Using membrane contactors for fruit juice concentration

Osmotic evaporation is a membrane process that has fascinating advantages over conventional processes for the production of fruit juice concentrates since it has the ability to concentrate solutes to very high levels with minimal thermal or mechanical damage. Our purpose was to compare and analyse the results obtained in the concentration of a sucrose solution used as model juice. Two different membrane contactors with different specific areas and number and dimensions of fibres/tubes were used. The hydrodynamic conditions that maximize the water flux were previously determined by using a series resistance model. For a determined range of Reynolds number, the boundary layer mass transfer resistances can be neglected and there is only the contribution of the membrane resistance. The concentration of a sucrose solution from 12degrees Brix to 60degrees Brix, used as a model fruit juice, was carried out. The water flux decreased due to the progressive reduction of the driving force. The overall mass transfer coefficient, K-p, remained constant throughout the experiment, except for one of the contactors used where there was a reduction due to the concentration polarization caused by the increase of the sucrose solution's viscosity.