External diffusion control in the gas-phase dehydrogenation of hydrocarbons on a catalyst pellet

External-diffusion gas-phase mass transfer in the catalytic hydrogenation of hydrocarbons was studied theoretically and experimentally. For the model of a stationary diffusion film around a catalyst pellet, an approximate solution of Maxwell-Stefan equations was obtained, which allowed the multicomponent diffusion problem to be reduced to a Fick equation involving a pseudobinary effective diffusion coefficient. A comparison was made between the theoretical and experimental results for the hydrogenation of α-methylstyrene, octene, and their mixtures.     

Biosynthesis of eicosapentaenoic acid in the sea urchin Psammechinus miliaris

The sea urchin Psammechinus miliaris (Gmelin) (Echinodermata: Echinoidea) was shown by using a deuterated tracer (D₅−18∶3n−3) and quantitation by negative chemical ionization gas chromatography-mass spectrometry to convert 18∶3n−3 to 20∶5n−3. The rate of conversion was very slow, corresponding to 0.09 μg/g tissue/mg 18∶3n−3 eaten over 14 d. Deuterated arachidonic acid (D₈−20∶4n−6) was also included in the diet to give a measure of the relative amounts of diet eaten by the different animals. The recovery of this fatty acid in tissue lipids was 33.7% compared with only 0.95% recovery of D₅−18∶3n−3 and its anabolites, indicating that the majority of the D₅-tracer was catabolized. Considerable elongation of D₅−18∶3n−3 into 20∶3n−3 and a trace of 22∶3n−3 was found, and these were accompanied by minor amounts of the intermediates 18∶4n−3 and 20∶4n−3. No deuterated 22∶6n−3 was found.     

Biosynthesis and tissue deposition of docosahexaenoic acid (22∶6n−3) in rainbow trout (Oncorhynchus mykiss)

Rainbow trout (Oncorhynchus mykiss) weighing ca. 5 g and previously acclimated for 8 wk on a diet comprising vegetable oil (11%), fish meal (5%), and casein (48%) as the major constituents were fed a pulse of diet containing deuterated (D₅) (17,17,18,18,18)-18∶3n−3 ethyl ester. The synthesis and tissue distribution of D₅-22∶6n−3 was determined 3,7,14, 24, and 35 d after the pulse. The whole-body accumulation of D₅-22∶6n−3 was linear over the first 7 d, corresponding to a rate of 0.54±0.12 μg D₅-22∶6n−3/g fish/mg D₅-18∶3n−3 eaten/d. Maximal accretion of D₅-22∶6n−3 was 4.3±1.2 μg/g fish/mg of D₅-18∶3n−3 eaten after 14 d. The amount of D₅-22∶6n−3 peaked in liver at day 7, in brain and eyes at day 24, and plateaued after day 14 in visceral and eye socket adipose tissue and in the whole fish. The majority of D₅-22∶6n−3 was found in the carcass (remaining tissues minus the above tissues analyzed separately) at all times. On a per milligram lipid basis, liver and eyes had the highest concentration of D₅-22∶6n−3. The experimental diet also contained 21∶4n−6 ethyl ester as a marker to estimate the amount of food eaten by individual fish. From such estimates it was calculated that the great majority of the D₅-tracer was catabolized, with the combined recovery of D₅-18∶3n−3 plus D₅-22∶6n−3 being 2.6%. The recovery of 21∶4n−6 was 57.6%. The concentration of 22∶6n−3 in the fish decreased during the 13-wk period, and the amount of 22∶6n−3 synthesized from 18∶3n−3 was only about 5% of that obtained directly from the fish meal in the diet.     

