- The Filtration Society - http://www.filtsoc.org -

Volume 9, Issue 2

ELECTROPOSITIVE FILTRATION TECHNOLOGY IN AUTOMOBILE MANUFACTURING APPLICATIONS
F. Tepper, H. Frank and R. Lancaster (pages 108-111)

Argonide Corporation began as an organization focused on the production and sale of nanopowders. By definition, nanopowders are extremely small particles (less than 0.1 micron) of materials such as nickel, copper, iron, alumina, gold, etc. These materials are in demand by research and development groups within both the public and private sectors. To date, the company is still involved in this active, although limited arena. It became clear that the future success of Argonide was not in nanomaterials themselves, but in full-scale commercialization of a product based on nanotechnology. Through several years of extensive R&D, discussions with the U.S.E.P.A. (US Environmental Protection Agency), and the use of several grants from NASA, we created a nonwoven filter media.

FILTRATION TECHNOLOGY – ITS IMPACT UPON OUR LIVES AND THE ENVIRONMENT
D. Dubbin (pages 112-117)

In these times when global warming poses such a challenge for this and future generations it is perhaps worth reflecting how advances in filtration technology have impacted upon our lives and the environment in a positive way. Not for the sake of complacency, but to illustrate how we as engineers and scientists have made a real difference over the recent past and how we must re-double our efforts in the future. In this short paper the author has considered some examples of gas and liquid technology which impact upon our lives.

CLOSED LOOP CONTROLLER IN A DWELL TIME-BASED GAS FILTRATION SYSTEM
M. Marcelo, A. Malino, J. Mercurio, M. Retirado and B. Sicat (pages 117-119)

This paper reports the development of a dwell time-based closed loop controller for a gasoline exhaust filtration system. The ppm content of the gas entering a chamber is measured. Gases that fall below a set threshold are passed on to the succeeding stage without processing, while those that are above the threshold are circulated by the system to an activated filtering loop until such a time that the concentration has fallen below the threshold. The resulting dwell time in order to attain an acceptable ppm is found to be a function of the initial ppm level.

FROM WARFARE TO HEALTHCARE
J. Taylor (pages 120-122)

Activated carbon cloth was invented by the UK Ministry of Defence for protection against chemical, biological and nuclear threats. However, today the world’s largest applications are in the medical field although that is about to change. This paper is intended to give a brief introduction to the development of activated carbon cloth (ACC), its manufacture and applications including non-particulate filtration of gases and liquids. All references to activated carbon cloth are based on ZORFLEX® ACC (ZORFLEX® is a registered trademark of Chemviron Carbon Limited).

ADSORPTIVE FILTER MEDIA (AFM)
H. Patzelt (pages 123-128)

Effective control of gaseous pollution requires filtration media developed specifically to capture the smallest concentrations of a range of ‘target’ molecules. The ability to combine particle filtration materials will result in extended filter lifetime in environments containing both particulate and gaseous pollutants. The layering together of various filtration products, often termed ‘Combination Filter Media’ (Combi), allows the filter manufacturer to customise their products for greater pollution adsorption capacity in challenging environments.

INORGANIC MEMBRANES FABRICATED BY AIR PLASMA SPRAY COATING
K.-L. Tung (pages 128-132)

Environmental protection awareness and higher energy costs in recent decades have made membrane technology more economically competitive with conventional separation processes such as absorption, adsorption, distillation, or solvent extraction. While the market of the global membrane industry varies from one estimate to another, it is reported that the total sales of membrane modules, excluding the pumps, valves, instruments, or fluid pipe work external to the housing of the module, were estimated to have been just over $8 billion in 2003 and were expected to exceed $24 billion in 20081. The market forecasts include both organic polymeric membrane and inorganic ceramic or metal membranes.

CHANGES IN SLURRY CONCENTRATION DURING THE INITIAL STAGES OF FILTRATION
A. Genç and I. Tosun (pages 133-138)

The variation in slurry concentration within the filter chamber during the startup of constant pressure filtration experiments and its effect on the cake length and filtrate volume are studied. Theoretical equations relating slurry concentration to cake length and filtrate volume are developed by using the equations of continuity together with the jump conditions at the cake-slurry interface. Comparison with experimental values indicates that the change in slurry concentration within the filter chamber, especially during the initial stages of filtration, should be taken into consideration in the evaluation of model parameters from experimental data.

