Adsorptive microfiltration membranes

Still other types of chemically functional membranes—particularly adsorptive microfiltration membranes containing affinity ligands or other complexants bound to interior pore wall surfaces—are capable of... 

Membrane absorbers are continuous chromatographic supports, which circumvent some of the above-mentioned problems of particulate stationary phases. They were originally derived from membrane (filtration) technology. The immobilization of interactive (ionic, hydrophobic, or biospecific) groups on the surface of microfiltration membranes was found to increase the selectivity of certain separation procedure. Ideally such activated membranes, or membrane adsorbers, allow the selective adsorption of certain substances and substance classes, which may subsequently be eluted by means of a stepwise change of the mobile phase (elution buffer). More complete information on the various types of modern membrane technology can be found in some recent reviews [e.g., 31-33]. 

The second category of microporous membranes is the depth filter (b), which captures the particles to be removed in the interior of the membrane. The average pore diameter of a depth filter is often 10 times the diameter of the smallest particle able to permeate the membrane. Some particles are captured at small constrictions within the membrane, others by adsorption as they permeate the membrane by a tortuous path. Depth filters are usually isotropic, with a similar pore structure throughout the membrane. Most microfiltration membranes are depth filters. 

In filtration of gas-borne aerosol particles by microfiltration membranes, capture by adsorption is usually far more important than capture by sieving. This leads to the paradoxical result that the most penetrating particle may not be the smallest one. This is because capture by inertial interception is most efficient for larger particles, whereas capture by Brownian motion is most efficient for smaller particles. As a result the most penetrating particle has an intermediate diameter, as shown in Figure 2.35 [55,56],... 

The mechanisms of microfiltration membrane fouling were investigated in wine and model solutions (Vernhet and Moutounet 2002). The sharp decline observed in microfiltration fluxes within the first minutes of the process could not be attributed to adsorption alone. They can be explained by a two step mechanisms involving first interaction of the wine constituents with the membrane, quickly followed by their aggregation at the pore entrance (Vernhet and Moutounet 2002). 

Vernhet, A., Bellon-Fontaine, M. N., Brillouet, J.-M., Roesink, E., Moutounet, M. (1997). Wetting properties of microfiltration membrane determination by means of the capillary rise technique and incidence on the adsorption of wine polysaccharide and tannins. /. Membrane Sci. 128, 163-174. 

Dextran is mainly used as a coating material on available microfiltration membranes. Breifs and Kula [36] reported the use of dextran-coated nylon membranes as affinity media. The ligand was first coupled with dextran (both by adsorption and... 

Kim M, Kojima J, Saito K, and Furusaki S. Reduction of nonselective adsorption of proteins by hydrophilization of microfiltration membranes by radiation-induced grafting. Biotechnol. Prog. 1994 10 114—120. 

Brose, D.J. Henricksen, G. A quantitative analysis of preservative adsorption on microfiltration membranes. Pharm. Tech Europe 1994, 42-49. 

M. Kim, K. Saito, S. Furusaki and T. Sugo, Comparison of BSA Adsorption and Fe Sorption to the Diol Group and Tannin Immobilized onto a Microfiltration Membrane, J. Membrane Sci., 85 (1993) 21. 

Two microfiltration membranes (Millipore, hydrophilic (GVWP) and hydrophobic (GVHP)) with nominal pore sizes of 0.22 (tm were used. The hydrophilic membrane is a modified hydrophobic membrane. The hydrophilic membrane was chosen for most experiments because hydrophilic membranes have a reduced adsorption capacity towards hydrophobic organics Qucker and Clark(1994)). The membrane material is a modified polyvinylidene fluoride (PVDF). 

Tremendous opportunity exists for hybrid processes consisting solely of membrane processes or a combination of membrane and non-membrane processes. Of the large number of potential combinations, studies of several are reported in the literature including nanofiltration with reverse osmosis [99] nanofiltration with electrodialysis [100] ultrafiltration with nanofiltration and reverse osmosis [101] ultrafiltration with membrane distillation [102] nanofiltration with reverse osmosis and a microfiltration membrane-based sorbent [103] microfiltration with flotation [104] microfiltration and ultrafiltration with ozone and activated carbon adsorption [105] and membrane processes with photocatalysis [106-107]. Despite the activity in this area, a comprehensive approach to designing hybrid systems does not exist future work would benefit from the development of such a design framework. 

There are a number of other techniques besides cut-off measurements for characterising ultrafiltration membranes. However, typical methods for microfiltration membranes, such as mercury intrusion or scanning electron microscopy cannot be used for the characterisation of ultrafiltration membranes. For this reason, other techniques have been developed such as thermoporometiy, liquid displacement and permporoinetry as have been discussed in chapter IV. Other more general techniques which are applicable are gas adsorption-desorption, permeability measurements and modified cut-off measurements. v, ... 

If the size of the obtained polymer-heavy metal binding is suitable, the microfiltration membranes can be applied. For example, As(V) ions have been removed by adsorption onto chitosan in a continuous stirred tank reactor (CSTR) coupled with a microfiltration immersed-membrane unit using 350 hollow organic fibers, with a cutoff of 0.2 xm and a surface area of 0.2 m (Gerente et al,... 

The technology is a combination of biodegradation, adsorption onto activated carbon, and microfiltration. It uses microbes grown on active powdered carbon as a prefilter and to degrade organics and a cross-flow membrane filter to remove biomass, viruses, and suspended impurities. 

Microfiltration. Various membrane filters have been used to remove viral agents from fluids. In some cases, membranes which have pores larger than the viral particle can be used if the filtration is conducted under conditions which allow for the adsorption of the viral particle to the membrane matrix. These are typically single-pass systems having pore sizes of 0.10—0.22 m. Under situations which allow optimum adsorption, between 10—102 particles of poliovirus (28—30 nm) were removed (34—36). The formation of a cake layer enhanced removal (35). The titer reduction when using 0.10—0.22 Jim membrane filters declined under conditions which minimized adsorption. By removal standards, these filters remove viruses at a rate on the low end of the desired titer reduction and the removal efficiency varies with differences in fluid chemistry and surface chemistry of viral agents (26). 

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