Utilization of PET (waste) via hydrothermal co–gasification with sorghum for hydrogen rich gas production

Abstract

In this study, the applicability of hydrothermal biomass co–gasification for utilizing polyethylene terephthalate (PET) based waste was investigated. For this purpose, hydrogen rich gas production was realised by hydrothermal co–gasification of sorghum biomass with virgin and waste PET mixtures at 500 °C, and the gasification performances were compared. The feedstock/water ratio (%, w/v) was significantly effective on the gasification process in terms of gas yields, gas, and liquid product distributions. Synergistic effects were observed in hydrogen formation in co–gasification of PET and sorghum. The amount of hydrogen obtained from the co–gasification of PET and sorghum was 4.0 mol H2/kg feed higher than the sum of total amount of hydrogen obtained from the individual gasification of PET and sorghum. GC/MS analysis showed that liquid contents were also affected from experimental conditions. The use of catalysts increased the gasification and carbon conversion yields regardless of the type. Although KOH was the most effective single catalyst on hydrogen yield, the catalyst combinations were more effective with promoted activities in terms of hydrogen yields and CO2 capture. Hydrogen yield, which was 12.9 mol H2/kg feed without catalyst, increased to 31.0 (±0.9) mol H2/kg in the presence of K2CO3/CaO catalyst combination for virgin PET/sorghum mixtures and 28.1 (±0.3) mol for PET waste plastics/sorghum mixtures. For the PET waste plastics/sorghum mixtures with the binary catalyst combinations (K2CO3/CaO and KOH/CaO), the CO2 mole fractions of the product gas mixtures were below 1% and the hydrogen contents of the obtained gas mixtures were above 90%. The results of the study show that pet–based plastic wastes can be effectively utilized to produce hydrogen rich gas, by co–gasification with biomass.