DE2505253C3 - Process for the hydrodimerization of an olefin compound - Google Patents

Description

Trodenal corrosion products tend to get into the electrolysis medium to enter and accumulate there in such a way that it is deposited on the cathode which increases the formation of molecular hydrogen at the expense of the current efficiency of the process and the selectivity of the reaction with respect to the desired hydrodimerized product gradually increases lowers As is known from Belgian patent specification 8 04365, the formation of molecular Hydrogen and anode corrosion in such processes are essentially inhibited by that a nitrile carboxylic acid compound, for example an alkali metal salt of ethylenediaminetetraacetic acid, is introduced into the electrolysis medium It is believed that such compounds remove the heavy metals in the electrolytic medium sequester and thereby inhibit the formation of the metal deposit rings on the cathode, which normally lead to an increase in the formation of molecular Keep hydrogen in the cell. Furthermore, in this Patent stated that it is possible by introducing such a compound into the electrolysis medium, the process over longer periods of operation perform at current densities and temperatures which are considerably higher than the temperatures use the method of Canadian Patent 813 877 or US Patent 36 16 321 is restricted

It was found, however, that despite the presence of such a compound in a substantial Concentration in the electrolysis medium causes the accumulation of heavy metals by the electrodes originate and in particular (forch & erosion of the anode are normally released in the medium by an increasing deterioration in the performance of the process, such as the selectivity of the Product accompanying the current efficiency, etc. One can, as described, the occurrence of such Delay deterioration and reduce its severity if a heavy metal sequence is introduced into the medium. introduces strierungsmittel and it can also in some cases - as mentioned - through use of a polyphosphate can be achieved to inhibit anode corrosion, but it is in an im Technical scope carried out working process desirable to avoid such a deterioration of the process to a wider extent than this by simply adding a sequestering agent to the initially used electrolysis medium or even by maintaining a specific concentration of such a sequestering agent in so the medium can be reached during the electrolysis. It is perfectly clear that the production costs of the desired product are the lower, the more Maintain the selectivity of the product longer and the longer and more complete the current efficiency lowering formation of molecular hydrogen can be inhibited. Such improvements to the Process are the subject of the invention.

It has now been found that in the process described at the outset according to the patent 23 44 294, in which heavy metals enter the medium in substantial quantities during electrolysis, the undesirable properties of the heavy metal in the medium, such as increased formation of molecular hydrogen and the possible reduction in the desired selectivity of the product can be significantly reduced by the fact that the nitrile carboxylic acid compound to the medium At the beginning and during the electrolysis added in an amount sufficient to ensure that an excess of free Nitrile carboxylic acid compound via the virtually complete solution of the electrolysis imported heavy metal wifd required amount of nitrile carboxylic acid compound to be maintained in the medium, and that one also the concentration of heavy metal dissolved in the medium by releasing it part of the electrolysis medium and replacement with one less concentrated in heavy metal ions Electrolyte or precipitation of the heavy metal ion from the withdrawn part of the electrolysis medium after the organic substance has been separated off between about 2 and about 50, preferably 4 and 30 ΐπΜοΙ keeps constant

Not necessarily in all cases, but typically when heavy metal is in a major one Amount passes into the medium when it is soluble in the initially used electrolysis medium the free nitrile carboxylic acid compound in excess compared to that for sequestering the heavy metal required amount to the medium during the electrolysis. This embodiment is special but not exclusively, suitable when the process is carried out and in an undivided cell Adipic acid dinitrile diirch hydrodimerization of Acrylonitrile is to be produced.

To the olefin compounds that can be hydrodimerized with the process according to the invention, include olefinic compounds that are used for reductive coupling by electrolysis in aqueous media are suitable. At present, most common such reactants are substituted olefin compounds such as those of the general formula

R R

I I

R-C = C-CN

where R is a hydrogen atom or a Q-Q-alkyl group (e.g. a methyl, ethyl, n-propyl, isopropyl, η-butyl, isobutyl or tert-butyl group), where at least one of the radicals R represents a hydrogen atom. Such compounds include for example acrylonitrile, methacrylonitrile, croton nitrile, 2-methylenebutyronitrile, 2-pentenenitrile, 2-methylenevaleronitrile, 2-methylenhexanenitrile, tiglinic acid nitrile and 2-ethylidene hexanenitrile.

The hydrodimerization products of these compounds have the general formula

NC-CHR-CR ₂ -CR ₂ -CHR-Cn

in which R has the meanings given above and are, for example, adiponitrile and 2,5-dimethyladiponitrile. These hydrodimers can be used as Monomers or used as intermediates, which are converted into monomers by known processes are convertible, which in turn are used to produce high molecular weight polymers including Polyamides and polyesters are suitable. Other examples of olefin compounds produced after Processes according to the invention can be hydrodimerized, as are the products produced thereby in U.S. Patents 3,193,475 to 3t 93479 and 31 93 481 to 31 93 483 mentioned above.

The invention is now with regard to the electrolysis of a liquid aqueous electrolysis medium

ums, that the previously designated olefin compounds contains, described. Such an electrolysis medium can be an aqueous, essentially single-phase solution or a multiphase mixture which is such aqueous solution, which is preferably the continuous Phase of the mixture and containing an undissolved organic phase typically, but not necessarily, dispersed in the aqueous solution gases like vaporized reactants, oxygen formed at the anode and in most cases at the Hydrogen formed at the cathode is normally present in small proportions.

If present, the organic phase can be up to constitutes about 25% or more of the medium and in some preferred embodiments of the method of the invention constitutes the organic phase at least about 10% (e.g., between about 12 and about 20%) of the medium. In some embodiments, continuous processes that utilize the recycling of the comprise unreacted olefin compound, such an organic phase usually consists predominantly (most often at least about 65% and typically at least about 75%) from the olefin compounds intended for hydrodimerization and the hydrodimerized product, with small amounts of reaction by-products, water, etc. may optionally be present. In the hydrodimerization of acrylonitrile, an organic phase generally contains at least about 10%, preferably between about 15 and about 50% and generally preferably between about 20 and about 40% Acrylonitrile. In each case, the concentrations of the constituents relate to those dissolved in the aqueous Solution phase of the electrolysis medium, as explained above, are present on the specified aqueous Solution as such and not on the total of the salary the aqueous solution and the undissolved organic phase, which, as mentioned, can be present in the electrolysis medium, but does not have to be present. On the other hand, the percentages by weight are related to here undissolved organic phase described on the total weight of the aqueous solution and the undissolved organic phase in the electrolysis medium.

With regard to the constituents of the aqueous solution in the electrolysis medium, the olefin compounds intended for hydrodimerization are at least in present in amounts such that electrolysis of the medium can result in a substantial amount of the desired hydrodimerized product. These Amount is generally at least about 0.1%, typically at least about 03%, and preferably at least about 1% of the aqueous solution. The introduction of one or more additional Ingredients that increase the solubility of the olefin compounds in the solution can enable the To carry out the process with a solution containing relatively high amounts of the olefin compound, e.g. B. at least about 5%, or even 10% or more. But in many embodiments of the invention, the aqueous solution less than about 5% (e.g., no more than 43%) of the olefin compound and in some Embodiments preferably no more than about 23% of the olefin compound.

The minimum amount of the quaternary ammonium cations see ^r small. In general, they only have to be present in an amount which is sufficient to form the desired product selectivity. In most cases, the auaternären ammonium cations in concentrations of at least 10 mol ~ ⁱ I pm of the aqueous solution and even typically of at least about 10 ^-4 moles per liter of solution are present. While in some instances, as noted, greater amounts may be present, the quaternary ammonium cations are generally in a concentration of less than about 0.5 moles per liter, and even more often in a concentration not greater than about 10- 'moles per I is present in the aqueous solution. According to a preferred embodiment, the concentration of the quaternary ammonium cations in the solution is at least about ⁴ 5-10- MoI per liter but not more than about 5- 10 ² MoI per I.

