Low temperature oxidative asphaltenes liquefaction for petrochemicals: fact or fiction?
Asphaltene is the heavy and heteroatom rich fraction of petroleum that is rejected during a solvent deasphalting process. In patent literature there are claims that state that this material can be converted into an aromatic petrochemical feedstock by oxidative liquefaction at low temperature. To evaluate the validity of these claims, asphaltenes from an industrial solvent deasphalting process were oxidized with dry and water saturated air at temperatures in the range 45 100 degC. Infrared spectroscopy of the oxidized product confirmed that oxygen was incorporated as C=O and C O. Under all experimental conditions studied little oxidative degradation was observed that would lead to the production of a petrochemical feedstock. Nevertheless, some observations of scientific value were made about the low temperature conversion of asphaltenes. During autoxidation with dry air, the n pentane insoluble fraction increased. On the contrary, when oxidation was conducted with water saturated air, the formation of additional n pentane insoluble material was suppressed. Mild heating of asphaltenes under nitrogen atmosphere also caused the n pentane insoluble content to increase. Spectroscopic evidence showed that esters are formed during oxidation at ~100 degC. The temperature dependence of this reaction was explained and a possible reaction pathway for cycloalkane to ester conversion was presented. Ester selectivity was determined by the competition between hydrogen abstraction and b scission of the alkoxy radical.
Applied Petrochemical Research