Hydroisomerization selectivity

In terms of hydroisomerization selectivity, it was found that Pt/ZSM-22 exhibits highest selectivity for the conversion of n-alkanes to 2-methyl-branched isomers 308,309). For example, the dibranched isomers from n-decane are particularly rich in 2,7-dimethyloctane. On the other hand, 3-, 4-, and 5-methylnonane isomers are significant even at a low conversion level on Pt/H-USY zeolite. On Pt/H-USY, the composition of the methyl-nonane product fraction approaches thermodynamic equilibrium at medium levels of conversion through methyl shifts. In addition, ethyloctanes are observed as primary products on Pt/H-USY via substituted protonated cyclobutane, but they are absent from the reaction products with Pt/ZSM-5... 

Hierarchical micro/mesopore structure can be obtained by forming composite from delaminated layered-stmcture zeohte and a mesoporous MTS material. At the same space time the bifunctional zeolite catalyst, having hierarchical micro/mesoporous stractme, show lower n-C hydroconversion activity and higher hydroisomerization selectivity than the corresponding microporous zeolite catalyst. 

The hydroisomerization of heavy linear alkanes is of a great interest in petroleum industry. Indeed, the transformation of long chain n-alkanes into branched alkanes allows to improve the low temperature performances of diesel or lubricating oils [1-3]. On bifunctional Pt-exchanged zeolite catalysts, n-CK, transformed into monobranched isomers, multibranched isomers and cracking products [4], The HBEA zeolite based catalyst was more selective for isomerization than those containing MCM-22 or HZSM-5 zeolites [4], This was explained on one hand by a rapid diffusion of the reaction intermediates inside the large HBEA channels, and on the other hand by the very small crystallites size of this zeolite (0.02 pm). 

An increase in the zeolite crystallites size would very likely produce substantial changes in the physicochemical properties of the catalyst and consequently on the selectivity for hydroisomerisation. Since the effect of the zeolite crystallites size in the nanoscale range cannot be predicted theoretically, n-hexadecane hydroisomerization was carried out on PtHBEA catalysts with different zeolite crystallites sizes. 

Hydroisomerization of n-octane over Pt-containing micro/mesoporous catalysts obtained by recrystallization of zeolites BEA and MOR was investigated in the temperature range of 200-250 °C under 1-20 bar. Composite materials showed remarkably high activity and selectivity with respect to both pure microporous and pure mesoporous materials. The effect is due to high zeolitic acidity combined with improved accessibility of active sites and transport of bulky molecules provided by mesopores. 

The development of composite micro/mesoporous materials opens new perspectives for the improvement of zeolytic catalysts. These materials combine the advantages of both zeolites and mesoporous molecular sieves, in particular, strong acidity, high thermal and hydrothermal stability and improved diffusivity of bulky molecules due to reduction of the intracrystalline diffusion path length, resulting from creation of secondary mesoporous structure. It can be expected that the creation of secondary mesoporous structure in zeolitic crystals, on the one hand, will result in the improvement of the effectiveness factor in hydroisomerization process and, on the other hand, will lead to the decrease of the residence time of products and minimization of secondary reactions, such as cracking. This will result in an increase of both the conversion and the selectivity to isomerization products. 

Paracrystallinity, Cu/ZnO/AIjOj, 31 295 2"-Paracyclophanes, 32 453 Paracyclophanes, macrocycles, 29 206-208 Paraffin, see also Alkanes alkylation, 10 165, 27 98 carbon selectivity, bed residence time effects, 39 249-250 cracking, 39 283 cyclization, 28 295 rates, 28 301, 302 double cyclization, 28 312-314 in exhaust gases, 24 66, 67 hydrogenolysis, 30 43-44 hydroisomerization, 39 183 oxidation, 32 118-121 solubility enhanced hydrogeolysis, 39 285 Parahydrogen conversion rate correlations, 27 48-50... 

Soualah, A., Lemberton, J.L., Pinard, L., Chater, M., Magnoux, P., and Moljord, K. (2008) Hydroisomerization of long-chain n-alkanes on bifunctional Pt/zeolite catalysts effect of the zeolite strucmre on the product selectivity and on the reaction mechanism. Appl. Catal. A., 336, 23-28. 

Of course, certain features of overall kinetics are inaccessible via a cluster model method, such as the influence of pore structure on reactivity. The cluster model method cannot integrate reaction rates with concepts such as shape selectivity, and an alternative method of probing overall kinetics is needed. This has recently been illustrated by a study of the kinetics of the hydroisomerization of hexane catalyzed by Pt-loaded acidic mordenite and ZSM-5 (211). The intrinsic acidities of the two catalysts were the same, and differences in catalyst performance were shown to be completely understood on the basis of differences in the heat of adsorption of hexene, an intermediate in the isomerization reaction. Heats of adsorption are strongly dependent on the zeolite pore diameter, as shown earlier in this review (Fig. 11). 

