Toluene from methylcyclohexane

Here M and T represent methylcyclohexane and toluene in the gas phase, and Ttt represents adsorbed toluene. The first step in the above reaction sequence represents the adsorption of methylcyclohexane with subsequent reaction to form toluene, while the second step is the desorption of toluene from the surface. Very likely the first step represents a series of steps involving partially dehydrogenated hydrocarbon molecules or radicals. However, at steady-state conditions the rates of the intermediate steps would all be equal, and the kinetic analysis is, therefore, not complicated by this factor. To account for the near zero-order behavior of the reaction, it was suggested that the active catalyst sites were heavily covered with... 

The functional form of the rate equation in Equation (5.3.18) is identical to that of Equation (5.3.17), illustrating that two completely different sets of assumptions can give rate equations consistent with experimental observation. Clearly, more information is needed to discriminate between the two cases. Additional experiments have shown that benzene added to the methylcyclohexane feed inhibits the rate only slightly. In the first case, benzene is expected to compete with methylcyclohexane for available surface sites since M is equilibrated with the surface. In the second case, M is not equilibrated with the surface and the irreversibility of toluene desorption implies that the surface coverage of toluene is far above its equilibrium value. Benzene added to the feed will not effectively displace toluene from the surface since benzene will cover the surface only to the extent of its equilibrium amount. The additional information provided by the inclusion of benzene in the feed suggests that the second case is the preferred path. 

Still larger quantities of aromatic hydrocarbons are needed, and these are synthesized from alkanes through the process of catalytic reforming (Sec. 9.3). This can bring about not only dehydrogenation as in the formation of toluene from methylcyclohexane, but also cyclization and isomerization as in the formation of toluene from //-heptane or 1,2-dimethylcyclopentane. In an analogous way, benzene is obtained from cyclohexane and methylcyclopentanc, as well as from the hydrodealkylation of toluene. 

Table 3.1 Partition coefficients (P,) at T — 24 °C in the perfluoro(methylcyclohexane)/toluene system, fluorophilicity parameters (f), and fluorine content (fluorine as a percentage of molecular weight) of a variety of fluorinated and non-fluorinated compounds (data modified or calculated from Ref. [17]).

An example of an extractive distillation process is the separation of methylcyclohexane (MCH) from toluene using a phenol solvent, as shown in Figure 12.17. Since MCH boils at 101.0°C and toluene boils at 110.7°C (1 atm), their separation by ordinary distillation is very difficult even though they do not form an azeotrope. Phenol is an effective solvent, since it has a structure more similar to the aromatic than to MCH (a naphthene), and it is relatively nonvolatile. The rectification... 

The product distribution from the TAP experiments is shown in Table 2. After pulsing methylcyclohexane, mainly toluene, benzene, methane and hydrogen are observed together with other luiidentifred products in smaller quantities. Figure 1 shows the transient responses of methylcyclohexane, toluene and benzene on a pulse of methylcyclohexane at 923 K. The times at which the maxima occur for the responses of toluene and benzene are rather close. 

FIGURE 5.5-5 Flow diagram for the extractive dislillation separation of toluene from methylcyclohexane... 

A sample of methylcyclohexane is suspected of being contaminated with toluene, from which it had been prepared by hydrogenation. At 261 nm, toluene has a molar absorptivity e = 224, whereas methylcyclohexane does not absorb at that wavelength (e = 0). An ultraviolet spectrum of the contaminated methylcyclohexane (obtained in a 1.0 cm cell) shows an absorbance A = 0.65 at 261 nm. Calculate the concentration of toluene in the methylcyclohexane. 

The octane number of toluene is 124 and of methylcyclohexane is 104. Since the density of the aromatic (0.862 g/mL) is higher than for the MCH (0.765 g/mL), there is a decrease in liquid volume due to this reaction. Because of this, the maximum yield in toluene from MCH is 83% by volume. Owing to the hydrogen loss, there is also a decrease in the weight of the product compare to the feed. 

Note that the concentration Cus has been assumed to be small in deference to the observation that the aromatics affect the rate only modestly. With this formulation, the activation energy of = 30 kcal/mol is that of desorption of the strongly bound toluene. From the rate constant ratio (ki/ks), it is seen that the activation energy for the chemisorption of methylcyclohexane is 11 kcal/mol. They went on to show that the ratio of preexponential factors determined from experimental data compared reasonably well with a value calculated from transition state theory. 

Returning back to the differences between 4 and 5, Figure 2.6 provides interesting information for discussion. The decrease of the temperature from room temperature to 160 K, which is near the freezing point of the solvents used, leads to a shift of the equilibrium toward the keto tautomer in methylcyclohexane/toluene in both compounds and to negligible changes for 4 in ethanol [43]. 

The presence of soluble Rh nanoparticles after catalysis is demonstrated by TEM. The kinetic of the catalytic reaction was found to be zero-order in respect to the substrate and first order with respect to hydrogen and catalyst. Curiously, under the same conditions (60 °C, 7 bar H2), ethylcyclohexane is not detected at the end of phenylacetylene hydrogenation and the formation of methylcyclohexane from toluene was only obtained under drastic conditions 40 bar H2 and 80 °C. 

Likewise it is possible to differentiate between substituted and unsubstituted alicycles using inclusion formation with 47 and 48 only the unbranched hydrocarbons are accommodated into the crystal lattices of 47 and 48 (e.g. separation of cyclohexane from methylcyclohexane, or of cyclopentane from methylcyclopentane). This holds also for cycloalkenes (cf. cyclohexene/methylcyclohexene), but not for benzene and its derivatives. Yet, in the latter case no arbitrary number of substituents (methyl groups) and nor any position of the attached substituents at the aromatic nucleus is tolerated on inclusion formation with 46, 47, and 48, dependent on the host molecule (Tables 7 and 8). This opens interesting separation procedures for analytical purposes, for instance the distinction between benzene and toluene or in the field of the isomeric xylenes. 

