Hydrodesulfurization of straight-run and secondary diesel fuels

Abstract

The degree of desulfurization of diesel cuts is a function of their distillation to a significant degree, since it determines the content and group composition of sulfur compounds.At Novokuibyshevskii OR OJSC, the diesel fuel straight-run cut (DSRC) from AVT units is the basic component of feedstock for hydrotreating units. A high end point t EP -above 370°C -is characteristic of this cut.The most typical DSRC -with a total sulfur content of 0.84 wt. % -was used for the studies. The proportion of residual sulfur in it is 90%. DSRC was distilled with a fractionation tower (50 theoretical plates) into narrow cuts, °C: IBP-180, 180-240, 240-260, and 260-EP. The yield of >260°C cut was approximately 80 wt. % and the yield of the >240°C cut was approximately 90 wt. %. The cut distilling under 240°C contained 0.3 wt. % total sulfur, the 240-260°C cut contained 0.42 wt. %, and the 260-EP cut contained 0.88 wt. % total sulfur, i.e., there was more than 83% sulfur in the >260°C cut. Light catalytic gasoil (LCG) is another component of the hydrotreating feedstock. Its content in the feedstock can attain 4.5-7.3 wt. %. The end point of this component is approximately 25-30°C lower than for the basic component.Distillation of LCG is: 75 wt. % distills at a temperature above 260°C, and 86.6 wt. % distills above 240°C. The total sulfur content in LCG is 1.04 wt. %, i.e., much higher than in DSRC. In the IBP-180, 180-240, 240-260°C and 260°C-EP narrow cuts, it is respectively 0.29, 0.56, 0.65, and 1.20 wt. %.The 260-346°C cut has the highest sulfur content, 86.5%. LCG is characterized by a high iodine number and aromatics content, 28 g I 2 /100 g and 36 wt. %, respectively. Light delayed coking gasoil (LDCG) with almost the same end point as LCG (~350°C) and a higher total (1.51 wt. %) and residual (1.21 wt. % sulfur content) are also used as a component of hydrotreating feedstock. More than 90% of the total sulfur is contained in the 240°C-EP cut . LDCG has the highest iodine number, 71.6 g I 2 /100 g and contains 32 wt. % aromatics. Hydrotreating of DSRC, LCG, LDCG, and their IBP-270°C and 270°C-EP narrow cuts was investigated in laboratory conditions with NKYu-220 aluminum-nickel-molybdenum catalyst developed for this purpose. This catalyst is characterized by high hydrodesulfurizing activity for a relatively low content of active components. In addition, it is distinguished by a high strength index -a minimum of 30 N/mm.