CA1039231A - Electrolytic hydrodimerization process improvement - Google Patents

Abstract

ELECTROLYTIC HYDRODIMERIZATION PROCESS IMPROVEMENT

ABSTRACT OF THE DISCLOSURE
In a process for hydrodimerizing an olefinic nitrile, amide or ester by electrolyzing an aqueous solution of the olefinic starting material, quaternary ammonium cations and a conductive salt, formation of hydro-gen at the cathode can be substantially inhibited and the current efficiency of the process can be thereby significantly increased by including in the solution a nitrilocarboxylic acid compound such as ethylenediaminetetra-acetic acid or a salt thereof. Particularly good results are obtained when the solution also contains a boric acid, a condensed phosphoric acid or an alkali metal or ammonium salt thereof.

Description

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.ELECTROLYTIC HYDRODIMERIZ-ATION PROCESS IMPROVEMENT

! BACKGROUND OF THE INVENTION
Production of paraffinic dinitriles, dicarboxamides or di-carboxylates by electrolytic hydrodimerization of an alpha, beta-olefinic nitrile, carboxamide or carboxylate is well known, e.g.
from U.S. Patent Nos. 3,193,481 through 3,193,483 which issued `to Manuel M. Baizer on July 6, 1965. Although the process has been sufficiently attractive that it has been in commercial use for over seven years, efforts to develop improvements thereon -- 10 have been continued with particular emphasis on lowering electric power costs and mitigating electrode corrosion and fouling tendencies because of which it has been heretofore commercially preferabl~ to carry out the process with a cell-dividing membrane.
With the objectives of maintaining high electrolyte con-ductivity while employing an electrolysis medium containing organic salts in a proportion small enough for attractive use of a single-compartment (membraneless) cell, one approach to improvement of the process has been to use as the electrolysis medium an a~ueous solution of a mixture of quaternary ammonium and alkali metal salts together with the olefinic compound to be hydrodimerized. ~owever, all known variations of the process are characterized by some degree of inefficiency in use of the electrolyzing current, and this problem is typically even more significant in thoæ process variations that utilize such an undivided cell.

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C-14-5d~-0160 ' For example, not all of the electroreduction that occurs at the cell cathode takes the form of the desired hydroclimeriza-tion reaction.
Instead, a minor but significant proportion thereof normally resu~ts in generation of molecular hydrogen. This hydrogen ordinarily accumulates in the electrolysis offgas together with the oxygen produced at the anode and, in fact, the proportion of hydrogen in the offgas is a fairly accurate indicator of the proportion of consumed electrolysis current that was wasted on such hydrogen production. At relatively low concentrations of hydrogen in the offgas, the percentage by volume of hydrogen in the 10 offgas is generally about twice the percentage of current consumed in the electrolysis but wasted on undesired production of molecular hydrogen.
More specifically, the percentage of current consumed in the electrolysis but wasted on undeslred production of molecular hydrogen is normally equal to fiMy times the percentage by volume of hydrogen in the offgas divided by one hundred less the percentage by volume of hydrogen in the offgas, i. e., 50 x %H2/(100-%H2). For example, a concentration of 10%
by volume of hydrogen in an electrolysis offgas usually indicates that about 5, 5% of the current consumed in the electrolysis was wasted on rnolecular hydrogen production ancl, accordingly, that the current 20 efficiency of the hydrodimerization process was not possibly any greater than about 94. 5%.
Obviously, the higher the proportion of the electrolyzing current that produces molecular hydrogen rather than the desired hydrodimer, the greater the cost of production of a given quantity of the hydrodimer will be. Accordingly, a process improvement whereby an olefinic compound from the aforementioned class can be electrolytically hydrodimerized with a resultingly lowered production of molecular hydrogen and a thereby increased current efficiency is highly desirable, and it is an ob~ect of this . ~

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~3~3~L i invention to provide such an improvement. Aclditional objectives of the invention will be apparent from the following description and Examples in which all percentages are by weight except where otherwise noted.
SUMMARY OF THE INVENTION
It has now been discovered that in a process for hydrodimerizing an olefinic compound having the formula R2C=CR-X wherein -X is -CN, .;
-CONR2 or -COOR', R is hydrogen or R' and R' is Cl-C4 alkyl by electrolyzing an aqueous solution having dissolved therein at least about 0. l~o by weight of said ole1nic compound, at least about 10-5 gram mol 10 per liter of quaternary ammonium cations and at least about 0.1% by weight of conductive salt in contact with a cathode surface having a cathode potential sufficient for hydrodimerization of said olefinic compound, formation of hydrogen at the cathodic surface can be substantially inhibited, and the current efficiency of the process thereby significantly increased, by including in the solution at least one nitrilocarboxylic acid compound such as, for example, a nitriloacetic or nitrilopropionic acid compound having the formula Y2N~ Z--YN ~ CH2 ~ COOM wherein Y is hydrogen, +CH2~cOoM~ ~CH2 )m~l OH or Cl-C20 alkyl, Z, is a divalent C2-C6 hydrocarbon radical, M is hydrogen, alkali metal or 20 ammonium, m is 1 or 2, n is an integer from 0 to 4 and at least one Y is ~CH2 ~COOM or ~-~CH2 ) +1 OH. Particularly good results are obtained when the solution also contains a small amount of a boric acid, a condensed phosphoric acid or an alkali metal or ammonium salt thereof.
These improvements of the process are especially, though not exclusively :
useful when the process is carried out in a single-compartment cell, and in the production of adiponitrile, a nylon 66 intermediate, by the hydro-dimerlzation of acrylonitrile.
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DETAILED DESCRIPTION (~)F THE :[NVENTION
Olefinic compounds that can be hydrodimerized by the improved process of this invention include those having the structural formula R2C=CR-X wherein -X is -CN, -CONR2 or -COC)R', 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 an alkyl group containing a given number of -: , 10 carbon atoms while at least one other R', if present, is an alkyl group containing a different number of carbon atoms, Such compounds include olefinic nitriles such as, for example, acrylonitrile, methyacrylonitrile, crotononitrile, 2-methylenebutyronitrile, 2-pentenenitrile, 2-methylene-valeronitr1le, 2-methylenehexanenitrile, tiglonitrile or 2-ethylidene-hexanenitrile; olefinic carboxylates such as, for example, methyl acrylate, ethyl acrylate or ethyl crotonate; and olefinic carboxamides such as, for example, acrylamide, methacrylamide, N, N-diethylacryl-amide or N, N-diethylcrotonamide. Products of hydrodimerization of such compounds include those having the structural formula 20 X-CHR-CR2-CR2-CHR-X wherein X and R have the aforesaid significance, i. e., paraffinic dinitriles such as, for example, adiponitrile and ' 2, 5-dimethyladiponitrile; paraffinic dicarboxylates such as, for example, -;~ dimethyladipate and diethyl-3, 4-dimethyladipate; and paraffinic dicarbox-amides such as, for example, adipamide, dimethyladipamide and N, N'-dimethyl-2, 5-dimethyladipamide. All of such hydrodimers are useful in the manufacture of high molecular weight condensation polymers, e. g. by reaction with dihydroxy or dicarboxylic compounds, and in the case of the dinitriles, as intermediates which can be hydrogenated by '~ ' .

