Uptake of n-hexane

As a non-invasive method, however, PFG NMR also provides excellent conditions for the measurement of molecular diffusivities under transient conditions. As an example. Fig. 18 shows the results of space- and time-resolved self-diffusion measurements over a bed of activated zeolite Na-X during the uptake of n-hexane [163]. Taking into account that, due to the finite size of... 

Fig. 23 Monitoring the absorbance of an H-ZSM-5 sample during uptake of n-hexane at 398 K via micro-FTIR spectroscopy 3.1mbar partial pressure of n-hexane in a helium flow (100 mlmin )...

Fig. 25 Uptake of n-hexane under 3.1 mbar partial pressure with helium as carrier gas at various sorption temperatures monitored via micro-FTIR spectroscopy. Solid lines calculated uptake curves symbols A = 398 K, <> = 423 K, o = 448 K, = 473 K...

The permeability of human skin to n-hexane has been determined in vitro in flow-through diffusion cells (Loden 1986). Pieces of full-thickness human skin were exposed to 3H -hcxane in human serum, and the appearance of label in the trans compartment measured for 0.5 or 12 hours. The skin was then sectioned with a microtome into 0.25 mm slices and the quantity of label in the skin measured. The rate of resorption (uptake of substance by the receptor fluid beneath the skin [i.e., the amount that passes through the skin]) was calculated. The rate of resorption for n-hexane through human skin was calculated to be 0.83 ( g cm2/hr). The permeability of n-hexane through human skin was much lower (approximately 100-fold) than for other chemicals tested in this study. For example, rates of resorption (in g cm2/hr) were 99 for benzene and 118 for ethylene glycol. 

Fig. 1 shows the uptake of pure hexane and decane frx)m their mixture with iso-octane on ZSM-S. The amounts adsorbed in the zeolite remain constant after 20 hours, indicating that the experiments were performed under equilibrium conditions. In order to verify that iso-octane can be used as inert solvent, a comparative experiment was performed in which the binary adsorption isotherm of hexane and decane was determined using isooctane and l,3,S-trimethyl benzene as respective solvents. The same adsorption isotherms are obtained with both solvent (Fig. 1 b), demonstrating that iso-octane does not interfere with the adsorption of the linear alkanes, and that the relative adsorption of the short and long n-alkanes is not influenced by the nature of the solvent, given that the solvent is not able to enter the pore system. 

Figure 4. IR absorbance spectrum of sample A after uptake imder 3.1mbar of n-hexane, conditions otherwise unchanged.

Figure 5. Uptake imder 3.1 mbar of n-hexane in HZSM-5, sample A at various sorption temperatures. Solid lines calculated uptake curves, symbols A - 398 K, 0 - 423 K, o - 448 K and -473K.

The decomposition of the zeolite frameworks was monitored by IR spectroscopy and calculated on the basis of n-hexane, nitrogen, and water sorption uptake. 

P-08 -Transient uptake measurements using an oscillating microbalance effect of acid leaching on the diffusivity of n-hexane in Pt/H-Mordenite... 

Radioactivity distribution. The N-hexane lipido/sterolic extract (LSESr) supplemented with [ C]-labeled oleic or lauric acids or P-sitosterol was administered orally to rats. The highest level of radioactivity uptake was LSESr supplemented with [ C]-labeled oleic acid. Ratios of radioactivity in tissues compared to plasma showed an uptake of radioactivity greater in prostate as compared with other genital organs, i.e., the seminal vesicles or to other organs such as... 

The evidence for 4 was based upon measurements of the uptake of ethylene (after degassing and readmission of ethylene several times to the system.) Hay found that the system absorbed more ethylene (25 times) than the solubility of ethylene in hexane would predict. However, one cannot help but wonder whether or not the solubility of ethylene in n-BuLi-hexane or n-BuLi-hexane-TMEDA might be different from that of ethylene in hexane alone. 

A 2.42 g (0.01 mole) of ethyl N-(p-cyanoethyl)indole-2-carboxylate is suspended in acetic anhydride (20 ml). The suspended compound is hydrogenated on a Parr shaker in the presence of Raney nickel. The uptake of hydrogen is complete after 1.5 h. The product recovered is recrystallized from benzene-hexane. The product obtained is ethyl l-(3-acetamidopropyl)indole-2-carboxylate, melting point 83.5°-84.5°C. 

