Hydrogen production from the steam reforming of phenol-pet solution using nickle-palladium supported catalyst

Abstract

As a sustainable and renewable energy carrier, hydrogen is considered as a key future fuel to make the low carbon energy schemes present. In recent years attention has been given for conversion of waste materials, including plastics towards production of hydrogen. Studies in this field are important because it resolves numerous problems brought about by plastic waste. Polyethylene terephthalate (PET) is one of the major products of plastic waste which constitutes a major threat to the environmental conservation efforts and living organism. Phenol has been chosen in this study as a solvent for PET toward hydrogen production since phenols are unwanted liquid by product of bio-oil from the biomass pyrolysis process. This study is to investigate catalytic steam reforming of phenol with dissolved PET over bimetallic nickel-palladium (Ni-Pd) supported on ?-aluminium oxide (?-Al2O3), lanthanum oxide (La2O3), zirconium oxide (ZrO2) and zeolite (ZSM-5) for hydrogen production. The scope of this research was based on the catalyst characterization, catalyst testing, process parametric study and reaction mechanism. The PET dissolution was screened in various solvents, and it was found that phenol is the most suitable solvent for this study. The catalytic steam reforming was carried out on the PET-phenol solution using a fixed bed reactor at atmospheric pressure. Developing a highly active and stable catalyst for hydrogen production from the steam reforming of waste products was the aim of this study. Supported Ni/Pd was prepared by impregnation method and screened on the steam reforming process. Ni-Pd/Al2O3-La2O3 was found to be the promising catalyst, as it was able to obtain as high as 95.6% phenol conversion, 69.5% hydrogen selectivity and remarkable performance even after 36 h. An in depth study of Ni-Pd/Al2O3-La2O3 catalyst was carried out from catalytic screening. Phenol concentration of 10 wt. %, temperature as low as 800 oC and total feed flow rate of 0.4 ml/min resulted in the highest hydrogen selectivity and highest PET-phenol conversion. Analysis on products composition indicated that steam reforming of PET-phenol generally produced aliphatic, high amount of aromatic compounds, together with moderate amount of cyclic compounds. The reaction conditions also led to alkylation of phenol by the reforming products from PET-phenol solution in the presence of the catalyst. Based on the product formation in the proposed reaction mechanism, free radical and carbenium ion mechanisms are of high chance to occur. In the parametric study five factors considered were temperature, feed flow rate of phenol+PET+water, N2 flow rate, phenol concentration, as well as concentration of PET solution, while the responses were phenol conversion (Y1) and hydrogen selectivity (Y2). The result from the parametric study indicated that all the main independent variables have a significant influence on the dependent variable of Y1 and Y2 with the range of 47.2-97.6% and 49-71%, respectively. The most effective parameters in this study were temperature of 800 oC and PET concentration of 7 wt. %. In conclusion, this study explored new thought toward useful product from waste plastic materials. It provides a promising clean technology, which employed PET waste and phenol in the catalytic steam reforming toward production of hydrogen.