Synthesis and efficient use of low-cost natural red clay catalyst for the production of upgraded fuel oil using pyrolysis of waste expanded polystyrene and in situ vapour phase hydrogenation

Abstract

The waste expanded polystyrene (WEPS) was subjected to the pyrolysis and in situ hydrogenation process in a laboratory fabricated innovative reactor on a red clay catalyst in the temperature range of 400°C to 700°C. Five different catalysts were synthesized from the eco-friendly and non-toxic red clay, that is, red clay in natural form (RC), red clay calcined at 600°C (RC-600), red clay calcined at 700°C (RC-700), red clay calcined at 800°C (RC-800), and red clay calcined at 900°C (RC-900). The catalytic pyrolysis of WEPS, in situ hydrogenation, and aromatization were performed keeping the synthesized catalyst in different reactor arrangements, that is, liquid phase/X-type, vapour phase/Y-type, and multiphase/XY-type. The raw and calcined red clay catalysts were characterized by various characterization techniques such as SEM-EDX, BET, XRD, and FTIR. The calcination temperature greatly influenced the surface morphology and surface area of the red clay catalysts. The surface morphology of calcined red clay catalyst RC-800 shows nano cluster form of particles with very high porosity. The highest surface area of 29.25 m2/g and highest silica content of 56.82 wt% were found for the RC-800 catalyst. Furthermore, the XRD analysis ensured the presence of illite-micas, α-quartz, κ-kappa alumina, δ-delta alumina, and θ-theta alumina in the RC-800 catalyst only. The presence of strong Bronstedacid sites in RC-800 catalyst was confirmed by the FTIR analysis. The highest liquid yield of 94.37 wt% was obtained for the thermal pyrolysis of WEPS at the optimum temperature of 650°C and heating rate of 15°C/min. The maximum BTE content of 11.38 wt% was recorded for the pyrolysis oil obtained from the thermal pyrolysis of WEPS at the same optimum conditions. On the other side, the highest liquid yield of 88.82 wt% was obtained for the X-type pyrolysis at the optimum temperature of 600°C and heating rate of 15°C/min using red clay catalyst RC-800. The Y-type and XY-type pyrolysis produced maximum liquid yield of 80.81 wt% and 79.47 wt%, respectively, at the optimum temperature of 550°C and at heating rate of 15°C/min using the same red clay catalyst RC-800. However, the multiphase/XY-type pyrolysis produced the highest BTE content of 27.62 wt% and lowest styrene content (60.75 wt%) at a temperature of 550°C using RC-800 catalyst among all types of pyrolysis. The maximum styrene content of 84.74 wt% was found in pyrolysis oil obtained from thermal pyrolysis of WEPS at optimum conditions. The styrene content obtained reduced significantly from 68.83 wt% to 60.75 wt% when the reactor arrangement was changed from X-type to XY-type. The pyrolysis oil obtained from XY-type/multiphase pyrolysis was found suitable for the use in internal combustion (IC) engine. © 2022 John Wiley & Sons Ltd.