaned

Season number

862
871

Melting point

(Cl

163
i66

TECi-

color

300
120

Example 4

Raw TMSA. which had been produced by the nitric acid oxidation of pseudocumene. is enlsvässcrt at 200 to 240 ° C; the resulting crude TMSA is distilled under a pressure less than 50 mm Hg. Into an autoclave equipped with a stirrer. 100 g of the distilled TMSA were dissolved in 800 g of benzene at 180.degree. The resulting solu- _4f) cooled solution svird to room temperature, the crystallized anhydride isolated and dried under reduced pressure. 91.7 g of purified TMSA are obtained. The results are given in Table VI.

45

Table Vl

Trimicllithsaries So before the acid Enamel TEG- anhydride crystallization .... number Point color after the (C) crystallization .... 874 165 200 874 167 85

From the values given in Table VI one can see that they 'get better results, If this is the crystallization process according to the invention used together with the described distillation process.

Example 5

The distilled TMSA used in Example 4 is recrystallized from acetic acid. The crystallization s is performed under such conditions. Yes, the amount of crystallized trimethylic acid anhydride 10 weight pro / ent. calculated on the vinegar

409 635 312

acid solution. The results are shown in Table VII specified.

The thus recrystallized TMSA (100 g) is dissolved in 800 g of benzene at 180 ⁰ C. The resulting lo-

10

solution is cooled to room temperature, the crystallized anhydride is isolated and reduced at reduced Print dried at 80 ° C. The results are given in Table VII.

Table VII

Recrystallized
Trimellitic acid
anhydride acid
number Enamel
Point
( ⁰ C) TEG-
color from acetic acid
from acetic acid and
then from benzene .. 872
873 165
167 180
70

Example 6

Crude TMSA, which had been produced by nitric acid oxidation of pseudocumene, is dewatered ^{at 235 ° C. under atmospheric pressure.} 100 g of the crude TMSA obtained in this way are dissolved in 900 g of benzene at an elevated temperature of 180 ^° C. in an autoclave equipped with a stirrer. The resulting solution is cooled to room temperature to crystallize the anhydride. The resulting purified TMSA is re-subjected to the recrystallization procedure described above. The results of the examination of each product obtained by one crystallization and by repeating the crystallization are shown in Table VIII. The triethylene glycol, which is used to determine the TEG color

»5 values is used, had a TEG color value of 40.

Table VIII

Trimellitic anhydride acid
number Enamel
Point TEG-
color CC) raw product (before the Recrystallization) 871 161 higher than 500 Product after a Recrystallization .. 873 165 90 Product that one after twofold um crystallization obtained 874 167 70

From the results shown in Table VIII, there is given 45 benzene and the two mixtures in one can be seen that a satisfactory cleaning stainless steel autoclave can be solved with heating.

The solution in 1,2,4-trichlorobenzene required 1000 % of the solvent and a temperature of 216 ° C. since the trichlorobenzene is not particularly capable of dissolving the trimithic anhydride, while on the other hand 400 g of benzene and a temperature above

obtained when the crystallization process according to the invention is carried out only once.

Comparative example 2

100g of technical trimellitic anhydride (TEG color value 300, melting point 163 ° C, acid value 862), As used in the present example 1, 400 g of benzene and 1000 g of 1,2,4-trichloro-180 ° were added C was sufficient for the first sample. The results obtained after recrystallization are in dei Table IX below summarized.

Table IX

Messed up F. (<= C) acid solvent Trimellitic anhydride 167 worth TEG- 870 Kind of amount Color 164 Benzene 400 g 150 869 1,2,4-trichloro 163 benzene 1000 g 350 862 Starting trimellitic acid anhydride .... 300

"« ■

As can be seen from the table, there is no possible reason for ii ^: .e deterioration of the TEG color value

borrowed, using 1,2,4-trichlorobenzene that is due to the 1,2,4-trichlorobenzene itself,

To purify starting trimellitic anhydride, much- which discolored the trimellitic anhydride and the

the more this the TEG color value against the container is slightly corroded,

deteriorated above that of the crude anhydride. The 5th

Claims (2)

