Upgrading spent liquors from NSSC process: III. Separation of spent liquors components by Ultrafiltration

AREA, M.C., MARTOS, M.S., FELISSIA, F.E., VENICA, A.D., VALADE, J.L.

Orlando, USA

Congreso; Tappi Pulping Conference; 1999

TAPPI

The present study examines the fractionation of NSSC spent liquors using membranes with different chemical composition and pore sizes. The experiments evaluated the use of this method for separating neutral sulfite spent liquors hemicelluloses from lignosulfonates with the aim of recovering theses by-products. Four ultrafiltration membranes with molecular weights cut-off of 500, 2000, 3000 and 10000 Dalton (AMICON type YC05, YM2, YM3 and PM10 respectively) were used. The fractions obtained by ultrafiltration and the original spent liquor were hydrolyzed and hemicellulose content was estimated by HPLC as xylans. Ultrafiltration behavior of spent liquor was estimated by determining molecular weights of the obtained fractions (retentate and permeate) by GPC (IR and UV detection) and lignosulfonate and ash content. BOD and COD of the original spent liquor and of some of the ultrafiltration fractions were also determined. The results showed that, for the separation of lignosulfonates, the membrane with a pore size of 3000 Dalton (YM3) gave the best results, with the lowest rejection of lignosulfonates. Permeates containe lower amounts of hemicelluloses than that of lignosulfonates, organic acids and ashes. The membranes with smaller pores retained more lignin, acetic acid and ash than YM3 and PM10 membranes. Trials at different concentrations show no difference between 1% and 7%. Definitive trials involved re-dilution of the YM filter retentates and further separation of ashes with the YC05 membrane.