Sustainable valorization of Stenochlaena palustris residues to bioenergy and green chemicals via pyrolysis: thermal decomposition, kinetic analysis, and product distributions.

Stenochlaena palustris, a species of fern, is commonly found in the wetland regions. Local communities in Southeast Asia typically only process their young leaves for food and medicine, discarding the older leaves and stems, resulting in residues accumulation. For the first time, pyrolysis of these residues was studied to investigate its potency as the source of energy and chemicals. The thermogravimetry data revealed that the decomposition of Stenochlaena palustris residues primarily took place at 213-550 °C, with three distinct decomposition temperature regions: hemicellulose (213-285 °C), cellulose (285-400 °C), and lignin (400-550 °C). The Coats-Redfern method was applied to thermogravimetry data to calculate the kinetic parameters (activation energy, pre-exponential factor, and reaction order). The calculated data of Stenochlaena palustris residues pyrolysis using this kinetic model was in a good agreement with the experimental data from thermogravimetry analysis. Furthermore, the pyrolysis experiment was conducted to investigate the influence of temperature on the product yield and its chemical compounds distribution. As the temperature increased from 500 to 600 °C, the yield of char decreased but the yield of gas increased. While the liquid yield shows slightly increased as the temperature increased from 500 to 550 °C, but continually decreased as further heated up to 600 °C. At 550 °C, the resulted bio-oil had higher relative content of phenolic compounds, hydrocarbons, and lower nitrogen compounds. The combination of kinetics, and pyrolysis properties concluded that Stenochlaena palustris residues potentially becomes a useful source of bioenergy or chemicals through pyrolysis.