The quaternary ammonium cations present in such quantities are positively charged ions that are a have pentavalent nitrogen atom that immediately is connected to other atoms (e.g. carbon atoms) with saturation of V5 of its valence. Such Cations can be cyclic, as in the case of the piperidinium, pyrrolidinium, and morpholinium cations but in general those in which the nitrogen atom is directly linked to four monovalent organic Groups is connected, preferably avoiding olefinically unsaturated groups. They are preferably hydrocarbon groups (for example Alkyl groups or aryl groups), trihydrocarbylammonium-substituted derivatives of such groups and Combinations thereof so that the Ipnen an average of 4 to 48, preferably about 6 to about 36 and in particular have about 7 to about 28 carbon atoms. Suitable aryl groups typically contain 6 to 12 carbon atoms, and preferably only an aromatic ring such as a phenyl or benzyl resL Suitable alkyl groups can be straight, branched, or cyclic, and each can typically be 1 to. 12 carbon atoms contain. Although quaternary ammonium cations, which have a combination of such alkyl and aryl groups (for example benzyltriethylamine • nonium cations) can be used many embodiments of the invention are preferably carried out with tetraalkylammonium cations and it generally superior results are obtained using such cations as at least three C2 - Ce alkyl groups and a total of 8 contain up to 24 carbon atoms in the four alkyl groups, e.g. B. Diethyldipropyl-, Äthyltripropyl-, Äthyltributyl-, Äthyltriamyl-, Äthyltrihexyl-, Octyltriethyl-, Tetrapropyl, methyltripropyl, decyltripropyl, methyltributyl, tetrabutyl, amyltributyl, tetraamyl, Tetrohexyl, ethyltrihexyl, diethyldioctylammonium cations and many others mentioned in the above U.S. Patents 3,193,475 to 3,193,479 and 31 93 481 to 31 93 483 are described * ius are particularly expedient for economic reasons general tetraalkylammonium cations in which each alkyl group contains 2 to 5 carbon atoms, e.g. 3. Diethyldiamyte, tetrapropyl, tetrabutyl, amyl tripropyl or tetraamylammonium cations. Such cations can be incorporated in any suitable manner Electrolysis provided aqueous solution are introduced, for example by dissolving the quaternary Ammonium hydroxide or its salt in the solution in a form to form the desired quaternary Ammonium cation concentration appropriate amount.

The type of conductive salt used is not a critical factor in gaining the benefits thereof

Invention. The conductive salt can therefore be a quaternary ammonium salt. be that so far at im Electrolytic hydrodimerizations carried out on an industrial scale was used, for example a tetraalkylammonium, (for example tetraalkylam-, monium) sulfate. -alkyl sulfate (for example ethyl sulfate) or -arylsulfonate (for example -toluenesulfonate) - Although organic salts of this general kind as Conductive salts can be used in divided or undivided cells. it is in general preferred to add other conductive salts such as an alkali metal *; !! / in mostly undivided cells use. Of the alkali metal salts are lithium and especially sodium and potassium salts generally preferred from an economic point of view.

Salts of inorganic and / or polybasic acids, for example a

phate, borate, perchlorate, carbonate or sulfate and especially incompletely substituted salts of this type, ie salts in which the anion has at least one valence saturated by hydrogen and at least one further valence saturated by an alkali metal. Examples of such salts include 2, disodium phosphate (NaIHPO ₄ ), sodium _{hydrogen phosphate (KH 2} PO ₄ ). Sodium bicarbonate (NaHCOj) and dipotassium borate (K ₂ HBOj). Likewise suitable are the alkali metal salts of condensed acids such as pyrophosphoric, metaphosphoric, metaboric, pyoboric acid and the like (for example sodium pyrophosphorus, potassium metaborate, borax etc.) and / or the products of the partial or complete hydrolysis of such condensed acidic 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 can correspond to a mixture of two or more salts of this type, for example a mixture of sodium hydrogen phosphate and disodium phosphate; accordingly, such salt mixtures (namely mixtures of salts of different cations, for example different alkali metals and / or different acids) also fall within the scope of the term “conductive salt”, “alkali metal phosphate, borate or carbonate”. as used here. The alkali metal salts can be dissolved as such in the solution or added in some other way, for example as alkali metal hydroxide together with the acid required to neutralize the hydroxide to the desired pH.

The concentration of the conductive salt in the solution should at least be sufficient to increase the electrical conductivity of the solution significantly above its conductivity in the absence of a salt. In most cases a concentration of at least about 0.1% is preferred. Greater conductivity is achieved by dissolving at least about 1% of the conductive salt, and preferably at least about 2% of such a salt, in the solution. In many cases, the eo preferred process conditions using a solution which contains more than 5% in dissolved form (typischenveise at least 5.5%) of the conductive salt. When an alkali metal salt is used as the conductive salt, the maximum amount of the salt in the solution is typically limited only by its solubility in the solution, which varies with the particular salt used. In the case of salts such as sodium or potassium phosphates and / or borates, it is generally most convenient that the solution contain between about 7 and about 20 percent of such a salt or a mixture of salts.

As mentioned earlier, the present invention is concerned with the undesirable effects of the Deterioration of the potential due to a heavy metal released during electrolysis (for example from a Electrode) passes into the electrolysis medium. Under heavy metal are metals with a specific Weight of more than 4.0 to understand how beUpieUvkeise Iron. Cadmium, lead. Zinc. Nickel. Mercury manganese, copper, cobalt, chromium. Titanium, thallium Vanadium, molybdenum. Ruthenium. Antimony. Bismuth, platinum and palladium. The expression continues "Heavy metal that passes into the medium" for a heavy metal that enters the liquid medium in the sense occurs that it can move freely there, for

i_ / Mti.r. ». iiii.i! visu 1.1111.111.-H-11 »τ \ .t ι ■ it ta II. ua3 all ClIfCl surface of the device is fixed. through which or in which the liquid medium circulates (e.g. the anode or cathode of an electrolytic cell in which the medium is electrolyzed). The term transfer of the metal into the medium in "a substantial amount" or at a "substantial rate" means that the amount or rate is great enough. to disrupt the electrolysis process. for example by the formation of molecular hydrogen or by the fact that the product selectivity is adversely affected if the metal is not prevented from exerting an adverse effect, for example by removal from the medium od. The like. The absolute amounts or ratios that can produce such effects vary substantially with the particular process variant, the specific hydrodimerization reaction desired, and many other process conditions. Before entering the electrolysis medium, the heavy metal can be essentially pure or in a bound form, for example as a compound (for example as an oxide or salt) or as an alloy of the metal. In general, metals with low hydrogen overvoltage have a greater adverse effect on potential, such as iron. Nickel, tungsten. Cobalt and molybdenum, or in other words. Metals that are not typically preferred as cathode materials for hydrodimerization

However, it has also been found that metals with high hydrogen overvoltage and even metals that The process behavior is disadvantageous, potentially as cathode materials for hydrodimerization if they are present in substantial concentrations in the electrolysis medium without being sequestered or removed. That is to say that heavy metals that result from the Cathode enter the medium, redeposited in a form or state on the cathode that differ from the original shape or condition (when the metal was still part of the cathode) differentiate.

This heavy metal can be as a result of a Erosion or corrosion of the process device. like electrodes, leads, etc., by chemical or electrochemical attack or otherwise enter the medium and can eventually be used as ions. Oxides, hydroxides. Salts such as (depending on the anions of the medium) phosphates, borates, carbonates, Sulfates, etc. or as more complex compounds in

enter the medium, although their chemical and / or physical form and even possibly its valence state in the medium May be subject to changes if they enter or exit the medium (on Example when they are deposited on the cathode of the cell). For example, this can be done on the surface A ferrous metal anode (i.e. an anode containing iron, e.g. carbon steel, stainless steel or other ferrous alloys. Contains iron oxides such as magnetite or other iron compounds) iron present as a result of corrosion by an electrolytic medium containing phosphate ion Form iron phosphate and enter the medium or as a finely divided (e.g. colloidal) solid Compound, such as iron hydroxide, may be present in the medium and may later appear in the form of oxides the cathode are deposited.

