Performance evaluation of HDS catalysts by distribution of sulfur compounds in naphtha

This paper presents results of pilot plant evaluation of two commercial hydrodesulfurization (HDS) catalysts and demonstrates the use of trace sulfur analysis and distribution of sulfur compounds for reliable and better catalyst evaluation. Straight-run naphtha (SRN) and a blend of SRN and hydrocracked naphtha containing 897 and 534 ppm sulfur respectively were analysed for sulfur compound distribution by gas chromatography with flame photometric detection and hydrocarbon type composition by a PONA analyser. G.c.-f.p.d. analysis indicated the presence of 52 sulfur compounds, including mercaptans (55.7%), thiophenes and sulfides (43.1%), disulfides (1.1%) and traces of polysulfides, hydrogen sulfide and elemental sulfur. Pilot plant experiments were carried out with two catalysts at 220-350°C, space velocities of 10 and 13 h^-1 and gas rates of 67 and 8011^-1. Total and mercaptan sulfur in the product passed through a minimum with increasing temperature. The optimum temperature was 320°C for SRN and 300°C for the blend naphtha. Thiophenes, forming a major portion of the sulfur in the product, could be removed by hydrotreating at >280°C. At higher temperatures, methyl mercaptan increased, owing to hydrogen sulfide recombination reactions. One of the catalysts performed better than the other.