Special Topics on Membranes
Homework 7
1. 3 Points
Name 2 important commercial dialysis applications.
2. 3 Points
Name a functional group for cation-exchange membranes and a functional group for anion-
exchange membranes.
3. 5 Points
Show typical plot of current vs. voltage for electrodialysis.
4. 10 Points
A 25-micron cellophane membrane is used in an artificial kidney to remove urea from
blood. The blood contains 0.18 g/1 urea whereas the dialysate has a negligible concentration of
urea. For urea, this membrane has a diffusivity of 3 x 10-7 cm2/s and a distribution coefficient of
1.6. The mass transfer coefficients on the blood side and in the dialysate are 0.8 x 10-3 cm/s and
3 x 10-3 cm/s, respectively. Calculate the urea flux and the boundary layer resistances in terms of
the percent of the overall resistance.
5. 10 Points
Surface water containing a sodium chloride concentration of 1 g/1 is desalted with
electrodialysis to 200 ppm for irrigation. The electrodialysis system consists of 80 cell pairs with
an average resistance of 0.05 each cell pair and an electrical efficiency of 0.91. Calculate the
current and electrical potential required for the membrane process to produce 300 m3/day of
irrigation water.
6. 10 Points
In an elecrodialysis, the current density (i) and voltage (electrical potential E) values were
determined by the use of a 0.2 M sodium chloride solution at room temperature as follows:
i (mA/cm2) E (V)
4 0.03
8 0.07
12 0.11
16 0.21
20 0.51
24 0.85
(1) Determine the limiting current density.
(2) If sodium sulfate is used instead of sodium chloride at the same concentration, will the
limiting current density increase or decrease?
,
Homework 7
1. 3 Points
Name 2 important commercial dialysis applications.
2. 3 Points
Name a functional group for cation-exchange membranes and a functional group for anion-
exchange membranes.
3. 5 Points
Show typical plot of current vs. voltage for electrodialysis.
4. 10 Points
A 25-micron cellophane membrane is used in an artificial kidney to remove urea from
blood. The blood contains 0.18 g/1 urea whereas the dialysate has a negligible concentration of
urea. For urea, this membrane has a diffusivity of 3 x 10-7 cm2/s and a distribution coefficient of
1.6. The mass transfer coefficients on the blood side and in the dialysate are 0.8 x 10-3 cm/s and
3 x 10-3 cm/s, respectively. Calculate the urea flux and the boundary layer resistances in terms of
the percent of the overall resistance.
5. 10 Points
Surface water containing a sodium chloride concentration of 1 g/1 is desalted with
electrodialysis to 200 ppm for irrigation. The electrodialysis system consists of 80 cell pairs with
an average resistance of 0.05 each cell pair and an electrical efficiency of 0.91. Calculate the
current and electrical potential required for the membrane process to produce 300 m3/day of
irrigation water.
6. 10 Points
In an elecrodialysis, the current density (i) and voltage (electrical potential E) values were
determined by the use of a 0.2 M sodium chloride solution at room temperature as follows:
i (mA/cm2) E (V)
4 0.03
8 0.07
12 0.11
16 0.21
20 0.51
24 0.85
(1) Determine the limiting current density.
(2) If sodium sulfate is used instead of sodium chloride at the same concentration, will the
limiting current density increase or decrease?
,