Frfinriiinaccrpmär When riip frpip NlitrurarhrtncäiirA-

connection to the electrolysis medium by adding again by regenerating the nitrile carboxylic acid compound from a heavy metal complex in the medium (for example by separating the metal from the complex with a heavy metal precipitating agent, such as a sulfide, ferricyanide or the like) are supplied, while in other systems the free nitrile carboxylic acid compound after regeneration fed back to the medium from the heavy metal complex separated from the medium can be.

Addition of the free nitrile carboxylic acid compound to the medium can also be continuous or discontinuous and at any suitable point of the system, for example to a part of the medium that is subject to electrolysis, or (im generally preferred for continuous systems) to part of the medium that comes from the electrolysis was withdrawn and is to be fed back into the circuit for further electrolysis.

As already stated, the objects of the invention are achieved by maintaining an excess of free nickel carboxylic acid compound in the electrolysis medium and by also keeping the concentration of the heavy metal dissolved in the medium essentially constant. The excess should preferably be sufficient to sequester at least about 2 mmol heavy metal per liter of medium. Excess is to be understood as meaning the measurable amount of the nitrile carboxylic acid compound which is sufficient to sequester further heavy metal which is added to the medium in sequesterable form, the amount (preferably substantially) being greater than the amount of the free nitrile carboxylic acid compound which is in static equilibrium is present with the heavy metal in the medium Usually and especially with the generally preferred nitrile carboxylic acid compounds that have a relatively high equilibrium constant (ie log K for an equimolar mixture of metal ions and sequestering agent, as defined by M arte 11 and Calvin, "Chemistry of the Metal Chelate Compounds ", Prentice Hall, Ine, Engelwood Cliffs, NY 1952), the concentrations of the free nitrile carboxylic acid compound in static equilibrium with the heavy metals in the medium are so low that they are of practically no importance; consequently, a substantial concentration of the free nitrite carboxylic acid compound measured in a given medium can essentially be referred to as the excess concentration of the free nitrite carboxylic acid compound in the medium. However, it should be pointed out that this excess of free Nitrilcarbonsäureverbindung in a dynamic ^r, see balance with a heavy metal in the medium may be present, /. B. in a system in which the nitrile carboxylic acid compound is continuously withdrawn or otherwise lost from the medium and free nitrile carboxylic acid compound continuously

ίο is supplied. Such a dynamic equilibrium concentration of free nitrile carboxylic acid compound can be much larger than the usual static ones Equilibrium concentrations at this compound in such media and there should not be confused the two types of equilibrium concentrations be with the presence of excess free nitrile carboxylic acid compound, as is the case according to the invention is applied. The determination of the concentrations of the Niirücärborisäursverbindungen "" "'in free cd ** r" ^ **; - ger Form) can be made according to known methods, the various already mentioned in Publications and in Keys to Chelation, Dow Chemical Company, Midland. Michigan, published 1969 are.

In order to "maintain excess free nitrile carboxylic acid compound in the medium" must during the course of the process generally excess free nitrile carboxylic acid compound in the medium to be available. Disruptions and other procedural changes

jo ments can indicate the lack of excess free Result in nitrile carboxylic acid compound temporarily and / or for relatively short periods of time, but it must be at least for about 80%, preferably at least for about 90%, and most preferably for at least about 90%

j5 for about 100% of the time the medium is is electrolyzed, excess free nitrile carboxylic acid compound will be present in the medium. This Time can be as little as 10-20 hours for some (for example batch) procedures or several thousand hours or more with others Executions (generally carried out continuously) be. The particularly desirable concentration changes with the other process conditions. In many preferred embodiments Men, the excess of free nitrile carboxylic acid compound is advantageously suitable for at least sequester about two (and preferably at least about four) mfviol heavy metal per liter of medium. In most embodiments of the invention, it is advantageous to the medium during the electrolysis to add free nitrile carboxylic acid compound in excess of the amount that is suitable for to sequester the heavy metal in quantity, like this one during the same or an equivalent Time segment of the electrolysis passes into the medium. As used in this specification, the term "suitable or capable of sequestering" means a lot Heavy metal under conditions favorable to sequestration, for example when the heavy metal is in an amount is in easily sequesterable form, intimately with the free nitrile carboxylic acid compound Contact comes and has time for sequestration in order to achieve the best possible conditions of static equilibrium to achieve, etc. In some cases, such equilibrium conditions under the hydrolysis conditions cannot be reached and accordingly a certain amount of heavy metal cannot by the amount of free nitrile carboxylic acid added

re-connection will be completely sequestered for this Would be "suitable or capable". In fact, it is shown below that there are embodiments of Invention exist in which a substantial proportion of the heavy metal transferred into the medium is not sequestered or at least not as sequestered is maintained, despite the presence of the free nitrile carboxylic acid compound in the electrolysis medium in an amount that is advantageous thereto would be sufficient to sequester the metal carried over into the medium. Rs must also be pointed out that the amount of heavy metal that is transferred into the medium and the amount of free nitrile carboxylic acid compound that is added "during the electrolysis" relate to any specific period of time relate to the electrolysis and not just to the electrolysis during the entire duration of a batch or continuous process or from

that is, the process according to the invention is carried out by adding free nitrile carboxylic acid compound during any period of electrolysis in an amount suitable to be carried into the medium to sequester heavy metal transferred during this period.

Furthermore, the term "soluble in the initial electrolysis medium" as used herein stands for the solubility in the electrolysis medium used at the beginning of any such period of time Electrolysis. It should be noted, however, that the amount of a heavy metal contained in such Medium is soluble. may decrease during electrolysis. For example, if that Initial medium contains a nitrile carboxylic acid compound, this decomposes during electrolysis and accordingly a heavy metal that is present in the medium during a substantial period of time If electrolysis occurs, it will not be soluble in it to as great a degree as the metal at the start of this Would have been soluble for a period of time. In this respect, as well as a substantial concentration of heavy metal, dissolved in the Aniangseiekt.uiysenmedhiin, present may be, it should be pointed out that an amount of heavy metals is greater than the amount soluble in the initial electrolysis medium «refers to the amount by which this occurs during a given During the period of electrolysis, the heavy metal that has entered the medium exceeds the amount in the Medium in addition to the amount that would be soluble in the "initial electrolytic medium" at the start of this Was resolved for a period of time.

Keeping the heavy metal concentration constant can be achieved in various ways, for example Example! by being part of the medium withdraws from the system during electrolysis and replaces it with a second part, the one has a lower concentration of dissolved heavy metal than the removed part, or by having the sequestered or otherwise dissolved heavy metal precipitates and then the precipitate (for Example by filtration, centrifugation or the like) removed. In fact, the procedure is carried out by Invention according to a preferred embodiment, in which a liquid aqueous electrolysis medium, the which contains olefin compounds and excess free nitrite carboxylic acid compounds, in a Hekirorysenic zone of electrolysis for hydrodimerization is subjected, the heavy metal being transferred to the medium in substantial amounts, in the manner by withdrawing part of the electrolyzed medium from this zone from the withdrawn part (for example, by decanting one of the product containing organic phase from a multiphase electrolysis medium) the hydrodimerized product is separated and replaced by fresh olefin compounds replaced, dissolved heavy metal removed from the withdrawn part (for example by cleaning a

ίο fraction of the withdrawn part that contains dissolved heavy metal, or by precipitation and then by Filtering or centrifuging the precipitated material from the withdrawn part), any purified Fraction from this part through another, similar one Replaced electrolysis medium, which has a lower concentration of dissolved heavy metal than that purified fraction, then the withdrawn part of the zone for further electrolysis in the circuit again

Feeds And thy mcuiiini «τ'απΓΕϊηι ιΐ £ Γ tLiciiiruijsc

μ adds sufficient free nitrile carboxylic acid compound, to maintain excess free nitrile carboxylic acid compound in the medium.

