High-Flux Cellulose Acetate Membranes

Abstract

Three routes to increase the permeate flux of asymmetric cellulose diacetate membranes of the Loeb-Sourirajan type are investigated: increasing the hydrophilicity of the membranes; increasing their compaction stability; employing a swelling agent which allows for higher solvent-to-polymer ratio in the casting solution. The effect of casting solution composition on flux and rejection of formamide-modified cellulose acetate membranes is shown in Figure 1, illustrating the general capability of this membrane type as function of solvent concentration. Membranes of casting solution composition cellulose diacetate/acetone/formamide 23/52/25 (solvent-to-polymer ratio 2.26) were used as reference membranes in this work. Increased Hydrophilicity Effect of Hydrophilic Bentonites. All membrane models imply a direct relation between flux and membrane water content. The gross water content of the membranes can be increased by incorporating pre-gelled hydrophilic bentonites into the membranes. The useful bentonite concentration i s limited by the fact that pre-gelation introduces water into the casting solution (1).