Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B3/00—Electrolytic production of organic compounds
  • C25B3/20—Processes
  • C25B3/29—Coupling reactions
  • C25B3/295—Coupling reactions hydrodimerisation

Definitions

• the selectivity with which the hydrodimer is produced is surprisingly high when the solution contains less than about by weight of the olefinic compound, more than 5% by weight of the alkali metal salt and/or alkali metal cations constituting more than half of the total weight of all cations in the solution and the solution is electrolyzed in contact with a cathode consisting essentially of cadmium.
• one approach to improvement of the process has been to carry out the electrolysis in an aqueous solution of a mixture of quaternary ammonium and alkali metal salts together with the olefinic compound to be hydrodimerized.
• adiponitrile is produced by electrolyzing a neutral aqueous solution of acrylonitrile, an alkali metal salt of a polyvalent acid such as phosphoric, boric or sulfuric and a small quantity of a quaternary ammonium salt.
• good selectivities can be achieved when such a process is carried out in an undivided (membraneless) cell having a graphite cathode.
• the aqueous solution has dissolved therein at least about 0.1% of the olefinic compound, quaternary ammonium cations in a concentration of at least about 10- gram mol per liter and at least about 0.1% of alkali metal salt sufiicient to provide alkali metal cations constituting more than half of the total weight of all cations in the solution.
• the aqueous solution has dissolved therein at least about 0.1% of the alkali metal salt, quaternary ammonium cations in a concentration of at least about 10 gram mol per liter and at least about 0.1% but less than about 5% of the olefinic compound.
• the aqueous solution has dissolved therein at least about 0.1% of the olefinic compound, quaternary ammonium cations in a concentration of at least about l gram mol per liter and at least about 5% of the alkali metal salt.
• fouling of the cathode proceeds very slowly and the hydrodimer selectivity remains high for an exceptionally long time when the cathodic surface has a centerline average not greater than about 90 microinches.
• Each of the embodiments of the invention is particularly useful in the preparation of adiponitrile, a nylon 66 intermediate, by the hydrodimerization of acrylonitrile.
• 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 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, methacrylonitrile, crotononitrile, 2 methylenebutyronitrile, 2 pentenenitrile, 2 methylenevaleronitrile, 2 methylenehexanenitrile, tiglonitrile or 2 ethylidenehexanenitrile; olefinic carboxylates such as, for example, methyl acrylate, ethyl acrylate or ethyl crotonate; and olefinic carboxamides such as, for example, acrylamide, methacrylamide, N,N- diethylacrylamide or N,N-diethylcrotonamide.
• olefinic nitriles such as, for example, acrylonitrile, methacrylonitrile, crotononitrile, 2 methylenebutyronitrile, 2 pentenenitrile, 2 methylenevaleronit
• Products of hydrodimerization of such compounds have the structural formula X-CHRCR CH CHRX wherein X and R have the aforesaid significance, i.e., paraffinic dinitriles such as, for example, adiponitrile and 2,5 dimethyladiponitrile; parafiinic dicarboxylates such as, for example, dimethyladipate and diethyl 3,4 dimethyladipate; and paraflinic dicarboxarnides 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.
• 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 an alkali metal salt.
• the electrolysis medium can be a single-phase aqueous solution containing essentially no undissolved organic phase, by which is meant that the solution may contain no undissolved organic phase or, alternatively, a minute proportion of undissolved organic phase, such as might remain entrained in the aqueous solution despite the latter being permitted to stand without agitation after electrolysis and cooling to separate a product-containing organic phase, but the presence of which does not have any significant effect on the olefinic compound conversion per pass or hydrodimer selectivity achieved when the separated aqueous phase is recycled for further electrolysis in accordance with the process of this invention.
• Such a minute proportion would be generally less than 5% (e.g. not more than 4.5%) of the aqueous solution, more typically less than about 2% (e.g. not more than 1.8%) of the aqueous solution and preferably less than 1% (e.g. not more than 0.8%) of the aqueous solution.
• the invention can be carried out by electrolyzing an aqueous solution of the type described hereinbefore but having dispersed therein an undissolved organic phase in a larger proportion (e.g. from about 5% up to 20% or even 50% or more of the aqueous solution) which may or may not significantly affect the conversion per pass or hydrodimer selectivity depending on other conditions of the process.
• concentrations of the recited constituents of the aqueous solution to be electrolyzed are with reference to the recited aqueous solution alone and not the combined contents of said aqueous solution and an undissolved organic phase which, as aforesaid, may be present in the aqueous solution as the process of this invention is carried out.
• the olefinic compound to be hydrodimerized will be present in at least such a proportion 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 solution, more typically at least about 0.5% of the aqueous solution and, in some embodiments 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.
