Investigation of aqueous biphasic systems for the separation of lignins from cellulose in the paper pulping process

In efforts to apply a polymer-based aqueous biphasic system (ABS) extractio n to the paper pulping process, the study of the distribution of various li gnin and cellulosic fractions in ABS and the effects of temperature on syst em composition and solute partitioning have been investigated. The partitio ning of three lignin species (Indulin AT, Indulin C, acid Rear 85A) have be en studied in ABS prepared from stock solutions of 40% (w/w) poly(ethylene glycol) (PEG)-2000 and increasing concentrations of K2CO3, (NH4)(2)SO4, and NaOH. The partitioning of these lignins is affected by the free energy of hydration of the salt forming the ABS, the tie line length, and the dissoci ation of the sulfonic acid and hydroxyl groups of the distributed solutes. The partitioning of fibrous cellulose and diethylaminoethyl cellulose have been studied in 40% (w/w) PEG-2000-(NH4)(2)SO4 ABS. The hydrophilic nature of these species is important in terms of their phase preference when desig ning a polymer-based aqueous biphasic extraction process for use in a paper pulping process. Both cellulosic samples do not dissolve, but rather repor t to the salt-rich phase of an ABS. In both chemical pulping and Organosolv pulping, temperatures in excess of 120 degrees C are needed to solubilize the lignin from the cellulose fraction of wood. To study the effects of tem perature on the phase diagram and solute partitioning, phthalic acid and (N H4TcO4)-Tc-99 (as system probes) have been partitioned in 40% (w/w) PEG-200 0-(NH4)(2)SO4 ABS at known tie line lengths as a function of temperature. T emperature does not appear to affect the partitioning results beyond the ex pected increase in phase divergence as temperature is increased. The PEG-20 00 polymer itself appears to be stable to chemical pulping conditions. (C) 2000 Elsevier Science B.V. All rights reserved.