Concentration of aqueous solutions of organic components by reverse osmosis: II. Influence of transmembrane pressure and membrane type on concentration of different alcohol solutions by reverse osmosis

Aroma compounds are heat-sensitive and volatile components, which are lost with co-vapour during concentration by evaporation. The application of reverse osmosis for concentration of alcohol solutions, that are components of apple juice aroma, was investigated. Influence of membrane type, processing pressure parameters and volume concentration of different alcohols (0.1% v/v, 1% v/v, 2% v/v) was studied. The effect of the molecular structure and molecular mass on concentration of model solutions of alcohols by reverse osmosis, and influence of activity and activity coefficient on concentration were also investigated. The investigation was carried out with model solutions of alcohols (methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, n-pentanol, isopentanol). Reverse osmosis concentration was carried out on laboratory equipment with plates and frames using two types of composite membranes. In defined time intervals, during the concentration process, samples of permeates and retentates were taken. Aroma volatile compounds—alcohols in the permeate and retentate were determined by gas chromatography with a mass detector (GC/MS) using a “head space” technique. The results of this research give a deeper insight into mechanisms of retention of aroma compounds by the membrane during concentration of water solutions by reverse osmosis. Examined alcohol solutions could be also concentrated successfully by reverse osmosis. Membrane type HR 98 PP showed greater retention of alcohols by the membrane and lower permeability. Higher concentration factor in retentate and lower recovery in permeate, was achieved with a bigger portion of alcohols in the feed solution, greater molecular mass and alcohols of iso-forms. Membrane selectivity increased with pressure increase and retention of alcohols was greater in the retentate than in permeate.