DE1568345B - Process for working up aqueous, bromine-containing acetic acid - Google Patents

Description

3 4

easy way to eliminate the corrosion without the need for 1 1

special materials and apparatus are used for this purpose

requirement. In the overhead product of a catalytic air

According to the invention, this object is achieved by oxidizing p-xylene, as it is in general

solved that the mixture is described at elevated temperature 5 part of this application, are 70 mg

with finely divided metals, which contain total bromine per kg of solution in the voltage series. Of which lie

between including magnesium and iron are 20 mg as ionogenically bound bromine.

stirs, cleans with an anion exchanger and 1000 g of this solution with 5 g iron file

then separates by distillation in a manner known per se. added, heated to boiling temperature with stirring

If the p-xylene air was held for 40 minutes, the mixture worked. The subsequent anaoxidation in the presence of acetic acid and in lytic examination shows that now the In the presence of heavy metal salts and bromine ions, all of the bromine (70 mg) inorganically bound over a temperature of about 180 to 190 ° C and is.

continuously through a pressure of 10 to 20 atü.

leads to the following composition: 13 exchange column, d = 30 mm, content 100 cm ³ with

Acetic acid 91 ° / ^{e 'ner} rate of 0.5 l / h sent. the

Water ' g 0; ° ion exchanger consists of a commercially available one

YyJ ₀ I 1 ° / ° Anion exchanger in the acetate form. After passing

Total bromine '' V "'''"."''' ^{/ O} Λ _k running through the column, the bromine content is in excess

(organic + inorganic) 70 mg overhead ² ° top product: <0.1 mg / kg.

Bromine (inorganic) 20 mg j product With a throughput of 20 1/100 ecm exchanger is

⁰ ' ^r no bromine breakdown can yet be detected. The Aus

The composition of these mixtures can be easily regenerated with caustic soda

borrowed, depending on the oxidation and process conditions, whereby by washing with acetic acid

vary both what the ratio of acid 25 is produced again to the acetate form,

to water and alkyl aromatic as well as what the bromine.

share and its subdivision into organic and anor- gional game

Ganically bound bromine concerns. , 1000 g of the overhead described in Example 1 -

It is advisable to work at 30 to 118 ° C. Self-product is mixed with 1 g of magnesium and

Understandably, this temperature can also rise above, or for about 20 minutes with stirring at the boiling point

are fallen short of, but usually no heating. The metal goes into solution, and that

procedural advantage is connected. All of the bromine is preferably in inorganically bound form.

becomes the boiling point of the mixture. The further processing of this solution is carried out as

Magnesium, indicated in example 1, is preferably suitable as a metal.

Aluminum, manganese, zinc and iron. 35 This result is surprising as it is not

The list in succeeds in solving the given task in that

Smith - D'A η s, introduction to the general one of the overhead product only the inorganic

and inorganic chemistry, XI. Edition (1947), ruffling bromine compounds by means of the ion equilibrium

G. Braun / Karlsruhe, p. 634.

The metals mentioned are distinguished by the fact that treatment has been carried out.

that they are in the form of their salts with the most varied are the overhead solvents used in Example 1 Form anosolvo acids (F. Hein, product directly on the ion exchange column, Chemical coordination theory, S.HirzelVerlagLeipzig, there are no more bromine ions after the run 1950, p. 303). detectable, on the other hand it is organically bound

The metals should, in order to act quickly, in a good 45 bromine still in the initial concentration of

distributed form, for example as a powder or in 50 mg / kg.

In the form of fine chips. The mixture that has been pretreated in this way is then used

The metals are preferably used in quantities in a chromium-nickel steel apparatus for the purpose

between 0.1 and 20 g, in particular between 0.5 of the distillation, is then readjusted

and 5 g, based on 1000 g of solution to be worked up, 50 very short time that again ionogen-bound

one. For this treatment, depending on the presence of bromine, you need a concentration

on the bromine content of the mixture, on the temperature that largely corresponds to the original (total

and of the type, amount and distribution of the metal bromine: 50 mg, inorganic bromine: 20 mg). In order to

a time of 0.1 to 1 hour. You can see that but the initial, serious cor-

End of implementation because all of the bromine remains unresolved,

when titrating with AgNO ₃ in nitric acid.

Solution is recorded quantitatively as bromide. Comparative example 3

Suitable anion exchangers are the commercially available ones derived from the oxidation of p-xylene

usual products. Contains base body of this exchanger overhead product

Resins are condensation and polymerization pro- 60 90 ° / acetic acid

products into which exchange-active (basic) groups g ^ S / v / _water

are built in. 1 ^ 5 ° /! p-xylene.

You can do that after this cleaning

Distill overhead product in the usual way, without the _{bromine content in the} overhead product being:

that the scoured corrosion occurs, with 65

the usual columns made of copper, total bromine] per kg

Chromium-nickel steels or stainless alloys (organic + inorganic) 82 mg \ overhead

can turn. Bromine inorganic 36 mg J product.

a) 21 of the overhead product of the above composition are mixed with 10 g of sodium acetate and boiled in a glass flask under reflux (boiling point 118 ° C.). A chrome-nickel steel strip is placed in the flask, 30 mm wide, 90 mm high, 2 mm thick, hung so that it is half immersed in the solution. After a running time of 200 hours are in the submerged part of the sheet, mainly on the liquid-vapor interface and at the cut surface of the sheet metal strip, next to a weak one Etching, pitting to be observed.

b) The experiment is repeated with the same overhead product, but according to Example 1 was pretreated with an iron file and then passed through an ion exchanger. After a Running time of again 200 hours is only a weak point on the metal strip, but no pitting was observed.

c) Finally, the overhead product before the start of the experiment - without pre-treatment with iron files - only with an ion exchanger given, the corrosion takes place in the same way as with the untreated overhead product [experiment a)], d. that is, pronounced pitting corrosion occurs

ίο on.

