Isomerization pentane

Pentane isomerization was used to increase the critical supply of aviation gasoline toward the end of the war. Two processes—one developed by Shell and one by Standard Oil Company (Indiana)—were commercialized. The pentane processes differ from butane isomerization mainly in the use of somewhat milder conditions and an inhibitor to suppress side reactions. In general, the problems of the butane processes are inherent also in pentane isomerization, but the quality of the feed stock is less important. Olefins can be as high as 0.2 %, although 0.05 % is preferable. The hexane content should not exceed about 5%, and sulfur and water contents should be as low as in the butane process. Catalyst life is much shorter than in the butane processes only about 30-50 gallons of isopentane are produced per pound of aluminum chloride. 

The molten catalyst contains only about 2% aluminum chloride and has a lower solidification point than the butane catalyst. Typical reactor 

Catalyst form Dissolved in SbCls Liquid complex 

Reactor material Nickel Hastelloy B or Lumnite cement 

and the conditions mentioned, a minimum partial pressure of about 60 p.s.i. is required to prevent disproportionation. Under milder conditions, somewhat lower partial pressures will serve, but conversion is much lower. Hydrogen pressures above 100 p.s.i. tend to suppress isomerization. A total reactor pressure of 300 p.s.i. is sufficient to obtain the desired hydrogen partial pressure at operating conditions. 

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Example B.I. Parameter estimation for pentane isomerization (after Kittrell (1972))... 

Many kinetic equations can be suitably linearized to the form of Eq. (20). For example, Eq. (1) can be transformed logarithmically, or Eq. (2) can be transformed reciprocally. Two equations proposed for describing pentane-isomerization data (Cl, Jl) are the single site... 

An analysis of variance can also be used to test the adequacy of more theoretical models. For example, two models considered in Section III for pentane isomerization are the single-site and dual-site models of Eqs. (30) and (31). These were linearized to provide Eqs. (32) and (33). The overall fit of these equations to the data may now be judged by an analysis of variance, reported in Tables V and VI (K3). It is seen that Eq. (33) fits the data quite... 

Koradia, P., Kiovsky, J.R., and Asim, M.Y. (1980) Optimization of SiOy/AlyOy, mole ratio of mordenite for n-pentane isomerization. . Catal., 66, 290-293. 

Recent data on other alloys confirm the overall classification presented above, but at the same time lead to some refinement of the picture. For example, the most diluted Pt-Au alloys revealed isomerization, identified as running via 3C intermediates. This evidence was obtained (248) by establishing the fact that pentane isomerizes on most diluted Pt-Au alloys with 100% selectivity, whereas this molecule can only isomerize via the 3C complexes. This conclusion has been confirmed by the isotopic labeling method (269). It is therefore reasonable to assume that this isomerization can also proceed on isolated Pt sites, as can a part of dehydrocyclization and the dehydrogenation. We must conclude on the basis of this information that on metals like Pt, the fast multisite and the slow one-site mechanisms of hydrocarbon reactions may operate in parallel with each other. 

Pentane isomerization was carried out on a much smaller scale. Isopentane, because of its high octane number and good lead response, was blended directly into aviation gasoline. It also served to increase the volatility of blends containing such high-boiling components as alkylate. 

The other commercialized pentane isomerization process is that of the Standard Oil Co. (Indiana) (20). This process differs from the Indiana-Texas butane process in that the aluminum chloride is introduced as a slurry directly to the reactor and that about 0.5% by volume of benzene is added continuously in the feed to suppress side reactions. Temperature, catalyst composition, space velocity, and hydrogen chloride concentration are generally similar to those in the corresponding butane process, but the reactor pressure is about 100 pounds lower. The Pan American Refining Co. operated the Indiana pentane isomerization process commercially during the last nine months of the war and produced about 400 barrels of isopentane per calendar day. 

The ability of water molecules to promote a reaction depends on many factors. In most cases, zeolites with monovalent cations have low activity. However, the addition of water molecules to X and Y zeolites with monovalent ions increased the isomerization of cyclopropane (63). De-cationized zeolites can be promoted readily with water, and the process is reversible (2, 60, 64). It was shown (2) that the promoting ability of water molecules in faujasites is less when the Si02/Al203 increases. Dealu-minated faujasites are even more difficult to promote. For erionite and mordenite the maximum effect of water was observed only after treatment with liquid water and subsequent heating (2). The effect of water on zeolites saturated with polyvalent cations is less pronounced (65, 66, 67). However, the presence of multivalent cations stabilizes the catalytic activity. Water and alcohols were reported to promote ion exchanged zeolites for n-pentane isomerization (68) and n-hexadecane hydrocracking (69). 

Catalysts Based on Mordenite. Isomerization of paraffins over H-mordenite based catalysts has been described (6, 7,14, 0, 21). Minachev (7) reports that cyclohexane isomerization activity of Na-H-mordenite catalysts increases linearly with H+ concentration in the zeolite for 25-94% exchange. He further observed that H-mordenite is deactivated by other cations such as Li, K, Mg, Cd, Zn, and Al. This agrees with Bryant s work (6) he reported that, compared with Pd-H-mordenite, samples in which hydrogen was partly replaced by Ca or Zn had an appreciably lower n-pentane isomerization activity. 

