Characterization of carbon deposits on used hydrotreating catalysts by Curie-point pyrolysis

Curie-point pyrolysis is applied to the characterization of the carbonaceous material deposited on used hydrotreating catalysts. Basically, the carbonaceous material can be divided in an extractable and non-extractable fraction. The extractable fraction consists of adsorbed molecules from the feed, mainly alkanes and small aromatic compounds. The non-extractable fraction is subdivided into strongly adsorbed feed molecules, a carbon fraction resistant to pyrolysis at 1043 K and a sulphur-containing fraction. The division between the extractable and non-extractable fraction is dependent on the extraction agent. Dichloromethane appears to produce a larger extractable fraction than benzene or hexane.