Carbon tetrachloride, adsorption

Fig. 2 shows the isotherms of n-hexane, benzene and carbon tetrachloride adsorption on silica from their mixtures and on Fig. 3 the isotherms of dioxane, acetone and water adsorption from their mixtures on hydroxylated silica are presented. Fig. 4. shows the... 

Alumina-zirconia and alumina-titania mixed oxides were prepared by coprec itation of thdr corresponding chlorides. Samples were synthezised at several concentrations, dried and calcined at ten eratures between 400°C and 800T. All dried samples showed the bayeiite structure, which upon calcination became first amorphous and later AljOj. Anatase was observed only on the high content, high calcination temperature sample, but no mystalline phase of zirconia was detected. Surface areas of mixed oxides were higher than for alumina single oxide, and decreased with ten ierature. Carbon tetrachloride adsorption increased with TiO content, but the opposite effect was observed on alumina-zirconia samples. 

Carbon tetrachloride adsorption was measured at 28 C with a microbalance giv ing a linear BET plot from which the specific area agreed with that by nitrog adsorption. There was no chemical interaction (76). Carbon dioxide at the tempera. ture of -78 C can be used in the same equipment as employed for nitrogen at - 196 C and gives the same results within 10% (77). 

For other adsorptives the experimental evidence, though less plentiful than with nitrogen, supports the view that at a given temperature the lower closure point is never situated below a critical relative pressure which is characteristic of the adsorptive. Thus, for benzene at 298 K Dubinin noted a value of 017 on active carbons, and on active charcoals Everett and Whitton found 0-19 other values, at 298 K, are 0-20 on alumina xerogel, 0-20-0-22 on titania xerogel and 017-0-20 on ammonium silicomolybdate. Carbon tetrachloride at 298 K gives indication of a minimum closure point at 0-20-0-25 on a number of solids including... 

A factor militating against the use of other adsorptives for pore size determination at the present time is the lack of reliable r-curves. The number of published isotherms of vapours such as benzene, carbon tetrachloride or the lower alkanes, or even such simple inorganic substances as carbon dioxide, on a reasonable number of well-defined non-porous adsorbents, is very small. 

Fig. 4.25 Adsorption isotherms showing low-pressure hysteresis, (a) Carbon tetrachloride at 20°C on unactivated polyacrylonitrile carbon Curves A and B are the desorption branches of the isotherms of the sample after heat treatment at 900°C and 2700°C respectively Curve C is the common adsorption branch (b) water at 22°C on stannic oxide gel heated to SOO C (c) krypton at 77-4 K on exfoliated graphite (d) ethyl chloride at 6°C on porous glass. (Redrawn from the diagrams in the original papers, with omission of experimental points.)...

For the experiments referred to in Fig. 4.25(a), McEnaney was able to show, on reasonable assumptions, that the stress induced by adsorption swelling should be sufficient to fracture the carbon over short distances. A memory effect in the carbon network would lead to trapping of some adsorbed carbon tetrachloride molecules during the desorption run. 

As remarked on p. 214, the validity of the nonane pre-adsorption method when adsorptives other than nitrogen are employed for determination of the isotherms, has been examined by Tayyab. Two organic adsorptives, /i-hexane and carbon tetrachloride, which could be used at or near room temperature, were selected and the adsorbents were the ammonium salts of... 

Fig. 4J1 Adsorption isotherms on ammonium phosphomolybdate powder. (1), (2), before pre-adsorption of nonane (3), (4) after preadsorption of nonane. (1), (4), nitrogen (77 K) (2), (3), carbon tetrachloride (298 K). Adsorption is expressed in mm (liquid).

Fig. 4J2 Adsorption isotherms of carbon tetrachloride (at 298 K) on ammonium phosphotungstate compact, (1) before, (2) after preadsorption of n-nonane. (3) is the isotherm of nitrogen, after preadsorption, for reference. Open symbols, adsorption solid symbols,...

Fig. 5.9 Adsorption isotherms of carbon tetrachloride at 20 C on various samples of silica. (A) Fransil (nonporous particles) (B) TK 800 (nonporous particles) (C) a mesoporous gel (D) a microporous gel.

Removal of Refractory Organics. Ozone reacts slowly or insignificantly with certain micropoUutants in some source waters such as carbon tetrachloride, trichlorethylene (TCE), and perchlorethylene (PCE), as well as in chlorinated waters, ie, ttihalomethanes, THMs (eg, chloroform and bromoform), and haloacetic acids (HAAs) (eg, trichloroacetic acid). Some removal of these compounds occurs in the ozone contactor as a result of volatilization (115). Air-stripping in a packed column is effective for removing some THMs, but not CHBr. THMs can be adsorbed on granular activated carbon (GAG) but the adsorption efficiency is low. 