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known processes to prepare paraffinic diamines that are similarly useful in the manufacture of high molecular weight condensation `;
polymers. Other examples of the various olefinic compounds that can be hydrodimerized by the process of this invention and the hydrodimers thereby produced are identified in the aforecited U.S~ Patent Nos. 3,193,481-483.
The invention is herein described in terms of electrolyzing an aqueous solution having dissolved therein certain proportions of the olefinic compound to be hydrodimerized, quaternary ammonium cations and a conductive salt. Such use of the term "aqueous solution" does not irnply, however, that khe electrolysis medium may not also contain an undissolved organic phase. To the con-trary, the process of this invention can be quite satisfactorily carried out by electrolyzing the aqueous solution in an electroly-sis medium containing the recited aqueous solution and a dis-persed but undissolved organic phase in any proportions at which the aqueous solution is the continuous phase of the electrolysis medium. Hence in some embodiments of the invention, the aqueous solution may be suitably electrolyzed in an electrolysis medium containing essentially no undissolved organic phase, by which is meant either no measurable amount of undissolved organic phase or a minute proportion of undissolved organic phase having no significant effect on the hydrodimer selectivity achieved when the aqueous solution is electrolyzed in accordance with the process of this invention. Such a minute proportion, if present, would be typically less than 5% of the combined weight of the aqueous solution and the undissolved organic phase in the electrolysis medium. In other embodiments, the process of this invention can be carried out by electrolyzing the aqueous solution in an electrolysis medium consisting essentially of the recited aqueous solution and a dispersed but undissolved organic phase in a larger proportion (e.g. from about 5 to 25% or ~ 9~Z3~ :`
more of the combined weight of the aqueous solution and the undissolved organic phase in the electrolysis medium) which may or may not signifi-cantly affect the hydrodimer selectivity depending on other conditions of the process. In continuous process embodiments involving recycle of ~ ;
unconverted olefinic compound and whether present in a minute or larger proportion, such an organic phase would be normally made up mainly (most commonly at least about 75%) of the olefinic compound to be hydrodimerized and the hydrodimer product with some small amounts of organic hydro- ;
dimerization by-products, quaternary ammonium cations, etc. possibly also present. Typically, such an organic phase contains at least about lO~o, :
preferably between about 15% and about 50%, and even more desirably between about 20% and about 40~/o of the oleeinic compound to be hydro-dimerized. In any event, however, the concentrations of the constituents dissolved in the aqueous solution to be electrolyzed, as set forth in this specification and the appended claims, are with reference to the recited :
aqueous solution alone and not the combined contents of said aqueous so-lution and an undissolved organic phase which, as aforesaid, may be present but need not be present in the electrolysis medium as the process of this invention is carried out. On the other hand, the weight percentages 20 of undissolved organic phase described in this disclosure ~including the Examples) and the appended claims are based on the combined weight of the aqueous solution and the undissolved organic phase in the electrolysis medium.
Referring now to the constituents of the aqueous phase, the olefinic `~
compound to be hydrodimerized will be present in at least such a pro-portion that electrolysis of the solution, as described herein, will result in a substantial amount of the desired hydrodimer being produced. That proportion is generally at least about 0.1% of the aqueous solu-tion, more C-14-54-0160 ~

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typically at least about 0. 5% of the aqueous solution and, in some embodi-ments 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 compound in the solution may permit the carrying out of the process with the solution containing relatively high proportions of the olefinic compound, e. g. at least about 5% or even 10%
:: or more, but in most 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 many of those embodiments, preferably not more than ; 10 about 1. 8% of the olefinic compound.
The minimum required proportion of quaternary ammonium cations is very small. In general, there need be only an amount sufficient to provide the desired hyclroclimer selectivity (typically at least about 75%) although much higher proportions can be present if desired or- convenient.
. In most cases, the quaternary ammonium cations are present in a concen-tration of at least about 10-5 gram mol per liter of the aqueous solution. ~;
l~ven more typically their concentration is at least about 10-4 gram mol `
per liter of the solution and, in many embodiments, preferably at least about 10-3 gram mol per liter. l~lthough higher proportions may be 20 present in some cases, as aforesaid, the quaternary ammonium cations are generally present in the aqueous solution in a concentration lower than about 0. 5 gram mol per liter and even more usually, in a concen-tration not higher than about 10 1 gram mol per liter. In some preferred embodiments, the concentration of quaternary ammonium cations in the solution is at least about 2 x 10-3 gram mol per liter but not more than about 5 x 10-2 and, in many cases, not more than about 2 x 10-2 gram mol per liter.
The quaternary ammonium cations that are present in such ''' :.

` - 8 -,: : , 3~`~31 concentrations are those positiveIy~charged ions in which a nitro-gen atom has a valence of five and is directly linked to other ~' ' atoms (e.g. carbon) satisfying four fifths of that valence. Such cations may be cyclic, as in the case of the piperidiniums, ' ' pyrrolidiniums and morpholiniums, but the~ are generall~ of the type in which the nitrogen atom is directly linked to a total of four monovalent organic groups from the group consisting of alkyl and ar~lradicals and combinations thereof. The aryl groups con-tain typically from six to twelve carbon atoms and preferably ~ ;
only one aromatic ring as in, for example, a phenyl or benzyl radical. The'alkyl groups can be'straight-chain, branched or ; cyclic and each typically contains from one to tweIve carbon atoms.
Although'~uaternary ammonium cations containing a combination of such alkyl and ar~l groups (e.g. benz~ltriethylammonium ions) can be used, many embodiments of the'invention are pre~erably carried ;'' out with'tetraalkylammonium ions and superior res'ults are general-ly obtained with'the use of those'containing at least three C2-C6 ' alkyl gxoups and a total of from 8 to 24 carbon atoms in the four alkyl groups, e.g. tetraethyl-, ethyltripropyl-, ethyltributyl-, ethyltriamyl-, ethyltrihexyl-, octyltriethyl-, tetrapropyl-, methyltripropyl-, decyltripropyl~, meth~ltributyl-, tetrabutyl-, amyltributyl-, tetraamyl-, tet'rahe'xyl-, ethyltrihexyl-, diethyl-dioctylammonium and many others such'as the bis-quaternar~ com~
pounds - e.g. N-trimethyl-N'-trimethylenediammonium di-p-toluene-sulfonate'referred to in the'a~orecited U.S. Patent Nos. 3,193,481-483'as well as other references such as U.S. Patent 3,6B9,382 issued September 5, 1972 to Fox et al. Most practical from the economic standpoint are generall~ those tetraalkylammonium ions in which each alkyl group contains two to five carbon atoms, e.g.
diethyldiamyl-, tetrapropyl-, tetrabutyl-, amyltripropyl-, tetra-amylammonium r etc. Such'cations can be'incorporated into the a~ueous solution to be eIectrolyzed in any convenient manner, ' e.g. b~ dissolving the quaternary ammonium hydroxide or a salt thereof in the solution in the amount _g_ "

