High external surface Pt/zeolite catalysts for improving polystyrene hydrocracking

Progress and perspective for conversion of plastic wastes into valuable chemicals

Today, discarded plastics in nature have caused serious "white pollution", however these plastic wastes contain abundant carbon resources that could serve as the feedstock to produce commodities. Because of this, it is requisite to convert these plastic wastes into valuable chemicals. Herein, the state-of-the-art techniques for plastic conversion are divided into two categories, those performed under violent conditions and mild conditions, in which the conversion mechanisms are discussed. The strategies under violent conditions are closer to practical application thanks to their excellent conversion efficiencies, while the strategies under mild conditions are more environmentally friendly, showing enormous development potential in the future. We summarize in detail the pyrolysis, hydropyrolysis, solvolysis and microwave-initiated catalysis for bond cleavage in plastic wastes at temperatures ranging from 448 to 973 K. Also, we overview the photocatalysis, electrocatalysis and biocatalysis for bond cleavage in plastic wastes at near and even normal temperature and pressure. Finally, we present some suggestions and outlooks concerning the improvement of current techniques and in-depth mechanisms of investigation for conversion of plastics into valuable chemicals.

Fuel production from waste polystyrene via pyrolysis: Kinetics and products distribution

In the present study polystyrene waste (PS) was collected from a drop off site in a local market and pyrolyzed at heating rates of 5, 10, 15 and 20 °C/min and temperature range 40-600 °C under nitrogen condition. The apparent activation energy (Ea) and pre-exponential factor (A) were determined using 6 different kinetic methods. Activation energy and pre-exponential factor were found in the range of 82.3 - 202.8 kJmol^-1 and 3.5 × 10⁶-7.6 × 10¹⁴ min^-1 respectively. The results demonstrated that the calculated values of Ea and A vary with fraction of conversion, heating rates and the applied model. Moreover, pyrolysis of waste polystyrene was carried out in an indigenously manufactured furnace at temperatures ranging from 340 to 420 °C. The composition of liquid and gaseous fractions was determined using gas chromatography-mass spectrometry. Temperature and reaction time were optimized and the results revealed that temperature of 410 °C and exposure time of 70 min are the best conditions for maximum fuel oil production. Methane and ethane were found as the main products in the gas phase constituting about 82% of the gaseous fraction. The liquid products composed of broad range of C₂ - C₁₅ hydrocarbons depending on the pyrolytic parameters. A comparison of the composition of pyrolysis oil with standard parameters of diesel, gasoline and kerosene oil suggested that pyrolysis oil from polystyrene waste holds great promise for replacing fuel oil.

Selective conversion of polystyrene into renewable chemical feedstock under mild conditions

The aim of this work is to prepare catalysts for energy efficient conversion of polystyrene (PS) and its waste into valuable products with high conversion at 250 °C. The FeCo/Alumina bimetallic catalyst was synthesized by aqueous impregnation and structurally determined using scanning-transmission electron microscopy, temperature programmed desorption, X-ray diffraction, and X-ray photoelectron spectroscopy. Successfully, we have achieved up to 91% liquid yield with selectivities for styrene monomer (SM) up to 45 wt% and ethylbenzene (EB) up to 55 wt%, depending on the exposure time at 250 °C by FeCo/Alumina which is comparable to those of reactions at high temperatures (≥350 °C). Further increase of catalyst loadings from 200 to 400 mg also led to the decrease in styrene yield and increase in ethylbenzene yield. The analysis of the resulting clear liquid by gas chromatography/mass spectrometry (GC/MS) indicates the generation of products in the gasoline range.