That the concentration of the heavy metal dissolved in the medium is kept essentially constant does not necessarily mean that the concentration is in a particularly narrow range must be kept. In fact, it is possible to conduct the process so that the concentration of the dissolved heavy metal in the medium by up to 100% or, in terms of height, can deviate even more from the standard value. However, that means that the dissolved heavy metal concentration is normally kept below a maximum that is essential is less than the concentration on which that otherwise dissolved heavy metal during the continued Transfer of the metal into the medium would increase, and that sufficient free nitrile carboxylic acid compound is added to keep this in excess in the medium to maintain. In most embodiments of the Processes that employ long operating times will have an essentially stable concentration of ^: Heavy metal dissolved in the medium, recognizable by the considerable persistence with which it remains below a given maximum concentration

The expression "dissolved heavy metal" as it is used here is used, stands for the heavy metal that is when passing the medium through a membrane filter with a standard porosity of 0.45 πιμιπ can not be separated It can therefore in typical Systems determine the concentration of dissolved heavy metal in the electrolytic medium simply by conventional analysis (e.g., by atomic absorption) Sample of the medium passed through such a riter can be determined. With specific systems the measures to keep the concentration of dissolved heavy metal constant depend on various factors. In the case of the nitriicarboxylic acid compounds used, such as ethylenediaminetetraacetic acid (EDTA) and N-Hydroxyäthyläthylendiamintriessig acid (HEDTA) it is generally desirable the concentration of heavy metal dissolved in the medium between about 2 and about 50 (preferably between about 4 and about 30} mmol per liter increases keep. For example, if the heavy metal Eiser! is BhJ the medium has a typical specific gravity of about 1.08 g / cm ³ , this corresponds to a concentration of dissolved iron in the medium between about 100 and about 2500 ppm (preferably between

about 200 and about 1500 ppm).

In many cases, and especially with some undivided cells, one carries the excess free Nitrile carboxylic acid compound to the medium in such an amount that it is suitable for the To sequester heavy metal in at least 1.5 times the amount which during the electrolysis in the Medium crosses. This amount is usually determined from the measured concentrations of the metal in the Electrolysis medium calculated or quantitatively from the metal loss of one or more electrodes certainly. Since the metal loss of a Process anode is usually closely related to the amount of current drawn by the in contact with the The medium standing on the anode is often used as the basis for calculating the metal losses and for the addition of free nitrile carboxylic acid, it is expedient to add this to the ratio of mmol / Faraday (F) current relate. For example, when using anodes made of a ferrous metal (such as Carbon steel) are made, the added free nitrile carboxylic acid is generally able to at least about 0.1 millimole of iron or other heavy metal per Faraday of current passed through the medium sequester. As a large number of nitrile carboxylic acid compounds is capable of sequestering heavy metals on a 1: 1 mole basis, they are the Electrolysis medium of most undivided cells containing such anodes, preferably similar ones molar amounts added, in particular in amounts of at least about 0.1 mmol of free nitrile carboxylic acid compound per Faraday of current passed through the medium.

With regard to the application of the method of the present invention in mostly undivided cells corrosion of the anode and thus the tendency for heavy metals to deposit on the cathode are advantageously inhibited by using a boric acid, a condensed phosphoric acid or their Brings alkali metal salts into the electrolytic medium. Boric acid or borate can be added to the medium as ortho-boric acid, metaboric acid or pyrobic acid and then neutralized to the desired pH value, for example with an alkali metal hydroxide, or they can be used as fully or incompletely substituted alkali metal salts of such Acid (for example in the form of disodium or monosodium orthoborate, potassium metaborate, sodium tetraborate or the hydrated form thereof (commonly referred to as borax) may be added. the condensed phosphoric acid or the phosphate can be used as polyphosphorus (for example pyrophosphorus or Triphosphoric acid can be added and then neutralized to the desired pH or them can be used as completely or incompletely substituted alkali metal salts of these acids (for example in the form of tetrasodium pyrophosphate. Potassium hexametaphosphate or sodium triphosphate) can be added. Further details regarding the use of a boric acid or a condensed phosphoric acid or Their salts in hydrodimerization processes can be found in the aforementioned Belgian patent 8 04 365 remove.

In most cases, the pH of the batch is right of the electrolysis medium used in the present invention is above 2, and is preferably at least about 5, especially at least about 6, and more preferably at least about 7th especially when the process is carried out in an undivided cell with a metal anode. The total pH should generally not be higher than about 12, typically not higher than about 11 and at ■; Use of sodium and / or potassium phosphates generally not much higher than about 10 lie.

The electrolysis medium should have a temperature which is compatible with the liquid state of the medium, ie it must be above the freezing point but below the boiling point at the pressure used. Good results can be achieved at temperatures between about 5 and about 75 ° C, or * even at higher temperatures if pressures are significantly above

'5 applied over 1 atmosphere can be obtained. The optimum temperature range will vary with the specific olefin compound and hydrodimer, among other things. In the hydrodimerization of acrylonitrile to adiponitrile are usually tiektrolysentemperaturen of at least about 25 ⁰ C preferred, and those particularly desirable from about 40 to about 65 ° C.

Indeed, a particular advantage of the present invention is that it is very satisfactory at temperatures above 40 "C (the maximum temperature specified in US Pat. No. 3,616,321) can be used because the conductivity of the electrolysis medium varies significantly with the Temperature increases and therefore the electricity costs of the

μ method are generally lower at temperatures of more than 40 ⁰ C than at lower temperatures.

It is known that the electrolytic hydrodimerization of olefin compounds in contact with a

j "; cathode surface must be performed, the sufficient for the hydrodimerization cathode potential comprising Generally, no minimum current density can be provided in which the invention may be carried out in most cases, a current density of at least about 1 A / dm ^{2 of} cathode surface. preferably to use at least about 5 A / dns ^2. Although higher current densities may be appropriate in some cases, those used here are generally not higher than about 150 A / dm ² and often not higher than about 75 A / dm ² Among the other process variables, current densities no greater than about 50 A / dm ² are preferred for some embodiments, but where it is a significant advantage

The invention is such that it can be performed particularly satisfactorily at current densities of at least about 10 A / dm ² cathode surface and in some cases at current densities up to about 25 A / dm ² or higher.

A liquid permeable cathode is usually preferred. When using a With such a cathode, the aqueous medium intended for electrolysis generally flows between the anode and cathode at a linear velocity with respect to the adjacent cathode surface of at least about 0304 meters per second, preferably at least about 0.608 meters per second, and most preferably at least between about 0314 and about 2438 meters per second, although speeds up to 6.1 meters per second or more can be applied.

The distance between the anode and the cathode can be very small, for example about 0.1 inch or less or as large as 1.27 cm or more, whereby

usually a distance between about 0.152 and about 0.635 cm is most appropriate.

The cathode surface can be any Material that is suitable for the required cathode potential and that does not have a not to:> tolerant speed is loosened or corroded. So the process can in general with a Cathode are made, which is essentially cadmium. Mercury. Thallium, lead, zinc, manganese, Tin (which is unsuitable for some olefin compounds is) or contains graphite, which is to be understood as meaning. that the cathode surface has a high percentage (im generally at least about 95%, and preferably at least about 98%) of the metal or one A combination (for example an alloy) of two or more such materials contains - but it can continue a? contain minor amounts of one or more other ingredients provided that these do not affect the nature of the cathode surface change so as to obviate the benefits of the present invention. Such other ingredients are when they are in substantial concentration are present, preferably other materials r.rit relatively high hydrogen overvoltages.