The mechanism and kinetics of pentane, hexane, and cyclohexane isomerization over Pd-H-mordenite have been extensively investigated by Bryant (6), Hopper (21), and Beecher (20). They assume a conventional dual function mechanism as described earlier. Bryant (6) pointed out that H-mordenite itself has a high activity for pentane isomerization and that impregnation of a noble metal does not change the rate of the isomerization reaction. This exceptional activity of mordenite has since been reported by Benesi (14) and Minachev (7) as well. In Mina-chev s paper the reaction mechanism of n-pentane isomerization over H-mordenite is discussed in some detail. The rate of reaction is inversely proportional to the hydrogen pressure, and it is concluded that the reaction proceeds according to the following scheme ... 

Figure 2. n-Pentane isomerization activity of mordenite. Platinum stabilizes conversion and increases selectivity. 

Fig. 5. Isomerization rate versus pentene partial pressure (S4). Comparison of n-pentane isomerization rate over platinum-alumina catalyst with the rate of skeletal isomerization of 1-pentene over the platinum-free catalyst 372°C.

Thus, at 372°C. and over the range of pressures and hydrogen to n-pentane ratios covered in the investigation, it appears that the proposed mechanism can account in large part for the observed kinetic data. However, Starnes and Zabor (S8) have proposed an alternative mechanism, based on their studies of n-pentane isomerization over platinum-alumina-halogen catalysts. They postulate that the paraffin is adsorbed on platinum sites with dissociation of a hydrogen atom, followed by polarization of the adsorbed species. 

After the war the need for aviation alkylate declined rapidly, and most of the isomerization units closed down. During the motor gasoline octane race in the 1950 s, a number of butane isomerization units were placed on stream. Several pentane isomerization units were placed on stream in the 1960 s, and it is believed that only one or two plants today are being used to isomerize a C5/C6 straight run cut (41). 

Pentane Isomerization—Isomerization of n-C5 appears to be the most attractive for the C4-C7 paraffins. By recycling n-C5 the unleaded RON... 

Figure 5.11. Variation of the composition of the catalytic phase as a function of the SbF5 concentration in the n-pentane isomerization in HF—SbF5.90 T — 15°C, pm = 5 bars, volume of the catalytic phase = 57 ml. , Mass of C5+, o, mass of C5H (Freon-113 extract) a, % weight of Cs+ + C5H (methylcyclopentane extract).

Pentafining a pentane isomerization process using a regenerable platinum catalyst on a silica-alumina support and requiring outside hydrogen. 

Pt-Re A1203 support Partial coke burning. C6H6 hydrogenation and n-pentane isomerization. 

In order to follow the catalytic recovering produced by the burning of coke, partially regenerated catalyst samples were submitted to standard reaction tests for benzene hydrogenation (metallic function) and normal pentane isomerization (acid function). Benzene hydrogenation was done at 423 K, 0.1 MPa, WHSV = 2 h 1, and molar ratio H2/Bz = 20. 200 mg of catalyst were loaded, which was reduced at 533 K with H2 for 2 h before the test. The isomerization of n-pentane was performed at 773 K, 0.1 MPa, WHSV = 2 h 1 and molar ratio H n = 6. 200 mg of catalyst were loaded, and were reduced with hydrogen at 773 K for 2 h before the test. 

Figure 4. Relative metallic or acidic activity as a function of relative residual carbon content on the "burned1 catalyst. The unity of catalytic activity is the percentage of cyclohexane produced by hydrogenation of benzene (a), or i-pentane produced by n pentane isomerization (b), over the completely decoked catalyst. The unity of residual carbon is the percentage of carbon in the initial catalyst (Table 1). I, catalyst I burnt with ozone-air II, catalyst II burnt with 02-N2 III, catalyst III burnt with 02-N2.

Keywords alkanes-isomerization iron-promoter n-pentane-isomerization platinum-promoter selectivity tungsten oxide zirconia-tungstated-acidity zirconia-tungstated-redox properties... 

When iron is added as a second promoter, the performance of PtFeWZ catalysts is dramatically improved in the presence of dihydrogen in the feed.19,21 Under identical reaction conditions, PtFeWZ(S) is characterized by an n-pentane isomerization rate of 9 x 10 x mol s 1 m 2. Whereas the PtWZ catalyst is characterized by a nearly stable selectivity of about 95% (see Table 2), the PtFeWZ(S) catalyst develops a selectivity (increasing with TOS) of up to 98%, and PtFeWZ(N) shows a stable selectivity greater than 99%. The suppression of the hydrogenolysis products, which are formed on the platinum in PtWZ by the addition of iron as a second promoter, might be a consequence of the suppression of the formation of metallic platinum. Furthermore, the redox properties of the Fe3+/Fe2+ pair in the surface solid solution (see above) might... 

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