Oscik and Chojnacka [63] use TEC adsorption in the investigation of six aromatic hydrocarbons (naphthalene, diphenyl, anthracene, pyrene, chrysene, and acenaphthene) on silica gel G by elution with different binary mobile phases (trichloroethylene-benzene, carbon tetrachloride-benzene, n-heptane-trichloroethylene. 

It is known that alumina is chlorinated exothermically at above 200° C by contact with halocarbon vapours, and hydrogen chloride, phosgene etc. are produced. It has now been found that a Co/Mo-alumina catalyst will generate a substantial exotherm in contact with vapour of carbon tetrachloride or 1,1,1-trichloroethane at ambient temperature in presence of air. In absence of air, the effect is less intense. Two successive phases appear to be involved first, adsorption raises the temperature of the alumina then reaction, presumably metal-catalysed, sets in with a further exotherm. 

The adsorption of block and random copolymers of styrene and methyl methacrylate on to silica from their solutions in carbon tetrachloride/n-heptane, and the resulting dispersion stability, has been investigated. Theta-conditions for the homopolymers and analogous critical non-solvent volume fractions for random copolymers were determined by cloud-point titration. The adsorption of block copolymers varied steadily with the non-solvent content, whilst that of the random copolymers became progressively more dependent on solvent quality only as theta-conditions and phase separation were approached. 

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. 

The experimental entropies of adsorption were calculated after obtaining the free energies of adsorption at 0 = /% from the gas pressure in equilibrium with half the amount of adsorbate required to form the monolayer. The same principles were used to obtain the figure for the entropy of adsorption of O2 on unreduced steel. The values for carbon tetrachloride were taken directly from Foster s paper (4). The results for adsorption in chabazite were obtained from the work of Barrer and Ibbitson (15) with the slight modification needed to allow for the different standard states in the two phases used by them. The figures in the last column... 

S.A. (1980) Infrared study of the adsorption of carboxylic acids on hematite and goethite immersed in carbon tetrachloride. J. Chem. Soc. Faraday Trans. I. 76 302-313 Buerge, I.J. Hug, S.J. (1999) Influence of mineral surfaces on chromium(VI) reduction by iron(II). Environ. Sci. Techn. 33 4285-4291 Buerge-Weirich, D. Hard, R. Xue, H. Behra, P. Sigg, L. (2002) Adsorption of Cu, Cd and Ni on goethite in the presence of natural groundwater ligands. Environ. Sci. Techn. 36 328-336... 

For this reason, additional studies on carbon tetrachloride flux rates into and out of surface water, as well as refined quantitative estimates of aquatic fate processes would be valuable. The chemical is expected to evaporate rapidly from soil due to its high vapor pressure and may migrate into groundwater due to its low soil adsorption coefficient. No data are available on biodegradation in soil. Additional studies to determine degradation rates and the extent to which adsorption has occurred would be useful. These data are also useful in evaluating the impact of carbon tetrachloride leaching from hazardous waste sites. 

Bioavailability from Environmental Media. Carbon tetrachloride can be absorbed following inhalation, oral, or dermal exposure. No data were located regarding the potential effects of environmental media (air, water, soil) on the absorption of carbon tetrachloride. Flowever, since soil adsorption is considered to be relatively low for carbon tetrachloride, it seems unlikely that soil would have a significant effect on its bioavailability. Additional studies are needed to determine the extent of bioavailability from contaminated air, drinking water, and soil at hazardous waste sites. 

Only nonpolar solvents, e.g., cyclohexane (most commonly employed with silica gel and silicic acid), methylcyclohexane, methylpentane, and carbon tetrachloride, can be utilized in these slurries since solvents of greater polarity will compete with the intended adsorbate for available binding sites and will result in incomplete sustrate adsorption. 

A comparison of husD and fe/M/t) values for sample 3 are particularly instructive. The heat values for the immersion of monolayer-covered samples in toluene, cyclohexane, and carbon tetrachloride are three to four times less than the heat values for the bare samples and are also significantly less than the surface enthalpies of the respective liquids. Apparently, the attractive forces of the covalent carbon atoms in the surface are highly localized. In addition, the interaction of first-layer molecules with those in the second layer is less than between the liquid molecules in adsorbed monolayer, as indicated by the 7 s (14)- The net energy of adsorption... 

The separation mechanisms, which were operative in the above experiments, will be discussed below. Carbon tetrachloride is a good solvent for all types of polybutadienes, and the separation with this solvent should have proceeded according to the adsorption mechanism. On the other hand, cis-1,4 and 1,2-vinyl poly butadiene were soluble in amyl chloride even below —5 °C but tram-1,4 polymer was insoluble in this solvent below ca. 40 °C. This suggests that the separation with this solvent would have proceeded according to the solubility-controlled mechanism. 

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