Reverse osmosis membranes for water desalination based on cellulose acetate extracted from Egyptian rice straw

Abstract

Cellulose diacetate (CDA) and cellulose triacetate (CTA) were extracted from Egyptian rice straw. Reverse osmosis (RO) membranes were prepared from this CDA using phase inversion technique. The structural, crystalline, morphological, and hydrophilic properties of the prepared membranes were characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance (1HNMR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and contact angle measurements, respectively. The NMR spectra revealed a degree of substitution of 2.8 for CTA and 1.75 for CDA. The values of water flux and salt rejection for CA-RO membrane without annealing, tested in 10,000 ppm NaCl, were 7.1 L/m2 h and 87.4%, respectively, while the water flux of 4.76 L/m2 h and a salt rejection of 93.3% were obtained for the annealed CA-RO membrane at 14 bar. The annealed CA-RO membranes showed an asymmetric structure with ridge-and-valley on the top layer and macrovoid structures in the support layer as revealed by SEM. The CA-RO membranes grafted with 15 wt% of 2-acrylamidopropane-2-methyl sulfonic acid produced a salt rejection of 93.5% and a water flux of 8.3 L/m2 h. It was concluded that both the annealing and grafting processes enhanced the performance of the CA-RO membranes.