Effect of CaO Additives on PET Steam Gasification in Bubbling Fluidized Bed

The growth of polyethylene terephthalate (PET) consumption for beverage bottles, packaging and textiles and their ineffective recycling procedures globally causes serious environmental problems. Steam gasification could be one possible way to recover materials from end-of-life PET, and CaO could catalyze the hydrogen production. The objective of this research was to study the effect of CaO on PET the gaseous products from steam gasification experimentally. CaO/PET mass ratios 0, 1, 2, 3 and 4 were fed in batch into a bubbling fluidized bed reactor at 750°C. N₂ and steam were employed as fluidization gas and steam to PET mass ratio was 2.5. After the tar and water vapor removal by impinger bottles with isopropanol, the product gas was analyzed by an online syngas analyzer. The results showed that hydrogen yield doubled (from 10.6 mol/kg PET to 21.9 mol/kg) when CaO/PET ratio increased from 0 to 4. CO₂ yield also increased with increasing CaO/PET ratio instead of decreasing because CaCO₃ decomposition is more active at 750 °C. However, at higher CaO/PET ratios, the yield seems to reach a constant level at 15 mol/kg. CO, CH₄ and other non-condensable hydrocarbon gases varied slightly with CaO/PET ratios where only CO rose 2 mol/kg PET comparing with no CaO addition. The batch feeding, 1g/min PET and corresponding ratio CaO, is reflected by the instantly measured periodical peaks of product compositions. Similar amplitudes in each product indicate a relatively stable gasification process. Moreover, in each period, H₂ and CO₂ have opposite trends as CH₄ and CO which could be due to the water-gas shift reaction. The results could be applied for hydrogen production from end-life PET steam gasification.