CA1039233A - Reductive coupling process improvement - Google Patents

Abstract

REDUCTIVE COUPLING PROCESS IMPROVEMENT
ABSTRACT OF THE DISCLOSURE
In a process in which olefinic reactants are reductively coupled by electrolyzing a liquid aqueous medium containing the reactants and a heavy metal passes into the medium during the electrolysis, undesirable effects of the heavy metal in the medium can be substantially lessened by adding sufficient free heavy metal sequesterant to the medium during the electrolysis to maintain excess free sequesterant in the medium.

Description

1~392~3 REDUCTIVE COUPLING PROCESS D~/IPROVEMENT
, .

BACKGROUND OF THE INVENTION
Electrolytic reductive coupling of like or umlike olefinic reactants and particularly production of paraffinic dinitr iles, dicarboxamides or dicarboxylates by electrolytic hydrodimerization of alpha, beta-olefinic nitriles, carboxamides or carboxylates are well known, e. g. from U. S.
Patents 3, 193, 475-79 and 3, 193, 481-83 issued July 6, 1965 to M. M. Raizer. Although the process is sufficiently attracti~e that it has been in commercial use for over eight years, efforts to improve it have 10 been continued with particular emphasis on eliminating expenses associated with the heretofore commer cially pref'erred use of cells divided into anolyte ~`
and catholyte compartments by a cation-permeable membrane.
For example, Canadian Patent 813, 877 issued May 27, 1969 to A. P. Tomilov et al. discloses that comparable yields of adiponitrile can , be produced by electrolyzing a neutral aqueous solution of acrylonitrile, an alkali metal salt of a polybasic acid and a quaternary ammonium salt in an undivided cell having a graphite cathode and a 99% iron oxide anode at a current density of 4 amps per square decimeter and a temperature of 15-18C. Cornmercial use oE a current density that low, 20 however, would require excessive capital investment for electrolytic cells, and use of a temperature that low would require expensive refrigeration of the electrolysis medium. Good adiponitrile yields are initially -~
available at higher temperatures and current densities but as shown in Example 2, Experiment 1 of U. S. Patent 3, 616, 321 issued October 26, 1971 to A. Verheyden et al., continued electrolysis of a solution similar to that of the Canadian patent for several hundred hours at a substantially higher current density (7. 9 amps/dm2) results in an ~;,~
~.-~9 , C- ~ 4-54-01 73 il~3~3 ~ - ~
.. ,, . ~ ~
unacceptably h1~h anode corrosion rate ~2.2 mm/yr) and an ad~po~
nitrile yield which, over the len~th of the run, avera~es much : lower than those reported in the Canadian patent ~or operation ~, ~
.- ~ .. ..
- at 4 amps/dm'.
One approach to control of such anode corrosion is described in U.S. 3,616,321 which discloses that in production of adipo-nitrile by electrolys~s of an aqueous emulsion of acrylonitrile, an alkali metal phosphate and a quaternary ammonium salt at current densities up to 20 amps/dm2 and temperatures up to 40C~
10 ~preferably ne~r room te~perature) In an undivided cell havin~ :
a ~raphite cathode and an iron or ma~netlte anode, corrosion of the anode can be substantially inhibited by usin~ an ~nitial electrolysis medium containin~ an alkali metal polyphosphate.
l It can also be seen from Example 2, Experiment 2 o~ that patent, i however, that althou~h the anode corrosion rate was lowered when :
.I the polyphosphate was present, the averape adiponitrile yield ~. :
. and current efficiency over 215 hours of operation (74.7% and 1, 70.5%, respect~vely) were even lower than those realized at the ;~
same current density ~7.9 amps/dm2) but without the polyphosphate ~;
present.
It has also been discovered that in runs of the len~th preferred for practical commercial operation, at least a portion : of tha products of corroslon of heavy metal electrQdes employed in such processes tend to pass into the electrolysis medium and accumulate there ~n forms such that they become deposited on ~ ~:
the cathode, lncrease the ~eneration of molecular hydro~en at the expense of process current efficiency and ~radually lower `~
the reaction selectivlty for the desired coupled product.
; As described in Bel~ium Patent No, 804,365, molecular hydro~en formation and anode corros~on in such processes can be ` ~. . ,.. ,., ,.... . . . `
, ,i . . `

C-14-54-0173 ~

1~39~33 ~ :
substantially inhibited by including in the electrolysis medium a nitrilo- -carboxylic acid compound such as, for example, an alkali metal salt of ethylenediaminetetraacetic acid. As disclosed in that patent, it is believed that such compounds sequester heavy metals in the electrolysis medium and thereby inhibit formation of the metallic deposits on the ' ;~
cathode which normally accompany increases in the formation of molecular hydrogen in the cell. Also as shown in that patent, the inclusion of such a compound in the electrolysis medium permits the carrying out of the process for long periods of operation at current densities and temperatures considerably higher than those to which practical use of the process of Canadian 813, 877 or U. S. 3, 616, 321 is restricted and accordingly, the improvement described in that p a t e n t .
is a very significant advance in the art.
It has been found, however, that even with such a compound maintained in the electrolysis medium in substantial concentration, accumulation in the medium of heavy metals from the electrodes, and especially from corrosion of the anode, is normally eventually accompa~
nied by a deterioration of process performance characteristics such as product selectivity, current efficiency, etc. The advent of such deterioration can be delayed and its severity lessened, as aforesaid, by including a heavy metal sequesterant in the medium and in some cases, this may be accomplished to a degree by inclusion of a polyphosphate as previously suggested for anode corrosion control, but it is desired for ...
commercial operation to prevent such process deterioration to an extent ;
greater than that accomplished by merely including a sequesterant in the ;~
initial electrolysis medium or even by maintaining such a sequesterant in the medium in a specified concentration throughout the electrolysis.
Clearly, the longer product selectivity can be maintained and the longer ~:: -- , . ................... . .
~, 1039~33 and more ~ull~ the cu~rent e~iciency-lo~erin~ ~ormat~on o~
molecular hydrogen can ~e l~n~b~ted, t~e lower t~e production cost of the desired coupled product will he. Such improve--ments in the process are objects of this invention. Other objects of tRe ~nvention will ~e apparent from the following descr~ption, examples and claims in which all percentages are by weight except where noted ot~erwise.
SUMMAR~ OF THE INVENTION
In a preferred emb~diment of the present invention, there is provided, in a process in which olefinic reactants having the formula R2C~CR-X in which -X is -CN, -CONR2 or -COOR', R is hydrogen or R' and R' is Cl-C4 alkyl are reduc-tively coupled by electrol~zing a liquid aqueous medium having a pH of between 2-12 and a temperature between about 5C to about 75C containing the reactants in contact with an electrode comprising a heavy metal that passes into the medium in sub-stantial amount during the electrolysis, the improvement which comprises adding sufficient free sequesterant of said heavy metal to the medium during the electrolysis to maintain excess free sequesterant of said heavy metal in the medium.
In greater detail, it has no~ been discovered that in a process in which olefinic reactants are reductively coupled by electrolyzing a liquid aqueous medium containing the reactants and substantial heavy metal passes into the medium during the electrolysis, undesirable effects of the heavy metal in the medium such as, for example, increased molecular hydrogen formation and eventual lowexing of the desired product selec-tivity, can be substantially lessened by adding to the medium during the electrolysis free heavy metal sequesterant sufficient to maintain excess free sequesterant in the medium. Not ~ t ~ - 5 -103~ 33 necessarily in all cases but typ;cally when t~ he~y~ ~etal passes into the med~um in an amount ~xeater than t~at soluble in the initial electrolys~s medium, free heavy metal seques-terant in excess o~ that capable of sequestering the heavy metal in that amount is added to the medium during the elec-trolysis. This improvement ~s especially thou~h not exclu~
sively use~ul when the process is carried out in an undivided cell, and in the production o~ adiponitrile, a nylon 66 inter-mediate, by the hydrodimerization of acrylonitrile.
DETAILED DESCRIPTION OF THE IN~TENTIoN

The reactants that can be reductively coupled by the process of this invention include any like or unlike olefinic compo~mds capable of being reductively coupled by electrolysis in aqueous media. Most ;

:

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~(~3~3~233 :::
commonly at present, such reactants are substituted olefinic compounds such as those having the structural formula R2C=CR-X wherein -X is ;

-CN, -CONR2 or -COOR', R is hydrogen or R' and R' is Cl-C4 alkyl (i. e., methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or tert-butyl). ;~

Compounds having that formula are known as having alpha, beta mono-unsaturation and in each such compound, at least one R may be R' while at least one other R is hydrogen and at least one R', if present, may be --,, .;I ~
an alkyl group containing a given number of carbon atoms while at least one other R', if present, is an alkyl group containing a different number 10 of carbon atoms. Such compounds include olefinic nitriles such as, for : , ,; . , example, acrylonitrile, methacrylonitrile, crotononitrile, 2-methylene-butyronitrile, 2-pentenenitrile, 2-methylenevaleronitrile, 2-methylene-hexanenitrile, tiglonitrile or 2-ethylidenehexanenitrile; olefinic , carboxylates such as, for example, methyl acrylate, ethyl acrylate or ; ethyl crotonate; and olefinic carboxamides such as, for example, acrylamide, methacrylamide, N,N-diethylacrylamide or N, N-diethyl-crotonamide. Products of hydrodimerization of such compounds include those having the structural formula X-CHR-CR2-CR2-CHE~-X wherein ;~
X and R have the aforesaid significance, i. e., paraffinic dinitriles such 20 as, for example, adiponitrile and 2, 5-dimethyladiponitrile; paraffinic dicarboxylates such as, for example, dimethyladlpate and diethyl-3, 4 i dimsthyladipate; and paraffinic dicsrboxamides such as, for example, adipamide, dimethyladipamide and N, N'-dimethyl-2, 5-dimethyladipamide. `

:, - .
Such hydrodimers can be employed as monomers or as intermediates convertible by known processes into monomers useful in the manufacture of high molscular weight pGlymsrs including polyamides and polyesters.

