US3488267A - Electrolytic production of adiponitrile - Google Patents

Description

Jan. 6, 1970 w. J. SLQAN 3,488,267

ELECTROLYTIC PRODUCTION OF ADIPONITRILE Filed June 25, 1963 FIGo \INVENTOR WALTER JOHN SLOAN ATTORNEY United States Patent ABSTRACT OF THE DISCLOSURE Process for the production of adiponitrile which comprises passing a direct electric current through an electrolyte containing acrylonitrile, a quaternary ammonium compound and water.

This invention relates to the production of adiponitrile from acrylonitrile. Specifically, this invention relates to the production of adiponitrile by passing a direct electric current through an electrolyte containing acrylonitrile using at least one quaternary ammonium compound in the electrolyte.

It is known that acrylonitrile can be reacted to produce adiponitrile by means of potassium amalgam which is produced electrolytically. The amalgam then reacts chemically with acrylonitrile and hydrochloric acid to form adiponitrile. It is an object of this invention to provide an alternative process for the production of adiponitrile which does not require the use of amalgam. It is a further object of this invention to provide a process for the production of adiponitrile at high current efliciency. Other objects of this invention will be apparent to one skilled in the art from the remainder of the specification.

Theabove objects are accomplished according to the present invention by passing a direct electric current through acrylonitrile containing from about 1 to about 3.8% by weight water and a quaternary ammonium compound. The process of this invention may be carried out with or without a diaphragm in the electrolytic cell. If a diaphragm is to be used, it is preferable to employ a cationic permselective membrane (that is, a membrane that is only cation-permeable). Such diaphragms are known in the art and arecommercially available. If a cationic permselective membrane is used, an anolyte may be employed that contains no acrylonitrile. This can be advantageous for under some conditions the anodic oxidation products tend to cause polymerization of the acrylonitrile. However, a diaphragm is not necessary to the successful operation of the process of this invention.

In' the drawings FIGURE 1 shows a cross-sectional view through a diaphragmed electrolytic cell suitable for use in carrying out the process of the present invention.

FIGURE 2 shows a cross-sectional view through an electrolytic cell without a diaphragm that is suitable for carrying out the process of the present invention.

The quaternized ammonium compounds found to be useful as electrolytes for the process of the present invention have the following general formula:

where R is an organic radical having 2-8 carbon atoms, and X- is a member of the class consisting of Cl, Br, I, and R 80 where R is a monovalent alkyl group containing between 1 and 6 carbon atoms. Specific examples of compounds known to be useful are: tetraethyl ammonium bromide, tetrabutyl ammonium iodide, tetrabutyl ammonium bromide, tetraethyl ammonium ethyl sulfate. In general, quaternized ammonium compounds useful in the instant process must be good conductors when dissolved in moist acrylonitrile and be stable at a potential of at least about 2.0 volts.

3,488,267 Patented Jan. 6, 1970 The process of this invention is carried out at a cathode current density of between about 50 and about 200 amp/ft. and at a measured voltage (cathode to catholyte) of between about 1.2 and 15.0 volts. The process is preferably carried out Within the temperature range of 30 to 70 C. because the conductivity of the electrolyte is greatest at this temperature. The optimum temperature is about 45 C. The pH of the system is critical only in that the pH should be on the acid side, i.e., less than 6, for higher pH may cause polymerization of the acrylonitrile. The concentration of the quaternary ammonium compound in the moist acrylonitrile can vary over wide limits depending on the particular compound employed, but about 430% by weight of the moist acrylonitrile is satisfactory in most cases (concentrations of about 6 to 15% by weight are preferred).

It is highly desirable, when carrying out the process of this invention in either an undiaphragmed' cell, or in a diaphragmed cell, to agitate the portion of the cell in which the acrylonitrile is undergoing conversion. Agitation avoids areas of high pH and reduces the degree of polarization, resulting in increased yields. The degree of agitation useful in the present process varies from a Reynolds number of about 12,000 to about 200,000, preferably about 50,000 to about 125,000.

