Hydrothermal carbonization of dried olive pomace: Energy potential and process performances

Hydrothermal carbonization (HTC) of dried olive pomace (DOP) was performed in subcritical water under HTC conditions (180-250 degrees C) to assess the potential of the generated hydrochar to produce energy. The effects of process parameters (holding time, temperature and DOP/water weight ratio) on the yield and the quality of the hydrochar were examined. The mass yield of hydrochar was between 56% and 71% and its HHV increased by more than 23% compared to the HHV of DOP giving a hydrochar similar to a lignite-type coal. The results reveal that a 30 min treatment at 215 degrees C with a DOP/water weight ratio of 1/6 maximizes the energy yield (83%) of the HTC process. Both the DOP and the hydrochar were characterized by ultimate, proximate and thermogravimetric analyses. The ultimate and thermogravimetric analyses showed that the hydrochar is more carbonaceous and more thermally stable than untreated DOP. The HTC conversion of raw DOP was carried out by dehydration reactions. The proximate analysis showed that hydrochars contained lower ash and volatile matter compared to the raw DOP.