Paraffinic hydrocarbons, isomerization

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). 

Wiener H (1947b) Correlation of heats of isomerization, and differences in heats of vaporization of isomers, among the paraffin hydrocarbons. J. Am. Chem. Soc. 69 2636-2638. 

Isomerization the conversion of a normal (straight-chain) paraffin hydrocarbon into an iso (branched-chain) paraffin hydrocarbon having the same atomic composition. 

The octane number improvement obtained by isomerization of paraffin hydrocarbons is not great since the amounts of the more highly branched paraffins formed at equilibrium are small at the temperatures employed in catalytic reforming (5). Naphthene isomerization, on the other hand, plays a more important role in reforming. In most naphthas about 50% of the naphthene hydrocarbons are of the cyclopentane type (4) so that in order to obtain the maximum aromatic formation, isomerization of these rings to cyclohexane rings must be promoted by the catalyst. 

Isomerization has long been familiar to organic chemists, but reactions of this type have become important in petroleum chemistry only in relatively recent years. Not until 1933 did the first paper on the isomerization of individual paraffinic hydrocarbons appear in the scientific literature (11). 

Isomate process a continuous, nonregenerative process for isomerizing C5-C8 normal paraffinic hydrocarbons, using aluminum chloride-hydrocarbon catalyst with anhydrous hydrochloric acid as a promoter. 

Due to the high concentration of linear n-paraffin hydrocarbons in fnel derived from PE, it is desirable to isomerize them in order to lower the cloud point and the freezing point of the fuel. The branched isomers do not exhibit the same tendency to crystallize as linear paraffins, so that wax crystals do not form nntil lower temperatures are reached. 

Diffiisional restrictions increase the effectiveness of olefin interception sites placed within catalyst pellets. Very high olefin hydrogenation turnover rates or site densities within pellets prevent olefin readsorption and lead to Flory distributions of lighter and more paraffinic hydrocarbons. Identical results can be obtained by introducing a double-bond isomerization function into FT catalyst pellets because internal olefins, like paraffins, are much less reactive than a-olefins in chain initiation reactions. However, light paraffins and internal olefins are not particularly useful end-products in many applications of FT synthesis. Yet, similar concepts can be used to intercept reactive olefins and convert them into more useful products (e.g., alcohols) and to shift the carbon number distribution into a more useful range. In the next section, olefin readsorption model simulations are used to explore these options in the control of FT synthesis selectivity. 

With the higher members of the paraffin hydrocarbons we have isomerism, due to the different positions in which the two hydroxyl groups are found. Propane, for example, yields two di-hydroxy derivatives, viz.,... 

Wiener, H. (1947a). Correlation of Heat of Isomerization, and Differences in Heats of Vaporization of Isomers, among the Paraffin Hydrocarbons. J.Am.Chem.Soc., 69,2636-2638. 

In catalytic cracking many reactions take place simultaneously. Cracking occurs by C-C bond cleavage of paraffins, dealkylation etc. Isomerization and even condensation reactions take place. These reactions occur via positively charged hydrocarbon ions (carbocations). The nature of the carbocations is the subject of debate. For the cracking of paraffinic hydrocarbons it is usually assumed that carbenium ions are the crucial intermediates, which decompose via beta fission into olefins and (smaller) carbenium ions (see Chapter 4, Section 4.4). A typical reaction mechanism for catalytic cracking (and hydrocracking) imder the relatively mild conditions used in FCC is shown overleaf. 

Branched chain a linear series of carbon atoms occurring in paraffinic hydrocarbons and some alcohols that is isomeric with its straight chain counterpart and has a subordinate chain of one or more carbon atoms ... 

In a recent patent Kramer and Leder (1975) describe an SCF reaction scheme for isomerizing short-chain paraffinic hydrocarbons (4-12 carbon atoms). The reaction medium consists of CO2, HBr, or HCl (as a promoter), a paraffinic hydrocarbon, and a Lewis acid catalyst (e.g., AlBr3, AICI3, BF3). 

By the use of these graphs, an approximation may be made of the isomeric monochloride compositions obtained by chlorination of a number of paraffin hydrocarbons. 

In catalytic dewaxing, linear alkanes are separated from branched hydrocarbons by cracking the molecules over zeolites with micropores that access linear alkanes only, but not branched molecules. Branched alkanes are desired as high octane gasoline components. A low reaction temperature (200° C) is preferred for the isomerization reaction because isomerization is an exothermic reaction. In this reaction linear paraffins are isomerized and more branched molecules are produced. 

Paraffin skeletal isomerization is the second of the reaction-producing high-octane hydrocarbons, though TMPs cannot be obtained by using diverse isomerization catalysts, even the Pt/Cl-Al Oj, has been used on the industrial scale in n-butane isomerization... 

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