Four commercial Saudi Arabian crude oils were characterized by thermogravimetry (TG) and differential thermal analysis (DTA).
These crude oils, Arab Berri (AB), Arab Light (AL), Arab Medium (AM) and Arab Heavy (AH), were also subjected to the traditionally
employed true boiling point (TBP) distillation and simulated distillation (SIMDIST). The TG/DTA data show that the hydrocarbons
present in these crude oils fall into four groups: the volatiles, the low molecular weight, the medium molecular weight and
the high molecular weight compounds. These four types of hydrocarbons were observed to display certain trends, such that the
volatile and low molecular weight hydrocarbons increased, while the medium and high molecular weight hydrocarbons decreased
with the lightness of the crude. The volatile contents of AB, AL, AM and AH crude oils up to 280�C were 50.1, 42.2, 42.3 and
38.5 mass percent, respectively. This confirms that AB is the lightest of these crude oils with maximum volatile content.
The mass percentage loss from the TG results is in good agreement with the percentage distilled from TBP (ASTM D 2892) and
SIMDIST. During evaporation, the TG mass loss follows a similar trend to those of the TBP and SIMDIST results and thus behaves
like distillation. During the oxidative degradation, the TG curve shows a higher mass loss as compared to the distillation
data. The higher deviation of the TG mass loss and percentage distilled at the higher-temperature end of the curve may be
attributed to the higher content of asphaltenes and carbonaceous material present in AH as compared to the AB crude oil. At
around 200�C, the TG mass loss curve intersects the TBP and SIMDIST curves and shows a derivation from distillation behaviour.
This intersection temperature of the TG and distillation curves is observed to decrease with the heaviness of the crude and
can be an indication of the onset of thermal degradation of hydrocarbons present in the crude oil. On the whole, the TG data
closely resemble the distillation results.