COMPETITIVE EFFECTS OF HETEROATOM CONTAINING COMPOUNDS IN THE HYDRODEMETALLISATION OF VANADYL-TETRAPHENYL-PORPHYRIN

Heavy oil residua contain large amounts of hetero-atoms, such as sulfu r, nitrogen, oxygen and metals. The metals, mainly vanadium and nickel , are removed by catalytic hydrotreatment. Sulfur, nitrogen and oxygen containing compounds present in heavy oil residua can influence the r ate at which the metals are removed, since they can adsorb competitive ly on the active site of the catalyst. Hence, the rate of the hydrogen ation and ring cleavage steps in the hydrodemetallisation of the organ o-metallic compounds may be slowed down. In the present work the compe titive effect of hetero-atom containing compounds which are analogues of those occurring in heavy oil residua, i.e. quinoline, ammonia, benz ofuran, water, dibenzothiophene and anthracene, has been investigated on the hydrodemetallisation of vanadyl-tetraphenyl-porphyrin. The spik ed amount of hetero-atoms has been chosen near to those occurring in o il residua. The added hetero-atom containing compounds appeared to dec rease the rate of metal removal. An increasing effect on the hydrogena tion steps was found in the following sequence: dibenzothiophene < qui noline < anthracene approximate to benzofuran < ammonia approximate to water. For the lumped ring cleavage step the effect increased in the following sequence: dibenzothiophene < anthracene approximate to quino line approximate to benzofuran < ammonia < water. The effect of quinol ine, benzofuran, dibenzothiophene and anthracene is caused by competit ive adsorption on the active sites of the catalyst. Water and ammonia, which have the most pronounced effect, are suggested to be co-ordinat ed to the vanadyl group in the porphyrin and, therefore, decrease the rate of metal removal. It is concluded that competitive adsorption of the reaction products from the ring cleavage of VO-TPP is negligible a nd that the presence of hetero-atom containing compounds in realistic feedstocks can decrease the rate of metal removal significantly. (C) 1 998 Elsevier Science Ltd. All rights reserved.