Metalorganic chemical vapor deposition of Sr x TiyO z thin films by using mixed metal precursorsO z thin films by using mixed metal precursors

Strontium titanate (Sr _x Ti _y O _z ) thin films were prepared by a chemical vapor deposition method using gaseous compounds, obtained by vaporizing a solid mixture of Sr(dpm)₂ and Ti(O-iPr)₂(dpm)₂ in one step, as the metal sources. The compositions of the films changed in proportion to the ratio of the precursors in the solid mixture, which is contrary to the case of films obtained from a mixture of individual precursor vapors. In the latter case, the film composition was not proportional to the mixing ratio of the precursors. The strontium titanate concentration in the film was changed by the deposition temperature even when the Sr/Ti ratio of the feed was fixed, i.e., the Sr/Ti ratio in the film decreased at high temperatures. An SrTiO₃ film, with an Sr/Ti ratio of 1/1, was obtained at 450 ‡C by using vapors from a solid mixture containing the metal precursors at a Sr/Ti of 1/1. The temperature, 450 ‡C in this case, was lower than that for producing the same film composition by a liquid injection method, 550 ‡C. The decomposition of the Ti and Sr precursors included in the solid mixture and possible reactions between them at elevated temperatures were investigated by thermogravimetry, differential scanning calorimetry, and mass spectrometry. When the solid mixture was heated, the Sr-O bond, that connected Sr to the dpm ligand, was dissociated at temperatures lower than 100 ‡C and the isopropoxide ligand of the Ti precursor was dissociated from the Ti atom at temperatures below 150 ‡C. At 162 ‡C, Ti(O-iPr)₂(dpm)₂ melted, forming an oligomer by reaction with surrounding Ti and Sr precursors. This reaction was confirmed by the presence of a mass peak at m/e=585, corresponding to a hetero-metallic compound containing Sr and Ti. The hetero-metallic compound vaporized at temperatures below 200 ‡C and eventually participated in the formation of a SrTiO₃ film.     

Effect of temperature on the incorporation into phospholipid classes and metabolismvia desaturation and elongation of n−3 and n−6 polyunsaturated fatty acids in fish cells in culture

The incorporation of 18∶2n−6, 18∶3n−3, 20∶4n−6 and 20∶5n−3 was greater at 10°C than at 22°C in Atlantic salmon (AS), rainbow trout (RTG-2) and turbot (TF) cells. However, there were generally no significant differences between the amount of incorporation of all four polyunsaturated fatty acids (PUFA) into total lipid within a cell type at either 22°C or 10°C. The distributions of the PUFA between individual phospholipid classes at 22°C was essentially the same in AS and TF cells—with the C₁₈ PUFA the order of incorporation in these cells was phosphatidylcholine (PC) > phosphatidylethanolamine (PE) > phosphatidic acid/cardiolipin (PA/CL); with 20∶4n−6 the order was PE and phosphatidylinositol (PI)>PC; with 20∶5n−3, PE>PC. In RTG-2 cells at 22°C the distributions of the C₁₈ PUFA were similar to the other cell lines, but with 20∶4n−6 the order was PC>PI>PE, and with 20∶5n−3 it was PC>PE. At 10°C the incorporation of C₁₈ PUFA into PC increased and into PE and PA/CL decreased, in general, in all cell lines. Incorporation of 20∶5n−3 into PC and PE was increased and decreased at 10°C, respectively, in AS and TF cells, whereas in RTG-2 cells the changes at 10°C were opposite i.e., increased in PE and decreased in PC. With 20∶4n−6, incorporation into PC at 10°C was increased in all cell lines with decreased incorporation into PI in AS and RTG-2 cells and into PE in AS and TF cells, whereas incorporation of 20∶4n−6 into PE increased in RTG-2 cells. The metabolismvia desaturation and elongation of the n−3 PUFA was greater than that of the equivalent n−6 PUFA in all cell lines, irrespective of temperature. There was less conversion of the C₁₈ PUFA at 10°C than at 22°C in RTG-2 and TF cells, but the conversion of 18∶3n−3 by AS cells was increased at 10°C. Temperature had no effect on the conversion of the C₂₀ PUFA.     

