US3616321A

US3616321A - Process for the production of adiponitrile

Info

Publication number: US3616321A
Application number: US830521A
Authority: US
Inventors: Albert Verheyden; Jean Walravens
Original assignee: UCB SA
Current assignee: UCB SA
Priority date: 1968-06-06
Filing date: 1969-06-04
Publication date: 1971-10-26
Anticipated expiration: 1988-10-26
Also published as: NL6908359A; BG16183A3; AT289056B; IL32339A0; DE1928748B2; CS154624B2; BE734090A; NO130430B; LU58763A1; GB1233266A; FR2010513A1; CH502312A; IL32339A; DE1928748A1; SE367820B; NL159366B; PL80063B1

Abstract

Process of hydrodimerization of acrylonitrile to adiponitrile by the direct electrolytic route, by passing a direct electrical current through an electrolytic cell having the anode and cathode in contact with the electrolytic medium, which comprises using an initial electrolysis medium consisting essentially of (a) acrylonitrile, (b) water, (c) at least one alkali salt selected from the group consisting of the alkali salts of condensed polyphosphoric acids of the formula

Description

United States Patent [72] Inventors Albert Verheyden Saint-Denis-Westrem; Jean Walravens, Watermael-Boitsiort, both of Belgium [2]] Appl. No. 830,521

[22] Filed [45] Patented June 4, 1969 Oct. 26, 1971 [73] Assignee UCB Societe Anonyme Salnt-Gelles-lez-Brussels, Belgium [32] Priority June 6, 1968 [33] Great Britain [54] PROCESS FOR THE PRODUCTION OF [56] References Cited UNITED STATES PATENTS 3,458,559 7/1969 Holland et al. 204/73 Primary Examiner-F. C. Edmundson Attorney-Wenderoth, Lind & Ponack ABSTRACT: Process of hydrodimerization of acrylonitrile to adiponitrile by the direct electrolytic route, by passing a direct electrical current through an electrolytic cell having the anode and cathode in contact with the electrolytic medium, which comprises using an initial electrolysis medium consisting es sentially of (a) acrylonitrile, (b) water, (c) at least one alkali salt selected from the group consisting of the alkali salts of condensed polyphosphoric acids of the formula n H -,PO,(n-I) H 0 (1) in which n has a value of from 2 to I00, and the alkali salts of polymetaphosphoric acids of the formula II II RII in which n has a value of from 2 to 100, (d) a surface-active substance, and (e) at least one acidic salt of an alkali metal and ofa polyacid, the ratio by weight of (e) to (c) being com prised between 99.9/0.l and 0/100.

PROCESS FOR THE PRODUCTION OF ADIPONITRILE The present invention is concerned with a process .for the production of adiponitrile from acrylonitrile.

It is well know to produce adiponitrile by the hydrodimerization of acrylonitrile either by operating in the presence of a metal amalgam or by the direct electrolytic route.

For the direct electrolytic hydrodimerization of acrylonitrile to give adiponitrile, which is what the present invention is concerned with, there are already known several methods. Thus, it has been proposed to carry out the cathodic hydrodimerization of acrylonitrile in a concentrated aqueous solution of tetramethyl ammonium toluene sulfonate on a cathode having a hydrogen over voltage greater than that of copper (Belgian Pat. specification Nos. 631,302 and 640,836). Another process consists in hydrodimerizing acrylonitrile by the electrolysis of a inixture of acrylonitrile and of a small quantity of water saturated by an electrolyte, such as lithium bromide, on a platinum electrode (Belgian Pat. specification No. 649,625).

These known processes present a number of disadvantages: high terminal voltages because of the low conductivity of the system, formation of polymers to the detriment of the selectivity of adiponitrile, consumption of the platinum electrode which greatly increases the cost of the product and difficulties of recovery caused by the dissolution of the electrolyte in the reaction product.

Subsequently, an improvement was achieved according to which it was suggested to carry out the electrolytic hydrodimerization of acrylonitrile emulsified in an alkaline aqueous solution contained in an electrolysis device, without a diaphragm, furnished with a graphite cathode (French Pat. specification No. 1,401,175), a procedure which coped, to a large extent, with the difficulties mentioned above. Nevertheless, the yields of adiponitrile obtained by this process do not reach 75 percent of the theoretical value and, to avoid the saponification of the nitrile groups by the alkali, the process must be carried out at a low temperature (about C.) which results in the consumption ofa large amount of energy for the refrigeration of the electrolytic solution.

