Resin regeneration process

Hydrogen chloride is stripped from spent basic ion exchange resin by treatment with a solution of a tertiary amine in an amide solvent. The eluent solution is treated with anhydrous ammonia to precipitate ammonium chloride. The solution of tertiary amine in amide solvent is separated from the precipitate and may be used to regenerate spent resin.

BACKGROUND OF THE INVENTION 
Poly(m-phenylene isophthalamide) is synthesized by the reaction of 
isophthaloyl chloride and m-phenylene diamine in dimethylacetamide (DMAc). 
Hydrogen chloride, a byproduct of the reaction, is corrosive and has an 
adverse effect on the polymer. The hydrogen chloride can be removed by 
contacting the solution with an ion-exchange resin in base form resulting 
in an HCl-free solution generally suitable for spinning. The present 
invention deals with regeneration of the spent or exhausted ion exchange 
resin. 
SUMMARY OF THE INVENTION 
The present invention provides a process for regenerating a bed of spent 
basic ion exchange resin in hydrogen chloride salt form and recovering the 
regenerant solution comprising: 
a) passing a regenerant solution comprising a tertiary amine in an amide 
solvent through the bed to regenerate the spent resin and form an amide 
solution of the hydrogen chloride salt of the tertiary amine; 
b) treating the resulting solution with anhydrous ammonia to precipitate 
ammonium chloride and form a solution consisting of the tertiary amine in 
amide solvent; and 
c) separating the regenerant solution from the precipitate. 
DETAILED DESCRIPTION OF THE INVENTION 
The present invention concerns the regeneration of a weakly basic ion 
exchange resin that is spent by virtue of adsorption of hydrogen chloride. 
Weakly basic anion exchange resins, such as Amberlyst.RTM. A-21 (Rohm & 
Haas, Philadelphia, Pa.) which bears tertiary amine functional groups, are 
useful in this process. Regeneration is achieved by passing an anhydrous 
solution of a tertiary amine, such as tri-n-butylamine in an amide 
solvent, conventionally DMAc, through a column of the spent resin which 
would be in the HCl-salt form. As the solution passes through the column, 
the HCl is stripped from the ion exchange resin converting it back to the 
free base form. The HCl forms a salt with the tertiary amine and is 
carried away by the anhydrous amide solution. The effluent comprising the 
tertiary amine hydrochloride in amide solvent is then neutralized with 
anhydrous ammonia and the ammonium chloride which forms is removed by 
filtration. The filtrate is now ready for use for resin bed regeneration. 
The solvent content of the filtrate can be reduced if desired by low 
temperature vacuum distillation or other means. 
If the resin had been previously treated with a polymer solution containing 
HCl, it is desirable to flow anhydrous DMAc through the spent resin until 
the effluent is free of residual polymer before treatment with the 
tertiary amine solution. The solution of tertiary amine in amide solvent 
is then flowed through the spent resin to convert the resin to the free 
base form. Flow is continued until the effluent contains little or no HCl 
salt of the tertiary amine. The column is then rinsed with the amide 
solvent and is once again ready for adsorption of HCl. 
The following example is illustrative of the invention.

EXAMPLE 
A jacketed flask approximately 10.2 cm in diameter and 30 cm in height with 
an inlet port at the top and an exit port at the bottom, is filled to a 
height of 21 cm with weakly basic A-21 ion exchange resin available from 
Rohm & Haas Co. This resin is conditioned with two bed volumes of 1.5N 
aqueous sodium hydroxide followed by a water wash and then two bed volumes 
of 2N HCl, followed by water rinsing until the effluent of the column is 
neutral. The above conditioning procedure is repeated. Following the water 
rinse the column is rinsed with 5 bed volumes of anhydrous DMAc to prepare 
the column for anhydrous non-aqueous conditions. 
To a jacketed 3L three-necked flask is added approximately 1000 grams of a 
13% polymer solids solution of poly(m-phenylene isophthalamide) in DMAc 
containing about 4% of HCl. The jacketed flask containing polymer and the 
jacketed flask containing the resin are heated using a circulating water 
bath of 70.degree. C. The polymer solution is stirred and pumped into the 
inlet port of the resin-containing flask at a rate of approximately 14 
g/min. The eluent leaving the exit port of the flask containing the resin 
is tested periodically for polymer (by sampling and testing for polymer 
via precipitation). Once polymer is detected, the effluent is collected in 
a separate container. Polymer is collected until very little polymer is 
detected in the effluent. The collected material is a solution of 
poly(m-phenylene isophthalamide) in DMAc. 
Anhydrous DMAc is flowed through the resin until the effluent is polymer 
free. Next, approximately 1800 ml of a 12% solution of amine (TBA) in DMAc 
is flowed through the column. After all the TBA solution has been passed 
through the column, the column is rinsed with 1500 ml of DMAc. The 
effluent is collected. The resin is now in the free amine state and ready 
for adsorption of HCl. 
Solvent is removed from the effluent solution by low temperature vacuum 
rotary evaporation until the concentration of tri-n-butylamine 
hydrochloride is determined to be 12% as tri-n-butylamine. This solution 
is treated with approximately 14 grams of anhydrous ammonia gas and 
ammonium chloride precipitates from solution. The ammonium chloride is 
separated from the solution via filtration. The tri-n-butylamine-DMAc 
solution is now ready to be used for resin bed regeneration.