~, ~

~ 1039~33 `- Other examples o the various olefinic reactants that can be reduc-tively coupled by the process of this invention and the coupled products thereby produced are identi~ied in the aforecited U. S.
Patents Nos. 3,193,475-79 and 3,193,48L-83.
The invention is herein described in terms of electroly-zing a liquid aqueous medium containing the aforementioned olefinic reactants. Such an electrolysis medium can be an essentially single-phase aqueous solution or a multi-phase mixture comprising such an aqueous solution which is preferably the continuous phase of the mixture and an undissolved organic phase which is typically but not necessarily dispersed throughout the aqueous solution.
Gases such as vaporized reactant, oxygen formed at the anode and in most cases, hydrogen formed at the cathode are also normally present in the medium in minor proportion. When present, the organic phase may constitute up to about 25% or even more of the combined weight of the aqueous solution and undissolved organic phase and in some attractive embodiments of the process improved as described herein, the organic ~ase constitutes at least about 10~ (e.g. between about 12% and about 20%) of the medium. In some continuous process embodiments involving recycle of uncon-verted olefinic reactant, such an organic phase is normally made up mainly (most commonly at least about 65% and even more typically at least about 75%) of the olefinic reactants to be coupled and the reduced coupled product with some minor amounts of reaction by-products, water, etc., possibly also present. In the hydrodimer-ization of acrylonitrile, such an organic phase generally contains at least about 10%, preferably between about 15~ and about 50~, and even more generally between about 20% and about 40~ acryloni-trile. In any event, however,the ~ncentrations of the constitu-ents dissolved in the aqueous solution phase of the electrolysis ri ., C - 1 4 - 5~ 1 73 ~3~33 medium as set forth herein are with reference to the recited aqueous ; solution alone and not the combined contents o-f -the aqueous solution ,~ and an undissolved organlc phase which, as aforesaid, may be present but need not be present in the electrolysi= m~dium as the invention is - carried out. On the other hand, the weigm percentages of undissolved ~;
organic phase described herein are based on the combined weight of the aqueous solution and the undissolved organic phase in the electrolysis ;
medium .
Referring to the constituents of the aqueous solution in the electrolysis medium, the olefinic reactants to be coupled are present in at least such a proportion that electrolysis of the medium, as described ~; herein, will result in a substantial amount of the desired coupled product being produced. That proportion is generally at least about 0.1%, more typically at least about 0. 5% and, in some embodirnents of the ~
' .: .
-invention, preferably at least about 1% of the aqueous solution. Inclusion ~ `
of one or more additional constituents which increase the solubility of the olefinic reactants in the solution may permit the carrying out of the process with the solution containing relatively high proportions of the reactants, e. g. at least about 5% or even 10% or more, but in many embodiments of the invention, the aqueous solution contains less than about 5% (e. g. not more than 4. 5%) of the olefinic compound and, in some of those embodiments, preferab1y not more than about 2. 5% of the olefinic reactants.
` In some proces= embodiments utllizing quaternary ammonium cations, e. g. to direct the reaction toward the desired coupled product, the minimum required proportion of those cations is very small. In general, there need be only an amount sufficient to provide the desired product selectivity (typically at least about 75% and preferably at least ''` ~' ~39~33 ~:
about 80% in the coupling of most olefinic nitriles, carboxylates or carboxamides) although much higher proportions can be present iE desired or convenient. In most cases, the quaternary ammonium ions are present in a concentration of at least 10~5Irlole per liter of the aqueous solution ;~
and even more typically at least about 10~4mole per liter of the solution.
Although higher proportions may be present in some cases, as aforesaid, the quaternary ammonium ions are generally present in the aqueous solution in a concentration lower than about 0. 5mole per liter and even ~;
more usually, in a concentration not higher than about 10-1mole per liter.
In some preferred embodiments, the concentration of quaternary ammonium ions in the solution is at least about 5 x 10~4 mole per liter ~, , ; but not more than about S x 10~2mole per liter. -~
The quaternary ammonium ions that may be present in such `
concentrations are those positively-charged ions in which a nitrogen atom has a valence of five and is directly linked to other atoms (e. g. carbon) ;
satisfying four fifths of that valence. Such ions may be cyclic, as in the case of the piperidiniums, pyrrolidiniums and morpholiniums, but they are generally of the type in which the nitrogen atom is directly linked to ;
four monovalent organic groups preferably devoid of olefinic unsaturation and desirably selected from the group consisting of hydrocarbyl (e, g.
alkyl, aryl, etc. ) radicals, trihydrocarbylammonium-substituted derivatives of such radicals and combinations thereof such that the ions ;~
; have an average total carbon atom content of from ~ to 48, preferably - from about 6 to about 36 and even more desirably from about 7 to about 28. Suitable aryl groups contain typically from six to twelve carbon atoms and preferably only one aromatic ring as in, for example, a phenyl or benzyl radical. Suitable alkyl groups can be straight-chain, branched or cyclic and each typically contains from one to twelve carbon atoms.

_ 9 ... . . . . . .
s ~-14-54-01 73 Although quaternary ammonium ions containing a combina-tion of such alkyl and aryl groups (e. g. benzyltriethylammonium ions) can be used, many embodiments of the invention are preferably carried out with tetra-alkylammonium ions and superior results are typically obtained with the use of those containing at least three C2-C6 alkyl groups and a total of from ~ to 24 carbon atoms in the four alkyl groups, e. g. diethyldipropyl-, ethyltripropyl-, ethyltributyl-, ethyltriamyl-, ethyltrihexyl-, octytriethyl-, tetrapropyl-, methyltripropyl-, decyltripropyl-, methyltributyl-, ' tetrabutyl-, amyltributyl-, tetraamyl-, tetrahexyl-, ethyltrihexyl-, diethyldioctylammonium and many others referred to in the aforecited U. S. Patent Nos. 3,193, 475-79 ancl '481-83. Most practical fr-om the economie standpoint are generally those tetraalkylammonium ions in which each alkyl group contains two to five carbon atoms, e. g.
diethyldiamyl-, tetrapropyl-, -tetrabutyl-, amyltripropyl-, tetraamyl-ammonium, etc. Such cations can be incorporated into the aqueous solution to be electrolyzed in any convenient manner, e. g. by dissolving the quaternary ammonium hydroxide or a salt thereof in the solution in the amount required to provide the desired quaternary ammonium ion eoncentration. It should be noted, however, that quaternary ammonium ions in the electrolysis medium are but one way in which the selectivity of the process for certain reduced coupled products can be improved and their presence in the medium is not a prerequisite for utility of the present invention.
The type of conductive salt employed is likewise not usually a critical factor in realization of advantages of this invention. Hence the conductive salt can be a quaternary ammonium salt of the kind used heretofore in commercial practice of the electrolytic reductive coupling precess, for example a tetraalkylammonium (e. g. tetraethylammonium) .. .. . .

C-14-5~-0173 .
~03~
sulfate, alkylsulfate (e. g. ethylsulfate) or arylsulfonate (e. g. toluene sulfonate). Although organic salts of that general type can be employed as conductive salts in a divided or an undivided cell, it is ~-generally preferred to use other conductive salts such as, for example, an alkali metal salt, in most undivided cells. When alkali metal salts are used, those of lithium and especially sodium and potassium are generally preferred for economic reasons. ;
Also preferred for such use are salts of inorganic and/or polyvalent acids, e. g. a tetraalkylammonium or alkali metal ortho~
phosphate, borate, perchlorate, carbonate or sulfate, and particularly incompletely-substituted salts of that type, i. e., salts in which the anion has at least one valence satisfied by hydrogen and at least one other valence satisfied by an alkali metal. Examples of such salts include disodium phosphate (Na2E~P04), potassium acid phosphate (KH2P04), ;, sodium bicarbonate (NaHCO3) and dipotassium borate (K2HBO3). Alsouseful are alkali metal salts of condensed acids such as pyrophosphoric, !~ ~
metaphosphoric, metaboric, pyroboric and the like (e. g. sodium pyro-phosphate, potassium metaborate, borax, etc. ) and/or the products of partial or complete hydrolysis of such condensed acid salts. Depending on the acidity of the aqueous solution in the electrolysis medium, the " , stoichiometric proportions of such anions and alkali metal cations in the solution may correspond to a mixture of two or rnore of such salts, e. g.
. :~
a mixture of sodium acid phosphate and disodium phosphate, and accordingly, such mixtures of salts ~as well as mixtures of salts of .
different cations, e. g. different alkali metals, and/or different acids) -are within the scope of the expressions "conductive salt, " "alkali metal phosphate, borate or carbonate, " etc., as used herein. Any of the alkali metal salts may be dissolved in the solution as such or otherwise, e. g.
:~.

