Microfiltration membrane manufacturers

The bubble point test is simple, quick and reliable and is by far the most widely used method of characterizing microfiltration membranes. The membrane is first wetted with a suitable liquid, usually water for hydrophilic membranes and methanol for hydrophobic membranes. The membrane is then placed in a holder with a layer of liquid on the top surface. Air is fed to the bottom of the membrane, and the pressure is slowly increased until the first continuous string of air bubbles at the membrane surface is observed. This pressure is called the bubble point pressure and is a characteristic measure of the diameter of the largest pore in the membrane. Obtaining reliable and consistent results with the bubble point test requires care. It is essential, for example, that the membrane be completely wetted with the test liquid this may be difficult to determine. Because this test is so widely used by microfiltration membrane manufacturers, a great deal of work has been devoted to developing a reliable test procedure to address this and other issues. The use of this test is reviewed in Meltzer s book [3],... 

The physical characterisation of membrane structure is important if the correct membrane is to be selected for a given application. The pore structure of microfiltration membranes is relatively easy to characterise, SEM and AFM being the most convenient method and allowing three-dimensional structure of the membrane to be determined. Other techniques such as the bubble point, mercury intrusion or permeability methods use measurements of the permeability of membranes to fluids. Both the maximum pore size and the pore size distribution may be determined.1315 A parameter often quoted in manufacturer s literature is the nominal... 

S-layer ultrafiltration membranes (SUMs) are isoporous structures with very sharp molecular exclusion limits (see Section III.B). SUMs were manufactured by depositing S-layer-carrying cell wall fragments of B. sphaericus CCM 2120 on commercial microfiltration membranes with a pore size up to 1 pm in a pressure-dependent process [73]. Mechanical and chemical resistance of these composite structures could be improved by introducing inter- and intramolecular covalent linkages between the individual S-layer subunits. The uni-... 

Recently, some membrane manufacturers have attempted to produce anisotropic microfiltration membranes in which the open microporous support is a built-in prefilter. Unlike most other applications of anisotropic membranes, these membranes are oriented with the coarse, relatively open pores facing the feed solution, and the most finely microporous layer is at the bottom of the membrane. The goal is to increase filter life by distributing the particle load more evenly across the filter than would be the case with an isotropic porous membrane. 

Metal oxides, used for manufacturing of ceramic nanofiltration membranes, are intrinsically hydrophilic. This limits the use of these membranes to polar solvents filtration of nonpolar solvents (n-hexane, toluene, cyclohexane) usually yields zero fluxes. Attempts have been made to modify the pore structure by adding hydrophobic groups, for example, in a silane coupling reaction [38, 43]. This approach is similar to modifications of ultrafiltration and microfiltration membranes... 

Microfiltration membranes usually have a nominal pore diameter in the range of 0.1-10 pm. However, the membrane specification is not an absolute parameter. The membranes usually present a pore size distribution around the nominal value and the shape of the bioparticles can determine whether they are retained or pass through the membrane. The membranes are manufactured from polymers, such as Teflon, polyester, PVC (polyvinyl chloride), Nylon, polypropylene, polyethersulfone, and cellulose, or from inorganic materials, such as ceramic and sinterized stainless steel. 

Addition of a Nonsolvent to a Homogeneous Polymer Solution. This technique is widely used today for the preparation of symmetric microfiltration membranes as well as for manufacturing asymmetric "skin-type" ultrafiltration or reverse osmosis membranes (7). The preparation procedure can again be rationalized with the aid of a three-component isothermic phase diagram shown schematically in Figure 3. 

APPENDIX LIST OF MEMBRANE MANUFACTURERS (MICROFILTRATION AND ULTRAFILTRATION)... 

This chapter focuses on the chemical processing of ceramic membranes, which has to date constituted the major part of inorganic membrane development. Before going further into the ceramic aspect, it is important to understand the requirements for ceramic membrane materials in terms of porous structure, chemical composition, and shape. In separation technologies based on permselective membranes, the difference in filtered species ranges from micrometer-sized particles to nanometer-sized species, such as molecular solutes or gas molecules. One can see that the connected porosity of the membrane must be adapted to the class of products to be separated. For this reason, ceramic membrane manufacture is concerned with macropores above 0.1 pm in diameter for microfiltration, mesopores ranging from 0.1 pm to 2 nm for ultrafiltration, and nanopores less than 2 nm in diameter for nanofiltration, per-vaporation, or gas separation. Dense membranes are also of interest for gas... 

This chapter will focus on three types of membrane extracorporeal devices, hemodialyzers, plasma filters for fractionating blood components, and artificial liver systems. These applications share the same physical principles of mass transfer by diffusion and convection across a microfiltration or ultrafiltration membrane (Figure 18.1). A considerable amount of research and development has been undertaken by membrane and modules manufacturers for producing more biocompatible and permeable membranes, while improving modules performance by optimizing their internal fluid mechanics and their geometry. 

Commercial as well as potential uses of inoiganic membranes multiply rapidly in recent years as a result of the continuous improvement and optimization of the manufacturing technologies and applications development for these membranes. Most of the industrially practiced or demonstrated applications fall in the domains of microfiltration or ultrafiltration. Microfiltration is applied mostly to cases where the liquid streams contain high levels of particulates while ultrafiltration usually does not involve particulates. While their principal separation mechanism is size exclusion, other secondary mechanisms reflecting the solution-membrane interactions such as adsorption are often operative. Still under extensive research and development is gas separation which will be treated in Chapter 7. 

Separation of manufactured sohds from process liquids and recycling of these liquids (water or organic solvents) is an interesting way to valorize by-products and to minimize the production of liquid effluents in a number of industries. Microfiltration ceramic membranes have been aheady used for the recovery of particles in the ceramic industry and in drilling operations, of pigments in paint and ink industries, and have potential applications in a wide variety of liquid-solid separation... 

The literature describes numerous manufacturing methods for synthetic membranes. A recent review by Pusch and Walch (1) considers membranes from a number of techniques for manufacturing membranes and discusses applications ranging from microfiltration to desalination to gas separation. In this paper, a thermal phase-separation technique of preparing membranes Is presented. The method Is a development of an Invention described In US Patent 4,247,498 by Anthony J. Castro (,2). This technique Is similar In many respects to the classical phase-inversion methods however, the additional consideration of thermal solubility characteristics of the poly-mer/solvent pair offers new possibilities to membrane production. 

Polymeric membranes are prepared from a variety of materials using several different production techniques. Table 5 summarizes a partial list of the various polymer materials used in the manufacture of cross-flow filters for both MF and UF applications. For microfiltration applications, typically symmetric membranes are used. Examples include polyethylene, polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) membrane. These can be produced by stretching, molding and sintering finegrained and partially crystalline polymers. Polyester and polycarbonate membranes are made using irradiation and etching processes and polymers such as polypropylene, polyamide, cellulose acetate and polysulfone membranes are produced by the phase inversion process.f Jf f ... 

In the last process step, fine particles are removed by the microfiltration unit. In the manufacture of highly integrated electronic devices, particles from the solvents used in these processes must be removed to improve product yields and suppress wafer contamination defects. For example, particles with >0.05-pm diameter should be removed to the extent of less than 10 particles per milliliter from solvents used in 16-Mbit level production lines [247]. Accordingly, the level of the microfiltration unit affects total system performance therefore, the unit should be equipped with an appropriate filtration membrane, although only a few membranes with sufficient performance are available [248]. In the solvent a very low level of dissolved metals and low total organic carbon (TOC) is desired. Moreover, high chemical resistance of the filtration membrane is also needed. 

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