Benzene isosteric heats

Fig. 2.15 Isosteric heat of adsorption of nitrogen on molecular (low-evergy) solids and on carbons (high-energy solids), plotted as a function of i/n . (A) Diamond (B) gruphitized carbon black. P.33 (D) Benzene (E) Teflon. The curve for amorphous carbon was very close to Curve (A). (Redrawn from a Figure of Adamson . )...

Snurr et al. (192) used biased GC-MC simulations to predict isotherms, isosteric heats of adsorption, and locations of benzene and p-xylene at various concentrations. The suitability of a bias method is clear, at low coverages to prevent trial insertions overlapping with the zeolite walls and at high coverages to prevent overlap with other sorbate molecules. (Slightly different bias schemes were used for the two extremes of concentrations.) Interactions between sorbates and zeolites—both of which were considered to be rigid—were modeled with parameters from the literature (79, 87). Electrostatic interactions were included to account for the quadrupole moment of the sorbates. Sorbate-sorbate interaction parameters were taken from Shi and Bartell (194) for benzene and from Jorgensen et al. (195) for p-xylene. 

Sorbate sorbate interactions were found to be negligible in the ORTHO regime of the isotherm molecules occupy intersections and are too far away from each other to interact. At higher loadings, in the PARA region of the isotherm, the sinusoidal channels become filled, and the significant sorbate-sorbate interactions between neighboring benzene molecules result in an increase of the isosteric heat of adsorption. 

The objective of this study is to compare the strengfti of adsorptive interaction between adsorbents and thiophene/benzene. Extremely low partial pressures at less than 10 atm would be necessary to meet this objective if isotherms were measured at ambient temperature, because the isotherms at ambient temperature are fairly flat and are difficult to compare. However, it is very difficult to obtain and control such low partial pressures experimentally. Therefore, single component isothoms for benzene and thiophene were measured at 90, 120 and 180 °C using standard gravimetric methods. A Shimadzu TGA-50 automatic recording microbalance was employed. Isosteric heats of adsorption were calculated using the Clausius-Clapeyron equation from isotherms at different temperatures. 

In a recent paper, Chiang et al. [22] reported values of the free energy, enthalpy, and entropy of adsorption of volatile organic compounds (exemplified by benzene and methylethylketone) on seven samples of activated carbon. The starting point for their development was Eqn (3.11) for the isosteric heat of adsorption. Linders et al. [23] determined adsorption heats from the adsorption equilibrium constant and found that these values agree quite well with those obtained from uptake experiments using the integrated form of Eqn (3.11). They analyzed the experimental data obtained for -butane adsorbed on two commercial activated carbons (Kureha and Sorbonorit B3) and for hexafluoropropylene adsorbed on activated carbon. 

Plot the isosteric heat of adsorption vs the amount adsorbed from the following data of Shen and Smith for benzene on silica gel. Using a constant value of 34.8 X 10 cm" for the surface area occupied by one benzene molecule, convert the coordinate showing the amount adsorbed to fraction of the surface --------covered- -t0tal-sur-faee-area-=-832-m /g)7--------------------------------------... 

Abstract Infrared spectroscopic methodsfor the measurement of adsorption and adsorption kinetics of some aromatics (benzene, ethylbenzene, p-xylene), pyridine, and paraffins in solid microporous materials such as zeolites (MOR, ZSM-5, silicalite-1) are described as well as the evaluation of the spectroscopically obtained data. The adsorption isotherms are of the Langmuir-Freundlich type. Isosteric heats of adsorption, transport diffusivities, and activation energies of diffusion as deduced from the spectroscopic measurements are compared with literature data as far as available, and they are found to be in reasonable agreement with results provided by independent techniques. Special attention is paid to sorption and sorption kinetics of binary mixtures, especially the problems of co- and counter-diffusion. ... 

Table 2 Isosteric heat, Qiso, and microcalorimetrically measured heat of adsorption, of benzene, ethylbenzene, and p-xylene in H-ZSM-5 ...

The adsorption isosteres for ethylbenzene (see Figure 18), adsorbed from a benzene/ethylbenzene mixture into H-ZSM-5, provided isosteric heats of... 

The first attempts to predict macroscopic properties such as Henry constants, initial isosteric heats of adsorption, or changes in the standard differential entropies for noble gases, H2, N2, O2, CO, H2O, NH3, CO2, n-alkanes up to Cg, ethylene, acetylene, and benzene in silicalite were performed by Kiselev and coworkers about 20 years ago.224-227 These workers used potential param-... 

The activation energy thus determined is compared with the heat of adsorption for each gas obtained by van Hoff plot (Fig. 3.12) in Fig. 4. IS. The activation energy for rare gases, methane and benzene and for hydrocarbons except methane have different proportionality constants to the isosteric heat of adsorption, Qa. 

Because the isosteric heat of adsorption of benzene on the zeolite NaX is... 

Replacement of a benzene ring by its isostere, thiophene, is one of the more venerable practices in medicinal chemistry. Application of this stratagem to the NSAID piroxicam, gives tenoxicam, 136, a drug with substantially the same activity, nie synthesis of this compound starts by a multi-step conversion of hydroxy thiophene carboxylic ester 130, to the sulfonyl chloride 133. Reaction of that with N-methylglycinc ethyl ester, gives the sulfonamide 134. Base-catalyzed Claisen type condensation serves to cyclize that intermediate to the p-keto ester 135 (shown as the enol tautomer). The final product tenoxicam (136) is obtained by heating the ester with 2-aminopyridine [22]. 

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