Cycloparaffins, reaction

The principal class of reactions in the FCC process converts high boiling, low octane normal paraffins to lower boiling, higher octane olefins, naphthenes (cycloparaffins), and aromatics. FCC naphtha is almost always fractionated into two or three streams. Typical properties are shown in Table 5. Properties of specific streams depend on the catalyst, design and operating conditions of the unit, and the cmde properties. 

Nitrations are highly exothermic, ie, ca 126 kj/mol (30 kcal/mol). However, the heat of reaction varies with the hydrocarbon that is nitrated. The mechanism of a nitration depends on the reactants and the operating conditions. The reactions usually are either ionic or free-radical. Ionic nitrations are commonly used for aromatics many heterocycHcs hydroxyl compounds, eg, simple alcohols, glycols, glycerol, and cellulose and amines. Nitration of paraffins, cycloparaffins, and olefins frequentiy involves a free-radical reaction. Aromatic compounds and other hydrocarbons sometimes can be nitrated by free-radical reactions, but generally such reactions are less successful. 

The conversion proceeds through dimethyl ether as an intermediate and the products are paraffins, aromatics, cycloparaffins, and +olefins, all of which must involve alkylation reactions catalyzed by the strong acid function of the zeoHte. This technology represents a significant advancement in the potential for using coal as a raw material for gasoline and hydrocarbons. 

During the cracking process, fragmentation of complex polynuclear cyclic compounds may occur, leading to formation of simple cycloparaffins. These compounds can he a source of Ce, C7, and Cg aromatics through isomerization and hydrogen transfer reactions. 

Scheme A. This scheme is typical of the hydrocarbons, which are oxidized with the production of secondary hydroperoxides (nonbranched paraffins, cycloparaffins, alkylaro-matic hydrocarbons of the PhCH2R type) [3,146]. Hydroperoxide initiates free radicals by the reaction with RH and is decomposed by reactions with peroxyl and alkoxyl radicals. The rate of initiation by the reaction of hydrocarbon with dioxygen is negligible. Chains are terminated by the reaction of two peroxyl radicals. The rates of chain initiation by the reactions of hydroperoxide with other products are very low (for simplicity). The rate of hydroperoxide accumulation during hydrocarbon oxidation should be equal to ...

This holds not only for aromatic and olefinic compounds but also for cycloparaffins which likewise take part in the Friedel-Crafts reaction. 

Attention will be focussed on three typical chemical reaction schemes. For the first illustration, two parallel competing reactions are considered. For instance, it may sometimes be necessaru to convert into a desired product only one component in a mixture. The dehydrogenation of six-membered cycloparaffins in the presence of five-membered cycloparaffins without affecting the latter is one such example of a selectivity problem in petroleum reforming reactions. In this case, it is desirable for the catalyst to favour a reaction depicted as... 

The initial dehydration reaction is sufficiently fast to form an equilibrium mixture of methanol, dimethyl ether, and water. These oxygenates dehydrate further to give light olefins. They in turn polymerize and cyclize to form a variety of paraffins, aromatics, and cycloparaffins. The above reaction path is illustrated further by Figure 3 in terms of product selectivity measured in an isothermal laboratory reactor over a wide range of space velocities. ( 3) The rate limiting step is the conversion of oxygenates to olefins, a reaction step that appears to be autocatalytic. In the absence of olefins, this rate is slow but it is accelerated as the concentration of olefins increases. 

Of the main reactions, aromatization takes place most readily and proceeds ca 7 times as fast as the dehydroisomerization reaction and ca 20 times as fast as the dehydrocyclization. Hence, feeds richest in cycloparaffins are most easily reformed. Hydrocracking to yield paraffins having a lower boiling point than feedstock proceeds at about the same rate as dehydrocyclization. 

In 1951, Titov and Shchitov [103] when examining the action of nitric anhydride on normal paraffins and cycloparaffins, found that in the presence of an inert solvent the reaction already started at 0°C, with the evolution of heat. Nitric acid esters were formed in the reaction which, according to the authors, proceeded through the following stages ... 

In the solution process, the reaction is carried out in the presence of an inert hydrocarbon which dissolves the polymer as it is formed. The solvent may contain a portion of cycloparaffin. Both monomer and polymer remain in solution during the reaction while the catalyst is maintained in suspension by agitation. Reaction temperatures range from about 125°-175°C. and reaction pressures from 20-30 atm. The reactor product is withdrawn, and monomer is flashed off and recycled. Suspended catalyst is then removed by filtration, and solvent is flashed from the filtrate with steam. 

The tritonation of the C3— 3 cycloparaffins with HeT+ ions was investigated by Cacace et al. (1968a, 1969) who sought, through the analysis of the tritiated reaction products and the determination of their structure, to gather direct evidence on the formation of gaseous cycloalkanium ions, whose long-postulated existence had not been experimentally verified. 

These conclusions, and especially the strong evidence for the existence of gaseous cycloalkanium ions, can usefully be compared with the considerable body of information on the protonated cycloparaffins, obtained from inass-spectrometric studies, kinetic investigations on the reactions of radiolytically formed ions with cycloalkanes, and the solution chemistry of cycloparaffins in strong Bronsted acids. 

