Microfiltration polyethylene

The microalgae are cultured in bioreactors under solar or artiflcial light in the presence of carbon dioxide and salts. The bioreactors may be closed systems made of polyethylene sleeves rather than open pools. Optimal conditions for pigment production are low to medium light intensity and medium temperatures (20 to 30°C). Pigment extraction is achieved by cell breakage, extraction into water or buffered solution, and centrifugation to separate out the filtrate. The filtrate may then be partly purified and sterilized by microfiltration and spray dried or lyophilized. 

In micro- and ultrafiltrations, the mode of separation is by sieving through line pores, where microfiltration membranes filter colloidal particles and bacteria from 0.1 to 10 mm, and ultrafiltration membranes filter dissolved macromolecules. Usually, a polymer membrane, for example, cellulose nitrate, polyacrilonytrile, polysulfone, polycarbonate, polyethylene, polypropylene, poly-tretrafhioroethylene, polyamide, and polyvinylchloride, permits the passage of specific constituents of a feed stream as a permeate flow through its pores, while other, usually larger components of the feed stream are rejected by the membrane from the permeate flow and incorporated in the retentate flow [10,148,149],... 

Microfiltration membranes can be used as pretreatment for other membrane technologies and to remove microbes and total suspended sohds (TSS) including fibers and particles. Retention of salts and dissolved organics is negligible, if they are not bound to the suspended sohds. MF can be used for the recovery of coating color pigments. MBRs generally use UF or MF membranes. The materials used in microfiltration are polyvinylidenefluoride (PVDF), polypropylene, polyethylene, polysulfone, polyether suUbne, Teflon, and ceramic materials. 

Polyethylene-co-vlnylaloohol/polyethylene-co-vinylacetate (PVA) polymers have been fabricated into membranes for both hemodialysis and microfiltration. The fabrication procedure and physical properties of the finished membrane material have not been published. Both the PMMA and PVA membranes have been developed in Japan, where most of the application studies have been performed. 

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 ... 

During sintering, a powder of particles of a given size is pressurized at elevated temperatures in a preformed shape so that the interface between the particles disappears. Microfiltration membranes can thus be obtained from PTFE (polytetra-fluoroethylene), PE (polyethylene), PP (polypropylene), metals, ceramics, graphite and glass, with pore sizes depending on the particle size and the particle-size distribution. Porosities up to 80% for metals and 10-20% for polymeric membranes can be reached with pore sizes varying between 0.1 and 10 pm. Most of these materials have excellent solvent and thermal stability. 

Al-Obeidani, S., Al-Hinai, H., Goosen, M.F.A., Sablani, S., Taniguchi, Y., and Okamura, H. 2008. Chemical cleaning of oU contaminated polyethylene hollow fiber microfiltration membranes. J Membr Sci. 307 299-308. 

Early systems based on visible light used high-zoom video cameras positioned to view the membrane from the side. The ability to continuously record, in real time, activity at the membrane surface made this type of system ideal for in situ imaging of cake deposition, provided the particles were sufficiently large. A 15 x zoom video camera was used to record in situ particle motion of large polyethylene particles (125-180 pm) dose to a stainless steel mesh filter 3]. The particles in this study were much larger than those typically found in microfiltration applications. Another study [4] used a similar system to record the deposition of more realistic caldte (2.6 pm, 25 pm) and anatase (0.5 pm) particles. Individual particles could not be resolved and only a cake thickness was quoted. In both studies the cakes thicknesses were in the millimeter range. 

Sawada Y, Fujii R, Igami I et al. Removal of endotoxin from water by microfiltration through a microporous polyethylene hollow fiber membrane. Appl Environ Microbiol 1986 51 813-820. 

In order to study nano- and ultra-filtration membranes some linear polymers could be chosen such as polyethylene glycols or dextranes. However, their linearity makes size designation difficult which is not the case for globular macromolecules such as proteins. In the case of microfiltration membranes particles of latex, silica, alumina, etc., can be used. 

Combining earlier work in which they had prepared microfiltration membranes from melt-extruded polyethylene (PE) with pore sizes in the region of 0.045 jtim, Elyashevich et al. [1041] deposited P(ANi) onto these PE microporous membranes, used as supports or hosts. They found that the combined PE-P(ANi) membranes had conductivities of 0.2 S/cm, and showed promise as gas separation membranes which were sturdier and more durable than free-standing P(ANi) membranes. 

The thermal phase inversion process is also employed for ultra- and microfiltration membranes. Crystalline polymers such as polyethylene and polypropylene are generally preferred as solutions these can be prepared at temperatures above the melting point, but cooling below the melting point will yield rapid crystallization and phase separation. These membranes are often employed in microfiltration and dialysis applications. 

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