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
• • 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

Definitions

• ABSTRACT Electrochemical hydrodimerization of acrylonitrile to adiponitrile in an electrochemical, preferably undivided, cell containing acrylonitrile dissolved in an aqueous electrolyte, wherein ammonia is added to the cell and oxidized at or near the anode.
• This invention relates to the electrochemical hydrodimerization of acrylonitrile to adiponitrile, wherein ammonia is oxidized at or near the anode. More particularly, this invention relates to the electrochemical hydrodimerization of acrylonitrile to adiponitrile in an undivided cell, wherein ammonia is oxidized at or near the anode.
• Adiponitrile is a very important intermediate in the production of nylon 6,6. Accordingly, there has been considerable research on new methods of producing this monomer. During the last years, interest has focused on various electrochemical methods of producing adiponitrile from acrylonitrile. (See, for example, Monsanto US. Pat. Nos. 3,193,476 to 483 and Asahi British No. 1,169,525.) The Apr. 17, 1970 European Chemical News reports at page 47 that Monsanto has a 45 million pound per year plant using a divided-cell hydrodimerization process for producing adiponitrile.
• the principal reaction at or near the cathode is and the principal reaction at or near the anode is H O 2H +1/2O 2e
• the solutions must be conductive (contain an electrolyte) and the anode reaction must either be compatible with the cathode reaction or isolated from it.
• electrolytes stable at one electrode are usually unstable at the other and products of one electrode reaction are usually reactive at the opposite electrode.
• the preferred electrolytes (tetraalkyl ammonium sulfonates) used in the Monsanto patents have the additional functions of promoting the solubility of acrylonitrile and preventing electroreduction of water at the cathode.
• These patents prefer the use of a divided cell (cg, a cation exchange membrane), thereby preventing destruction of electrolyte, acrylonitrile and adiponitrile at the anode.
• the general object of this invention is to provide a new electrochemical process for producing adiponitrile from acrylonitrile.
• the principal object of this invention is to provide a new electrochemical undivided cell process for producing adiponitrile from acrylonitrile.
• the objects of this invention can be attained by the electrochemical hydrodimerization of acrylonitrile to adiponitrile in an electrochemical cell containing acrylonitrile dissolved in an aqueous electrolyte, wherein ammonia is added to the solution in an amount at least equal to that stoichiometrically required for service as a proton replenisher.
• the present invention like US. Pat. No. 3,699,020, which is incorporated by reference, makes use of the fact that ammonia can be oxidized electrochemically at a lower voltage than water.
• ammonia can be oxidized electrochemically without danger of oxidizing electrolyte, acrylonitrile or adiponitrile at the anode, it is possible to carry out the process in an undivided cell. Accordingly, when an undivided cell is employed in the process of this invention, there is no substantial buildup of hydroxyl ions in the cathode chamber eliminating the alkalinity-control problems of the divided cell; there is less heat buildup, lower power costs, lower equipment investment and the possibility of recovering more concentrated adiponitrile compositions.
• electrochemical reaction in the present process can be represented as:
• Suitable electrolyte salts include tetraalkyl ammonium salts such as tetraethylammonium bromide, tetramethyl ammonium chloride, tetrapropylammonium bromide, tetrabutylammonium bromide, tetraethylammonium paratoluene sulfonate, etc. Of these, best results have been obtained with the bromides, particularly tetraethylammonium bromide.
• acrylonitrile can be added to the electrolysis cell through a separate dip tube. 1f the solution is continuously re moved from the cell for recovery of adiponitrile and/or for cycling through a cooling system, acrylonitrile can be injected into the recycled solvent-electrolyte.
• Ammonia is consumed in my process and accordingly should alwaysbe present in some excess concentration over that stoichiometrically required for the electro-reduction.
• a high concentration of ammonia lowers selectivity.
• carbon anodes preferably graphite anodes
• the carbon may be impregnated with a metal; e.g., platinum, although metals tend to oxidize and then plate out on the cathode.
• the cathode must be a material exhibiting a high hydrogen over-voltage such as lead, mercury, aluminum, tin, zinc and cadmium. Lead and mercury are especially suitable.
• ammonia is the most easily oxidized entity so t l rat oxidation of halide ion is essentially eliminated.
• an impressed current density in the range from about 30 to about 1000 amps/Ft and preferably from 300 to 500 amps/Ft may be employed.
