Methanol, adsorption isotherms

The slopes of the isotherms for the various substances are approximately identical in the central part and close to the slope of the hydrogen adsorption isotherm. On iridium the methanol adsorption isotherms are satisfedby the Freundlich equation, where the power in the equation of the isotherm is close to that in the isotherm for hydrogen adsorption on iridium. The adsorption isotherms for methanol and hydrogen on rhodium are the same in nature. These results lead to the conclusion that the dependence of 0 andc is determined not by the nature of the adsorbed substance but by the nature and character of inhomogeneity in the catalyst surface. 

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],... 

The reason for enhancement of adsorption performance of PA/AC was considered to be due to combination effect of increase of BET surface area and chemical modification by the treatment with PA. Consequently, lwt%-PA/AC was determined to be a best candidate as an adsorbent for removing benzene, toluene, p-xylene, methanol, ethanol, and iso-propanol. Therefore, lwt%-PA/AC was used as the adsorbent to investigate the adsorption isotherm, adsorption and desorption performance. 

Assume that the coverages of H, CO, and methanol are given by the Langmuir adsorption isotherm in which CO, H2, and methanol adsorption compete for the same sites, and the intermediates HjCO S are present in negligible quantities. 

The retention of analyses in RP-HPLC markedly depends on the adsorption of the organic constituent of the mobile phase on the surface of the stationary phase. The excess adsorption isotherms of ACN, THF and methanol were measured on silica support modified with C, C6, C8, C10, C12 and C18 monomeric phase and a model was developed for the description of the retention of solutes from the binary mobile phase. The dependence of the retention factor on the partition coefficient can be described by... 

The formation of silicon-flvxyride bonds on the surface of silica after treatment with hydrogen fluoride was never proven directly. However, there is a pronounced change in the adsorption and wetting properties. The silica becomes hydrophobic as was mentioned in a patent to Kimberlin (279a). Neimark and collaborators (279b) found a type V isotherm in the methanol adsorption on silica gel which had been treated with a solution of SiF in absolute alcohol. Wilska (280) obtained a water-repellent silica when solutions of HaSiPg were precipitated with ammonia. The Si—F bond is hydrolyzed only slowly. A considerable fluorine content of 7-10% F was reported in an older patent (281) for a silica that had been prepared by hydrolysis of SiF. ... 

It must be remembered, in interpreting adsorption isotherms on coal, that coal expands sizably when temperature is increased, and coal swells appreciably during adsorption. These factors are relatively unimportant for porous inorganic solids. On heating from —195°C. to room temperature the volume of coal expands about 10%, and at least more or less consistent with this, pore openings at —195°C. seem to be 4A. while at room temperature they are about 5A. Further, on adsorption of water or methanol the volume of coal increases 10-20%, and with some exceptional polar adsorbates coal eventually dissolves. 

We have also compared the determination of the adsorption isotherms with those from a standard gravimetric technique. The precision of the data obtained by the gravimetric technique was found to be lower than that obtained by the FT-IR technique, particularly at very low silane concentrations (about 5%, and 3% at 0.4 g/100 ml concentration for the gravimetric and the FT-IR techniques, respectively). This is because very small weights of the silanes cannot be measured accurately and the silane is volatile. The effects of suspended silica particles in the solution were also examined by centrifuging methanol solutions... 

With binary and ternary supercritical mixtures as chromatographic mobile phases, solute retention mechanisms are unclear. Polar modifiers produce a nonlinear relationship between the log of solute partition ratios (k ) and the percentage of modifier in the mobile phase. The only form of liquid chromatography (LC) that produces non-linear retention is liquid-solid adsorption chromatography (LSC) where the retention of solutes follows the adsorption isotherm of the polar modifier (6). Recent measurements confirm that extensive adsorption of both carbon dioxide (7,8) and methanol (8,9) occurs from supercritical methanol/carbon dioxide mixtures. Although extensive adsorption of mobile phase components clearly occurs, a classic adsorption mechanism does not appear to describe chromatographic behavior of polar solutes in packed column SFC. 

