Simple Model for Predicting the Cutting Temperature between Light and Heavy Fractions in Fluid Catalytic Cracking Naphtha Selective Hydrodesulfurization Processes

摘要

In selective hydrodesulfurization processes for hydro-upgrading fluid catalytic cracking (FCC) naphtha with high olefin and sulfur contents, it is a common practice to split the feeding full-range FCC naphtha into a light fraction and a heavy fraction. This operation can effectively alleviate olefin saturation and thereby octane loss. Thus, the determination of a suitable cutting temperature plays a vital role in guaranteeing the success of the operation. Starting by fractionating two FCC naphthas into nine narrow cuts, this paper shows that, despite the great differences in the properties of the two FCC naphthas, both hydrocarbons and sulfides have almost the same distributions in the nine cuts. More importantly, it was observed that the distribution of sulfides in the narrow cuts is irrelevant to their true boiling points because of the formation of azeotropes between sulfides and hydrocarbons. On the basis of these findings, a simple model for estimating thiophene content in light FCC naphtha and, thereby, determining the cutting temperature was deduced and its applicability was verified using three other FCC naphthas sampled from different refineries. The salient feature of the model lies in that it only uses the total thiophene content of the feeding FCC naphtha to perform the estimation without the necessity to carry out time-consuming and cost-expensive pre-hydrogenation and fractionation tests. Thus, it can provide in-prior estimation for the design and operation optimization of FCC naphtha hydro-upgrading processes.