When the process of this invention is carried out in a diaphragmed cell, the diaphragm is preferably a cation permselective diaphragm. Suitable ion exchange membranes are commercially available. Useful membranes can be made by sulfonating a copolymer of styrene and divinyl benzene, and blending the product with polyethylene. The blend is then formed into a sheet of about .045 inch thickness. Sulfonated copolymers of styrene and divinyl benzene may be ground and mixed with sulfonated polyethylene dissolved in a suitable solvent and cemented as a sheet to Dynel (a copolymer of vinyl chloride and acrylonitrile) monofilament fabric. Some membranes require pre-soaking prior to use. This can be accomplished by techniques known in the art, for example the membrane is installed in the cell, and then treated with aqueous H (5%). This treatment avoids uneven swelling and buckling. The anolyte in the diaphragmed cell is an aqueous acid. Sulfuric acid at concentrations of 25 to 45% is highly satisfactory. Also dilute hydrochloric acid can be used, when satisfactory means are available to remove the chlorine. Aqueous organic acids such as ethyl sulfuric acid and p-toluene sulfonic acids are also satisfactory.

Cathode materials suitable for the process include lead, platinum, palladium, copper, nickel, chromium on brass, and silver. Platinum, lead, silver and copper are the preferred cathode materials. The anode may be of any relatively inert conductor; platinum and carbon are highly satisfactory.

The catholyte, or in the case of an undiaphragmed cell, the electrolyte, may contain (in addition to acrylonitrile, water, and quaternary ammonium compounds) other materials that do not substantially affect the basic composition. For example, cosolvents for the quaternary ammonium compound, may be included. Specifically, dimethyl formamide, methanol, or isopropanol may be added to the catholyte as cosolvents fon the ammonium compound.

When carrying out the process of this invention for extended periods of time, it is usually desirable to peri odically or continuously add acid, such as sulfuric or hydrobromic, to the electrolyte in order to maintain the pH below 6.

The drawings diagrammatically illustrate alternative apparatus suitable for carrying out the process. FIG- URE 1 shows an electrolytic cell designated 1, having a cathode 2 in catholyte 3, and an anode 4 in anolyte 5.

The anolyte and the catholyte are separated by a cation permselective diaphragm 6. The cathode compartment of the cell contains an agitator 7. Suitable inlet means 8 and outlet means 9 are provided for the cathode compartment. The anode compartment has inlet means 10 and outlet means 11. The cell is also provided with suitable vents 12 and 13 to remove the gaseous electrolytic products.

FIGURE 2 diagrammatically shows an undiaphragmed electrolytic cell suitable for use in the process of this invention. The cell 1 is provided with a cathode 2, an anode 4, an agitator 7, an inlet means 8, an outlet means 9, and vents 12 and 13. Additionally, inlet means 14 is provided to allow the introduction of acid to keep the pH acidic.

In operation either of the cells may be run in a batchwise fashion or continuously. That is, electrolyte (moist acrylonitrile and quaternary ammonium compound) may be introduced continuously through inlet 8 and Withdrawn continuously through outlet 9; or the electrolyte may be introduced through inlet 8, electrolyzed and withdrawn as a batch through outlet 9. In either instance, the adiponitrile is separated from the acrylonitrile, water, and quaternary ammonium compound by further processing after removal through outlet 9. I

In the following examples which illusrate the invention, all parts and percentages are in parts 'by weight unless otherwise stated.

EXAMPLE I Into the cathode compartment of a cell having a diaphragm of Amberplex C1 (an ion exchange membrane made by blending a sulfonated copolymer of styrene and divinyl benzene with polyethylene, and then forming a sheet of the blend), 350 ml. of a moist acrylonitrile, approximately 3.6% by weight water, containing about 7.5% by weight tetraethyl ammonium bromide was introduced. Into the anode compartments, 30% by weight H 50 was simultaneously introduced. The membrane had an area of approximately 0.024 sq. ft. The membrane had a thickness of approximately 0.045 in. The catholyte was vigorously agitated by means of a stirrer and voltage of approximately 8.4-9.0 volts applied between a platinum anode and a lead cathode for about 4.8 hours. The cathode current density was about 50 amp/ftP. The cathode to catholyte potential drop was measured as 3.2 volts. The temperature was approximately 30 C. The pH varied from 1 to 5. The current efficiency was about 81% calculated with regard to amount of acrylonitrile converted to adiponitrile. 79% of the tetraethyl ammonium bromide was recovered from the catholyte.

