Pervaporation performance of a composite bacterial cellulose membrane: dehydration of binary aqueous–organic mixtures

Acetobacter xylinum (Gluconacetobacter xylinus) is a bacterium that produces extracellular cellulose under static culture conditions. The highly reticulated cellulose matrix along with the entrapped cellulose-forming bacteria is commonly referred to as a pellicle. The processed bacterial cellulose membrane/film was modified into a composite bacterial cellulose membrane (CBCM) for pervaporation separation of aqueous–organic mixtures. The CBCM was prepared by coating with alginate or alginate+polyvinylpyrrolidone and cross-linking with glutaraldehyde. The pervaporation performance was determined using aqueous–organic mixtures such as, 1:1 (v/v) water–ethanol, water–isopropanol and water–acetone. The pervaporation performance of the CBCM was more effective for zeotropic mixtures (water–acetone) in comparison to the investigated azeotropic mixtures (water–ethanol and water–isopropanol). The selectivity of CBCM was found to be 4.8, 8.8, 19.8 for water–ethanol, water–isopropanol and water–acetone mixtures, respectively. The permeation flux for the water–acetone mixture was found to be 235 ml/m2/h. The present investigation demonstrated that the CBCM could be employed to concentrate azeotropic as well as zeotrope forming binary mixtures by preferential pervaporation of water, with low energy requirements in contrast to the established method of distillation. In addition, the effects of feed composition, operating temperature, membrane thickness, and method of CBCM preparation on pervaporation performance have been evaluated. Investigations with the CBCM revealed that 94.5% ethanol, 98% acetone and 98.5% isopropanol concentrations could be attained from the initial 50% aqueous mixtures of these chemicals by way of pervaporation. In the case of the isopropanol–water mixture the resolving property of the membrane was more evident as the concentration arrived at was 98.5%, in contrast to other binary mixtures. The surface characteristics of the CBCM were revealed by scanning electron microscopy. In view of its properties the CBCM can be useful for pervaporation separation of these chemicals at moderate temperatures and pressure. The CBCM could be employed in the downstream processing of heat-labile and flavor-imparting volatile molecules in the field of food biotechnology and fabrication of membrane bioreactors for on-line product purification. Further studies are under progress to use the membrane for the immobilization of food processing enzymes.