Hydrocarbon distribution surface area

These conditions were compared because any effect resulting from exposure to a large surface of stainless steel would not require comparably rapid sampling flow. In other words, the effect of increased surface area alone could be observed. The hydrocarbon distribution at each temperature with and without added stainless steel wool is shown in Table V. Table V indicates that the preponderance of methane and absence of acetylene is not affected at 800°C. To interpret the apparent shift, however, at 500°C it is necessary to compare the relative concentrations of all samples. This is shown in terms of their ratios in Table VI. It will be noted that the effect of the stainless steel hot zone is relatively constant and appreciable for the times and temperatures of exposure. At 800°C, no acetylene is present, as expected for temperature as shown in Table III above while at 500°C the time-related suppression of acetylene previously observed in Table II above is also more strongly enhanced by the increased stainless steel surface area. We interpret this to mean that acetylene disappears much more rapidly than methane under these conditions and that the disappearance is related to the surface area of the stainless steel hot zone. 

The approach to calculate the van der Waals and cavity terms from the molecular surface areas can be used for the calculation of partition coefficients. The results show that for the distribution of hydrocarbons between water and n-octanol the calculated partition coefficient is linear in carbon number. Qualitatively similar data are obtained for the distribution between other solvents and water and the results can be used to predict the retention in liquid>liquid chromatography. On the other hand, if retention in RPC occurs due to reversible binding at the surface of the stationary phase, the significant parameter is not the total surface area of the eiuite but rather the net decrease in the molecular surface area of the stationary phase ligates and that of the eiuite upon binding, i.e., the contact area in the complex. 

Distribution of a polar compound between the bulk eluent and the surface of the active adsorbent can be used to load the porous column packing with variable amounts of a stationary phase. Eventually, a column containing an active adsorbent can be tran ormed into a "liquid-liquid partition column. In some cases, such as with prepacked columns, this is the only way to prepare a partition-qhromatographic system. If ternary mixtures containing a hydrocarbon, e.g., heptane or isooctane, an alcohol such as ethanol or isopropanol, and water are used, the polar constituents of this mixture are preferentially adsorbed by the stationary phase, especially if its surface area is large. In this case the eluent mixture decomposes and forms a polar stationary liquid rich in water and alcohol in the pores of the stationary phase. Tl greater the polarity differences between the components of the eluent, and the greater... 

Eadie, in Ref 69, reports on a considerable amount of work done on the ability of beeswax and paraffin wax to remain coated on HMX surfaces when immersed in liq TNT. Thru measurements of contact angles, a technique used earlier on RDX/wax systems reported on by Rubin in Ref 23, it was determined that the TNT preferentially wets the HMX and the wax is stripped away. He concludes that the most important property of a desensitizing wax is that it should be readily dispersed uniformly thruout the TNT phase. He also suggests that a better desensitizer for investigation for use would be a wax or substituted hydrocarbon having a low interfacial tension with TNT. The smaller the wax droplet size the more efficiently it will be distributed and the more effectively it should desensitize. Williamson (Ref 64) in his examination of the microstructures of PETN/TNT/wax fusion-casts detected that wax is dispersed thru the cast as isolated descrete globules which he refers to as blebs or irregular or streak-like areas, surrounded by TNT (see also Ref 54)... 

This and similar instruments (3,4) that allow one to study reaction rates and product distributions on small-area crystal and catalyst surfaces have been used in our studies of the mechanism of heterogeneous catalysis and the nature of active sites. These studies, which concentrated primarily on hydrocarbon reaction as catalyzed by platinum crystal surfaces, will be reviewed in the next section. 

Example 13.4. The result of a typical X-ray measurement is shown in Fig. 13.10 for a galactocerebroside [605], The plot on the left side shows the normalized reflected X-ray beam intensity versus the incident angle a for two different film pressures. The pressure-area isotherm is shown in the inset, together with the points of measurement a and b. On the right side are the extracted electron density profiles normal to the film surface taken at the same film pressures. At 0 A we find the monolayer surface (top of the alkyl chains), a depth of -40 A corresponds to pure water. In between is the film. The measurement is so sensitive that we even find two different electron densities within the monolayer. This is illustrated by the dashed boxes denoted by film 1 and film 2 (shown for curve b only) which represents the simplified electron density distribution in the so-called two-box model. A box is defined as a part in the film of a certain thickness where the electron density is constant. In the two-box model the film is divided into two layers. Film 1 represents the hydrocarbon tails, film 2 corresponds to the mean electron density of the head groups. 

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