required to provide the desired quaternary ammonium cation concentration.
The type of conductive salt employed is not usually critical to inhibition of hydrogen formation by use of a nitri:Locarboxylic acid compound as described herein. Hence the conductive salt can be a quaternary ;:
ammonium salt of the kind used heretofore in commercial practice of the ;
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- electrolytic hydrodimerization (EHD) process, for example a tetraalkyl-ammonium (e. g. tetraethylammonium! sulfate, alkylsulfate (e. g. ethyl-sulfate) or arylsulfonate (e. g. toluene sulfonate). Although organic salts of that general type can be employed as the conductive salt in a divided 10 or single-compartment cell, it is generally preferred to use an alkali metal conductive salt, i. e., a salt of sodium, potassium, lithium, cesium ;;or rubidium, in single-compartment EHD cells. When such a salt is used, those of lithium and especially sodium and potassium are generally preferred for economic reasons.
Also preferred for such use are the salts of inorganic and/or polyvalent acids, e. g. a tetraalkylamm3nium or alkali metal ortho-phosphate, borate, perchlorate, carbonate or sulfate, and particularly an incompletely~substituted salt of that type, i. e., a salt in which the ; ~ ~ `
anion has at least one valence thereof satisfied by hydrogen and at least 20 one other valence thereof satisfied by an alkali metal. Examples of such ,`
;' salts include disodium phosphate tNa2HPO4), potassium acid phosphate(K~2PO4), sodium bicarbonate ~NaHCO3) and dipotassium borate ~.
(K2HBO3). Also useful are the alkali metal salts of condensed acids such as pyrophosphoric, metaphosphoric, metaboric, pyroboric and the like `
(e. g. sodium pyrophosphate, potassium rnetaborate, borax, etc. ) and/or the products of partial or complete hydrolysis of such condensed acid salts. I~epending on the acidity of the aqueous solution to be electrolyzed, the stoichiometric proportions of such anions and alkali metal cations in - lQ -3~
the solution may correspond to a mixture of two or more OI 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. difEerent alkali metals, and/or different acids) are intended to be within the scope of the expressions "conductive salt"
and "alkali metal phosphate, borate, perchlorate, carbonate or sulfate"
as used in this specification and the appended claims. Any of the alkali metal salts may be dissolvedin the aqueous solution as such or otherwise, e. g. as the alkali metal hydroxide and the acid necessary to neutralize 10 the hydroxide to the extent of the desired acidity of the aqueous solution.
The concentration o~ 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 advantageous conductivity levels are achieved when the solution has `~
dissolved therein at least about 1% of the conductive salt or, even more preferably, at least about 2% of such a salt. In many cases, optimum process conditions include the solution having dissolved therein more than 5% (typically at least 5. 5%) of the conductive salt. When an alkali 20 metal conductive salt is used, the maximum amount of salt in the solution is typically limited only by its solubility therein, which varies with the particular salt employed. With salts such as sodium or potassium phosphates, it is generally most convenient when the solution contains ~;
between about 8% and about 13% of such a salt or mixture thereof.
As aforesaid, generation of molecular hydrogen at the cathode of a li process of the type discussed herein can be substantially inhibited by ' including in the aqueous electrolysis medium at least one nitrilocarboxylic acid compound such as, for example, a nitriloacetic or nitrilopropionic .'` ':

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acid compound having the formula Y2N~ Z -YN ~ CE~2 ~ COOM
wherein Y is a monovalent radical such as hydrogen, ~ CH2~ COOM, +CH2 )m+l OH or Cl -C20 alkyl (e. g. ethyl, n-propyl, tert-butyl, n-hexyl, n-decyl, etc. ); Z is a divalent C2-C6 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 most desirably, sodium or potassium) or amrnonium; m is 1 or 2; n represents the number of repeating ~ Z--YN-~ groups, if any, and may be 0, 1, 2, 10 3 or 4; and at least one Y in said formula is ~CH2~COOM or +CH2 )m, lOH, i, e., the nitrilocarboxylic acid compound contains at least one ~CH2 ~COOM or +CH2 )`m+l OH group in addition to the ~ CH2 ~ COOM group on the right-hand end of the generic nitrilo-carboxylic acid compound formula as shown hereinbefore. At least one such additional ~ CH2 ~ COOM or ~CH2 )m+l OH group is y desirably attached to the nitrogen atom on the left-hand end of that generic 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 of the nitrogen atoms in the 20 repeating ~ Z--YN ~ units may have such an additional ~CH2 ~ COOM
or ~ CH2 ~ OH group attached thereto.
Preferably, but not necessarily, there are at least two -~CH2 ~ COOM groups in the nitrilocarboxylic acid compound employed in this invention. It is also generally desirable for each Y in the compound to be ~CH2 ~ COOM or ~ CH2 ~ OH, for Z to be C2-C4 alkylene -and for n to be 0, l, 2 or 3 (even more desirably 0, 1 or 2 and most preferably 1 or 2). Representative of such compounds are nltrilotriacetic acid, N-hydroxyethylethylenediaminetriacetic acid, diethylenetriamine-`',:. ~ , :, .... .

~ C-14-54-0160 ~39~3~ :

pentaacetic acid, N, N-di(2-hydroxyethyl)glycine, ethylenediaminetetra-propionic acid and, typically most favored, ethylenediaminetetraacetic acid (hereinafter sometimes represented as EDTA). In the low concen- ~ ~`
trations generally employed, they may be added to the electrolysis medium of the present process as acids orJ usually more conveniently, as partially or fully neutralized salts thereof (e. g. the ammonium or alkali metal salts of such acids). In accordance with procedures known in the art, alkali metal salts of such nitrilocarboxylic acid compounds can be ;
prepared by reacting the appropriate amine (e. g. ethylenediamine) with :, an alkali metal salt of chloracetic acid in the presence of an alkali metal hydroxide, or with hydrogen cyanide and formaldehyde and then an alkali ~
metal hydroxide, or with ethylene glycol to provide hydroxyethyl `
substituents on the nitrogen atom(s) of the amine and then reacting the hydroxyethyl-substituted amine with an alkali metal hydroxide in the presence of cadmium oxide to convert the hydroxyethyl substituents to ;;
alkali metal acetate substituents in the proportion desired, or with acrylo-nitrile in the presence of a base (e. g. sodium hydroxide) and then h~rdrolyzing the cyanoethylated amine in the presence of an alkali m~tal ; ! hydroxide, ~`
The minimum concentration of the nitrilocarboxylic acid compound in the aqueous electrolysis medium is only that sufficient to inhibit formation of molecular hydrogen at the cathodic surface of the process.
In general, at least about 0. 025 millimol of the nitrilocarboxylic acid compound per liter of the solution is desirable and at least about 0.1 millimol per liter is preferred. In most cases having greater attraction ~-~
' for commercial use, at least about 0. 5 millimol per liter is more desirable and at least about 2. 5 millimols per liter usually provide even better results. Generally, not more than about 50 millimols per liter are ~ ~03~3~ :
required, although higher concentrations may be employed if desired.
Even more typically, economic results are better when -the concentration of the nitrilocarboxylic acid compounds in the solution is not greater than 25 millimols per liter. With reference to such concentrations, it should be understood that the nitrilocarboxylic acid compounds used herein may degrade under the conditions of the process, e. g, to compounds that have lower molecular weight and/or fewer ~H2 ~COOM or ~CH2 ) +1 OH groups but which nevertheless provide the advantages of this invention in substantial measure, and accordingly such degradation : . j 10 products should be considered as equivalent to the undegraded nitrilo-carboxylic acid compounds to the extent that they provide the advantages thereof, when measuring or otherwise identi~ying a nitrilocarboxylic acid compound concentration with reference to the process oE this invention.
Mixtures of two or more of the aforedescribed nitrilocarboxylic acid compounds may also be used in the process of this invention and accordingly, such mixtures are meant to be within the scope of the ~ -expression "a nitrilocarboxylic acid compound" as used in this disclosure ; and the appended claims.
In substantial measure when carrying out the present process in a 20 cell divided by a cation-permeable membrane and particularly when carrying out the process in a single-compartment cell, generation of hydrogen at the cathode is even more significantly inhibited by including in the electrolysis medium a boric acid, a condensed phosphoric acid or an alkali metal or ammonium salt thereof. The boric acid or borate may be added to the solution as orthoboric acid, metaboric acid or pyroboric - acid and then neutralized to the desired solution pH, e. g. with an alkali metal (preferably the cation of the conductive salt) or ammonium hydroxide or as a completely or incompletely substituted alkali metal or ammonium . .

