1995 Volume 21 Issue 6 Pages 1110-1119
Effects of preasphaltene and ash content on catalyst deactivation were investigated with a Ca-Ni-Mo/Al2O3 developed for secondary hydrogenation in two-stage brown coal liquefaction. Compared with Ni-Mo/Al2O3, little catalyst deactivation was observed with Ca-Ni-Mo/Al2O3 owing to a small carbonaceous deposit, even in the case of including large amounts of preaspaltenes, while a significant decrease in catalytic activity was observed with an increase in the ash content.
It appeared that Na and K in ash having a small particle size could easily penetrate into the catalyst pore, resulting in poisoning of active sites. A remarkable change in surface area or pore structure was observed on the used catalyst collected from the inlet of a fixed bed reactor.
It was found that the possibility of pore blockage by metal deposition may be ruled out, as the reduction in pore volume was mainly caused by carbonaceous deposition. These results suggest that initial deposition of carbonaceous materials and alkaline metals (Na, K) on the catalyst could cause catalyst deactivation in the initial stage.