Cellulose acetate, cellulose acetate propionate and cellulose acetate butyrate membranes for water desalination applications

The most common reverse osmosis (RO) membranes that achieved economic water desalination applications are made of cellulose acetate (CA). Cellulose acetate propionate (CAP) and cellulose acetate butyrate (CAB) have been blended with CA as innovative combinations to produce RO membranes through phase inversion technique. The relation between membranes compositions, structure, morphology, hydrophilicity and applicability were examined. Scanning electron microscope and Fourier transform infrared were used to evaluate the microstructure of these membranes. Hydrophilicity, strength, salt rejection and flow permeates were tested using a cross-flow reverse osmosis system and contact angle calculations. The contact angle measurements showed an increase from 56° for CA membrane to 71° for CAP membrane and 74° for CAB membrane. The hydro-phobicity of such membranes increased as CAP and CAB loadings increased. The salt rejection of pristine RO membranes increased from 93.2% with permeate of 1.4 L/m² h for CA membrane to 96.8% with permeate of 1.07 L/m² h for CAB membrane and 97.8% with permeate of 18.62 L/m²hr for CAP membrane. The salt rejection of supported membranes onto a nonwoven polyester fabric decreased from 92.8% with permeate of 3.78 L/m² h for CA/0.5 wt% CAP to 91.4% with permeate of 6.05 L/m²  h for CA/0.5 wt% CAB and 88.5% with permeate of 5.84 L/m²  h for CA/0.1 wt% CAP/0.1 wt% CAB.