Mass transfer coefficient determination method for high-recovery pressure-driven membrane modules

A mass transfer coefficient determination method, based on the velocity variation method, is developed for pressure-driven membrane modules with large membrane area and high recovery rates. The method was used to measure mass transfer coefficients in the nanofiltration spiral-wound module Filmtec NF200-2540 (DOW-USA), with a membrane area of 2.6 m2, using two aqueous solutions of glycerol and xylose at 25ºC with a concentration of ca. 2 kg/m3. The permeate concentration was measured for circulation Reynolds numbers in the range 70–270 (based on the channel height and on the average feed velocity) and for a permeate flux of 69.2 l/m2h. The water recovery rate varied between 15% and 48% in the experiments. The intrinsic rejection coefficients of the membrane were determined for the two solutes by the developed extrapolation procedure to infinite Reynolds number. Based on these values and on the experimental data, the mass transfer coefficients were determined for the two solutes (950 < Sc < 1170) and for the different Reynolds number tested (70 < Re < 270) and the mass transfer correlation Sh = 0.33 Re0.5 Sc0.33 was obtained for this system.

A mass transfer coefficient determination method, based on the velocity variation method, was developed for pressure-driven membrane modules with large membrane area and high recovery rates. The method is based on the measurement of the solute concentration in the permeate as a function of the circulation Reynolds number, at constant transmembrane pressure. The extrapolation procedure to obtain the mass transfer coefficient requires that the intrinsic rejection must be independent of the circulation Reynolds number. For aqueous binary solutions of neutral solutes, this can be achieved if the transmembrane pressure is kept constant during the procedure of variation of the circulation Reynolds number. The method was adequate to measure mass transfer coefficients for the nanofiltration spiralwound module Filmtec NF200-2540 (Dow-USA), with a membrane area of 2.6 m 2, using two aqueous solutions of glycerol and xylose at 25ºC with a concentration of ca. 2 kg/m3, for water recovery rates between 15% and 48%. For this spiralwound module, the mass transfer correlation Spiral-wound module Fimtec NF200-2540 T = 2 5 ºC 0,5 glycerol (2.05 kg/m ) c Ap / c A 0 0,4 0,10 xylose (2.15 kg/m ) 0,05 A pproxim ate solution ( Eq. 9) 0,00 E xact solution Re Fig. 4. Comparison between the approximate [Eq. (9)] and exact prediction of the dimensionless permeate concentration.