Pentane adsorbed

Normal pentane has an oetane number of 62, while iso-pentane has an octane number of 90 The n-pentane adsorbs onto the platinum, where it is dehydrogenated to form n-pentene. The n-pentene desorbs from the platinum arid adsorbs onto the almnina, where it is isomerized to i-pentene, which then desorbs and subsequently adsorbs onto platinum, where it is hydrogenated to form i-pentane. That is,... 

Normal pentane has an octane number of 62. while /so-pentane, which is nK/re Cs 10% compact, has an octane number of 90 The n-pentane adsorbs onto the platt-... 

The data may then be expressed in conventional ir-versus-tr or ira-versus-ir plots, as shown in Fig. Ill-17. The behavior of adsorbed pentane films was that of a nonideal two-dimensional gas, as can be seen from the figure. 

Fig. 2.12 Plot of the calorimetric difTeFential enthalpy of adsorption A h) against amount adsorbed (n), for (u) n-pentane, (f)) /i-hexane, (c) n-heptane, d) n-octane, all adsorbed on graphitized car n black. The point corresponding to n = is marked on each curve. (Courtesy Kiselev.)...

Fig. 2.17 The adsorption of pentane on different adsorbents, (a) Effect of the nature of the adsorbent on the shape of the isotherm (each isotherm is labelled with the name of the adsorbent), (b) Dependence of ajpentane) on the value of parameter C. (Courtesy Kiselev and Eltekov. )...

The strength of dispersion interaction of a solid with a gas molecule is determined not only by the chemical composition of the surface of the solid, but also by the surface density of the force centres. If therefore this surface density can be sufficiently reduced by the pre-adsorption of a suitable substance, the isotherm may be converted from Type II to Type III. An example is rutile, modified by the pre-adsorption of a monolayer of ethanol the isotherm of pentane, which is of Type II on the unmodified rutile (Fig. 5.3, curve A), changes to Type III on the treated sample (cf. Fig. 5.3 curve B). Similar results were found with hexane-l-ol as pre-adsorbate. Another example is the pre-adsorption of amyl alcohol on a quartz powder... 

Dried with Linde type 5A molecular sieves or Na2S04 and fractionally distd at reduced pressure. Alternatively, it was refluxed with, and distd from, BaO. Also purified by fractional crystn from the melt and distd from zinc dust. Converted to its phosphate (m 135°) or picrate (m 223°), which were purified by crystn and the free base recovered and distd. [Packer, Vaughn and Wong J Am Chem Soc 80 905 1958.] The procedure for purifying via the picrate comprises the addition of quinoline to picric acid dissolved in the minimum volume of 95% EtOH to yield yellow crystals which are washed with EtOH and air dried before recrystn from acetonitrile. The crystals are dissolved in dimethyl sulfoxide (previously dried over 4A molecular sieves) and passed through a basic alumina column, on which picric acid is adsorbed. The free base in the effluent is extracted with n-pentane and distd under vacuum. Traces of solvent are removed by vapour phase chromatography. [Mooman and Anton J Phys Chem 80 2243 1976.]... 

A vapor phase process for deparaffmization of light gas oils performed by the BP works in this way The gas oil, boiling range 230-320°C, is passed over a 5-A molecular sieve at 320°C and a pressure of 3.6 bar. The space velocity is 0.63 vol liquid gas oil per vol molecular sieve and per hour, [liquid hourly space velocity (lhsv) = 0.63] the adsorption period takes 6 min. Together with the gas oil vapor 120 vol N2 per vol liquid gas oil is led over the sieve as carrier and purge gas. After the adsorption period the loaded molecular sieve is purged at the same temperature with pure N2 for 6 min. Subsequently, the adsorbed /z-alkanes are desorbed by 1 vol liquid /z-pentane per vol molecular sieve and per hour. The /z-pentane is recovered from the /z-alkane//z-pentane mixture by simple distillation [15]. The IsoSiv process of the Union Carbide Corporation works in a similar way [16]. The purity of the isolated /z-alkanes is >98%. 

Another piece of information available concerns the surface intermediates. By using the l C labelling and by monitoring the reaction of a molecule which is an "archtype" for two types of complexes the following has been established (31-33) i) dilution of Pt by Cu increases the relative contribution to isomerization of the 5-C-intermediates (something like an adsorbed methylcyclo-pentane) in comparison with that of 3C-intermediates. ii) The contribution of various types of the 3C-(ay) and 2C-(aB) intermediates to the overall reaction is independent of the Cu-content, but with Cu increasing, the proportion increases to which the 3C-(ay) intermediates are hydrogenolysed (as compared with their isomerization). 

