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both having average macropore peaks at 3600 and 2692 A ˚ ,respectively.The active phase in the sulfidic NiMo catalyst is usuallydescribed as the so-called Type I and Type II ‘‘NiMoS’’ phase.The typical properties of the ‘‘Type I’’ phase are the lower Scoordination of Mo and Ni, and the high dispersion of theFig. 3. Reaction-temperature monitoring upon heavy residue hydroconversionusing AMAC and ComCat catalysts. Right part of dotted vertical line isstationary regime. underlying MoS2, mostly single slabs, having maintained theirMo–O–Al interactions with the support. ‘‘Type II’’ phase hashigher intrinsic activity than ‘‘Type I’’ in an HDN reaction [13].Carbon-supported CoMoS (or NiMoS) structures are moreweakly bound to the support than typical alumina-supportedCoMoS [14,15]. CoMoS structures found in carbon-supportedcatalysts had properties much like Type II CoMoS [15,16],inagreement with the observation that support interactions areless important for Type II than for Type I CoMoS [17].In general, macropores are beneficial in removing heavymetals, such as Ni and V, which are present as porphyrine-likecompounds in heavy oils, as can be observed in Figs. 8 and 9.AMAC-catalysts containing macropores were more efficient inhydrodemetallization than the unimodal AMAC-117, clearlyindicating the importance of macropores in increasing metalsremoval levels. Worth mentioning is the case of Vanadium, themost catalyst-deleterious metal. In Fig. 9, HDV levels between160 and 350 h are approximately 93% in AMAC-128 and 88%in ComCat, though they showed similar HDV levels whendeactivation became pronounced. However, AMAC-142, inspite of having macropores at avg. 2690 A ˚ , behaved somewhatlower than AMAC-128.A tendency to form sediments in AMAC-117, -142, andComCat is shown in Fig. 10. Formation of total sediments wasgreatly suppressed in AMAC-117 and -142 in comparison withthat in ComCat, especially during the high-activity period(150–300 h), remaining low and stable throughout thetest. Presumably, carbon black in AMAC catalysts aids insuppressing Al2O3 acidity, which contributes to sedimentformation. Notice that when deactivation advances in ComCat,e.g., when coke is deposited on the Al2O3 surface, sedimentsare greatly diminished.Fig. 10. Evolution of total sediments in the product on AMAC and ComCatcatalysts. Conradson carbon residue (CCR) is a standard petroleumcoking test for characterizing the coke forming tendency ofpetroleum liquids, and it is an indicator of a catalyst’scarbonizing nature when all reaction conditions remainconstant, as in the case presented here. The evolution ofCCR levels in AMACs and ComCat is shown in Fig. 11, whereCCR levels fall rapidly below 130 h of operation because ofhigh activity and a reaction temperature increase (e.g., non-stationary period), while CCR levels are practically stableabove 140 h of operation. AMAC-128 showed the lowest levelsof CCR formation. AMAC-117 showed similar CCR levels toComCat, but the former contains carbon black and nomacropores. AMAC-142 yielded more CCR than the otherAMAC catalysts, probably due to the low carbon black content(see Table 2).Yields to different hydrocarbon fractions, after 200 h ofoperation, are presented in Table 3. AMAC catalysts showed ahigher tendency to form lighter fractions in comparison withthose of ComCat; but a combination of carbon black and largermacropores (i.e., AMAC-142) gave the best results in naphtha,kerosene, and diesel yields.4. ConclusionsAlumina modified with amorphous carbon black can be agood alternative as a support for H-OilTM catalysts, especiallyin decreasing sediment formation. Addition of carbon black toalumina, after almost inert atmosphere pyrolysis, results inshaped strong particles, suitable for high colliding-attritionapplications,
such as those of ebullated bed reactors.Appropriate mixing and extrusion conditions allow formationof about 22% of total pore volume as macropores. HDS andHDN can be upgraded when combining carbon black andmacropores. The presence of carbon black may be promoting arelative abundance of Type II sites in NiMoS species, which aremore active than Type I. Macropores are particularly beneficialin removing heavy metals, such as Ni and V, which are presentas porphyrine-like compounds in heavy oils; AMAC-catalystscontaining macropores were more efficient in hydrodemetalli-zation than AMAC containing no macropores. Yields tovaluable light oil fractions, such as naphtha and kerosene,increased using AMAC catalysts.AcknowledgementThis study was supported and partly funded by the JapanInternational Cooperation Agency (JICA).References[1] I.A. Wiehe, Ind. Eng. Chem. Res. 31 (1992) 530.[2] V.J. Nowlan, N.S. Srinivasan, Fuel Sci. Tech. Int. 14 (1996) 41.[3] D.E. Sherwood, Jr., US Patent 5,827,421 (1998) and references therein.[4] E.B. Cornelius, T.H. Milliken, G.A. Mills, A.G. Oblad, J. Phys. Chem. 59(1955) 809.[5] J.A. van Veen, E. Gerkema, A.M. van der Kraan, A. Knoester, J. Chem.Soc. Chem. Commun. 1684 (1987).[6] Z. Vit, Fuel 72 (1993) 105.[7] E. Hillerova ´, M. Zdrazil, Catal. Lett. 8 (1991) 215.[8] A. Drahodarova, Z. Vit, M. Zdrazil, Fuel 71 (1992) 455.[9] T. Kabe, A. Ishihara, W. Qian, Hydrodesulfurization and Hydrodenitro-genation, Chemistry and Engineering, Kodansha Wiley–VCH, 1999,, p.227.[10] A. Segawa, K. Watanabe, Y. Shibata, T. Yoneda, in: B. Delmon, G.F.Froment, P. Grange (Eds.),