Abstract
A kinetic analysis of non-catalytic pyrolysis (NCP) and catalytic pyrolysis (CP) of polypropylene (PP) with different catalysts was performed using thermogravimetric analysis (TGA) and kinetic models. Three kinds of low-cost natural catalysts were used to maximize the cost-effectiveness of the process: natural zeolite (NZ), bentonite, olivine, and a mesoporous catalyst, Al-MCM-41. The decomposition temperature of PP and apparent activation energy (Ea) were obtained from the TGA results at multiple heating rates, and a model-free kinetic analysis was performed using the Flynn–Wall–Ozawa model. TGA indicated that the maximum decomposition temperature (Tmax) of the PP was shifted from 464 °C to 347 °C with Al-MCM-41 and 348 °C with bentonite, largely due to their strong acidity and large pore size. Although olivine had a large pore size, the Tmax of PP was only shifted to 456 °C, because of its low acidity. The differential TG (DTG) curve of PP over NZ revealed a two-step mechanism. The Tmax of the first peak on the DTG curve of PP with NZ was 376 °C due to the high acidity of NZ. On the other hand, that of the second peak was higher (474 °C) than the non-catalytic reaction. The Ea values at each conversion were also decreased when using the catalysts, except olivine. At <0.5 conversion, the Ea obtained from the CP of PP with NZ was lower than that with the other catalysts: Al-MCM-41, bentonite, and olivine, in that order. The Ea for the CP of PP with NZ increased more rapidly, to 193 kJ/mol at 0.9 conversion, than the other catalysts.
Highlights
Polypropylene (PP) is a well-balanced general-purpose engineering plastic with excellent chemical resistance, high purity, low water absorption, and good electrical insulation properties
This study examined the degradation kinetics of PP, with both non-catalytic pyrolysis (NCP) and CP with the inexpensive catalysts, natural zeolite (NZ), bentonite, and olivine
Al-MCM-41 had the highest acidity among the catalysts, followed in order by NZ and bentonite
Summary
Polypropylene (PP) is a well-balanced general-purpose engineering plastic with excellent chemical resistance, high purity, low water absorption, and good electrical insulation properties. Owing to its good physicochemical properties, PP is used widely as a packaging material for consumer goods, internal cases, and containers for electronic products. Worldwide PP production has increased rapidly in recent decades, and its waste exceeds. Waste PP is difficult to degrade biologically and is converted into microplastics, endangering human health. The sudden increase in mask use during the recent COVID-19 pandemic accelerated the accumulation of PP waste in the environment [2]. PP has a good potential to be converted to valuable energy sources or chemical feedstocks, most of it is disposed of by incineration; more desirable treatments are needed [3]
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