C-14-54-Ol 73 ~ 03~33 ::
as the alkali metal hydroxide and the acid necessary to neutralize the hydroxide to the desired solution pH.
The concentration of conductive salt in the solution should be at least sufficient to substantially increase the electrical conductivity of the solution above its conductivity without such a salt being present. In most cases, a concentration of at least about 0.1% is favored. More advan-tageous conductivity levels are achieved when the solution has dissolved therein at least about 1% of the conductive salt or, even more typically, at least about 2% of such a salt. In many cases, preferred process 10 conditions include the solution having dissolved therein more than 5%
(typically at least 5. 5%) of the conductive salt. When an alkali metal conductive salt is used, the maximum amount of salt in the solution is typically limited or~ly by its solubility therem, which varies with the particular salt employed. With salts such as sodium or potassium phos-phates and/or borates, it is generally most convenient for the solution to contain between about 7% and about 20% of such a salt or mixture thereof.
As aforesaid, the present invention has to do with lessening potential undesirable effects of a heavy metal which passes into the electrolysis medium (e. g. from an electrode) while the medium is being electrolyzed.
20 In this context, heavy metal means a metal of specific gravity greater than 4. 0 such as, for example, iron, cadmium, lead, zinc, nickel, mercury, manganese, copper, cobalt, chromium, titanium, thallium, vanadium, molybdenum, ruthenium, antimony, bismuth, platinum or palladium. Also as used herein, heavy metal that "passes into the medium" represents heavy metal that enters the liquid medium in the sense of becoming free to circulate with and within the medium, as distinguished from heavy metal affixed to a surface of process apparatus through which or in which the liquid medium is circulated (e. g. the anode or cathode of an electrolytic :. . ~ . . . :.

~ 39~33 cell in which the medium is electrolyzed) and passage o~ the metal into the medium in "substantial amount" or at a "substantial rate" means that the amount or rate is great enough that in the course of the electrolysis, process performance characteristics such as, for example, molecular hydrogen formation or product selectivity would be substantially adversely affected unless the metal is rendered incapable of having such adverse effect, e. g. by removal from the medium or otherwise. The absolute amounts or rates that would have such effects vary greatly with the particular metals involved, the specific reductive coupling reaction 10 desired and many other process conditions, Prior to passage into the electrolysis medium, the heavy metal may be substantially pure or in a combined form such as a compound (e, g. an oxide or salt) or an alloy of that metal. In general, the metals having greater potential for adverse effects on the process after passage into the medium are those with low hydrogen overvoltage such as, for example, iron, nickel, tungsten, cobalt and molybdenum or, in other ~-words, metals not typically preferred as cathode materials for reductive coupling processes. In many embodiments, the invention is particularly ;
concerned with heavy metals from the anodes of electrolytic cells 20 employed in reductive coupling processes and particularly the anodes of most undivided cells used in such processes.
It has also been found, however, that metals of high hydrogen ~
overvoltage and even metals potentially useful as reductive coupling -cathode materials may also eventually affect process performance adversely if present in the electrolysis medium in substantial concentration without being rendered incapable of doing so. This may indicate that heavy metals which pass into the medium from the cathode are potentially re-deposited on the cathode in forms or states somewhat different from those ... . ,, ~ ,..... . . . . .

3~33 in which they were originally part of the cathoàe. In some embodiments, at any rate, the invention is importantly concerned with a heavy metal from the process cathode and accordingly, the process improvement of this invention may relate to metals passing into the medium from the process anode, cathode or both.
Such metals may pass into the medium as a result o~ erosion or corrosion of process apparatus such as electrodes, piping, etc., by chemical or electrochemical attack or otherwise and hence may enter the medium as ions, oxides, hydroxides, salts such as (depending on anions 10 in the medium) phosphates, borates, carbonates, sulfates, etc., or more complex compounds, although their chemical and/or physical forms and even possibly their valence states may undergo significant changes in the medium and/or as they pass into the medium or out of it (e. g. if deposited on the cathode of the cell). For instance, iron at the surface of a ferrous metal anode (i. e., an anode comprising iron, e. g. as in carkon steel, stainless steel or other iron-containing alloys, iron oxides such as magnetite, or other iron compounds) may form an iron phosphate as a result oE corrosion by a phosphate anion-containing electrolysis medium, pass into or be otherwise later present in the medium as a 20 finely divided (e. g. colloidal) solid compound such as an iron hydroxide, and be later deposited on the cathode as one or more oxides of iron.
Heavy metal sequesterants that are useful in the present invention may be any of various well-known compounds that combine with a metal to form soluble complexes in the presence of other chemicals that would otherwise tend to precipitate the metal ion. Preferred in some cases are sequesterants that are at least partly organic, i. e., sequesterants containing at least one organic component such as, for example, a carboxyl radical or an amino- or hydroxy-substituted hydroca-rbyl ... ~. .. . .

~, C-14-54-01 73 1(~3~
(e. g. alkyl) radica:l. Especially preferred are the aminocarboxylic acid compounds containing one or more amine groups and at least one carboxylic acid radical such as, for example, the nitriloacetic and nitrilopropionic acid and glycine compounds having the formula Y2N~ Z--YN~ R"-COOM wherein Y is a monovalent radical such as hydrogen, -R~-COOM, ~CH2 trn+l OH or Cl-C20 alkyl (preferably Cl-C10 alkyl such as ethyl, n-propyl, tert-butyl, n-hexylJ n-decyl, etc. ); -E~"- is +CH2~ or ~ CHR"'~; R"' is hydroxy, -COOM, ~ CH2~m COOM or Cl-C8 alkyl, hydroxyalkyl (e. g. hydroxyethyl) or ;
10 hydroxyphenyl (e. g. ortho-hydroxyphenyl); Z is a divalent C2-C
hydrocarbon (e. g. alkylene) radical such as, for example, n-hexylene, n-butylene, iso-butylene or, generally more desirably, ethylene or n-propylene; M is a monovalent radical such as hydrogen, an alkali metal ~e. g lithium or, usually more desirably, sodium or potassium) or ;
ammonium; m is 1 or 2; n represents the number of repeating ~ Z--YN-~ groups, if any, and may be 0, 1, 2, 3 or 4; and at least one Y in the formula is -R"-COOM or ~CH2~1 OH, i. e., the compound contains at least one -R"-COOM or ~ CH2 ~;~ OH group in addition to the -R"-COOM group on the right hand end of the formula as :
20 shown hereinbefore. At least one such additional -R"-COOM or ~CH2 ) 1 OH group is usually desirably attached to the nitrogen atom at the left-hand end of the formula but when n is 1, such an additional group may be attached (alternatively or otherwise) to the nitrogen atom in the ~Z--YN~ unit, and when n is 2, 3 or 4, any one or more ae the .
nitrogen atoms in the repeating -~ Z--YN~ units may have such an `
additional -R"-COOM or ~CH2 ~1 OH group attached thereto.
Preferably, but not necessarily, the sequesterant is an amino-polycarboxylic acid compound, i. e., one in which there are at least two ,' ".~ , ' ~

5 ~
' '' ' ~3~33 --~"-COOM groups It is also generally desirable for Z to be C2-C4 aL~tylene and for n to be 0, 1, 2 or 3 (even rnore desirabl~ 0, 1 or 2 and most preferably 1 or 2). Representative of such compounds are nitrilo-triacetic acid, diethylenetriaminepentaacetic acid, N, N-di(2-hydroxyethyl)-` glycine, ethylenediaminetetrapropionic acid, N, N'-ethylenebis~2-(o-hydroxy-phenyl)~glycine and, typically most favored, ethylenediaminetetraacetic acid and N-hydroxyethylethylenediaminetriacetic acid (hereinafter sometimes represented as EDTA and HEDTA, respectively). In the ~ow concentrations generally employed, they may be added to the electrolysis mediurn as acids or, usually more conveniently and particularly at the alkaline pH's favored for most embodiments of the invention, as partially or fully neutralized salts thereof (e. g. the t~ater-soluble amrnonium or alkali metal salts of such acids).
Known procedures for preparing aminocarboxylic acid compounds such as those just mentioned are referred to generally ~n the aforementioned .~ . .
Belqium Patent tJo. 804,365. For example, alkali metal salts of such compounds can be prepared by reacting an appropriate amine (e. g.
ethylenediamine) with an alkali metal salt of a chloracetlc acid in the presence of an alkali metal hydroxide, or with hydrogen cyanide and ~ormaldehyde and then an alkali metal hydroxide, or with ethy]ene glycol to provide hydroxyethyl substituents on nitrogen atom(s) of the arnine and ` then reacting the hydroxyethyl-substituted amine ~ith an alkali metalhydroxide in the presence of cadrniurn oxide to convert the hydroxyethyl substituents to alkali metal acetate substituents in the proportion desired, or ~ith acrylonitrile in the presence of a base (e g. sodium hydroxide~
and then hydrolyzing the cyanoethy]ated amine in the presence of an alkali rr.efal hydroxide. Other sequesterants suitable ~or use in the present -invention include o<-hydroxy carboxy]ic acids such as citric, tartaric, g]uconic, etc.; 3, S-disulfopyrocatechol; pyridines such as 2-aminometh ~ . .