Neutral metal carbonyl clusters exemplified by Ir4(CO)i2, IrelCOlie, and Rh6(CO)i6 are adsorbed intact from solution (e.g., n-pentane) onto more-or-less neutral supports such as y-Al203 or Ti02. The clusters on these supports can often be extracted intact into solutions such as tetrahydrofuran. 

For propane, n-pentane and n-hexane the differential heats of adsorption over FER dropped more rapidly, right after 1 molecule was adsorbed per Bronsted acid site. Similar results were obtained with TON. In contrast, with MOR and FAU the drop in the differential heats of adsorption for n-alkanes occurred at lower coverages, indicating that only a certain fraction of the Bronsted acid sites were accessible to the adsorbing alkane probe molecules. With MFI the drop did not occur until 2 molecules of n-alkane were adsorbed per Bronsted acid site, suggesting perhaps a higher stoichiometry of about two n-alkanes per Bronsted acid site. In the cases of i-butane and i-pentane the drop occurred around one alkane per Bronsted acid site. Finally, n-butane adsorption isotherms measured over TON framework type catalysts having three different A1 contents (Si/Al2 = 90, 104, 128) showed Henry coefficients to increase with increase in the A1 content [5], Based... 

We then designed model studies by adsorbing cinchonidine from CCU solution onto a polycrystalline platinum disk, and then rinsing the platinum surface with a solvent. The fate of the adsorbed cinchonidine was monitored by reflection-absorption infrared spectroscopy (RAIRS) that probes the adsorbed cinchonidine on the surface. By trying 54 different solvents, we are able to identify two broad trends (Figure 17) [66]. For the first trend, the cinchonidine initially adsorbed at the CCR-Pt interface is not easily removed by the second solvent such as cyclohexane, n-pentane, n-hexane, carbon tetrachloride, carbon disulfide, toluene, benzene, ethyl ether, chlorobenzene, and formamide. For the second trend, the initially established adsorption-desorption equilibrium at the CCR-Pt interface is obviously perturbed by flushing the system with another solvent such as dichloromethane, ethyl acetate, methanol, ethanol, and acetic acid. These trends can already explain the above-mentioned observations made by catalysis researchers, in the sense that the perturbation of initially established adsorption-desorption equilibrium is related to the nature of the solvent. 

Fia. 3. Contractions and expansions of an activated carbon rod as a function of pressure-volume units of adsorbed material. Key O, ethane X, n-propane , n-butane V, n-pentane , 2,2-dimethyl propane -H, carbon tetrachloride. (73). 

Kiselev and Eltekov established that the BET C value influences the adsorbate cross-sectional area. They measured the surface area of a number of adsorbents using nitrogen. When the surface areas of the same adsorbents were measured using n-pentane as the adsorbate the cross-sectional areas of n-pentane had to be revised in order to match the surface areas measured using nitrogen. It was found that the revised areas... 

The idea of the evidence is rather simple and can be elucidated by means of the following experiment. Let us consider, for example, a molecule of 2-methylpentane labeled in a branched position by 13C 2-methyl- 13C(2)-pentane. If the consecutive reactions in the adsorbed state are with a given metal of low extent, and this is certainly true for Pt or Pd, then the appearance, among the product, of 3-methyl-l3C(3)-pentane is very strong evidence of the operation of the 5C (cyclic) intermediates. Only via a ring closure at one place and an opening at another place of the molecule can a label move simultaneously with the branch. On the other hand, when the branch and labeled atom become separated by isomerization, this is evidence of the operation of the 3Cay complexes (see Fig. 5). 

That products of intermediate oxidation level can be detected in the photocatalytic reactions of hydrocarbons and fossil fuels is also consistent with a surface bound radical intermediate . Photocatalytic isotope exchange between cyclopentane and deuterium on bifunctional platinum/titanium dioxide catalysts indicates the importance of weakly adsorbed pentane at oxide sites. The platinum serves to attract free electrons, decreasing the efficiency of electron-hole recombination, and to regenerate the surface oxide after exchange. Much better control of the exchange is afforded with photoelectrochemical than thermal catalysis > ) As before, hydrocarbon oxidations can also be conducted at the gas-solid interface... 

The coating material (about 75ml per l(X)ml of column packing) is applied as a solution in a suitable solvent such as methylene chloride, acetone, methanol or pentane, which is then allowed to evaporate in air, over a steam-bath, or in a vacuum oven (provided the adsorbed substance is sufficiently non-volatile). The order in which a mixture of substances travels through such columns depends on their relative solubilities in the materials making up the stationary phases. 

---