Pyrolysis of macroalgae biomass from Nitella hyalina and its thermokinetics

Abstract

In the context of the developing circular economy, algae biomass emerges as a promising and renewable source of bioenergy. Algae play a vital role in our marine environment and hold great potential for the production of biomaterials and bioenergy. This study explores the bioenergy potential of macroalgae Nitella hyalina through thermogravimetric analysis (TGA), utilizing slow heating rates of 5, 10, and 20 °C min⁻¹, ranging from room temperature to 800 °C. The pyrolysis of biomass can be divided into four distinct zones based on molecular transformation. To comprehensively examine the kinetics and mechanisms of thermal decomposition, a stepwise approach based on master plots and iso-conversional methodologies was employed. The TGA/DTG analysis revealed three distinct pyrolysis peaks, with the highest pyrolysis rates occurring at temperatures between 230–250 and 650–735 °C. The activation energy, computed using iso-conversional methods, ranged from 172.80 to 362.13 kJ mol^–1. Thermodynamic investigations of the Nitella biomass indicated an enthalpy in the range of 186.93 ± 0.16 to 363.29 ± 0.34 kJ mol^–1, and Gibbs free energy values ranging from 145.84 ± 1.57 to 278.18 ± 3.86 kJ mol⁻¹. These values indicated a suitable bioenergy production from biomass valorization of macroalgae biomass. Additionally, the change in entropy (∆S) values fell within the range of − 51.34 ± 0.39 to 93.85 ± 0.38 J.mol⁻¹ K^-1, showing a positive disorder of the decomposed molecules. This study demonstrates that macroalgae biomass holds significant potential as a sustainable source for bioenergy production.