C-14-~4-0173 ~ 3~ 3 pyridine, N-hydroxyethyl-2-aminomethylpyridine, 2-aminomethylpyridine-N-monoacetic acid, ethylenebis-N, N-(2-aminomethyl)-pyridine-N, N'-diacetic acid, etc., and many other compounds k;nown in the art as metal sequ0sterants, chelating agents, complexing agents or the like. See "Organic Sequestering Agents" by Chaberek and ~artell, John Wiley & Sons, Inc., New York, 1959; "Chelating Agents and Metal Chelates" edited by Dwyer and Mellor, Academic Press, New York, 196~; and "Chemistry of the Metal Chelate Compounds" by Martell and Calvin, Prentice-Hall, Inc., Engelwood Cliffs, N.J., 1952.
10As aforesaid, objects of this invention are achieved by additon to the medium of free heavy metal sequesterant, by which is meant heavy metal sequesterant not sequestering heavy metal to the fullest extent of its capability in that medium. Illustrations of free sequesterant include, for example, the acid forms of such compounds, alkali metal or ammonium ~;
salts thereof and their nonsequestering or incompletely-sequestering ions in solution. In this invention, free sequesterant may be added to the medium by newly combining free sequesterant with the medium or by regenerating free sequesterant from a heavy metal complex within the medium (e. g. by separating the metal from the complex with a heavy 20 metal precipitating agent such as a sulfide, ferricyanide or the like) while in other systems, free sequesterant mQy be readded to the medium a:~ter being regenerated from a heavy metal complex previously separated from the medium. In any systems, addition of free sequesterant to the medium ~nay be continuous or intermittent and at any convenient point in the system :;such as, for example, to a portion of the medium that is undergoing ; -electrolysis or ~generally preferred in continuous systems) to a portion of the medium that has been withdrawn from electrolysis and is being recirculated for further electrolysis.
' .. . .
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C-l 4-5~-01 73 ~L(D39233 ~
Also as aforesaid, objects of the inventioll are achieved by maintaining in the electrolysis medium excess free heavy metal sequesterant, by which is meant a measurable capability of sequestering more of a heavy metal added to the medium in sequesterable form, said capability being in excess (preferably substantially) of any metal-sequestering capability provided by free sequesterant in static equilibrium with the heavy metal in the medium. Normally, and especially with the generally preferred sequesterants having relatively high equilibrium -constants (i. e., log K for an equimolar mixture of metal ion and sequesterant, as defined in the aforecited text by Martell and CaLvin), concentrations of free sequesterant in static equilibrium with heavy metals in the msdium are so small that they have no practical significance;
:~
hence a substantial concentration of free sequesterant measured in a given medium may be taken as essentially the same as the excess free sequesterant concentration in that medium. It should be noted, however, that excess free sequesterant may exist in dynamic equilibrium with a heavy metal in the medium, e. g. in a system in which the sequesterant is continuously withdrawn or otherwise lost from the medium and free sequesterant is continuously added. Such a dynamic equilihrium concen-20 tration of free sequesterant may be much larger than the usual static equilibrium concentrations of free sequesterant in such media, and the ~ -two types of equilibrium concentrations should not be confused with reference to the presence of excess free sequesterant as employed in this invention. Measurements of concentrations of sequesterants (free or otherwise) can be made by well-known techniques described in various publications including those mentioned hereinbefore and "Keys to Chelation, "
` Dow Chemical Company, Midland, Michigan/ 1969.

: ~3~33 ~:

To maintain excess free sequesterant in the medium, as the term is used herein, means to have excess free sequesterant generally present in the medium throughout the operation of the process. Upsets and other process variations may result in the absence of excess free sequesterant for temporary and/or relatively short periods of time, but excess free sequesterant is typically maintained in the medium at least about 80%, preferably at least about 90% and most desirably about 100%
of the time the medium is being electrolyzed which may be as short as 10-20 hours in some (e. g batch) process embodiments or as long as several thousand hours or longer in other (generally continuous) embodiments. The most desirable concentration of excess free '!
sequesterant will vary with many other process conditions but in many preferred embodiments, the excess free sequesterant is aclvantageously capable of sequestering at least about two (and preferably at least about four) mill~les of heavy metal per liter of the medium.
In most embodiments of the invention it is advantageous to add to the medium during the electrolysis free heavy metal sequesterant in excess of that capable of sequestering the heavy metal in the amount passed into the medium during the same or an equivalent period of the electrolysis. In this context, "capable of sequestering" an amount of the heavy metal means under sequestration~favoring conditions including, `
for example, the amount of heavy metal being present in readily `-sequesterable form, intimate contacting of the heavy metal and free sequesterant, time for the sequestration to closely approach the ' conditions of static equilibrium, etc. In some cases, such equilibrium -~ conditions may not be reached under the electrolysis conditions and .! accordingly, a given amount of heavy metal may not be fully sequestered :, ' ' . : : . : . . - , .. :., . : ~
.. . . .. . . . . , . . , ~

~- C~ 5as-01 73 ~a~39~3 by an amount of added free sequesterant that is "capable" of doing so, as that term is used herein. As shown hereinafter, in fact, there are embodiments of the invention in which a substantial proportion of the heavy metal passed into the medium is not sequesterecl or at least not maintained sequestered throughout its presence in the electrolysis medium despite the added free sequesterant having advantageously had the capability of sequestering the metal in the amount passed into the medium.
It should also be noted that the amount of heavy metal passed into the medium ~nd the amount of free sequesterant added "during the electrolysis"
may be considered with reference to any specific interval of electrolysis and need not refer only to electrolysis throughout the duration of a batch or continuous operation or from the beginning of such a operation or to the end of such an operation. Hence the invention is practiced by adding free sequesterant during any given period of electrolysis in an amount capable of sequestering the heavy metal passed into the medium during that interval.
Also as used herein, the term "soluble in the initial electrolysis medium" has reference to a solubility in the electrolysis medium employed at the beginning of any such interval of electrolysis. It should be noted, however, that the amount of a heavy metal that is soluble in such a medium may decrease during the electrolysis, e. g. if the initial medium contained a sequesterant subject to degradation during the electrolysis, and accordingly, a heavy metal passed into that medium during a substantial interval of electrolysis may not be soluble in as great an amount therein as the metal would have been at the beginning `
of that interval. Inasmuch as there may also be a substantial concen-tration of heavy metal dissolved in the initial electrolysis medium, it - . ~

-~ C 14-54-0173 :' ~39~33 should be understood that an amount of heavy metal "greater than that soluble in the initial elec-trolysis meclium" has reference to the amount by which the heavy metal passed into the medium ~uring a given interval ~j of electrolysis exceeds that amount, if any, which is soluble in the - .
medium in addition to the amount, if any, which was dissolved in the "initial electrolysis medium" at the beginning of that interval. ~ ~ ~
As mentioned before, various sequesterants and especially many ~ -of those containing organic radicals are subject to degradation in the : ;
electrolysis medium, e. g. by hydrolysis or oxidation, particularly at !`~
the anode in process embodiments utilizing undivided cells.
Some of the degradation products may have significant sequestering capability and hence comprise fr ee sequesterant as that term is used herein. It will be appreciated, therefore, that partly because of such . , , degradation, determinations of free sequesterant presence or concen~
. . .
tration are often more importantly made as measurements of sequestering capability rather than as qualitative or quantitative analyses for specific sequesterant compounds or radicals thereof. ~ ~ ;
In some systems it may be practical to let the concentration of ;~
heavy metal dissolved in the electrolysis medium gradually increase during the operation of the process while adding free seq lesterant sufficient to dissolve heavy metal passing into the medium and also ,: . .
maintain the desired excess of free sequesterant, e. g. when the medium can be satisfactorily discarded thereafter. In other systems, however, -including some in which l:he sequesterant may degrade in the electrolysis medium and especially when such degradation may occur in a direct ~ `~
relation to the concentration of sequesterant in the medium, it may be preferable to hold the concentration of heavy metal dissolved in the medium essentially stable and thereby hold essentially stable the ., .

i: . : ,-, . . . . .
: . . .. , . , - . : ~ . .
~ :'.. . .. .. ,, . .: .
... . .. . . . .

-~~ C-14-54-0173 . .

~0;~9~33 concentration of sequesterant needed to maintain excess free sequesterant in the medium. That may be done in various ways such as, for e~ample, by purging a portion of the medium from the system during the electroly-sis and replacing it with a second portion having a lower dissolved heavy metal concentration than the portion purged, or by precipitating heavy metal sequestered or otherwise dissolved in the medium and then removing the precipitate (e. g. by filtration, centrifuging or the like). In fact, it is a ~ ~
preferred embodiment of the invention in which a liquid aqueous electrolysis ;; `
medium comprising the olefinic reactants and excess free heavy metal sequesterant is subjected in an electrolysis zone to electrolysis by which the reactants are reductively coupled and during which a heavy rnetal passes into the medium in substantial amount, a portion of the electrol~zed medium is then withdrawn from said zone, reduced coupled product is separated from said withdrawn portion (e. g. by decanting a product-containing ~
organic phase from a multi-phase electrolysis m~dium) and replaced with -fresh olefinic reactant, dissolved heavy metal is removed from said withdrawn portion (e. g. by purging a fraction of said withdrawn portion containing dissolved heavy metal or by precipitating and -then filter ing or centrifuging the precipitated metal from said wi-thdrawn portion), 20 any purged fraction of said withdrawn portion is replaced with otherwise-similar electrolysis medium having a lower dissolved heavy metal concentration than the fraction purged, said withdrawn portion is thereafter recycled into said zone for more of said electrolysis and sufficient free heavy metal secluesterant is added to the medium during the electrolysis to maintain excess free sequesterant in the medium.

'' ~L~39~33 Holding the concentration of heavy metal dissolved in the medium essentially stable, as the term is used herein7 does not necessarily mean holding that concentration within an especia]ly narrow range and, ;
in fact, it embraces process operation in which the concentration of heavy metal dissolved in the medium may vary from its norm up to 1 OO
or, on the high side, even more. It does mean, however~ that the dissolved heavy metal concentration is held normally below a maximum substantially lower than the concentration to which the dissolved heavy metal would otherwise increase during continued passage of the metal `
into the medium and addition of free sequesterant sufficient to maintain `
excess free sequesterant in the mQdium. In most process embodiments involving extended periods of operation, an essentially stable concentration of heavy metal dissolved in the rnedium is recognizable by the substantial consistency with which it remains below a given " ~
maximum concentration. `- -As used herein, dissolved heavy metal means heavy metal not . separated from the medium by passage of the medium through a membrane-type filter having a standard porosity rating of 0. 45 millimicron. Hence - -for typical systems, the concentration of heavy metal dissolved in the electrolysis medium can be simply determined by conventional analysis (e. g. atomic absorption) of a sample of the medium that has been passed -through such a filter. In specific systems, the relative desirability of ~ -the various techniques for holding the concentration of dissolved heavy metal stable will be based on several factors but with many organic sequesterants including aminocarboxyl compounds such as EDT~ and HEDTA, it has been found most desirable to maintain the concentration ~ ..

