Journal of Catalysis 210, 445–452 (2002) doi:10.1006/jcat.2002.3700 Molecular Competition of C 7 and C 9 n-Alkanes in Vapor- and Liquid-Phase Hydroconversion over Bifunctional Pt–USY Zeolite Catalysts Joeri F. M. Denayer, ∗,1 Bruno De Jonckheere,† Myriam Hloch,† Guy B. Marin,‡ Gina Vanbutsele,† Johan A. Martens,† and Gino V. Baron ∗ ∗ Dienst Chemische Ingenieurstechniek, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium; †Centrum voor Oppervlaktechemie en Katalyse, Katholieke Universiteit Leuven, Kasteelpark Arenberg 23, B-3001 Louvain, Belgium; and ‡Laboratorium voor Petrochemische Techniek, Universiteit Gent, Krijgslaan 281, B-9000 Ghent, Belgium Received March 14, 2002; revised May 28, 2002; accepted May 28, 2002 Molecular competition effects in the hydroconversion of an equimolar heptane/nonane mixture were studied in liquid-phase re- action conditions in a ﬁxed-bed reactor ﬁlled with a Pt–ultrastable-Y (USY) catalyst. Liquid-phase conditions were attained by feed- ing the hydrocarbon mixture with hydrogen dissolved in it at 100 bar and 230 ◦ C. Comparative vapor-phase experiments were run at 230 ◦ C, a pressure of 4.5 bar, and a hydrogen-to-hydrocarbon ratio of 13. Whereas catalytic experiments in the vapor-phase showed a marked referential conversion of nonane over heptane, in liquid-phase the differences in conversion rate between nonane and heptane were much less pronounced. Adsorption-reaction mod- els were used to explain the difference. For this purpose, intrinsic kinetic constants for heptane and nonane were derived from exper- imental data from vapor-phase conversions of the n-alkanes indi- vidually, using an adsorption-reaction model with independently determined adsorption equilibria, and assuming the classic bifunc- tional reaction scheme. The liquid-phase conversion of the heptane/ nonane mixture was predicted very well using these intrinsic re- action kinetics derived from the vapor-phase experiments and as- suming no adsorption preference between heptane and nonane. In contrast to this, the conversion of the heptane/nonane mix- ture in the vapor phase could only be appropriately described by a model involving adsorption according to a Langmuir-with- interaction model, favoring adsorption of the heaviest compound. In liquid-phase reaction conditions and at saturation of the Pt– USY zeolite pores with n-alkanes, there is no such selective adsorp- tion of the heaviest compound. In liquid-phase, the conversion of the mixture reﬂects the intrinsic reaction kinetics of the individual compounds. c  2002 Elsevier Science (USA) Key Words: hydrocracking; alkane; Pt/USY zeolite; liquid phase; kinetic modeling. INTRODUCTION Bifunctional zeolite catalysts are applied in several petroleum reﬁnery operations, designated as hydroconver- 1 To whom correspondence should be addressed. Fax: +32 2 6293248. E-mail: Joeri.Denayer@vub.ac.be. sion processes. The most important zeolite-based petro- chemical hydroconversion processes are isomerization of light naphtha, iso-dewaxing, and hydrocracking of heavy fractions (1). The hydroconversion of hydrocarbon molecules on platinum-loaded acid zeolite catalysts is an appealing research subject in view of these important indus- trial applications. Experimental investigations in academic laboratories are typically performed with pure model com- ponents or simple mixtures thereof as feedstock, and under reaction conditions where the hydrocarbon compounds are in the vapor phase. (2–5). Industrial hydroconversion pro- cesses are mostly run under three-phase, or even in some cases under liquid-phase conditions and with feedstocks that are extremely complex mixtures of large numbers of different hydrocarbon compounds (1). At the relatively mild reaction temperatures relevant to these hydroconversion processes, even under vapor- phase reaction conditions, the zeolite pores are ﬁlled with physisorbed molecules to a signiﬁcant extent. In earlier work, adsorption equilibria of a broad range of hydrocar- bon components were determined on ultrastable-Y (USY) zeolites under catalytic conditions. It was found that Henry adsorption constants increase exponentially with the alkane carbon number (6, 7). This adsorptive discrimination of long alkanes in favor of shorter alkanes is most pronounced in the Henry regime and decreases when the pores are more ﬁlled with hydrocarbon molecules at increasing vapor pres- sures (8). USY-type zeolite contacted with liquid alkanes does not show any difference in afﬁnity toward alkanes of different molecular weight (9). These investigations showed that on USY-type zeolite, adsorption selectivity depends strongly on the loading of the micropores and on the aggre- gation state of the alkane contacted with the zeolite. In con- trast to the vast amount of literature dealing with hydrocon- version processes of model compounds in the vapor-phase, only very few experimental studies dealing with liquid- phase reaction conditions have been reported (10, 11). Reaction pathways of bifunctional catalytic conversions of model hydrocarbon compounds were experimentally 445 0021-9517/02 $35.00 c  2002 Elsevier Science (USA) All rights reserved.