Grafting and catalytic activity The dependence of grafting and catalytic activity on the pore size of nylon membranes grafted with different DGDA concentrations and loaded with ]~-galactosidase is discussed. Membrane pore sizes were 0.2 t.tm, 1.2 I-tm and 3.0 pm. Grafting and enzyme activity, all other experimental conditions being the same, decrease with the increase of membrane pore size. The membranes have been characterised also with reference to pH and temperature. The experimental conditions giving the best performance for each of the three membranes have been identified. In all cases the membranes giving the best results are those having 0.2 }.tin pore size. The advantages of using in non-isothermal bioreactors a single membrane, which is both catalytic and hydrophobic at the same time, are also indicated. M.S. Mohy Eldin, A. De Maio, S. Di Martino, U. Bencivenga, S. Rossi, A. D'uva, ES. Gaeta, D.G. Mita: Advances in Polymer Technology 18(2) (Summer 1999).
Mass transfer coefficient and variations The modified Sherwood number relationship, including the effects of property variations and suction by the membrane for laminar flow, in a rectangular channel, are presented in this work. The modified relationship is used to predict the permeate flux of ultrafiltration data of bovine serum albumin and dextran, taken from the literature. The exponent n of the correction factor (Sc/SCm)nWas found to be 0.01 for bovine serum albumin, for all feed concentrations. For dextran, n was found to vary with feed concentration (0.013 for 5%, and 0.026 for 10% solutions). The analysis is also valid for the imperfect membranes. Results are also presented for the simultaneous prediction of permeate flux and permeate quality in terms of the observed retention. Finally, a parametric study of flux and observed retention is carried out to
infer the influences of various operating and membrane performance parameters. S. De, P.K. Bhattacharya:
Separation & Purification Technology 16(1) 61-73 (10 June 1999).
Simulation of unstirred batch UF process A mass transfer model based on a concentration boundary layer, as suggested by film theory, is proposed in this study. The mass transfer coefficient for the case of an unstirred batch cell was predicted using an extrapolation technique based on a suitable curve-fitted equation. The parabolic partial differential equation resulting from the unsteady state mass balance over the concentration boundary layer was solved by a numerical technique using a second order implicit method. The solution process also couples the osmotic pressure model for the prediction of flux and an equation from irreversible thermodynamics for the prediction of real rejection. All equations were solved simultaneously by the multidimensional Newton-Raphson technique, using Broyden's correction factor to enhance the rate of convergence. The final predicted flux and rejection was found to be in good agreement with the experimental data, and the absolute average deviation in both cases was found to be well within 10%. S. Ghose, A. Poddar, S. Datta, C. Bhattacharjee: Separation & Purification Technology 16(1) 75-81 (10 June 1999).
Oil removal using PVDF membranes A microporous hydrophobic membrane allows the permeation of an oil phase at almost zero pressure and retains the water. The separation of dilute oil-in-water mixtures using flat sheet hydrophobic PVDF membranes has been investigated using an unstirred laboratory-scale, semi-batch experimental system, operated at 40°C. The flat-sheet membranes
were prepared in the laboratory by an immersion precipitation method and were characterised in terms of a mean pore radius, porosity and breakthrough pressure. The oil-in-water mixture contains 1% kerosene in distilled water. The experimental work essentially entails the study of the effects of various system parameters on the oil/water separation characteristics. In particular, the effects of feed flowrate, the operating pressure and pore size and porosity of the membrane were studied. The experimental results can be predicted reasonably well using the Hagen-Poiseuille equation at a high vertical velocity, and the percentage of oil removed can be as high as 77% under normal experimental conditions. J. Kong, K. Li: Separation & Purification Technology 16(1) 83-93 (10 June 1999).
Acrylic threedimensional networks The retention process of the Cu(II) and Ni(II) cations from CuSO 4 and NiSO 4 aqueous solutions by eight acrylic ion exchangers was studied. Mso, the elution process of these cations with 0.5 mol/l HCI solution was analysed. The quantitative retention and elution, as well as the development aspects of the two processes were observed using the column method. Seven ion exchangers contained weak base, weak acid, and amphoteric functional groups, these being known as chelating agents. Also, an ion exchanger with carboxylic groups, as a model, was taken in this study. The experiments show that the ion exchangers can be divided into three types. These are: bad chelating agents; chelating ion exchangers with the limited efficiency; and ion exchangers with good chelating properties and a high application efficiency. It is considered that the ion exchanger with hydroxamic functional groups falls into the latter class. Also, the experimental data prove that for both Cu(II) and Ni(II) cations, the volume of the purified effluent is higher than the HCI volume needs for their complete elution. S. Maxim, A. Flondor, I. Bunea, C. Luca, I. Rabia, J. Zerouk, E Iayadene, H. Guettaf: Journal of
Applied Polymer Science 72(11) 1387-1394 (13 June 1999).
Shear filtration A novel rotary microfiltration technique, specifically designed for the separation of animal cells has been developed. The concept allows the independent adjustment of wall shear stress, transmembrane pressure, and residence time, allowing straightforward optimisation of the microfiltration process. By using a smooth, conical rotor, it is possible to establish a controlled shear field in which animal cells experience a significant hydrodynamic lift away from the membrane surface. It is shown in preliminary experiments that sllearinduced cell-rupture speeds up membrane clogging. However, a threshold value of shear stability exists, which depends on the frequency of passing the shear field, the residence time in the shear field, as well as on cell status. J.H. Vogel, K.-H. Kroner: Biotechnology & Bioengineering 63(6) 663-674 (20 June 1999).
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