~3~3 ::
,:
of heavy metal di~solved in the medium between about 2 and abou-t S0 (preferably between about 4 and about 3()) millimoles per liter corresponding, for example when the heavy metal is iron and the medium has a typical specific gravity of about 1. 0~, to a concentration ' of iron dissolved in the medium between about 100 and about 2500 ppm ~;
~preferably between about 200 and about 1500 ppm). .-~
With most of such degradable sequesterants, particularly in some undivided cells and in order to maintain excess free sequesterant ~
in the me~ium together with a dissolved heavy metal withdrawal (e. g. ~ .
purge) rate that is not economically impractical, it is also commonly : .
preferable that the free sequesterant added to the medium is capable of ~ :
sequestering the heavy metal in at least about 1. 5 times the amount that passes into the medium cluring the electrolysis, which amount may be usually calculated from measured concentrations of the metal in the electrolysis medium or from the quantitatively observed loss of the metal from one or more electrodes. In fact, since loss of metal from a . `
process anode is usually closely related to the quantity of electric ~
. current passed through the medium in contact therewith, it is often ~ .
convenient to base calculations of metal loss and free sequesterant ~ . .
20 addition in terms of millimoles per Faraday of such current. For example, with the use of an anode made of a ferrous metal such as carbon .
steel, the added free sequesterant is generally most desirably capable of sequestering at least about 0.1 millimole of iron or other heavy metal per Faraday of current passed through the medium. Inasmuch as a great :
many sequesterants are capable of sequestering heavy metals on a one-to-one mole basis, those sequesterants (including aminocarboxyl ~.

- 24 - ::;

C ~ S ~ - 0 ~ 7 .

- cornpounds such as EDTA and HEDTA) are desirably added to the electrolysis medium in most undivided cells having such anodes în `~ sirnilar molar amounts, i. e., at least about 0.1 millimole of free sequesterant per Faraday oi current passed through the medium.

In conjunction wi~h use of the present invention in most undivided cells, corrosion of the anode and hence the tendency towa~d deposi tion of heavy metals on the cathode can be advan-tageously inhibited by including in the elect rolysis medium a - boric acid, a condensed phosphoric acid or an alkali metal salt thereof . The boric acid or borate may be added to the ~.
medium as orthoboric acid, metaboric acid or pyroboric acid - and then neutralized to the desired pH, e.g. with an alkali metal hydroxide or aS a comple tely or incompletely substituted u alkali met al salt o such an acid (e . g . disodium or monosodium 1 orthoborate, potassium metaborate, sodium tetraborate or the :1 hydrated form thereof commonly called borax). The condensed .. . .
~hosphoric acid or phosphate may be added as a polyphosphoric (e. g. pyrophosphoric or triphosphoric) acid and then neutralized .. to the desired pH or as a completely or incompletely substituted aL"ali metal salt thereof (e. g. tetrasodium pyrophosphate, .; potassium hexametaphosphate or sodium triphosphate). Further details concerning such use oi a boric or condensed phosphoric acid or salt thereof in reductive coupling processes as described hereinbefore are included in the aiorementioned Bel~ium Patent ~o.
; 804, 365.
In most cases, the pH of the bulk oi the electrolysis medium employed in the present invention is greater than t~vo, preferably at least about five, more preferably at ]east about six and most conveniently ; .. ~i,~

C-1~-54-01 73 9~33 at least about seven, especially when the process is carried out ~;
in an undivided cell having a metallic anode. On the other hand~
the overall pH is generally not higher than about twelve, typically not higher than about eleven and, with -the use of sodium and/or potassium phosphates, generally not substantially higher thcm about ten.
The temperature of the electrolysis medi~m may be at any level compatible with the liquid state of the medium, i. e., above its freezing ~ ~ ~
point but below its boiling point under the pressure employed. Good :
results can be achieved between about 5 and about 75C. or at even~; -higher temperatures if pressures substantially above one atmosphere `
are employed. The optimum temperature range will vary with the specific olefinic reactant and hydrodimer, among other factors, but in ' hydrodimerization of acrylonitrile to adiponitrile, electrolysis temper-. .. .
atures of at least about 25 are usually preferred and those between about 40 and about 65C. are especially desirable. In fact, it is an especially -advantageous feature of the present invention that it can be employed very satisfactorily at temperatures above 40C. (the maximum ~ -temperature indicated feasible in the disclosure of U. S. 3, 616, 321) because electrolysis medium conductivity typically increases with temperature and the power costs of the process are therefore generally smaller above 40C. than at lower temperatures.
As is well known, electrolytic reductive coupling of olefinic `;~
reactants (including those mentioned hereinbefore) is carried out in -contact with a cathodic surface having a cathode potential sufficient `
for reductive coupling of those reactants. In general, there is no minimum current density with which the invention can be carried out but in most casesJ a current density of at least about 1 amp per square

- 2 6 -~(339~33 ~:

.. ~ C-14-54-0173 '; ~, '- ' decimeter (amp/dm2) of the cathodic surface is used and at least about 5 amp/dm2 is usually preferred, Alt;hou~h hi~her current :.:
densities may be practical in some ~nstanc:es, those ~enerally :~ employed herein are not hl~her than about 150 amp/dm2 and even more typically not above about 75 amp/dm2. Dependin~ on other .. .:
process variables, current densities not hi~her than about 50 ~ .
: amptdm2 may be preferred in some embodiments, but it is a `~
si~niflcant advanta~e of the invention that it can be carried out typically most sat~sfactorily at current densities of at least about 10 amp/dm2 of cathodic surface and in some cases at ~ :
current densities up to about 25 amp/dm2 or even hi~her, ;. ~`
Althou~h not necessary, a liquid-impermeable cathode is usually pre~erred. With the use of such a cathode, the aqueous medium to be electrolyzed is ~enerally passed between the anode and cathode at a linear velocity with reference to the adjacent - ~:
cathodic surface of at least about 0.3 meters per second, ;
preferably at least about 0.6 meters per second and even more preferably between about 0.9 and about 2.4 meters per second althou~h a velocity up to 6 meters per second or hi~her can be employed, if des~red, The ~ap between the anode and cathode can be very narrow, e,~ about 0,10 centimeters or less, or as wide as 1.27 centimeters or even wider, but is usually most conveniently of a width between about 0.152 and about 0.635 centimeters.
The cathodic surface can be made of virtually any material at which the requisite cathode potential can be provided and which is not dissolved or corroded at an intolerable rate, ~or example, the process can be ~enerally carried out with a cathode consistin~
essentlally of cadmium, mercury, thallium, lead, zinc, man~anese, tin (possibly not su~table with some nitrile reactants) or ~raphite, by whtch is meant that the cathodic surface contains .. . . . . . . ~ ~ .

C-14-54-0173 ~039~33 ~

a hi~h percenta~e (~enerally at least about 95~ and preferably at least about 98~) of one or a comb~nation (e.~. an alloy~ of two or more of such materials. but it may contain a small amount of one or more other constituents that do not alter the nature ~;
of the cathodic surface so as to prevent substantial realization ~ ;
of the advanta~es of the present invention~ particularly as descr~bed herein. Such other constituents, if present in substantial concentration, are preferably other materials havin~
relatively hi~h hydro~en overvolta~es, ~enerally of particular preference are cathodes consistin~ essentially of cadmium~ lead, zinc, man~anese, ~raphite or an alloy of one of such metals, and especially cathodes consistin~ essentially of cadmium. Best results are usually obtained with a cathodic surface havin~ a cadmium content of at least about 99~5~, even more typically at least about ~9~8~ and most desirably at least about 99.9%
as in ASTM Desi~nation B~40-66T (issued l9h6).
Cathodes employed in this invention can be prepared by various techniques such as, for example, electroplatin~ of the desired cathode material on a suitably-shaped substrate of 2n some other material, e.~. a metal havin~ ~reater structural ri~idity, or by chemically, thermally and/or mechanically bondin~ a layer of the cathode material to a similar substrate.
Alternatively, a plate, sheet, rod or any other suitable ;~
confi~uration consistin~ essentially of the desired cathode material may be used without such a substrate, if convenient.
The process of this invention can be carried out in a divided -~cell havin~ a cation-permeable membrane, diaphra~m or the like separatin~ anode and cathode compartments of the cell in such a way ~'~

. ~ ~
:.'. . . - ~ ~ .,.

