Uptake of cyclohexane

There was always an induction period of 10 to 20 min before the benzene product reached its steady-state rate of production as detected by the mass spectrometer after the introduction of cyclohexane onto the crystal surface. This is shown in Fig. 22 for several catalyst temperatures. The catalyst was initially at 300 K. When steady-state reaction rates were obtained, the catalyst temperature was rapidly increased (in approximately 30 sec) to 423 K and the reaction rate monitored. This was repeated with heating to 573 and 723 K. The benzene desorbed during rapid heating of the catalyst surface is approximately 1 x 1013 molecules or less and represents only a small fraction of the carbon on the surface. The steady-state reaction rates at a given temperature are the same whether the catalyst was initially at that temperature or another. This induction period coincides with a higher than steady-state uptake of cyclohexane. A mass balance calculation on carbon, utilizing the known... 

Figure 5. Uptake of cyclohexane at 25°C and p/pQ = 0.95 by chromia pillared montmorillonites (A) Cr3 53-...

SBS Interphase. Since 20°C is below the 0-temperature for the polystyrene-cyclohexane systems, it was expected that the PBD phase would be permeable to cyclohexane, but the PS domains would be relatively impermeable. (It is known that PS swells almost fourfold in liquid cyclohexane and that SBS may be dissolved even in cyclohexane. However, the maximum uptake of cyclohexane vapor by SBS was approximately 40% of its original weight. Furthermore, a sample of pure PS did not absorb any vapor within the time scale of these experiments. It was concluded then that the pure PS domain was not penetrated by cyclohexane vapor in these experiments and that, except for the interface, the PS domains may be considered an impermeable phase dispersed within a permeable continuum.) Thus the diffusion coefficient would be expected to reflect the structure of the PBD phase and to be characteristic of diffusion in elastomers (i.e., Fickian diffusion). 

A solution of 4,4-dimethyl-5a-androst-l-en-3-one (128, 14 mg) in cyclohexane (3 ml) is stirred in a microhydrogenation apparatus in the presence of 10 % palladium-on-charcoal (15 mg) at atmospheric pressure and room temperature. The uptake of one eq of deuterium (1.15 ml) is complete in about 1 min and no more deuterium is consumed. After 5 min the catalyst is removed by filtration, and the solvent evaporated under reduced pressure. The resulting l<, 2< -d2-4,4-dimethyl-5a-androstan-3-one (129, 13 mg, 93%), mp 120-122°, exhibits 87% isotopic purity and 13% d species. ... 

Oxidation of cyclohexane was also studied using homogeneous complex of Ru(lll) with 1,2 DAP under similar condition (Table 8). However for convenience same quantity of catalyst could not be used as the same quantity of unbound catalyst gave immeasurable oxygen uptake. Inspite of using larger amount ofRu (III), a lower reaction rate was observed as compared to polymer supported catalyst. Effect of various parameters such as concentration of substrate and catalyst, temperature, amount and nature of solvent is seen and the results are summerised in Table 8. The energy of activation was found to be 7.04 Kcal mof. 

Specific roles of the so-called co-surfactants (commonly, but not necessarily alcohols) have been examined by various workers [122, 126, 136] some points are discussed here. For example, a critical thermodynamic analysis in conjunction with experimentations led Eicke [ 136] to the conclusion that a co-surfactant should decrease the interfacial free energy under isothermal conditions, while causing an uptake of water into the microemulsion and extension of its domain. The anionic surfactant AOT assists the formation of large reverse microemulsion domains (high water uptake) in different ternary systems without help from a co-surfactant (Section 2.2), but cationic surfactants do generally need this fourth component. In spite of this, enhanced solubilization by the addition of (small quantities of) a co-surfactant has been observed by various workers in AOT systems. Eicke [136] used cyclohexane, benzene, carbon tetrachloride and nitrobenzene in the system AOT/ isooctane/water and found considerable water uptake (the fraction of the oil phase, i.e. isooctane was 0.8 or more). With increasing polarizability or polarity of the CO-surfactant, the water uptake decreased. 

Figure 6. Periodate uptake (10 f) and malonaldehyde formation (MA) during the oxidation of 1,3,5/2,4-cyclohexane pent ol with sodium metaperioaate (c.f.

The compound (10 ml) was hydrogenated in 10 ml methylcyclohexane (cyclohexane for toluene) at 80°C (100°C for o-xylene) and the initial hydrogen pressure of 7.8 MPa over the catalyst containing 0.08 g of catalytic metal and prepared before use. The rates (at the initial stage) were obtained by an extrapolation method to get rid of an unstable hydrogen uptake at the initiation. 

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