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salt of such an acid (e. g. disodium or monosodium orthoborate, potassium metaborate, sodium tetraborate or the hydrated rorm thereof commonly called borax). The condensed phosphoric acid or phosphate may be added as a polyphosphoric (e. g. pyrophosphoric or triphosphoric) acid and then neutralized to the desired solution pH or as a completely or incompletely substituted alkali metal or ammonium salt thereof (e. g.
tetrasodium pyrophosphate, potassium hexametaphosphate or ammonium triphosphate).
In general, the condensed phosphoric acids and their alka:Li m~tal .
10 or ammonium salts tend to hydrolyze in the electrolysis medium at rates dependent on their concentration, the solution pH, etc. It is believed, however, that the products of such hydrolysis continue to inhibit the generation of hydrogen at the cathode so long as they remain condensed ; ~ :
to at least some degree, i. e., so long as they have not been hydrolyzed to the orthophosphate form, and hence the preferred concentrations of such condensed phosphoric acid compounds are herein expressed in terms of weight percent of a condensed phosphoric acid (which may be the one originally added to the solution or hydrolysis products thereof having a lower but conventionally recognizable degree of molecular condensation) .

20 or the molar equivalent of an alkali metal or ammonium salt thereof.

When such a condensed phosphoric acid is used in the process of this . .
invention, and particularly in a single-compartment cell having a metallic anode (e. g. an anode comprising a ferrous metal such as carbon steel, alloy steel, iron or magnetite), it is generally advantageous for the solution to contain at least about 0. 01%, preferably between about 0. 02%
and about 3%, and often most desirably between about 0. 02% and about

2% of the condensed phosphoric acid or the molar equivalent (molecularly equivalent amount) of an alkali metal or ammonium salt thereof.

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The aforementioned boric acids and alkali metal or ammonium salts thereof, on the other hand, tend to relatively rapidly form in the electrolysis medium a variety of boron-containing ions havmg relatlve proportions normally dependent on their concentrations, the solution pH, etc., and generally including both uncondensed (i. e., orthoborate) and , condensed (e. g. metaborate, tetraborate, polymeric, ring-containing, etc. ) ions, regardless of whether the acids and/or salts originally added to the electrolysis medium were in condensed or uncondensed form at ~ ;
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that time. In other words, condensed borates (e. g. tetraborates) ~-normally convert in the electrolysis medium in part to orthoborate ions and in part to other condensed borate ions, while orthoborates added as ~
such generally form various condensed borate ions, depending largely ~ `
on the solution pH, etc. In any event, it appears that the boron-containing ions are effective for purposes of this invention whether they are present in condensed or uncondensed forms or a mixture thereof and accordingly, ~-preferred concentrations of the boric acids or salts are herein expressed (on the basis of one liter of solution) in terms of gram atoms of boron which may be present in the ionic form of condensed or uncondensed borates or other boron-containing moieties provided by interaction ` -~;
between the electrolysis rnedium and the boric acids and/or salts added thereto. When such boric acids or salts are used in the process of this invention, and particularly in a single-compartment cell having a ~.:
metallic anode (e. g. an anode comprising a ferrous metal such as ;1 carbon steel, alloy steel, iron or magnetite), it is generally desirable for the boron concentration in the electrolysis medium to be at least about 0. 01 and preferably 0. 02 gram atom of boron per liter of solution.
It is generally not necessary that the boron concentration in the solution be greater than about 0. 9 gram atom per liter and in many cases it need ~03~ 3~ ~
not be greater than about 0. 5 gram atom per liter, although higher concentrations are not necessarily detrimental and may be advantageous, e. g. if it is intended that a boric acid salt provide a substantial portion of the electrical conductivity of the electrolysis medium, In most cases, the pH of the bulk of the electrolysis medium is greater than two, preferably at least about five, more preferably at least about six and most conveniently at least about seven, especially when the process is carried out in a single-compartment cell having a metallic anode. On the other hand, the overall solution pH is generally 10 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 than about ten.

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, The temperature of the solution may be at any level compatible ,~ with existence as such of the solution itself, 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 compound and hydrodimer, among other factors, but in 20 hydrodimerization of acrylonitrile to adiponitrile, electrolysis temperatures of at least about 25 are usually preferred and those between about 40 and about 65C. are especially desirable.
As is well-known, electrolytic hydrodimerization of an olefinic compound having a formula as set forth hereinbefore must be carried out in contact with a cathodic surface having a cathode potential sufficient for hydrodimerization of that compound. In general, there is no minimum current density with which the present process can be carried out at such a cathodic surface but in most cases, a current densit;s~ of at least about ., ~

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:1~39;~3~l 0. 01 amp per square centimeter of the cathodic surface is used and a current density of at least about 0. 05 amp per square centimeter of the ; cathodic surface is usually preferred. Although higher current densities may be practical in some instances, those generally employed in the present process are not higher than about 1. 5 amps per sqware centimeter .. . .
and even more typically not higher than about 0. '75 amp per square centi- ~-meter of the aforedescribed cathodic surface. Depending on other - ~ -process variables, current densities not higher than about 0. 5 amp per square centimeter may be preferred in som~ embodiments of the process.
Although not necessary, a liquid-impermeable cathode is usually -preferred. With the use of such a cathode, the aqueous solution to be electrolyzed is generally passed between the anode and cathode at a linear velocity with reference to the adjacent cathodic surface of at least about one foot per second, preferably at least about two feet per second ~;
and even more preferably between about three and about eight feet per ,: . , second although a solution velocity up to twenty feet per second or higher can be employed, if desired. The gap between the anode and cathode can be very narrow, e. g. about 40 mils or less, or as wide as one-half inch ;
or even wider, but is usually most conveniently of a width between about ; 20 60 mils and about one-quarter inch. In the process of this invention, the cathodic surface can be made of virtually any material at which the requi-site cathod~ potential can be provided and which is not dissolved or corroded at an intolerable rate. In general, the process can be carried out with a cathode consisting essentially of cadmium, mercury, thallium, lead, -~
zinc, manganese, tin or graphite, by which is meant that the cathodic surface contains a high percentage (generally at least about 95% and preferably at least about 98%) of one or a combination (e. g. an alloy) of two or more of such materials, but it may contain a small amount of one .,~
. " . . . .

~; ,, ~ 1~39Z3~ :
or more other constituents that do not alter the nature ol the cathodic surface so as to prevent substantial realization of the advantages of the present invention, particularly as described herein. Such other consti-tuentsJ if present, are desirably other m~terials having relative]y high hydrogen overvoltages but preferably not such materials of relatively low hydrogen overvoltage as copper or nickel in a concentration substantially higher than about 0. 05% or, even more desirably, about û. 02%, based on the total composition of the material of which the cathodic surface is :- :
composed. ~f particular preference are cathodes consisting essentially ;~ 10 of cadmium, lead, zinc, manganese, tin, graphite or an alloy of one of such metals, and especially cathodes consisting essentially of cadmium.
,, ~ . .
Best results are usually obtained with a cathodic surface having a cadmium content of at least about g9. 5%, even more typically at least about 99. 8%
and m~st desirably at least about 99. 9% as in ASTM Designation B440-66T ;
,, .; . ~
(issued 1966).
Cathodes employed in this invention can be prepared by various techniques such as, for example, electroplating of the desired cathode material on a suitable-shaped substrate of soms other material, e. g. a metal having greater structural rigidity, or by chemically, thermally 20 and/or mechanically bonding a layer of the cathode material to a similar substrate. Alternatively, a plate, sheet, rod or any other suitable configu-ration consisting essentially of the desired cathode material may be used ~^
without such a substrate, if convenient.
, The process of this invention can be satisfactorily carried out in a divided cell having a cation-permeable membrane, diaphragm or the like separating the anode and cathode compartments of the cell in such a way that the aqueous solution containing the olefinic compound to be hydro-dimerized is not in contact with the anode of the cell. However, it is ''. : .

