Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C255/00—Carboxylic acid nitriles
• • 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

• Adiponitrile can be produced by electrohydrodimerizing acrylonitrile.
• the electrohydrodimerization is carried out in an electrolytic cell having an anode chamber and a cathode chamber separated by an ion exchange resin.
• Acrylonitrile is dissolved in an aqueous quaternary ammonium salt solution.
• This solution i.e., catholyte
• a dilute acid solution i.e., anolyte
• An electrical potential is established between the anode and cathode sufficient to produce a unidirectional current flow.
• acrylonitrile is reductively dimerized to adiponitrile at the cathode.
• the catholyte is then extracted with acrylonitrile to remove adiponitrile plus a small quantity of certain byproducts, e.g., propionitn'le, bis-cyanoethylether, hydroxypropionitrile, etc.
• the acrylonitrile plus other products is in turn water-Washed to remove any dissolved quaternary ammonium salt.
• the aqueous quaternary ammonium salt raflinate from the acrylonitrile extraction plus any aqueous quaternary ammonium salt solution obtained from water-washing the acrylonitrile extract are evaporated to the proper quaternary ammonium salt concentration before the quaternary ammonium salt solution is returned to the catholyte circulating system.
• the salt employed in the electrohydrodimerization of acrylonitrile to adiponitrile must serve two functions: one, the salt must conduct electrical current and, two, it must act to dissolve acrylonitrile in the aqueous solution of salt, i.e., the salt must be hydrotropic.
• Quaternary ammonium salts have been found to be admirably suited for such purposes. Included among the suitable quaternary ammonium salts are, generally, tetraalkylammonium sulfates, tetralkylammonium aryl sulfonates, and tetraalkylammonium alkyl sulfates.
• Two specifically useful salts are tetramethylammonium toluene sulfonate and tetraethylammonium ethyl sulfate.
• quaternary ammonium salt solution must be kept substantially free of impurities.
• One impurity formed in the electrohydrodi- Inerization process is polyacrylonitrile. Most of this material is removable by ordinary filtration or like processes for removing solids from liquids. Nevertheless, small quantities of polyacrylonitrile partially hydrolyze to produce a polymer having sufiicient carboxylate groups to make it readily soluble in quaternary ammonium salt solution.
• a further object is to substantially remove organic impurities, especially polyacrylonitrile, from an aqueous solution of quaternary ammonium salt.
• a still further object is to improve, by reducing all cathode fouling, the product yield in the electrohydrodimerization of acrylonitrile to adiponitrile.
• the above objects are achieved by providing a process wherein the above noted partially hydrolyzed polyacrylonitrile is removed from an aqueous solution of a hydrotropic quaternary ammonium salt by means of a procedure including precipitating the polyacrylonitrile by adjusting the salt concentration of the solution to not more than about 55 weight percent and adjusting the pH of the aqueous solution to not more than about 7. This precipitated material is then separated from the aqueous salt solution.
• the treated quaternary ammonium salt solution have a concentration of not more than about 55 weight percent and a pH of notlmore than about 7, i.e., be neutral or acidic.
• concentration not more than about 55 weight percent
• pH notlmore than about 7
• concentration is more than 55 weight percent then it is only necessary to decrease the salt concentration to achieve the proper precipitating conditions.
• both concentration and pH are above the maximum limits then it is necessary to lower the salt concentration, i.e., dilute the solution, and to put suflicient acid in the solution to make it acidic.
• the order in which the concentration adjustment and pH adjustment takes place may vary.
• the solution can be made acidic then have the concentration adjusted or the concentration can be adjusted, then the solution can be made acidic.
• the salt concentration is greater than about 55 weight percent and the pH is greater than 7, i.e., alkaline, the solution can be simultaneously diluted and acidified with a proper quantity of an aqueous acid solution.
• the most effective precipitation occurs when the pH is not more than about 7 and the salt concentration is not more than about 40 weight percent.
