Adsorption cyclohexane

Examples 28 and 29 are for deuterium-hydrogen exchange reactions. The reaction in Example 28 was carried out at a temperature low enough so that the only reaction after adsorption was that of CgHj (ads) with D (ads), followed by desorption. Sarkany, Guczi, and Tetenyi (54) suggested for their reaction that the rate-determining step was cyclohexane adsorption. The log L values indicate that dissociative adsorption of cyclohexane (Step 2, cyclohexane), for which log L = 19, is possible. But some surface freedom of cyclohexane is required. Dissociative adsorption of D2, for which log L = 15, seems more likely. 

Haaland also measured the infrared spectra of benzene adsorbed on Pt/Al203 that had been regenerated after previous benzene/cyclohexane adsorptions (247) the surface was thought to retain structured carbonaceous deposits. In this case, the broad yCH feature was centered at ca. 3030 cm 1 (with components at 3042, 3031, 3024, and 3014 cm 1) rather than 3040 cm 1 for the species on the freshly prepared catalyst, and a weaker companion band occurred at 2947 cm-1. The benzene absorption bands at wavenumbers <1500 cm 1 were little changed in position but become more prominent in room-temperature spectra in which the 2947-cm 1 feature was weakened. Spectra measured over the range 300-650 K showed that the 2947-cm 1 feature disappeared at 435 K, whereas the vCH aromatic bands retained considerable intensity at temperatures up to 560 K. 

Figure 5. Pulse chromatograms for cyclohexane adsorption on activated carbon...

Benzene and cyclohexane adsorption was studied on Na- and H-mordenite in a chromatographic thermodesorption unit (3) at various rates of programmed temperature changes. 

The sensitivity of lattice modes to structural changes is illustrated by the recent study of Mueller and Connor [25] on the effects of cyclohexane adsorption on the structure of MFI zeolites. The adsorption of molecules such as paraxylene and benzene into MFI zeolites causes a structural transition from monoclinic to orthorhombic symmetry, which has been characterized by X-ray powder diffraction and 29 si NMR spectroscopy [26]. Cyclohexane has a slightly larger kinetic diameter than benzene or paraxylene (0.60 nm compared with 0.585nm), but does not cause the same structural transition. Cyclohexane adsorption does however affect the zeolite lattice mode vibrational frequencies. Figure 7 shows spectra taken from reference 25 before and after (upper spectrum) adsorption of cyclohexane in a low aluminium MFI zeolite. 

Fig. 13. Cyclohexane adsorption vs temperature of calcination for modified faujasite catalysts.

Siemieniewska, T., et ah. Application of the Dubinin-Astakhov equation to evaluation of benzene and cyclohexane adsorption isotherms on steam gasified humic acid chars from brown coal. Energy Fuels, 4(1), 61-69(1990). 

Fig. XI-5. Adsorption isotherm from Ref. 61 for polystyrene on chrome in cyclohexane at the polymer theta condition. The polymer molecular weights x 10 are (-0) 11, (O) 67, (( )) 242, (( )) 762, and (O) 1340. Note that all the isotherms have a high-affinity form except for the two lowest molecular weights.

For adsorption on Spheron 6 from benzene-cyclohexane solutions, the plot of N N2/noAN2 versus N2 (cyclohexane being component 2) has a slope of 2.3 and an intercept of 0.4. (a) Calculate K. (b) Taking the area per molecule to be 40 A, calculate the specific surface area of the spheron 6. (c) Plot the isotherm of composition change. Note Assume that is in millimoles per gram. 

Fig. 5.8 Adsorption isotherms at 25°C of benzene and cyclohexane on a mesoporous silica gel. Curve (A), benzene curve (B), cyclohexane. Solid symbols denote desorption.

Example 4 Application of Isotherms Thomas [Ann. N.Y. Acad. Sci., 49, 161 (1948)] provides the following Langmuir isotherm for the adsorption of anthracene from cyclohexane onto alumina ... 

Furusawa and Yamamoto [16] studied the adsorption process of polystyrene samples (M ranging from 16700 to 2xl06) with narrow molecular weight distribution (Mw/M = 1.01-1.07) at the -conditions (cyclohexane, 35 °C). Controlled pore glass with pore diameter of 1000 A was used as an adsorbent. 

This is the same case with which in Eqs. (2)-(4) we demonstrated the elimination of the time variable, and it may occur in practice when all the reactions of the system are taking place on the same number of identical active centers. Wei and Prater and their co-workers applied this method with success to the treatment of experimental data on the reversible isomerization reactions of n-butenes and xylenes on alumina or on silica-alumina, proceeding according to a triangular network (28, 31). The problems of more complicated catalytic kinetics were treated by Smith and Prater (32) who demonstrated the difficulties arising in an attempt at a complete solution of the kinetics of the cyclohexane-cyclohexene-benzene interconversion on Pt/Al203 catalyst, including adsorption-desorption steps. 

The quantitative solution of the problem, i.e. simultaneous determination of both the sequence of surface chemical steps and the ratios of the rate constants of adsorption-desorption processes to the rate constants of surface reactions from experimental kinetic data, is extraordinarily difficult. The attempt made by Smith and Prater 82) in a study of cyclohexane-cyclohexene-benzene interconversion, using elegant mathematic procedures based on the previous theoretical treatment 28), has met with only partial success. Nevertheless, their work is an example of how a sophisticated approach to the quantitative solution of a coupled heterogeneous catalytic system should be employed if the system is studied as a whole. 

In a poor solvent (cyclohexane at 5°C), a polymer chain takes on a condensed globular state because constituent molecules are repulsed by the solvent molecules. Nanofishing of this chain revealed a perfectly different force-extension curve, as shown in Figure 21.5. It was observed that constant force continued from about 30 to 130 nm after nonspecific adsorption between a... 

Adsorption phenomena from solutions onto sohd surfaces have been one of the important subjects in colloid and surface chemistry. Sophisticated application of adsorption has been demonstrated recently in the formation of self-assembhng monolayers and multilayers on various substrates [4,7], However, only a limited number of researchers have been devoted to the study of adsorption in binary hquid systems. The adsorption isotherm and colloidal stabihty measmement have been the main tools for these studies. The molecular level of characterization is needed to elucidate the phenomenon. We have employed the combination of smface forces measmement and Fomier transform infrared spectroscopy in attenuated total reflection (FTIR-ATR) to study the preferential (selective) adsorption of alcohol (methanol, ethanol, and propanol) onto glass surfaces from their binary mixtures with cyclohexane. Om studies have demonstrated the cluster formation of alcohol adsorbed on the surfaces and the long-range attraction associated with such adsorption. We may call these clusters macroclusters, because the thickness of the adsorbed alcohol layer is about 15 mn, which is quite large compared to the size of the alcohol. The following describes the results for the ethanol-cycohexane mixtures [10],... 

Fig.3.1.9 (a) The adsorption-desorption isotherm (circles, right axis) and the self-diffusion coefficients D (triangles, left axis) for cyclohexane in porous silicon with 3.6-nm pore diameter as a function of the relative vapor pressure z = P/PS1 where Ps is the saturated vapor pressure, (b) The self-diffusion coefficients D for acetone (squares) and cyclohexane (triangles) as a function of the concentration 0 of molecules in pores measured on the adsorption (open symbols) and the desorption (filled symbols) branches. 

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