Isobutane, branched hydrocarbon

This phenomenon is also observed during the hydrogenolysis of branched hydrocarbons such as isobutane carried out under the same conditions an excess of 8% of methane versus propane is observed. With neopentane the excess of methane versus isobutane reaches 15%. 

In contrast with these results, catalytic cracking yields a much higher percentage of branched hydrocarbons. For example, the catalytic cracking of cetane yields 50-60 mol of isobutane and isobutylene per 100 mol of paraffin cracked. Alkenes crack more easily in catalytic cracking than do saturated hydrocarbons. Saturated hydrocarbons tend to crack near the center of the chain. Rapid carbon-carbon double-bond migration, hydrogen transfer to trisubstituted olefinic bonds, and extensive isomerization are characteristic.52 These features are in accord with a carbo-cationic mechanism initiated by hydride abstraction.43,55-62 Hydride is abstracted by the acidic centers of the silica-alumina catalysts or by already formed carbocations ... 

In water, isobutane is fifty times better bound than isobutene, and ten times better than n-butane. These results confirm the preference of the cryptophane cavity for tetrahedral structures, and show that branched hydrocarbons are much better substrates than linear ones. Separation processes based on such molecular... 

The conventional isosynthesis for producing branched hydrocarbons appears to be mainly of academic interest, especially in this country. It was developed on a laboratory scale in Germany when there was an extreme need for isobutene and isobutane, as a starting material for the production of aviation fuels. As shown in Table 11-11, about 57 per cent of the Cj- -product is Cj and C4 hydrocarbons, and 80 per cent of the C4 is branched. Rather severe operating conditions include a temperature of 400-450°C and pressure of 100-300 atm. The common Fischer-Tropsch catalysts are not satisfactory for the isosynthesis. The more recent development to yield aromatics may be of commercial value at some time. 

The isomerization of n-butane to isobutane is of substantial importance because isobutane reacts under mild acidic conditions with olefins to give highly branched hydrocarbons in the gasoline range. A variety of useful products can be obtained from isobutane isobutylene, t-butyl alcohol, methyl t-butyl ether and t-butyl hydroperoxide. A number of methods involving solution as well as solid acid catalysts have been developed to achieve isomerization of n-butane as well as other linear higher alkanes to branched isomers. 

An isomer of butane, for example, has the same molecular formula as the straight-chained compound shown in Figure 14-2, C4H10, but a different bonding pattern. This isomer is mostly referred to by the common name isobutane and is what I call a branched hydrocarbon. Check out Figure 14-3 to see it shown in a variety of ways. 

Gas mixture separation processes are based on the specific pore size distribution of CMS, which permits diffusion of different gasses at different rates. These processes aim to either recover and recycle valuable constituents from industrial waste gases, or to separate small gas molecules by preferential adsorption. The latter is at present the most important large scale application of CMS. Separations that have been accomplished include oxygen from nitrogen in air, carbon dioxide from methane in natural gas, ethylene from ethane, linear from branched hydrocarbons (such as n-butane from isobutane), and hydrogen from flue gases [6]. 

This Is used In some petroleum refineries to convert alkenes and Isobutane Into higher molecular-weight branched hydrocarbons that have higher octane ratings for gasoline. 

Nonselective polymerization involves the polymerization of propene, the butenes, and about one-fifth of the ethene whereas selective polymerization employs only the butenes or in some cases only isobutene. The gasoline from selective operation is primarily 2,2,4-trimethylpentene or similar branched hydrocarbons (Codimer) which have a high octane number (92 to 103). The Codimer may be hydrogenated to make isooctane. Obviously, special methods of feed preparation or fractionation must be employed for selective operation, and the same applies to alkylation which is frequently applied to only the butylenes and isobutane. 

Alkanes are a class of saturated hydrocarbons with the general formula C H2n. -2- They contain no functional groups, are relatively inert, and can be either straight-chain (normal) or branched. Alkanes are named by a series of IUPAC rules of nomenclature. Compounds that have the same chemical formula but different structures are called isomers. More specifically, compounds such as butane and isobutane, which differ in their connections between atoms, are called constitutional isomers. 

The paraffin hydrocarbon containing four carbon atoms is called butane, but two 4-carbon (C4) paraffins are possible. The butane with its carbons in a line is known as normal butane or n-butane. The branched chain butane is isobutane or i-butane. Although each compound has the formula C4H10, they have different properties for example, n-butane boils at -0.5°C while isobutane boils at -11.7°C. n-Butane and i-butane are isomers of each other. The straight-chain paraffin is always called the normal form. 

Fig. 12.4. Vapor-to-water transfer data for saturated hydrocarbons as a function of accessible surface area, from [131]. Standard states are 1M ideal gas and solution phases. Linear alkanes (small dots) are labeled by the number of carbons. Cyclic compounds (large dots) are a = cyclooctane, b = cycloheptane, c = cyclopentane, d = cyclohexane, e = methylcyclopentane, f = methylcyclohexane, g = cA-l,2-dimethylcyclohexane. Branched compounds (circles) are h = isobutane, i = neopentane, j = isopentane, k = neohexane, 1 = isohexane, m = 3-methylpentane, n = 2,4-dimethylpentane, o = isooctane, p = 2,2,5-tri-metbylhexane. Adapted with permission from [74], Copyright 1994, American Chemical Society...

Table I gives the compositions of alkylates produced with various acidic catalysts. The product distribution is similar for a variety of acidic catalysts, both solid and liquid, and over a wide range of process conditions. Typically, alkylate is a mixture of methyl-branched alkanes with a high content of isooctanes. Almost all the compounds have tertiary carbon atoms only very few have quaternary carbon atoms or are non-branched. Alkylate contains not only the primary products, trimethylpentanes, but also dimethylhexanes, sometimes methylheptanes, and a considerable amount of isopentane, isohexanes, isoheptanes and hydrocarbons with nine or more carbon atoms. The complexity of the product illustrates that no simple and straightforward single-step mechanism is operative rather, the reaction involves a set of parallel and consecutive reaction steps, with the importance of the individual steps differing markedly from one catalyst to another. To arrive at this complex product distribution from two simple molecules such as isobutane and butene, reaction steps such as isomerization, oligomerization, (3-scission, and hydride transfer have to be involved.

The conversion of a chemical with a given molecular formula to another compound with the same molecular formula but a different molecular structure, such as from a straight-chain to a branched-chain hydrocarbon or an alicyclic to an aromatic hydrocarbon. Examples include the isomerization of ethylene oxide to acetaldehyde (both C2H40) and butane to isobutane (both C4H10). 

Alkylation in the petroleum industry, a process by which an olefin (e.g., ethylene) is combined with a branched-chain hydrocarbon (e.g., isobutane) alkylation may be accomplished as a thermal or a catalytic reaction. 

Sulfuric acid alkylation an alkylation process in which olefins (C3, C4, and C5) combine with isobutane in the presence of a catalyst (sulfuric acid) to form branched-chain hydrocarbons used especially in gasoline blending stock. 

Alkanes are straight-chained or even branch-chained hydrocarbon molecules made up of methyl groups having the formula CnH2n+2i such as butane, isobutane, and pentane. 

Hydrocarbons (multibranched chain) from singly branched and straight-chain hydrocarbons KBaX Isobutane [152]... 

---