Feedstock Recycling of Plastics to Liquid Fuel Using Zeolite Y
Catalysts
GMSARN International Conference on Sustainable Development: Issues and Prospects for the GMS 12-14 Nov. 2008
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Waste plastics can be reused as valuable resources according to the treatment technologies. The mechanical recycles for the production using the same material can be recommended as a desirable technology because this makes no more pollution problems. But it is very difficult to separate various waste plastics with dust and metals into one-component raw material which can be recycled without any problems. So thermal recycle technologies are the objects of interest used as alternatives for the mechanical recycle technologies.
In these technologies, pyrolysis may be favorably used for oil and monomer recovery from waste plastics. Also, this technology has more advantages than combustion technology in the view of discharging less pollutant. Especially, it can be more attractive than any other technologies because it is able to make light oil to be directly used for the industrial fuel.
But, all kinds of plastics attributed to the series of thermoplastics are not easily converted into oil product by pyrolysis. To pyrolyze plastics such as polyethylene (PE) and polypropylene (PP) of olefin series, the catalysts with high cracking property are needed.
Recycling is one of the three ways for utilization and minimalization of the huge amount of wastes. The others are landfilling and incineration with or without energy recovery. Neither landfilling nor incineration can solve the growing problem of huge amount of wastes, e.g. directives exist to maximalize the mass of the deponable wastes. In 2005 it will be 40% of the total amount of wastes arisen in 1993.
End gases with high content of toxic and handful compounds can be arisen in case of incineration, therefore incinerators need special filter system with high efficiency which can only decrease their concentration, but not eliminate. The slug of incineration containing toxic ash as well can also cause environmental problems.
Several methods have been suggested for solving the problem of waste plastics, but some of them are still in their initial stages, or produce further environmental pollution.
One of the prospective ways of the utilization of the waste polymers is chemical (thermal) treatment which is named tertiary recycling in the literature- where long alkyl chains are broken into a mixture of lighter hydrocarbons. Further utilization of these hydrocarbons has also not been solved yet. One possibility of their utilization is fuel like application or blending in fuel as mixing components. Many researches study their application as fuel.
This hydrocarbon mixture having high olefin content can be saturated with hydrogen, and perhaps isomerized by the use of catalysts. These steps result in a high quality synthetic diesel fuel, with high cetane number, and theoretically these fuels are free from sulphur, nitrogen and metals. The treatment might be only
thermal or catalytic.
Cracking reactions are endothermic, and have need energy. The required heat and temperature can be reduced with catalysts, but the disposal and the activation loss or regeneration of the catalysts could cause some problems.
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Catalytic Activities of Zeolite Y
The cracking process was carried out by using the prepared zeolite Y as catalyst at the temperature of 232-343 °C for 3 hours. The cracking process was done by using the catalyst to recycled polyethylene plastic ratio of 1:10 and the cracking conditions are shown in Table 5.
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