Chapter 4Recovery of Monomers

4.1 Process for Obtaining a Polymerizable Monomer

A process for obtaining a polymerizable monomer can be performed by(1):

  1. Contacting a waste of thermoplastic acrylic and styrenic resin with a fluid heat transfer medium,
  2. Cooling the resulting decomposed product, and
  3. Subjecting it to distillation.

This method uses not only a molten mixed metal as an inorganic heat transfer medium, but also an additional organic heat transfer medium, so that the plastic waste does not just float on the molten metal.

Inorganic heat transfer media are mixtures or alloys of zinc, bismuth, tin, antimony, and lead, which are molten at very low temperatures alone, or in the presence of added inorganic salts, such as sodium chloride, etc., which are molten at less than 500°C.

The molten organic medium is a thermoplastic resin. Examples are other waste resins such as atatic poly(propylene) (PP), other polyolefins, or tar pitch. The added thermoplastic is also partially thermally decomposed into products that end up together with the desired monomers, and, therefore, distillation and other procedures must be used to obtain the purified monomer (1).

However, since this method is experienced with acrylic polymers which are known to decompose thermally into their corresponding monomers, no means for identifying catalyst and temperature conditions are mentioned that permit the decomposition of that polymer in the presence of others, without substantial decomposition of the other ...

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