• the aqueous solution contains less than about 5% (e.g. not more than 4.5%) of the olefinic compound and, in most of those embodiments, preferably not more than 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 hydrodimer selectivity (e.g. at least about although much higher proportions can be present if desired or convenient. In most cases, the quaternary ammonium cations are present in a concentration of at least about 10- gram mol per liter of the aqueous solution. Even more typically their concentration is at least about 10" gram mol per liter of the solution and, in many embodiments, preferably at least about 10* gram mol per liter.
• 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 concentration not higher than about 0.1 gram mol per liter.
• the concentration of quaternary ammonium cations in the solution is at least about 2 10 gram mol per liter but not more than about 5 1() and, in many cases, not more than about 2 10 gram mol per liter.
• the quaternary ammonium cations that are present in such concentrations are those positively-charged ions in which a nitrogen atom has a valence of five and is directly linked to other atoms (e.g. carbon) satisfying four fifths of that valence.
• Such cations may be cyclic, as in the case of the piperidiniums, pyrrolidiniums and morpholiniums, but they are generally of the type in which the nitrogen atom is directly linked to a total of four monovalent organic groups from the group consisting of alkyl or aryl radicals or combinations thereof.
• the aryl groups contain typically from six to twelve carbon atoms and preferably only one aromatic ring as in, for example, a phenyl or benzyl radical.
• the alkyl groups can be straight-chain, branched or cyclic and each typically contains from one to twelve carbon atoms.
• quaternary ammonium cations containing a combination of such alkyl and aryl groups e.g. benzyltriethylammonium ions
• many embodiments of the invention are preferably carried out with tetraalkylammonium ions and superior results are generally obtained with the use of those containing at least three C -C alkyl groups and a total of from 8 to 24 carbon atoms in the four alkyl groups, e.g.
• the alkali metal salts which can be employed in the invention are those of sodium, potassium, lithium, cesium and rubidium. Generally preferred for economic reasons are those of lithium and especially sodium and potassium. They may be salts of a monovalent acid, e.g. a perchlorate, a nitrate or a halide such as a chloride or bromide. In some cases, e.g. where corrosion control is more of a factor, it may be desirable to use an alkali metal salt of a polyvalent acid, e.g. an orthophosphate, borate, carbonate or sulfate, and particularly an incompletely-substituted salt of that type, i.e.
• a polyvalent acid e.g. an orthophosphate, borate, carbonate or sulfate
• salts in which the anion has at least one valence thereof satisfied by hydrogen and at least one other valence thereof satisfied by an alkali metal examples include disodium phosphate (Na HPO potassium acid phosphate (KH PO sodium bicarbonate (NaHCO dipotassium borate (K HBO and sodium acid sulfate (NaHSO).
• Na HPO potassium acid phosphate KH PO sodium bicarbonate
• K HBO and sodium acid sulfate NaHSO
• alkali metal salts of condensed acids such as pyrophosphoric, metaphosphoric, metaboric, pyroboric and the like (e.g. sodium pyrophosphate, potassium metaborate, etc.).
• the stoichiometric proportions of such anions and alkali metal cations in the solution may correspond to a mixture of two or more of such salts, e.g. a mixture of sodium acid phosphate and disodium phosphate, and such a mixture of salts is intended to be within the scope of the expression alkali metal salt as used in this specification and the appended claims.
• Any of the alkali metal salts may be dissolved in the aqueous solution as such or otherwise, e.g. as the alkali metal hydroxide and the acid necessary to neutralize the hydroxide to the extent of the desired acidity of the aqueous solution.
• the concentration of alkali metal salt in the solution should be at least sufiicient to substantially increase the electrical conductivity of the solution above its conductivity without such a salt being present.
• the solution has dissolved therein at least about 0.1% of the alkali metal salt. More advantageous conductivity levels are achieved when the solution has dissolved therein at least about 1% of alkali metal salt or, more preferably, at least about 2% of such a salt.
• optimum process conditions include the solution having dissolved therein more than 5% (typically at least 5.5%) of alkali metal salt.
• alkali metal salt in the solution is 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 12% of such a salt or mixture thereof.
• the acidity of the solution need only be such that a neutral or alkaline condition prevails at the cathode. Since there is normally an acidity gradient across the cell, pH at the anode can be lower than seven, if desired. In most cases, however, pH of the overall solution should be at least about two, is preferably at least about five and when the solution is in contact with certain metals subject to corrosion, is most conveniently at least about seven. Also in most cases, the overall solution pH is not higher than about twelve, typically not higher than about eleven and, with the use of sodium and/or potassium phosphates, generally not higher than about nine.
