Hydrogenation methylcyclopentane

Some processes use only one reactor (57) or a combination of liquid- and vapor-phase reactors (58). The goal of these schemes is to reduce energy consumption and capital cost. Hydrogenation normally is carried out at 2—3 MPa (20—30 atm). Temperature is maintained at 300—350°C to meet a typical specification of less than 500 ppm benzene in the product at higher temperatures, thermodynamic equiUbrium shifts to favor benzene and the benzene specification is impossible to attain. Also, at higher temperatures, isomerization of cyclohexane to methylcyclopentane occurs typically there is a 200 ppm specification limit on methylcyclopentane content. 

The illustrated unit can be used to study vapor-phase reforming of kerosene fractions to high octane gasoline, or hydrogenation of benzene, neat or in gasoline mixtures to cyclohexane and methylcyclopentane. In liquid phase experiments hydrotreating of distillate fractions can be studied. The so-called Solvent Methanol Process was studied in the liquid phase, where the liquid feed was a solvent only, a white oil fraction. 

Selected Properties of Hydrogen, Important Ci-Cio Paraffins, Methylcyclopentane and Cyclohexane ... 

The values of the adsorption coefficient of hydrogen for both reactions were practically identical (1.9 and 2.1 atm-1). Here, the selectivity of the branched reactions depends on the partial pressure of methylcyclopentane. This difference may be accounted for by assuming that either the cleavage of the C—C bond of methylcyclopentane in the (3-position and in the 7-position with respect to the methyl group does not take place on the same sites of the surface of platinum (or on the sites of the same activity), or that the mechanism of hydrogenolysis is more complex than that ex-... 

Finally we mention that aromatic bromides can be debrominated by hydrogen and a metal(o)-in-zeoite system (ref. 33). Over e.g. Cu(0)-Y bromobenzene is converted into benzene whereas over Pt-H-beta (200 °C) quantitative hydrodebromination is followed by hydrogenation and isomerization towards methylcyclopentane (Fig. 12). In this way undesired aromatic bromides can be recycled. 

Bodner and Domin (2000) demonstrated the inability of many university students to interpret abbreviated structural portrayals with some atoms implied, rather than shown. The students were asked to predict the major products of the reaction of bromine with methylcyclopentane portrayed as in Fig. 1.2, and to estimate the ratio of the products if bromine radicals were just as likely to attack one hydrogen atom as another. Most of the 200 students predicted three products, with a relative abundance 3 2 2 (Fig. 1.4). 

Methylcyclopentane is a powerful probe molecule for the study of metal surfaces. The product distribution on platinum depends on the following factors particle size 491 reaction conditions 492-494 carbonaceous residues,492,493,495 and the extent of the interface between the metal and the support.492,493,495 The hydrogenolysis rate of methylcyclopentane depends on the hydrogen pressure.496,497 The rate exhibits a maximal value as a function of hydrogen pressure on EuroPt catalysts.498 The hydrogenolysis of methylcyclopentane has also been studied over Pt-Ru bimetallic catalysts.499... 

In work under very mild reaction conditions (<300°C) cyclic C6 products always strongly predominate over cyclic C products. This is kinetic rather than thermodynamic in origin, since at 277°C and starting with a reaction mixture containing 50 Torr hydrogen and 5 Torr n-hcxane, for instance, equilibrium in the formation of methylcyclopentane would yield 1.86 Torr of the latter, in benzene 4.99 Torr, and in cyclohexane 0.59 Torr... 

The catalytic performances obtained during transalkylation of toluene and 1,2,4-trimethylbenzene at 50 50 wt/wt composition over a single catalyst Pt/Z12 and a dualbed catalyst Pt/Z 121 HB are shown in Table 1. As expected, the presence of Pt tends to catalyze hydrogenation of coke precursors and aromatic species to yield undesirable naphthenes (N6 and N7) side products, such as cyclohexane (CH), methylcyclopentane (MCP), methylcyclohexane (MCH), and dimethylcyclopentane (DMCP), which deteriorates the benzene product purity. The product purity of benzene separated in typical benzene distillation towers, commonly termed as simulated benzene purity , can be estimated from the compositions of reactor effluent, such that [3] ... 

Aluminum chloride, used either as a stoichiometric reagent or as a catalyst with gaseous hydrogen chloride, may be used to promote silane reductions of secondary alkyl alcohols that otherwise resist reduction by the action of weaker acids.136 For example, cyclohexanol is not reduced by organosilicon hydrides in the presence of trifluoroacetic acid in dichloromethane, presumably because of the relative instability and difficult formation of the secondary cyclohexyl carbocation. By contrast, treatment of cyclohexanol with an excess of hydrogen chloride gas in the presence of a three-to-four-fold excess of triethylsilane and 1.5 equivalents of aluminum chloride in anhydrous dichloromethane produces 70% of cyclohexane and 7% of methylcyclopentane after a reaction time of 3.5 hours at... 

To account for the exchange and isomerization of a number of poly-methylcyclopentanes, Rooney et al. (3S) postulated that intermediates corresponding to the w-allyl structures written above were not only able to abstract hydrogen from the surface as in the classical mechanism, but also could accept an atom from molecular hydrogen according to an Eley-Rideal mechanism (Fig. 26). 

