Pyrolysis of polystyrene using low-cost natural catalysts: Production and characterisation of styrene-rich pyro-oils

Abstract

This work aims to study the catalytic pyrolysis of polystyrene (PS) in order to obtain a styrene-rich liquid appealing for re-polymerisation processes. The process was performed in a fixed-bed reactor using low-cost materials such as ilmenite, olivine, calcium oxide (CaO) and dolomite as catalysts at 600 ºC. A non-catalytic test with sand was also conducted for comparison purposes. The resulting pyro-oil yield was between 89 and 96 wt%, and consisted mainly of styrene monomer, styrene dimer and styrene trimer, as well as other light aromatic compounds depending on the catalyst used. Olivine and CaO were capable to increase the styrene monomer concentration in the pyro-oil by about 10–12 % compared to non-catalytic pyrolysis, reaching up to 74.5 and 71.4 wt%, respectively. Furthermore, these catalysts reduced the concentration of styrene dimer and styrene trimer in the pyro-oil, which could be useful for further re-polymerisation processes. However, the presence of polyaromatics (PAHs) in the pyro-oils obtained from ilmenite, olivine and CaO was also identified, and other families such as mono-aromatics, di-aromatics, BTX, and nitrogen heterocyclic compounds were also increased in all pyro-oils obtained with catalysts compared to those obtained by non-catalytic pyrolysis. In addition, several inorganic species in the pyro-oil were reduced by the addition of the catalysts. This effect was observed after the addition of olivine and CaO, especially in the reduction of S, Mg, Ca and Fe. These results clearly demonstrate the potential of pyrolysis to convert PS waste into valuable building blocks for the production of new plastics.