Ultrafiltration membrane replacement

Membrane Characterization The two important characteristics of a UF membrane are its permeability and its retention characteristics. Ultrafiltration membranes contain pores too small to be tested by bubble point. Direc t microscopic observation of the surface is difficult and unreliable. The pores, especially the smaller ones, usually close when samples are dried for the electron microscope. Critical-point drying of a membrane (replacing the water with a flmd which can be removed at its critical point) is utihzed even though this procedure has complications of its own it has been used to produce a Few good pictures. 

SPEC was essentially able to market their Zr02-based ultrafiltration membranes to an already existing market in the sense that these membranes replaced polymeric UF membranes in a number of applications. They also developed a certain number of new applications. For Ceraver, the situation was different. When the Membralox membranes were first developed, microfiltration was performed exclusively with dead-end polymeric cartridge filters. In parallel to the development of inorganic MF membranes, Ceraver initiated the development of cross-flow MF with backflushing as a new industrial process. 

Because of the challenging environment in which ultrafiltration membranes are operated and the regular cleaning cycles, membrane lifetime is significantly shorter than that of reverse osmosis membranes. Ultrafiltration module lifetimes are rarely more than 2-3 years, and modules may be replaced annually in cheese whey or electrocoat paint applications. In contrast, reverse osmosis membranes are normally not cleaned more than once or twice per year and can last 4-5 years. 

The membranes used for analytical pervaporation are hydrophobic membranes of the types usually employed in ultrafiltration and gas-diffusion processes. In practice, PTFE is the most frequently used membrane material, followed by hydrophobic polyvinylidene-fluoride (PVDF). Ultrafiltration membranes are very thin, which, in combination with the large surface area of both the donor and acceptor chamber, leads to their easy bending. This results in changes in the ffux of the permeating component through an altered membrane area and hence in changes in the efficiency of the process. As a result, membranes must be replaced fairly often. Because of their thickness, gas-diffusion membranes are not so easily bent, so the same membrane can be used over long periods. The pore size of the... 

Microfiltration and ultrafiltration membranes allow flow capacities of 150 to 500 liters/m per hour when operating on water. This is expressed as water flux for each membrane type. Naturally the flow capacity for juices is lower. After cleaning of a membrane the water flux should reach its original capacity and it serves as an indication whether the membrane was properly cleaned. It is also an indication for when a membrane needs replacement once it plugs over longer periods. 

Polyamide-6 (Nylon-6, Perlon) and polyamide-6.6 (Nylon-6.6) are the most well known polyamides. Polyamide-based filaments find wide spread applications as yarns for textile or industrial and carpet materials [70], However, nylon-based textiles are uncomfortable to wear and difficult to finish due to their hydrophobic character. This characteristic also leads to fouling of PA-based ultrafiltration membranes by proteins and other biomolecules which increases the energy demand for filtration and requires cleaning with aggressive chemicals or replacement [71-73], Consequently the enhancement of the hydrophilicity of nylon is a key requirement for many applications and can be achieved by using plasma treatment [74-76], As a promising alternative, enzymatic hydrophilization of PA requires less energy and is not restricted to planar surfaces. 

Separation processes such as ultrafiltration and micro filtration use porous membranes which allow the passage of molecules smaller than the membrane pore size. Ultrafiltration membranes have pore sizes from 0.001 to 0.1 )im while micro filtration membranes have pore sizes in the range of 0.02 to 10 im. The production of these membranes is almost exclusively based on non-solvent inversion method which has two essential steps the polymer is dissolved in a solvent, cast to form a film then the film is exposed to a non-solvent. Two factors determine the quality of the membrane pore size and selectivity. Selectivity is determined by how narrow the distribution of pore size is. In order to obtain membranes with good selectivity, one must control the non-solvent inversion process so that it inverts slowly. If it occurs too fast, it causes the formation of pores of different sizes which will be non-uniformly distributed. This can be prevented either by an introduction of a large number of nuclei, which are uniformly distributed in the polymer membrane or by the use of a solvent combination which regulates the rate of solvent replacement. 

Recently a cationic electrodeposit paint with better anti-corrosion properties has been developed and is replacing anionic electrodeposit paint. This has made it necessary for the ultrafilter maker to develop a new ultrafiltration membrane, because conventional membranes suitable for anionic electrodeposit paint suffer some decline in filtration rate with the passage of time, when they are used for cationic electrodeposit paint. This problem has been solved by developing a modified membrane for cationic electrodeposite coating. This new membrane shows better flux stability than the conventional type. 

