Petroleum pitches, by-products of oil refining, are interesting materials from which it is possible to obtain useful compounds, like cokes and hydrocarbons. Cokes can be used as starting materials of active carbons, while hydrocarbons have a utilization closely related to their molecular weight and structure. In the present investigation the process of pyrolysis of certain pitches is studied (in different thermal conditions, gaseous atmospheres and catalysts) in order to obtain good quality cokes.The study was carried out by a thermogravimetric apparatus having high sensibility and very fast response time (in order to obtain information in the first instants of the pyrolysis reaction) as well. Gaseous, atmospheres, where the pitch samples were heated, were carbon dioxide, nitrogen and argon (pure or containing small and controlled amounts of oxygen) or hydrogen (pure or mixed with nitrogen). The obtained cokes were accurately classified (by determining their elementary composition) and submitted to surface characterization (by determining BET surface area, meso and macropore distribution, surface oxygenated functional groups, etc.). Surface characteristic are related to type of thermal treatment. Cokes were washed with Hcl and HF boiling aqueous solution in order to minimize their content of metal derivatives (ashes); then they were submitted to certain selective oxidation processes with boiling nitric acid solutions, air (at 350 °C) and N_2 containing small amounts of O_2 (at 800 °C) with the aim to obtain surface oxygenated groups with selective chemical structures.The cokes, thus treated were accurately characterized and submitted to adsorption/desorption processes of several chemical compounds (testing their general sorption capacities and the degradation, in time, of their starting properties). The results were correlated to the type of parent pitch, the thermal treatment used (temperature, heating rate and conditions etc.) and to the composition of the gaseous atmosphere of pyrolysis. Interesting results are obtained by comparing the behaviours of the pitch cokes with the similar ones obtained from ordinary commercial active carbons.
展开▼