C~ 54-01 73 , 1~39~33 `;
. . ;
that electrolysis medium in direct physical contact with a cathode of the .~.~; . .
cell is not in simultaneous direct contact with an anode of the cell. ~ -~:
It is especially advantageously used, however, in cells not divided in that manner, i. e., in cells in which the electrolysis medium is simultaneously in direct physical contact with an anode and cathode of the cell. In fact, it is a preferred embodiment of the invention which ;
. .. ~ .
is carried out in an undivided cell ~aving an anode comprising a ferrous metal with an alkali metal phosphate, borate or carbonate conductive salt and an electrolysis medium having a pH not substantially 10 below seven. Of particular interest are embodiments employing an anode consisting essentially of carbon steel, exemplary compositions of which are listed in the 1000, 1100 and 1200 series of American Iron and Steel Institute and Society of Automotive Engineers standard steel composition numbers, many of which may be found on page 62 of Volume 1, Metals Handbook, 8th Edition (1961) published by the American Society for Metals, Metals Park, Ohio.
In general, carbon steels advantageously used as anode materials in the process of this invention contain between about 0. 02%
carbon (more typically at least about 0. 05% carbon) and about 2%
carbon. Normally, carbon steels such as those of the AISI and SAE
1000 series of standard steel composition numbers are preferred and ~-those containing between about 0.1`% and about lo 5% carbon are typically most desirable. Regardless of the material from which it is made, each anode in the cell may be in the form of a plate, sheetJ
strip, rod or any other configuration suitable for the use intendecl.
In one embodiment, the anode is in the form of a sheet (e. g. of carbon steel) essentially parallel to and closely spaced from a cathodic ,, : ~ :, :

~(~39~33 surface of approximately the same dimensions. Potentially advantageous in some cases in the use of a multi-cell package comprising a series of substantially parallel plates or sheets made ' ol a self-supporting material (e. g. iron or steel) having surfacesfacing in one direction composed of a suitable anode material (e. g. magnetite or a steel supporting material) and the surfaces facing in the other direction covered with a suitable cathode material (e. g.
cadmium or other metal conveniently electroplated or otherwise coated on the supporting material) so as to permit passage of electrolysis medium through a plurality ol channels between such p]ates or sheets and simultaneous use of each plate or sheet in the series as an anode and cathode in the manner conventionally referred to as use of bipolar electrodes.
In the following specific examples, the heavy metals present in the electrolysis medium in significant proportions were iron and cadmium, the latter of which is known from pub-' lished data and experimental comparison to be sequestered in the same molar proportions as iron and in essentially complete preference to iron by the particular kinds of sequesterant employed. Accordingly, electrolysis medium capabilities for dissolving additional cadmium or iron in the follo~/ing examp]es were de~termined as follows: (1) A representative sample of the electrolysis m~dium uas ;-diluted and then filtered to remove essentially all solids by passage through a membrane-type fi~ter having a standard porosity rating of 0. 45 millimicronJ (2) the weight concentrations of iron and cadmium in a first portion of the filtered sample u~ere ind;vidually measured by atomic absorption, (3) a finely-divided cadmium compound (e. g. oxide ` C-14-54-0173 ~K~9~3;~
.
or phosphate) was added to a second portion of the sample in excess of its solubility therein after which that portion \~as thorou~hly a~itated for several hours, refiltered and analyzed for its ~Jei~ht concentration of cadmium in the manner employed for the first portion of the sample, (4) the ~lei~ht concentrations of cadmium and iron measured as just described were converted to molar concentrations and (5) the sum of the molar concentrations~
of iron and cadmium ;n the first portion of the sample wa~
subtracted from the molar concentration of cadmium in the second , 10 portion of the sample with the difference representin~ the ` molar concentration in ~hich the aforementioned representative sample had the capability of dissolvin~ iron or cadmium in addition to the iron and cadmium actually dissolved in that sample of the medium.
.~ Also in the followin~ specific examples, wh;ch are included to illustrate and not to delimit the invention, acrylonitrile and adiponitrile are yenerally represented by AR and ADN, respectively.
Example I
_ _ In a continuous process, a liquid electrolysis medium composed about 99% by (1) an a~ueous solution havin~ dissolved therein about 1.7X AN, 1.2% ADN, 10% of a mixture of sodium orthophosphates correspondin~ to the solution pH of 9 and bet~leen 4 and 9 x 10-3 mole per liter of ethyltributylammonium ions and about 1% by (2) a dispersed but undissolved or~anic phase containin~ about 31% ANs 52-53X ADN, 8-9% AN dimerization byproducts and 8% ~later was circulated at 55C. and 1.22 meters per second throu~h an undiv~ded electrolytic cell havin~ an AISI
1020 carbon steel anode separated by a ~ap of n.238 centimeters from a cadmium (at least 99.9~ Cd) cathode and electrolyzed as it ,~`~'i' passed throu~h the cell W~th a current dens~ty of 20 amptdm2 of the surface of the anode or cathode. Or~an~c phase containin~
product ADN, byproducts and unreacted AN was separated from the :' . ;
electrolyzed medlum and make-up AN was added after ~Ihich the medium was rec1rculated throu~h the cell and elec~rolyzed a~ain under the condit~ons just described. In~tially~ the medlum contained dlssolved ~ron and cadmium in concentrations of 4.75 and 0.24 millimoles per l~ter, respectively~ and tetrasodium ethylenediaminetetraacetate (Na4EDTA) and de~radation products thereof in proportions such that the med~um was capable of dlssolv~n~ an addlt10nal 5.8 ~illimoles per liter of iron andtor cadm~um but no more than that amount. For each ~araday of current passed throu~h the med~um, 0.28 mill~mole of Na4EDTA was ; added to the c1rculatin~ medium and 13.2 ~rams of the solution were pur~ed from the system and replaced with water containin~
sufficlent dissolYed ethyltributylammonium ions and sodium orthophosphates to maintain the concentrations of those con-:
stituents of the solution at the aforedescribed levels and the total volume of the medium essentially constant. Under those cond~tions, the anode and cathode corroded at avera~e rates tapproximately 0.063 and 0.007 centimeters per year, respectively) ; such that 0.139 millimole of iron and 0.008 millimole of cadmiumpassed into the med~um per ~araday of such current whereby the iron and cadmium passed into the medium during the electrolysis .
exceeded 5.8 millimoles per liter of the medium during the first 185 hours of electrolysis, addition of the 0.28 millimole of Na4-EDTA per Faraday maintained in the aqueous phase of the medium excess free sequesterant providing an average sequestering capa-bility of two millimoles of iron or cadmium per liter of the , , ~-14-54-0173 ~392~3 solut~on const~tutln~ ~hat aqueous phas~with~ concen~rations of iron and cadmium dlssolved in the solut~onbeing helds ~ ~ in the ran~es of 206-378 and 28-35 ppm (4-7.3 and 0.27~0.34 milli-;; moles per liter~ respect~vely, wh11e about 40X of the iron passin~ from the anode into the electrolys~s medium formed solids removable by f~ltration. ~or 358 hours of electrolysis under those conditions, AN was converted to ADN with an avera~e selectiv~ty of 86.5%~ the volta~e drop across the cell was stable between 3.9 and 4.0 volts and the volume percenta~e of hydro~en ~0 1n the electro1ysis off~as avera~ed 8X.
D At that time the pur~e rate was lowered to 4.4 ~rams per ~araday. Iron and cadm~um continued passin~ into the electrolysls medium at essent~ally the same avera~e rates as before but surprisin~ly, the concentration of iron dissolved in the solution did not increaseO Instead, that concentration held stable in the ran~e of 290-320 ppm (5.6-6.2 m~ moles per ., .
liter~ wh~le about 80-85X of the iron passin~ from the anode into the electrolys~s medium formed solids re~ovable by filtration. At the lowered pur~e rate, add~tion of the 0.28 mill~mole of Na4EDTA per Faraday maintained in the aqueous phase excess free sequesterant havin~ an avera~e iron or cadmium sequesterin~ capab~lity o~ 4.3 mill~moles per l~ter of solut~on i and the concentration of cadmium dissolved in the solution was stable in the ran~e of 70-80 ppm (0.68-0.77 millimoles per liter).
Durin~ an addit~onal 191 hours of electrolysis under those conditions, AN waj converted to ADN with an avera~e selectivity o~ B7X, the volta~e drop remained below 4 volts and the Yolume percenta~e of hydro~en in the off~as avera~ed less than lOX.

C-14-54-01 73 ~39,f~33 Comparatlve Example A
An electrolysis medium essentially 1i5~e that of Example I ::~
was electrolyzed under conditions essentially the same as those of Example I except for an intermediate pur~e ratc of 8.06 ~rams per Faraday and a lower Na4EDTA addition rate of 0.085 millimole per ~arada,y. Under those conditions, the concentrations of iron and cadmium dissolved in the solution ~ere stable at about , 260 and 40 ppm (5 and n.39 millimoles per liter) respectively, '' ;'~
but with iron and cadmium passin~ in~o the electrol,ysis medium ,~
at avera~e reates at least as ~reat as those in Example I, the Na4EVTA addition rate was not suf~icient to maintain excess ~ree senuesterant in the medium and after 16fi hours of elec- `3~
trolysis, corrosion of the anode accelerated to a much hi~her '' rate, the ADN selectivity had declined to 84~, t~le volta~e ~''- ', drop across the cell had increased to 4.4 volts and the volume ',,~
percenta~e of hydro~en in the off~as had risen to 26%.
Example II
__________ .
In a continuous process~ a liquid electrolysis medium : ~ ' composed about 99% by (1) an aqueous solution havin~ dissolved therein between 1.3% and 1.6% AN, about 1.2% ADN, between 4 and 10 x 10-3 mole per liter of ethyltributylammonium ions, lOX of ~`' a mixture of sodium orthophosphates and the sodium borates ~ ~ , produced by neutralizin~ orthoboric acid in an amount correspondin~
to 2% of the solution to the solution pH of 8,5 and about 1% by (2) a dispersed but undissolved or~anic phase containin~ about ';~
24-30X AN, 54-60~ ADN~ 8% AN dimerization byproducts and 8%
water was circulated at 55C. and 1.22 meters per second throu~h ' an undivided electrolytic cell havin~ an AISI 1020 carbon steel anode separated by a ~ap of 0.178 centimeters from a cadmium ...

.

