Hydrocracking of n-decane

Hydroisomerization/ hydrocracking of n-decane A1 Ga-(Be, M) impr. The order of activity found was USY >A1-Be > Ga-M > Al-M. A direct relationship between catalytic activity and Bronsted acidity associated with the Al and Si in the tetrahedral layers of Be. 52... 

Chromia pillared montmorillonite with 1.0 -1.1 nm gallery height and a high specific surface area has been prepared successfully by using an elevated temperature (368 K) for the formation of hydroxy-chromium polycations [2]. This catalyst possesses significant activity in the hydrocracking of n-decane. Previously, we synthesized... 

Such an independent measure is the selectivity of bifunctionally catalyzed consecutive reactions, e.g., the isomerization followed by hydrocracking of n-decane. By model calculations one can show that for a bifunctional catalyst limited in the acid function, the selectivity for intermediate product is high and does not change upon variation of the activity of the metal function. Large changes in selectivity because of such variations are expected for catalysts where neither the metal function nor the acidic function is ratelimiting. If a bifunctional catalyst is really limited in the metal function, this limitation is accompanied by a very low selectivity for intermediate products. 

The actual butane content of the product from the hydrocracking of n-decane can be substantially higher than that calculated on the above simple basis. For example, at 288°C and 82 atm, about 25 moles of "excess butane are formed from n-decane over a nickel sulfide on silica-alumina catalyst. This result indicates that reactions other than simple scission are involved, such as the apparent disproportionation process discussed above. In the above example, butane would not be the only species formed by such reactions. However, because butane is the most common product from cracking, it is the one to appear in excess in this material balance calculation. 

Figure 4 - Isoparaffin to n-paraffin ratios in the product from hydrocracking of n-decane using strongly acidic catalysts.

Because of the small pores in zeolitic catalysts, reaction rates may be controlled by rates of diffusion of reactants and products. Beecher, Voorhies, and Eberly (4) studied hydrocracking of mixtures of n-decane and Decalin with mordenite catalysts impregnated with palladium. They found that acid leaching of the mordenite produces an aluminum-deficient structure of significantly higher catalytic activity. At least part of this improvement appears to be caused by the decrease in diffusional resistance. They observed that with this type of catalyst, the effective catalyst pore diameter appears to be smaller than calculated owing to the strong interaction or adsorption of hydrocarbon molecules on the pore walls. 

The platforming catalyst was the first example of a reforming catalyst having two functions.43 44 93 100-103 The functions of this bifunctional catalyst consist of platinum-catalyzed reactions (dehydrogenation of cycloalkanes to aromatics, hydrogenation of olefins, and dehydrocyclization) and acid-catalyzed reactions (isomerization of alkanes and cycloalkanes). Hyrocracking is usually an undesirable reaction since it produces gaseous products. However, it may contribute to octane enhancement. n-Decane, for example, can hydrocrack to C3 and C7 hydrocarbons the latter is further transformed to aromatics. 

When metal centers act in conjunction with acid sites on the zeolite, bifunctional catalysis can occur (e.g., Pd/HY). This type of catalysis is used mainly for the hydrocracking and isomerization of long-chain n-alkanes. For example, the rates of formation of 2- and 5-methylnonane isomers obtained from n-decane isomerization over bifunctional zeolite catalysts depend on the size and structure of the zeolites used. This reaction has been developed as a test reaction to characterize zeolite structures (17-19). 

The Mobil process for catalytic dewaxing by selective hydrocracking of wax molecules arose from that company s development work on zeolites and the discovery of the remarkable selectivity exhibited by these catalysts some 20 years prior to first commercialization. In 1960 Weise and Frilette, of the then Socony Mobil Research and Development Laboratories,1 reported that n-decane cracked readily to lighter paraffins over the sodium form of a zeolite known as 13X, whereas the bulkier molecules, a-pinene and isopropylbenzene, underwent no reaction (Figure 10.1). 

Product distributions from the hydrocracking of typical normal paraffins with nickel sulfide on silica alumina catalyst (34, 59) are shown in Figure 1 (n-hexadecane) and Table I (n-decane). Table I also includes results with silica-alumina and with nickel on silica-alumina (discussed later). 

On the other hand, R-exchanged zeolites have also been used in combination with a metal function, for carrying out the isomerization and hydrocracking of paraffins and cycloalkanes. This is the case for isomerization of n-hexane to isohexane and 2,2-dimethyl-butane (Rabo et al. 1961) the isomerization of n-undecane to mixed Ci 1 isomers at 275°C on Pt/Ce-Y zeolite (Weitkamp et al. 1985) the isomerization of c (7o-exo-tricyclo[5.2.1.02,6]-decane or exo-tricyclo[6.2.1.02,7]-undecane into adamantane or 1-methyladamantane, respectively, on R-Y at 150-270°C (Lau and Maier 1987) the isomerization of tetrahydrodicyclopentadiene into adamantane on Re-Y in a H2/HC1 atmosphere at 250°C (Honna et al. 1986) or the double bond relocation of 2-alkyl acrolein into fran.j-2-methyl-2-alkenals over Ce,B-ZSM-5 (Fisher et al. 1986). Recently, it has been reported that Ce-promoted Pd/ZSM-5 is an active and selective catalyst in the dehydroisomerization of a-limonene to / -cymene (Weyrich et al. 1997). 

For the hydroconversion of -heptane and n-decane, the group of Jacobs [96,165-169] reported a hnear relation between the rates of hydroisomerization normalized to the concentration of tetrahedral A1 and the concentration of pentacoordinated and tetrahedrally distorted A1 (analyzed by Al MAS NMR) [166]. This emphasizes that the interaction of extraframework aluminum species with Bronsted acid sites creates more active sites. The work by Blomsma et al. [96,165,167] shows that hydroconversion of n-heptane over Pd/H-Beta zeolites is a combination of classic bifimctional hydrocracking and cracking of dimerized C7 species. 

Steyns, M. and Froment, G.F. (1981) Hydroisomerization and hydrocracking Kinetic analysis of rate date for N-decane and N-dodecane , Ind. Eng. Chem. Prod. Res. Develop. 20,660-668. 

---