Impact factors for flux decline in ultrafiltration of lignocellulosic hydrolysis liquor

Abstract Ultrafiltration (UF) is an effective approach for the separation and purification of organic components dissolved in lignocellulosic pre-hydrolysis liquor (PHL). However, flux decline has been a problem that restricts UF industrial applications. Here, the main impact factors for flux decline on UF processing of PHL are examined. Flux decline curves for four UF membranes having different molecular weight cut-offs (MWCOs) indicated that the largest MWCO UF membrane had a faster flux decline rate because of its better ability to concentrate PHL. Using a 10-kDa UF membrane, the normal UF procedure was modified three different ways to study the independent factors affecting flux, including retentate concentration, charge density, and membrane fouling. The results indicated that membrane fouling was a main impact factor causing flux decline in the early stages of UF, and then charge and concentration effects gradually intervened. Relative to the latter factors, membrane fouling displayed a more regular behavior, with a good linear relationship between flux and operating time. Micro-computed tomography, scanning electron microscopy, and atomic force microscopy were used to characterize fouled membranes. It was revealed that surface contamination plays a more dominant role in flux decline than does internal contamination.