Natural isobutane

Because the protonation of ozone removes its dipolar nature, the electrophilic chemistry of HOs, a very efficient oxygenating electrophile, has no relevance to conventional ozone chemistry. The superacid-catalyzed reaction of isobutane with ozone giving acetone and methyl alcohol, the aliphatic equivalent of the industrially significant Hock-reaction of cumene, is illustrative. 

Butanes are naturally occurring alkane hydrocarbons that are produced primarily in association with natural gas processing and certain refinery operations such as catalytic cracking and catalytic reforming. The term butanes includes the two stmctural isomers, / -butane [106-97-8] CH2CH2CH2CH2, and isobutane [79-28-9], (CH2)2CHCH2 (2-methylpropane). 

In 1987 nonmotor fuel uses of butanes represented ca 16% of the total consumption. Liquid petroleum gas (LPG) is a mixture of butane and propane, typically in a ratio of 60 40 butane—propane however, the butane content can vary from 100 to 50% and less (see Liquefied petroleum gas). LPG is consumed as fuel in engines and in home, commercial, and industrial appHcations. Increasing amounts of LPG and butanes are used as feedstocks for substitute natural gas (SNG) plants (see Fuels, synthetic). / -Butane, propane, and isobutane are used alone or in mixture as hydrocarbon propellents in aerosols (qv). 

The overhead product from the lean-oil fractionator, consisting of propane and heavier hydrocarbons, enters the depropanizer. The depropanizer overhead product is treated to remove sulfur and water to provide specification propane. The depropanizer bottoms, containing butane and higher boiling hydrocarbons, enters the debutanizer. Natural gasoHne is produced as a bottom product from the debutanizer. The debutanizer overhead product is mixed butanes, which are treated for removal of sulfur and water, then fed iato the butane spHtter. Isobutane is produced as an overhead product from the spHtter and / -butane is produced as a bottoms product. 

The hydrocarbon cracking operations that generate feed olefins generally do not produce sufficient isobutane to satisfy the reaction requirements. Additional isobutane must be recovered from cmde oil or natural gas Hquids or generated by other refinery operations. A growing quantity of isobutane is produced by the isomerization of / -butane [106-97-8]. 

Liquefied Petroleum Gas The term liquefied petroleum gas (LPG) is applied to certain specific hydrocarbons which can be liquefied under moderate pressure at normal temperatures but are gaseous under normal atmospheric conditions. The chief constituents of LPG are propane, propylene, butane, butylene, and isobutane. LPG produced in the separation of heavier hydrocarbons from natural gas is mainly of the paraffinic (saturated) series. LPG derived from oil-refinery gas may contain varying low amounts of olefinic (unsaturated) hydrocamons. 

The most common fuels were divided into three groups according to reactivity. The low-reactivity group included ammonia, methane, and natural gas hydrogen, acetylene, and ethylene oxide were classified as highly reactive. Those within these extremes, for example, ethane, ethylene, propane, propylene, butane, and isobutane, were classified as medium-reactivity fuels. 

Like propane, butanes are obtained from natural gas liquids and from refinery gas streams. The C4 acyclic paraffin consists of two isomers n-butane and isobutane (2-methylpropane). The physical as well as the chemical properties of the two isomers are quite different due to structural differences, for example, the vapor pressure (Reid method) for n-butane is 52 Ib/in., while it is 71 Ib/in. for isobutane. This makes the former a more favorable gasoline additive to adjust its vapor pressure. However, this use is declining in the United States due to new regulations that reduce the volatility of gasolines to 9 psi, primarily by removing butane. ... 

Like propane, n-hutane is mainly obtained from natural gas liquids. It is also a hy-product from different refinery operations. Currently, the major use of n-hutane is to control the vapor pressure of product gasoline. Due to new regulations restricting the vapor pressure of gasolines, this use is expected to he substantially reduced. Surplus n-butane could be isomerized to isobutane, which is currently in high demand for producing isobutene. Isobutene is a precursor for methyl and ethyl tertiary butyl ethers, which are important octane number boosters. Another alternative outlet for surplus n-butane is its oxidation to maleic anhydride. Almost all new maleic anhydride processes are based on butane oxidation. 

The co-refining synergy of natural gas liquids and Fe-HTFT was exploited for alkylate production. The natural gas liquids serve as a source of butane that can be hydroisomerized to yield isobutane that is alkylated (HF process) to produce a... 

