Comparative kinetic study of the pyrolysis of mandarin and pineapple peel

• The activation energies for the pyrolysis of the mandarin and pineapple peel were estimated.
• Analysis of pyrolysis oils was achieved via GC/MS and IR spectroscopy.
• The fact that the activation energy value decreased rapidly for both biomasses between 350 and 460 °C confirms mechanisms of radical reactions.
• Average degrees of unsaturation for oils prepared at 460 and 600 °C were obtained. Comparisons were carried out.

This study focuses on the pyrolysis processes of fruit peels as energy sources. These pyrolysis processes for mandarin and pineapple peels were analyzed by profiles of conversion vs. temperature and DTG curves. Five kinetic stages were observed, each with a different activation energy calculated by utilizing the Coats and Redfern method and assuming a first order model. The mandarin peel process showed a higher activation energy during the first and second stages of the pyrolysis. Consequently, mandarin peel was selected over pineapple peel for further studies. Other models such as diffusion and nucleation also fitted the data and as a result, the nonlinear integral isoconversional method was implemented to get more accurate activation energies. In the range of 350 and 460 °C, there was a rapid decrease in activation energy that was attributed to the radical recombination as the dominant mechanism. Experiments of pyrolysis with the mandarin peel were carried out in the pyrolytic reactor to verify these findings. The pyrolysis oils obtained at 460 and 600 °C were analyzed by GC–MS and FTIR Spectroscopy. The results showed that the pyrolysis oil obtained at 460 °C had a higher average degree of unsaturation. Once the pyrolysis went through temperatures higher than 460 °C, the average degree of unsaturation decreased. Although the oil obtained at 460 °C showed a higher average degree of unsaturation, it was not enough to show a substantially higher calorific value than the oil obtained at 600 °C. The significant difference in the calorific values could be potentially observed in the biochars obtained at the temperatures already mentioned.