• the preferred acids used to acidify the salt solution are those whose anion corresponds to the anion of the quaternary ammonium salt being treated, for instance, when tetraethylammonium ethyl sulfate is the salt the acid should be ethyl sulfuric acid.
• the procedure can be performed in batch form or it can be performed upon a continuous stream.
• the methods for separating the precipitated material from the salt I solution include filtering, centrifuging, and other like processes well known to persons skilled in the art..
• Example I A quantity of tetramethylammonium toluene sulfonate that had been recycled 25 times through the electrolytic cell employed to electrohydrodimerize acrylonitrile to adiponitrile was so concentrated by a series of concentration and crystallization procedures until the level of organic impurities present in the aqueous salt was approximately equivalent to that quantity of organic impurities that would have been present if the salt had been recycled about times.
• This salt having a large quantity of organic impurities therein, was then employed as the supporting electrolyte in the catholyte used in electrohydrodimerizing acrylonitrile to adiponitrile.
• the catholyte included 25 weight percent acrylonitrile (45.9 weight percent tetramethylammonium toluene sulfonate, and 29.1 weight percent water.
• the pH was 9.0.
• the diluted salt solution from which the partially hydrolyzed polyacrylonitrile had been removed was reconcentrated and had the pH readjusted, and had enough acrylonitrile added thereto to produce a catholyte substantially equivalent to that described above, i.e., the pH was adjusted to about 9.0 with tetramethylammonium hydroxide, acrylonitrile concentration to about 25 weight percent, tetramethylammonium toluene sulfonate concentration to about 45.9 weight percent and about 29.1 weight percent of thecatholyte was water.
• This catholyte was used in the same cell as was the contaminated electrolyte and was run for the same period of time, six hours.
• Table l were obtained. All amounts are given as weight percent based on the total product weight.
• Example 11 TABLE 2. COMPARATIVE POLYMER REMOVAL RESULTS Salt concentra- Amount of polymer tion, weight pH removed, weight perpercent cent based on diy salt Thus, it is clear that once the pH of the diluted salt becomes greater than 7.0 polymer removal becomes negligible. However, as can be seen from Example 1, best results are obtained when the salt concentration and pH 5 are lower. than set out in this example.
• the primary advantage of this invention is the significant improvement in adiponitrile yield.
• a second advantage is the increased useful life span of a particular cathode, i.e., the cathode becomes fouled at a much slower rate when the electrolyte is substantially free of organic impurities-such as polyacrylonitrile, thus increasing the periods between cathode cleanmg.
• hydrotropic quaternary ammonium salt is a tetraalkylammonium aryl sulfonate.
• a process for removing partially hydrolyzed polyacrylonitrile from an aqueous salt solution of ,a hydrotropic quaternary. ammonium salt comprising, in combination, the steps of:
• quaternary ammonium salt is a tetraalkylammonium alkyl 5 6 (b) separating said polyacrylonitrile from said aqueous References Cited Solution UNITED STATE PAT N s 7.
• the hydrotropic qua- S E T ternary ammonium salt is tetraethylammonium ethyl 3,193,481 7/1965 Bauer 204 '73 Sulfate 5 CHARLES B. PARKER, Primary Examiner.
• hydrotropic quaternary ammonium salt is tetramethylammonium toluene BERNARD BILLIAN, Assistant Examiner.

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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)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)

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Cited By (4)

Citations (1)

• 1965
  • 1965-05-10 US US454740A patent/US3335162A/en not_active Expired - Lifetime
• 1966
  • 1966-05-03 IL IL25695A patent/IL25695A/en unknown
  • 1966-05-03 LU LU51019A patent/LU51019A1/xx unknown
  • 1966-05-03 GB GB19571/66A patent/GB1153194A/en not_active Expired
  • 1966-05-05 BE BE680551D patent/BE680551A/xx unknown
  • 1966-05-09 AT AT435566A patent/AT265234B/de active
  • 1966-05-09 NL NL6606313A patent/NL6606313A/xx unknown
  • 1966-05-09 DK DK236266AA patent/DK117696B/da unknown
  • 1966-05-10 CH CH674366A patent/CH469654A/de unknown
  • 1966-05-10 DE DE19661593014 patent/DE1593014A1/de active Granted
  • 1966-05-10 JP JP41029162A patent/JPS496296B1/ja active Pending

Patent Citations (1)

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