In this study, the effect of binary and ternary systems, solvent/feed (S/F) ratio (20-100 w/w), time (2-3 h) and pressure (10-200 bar) were tested with subcritical and supercritical CO2 to produce valonea tannin from acorn cups. The best yield of phenolic contents (PCs) of the valonea tannin (34.73 +/- 0.02 wt%) was obtained by H2O/CO2 binary system under the conditions of S/F = 100 (w/w) at 100 bar for 3 h with supercritical CO2. Phase equilibria of H2O/CH3OH/CO2 ternary system with different solvent fractions at different temperatures and pressures were also imaged in the high pressure view cell, where liquid-liquid-vapor phase behaviors were observed for all ratios of H2O and CH3OH from 60 to 100 degrees C and 60 to 250 bar. High tannin content isolated in a short time will decrease the waste load and provide great advantage in terms of reducing the cost of the tannin used in leather industry. (C) 2015 Elsevier B.V. All rights reserved.