Thermo-catalytic pyrolysis is considered as a promising process for the chemical recycling of waste polymeric materials aiming at converting them into their original monomers or other valuable chemicals. In this regard, process parameters and reactor type can play important roles for an enhanced recovery of the desired products. Polystyrene (PS) wastes are excellent feedstocks for the chemical recycling owing to the capability of PS to be fully recycled. In this respect, the present work deals with the thermo-catalytic pyrolysis of PS in batch and semi-batch reactor setups. The main goal was to perform a comprehensive study on the depolymerisation of PS, thereby investigating the effect of reactor type, catalyst arrangement, feed to catalyst ratio and residence time on the yields of oil and styrene monomer (SM). A further goal was to identify the optimum operating conditions as well as reactor type for an enhanced recovery of oil and SM. It was demonstrated that the semi-batch reactor outperformed the batch reactor in terms of oil and SM yields in both thermal (non-catalytic) and catalytic tests performed at 400°C. Furthermore, it was shown that the layered arrangement of catalyst (catalyst separated from PS) produced a higher amount of oil with higher selectivity for SM as compared to the mixed arrangement (catalyst mixed with PS). Moreover, the effect of carrier gas flowrate on the product distribution was presented.

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Polystyrene (PS) is an important plastic material, which is widely used in packaging, home, construction, electrical appliances, medical equipment etc. The widespread use of PS generates large amounts of PS wastes, which is due to poor recycling rates globally end up in landfills as well as in the oceans. The increasing amounts of wastes polystyrene and other wastes plastics thus represent a serious threat to the environment, and also to human and animal health. Chemical recycling is an environmentally friendly approach that can be applied for the recycling of plastics. For chemical recycling, thermal or thermo-catalytic pyrolysis/degradation can be used. During the degradation process, polymeric materials are converted into their monomers or other valuable compounds. This paper deals with the synthesis of α-Fe2O3 nanoparticles and their use as catalyst in thermo-catalytic degradation of PS in a semi-batch reactor. The aim was to study the influence of synthesis parameters on the catalytic properties of α-Fe2O3 in PS degradation. The α-Fe2O3 catalyst samples were prepared by the chemical precipitation method using FeCl3.6H2O as a precursor salt and NaOH as precipitating agent and by calcining the precipitates at different temperatures. All catalyst samples prepared were characterized by XRD and physisorption of nitrogen. It is shown that by increasing the calcination temperature of precipitates, pure α-Fe2O3 (hematite phase) can be obtained. Furthermore, it is demonstrated that PS degradation using pure hematite as catalyst in comparison with mixed phase or non-catalytic degradation gives higher yields of oil and styrene monomer.

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