Generation of H2 gas from polystyrene and poly(vinyl alcohol) by milling and heating with Ni(OH)2 and Ca(OH)2

Abstract

A two-step process to generate H2 gas; first by milling polystyrene (PS) or poly(vinyl alcohol) (PVA) with Ni(OH)2 and Ca(OH)2, followed by heating of the milled product in the second-step was performed in this work. Polymer and hydroxide mixtures obtained after milling for 60 min and heating to 700 °C showed H2, CH4, H2O, CO, and CO2 as the main gaseous products with H2 as the dominant gas generated between 350 and 500 °C. Analysis of the gaseous products by TG–MS and gas-chromatography, and solid products by TG–DTA and XRD shows that CO2 gas was fixed as CaCO3 at temperatures between 350 to 600 °C allowing generation of H2 gas with concentrations over 95% for PS and over 98% for PVA. The results in this study show that milling of solid based hydrocarbon compounds with nickel and calcium hydroxides allows dispersion of nickel to hydrocarbon surfaces and facilitates C–C bond rupture in polymer(s) during heating at temperatures below 500 °C, at the same time calcium adsorbs CO2. This process could be developed to treat hydrocarbon based wastes such as plastics, biomass or combinations at low temperatures avoiding syngas purification and separation steps.