MEMBRANE CHARACTERISATION

From an applications view point, it should be noted that the membranes are negative over most of the relevant pH range. Similar results were obtained by Kim et al. (1994), who measured the zeta potential through the pores rather than along the surface. However, the isoelectric points determined by those authors were 3.7 and 4.4 to 5.3 for the GVWP and GVHP membranes, respectively. 

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W.R. Bowen, N. Hilal, R.W. Lovitt and C.J. Wright, A new technique for membrane characterisation direct measurement of the force of adhesion of a single particle using an atomic force microscope, J. Membrane Sci. 139 (1998) 269-274. 

Dinis da Costa JC, Lu GQ, Rudolph V, and Lin YS. Novel molecular sieve silica (MSS) membranes characterisation and permeation of single-step and two-step sol-gel membranes. J. Membr. Sci. 2002 198 9-21. 

V.T. Zaspalis and A.J. Burggraaf, Inorganic membrane reactors to enhance the productivity of chemical processes, in R.R. Bhave (Ed.), Inorganic Membranes Characterisation and Applications, von Nostrand Reinhold, New York, 1991, pp. 177-208. 

Fig. 4.1. Methodology for membrane characterisation. Listing methods and related parameters.

The application of ion beam analysis techniques to determine pore size and pore volume or density of thin silica gel layers was first described by Armitage and co-workers [114]. These techniques are non-destructive, sensitive and ideally suited for the analysis of thin porous films such as membrane layers (dense support is needed for backscattering). However, apart from a more recent report on ion-beam analysis of sol-gel films [115] using Rutherford backscattering and forward recoil spectrometry, ion beam techniques have not been developed further despite their potential for membrane characterisation. This is probably due to the limited availability of ion beam sources, such as charged particles accelerators. 

This method, using a microfocused beam, has unique advantages over other techniques which could be very useful in membrane characterisation. Thus in the above work examples of measurements made on gel layers as a function of sampling depth (from 3 pm to 100 pm) and as a function of distance across the sample were illustrated. It will also be noted that the technique is equally appropriate for measurements in the micro and mesoporous ranges. 

Rejection measurements with reference molecules like dextrans, proteins or polyglycols are often used by membrane manufacturers. A parameter extensively used for membranes characterisation is the "cut-off" value, which is... 

A variety of other static characterisation methods have been described in this chapter which are not listed in Table 4.2. Many of these are new and in a state of rapid evolution, as for example those involving NMR and radiation scattering. Whilst appropriate for research investigations they do not seem yet to be appropriate as a means of general characterisation. However with the rapid progress under way in these areas, some of these techniques we feel may in the future be ideally suited to membrane characterisation. 

The potential of the WGS membrane reactor in CO2 control in IGCC installations has been studied in greater detail [57]. The possibilities of the reactor and demands set for the membranes have been determined by carefully assessing the process integration options, by experimental membrane characterisation and by using a membrane reactor model. 

T. Buttler, C. Nilsson, L. Gorton, G. Marko-Varga, T. Laurell, Membrane characterisation and performance of microdialysis probes intended for use as bioprocess sampling units, J. Chromatogr. A 725 (1996) 41. 

Capannelli, G., Becchi, I., Bottino, A., Moretti, P., and Munari, S., Computer driven porosimeter for ultrafiltration membranes Characterisation of Porous Solids, Elsevier, Amsterdam, 1988. p. 283. 

The pure water fluxes are very different at the low MWCOs (PLAC, PLBC and PLCQ fluxes and permeabilities are lower than those of NF membranes (see Chapter 7). The higher MWCO membranes are well below the MF pure water fluxes (see Chapter 5), but certainly in the area of MF fluxes in full-scale systems. This demonstrates the continuity in membrane characterisation. 

The use of membranes in cartridge microfihration has be discussed already in Chapter 6, Section 6.6. That section also contained a number of test procedures enq)loyed for membrane characterisation which will not be repeated here. This chapter provides details of membrane configuration other than cartridges, mathematical models to assist in the understanding and control of the processes. Industrial applications or investigations of microfiltration and to a lesser extent ultrafiltration are also discussed. 

Differences in membranes and membrane strucmres will be explained in greater detail in chapters II, m, IV, V and VI, respectively where materials, membrane formation, membrane characterisation, membrane transpon and membrane processes are described. 

Before describing the membrane characterisation methods available and the purpose for which they can be employed, it is important to realise the wide range of pore sizes which must be covered (sec table I -. I). In general, it may be stated that membrane characterisation becomes progressively more difficult as the pore size decreases. Various pore sizes have their own methods of characterisation methods. Again, the membranes will be classified in two main groups, which have been depicted schematically in figure IV-1. 

Electron microscopy (EM) is one of the techniques that can be used for membrane characterisation. Two basic techniques can be distinguished scanning electron microscopy (SEM) and transmission electron microscopy (TEM). 

The same type of developments is in current for ultra and microfiltration applications membrane characterisation device coupled with data-base and numerical code. 

MasseUn, I, Durand-Bourlier, L., Laine, J.-M., Sizaret, P. Y., Chasseray, X., and Lemordant, D. (2001). Membrane characterisation using microscopic image analysis. J. Membr. Sci. 186, 85. 

Zhang, W. and HaUstrom, B. (1990). Membrane characterisation using the contact angle technique, I. Methodology of the captive bubble technique. Desalination 79, 1. 

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