Several nanofiltration and reverse osmosis membranes were screened for separating acetic acid from model solutions. Flux increased with pressure and temperature and decreased with pH and concentration of acetate. Rejection increased with pH, probably depending on the degree of dissociation of the acetate. At higher pH, acetate rejection could be correlated with NaCl rejection. Of all the membranes screened, the best for separation of acetate were NTR729, DS5 and PZ. At pH 5.6 and 50 degrees C, the NTR729 had an average acetate rejection of 40%, glucose rejection of 99% and flux of 601 m(-2) h(-1) at 250 psig.