Quaternary recycling

This process includes the recovery of energy content only. Most plastic waste has a high heat content so can be incinerated the generation of heat energy is the only advantage of this process. The solid waste problem is not solved by this process in fact it leads to the issue of air pollution. 

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Explain the recycling hierarchy indicated by the terms primary, secondary, tertiary and quaternary recycling. 

The advantage of pyrolysis over combustion (quaternary recycling) is a reduction in the volume of product gases by a factor of 5-20, which leads to considerable savings in the gas conditioning equipment. Furthermore, the pollutants are concentrated in a coke-like residue matrix. It is possible to obtain hydrocarbon compounds as gas or oil. 

Tertiary recycling involves chemical breakdown of nylon or PET for repolymerisation. This requires either clean, sorted pre-consumer waste or post-consumer waste, sorted by fibre type, as a feedstock. In quaternary recycling, the embedded energy of textiles can be reclaimed through incineration (Wang, 2010). This final approach is not addressed in this chapter. 

Quaternary recycling is the useful retrieval of the energy content of scrap plastic by its use as a fuel to produce products such as steam, electricity, and so forth. ... 

Recycling processes for plastics can be classified in a variety of ways. One categorization differentiates between primary, secondary, tertiary, and sometimes quaternary recycling. 

Flame retardant additives can also modify the types of products that are released during incineration of waste polymers and in this way the flame retardants are contaminants which also affect the quaternary recycling of polymers (that is, the incineration of polymers to recover heat). For example, the thermal degradation of polyurethane, PU, can produce a complex mixture of products. However, in the presence of a common phosphorus-based flame retardant (such as ammonium polyphosphate), aniline (which is quite toxic) becomes a relevant volatile combustion product. ... 

Data relating to the nature and quantities of plastics wastes arising from industrial processes and municipal refuse have been reviewed [1,2], together with a consideration of the economics and appropriateness of primary, secondary, tertiary and quaternary recycling respectively. 

Processes that do not rely on the melting of plastic recyclate relate to large scale predominantly tertiary and quaternary recycling. Thermoset matrix composites recycling also falls within this description, and the principal recycling routes for thermoset matrix composites are outlined below. 

Tertiary or quaternary recycling, (recovery of chemicals or energy), should only be considered when other types of recycling are not economically or technologically feasible. In tertiary recycling, waste plastics are converted to either monomers or fuels or petrochemical feedstocks. Conversion to monomers by solvolytic methods is feasible for condensation polymers but often requires pure polymer streams. Sorting and cleaning of the waste stream increases the cost of the process. 

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