In general, cathodes consisting essentially of cadmium, lead, zinc are particularly preferred. Manganese, graphite or an alloy made of such metals. Cathodes which essentially contain cadmium are particularly preferred. best Results are usually obtained with a cathode surface having a cadmium content of at least about 99.5%. even typically at least about 993%, and especially at least about 995% according to ASTM regulation B440-66T.

The cathodes used in this invention can be manufactured by various methods such as by electroplating the desired cathode material on a suitable molded substrate of a different material, for example a metal with greater structural Strength, or by chemical, thermal and / or mechanically applying a layer of the cathode material to a similar substrate. Man but can also be a plate, a film, a rod or any other suitable body, which in the consists essentially of the desired cathode material without using such a substrate.

The method of this invention can be carried out in a divided cell having a cation permeable cell Membrane, a diaphragm or the like. To separate the anode compartment from the cathode compartment of the cell in one be carried out in such a way that the electrolysis medium, which is in direct physical Contact is made with a cathode of the cell, not at the same time directly with an anode of the cell Contact is available. Advantageously, cells are used in which the electrolysis medium is in simultaneous direct physical contact with an anode and cathode of the cell is located. Indeed, according to a preferred embodiment of the invention, the method is carried out in a Undivided cell carried out, which has an anode, which a ferrous metal with an alkali metal phosphate, boral or carbonate as a conductive salt contains, and contains an electrolysis medium, its pH value is not significantly below 7. Embodiments are of particular interest in which a Anode is used, which consists essentially of carbon steel, such preparations are specified in the 100Ό, 1100 and 1200 series of numbers (for standard steel preparations) of the American Iron and Steel Institute and Society of Automotive Engineers !, many of which are on page 6Z Volume 1, Metals Handbook, B. Edition (1961), published by American Society for Metals, Metals Park, Ohio, are indicated.

In general, the carbon steels contain that are advantageously used as anode materials in the method according to the invention, between about 0.02% (typically about 0.05%) and about 2% carbon. Usually carbon steels such as those of the AlSI and SAE 1000 series are used of standard steel preparations are preferred and those containing between about 0.1 and about 1.5% carbon are particularly preferred. Regardless Anyone can rely on the material from which it is made Anode in the cell in the form of a plate, foil, a strip, a rod or any other shape suitable for the purpose to have. According to one embodiment, the anode has the shape of a foil or plate (for example made of Carbon steel) and is parallel to and closely spaced from a cathode face of approximately the Equipped with the same dimensions Potentially advantageous in some cases is the use of a Multi-cell packing. This contains a series of essentially parallel plates or foils, which are made of a self-supporting material (for example iron or steel) and in one direction Have surfaces made of a suitable anode material (for example magnetite or the steel carrier material) and in the other direction have surfaces that are coated with a suitable Cathode material are covered (for example cadmium or another metal that is suitably electroplated or otherwise applied to the carrier material is) so that it is possible. the electrolysis medium through a multitude of channels between such plates or to let foils flow and at the same time like each plate or foil in the series as anode and cathode to use bipolar electrodes.

In the specific examples below, the heavy metals present in the electrolytic medium are iron and cadmium, starting from the latter published values and by experimental comparison it is known that it is in the same molar Proportions such as iron is sequestered and essentially completely in terms of the used Nitrile carboxylic acids coincide with iron.

Accordingly, the ability of the electrolysis medium to dissolve additional cadmium or Iron determined in the following examples as follows:

(1) A comparative sample of the electrolytic medium is diluted and then filtered to substantially remove all solids contaminating the membrane-type filter with a Sundard porosity of 0.45 πΊμπι had passed through:

(2) the weight concentration of iron and cadmium in a first portion of the filtered sample measured individually by atomic absorption;

(3) a finely divided cadmium compound (for example oxide or phosphate) becomes a second part the sample is added in excess to its solubility, after which this part becomes several

909 616/276

Stirred thoroughly for hours, filtered again and analyzed for its weight concentration of cadmium in the same way as for first part of the sample took place;

(4) the weight concentrations of cadmium and iron measured in the manner described are converted into molar concentrations; and

(5) becomes the sum of the molar concentrations of iron and cadmium in the first part of the sample subtracted from the molar concentration of cadmium in the second part of the sample, the Difference in the molar concentration indicates the extent to which the comparison sample described above nor the ability to dissolve iron or is cadmium in addition to the iron and the Has cadmium, which was actually already dissolved in the sample of the medium.

Furthermore, in the following specific examples, which are only intended to illustrate the Invention are intended to serve. Acrylonitrile and adipic dinitrile are generally referred to as AN and ADN, respectively

25th

30th

35

example 1

In a continuous process, a liquid electrolysis medium is left out

1) about 99% of an aqueous solution containing about 1.7% AN, 1.2% ADN, 10% of a mixture of sodium orthophosphates, which corresponds to a pH of the solution of 9, and between 4 and 9 · 10 ^-3 Mol / l contains dissolved ethyltributylammonium ions, and

2) about 1% of a dispersed but undissolved organic phase containing about 31% AN, 52-53% ADN, contains 8 - 9% AN dimerization by-products and 8% water,

circulate through an undivided electrolytic cell at 55 ° C and at 1.22 m / sec. This cell contains an AISI 1020 carbon steel anode placed 0.238 cm from a cadmium cathode (at least 993% Cd). As it passes through the cell, the medium is ^{electrolyzed with a current density of 20 A / dm 2} surface of the anode or cathode. The organic phase, which contains ADN, by-products and unreacted AN, is separated from the electrolyzed medium. To make up certain AN is added, after which the medium is again circulated through the cell and the electrolysis is continued under the conditions described. Initially, the medium contains dissolved iron and cadmium in concentrations of 4.75 and 0.24 mmol / l and tetrasodium ethylenediamine tetraacetate (Na ₄ EDTA) and its degradation products in such proportions that the medium contains another 5.8 mmol / l iron and / or Can dissolve cadmium, but not more than this amount. For each Faraday current passed through the medium, 0.28 mmol of Na ₄ EDTA are added to the circulating medium and 13.2 g of solution are withdrawn from the system and replaced with water containing sufficient dissolved ethyltributylammonium ions and sodium orthophosphate to reduce the concentrations of these constituents of the solution to the aforementioned values and the total volume of the medium is essentially constant to keep. Under these conditions, the anode and cathode corrode at average speeds of about 0.063 and 0.007 cm / year, respectively, so that 0.139 mmol of iron and 0.008 mmol of cadmium per Faraday current are transferred into the medium and the iron and cadmium transferred during the electrolysis 5.8 mmol / l of medium during the first 185 hours of electrolysis. By adding 0.28 mmol of Na ₄ EDTA, an excess of free nitrile carboxylic acid compound with an average sequestering capacity of 2 mmol of iron or cadmium / I solution can be maintained in the aqueous phase of the medium. This is achieved in that the aqueous phase and the concentrations of dissolved iron and cadmium in the solution are stable in the ranges of 206-378 and 28-35 ppm (4-7 3 and 0.27-034 mmol / l) are, while about 40% of the iron that passes from the anode into the electrolytic medium forms removable solids by filtration. After 358 hours of electrolysis under these conditions, the AN is converted into ADN with an average selectivity of 86.5%. The voltage drop in the cell is constant between 33 and 4.0 V and the volume percentage of hydrogen in the waste gas from the electrolysis is 8% on average.