The comparative experiment shows that the prior art mode of operation does not cause any corrosion volatile bromine compounds prevent, but are unable to, the much more serious pitting corrosion to prevent.

Claims (1)

1 2 solution delay the reaction considerably or completely Claim: block. When using stainless steels in the Iron values of this kind become fast in the distillation stage Process for working up aqueous, bromine achieved. The copper ion concentration must also not rise significantly above 150 ppm containing compounds and alkyl aromatics. This means acetic acid from the liquid phase oxidation of but that the acetic acid, which has been identified in such apparatus for alkylaromatics with air, is not readily drawn into the fact that the mixture can be recycled when the oxidation process is increased.
Temperature with finely divided metals in it is known to have the most destructive effect seeks to prevent the series of voltages between, including the magnitude of the bromine, by the sium and iron are, stirred up, with a distillation work-up of the bromine-containing over-anion exchanger cleans and then makes the top product in itself in a distillation plant, known way separates by distillation. which is made of special materials. When such come titanium, tantalum, zirconium, silver and 15 the well-known alloy of nickel, molybdenum and Chrome in question. The use of the materials listed is associated with very high costs, which are absolutely are suitable to the economics of the whole The invention relates to a method for reconditioning 20 the method in question. Processing of aqueous, bromine compounds and alkyl aromatics is also from the German Auslegeschrift 1 092 897 containing acetic acid from the liquid phase oxy- a process for working up low molecular weight of alkyl aromatics with air. laren saturated fatty acids known which one Such acetic acid falls when the liquid contains an inorganic bromine compound. Here phase oxidation of alkyl aromatics such as p-xylene 25, the fatty acid is distilled in the presence of in acetic acid solution with air in the presence of oxides, hydroxides or salts of weak acids Manganese or cobalt salts at an elevated temperature of various metals. in accordance with US Pat. No. 2,245,528 when this occurs when ionically dissolved bromides are added the oxidation in the presence of a heavy metal - a metal oxide or with the salt of a weak one bromides (U.S. Pat. No. 2,276,774) or from 30 acid predictably with the formation of metal bromides Hydrogen bromide or a compound that under order that hold the bromine; therefore it is not overdone Working conditions forms hydrogen bromide (it is surprising that the acid is freed from the bromide, table patent 578 608), executes. Moreover, almost all the examples are exclusive of that The reaction mixture is usually based on borrowing mixtures containing acetic acid and inorganic Separation of the crude oxidation product, containing 35 niche bromides, and acting in all cases z. B. the terephthalic acid, or continuously one it evidently to mixtures, which from model mixture are composed of acetic acid, unreacted p-xylene substances, but none and the water of reaction formed as an overhead product corresponds to such solutions as they are withdraws from the reactor. in the liquid phase oxidation of p-xylene did- Because this overhead product receives valuable starting points. Such is the tetrabromoethane in his substances for the oxidation process - acetic acid and corrosive effect in no way comparable with p-xylene - contains, it requires a further core brominated aromatics, which in the oxidation work. The mixture is expediently separated into the p-xylene as an undesired by-product a downstream distillation into an azeotrope. Top product from xylene and water, from which one 45 These core brominated aromatics can be used as both Xylene used again and the water discarded, for example with sodium acetate not harmless and into an anhydrous acetic acid, which can be made from. Rather, they exert their harmful effects Swamp pulls off. by leaning against the metal walls and This discharge of the water of reaction is decomposed by the structures of the apparatus, with the metal of particular importance, since higher water concentrations are corroded with pitting, and only then trations in the reaction mixture the further oxidation resulting inorganic, ionogenic bromide can can inhibit completely. then away with the specified metal connections The overhead product now contains, however, conditional catch. But then it is too late, because the corrosion caused by the presence of bromine during the oxidation is not undone by it,
noticeable amounts of bromine compounds, some 55 This is also shown by comparative example 3, which is of an inorganic nature. These bromine compounds follow that a solution that is technically difficult to work up the oxidation by distillation is taken and the aromatically gebun-overhead product considerably, since even Verdenes contains bromine, in the presence of z. B. Sodium turn of the usual chemically resistant metals acetate can well concentrate and distill that such as copper or stainless steels or alloys 60 during this narrowing but in the presence of the greatest extent of corrosion in the form of buffer substance, the old corrosion still takes place. Pitting can occur. It should also be taken into account that the basis of the present invention is that the corrosion not only progresses correct knowledge of the connections that it This leads to serious damage to the apparatus, but that does not depend so much on the solutions to make the Oxy-65 distillable even under the action of the dissolved metals, without the release of hydrogen bromide dation sequence blocked. So is from the German with passes, but on the solutions of Auslegeschrift 1 087 589 known that iron concentrations to free their corrosion activity. At the same time solves trations of 300 mg or 1000 mg / kg reaction, the invention surprisingly the task of one