DE1242211B - Process for the continuous production of pure benzene dicarboxylic acids - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

CAma

Int. Cl .:

C07c

German class: 12 ο -14

/ jO2.0

Number: 1242 211

File number: C 26626IV b / 12 ο

Filing date: April 4, 1962

Open date: June 15, 1967

The invention relates to a process for the continuous production of pure benzene dicarboxylic acids, the oxidation of corresponding xylenes with the help of ammonium sulfate and an inorganic one Sulfur compound in which the sulfur 5 has a valence below 6 has been obtained was. Of the benzenedicarboxylic acids, terephthalic acid in particular has a considerable technical level Importance in the production of polyethylene terephthalate.

In the manufacture of polyethylene terephthalate by reacting terephthalic acid with ethylene glycol there is an essential requirement that the terephthalic acid be in a state of very high purity is present when there are satisfactory reaction rates and a technically acceptable one Polycondensate are to be obtained.

Benzene dicarboxylic acids can, for. B. by oxidation of dialkylbenzenes with oxygen or oxygen-containing gases in the presence of aliphatic carboxylic acids as solvents and heavy metal compounds as catalysts or, as already indicated above, by oxidation Xylenes with the help of ammonium sulfate and an inorganic sulfur compound in which the Sulfur has a valence below 6. However, they contain according to this procedure or other known procedures, the crude benzene dicarboxylic acids obtained have a high Content of impurities. There are methods of treating these crude benzene dicarboxylic acids for the achievement of a higher level of purity is known, but this is usually difficult and expensive and are generally not suitable, the high required for the reaction with ethylene glycol To achieve purity standards in order to obtain suitable polycondensates, for example in synthetic fiber production, to create.

It is a process for separating accompanying substances from solid crystalline substances or mixtures of substances, ζ. Β. Terephthalic acid, known from solvent treatment, in which the solvent treatment is carried out after the crystalline substances or mixtures of substances in the presence a small amount of a solvent for these substances and / or some adsorbents Time have been heated to temperatures below the decomposition temperature or the melting point of the substances or mixtures of substances.

Furthermore, a method for purifying terephthalic acid is known in which the crude acid on a Temperature not heated below 350 ° C is a process for the continuous recovery of purer Benzene dicarboxylic acids

Applicant:

Monsanto Company, St. Louis, Mo. (V. St. A.)

Representative:

Dr. E. Wiegand and Dipl.-Ing. W. Niemann,

Patent Attorneys, Munich 15, Nussbaumstr. 10

Named as inventor:
Eugene Lee Ringwald,
Cary, NC (V. St. A.)

Claimed priority:

V. St. v. America April 25, 1961 (105 445)

and optionally the decomposition products of the impurities from the terephthalic acid by dissolution the purified terephthalic acid and the decomposition products in alkali and recovery of terephthalic acid can be removed by precipitation with a mineral acid.

Furthermore, there is a method for purifying a carboxylic acid containing nitrogen compounds known as impurities, in which the nitrogen compounds by treating the impure Carboxylic acid in alkali solution with gaseous sulfur dioxide converted into water-soluble products will.

However, the known methods have not led to the desired success.

Finally, it is known to produce crude benzene dicarboxylic acids by a batch process the high level of purity that comes as standard for use when implementing with clean Ethylene glycol for the production of linear polyesters, which are suitable for synthetic fiber production are required. However, although the known method is very effective, it is large-scale Due to its nature, production as a single batch process is not easily accessible.

It has now been found, surprisingly, that benzene dicarboxylic acids obtained by oxidation corresponding xylenes with the help of ammonium sulfate and an inorganic sulfur compound, in which the sulfur has a valence below 6,

709 590/333

3 4

had been obtained, continuously, in particular resulting diammonium sulfate an easier ab-

on the polyester separation of the precipitated benzenedicarboxylic acid required for further processing

fibers can bring the required degree of purity, possible. But it can also be ammonium chloride,

if you have a raw, in a known manner, which is formed when using hydrochloric acid,

Treating with activated charcoal, decolorized, aqueous am- 5 are separated off well. Preferred is the sulfur

moniacal solution of a benzene dicarboxylic acid with acid in aqueous solution with a concentration

eiöeP * §acid ionization constant greater than that of 10 to 20% used.

