ABSTRACT
The regeneration of volatile organic solvents via dehydration tests, from 90 wt %, was evaluated by pervaporation using an on-line near-infrared (NIR) spectrometer. Experiments were performed using a bis(triethoxysilyl)methane (BTESM)-based ceramic HybSi® membrane at temperatures of 20, 30 and 40 °C. The presence of an on-line NIR allows continuous monitoring of the process without sampling, and quickly estimates mass fractions of species in the retentate. Dehydration tests were performed at 30 °C in order to confirm the on-line NIR reproducibility, and closely matched results obtained with an off-line densimeter. These results validated the usefulness of the on-line NIR and provided the same precision whatever the mass fraction in the retentate. A good on-line reproducibility was found, with an agreement between the on-line NIR and off-line densimeter, obtaining an average deviation of ±0.058 wt %, ±0.17 wt % and ±0.049 wt %, respectively, at 20, 30 and 40 °C.
ABSTRACT
Due to their numerous biological properties, natural sulfated polysaccharides have attracted the interest of the food and pharmaceutical industries. Membrane processes were thought to be especially suitable for their production at industrial scale. The aim of this study was to evaluate the effect of sodium chloride, often used as a preservative and a precipitation adjuvant, on the ultrafiltration of sulfated pentasaccharides. In pure water, results showed a complete retention of the polymers on membranes with molecular weight cut-off up to eight times the molecular weight of the studied pentasaccharides. When NaCl was added to a concentration of 0.5 mol L(-1), retention rates decreased significantly (≈-50%). As no relevant modification of the molecules size was observed through hydrodynamic radius measurements, these variations of selectivity were fully attributed to the screening of membrane surface charges by the electrolyte. Therefore, optimising the ultrafiltration of charged molecules need absolutely exammining electrostatic interactions.
