Modeling Fixed-bed Multicomponent Adsorption as a step to achieve Ultra-Low Sulfur Diesel

The elimination by selective adsorption of nitrogen-heterocyclic compounds (NHC) in diesel may be considered as a strategic step prior to hydrodesulphurization (HDS), to achieve ultra-low sulfur diesel (ULSD). NHC compete favorably with sulfurheterocyclic molecules (SHC) for sites in CoMo/Al2O3 and NiMo/Al2O catalysts at typical HDS operating conditions. It is also known that NHC and SHC adsorb favorably on various solids supports at mild conditions. These encourage the design of a process for the adsorption of both NHC and SHC contained in diesel prior to HDS to achieve ULSD. To this goal, a detailed process model has been developed for the simulation of the transient non-isothermal operation of a pilot-scale fixed-bed for the continuous adsorption and desorption stages treating a diesel with 500 ppm of a mixture of NHC and SHC. Model simulations of a continuous three-stage adsorption-desorption operation shows that the process can be successful, if an adequate combination of adsorbent, solvent and temperature is found, and best performance is achieved when using small microporous particles with large pore diameters.