those \ ler benzenedicarboxylic acid continuously with Surprisingly, it has been shown that Prosolcher ^ Speed brings that duct losses largely avoided and the product der pH ^ vert is kept between 1 and 3.6, and io quality can be considerably increased if the precipitated benzenedicarboxylic acid known in one the pH while touching the di-way worked up. In a special execution ammonium salt solution with the to precipitate the In the form of the process according to the invention, a benzene dicarboxylic acid from the solution is used pH value between 2 and 3 maintained. Acid between 1 and 3.6 and preferably between

In practice, the raw 15 2 and 3 is set. This can advantageously be achieved by using benzene dicarboxylic acid be handed over in their ammonium salt that one led the reactants. As the duration of the dissolution of the crude with stirring in a reaction vessel with such Acid in the aqueous ammonia forming the rate gauges to the resulting mixture Keeping acid salt of the particle size of the crude benzene within the desired pH range Depending on the dicarboxylic acid, it is expedient in 20 To indicate the pH value within the reaction ratio small particle size, d. H. A pH meter can be used with a diameter of about 0.15 mm or less, with the electrodes inside the reaction vessel below, introduced, with the salt used to facilitate the use.

advantageously a stoichiometric amount, the precipitated, the benzene dicarboxylic acid

the paste-like mixture required for complete neutralization of the benzene is fed to a separating device

dicarboxylic acid charge is required, overflow, preferably a centrifuge, fed. the

lowing amount of ammonia is used. Bis- separated benzenedicarboxylic acid is then by

while a molar excess of ammonia can lead to one or more washing and filtration zones

up to 30% beneficial. leads to a common drying

Appropriately, the solution obtained, for. B. is pumped with 30 voltage device.

a concentration of about 10% of the diammo- The process is filtered based on the drawing in more detail in order to explain all insoluble substances, which separate them in a schematic representation, with a filter aid, device and the process sequence for the practically diatomite, if necessary can be. The table shows the implementation of the invention.
Filter medium usually in an amount of 1 to 3%. Crude benzene dicarboxylic acid is present based on the weight of the benzene dicarboxylic acid used via line 2 in a horizontal carboxylic acid. brought mixed flow dissolver 3 introduced. In this

The solution of the diammonium salt possesses a vessel becomes aqueous ammonium hydroxide from the yellow to dark brown color. To decolorize container 4 via line 5 together with a therefore the solution passed through a bed of activated carbon. 40 filter aid (kieselguhr), which is from the Trich-Optimal Results can be obtained when using a ter 6 introduced through the line 7, pumped, finely divided activated carbon, which is produced by a close-meshed The aqueous ammonium hydroxide solution in the sieve, for example the commercially available Pittsburgh container 4 is made by inserting into the container Type OL, and preferably one particle size, goes from line 8 to ammonia and from line 9 of about 0.297 to 0.84 mm, 45 introduces water. After the dissolution of the raw Benden. Usually it is desired that the activated carbon zoldicarboxylic acid is over the resulting solution the acid salt solution in an amount of about 1 to line 10 through the filter 11 to separate the 2% based on the weight of the benzene dicarbon filter aid. From the filter 11 is the acid, add. Although various Vorrich- solution transferred to the holding container 12, from lines, which for the treatment with activated carbon 50 which they via line 13 in and through the are used, the activated carbon adsorption tower 14 is generally used for the separation of Turning a column charged with activated charcoal is pumped soluble color bodies. The discolored or a tower is preferred, through which or by solution is then from the top of the tower which the solution is pumped or removed down to base 14 and passed through filter 15 and can be guided by gravity. The decolorized 55 is then placed in the holding container 16. The solution can now be passed through a filter, a centrifuge. or a similar device for separating ad- saline solution in the device 17 with stirring of the same-sorbed or absorbed coal particles simultaneously with aqueous sulfuric acid, which from leads to be. is inserted into the container 18, measured. That

As indicated above, the benzene dicar is 60 simultaneous metering of these reactants

Boric acid from the decolorized diammonium salt solution is carefully regulated to keep throughout

precipitated by treating them with an acid with a pH between 2 and 3 in the period

Ionization constant, which is greater than that of the device 17 to be maintained. For pH value adjustment

Benzene dicarboxylic acid is brought into contact. A pH measuring device (not

Suitable for this are: sulfuric acid, nitric acid, hydrochloric acid, 65 shown) with inserted inside the device

acid, sulphurous acid, acetic acid and ant electrodes are used. Mixing the solution

acid. Sulfuric acid is generally preferred, with the diammonium salt of benzene dicarboxylic acid

because it is relatively cheap and also because that of the sulfuric acid in the device 17 leads to