1 2 chemical, but also to the physical claims: shafts are very similar, and these impurities crystallize together with the trimellitic anhydride 1. Process for the purification of by nitric and give the recrystallization products acid oxidation of 1,2,4-tri-lower-alkyl-benzoI 5 yellow hue. These colored or color-forming and subsequent dehydration produced tri-impurities cannot be separated, mellitic anhydride by recrystallization from even if the solution before crystallizing with an organic solvent, thereby treating activated carbon. The Japanese patent publication 2454/1969 anhydride in benzene, which may affect up to jo a process for the preparation of trimellitic 20 percent by weight of another organic acid anhydride, which consists in the fact that one tri- Contains solvent, to a temperature that heats mellitic acid in trichlorobenzene and dehydrates not lower than the melting point of the crude aned, however, this publication is in no way hydrids is, heated and the resulting solution can be seen whether trichlorobenzene and even more benzene to a temperature below the melting point 15 also for the purification of trimellitic anhydride, of the crude anhydride cools. which is caused by the dehydration of nitric 2. The method according to claim 1, characterized in that the tri-acid oxidation of trialkylbenzene obtained by producing the trimellitic anhydride to mellitic acid would be suitable. Experiments to determine the effectiveness of benzene were heated to 170 to 250 ° C together with 1 to 1 times the amount by weight and the ent- 20 trichlorobenzene as a kneading agent for tristandene solution to a temperature in the range of melietic anhydride, which, starting from 10 to 100 ° C, was heated ⁰ C. Nitrousic acid oxidation obtained from pseudocumene was carried out, which was found to be almost ineffective, as described in the following 25 benen comparative example 2 can be seen. The process according to the invention described below cannot; on crude trimellitic acid A common industrial process for the production of anhydrides use, which au * one by trimellitic anhydride is that one oxygen oxidation in the presence of heavy metals in 1,2,4-Trialkylbenzo !, z. B. pseudocumene, with salt ions (especially Ca and Mn) in the liquid phase oxidized pitric acid and the resulting trimellitic trimellitic acid originate, since here completely acidic from thermal dehydration at temperature different impurities are present,
Doors in the range from the melting point of the trimellitic By erfindungsgomäße method, the acid is subjected to 300 ⁰ C. (The production of nitrogen-containing crude trimellitic anhydride by trimellitic acid by oxidation with nitric acid is a single recrystallization from a solvent readily available, for example in the U.S. Patents 3,165,548, which was previously used for this purpose and 3,278,592 and the British patents has not yet been used, purified, it being described under 662 229 and 887 731.) High crystallization rate with high pure crude trimellitic acid, which is obtainable by oxidation with degree of stability. Nitric acid was produced, can be prepared by the 40 The present invention relates to a method for known process almost completely dehydrated purification of by nitric acid oxidation of by adding the acid preferably to 200 1,2,4-tri-lower alkyl-benzene and subsequent ent- Trimellitic anhydride produced up to 300 ^° C. under normal pressure or, if desired, washing heated under reduced pressure until the release occurs by recrystallization from egg learning water is no longer recognizable. Dementia, which is characterized by the fact that one The resulting trimellitic anhydride is trimellitic anhydride in benzene, the given essentially free of unreacted trimellite if up to 20 percent by weight of another organic acid: however, it contains impurities that can be seen from the solvent, at a temperature Nitric acid oxidation, namely nitrogen, which is lower than the melting point of the crude Substance-containing colored or coloring impurities are 50 anhydride, heated and the resulting solution gen. to a temperature below the melting point To purify such a crude trimellitic acid, cool the crude anhydride. anhydrids can be used because of its low volatility and the crude trimellitic anhydride because of the difficulty of producing such nitrogenous processes by splitting off water from a trimellitic impurities obtained by distillation or acid obtained by oxidation of nitric acid, e.g. B. To remove sublimation, a treatment such as that used for pseudocumene (1,2,4-trimethylbenzene), 1,2,4-tri- the purification of other benzenecarboxylic anhydrides, ethylbenzene, 1,2-dimethyl-4-isopropylbenzene or z. B. Phthalic anhydride, is applicable, was not produced by 1,2,4-Tii-isopropylbenzene, be guided. There has been a method for cleaning. Surprisingly, it has been found that the use of crude trimellitic anhydride, 60 the colored or coloring materials used in the that consists in having the crude anhydride from crude trimellitic acid hydride (TMSA), organic solvents such as ketones, ethers made from by nitric acid reoxidation and esters, recrystallized (cf. for example the trimellitic acid obtained, an extremely high solubility U.S. Patent 3,032,559). If they have the raw smoothness in benzene, even at low temperatures hydride by oxidation with tri-temperature nitric acid; the impurities of an acidic alkylbenzene are the main pollutants - heavy metal ions - originating from processes Nitrobenzenecarboxylic anhydrides, which the TMSA behave fundamentally differently. Trimellitic anhydride not only in relation to the while so trimellitic anhydride in benzene