Another example of secondary shape selectivity is shown by John and co-workers (77,73). They found that the hydroisomerization/hydroeracking of n-hexane over Pt/H-mordenite is significantly inhibited by the presence of benzene. They also found a correlation between the aromatic size relative to zeolite pore size on the inhibition of the hexane reaction and the changes in isomer selectivities. Figure 4 illustrates the relation between the various aromatics co-fed and the n-hexane isomerization rates on H-mordenite. From Figure 4, it is shown that as the kinetic diameter of the aromatics is increased, the isomer formation rate appears to pass through a minimum. This result can be explained by considering the size of the zeolite pore and the kinetic... 

The noble metal component may be either palladium or platinum the effect of the concentration of both metals on methylpentane as well as on dimethylbutane selectivity in C6 hydroisomerization on lanthanum and ammonium Y-zeolite with Si/Al of 2.5 has been studied by M.A. Lanewala et al. (5). They found an optimum of metal content for that reaction between 0.1 and 0.4 wt.-%. The noble metal has several functions (i) to increase the isomerization activity of the zeolite (ii) to support the saturation of the coke precursors and hence prevent deactivation, as was shown by H.W. Kouvenhoven et al. (6) for platinum on hydrogen mordenite (iii) to support the hydrodesulfurization activity of the catalysts in sulfur containing feedstocks. 

From the thermodynamic point of view, the hydroisomerization reaction is not pressure sensitive. However, because the catalyst contains the acid function, hydrocarbon cracking is an unavoidable side reaction. The cracking reaction however should depend on the total pressure. Table 7.4 shows laboratory results obtained in a bench scale reactor at 250°C (482°F), H2/HC = 1 with a synthetic feedstock containing 50wt% of n.Cs, 25 of iCs, 20 of n C6, 5 of methylcyclopentane and no heptane (Feed 1). At a liquid hour space velocity (LHSV) of 2h an increase of the total pressure from 20 bar to 30 bar reduces the cracking selectivity S = Z C4/Z HC from 1.6 to 1.1 wt.-%, whereas at a LHSV of 1 h 1 no effect can be observed. 

Table 7.5 Effect of pressure on cracking selectivity in hydroisomerization of synthetic feedstock on Pt-H-MOR Conditions T=250 °C, Total pressure = 20 bar, LHSV = 2 h 1, Feed 2...

Commercial zeolite based hydroisomerization catalysts comprise alumina bound and platinum impregnated dealuminated mordenite. The activity and selectivity of the hydroisomerization of n-paraffins is strongly influenced by acid leaching. The influence of silica to alumina ratio has been studied for pentane isomerization over platinum mordenite many times since one of the first papers published (6). 

Laboratory studies have shown that omega (MAZ structure type) based paraffin hydroisomerization catalyst shows higher activity than mordenite based catalyst and better selectivity, i.e. higher octane due to higher yield of di-branched paraffins compared to mordenite performance (17). The isomerization of a C5/C6 cut at 15 bar results in a final calculated RON of 80.4 for the alumina bound dealuminated PtH-MOR catalyst supplied by IFP with undisclosed (most likely similar) Si/Al ratio, measured at 265 °C compared to a RON value of 80.9 for an alumina bound dealuminated PtH-MAZ catalyst with bulk Si/Al = 16, measured at 250 °C. Both measurements were performed in a bench-scale tubular reactor with a volume of 50 cm3 of 2 mm diameter extrudates with WHSV of 1.5 h and H2/HC of 4. This... 

Description Crude C4 streams are converted into propylene and an isobutylene-rich stream in three IFP process steps (1) butadiene and C4 acetylenes selective hydrogenation and butenes hydroisomerization, (2) isobutylene removal via distillation or MTBE production and (3) metathesis (Meta-4). 

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. 

CDTECH Isobutylene Raffinate 1 Selective hydrogenation of butadiene and hydroisomerization of butene-1 to butene-2 via catalytic distilation to recover isobutylene 1 1994... 

IFP/Chinese Petroleum Corp. Propylene FCC and steam-cracker C4cuts Meta-4 upgrades pyrolysis C4 cuts to propylene has attractive ROI when combined with IFP selective hydroisomerization unit 1 NA... 

Furthermore, since the C4 cuts employed exhibit a 1-butcne percentage of about 10 to 15 per cent weight, this graph also shows that, to achieve effective conversion, it is necessary to operate at less than ISO C. In practice, the operation is conducted at about lOCPC, which maintains a residual 1-butene content of about 5 per cent weight in the effluenL la these conditions, however, the reaction rate becomes slow. Catalysts are used to accelerate it, usually based on precious metals deposited on inert alumina (palladium, rhodium etc.), whose operation is considerably improved in a hydrogen atmosphere. This also permits the selective hydrogenation of the residual butadiene, and explains why this conversion is called hydroisomerization. 

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