Figure 34 shows the results for alcohol (methanol, ethanol, 1-propanol and 1-butanol), ketone (acetone and diacetyl), terpene (pinene and linalool), aldehyde (n-nonyl aldehyde) and ester (acetic acid n-amyl ester and n-butyric acid ethyl ester) of various concentrations. Because of the linear characteristics of the CTL-based sensor, the plots are located in a similar region for a certain type of gas of various concentrations where the Henry-type adsorption isotherm holds. Thus, we can identify these gases with various concentrations by simple data-processing. 

Since the chloroanilines are sufficiently retained (k >5) in a 10 % v/v methanol water eluent, and the Ibuprofen enantiomers are sufficiently retained in a 30 % v/v acetonitrile buffer eluent, these solvents were selected as carrier solvents for the displacement chromatographic separations. Also, these solvents were used to determine the adsorption isotherms of p-nitrophenol and 4-t-butylcyclohexanol on beta-cyclodextrin silica. The isotherms were determined from frontal chromatographic measurements as described in (56). The isotherms are shown in Figs. 7 and 8. Since both isotherms are downwardly convex, p-nitrophenol and 4-t-butylcyclohexanol might prove useful displacers for our test solutes, provided that they are more strongly adsorbed that the solutes. 

Adsorption isotherms of p-nitrophenol and the most retained isomers of chloroanilines. Conditions 15 cm x 4.6 mm ID column packed with beta-cyclodextrin-silica solvent 10 % v/v methanol water temperature 30 C. 

Parameters of the porous structure of titania samples (pores volume Vs, specific surface area Ssp) were calculated using BET theory [34] from the adsorption isotherms of methanol. The average pore diameter (Dp) values were estimated from the differential curves of pore size distribution. 

A classical volumetric adsorption apparatus equipped with absolute capacitance pressures transducers can be used for the estimation of adsorption isotherms in the pressure range 10-3 mbaradsorption measurements the carbon black samples are extracted with toluene and water/methanol (1 1) and after drying degassed overnight at 200 °C at a pressure below 10 4 mbar. The time allowed for equilibrium of each point of the isotherm is 5-90 min depending on the sample and the adsorbed amount. 

The surface areas of the various specimens estimated by applying the Brunauer, Emmett, and Teller equation (4) to the initial adsorption isotherms and using the value of 18 sq. A. (14) are compared with the surface areas calculated from the adsorption of cyclohexane in Table I. The surface areas calculated from the total adsorption of methanol on lepidocrocite as well as its products formed by... 

Figure 10.15. Adsorption isotherms of methanol, ethanol, propanol and butanol on a-Al203 (2.7 m2 g 1) (from Barto et al., 1966).

Type II character, whereas the latter was predominantly Type I. This difference is not surprising, hut it is more difficult to explain the magnitude of the derived external area. Thus, a value of c. 300 m2 g-1 was obtained from the methanol isotherms, whereas tire BET-nitrogen value was only 140 m2 g 1. It seems therefore that there may be an overestimate of the extent of the methanol adsorption on the external surface. 

Determinations of the adsorption isotherms for a number of organic solvent-water systems in contact with hydrocarbonaceous stationary phases have shown that a layer of solvent molecules forms on the bonded-phase surface and that the extent of the layer increases with the concentration of the solvent in the mobile phase. For example, methanol shows a Langmuir-type isotherm when distributed between water and Partisil ODS (56). This effect can be exploited to enhance the resolution and the recoveries of hydrophobic peptides by the use of low concentrations, i.e., <5% v/v, of medium-chain alkyl alcohols such as tm-butanol or tert-pentanol or other polar, but nonionic solvents added to aquo-methanol or acetonitrile eluents. It also highlights the cautionary requirement that adequate equilibration of a reversed-phase system is mandatory if reproducible chromatography is to be obtained with surface-active components in the mobile phase. 

