ELECTROCHEMICAL DETERMINATION OF TRACE SULFUR COMPOUNDS IN PETROLEUM PRODUCTS

Sulfur level in petroleum products is of great concern all over the world as it is accounted for problems in storage, processing, transportation and, most importantly, environmental pollution. In recent years, allowable sulfur levels in many petroleum products such as transportation fuels have been drastically lowered by national regulations to combat air pollution. Thus, an ability to determine the trace level of sulfur compounds is necessary.

This research describes a trace-level sulfur determination in petroleum products using electrochemical technique where bismuth electrode was for the first time introduced as a working electrode, aiming to be as an alternative electrode for a classic mercury electrode. Diphenyldisulfide and butanethiol were chosen as model analytes in this study. The diphenyldisulfide represents sulfur compounds at nanomolar level (4 ppb) while butanethiol represents sulfur compounds at a concentration of 3 orders of magnitude higher. Simultaneous measurements of both levels were beautifully achieved in a single scan. Effects of bismuth concentration and electrolyte including deposition potential and time on the measured signals will be demonstrated. Under optimal conditions, dynamic linearity ranges of both compounds were obtained. The detection limits of diphenyldisulfide and butanethiol were 12.9 nM and 1.4 µM, respectively. This method was applied for sulfur determination in kerosene and jet fuel used in Thailand. The results indicated that kerosene contained 89.8±0.1 nM diphenyldisulfide and 4.9±0.3 µM butanethiol while jet fuel contained 249.7±0.1 nM diphenyldisulfide and 10.9±0.3 µM butanethiol. The proposed method demonstrates that bismuth electrode could be used as a mercury electrode replacement in petroleum medium and trace-level sulfur determination is possible on this electrode.