Evaluation of olive stone for syngas production -integrated with CO2 capture by waste materials- and for amelioration of agricultural soil

Abstract

A building waste material and an agro-industrial waste were investigated as CO₂ sorbents during the steam gasification of olive stone. Using a fixed-bed setup connected to a differential thermogravimetric–mass spectrometry system made it possible to determine key features, including the composition and energy content of the generated gas, as well as the yields of syngas and hydrogen. As an alternative application of the biochar, the possibility for soil amendment was examined by carrying out column leaching experiments. Upon steam gasification of the char, the building waste sorbent captured up to 94.1% of CO₂ emissions, whereas the olive stone ash sorbent captured up to 91.4% of CO₂. The building waste presented a higher overall performance, raising the mole fraction of H₂ to 73.3% at a Ca/C=2, the H₂/CO ratio to 3.35, the higher heating value of the generated gas to 13.4 MJ/m³, and the syngas yield to 1.74 m³/kg. Upon biochar leaching through the soil, the release of nitrates was quite low, whereas that of phosphates was considerable. Nutrient elements K, Na, and Mg were extracted in higher amounts from the biochar. The leachability of heavy metals was very low. Overall, the steam gasification of olive stone, integrated with CO₂ capture by waste materials, was very beneficial. An alternative application of biochar to the soil could improve the amendment when mixed with composts.