However, the inconveniencies of the above-mentioned process have, to a large extent, been overcome by a recent process (Belgian Pat. specification No. 684,436) in which the electrolysis is carried out in an emulsion in an electrolyte containing incompletely substituted salts of an alkali metal and of a polyacid, as well as surface-active substances. The electrolysis apparatus used is of the type without a diaphragm in which there is used an anode constituted by an iron oxide supported on metallic iron and possibly containing up to percent of oxides of silicon and up to 10 percent ofoxides of titanium. By incompletely substituted salts of an alkali metal and of an inorganic or organic polyacid, there are intended the sulfates, borates, perborates, phosphates, oxalates and the like of the alkali metals.

The process according to Belgian Pat specifications No. 684,436 provides a remarkable technical advance in that it enables excellent yields to be obtained not only as referred to the acrylonitrile consumed but also as to the amount of electricity supplied to the system. However, a major disadvantage is that the iron oxide anode is subjected to a very considerable degree of corrosion during the course of the electrolysis. This corrosion necessitates the frequent replacement of the anodes, which represents a very heavy expense to the point of compromising the industrial application of the invention. Consequently, there is a very great interest in preserving substantially all of the advantages provided by this process, while reducing the corrosion of the anode to a minimum. lt is this which constitutes the object of the present invention.

According to the present invention, we have found that the electrolyte used according to the process of Belgian Pat. specification No. 684,436 is responsible for the corrosion of the iron oxide anode and that, if the salts of the electrolyte are replaced wholly or partially by the alkali metal salts of polycondensed phosphoric acids, it is possible to maintain substantially all of the advantages of this process, while reducing the corrosion of the iron oxide anode to an amount which is technically acceptable.

The process according to the present invention for the hydrodimerization of acrylonitrile to adiponitrile by the direct electrolytic route, by passing a direct electrical current through an electrolytic cell having the anode and cathode in contact with the electrolytic medium, comprises using an initial electrolysis medium consisting essentially of (a) acrylonitrile, (b) water, (c) at least one alkali salt selected from the group consisting of the alkali salts of condensed polyphosphoric acids of the formula:

nH PO -(nl )H O (l) in which n has a value of from 2-100, and the alkali salts of polymetaphosphoric acids of the formula n H M in which n has a value of from 2-100 (d) a surface-active substance and (e) possibly at least one acidic salt of an alkali metal and ofa polyacid.

By alkali salts of condensed polyphosphoric acids of formula (1), there are intended the sodium, potassium, lithium, ammonium and quaternary ammonium salts of acids, such as pyrophosphoric acid (H,P O,-), triphosphoric acid (H P O tetraphosphoric acid (H -P 0 polyphosphoric acids containing from 5 to 100 phosphorus atoms, and mixtures thereof.

'By alkali salts of polymetaphosphoric acids of formule (11), there are intended the sodium, potassium, lithium, ammonium and quaternary ammonium salts of acids, such as dimetaphosphoric acid (H P- O), tn'metaphosphoric acid (11 F 0 tetrametaphosphoric acid (H,P.oa). metaphosphoric acids containing from 5 to 100 phosphorus atoms and mixtures thereof.

The alkali salts of the condensed polyphosphoric acids of formula (1) and of the metaphosphoric acids of formula (11) may also be used in the form of mixtures with one another in any desired proportions; furthermore, there can be used the alkali salts of these acids such as are available commercially, for example, under the names of Graham's salt, Kurrol salt, sodium hexametaphosphate, SQ salt sold by Monsanto (Na,,P 0 and the like.

By acidic salts of alkali metals and of polyacids, there are intended the salts of a polyacid, such as sulfuric acid, boric acid, perboric acid, phosphoric acid, oxalic acid or the like, which is incompletely substituted, containing at least one hydrogen cation. Thus, there may be mentioned monoand disodium orthophosphates, monoand dipotassium orthophosphates, sodium hydrogen sulfate, monopotassium oxalate and the like, as well as mixtures thereof.