3l(~39~3~3 ~at least 99.9% Cd~ cathode and electrol~zed as it passed through the cell with a current dens~t~ of 16 amp~dm2 o~ the surface of the anode or cat~ode. Organ~.c phase containing product ADN, byproducts and unreacted AN was separated from the electrolyzed medium and make-up AN was added after which the medium was re-circulated t~rough the cell and electrolyzed agai~ under the con-ditions just described. In~tially, the medium contained about . 6.8 millimoles per liter o~ dissolved iron and Na4EDTA and de-gradation products thereof in proportions such that the medium was capable of dissolving an additional 4.9 millimoles per liter of iron and/or cadmium but no more than that amount. For each Faraday of current passed khrough the medium, 0.4 millimole of Na4EDTA was added to the circulating medium and 12 grams of the solution were purged from the system and replaced.with water con-taining sufficîent dissolved ethyltributylammonium ions and sodium orthophosphates and borates to mainta.in the concentrations of those constituents of the solution at the aforedescribed levels and the total volume of the medium essentially constant.
.~ Under those conditions, the anode and cathode corroded at averagerates ~approximately 0.033 and 0.007 centimeters per year, res-pectively) such that 0.09 millimole o~ iron and 0.009 millimole of cadmium passed into -the medium per Faraday of such current whereby the iron and cadmium passed into the medium during the electrolysis exceeded 4.9 millimoles per liter of the medium during the first 46 hours of electrolysis, addition of the 0.4 ' millimole of Na4EDTA per Faraday maintained in the aqueous phase .~ of the medium excess free sequesterant providing an average sequestering capability o~ 2.5 millimoles of iron or cadmium per liter o~ the solution constituting that aqueous phase with the concentrations of iron and cadmium dissolved in the solution - 35 _ "

, ~3~33 bein~ ~eld stable in the xanges o~ 326~450.and 35-90 ~pm. (6.3-8.7 and 0.34~0.87 millimoles pex literl xespect~vely. ~fter 232 hours of electrolysis it was ~ound that AN had been converted to ADN with a selectivity ~etween 87.5~; and 88.1~ throughout the run, the voltage drop across the cell (3.73 volts) had not risen since the Beginning of the run andthe volume percentage of hydro-~en in the offgas had averaged 4-5% ~ith a maximum of 6% and a final value of 5.5%~

EXAMPLE III

~hen there was carried out for 429 hours a process essentially the same as that of Example II except that the elec- .:.
trolysis medium initially contained dissolved iron and cadmium in concentrations of about 11.1 and ~.4 millimoles per liter, respectively, the Na4EDTA addition rate was 00495 millimole per Faraday and the current density was 18.5 ampfdm2, the anode and cathode corroded at average rates tapproximately 0.055 and 0.010 centimeters per year, respectively) such that 0.132 milli-mole of iron and 0.012 millimole of cadmium passed into the medium per Faraday of current passed throughthe medium whereby the iron and cadmium passed into the medium during the first 31 hours of the electrolysis exceeded 4.9 millimoles per liter of the medium, addition of the 0.495 millimole of Na4EDTA per Faraday maintained in the aqueou6 phase of the medium excess free sequesterant providing an average sequestering capability of 5.75 millimoles of iron or cadmium per liter of the solution constituting that aqueous phase with the concentrations of iron and cadmium dissolved in the solution being held stable in the ranges of 455-570 and 94-178 ppm ~8.8-11.0 and ~.9-1.7 millimoles ~r~

C- l ~ ~ 5~ ~ O 1 7 3 233 ~ ~
per liter) respective1y. Under those conditions, AN was con- ''~`
verted to ADN with avera~e and final selectivi~ies of 88% and 87~1% respectivel,y, the volta~e drop across the cell ~ias stable at 3.~4-3,9 volts and the volume percenta~e of hydro~en in the off~as avera~ed about 10% with a final value of 16.4 Example IV
In a continuous process, a liquid electrolysis medium composed about 99X by (1) an aqueous soluti~n havin~ dissolved there~n about 1-1.5% AN, 1.2% ADN, 12,2% of a mixture of ~ , potassium orthophosphates, 7.5-16 x 10 3 mole per liter of ethyltributylammonium ions and the sodium borates produced by neutralizin~ orthoboric acid in an amount correspondin~ to 2% , ' of the solution to the solution pH of 805 and about 1% by ~?) '' a dispersed but undissolved or~anic phase containin~ 18-27% AN, 57-66X ADN. 8% AN dimerization byproducts and 8% water was circulated at 55C, and 1.22 meters per second throu~h an undivided electrolytic cell havin~ an AISI 1020 carbon steel anode separated by a ~ap of 0.178 centimeters from a cadmium (at least 99.9% Cd) cathode and electrolyzed as it passed throu~h the cell with a current density of 16 amp/dm2 of the ' sur~ace of the anode or cathode. Or~anic phase containin~ product ADN, byproducts and unreacted AN was separated from the elec-trolyzed medium and make-up AN ~as added after which the medium was recirculated throu~h the cell and electrolyzed a~ain under the conditions just described. Initially, the medium con~ained dissolved iron in a concentration of 13~7 millimo1e per liter and Na4EDTA and de~radation products thereof in proportions such that the medium was incapable of dissolvin~ any additional iron or cadmium. For each ~araday of current passed throu~h the .. .
. - .. . . . .

C-14-54-Q173 1~39?~33 medium, Q.4 millimole of Na~EDTA was added to the circulatin~
medium and 12 ~rams of the solution were pur~ed from the system and replacedwith water conta~nin~ sufficient dissolved .
ethyltributylammonium ions. potassium orthophosphates and sod;um :
borates to maintain the concentrations of those constituents of the solution at the aforedescribed levels and the total volume -of the med~um essentially constant. Under those conditions, the anode and cathode corroded at avera~e rates (approx~mately ~
0.038 and o.on7 centimeters per year, respect~vely) such that .
0.104 millimole of iron and 0.009 millimole of cadmium passed into the medium per Faraday of such current, addition of the ; 0.4 millimole of Na4EDTA per ~araday maintained in the aqueous phase of the medium excess ~ree sequesterant providing an aver- :~
- age sequestering capabillty of three millimoles of iron or cad- :
m~um per liter of the solution constituting that aqueous phase ;
with the concentration~ o-E iron and cadmium dissolved in the solution being held stable in the ranges of 519-708 and 209-475 ~0.3-14.1 and 2.1-4.7 millimoles per liter) respectively.
A~ter 233 hours of electrolysis under those conditions, it was found that AN had been converted to ADN with an average and final selectivity of 88%, the~Dltage drop across the cell (3.65 volts) had not risen since the beginning of the run and the volume percentage of hydrogen in the offgas had averaged 3-4~ 1 with a final value of 4.4%. .
Example V I .
_ _ _ _ _ _ _ _ 1. In a continuous process~ a liquid electrolysis medium composed about 85.4X by (17 an aqueous solution havin~ dissolved therein about 1~7~ AN, 1.2X AD~J, lOg of a mixture of sodium orthophosphates, 2-5 x 10-3 mole pPr liter of ethyltributYl-ammonium ions and the sodium borates produced by neutralizin~

C-14-5~-0173 ~3 ~ ~ 3 ~

orthoboric acid ~n an amount correspondin~ to 1.8% of the solution to the solutlon pH of R.5 and about 14.6% by (2~ a dispersed but undissolved or~anic phase containin~ about 31% ;~
AN~ 53-54~ ADN, 7-8% AN dimerization byproducts and 8% water was circulated at 55C. and 1,22 meters per second throu~h an undivided electrolytic cell havin~ an AISI 1020 carbon steel anode separated by a ~ap of 0.178 centimeters from a cadmium (at leas~ 99.9% Cd) cathode and electrolyzed as it passed throu~h the cell with a current density of 18.5 amp/dm2 of the surface ~o of the anode or cathode. Or~anic phase containin~ product ADN, byproducts and unreacted AN was separated from the electrolyzed medium and make-up AN was added after whlch the medium was recirculated throu~h the cell and electrolyzed a~ain under the conditions just described. Initially, the electrolysis medium contained dissolved iron and cadmium in concentrations of 9,0 and 2.75 millimoles per liter, respectively, and Na4EDTA and de~radation products thereof in proportions such that the medium was capable of dissolvin~ an additlonal 5,25 millimoles per liter of iron and/or cadmium but no more than that amount.
~or each ~araday of current passed throu~h the medium, 0.4 millimole of Na4EDTA was added to the circulatin~ medium and 12 ~rams of the solution were pur~ed from the system and replaced with water containin~ sufficient dissolved ethyltributylammonium ions and sodium orthophosphates and borates to maintain the concentrations of those constituents of the solution at the aforedescribed levels and the total volume of the medium essentially constant. Under those conditions, the anode and ;~
cathode corroded at avera~e rates (approximately 0.05 and 0.007 centimeters per year, respectively) such that 0.12 millimole of :
-39~

,.
: . .: . . -.

1~!39~33 iron and 0.008 millimole ~ cadmium passed into the medium per Faraday of such current wh~reby the iron and cadmium pas~ed into the medium during the electrolys:is exceeded 5.~5 milli-moles per liter of the medium during the first 37 hours of electrolysis, addition of the 0.4 mil:Limole of Na4EDTA per Faraday maintained in the aqueous phase of the medium excess free sequesterant providing an average sequestering capability of 5.25 millimoles of iron and cadmium per liter of the solu-tion constituting that aqueous phase with the concentrations of iron and cadmium dissolved in the solution being held stable in the ranges of 465-490 and 170-288 ppm (9-9.5 and 1.6-2.8 millimoles per liter) respectively. After 69 hours of elec-trol~sis under those conditions, it was found that AN had been converted ko ADN with average and final selectivities of 87.8%, t~e voltage drop across the cell had been stable below 4 volts and the volume percentage of hydrogen in the offgas had aver-aged 3-4% with a final value of 6%.

