Thermal behaviour of impregnated olive stones with phosphoric acid via TGA-MS

Abstract

This study aims to investigate the thermal behaviour of raw and phosphoric acid impregnated olive stones via coupled thermogravimetric analysis-Mass spectrometry (TGA-MS) during pyrolysis. The impregnated material was prepared at three H$_{3}$PO$_{4}$/precursor weight ratio of 0.5; 1 and 1.5; for various impregnation time of 3, 6 and 9 h, which was then subjected for thermal analysis. TGA profiles were obtained under dynamic conditions in temperature range 25 °C to 750 °C with a heating rate of 10 °C/min, using pure nitrogen as an inert gas. Thermal degradation of olive stones was observed in three stages namely dehydration, active and passive pyrolysis. Two-steps degradation of raw olive stone occurred, whereas the impregnated material displayed only one step. Addition of phosphoric acid sharply reduced the onset temperature of the main decomposition step. Onset temperatures decreased with increasing rate or time of impregnation. It could conclude that 3 h is sufficient as time of impregnation for activated carbon production. Examination of the main gas products were carried out using coupled TGA-MS. The principal permanent gases detected were H$_{2}$, H$_{2}$O, CO, CO$_{2}$ and the light hydrocarbons C$_{2}$H$_{6}$ and CH$_{4}$. Different kinetic scenarios of raw and impregnated olive stones were observed. The above results should be useful to understand the pyrolysis mechanism of phosphoric acid impregnated olive stone for improving activated carbon production.

Keywords

• TGA-MS
• Olive stone
• Impregnation ratio
• Chemical treatment
• Activated carbon