Isomerization hydrocarbons

In addition to separating product from catalyst, excess ligand and reaction solvent, one must also separate byproducts arising from the reactants or products. For example in hydroformylation, one must separate saturated hydrocarbon, isomerized alkene and aldehyde dimers and trimers. 

Isomerate A continuous hydrocarbon isomerization process for converting pentanes and hexanes to highly branched isomers. Developed by the Pure Oil Company, a division of the Union Oil Company of California. The catalyst, unlike those used in most such processes, does not contain a noble metal. 

With gem-dimethyl hydrocarbons, isomerization and demethylation compete with each other. Isomerization predominates in the presence of acidic centers. Over platinum supported by acidic alumina 1,1-dimethylcyclo-hexane gave 18% toluene and 60% o-xylene (percentages of the total aro-... 

For the reaction with u-heptane, Friedmann again postulated the hydrocarbon isomerization. He obtained two products, C HjoS (A) and C7HJS2 (B). The structure of methylthieno[2,3-6]thiophene was ascribed to product B, though again there seems to be no reason to neglect the isomeric methylthieno[3,2-t]thiophene structure. 

G.l.c. papers of interest include the classification of 22 acyclic monoterpenoid alcohols according to retention indexes, resolution of cyclic ketones [e.g. ( )-menthone, ( )-isomenthone] as diethyl (+)-tartrate acetals, and the use of lanthanide shift reagents to resolve non-terpenoid racemic epoxides.The occurrence and prevention of monoterpenoid hydrocarbon isomerization during silica gel chromatography has been examined and the separation of monoterpenoids and sesquiterpenoids by gel permeation chromatography is reported. Monoterpenoid hydrocarbons have been selectively extracted from essential oils using dimethylsilicone. ... 

Olefin Isomerization. One other type of hydrocarbon isomerization is on the threshold of commercialization—namely, that of olefins. Processes for olefin isomerization were first developed some 15 years ago (11, 14, 20) after it was recognized that highly branched olefins have higher octane numbers than do their straight-chain isomers, and that the octane numbers of olefins increase as the double bond moves toward the middle of the molecule. 

Pericyclic reactions are unimolecular, concerted, uncatalyzed transformations. They take place in a highly stereoselective manner governed by symmetry proper-ties of interacting orbitals. - Characteristic of all these rearrangements is that they are reversible and may be effected thermally or photochemically. The compounds in equilibrium are usually interconverted through a cyclic transition state,224 although biradical mechanisms may also be operative. A few characteristic examples of pericyclic rearrangements relevant to hydrocarbon isomerizations are presented here. 

The thermodynamic ratio for the neutral hydrocarbon isomerization is very different as compared with the isomerization of the corresponding ions. The large energy difference (> 10 kcal mol-1) between secondary cyclohexyl cation 22 and the tertiary methylcyclopentyl ion 23 means that in the presence of excess superacid, only the latter can be observed [Eq. (5.47)]. 

In unsaturated hydrocarbons, isomerism can occur because of the position of the double or triple bond. 

This is a mechanism of polyolefin cracking. The main polymer chains are reduced by reaction with protons or other carbonium ions, followed by chain scission giving C30-C50 oligomeric hydrocarbons [7], As a result of further, secondary cracking reactions by P-scission of C30-C50 hydrocarbons, gas and lower-molecular liquid C10-C25 hydrocarbons are produced. Other reactions are double bond and saturated hydrocarbon isomerization as well as methyl group shift . 

The hydrogen form of mordenite is an extremely active catalyst in paraffin hydrocarbon isomerization as well. For example, 50% of n-pentane at 280 °C and 30 atm undergoes isomerization to produce isopentane. To attain the same degree of hydrocarbon isomerization with H-mor-denite as compared with bifunctional catalysts involving Pt, Pd, and Ni per AI2O3 or zeolite, the temperature should be 70°-120° lower 14). 

Pseudo-cumene, 1-2-4-Tri-methyl Benzene.—The second hydrocarbon, isomeric with mesitylene, and therefore tri-methyl benzene, is known as pseudo-cumene. It occurs also in coal tar, and resembles mesitylene in its properties. Its boiling point is 169°. Its structure is proven to be 1-2-4-tri-methyl benzene from the following reactions. 

Gallium oxides and Ga-containing materials are catalytically active in a variety of reactions, including hydrocarbon isomerization, dehydrogenation and aromatization,... 

