Dynamics of Pyridine Adsorption on Hydrotreating Catalysts

Abstract

The adsorption of pyridine on two Ni-Mo/alumina hydrotreating catalysts <HDN-60 and Shell 324) was investigated. Equilibrium and dynamic adsorption data were collected at 100, 200, 250, 300, 400, and 450 C in the pyridine partial pressure range of 533-800 N/m2 (4-6 mm Hg). The equilibrium results described two kinds of adsorption: physical adsorption at temperatures below 250 C and chemisorption which was predominant at temperatures above 250 C. The initial rate of adsorption at low temperatures was larger than that at high temperatures and the time to reach equilibrium at low temperatures was shorter than that at high temperatures. Pyridine adsorption at the temperatures studied demonstrated a 30-60 % irreversibility. A reversible adsorption model demonstrated different types of adsorption from the dynamic study. At temperatures below 250 c, there were three types of adsorption and at higher temperatures, four or five types of adsorption occurred in the process. Temperature programmed adsorption of pyridine on catalyst showed a strong adsorption at temperatures higher than 420 C. This high temperature adsorption may be attributed to coke formation.