19 - ' , .

C - 1 4 - 5~ - 01 60 ;

~ lfl)39~3~ ~ .
especially advantageously carried out in a cell that is not divided in that manner, i. e., in a cell in which the anode or anodes and the cathode or cathodes are in direct physical contact with the solution being electrolyzed.
In fact, and particularly without the presence of a boric or condensed phos-; . ~~
phoric acid or salt thereof in the preferred concentrations described hereinbefore, it has been found that the aforementioned nitrilocarboxylic acid compounds, and especially in the concentrations cited hereinbefore, .
generally substantially inhibit the corrosion of metallic anodes when used in such undivided cells. AnQdes whose corrosion may be thereby inhibited , include those composed of, for example, platinum, ruthenium~ nickel, lead, lead dioxide and, of particular advantage when the conductive salt ~;
, is a phosphate, borate or carbonate, fefrrous materials such as carbon steels, alloy steels, iron and magnetite.
f f In fact, it is an especially preferred embodiment of the invention ~ ~
.:
which is carried out in a single-compartment cell having an anode comprising a ferrous metal and with the use of an alkali metal phosphate, borate or carbonate conductive salt and an electrolysis medium having a pH not substantial~y below seven. Of great interest from the economic standpQint are those embodiments employing an anode consisting essentially of carbon steel, exemplary compositions of which are listed in the 1000, : ;
1100 and 1200 serles 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 Volurne 1, Metals Handbook, 8th Edition (1~61) published py the American Society for Metals, Metals Park, Ohio.
In general, the carbon steels that are 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 C-14-54-0160 `

1~3~;~3~

.
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 1. 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, sheet, strip, rod or any ~
":
other configuration suitable for the use intended. In a preferred embodi-ment, however, the anode is in the form of a sheet (e. g. of cold-rolled . . ~ .
carbon steel) essentially parallel to and closely spaced from a cathodic surface of approximately the same dimensions.
, . ..
Although the invention described and claimed herein is not to be !~' ' regarded as limited to any particular mechanism proposed therefor, it is presently believed that the nitrilocarboxylic acid compounds (and probably to a lesser extent, if present, the boric and/or condensed phosphoric acid compounds) at least partially sequester heavy metals which tend to accumu--: ::
late in the electrolysis medium (e. g. as a result of corrosion of the cathode ~--and/or, with use of an undivided cell, corrosion of the anode) and that such sequestration inhibits the deposition of those metals on the cathode of the ., cell. It is further believed that unsequestered heavy metals (or oxides and/ ;` ~ ~
. ~ .
or hydroxides thereof) tend to form colloidal particles in the electrolysis 20 medium and aMer such depositionJ alter the nature of the cathodic surface so as to increase the generation of molecular hydrogen at the expense of process current efficiency. Those beliefs are mainly based on observations that increases in hydrogen production normally accompany increased depo~
;l sition on the cathode of a relatively dense precipitate which has been identi~

' fied as essentially completely composed of such heavy metals ~principally .:
iron in an undivided cell having a steel anode) and their oxides and hydroxides, and that deposition of the precipitate is substantially inhibited ~`~
; by use of the process improvement described and claimed herein. `

., ~, . ~ ~ , :
,:.;. , . :

' ~' '.

~39f~3~
The following specific examples of the process of this invention are included for purposes of illustration only and do not imply any limitations on the scope of the invention.
;~ Example I
- In a continuous process, an aqueous solution having dissolved therein approximately 1. 5% acrylonitrile, 1. 2% adiponitrile, 0. 2% acrylo-nitrile EHD byproducts, 4 x 10-3 gram mol per liter of ethyltributyl-ammonium cations, 10% of a mixture of incompletely-substituted sodium `
orthophosphates corresponding to the solution pH of 9 (approximately ~ ;
Nal 9Hl lPO4), 0. 3% of tetrasodium pyrophosphate and 0. 018~o (0. 5 millimols per liter) of the tetrasodium salt of ethylenediaminetetraacetic acid (EDTA) was circulated at 55C. and a velocity between 4 and 4. 5 feet per second through an undivided electrolytic cell having an AISI 1020 , (0. 2%) carbon steel anode separated by a gap of about 90 mils from a cathode composed of cadmlum conforming to ASTM Designation B440-66T (at least 99. 9% Cd). The solution, which also had entrained ;
therein approximately 0. 8% by weight of an organic phase containing about 55% adiponitrile, 28% acrylonitrile, 9% acrylonitrile EHD by-' products and 8% water, was electrolyzed as it passed through the cell with 20 a voltage drop across the cell of about 3. 8 volts and a current density of about 0.16 amp per square centimeter of cathodic surface and then fed into a decanter for equilibration with an accumulated upper layer having approximately the composition of the aforedescribed organic phase and withdrawal of equilibrated lower (aqueous) layer for recycle through the cell. After 182 hours of electrolysis during which acrylo-nitrile and water were continuously added to the circulating aqueous `I solution and an equivalent amount of product was continuously removed Il from the decanter upper layer, it was found that acrylonitrile in the solution .

- 1 4 - ~4 -01 60 . ,;

~1)3~3~l ;
had been converted to adiponitrile with an average molar selectivity of ~:
87. 6%, the carbon steel anode had corroded at the average rate of 18 mils per year and the volume percentage of hydrogen in the electrolysis offgas ~ .
had averaged 6. 4% with a final value of 8. 4%.
Comparative Example A ~ .
When Example I was repeated except that the tetrasodium salt of :
EDTA was omitted, it was found after 78 hours that the average adiponitrile .

. molar selectivity had been 86. 6%, the anode had corroded at essentially . .
the same average rate and the volume percentage of hydrogen in the offgas had averaged 11. 3% with a final value of 24. 3%.
Example II
In a continuous process, an aqueous solution having dissolved therein approximately 1. 6% acrylonitrile, l. 2% adiponitrile, 0. 2% :
acrylonitrile EHD byproducts, ethyltributylammonium cations in a concentration that varied between 9 and 25 x 10-3 gram mol per liter, . ~ :
9% of a mixture of incompletely-substituted sodium orthophosphates :
corresponding to the solution pH of 9, 0.1% of tetrasodium pyrophosphate and 0. 05% tl. 4 millimols per liter) of the tetrasodium salt of EDTA was circulated at a temperature between 50 and 55C. and a velocity between 20 three and four feet per second through an undivided electrolytic cell having an ~ISI 1020 carbon steel anode separated by a gap of 125 mils .;~
from a cathode composed of a rolled sheet of cadmium having the composition described in Example 1. The solution, which also had ~ ~ .
.
entrained therein approximately 4% by weight of an organic phase containing about 54% adiponitrile, 29% acrylonitrile, 9% acrylonitrile EHD byproducts and 8% water, was electrolyzed as it passed through the cell with a voltage ~

drop across the cell of 4. 5 volts and a current density of 0. 23 amp per ` i`
'~
square centimeter of cathodic surface and then fed into a decanter for

3~3~ ~ :
equilibration and recycle o ower layer as in Example I. After 325 hours ~.
of electrolysis during which acrylonitrile and water were continuously added to the circulating solution and an equivalent amount of product was continuously removed, it was found that acrylonitrile in the solution had been converted to adiponitrile with an average molar selectivity of 86.1%, ~ ~
the steel anode had corroded at the average rate of 35 mils per year and ~:
, .-; .~ , the volume percentage of hydrogen in the electrolysis offgas had been . stable throughout the run at 8 to 10%. ~:

Example III

.. 10 In a continuous process, an aqueous solution having dissolved ,...................................................................... ...
therein approximately 1. 6~o acrylonitrileJ 1. 2% adiponitrile, 0. 2%

