A Study on Waste Plastic Pyrolysis using Metal Supported Catalysts

Abstract

Energy demands of Pakistan are not fulfilled by conventional energy sources such as hydel and thermal. Renewable energy sources also failed to provide a solution to energy crisis in Pakistan due to several economic and technical shortcomings. Waste plastic present in municipal solid waste in this context, has huge potential to produce iesel/gasoline providing an alternate energy source and clean the environment by reducing the pollution. Several processes, such as mechanical recycling, incineration, reusing, landfilling and energy recovery method, are employed by the waste plastic management to dispose waste plastic. Pyrolysis is the most desired energy recovery method that converts plastic into automobile fuels. This study will present our efforts to convert waste plastic into hydrocarbon fuels through pyrolysis process to eliminate the environmental problem from waste plastic and provide the alternate transportation fuel. This extensive study was performed in three steps. In the first step catalyst were synthesized, in second step the plastic sample was thermally degraded (thermal pyrolysis) and finally the catalytic degradation of the plastic was performed. Plastic sample was characterized using Thermogravimetric analysis (TGA) which shows that the degradation starts at around 340 °C. The catalysts for the catalytic cracking were prepared using two step method, first by preparing two supports of CeO2 and ZrO2 through solution combustion synthesis using urea and glycine as fuel separately followed by the impregnation of nickel metal through incipient wetness impregnation method. Four different Ni loadings i.e. 2%, 5%, 10% and 15%, were prepared using different weight percentages of nickel nitrate. Catalysts of sixteen types were prepared with the combination of these two techniques. The catalysts were then finally calcined at 400 °C for 3 hours in the muffle furnace to remove any impurity present. The catalyst was then characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. XRD confirmed the synthesis of prepared xi catalysts. SEM analysis of the catalyst revealed that there are macro pores in the catalyst particles. FTIR results of the catalysts supports the XRD results of the samples reveals the functional groups present. Thermal pyrolysis was performed at different temperature from 400 °C to 700 °C with an interval of 50 °C to find the best optimum temperature that gives the maximum oil yield. The temperature 500 °C selected for the catalytic pyrolysis because the plastic gives maximum oil at this temperature of about 17.7g from 20g sample. Then 16 different experiments were performed using catalytic cracking approach with 16 prepared catalysts at 500 °C. The plastic to catalyst ratio was set to 40:1 in every experiment of catalytic pyrolysis of the plastic. The produced oil was characterized using UV-vis and FTIR spectroscopy which reveals that the oil is in the hydrocarbon fuel range.