• Cell voltage will accordingly vary within the range from 2 to 10, and desirably 3 to 6, volts. Failure to supply ammonia to the system results in oxidation of the halide, formation of copious precipitates, decreased selectivity and low current efficiency.
• Electrolysis temperature is not a critical variable and hydrodimerization may readily be conducted within the range from 70 to 140F.
• the solvent-electrolyte solution must be fluid at the selected temperature and the solubility of ammonia must be adequate to satisfy mass transfer (stoichiometric) requirements. Operation at or near room temperature (80 to 120 F.) is preferred.
• part of the solution may be continuously removed from the cell, passed through a cooling coil and returned to the cell.
• the impressed voltage is increased to maintain the desired current density whenever there is a slow corrosion of the graphite anode (for example, a loss amounting to about 0.0005 inch per 24 hours).
• Salt consumption is low, although it tends to increase at low water concentrations while hydrogen evolution occurs at high water concentrations.
• No separator is required in this system. Indeed, presence of a separator to afford compartments and minimize mixing between reagents could lead to an inoperable system by effecting precipitation of, for example, ammonium bromide on the separator frit, and thus gradually shut off the electrochemical reaction.
• the cell contents can be transferred to a still and heated under mild vacuum to remove aprotic solvent, water, ammonia, acrylonitrile and adiponitrile. Tetraalkyl ammonium salt is recovered from the residue.
• my process comprises the use of banks of electrolytic cells, each bank including a plurality of cells arranged in a line and having abutting walls to conserve space. Each cell is relatively narrow and deep and fitted with thin, flat facing electrodes disposed vertically.
• One such cell-bank has a number of bielectrodes (anode-cathode pairs sealed back to back) of carbon and lead (or some other high hydrogen-overvoltage metal) punched in the center, faced at either end with a separate anode and cathode, and spaced by plastic inserts.
• Solution is introduced at the center of the separate cathode (or anode) and then flows, in parallel, between the bielectrics and out to a reservoir.
• An exit line transports solution from the reservoir and, after addition of ammonia and acrylonitrile. back to the cell-bank.
• EXAMPLE I An electrolytic cell was fitted with disc electrodes 4.5 inches in diameter and A inch thick. A graphite anode was disposed horizontally near the bottom of the cell. A lead cathode was punched out at its center to receive a hollow cylindrical support rod and was maintained parallel to and above the anode by insulating spacers placed therebetween. The separation between the electrodes was 0.03 inch. A suction tube was extended from the cell to a circulating pump. The effluent line from the pump passed through a cooling bath and adapted to returning to the cell through the hollow support rod. The effluent line contained Ts for continuously adding ammonia and acrylonitrile downstream from the cooling coil. Sheathed wires connected the electrodes to a DC. power source.
• a voltmeter and an ammeter were provided in the circuit.
• the cell was filled with a solution containing 40 grams acrylonitrile. grams water, grams tetraethylammonium bromide and grams acetonitrile. Five thousand c.c. ammonia (3.8 grams) was then added to provide a 0.3 molar solution of ammonia.
• the composition was electrolyzed at 35A (350 ma/cm 4.1 volts (average) and 29C. for 2 hours while adding ammonia at cc/min and acrylonitrile at 1.0 g/min. After two hours, by analysis, the electrolysis solution contained 21% by weight adiponitrile, selectivity was 92%, current efficiency was 83% and conversion was 77%.
• Example 1 was repeated, except that the solution was electrolyzed at 40A (400 ma/cm"), 4.8 volts (average) and 26C. for 2 hours while adding ammonia at cc/min. and acrylonitrile at 1.3 g/min. After two hours, by analysis, the electrolysis solution contained 24% by weight adiponitrile, selectivity was 91%, current efficiency was 83% and conversion was 77%.
• aqueouselectrolyte composition comprises acetonitrile as a component.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)

Priority Applications (6)

Applications Claiming Priority (1)

Publications (1)

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Family Applications (1)

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Cited By (3)

Citations (3)

• 1973
  • 1973-09-10 US US395720A patent/US3871976A/en not_active Expired - Lifetime
• 1974
  • 1974-08-14 CA CA206,966A patent/CA1040581A/fr not_active Expired
  • 1974-08-27 DE DE2441036A patent/DE2441036C2/de not_active Expired
  • 1974-09-04 FR FR7430075A patent/FR2243275B1/fr not_active Expired
  • 1974-09-04 GB GB38684/74A patent/GB1479699A/en not_active Expired
  • 1974-09-09 JP JP49103758A patent/JPS5825753B2/ja not_active Expired

Patent Citations (3)

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