DE1932037C3 - Process for the electrolytic production of adipic acid dinitrile - Google Patents

Description

3 4

aqueous phase of this part acrylonitrile and adipine and catholytes removed from the cell formed wersäuredimtril is removed, with removal of the metal ions contained in the can, is preferred, gaseous carbon-aqueous phase by precipitation by exhaust dioxide in the catholyte entering the cell and then lead the pH in one line and then make it alkaline, not higher than 4, whereupon the aqueous phase 5 because the concentration of the at the interface of the in the storage vessel and the separated acrylonitrile in the cathode formed alkali is very high, so that the the storage vessel can be returned, the rate of precipitation of the carbonates is strong is characterized in that gaseous coal can be increased.

Dioxide in excess into the aqueous phase with a preferably used as a diaphragm in the electrical

pH not lower than 10, the precipitated 10 lysis cell uses an anion exchange membrane,

Carbonates are removed, and unreacted gaseous as this comes from the anode compartment

Carbon dioxide removed by blowing out. Hydrogen ions and other ions are prevented from doing so

The inventive cleaning of the catholyte will migrate into the cathode compartment. For the

is used in a process for electrolytic hydro- process according to the invention can advantageously be

dimerization of acrylonitrile in a conventional ion exchange membrane through a diaphragm

phragma can be used in an anode compartment and in a cathode compartment. For example, mem-

Room-divided electrolysis cell is used. burn n. with quaternary ammonium groups, which through

When removing metals by precipitation in chloromethylation of a styroi-divinyibenzene-copoly-form of their carbonates, it is generally possible that mer matrix and subsequent quaternization er the precipitation of the metals in a low pH-Bao, or by copolymerizing rich Because of the formation of bicarbonates, which have higher styrene, vinylpyridine and divinylbenzene and subsequently have solubility than the carbonates, only inadequate quaternization of the membranes obtained takes place. finally membranes with uniform and non-

In order to prevent this, according to the invention, the uniform composition with a built-in alkalinity of the catholyte, specifically at a pH of a ₅ core material, is advantageously used.
set of not less than 10. This setting Although anion exchange membranes, such as the pH value, can be most preferred as the diaphragm before, during or after the inputting of gaseous carbon dioxide into the cathode, diaphragms other than anion auslytes can also be used. exchanger membranes are used. If, however, a catholyte 30 containing acrylonitrile is possible, for example, to make a cation exchanger membrane alkyl, in particular to use it as a diaphragm on a branch, if the anolyte is brought to a pH above 10, the acrylonitrile contained therein tends to be a neutral or alkaline solution of a carrier , is used in Biscyanäthyläther electrolytes.

transferred or polymerized or hydrolyzed to As a cathode, any materials can be with a. It is therefore preferred to use low hydrogen overvoltage, which is resistant to treating a catholyte from which acrylonitrile is capable of corrosion, in accordance with the present invention. Before previously added materials for a cathode by distillation or similar processes include, for example, removed. _we j _se iron, stainless steel, nickel sheet and nickel

In the method according to the invention, clad iron sheet is advantageously used.

A catholyte purified by electrolysis of 40 .mu.m in the process according to the invention

Acrylonitrile and adipic dinitrile in the form of an alkalinity of a catholyte containing metal ions

Suspension was obtained, which not only increase from acrylic, another method can be applied

nitrile, but also from adipic acid dinitrile according to Me-, after which the catholyte through an exchanger

methods such as settling, centrifugation, thermal condensation membrane of the hydroxyl group type is conducted,

sation, filtration-condensation, etc., have been freed 45 In this process, the anion exchange

is. Such catholytes are in the Belgian patent membrane after use using

67 08 254. Since when using sodium hydroxide or aqueous ammonia regenerate

these catholytes mentioned are the undesired hy- riert. In this case, however, the

drolysis of adipic dinitrile and by electrolysis formation of a carrier electrolyte with an oleophilic one

formed by-products, such as propionitrile and 2-cyano 50 anion, such as aryl sulfonate, not preferred

