Hydrodesulfurization of Model Systems Using Slurry-Phase Catalysts

Abstract

The activity and selectivity of slurry phase catalysts composed of iron, molybdenum, nickel, and cobalt for hydrodesulfurization (HDS) of sulfur-containing compounds were investigated. The sulfur compounds which represent sulfur containing moieties in coal were benzothiophene, dibenzothiophene, and 5-methyl-8-(1-methylethyl)dibenzothiophen-4-ol (MMDH). Slurry-phase iron naphthenate (FeNaph) and iron acetylacetonate (FeAcAc) at 1000 ppm of Fe yielded 63 and 43% desulfurization of benzothiophene, respectively, but did not convert any dibenzothiophene. Molybdenum naphthenate (MoNaph) at 1000 ppm Mo, by contrast, totally desulfurized both benzothiophene and dibenzothiophene. Combining MoNaph with either FeNaph or FeAcAc at 500 ppm of each metal resulted in synergetic activity also totally desulfurizing benzothiophene. Combinations of cobalt naphthenate or nickel octoate with FeNaph yielded more HDS and more hydrogenation than with either catalyst individually. The substituted dibenzothiophene MMDH was more reactive than dibenzothiophene under these reaction conditions. Catalytic hydrotreatment with MoNaph and excess S resulted in hydrocracking, desulfurization, deoxygenation and hydrogenation reactions while FeNaph and excess S promoted desulfurization but lesser amounts of the other reactions. Synergism occurred with the combination of FeNaph and MoNaph and excess sulfur, yielding increased amounts of hydrocracking, hydrogenation, and heteroatom removal reactions. Reaction pathways for MMDH were postulated under both catalytic and noncatalytic conditions.