Precipitation of benzene dicarboxylic acid and formation of ammonium sulphate. Formed slurry of benzenedicarboxylic acid and ammonium sulphate is herein via line 18 to centrifuge 19 α out where the benzenedicarboxylic acid is separated from the ammonium sulfate from the apparatus 17th The isolated benzenedicarboxylic acid is then subjected to a first water wash with the aid of a water stream from line 9 in the countercurrent principle, while the ammonium sulfate solution is drawn off and passed with waste water through line 20 to a drainage duct or a collecting zone. After washing, the benzene dicarboxylic acid cake is removed at intervals and transferred via line 21 into container 22, where it is slurried again with washing water which is introduced into the container from filter 24 via line 23. The reslurried benzene dicarboxylic acid is then transferred from container 22 through line 25 to filter 24 where the filter cake is washed again. The filtered benzenedicarboxylic acid is then brought via line 26 into the container 27, where the previous operation, the formation of a slurry, the filtering and washing is repeated. The benzene dicarboxylic acid is again slurried by introducing washing water into the container 27 from the line 28, whereupon the slurry is fed via the line 29 to the filter 30 to be filtered and washed. The wet benzene dicarboxylic acid is then brought to the dryer 31, where drying is carried out in a conventional drying device, for example an oven dryer with circulating air.

The invention is explained in more detail below with reference to examples, the above-described Cleaning unit according to the drawing is used.

40

example 1

Crude terephthalic acid, which is obtained by the oxidation of p-xylene by the above-mentioned sulfur ammonium process had been obtained, was together with a solution of aqueous ammonia and a filter aid (kieselguhr) in one Introduced mixed flow dissolver with a volume of about 1650 ml. The total amount of used Reactant was 162.22 kg of crude terephthalic acid, 36.6 kg of ammonia and 3.54 kg Filter aid. Ammonia was in the form of an aqueous solution with an ammonia concentration of about 2 weight percent is used. The aqueous acid introduced at a rate to to result in a 10 molar excess of ammonia in the reaction mixture. This became a 10% aqueous solution of diammonium terephthalate was obtained. At a throughput speed of 0.454 kg per hour of crude terephthalic acid was the residence time in the mixed flow dissolver about 15 minutes.

The diammonium terephthalate solution was decolorized by passing it through a tower of activated carbon of the Pittsburgh type OL having a particle size in the range of 0.297 mm to 0.84 mm. the The amount of charcoal by weight used for decolorization was 2.4 kg, which is 1.47% based on weight the initially used crude terephthalic acid.

To recover the terephthalic acid from the decolorized diammonium terephthalate solution, 95.7 kg of sulfuric acid used in a 20% aqueous solution. The aqueous sulfuric acid and the diammonium terephthalate solution was added with stirring in an apparatus at such speeds measured to keep the pH of the slurry between 2-3.

The reaction mixture containing the recovered terephthalic acid became continuously one Centrifuge fed to separate the terephthalic acid from the ammonium sulfate solution.

After separation, the terephthalic acid was washed and washed with water at a temperature of Slurried about 90 ° C to facilitate the subsequent filtration stages. After filtration, reslurry and again filtration, the wet terephthalic acid was placed in a circulating hot air oven dried.

146.3 kg of terephthalic acid were thereby obtained, which corresponded to 90.5% of the amount of crude acid used, obtain. The time required to carry out this experiment was 381 hours.

In order to determine the effectiveness of the cleaning method according to the invention, a sample was taken the terephthalic acid obtained in the cleaning experiment described above is used to to produce a polycondensate by reaction with ethylene glycol in the following way: A slurry from 66.4 g of purified terephthalic acid and 248 g of ethylene glycol was in an autoclave made of stainless steel at a temperature of 221 to 231 ° C and under a pressure of 1.76 to 1.90 atü heated in a nitrogen gas atmosphere for 20 minutes. During the between the acid and the Glycol-induced reaction, 38 ml of distillate was collected. The reaction mixture obtained was placed in a stainless steel vessel with 60 mg of zinc acetylacetonate, which was used as a polycondensation catalyst was added, transferred. While stirring the mixture at 285 ° C. became excess Separated glycol by distillation. Then the reaction mixture was at the same temperature exposed to a pressure of 0.3 mm of mercury for 70 minutes. The polycondensate obtained was white in color and had a melting point of about 250 ° C. Well threads were spun directly from the autoclave and stretched to standard textile draw ratios. the Fiber formation and tensile properties were excellent.

