Efficiency of ultrafiltration purification of solutions of polymeric colorants by inorganic base addition
AssigneeDynapol
InventorsRobin G. Booth, Anthony R. Cooper
Life of this patent
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Abstract
The ultrafiltration purification of aqueous solutions of polymeric colorants, wherein low molecular weight impurities are removed in an ultrafiltrate leaving a purified polymeric colorant-bearing retentate, is carried out with improved efficiency when during at least 2 diavolumes of ultrafiltration, the pH of the retentate is maintained above about pH 9.0.
Claims18
In the process for purifying a solution of a polymeric colorant wherein an aqueous feed solution comprising polymeric colorant of molecular weight above 1000 Daltons polymeric colorant and polymeric colorant precursors and degradation products and inorganic salts of molecular weight below 1000 Daltons is brought in contact with a semipermeable membrane under ultrafiltration conditions in a diafiltration mode for a plurality of diavolumes thereby forming an ultrafiltrate comprising polymeric colorant, polymeric colorant precursors and degradation products and inorganic salts of molecular weight below 1000 Daltons and a retentate comprising polymeric colorant of molecular weight above 1000 Daltons, the improvement which comprises maintaining the pH of the feed solution above pH 9.0 for at least 2 diavolumes by addition of base directly to said ultrafiltration feed, said ultrafiltration feed comprising at least 50% by weight water, and said base being only an alkali metal or alkaline earth metal inorganic base.
The process for purifying a solution of a polymeric colorant which comprises:
- (A) Contacting an at least 50% by weight water aqueous feed solution comprising aqueous solvent, from 0.1 to 40% by weight basis total solution of dissolved polymeric colorant of molecular weight above 1000 Daltons, from 0.04 to 10% by weight basis total solution of dissolved organic materials of molecular weight below 1000 Daltons said materials including salts, polymeric colorants of molecular weight below 1000 Daltons and polymeric colorant precursors and degradation products with a semipermeable membrane at an inlet pressure of from 25 to 200 psig, and a temperature of from 10.degree. C. to 100.degree. C. and a feed pH of from 9.0 to 13, thereby forming an ultrafiltrate solution rich in materials of molecular weight below 1000 Daltons, and a retentate solution rich in polymeric colorant of molecular weight above 1000 Daltons;
- (B) Adding directly to said retentate aqueous solvent and base in an amount to maintain the water content at at least 50% by weight and its pH within the range of 9.0 to 13, and form a pH-adjusted retentate, said base being only an alkali metal or alkaline earth metal inorganic base;
- (C) Repeating the contacting of Step (A) using as feed the pH-adjusted retentate thereby forming a second ultrafiltrate and a second retentate;
- and (D) Recovering as said second retentate, a purified solution of polymeric colorant.
Dependencies are inferred from the claim text.