Benzene molecular adsorption

Changes in relative peak intensity and marginal line shifts have been observed for benzene adsorbed on porous glass (26). More significantly, infrared spectroscopic evidence had been found in the appearance of inactive fundamentals for the lowering of molecular symmetry of benzene on adsorption on zeolites (47). 

Two different adsorbents, activated carbon Norit R 0.8 Extra (Norit N.V., The Netherlands) and molecular sieve (type 4A, Merck), were used to study tert-butylbenzene, cyclohexane, and water vapour breakthrough dynamics. Structural parameters of the carbon adsorbent were calculated from benzene vapour adsorption-desorption isotherms measured gravimetrically at 293 K using a McBain-Bakr quartz microbalance, and nitrogen adsorption-desorption isotherms recorded at 77.4 K using a Micromeritics ASAP 2405N analyzer described in detail elsewhere.22,24 Activated carbon Norit has a cylindrical... 

In this work, vapor-phase benzene/thiophene adsorption isotherms were investigated to develop new sorbents for desulfurization. Among the sorbents studied, Cu(I)-Y and Ag-Y exhibited excellent adsorption performance (capacities and separation ctors) for desulfurization. This enhanced performance compared to Na-Y was due to the n-complexation of thiophene with Cu and Ag. Molecular orbital calculations confirmed the relative strengths of n-complexation thiophene > benzene and Cu > Ag. ... 

A study was made of the ultraviolet spectra of benzene, alkyl-, amino-, and nitro-derivatives of benzene, diphenyl-amine, triphenylmethane, triphenylcarbinol, and anthra-quinone adsorbed on zeolites with alkali exchange cations, on Ca- and Cu-zeolites, and on decationized zeolites. The spectra of molecules adsorbed on zeolites totally cationized with alkali cations show only absorption bands caused by molecular adsorption. The spectra of aniline, pyridine, triphenylcarbinol, and anthraquinone adsorbed on decationized zeolite and Ca-zeolite are characterized by absorption of the corresponding compounds in the ionized state. The absorption bands of ionized benzene and cumene molecules appear only after uv-excitation of the adsorbed molecules. The concentration of carbonium ions produced during adsorption of triphenylcarbinol on Ca-zeolite and on the decationized zeolite depends on the degree of dehydroxyla-tion of the zeolite. 

Adsorption on Decationized Zeolites. There is great similarity in the spectral characteristics of adsorption on Ca-zeolites and on decationized zeolites. The adsorption of such molecules as benzene (Figure 4), and cumene (10) on these zeolites is characterized only by molecular adsorption. 

On the other hand, adsorbents A and B modified with ODS and adsorbent C unmodified or modified with ODS as well as with ODS+HMDS exhibit higher adsorption capacity. Benzene shows similar adsorption behavior [68]. The above facts are due to the specific structure of adsorption sites which is formed after the chemical modification of the adsorbents. Adsorption energy sites constitute of spacially arranged CH, CH2 and CH3 groups of the octadecyl radical, chemically bonded to the surface of the silica gel and, in the case of carbosils of components of the carbon deposit (i.e. CH, CH2, CH3) planary distributed on the surface of the supporting material. There is an essential difference in the mechanism of the molecular adsorption on chemically modified and unmodified adsorbents [30]. The surface of chemically unmodified adsorbents can be considered as planar, i.e. two-dimensional, while that of the modified sorbents as three-dimensional. 

The Q-TG mass loss and the Q-DTG differential mass loss curves of liquids as a fiinction of temperature from the N-1, N-2 and N-3 carbon nanotube surfaces are presented in Figure 11. The characteristic inflections in the Q-DTG curves correspond to the individual stages of thermodesorption of the selected liquids from nanotube surfaces. The Q-DTG curve is a type of spectrum of thermodesorption process, describing the energetic states of polar and nonpolar molecules on the surface. The spectrum indicates long wide peaks with the minima near 70 (N-l/benzene), 115 (N-2/n-octane) and 120 C (N-3/n-butanol) and a few other small peaks. The data presented in Table 2 show that the samples are highly sensitive to water vapour because the mechanism of molecular adsorption depends largely on the activated surface centres. 

Bipyridine-bridged [Mn(l) and Re(l)] molecular rectangles QCM Toluene 4-fluorotoluene benzene fluorobenzene Adsorption Benkstein et al. (2000)... 

