Polyesters membrane technology

The key to the reverse osmosis (RO) process is a suitable semipermeable membrane. Improvements in membrane technology now mean that the process can apply to industrial-scale plants. Common contemporary membrane selections are made of cellulose-based polymer or a polyamide layer applied to a microporous poljmier fllm. This membrane is bonded to a porous polyester sheet for structural stiffiiess. This composite is rolled into a spiral. Spun hollow fine fibers are the finished product. The semipermeable layer is on the outside of the fibers. The total thickness of the composite is about 24 pm. The outside diameter of the tube is about 95 pm, making for a large surface area for rejecting salt. The fibers are made into bundles that are sealed with epo in a fiberglass pressure container. 

GE-Osmonics (part of GE Water Technologies) commercializes the Desal 5 nanofiltration membranes, used for removal of hardness and other contaminants, alcohol recovery from aqueous solution and removal of salt from salt whey. The membrane has 4 layers, a polyester nonwoven, an asymmetric micro-porous polysulfone and two proprietary thin films, which might be based on sulfonated polysulfone and polypiperazineamide [34]. A comparison between DesaF 5 and NF270 for nanofiltration has been reported by [44] (Tab. 4.3). 

Reducing the section thickness to the level of foils and films allows many more polymers to become transparent. Although films technology is very highly developed nowadays, it has only a few points of contact with automotive design, e.g., in the use of oriented polyester film for membrane touch switches and instrument panel display. 

The source of the new technology is MacDermid Autotype, where the antimicrobial protection is built into the hard-coat layer, which enables the protection to be built into traditional flat panel displays, membrane keypads, touch screens and fascia panels. The manufacturing process follows traditional lines and comprises a flexible polyester base, primed on the underside with an ink adhesion layer, for high definition screen and ink-jet printing, and coated on the outside with an exceptionally tough hard-coat layer. 

Within the aromatics e.g. benzene, toluene and xylene) the xylenes are used as a feedstock for the production terephthalic acid and dimethyl terephthalate, both monomers that are used for the production of polyethylene terephthalate (PET), which is the main constituent of plastic bottles and polyester clothing. There are three very close boiling isomers of xylene ortho-, meta- and para-) and it is mainly p-xylene that is used for PET production. The fractionation processes for all existing xylene isomers (crystallization or simulated moving bed) are expensive technologies and it is of interest to study the potentials of membranes for such a separation. 

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