JPS5825753B2 - Adiponitrile - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to the electrochemical hydrodimerization of acrylonitrile to adiponitrile in which ammonia is oxidized at or near the anode.

More particularly, this invention relates to the electrochemical hydrodimerization of acrylonitrile to adiponyl-IJ in a membraneless electrolytic cell in which ammonia is oxidized at or near the anode.

Adiponitrile is a very important intermediate in the production of nylon 6.6.

Therefore, considerable research is being done to develop new methods for producing this monomer.

During the last decade, interest has focused on various electrochemical methods for producing adiponitrile from acrylonitrile.

(For example, U.S. Patents 3,193,476-483 to Monsanto and British Patent 1,169,52 to Asahi Kakai)
Please refer to Specification No. 5.

) European Chemical News, April 17, 1970
On page 47, it is reported that Monsanto has a factory that produces 45 million pumps of adiponitrile per year using the diaphragm cell hydroquantization method.

It is.

As in all electrochemical reactions, the solution must be electrically conductive (must contain an electrolyte).

And the anodic reaction must be compatible with the cathodic reaction or must be isolated from it.

However, an electrolyte that is stable at one electrode is usually unstable at the other electrode, and the products of one electrode reaction are usually reactive at the opposite electrode, so electrochemical systems in which cathodic and anodic reactions are compatible is difficult to design.

The preferred electrolyte used in Monsanto's patented method (
Tetraalkylammonium sulfonates) have the additional function of promoting solubility of acrylonitrile and preventing electroreduction of water at the cathode.

These patented methods preferably use a diaphragm electrolyte cell (eg, a cation exchange membrane), thereby preventing decomposition of the electrolytes, acrylonitrile and adiponitrile, at the anode.

There are several disadvantages to using diaphragm cells.

For example, U.S. Patent No. 3,193,481, column 5, column 6.
In line 6 to column 6, line 27, it is pointed out that the alkalinity of cathodic decomposition deposits increases.

This alkalinity must be regulated to avoid side reactions.

In addition to the high cost, power losses and heat generation are relatively high in the case of diaphragm cells.

The total voltage drop for a diaphragm cell is at least twice that of a cell without a diaphragm, and the specific resistance drop is three times as high.

Furthermore, on a commercial basis. Due to the higher electrical demands as the solution viscosity increases, the product increase is limited to about 15% by weight for membrane vessels.

For example, in an electrolytic cell without a diaphragm, the adiponitrile concentration is about 15
When increasing from 30% by weight, the voltage increases by about 1.5μ.

In the case of a diaphragm electrolytic cell, other things being equal, the voltage increases by about 5μ.

Therefore, power costs are substantially higher in diaphragm electrolysers.

Moreover, heat build-up and chemical attack in hot solutions shorten the lifetime of the membrane.

The general object of this invention is to provide a new electrochemical process for producing adiponitrile from acrylonitrile.

The main object of this invention is to provide a new electrochemical membraneless cell method for producing adiponitrile from acrylonitrile.

Other purposes will become apparent below.

The purpose of this invention is to add ammonia to the solution in an amount at least equal to the amount stoichiometrically required to serve as a proton replenisher (acrylonyl I-IJ) dissolved in an aqueous electrolyte solution.

A distant relative can be obtained by electrochemical hydrogenation of acrylonitrile to adiponitrile in an electrochemical cell containing

This invention relies on the fact that ammonia can be electrochemically oxidized at lower voltages than water, similar to the method described in U.S. Pat. No. 3,699,020, incorporated herein by reference. Take advantage of.

Since ammonia can be oxidized electrochemically without the risk of oxidizing the electrolyte, acrylonitrile or adiponitrile of the anode, the process of the invention can be carried out in membraneless electrolytic cells.

Therefore, when using a diaphragmless electrolytic cell in the method of the present invention, there is virtually no increase in hydroxyl ions in the cathode chamber, and the problem of alkalinity control in the case of a diaphragm electrolytic cell is eliminated; heat gain is small and electricity costs are reduced. is low, and equipment investment is small.

And there is the possibility of recovering a more concentrated adiponitrile composition.

In some detail, the electrochemical reaction in the method of this invention can be expressed as follows.

As shown above, the electrochemical method of this invention uses water (
(continuously regenerated) and the presence of an electrolyte salt (which must be soluble in a combination of water and a neutral solvent) are required.

Generally, the higher the concentration of water, the higher the current density.

Therefore, water should represent at least 15% by weight of the electrolytic composition.

various neutral solvents, such as acetonate). can be added to the system to increase the solubility of acrylonitrile in the aqueous electrolyte solution.

Suitable electrolyte salts include tetraalkylammonium salts such as tetraethylammonium bromide, tetramethylammonium chloride, tetrapropylammonium bromide, tetrabutylammonium bromide, tetraethylammonium valatoluenesulfonate, and the like.

In these cases, the best results have been obtained using promids, especially tetraethylammonium bromide.

Since acrylonitrile is consumed in the process of this invention, it can be added to the electrolytic cell through a separate dip tube.

Acrylonitrile can be injected into the recycled solvent/electrolyte if the solution is continuously removed from the cell for adiponitrile recovery and/or circulation through a cooling system.

Since ammonia is consumed in the process of this invention, it must therefore always be present in a concentration somewhat in excess of the amount stoichiometrically required for electroreduction.

However, high concentrations of ammonia reduce selectivity.

Therefore, the solvent/electrolyte system contains approximately 0.1 to 0 ammonia.
．． It has proven convenient to maintain it at 5 mol, preferably between 0.2 and 0.3 mol.

This concentration can be approximately maintained by continuously bubbling ammonia into the solution contained in the electrolytic cell during reduction.

