Determination of Nitrogen Content in Crude Oil and Petroleum Products of Isfahan Refinery by Three Techniques of Titration, pH Metric Titration and Nessler and Comparison of Their Results

In this study, the Nitrogen content of crude oil and petroleum products of Isfahan refinery were determined using three methods of pH meter titration, Nessler method, and titration with sulfuric acid. Results were compared in terms of accuracy and precision. In the first method (pH metric titration), samples were digested by concentrated sulfuric acid and distilled by micro-Kjeldahl apparatus and the distillate was titrated using a pH meter. In the second method (Nessler) samples were distilled using the micro-Kjeldahl apparatus and were measured spectrophotometrically utilizing Nessler reagent. The third technique was based on a combination of micro-Kjeldahl distillation by sulphuric acid and direct titration in the presence of methyl red indicator. For a lighter portion of the crude oil, a primary  liquid-liquid extraction step in a separatory funnel by sulphuric acid was performed. Statistical results showed that all three methods have the same accuracy. Analysis time for direct titration is the most time-consuming method, while Nessler was the shortest. However, Nessler is the most complicated technique among others. According to the results obtained by Nessler, the nitrogen content of oil feed was between 1.0 to 1.3 g/.L, while it was at the range of 0.1 to 4300.0 mg/.L in petroleum products which is in the normal global range. Finally, statistical analysis showed that pH metric titration method is a proper technique for such applications with relatively good reproducibility. The Nessler-photometric method is also satisfactory, especially for low nitrogen content samples, but its precision is lower than the former method. Direct titration has the worst precision among three methods.