IL29389A - Process of removing hydrolyzed polyacrylonitrile from an aqueous mixture - Google Patents

Description

mil Patents Form Ho. 3 PATENTS AND DESIGNS ORDINANCE.

SPECIFICATION.

PRG!S AIJ A£JBB008 HXJHJOSE* I/WE, cxiBtiae u&Sei? tlic lawo of tho State of Doiam3?ot t¾ » of do hereby declare the nature of this invention and in what manner the same is to be performed, to be particularly described aud ascertained in and by the following statement : - This invention relates to a process of removing hydrolyzed polyacrylonitrile from an aqueous mixture consisting essentially of a quaternary ammonium salt, adiponitrile , acrylonitrile and hydrolyzed polyacrylonitrile. More specifically , this invention relates to a process of removing hydrolyzed polyacrylonitrile from such an aqueous mixture by introducing the a ueous mixture into a decanter wherein the mixture is separated into ah organic phase (comprising adiponitrile and the acrylonitrile) and a '.vater phase (comprising quaternary ammounium salt), the phases separated by an interface (the interface consisting essentially of an emulsion containing the hydrolyzed polyacrylonitrile) and withdrawing a portion of the interface to separate the hydrolyzed polyacrylonitrile from the aqueous mixture.

Adiponitrile can be continuously produced by electrochemical dimerization of acrylonitrile to adiponitrile. This process is effected in an electrolytic cell containing at least one anode chamber and at least one cathode chamber the chambers separated by an ion exchange membrane. In brief, the process comprises circulating an anolyte comprised of a dilute acid solution through the anode chamber 3 circulating a catholyte comprised of acrylonitrile dissolved in an aqueous quaternary ammonium salt solution through the cathode chamber , and establishing an electrical potential between the anode and the cathode sufficient to produce a unidirectional current flow and thus to reductively dimerize the acrylonitrile to adiponitrile at the cathode. The electrical potential causes the hydrogen ions of the dilute acid solution to migrate through the ion exchange membrane to make available to adipontrile. As the dimerizatlon progresses a portion of the catholyte exiting from the cathode chamber is withdrawn arid an equal portion of make-up quaternary ammonium salt solution containing acrylonitrile is added to the catholyte to maintain a constant volume catholyte stream.

The portion of the catholyte which is withdrawn from the catholyte stream contains water* quaternary ammonium salt, adiponitrile, acrylonitrile and a small quantity of by-products , e.g. propionitrile , bis-cyano-ethylether, hydroxyproplonitrile , etc. and a small quantity of hydrolyzed polyacrylonitrile. Adiponitrile , the desired product, is separated from the catholyte and the quaternary ammonium salt is returned to the electrolytic cell in the catholyte stream.

The quaternary ammonium salt employed in the catholyte of the electrolytic cell must serve two functions. i.e., the salt must provide ions in aqueous solution for conducting an electrical current and the salt must be capable of increasing acrylonitrile solubility.

Suitable quaternary ammonium salts include tetraalky-ammonium alkyl sulfates, tetraalkylammonium sulfate, tetraalkylammonium aryl sulfonates, etc.

For efficient operation vjithin the electrolytic cell, the quaternary ammonium salt in the catholyte stream must be kept substantially free of harmful, impurities.

Such a harmful impurity is hydrolyzed polyacrylonitrile.

For example, small smounts of this harmful impurity, e.g. about 0.15? based on the weight of the catholyte stream, can cause deposits on the cathode and, as a result, substantially acrylonitrile to adiponitrile.

It is therefore an object of this invention to provide a process of removing hydrolyzed polyacrylonitrile from an aqueous mixture consisting essentially of a quaternary ammonium salt, adiponitrile, acrylonitrile and hydrolyzed polyacrylonitrile.

Another object of this invention is to substantially reduce cathode fouling in an electrochemical cell used in the electrochemical dimerization of acrylonitrile to adiponitrile.

A still further object of the invention is to improve the efficiency of the electrochemical dimerization of acrylonitrile to adiponitrile.

Other objects of this invention will become apparent as the invention is fully developed within the specification.

These and other objects of this invention are accomplished by providing a process of removing hydrolyzed polyacrylonitrile from an aqueous mixture consisting essentially of a quaternary ammonium salt, adiponitrile, acrylonitrile and hydrolyzed polyacrylonitrile comprising containing the mixture at a temperature up to about *Ι5ο0. and for at least about one hour to form a water phase and an organic phase the phases separated by an interface, and withdrawing a portion of the interface as the hydrolyzed polyacrylonitrile. The interface is not a definitely defined interface but is an emulsion of the organic and water phases and consists essentially of hydrolyzed polyacrylonitrile.

