Polymers fouling

Solution Polymer fouling is generally a problem in suspension polymerization reaetors. Supplemental heat-transfer area in the form of coils is generally avoided because of the dififleulty eneountered in cleaning the area between coils and the vessel wall. 

Modification of the membranes affects the properties. Cross-linking improves mechanical properties and chemical resistivity. Fixed-charge membranes are formed by incorporating polyelectrolytes into polymer solution and cross-linking after the membrane is precipitated (6), or by substituting ionic species onto the polymer chain (eg, sulfonation). Polymer grafting alters surface properties (7). Enzymes are added to react with permeable species (8—11) and reduce fouling (12,13). 

Butadiene is also known to form mbbery polymers caused by polymerization initiators like free radicals or oxygen. Addition of antioxidants like TBC and the use of lower storage temperatures can substantially reduce fouling caused by these polymers. Butadiene and other olefins, such as isoprene, styrene, and chloroprene, also form so-called popcorn polymers (250). These popcorn polymers are hard, opaque, and porous. They have been reported to... 

Membrane Limitations Chemical attack, fouling, and compaction are prominent problems with RO and NF membranes. Compaction is the most straightforward. It is the result of creep, slow cold flow of the polymer resulting in a loss of water permeability. It is measured by the slope of log flux versus log time in seconds. It is independent of the flux units used and is reported as a slope, sometimes with the minus sign omitted. A slope of—0.001, typical for noncelhilosic membranes, means that for every threefold increase in log(time), 10 seconds, a membrane looses 10 percent of its flux. Since membranes are rated assuming that the dramatic early decline in permeability has already occurred, the further decline after the first few weeks is veiy slow. Compaction is specific to pressure, temperature, and envi-... 

Application all services except extremely coking, polymer formation or other high fouling conditions. Use for extremely low flow conditions where tray must remain wet and maintain a vapor seal. 

Packed towers are used in some distillation operations in preference to plate towers. Usually the selection requires an understanding of the fouling characteristics of fluids of the system. These towers have been used even in polymer forming operations. However, other contacting devices can be cleaned easier. For some processes the packed tower is much more effective as well as cheaper than a tray tower. 

SS/MA is very useful in cleaning boilers on-line that have been fouled as a result of out-of-control phosphate programs. It is a first-class polymer for operating phosphate programs with high FW hardness and voluminous amounts of sludge in the bulk BW. 

Several cleaning methods are used to remove the densified gel layer of retained material from the membrane surface. Alkaline solutions followed by hot detergent solutions are indicated for organic polymer colloids and gelatinous materials fouling. Ferrous deposits, t3 pical in water treatments, are usually removed with a citric or hydrochloric wash. [35]. 

Fouling is a major problem encoimtered during radical polymer formation [125]. High molecular-weight polymers, potentially of branched nature, form during polymerization and precipitate owing to their insolubility in the solvent. 

Fouling is only one result stemming from the influence of mixing on establishing local concentration profiles and their impact on the course of reaction [125]. Hence, in a more comprehensive view, micro mixing can affect the local concentration of initiator, monomer and additives. This should have an impact on the molecular weight distribution of the polymer formed. 

In turn, the interdigital micro mixer mixes much faster, provides more unique concentration profiles before reaction takes place and consequently changes the course of the reaction [125]. As a result, no high-molecular-weight polymer fraction is observed by GPC measurement and no fouling occurs, although the specific wall surfaces of the micro device are expected to promote deposition. 

Membranes UF membranes consist primarily of polymeric structures (polyethersulfone, regenerated cellulose, polysulfone, polyamide, polyacrylonitrile, or various fluoropolymers) formed by immersion casting on a web or as a composite on a MF membrane. Hydrophobic polymers are surface-modified to render them hydrophilic and thereby reduce fouling, reduce product losses, and increase flux [Cabasso in Vltrafiltration Membranes and Applications, Cooper (ed.). Plenum Press, New York, 1980]. Some inorganic UF membranes (alumina, glass, zirconia) are available but only find use in corrosive applications due to their high cost. 

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