Steam gasification of polyethylene terephthalate (PET) with CaO in a bubbling fluidized bed gasifier for enriching H₂ in syngas with Response Surface Methodology (RSM)

Polyethylene terephthalate (PET) is widely used as packaging and textile materials. Although PET bottles recycling is mature in many countries, steam gasification could be a solution to recover valuable products from end-of-life PET. CaO has been investigated as an absorbent to capture CO₂ and improve H₂ production in gasification but mostly it was analyzed as an individual effect. As the main novelty, this work studied not only the individual effect of temperature, steam/PET ratio and CaO/PET ratio on gas products, tars, and char but also the combined interaction of them on gas yields using response surface methodology in PET steam gasification with CaO. The experimental work was conducted in a bubbling fluidized bed gasifier and mathematical models were fitted with considering all significant terms. The results showed that H₂ yield was doubled at 800 °C but increasing by 44% at 750 °C when the CaO/PET ratio raised from 0 to 2.0. Thus, temperature, CaO, and their interaction had significant effect on H₂ yield, which was also reflected by the P-values calculated from the coefficients of the mathematical models. Tar analysis showed that benzene accounted for 80 wt% in tar products and adding CaO can reduce benzene by 34%. However, CO₂ increased with adding CaO at temperatures of 700 °C – 800 °C implying that CaO mainly functioned as a catalyst instead of an absorbent. The models fitted well in R² and model validations with non-model-fitting points. Therefore, the models can be applied for the prediction of gas product yield in the studied range.