Catalysis Hydroisomerization

Since ITQ-4/SSZ-42/MCM-58 have been prepared as aluminosilicates with Si/Al ratios of 20 to °°, which possess Brpnsted sites, there is potential for acid catalysis. Some preliminary accounts of catalytic cracking, hydrocracking, dewaxing, alkylation, hydroisomerization, and reforming reactions have been reported (47, 62-64). 

While the rate of cleavage is given by temperature, acidity of the catalyst and concentration of i-alkyl cations, the rate of desorption is assumed to be enhanced by the steady state concentrations of n-alkenes, i. e., a high dehydrogenation activity of the catalyst favors hydroisomerization. This is the concept of competitive chemisorption which in ideal bifunctional catalysis keeps the residence times of the alkylcarbenium ions low. 

The chain length of n-alkanes has a marked influence on reactivities for hydroisomerization, and especially for hydrocracking. To a very small extent a methane and ethane abstracting mechanism, probably hydrogenolysis as predicted in a basic work on bifunctional catalysis (14), is found to be superimposed when lower carbon number feeds (C, Cg, Cg) are used. n-Hexane is excluded from ideal hydrocracking. On the Pt/Ca-Y-zeolite catalyst it is cracked via a mechanism that is mainly hydrogeno-lytic. 

Application Increase the value of steam cracker C4 cuts via low-temperature selective hydrogenation and hydroisomerization catalysis. Several options exist removal of ethyl and vinyl acetylenes to facilitate butadiene extraction processing downstream conversion of 1, 3 butadiene to maximize 1-butene or 2-butene production production of high-purity isobutylene from crude C4 cuts total C4 cut hydrogenation and total hydrogenation of combined C3/C4 and C4C5 cuts for recycle to cracking furnaces or LPG production. 

In 1960, Weisz, Frilette, and co-workers first reported molecular-shape selective cracking, alcohol dehydration, and hydration with small pore zeolites (6,7), and a comparison of sodium and calcium X zeolites in cracking of paraffins, olefins, and alkylaromatics (8). In 1961, Rabo and associates (9) presented data on the hydroisomerization of paraffins over various zeolites loaded with small amounts of noble metals. Since then, the field of zeolite catalysis has rapidly expanded,... 

FIGURE 10.25 Hydroisomerization of n-hexadecane over Pt-SAPO-11 and Pt-silica-alumina catalysts monosubstituted methyl pentadecane contents versus pour point. Source S. J. Miller, Studies on Wax Isomerization for Lubes and Fuels, Studies in Surface Science and Catalysis 84 2319-2326 (1994). With permission. 

Source R. J. Taylor and R. H. Petty, Selective Hydroisomerization of Long Chain Normal Paraffins, Applied Catalysis A General 119 121-138 (1994). With permission. 

MTT zeolites with aluminosilicate core and siliceous overlayer were synthesized in a two-step synthesis, whereby core material in its mother liquor was combined with siliceous synthesis gel. A substantial weight gain of up to 140% was obtained. The activity in decane hydroisomerization reflects the Si/Al ratio of the external surface in accordance with pore mouth and key-lock catalysis. 

Martens. J.A. Vanbutsele, G. Jacobs, P.A. Denayer, J. Ocakoglu, R. Baron. G. Munos Arroyo, J.A. Thybaut, J. Marin, G.B. Evidences for pore mouth and key-lock catalysis in hydroisomerization of long n-alkancs over 10-ring tubular pore bifunctional zeolites. Catal. Today 2001, 65. 111-116. 

Hydroisomerization and hydrocracking of n-heptane on PtH zeolites. Effect of the porosity and of the distribution of metallic and acid sites Catalysis Today 1, 415-433. 

To illustrate the use of Elq. (4.1) in zeolite catalysis, we will discuss the results of theoretical and experimental studies of the hydroisomerization reaction of hexanel L In order to exclude diffusion limitation, two conditions have to be met. First, the Biot condition must be satisfied when the rate of desorption is limiting ... 

Molecular heats of adsorption play a role in many catalytic reactions. Figure 6.23 illustrates this for an isomerization reaction catalyzed by a solid acid. As explained in Chapter 3, the hydroisomerization of alkanes on a zeolite-supported metal proceeds through a bifunctional reaction mechanism, in which the metal has the function of activating C-H bonds and H2 at a low reaction temperature. The alkane-alkene equilibrium is established by metal catalysis, and the alkene is protonated and isomerized by the acidic protons of the zeolite... 

From Ihopoulou, E.F., Heracleous, E., Dehmitis, A., Lappas, A.A., 2014. Producing high quality biofuels Pt-based hydroisomerization catalysts evaluated using BtL-naphtha surrogates. Applied Catalysis B 145, 177—186. 

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