Shear controlled model of the ultrafiltration of soy suspensions

摘要

The ultrafiltration of the aqueous extract of full-fat soy flour was investigated as a complex suspension of proteins, lipids and carbohydrates where the foulant layer is the major resistance. Ultrafiltration was performed on both homogenised and unhomogenised soy extracts using a flat plate module and two polysulphone membranes. The permeate flux profiles for constant recirculation flow exhibited a combination of falling-flux and constant-flux regions. The mass transfer model was not applicable to these profiles. Both regions were modeled by the shear controlled model J = J_iτ_r~nae~(-bC). The model was also effective in correlating the flux where the retentate flow was reduced for increasing concentration at constant pressure drop over the module. Wall shear stress had a larger effect on the permeate flux for the homogenised extract (n = 0.7) than for the unhomogenised extract (n = 0.5). The wall shear stress was shown to have minimal effect on displacing the foulant layer. The major effect of the wall shear stress was to sweep away the gel layer preventing it from binding to the foulant layer.