Formation of oxygen structures by ozonation of carbonaceous materials prepared from cherry stones: II. Kinetic study Original Research Article

In this second part, the kinetics of the ozonation process of a char prepared from cherry stones (CS) is investigated. The char was obtained by heat treatment of CS at 600°C for 2 h in nitrogen. The effects of reaction time, partial pressure of ozone, and mass transport phenomena on the formation of oxygen complexes are studied. The surface chemistry of the samples was examined by FT-IR spectroscopy and the elemental chemical analysis was also determined for some samples. Results showed that the ozonation of the char led to oxygen chemisorption and to carbon gasification. The amount of oxygen complexes formed in the chemisorption stage (i.e., OH groups, CO structures, and ether structures) was found to be very sensitive to the increase in the ozonation time. The type of oxygen complexes was also time dependent. Ozonated products with relatively high concentrations of CO groups and ether structures were prepared by applying high ozone doses, whereas the formation of OH groups was favored at low ozone contents. The particle size did not influence the surface chemistry of the ozonated products. Only when the gas flow rate was lower than 40 l h−1, restrictions to ozone mass transport developed. For kinetics of the char ozonation process, a mechanism based on the Langmuir–Hinselwood adsorption–desorption model was proposed, and the intrinsic reaction rates were calculated as a function of ozonation temperature. The activation energy for the ozonation stage of the char was equal to 41.6 kJ mol−1.