As will be shown in the following examples, the salts used according to the present invention may replace wholly the partially substituted salts of alkali metals and of polyacids, especially the acidic alkali metal orthophosphates. However, as some of the salts according to the present invention are more expensive, especially with regard to the alkali orthophosphates, and as, on the other hand, their lower ionization, increases the terminal voltage, it is intended, according to the present invention, to use mixtures, on the one hand, of acidic salts of alkali metal and of polyacid and, on the other hand, of salts of acids according to formulas (l) and (11) in which the amount of polyphosphates according to the present invention is sufficient to maintain the corrosion of the anode at an acceptable level. Indeed, we have, surprisingly, found that the amount of polyphosphate may be relatively low, without prejudicing the anticorrosive effect. Thus, the ratio by weight between the acidic salts of alkali metal and of polyacid and of the polyphosphates used according to the present invention may be 99.9/01 to 0/100, advantageously 99/1 to /20, and preferably 95/5 to /15.

The concentration by weight of the polyphosphates (or of the mixture of polyphosphates and of acidic salts of alkali metal and of polyacid) in the aqueous electrolytic solution may'vary from 0.5 percent up to the concentration corresponding to saturation.

As surface-active substances, there may be used quaternary ammonium salts or pyridinium salts, such as acidic bistetraethyl-amrnonium phosphate, penta-tetraethyl-ammonium tripolyphosphate or acidic bis-methyl-pyridinum phosphate or the like. The concentration of these surface-active substances in the aqueous electrolytic solution may vary from 0.05 to 5 percent by weight, preferably from 0.2 to 2 percent Apart from the polyphosphates (and possibly of the acid salts of an alkali metal and of a polyacid) and the surface-active substances, the initial electrolytic solution essentially contains water. However, there may also be added a small quantity of a base or of an acid in order to maintain a definite pH value, this pH value advantageously being maintained between 5 and 10, preferably between 8 and 9.

In the course of the electrolysis, a mixture of emulsified acrylonitrile and of the initial aqueous electrolytic solution is circulated through the electrolysis apparatus, the volumetric ration between the aqueous phase and the acrylonitrile phase being maintained within the limits of 1:1 and 6: l.

This anode is surrounded by two cathodes made of graphite and of the same dimensions, placed on both sides of the anode at a distance ofl cm.

The supply of current is made by means of steel threaded rods screwed to the upper part ofeach electrode.

The assembly of the three electrodes is fixed vertically in the beaker.

The apparatus is provided with [.8 liters of the electrolytic solution to be tested. A temperature of 20 C. is maintained and there is passed through a continuous current of 14 amperes. The current density is in the region of 7 amperes/dmf". Every 24 hours, the electrolysis is interrupted for the time necessary to remove the anode, rinse it, dry and weigh it. The anode is then replaced and the electrolysis resumed under the same conditions.

in the following table I, there are set out the results thus obtained by expressing the rate of corrosion of the anode in mm. loss of thickness per year.

The first experiment is a comparative one carried out with an TABLE I Experiment number KzEPO 5.6 5.6 5.3 4.8 KsPzOnL 0. 06 0.3 1.14 (Et NhllPOt 1 1 1 1 Hexarnetaphosphatc Phosphate SQ NB P207 Rate of corrosion, mmJyear:

irst day 5.31 12.31 1.09 0.48 0. 3.14 0.96 0.51 0.16 O. 2. 0. 96 0. 48 0.16 0. 2. 53 1.06 0.32 0.03 0. Terminal voltage 5 5 5 5. 6

The temperature during the electrolysis is maintained within the limits of 0 C., to 40 C., preferably within the region of room temperature.

The linear velocity of circulation of the emulsified mixture is between 0.1 and l m./sec.

it is preferred to use an electrolysis apparatus without a diaphragm, having graphite cathodes and magnetite anodes, with or without a metallic support. The current density is l20 amperes/dm. and the voltage is comprised between 4 and volts preferably between 4 and 7 volts.

The process according to the present invention is equally applicable to anodes made of materials other than iron oxide, for example, anodes made of metallic iron or the like.

In general, the electrolysis is carried out in a manner such that the conversion of the acrylonitrile is -70 percent, preferably -50 percent. Below 20 percent, the economy of the process according to the present invention or the production ratio is too poor for industrial use, while when the conversion is increased beyond 70 percent, the selectivity of adiponitrile is less good.

The process according to the present invention may be carried out as well discontinuously as continuously.

