Flux enhancement during Dean vortex tubular membrane nanofiltration: 13. Effects of concentration and solute type

Controlled centrifugal instabilities (called Dean vortices) resulting from sufficient flow in composite polyamide-poly(ether sulfone) helical membrane tubes have been used to reduce concentration polarization during nanofiltr ation. These vortices enhance back-migration through convective flow away f rom the membrane-solution interface and increased shear at the membrane-sol ution interface and allow for increased membrane permeation rates. As a res ult, solute concentrations at the membrane-solution interface and resulting osmotic-driven back flow are reduced. The performance of two sets of modules (designated Set II and Set III), eac h set containing a prototype vortex generating helical tubular nanofiltrati on (NF) element and a conventional linear element was evaluated. Nanofiltra tion of aqueous solutions of inorganic salts (including KCI, K2SO4 and K3PO 4) and amino acids of similar molecular weight (including glutamic acid, gl utamine and lysine) was performed with Set II. These experiments, designed to evaluate the effects of solute type, were conducted at the same energy c onsumption and transmembrane pressures. Both membrane swelling and charge e ffects were evident as a function of varying the pH during membrane filtrat ion of both inorganic salts and aminoacids. Both flux and rejection were hi gher for the helical module than the linear module during amino acid nanofi ltration. A new modified phenomenological model was shown to be effective for predict ive purposes for cases of responsive concentration polarization. Its applic ability is validated by performing nanofiltration of aqueous MgSO4 solution s with a new set of modules designated as Set In. Modules of Set III contai ned dissimilar helical and linear elements. The model was then tested again st the results obtained previously. (C) 1999 Elsevier Science B.V. All righ ts reserved.