äthyladipinsäuredinitril, can be prevented, even added, because thereby the regeneration of the anion

if the exchanger membrane is made difficult during the process according to the invention.

pH values are increased to 10 or more, the There is another method for alkaline-

Using such catholytes as a starting material make a catholyte, according to which the alkalinity

preferred. 55 by adding sodium hydroxide, slaked lime

The following is intended to increase the type of implementation of one or similar connections. When

Series of process steps are explained, which quaternary ammonium sulfate as a carrier electrolyte

comprise the cleaning method according to the invention. are used, the addition of deleted

First of all, the method for making lime alkaline should be particularly preferred, since the alkalinity increases with the

of a catholyte by electrolysis can be explained. 60 precipitation of calcium sulfate is increased.

A freed of acrylonitrile, containing metal ions- To increase the alkalinity of a catholyte

the catholyte is in the cathode compartment of an electrode. The method according to the invention can also be used

lysis cell introduced by an anion exchange method described numerous other methods

Find membrane in an anode space and a cathode use.

space is divided. Since hydrogen gas 65 at the cathode

is generated, the pH of the catholyte is increased. Catholyte is used, which has a sulfate ion

Although it contains metal carbonates by introducing gaseous carrier electrolyte, the alkali metal

carbon dioxide, which has been made alkaline in this way, can be increased to a pH value of more than 10

after the acrylonitrile has been removed therefrom. When applied to a catholyte in the form a suspension, it is preferred to first remove acrylonitrile therefrom, then the phases of the catholyte to be separated into an oil phase and an aqueous phase and in a third stage the alkalinity is just the same Adjust the separated aqueous phase to a pH of more than 10 by the methods described and finally to introduce gaseous carbon dioxide.

Although a higher alkalinity of the catholyte is desirable for the process according to the invention, since the higher the alkalinity, the more pronounced the precipitation of the carbonates occurs, but it is economical A pH of about 11-13 is preferred. In addition, the Concentration of the supporting electrolyte not higher than 25%, since the rate of precipitation of the The higher the carbonate. the lower the concentration of the carrier electrolyte in the one to be treated Catholyte is.

To accelerate the removal of iron ions from a catholyte, the alkalinity should first of the catholyte increased and then the procedural measure of the passage of gaseous Carbon dioxide can be carried out in combination with a process step in which the catholyte exposed to air so that iron ions present are oxidized.

The carbonates and / or hydroxides thus formed in accordance with the process according to the invention are then removed from the catholyte by sedimentation, filtration or centrifugation.

The catholyte treated according to the invention has a pH of more than 10. However, it is necessary that a used for the production of adipic acid dinitrile by electrolytic hydrodimerization of acrylonitrile Catholyte has a pH value of less than 10 to prevent the formation of biscyanoethyl ether as a by-product to prevent. Therefore, the treated catholyte becomes the desired one by adding acid pH brought.

If the presence of ions formed from carbon dioxide in a catholyte is undesirable, Carbon dioxide gas can be removed from it by blowing air after it has got the pH up has decreased a value of less than 4.

As already stated, according to the invention the concentration of metal ions in a catholyte, obtained in the production of adipic acid dinitrile by electrolytic hydrodimerization of acrylonitrile was, at a lower value, for example less than about 2 parts per million parts (ppm) and consequently the precipitation of metals on the cathode surface can be reduced. For this reason, adiponitrile can be obtained in high yields for a long period of time will.

The process according to the invention can be based on that described in the US Pat. No. 3,193,481 mentioned Apply method according to which an aqueous solution containing acrylonitrile and adipinitrile in contains high concentrations, using a quaternary ammonium salt with oleophilic Anions as a carrier electrolyte that is subjected to electrolytic hydrodimerization.

The method according to the invention can also be applied to that in the Belgian patent already mentioned 67 08 254 apply method in which the electrolysis using a quaternary ammonium salt is carried out with non-oleophilic anions as a carrier electrolyte, and Acrylonitrile and adipic dinitrile are in the form of a suspension.

