IL33153A - Process of purifying aqueous zncl2 solutions used as spinning solvents for acrylonitrile polymers - Google Patents

Description

PROCESS OF PURIFYING AQUEOUS ZnCl2 SOLUTIONS USED AS SPINNING SOLVENTS FOR ACRYLONITRILE OLYMERS e A process is presented for oxalate impurities from aqueous solutions used as solvents in the wet spinning of acrylonitrile polymers involves the adjustment of the pK of the solution and the addition of permanganate to oxidize oxalate This process prevents the formation of oxalates that tend to clog spinnerette orifices and interrupt the spinning Disclosure This invention relates to a process for improving the spinning of polymers by preventing the formation of insoluble impurities that tend to obstruct spinnerette Previously it was known that various metallic impurities produced adverse effects when present in solutions used as solvents in the spinning of acrylonitrile Various methods have been presented for removing impurities from these solvents by oxidation to form insoluble and the form precipitates removable by Various have been used for this Such methods remove interferrng inorganic Typical agents that have been employed are the various peroxides disclosed in Patent and potassium ganate disclosed in Patent For reasons which have not previously been too it has been found that such use of the permanganates of the prior art for purification of solvents used the polymerization and spinning of polymers has resulted in frequent clogging of the spinnerette necessitating frequent stoppage and cleaning the spinnerettes In the light of the present it is believed that the use of such oxidizing agents to remove undesirable metallic impurities resulted in reactions with residual and their derivatives which the formation of metallic salts of oxalic acid in deposited out on the spinnerette head and clogged its It an object of this invention to provide a new and useful process for preventing the clogging of spinnerette orifices in the spinning of acrylonitrile Another object of this invention is to provide a process for preventing the clogging of spinnerette head Additional objects and advantages of the present tion will be apparent by reference to the following detailed description In accordance with the present there is vided a new and useful process for preventing the clogging of spinnerette orifices which involves the steps adjusting the pH of the ZnCl2 solution to be used in the spinning of polymers to a value between about and about adding sufficient to oxidize oxalate ions present in said adjusting the of the resulting solution to a value between about and about adding sufficient to oxidize the ions present in said and filtering the resulting solution to remove insoluble This process is carried out in the following The solution that is to be treated is first stripped of residual the pH of the solution is lowered by the addition of an acid such as Sufficient acid is added so that the solution being treated has a in the range of about to and preferably to when made on made up of one volume of solution diluted by nine volumes of distilled water other equivalent After the pH an aqueous potassium permanganate solution is slowly added to the solution undergoing This ganate solution is added until the color of the solution indicates a temporary pink This pink color slowly fades into a turbid and eventually the solution becomes clear and This clear and colorless solution contains manganous ions formed in the oxalate oxidation the reaction between the added permanganate and the It is usually desirable to remove these and this is accomplished by first adjusting the pH of the acrylonitrile polymer solvent to about to and preferably to This pH adjustment is c tied out by adding or those skilled in the Further potassium tion is then added to the resultant batch until the color of the solution indicates that a characteristic pink has been Normally this will require about of the permanganate used in the oxalate oxidation this point in the the acrylonitrile polymer solvent is purified of oxalate ions as the ions occurring as a result of the It is then normal to filter the batch to remove various metallies The solutions that may be treated by the process of this invention are polymer solvents or coagulating solutions must be treated with an oxidizing agent to remove metallic These solutions contain various concentrates of The aqueous solution may be first adjusted a concentration of from to zinc chlori prior to the pli adjustment to a value about and about By treating such solutions according to the process this it has been possible to continue spinning for more than four times longer changing or cleaning the spinnerette than was possible prior to this Certain precautions are necessary to obtain the best result with the process of this Proper temperature control appears to be since high teraperatures may encourage other reactions at the expense of the oxalate oxidation To insure that this does not the temperature of the being treated should be maintained within the limits of about to A temperature of about is at that temperature the reaction with oxalate An excess of permanganate should also be amount of oxalate is attacked by the permanganate used in this process and to avoid other side Control of the is also since there is a definite decrease in oxalate oxidation with a pH slightly above For optimum results in the oxalate oxidation the pH of the solution should be in the vicinity of The invention may be more fully understood by ence to the All parts and percentages unless otherwise These examples are illustrative of certain embodiments designed to teach those skilled in the art to practice the invention and to represent the best mode contemplated for carrying out the invention and are not intended to limit the scope of the invention in any EXAMPLE 1 This example illustrates the use of the process of this invention for treating aqueous coagulating solutions To 250 ml of aqueous ing traces of aeryIo itrile and oxalates ml of N was added to adjust the pH to To this ml of was slowly as the solution was well An of was The last drop of required 30 seconds for the disappearance of the pink is when the pink color persists for 40 to 50 seconds and the solution turns rather than To this solution ml of N was added stirring to adjust the to To ml of K was with After standing a to permit coagulation to the was filtered with suction a A era diameter filter to remove various metallic The original sample contained ppm oxalate and The from the above treatment contained 35 ppm oxalate ion and 17 p m Upon correction for the equivalent concentrations at the initial zinc chloride concentration are 38 ppm oxalate and 19 ppm Mn All rements were made on 1 volume of diluted with 9 volumes of distilled wate or the equivalent dilution of other This process was carried out at ambient or room EXAMPLE 2 This example illustrates the results obtained by the process of this invention on various spinning solvent batches freed of all but traces of The tests were ducted on polymeri ation grade aqueous which contained traces of aerylonitrile and The oxalate content the untreated tions ranged from ppm Cl2 The oxalate content was reduced by potassium permanganate treatment of this invention as PPM Oxalate Batch Initi l Final Removed 1 390 80 2 373 50 363 90 4 329 34 5 300 98 6 439 0 7 431 38 8 450 9 434 0 10 322 38 11 439 32 EXAMPLE 3 This example illustrates the importance of maintaining the proper H during the oxalate oxidation In this the treatment was carried out in a manner similar to that in Example Reagent grade aqueous solution containing oxalate used and the pH of the solution was At a pH of the oxalate oxidation process was only efficient based upon the weight of added to the a a pH of the oxidation was close to 4 This example illustrates the suitability of the process for long term Coagulation bath solutions freed of all but traces of monomers were treated in a manner similar to Example 2 over an extended period of This treatment was carried out The following were PPM Oxalate Untreated 44 228 32 224 After the above solution had been used and reused in a closed and coagulating a batchwise treatment was carried out one week later on a sidestream over a period of 5 The following analyses were tions may on as insufficientOCRQuality