Pyloric ceca are significant sites of newly synthesized 22∶6n−3 in rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)

In this pulse-chase study, rainbow trout fed a diet containing deuterated (D₅) (17,17,18,18,18)-18∶3n−3 ethyl ester accumulated D₅-22∶6n−3 in pyloric ceca to a greater extent than in liver 2 d post-dose. The ratio of newly synthesized D₅-22∶6n−3 in ceca to that in liver 2 d after feeding D₅-18∶3n−3 was 4.7±1.2 when expressed as per mg tissue and 5.2±2.4 when expressed as per mg protein. The amount of D₅-22∶6n−3 in ceca then declined whereas that in liver and blood increased, with the ratio of ceca to liver falling to 1.7 and 1.4, respectively, by day 5 and approaching unity by day 9. A crude cecal mucosa fraction contained 123±50 ng D₅-22∶6n−3/mg protein/mg D₅-18∶3n−3 eaten 2 d after feeding the tracer, compared with 35±21 ng D₅-22∶6n−3/mg protein/mg D₅-18∶3n−3 eaten in liver. Three days later the amount in cecal mucosa had fallen by one-third and that in liver had increased threefold. Most of the D₅-18∶3n−3 was catabolized very rapidly. The ratio of D₅-18∶3n−3 to 21∶4n−6 (a relatively inert FA marker) in the diet was 4.0, but this fell to 0.30 in ceca and ca. 0.8 in liver, blood, and whole carcass one day after feeding. These results indicate that ceca are active in the synthesis of 22∶6n−3 and the oxidation of 18∶3n−3.     

Diffusivity of alkanes in polystyrene

Gravimetry is used to study the diffusivity of a homologous series of linear alkanes (C_n, with n = 8, 10, 12, 14 and 16) in amorphous polystyrene at temperatures ranging from 45 °C to 145 °C, i.e. both below and above the polymer glass transition temperature (100 °C). All the mass uptake results obtained are well described by a simple Fickian model (for t < t_1/2) and are used to calculate the corresponding diffusion coefficients (D) using the thin-film approximation of the Fickian equation. For all the alkanes considered, the temperature dependency of the diffusion coefficients is non-Arrhenius in character, over the broad temperature intervals considered. For any particular temperature log(D) varies linearly (R² > 0.993, for all temperatures) with respect to the number of carbon atoms (n) in the alkyl chain, log(D) decreasing when n increases. For each liquid penetrant, over the temperature intervals considered, its log(D) also increases linearly (R² > 0.996 for all the systems) with the decrease in the penetrant’s liquid viscosity.     

Temperature programmed decomposition of sillica-supported MgCl2/THF/TiCl4 catalyst and effect of thermal treatment on ethylene polymerization rate

Silica supported MgCl₂/THF/TiCl₄ catalyst (SiO₂/MgCl₂/THF/TiCl₄) was prepared, and then decomposed thermally. The amount of produced gas [tetrahydrofuran (THF) and 1,4-dichlorobutane (DCB)] was measured with gas chromatography (GC) and mass spectrometer. SiO₂/MgCl₂/THF/TiCl₄ catalyst started to decompose around 85‡C, and further decomposed at 113, 150 and 213‡C. THF was mainly produced, but very small amount of DCB evolved during temperature programmed decomposition (TPD), while unsupported MgCl₂THF/TiCl₄ produced DCB significantly. Polymerization rate of ethylene with SiO₂/MgCl₂/THF/TiCl₄ decreased when it was preheated at 85 and 110‡C for 5 and 60 min, respectively, while that of unsupported MgCl₂/THF/TiCl₄ increased after same pretreatment condition. It can be suggested that Mg/Ti bimetallic complex anchored on the surface of silica through OH group of it has weak interaction between Mg and Ti species.     

