Profiling Alkyl Phosphates in Petroleum Samples by Comprehensive Two-dimensional Gas Chromatography with Nitrogen-phosphorus Detection (GC×GC-NPD)

The profiling of alkyl phosphates in petroleum samples is of particular interest to refineries that process conventional crude oil derived from the Western Canadian Sedimentary Basin and other similar geologies. This is due to alkyl phosphate-based additives used during crude oil recovery processes and the subsequent contamination of the produced oil. Phosphate contamination causes numerous problems for refineries, including equipment fouling, the poisoning of catalysts, and potential impacts on downstream processes or consumers if these phosphates enter petroleum product streams. These issues have occurred at a number of facilities across Canada with the impacts measured in the tens of millions of dollars. In response, the Canadian Association of Petroleum Producers and the Canadian Crude Quality Technical Association have specified a limit of 0.5 μg/mL total distillable phosphorus in feedstock. This limit is monitored using inductively coupled plasma – optical emission spectroscopy (ICP-OES), a technique plagued with poor precision and a high limit of detection (0.5 ± 1 µg phosphorus/mL), thus making the current specification difficult to enforce. Furthermore, this method cannot provide speciation information, which is critical for developing an understanding of the challenge of alkyl phosphates at a molecular level. This thesis approaches these challenges using comprehensive two-dimensional gas chromatography with post-column Deans switching to allow for effluent flow switching between a flame ionization detector and a nitrogen-phosphorus detector (GC×GC-FID/NPD). Using trimethylsilyl derivatization, splitless injection, and concurrent backflushing, the GC×GC-FID/NPD method developed and optimized herein, represents the only analytical technique currently capable of: 1) separating the alkyl phosphates from each other and from the crude oil matrix; and 2) speciating and quantifying the phosphates reproducibly in petroleum samples at trace levels (levels two to three orders of magnitude below those achievable by ICP-OES). Overall, this work presents a significant step towards a routine, robust method for profiling trace alkyl phosphates in industrial petroleum and process samples in a production environment. In addition, this thesis presents preliminary results from the first-ever detailed study of alkyl phosphate contamination in a refining environment. The final results of this study will hopefully provide the chemical information needed to contemplate future mitigation strategies for handling the “phosphate problem”. This will be important to refineries across Canada that struggle with issues of equipment fouling. A mitigation strategy would be, quite literally, a multimillion-dollar idea for the Canadian petroleum industry.

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