EXAMPLE II The process of Example I was repeated using a catholyte containing 26.9% by weight tetraethyl ammonium ethyl sulfate instead of the tetraethyl ammonium bromide. The anolyte was an aqueous solution 12% by weight of ethyl sulfate C H SO I-I. A voltage of 8.4-9.4 volts was applied between a platinum anode and a lead cathode. The cathode to catholyte potential drop was measured as 2.4 to 2.9 volts. The pH of the catholyte was less than 1. The current density at the cathode was 100 amp/ sq. ft. The process was carried out using vigorous agitation and the time was 3.7 hours. The amount of water in the catholyte at the start of the run was about 3.0% by weight. The current efficiency calculated with regard to the amount of acrylonitrile converted to adiponitrile was 73.5%.

EXAMPLE III and the cathode was platinum. A 48% solution of hydrobromic acid was periodically added to the electrolyte to maintain the pH between 1 and 3.5. The product was recovered and analyzed. The current efiiciency for the production of adiponitrile was 34%.

EXAMPLE IV In a cell, such as illustrated in FIGURE 2, an electrolyte consisting of 44.4.parts acrylonitrile, 44.5 parts dimethyl formamide ,(a cosolvent for the quaternary ammonium compound), 7.6 parts tetraethyl ammonium bromide, and 3.5% water, was electrolyzed with mild agitation at a cathode current density of 65 amp/ft. for 60 minutes using a platinum cathode and a platinum screen anode. Hydrogen gas was introduced in the anode region in an effort to minimize the polarization. A 48% solution of hydrobromic acid was introduced periodically into the electrolyte to maintain the pH at about 2.2. The product was removed and analyzed. The current efficiency for the production of adiponitrile was 12.5%

EXAMPLE V An electrolyte of 87.2 parts acrylonitrile, 9.8 parts tetraethyl ammonium ethyl sulfate, and 3.0 parts water was electrolyzed with mild agitation in a cell such as that shown in FIGURE 2, at a potential of 9.6 volts, at a cathode current density of 65 amp/ft. for 34 minutes. The pH remained about 0; no acid was added. Both the anode and cathode were platinum. The product was analyzed and the current efiiciency for the production of adiponitrile was calculated to be 52%.

Two methods were used for product work-up. Method I was used when low rrielting quaternary ammonium compounds were used, i.e.,- melting point not in excess of about 200 C. In both methods, the content of adiponitrile was confirmed by chromatographic analysis.

Method I 1.0 N NaOH was added to the product of the electrolytic process to raise the solution pH to 5. The material was distilled and an organic cut (primarily acrylonitrile) was collected until a head temperature of 99 C. was reached. The cooled pot contents were then filtered and the residue weighed. The water was then removed from the filtrate by distillation at atmospheric pressure until a head temperature of 110 C. was reached, followed by distillation at 40 mm. Hg. To remove final traces of water, 300 ml. of chloroform was added to the pot and a waterchloroform azeotrope taken ofi until the condensate appeared clear. The pot contents were cooled and filtered to remove insoluble sodium salts. Most of the chloroform was removed from the filtrate over a steam bath at atmospheric pressure, the remaining traces being taken off under vacuum. About 300 m1. of benzene was then added to the pot and the distillate removed until a head temperature of C. was reached. The pot contents were then cooled and the quaternary ammonium compounds crystallized, filtered, dried, and weighed. The benzene solution was then evaporated, leaving adiponitrile and high boilers. The adiponitrile was recovered by distillation.

Method II The pH of the organic product from electrolytic cell was adjusted to 3.54.5 and then filtered. The filter cake was dried and weighed. The organic liquid was extracted with water and methylene dichloride, the water washes being extracted with methylene dichloride and the methylene dichloride extract being washed with water. The aqueous layers were consolidated at the end of the extraction, and the organic layers were separately consolidated.

The water was stripped from the combined aqueous layers, leaving as a product dried quaternary ammonium compound.

