Measurement of Cracking Kinetics of Pure Model Compounds by Thermogravimetric Analysis

Abstract

Determination of cracking kinetics by thermogravimetric analysis (TGA) is attractive but requires careful experimental design to ensure consistent results. Here, we examine three methods for determining kinetic parameters by TGA: differential analysis at a constant heating rate (differential), temperature for constant conversion at multiple heating rates (isoconversional), and maximum rate at multiple heating rates (peak temperature). The test compounds used in this study are based on pyrene, with boiling points high enough that mass loss was dominated by the reaction rather than evaporation. The methods using multiple heating rates gave comparable results to each other but were very different from the results from the differential method. The results of the differential method were insensitive to the heating rate and consistent with kinetics of cracking reported in the literature for similar structures. The differential analysis method for cracking of model compounds was the best approach, because the methods of multiple heating rates consumed more sample and were reported in the literature to be very sensitive to minor experimental errors. The conversion in a microreactor experiment was accurately predicted using the kinetics from the differential TGA method, suggesting a consistent reaction rate in these two different reactions. Hence, the differential approach was concluded to be much more accurate when compared to isoconversional and peak temperature methods.

A study of the combustion chemistry of petroleum and bio-fuel oil asphaltenes

“…bond-dissociation energies. This is in agreement with our earlier work but using a different HFO and the low values result from the parallel radical attack and sequential reaction paths and is consistent with other work with model compounds [18].…”

“…The two petroleum asphaltenes have similar mass loss profiles and they have, as shown in experimental results here for the loss of the volatiles follow kinetic rates which are similar to those found in our previous studies [15] and by other research groups [17][18][19] as discussed later.…”

“…Evidence for this comes from, for example, the pyrolysis of n-pentadecylbenzene which gave rise to toluene and alkane/alkenes, and from dodecylbenzene which gave rise to undecene/undecane, toluene and ethylbenzene [24]. These peaks are still seen at 900 o C (Fig 2 a) although they much more prominent at lower temperatures such as 500 o C as previously shown [11,15,18], but by 1000 o C they are not so visible as the aromatic structures decompose (Fig. 2b).…”

Incorporation of steroidal biomarkers into petroleum model compounds

“…Given the incredible diversity of structures present in a natural sample, however, global analyses can be difficult to generalize, because the analytical results may not correlate with the constitution of the bulk sample. We and others have opted for an alternative approach to study asphaltene behavior, particularly with respect to aggregation phenomena. Rather than the top–down approach to analysis, we consider instead a ‘bottom–up’ approach, which is accomplished through the synthesis and study of complex archipelago model compounds of rigorously defined structures.…”

Characterization of Petroleum Residues with Varying Cutting Depth and Corresponding Vacuum Distillates Derived from Laboratory Deep-Vacuum Fractionation of Unconventional Heavy Oil for an Instructive Utilization Guideline

“…All DSC and TGA experiments were performed with the prospection of a pure flowing nitrogen gas for the sophisticated system. As suggested by J. V. Dubrawski 25 and Alshareef et al, 26 the thermal analysis system was heated at a constant rate (15 K/min) to 650 °C for the moderate heat up time and necessarily accurate thermal data.…”