Improving kinetic analysis of sequential and parallel reactions of hydrodesulfurization of dibenzothiophenes by establishing reasonable boundaries for reaction rate constants

Hydrodesulfurization (HDS) of dibenzothiophene (DBT), hydrogenation (HYD) o f biphenyl (BP) and 3,3'-dimethylbiphenyl (3,3'-DMBP) and their competitive reactions were carried out over a novel Co-Mo/carbon catalyst. Studies wer e made with a batch stirred micro-autoclave reactor, 100 ml, at temperature s of 300-320 degrees C and 2.9 MPa H-2. The HDS reactions were found to pro ceed via a network of sequential and parallel reactions and a computer mode l was developed which could be used to determine all the individual rate co nstants in the reaction scheme by matching experimental product composition data to theoretical curves as a function of conversion and/or reaction tim e. Unfortunately, with limited data, many different sets of rate constants can provide good matches with the experimental data. In order to obtain a u nique solution for the set of rate constants two boundaries were found nece ssary. One is the relative hydrogenation activity of DBT to that of bipheny l which can be established with separate competitive experiments. The other is to consider the thermodynamic limitations, on the reactions of refracto ry sulfur compounds which proceed via ring hydrogenation. The rates of hydr ogenation of BP and 3,3'-DMBP were found to be much lower than the rates of HDS of DBT. In addition, it was established that there was almost no inhib ition on the HDS of DBT by BP and/or 3,3'-DMBP. (C) 1999 Elsevier Science B .V. All rights reserved.