Pyrolysis kinetics and characteristics of the mixtures of waste ship lubricating oil and waste fishing rope

Kinetic investigations on the pyrolysis of a mixture of waste ship lubricating oil (WSLO) and waste fishing rope (WFR) were carried out using a thermogravimetric analyzer (TGA) at a heating rate of 0.5 ‡C/min, 1.0 ‡C/min and 2.0 ‡C/min. WSLO and WFR were mainly decomposed at the temperature of range of 400 ‡C to 455 ‡C and 370 ‡C to 410 ‡C, respectively. The WSLO/WFR mixture was mainly decomposed at the temperature range of 300 ‡C and 450 ‡C, which is a lower temperature than that for the WSLO or the WFR alone at each heating rate. The ranges of apparent activation energies of the WALO/WFR mixture were between 137 kJ mol^-1 and 197 kJ mol^-1 at conversions in the range of 10–95%. The mixture of WSLO and WFR was pyrolyzed in a micro-scale tubing reactor at 440 ‡C for 60 min and 80 min. The yield of pyrolyzed gases increased from 2.13 wt% to2.29 wt% with reaction time. The selectivity to C₇ hydrocarbons was shown in the pyrolyzed oil of the mixture.     

Homogenous catalysis in the reactions of olefinic substances. V. Hydrogenation of soybean oil methyl ester with triphenylphosphine and triphenylarsine palladium catalysts

Some palladium complexes containing coordinated triphenylphosphine or arsine have been found to be effective and selective catalysts in the homogeneous hydrogenation of soybean oil methyl ester. The characteristic features of the catalysis are 1) isomerization ofcis double bonds totrans double bonds, 2) migration of isolated double bonds to form conjugated dienes, 3) selective hydrogenation of poly olefines to mono olefines without hydrogenation of mono olefine, 4) ester exchange of methyl ester to butyl ester, 5) effective hydrogenation and isomerization by methanol in the absence of elemental hydrogen. The catalytic activity of a variety of palladium complexes decreases in the following order: (ϕ₃P)₂PdCl₂+SnCl₂·2H₂O>(ϕ₃P)₂PdCl₂+GeCl₂>(ϕ₃P)₂Pd(CN)₂> (ϕ₃As)₂Pd(CN)₂>(ϕ₃P)₂PdCl₂≫(ϕ₃As)₂PdCl₂. However, neither K₂PdCl₄ with SnCl₂·2H₂O nor (ϕ₃P)₂Pd(SCN)₂ was effective for hydrogenation. The hydrogenation and isomerization of soybean oil methyl ester have been examined under various conditions using a mixture of (ϕ₃P)₂PdCl₂ and SnCl₂·2H₂O. Under nitrogen pressure, in benzene and methanol as a solvent, both isomerization and hydrogenation of soybean oil methyl ester proceeded less effectively than under hydrogen pressure. This work was done under contract with the USDA. Earlier articles in the series are: I, Inorg. Chem.4, 1618 (1965): II, Proceedings of the Symposium on Coordination Chemistry (Tihany, Hungary, 1964), Edited by M. T. Beck, Budapest, 1965; III, JAOCS43, 337 (1966); IV, Advances in Chemistry Series, American Chemical Society, in press.     

Conversion of linoleic acid to 10-hydroxy-12(Z)-octadecenoic acid byFlavobacterium sp. (NRRL B-14859)

A new microbial isolate,Flavobacterium sp. strain DS5, converts linoleic acid into 10-hydroxy-12(Z)-octadecenoic acid (10-HOA) with 55% yield. The product was characterized by gas chromatography (GC), GC/mass spectrometry, nuclear magnetic resonance and Fourier transform infrared spectroscopy. The specific optical rotation of 10-HOA is [α] _D ²⁴ =−5.58 (methanol). The optimum time, pH and temperature for the production of 10-HOA were 36h, 7.5 and 20–35°C, respectively. The enzyme(s) that converts linoleic acid to 10-HOA is soluble and located intracellulary in strain DS5. Two minor products, 10-methoxy-12-octade-cenoic acid and 10-keto-12-octadecenoic acid, were also identified. 10-HOA was further metabolized by strain DS5. Among the unsaturated fatty acids studied, the order of reactivity for the DS5 enzyme(s) is oleic>palmitoleic> linoleic>linolenic>γ-linolenic>myristoleic acid.     