. acrylonitrile EHD byproducts, 5. 8 x 10-3 gram mol per liter of ethyltri-"
butylamrnonium cationsJ 10% of a mixture of incompletely-substituted sodium orthophosphates corresponding to the solution pH of 9J 0.1% of :

: ~ tetrasodium pyrophosphate and 0. 05% (1. 4 millimols per liter) of the ~ tetrasodium salt of EDTA was circulated at 55C. and a velocity between ~;

4 and 4. 5 feet per second through an undivided electrolytic cell having an , . .
AISI 1020 carbon steel anode separated by a gap of 107 mils from a ` cathode composed of a rolled sheet of cadmium having the composition : 20 described in Example I. ~he solutionJ which also had entrained therein approximately 1% by weight of an organic phase containing about 54~0 adiponitrileJ 29% acrylonitrileJ 9% acrylonitrile EHD byproducts and 8%
i waterJ was electrolyzed as it passed through the cell with a voltage drop ,',;! of 4, 7 volts and a current density of 0. 27 amp per square centimeter of . :-:! cathodic surface and then fed into a decanter for equilibration and recycle of lower layer as in Examples I and II. After 776 hours of electrolysis during which acrylonitrile and water were continuously added to the cir-culating solution and an equivalent amount of product was continuously -t4-54-()160 ~ ~39;~3~
removed, it was found that acrylonitrile in the solution had been converted to adiponitrile with an average molar selectivity of 86.1%, the steel anode ; ::
had corroded at the average rate of 34 mils per year and the volume percentage of hydrogen in the electrolysis offgas had gradually increased but to a final value no greater than 15%.
Example IV .
,.
In a continuous process, an aqueous solution having dissolved therein approximately 1. 4% acrylonitrile, 1. 2% adiponitrile, 0. 2%
acrylonitrile EHD byproducts, 6. 8 x 10-3 gram mol per liter of 10 ethyltributylammonium cations, 10% of a r~lixture of incompletely-substi-tuted sodium orthophosphates corresponding to the solution pH of 9, 0. 4% (11. 3 millimols per liter) of tetrasodium ethylenediaminetetraacetate :
and 2% of sodium tetraborate ~Na2B4{)7) corresponding to 0. 43 gram atom of boron per liter of the solution was circulated at 55~C. and a velocity ~:
of f~ur feet per second through an undivided electrolytic cell having an AISI 1020 carbon steel anode separated by a gap of 93 mils from a cadmiurn cathode having the composition described in Example I. The solution, which also had entrained therein approximately 0 8% by weight of an organic phase containing about 58% adiponitrile, 25. 5% acrylo- ~ :
20 nitrile, 8. 5% acrylonitrile EHD byproducts and 8% water, was electrolyzed as it passed through the cell with a voltage drop across the cell averaging 3. 85 volts and a current density of 0.16 amp per square centimeter of ;`~
cathodic surface in contact with the solution and then fed into a decanter ~ .-for equilibration and recycle of lower layer as in the previous Examples.
, After 288 hours of electrolysis during which acrylonitrile and water were :~
. continuously added to the circulating solution and an equivalent amount of product was continuously removed, it was found that acrylonitrile in the solution had been converted to adiponitrile with an average molar ''~

'!' ` ' . ~ ' ~L~3~3~
selectivity of 87. 7~0, the carbon steel anode had corroded at the average . rate of 15 mils per year and the volume percentage o:E hydrogen in the electrolysis offgas had averaged less than 10%.

Example V :
. ., -, . In a continuous process, an aqueous solution having dissolved -~
therein approximately 1.1% acrylonitrile, 1.1% adiponitrile, 0. 2%
.~. acrylonitrile EHD byproducts, ethyltributylammonium cations in a :
concentration that varied between 5.1 and 8. 7 x 10-3 gram mol per liter, :. 10. 3% of a mixture of incompletely-s~bstituted sodium orthophosphates corresponding to the solution pH Oe 9 and 0. 3~0 (8. 5 millimols per liter) of the tetrasodium salt of EDTA was circulated at 50-55C. and a velocity of 4. 5 feet per second through an undivided electrolytic. cell having an AISI 1020 carbon steei anode separated by a gap of 107 mils :l from a cathode composed of cadmium having the composition described ;
in Example I. The solution, which also had entrained therein .
approximately 4~0 by weight of an organic phase containing an average of ;' about 61% adiponitrile, 21% acrylonitrile, 10% acrylonitrile EHD byproducts and 8% water, was electrolyzed as it passed through the cell with a voltage drop across the cell averaging 4. 35 volts and a current density averaging about 0. 22 amp per square centimeter of cathodic surface ; -~
and then fed into a decanter for equilibration and recycle of lower layer as in previous Examples. After 159 hours of electrolysis during which acrylonitrile and water were continuously added to the circulating solution and an equivalent amount of product was continuously removed, it was found that acrylonitrile in the solution had been converted to ~ :
adiponitrile with an average molar selectivity of 88. 3%, the carbon steel anode had corroded at the average rate of 50 mils per year and the volume percentage of hydrogen in the electrolysis offgas had averaged 5%.
';

-.,.- . :
:~ .