Kim et al. (2007b) tested three different ultrafiltration membranes (Amicon Corp.) for power generation in two different types of two-chambered MFCs. They found that these membranes had high internal resistances, and thus produced less power than the CEM or AEM membranes (Table 5.1). The 0.5 K membrane had extremely high internal resistance values. As a result, power was only 5 mW/m in two-chamber bottle reactors whereas the other membranes did not appreciably impact power generation as they all produced 33-38 mW/m. In the cube reactors, where internal resistance was lower due to a closer electrode spacing and the use of an air cathode, the 1 K membrane produced only slightly less power than the CEM membrane. Thus, in theory it may be possible to replace the CEM membrane with a more conventional ultrafiltration membrane in an MFC, but membranes must be developed that result in lower internal resistances. 

SPPO was first prepared by sulfonating PPO of intrinsic viscosity of 1.58 dL/g in chloroform at 2S C. Solutions of SPPOH in different solvents like ethoxyether and butoxyether were coated onto the surface of commercial polyethersulfone ultrafiltration membranes. All coated membranes were dried at 60° C for overnight. TFC membranes prepared from a solution of SPPO in ethoxyethanol demonstrated higher permeances and permeance ratios for CO2/CH4 gas pair. These membranes were immersed in solutions of alkali metal hydroxide or alkaline earth metal hydroxide of 0.1 to IN concentrations, depending on the solubility of the respective hydroxide in water. When the solubility was low, the solution saturated with hydroxide was used. The TFC membranes were kept immersed for 48 hours at room temperature to complete the exchange of the proton with metal cations. Solutions of magnesium nitrate and aluminium chloride were used to replace the proton with Mg and AF respectively. 

Until the early 1960s, laboratory iavestigators rehed on dialysis for the separation, concentration, and purification of a wide variety of biologic fluids. Examples iaclude removal of a buffer from a proteia solution or concentrating a polypeptide with hyperosmotic dialysate. Speciali2ed fixtures were sometimes employed alternatively, dialysis tubes, ie, cylinders of membrane about the si2e of a test tube and sealed at both ends, were simply suspended ia a dialysate bath. In recent years, dialysis as a laboratory operation has been replaced largely by ultrafiltration and diafiltration. 

Membranes used for the pressure driven separation processes, microfiltration (MF), ultrafiltration (UF) and reverse osmosis (RO), as well as those used for dialysis, are most commonly made of polymeric materials. Initially most such membranes were cellulosic in nature. These ate now being replaced by polyamide, polysulphone, polycarbonate and several other advanced polymers. These synthetic polymers have improved chemical stability and better resistance to microbial degradation. Membranes have most commonly been produced by a form of phase inversion known as immersion precipitation.11 This process has four main steps ... 

In the hemofiltration HF (i.e., ultrafiltration see Section 8.3) of blood, using an appropriate membrane, all of the solutes in plasma below a certain molecular weight will pass into the filtrate at the same rate, irrespective of their molecular sizes, as occurs in the human kidney glomeruli. Since its first proposal in 1967 [14], HF has been studied extensively [15-17]. Although a dialysate solution is not used in HF, the correct amount of substitution fluid must be added to the blood of the patient, either before or after filtration, to replace all the necessary blood constituents that are lost in the filtrate. This substitution fluid must be absolutely sterile, as it is mixed with the patient s blood. For these reasons, HF is more expensive to perform than hemodialysis, and so is not generally used to the same extent. 

In what concerns ultrafiltration, it has replaced size-exclusion chromatography in almost all final formulation processes. Charged ultrafiltrafion membranes, in conjunction with optimum operating parameters, as previously discussed, can also be used to enable protein purification with HPTFF. In fact, recent developments in membrane chromatography and FIPTFF enable, for the first time, complete purification of proteins using membrane systems [1],... 

The goal of ultrafiltration, in contrast to microfiltration, is to retain protein molecules by the membrane while passing smaller solutes through the membrane with the permeate. Ultrafiltration experiments were performed with polysulfone membranes (30,000-Dalton mol wt cutoff). Figure 9 shows a comparison of the permeate flux vs time obtained during ultrafiltration of cellulase in the presence and absence of SMY that was periodically removed by backflushing and then replaced with a new SMY. 

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