A comparative study of the thermal decomposition of apple pulp in the absence and presence of phosphoric acid

Abstract

Apple pulp pyrolysis in the presence of phosphoric acid (chemical activation) represents a promising way for utilisation of this residue from apple juice and cider production. Thermogravimetry and infrared spectroscopy have been used to compare the pyrolysis behaviour of apple pulp, alone and impregnated with 60 wt.% H 3PO 4. Phosphoric acid promotes the degradation of the biopolymers constituting apple pulp, lowering the temperatures necessary for their degradation. At low temperatures, the main chemical transformation is dehydration leading to anhydrocellulose. The chemical structure collapses during cellulose degradation (300–350 °C in absence of phosphoric acid and 155–205 °C in presence of phosphoric acid). At higher temperatures progressive aromatisation and decarboxylation of the char take place. At 500 °C, carbonyl bands are only found in the spectra of chars from apple pulp impregnated with phosphoric acid, indicating that this reagent introduces oxygenated functions (alcohol and/or ether) into the solid pyrolysis residues.