C-14-S4-0160 ~
' ~(1 39~31 Example VI
In a continuous process, an aqueous solution having dissolved therein an average of approximately 1.1% acrylonitrile, 1.1% adiponitrile, 0. 2% acrylonitrile EHD byproducts, 1. 7 x 10-3 gram mol per liter of tetrabutylammonium cations, 12. 2% of a mixture of incompletely-substi-tuted sodium orthophosphates corresponding to the solution pH of 10 ( ppr ximately Na2. l~o. gP4) and 0. 3% (8. 5 millimols per liter) of the tetrasodium salt of EDTA was circulated at 50C. and a velocity of four feet per second through an undivided electrolytic cell having an AISI 1020 10 carbon steel anode separated by a gap of 107 mils from a lead cathode.
The solution, which also had entrained therein approximately 4% by weight of an organic phase containing an average of about 61% adiponitrile, 21%
acrylonitrile, 10% acrylonitrile EHD byproducts and 8% water, was electrolyzed as it passed through the cell with a voltage drop across the cell averaging 4. 25 volts and a current density of 0. 22 amp per square centimeter of cathodic surface and then fed into a decanter for equili~
bration and recycle of lower layer as in previous Examples. After 154 hours of electrolysis during which acrylonitrile and water were con-tinuously added to the circulating solution and an equivalent amount of 20 product was continuously removed, it was found that acrylonitrile in the solution had been converted to adiponitrile with an average molar ` selectivity of 82. 2%, the steel anode had corroded at the average rate of about 60 mils per year and the proportion of hydrogen in the electrolysis offgas had averaged about 2% by volume.
` Comparative Example B
In a continuous process, an aqueous solution having dissolved therein approximately 2% acrylonitrile, 1% adiponitrile, 0. 2% acrylo-nitrile EHD byproducts, 1. 6 x 10-2 gram mol per liter of ethyltributyl-' : ' . i .. ... . .. .
.... . , .. .. .. . . , ~-14-54-0160 ~39~23~
ammonium cations and 11. 3% of a mixture of incompletely-substituted ::
sodium orthophosphates corresponding to the solution pH of 10 and devoid of any nitrilocarboxylic acid compound was circulated at 502C. and a velocity of four feet per second through an undivided electrolytic cell having an AISI 1020 carbon steel anode separated by a gap of 107 mils from a lead cathode of the type employed in Example VI. The solution, which also had entrained therein approximately 4% by weight of an organic phase containing an average of about 47% adiponitrile, 37% acrylonitrile, 8~o acrylonitrile EHD byproducts and 8% water, was electrolyzed as it passed through the cell with a voltage drop across the cell averaging 4. 6 volts ancl a current density of 0. 22 amp per square centimeter OI cathodic surface ancl then fed into a decanter for equilibration and recycle of lower layer as in previous Examples. After 22 hours of electrolysis during which acrylo~
nitrile and water were continuously added to the circulating solution and an equivalent amount of product was continuously removed, it was found that acrylonitrile in the solution had been converted to adiponitrile with an average m~lar selectivity of 79. 4%, the steel anode had corroded at the average rate of 400 mils per year and the volume percentage of hydrogen in the electrolysis offgas was 22%.
Example VII
In a continuous process, an aqueous solution having dissolved ~ -therein approximately 1. 5% acrylonitrile, 1. 2% adiponitrile, 0. 2% ~ ~ .
acrylonitrile EHD byproducts, ethyltributylammonium cations in a concentration that varied between 2 and 9 x 10-3 gram mol per liter, 10% of a mixture of incompletely-substituted sodium orthophosphates having an average formula of approximately Nal 8H1 2PO4, 0. 5%
(14. 2 millimols per liter) of tetrasodium ethylenediaminetetraacetate and the mixture of sodium borates produced by neutraliging o:rthoboric -14-54-()160 3~3~l :
acid in an amount corresponding to 2% of the solution ((~. 36 gram ~toms of boron per liter of the solution) with sodium hydroxide to the solution pH of 8. 5 was circulated at a temperature of 55C. and a velocity of four feet per second through an undivided electrolytic cell having an AISI .:
1020 carbon steel anode separated by a gap of 70 mils from a cathode composed of a rolled sheet of cadmium conforming to AST~ Designation B44r)-66T (at least ~9. 9% Cd). The solution, which contained no ~ ~
: measurable amount of undissolved organic phase, was electrolyzed as it .~ .
passed through the cell with a voltage. drop across the cell of 3. 8 volts and 10 a current density of 0.16 amp per square centimeter of cathodic surface .
and then fed into a decanter for equilibration with an accumulated upper layer containing about 55% adiponitrile, 28% acrylonitrile, 9% acrylonitrile EHD byproducts and 8% water and withdrawal of equilibrated lower (aqueous) ;;
layer for recycle through the cell. After 459 hours of electrolysis during which acrylonitrile and water were continuously added to the circulating : ~
solution and an equivalent amount of product was continuously removed, it :: -. was found that acrylonitrile in the solution had been converted to adiponitrile :
with an average rrlolar selectivity of 87. 7%, the steel anode had corroded at :~
the average rate of 13 mils per year and the volume percentage of hydrogen in 20 the electrolysis offgas had been stable throughout the run at less than 8%.
Example VIII
In a continuous process, an aqueous solution having dissolved therein ;
~ approximately 1. 7% acrylonitrile, 1. 2% adiponitrile, 0. 2% acrylonitrile .... EHD byproductsJ between 2 and 4. 8 x 10-3 gram mol per liter of ethyltributyl-ammonium cations, 10% of a mixture of incompletely-substituted sodium orthophosphates having an average formula of approximately Nal 8H1 2PO4, and about 0. fi% (17. 0 millimols per liter) of tetrasodium ethylenediamine-tetraacetate and the mixture of sodium borates produced by neutralizing .... . . . . .

C-1~-54-0160 ~L~35~3~
orthoboric acid in an amount corresponding to 1. 8% of the solution ~0, 32 gram atom of boron per liter of the solution) to the solution pH Oe 8. 5 was circulated at a temperature of 55~C. and a velocity of Eour feet per second through an undivided electrolytic cell having an AlSI 1020 carbon steel anode separated by a gap of 70 mils from a cathode composed of cadmium con-forming to ASTM Designation B440-66T (at least 99. 9% Cd). The solution, which also had dispersed therein approximately 14. 6% by weight of an organic phase containing about 52% adiponitrile, 31% acrylonitrile, 9% ~;
acrylonitrile EHD byproducts and 8% water, was electrolyzed as it passed 10 through the cell with a voltage drop across the cell of 3. 95 volts and a current density of 0.185 amp per square centimeter of cathodic surface and then fed into a decanter for equilibration with an accumulated upper layer having the composition of the aforedescribed organic phase and then withdrawal of lower (aqueous) layer from the decanter for recycle through the cell as just described. Throughout the operation of the process and for each Faraday of current passed through the cell, 12 grams of lower layer from the decanter were purged from the system and replaced with water containing sufficient dissolved ethyltributylammonium cations, tetrasodium ethylenediaminetetraacetate and sodium orthophosphates and borates to 20 maintain the concentrations of those constituents of the aqueous solution at the aforedescribed levels After 69 hours of electrolysis during which acrylonitrile was continuously added to the system and an equivalent amount of product was continuously removed from the decanter upper layer, it was found that acrylonitrile in the system had been converted to adiponitrile with a molar selectivity of 87. 8%J the steel anode had corroded at the average rate of 20 mils per year and the volume percentage of hydrogen in the electrolysis offgas had been no greater than 7% throughout the run.

Claims (36)