On a practical basis, this process is useful for removing ze t e - ing essentially of a quaternary ammonium saltj adiponltrile . acrylonitrile . and hydrolyzed polyacrylonitrile and also for separating therefrom and refining the quaternary ammonium salt, the acrylonitrile and adiponltrile; the process comprising 1) introducing into a decanter an aoueous mixture consisting essentially of a quaternary ammonium salt } adiponltrile acrylonitrile, and hydrolyzed polyacrylonitrile wherein the mixture is separated into an organic phase (comprising adiponltrile and acrylonitrile) and a water phase (comprising quaternary ammonium salt) s the phases separated by an interface consisting essentially of an emulsion containing the hydrolyzed polyacrylonitrile;; 2) withdrawing a portion of the water phase and washing said water phase with acrylonitrile to extract any adiponitrile in the water phase and passing the acrylonitrile plus any extracted adiponitrile into the organic phase of the decanter, the water phase consisting essentially of refined quaternary ammonium salt- 3) withdrawing a portion of the organic phase and washing said organic phase with water to extract any quaternary ammonium salt in the organic phase and passing the water plus any extracted quaternary ammonium salt into the water phase of the decanter s the or anic hase bein essentiall refined and consisting essentially of adiponitrile and acrylonitrile; and *0 withdrawing a portion of the interface and filtering the interface portion to remove hydrolyzed polyacrylonitrile and passing the filtrate into the water phase of the decanter .

This practical aspect of the process provides for the removal of hydrolyzed polyacrylonitrile, for the refining and separation of the quaternary ammonium salt and combination of the adiponitrile and the acrylonitrile.

The attached drawing shows the preferred embodiment of the process. It is to be understood that this drawing is not to be considered as a limitation of the invention, but is presented to show an assembly of equipment in which the process may be practiced.

Peed 2 of an aqueous mixture consisting essentially of a quaternary ammounium salt Λ adiponitrile, acrylonitrile and hydrolyzed polyacrylonitrile is passed into decanter wherein the mixture is separated into an organic phase (comprising adiponitrile and acrylonitrile) , a water phase (comprising quaternary ammonium salt), the phases separated by an Interface (the interface not being definitely defined but consisting essentially of an emulsion of the organic phase and the water phase and consisting essentially of hydrolyzed polyacrylonitrile). The decanter is operated at a temperature up to about ¾5°C., and preferably from about 20--35°C> and the hold -up time of the liquid in the decanter is at least one hour. A portion of the interface is withdrawn polyacrylonltrile is removed and the filtrate 10 is passed into the water phase of decanter . A portion of the water phase in decanter 4 is withdrawn by stream 12, passed through acrylonitrile scrubber 28 wherein the water phase is scrubbed with acrylonitrile stream 16 to remove any adiponitrile or acrylonitrile, the scrubbed water phase leaves scrubber 28 by stream 1 as an aqueous solution of refined quaternary ammonium salt,, and the acrylonitrile plus any extracted adiponitrile leaves scrubber 28 by line 18 and is returned to the organic phase of decanter . A portion of the organic phase in decanter H is vrithdrawn by stream 20» washed with water in water scrubber 30 to remove any quaternary ammonium salt;, the wash water plus any extracted quaternary ammonium salt exits scrubber 30 by stream 26 and is returned to the water phase of decanter H and the washed organic phase leaves scrubber 30 by stream 22 as refined adiponitrile and acrylonitrile.

As previously mentioned a hydrolyzed polyacrylonltrile is undesirable in the catholyte stream of an electrolytic cell wherein acrylonitrile is dimerized to adiponitrile. Such hydrolyzed polyacrylonltrile decreases the efficiency of the dimerization by fouling the cathode and, if the hydrolyzed polyacrylonltrile is permitted to remain in the processing streams, it will form emulsions which adversely affect the extraction of the products in the exiting catholyte stream.

Hydrolyzed polyacrylonltrile can be removed from a catholyte stream^ the catholyte stream consisting essentially of an aqueous mixture of a quaternary ammonium - acrylonitrile, by a process comprising containing the mixture at a temperature up to about 45°C. and for at least about one hour to form a water phase and an organic phase , the phases separated by an interface, and withdrawing a portion of the interface as the hydrolyzed polyacrylonitrile .

Preferabl , the mixture can be contained at a temperature within the range of from about 20 -35°C. and for a time of at least about one hour. The organic phase comprises adiponitrile and acrylonitrile and the water phase comprises quaternary ammonium salt. The organic phase and the water phase is separated by the interface, the interface not being definitely defined but consisting essentially of an emulsion containing part of the organic phase and part of the water phase and consisting essentially of hydrolyzed polyacrylonitrile.

Impurities e.g. propionitrile , bis -cyanoethylether , hydroxy-propionitrile, and other by-products obtained from the dimeri-zation of acrylonitrile to adiponitrile are present in the organic phase and water phase, depending on the solubility thereof -generally speaking these impurities are not harmful to the process and are permitted to remain in the processing streams .

