The effect of anti-foam agents on the ultrafiltration of a protease solution

Polydimethylsiloxane and polypropylene glycol-based anti-foam agents adversely influence the ultrafiltration rate of a protease solution with polysulfon membranes. Four propietary agents have been compared, of which Rhodosil 426 R (ex Rhone Poulenc, France), an emulsion of polydimethylsiloxane, proved to have the least influence. With this agent, the relative filtration flux of a protease solution decreased by a factor of two for concentrations of anti-foam agent higher than 0.25 cm³/dm³. A simple, quasisteady-state model developed on the basis of data obtained from total recycle experiments with this anti-foam agent, well predicted the temporal variation of protease concentration during batch ultrafiltration experiments with and without Rhodosil 426 R.List of Symbols A _uf m² total membrane area - C _af dm³/m³ concentration of anti-foam agent - C _af,0 dm³/m³ initial concentration of anti-foam agent in the feed solution - C _e kg/m³ protease powder concentration - C _e,0 kg/m³ initial protease powder concentration in the feed solution - J m³/s ultrafiltration rate - J _w m³/m²s water flow for a clean membrane under processing conditions - R _af rejection coefficient for anti-foam agent - R _e rejection coefficient for protein - RF % relative filtration rate - t s filtration time - V m³ concentrate volume - V ₀ m³ volume to be concentrated - V _t m³ end volume