• 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 75 C. 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 hydrodimerization of acrylonitrile to adiponitrile, an electrolysis temperature between about 25 and about 65 C. is usually preferred.
• a liquid-impermeable cathode is usually preferred.
• the aqueous solution to be electrolyzed is generally passed along the surface thereof 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, if desired, 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 generally of a width between about 60 mils and about onequarter inch.
• 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 sufiicient for hydrodimerization of that compound.
• a current density of at least about 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.
• the process of this invention is carried out with a cathodic surface consisting essentially of cadmium, meaning that the cathodic surface contains a very high percentage of cadmium (generally at least about more typically at least about and preferably at least about 98%) but that it may contain a small amount of one or more other constituents that do not alter the nature of the cadmium cathode so as to prevent it from providing the advantages of the present invention, particularly as described herein.
• Such other constituents, if present, are desirably other materials having relatively high hydrogen overvoltages, e.g.
• thallium, mercury, manganese, lead, zinc, tin, graphite, etc. but preferably not such materials of relatively low hydrogen overvoltage as copper or nickel in any concentration higher than about 0.05% or, even more desirably, about 0.02%, based on the cadmium in the cathodic surface.
• such other materials are present in a relatively high concentration such as, for example, from about 0.5% up to about or higher, they are preferably lead and/or mercury.
• the cathodic surface has a cadmium content of at least about 99.5%, even more typically at least about 99.8% and most desirably at least about 99.9% as in ASTM Designation B440-66T (issued 1966).
• Cathodes employed in this invention can be prepared by any of various techniques such as, for example, electroplating of cadmium on any suitably-shaped substrate of some other material, e.g. a metal having greater structural rigidity, or by chemically, thermally and/or mechanically bonding a layer of cadmium or an alloy thereof containing one or more of the aforementioned other optionallypresent cathode constituents to a similar substrate.
• a plate, sheet, rod or any other suitable configuration consisting essentially of cadmium may be used without such a substrate, if desired.
• 1,014,428 process embodiments using a cadmium cathode is normally at least about 75 i.e., at least about 75% of the mols of converted olefinic starting material are converted to the desired dinitrile, dicarboxylate or dicarboxamide.
• the molar selectivity of the present process is at least about 80% and, in some instances including certain embodiments employed in hydrodimerization of acrylonitrile to adiponitrile, as high as 85% or even higher.
• 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 undergoing electrolysis is not in contact with the anode of the cell and products of anode corrosion, if any, are substantially prevented from migrating to the cathode of the cell.
• the process can also be carried out in a cell that is not divided in that manner, i.e., in an electrolytic cell in which the aforedescribed aqueous solution is in contact with the anode of the cell while it is in contact with the cathode of the same cell, and in which the anode is composed of a material not corroded by the solution at a substantial rate (e.g. at least about 10 inch per year) such as, for example, one of the materials conventionally regarded as corrosion-proof (e.g. platinum, various alloys of platinum, other precious metals and alloys thereof, lead dioxide, carbon, etc.).
• a substantial rate e.g. at least about 10 inch per year
• anode corrosion products normally do not reach the cathode of the cell in a quantity large enough to plate out on or foul the cathode to a degree sulficient to greatly lower the hydrodimer selectivity of the process and it has been found that the surface smoothness of the cathode is generally not of critical importance to longterm maintenance of high selectivities when that is the case.
• the process of this invention can be carried out in an undivided cell in which the anode is in contact with the aqueous solution, as aforesaid, and the anode is composed of a material which, depending on process conditions such as the particular alkali metal salt employed, the solution temperature, etc., may or may not be corroded by the solution at a substantial rate under the electrolysis conditions.
• Such less corrosion-resistant anode materials include the ferrous metals such as iron and steel, magnetite, nickel, nickel silicide and, in fact, any metal or alloy capable of being passivated, particularly if the solution undergoing electrolysis is alkaline or at least not strongly acidic (i.e., pH not substantially below seven).
• the centerline average of the cathodic surface employed in this embodiment of the present process is desirably less than about 70 microinches, preferably less than about 50 microinches and, for superior results in many cases, less than about 30 microinches, all determined in accordance with the definition in the aforecited ASA publication.
• Centerline average can be measured by various procedures and types of apparatus, exemplary of which are the Rank Taylor Hobson Talysurf 4 and the procedures described in the Talysurf 4 Operators Handbook distributed by Rank Precision Industries Ltd., Metrology Division, PO. Box 36, Sheffield House, Lee Circle, Sheffield LE1 9JB, England and in the USA. by Engis Equipment Company, 8035 Austin Avenue, Morton Grove, Ill.
