Pyrolysis kinetics and physicochemical characteristics of skin, husk, and shell from green coconut wastes

The green coconut (Cocus nucifera) is widely consumed in the world; however, its processing generates a large amount of waste, which presents a high energetic potential. The coconut waste is composed of skin, husk, and shell, where each part can be showing different physicochemical and thermal characteristics. Thus, this study presents the physicochemical and thermal characteristics of skin, husk, and shell of green coconut waste. The physicochemical behavior was evaluated by proximate analysis and ultimate analysis, while the thermal behavior was evaluated by thermogravimetric analysis under five different heating rates (5, 10, 15, 20, and 30 °C min⁻¹). In addition, from the thermogravimetric data was evaluated the activation energy (E_a) by using Friedman and Ozawa–Flynn–Wall (OFW) methods. The physicochemical and thermal characteristics presented by each part of the coconut indicate that the material can be used completely due to the great similarity between the heating value of each part of the coconut (HHV_skin = 18.98 MJ kg⁻¹, HHV_husk = 18.15 MJ kg⁻¹, and HHV_shell = 18.64 MJ kg⁻¹), although they different contents of moisture and ash. A different thermal behavior of each part of the coconut was also observed, being associated with the possibility of different components in its structures, which directly influences the E_a value. Based on the E_a values, the husk shows a better applicability for pyrolysis process, due to lower energy required per mol of biomass.