The following examples are given for the purpose of illustrating the present invention:

EXAMPLE 1.

a. Comparative experiments for the corrosion of magnetite anodes.

The apparatus for measuring the rate of corrosion of the anodes comprises a beaker provided with means for cooling and a mechanical stirrer.

The magnetite anode subjected to the experiments is a square plate of steel or of Armco iron, the edges of which are 10 cm. long and the thickness of which is l cm., entirely covered with a coating of magnetite with a thickness of about 1 mm., obtained by the superficial oxidation of the metal in water vapor at a temperature of 1,000 C.

electrolyte of the kind used according to Belgian Pat. specification No. 684,436. It can be seen that the corrosion of the electrode made of iron oxide brought about by this electrolyte is considerable.

In experiments 2-5, in which the acidic potassium orthophosphate is replaced by an increasing amount of potassium tripolyphosphate, it is observed that the corrosion decreases with the increasing amount of tripolyphosphate and that on the fourth day it is not more than l/th of the corrosion according to the first experiment. A comparison of experiments l and 4 also shows that it is possible to reduce eightyfold the rate of corrosion by replacing only 20 percent of the orthophosphate by polyphosphate.

Experiments 6, 7 and 8 show that with other polyphosphates or polymetaphosphates, there is also obtained, according to the present invention, a considerable diminution of the corro- SlOl'l.

Experiments 9, l0 and l 1 point out that at very low doses of sodium hexametaphosphate the decrease of corrosion is already considerable.

b. Comparative experiments for the corrosion of iron anodes. When the magnetite anode of the experiment carried out as in example 1 (a) is replaced by an iron anode, the results represented in the following table ll are obtained:

TABLE II Experiment number PP mtoenoaen How:

NOTE: The favorable effect of replacing a part of KQIIPOJ by K P Om can clearly been seen from this table.

EXAMPLE 2.

ELECTROLYTIC HYDRODIMERISATION OF ACRYLONITRILE IN PRESENCE OF POLYPHOSPHATES.

In a semiindustrial electrolytic cell made of polypropylene of the filter press type comprising 6 compartments, each of which is delimited by a flat graphite cathode with an effective area of 3.4 dm. and by a flat steel anode covered with a coating of magnetite, which also has an effective surface area of 3.4 dmF, having a distance between the cathodes and anodes of 5 mm., there is carried out the electrolysis of an emulsion containing acrylonitrile and the aqueous solution (electrolyte). The composition of this emulsion and the conditions of electrolysis are given in the following table III.

In experiment No. l, the composition of the electrolyte is of the type used in Belgian Pat. specification No. 684,436; it contains, in particular, acidic dipotassium orthophosphatev In the second experiment, which is according to the present invention, a part of the acidic dipotassium orthophosphate of the first experiment is replaced by potassium tripolyphosphate.

In the third experiment, according to the present invention, a part of the acidic dipotassium orthophosphate of the first experiment is replaced by sodium hexametaphosphate.

In the fourth experiment, according to the present invention, the whole of the dipotassium orthophosphate is replaced by potassium tripolyphosphate.

In the four experiments, the electrolysis device functions in a continuous manner, with a constant supply of acrylonitrile and of water (to compensate for the electrolytic decomposition of this latter) and a continuous removal, by decantation, of an organic phase containing unchanged acrylonitrile,

adiponitrile, propionitrile and the products of hydro oligomerisation. The pH value is permanently controlled and maintained at 8.4.

In the following table:

AN=Acrylonitrile. ADN=Adiponitrile. PN=Propionitrile. Efi. ADNlAN=Percent of the number of moles of ADN formed referred to the number of moles of AN supplied.

Efi. PNlAN=Percent of the number of moles of PN formed, referred to the number of moles of AN supplied.

Efi. Hydr. Fraction in percent otAN supplied which is transformed into hydrooligomers.

Yield ADN/AN=Quotient in percent of the efficiency of ADN by the conversion of AN.

Yield ADN/Elec.=Ratio in percent between the number of moles of ADN formed and the number of taradays provided to the cell in the course of the electrol sis.