Fig. 1. Yields of benzene and methylcyclopentane from n-hexane (mole % in the effluent) as a function of the hydrogen percentage in the carrier gas (the other component being He). Pulse system, catalyst 0.4 g Pt black, T = 360°C (27a).

The increase in hydrogen pressure should suppress both benzene and methylcyclopentane formation. Equilibrium composition for the five hexane isomers, methylcyclopentane, and benzene in sixfold hydrogen excess consists of nearly 100% of benzene at about 400°C (673 K) at 3 atm and at about 600°C (873 K) at 20 atm. Cyclohexane and unsaturated products should be present in concentrations between 10" and 10" mole %. In fact, less cyclohexane and more unsaturated products are observed (30). 

The yields of both benzene and methylcyclopentane show maxima as a function of the hydrogen pressure. Whereas thermodynamics permit a very broad maximum in methylcyclopentane concentration, the yields of benzene should increase monotonically. 

Over platinum black, -hexane gives 2- and 3-methylpentanes, methylcyclopentane, and benzene. Actual concentrations are compared in Fig. 2 with equilibrium ones as a function of hydrogen pressure. Unreacted n-hexane is ignored since it would not be able to equilibrate with all its products. Realistic values are obtained if methylcyclopentane plus isomers are compared with the amount of benzene. These, however, correspond to much higher effective hydrogen concentrations than measured in the gas phase (31). 

The formation of methylcyclopentane from hexanes proceeds in the presence of hydrogen only (27, 27a). A singly dissociated surface intermediate is suggested by the hydrogen order of about — 1 on the right-hand side of the bell-shaped curves over platinum black between 300° and 360°C (Fig. 6) (77). 

Fig, 6. Rates of methylcyclopentane formation from 3-methylpentane, as a function of hydrogen pressure. Static-circulation system catalyst, 0.16 g platinum black hydrocarbon pressure, 5 Torr (77). 

Fig. 7, Percent selectivity of hydrogenative C, ring closure as a function of the hydrogen content of the carrier gas. Pulse system catalyst, 0.4 g platinum black T = 360°C. Starting hydrocarbons ( ) 3-methylpentane ( ) 3-methyl-1-pentene (T) tra . -3-methyl-2-pentene (A) di-2-methyl-2-pentene. Selectivity is expressed as methylcyclopentane (MCP) % in the total C5 cyclic product (MCP + MCPe) (55).

Figure 3.8 Conversion with time in the hydrogenolysis of cycloalkanes (19Torr, 14.5 equiv.) catalyzed by (=SiO)2TaH (3) at 160°C under hydrogen (470Torr) cycloheptane ( ), methylcyclohexane ( ), cyclohexane ( ), methylcyclopentane (A) and cyclopentane (x).

Earlier work on the exchange of methylcyclopentane and methylcyclo-hexane over nickel catalysts at 150°-200° had not shown any discontinuities in the distribution pattern of the products (S9). There was a uniform rise up to a maximum for the fully deuterated species. This is not surprising, since similar behavior was noted with cyclopentane and cyclohexane under the same conditions. At these high temperatures the interchange reaction occurs sufficiently readily to mask any division of the hydrogen atoms into sets. 

Fig. 1. Reaction composition profile. Reforming at 794 K, 2620 kPa. Zone A dehydrogenation zone zone B isomerization zone zone C hydrogenation and cracking zone. [Charge stock A, hexane (HEX) , benzene (BENZ) V, cyclohexane (CH) O, methylcyclopentane (MCP).]...

Experimental conditions were 727, 756, and 794 K isothermal reactor temperature 827-, 1220-, and 2619-kPa hydrogen pressure 138- and 345-kPa hydrocarbon pressure and 1 to 26 liquid hourly space velocity. (See Section II for definition.) Charge stocks consisted of three C6 component blends (blends included 53/19/23/5, 25/75/0/0, and 0/0/50/50 wt. % hexane/methylcyclopentane/cyclohexane/benzene), C6 to C7 component naphthas (322-366 K TBP Kirkuk, Mid-Continent, and Nigerian), a C6 to C8 component naphtha (322-416 K TBP Mid-Continent), and C6 to C12 component naphthas (322-461 K TBP Arab Light, Mid-Continent, and... 

Hh Heat of adsorption for hydrogen, kJ/gmole H, hexane MCP, methylcyclopentane... 

Benzene, naphthalene, toluene, and the xylenes are naturally occurring compounds obtained from coal tar. Industrial synthetic methods, called catalytic reforming, utilize alkanes and cycloalkanes isolated from petroleum. Thus, cyclohexane is dehydrogenated (aromatization), and n-hexane(cycli> zation) and methylcyclopentane(isomerization) are converted to benzene. Aromatization is the reverse of catalytic hydrogenation and, in the laboratory, the same catalysts—Pt, Pd, and Ni—can be used. The stability of the aromatic ring favors dehydrogenation. 

In several examples the reductive halide-hydrogen exchange has been studied on a preparative scale. For example, the indirect electroreduction of 2-chloropyridine in DMF using anthracene as mediator gives pyridine in 83-86 % yield 2 . For the dehalogenation of 1-chlorohexane (80% yield), naphthalene is applied as redox catalyst. Similarly, 6-chloro-hexene yields 1-hexene (60%) and methylcyclopentane (25%), which is the product of the radical cyclization . The indirect electrochemical reduction of p- and y-bromocarboxylic esters forms coupling and elimination products besides the dehalogenated products... 

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