The inventive method is also

largely in connection with processes other than those described above for the preparation of adiponitrile from acrylonitrile can be used by electrolysis.

In general, when performing the

method according to the invention, the concentration of acrylonitrile and adipic dinitrile in the catholyte, the type and concentration of the salt used as the support electrolyte are not subject to any restriction.

According to the invention, a catholyte does not have to be heated to any particularly high temperature, and the purification of the catholyte, namely the Ent-2 = Removal of metals from this, can be carried out at about room temperature or at one temperature in which the electrolysis is carried out. The inventive method is therefore not accompanied by the disadvantages of the previously known methods.

Another advantage of the method according to the invention is that the removal of the precipitates metal carbonates can be carried out more easily than metal hydroxides, since generally metal carbonates have a lower solubility in water than metal hydroxides.

The operation of the method according to the invention is described below with reference to the drawing which illustrates a typical flow sheet of the process of the invention. the However, the invention is not intended to be limited to the particular embodiment described.

In the figure, the number 2 denotes an electrolytic cell which is subdivided into a cathode compartment and an anode compartment with the aid of a cation exchange membrane and is used for the production of adipic acid dinitrile by electrolytic hydrodimerization before acrylonitrile. An anolyte in cell 1 is circulated between the anode compartment of cell 2 and an anolyte tank 1. A catholyte is circulated between the cathode compartment of the cell 2 and a catholyte tank 1.

The catholyte consists of an aqueous phase

which is an aqueous solution as its main component:

S "contains quaternary ammonium salt and an oil phase that is mainly acrylic suspended in it

contains nitrile and adipic dinitrile.

Part of the catholyte from the catholyte tank '. is introduced into an acrylonitrile stripper 4, in which the acrylonitrile is distilled and from which the acrylonitrile distilled in this way is returned to the catholyte tank 3 separated in two phases by an oil phase consisting predominantly of adipic acid dinitrile is fed through line 6 to a cleaning process. The aqueous phase is passed into a tank 7.

The number 10 denotes an electrolytic cell which is converted into a The anode compartment and a cathode compartment are subdivided and are intended to reduce the alkalinity from tank 7 supplied catholyte to increase

An anolyte is circulated between the anode compartment of the cell 10 and an anolyte tank 11. The catholyte in the cell 10 is supplied from the tank 7 and between the cathode compartment of the cell 10 lind the tank 7 out in the circuit. Gaseous carbon dioxide is fed into the tank 7 through a line 8 blown in and gaseous hydrogen generated in the cell 10 is withdrawn from a line 9.

Part of the liquid in the tank 7 is fed into a tower 12 provided with packing elements, in which the liquid is brought into contact in countercurrent with air 13 in order to be present in the catholyte To oxidize iron ions.

Then formed metal carbonates and / or hydroxides are filtered off in a filter 14 and that of Catholyte freed from impurities is stored in a tank 15, and the pH value is adjusted there by adding Bred acid from line 16 to a value of about 4. The adjusted catholyte is then in a headed tower 18 provided with packings, where it is brought into contact with air in countercurrent, «It is fed from a line 17, and thereby carbon dioxide is removed. The obtained purified Catholyte is fed back into the catholyte tank 3.

The following examples serve to more fully illustrate the invention.

example 1

According to the flow diagram in the drawing, the anolyte tank 1 with 2 η-sulfuric acid and the catholyte tank 3 is filled with an emulsion of the following composition:

Oil phase

Acrylonitrile 20

Adipic acid dinitrile 70

By-products of electrolysis 5

Water 5

Aqueous phase

Tetraethylammonium sulfate 10

Acrylonitrile, adipic dinitrile and

By-products of electrolysis ... 8

Water rest

pH - 4

Volume ratio of oil phase to

aqueous phase 2: 8

An alkali formed with an electrical current efficiency of about 50 "". Then line 8 Carbon dioxide gas is introduced into the catholyte while the pH of the catholyte in the tank 7 was kept at a value of 12.

