Mass transfer in the membrane phase contactor with an enzyme gel layer immobilized on a membrane

In the membrane phase contactor, the rate of reagent mass transfer from organic phase (a reservoir) to water phase (a reaction phase) depends on the three different resistances: the organic phase resistance, the resistance generated by the membrane and the water phase resistance. In the case when the enzyme is immobilized on the membrane surface and forms a gel layer, an additional mass transfer resistance is generated that could have an important influence on total mass transfer rate. Its value is directly proportional to the layer thickness and assumes particularly high values in the system where the distribution coefficient is much higher than unity. Since the gel layer thickness affects simultaneously the process yield, the decision concerning the amount of protein immobilized on the surface should be considered in detail.

After identification of the particular resistances, it seems that the mass transfer in continuous phases could be only slightly improved with the increase of phase flow rates. The part of particular resistance in total mass transfer depends on the system properties (by means of partition coefficient) and the thickness of membrane and enzyme gel layer. The percentage of particular mass transfer resistance for two selected cases differing in the membrane character used, at Qw= 6.0×10–7 m3 s–1, Qo= 6.0×10–7 m3 s–1, dm= 1.0×10–4 m, s = 5.0× 10–7 m) was determined. It was shown (Fig. 6) that the resistance generated by the organic phase and the hydrophobic membrane filled with an organic phase had the least important influence on the total mass transfer rate. The resistance of the gel layer could be predominant. Its percentage in the considered case is equal to ca. 30–40% of the total resistance. The percentage could much increase at a higher amount of protein accumulated on the surface. It is also worth noting that in many hydrophilic membrane 27% (a) hexane 4% protein gel 36% (b) hydrophobic membrane 9% water 40% isooctane 15% Fig. 6. Influence of particular mass transfer resistance on the total resistance in mass transfer of glycidyl butyrate in hexane–PA–water: (a) and isooctane–PP–water; (b) system (Qw = 6.0×10–7 m3 s–1, Qo = 6.0×10–7 m3 s–1, dm = 1.0×10–4 m, s = 5.0×10–7 m).