The study of the weathering of diesel fuel samples by Gas Chromatography
Nowadays fossil fuels including crude oil and its’ derivatives provide most part of the power supply worldwide. Therefore these petrochemical products are frequently discovered as contaminants in the environment. In order to determine the liability related to a hydrocarbon contamination and to determine the degree of the required remediation chemical fingerprinting methods are applied. The key factor to successfully apply chemical fingerprinting is to master the insight of how the weathering processes affect the chemical composition of the pollutants....During my work I started to study the weathering processes which have a short term effect, namely evaporation and dissolution. I studied the possibilities in the experimental design of modelling diesel oil – distilled water systems. The significance of my work is confirmed by the fact that no standardized method is available for these model experiments.
To successfully model evaporation it is crucial to ensure that from the diesel oil – distilled water system only the diesel oil can evaporate. In the case of modelling dissolution the key factor is the application of a gas-tight system. The first goal of my work was to find the parameter set (both in magnetic stirring and shaking experiments) which satisfies the previously stated principles. The criteria of dissolution experiments can be easily achieved thus the detailed examination was not necessary. Thus the first experiments was designed to investigate the influence of shaking and magnetic stirring at different evaporation temperatures. It was proved soon that these conditions have asignificant effect on the criteria of modelling evaporation. The further experiments was carried out with the parameter set which was found to be suitable to compare the two different designs, the magnetic stirring and the shaking. The comparison was based on the effect of the different designs on the mass loss and the composition of the compound classes relevant in chemical fingerprinting. The composition of these compound classes in the weathered diesel oils (the samples obtained with the optimized model experiments) was measured with GC-MS. The distribution of individual compounds in the compound classes was studied. The change in the composition of compound classeswas monitored during the model experiments. We assessed the compositions as normalized percentagedistributions of individual compounds in the corresponding compound class.
Based on both the GC-MS measurements and the mass loss data the importance of the properexperimental design was proved. In the case of dissolution only magnetic stirring provided significant differences in the solubility of different compound classes. On the other hand the examination of the diesel oil – distilled water evaporation system can be carried out only with a shaking machine, because this design excludes the influence of dissolution.
Author: Kristóf Szilágyi, Chemistry MSc student