NANOFILTRATION: A METHOD FOR IMPROVING THE PURITY OF FUELS AND NON-AQUEOUS SOLVENTS
E.S. Tarleton and J.S. Low (pages 138-141)

This paper describes some of the principal features of solvent resistant nanofiltration and its potential in fuel processing. Experimental data for both fuel simulants and a petrol fuel are presented. The solute rejection mechanism for low polarity mixtures was size exclusion with a membrane cut-off in the region of 1-2 nm. The extent of solute rejection was dependent on the degree of membrane crosslinking, the membrane swelling induced by the feed and the filtration pressure. Nanofiltration experiments with the petrol fuel showed a good correlation with the data obtained for the fuel simulants, both in terms of permeate flux and solute rejection. Provided that higher polarity oxygenates were not present in the fuel, it was possible to remove undesirable poly-nuclear aromatic and organometallic solutes to an extent that was sufficient to significantly reduce valve deposits and emissions gases in engine tests.

INVESTIGATIONS ON THE MINIATURISATION OF PRESSURE FILTRATION PROCESSES
S. Jermann, A. Schreiner and R. Schneeberger (pages 142-147)

As a basic operation of mechanical process engineering, pressure filtration and its scale-up has been described in detail in the literature. However, the pharmaceutical development of active substances in particular calls for scale-up from relatively small quantities and is therefore dependent on conclusions from smaller filter equipment. In this study, results from laboratory Nutsche filters with filter surface areas of 1.4 cm2 and 9.6 cm2 were compared with results from a 20 cm2 Nutsche. It is shown that no reproducible and reliable data could be generated using the 1.4 cm2 Nutsche. While this was possible using the 9.6 cm2 Nutsche, the permeability was greater than with the recommended 20 cm2 Nutsche, so that a correction factor has to be introduced.

RECONSTRUCTION ALGORITHMS FOR THE INTERNAL PACKING DENSITY DISTRIBUTION OF FIBROUS FILTER MEDIA BASED ON TOMOGRAPHIC DATA
(pages 147-154)

Algorithms were developed to approximate the 3-dimensional internal packing density distributions of fibrous filter media at different levels of detail and complexity. Each algorithm uses certain input information derived from X-ray tomographic data of filter samples.

Algorithm 1 creates a binary media structure consisting of the true (i.e. tomographically determined) void distribution plus regions of uniform packing density. The average packing density of the media is maintained constant. Algorithm 2 creates a model fibrous structure of straight fibres of equal diameter and random length positioned randomly in space, while maintaining the true (i.e. tomographically determined) fibre orientation distribution. The number and length of the fibres on average adds up to the packing density of the filter. The model fibrous structure is recreated by a stationary Poisson process of convex bodies. Algorithm 3 distributes pores of random size and location within a homogeneous matrix, such that the average packing density again coincides with the true (i.e. tomographically determined) packing density. This algorithm is also based on a stationary Poisson process of convex bodies.

The capability of each algorithm to recreate the essential structural features of the media was tested against ‘reality’ by computing the respective overall pressure drop of the filter as well as the velocity distribution in the filter interior, and comparing with the results obtained for the ‘true’ packing density distribution of a sample measured by tomography. Compared to the assumption of a completely homogenous filter (which gives roughly 2 times the actual ∆p), all algorithms are closer to reality. The binary algorithm deviates in ∆p by a factor of 1.8; algorithm 3 comes within a factor of 1.6 of the true ∆p. The best approximation is by algorithm 2 which narrows the difference in ∆p to a factor of 1.4

YEAST MICROFILTRATION USING A MODIFIED SURFACE FILTER
M. Stillwell, R.G. Holdich and S. Kosvintsev (pages 155-160)

A microfilter is generally accepted as a filter capable of removing suspended material with diameter of between 0.1 and 10 μm from fluids. All filtration systems have to balance the requirement to present a high efficiency for particle removal with the intention of presenting a minimum resistance to fluid flow. These contradictory requirements have led to research on filter pore structure and shape as well as techniques for employing the filter to minimise particle deposition on top of, and within, the filter matrix. One successful filter design uses slotted pores, which pass through a lamina filter sheet, and present a non-tortuous flow channel for the pore. However, this type of filter is only feasible for pore sizes towards the top end of the microfiltration range, at least when constructed from robust engineering materials. For the filtration of fine particulates, using a microfilter, a tortuous pore channel filter is more applicable.

This paper presents the results of a series of tests using carefully sized glass beads that have been sintered under a variety of processing conditions to provide a series of microfilters. Parameters such as particle size distribution, bed depth, sintering temperature and time as well as bed support have been investigated, considering their effect on the filtration performance of sub-10 μm yeast cells suspended in water. Models for the resulting voidage of the sintered porous media and hence permeability are presented. Surface post-treatment of the glass beads by chemical means has also been investigated: investigating the influence of chemical surface properties on yeast adhesion