Plastic wastes partial oxidation

In spite of the above mentioned background on polymer oxidation, only a few works have been published on the subject of obtaining commercially valuable products by partial oxidation of plastic and rubber wastes. Several of these works are described below. 

Other possible oxidative treatments for the feedstock recycling of plastic and rubber wastes include partial oxidation with organic peroxides and decomposition by reaction with oxygen by thermooxidation or under supercritical water conditions. However, these latter alternatives have so far not been widely investigated. 

The situation at the metal interface, i.e. under a deposit or oxide scale where the oxygen partial pressure is low is shown in Fig. 24.12(a) and the situation at the gas interface, i.e. at the top of a deposit or oxide scale where the oxygen partial pressure is higher, is shown in Fig. 24.12(b). In both cases the levels of Cl, S, and K are held constant and the temperature varied. It is to be noted that these conditions will vary slightly from case to case. For example, an increase in the amount of plastic waste or demolition waste being co-combusted will increase the amount of Cl, while the amount of sulphur, sulphate or even coal or peat used in combustion will affect the S levels. Nevertheless, two significant features can be identified from these diagrams. 

A process akin to the allylic oxidation in activation is aromatic side chain oxidation to produce acids or anhydrides. Phthalic anhydride, an important intermediate in production of polyesters, plasticizers, and fine chemicals synthesis, can be produced via selective oxidation of -xylenes using vanadium oxide catalysts (Eqn. 3). This process today accounts for over 85% of the phthalic anhydride produced worldwide, and has largely displaced the partially wasteful and more expensive naphthalene-based route (Eqn. 4), by which nearly all PA was produced in 1960 (Figure 4). Nearly all of the phthalic anhydride produced today is used for manufacturing vinyl plasticizers, with a much smaller application in the fine chemicals industry. 

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