Development of a sulfur determination for petroleum by high temperature-coulometric Method

Abstract

An automatic apparatus has been developed for the rapid and accurate determination of the amount of sulfur in petroleum. In order to obtain accurate results of the sulfur contents, it is essential to burn petroleum sample smoothly without spattering or smoking. This is accomplished by modifying a sulfur analyser for iron and steel, which is based on high-temperature combustion by high frequency (H. F.) induction heating combined with coulometric titration. The characteristics of the analyser are (a) all the gaseous sulfur formed by combustion is carried into the absorption solution without condensing on the wall of the tubing; this is ensured by the use of a special flushing device and of an automatic recirculation and by special technique of heating the tube and (b) the programmed combustion of the sample enabling the smooth burning.
(1) The best conditions for placing sample in crucible are discussed. The sample is placed in a small cup (oil sampler) and after weighing, the cup with the sample is placed in a crucible and covered with a layer of Al₂O₃ and then a layer of iron powder.
(2) A programme control function is added to the H. F. power supply. At the beginning of the combustion, the heating power is set to a low value so that the burning take place at a low temperature. The heating power is then increased gradually until maximum power is reached and maintained.
(3) The shape of the combustion tube is modified. Instead of using the conventional straight type combustion tube with constricted end, a special combustion chamber with a spiral tube is used. This increases the path in the heated zone, ensuring the complete buring of the fine mist of the sample which escapes from the crucible on combustion.
With this apparatus the determination can be made automatically with high precision in 815 minutes.The repeatability for the residual fuel oil (mass fraction of sulfur =2.5% S) was 0.85% as coefficient of variation. The values of sulfur contents in petroleum obtained by this method agreed well with those obtained by the standard method.