Study on the formation, determination, and removal of elemental sulfur in ultra-low sulfur gas oil

• Oxidation of ammonium polysulfide formed elemental sulfur during the HDS process.
• (NH4)2Sn is formed when oil feed containing nitrogen and sulfur in the HDS process.
• NH4+ contained in the HDS catalyst can result in the formation of (NH4)2Sn.
• Na2S aqueous solution can be used to remove elemental sulfur in hydrotreated oil.

The question as to the formation of elemental sulfur in petroleum has never been definitely settled, although there are many references in the literature to the presence of elemental sulfur in distillates. In connection with studies on sulfur compounds in petroleum distillates, the presence and behavior of elemental sulfur in gas oil, especially in ultra-low sulfur gas oil are important. A rapid and accurate method for the analysis of elemental sulfur by GC–PFPD was developed and a series of experiments was carried out to clarify the formation mechanism of elemental sulfur. The results showed that (NH4)2Sn was found to be easily oxidized to free sulfur when contacted with air and the oxidation of ammonium polysulfide was the main formation mechanism of elemental sulfur in the hydrotreating of gas oil. It was revealed that nitrogen-containing molecules in the oil feed and NH4+ contained in the HDS catalyst can result in the formation of (NH4)2Sn. A method with high efficiency and selectivity to remove elemental sulfur from hydrotreated gas oil by Na2S washing was developed for analysis purpose.