A variety of solid acids besides zeolites have been tested as alkylation catalysts. Sulfated zirconia and related materials have drawn considerable attention because of what was initially thought to be their superacidic nature and their well-demonstrated ability to isomerize short linear alkanes at temperatures below 423 K. Corma et al. (188) compared sulfated zirconia and zeolite BEA at reaction temperatures of 273 and 323 K in isobutane/2-butene alkylation. While BEA catalyzed mainly dimerization at 273 K, the sulfated zirconia exhibited a high selectivity to TMPs. At 323 K, on the other hand, zeolite BEA produced more TMPs than sulfated zirconia, which under these conditions produced mainly cracked products with 65 wt% selectivity. The TMP/DMH ratio was always higher for the sulfated zirconia sample. These distinctive differences in the product distribution were attributed to the much stronger acid sites in sulfated zirconia than in zeolite BEA, but today one would question this suggestion because of evidence that the sulfated zirconia catalyst is not strongly acidic, being active for alkane isomerization because of a combination of acidic character and redox properties that help initiate hydrocarbon conversions (189). The time-on-stream behavior was more favorable for BEA, which deactivated at a lower rate than sulfated zirconia. Whether differences in the adsorption of the feed and product molecules influenced the performance was not discussed. 

Moreover, the efficiency of these catalysts could be modihed by tailoring the nature of the metal oxide support and/or reaction conditions (especially the reaction temperature). In this way, interesting conclusions can be obtained when comparing the isobutane/2-butene alkylation catalyzed on two of the most studied catalysts, that is, beta zeolite and sulfated zirconia, when operating at different reaction temperatures. (Table 13.2). ... 

Petkovic, L.M. and Ginosar, D.M. (2004) The efiect of supercritical isobutane regeneration on the nature of hydrocarbons deposited on a USY zeolite catalyst utilized for isobutane/butene alkylation. Appl. Catal. A, 275, 235-245. 

Isobutane can be isolated from the petroleum C4 fraction or from natural gas by extraction and distillation. 

Recent DFT calculations by Sarzi-Amade and his collaboratorsmay well have resolved this mechanistic difference between a biradicaloid TS (Scheme 7, path b) and a mechanism involving discrete long-lived free radicals (Scheme 8). Oxygen insertion into the C—H bond of isobutane by DMDO was studied computationally at the unrestricted B3LYP level. Transition structures that were diradicaloid in nature were found to lead to... 

In gas-phase oxidations of isobutane at around 350°C., several workers have reported that the products are about 80% isobutylene and 20% of a mixture of several oxygen compounds. Hay, Knox, and Turner (5) have reported that the nature, but not the total amount, of the oxygen compounds depends on the walls of the reaction vessel. They proposed that oxygen compounds arise from wall reactions. I have found that other workers show little enthusiasm for this conclusion, but the right answer is important. 

One of the most important challenges in the modern chemical industry is represented by the development of new processes aimed at the exploitation of alternative raw materials, in replacement of technologies that make use of building blocks derived from oil (olefins and aromatics). This has led to a scientific activity devoted to the valorization of natural gas components, through catalytic, environmentally benign processes of transformation (1). Examples include the direct exoenthalpic transformation of methane to methanol, DME or formaldehyde, the oxidation of ethane to acetic acid or its oxychlorination to vinyl chloride, the oxidation of propane to acrylic acid or its ammoxidation to acrylonitrile, the oxidation of isobutane to... 

When two different compounds have the same molecular formula but differ in the nature or sequence of bonding, they are called constitutional isomers. For example, ethanol and dimethylether have same molecular formula, C2HgO, but they differ in the sequence of bonding. Similarly, butane and isobutane are two constitutional isomers. Constitutional isomers generally have different physical and chemical properties. 

The wartime role of isomerization in the United States is summarized in Figure 1. Most of the units were built to supplement the natural supply of isobutane for alkylation. Domestic production of synthetic isobutane began in 1941 and rose in four years to more than 40,000 barrels per day. Most of the isomerization units were shut down when the military need for aviation gasoline dropped after the close of the war in Europe in May 1945. 

Anderson and Erskine (1) in 1924, relating to propane, n-butane, isobutane, n-pentane, isopentane, n-hexane, n-heptane, n-octane, and Ce and C7 branched paraffins in a natural gasoline... 

The nature of the methanol-zeolite interaction has been shown to be sensitive to a number of parameters and as such has proved to be a good benchmark for judging the reliability of quantum chemical methods. Not only are there a number of possible modes whereby one and two molecules interact with an acidic site (245), the barrier to proton transfer is small and sensitive to calculation details. Recent first-principles simulations (236-238) suggest that the nature of adsorbed methanol may be sensitive to the topology of the zeolite pore. The activation and reaction of methane, ethane, and isobutane have been characterized by using reliable methods and models, and realistic activation energies for catalytic reactions have been obtained. 

Another way to reduce the compressor discharge pressure is to render the refrigerant heavier, or less volatile. Adding isobutane to a propane refrigerant is one common example. Naturally, this will lower the suction pressure to the refrigerant compressor shown in Fig. 22.1, and increase the actual volume of vapor flow. If the compressor is speed-limited, this will not be practical. 

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