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The resolution of many technological problems with the acceleration and increase of efficacy of processes of solid-liquid separation systems require use of synthetic products of a polymeric nature which have, among others, two fundamental properties to provide adequate performance: high molecular weight and ionic (anionic or cationic) in their molecules. This family of products is included in the group known as polyelectrolytes.
These separation processes acquire great importance in such currently essential as water purification (as flocculating agents in the physicochemical treatment and dehydrating agents in the process of drying the sludge), paper manufacture (as retention and drainage agents activities on the bench), or mining and petrochemicals (as aids in separation of solids).
The specific field of water treatment (which speak generically of flocculants) is a high-volume market (now the production capacity of the largest manufacturers totaling more than 100,000 tons / year worldwide) and continuously rising, motivated mainly by the increasing environmental requirements which lead to a continuous increase in Treatment Plants of both urban and industrial wastewater.
By the qualifications of flocculants special features, you can only use a small number of commercially available monomers basis elements manufacture. Of all these, acrylamide has become the last thirty years in the basic unit on which has been based the whole chemistry of these products. In practice, acrylamide, acrylic acid chloride and acryloxy ethyl trimethyl ammonium, synthesized currently more than 95% of existing market flocculants.
The flocculants are obtained by various polymerization processes:
Gel-solid phase polymerization
Aqueous solution polymerization
Inverse emulsion polymerization (water in organic phase)
These production processes use a number of drawbacks associated with both the engineering process itself as with the characteristics of the products obtained to cause the course of the polymerization of acrylamide derivatives of high molecular weight is a field in which focus their efforts a large number of research teams worldwide. In the last three years there have been 123 patents in USA with the words ‘polyacrylamide’ and ‘water treatment’ in the basic text. Last year, 63 patents were registered with the terms ‘acrylamide’ and ‘water treatment’.
Among the problems of industrial production of flocculants for water treatment by the procedures we can now highlight the following:
High exothermicity. The enthalpy of polymerization of acrylamide is 19,800 cal / mole. The specific heat of the polyacrylamide is 0.5 cal / g ° C. Given the kinetic rapid polymerization that the monomer can occur, effective dissipation of heat generated (to properly monitor the progress of the reaction and to avoid temperature increases lead to undesired reactions or conditions out of control) has become a problem engineering center in such an industrial scale processes.
Too high levels of existing residual monomers in the final products. Because they are used in processes such as production of drinking water or sludge drying which are then used for livestock, the decrease in levels apart toxicity limits of these monomers is vital. For example, levels of residual acrylamide allowed in water intended for human consumption are at the proposed new European legislation around 0.1 micrograms per liter. In the usual dosage levels of these products, we are talking about maximum around 100 ppm of residual monomer (acrylamide) in the flocculants used in these treatments.
Difficult to obtain stable products of high molecular weight and high load. Especially flocculants high cationicity and high molecular weight are of great application and its potential is huge, being expensive and difficult production currently.
Difficult manageable obtain liquid products with a high content of active material and high molecular weights to different loads. The liquid products have notable advantages over solid state equivalent, as are its ease of handling, systems simpler and controllable production, end more uniform application, etc. But have the drawback that transportation costs expensive if the amount of active substance in the final product is not sufficiently high.
Thermodynamically unstable liquid products, in which phase separation occurs, degradation, etc. Within weeks of manufacture.