Claims (5)

What is claimed is:

1. In a wet spinning process for acrylonitrile polymer fibers in which the aqueous Z C^ coagulating 'solution or spinning solvent contains oxalates and is treated -witn an_ oxidizing agen -to remove metallic impurities, the improvement which comprises the steps of: (1) adjusting the pH of said Z CI^ solution to a value between about 1.0 and about 2.0; (2) adding KMnO^ to oxidize oxalate ions present in said solution; (3) adjusting the pH of the resulting solution to a value between about 5.0 and about 5.5? (4) adding sufficient KMnO^ ' to oxidize the metallic ions present in said solution; and (5) filtering the resulting solution to remove insoluble precipitates. ■

2. The process of Claim 1 in which the amount of KMnO^ added in step (4) to oxidize metallic ions is at least equal to 2/3 of the amount of MnO^ added in step (2) to oxidise oxalate ions .

3. The process of Claim 1 in which the pH is adjusted to a value of about 1. to about 1.6 just prior to the oxalate oxidation step.

4. The process of Claim 2 in which.' he aqueous ZnCJ^ solution is first adjusted to a concentration of from 30 ¾ to 50¾ zinc chloride prior to the pH adjustment of step (1) „ ?

5. . The process of Claim 4 in which the temperature is maintained between about 10°C and 40 °C.