Reverse osmotic concentration of aqueous 1, 2 propanediol solution was carried out, using cellulose acetate asymmetric membranes and composite membranes, PEC-1000, NS-100, and FT-30. Separation of 1, 2 propanediol and flux through the membranes were measured within the following ranges : concentration; 1 to 10 wt%, operating presssres; 3.92 to 6.86 MPa.
PEC-1000 membrane shows the best performance among the membranes tested. Its separation at 5wt% and 4MPa was above 99% At the same experimental condition, separation of FT-30 BWwas 89%, FT-30 SW 89%, NS-100 90%, and cellulose acetate heat treated at 90°C 92%, at 87°C 87%, and at 85°C 79%.
An analysis of data with Spiegler-Kedem's transport model was carried out to obtain membrane constants such as reflection coefficient σ, solute and hydraulic permeabilitics ω and L
p, concentration induced compaction coefficients for ω and L
p, β
s and β
v. Values of σ for composite membranes are 1.0, but for cellulose acetate less than 1.0. PEC-1000 shows the largest value of β
v, then FT-30, NS-100, and cellulose acetate shows the smallest.
Energy and membrane area required using the best membrane PEC-100 were calculated to concentrate 1, 2 propanediol from 1.8 wt% to 16 and 12 wt% by reverse osmosis. The energy per one kilogram of concentrated 1, 2 propanediol is proportional to the operating pressure and slightly depends on final concentration and concentration polarization, and is found 0.1 to 0.18 kWh. The membrane area is inversely proportional to the operating pressure and found 0.15, 0.25 and 0.65 m
2/kg 1, 2 propanediol/day for 10, 8 and 5 MPa at no concentration polarization.
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