AbstractThe accurate and reliable analysis of crude oil, weathered oil and oil-spill related environmental samples is extremely important in view of the distribution of oil pollution in the environmental. In this work the fractionation selectivity of column chromatography, extrography and supercritical fluid extraction was compared.
Column chromatography with a silica gel as stationary phase provided a means of fractionating a standard mixture of saturated and aromatic hydrocarbons and crude oils such that the aromatic profile could be determined by GC-MS. The recoveries of saturated, aromatic and polar compounds from crude oil are in the range of 60.6-70.3 %, 12.9-19.8 % and 7.1-9.4 % respectively, with relative standard deviations under 6 %.
The potential of extrography on silica gel as a fractionation technique of crude oil has been evaluated in terms of reproducibility and selectivity of separation. The recoveries of saturated, aromatic and polar compounds from crude oil are in the range of 59.3-72.0, 13.6-21.0 and 7.5-10.5 % respectively, with relative standard deviations under 6 %. The overlapping effects between the adjacent fractions were evaluated using GC-MS. It was found that extrographic fractionation produced a better separation than the column chromatographic technique.
The supercritical fluid extraction parameters determined in this study using spiked samples have shown to be effective starting conditions for fractionation of crude oil samples. These studies have shown that under optimized SFE conditions (density 0.75 g.cm"3 and temperature 40 °C ) crude oil can be selectively fractionated into saturated and aromatic compounds.
Comparatively, it was found that SFE provided an effective extraction within 56 minutes while the chromatography and extrography methods required 8-10 and 4-6 hours respectively. The total recovery of crude oils for column chromatography, extrography and SFE are in the range of 83.4-90.5 %, 89.4-95.9 % and 77.7-99.9 % respectively. The capability of SFE to fractionate mixtures containing homologous compounds with narrow molecular weight ranges has shown to be more effective than can be achieved with column chromatography and extrographic techniques.
Studies into the SFE of spiked aqueous matrices performed utilizing a liquid extraction cell showed that crude oil could be fractionated into saturated and aromatic compounds under the optimized conditions of pressure * 3000 Psi and 40 °C with a 15 minute extraction time and 2 cm" 3 min" 1 flow rate.
|Date of Award||Oct 1997|
|Supervisor||A. J. Berry (Supervisor)|