• anode corrosion may otherwise proceed at a relatively high rate, it may be desirable to also include in the electrolysis medium a small amount (generally between about 0.02% and about 2%) of an inhibitor of corrosion of the anode material employed (e.g. an alkali metal salt of a condensed acid such as pyrophosphoric, metaboric or the like when the anode material comprises a ferrous metal) and/or a similarly small amount of a chelating agent for the anode metal (e.g. a diacetic or polyacetic acid compound such as ethylenediaminetetraacetic acid, nitrilotriacetic acid or the like).
• an inhibitor of corrosion of the anode material employed e.g. an alkali metal salt of a condensed acid such as pyrophosphoric, metaboric or the like when the anode material comprises a ferrous metal
• a chelating agent for the anode metal e.g. a diacetic or polyacetic acid compound such as
• Example I In a continuous process, an aqueous solution having dissolved therein approximately 1.6% acrylonitrile, 1.2% adiponitrile, 0.2% acrylonitrile EHD byproducts, 5.8 10 gram mol per liter of ethyltributylammonium cations, 10% of a mixture of incompletely-substituted sodium orthophosphates corresponding to the solution pH of 9 (approximately Na H PO 0.1% of a ferrous 9 metal corrosion inhibitor (sodium pyrophosphate) and 0.05% of ethylenediaminetetraacetic acid was circulated at 55 C.
• aqueous solution having dissolved therein approximately 1.6% acrylonitrile, 1.2% adiponitrile, 0.2% acrylonitrile EHD byproducts, 5.8 10 gram mol per liter of ethyltributylammonium cations, 10% of a mixture of incompletely-substituted sodium orthophosphates corresponding to the solution pH of 9
• the solution which also had entrained therein less than 1% 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 4.7 volts and a current density of 0.27 amp per square centimeter of cathodic surface and then fed into a decanter for equilibration with an accumulated upper layer having approxi-- mately the composition of the aforedescribed organic phase and withdrawal of equilibrated lower (aqueous) layer for recycle through the cell.
• Example H In a continuous process, an aqueous solution having dissolved therein approximately 1.6% acrylonitrile, 1.2% adiponitrile, 0.2% acrylonitrile EHD byproducts, ethyltributylammonium cations in a concentration varying between 9 and 25 10- gram mol per liter, 9% of a mixture of incompletely-substituted sodium orthophosphates corresponding to the solution pH of 9 (approximately Na H POQ, 0.1% of a ferrous metal corrosion inhibitor (sodium pyrophosphate) and 0.05% of ethylenediaminetetraacetic acid was circulated at a temperature between 50 and 55 C.
• aqueous solution having dissolved therein approximately 1.6% acrylonitrile, 1.2% adiponitrile, 0.2% acrylonitrile EHD byproducts, ethyltributylammonium cations in a concentration varying between 9 and 25 10- gram mol per liter, 9% of a
• the solution which also had entrained therein less than 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 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 then withdrawal of equilibrated lower (aqueous) layer for recycle through the cell.
• Example III In a continuous process, an aqueous solution having dissolved therein approximately 0.8% acrylonitrile, 1.1% adiponitrile, 0.15% acrylonitrile EHD byproducts, 8X10 gram mol per liter of tetrabutylammonium cations, 13% of a mixture of incompletely-substituted sodium orthophosphates corresponding to the solution pH of 8 (approximately Na H PO and 0.05-0.1% of a ferrous metal corrosion inhibitor (sodium pyrophosphate) was circulated at 50 C.
• a ferrous metal corrosion inhibitor sodium pyrophosphate
• the solution which also had entrained therein less than 4% by weight of an organic phase containing about 64% adiponitrile, 17% acrylonitrile, 11% acrylonitrile EHD byproducts and 8% water, was electrolyzed as it passed through the cell with a voltage drop across the cell of 4.35 volts and a current density of 0.25 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 then withdrawal of equilibrated lower (aqueous) layer for recycle through the cell.
• a process for hydrodimerizing acrylonitrile which comprises electrolyzing an aqueous solution having dissolved therein from about 0.5 to about 1.8% by weight of acrylonitrile, from about 1% to about 12% by weight of sodium or potassium phosphate sufiicient to provide sodium or potassium ions constituting more than half of the total weight of all cations in the solution and tetra(C -C a1kyl)ammonium ions in a concentration of from about l0 to about 10- mol per liter in contact with a cathodic surface having a cathode potential sufficient for hydrodimerization of acrylonitrile and consisting essentially of cadmium with a current density between 12' about 0.01 and about 0.75 amp per square centimeter of said cathodic surface while passing the solution along said cathodic surface at a velocity of at least about two feet per second, said solution having a pH of at least about 7 and a temperature between about 5 and about C.

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• 1972
  • 1972-08-28 US US00284373A patent/US3830712A/en not_active Expired - Lifetime
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