Solution properties of polymacromonomers consisting of polystyrene

Summary Dynamic light scattering measurements have been made on 14 samples of a polymacromonomer consisting of polystyrene with 15 styrene side-chain units in cyclohexane at 34.5°C (the theta point) to determine the translational diffusion coefficient D as a function of molecular weight. The dependence of D on the main-chain length is analyzed on the basis of the wormlike chain by taking into account the end effect arising from side chains near the main-chain ends. The model parameters describing this dependence, i.e., the Kuhn segment length (11.5 ± 1.5 nm), the linear mass density (5600 ± 700 nm⁻¹), the diameter (5.2 ± 0.5 nm), and the end-effect parameter δ (2.5 ± 0.3 nm), are close to those determined previously from <S ²>_z (the z-average mean-square radius of gyration) and [η] (the intrinsic viscosity), leading to the conclusion that the wormlike chain model is capable of consistently explaining <S ²>_z, [η], and D of the polymacromonomer in the Θ solvent. Received: 8 February 2000/Accepted: 18 February 2000     

Chain elongation of polyunsaturated fatty acids by vascular endothelial cells: Studies with arachidonate analogues

This study has utilized radiolabeled analogues of arachidonic acid to study the substrate specificity of elongation of long-chain polyunsaturated fatty acids. Human umbilical vein endothelial cells were incubated for 2–72 hr in medium supplemented with 0.9–2.6 μM [¹⁴C]fatty acid, and cellular glycerolipids were analyzed by gas-liquid chromatography with radioactivity detection. Elongation of naturally occurring C₂₀ polyunsaturated fatty acids occurred with eicosapentaenoate (20∶5(n−3))>Mead acid (20∶3(n−9))>arachidonate (20∶4(n−6)). Chain length markedly influenced the extent of elongation of 5,8,11,14-tetraenoates (18∶4>19∶4>20∶4>21∶4); effects of initial double bond position were also observed (6,9,12,15–20∶4>4,7,10,13–20∶4. Neither 5,8,14- nor 5,11,14–20∶3 was elongated to the extent of 5,8,11–20∶3. Differences between polyunsaturated fatty acids were observed both in the initial rates and in the maximal percentages of elongation, suggesting that the content of cellular C₂₀ and C₂₂ fatty acids may represent a balance between chain elongation and retroconversion. Umbilical vein endothelial cells do not exhibit significant desaturation of either 22∶4(n−6) or 22∶5(n−3). By contrast, incubation with 5,8,11,14-[¹⁴C]18∶4(n−4) resulted in formation of both [¹⁴C]20∶5(n−4) and [¹⁴C]22∶5(n−4). The respective time courses for the appearances of [¹⁴C]22∶5(n−4) and [¹⁴C]20∶5(n−5) suggests Δ6 desaturation of [¹⁴C]22∶4(n−4) rather than Δ4 desaturation of [¹⁴C]20∶4(n−4).     

Dimorphism of water at 0‡c. refinement of the cluster-hygroscopic microstructure of water

The structural and physical behavior of water in the temperature range from 0 to 35‡C was examined. The possible enantiotropic mechanism of formation of two morphological modifications of (H₂O)₈ clusters at 0‡C (dimorphism of water) was demonstrated: liquid phase — body-centered cubic packing of the water molecules (bcc packing), ice — double tetrahedral (diamond) packing. The partial density of ice clusters at 0‡C is equal to 838 g/liter, and the maximum density of water is observed when (H₂O)₆ clusters predominate in the water. Translated fromKhimicheskie Volokna, No. 6. pp. 44–46, November–December, 1998.     