It is noted in this connection that the above-described washing treatment of the purified terephthalic acid and the process for producing the polycondensate by reaction of terephthalic acid with ethylene glycol are not the subject of the invention.

As already mentioned, the yields are largely influenced by the manner in which the diammonium salt solution is used and the acid used to precipitate the benzene dicarboxylic acid in the recovery device be brought together. If the reactants are introduced into the device at such speeds, that the mixture obtained at a pH between

see 1 to 3.5 and preferably between 2 and 3, end product losses will be substantial avoided.

To show the extent to which losses are caused by observing the specified pH regulation during the acid precipitation level are influenced, comparative experiments were carried out using the method described in FIG

Continuous cleaning unit shown in the drawing. The procedural details were accordingly, only allowing the pH of the mixture to be in the Acid regeneration device changed in each of the test runs. The results are in the following Table listed.

approach Raw acid added
(Grams per hour) Test duration
(Minutes) pH in the acid again
extraction device weight
the acid obtained Yield (° / o) 1
2
3 188
188
188 120
120
120 2.0
3.0
6.0 360.5
326.7
150.6 95
86
39

From the table above it can be seen that there is a substantial reduction in the yield, when the benzenedicarboxylic acid from the diammonium salt solution at a pH outside of of the range according to the invention is precipitated.

Further, since it was found that the pH control in the acid recovery step improves the purity of the affected end product, corresponding determinations were carried out. To this For this purpose, a series of polyester condensates was produced by reacting ethylene glycol with test samples of purified terephthalic acid. It were thereby terephthalic acid, which when adhering to the pH control according to the invention during the Purification was obtained, compared with terephthalic acid, which is also according to the invention Process had been purified, but with the difference that in the stage in which Terephthalic acid is deposited from the diammonium salt solution, exceeding the pH value the limits of the range indicated above, which are necessary for satisfactory results have been approved to a small extent. The polycondensates produced therefrom became threads spun, which have been subjected to color tests. The relative discoloration of the threads was measured as Measure taken for the purity of the terephthalic acid, which is used in the production of the polycondensates, from which the filaments were formed, was used since it is known that the purity of terephthalic acid influences the color of the polycondensates.

The one used to measure the color of the test polyester fibers The test method used was to determine its approximation to perfect white by Reflectance measurements were made with a spectrophotometer, using those of the standard Observer and Coordinate System of the International Commission on Illumination recommended test methods (See Handbook of Colorimetry, published in 1936 by Technology Press, Massachusetts Institute of Technology).

In the test results below, the polycondensates from which the fiber test samples were made were obtained in the same way. The one used to produce these polycondensates The terephthalic acid samples used were determined in the same way by the method according to the invention purified with the difference that the pH was varied during the precipitation of the terephthalic acid.

The white values listed in the table below indicate the degree of approximation to perfect white, for which the value 100 is taken.

Polycondensate
sample pH in the
Cleaning level White level
the fiber 1
2
3 2.5
3
4th 90.5
85.0
64

The results of the table above show that there is a remarkable improvement in quality the polycondensate is achieved when the pH is kept below about 3.5. Even a minor one Deviation causes a remarkable decrease in purity as shown in Sample 3 is at which a pH value of 4 was maintained.

Example 2

Crude isophthalic acid, which was obtained by the oxidation of m-xylene with sulfate, became together with a solution of aqueous ammonia and kieselguhr through a mixed flow dissolver of a volume of 1650 ml. The total amount of reactants fed passed from 162.5 kg of crude isophthalic acid, 36.6 kg of ammonia and 3.54 kg of kieselguhr. The aqueous ammonia solution was about 2 percent by weight. This aqueous ammonia solution was purchased in such an amount on the crude acid, fed that a 10 mole percent excess of ammonia in the reaction mixture was present, a 10% aqueous solution of diammonium isophthalate being formed. At a throughput rate of 0.45 kg per hour of crude isophthalic acid, the mean dwell time in the mixed current release about 15 minutes.

The diammonium isophthalate solution was decolorized by pumping it through a tower, which activated carbon (trade name: Pittsburgh type OL), with a particle size of 0.297 to 0.84 mm. The amount of charcoal used for decolorization was 2.4 kg, which is 1.47% by weight on the weight of the crude isophthalic acid.

In the recovery of isophthalic acid from the decolorized diammonium isophthalate solution 101.6 kg of sulfuric acid used in a 20% aqueous solution. The aqueous sulfuric acid and the diammonium isophthalate solution were combined with each other with stirring so that the pH of the slurry was maintained within 2-3.

