Thermal analysis of olive tree pruning and the by-products obtained by its gasification and pyrolysis: The effect of some heavy metals on their devolatilization behavior

Abstract

Abstract In this work, the effect of the presence of nickel and lead in thermal decomposition of olive tree pruning (OTP), OTP-char and OTP-ashes was studied by thermogravimetry. Experiments were conducted in two kinds of atmosphere (nitrogen atmosphere and oxidizing atmosphere with 20% of O2) at a heating rate of 10 °C/min. This investigation describes the chemical, physical and fuel properties of the OTP, which shows a similar composition to other lignocellulosic materials such as hazelnut husk and wood sawdust. In addition, SEM analysis indicated that OTP-char surface is higher than OTP surface with plenty of holes and channels. It makes the char an ideal support for metal retention specially for Pb metal (OTP retained 8.55 mg/g whereas OTP char retained 11.57 mg/g). On the other hand, metal retention occurred by adsorption or ion exchange, according to the IR spectrum of the samples. The results of thermogravimetric tests proved that the presence of lead did not have a strong effect on the decomposition of the samples, since TG and DTG curves were very similar. However, nickel increased the mass loss rate, accelerating the decomposition process, showing higher peaks in DTG curves. Additionally, for temperatures higher than 360 °C, the volatilization of the samples was improved in the nickel-polluted sample, achieving a higher mass loss, getting more energy from the biomass and reducing the quantity of residues left after the process.