Suppression of Sludge Formation by Two-stage Catalytic Hydrodesulfurization of Arabian Atmospheric Residue.

Abstract

Two-stage catalytic hydrodesulfurization of Arabian atmospheric residue was studied using commercial Co-Mo and Ni-Mo catalysts in a batch autoclave to achieve a high desulfurization level without producing (precipitated insoluble droplets in the product oil matrix). Single-stage reactions using a Co-Mo catalyst (KF-742) at 380 and 400°C for 3h under hydrogen pressure of ca. 100atm achieved desulfurizations of 62 and 75%, respectively, with a very little amount of sludge formed. A higher reaction temperature of 420°C enhanced the rate of desulfurization significantly up to 86%, but much sludge droplets were formed in the product oil. The two-stage hydrotreatment using KF-742 catalyst at 380°C-2h followed by 420°C-1h achieved high rate of desulfurization (84%) comparable to that of the single-stage reaction at 420°C-3h, and produced slightly less dry sludge in the product oil. A combination of using KFR-10 catalyst in the first stage, and KF-742 catalyst in the second stage, under the same two-stage reaction conditions, markedly decreased formation of sludge droplets, although the rate of desulfurization was also reduced slightly to 80%. A first stage reaction at 380°C-2h with KFR-10 catalyst followed by a second stage reaction at 410°C-2h with KF-742 catalyst improved the desulfurization level to 85% without increasing dry sludge. The mechanism of sludge formation and its suppression are discussed relative to severities of reaction conditions involved in the hydrotreatment which may also enhance the desulfurization.