It is desired that the pH of the aqueous mixture in the decanter be within the range of from about 2.5 to about 7.5. Within this range the particle size of the hydrolyzed polyacrylonitrile is larger and thus facilitates filtration of the interface portion containing the hydrolyzed polyacrylonitrile. More preferably, it is desired that the pH of the mixture be within the range of 3.5 - 6.5.

The hold-up time in the decanter should be in excess of one hour in order to effect adequate separation of the aqueous mixture into an organic phase and a viater phase and to allow the hydrolyzed polyacrylonitrile particles to move to the interface. The hold-up time is unlimited, but due to the economics of the process a minimum hold up time is preferred.

The following example is presented to illustrate the invention. Where percents are used, it is based on weight unless otherwise specified.

EXAMPLE Three aqueous mixtures representative of portions of exiting catholyte streams from the electrochemical dimeriza-tion of acrylonitrile to adiponitrile , the mixtures consisting essentially of a quaternary ammonium salt 5 adiponitrile s acrylonitrile and hydrolyzed polyacrylonitrile (the amounts in each mixture indicated in Table I), are introduced into a decanter. The conditions within the decanter, i.e. pH of the mixture, hold-up time of the mixture in the decanter, and temperature of the mixture in the decanter, are indicated in Table I. The aqueous mixture separates into an aqueous phase and an organic phase and an interface consisting essentially of an emulsion consisting essentially of hydrolyzed polyacrylonitrile separates the two phases. A portion of the interface is withdrawn from the decanter and the amount of hydrolyzed polyacrylonitrile filtered is indicated in Table Is the filtrate is returned to the aqueous phase in the decanter. Table I also indicated the % hydrolyzed polyacrylonitrile removed by the process: TABLE I Aqueous pH of °C. of Hold-up Time lbs of Hydrolyz Mixture Aqueous Aqueous in Decanter In Aqueous Mixture Mixture (hrs) Mixture 1 i .0 28 9.7 3.97 (1.8 Kg) 2 1 . 5 25 3.8 2.72 (1.23 Kg) 3 5·.3 35 2.3 2.28 (1.03 Kg) These above dat£ indicate that hydrolyzed polyacrylonitrile can be effec Although the invention is described by reference to particular embodiments and examples s it is to be understood that equivalent embodiments and variations may be apparent to those skilled in the art and thus be a part of the invention. Therefore Λ the invention should be broadly construed and should only be limited to the reasonable scope of the appended claims.

Claims (7)

HAVXEG ΗΌ7 particularly described and ascertained the nature of our said invention and what manner the same is to be performed, ve declare that w we claim is Ϊ

1. A process of removing hydrolyzed poly-acrylonitrile from an aqueous mixture consisting essentially of a quaternary ammonium salt3 adiponitrile 3 acrylonitrile and hydrolyzed polyacrylonitrile s characterized by maintaining the mixture at a temperature up to about 45°C. and for at least about one hour to form a water phase and an organic phase > the phases separated by an interface, and withdrawings a portion of the interface as the hydrolyzed polyacrylonitrile

2. The process of Claim 13 characterized in that the temperature of the mixture is from about 20° to about 35°C.

3. The process of Claim 1, characterized in that the pH of the mixture is from about 2.5 to about 7.5.

4. The process of Claim 1.. characterized by (1) introducing into a decanter an aaueous mixture consisting essentially of a quaternary ammonium salt, acrylonitrile s adiponitrile and hydrolyzed polyacrylonitrile wherein the mixture is maintained at a temperature U to about 4 °C . for at least one hour and wherein the mixture is separated into an organic phase and a water phase , the phases separated by an interface and the organic phase comprising adiponitrile and acrylonitrile 3 the water phase, comprising quaternary ammonium salt and the interface consisting essentially of an emulsion which consists essentially of hydrolyzed polyacrylonitrile. (2) withdrawin a portion of the water phase and washing said water phase with acrylonitrile to extract any adiponitrile in said portion of water phase and passing the acrylonitrile plus any extracted adiponitrile into the organic phase of the decanter; (3) withdrawing a portion of the organic phase and washing said portion of the organic phase with water to extract any quaternary ammonium salt in the organic phase and passing the water plus any extracted quaternary ammonium salt into the water phase of the decanter and (4) withdrawing- a portion of the Interface filtering the interface portion to remove hydrolyzed poly-acrylonitrile and passing the filtrate into the water phase of the decanter.

5. The process of Claim > characterized in that the temperature of the aqueous mixture in the decanter is within the range of from about 20°C. to about 35°C.

6. The process of Claim 4, characterized in that the pH of the aqueous mixture in the decanter is within the range offrom about 2.5 to 7.5·

7. The process of Claim 4, characterized in that the pH of the aqueous mixture in^ the decanter is within the range of from about 3.5 to 6.5. Dated this Twenty-ninth day of January 1968 Agent or pp icants,