Chemical Recycling to Monomers

Chemical recycling to monomers has the advantage that the monomers can be reused to produce virgin polymers, which are of higher value than their recycled counterparts. Processes have been developed to chemically recycle most functionalized polymers. However, because of the relatively high associated costs, many of these processes are not widely used on a commercial scale. For polymers containing C-0 bonds the process entails some form of hydrolysis or alcoholysis. Two such processes are outlined below. 

The hydrolysis option suffers from the requirement for expensive high-pressure equipment, whilst the lower energy (and capex) acidolysis process suffers from progressive poisoning of the phosphoric acid catalyst by impurities. Reaction with ammonia is quite versatile and can be used to recycle mixtures of both nylon 6 and nylon 6,6. From this, caprolactam, hexamethylene diamine, aminocapronitrile and adiponitrile can all be recovered by distillation. 

One of the most expensive and time-consuming aspects of polymer recycling is the separation process. It would therefore make economic sense if mixed plastics waste could be taken and recycled back to suitable feedstocks. The essential feature of feedstock recycling processes is the use of heat (thermolysis) to break bonds, similar to crude oil refining. The process may be carried out by heat alone (pyrolysis), in a hydrogen atmosphere, or in the presence of oxygen (gasification). In the latter case 

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