At this point, the removal speed for cleaning is reduced to 4.4 g / F. Iron and Cadmium continues to go in at essentially the same stated average rates the electrolysis medium over, but surprisingly the concentration of the dissolved Iron in solution not increased. Instead, the concentration remains in the range of 290-320 ppm (5.6-6.2 mmol / l) constant, while about 80-85% iron that from the anode into the electrolysis medium was transferred, forms removable solids by filtration. At the reduced cleaning speed is obtained by adding 0.28 mmol of NsuEDTA / F in the aqueous phase excess free nitrile carboxylic acid compound with an average iron or cadmium sequestration capacity of 43 mmol / l solution. The concentration of cadmium dissolved in the solution is in the range of 70-80 ppm (0.68-0.70mmol / l) constant. During an additional 191 hours of electrolysis under these conditions, it becomes ON converted to ADN with an average selectivity of 87%. The voltage drop remains below 4 V and the volume percentage of hydrogen in the exhaust gas is less than 10% on average.

Comparative example A.

An electrolysis medium which is essentially the same as that of Example 1 is electrolyzed under essentially the same conditions as in Example I, except that an intermediate _{cleaning draw of 8.06 g / F and a smaller addition of Na 4} EDTA of 0.085 mmol / F Under these conditions, the concentrations of dissolved iron and cadmium in the solution are constant at about 260 and 40 ppm (5 and 0.39 mmol / l); however, average rates of iron and cadmium transferred to the electrolytic medium are at least as great as in Example I. The rate of addition of Na ₄ EDTA is insufficient to maintain an excess of free nitrile carboxylic acid compound in the medium. After 166 hours of electrolysis, the corrosion accelerates

Anode considerably; the ADN selectivity drops to 84%, the voltage drop in the cell increases to 4.4 V. and the volume percentage of hydrogen in the Exhaust gas increases to 26%.

Example 2

In a continuous process, one lets in liquid electrolysis medium that consists of

IO

1) 99% of an aqueous solution between 13 and 1.6% AN, about 1.2% ADN, between 4 and 10 - 10 * MoIZI Äthyltributylammoniumionen, 10% of a mixture of sodium orthophosphates as well Sodium borates, obtained by neutralizing orthoboric acid in an amount equal to 2% of the Solution at a pH value of the solution of 84 corresponds, contains dissolved and from about

2) Γ% of a dispersed but undissolved organic Phase that is about 24-30% AN. 54-60% ADN, 8% AN-Dimerisserisserungsnebeaprodsiktc and 8% water contains,

circulate through an undivided electrolytic cell at 55 ° C and 1.22 m / sec. This contains an anode made of AISI 1020 carbon steel which is arranged at a distance of 0.178 cm from a cadmium cathode (at least 993% Cd). The electrolysis takes place in the cell with a current density of 16 A / dm ² surface of the anode or cathode. The organic phase, which contains ADN, by-products and unreacted AN, is separated from the electrolyzed medium and AN intended for replenishment is added. The medium is then again circulated through the cell and the electrolysis is continued under the conditions described. Initially, the medium contains about 6.8 mmol / l of dissolved iron and Na ₄ EDTA and its degradation products in such proportions that the medium is able to dissolve a further 43 mmol / l of iron and / or cadmium, but not more than this amount . For each Faraday current that is passed through the medium, 0.4 mmol of Na ₄ EDTA are added to the circulating medium and 12 g of the solution are removed from the system and replaced by water that contains sufficiently dissolved ethyltributylammonium ions and sodium orthophosphates and borates, in order to keep the concentrations of these components of the solution essentially constant at the values indicated above and the total volume of the medium. Under these conditions the anode and $ 0 cathode corrode at average velocities of (about 0.033 and 0.007 cm / Fahrenheit, respectively), ie 0.09 mmol of iron and 0.009 mmol of cadmium per Faraday current are passed into the medium during the electrolysis Conveyed iron and cadmium exceed 43 mmol / l of medium during the first 46 hours of electrolysis. By the addition of 0.4 mmol of Na ₄ EDTAZF an upper weft chen Sesquestrierungsvermögen can in the aqueous phase of the medium to be maintained free of sequestering agents having a durchschnittli- _M of 2.5 mmol of iron or cadmium / I solution, with the result that the aqueous phase and the concentrations of dissolved iron and cadmium in the solution are stable in the ranges of 326-450 and 35-90 ppm (63-8.7 and 0.34-0.87 mmol / l, respectively). After 232 hours of electrolysis, it can be seen that AN is converted to ADN with a selectivity between 873 and 88.1%. the voltage drop in the cell (3.73 V) has not increased since the start of the procedure and that the Volume percentage of hydrogen in the exhaust gas averages 4-5% with a maximum of 6% and a final value of 54%

Example 3

If a substantially similar procedure as in Example 2 is carried out for 429 hours, with the difference that the electrolysis medium initially contains dissolved iron and cadmium in concentrations of about 11 t and 2.4 mmol / 1, respectively, the Na ^ DTA addition rate 0.495 mmol / F and the current density 184 A / dm ² , the anode and corrode. Cathode with average velocities of about 0.055 and 0.010 cm / year, respectively. Thus 0.132 mmol of esen and 0.012 mmol of cadmium are introduced into the medium per Faraday of the current passed through the medium. The amounts of iron and cadmium transferred into the medium during the first 31 hours of electrolysis exceed 43 mmol / l of medium. By adding 0.495 mmol of Na ₄ EDTAZF, an excess of free Nitrilcarbonsäureverbmdung with an average Scsquestrierbarkeit of 5.75iriMol iron or cadmium / l solution is obtained in the aqueous phase of the medium, whereby it is achieved that the aqueous phase and the concentrations of dissolved Iron and cadmium in the solution are stable in the 455-570 and 94-178 ppm (8.8-11.0 and 03-UmMoJZI, respectively) ranges. Under these conditions, AN is converted to ADN with average and final selectivities of 88 and 87.1%, respectively, the voltage drop in the cell is stable at 3.84-33 V and the volume percentage of hydrogen in the exhaust gas carries an average of about 10% a final value of 16.4%.

Example 4

In a continuous process, a liquid electrolytic brain is drained from it

1) about 99% of an aqueous solution containing about I - AN, 1.2% ADN, 12 ^% of a mixture of potassium orthophosphate 74-16 - 10- ³ MoIZI Äthyltributylammoniumionen and sodium borates, which are herstelit by neutralizing orthoboric acid in an amount which corresponds to 2% of the solution at a pH value of the solution of 84, contains dissolved, and

2) about 1% of a dispersed but undissolved one

organic phase, the 18-27% AN, 57 6%

Contains ADN, 8% AN dimerization by-products and 8% water,

exists at 55 ° C and circulating at t, 22m per second through a non-divided electrolytic cell. The cell enthäit an anode made of AISI 1020 carbon steel, the cm at a distance of 0.178 (at least 993% Cd) of a Cadmhimkathode is arranged the electrolysis proceeds at a current density of 16 ¹ Mim surface of the anode or the cathode. The organic phase, which contains ADN, by-products and unreacted AN, is separated from the electrolyzed medium

conditions just described continues. Initially, the medium contains dissolved iron in a concentration of 13.7 mmol / l and Na ₄ EDTA and its degradation products in such proportions that the medium is not suitable for dissolving additional iron and cadmium. For each Faraday current that is passed through the medium, 0.4 mmol of Na ₄ EDTA is added to the circulating medium and 12 g of the solution are removed from the system for cleaning purposes and replaced by water containing sufficient amounts of dissolved ethyltributylammonium ions, potassium orthophosphate and sodium borate contains in order to keep the concentrations of these components of the solution at the above-mentioned level and the total volume essentially constant. Under these conditions, the anode and cathode corrode at average speeds of 0.038 and 0.007 cm / year, respectively, so that 0.104 mmol of iron and 0.009 mmol of cadmium are transferred into the medium per Faraday current. By adding 0.4 mmol of Na4EDTA / F, an excess of free sequestering agent with an average sequestering capacity of 3 mmol of iron or cadmium per liter of solution is maintained in the aqueous phase of the medium dissolved iron and cadmium in the solution remain stable in ranges of 519-708 and 209-475 (103-14.1 and 2.1-4.7 mmoles per liter, respectively). It is found that after 233 hours of electrolysis under these conditions, AN is converted to ADN with an average and final selectivity of 88%, the voltage drop in the cell (3.65 V) has not increased since the start of the process and that the volume percentage of hydrogen in the exhaust gas averages 3-4% at a final value of 4.4%