Nomiyama K, Nomiyama H. 1974a. Respiratory retention, uptake and excretion of organic solvents in man Benzene, toluene, n-hexane, trichloroethylene, acetone, ethyl acetate and ethyl alcohol. Int Arch Arbeitsmed 32 75-83. 

In this study, uptake kinetics have been investigated for the system n-hexane/HZSM-S by means of w/cro-FTIR, an extension of the conventional FTIR technique. We would like to summarize the major features of this technique as follows ... 

Fig. 2 n-Hexane sorption uptake of DAY-S treated 72 h in steam at saturation pressure... 

A partition coefficient is defined by the ratio of the concentrations of a compound in two immiscible phases that are at equilibrium. It is common, though not necessary, for one phase to be water and the second an organic solvent, such as hexane, benzene, ether, and so on. It is important to emphasize that Aqw is not the ratio of the solubilities of the compound in octanol and water, because, since the two liquids are at equilibrium, the octanol phase will be saturated with water and the water with octanol. The use of n-octanol dates from the late nineteenth century when water-octanol was chosen as a surrogate to reflect uptake of pharmaceuticals into organisms. In retrospect, this turned out to be a wise choice and over the past 30 years there has been a continuing interest in the study of initially stimulated... 

To illustrate the quality of the data, no accumulation and/or averaging of the absorbances were carried out. For the sorbates n-heptane (see Fig. 24), n-octane, and n-nonane similarly well-fitted uptake curves were obtained [32]. In Fig. 25, the uptake curves for n-hexane into sample No. 7 at various sorption temperatures are presented. The symbols denote the... 

From the uptake curves of the four n-paraffins (as shown, e.g., in Figs. 24 and 25 for diffusion of n-heptane and n-hexane, respectively) into H-ZSM-5 as a function of adsorption temperature, the corresponding Arrhenius plots were derived and are shown in Fig. 26. 

The reverse experiment showed that neopentane was, under the given conditions, unable to replace any of the preloaded n-hexane. Admission of neopentane did not change the steady-state concentration of the preloaded n-hexane, but led to an additional uptake of neopentane (see Fig. 32). 

Microporous zincophosphate crystals of zeolitic structure have been synthesized by Dutta and colleagues [335, 222] via multiple microemulsions. In the first investigation [335], these authors used two reverse microemulsions, based on the system AOT/n-hexane, containing (a) aqueous solution of Zn(N03)2.6H20 and (b) aqueous solution with H3PO4 and tetramethylammonium hydroxide (the latter was required for incorporation of the phosphate in the reverse micelle). For the Zn-micelle, the [AOT]/[H20] ratio was 13, while for the phosphate-micelle, the value went up to 21. Uptake of the constituents in the micelles was examined by chemical analysis. The two microemulsions were finally mixed at room temperature. Particles grew from 14 nm to - 150 nm in three days, and then became stable at --140 nm. 

Diffusivity and Mobflity Isotherms. The temperature and penetrant concentration dependence of the diffusion coefficient, D, has been measured for binary mixtures of PTMSP with n-pentane, n-hexane, ethanol and methanol Indeed, for each sorption step in the sequences of isothermal sorption experiments, the kinetics of mass uptake have been analysed and estimates of the corresponding diffusivity have been obtained from both small and long time sorption data, as indicated in a previous study (6). The relative difference in the values of the diffusion coefficients obtained through the use of long time and short time sorption data is less than 5% in the great majority of cases and is less than 10% in the worst cases. Indeed, when one compares the diffusion coeffident results obtained from two different experiments performed under the same conditions, the diffusivity values are only determined to within approximately 10%. 

The sorption and transport of four aliphatic hydrocarbons (n-hexane, n-heptane, n-octane and n-nonane) into NR crosslinked using conventional, efficient, dicumyl peroxide(DCP) and mixed sulphur/peroxide vulcanisation systems were investigated at temp, of 28 to 60C. The NR vulcanised by DCP exhibited the lowest penetrant uptake of the systems studied. It was observed that the kinetics of liquid sorption in every case deviated from the regular Fickian trend, characteristic of sorption of liquids by rubbers. The diffusion coefficient, activation energy of sorption, enthalpy, entropy and rubber-solvent interaction parameter were evaluated for the four systems from the swelling data. 30 refs. 

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