The analysis of experimental excess adsorption isotherms using equation (2-50) had shown unusual results [22]. The adsorbed layer thickness of acetonitrile adsorbed from water on different types of reversed-phase adsorbents calculated as the ratio of adsorbed layer volume and adsorbent surface area appears to be on average equal to 14 A, which is equivalent to approximately five monolayers of acetonitrile molecules adsorbed on the hydrophobic surface. At the same time, the adsorbed layer thickness of methanol adsorbed from water on the same adsorbents is equal to only 2.5 A, which is equivalent to the monolayer-type adsorption. 

Figure 4-43. Adsorption isotherms of alkylsulfates on Hypersil-ODS from methanol/water (20/80) with 0.02 M phosphate buffer at pH 6.0. (Reprinted from reference 119, with permission.)...

Adsorption of 19a on CdS was measured from methanolic solution. As observed for the adsorption of 2,5-DHF, the adsorption isotherm indicates the presence of mono- and multilayer adsorption. From the former a maximum surface concentration eq(max) of 20 X 10 mol g Can be estimated. At higher concentrations a linear correlation seems to be present. A similar behavior was observed also for the adsorption of chlorophenols on Ti02 [46]. Application of the Fliemenz model on the methanol-imine surface monolayer leads to an adsorption constant of 4400 + 950 and a <7° value of 4000 A. This is far too large, as indicated by comparison with 50 (14 x 3.5 A) estimated for a flat unsolvated molecule. This... 

Figure 1. Adsorption isotherms and corresponding Os plots for benzene, dichloromethane and methanol adsorption on Maxsorb M25 and M30, VK50 and Carbosieve.

Two kinds of pitch-based ACFs (P5 and P20 Osaka Gas Co.) were used. The microporous structure was determined by high-resolution N, adsorption isotherms at 77 K using a gravimetric method. The micropore structual parameters were obtained from high-resolution a, -plot analysis with subtracting pore effect (SPE) method. The average slit pore width w was determined from the micropore volume and the surface area. The adsorption isotherms of methanol and ethanol on carbon samples were gravimetrically measured at 303 K. The sample was preevacuated at 10 mPa and 383 K for 2h. 

The adsorption isotherms of methanol and ethanol on ACF samples at 303 K were shown in Figure 2. The horizontal axes are expressed by the logarithm of P/P to show explieitly the adsorption in the low relative pressure range. The ad.sorption isotherms of ethanol on both P5 and P20 have a greater uptake in the lower relative pressure than those of methanol. Therefore, the interaction of an ethanol molecule with the micropore is much greater than that of a methanol molecule. However, the methanol molecule can interact more strongly than a H,0 molecule, because almost no water molecule is adsorbed below P/P = 0.3." ... 

Figure 2. Adsorption isotherms of methanol and ethanol on P5 (a) and P20 (b) at 303 K. O and Methanol and Ethanol...

Figure 3.23 Use of the Fowler isotherm to account for experimental data. The adsorption isotherms of 2-phenylethanol and 3-phenylpropanol between spherical ODS silica (Vydac, Hesperia, CA), 10 fim, and a methanol/water 50 50 solution. Column dimensions, 2.1 x 250 mm. Data from J. Zhu, AM. Katti and G. Guiochon, J. Ghromatogr., 552 (1991) 71.

Figure 3.24 Experimental adsorption isotherms of nucleotides on ODS silica, (a) Nucleotides on ODS. 1, Guanosine 2 3 -cyclic monophosphate 2, adenosine 2 3 -cyclic monophosphate 3, adenosine monophosphate. Spherisorb ODS-2 100 mM phosphate buffer pH 7, 25° C. (b) 1, a-MSH 2, benzyl-dimethyl-dodecyl ammoniiun bromide (BDDAB) on Spherisorb ODS-2,25°C, eluted with 15% v/v aqueous methanol (—) or with 21% aqueous acetonitrile, 0.2% formic acid and 0.4% triethylamine, pH 7 (—). Reproduced mth permission from from J.-X. Huang and Cs. Horvath, ]. Chromatogr., 406 (1987) 275, (a) Fig. 6, (b) Fig. 7.

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