The reaction mixture was continuously fed to a centrifuge to remove the isophthalic acid to separate the ammonium sulfate. After the separation, the isophthalic acid was washed and washed with Water slurried at a temperature of about 90 ° for the subsequent filtering operations to facilitate. After filtering, reslurrying and filtering again, the Put moist isophthalic acid in an oven with circulating hot air to dry. The amount of Dry isophthalic acid recovered was 147.7 kg, which is 91.5% of the amount originally charged raw acid. The total time it takes to perform this experiment was 376 hours.

In order to determine the effectiveness of the cleaning method according to the invention, a sample of the isophthalic acid obtained above used for the preparation of a polycondensate.

A slurry of 66.4 g of the purified isophthalic acid and 248 g of ethylene glycol was heated in a stainless steel autoclave at a temperature of 221 to 321 ° C under a pressure of 1.76 to 1.90 atm for 20 minutes in an atmosphere of nitrogen . During this time 38 ml of distillate were collected. 60 mg of zinc acetylacetonate were added as a polycondensation catalyst to the reaction mixture obtained. While the mixture was stirred at 285 ° C, excess glycol was removed by distillation. The reaction mixture was then subjected to a pressure of <0.3 mm Torr at the same temperature for 70 minutes. The polycondensate obtained in this way had a white color and a melting point of about 250 ^° C. Threads were then spun directly from the autoclave and stretched to the standard textile stretching dimension. The fiber forming and stretching properties were excellent.

Example 3

Using a continuous cleaning unit as illustrated in the drawing the following experiment was carried out.

Crude phthalic acid, obtained by the oxidation of o-xylene with sulfate, was put together with a solution of aqueous ammonia and kieselguhr through a mixed flow dissolver with a volume of about 1650 ml. The total amount of reactants used passed from 162.22 kg of crude phthalic acid, 36.6 kg of ammonia and 3.54 kg of filter aid. ammonia was in the form of an aqueous solution with an ammonia concentration of about 2 percent by weight applied. The aqueous ammonia solution became with respect to the crude acid at such a rate or amount introduced that a 10% molar excess of ammonia was present in the reaction mixture. This led to a 10% aqueous solution of diammonium phthalate. With a throughput speed of 0.454 kg per hour the For crude phthalic acid, the mean residence time in the mixed flow dissolver was about 15 minutes.

The ammonium phthalate solution was decolorized by pumping it through a tower which Contained activated carbon. The activated carbon had a particle size of 0.297 to 0.84 mm.

The amount by weight of charcoal used for decolorization was 2.4 kg, corresponding to 1.47%, based on weight on the weight of the raw material used initially

ίο phthalic acid.

To regenerate the phthalic acid from the decolorized diammonium phthalate solution, 101.6 kg Sulfuric acid applied in 20% aqueous solution. The aqueous sulfuric acid and the diammonium phthalate solution were combined with stirring such that the pH of the slurry was held between 2 and 3.

The reaction mixture containing the regenerated phthalic acid was continuously passed through a centrifuge fed to separate the phthalic acid from the ammonium sulfate formed. After the separation the phthalic acid was washed and slurried with water at a temperature of about 90 ° C, to facilitate the subsequent filtration stages.

After filtering, reslurrying, and filtering again, the wet phthalic acid was placed in a hot air circulation oven fed for drying. The amount of recovered dried phthalic acid was about 144 kg, which is 89 per cent of the originally brought in Amount of raw acid corresponded. The total time it took to complete this experiment was 381 hours.

Claims (2)

Patent claims: 1. Process for the continuous production of pure benzene dicarboxylic acids, which are produced by oxidation corresponding xylenes with the help of ammonium sulfate and an inorganic sulfur compound, in which the sulfur has a valence below 6, were obtained, characterized in that one crude aqueous ammoniacal, decolorized in a known manner by treatment with activated charcoal Solution of a benzene dicarboxylic acid with an acid having a larger ionization constant than that brings the benzenedicarboxylic acid into contact continuously at such a rate that the pH is kept between 1 and 3.6, and the precipitated benzenedicarboxylic acid in known Way worked up. 2. The method according to claim 1, characterized in that one has a pH between 2 and 3 complies with. Considered publications:
German Auslegeschrift No. 1 025 875;
British Patent Nos. 695 170, 777 782; Legacy Patents Considered:
German Patent No. 1117 100. 1 sheet of drawings 709 590/333 6.67 © Bundesdruckerei Berlin