TABLE III Experiment Number Duration of electrolysis (hrs.) 227 215 117. 5 83 Percent composition of the initial aqueous phase emulsion:

3O 93. 46 93. 30 93. 30 93. 5 KIHPO4- 5. 57 5. 36 5. 36 KP30m 0 O. 33 0 5. 54: Na hexametaphosphat 0 0 0. 33 0 (EtlN)JHPOl 0. 96 O. 96 0. 97 O 4 )5 a 1o 0 0 0 O. 96 Initial organic phase AN AN AN AN Ratio by vol. aq. ph./org. ph. 2 2 2 2 Current intensity (amps) 157 157 158 158 Current density (amp/dm. c. 7.9 7.9 7. 9 7 Rate of circulation of emulsion (dm./

sec. 3 3 3 3 Supply of AN (g./hr.) 634 634 634 634 Supply of water (g./hr.) 72 78. 5 78.5 78. 5 Unchanged AN (percent) c. 51. 2 51.7 51. 9 52. 9 Efliciency ADN/AN (percent) 39. 0 36.1 37.4 35. 7 Efiiciency PN/AN (percent) 3. 6 4. 4 4. 35 3. 2 Efficiency HydrJAN (percent) 4. 8 7.8 8. 2 Yield ADN/AN (percent) 80.0 74. 7 77.8 75. 7 Yield ADN/elec. current (percent) 77. 8 70. 5 73.0 73. 6 Rate of corrosion of the magnetite (IDJIL/ year) 2. 2 0. 6 0. 3 1. 2 Terminal voltage 5. 8 6. 3 6. 3 6. 1 Specific conductivity of the emulsion (Q' CBL' 18. 10 l4. l0 l2. l0

The table shows that the yield of adiponitrile referred to the supplied acrylonitrile is appreciably maintained and that the yield of adiponitrile with reference to the electric current is subjected to a slight diminution. However, this small loss in yield is largely compensated by the diminution of the speed of corrosion of the anode which, compared with that found in experiment No. 1, is only about one half in experiment No. 4, is less than one third in experiment No. 2 and is less than one seventh in experiment No. 3.

EXAMPLE 3.

The experiment was carried out in a tubular electrolytic cell constituted by a cylindrical anode made of molten magnetite surrounded by a graphite tube which functions both as cathode and as container. The anode has a diameter of 6 cm. and an effective length of 61 cm., i.e., a surface of 11.3 dm. dm.? The cathode has an interior diameter of7 cm., i.e.. an effective surface of l3.2 dm.? The distance between the electrodes is 0.5 cm. The cell proper is completed by a tubing system with pumps, hydrocyclone and filter allowing the circulation of the reaction medium between the electrodes and the collection of the solid products resulting from the corrosion of the anode (phosphate+iron hydroxide). Cooling is effected by circulating brine in a double jacket surrounding the graphite tube.

The working conditions and the obtained results are given in the following table IV:

TABLE IV Experiment Number Percent composition of the emulsion:

Initial aqueous phase:

93. 3 93. 3 5. 7 5. 4 0 0. 3 1. 0 I. 0 Initial organic phase AN AN Ratio by vol. an. ph./org. ph. 2 2 Current intensity (amps) 90 90 Anodlc current density (amp/dm. 7. 95 7. 95 Cathodic current density (amp/dm. 6. 6. 80 Rate or circulation (dm./sec.) 3 3 Supply of AN (g./hr.) 372 393 Supply of water (g./hr.) 47 47 Unchanged AN (percent).. 53. 4 58. 3 Efficiency ADN/AN (percent)... 38. 8 34.6 Etiicicncy PN/AN (percent) 3.7 3.0 Etficiency Hydr./AN (percent) 4.1 4.1 Yield ADN/AN (percent) 83. 2 82. 9 Yield ADN/elcc. current (percent) 80. 2 75. 5 Rate of corrosion of tho magnetite anodes (mm./

year) 15. 4 0.3 Terminal voltage 5. 6 5. Q Specific conductivity of the emulsion (tr cmr -2.10' -2. 10-- This table shows that on replacing about 5% of K vHPO, by sodium hexametaphosphatc, practically the same yield of adiponitrile is maintained whereas the corrosion ofthe anode is fiftyfold diminished.

