Ultrafiltration membrane manufacturers

Cellulosic Membranes. In the first period, summarized In Table I, cellulose acetate (CA) was discovered as a highly selective material by Reid and co-workers ( 1) who found high sa t rejections, but unfortunately low permeate water fluxes (40 L/m d) through their membranes. In 1960, Loeb obtained widely scattered results during permeation measurements of CA ultrafiltration membranes manufactured by the German company Schleicher Schuell. This was first attributed to sealing problems, but later found to depend on the side of the membrane which was exposed to the feed water (2 ). 

Ultrafiltration membrane manufacturers frequently characterize their membranes using the cutoff concept rather than pore size. The nominal molecular weight cutoff (MWCO) is a performance-related parameter, defined as the lower limit of a solute molecular weight (e.g., dextran) for which the rejection is 95-98% (Boerlage, 2001). As the MWCO decreases, the mean pore diameter for most UF membranes has been foimd to decrease (Kim et al., 1990). However, the MWCO may be sharp or diffuse, that is, thoe is a range of MWCO, and in reality MWCO is only a rough indication of the membrane s ability to remove a given compound as molecular shape, polarity, and interaction with the membrane affect rejection (Mulder, 1996). Moreover, membrane surface characteristics (e.g., surface porosity and pore size distribution) may influence the apparent size of particles retained. 

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-... 

Traditionally, ultrafilters have been manufactured from cellulose acetate or cellulose nitrate. Several other materials, such as polyvinyl chloride and polycarbonate, are now also used in membrane manufacture. Such plastic-type membranes exhibit enhanced chemical and physical stability when compared with cellulose-based ultrafiltration membranes. An important prerequisite in manufacturing ultrafilters is that the material utilized exhibits low protein adsorptive properties. 

Membranes. Photopolymer chemistry is being applied to the design and manufacture of a variety of membrane materials. In these applications, photopolymer technology is used to precisely define the microscopic openings in the membrane as it is being formed or to modify an existing membrane. Some of the applications of photopolymer chemistry to membranes include the modification of ultrafiltration membranes (78) and the manufacture of amphiphilic (79), gas permeable (80), untrafiltration (81), ion-selective electrode (82) and reverse osmosis membranes. 

Ultrafiltration membranes are usually manufactured from tough plastic-based polymers, such as polyvinyl chloride or polycarbonate. A range of membranes are available which display different cut-off points (Figure 3.20). Membranes displaying cut-off points of 3, 10, 30, 50 and 100 kDa are most commonly used. Thus, if the protein of interest displays a molecular mass of 70kDa, it may be concentrated effectively by using an ultrafilter membrane displaying a molecular mass cut-off point of 50 kDa. Ultrafiltration is a popular method of concentration because ... 

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. 

The most widely used nominal pore size for ultrafiltration is 1 nm, which is estimated to retain compounds with MWs >1000 Da. The 1 nm pore-sized membrane isolates 20% of the total DOC in surface and deep ocean waters and up to 55% of the DOC in coastal and estuarine environments (Benner et ai, 1997 Carlson et ah, 1985 Guo and Santschi, 1996). Ultrafiltration membranes with a smaller pore size are rare and do not show reproducible retention characteristics filters with a larger pore size retain only a small fraction of total DOC and they are not widely used. In general, the actual MW retained and the isolation of reproducible quantities of DOC by ultrafiltration depends strongly on the membrane (e.g. construction material, manufacturer), sample type (e.g. river, coastal, open ocean), total DOC concentration, concentration factor, extent of desalting and operating conditions (Buesseler et al, 1996 Guo and Santschi, 1996 Guo et ai, 2000). Losses to the ultrafiltration membrane can also be significant (Guo et al., 2000) and depend primarily on the physiochemical characteristics of the particular molecule. 

Clarification of rough beer, vinegar and pasteurization of clarified beer by cross-flow ultrafiltration are also very common processes utilizing hollow fiber ultrafiltration. As seen in Table 1, an important number of membrane manufacturers specialize in medical and pharmaceutical applications. In pharmaceutical and biotechnology industries, hollow fiber membranes are used for the concentration, separation, and purification of physiological activators such as antibiotics, vaccines, enzymes, proteins and peptides, as well as blood purification (hemofiltration). As a physical barrier for bacteria and viruses, membranes are also a popular option for the production of purified water for hospitals and pharmacies. 

