A theory of ultradeep hydrodesulfurization of diesel in stacked‐bed reactors

Abstract

in Wiley Online Library (wileyonlinelibrary.com)Hydrodesulfurization catalysts have two types of active sites for hydrogenation and hydrogenolysis reactions. While hydrogenation sites are more active for desulfurizing refractory sulfur species, they are more susceptible to organonitrogen inhibition than hydrogenolysis sites. In contrast, hydrogenolysis sites are more resistant to organonitrogen inhibition but are less active for desulfurizing refractory sulfur species. This dichotomy is exploited to develop an ultradeep hydrodesulfurization stacked-bed reactor comprising two catalysts of different characteristics. The performance of such a catalyst system can be superior or inferior to that of either catalyst alone. A mathematical model is constructed to predict the optimum stacking configuration for maximum synergies between the two catalysts. The best configuration provides the precise environment for the catalysts to reach their full potentials, resulting in the smallest reactor and minimum hydrogen consumption. Model predictions are consistent with experimental results. A selectivity-activity diagram is developed for guiding the development of stacked-bed catalyst systems.Bottom curve: reference catalyst followed by new catalyst configuration; middle curve: mixed-bed; top curve: new catalyst followed by reference catalyst configuration.

Kinetics toward mechanism and real operation for ultra‐deep hydrodesulfurization and hydrodenitrogenation of diesel

“…Dibenzothiophene (DBT) and dibenzothiophenes (C1–C2‐DBT) with two alkyl substituents at neither 4‐ nor 6‐ position make up the lump S 2 , where predominant HDS reaction pathway is the direct desulfurization, a pathway resistant to the organonitrogen inhibition when the concentration of organonitrogen species is below 500 ppm 34‐36 . So similar to the lump S 1 , UHDS of S 2 still follows the first order rate equation, where the rate constant is modified by using Equation ) and to get Equation ). …”

Catalyst Stacking Technology as a Viable Solution to Ultralow Sulfur Diesel Production

“…Further reduction of the final content of sulfur from 300 ppm to 10 ppm requires an ultradeep HDS of 99.9%. However, this apparently small 2.9% difference in HDS would greatly affect overall production costs because it is constituted by the most refractory sulfur compounds, and the reactor volume is very sensitive when targeting high HDS conversion to reach ultralow sulfur levels . First, operating conditions must be toughened, i.e., increasing the reactor temperature and hydrogen partial pressure and lowering LHSV.…”

Deactivation of hydrodesulfurization catalysts during reactor startup

“…Commercially, bulk and supported catalysts have been used together in a custom‐designed stacked‐bed reactor for maximum synergies between the two catalysts . The key to the design of the stacked‐bed reactor is to strike a delicate balance between two conflicting catalytic functions: high hydrogenation function and high resilience to organonitrogen inhibition and poisoning . The resulting stacked‐bed catalyst system is more active than either catalyst alone, thus achieving significant savings in capital expenditures and hydrogen consumption .…”

“…The key to the design of the stacked‐bed reactor is to strike a delicate balance between two conflicting catalytic functions: high hydrogenation function and high resilience to organonitrogen inhibition and poisoning . The resulting stacked‐bed catalyst system is more active than either catalyst alone, thus achieving significant savings in capital expenditures and hydrogen consumption . As alluded to earlier, HDS catalytic process needs to be continuously improved to remove as much sulfur as possible over a catalyst cycle.…”