Mass transfer studies on cellulosic membrane for artificial kidney

Abstract

The mass transfer characteristics of cellulosic membranes nearly devoid of any charge or adsorption property are investigated. The membrane acts as size selective-sieve type barrier through which diffusion by concentration gradient and ultrafiltration by pressure difference take place simultaneously or alone depending on the driving forces between either side of the membrane. Overall membrane resistance (O.M.R) are determined by a dual closed-loop technique with which the effects of blood flow rate, dialyzate flow rate and molecular size on O.M.R. are examined. Ultrafiltration experiment in the range of 0.2-1.0 atm of pressure differences is performed by use of Amicon ultrafilter with which solute rejection is determined covering M.W. 60 (urea) to 44,000. (albumin) The increase of blood flow rate and dialyzate flow rate decreases O.M.R. due to the reduction of film-resistance. As M. W. increases O.M.R. increases. Solute radius (Stokes-Einstein radius) is found to be more reasonable parameter in estimating O.M.R. than molecular weight. The correlations for cellulosic membranes have the following formula. For membrane 1 (22$\mu$ thickness, Union Cellophane, Seoul, Korea) $$\log\,(R_o) = 2.224\,\log\,(r_o) + 0.745$$ For membrane 2 (38$\mu$ thickness) $$\log\,(R_o) = 1.326\,\log\,(r_o) + 0.945$$ where $R_o$ : overall membrane resistance (min/cm) $r_o$ : Stokes-Einstein radius, $\mbox{\AA}$ O.M.R. of membrane 1 is much higher than the reported value of Cuprophane which is clinically in use. So membrane 1 is not suitable for hemodialyzer membrane owing to its high O.M.R.. Membrane 2 is, on the other hand, approximately the same as Cuprophane in terms of membrane diffusive permembranes: But membrane 2 has low hydraulic permeability ($\frac{1}{2}$ times Cuprophane). There is no solute rejection for less than solute radius of 3.5$\mbox{\AA}$. Solute rejection increases rapidly ranging from M.W. 500 to 2000. Solute rejection profile shows sigmoid form with M.W. increase....