Early transition metal carbides with high surface area are active catalysts for various reactions such as hydrodenitrogenation(HDN) [1,2], hydrogenation [3,4], Fischer-Tropsch synthesis [5,6], hydrocarbon isomerization [7]. Synthesis of these materials has attracted great attention over the years and a number of procedures have been reported for the preparation of carbides with high surface areas suitable for catalysts. The most commonly employed method is temperature programmed reaction of metal oxide with a mixture of hydrogen and methane, which was developed by Boudart and co-workers [8-10]. 

Figure n.4 Schematic P-T diagram of the reacting mixture in the hydrocarbon isomerization process proposed by Leder, Kramer, and Solomon... 

Catalysts which promote carbonium ion reactions have long been used for hydrocarbon isomerization (2, 6). Although such catalysts promote aromatics isomerization (3), in the case of ethylbenzene, the predominant reactions are disproportionation and dealkylation (5). Pitts, Connor, and Leum (7) demonstrated that hydrogenated intermediates were required to isomerize both ethylbenzene and cumene over platinum-... 

Azulene, a bicyclic C,oHg hydrocarbon isomeric with naphthalene, was first reported as a tobacco smoke component by Ikeda (1857) and subsequently by Gilbert and Lindsey (1287, 1288), Lindsey (2365), and Lyons (2426). Despite improved analytical technology and hundreds of studies on the identification of PAHs in tobacco smoke, very few reports of its identification have appeared since those in the 1950s. This suggests... 

Isomeres of Terebenthene.—There exist a great number of bodies, the products of distillation of vegetable substances, which are known as essences, essential oils, volatile oils or distilled oils. They resemble each other in being odorous, oily, sparingly soluble in water, more or less soluble in alcohol and ether colorless or yellowish, inflammable, and prone to become resinous on exposure to air. They are not simple chemical compounds, but mixtures, and in many of them the principal ingredient is a hydrocarbon, isomeric with terebenthene, and consequently having the composition jiCioH,. Some contain hydrocarbons, others aldehydes, acetones, phenols, and ethers. 

CHI3, is treated with zinc is an argument in favor of the accepted structure of the hydrocarbon. The properties of certain substitution-products of acetylene have led to the view that derivatives of a hydrocarbon isomeric with acetylene and having the structure H2C =C may exist. 

Hydrocarbons Isomerism in Alkanes Nomenclature Reactions of Alkanes Cyclic Alkanes... 

As shown in Section 17.1, the various hydrocarbon isomerization mechanisms are clearly size dependent i.e. they take place on separated surface sites. Obviously, their relative importance should be dependent on the same weighted d-band center. This is summarized schematically in Fig. 17.6 [32]. 

Finally, the applications of various spectroscopic and structural probes made possible the investigation of catalyst surfaces at a more microscopic leveL Studies with idealized surfaces such as the faces of single crystals in an ultra-high vacuum apparatus allowed us to investigate the role of the surface in catalysis. This was completed by spectroscopic studies of supported metallic particles allowing us to characterize the size dependence of the electronic system. Specific active sites for hydrocarbon isomerization were evidenced and their appearance was linked to the lowered atomic coordination. 

Weisz [100] utilized Eq. 3.6.C-5 to determine the minimum distance between the two types of active sites in a bifunctional catalyst so that the reactive intermediates could be sufficiently mobile to result in an appreciable overall reaction rate (this was qualitatively discussed in Sec. 2.1). For the important case of hydrocarbon isomerizations, the first step on catalytic site 1 has an adverse equilibrium, but the second step on site 2 is essentially irreversible ... 

Weisz [100] utilized typical values of parameters and observed reaction rates for hydrocarbon isomerizations to show that grain sizes of less than I fan for catalyst one or two can have extremely low intermediate (R) partial pressures of 10 atm, which would be unobservable even though the overall reaction had a finite rate. Also, for n-heptane isomerization, the thermodynamic equilibrium concentration under typical conditions, can be used in Eq. h to compute the minimum catalyst grain siro, or intimate, required for appreciable reaction to occur, not influenced by diffiisional limitations. At a 40 percent conversion to isoheptanes at 470°C, the result was... 

Itaconic Acid.—The concentrated solution of the alkali salt electrolyzed by Aarland gave a hydrocarbon isomeric with allylene, C,H<, which is said to have the formula CH, = C = CH,. Along with this compound, some propylene was formed, while a portion of the acid was always regenerated. 

Similar reactivity to Pt in alcohol synthesis, methane dehydrogenation, and hydrocarbon isomerization Excellent hydrodesulfurization activity Promotes the water gas shift (WGS) reaction at low temperatures High resistance to coking even under stoichiometric fuel reforming conditions Shows the potential of being sulfur-tolerant High selectivity for hydrocarbon conversions... 

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