Pertrochemical products derived from crude oil and Fischer-Tropsch (FT) processes contain a
variety of compounds over a wide carbon number range and a large number of fuels and
chemicals are produced during product workup. The characterisation of these fuels and
chemicals as well as intermediate process streams is very important to control conversion
processes. The analysis of any one of these phases is very challenging. Typical oil phase
samples may contain thousands of compounds.
In many cases, complete characterisation of these complex samples is possible with
comprehensive two-dimensional gas chromatography (GC×GC), but even with the increase in
separation power obtained by comprehensive GC, peak co-elution still occurs when complex
samples are analysed. In this work chromatographic techniques were investigated and the
hyphenation of these techniques was evaluated, addressing some of the remaining analytical
challenges in petrochemical analysis.
The on-line hyphenation of supercritical fluid chromatography (SFC) to a GC×GC system as a
pre-separation technique was successfully developed to address the challenge of the
separation between cyclic and non-cyclic alkenes and alkanes. The developed SFC preseparation
method also pre-separated the sample of interest into other chemical groups
(saturates, unsaturates, oxygenates and aromatics) for further characterisation by GC×GC.
On-line hydrogenation after GC×GC separation was successfully developed to address the
challenge of distinguishing between isomeric cyclic and double bond containing compounds
with the same (two or more) double bond equivalents. The number of rings and alkene double
bonds in specific compounds could be determined from the mass spectra of the compounds
before and after hydrogenation in a complex petrochemical sample requiring GC×GC
A high temperature (HT)-GC×GC method was developed to replace titrimetric procedures
traditionally used for the control of oxidation processes of heavy paraffinic fractions. The
advantages of the developed HT-GC×GC method include the selective quantification of oxygenate classes and obtaining the concentration for each oxygenate class by carbon
number. This allows the optimisation of conditions used to oxidise heavy paraffinic fractions.
The challenge of the identification of oxygenates in these oxidised heavy paraffinic fractions
was also addressed with the development of a method that pre-separates the oxygenates
before subsequent analysis by gas chromatography mass spectrometry, with the use of a
supersonic molecular beam (GC-SMB-MS). The EI spectra with enhanced molecular ions
obtained by GC-SMB-MS aided tremendously in the identification of oxygenates and the
advantage of this procedure was illustrated, whereby the heavy oxygenates in an oxidised
heavy paraffinic sample could be better identified.
This study successfully addressed various analytical challenges in the field of petrochemical
analysis and the developed techniques may be useful for the comprehensive characterisation
of various streams in other areas of petrochemical analysis.