.
Exampl_e VI
In a continuous process, a li~uid electrolysis medium composed about 99% by (1) an aqueous solution havin~ dissolved therein between 1.4% and 1.8% AN, about 1.2% ADN, 10-11% of a mixture of sodium orthophosphatesJ about 1.4 ~ 10~3 mole per ! liter of ethyltributylammonium ions and the sodium borates produced by neutralizin~ orthoboric ac~d in an amount correspondin~ to 2X of the solution to the solution pH of 8.5 and about lX by (2) a dispersed but undissolved or~anic phase containin~ 27-32% AN, 53-5g% ADN. 6-7~ AN dimerization byproducts and B% water was circulated at 55C. and 1.22 meters per second throu~h an undivided electrolytic cell havin~ an AISI 1020 carbon steel anode separated by a ~ap of 0.178 centimeters fro~

1~3~3 a cadm~um (at least 9909X Cd) cathode ~and electroly7ed as ~t passed throuQh the cell w~th a current denslty of 18.5 amp/dm2 of the surfaoe of the anode or cathode. Or~anic phase containin~ produc~ ADN, byproducts and unreacted AN was separated from the electrolyzed medium and make-up AN was added after which.the medlum was recirculated throu~h the cell and electrolyzed a~ain under the conditions just descr~bed. Initially, the ~:
med~um cuntained d~ssolYed iron and cadmium in concentration~
of abou~t 12.8 and 2.7 millimoles per liter, respect~vely, and tr~sod~um hydroxyethylethylenediaminetriacetate (Na3HEDTA) and de~radat~on products thereof in proport~ons such that the medium was capable of dlssolv~n~ an add~t~onal 4.9 millimoles per 1iter of ~ron and/or cadm~um but no more than that amount. ~or each Faraday o~ current passed throu~h the ~ed~um, 0~495 millimole of Wa3HEDTA was added to the circulatin~ medium and 12 ~rams of the ~olution were pur~ed from the system and replaced with water conta~nin~ sufficient dissolved ~thyltributylammon~um ions and sodium orthophosphates and borates to mainta~n the concen~ra-tions of those constituents of the solution at the afore-described levels and the total volume of the medium essentially constant.
Under those conditions, the anode and cathode corroded at average rates tapproximately 0.059 and 0.020 centimeters per year, res-pectively) such that 0.14 millimole of iron and 0.022 millimole of cadmium passed into the medium per Faraday of such currentwhere-by the iron and cadmium passed into the medium during the electro-lysis exceeded 4.9 millimoles per liter of the medium during the first 27 hours of the electrolysis, addition of the 0.495 millimole of Na3HEDTA per Faraday maintained in the aqueous phase of the med-ium excess free sequesterant providing an average se~uesteriny il~l?3Y~233 capab~lity o~ 4.6 mill~moles o~ ~ron o;r cadm~ .per liter o~ the solution constituting that aqueous phase with the concentrations of iron and cadmium dissolved in the solution being held stable in the ranges of 538-668 and 106 279 ppm (lO.4-l2.9 and 1.0-2.7 millimoles per liter~ respectively and about 4~ o~ the iron passing from the anode in the medium ~ormed solids removable by filtration. For 241 hours o~ electrolysis under those condi-tions, AN was converted to ADN with average and final selectivi-ties o~ 89.3~ and 89.0% respectively, the voltage drop across the cell was stable at 3.9 volts and the volume percentage of hydrogen in the offgas averaged 4.5% with a final value of 5.4%.

Exam~le VII

When an electrolysis medium essentially identical to that of Example VI was electroly~ed under conditions essentially the same as those of Example VI for 362 hours, the anode and cathode corroded at average rates ~approximately 0.058 and 0.017 centi-meters per year, respectively) such that 0.137 millimole of iron -and 0.Ol9 millimole of cadmium passed into the medium per Ear~ay o~ current passed through the medium whereby the iron and cadmium passed into the medium during the electrolysis exceeded 4.9 milli-moles per liter of the medium during the first 28 hours of the electrolysis, addition of the 0.495 millimole of Na3HEDTA per Far-; aday maintained in the aqueous phase of the medium excess free sequesterant providing an average sequestering capability of 5.6 millimoles of iron or cadmium per liter of the solution constitu-ting that aqueous phase with the concentràtions of iron and cad-mium dissolved in the solution being held stable in the ranges of 506-558 and lO5-278 ppm 19.8-10.8 and l.0-2.7 millimoles per liter)respectively. Under those conditions, AN was converted .

C-14-5~-0173 ~3~33 - to ADN wlth avera~e and final select~vities of 8~,7% and 87.1%
respectively, the volta~e drop across the cell was stable at

3.9 volts and the volume percenta~e of hydro~en in the off~as avera~ed 7.2% with a final value of 8.5%.
Example VIII
In a continuous process, a liquid electrolysis medium composed between 85~9% and 87.5% by (1) an aqueous solution ; havin~ dissolved therein between 1.~% and 1.6% AN, about 1.2%
ADW, 9.6-9.9% of a mixture of sodium orthophosphates, 0.8-2~5 x 10 3 mole per liter of ethyltributylammonium ions and the sod~um borates produced by neutralizln~ orthoboric acid in an amount correspondin~ to about 2% of the solution to the solution pH of 8.5-9 and between 12.5% and 14.1% by (2) a dispersed but undissolved or~an1c phase conta~nin~ 26-29% AN9 54-59% ADN, 7-9% AN dimerization byproducts and 8% water was circulated at ~5C. and 1.158 meters per second throu~h an undivided electrolytic cell havin~ an AISI 1020 carbon steel anode separated by a ~ap o~ 0.228 centimeters from a cadmium (at least 9g.9% Cd) cathode and electrolyzed as it passed throu~h the cell with a current density of 20 amp/dm2 of the surface of the anode or cathode.
Or~anic phase containin~ product ADN, byproducts and unreacted ;~
AN WdS separated from the electrolyzed medium and make-up AN was added after which the medium was recircu~ated throu~h the cell and electrolyzed a~ain under the conditions just described.
Init~ally, the electrolysis medium contained dissolved iron and cadmium in concentrations of 6.9 and 1.25 millimoles per liter, respectively, and Na~EDTA and de~radation products thereof in proportions such that the med~um was capable of dissolvin~ an additional 2.75 millimoles per liter of iron and/or cadmium but -43- ;

. ... - . . .
;'. : ~ :, ' . , ~39~33 no more t~an that a~ount. Fo~ each Faxada~ o~ curxent passed through the medium, 0.475 m~llimole of Na4EDTA was added to the circulating medium and about 10 grams o~ the solution were purged ~rom the system and replaced with water containing sufi-cient dissolved ethyltributylammonium ions and sodium orthophos-phates and borates to mainta~n the concentrations Qf those con-st~tuents of the solution at theafore-described levels and the total volume of the medium essentially constant. Under those conditions, the anode and cathode corroded at average rates ~approximately 0.05 and 0.012 centimeters per year, respectively) such that 0.12 millimole of iron and 0.014 millimole of cadmium passed into the medium per Faraday of such current whereby the iron and cadmium passed into themedium during the electrolysis exceeded 2.75 millimoles per liter of the mediu~ during the first 102 hours of electrolysis, addition of the 0.475 millimole of Na4EDTA per Faraday maintained in the aqueous phase of the medium excess free sequesterant providing an average sequestering ~apa-bility of 3.6 millimoles of iron or cadmium per liter of the solution constituting that a~ueous phase with the concentrations of iron and cadmium dissolved in the solution being held stable in the ranges of 350-550 and 130-165 ppm (6.8-11.6 and 1.25-1.55 millimoles per liter) respectively. After 268 hours of electro-lysis under those conditions, it was found that AN had been con- -verted to ADN with average and final selectivities of 87~ and 88%
respectively, the voltage drop across the cell had been stable ;~
at 4 volts and the volume percentage of hydrogen in the offgas had averaged about 6.5% with a final value of 10.4%.

.

_ 44 -

Claims (8)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a process in which olefinic reactants having the formula R2C=CR-X in which -X is -CN, -CONR2 or -COOR', R is hydrogen or R' and R' is C1-C4 alkyl are reductively coupled by electrolyzing a liquid aqueous medium having a pH of between 2-12 and a temperature between about 5°C to about 75°C containing the reactants in contact with an electrode comprising a heavy metal that passes into the medium in substantial amount during the electrolysis, the improvement which comprises adding suffi-cient free sequesterant of said heavy metal to the medium during the electrolysis to maintain excess free sequesterant of said heavy metal in the medium.

2. The process of claim 1 wherein the added sequesterant is an aminocarboxyl compound.

3. The process of claim 2 wherein the excess free sequesterant is capable of sequestering at least about two milli-moles of heavy metal per liter of the medium.

4. The process of claim 1 wherein the heavy metal is iron and the added sequesterant is capable of sequestering at least about 0.1 millimole of iron per Faraday of current passed through the medium.

5. The process of claim 1 wherein acrylonitrile is the olefinic reactant and the liquid medium contains as the contin-uous phase thereof an aqueous solution of acrylonitrile, quater-nary ammonium ions and a conductive salt in a concentration of at least 0.1%.

6. The process of claim 5 wherein the liquid medium is in contact with a ferrous metal anode and the added sequesterant comprises an aminopolycarboxyl compound capable of sequestering at least about 1.5 times the iron passing into the medium.

7. The process of claim 6 wherein the added sequesterant comprises at least about 0.1 millimole of a salt of ethylene-diaminetetraacetic acid or N-hydroxyethylethylenediaminetriacetic acid per Faraday of current passed through the medium.

8. The process of claim 6 wherein the medium is electro-lyzed in contact with an essentially cadmium cathode.