Ultrafiltrative deinking of flexographic ONP : the role of surfactants

Abstract

Ultrafiltration is a potentially viable method of removing finely dispersed flexographic pigments from the deinking water loop. This work examines the effects of surface-active materials on ultrafiltration efficiency. A logarithmic relationship between permeate flax and pigment concentration was demonstrated at ink concentrations above 0.4%, permeation rates becoming independent of ink content at lower concentrations. The pressure independent ultrafiltration permeation rates observed at more highly concentrated ink dispersions were shown to be limited by mass-transfer effects, as predicted by the concentration-polarization model. Permeate flux at low ink concentration was limited by membrane fouling, which occurs because dilute ink dispersions have a low concentration of surface-active materials. Increasing the concentration of surfactant in dilute ink dispersions decreased the degree of membrane fouling. However, excessive surfactant decreased permeation rates because of mice//e formation. Clarification of concentrated ink dispersions (>0.4% ink solids) resulted in relatively stable permeation rates and less fouling. The inherently higher concentrations of surface-active materials in concentrated ink dispersions appear to retard fouling.

Citation

Upton, Bradley H. ; Krishnagopalan, Gopal A.; Abubakr, Said. 1999. Ultrafiltrative deinking of flexographic ONP : the role of surfactants. Tappi journal. Vol. 82, no. 11 (Nov. 1999).:p. 104-114 : ill.