A model integrates sections of an FCC naphtha post-treater for evaluating plant operating conditions to maximise octane-barrel at varying levels of desulphurisation

摘要

Fluid catalytic cracking(FCC)naphtha remains one of the largest contributors by volume to the gasoline pool(30-40%).Since Tier 3 regulations impose a maximum sulphur limit of 10 ppm in the final gasoline product,and more than 90% of the sulphur in gasoline comes from FCC naphtha,process technologists have improved catalyst formulations and process configurations over the years to produce low sulphur cracked naphtha while minimising the loss of octane due to olefin saturation.Feeding FCC naphtha to a conventional hydrotreater may reduce sulphur to acceptable levels,but it would also result in excessive olefin saturation,which is detrimental for the cracked naphtha octane-barrel.The good news is that olefin and sulphur concentrations are not distributed uniformly along the boiling range of an FCC naphtha.The lighter portion has a higher concentration of olefins and lower sulphur content in the form of mercaptans,compared to the heavier fraction,which has a lower olefin concentration and higher sulphur,mostly thiophenic refractory type species.FCC naphtha post-treating technologies take advantage of this uneven molecular spread to separate the full boiling range naphtha(FBRN)into two or three fractions with different treatment options.