We claim:

1. Process of hydrodimerization of acrylonitrile to adiponitrile by the direct electrolytic route, by passing a direct electrical current through an electrolytic cell having the anode and cathode in contact with the electrolytic medium, which comprises using an initial electrolysis medium consisting essentially of (a) acrylonitrile, (b) water, (c) at least one alkali salt selected from the group consisting of the alkali salts of condensed polyphosphoric acids of the formula in which n has a value of from 2 to I00, and the alkali salts of polymetaphosphoric acids of the formula n n fln in which n has a value of from 2 to I00, (d) a surface-active substance, and (e) at least one acidic salt of an alkali metal and ofa polyacid, the ratio by weight of (e) to (c) being comprised between 99.9/0.l and 0/l00.

2. Process as claimed in claim I, in which the ratio by weight ot(e) to (c) is comprised between 99/1 and 80/20.

3. Process as claimed in claim I, in which the ratio by weight of (e) to (c) is comprised between 95/5 and /15.

4. Process as claimed in claim I, in which the concentration 5. Process as c laimed in claim 1, in which the salts of formu la (1) are selected from the group consisting of sodium, potassium, lithium, ammonium and quaternary ammonium salts of pyrophosphoric, triphosphoric, tetraphosphoric and polyphosphoric acids containing from 5 to 100 phosphorous atoms and mixtures thereof.

6. Process as claimed in claim 1, in which the salts offormula (II) are selected from the group consisting of sodium, potassium, lithium, ammonium and quaternary ammonium salts of dimetaphosphoric, trimetaphosphoric, tetrametaphosphoric acids and metaphosphoric acids having 5 to 100 phosphorous atoms and mixtures thereof.

7. Process as claimed in claim 1, in which the salts of formula (1) are used in mixture with salts of formula (11).

8. Process as claimed in claim 1, in which the surface-active substance is selected from the group consisting of quaternary ammonium and pyridinium salts.

9. Process as claimed In claim 1, in which the surface-active substance is selected from the group consisting of acidic bistetraethyl-ammonium phosphate, penta-tetraethyl-ammonium tripolyphosphate and acidic bis-methylpyridinium phosphate.

10. Process as claimed in claim 1, in which the concentration of the surface-active substance in the aqueous electrolytic solution is comprised between 0.05 and 5 percent by weight.

11. Process as claimed in claim 1, in which the concentration of the surface-active substance in the aqueous electrolytic solution is comprised between 0.2 and 2 percent by weight.

12. Process as claimed in claim 1, in which the acidic salt of an alkali metal and of a polyacid is selected from the group consisting of acidic salts of sulfuric, boric, perboric, phosphoric and oxalic acids, which are incompletely substituted, containing at least one hydrogen cation.

13. Process as claimed in claim 1, in which the acidic salts of an alkali metal and of a polyacid is selected from the group consisting of acidic sodium and potassium salts of orthophosphoric acid, sodium hydrogen sulfate and 8 monopotassium oxalate.

14. Process as claimed in claim 1, in which an amount of base or acid is added to the water so as to maintain a pH value comprised between 5 and 10.

15. Process as claimed in claim 1, in which an amount of base or acid is added to the water so as to maintain a pH value comprised between 8 and 9.

16. Process as claimed in claim 1, in which, in the course of electrolysis, the volumetric ratio of the aqueous electrolytic solution to acrylonitrile is maintained between 1: 1 and 6:1

17. Process as claimed in claim 1, in which, in the course of electrolysis, the temperature is maintained within the limits of 0 C. and 40 C.

18. Process as claimed in claim 1, in which, in the course of electrolysis, the temperature is maintained within the region of room temperature.

19. Process as claimed in claim 1, in which the linear velocity of circulation of the emulsified mixture of the aqueous electrolytic solution and acrylonitrile in the electrolysis apparatus is comprised between 0.1 and 1 m./sec.

20. Process as claimed in claim 1, in which electrolysis is carried out in an electrolysis apparatus without diaphragm having graphite cathodes and magnetite or iron anodes.

21. Process as claimed in claim 1, in which the current density is comprised between 1 and 20 arnperes/dm. and the tension is comprised between 4 and 10 volts.

22. Process as claimed in claim 1, in which the current density is comprised between 1 and 20 amperes/dm. 1 and the tension is comprised between 4 and 10 volts.

23. Process as claimed in claim 1, in which the electrolysis is carried out in a manner such that the conversion of acrylonitrile is comprised between 20 and percent.

24. Process as claimed in claim Lin which the electrolysis is carried out in a manner such that the conversion of acrylonitriie is comprised between 40 and 50 percent.

