Simultaneous catalytic hydroprocessing of chlorine-, nitrogen-, and sulphur-containing aromatic compounds

With the aim of assessing catalytic hydrogenation as a promising method for the disposal of hazardous organic waste liquids, an experimental investigation on the simultaneous hydroprocessing of chlorine-, sulphur- and nitrogen-containing chemicals over a Ni-Mo/gamma-Al2O3 sulphided catalyst is presented. The model compounds chlorobenzene (CB), quinoline (Q) and benzothiophene (BT) were hydroprocessed one at a time or in admixture using hexadecane as reaction medium. The behaviour of these chemicals, in the hydrogenation runs carried out, gives useful information regarding the problems which could arise when organic industrial waste liquids containing chlorine-, nitrogen-, and sulphur-compounds are hydrotreated. The model compounds have been hydrotreated separately at T = 320 degrees C and in admixture at the temperatures 280, 300, 320, and 350 degrees C. The hydrogen pressure was kept constant at 40 bar. The experimental results show that both hydrodechlorination (HDCl) and hydrodesulphurization (HDS) processes were strongly inhibited by the presence of quinoline. On the contrary hydrodenitrogenation (HDN) of quinoline was not significantly influenced by the presence of both chlorobenzene and benzothiophene. The reason for this behaviour resides in the fact that the nitrogen compounds are strongly basic and adsorb preferentially on the acidic catalyst surface. Therefore, the sharing of the active surface was strongly in favour of the nitrogen compounds. In particular, it was found that decahydroquinoline (DHQ), which is the intermediate with the highest adsorptivity, played the dominant role in subtracting, in a substantial way, active sites to the HDCl and HDS processes. (C) 1998 Elsevier Science B.V.