Enhanced pervaporation dehydration of n-butanol using water hyacinth–derived cellulose acetate/chitosan composite membranes

n-Butanol is a promising biofuel with higher energy density and lower volatility than ethanol, yet its purification by distillation is limited due to azeotrope formation with water. Pervaporation (PV) using dense polymer membranes offers an energy-efficient alternative for butanol dehydration. This study develops cellulose acetate (CA)–chitosan (CT) composite membranes derived from water hyacinth cellulose, using blending and layer-by-layer (LbL) casting techniques on polyethersulfone (PES) supports. The membranes were systematically characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), contact angle measurements, swelling degree, and tensile strength analysis, followed by performance evaluation in butanol–water separation. FTIR analysis confirmed the formation of hydrogen bonding interactions between CA and CT, while SEM revealed distinct morphological features depending on the fabrication method: blended membranes exhibited a dense and homogeneous structure, whereas LbL membranes showed a rougher and more porous surface. Increasing CT content reduced membrane hydrophilicity and water uptake, leading to enhanced dimensional stability. In pervaporation performance, PES/CA–CT membranes achieved the highest separation factor of 4.82, whereas PES/CA/CT membranes exhibited the highest permeance of 25.01 L m⁻² h⁻¹ bar⁻¹ . Considering both permeance and selectivity, the PES/CT/CA membrane demonstrated the highest pervaporation separation index (PSI) of 79.13 L m⁻² h⁻¹ bar⁻¹ . These findings demonstrate that blending and layer-by-layer fabrication strategies produce distinct membrane morphologies and permeance -selectivity trade-offs during n-butanol dehydration. Furthermore, the use of water hyacinth-derived cellulose provides a value-added utilization pathway for an abundant invasive biomass resource in membrane fabrication.