Part of the resulting catholyte thus obtained was introduced into packing corridor 12 where it was vented. Subsequently, in the filter 14 Impurities removed from the catholyte and the

ίο pH value of the catholyte * in the tank 15 through Addition of sulfuric acid adjusted to a value of 4. By venting in the packed tower 18 residual carbon dioxide gas is removed and the purified catholyte obtained is then transferred to the catholyte tank 3 supplied.

The following effects were obtained by the treatment of the present invention.

In the above flow sheet, when no electrolytic cell was used and none was used Introduction of carbon dioxide took place, the concentration of calcium ions, magnesium ions. Lead ions and iron ions in the aqueous phase of the catholyte tank 3 are 15 ppm, 3 ppm, 5 ppm and 3 ppm, respectively.

The electrolytic hydrodimerization of acrylonitrile was in the electrolysis cell 2 under these described conditions for about 400 hours accomplished. As a result, the conversion of acrylonitrile to adiponitrile decreased about 85 ° ".

In contrast, when the electrolytic cell 10 was used and carbon dioxide was introduced, thereby increasing the concentration of the total content of metal ions such as calcium. Magnesium, lead and iron in the catholyte tank 3 was reduced to less than about 2 ppm, a high conversion of acrylonitrile to adipic dinitrile of 92 " _{o was maintained} even after the process was carried out continuously for about 400 hours.

In this example, the same effect as described was obtained when using a cation exchange membrane use as a diaphragm in the electrolysis cell and tetraethylammonium chloride as an anolyte! became.

45

50

Part of the emulsion was fed to the acrylonitrile stripper 4 to remove acrylonitrile therefrom, and the bottom fraction was separated by settling in the decanter 5. At this Instead, the concentration of acrylonitrile remaining in the aqueous phase was less than 0.05%.

The liquid, i.e. H. the acrylonitrile-free aqueous phase is fed to the electrolysis cell 10 as a catholyte. The electrolytic cell 10 comprised a stainless steel cathode, one of a Anode consisting of lead alloy and a diaphragm consisting of an anion exchange membrane. A 2 η sulfuric acid was used as the anolyte.

In this electrolytic cell, electrolysis was carried out with a current density of 10 A / dm ² , and it

Example 2

Example 1 was repeated using the same process steps, with the exception that: Instead of the electrolysis cell 10 and the anolyte tank 11, an anion exchange tower was provided de. An anion exchange resin that converts into a hydroxyl group resin with the help of sodium hydroxide was used after washing it thoroughly with water. The liquid au; Tank 7 was passed through a layer of the resin and carbon dioxide gas was introduced at the same time, wöbe the pH of the liquid was kept at a value of 1].

The same effect as Example] was obtained.

Example 3

In the method according to Example 1, the pH of the catholyte was ^{adjusted to about 13 by adding slaked lime in an amount of 5 km 3 of} the aqueous phase, instead of using the electrolytic cell 10, the anolyte tank 11 and tank 7.

After the precipitated calcium sulfate was filtered off, gaseous carbon dioxide was released into the liquid : it initiated to achieve a pH of 12, The resulting liquid was introduced into the packing arm 12.

10

The treatment described was the

the same effect as in Example 1 was achieved. In this example, the same effect could be achieved if Sodium carbonate was introduced into the liquid in place of carbon dioxide.

1 sheet of drawings

Claims (1)

