Model development for estimating microfiltration performance of bio-ethanol fermentation broth

Abstract

A membrane process is used for bio-ethanol purification from fermentation broths. Yeast cells are separated from a suspension containing yeast, glucose and ethanol using cross-flow microfiltration. Yeast cells are retained by the filter membrane with a mean pore size of 0.45μm and recycled back into the broth, while most of the glucose and ethanol penetrate through the membrane into the filtrate. The operating condition effects, such as cross-flow velocity and transmembrane pressure, on the filtration flux, cake properties and solute rejections are measured and analyzed. The filtration flux increases over 2-fold as the cross-flow velocity increases from 0.1 to 0.5m/s and increases 50% as the transmembrane pressure is increased from 20 to 100kPa at a fixed cross-flow velocity of 0.5m/s. The experimental data show that the filter cake plays the major role in determining the filtration resistance. The yeast cake exhibits a specific filtration resistance as high as 1014m/kg and a compressibility of 0.55. The glucose and ethanol rejections are both lower than 8% and increase slightly with increasing cross-flow velocity or transmembrane pressure. The cake formation and solute rejections are analyzed theoretically using a force balance model for particle deposition and the standard capture equation for depth filtration. Semi-empirical equations are derived and used for predicting the filtration flux, cake thickness and solute rejection directly from the operating conditions. The calculated results using the proposed models agree fairly well with the experimental data.