1. The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
   
   l. In a process for hydrodimerizing an olefinic compound having the formula R2C=CR-X wherein -X is -CN, -CONR2 or -COOR', R is hydrogen or R' and R' is C1-C4 alkyl by electrolyzing an aqueous solution having dissolved therein at least about 0.1%
   by weight of said olefinic compound, at least about 10-5 gram mol per liter of quaternary ammonium cations and in addition to said olefinic compounds and said quaternary ammonium cations, at least about 0.1% by weight of conductive salt in contact with a cathodic surface having a cathode potential sufficient for hydrodimerization of said olefinic compound, the improvement which comprises including in the solution, in a concentration sufficient to inhibit formation of hydrogen at the cathodic surface, a nitrilocarboxylic acid compound having the formula wherein Y is hydrogen, , or C1-C20 alkyl, Z is a divalent C2-C6 hydrocarbon radical, M is hydrogen, alkali metal or am-monium, m is 1 or 2, n is an integer from 0 to 4 and at least one Y is or , said concentration being between about .025 and about 50 millimols per liter.
2. 2. The process of Claim 1 wherein Y is or , Z is C2-C4 alkylene and n is an integer from 0 to 3.
3. 3. The process of Claim l wherein the olefinic compound is acrylonitrile and the cathodic surface is composed essentially of cadmium, lead, zinc, manganese, tin or graphite, said solution having dissolved therein at least about 0.5% by weight of said olefinic compound, at least about 10-4 gram mol per liter of C8-C24 tetraalkylammonium ions containing at least three C2-C6 alkyl groups and at least about 1% by weight of alkali metal phosphate, borate, perchlorate, carbonate or sulfate.
4. 4. The process of Claim 3 wherein Y is or , Z is C2-C4 alkylene and n is an integer from 0 to 3.
5. 5. The process of Claim 4 wherein the nitrilocarboxylic acid compound is selected from the group consisting of ethylenediaminetetra-acetic acid, ethylenediaminetetrapropionic acid, N-hydroxyethylethylene-diaminetriacetic acid, diethylenetriaminepentaacetic acid, nitrilotriacetic acid, N, N-di(2-hydroxyethyl)glycine and the alkali metal and ammonium salts of such acids and said concentration is between about 0.025 and about 50 millimols per liter.
6. 6. The process of Claim 1 wherein the solution contains a boric acid or alkali metal or ammonium salt, thereof in a concentration cor-responding to at least about 0. 01 gram atom of boron per liter of solution.
7. 7. The process of Claim 1 wherein the solution contains at least about 0. 01% by weight of a condensed phosphoric acid or a molecularly equivalent amount of an alkali metal or ammonium salt thereof.
8. 8. The process of Claim 1 carried out in a single-compartment cell having a metallic anode in contact with said solution.
9. 9. The process of Claim 8 wherein Y is or , Z is C2-C4 alkylene and n is an integer from 0 to 3.
10. 10. The process of Claim 8 wherein the solution contains a boric acid or alkali metal or ammonium salt thereof in a concentration cor-responding to at least about 0. 01 gram atom of boron per liter of solution.
11. 11. The process of Claim 8 wherein the solution contains at least about 0. 01% by weight of a condensed phosphoric acid or a molecularly equivalent amount of an alkali metal or ammonium salt thereof.
12. 12. The process of Claim 8 wherein the olefinic compound is acrylonitrile and the cathodic surface is composed essentially of cadmium, lead, zinc, manganese, tin or graphite, said solution having dissolved therein at least about 0.5% by weight of said olefinic compound, at least about 10-4 gram mol per liter of C8-C24 tetraalkylammonium ions containing at least three C2-C6 alkyl groups and at least about 1% by weight of alkali metal phosphate, borate, perchlorate, carbonate or sulfate.
13. 13. The process of Claim 12 wherein Y is or , Z is C2-C4 alkylene and n is an integer from 0 to 3.
14. 14. The process of Claim 12 wherein the alkali metal salt is a phosphate, borate or carbonate and the anode is ferrous.
15. 15. The process of Claim 14 wherein Y is or , Z is C2-C4 alkylene and n is an integer from 0 to 3.
16. 16. The process of Claim 15 wherein the nitrilocarboxylic acid compound is selected from the group consisting of ethylene-diaminetetraacetic acid, ethylenediaminetetrapropionic acid, N-hydroxyethylethylenediaminetriacetic acid, diethylenetri-aminepentaacetic acid, nitrilotriacetic acid, N,N-di(2-hydroxy-ethyl)glycine and the alkali metal and ammonium salts oE such acids and said concentration is between about 0.1 and about 50 millimols per liter.
17. 17. The process of Claim 14 wherein the solution contains a boric acid or alkali metal or ammonium salt thereof in a con-centration corresponding to at least about 0.01 gram atom of boron per liter of solution.
18. 18. The process of Claim 14 wherein the solution contains at least about 0.01% by weight of a condensed phosphoric acid or a molecularly equivalent amount of an alkali metal or ammonium salt thereof.
19. 19. In a process for hydrodimerizing acrylonitrile by electrolyzing an aqueous solution having dissolved therein at least about 0. 5% by weight of acrylonitrile, at least about 10-4 gram mol per liter of tetra(C2-C5alkyl)-ammonium ions and at least about 1% by weight of sodium or potassium phosphate, borate or carbonate in contact with a cathodic surface consisting essentially of cadmium or lead with a current density of at least about 0.01 amp per square centimeter of cathodic surface while passing the solution along the cathodic surface at a velocity of at least about one foot per second, said solution having a pH between about 5 and about 11 and a temperature between about 5° and about 75°C., the improvement which comprises including in the solution between about 0.1 and about 50 millimols per liter of a nitrilocarboxylic acid compound having the formula wherein Y is or , Z is C2-C4 alkylene, M is hydrogen, alkali metal or ammonium, m is 1 or 2 and n is an integer of 0 to 2.
20. 20. The process of Claim 19 wherein the nitrilocarboxylic acid compound is selected from the group consisting of ethylenediaminetetra-acetic acid, ethylenediaminetetrapropionic acid, N-hydroxyethylethylene-diaminetriacetic acid, diethylenetriaminepentaacetic acid, nitrilotriacetic acid, N, N-di(2-hydroxyethyl)glycine and the alkali metal and ammonium salts of such acids.
21. 21, The process of Claim 19 wherein the solution contains a boric acid or alkali metal or ammonium salt thereof in a concentration cor-responding to between about 0.02 and about 0.9 gram atom of boron per liter of solution.
22. 22. The process of Claim 19 wherein the solution contains between about 0. 02% and about 3% by weight of a condensed phosphoric acid or a molecularly equivalent amount of an alkali metal or ammonium salt thereof.
23. 23. The process of Claim 19 carried out in a single-compartment cell having a metallic anode in contact with said solution.
24. 24. The process of Claim 23 wherein the nitrilocarboxylic acid compound is selected from the group consisting of ethylene-diaminetetraacetic acid, ethylenediaminetetrapropionic acid, N-hydroxyethylethylenediaminetriacetic acid, diethylenetri-aminepentaacetic acid, nitrilotriacetic acid, N,N-di(2-hydroxy-ethyl)glycine and the alkali metal and ammonium salts of such acids.
25. 25. The process of Claim 23 wherein the anode is ferrous.
26. 26. The process of Claim 25 wherein the nitrilocarboxylic acid compound is selected from the group consisting of ethylene-diaminetetraacetic acid, ethylenediaminetetrapropionic acid, N-hydroxyethylethylenediaminetriacetic acid, diethylenetriamine-pentaacetic acid, nitrilotriacetic acid, N,N-di(2-hydroxyethyl)-glycine and the alkali metal and ammonium salts of such acids.
27. 27. The process of Claim 26 wherein the solution contains at least about 0.5 millimol per liter of the nitrilocarboxylic acid compound.
28. 28. The process of Claim 27 wherein the solution contains a boric acid or alkali metal or ammonium salt thereof in con-centration corresponding to between 0.02 and about 0.9 gram atom of boron per liter of solution.
29. 29. The process of Claim 27 wherein the solution contains between about 0.02% and about 3% by weight of a condensed phos-phoric acid or a molecularly equivalent amount of an alkali metal or ammonium salt thereof.
30. 30. In a process for hydrodimerizing acrylonitrile by electro-lyzing an aqueous solution having dissolved therein at least about 0.5%
    but less than about 5% by weight of acrylonitrile, between about 10-3 and about 10-1 gram mol per liter of tetra(C2-C5alkyl)ammonium ions and at least about 1% by weight of sodium or potassium phosphate in a single-compartment cell having a ferrous metal anode and a cathodic surface consisting essentially of cadmium with a current density of at least about 0.1 amp per square centimeter of cathodic surface while passing the solution along the cathodic surface at a velocity of at least about two feet per second, said solution having a pH between about 7 and about 10 and a temperature between about 40° and about 65°C., the improvement which comprises including in the solution between about 0.1 and about 25 millimols per liter of a nitrilocarboxylic acid compound selected from the group consisting of ethylenediaminetetraacetic acid, ethylenediaminetetra-propionic acid and the alkali metal and ammonium salts of such acids.
31. 31. The process of Claim 30, said solution having dissolved therein more than 5% by weight of sodium or potassium phosphate.
32. 32. The process of Claim 30, said anode consisting essentially of carbon steel.
33. 33. The process of Claim 32 wherein the solution contains at least about 2. 5 millimols per liter of the nitrilocarboxylic acid compound.
34. 34. The process of Claim 33 wherein the solution contains orthoboric, metaboric or pyroboric acid or a sodium or potassium salt thereof in a concentration corresponding to between about 0. 02 and about 0. 5 gram atom of boron per liter of solution.
35. 35. The process of Claim 33 wherein the solution contains between about 0. 02% and about 2% by weight of a metaphosphoric or pyrophosphoric acid or a molecularly equivalent amount of a sodium or potassium salt thereof.
36. 36. The process of Claim 30 wherein the aqueous solution is electrolyzed in an electrolysis medium consisting essentially of said aqueous solution and up to about 25% by weight of a dispersed but undissolved organic phase.