Production of carbonium ions gives the possibility to produce different hydrocarbons molecules, e.g. cycloparaffins and aromatics by cyclization and dehydrogenation reactions (Figure 4.2). In the first step presumably intramolecular reactions between carbonium ions and double bonds take place. 

The reactions taking place in the vapour phase also occur in the condensed phase, and their mechanisms are probably similar. However, as may be expected on the basis of the results obtained for the gas phase photolysis, the formation of olefins, cycloparaffins, and CO is of less importance, while that of the saturated aldehydes is more important in the liquid phase or solution, where energy dissipation by collision is more efficient. The decarbonylation products were shown to be only of minor importance in the photolysis of liquid cyclopentanone and cyclohexanone . The unsaturated aldehyde was found to be the main product in the liquid-phase photolysis of cyclopentanone (methyl cyclohexanone . Unsaturated aldehydes were also identified in the photolysis products of other cyclic ketones in the liquid phase as well as in solution . ... 

Several larger membered ring azocompounds have also been synthesized and their decomposition kinetics studied . Reported kinetic data are collected in Table 8. The decomposition products are the corresponding diaryl cycloparaffins and isomeric olefins. The cis isomers decompose with considerably lower activation energies than the trans isomers. This feature of the reaction has been attributed to the greater ease with which both aryl substituents achieve coplanarity with the C-N=N-C linkage in the transition state-and thereby stabilize the incipient diradical — in the cis than in the trans isomer. A similar effect was noted for the... 

The dehydrogenation of hexane to hexene or cyclohexane (reactions 5 and 6) only becomes appreciable at temperatures approaching 800 °K. The dehydrogenation to methylcyclopentane however appears to be thermodynamically feasible at temperatures as low as 350 °K. One cannot place too much reliance on this particular result since the affinity of formation of methylcyclopentane is known less accurately than the others. These three reactions, however, scarcely affect the synthesis of aromatic compounds in the reaction since the ethylenes and cycloparaffins are thermodynamically unstable relative to aromatic hydrocarbons above 550 °K, and they decompose spontaneously to form aromatics at this temperature. They can therefore only appear as intermediates in reaction (9) above 550 °K. 

Once formed, alcohols esterify to some extent with the acids generated in an oxidation reaction. Except for lactones, esters do not appear to be generated directly in oxidation mechanisms [10, 37, 38]. The Bayer-Villiger reaction of intermediate peracids and ketones is sometimes proposed as a source of esters [39] but it appears to be too slow to be a significant source except in the case of cycloparaffins [10, 40]. The ester group and its immediate neighboring groups appear to be remarkably resistant to oxidation. 

Realizations of such microcompartments are obtained in normal heterogeneous catalysis by using zeolite crystals as support material, e. g., in the formation of are-nes from cycloparaffins by use of Y-zeolite crystals as catalysts [15] or the hydro-isomerization of light paraffins by Pt-doped Y-zeolite [16]. Concentration effects, resembling channeling in enzyme-catalyzed reactions, are caused by the hindrance of the transport of larger molecules through the apertures between the cavities which form the three-dimensional pore texture of zeolite crystals. 

Reed reaction. Photochemical sulfonation of paraffins and cycloparaffins by sulfur dioxide and chlorine under irradiation with UV light. 

The use of organic halogen compounds as the starting products for the synthesis of other organic chemicals is too immense a field to do more than indicate some of the commercial applications. In his book I4S) on the chemistry of petroleum derivatives, Ellis includes a chapter on the production of alcohols and esters from alkyl halides, and also one on miscellaneous reactions of halo-paraffins and cycloparaffins. The manufacture of amyl alcohols and related products from the chlorides has been well covered 14 ) 1 )-A two-step process for the synthesis of cyclopropane by chlorinating propane from natural gas and dechlorinating with zinc dust was devised in 1936 152). A critical review of syntheses from l,3-dichloro-2-butene was published in Russia in 1950 (1-54). The products obtainable from the allylic chlorides are covered in a number of articles 14If 14 157). 

Medium pore aluminophosphate based molecular sieves with the -11, -31 and -41 crystal structures are active and selective catalysts for 1-hexene isomerization, hexane dehydrocyclization and Cg aromatic reactions. With olefin feeds, they promote isomerization with little loss to competing hydride transfer and cracking reactions. With Cg aromatics, they effectively catalyze xylene isomerization and ethylbenzene disproportionation at very low xylene loss. As acid components in bifunctional catalysts, they are selective for paraffin and cycloparaffin isomerization with low cracking activity. In these reactions the medium pore aluminophosphate based sieves are generally less active but significantly more selective than the medium pore zeolites. Similarity with medium pore zeolites is displayed by an outstanding resistance to coke induced deactivation and by a variety of shape selective actions in catalysis. The excellent selectivities observed with medium pore aluminophosphate based sieves is attributed to a unique combination of mild acidity and shape selectivity. Selectivity is also enhanced by the presence of transition metal framework constituents such as cobalt and manganese which may exert a chemical influence on reaction intermediates. 

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