Example 5

In a continuous process one lets in liquid electrolysis medium that consists of

1) about 85.4% of an aqueous solution containing about 1.7% AN, 1.2% ADN, 10% of a mixture of sodium orthophosphates, ^{2-5 · 10 -3} mol / l ethyltributylammonium ions and sodium borates, which are neutralized of orthoboric acid in an amount which corresponds to 1.8% of the solution at a pH value of the solution of 8.5 contains and

2) about 14.6% of a dispersed but undissolved organic phase containing about 31% AN, 53-54% Contains ADN, 7-8% AN dimerization by-products and 8% water,

consists of circulating through a non-divided electrolytic cell at 55 ° C and 1.22 m / sec. The cell contains an AISI 1020 carbon steel anode positioned 0.178 cm from a cadmium cathode (at least 993% Cd). The electrolysis is carried out with a current density of 18.5 A / dm ² , measured on the surface of the anode or cathode. The organic phase, which contains ADN, by-products and nichium-added AN, is separated from the electrolyzed medium and supplementary AN is added to it. The medium is then circulated through the cell again and the electrolysis is continued under the conditions described. Initially, the electrolysis medium contains iron and cadmium dissolved in concentrations of 9.0 or 2.75 mmol / l and Na ₄ EDTA and its degradation products in such proportions that the medium is suitable. to dissolve another 5.25 mmol / l iron and / or cadmium, but not more than this amount. For each Faraday current that is passed through the medium, 0.4 mmol of Na ₄ EDTA are added to the circulating medium and 12 g of the solution are used for purification removed from the system and replaced by water, the sufficiently dissolved ethyltributylammonium ions and sodium orthophosphates and borates contains around that Concentrations of these components of the solution at the specified content and the total volume of the To keep the medium essentially constant. Under these conditions the anode and corrode Cathode at average speeds of 0.05 and 0.007 cm / year, so that 0.72 mmol of iron and 0.008 mmol of cadmium per Faraday current into the Mediun? be convicted. The --iron and cadmium introduced into the medium during the electrolysis exceeded 5.25 mmol / l medium during the first 71 hours of the electrolysis. Addition of 0.4 mmol of Na ₄ EDTAZF is obtained in the aqueous

Phase of the medium contains an excess of free nitric carboxylic acid compound with an average sesquester capacity of 5.25 mmol of iron or Cadmium per liter of solution, which ensures that the aqueous phase and the concentrations dissolved iron and cadmium in the solution in the ranges of 465 - 490 and 170 - 288 ppm (9 - 93 and 1.6-23 mmol / l) are kept stable. After 69 hours of electrolysis under these conditions it is shown that daS AN with average and final selectivities of 87 ^% is converted to ADN, the voltage drop in the cell was stable at less than 4V and that the volume percentage of hydrogen in the exhaust gas was a final value of 6% averages 3–4%

Example 6

In a continuous process, a liquid electrolysis medium is left out

1) about 99% of an aqueous solution containing between 1.4 and 1.8% AN, about 1.2% ADN, 10-11% of a mixture of sodium orthophosphate, about 1,4 10- ³ MOUL Äthyltributylammoniumionen and sodium borates, which is prepared by neutralizing orthoboric acid in an amount which corresponds to 2% of the solution at a pH of 83 dissolved, and

2) about 1% of a dispersed but not dissolved organic phase containing 27-32% AN, 53-59% ADN, 6 - 7% AN dimerization by-products and contains 8% water

exists at 55 ° C and 1.22 m / sec by an undivided circulate electrolytic cell. The cell contains egg-ie

go Anode made of AJSI 1020 carbon steel, which is arranged at a distance of 0.178 cm from a cadmium cathode (at least 993% Cd). When passing through the cell, the medium has a current density of 183 A / dm ^{2 on the} surface of the anode or cathode Electrolyzed The organic phase, which contains ADN, by-products and nictitumgvisetztes AN, is of separated from the electrolyzed medium and supplemental AN is added to the medium. Then lets

the medium is recirculated through the cell and the electrolysis is continued under the conditions described. Initially, the medium contains dissolved iron and cadmium in concentrations of about 12.8 and 2.8 mmol / l and trisodium hydroxyäthyläthylcndi- i amintriacetat (NajHEDTA) and its degradation products in such proportions that the medium another 4.9 mmol per liter of iron and / or Can dissolve cadmium, but not more than this amount. For each Faraday current that is passed through the medium, 0.495 mmol of Na ₅ HEDTA are added to the circulating medium and 12 g of the solution are removed from the system for purification and replaced by water which contains sufficient amounts of dissolved ethyltributylammonium ions and sodium orthophosphates and borates to keep the concentrations of these components of the solution essentially constant at the values described and the total volume of the medium. Under these conditions, the anode and cathode corrode at average speeds of iin-> n danger 0.059 and 0.020 cm / year, so that 0.14 mmol of iron and 0.022 mmol of cadmium per Faraday current are transferred into the medium and that into the medium during the Iron and cadmium transferred to electrolysis exceed 4.9 mmol per liter of medium. >>

During the first 27 hours, the electrolysis 0.495 mmol Naj HRDTA / F was added, an excess can be maintained in free NitrilcarbonsäureverbimJung whereby in the aqueous phase of the medium, which has an average j ₀ sequestering of 4.6 mmol of iron or cadmium per liter of solution, whereby it is achieved that in the aqueous phase the concentrations of dissolved iron and cadmium in the ranges of 538-668 and 106-279 ppm (10.4-12.9 and 1.0-2.7 mmol / l) are stable and about 4% of the iron transferred from the anode into the medium forms removable solids by filtration. After 241 hours of electrolysis under these conditions, AN is converted to ADN with average and final selectivities of 89.3 and 89%, respectively, the voltage drop across the cell is stable at 3.9 V and the volume percentage of hydrogen in the exhaust gas averages 43% at a final value of 5.4%.

Example 7

When an electrolysis medium substantially identical to that of Example 6 is electrolyzed under substantially the same conditions as in Example 6 for 362 hours, the anode and cathode corrode at average speeds of about 0.058 and 0.017 cm / year, respectively, so that 0.137 mmol of iron and 0.019 mmol of cadmium are transferred into the medium per Faraday of the current passed through the medium. The amounts of iron and cadmium transferred into the medium during the electrolysis exceed 4.9 mmol / l medium during the first 28 hours of the electrolysis. By adding 0.495 mmol of Na ₃ HEDTA / F, an excess of free nitrile carboxylic acid compound with an average sesquester capacity of 5.6 mmol of iron or cadmium per liter of solution is obtained in the aqueous phase of the medium, which means that the aqueous phase and the concentrations of dissolved iron and cadmium in the solution are stable in the ranges of 506-558 and 105-279 ppm (9.8-10.8 and 1.0-2.7 mmol / l, respectively). Under these conditions, AN is converted to ADN with average and final cleklivities of 88.7% and 87.1%, respectively, the voltage drop through the cell is stable at 3.9 V and the volume percentage of hydrogen in the exhaust gas is in the Average 7.2%, with a final score of 8.5%.

