Depolymerization in supercritical fluids

Matsumura, S. (2003) Depolymerization and Polymerization of polyester and polycarbonate in supercritical fluid,... 

The supercritical fluid over its critical point has high density, such as in liquid state, and high kinetic energy as in a gas molecule. Therefore the reaction rate is expected to be higher than the reaction under liquid state conditions. PET is depolymerized quickly by solvolysis in supercritical water [35] or supercritical methanol [36]. The main products of PET depolymerization in supercritical methanol are dimethyl terephthalate (DMT) and ethylene glycol (EG), as shown in Figure 6.4. The depolymerization is carried out typically at temperatures between 543 and 603 K under pressures of 0.1-15 MPa for a reaction time of 3-60 min. For example, at 573 K, sample/methanol ratio 1/5 (by wt) and reaction pressure 14.7 MPa, DMT yield is reported [37] to be 98 per cent in 30 min. 

Depolymerization, e.g., polyethylene terephthalate and cellulose hydrolysis Hydrothermal oxidation of organic wastes in water Crystallization, particle formation, and coatings Antisolvent crystallization, rapid expansion from supercritical fluid solution (RESS)... 

Supercritical fluids are already used as alternative for classical separation processes such as extraction, adsorption, chromatography, and crystallization, as reaction media as in polymerization or depolymerization, as plasticization agents or simply as particles, fibers, or foams formation even some processes becoming commercial. A variety of polymers, including polyolefins. 

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