Permeation of water vapor through cellulose triacetate membranes in hollow fiber form

Abstract

AbstractA modification of the carrier gas method for measuring permeability of a hollow fiber to a vapor is described with particular application to water vapor permeation through asymmetric cellulose triacetate in hollow fiber from. Conventional methods are inadequate because the high flux of permeation vapor combined with its low pressure on the permeate side and the small diameter of the fiber lead to an excessive buildup of pressure in the permeate stream—in some cases so great as to render much of the fiber length ineffective. The method described in this paper involves the permeation from the outside to the inside of the fiber of a binary mixture consisting of the water vapor and a fairly highly permeable carrier (helium). There is a significant pressure drop along the fiber, but a theoretical treatment is presented to take this into account and to permit a determination of the vapor permeability. Experiments at 35°C over a range of water vapor pressures up to 1.7 cm Hg gave a water flux of 9 × 10−3 cc(S.T.P.)/cm2‐sec‐cm Hg, with an apparent slight decrease with increasing pressure. Over the same range of water vapor pressure the helium flux decreased from 2.3 × 10−4 to 1.85 × 10−4 cc(S.T.P.)/cm2‐sec‐cm Hg.