25. Process as claimed in claim 1, in which the electrolysis is carried out discontinuously.

26. Process as claimed in claim 1, in which the electrolysis is carried out continuously.

Claims

2. Process as claimed in claim 1, in which the ratio by weight of (e) to (c) is comprised between 99/1 and 80/20.
3. Process as claimed in claim 1, in which the ratio by weight of (e) to (c) is comprised between 95/5 and 85/15.
4. Process as claimed in claim 1, in which the concentration of the mixture (e)+(c) in the aqueous electrolytic solution is comprised between 0.5 percent by weight and the concentration corresponding to saturation.
5. Process as claimed in claim 1, in which the salts of formula (I) are selected from the group consisting of sodium, potassium, lithium, ammonium and quaternary ammonium salts of pyrophosphoric, triphosphoric, tetraphosphoric and polyphosphoric acids containing from 5 to 100 phosphorous atoms and mixtures thereof.
6. Process as claimed in claim 1, in which the salts of formula (II) are selected from the group consisting of sodium, potassium, lithium, ammonium and quaternary ammonium salts of dimetaphosphoric, trimetaphosphoric, tetrametaphosphoric acids and metaphosphoric acids having 5 to 100 phosphorous atoms and mixtures thereof.
7. Process as claimed in claim 1, in which the salts of formula (I) are used in mixture with salts of formula (II).
8. Process as claimed in claim 1, in which the surface-active substance is selected from the group consisting of quaternary ammonium and pyridinium salts.
9. Process as claimed in claim 1, in which the surface-active substance is selected from the group consisting of acidic bis-tetraethyl-ammonium phosphate, penta-tetraethyl-ammonium tripolyphosphate and acidic bis-methylpyridinium phosphate.
10. Process as claimed in claim 1, in which the concentration of the surface-active substance in the aqueous electrolytic solution is comprised between 0.05 and 5 percent by weight.
11. Process as claimed in claim 1, in which the concentration of the surface-active substance in the aqueous electrolytic solution is comprised between 0.2 and 2 percent by weight.
12. Process as claimed in claim 1, in which the acidic salt of an alkali metal and of a polyacid is selected from the group consisting of acidic salts of sulfuric, boric, perboric, phosphoric and oxalic acids, which are incompletely substituted, containing at least one hydrogen cation.
13. Process as claimed in claim 1, in which the acidic salts of an alkali metal and of a polyacid is selected from the group consisting of acidic sodium and potassium salts of orthophosphoric acid, sodium hydrogen sulfate and monopotassium oxalate.
14. Process as claimed in claim 1, in which an amount of base or acid is added to the water so as to maintain a pH value comprised between 5 and 10.
15. Process as claimed in claim 1, in which an amount of base or acid is added to the water so as to maintain a pH value comprised between 8 and 9.
16. Process as claimed in claim 1, in which, in the course of electrolysis, the volumetric ratio of the aqueous electrolytic solution to acrylonitrile is maintained between 1:1 and 6:1.
17. Process as claimed in claim 1, in which, in the course of electrolysis, the temperature is maintained within the limits of 0* C. and 40* C.
18. Process as claimed in claim 1, in which, in the course of electrolysis, the temperature is maintained within the region of room temperature.
19. Process as claimed in claim 1, in which the linear velocity of circulation of the emulsified mixture of the aqueous electrolytic solution and acrylonitrile in the electrolysis apparatus is comprised between 0.1 and 1 m./sec.
20. Process as claimed in claim 1, in which electrolysis is carried out in an electrolysis appAratus without diaphragm having graphite cathodes and magnetite or iron anodes.
21. Process as claimed in claim 1, in which the current density is comprised between 1 and 20 amperes/dm.2 and the tension is comprised between 4 and 10 volts.
22. Process as claimed in claim 1, in which the current density is comprised between 1 and 20 amperes/dm.2 and the tension is comprised between 4 and 10 volts.
23. Process as claimed in claim 1, in which the electrolysis is carried out in a manner such that the conversion of acrylonitrile is comprised between 20 and 70 percent.
24. Process as claimed in claim 1, in which the electrolysis is carried out in a manner such that the conversion of acrylonitrile is comprised between 40 and 50 percent.
25. Process as claimed in claim 1, in which the electrolysis is carried out discontinuously.
26. Process as claimed in claim 1, in which the electrolysis is carried out continuously.