If the solution is continuously removed from the tank for circulation through a cooling device, it is convenient to inject ammonia into the stream, preferably from a pumping device.

In the practice of this invention, carbon anodes, preferably graphite anodes, have been satisfactory.

This carbon may contain a metal 1, such as platinum.

However, the metal tends to oxidize and then precipitate on the cathode.

The cathode must be a material exhibiting a high hydrogen overpotential, such as lead, mercury, aluminum, soot, zinc, and cadmium.

Lead and mercury are particularly suitable.

In the preferred system of this invention, oxidation of halide ions is essentially eliminated since ammonia is the most easily oxidized moiety.

Generally, applied current densities of about 30 to about 1,0 OOA/sq. ft., preferably 300-500 A/sq. ft. can be used.

The sliding voltage therefore varies within the range of 2 to IOV, preferably 3 to 6 volts.

When ammonia is no longer supplied to the system, halide oxidation,
Formation of abundant precipitates 5 Decreased selectivity and current efficiency result.

Electrolysis temperature is not an important variable, hydrogenation is 70
This can be easily done within the range of ~140'F.

The solvent-electrolyte solvent must be fluid at the selected temperature and the solubility of ammonia must be sufficient to meet (stoichiometric) mass transfer conditions.

Operation at or near room temperature (800-120'F) is preferred.

During electrolysis. A portion of the solution can be continuously removed from the vessel, passed through a cooling coil, and returned to the vessel.

When the graphite anode slowly corrodes as the hydrogenation of this invention progresses [for example, the loss is about 0.0012
7 cm (0,0005 inches) for 724 hours], the applied voltage is increased to maintain the desired current density.

Salt consumption is low but tends to increase at low water concentrations, while hydrogen evolution occurs at high water concentrations.

No diaphragm is required in the device of this invention.

Indeed, the presence of a septum that provides compartmentalization and minimizes mixing between the reagents is important, e.g.
(epa rrator frit) which renders the device inoperable, and therefore:
Gradually stop the electrochemical reaction.

Once the reduction operation is complete, the vessel contents can be sent to a still and heated under light vacuum to remove the neutral solvent, water, ammonia, acrylonitrile, and adiponitrile.

The tetraalkylammonium salt is recovered from the residue.

In continuous operation, the method of the invention uses electrolytic cell banks, each bank containing a plurality of cells arranged in a row and having contact walls to the protected space.

Each chamber is relatively narrow and deep, and is equipped with vertically oriented thin, flat intercalating electrodes.

Such a tank bank has carbon and lead (preferably other high It has multiple bielectrodes (anode-cathode pairs sealed back-to-back) of hydrogen overvoltage (metals).

Introduce the solution into the center of a separate cathode (or anode).

Then, pour it into the tank in parallel between the plates.

A drain line takes the solution from this tank and returns it to the tank bank after addition of ammonia and acrylonitrile.

Within one tank bank, only the two end electrodes are electrically connected, ie the electrodes are arranged in series.

Electrical connections between tank banks may be in series or in parallel.

The solution flow pattern can be arranged in parallel within tank banks and in series between banks, if desired.

If necessary, solution cooling equipment can be provided outside the tank.

If necessary, all or part of the solution can be recycled.

The following examples are merely illustrative.

Example 1゜ Electrolytic cell with a diameter of 11.4 mm. cwt (4.5 inches) and a thickness of 0.635 CIrL (V4 inches).

A graphite anode was placed horizontally near the bottom of the tank.

A hole was drilled in the center of the lead cathode and a hollow cylindrical support rond was fitted, held above and parallel to the anode and insulated by a spacer placed between them.

The interelectrode distance was 0.076 cm (0.03 inch).

A suction tube was extended from the tank to the circulation pump.

The outflow line from the pump was passed through the cooling bath and returned to the vessel through a hollow support rond.

The outlet line included two feed lines for continuously adding ammonia and acrylonitrile to the flow from the cooling coil.

The electrodes were connected with covered wire and connected to the C0 power source. I put a voltmeter and an ammeter into the circuit.

In a tank, 40g acrylonitrile, 90g water, 120g
A solution containing 151 g of tetraethylammonium bromide and 151 g of acetonyl-IJ was charged.

Then 5.000 CC (3.8 g) of ammonia was added to give a 0.3 molar solution of ammonia.

This composition. Ammonia at i6om/min, 1.09
35A (350
mA/CrIt), 4, IV (average), 29°C
Electrolyzed for 2 hours.

When analyzed after 2 hours, the mold solution contained 21 wt □ adiponiyl, the selectivity was 92%, the current efficiency was 83%, and the conversion was 77%.

Example 2゜ Example 1. repeated.

However, the solution was heated at 40Ce/min while adding ammonia (180Ce/min) and acrylonitrile (1, 3, 9/min).
Electrolysis was carried out at A (400 mA/C1rL), 4.8 V (average), and 26°C for 2 hours.

When analyzed after 2 hours, the electrolyte contained 24% by weight of adiponyl, the selectivity was 91%, the current efficiency was 83%, and the conversion was 77%.

[Brief explanation of the drawing]

The accompanying drawing is a schematic cross-sectional view of a preferred electrolytic cell for carrying out the method of the invention. 1...Pump, 2...Graphite anode, 3.
...Cooler, 4...Condenser, 5...
...Glass container, 6...Lead cathode, 7...
...Acrylonitrile supply line.

Claims (1)

[Claims] 1. A method for electrochemically hydrodimerizing acrylonitrile to adiponitrile in an electrochemical bath containing acrylonitrile dissolved in an aqueous electrolyte solution, characterized by adding ammonia to a membraneless electrolytic cell and oxidizing it at or near the anode. .