Permeation of xylene isomers through nitrile gloves

The physical parameters of the xylene isomers (the positional isomers o-, m-, and p-xylenes and the skeletal isomer ethyl benzene) responsible for the differing permeation behavior of the isomers through lined unsupported 0.41 mm thick nitrile glove material were investigated. An ASTM type permeation cell at 30°C, constant mixing conditions, hexane liquid collection, and capillary column gas chromatography/mass spectrometry of samples taken from the collection side every ten minutes allowed break through times t_b and steady-state sections to be defined. While pure isomers had distinct break through times t_b(m-xylene = p-xylene < ethyl benzene = o-xylene), steady-state permeation rates P_s(p-xylene > m-xylene > ethyl benzene = o-xylene), lag times t_l(m-xylene < p-xylene = ethyl benzene < o-xylene), and diffusion coefficients D_p(m-xylene < p-xylene = ethyl benzene < o-xylene), such behavior was lost in a equal volume mixture (t_b, t_l, P_s, and D_p were equivalent). The average P_s of the mixture isomers of equal volumes did not differ from that expected from the individual pure isomer P_s values. The results for the pure isomers were attributed to o-xylene and ethyl benzene being similarly sterically hindered, the p-xylene being the flattest and most symmetrical molecule and having no dipole moment, and m-xylene being intermediate in steric structure. The pure isomer t_l were directly related to viscosity divided by the log octanol-water coefficient, while their log P_s was inversely related to dipole moment times the logarithm of the capacity factor for water for a reversed-phase high-performance liquid chromatography column. In an equivolume mixture of the isomers, isomer interactions caused equivalence for all permeation kinetic parameters, indicating that the kinetics of mixture constituents is not predictable from the behavior of the pure constituents, although mass transfer appears additive. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1713–1721, 1997     

Catalytic hydrogenation of benzene to cyclohexene on Ru(0 0 0 1) from density functional theory investigations

The catalytic hydrogenation of benzene on transition metal surfaces is of fundamental importance in petroleum industry. With the aim to improve its efficiency and particularly the selectivity to cyclohexene, in this contribution we perform periodic density functional theory calculations to determine the potential energy surface in the hydrogenation of benzene on Ru(0 0 0 1). By following the Horiuti–Polanyi mechanism with a step-wise addition of hydrogen adatoms, we investigate the adsorption of all the possible reaction intermediates and identify the most favored adsorption configuration for each intermediate. In particular, the most stable isomer for the same C₆H_n (n = 8, 9, 10) species are revealed as the most conjugated isomers, which are consistent with those in the gas phase. The elementary hydrogenation reactions of the most stable intermediates are then investigated under different H coverage conditions: the reaction barriers are calculated to be 0.68–0.97 eV at the low H coverage and 0.32–1.14 eV at the high H coverage. The high H coverage reduces significantly the overall barrier height of hydrogenation. With the determined pathway, we propose that the hydrogenation of benzene on Ru(0 0 0 1) follows the mechanism with the step-wise hydrogenation of neighboring C atoms in the ring, i.e., 1–2–3… hydrogenation. The selectivity to cyclohexene on Ru is also discussed, which highlights the importance of the π mode adsorption of benzene and also the adverse effect of secondary reaction process involving the readsorption and hydrogenation of cyclohexene.     

Fischer–Tropsch Synthesis: Deuterium Kinetic Isotope Study for Hydrogenation of Carbon Oxides Over Cobalt and Iron Catalysts

Abstract  

The hydrogenation of CO₂ using Pt promoted Co/γ-Al₂O₃ and doubly (Cu, K) promoted iron catalysts exhibits an inverse isotope effect (r ^H/r ^D < 1). The observed inverse isotope effect for hydrogenation of CO₂ shows that hydrogen addition to CO₂ should be involved in the kinetically relevant step. The systematic increase of inverse isotope effect with carbon number of products obtained during H₂–D₂–H₂ switching experiments suggests the possible existence of a common intermediate (CH _x O) for hydrogenation of CO₂ over both cobalt and iron FT catalysts. The magnitude of the inverse isotope effect is lower for CO₂ compared to CO hydrogenation under similar reaction conditions. The deuterium isotope effect does not provide a definite conclusion regarding the mechanism which CO₂ hydrogenation follows (alkyl, enol, or alkylidine mechanisms).     