Example 8

In a continuous process, a liquid electrolysis medium is left out

I) / between 85.9 and 87.5% of an aqueous solution containing between 1.4 and 1.6% AN, about 1.2 ^{0 /} <· ADN 9.6-9.9% of a mixture of sodium orthophosphates, 0.8-2.5 · 10 ^J mol / l ethyltributyliimmonium ions and sodium borates, which can be obtained by neutralizing orthoboric acid in a quantity

10 / n

k * ii

pH of the solution corresponds to 8.5-9, dissolved contains, and

2) / between 12.5 and 14.1% of a dispersed. but undissolved organic phase which is 26-29% AN, 54-59% ADN. 7-9% AN-Dimerisierungsnebcn-P ^{1--products',} and contains 8% water,

exists, at 55 ° C i »- .. i!, 158 m / sec circulate through an undivided electrolyte« <rhe cell. The cell contains an AISI 1020 carbon steel anode positioned 0.228 cm from a cadmium cathode (at least 99.9% Cd). Oif electrolysis takes place at a current density of 2OAZdIn 'surface of the anode or cathode. The organic phase, which contains ADN, by-products and unreacted AN, is separated from the electrolytic medium and supplementary AN is added. The medium is then allowed to circulate through the cell again and the electrolysis continues under the conditions described. Initially, the electrolysis medium contains dissolved iron and cadmium in concentrations of 63 or 1.25 mmol / l and Na ₄ EDTA and its breakdown products in such proportions that the medium can dissolve a further 2.75 mmol per liter of iron and / or cadmium, but not more than this amount. For each Faraday current that is passed through the medium, 0.475 mmol of Na ₄ EDTA are added to the circulating medium and about 10 g of the solution are removed from the system for cleaning and replaced by water that contains sufficiently dissolved ethyltributylammonium ions and sodium orthophosphates and borates In order to keep the concentrations of these constituents of the solution at the aforesaid level and the total volume of the medium essentially constant. Under these conditions, the anode and cathode corrode at average speeds of about 0.05 and 0.012 cm / year, respectively. so that 0.12 mmol of iron and 0.014 mmol of cadmium per Faraday current are transferred to the medium. The amounts of iron and cadmium introduced into the medium during electrolysis exceed 2.75 mmol / l of medium during the first 102 hours of electrolysis. By adding 0.475 mmol of Na ₄ EDTAZF, an excess of ar-free sequestering agent is obtained in the aqueous phase of the medium an average sesquestration capacity of 3.6 mmol of hiser or cadmium per liter of solution, whereby it is achieved that the aqueous phase and the concentrations ar

25 26

dissolved iron and cadmium in the solution in that 87 and 88%, respectively, are converted to ADN;

Range of 350 to 550 and 130- 165 ppm (11.6 6,8- the voltage drop in the cell at 4 V is stable _^and:

and 1.25-1.55 mmol / 1) are kept stable. After that the volume percentage of hydrogen in the i

268 hours of Flektrolysis under these conditions exhaust averages about 6.5% at one
/ it is agreed that AN with average and final selectivi- "<final value of 10.4%. _; ,

Claims (1)

Claim: Process for the hydrodimerization of an olefin compound of the general form! R R I I R-C = C-CN in which R is a hydrogen atom or a Ci- to Q-alkyl radical and at least one R radical is a hydrogen atom, by electrolyzing an aqueous solution which is ^{quaternary in dissolved form at least 0.1 percent by weight of the olefin compound, at least about 10 5} gmol / l Ammonium cations, at least 0.1 percent by weight of a conductive salt and 0.025 to 50 mmol / l of a nitrile carboxylic acid compound, namely ethylenediaminetetraacetic acid and / or ethylenediaminetetrapropionic acid and / or N-hydroxyethylethylenediamine triacetic acid and / or diethylenetriamine pentaacetic acid and / or nitrile and / or nitrile Contains (2-hydioxyäthyl) glycine and / or an alkali metal or ammonium salt of such acids, according to Patent 23 44 294, characterized in that the nitrile carboxylic acid compound is added to the medium at the beginning and during the electrolysis in an amount sufficient for an excess of free nitrile carboxylic acid compound over the practically complete solution of the The amount of nitrilocarboxylic acid compound introduced by the electrolysis is maintained in the medium, and that the concentration of the heavy metal dissolved in the medium is also maintained by withdrawing part of the electrolysis medium and replacing it with an electrolyte less concentrated in heavy metal ions or precipitating the heavy metal ion from the withdrawn part of the Electrolysis medium after separation of the organic substance essentially keeps constant between about 2 and about 50, preferably 4 and 30 mmol. The present invention relates to a process for the hydrodimerization of an olefin compound of the general formula R R R-C = C-CN in which R is a hydrogen atom or a Ci- to Ci-alkyl radical and at least one R radical is a hydrogen atom, by electrolyzing an aqueous solution which, in dissolved form, contains at least 0.1 percent by weight of the olefin compound, at least about ΙΟ- ⁵ gmol / l quaternary ammonium cations, at least 0.1 percent by weight of a conductive salt and 0.025 to 50 mmol / l of a nitrile carboxylic acid compound, namely ethylenediaminetetraacetic acid and / or ethylenediamine tetrapropionic acid and / or N-hydroxyethylethylenediamine triacetic acid and / or diethylenetriamine pentaacetic acid and / or diethylenetriaminepentaacetic acid and / or N, N-di (2-hydroxyethyl) glycine and / or an alkali metal or ammonium salt of such acids contains, according to patent 23 44 294. The preparation of paraffinic dinitriles by means of electrolytic hydrodimerization of a «^ -olefin nitrile is generally known and, for example, in the U.S. Patents 3,193,475-79 and 3,193,481-83. Although the procedure has been going on for a number of ίο Years of proven practice will continue Strive for improvements, in particular to lower the costs previously incurred with those in practice preferred used, through a membrane permeable to cations in anolyte and catholyte chambers divided cells were connected. For example, in Canadian Patent 8 13 877, it is described that increased yields are obtained Adipic acid dinitrile can thereby achieve dr £? one one neutral aqueous solution of acrylonitrile, one The alkali metal salt of a polybasic acid and a quaternary ammonium salt is electrolyzed in an undivided cell with a graphite cathode and a 99% iron oxide anode at a current density of 4 A / dm ² and a temperature of 15 to 18 ° C ^ However, technical application of such a low current density would require excessive capital an expensive cooling of the electrolysis cells and working at such a low temperature Make electrolysis medium required. Good at However, catch yields of adipic dinitrile are also to achieve at much higher temperatures and current densities, as shown in Example 2, Experiment 1 of Referring to US Pat. No. 3,616,321, continued electrolysis of a solution, similar to that of US Pat Canadian patent, for several hundred hours and at a significantly higher current density (7.9 A / dm ² ) leads to an unacceptably high anode corrosion rate (22 mm / year) and gives an adipic acid dinitrile yield that is in the through cut over the total duration of the process is much less than specified in the Canadian patent for a current density of 4 A / dm ^2. One way of combating such anode corrosion is in US Pat. No. 3,616,321 in which it is disclosed that in the production of adipic dinitrile by electrolysis of an aqueous emulsion of acrylonitrile, an alkali metal phosphate and a quaternary ammonium salt at current densities of up to 20 A / dm ² and temperatures of up to 40 ° C (preferably near room temperature) in an undivided cell with a graphite cathode and an iron or magnetite anode, the corrosion of the anode can essentially be inhibited by that an electrolysis medium is used at the beginning, containing an alkali metal polyphosphate. However, it can be seen from Example 2, Experiment 2, of the cited patent that, despite a reduction in the rate of corrosion of the anode due to the presence of the polyphosphate, the average yield of adipic acid dinitrile and the current efficiency during an operating time of 215 hours (with 74.7 and 70.5%, respectively) were lower than with the same current density (7.9 A / dm ² ), but without the use of the polyphosphate. It has also been shown that with longer periods of operation, which in practice in the technical Scope are preferred, at least a part of the heavy metal elec-