Aroma Stripping under various Forms of Membrane Distillation Processes: Experiments and modeling

Concentration of fruit juices by membrane distillation is an interesting process as it can be done at low temperature giving a gentle concentration process with little deterioration of the juices. Since the juices contains many different aroma compounds with a wide range of chemical properties such as volatility, activity coefficient and vapor pressure, it is important to know how these aroma compounds will eventually pass through the membrane.
Experiments have been made on an aroma model solution and on black currant juice in a lab scale membrane distillation set up which can be operated in various types of MD configurations: Vacuum Membrane Distillation , Sweeping Gas Membrane Distillation , Direct Contact Membrane Distillation and Osmotic Membrane Distillation. The influence of feed temperature and feed flow rate on the permeate flux and concentration factor for different types of aroma compounds have been measured for these MD configurations.
A general transport model for the flux of water and aroma compounds have been derived and compared with the experimental data. A reasonable agreement between the modelling and the experiments could be obtained. From the modelling it was possible to explain the large different in permeate flux and concentration factor that was observed for the different MD configurations. This is highly related to the heat and mass transfer resistances in the membrane as well as in the boundary layers adjacent to the membrane surface and how the driving force develops along the length of the membrane.