Initial Flux Decline Research Articles

Initial flux decline of the cellulose acetate butylate membranes with time under RO performance

Initial flux decline, i.e. compaction, has been investigated for the cellulose acetate butylate membrane prepared by varying casting condition. The compaction behavior of membranes prepared in a short evaporation period was different from that prepared in a long evaporation period. Compression tests showed that the membrane thinned by 30 ∼ 40% instantaneously when pressurized; afterwards it thinned gradually. This corresponded to the behavior of decline. It appears that a change in decline occurs reflecting membrane structure depending on casting condition. The results were discussed for a pore model based on Kozeny-Carman equation and on the viscoelastic deformation model.

Initial flux decline and initial rejection increase for swollen ionic membranes

AbstractDuring the initial stage of operation, membrance performance in hyperfiltration experiments will be time dependent. For swollen ionic membranes, fluxes show an initial decrease while rejections initially increase in magnitude. These phenomena, also referred to as compaction, can be described by a model proposed here in which the wet membrane thickness decreases in time as a combined response to stepwise changed process parameters pressure and concentration. The response has been described by a linear first‐order differential equation and worked out by use of known concepts of flux and rejection for swollen ionic membranes. Experimental data appear to be in good agreement with model predictions.