The combined organic layers were charged slowly through a separatory funnel into the distillation apparatus flashing the acrylonitrile and CH C1 off over a steambath. The separatory funnel was then removed, and a thermometer was installed where the separatory funnel had been and the distillation resumed at 40 mm. Hg for about five minutes after visible boiling had ceased. The pressure was then decreased to 5 mm. Hg, and distillation continued until a pot temperature of 70 C. was reached. The adiponitrile was then recovered by distillation.

In the foregoing examples the current efliciency to adiponitrile is the percentage of the current which is utilized in making adiponitrile. By-products included hydrogen gas, propionitrile, beta-hydroxy propionitrile and beta, beta-oxydipropionitrile, and polyacrylonitrile. The current efficiency can be determined as exemplified by the following sample calculation. In a run in which the average current is 2.8 amps and the duration is 156 minutes, the current density is 2.8 156 60=26,220 amp-sec. or 0.2720 faraday. If the electrolyte weighs 252 grams and has a concentration of 4.27% adiponitrile, the quantity of adiponitrile is 0.10 mol, and at two faradays per mol of adiponitrile the current efiiciency to adiponitrile is 0.10/(0.2720 2) which is 65%.

The adiponitrile produced by the disclosed process is useful as an intermediate in the production of nylon.

I claim:

1. A process for the production of adiponitrile which comprises passing a direct electric current at a potential between about 1.2 and 15 volts and at a cathode current density between about 50 and 200 amp/sq. ft. between a cathode selected from the class consisting of palladium, nickel, chromium on brass, platinum, lead, silver and copper, and an inert anode through an electrolyte consisting essentially of acrylonitrile, a quaternary ammonium compound and between about 1 and about 3.8% water, said electrolyte having a pH of less than 6 thereby forming adiponitrile and thereafter recovering the adiponitrile.

2. The process of claim 1 in which the quaternary ammonium compound has the formula R N+X where R is an organic radical having 2-8 carbon atoms and X" is a member of the class consisting of Cl, Br, I and R 50 where R is an alkyl group containing between 1 and 6 carbon atoms.

3. The process of claim 4 in which the quaternary ammonium compound is selected from the class consisting of tetraethyl ammonium bromide, tetrabutyl ammonium iodide, tetrabutyl ammonium bromide, and tetraethyl ammonium ethyl sulfate.

4. The process of claim 3 in which the anode and the cathode are separated by a membrane that is cation permselective.

5. The process of claim :4 in which the anode is surrounded by an aqueous acid electrolyte.

6. A process for the production of adiponitrile in an electrolytic cell having an anode compartment and a cathode compartment, said anode compartment being separated from said cathode compartment by means of a cationic permselective membrane, which comprises subjecting acrylonitrile consisting essentially of a quaternary ammonium compound and between about 1 and about 38% water to direct electric current in the cathode compartment of said cell thereby forming adiponitrile and thereafter recovering the adiponitrile.

7. The process of claim 6 in which the anode compartment of said cell contains an aqueous acid solution.

8. The process of claim 7 in which the aqueous acid solution is selected from the class consisting of sulfuric, hydrochloric, ethyl sulfuric, and p-toluene sulfonic.

9. A process for the production of adiponitrile in an electrolytic cell having an anode compartment and a cathode compartment, said anode compartment being separated from said cathode compartment by means of a cationic permselective membrane which comprises subjecting an electrolyte to the action of direct electric current, the electrolyte in the cathode compartment consisting essentially of between about 1 and about 3.8% water, quaternary ammonium compound, and acrylonitrile, whereby adiponitrile is formed in the cathode compartment of the cell, and recovering adiponitrile.

References Cited UNITED STATES PATENTS 2,726,204 12/1955 Park et al. 20472 FOREIGN PATENTS 566,274 1l/ 1958 Canada.

JOHN H. MACK, Primary Examiner H. M. FLOURNOY, Assistant Examiner 3 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,'+88,26T Dated January 6 l9'TO Inventor s) WALTER JOHN SLOAN It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

FCLAIM 3, column 5, line 46, "claim 4" should be claim 1 .1

"TIGNED AND SEALED SEP 151970 Amsfing 0mm mm 1:. sammm, JR.

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