Microwave pyrolysis of polymeric materials

Abstract

The consumption of polymeric materials is growing ceaselessly in the world even in spite of the financial crisis. World’s plastics production in 2009 was 2.3·108 tons and in Europe it was 4.5·107 tons whose 54% is disposed as waste. The annual average production of tires in Europe is more than 2.5 106 tons. In the 2008 in Italy were produced 3.5·106 tons of plastics among which 4.1·105 tons of tires, and 1.5·106 of waste plastics tons were collected for disposal. (Chen et al., 2007; Federazione Imprese e Servizi, Unione Nazionale Imprese Recupero [FISE UNIRE], 2009; PlasticsEurope, 2010). World rubber demand is foreseen to increase up to 4% annually to 26.5 million metric tons in 2011 (Freedonia, 2010). Therefore the disposal of waste polymers is a serious environmental problem against which public is becoming more aware. The interest of waste polymeric materials disposal is focused on new uses rather than land filling or incineration. Regarding scrap tires, a strong attention has been paid over last years to the claims for their recycling or reprocessing. In consideration of their complex composition, slow degradation rate in landfill, high calorific value and shape hindrance they may be burned hardly but otherwise they cannot send to landfill anymore and an alternative methodology must be eligible in order to dispose scrap tires. European Directive No. 31/1999 states that the disposal of scrap tires in landfills is banned with the exclusion of bicycle tires and tires with an external diameter greater than 1400mm. Since July 2006 the ban has been extended also to shredded tires. Waste plastics and tires are very attractive as a source of renewed raw materials and chemical substances. These products may be achieved by pyrolysis, heating usually in the absence, but sometimes in the presence, of an oxidative agent, and these processes may be viewed as a promising technology. The pyrolysis of polymeric materials or plastic-containing wastes including scrap tires is a possible answer to the problem of their disposal because it let recover of gas, oil and solid able to be employed as a source of products and energy. Therefore the relevance of the pyrolysis processes of plastic waste has been growing. A plethora of studies over the thermal degradation of polymeric materials are carried out using conventional heating method with internal or external heating source, under inert or oxidizing atmosphere. Generally the thermal decomposition needs operating temperature above 450°C (Kaminsky et al., 2004; Mastral et al., 2002; Whesterhout et al., 1998).