Viscosity-structure relationship of dilute triglycerides’ solutions correlation to retention time in reversed-phase liquid chromatography

The dynamic viscosity (η) of dilute solutions of the trigly-cerides triolein, trilinolein, trimyristin, tristearin and tripalmitin in benzene at temperatures in the range of 25–37°C can be expressed in terms of the viscosity of the solvent (η₀), the triglycerides’ concentration (C) and structural characteristics, such as the length of the carbon chains (CN) and the number of double bonds (DB). The simple empirical equation ln η=k₀+k₁ ln η₀+k₂ CN+k₃ DB+k₄ C satisfactorily describes (within the experimental error of 0.002 cp) the solution viscosity of triglycerides inp-xylene when using the coefficients derived from the benzene solutions. In addition, a relation is derived extending the application of the above-mentioned empirical equation to multicomponent dilute solutions. This last one describes the dilute solution viscosity of natural oils in benzene and agrees with the experimental values. Furthermore, the triglycerides that have equal partition numbers in reversed-phase liquid chromatography (RPLC) exhibit equal values for the solution viscosity. This relationship is similar to the equation expressing the retention time of RPLC in terms of the structure of the solute. Hence, it is suggested that the shape of the solute, which is a significant factor for the solution viscosity of triglycerides, also plays an important role in the retention mechanism of RPLC.     

Characteristics of the technological behavior of water and its structure

The moisture content in freshly spun fibre, which is correlated with the temperature dependence of the cluster composition of water, decreases significantly with an increase in the processing temperature from 20 to 60‡C. Agreement was demonstrated for different nonlattice close packings of spheres of the same radius with the same reduced density and contact number and the mixture structure of water in the form of cluster-hygroscopic supermolecular formations (H ₂O)_n, in which the number of molecules is a function of the temperature and varies from 〈6.7〉 (with a mole fraction of water of approximately 0.9 in the clusters) at 0‡C to 〈2.8〉 (0.43) at 100‡C. It was hypothesized that at a temperature of approximately 40 and 80‡C, resonance absorption of electromagnetic energy with a frequency equal to the natural frequency of water takes place. Destruction of the cluster microstructure of water in the energy absorption zone begins for an external electromagnetic field frequency above 600 GHz. Translated from Khimicheskie Volokna, No. 1, pp. 16–21, January–February, 1997.     

Binary gas diffusivity estimates from transient,one-dimensional sublimation–diffusion experiments in a spherical enclosure

Binary gas diffusivities D_AB’s are extremely useful in the analysis/design of mass transfer systems and to develop correlations. This study used an unsteady experimental method to determine D_AB’s in gas pairs starting with a sublimating solid (A) such as naphthalene or camphor and air (B). The cumulative fractional mass transferred from the surface of a solid A sphere placed concentrically within an isothermal spherical enclosure was followed gravimetrically with time. The experimental D_AB,exp for the gas pair was determined by nonlinear regression using the solution to a transient, one-dimensional (radial) diffusion model. The model’s Case 1 option assumed impermeability (no flux of gas A) at the enclosure’s outer surface, while Case 2 assumed zero concentration of gas A at the same location. For naphthalene–air, D_AB,exp overestimated the literature values, the errors ranging from ?110 to ?185% for Case 1 and ?21 to ?65% for Case 2. For camphor–air, the error in D_AB,exp was ?36% for Case 1 and ?16% for Case 2. D_AB,exp for camphor in atmospheric air is herein reported for the first time. Potential improvements to the experiments include automation of the sphere melt-casting process and tighter control of the enclosure’s environmental conditions. Likewise, the theoretical model could be extended to three dimensions with multicomponent diffusion to assess the effect of air humidity on the transport of gas A. This is the first attempt to determine D_AB,exp for naphthalene–air and camphor–air from an unsteady sublimation–diffusion experiment and to model the results using rigorous mass transport theory.