Membranes are being frequently employed in the manufacturing of pharmaceuticals in combination with a bioreactor for enzymatic reactions. In DSM such a combination has been studied for the production of S -ibuprofen, via the hydrolysis of the (R,S)-ibuprofen methylester coupled to a racemization of the unwanted enantiomer. The esterase used for the above conversion is strongly deactivated by the product. To solve this problem, an ultrafiltration membrane unit has been coupled to the reactor, to remove in situ the product formed. The application of the ultrafiltration has led to a twofold increase of the conversion/productivity, as shown in Fig. 11. 

Virtually the entire membrane manufacture today is based on laminate structures comprising a thin barrier layer deployed upon a much thicker, highly permeable support. Most are formed of compositionaUy homogeneous polysulfone, cellulose acetate, polyamides, and various fluoropolymers by phase inversion techniques in which ultrathin films of suitably permselective material are deposited on prefabricated porous support structures. Hydrophobic polymers as polyethylene, polypropylene, or polysulfone are often used as supports. A fairly comprehensive hst of microporous and ultrafiltration commercial membranes and produced companies are presented in Refs [107-109]. A review on inorganic membranes has been given in Ref. [110]. 

The majority of the ultrafiltration (UP) experiments have been performed using the laboratory unit shown in fig.2. The apparatus was constructed to use capillary membranes manufactured by the Berghof Institute (Tubingen, Germany). The physical properties of the membranes are given in Table I. 

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

Equipment used to produce biotech products should be qualified for design, installation, operation, and performance [15]. The aging and continued performance of re-used process materials such as column resins is an important consideration during the validation of a biotech process. Demonstration of microbial control during processing is also a critical component of process validation, particularly in difficult to clean equipment such as alBnity columns or ultrafiltration membranes. Finally, consistent and reasonable step yield of individual unit operations can be verified during consistency and commercial product manufacturing. 

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... 

Hollow fibers have been used since the 1960s in many applications such as reverse osmosis, ultrafiltration, membrane gas separation, artificial organs, and other medical purposes. There are several advantages to hollow fibers over the flat sheet membranes the most important is their high surface-to-volume ratio. The use of hollow fibers has become popular in many industrial sectors since Mahon first patented the hollow fiber membranes [56]. The morphology and performance of hollow fibers are complex functions of many parameters involved in their manufacturing. McKelvey summarized the effect of spinning parameters on the macroscopic dimensions of hollow fibers [57]. 

The manufacture of ultrafiltration membranes is possible on the basis of mix polysulfone-polyesteiketone [432, 433]. Transparent membranes obtained by means of cast from solution have good mechanical properties in both dry and hydrated state and keep analogous mechanical properties after exposition in water (for 24 h at 80 °C). The maximal conductivity of membranes at 23 °C is 4.2x lO Sm/cm while it increases to 0.11 Sm/cm at 80 °C. 

Table 1.6 lists the development of some membrane processes. The first commercial membranes for practical applications were manufactured by Sanorius in Germany after World War I, the know-how necessary to prepare these membranes originating from the early work of Zsigmondy [25]. However, these porous cellulose nitrate or cellulose nitrate-cellulose acetate membranes were only used on a laboratory scale and the same applied to the more dense ultrafiltration membranes developed at the same... 

Ultrafiltration is often applied for the concentration of macromolecular solutions where the large molecules have to be retained by the membrane while small molecules (and the solvent) should permeate freely. In order to choose a suitable membrane, manufacturers often used the concept of cut-off but this concept should be considered critically (see chapter IV). 

Composite membranes constitute the second type of structure frequently used in reverse osmosis while most of the nanofiltration membranes are in fact composite membranes. In such membranes the toplayer and sublayer are composed of different polymeric materials so that each layer can be optimised separately. The first stage in manufacturing a composite membrane is the preparation of the porous sublayer. Important criteria for this sublayer are surface porosity and pore size distribution and asymmetric ultrafiltration membranes are often used. Different methods have been employed for placing a thin dense layer on top of this sublayer ... 

Fig. 29. Rejection of test proteins as a function of molecular weight, in a series of ultrafiltration membranes with different molecular weight cutoffs. As these data show, membranes with complete sharp molecular weight are not found outside of manufacturers catalogs.

Since the middle 1970 s, KYNAR resins have also been used for the manufacture of microporous and ultrafiltration membranes. KYNAR fluoropolymer was selected for this application because it is resistant to many chemicals both at room temperature and elevated temperature. Because PVDF is approved by the Federal Drug Administration (FDA) for articles or components of articles intended for repeated use in contact with food, KYNAR filters and fluid handling systems are being used by the chemical and the food industry and are also being used by the semiconductor industry as well as in biomedical applications The latter two applications require particularly inert materials that will not contaminate the fluid with trace contaminants, and KYNAR PVDF does meet these extreme purity requirements. 

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