Concentration of licorice aqueous solutions using nanofiltration and reverse osmosis membranes

The aim of this work was to study the concentration of licorice aqueous solutions using reverse osmosis (FT 30) and nanofiltration (BDX N-90) membranes. The effects of transmembrane pressure, feed temperature, feed pH and cross-flow velocity on permeate flux and rejection were determined. A lab scale cross-flow set-up using flat-sheet configuration membrane was employed for all experiments. SEM micrographs showed the changes in the cross-section of RO and NF membranes at various pH solutions and surface alteration fouled during operating time. The applied transmembrane pressure, feed temperature, feed pH and cross-flow velocity were varied from 6 to 14 bar, 25–45 °C, 3–11 and 0.5–3.2 m/s, respectively. The obtained rejection values varied between 93 and 99.6%. The optimum operating conditions for concentration of licorice aqueous solutions using FT 30 reverse osmosis membrane were 1.8 m/s cross-flow velocity, 12 bar transmembrane pressure, 35 °C of feed temperature and pH 5. For BDX N-90 nanofiltration membrane the optimum conditions were 2 m/s cross-flow velocity, 10 bar transmembrane pressure, feed temperature 35 °C and pH 5. The membranes were tested for 10 h. The permeate flux was gradually decreased during the operating time and eventually reached a constant value.

Research highlights▶ Concentration of licorice aqueous solutions is feasible using membranes. ▶ Reverse osmosis (FT30) and nanofiltration (BDXN-90) membranes are applicable. ▶ Optimum operating condition for reverse osmosis were 1.8 m/s, 12 bars and 35°C. ▶ Optimum operating conditions for nanofiltration were 2 m/s, 10 bars and 35°C.