The hydrogenation of toluene, aniline, /r-toluidine, and 4-tert-butylaniline was examined over catalyst M1273. The reaction profile for the reactions is shown in Figure 2. From this it can be seen that the order of reactivity is aniline > toluene > /Moluidinc > 4-fer f-butylaniline. The hydrogenation products were methylcyclohexane from toluene, cyclohexylamine from aniline, 4-methyl-cyclohexylamine (4-MCYA) from /Holuidine. and 4-feri-butylcyclohexylamine (4-tBuCYA) from 4-tert-butylaniline. At 50 % conversion the cis trans ratio of 4-MCYA was 2, while tBuCYA it was 1.6. 

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] ... 

Naphthalene itself is solid at ambient temperatures (m.p. 80.5°C) but is dissolved easily in aromatic compounds such as toluene (refer Table 13.1) [10,12], so that the oily mixture can be handled as a "naphthalene oil." The naphthalene oil is catalytically hydrogenated to decalin and methylcyclohexane simultaneously. Decalin and methylcyclohexane are converted into hydrogen and naphthalene oil again by dehydrogenation catalysis. From the handling viewpoint, the naphthalene oil may be deemed as a preferential and practical material for hydrogen storage and transportation. 

As shown in Table 13.1, toluene is a candidate compound to form the naphthalene oil. To utilize the reaction pair of methylcyclohexane dehydrogenation/toluene hydrogenation as an additive component, it is, thus, necessary to generate hydrogen efficiently from methylcyclohexane under mild reaction conditions. 

Heat flow from any external thermo-source into the dehydrogenation reactor should take the role of affording the endothermic reaction heat and the evaporation heat of both reactant and product in addition to the apparent heat for raising their temperatures from the ambient up to the external heating one. Under assumptions of the sufficient amounts of active catalyst and the adequate feed rates of organic chemical hydride, the minimum required heat is obtained as shown in the example of methylcyclohexane at 285°C on the basis of 100% conversion of methylcyclohexane to toluene and hydrogen (Table 13.5). 

Methanol, toluene, methylcyclohexane and ethylbenzene were obtained from Merck at a purity of about 99.5 % and were used without further purification. The purity of these materials was checked by gas chromatography. 

Figure 1.6 ICH Class 2 solvents measured using GC. Purification of pravastatin sodium by preparative liquid chromatography. Reprinted from [15], copyright 2004, with permission from Elsevier. (Column 30 m X 0.53 mm i.d. 3 pm OVI-G43 (Supelco) carrier gas helium at 5 ml/min injection in split mode total flow 25 ml/min injector temperature 140 C flame ionization detector temperature 25C C and oven temperature 40°C for 20 min, to 240°C at 10°C/min, maintain at 240 C for 20 min. The components are 1 methanol, 3 acetonitrile, 4 dichloromethane, 5 hexane, 6 cw-l,2-dichloroeth-ylene, 7 nitromethane, 8 chloroform, 9 cyclohexane, 13 1,2-dimethoxyethane, 15 1,1,2-trichloroethyl-ene, 16 methylcyclohexane, 17 1,4-dioxane, 18 pyridine, 19 toluene, 20 2-hexanone, 21 chlorobenzene, 22 ethylbenzene, 23 m-xylene, 24p-xylene, 25 o-xylene, and 26 tetralin. The solvents are dissolved in DMF and heated at 80X for 60 min, and a sample of the headspace is injected.)...

A fourth type of petroleum isomerization, which was commercialized on a small scale, involves the rearrangement of naphthenes. In the manufacture of toluene by dehydrogenation of methylcyclohexane, the toluene yield can be increased by isomerizing to methylcyclohexane the dimethylcyclopentanes also present in the naphtha feed. This type of isomerization is also of interest in connection with the manufacture of benzene from petroleum sources. 

In the present study, we have confirmed the modification of the EGL for the CS from S2 induced by the change of solvent polarity by comparing the EGL in toluene (Tol) and methylcyclohexane (MCH) solution with that in THF. Moreover, we have compared the rate constants ()>p) of the S, state formation by S2 excitation with the decay rate constants (), ) of S2 state in ZP-I series and examined also solvent polarity effects on these rate constants comparing THF with Tol or MCH solutions. 

Component 1 in Singapore buildings was correlated with compounds associated with humans and their activities. Human effluents have been reported to contain isoprene (Ellin et al, 1974) while tetrachloroethylene is a VOC found in dry-cleaned clothes worn by building occupants (Wallace, Pellizzari and Wendel, 1991) or from the use of consumer products (Sack et al., 1992). Tetradecane, benzaldehyde, o-xylene, naphthalene are emissions from dry process photocopiers (Leovic et al., 1996). Component 2 with high loadings ofn-decane, n- undecane, toluene, styrene, n-nonane, 1,2,4-trimethyl benzene probably reflects the emissions of carpets and vinyl floorings (Yu and Crump, 1998). Component 3 was primarily correlated with heptane and methylcyclopentane, which could be due to the emissions of water-based paints. Finally, component 4 was associated with 2-methylpentane, hexane, cyclohexane, methylcyclohexane and limonene, which is reflective of the emissions of air fresheners and cleaning products (Sack et al., 1992). 

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