Ethanol surface concentration

The mixture of ethanol and concentrated sulphuric acid required in this and several subsequent preparations should always be prepared by adding the heavy acid to the ethanol. If the ethanol is added to the acid, it will tend to float on the surface of the acid, and the heat generated at the interface may blow the upper liquid out of the flask... 

The addition of ethylene to a CO-H flow on a Rh-CeO catalyst (fig. 4), which should enhance the surface concentration of C H groups increased the formation of propanol and propionaldehyde and decreased the ethanol and acetaldehyde production. 

The mass transfer term of k° is about 10.6% of k°. Considering that the second term will be even higher due to the lower surface concentration of ethanol during the reaction evolution, the contribution of the mass transfer term to k° can be considered minimal. This approximation, though rough, greatly simplifies the problem solution. Then... 

Correlation between the rate of ether formation from ethanol and the surface concentration of ethoxide species determined by IR spectroscopy [136]. 

In the case of solid or liquid solutions it is frequently observed that one component of the solution is present at a greater concentration in the surface region than in the bulk of the solution. Thus, for an ethanol-water system, die surface region will contain an excess of ethanol. The concentration of water will be higher at the surface than in the bulk, if the solute is sulfuric acid. Molybdenum oxide dissolved in glass will concentrate at the surface of the glass. The concentrating of solute molecules at a surface is called adsorption. 

Although DMVES reacts on silica surfaces [37], we have found it to adsorb on oxidized A1 only under specific conditions [4]. When spin cast on plasma alumina from solutions of either H20, acetone, or ethanol at concentrations 2.0 vol.% or greater, prohibitively thick films were obtained which adhered poorly to the alumina surface, evidenced by the fact they could be easily rinsed off with the above solvents. Lower solution concentrations resulted in no detectable adsorption. From these results we concluded that for DMVES to adsorb on alumina, the solutions must be dilute (<2.0 vol.%) and the exposure time increased. 

It has been shown that only those alcohols that form detectable surface alco-holate species on alumina undergo bimolecular dehydration with ether and water as reaction products (340). Thus, ether formation is the dominant reaction direction of methanol and ethanol at low temperatures, and the tendency toward ether formation is reduced as the chain length increases and chain branching occurs (28, 340). The same trends are observed for the stability and surface concentrations of the surface alcoholate species (27, 28, 47, 340). Alcoholate formation is due to a dissociative chemisorption step of the alcohol that occurs on A1—O pair sites (47, 340, 354-358). One is, thus, led to the conclusion that incompletely coordinated Al3+ ions and O2- ions are both important sites in the ether formation from alcohols and that their participation should be detectable by specific poisoning. 

The stop-effect was measured at 180 and 200°C with an ethanol initial concentration of 0.26 mol / m, at total flow rates of 1(X), 200 and 4(X) ml (NTP) / min. Before each experiment the catalyst was pre-treated in-situ at 415°C during 1 hour under inert gas flow, in order to remove the carboneous species adsorbed at the surface and to activate it. The transient experiments were carried out according to the following sequence 108 minutes ethanol / 830 minutes Ar. An infrared background spectrum was measured before each experiment, after the pre-treatment. A wafer of 27 mg was used in the cell, and the fixed-bed was filled with 483 mg of catalyst. 

In subsequent years, a new issue that bears on the composition of reformulated gasoline has surfaced. Concentrations of MTBE, presumably from gasoline leaks and spills that wash into natural waterways, have been found in drinking water. Because MTBE is not easily decomposed by natural processes or water treatment, it tends to remain where it has accumulated. It is reported to cause off tastes and odors in water. Also, it may be a carcinogen. In response to these concerns, a blue-ribbon panel of experts reviewed the evidence. In 2000, at their recommendation, efforts were begun to eliminate use of MTBE and promote further use of renewable oxygenates like ethanol. 

Whitesides and coworkers [435] have examined the preparation and properties of SAMs obtained by adsorption of long-chain alkanoic acids and alkanephosphonic acids as well as alkanehydroxamic acids onto metal oxide surfaces such as Ti02 and Zr02. Monolayers of octadecanoic acid and octadecanephosphonic acid were formed from solutions in either isooctane or ethanol with concentrations of 1 mM in... 

Kwon, M.Y. and Kim, J.J. (1990) Surface-enhanced Raman scattering of water in ethanol Electrolytic concentration dependence. Chemical Physics Letters, 169, 337-341. 

The type of behavior shown by the ethanol-water system reaches an extreme in the case of higher-molecular-weight solutes of the polar-nonpolar type, such as, soaps and detergents [91]. As illustrated in Fig. Ul-9e, the decrease in surface tension now takes place at very low concentrations sometimes showing a point of abrupt change in slope in a y/C plot [92]. The surface tension becomes essentially constant beyond a certain concentration identified with micelle formation (see Section XIII-5). The lines in Fig. III-9e are fits to Eq. III-57. The authors combined this analysis with the Gibbs equation (Section III-SB) to obtain the surface excess of surfactant and an alcohol cosurfactant. 

Fig. III-9. Representative plots of surface tension versus composition, (a) Isooctane-n-dodecane at 30°C 1 linear, 2 ideal, with a = 48.6. Isooctane-benzene at 30°C 3 ideal, with a = 35.4, 4 ideal-like with empirical a of 112, 5 unsymmetrical, with ai = 136 and U2 = 45. Isooctane-

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