1 2 Nickel, chromium and zinc. If these metals in one Claim: Catholyte are enriched, they tend to through a layer located on the cathode top Process for the production of adipic acid from concentrated alkali in their hydroxides via dinitrile by electrolysis of a catholyte that leads to 5 becoming and precipitating there, or Acrylonitrile, a carrier electrolyte and water under different conditions electrolytically to the free contains, by passing the catholyte through the metals to be reduced and afterwards in Electrolysis cell and a storage vessel in the form of a circulation to dissipate the metals on the cathode top, storing part of the catholyte suspension. continuously or intermittently from the previous io If the deposition of these metals even in advice vessel branched off and small amounts of, for example, about 50 mg / dm ^{2 from the aqueous phase} this part of acrylonitrile and adipic dinitrile occurs, the supply of acrylonitrile to the is removed, with removal of the obstructed in the aqueous electrode surface, which is too difficult Metal ions contained in the precipitation phase lead to major disadvantages, mainly in the phase and then adjusting the pH to not 15 formation of propionitrile as a by-product and the higher than 4, whereupon the aqueous phase finally insist on formation of gaseous hydrogen. on into the storage jar and the separated acrylic- this way the yield will also increase nitrile are returned to the storage vessel, adipic acid dinitrile and thus the electrical current characterized in that the yield is reduced and a contaminated product Gaseous carbon dioxide obtained in excess in the 20 .. aqueous phase at a pH not lower than 10 to remove these troublesome metal impurities, the precipitated carbonates are removed and a process has already been developed at unreacted gaseous carbon dioxide by which the catholyte was made alkaline and which as Blow out removed. Impurities present metals are precipitated by Eras heating in the form of hydroxides or oxides were (NL-AS 66 07 654). With this well-known Method for purifying a catholyte that consists of an aqueous solution of a hydrotropic quaternary ammonium salt and a pH range of The invention relates to a method for manufacturing 30 6 to 12, therefore the following process must of adipic acid dinitrile can be carried out by electrolysis of a ka steps: tholyte, the acrylonitrile, a carrier electrolyte and separation of the solution of the hydrotropic, quater- Contains water. natural ammonium salt from the catholyte, There are numerous methods of making adjustments to the pH of the separated solder Adipic acid dinitnl by electrolytic hydrodisolution of _an ammonium salt to a value of 7 of acrylonitrile known, such as _{or above and} the concentration of the ammo the sodium salt described in U.S. Patent No. 31 93 481 to 28 to 85%, Processes and other processes in which aqueous heating of the solution thus obtained to a temperature fige solution, the acrylonitrile and adipic dinitrile in a temperature of not more than 115 ⁰ C and contains high concentrations, using ₄ ° separating the impurities from the solution quaternary ammonium salts with oleophilic anions of _the ammonium salt,
is electrolyzed as a carrier electrolyte. According to the Belgian patent 67 08 254 This known method has the disadvantage that described and other known processes by the necessary heating under strongly alkaline acrylonitrile and adipic acid dinitrile in the form of 45 conditions cause undesired side reactions. a suspension using quaternary occur, such as the thermal decomposition of quaternary Ammonium salts with non-oleophilic anions as ammonium salts by Hoffmann degradation, hy- Electrolyte carrier electrolyte. drolysis of acrylonitrile, adipic dinitrile or of As from the USA.-Patent 31 93 480 out-by-products, and the polymerization of acrylic goes, has already been proposed, Adipinsäuredinitril 50 nitrile. by electrolysis of acrylonitrile in an electrolysis- The invention is based on the object Cell to produce, with the help of an ion exchanger, a process for the electrolytic production of membrane in an anode compartment and a cathode adipic acid dinitrile made of acrylonitrile available space is divided. In this known method put in the troublesome impurities from the the previously described solutions will be removed as quantitatively as possible as catholytes, tholyt used. without disruptive side reactions and decomposition However, if the aforementioned processes for electrical reactions occur. lytic, hydrogenating dimerization in industry This object is achieved according to the invention in that it is carried out on a scale over a longer period in that numerous metals are used in the catholyte with gaseous carbon dioxide as a precipitant for the metal impurities,
enriched, which consist of the materials from which the subject of the invention is a process anode, the electrolytic cell, the lines, the pumping for the production of adipic dinitrile by Elekpen and the associated device trolysis of a catholyte, the acrylonitrile, a carrier gene , as well as from the anolyte and electrodes and water used, by taking the water, or even from the device for the production of catholytes by the electrolysis cell and a Vorlung of the carrier electrolytes. These metal impurities include lead, iron, calcium, magnesium, silver, continuously or intermittently lead, iron, calcium, magnesium, silver, branched off from the storage vessel and from the