Iso-butane

The isomerization of butane to iso butane in superacids is illustrative of a protolytic isomerization, where no intermediate olefins are present in equilibrium with carbocations. 

Figure B-20. Iso-butane pressure-enthalpy diagram. (FromEdmister and Lee.. 4pp/reJ//yc/rocarho r/ierm fynawMt t. Vbl. i Second Edition, Gulf Publishing Company, Houston, TX, 1984.)...

LPG is a mixture of propane and n- and iso-butanes, plus small amounts of theu olefmie eounterparts. The main sourees are natural gas wells, gas from erude oil wells and the eraeking of etude oil. The requirements for eommereial LPG are defined in national standards and a stenehing agent is added for some uses. 

The first step in a gas processing plant is to separate the components that are to be recovered from the gas into an NGL stream. It may then be desirable to fractionate the NGL stream into various liquefied petroleum gas (LPG) components of ethane, propane, iso-butane, or normal-butane. The LPG products are defined by their vapor pressure and must meet certain criteria as shown in Table 9-1. The unfractionated natural gas liquids product (NGL) is defined by the properties in Table 9-2. NGL is made up principally of pentanes and heavier hydrocarbons although it may contain some butanes and very small amounts of propane. It cannot contain heavy components that boil at more than 375°F. 

Compute the isomerization energy between two forms of C4Hjq iso-butane and n-butane using AMI, PM3 and HF/6-31G(d). How does each model chemistry compare with the observed energy difference (iso-butane minus n-butane) of -1.64 kcal-moT ... 

Figure 14.7 Typical clnomatogram obtained by using the refinery analyser system shown in Figure 14.6. Peak identification is as follows 1, hydrogen 2, Cg+, 3, propane 4, acetylene 5, propene 6, hydrogen sulfide 6, iso-butane 8, propadiene 9, n-butane, 10. iso-butene 11, 1-butene 12, traw-2-butene 13, cw-2-butene 14, 1,3-butadiene 15, iso-pentane 16, w-pen-tane 17, 1-pentene 18, tro 5-2-pentene 19, cw-2-pentene 20, 2-inethyl-2-butene 21, carbon dioxide 22, ethene 23, ethane 24, oxygen + argon, 25, niti Ogen, 26, carbon monoxide.

Figure 12-24H. Mollier diagram of properties of iso-butane. (Used by permission Elliott Company. All rights reserved.)...

Alkyl substituted dinitropentanes. There are two such compds of interest 1,2-Dinitro-2-Methyl-Propane. See Vol 5, D1391-R and Vol 2, B368-R where it is described as Dinitro-iso-butane The Sodium salt of 1,1-Dtnitro-2 Methoxy-Pentene. CH3.CH2.CH2.CH(0CH3).C.(Na)(N02)2,... 

Typical conditions in a process using H2SO4 as the catalyst are 5-10 °C, 2-5 bar, iso-butane olefin ratios of 10, and a residence time in the reactor of 20-30 min. The catalyst consumption rate is high (about 100 kg of acid per ton of alkylate prod-... 

The reactions proceed via carbenium ions in a chain mechanism, initiated by the reaction between an olefin and an acid to C-C -C, which then reacts with iso-butane to give C-C C)-C. This carbenium ion is the central species in propagation steps to alkylated products such as 2,2-dimethylpentane and related products (Fig. 9.14). 

As one more common example of liquid fuels present reference may be drawn to liquified petroleum gas (LPG) or bottled gas or refinery gas. This fuel is obtained as a by-product during the cracking of heavy oils or from natural gas. It is dehydrated, desulfurized and traces of odours organic sulfides (mercaptans) are added in order to identify whether a gas leak has occurred. Supply of LPG is carried out under pressure in containers under different trade names. It consists of hydrocarbons of great volatility such that they can occur in the gaseous state under atmospheric pressure, but are readily liquifiable under high pressures. The principal constituents of LPG are n-butane, iso-butane, butylene and propane,... 

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