Pyrolysis of solid residues commencing from the olive oil food industry for potential hydrogen production

Exhausted olive oil husks derived from the olive oil extraction process were pyrolyzed in a nitrogen atmosphere. The experiments were performed in a continuous feed reactor at pressure slightly above atmospheric (103–104 kPa). The aim of this work was to convert the biomass pyrolysis gas into hydrogen by non-catalytic experiments and/or catalytic elimination of volatiles and tar in the presence of calcined dolomite to enhance the yield of hydrogen. The pyrolyzer was operated at 975 K during all runs, while the cracking temperature was varied between 973 and 1175 K. The particle size (dp) class of the exhausted olive oil husks varied between 0.5 and 1.0 mm with a biomass formula of CH1.97O0.73. The parameters studied were the temperature, space time, steam and catalysts (calcined dolomites) on gas composition and potential hydrogen production. Tar elimination was studied in presence of two calcined Swedish (Stråbruken AB and Närke-Ernströms Mineral AB) dolomites (OCa·OMg). The collection of liquid/tar phase, charcoal and the gas product obtained under steady-state conditions were examined. The results showed that an increase of the temperature in non-catalytic runs diminishes the total tar content. A first-order kinetic model was used to correlate the evolution of the major gaseous products and total volatiles. Thermochemical treatment of the exhausted olive oil husks produced relatively low yield of H2 (0.24–0.30 mol/kg dry exhausted olive husks). The overall effect of the calcined dolomite is to increase the hydrogen yield (0.90–1.20 mol/kg dry exhausted olive husks) by decreasing the tar yield.