Thermal decomposition of low-density polyethylene (LDPE) was monitored by thermogravimetry under N2 atmosphere in the presence of solid acid catalysts such as alumina (α-Al2O3, γ-Al2O3), crystalline silica-alumina (SA, molar ratio of Si/Al = 0.19) and amorphous silica-alumina catalysts (ASA, molar ratio of Si/Al = 4.9). Crystal structure and surface area of solid acid catalysts were measured by XRD and BET, respectively. The strength and distribution of acid sites of solid acid catalysts were estimated by NH3- TPD. It was observed that total acidity strength is in the order of ASA (1.77 μmmol NH3/ g) > AS (1.42 μmol NH3/ g) > γ-Al2O3 (1.06 μmol NH3/ g) > α-Al2O3 (0.06 μmol NH3/ g). Thermal degradation behavior of LDPE with and without solid acid catalyst was monitored by TGA, where heating rates (β) of 5, 10, and 20 °C/min were employed under an inert atmosphere, and their activation energies ( Ea), onset temperatures ( Tinitial), decomposition temperatures ( Tdecomp) were calculated and compared. The activation energy ( Ea) was evaluated using the Coats-Redfern method. Solid acid catalysts with stronger acidity and higher surface area showed a decrease in activation energy and onset temperature. Activation energy of LDPE over ASA catalyst is decreased to 97.3 kJ/mol from thermal decomposition of LDPE without catalyst of 117.2 kJ/mol under heating rate of 10 °C/min. The isothermal decomposition of LDPE was monitored at 300 °C for 3 h with a heating rate of 10 °C/min, where 13.1% and 24.2% wt. loss were observed over SA and ASA, respectively, while only 0.7% wt. loss was observed for LDPE without a solid acid catalyst.

Effect of acidity of solid acid catalysts during non-oxidative thermal decomposition of LDPE
    Abstract
        Graphical abstract
    1 Introduction
    2 Experimental
        2.1 Materials
        2.2 Catalyst characterization
        2.3 Thermogravimetric analysis
    3 Results and discussion
        3.1 Catalyst characterization
        3.2 Kinetic parameter calculation by TGA​
    4 Conclusion
    Acknowledgements 
    References

• Dipali P. Upare(Korea Institute of Energy Technology (KENTECH), Environmental and Climate Technology, Naju 58330, Republic of Korea)
• Chul Wee Lee(Korea Institute of Energy Technology (KENTECH), Environmental and Climate Technology, Naju 58330, Republic of Korea)
• Don Keun Lee(Korea Institute of Energy Technology (KENTECH), Environmental and Climate Technology, Naju 58330, Republic of Korea)
• Young Soo Kang(Korea Institute of Energy Technology (KENTECH), Environmental and Climate Technology, Naju 58330, Republic of Korea) Corresponding author