Some methods for pore structure analysis have been presented The adsorption of benzene and the evaluation of isotherms through the Dubinin - Radushkevich equation, the estimation of immersion heats in benzene, the adsorption of water at relative pressures of h=0.6 and 1.0, the size exclusion liquid chromatography with tracers of different molecular diameters and the one - point adsorption of nitrogen. Six active carbons are included in the investigations. It is not possible to obtain reliable values with the simple water adsorption method. The results obtained with other methods are compared with performances of adsorption of phenol from aqueous solutions as obtained from measuring equilibria and column dynamics. It is shown, that the rank of the results of pore structure analysis is the same as from the dynamic experiments. 

Molecular moments of inertia are about 10 g/cm thus 7 values for benzene, N2, and NH3 are 18, 1.4, and 0.28, respectively, in those units. For the case of benzene gas, a = 6 and n = 3, and 5rot is about 21 cal K mol at 25°C. On adsorption, all of this entropy would be lost if the benzene were unable to rotate, and part of it if, say, rotation about only one axis were possible (as might be the situation if the benzene was subject only to the constraint of lying flat... 

The standard entropy of adsorption AS2 of benzene on a certain surface was found to be -25.2 EU at 323.1 K the standard states being the vapor at 1 atm and the film at an area of 22.5 x T per molecule. Discuss, with appropriate calculations, what the state of the adsorbed film might be, particularly as to whether it is mobile or localized. Take the molecular area of benzene to be 22 A. ... 

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 . )...

Benzene, toluene, and a mixed xylene stream are subsequently recovered by extractive distillation using a solvent. Recovery ofA-xylene from a mixed xylene stream requires a further process step of either crystallization and filtration or adsorption on molecular sieves. o-Xylene can be recovered from the raffinate by fractionation. In A" xylene production it is common to isomerize the / -xylene in order to maximize the production of A xylene and o-xylene. Additional benzene is commonly produced by the hydrodealkylation of toluene to benzene to balance supply and demand. Less common is the hydrodealkylation of xylenes to produce benzene and the disproportionation of toluene to produce xylenes and benzene. 

The pore size of Cs2.2 and Cs2.1 cannot be determined by the N2 adsorption, so that their pore sizes were estimated from the adsorption of molecules having different molecular size. Table 3 compares the adsorption capacities of Csx for various molecules measured by a microbalance connected directly to an ultrahigh vacuum system [18]. As for the adsorption of benzene (kinetic diameter = 5.9 A [25]) and neopentane (kinetic diameter = 6.2 A [25]), the ratios of the adsorption capacity between Cs2.2 and Cs2.5 were similar to the ratio for N2 adsorption. Of interest are the results of 1,3,5-trimethylbenzene (kinetic diameter = 7.5 A [25]) and triisopropylbenzene (kinetic diameter = 8.5 A [25]). Both adsorbed significantly on Cs2.5, but httle on Cs2.2, indicating that the pore size of Cs2.2 is in the range of 6.2 -7.5 A and that of Cs2.5 is larger than 8.5 A in diameter. In the case of Cs2.1, both benzene and neopentane adsorbed only a little. Hence the pore size of Cs2.1 is less than 5.9 A. These results demonstrate that the pore structure can be controlled by the substitution for H+ by Cs+. 

Pyridine. Pyridine and its methyl substituted derivatives (picolines and lutidines) were found to polymerize electrochemically and, under certain circumstances, catalytically. This behavior was not expected because usually pyridine undergoes electrophilic substitution and addition slowly, behaving like a deactivated benzene ring. The interaction of pyridine with a Ni(100) surface did not indicate any catalytic polymerization. Adsorption of pyridine below 200 K resulted in pyridine adsorbing with the ring parallel to the surface. The infrared spectrum of pyridine adsorbed at 200 K showed no evidence of either ring vibrations or CH stretches (Figure 5). Desorption of molecular pyridine occurred at 250 K, and above 300 K pyridine underwent a... 

The elution volumes of polystyrene and benzene in the size-exclusion mode were 0.98 and 1.78 ml, respectively (Figure 1.4A). This means that separations by molecular size can be achieved between 0.98 and 1.78 ml in this system. In the normal phase mode the elution volumes of octylbenzene and benzene were 1.98 and 2.08 ml, respectively, in n-hexane solution (Figure 1.4B). This type of chromatography is called adsorption or non-aqueous reversed-phase liquid chromatography. These are adsorption liquid chromatography and non-aqueous reversed-phase liquid chromatography. The elution order of the alkylbenzenes in the reversed-phase mode using acetonitrile was reversed... 

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