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Vapor Pressure (vapor + pressure)
Terms modified by Vapor Pressure Selected AbstractsDetermination of Urea Nitrate and Guanidine Nitrate Vapor Pressures by Isothermal ThermogravimetryPROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 3 2010Jimmie Oxley Abstract Since the bombing of Pan Am Flight 103 over Lockerbie, Scotland in 1988, detection of military explosives has received much attention. Only in the last few years has detection of improvised explosives become a priority. Many detection methods require that the particulate or vapor be available. Elsewhere we have reported the vapor pressures of peroxide explosives triacetone triperoxide (TATP), diacetone diperoxide (DADP), and 2,4,6-trinitrotoluene (TNT). Herein we examine the vapor signatures of the nitrate salts of urea and guanidine (UN and GN, respectively), and compare them to ammonium nitrate (AN) and TATP using an isothermal thermo-gravimetric method. The vapor signatures of the nitrate salts are assumed to be the vapor pressures of the neutral parent base and nitric acid. Studies were performed at elevated temperatures (80,120,°C for UN, 205,225,°C for GN, 100,160,°C for AN, and 40,59,°C for TATP), enthalpies of sublimation calculated and vapor pressures extrapolated to room temperature. Reported vapor pressure values (in Pa) are as follows: GN ,,UN , Determining the Vapor Pressures of Diacetone Diperoxide (DADP) and Hexamethylene Triperoxide Diamine (HMTD)PROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 6 2009Jimmie Abstract The vapor signature of diacetone diperoxide (DADP) and hexamethylene triperoxide diamine (HMTD) were examined by a gas chromatography (GC) headspace technique over the range of 15 to 55,°C. Parallel experiments were conducted to redetermine the vapor pressures of 2,4,6-trinitrotoluene (TNT) and triacetone triperoxide (TATP). The TNT and TATP vapor pressures were in agreement with the previously reported results. Vapor pressure of DADP was determined to be 17.7,Pa at 25,°C, which is approximately 2.6 times higher than TATP at the same temperature. The Clapeyron equation, relating vapor pressure and temperature, was LnP (Pa)=35.9,9845.1/T (K) for DADP. Heat of sublimation, calculated from the slope of the line for the Clapeyron equation, was 81.9,kJ mole,1. HMTD vapor pressure was not determined due to reduced thermal stability resulting in vapor phase decomposition products. [source] Vapor pressures and thermodynamics of oxygen-containing polycyclic aromatic hydrocarbons measured using knudsen effusion,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2008Jillian L. Goldfarb Abstract Polycyclic aromatic hydrocarbons (PAHs) and their oxygenated derivatives (OPAHs) are ubiquitous environmental pollutants resulting from the incomplete combustion of coal and fossil fuels. Their vapor pressures are key thermodynamic data essential for modeling fate and transport within the environment. The present study involved nine PAHs containing oxygen heteroatoms, including aldehyde, carboxyl, and nitro groups, specifically 2-nitrofluorene, 9-fluorenecarboxylic acid, 2-fluorenecarboxaldehyde, 2-anthracenecarboxylic acid, 9-anthracenecarboxylic acid, 9-anthraldehyde, 1-nitropyrene, 1-pyrenecarboxaldehyde, and 1-bromo-2-naphthoic acid. The vapor pressures of these compounds, with molecular weights ranging from 194 to 251 g/mol, were measured using the isothermal Knudsen effusion technique in the temperature range of 329 to 421 K. The corresponding enthalpies of sublimation, calculated via the Clausius-Clapeyron equation, are compared to parent, nonoxygenated PAH compound data to determine the effect of the addition of these oxygen-containing heteroatoms. As expected, the addition of ,CHO, ,COOH, and ,NO2 groups onto these PAHs increases the enthalpy of sublimation and decreases the vapor pressure as compared to the parent PAH; the position of substitution also plays a significant role in determining the vapor pressure of these OPAHs. [source] Vapor pressures and enthalpies of sublimation of 17 polychlorinated dibenzo- p -dioxins and five polychlorinated dibenzofuransENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2004Xian-Wei Li Abstract An apparatus for vapor pressure measurement with a very small cell by the mass-loss Knudsen effusion technique was tested with solid benzoic acid and anthracene. The vapor pressure and enthalpy of sublimation results of the two reference compounds were in good agreement with accepted literature data. The vapor pressures at different temperatures of 17 polychlorinated dibenzo- p -dioxins (including dibenzo- p -dioxin) and five polychlorinated dibenzofurans (including dibenzofuran) were measured with the apparatus, and the enthalpies of sublimation of the 22 dioxins and furans were derived from the temperature dependence of vapor pressure. The results were systematically compared with the literature data. [source] Determination of physicochemical properties of tetrabromobisphenol AENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2008Hidetoshi Kuramochi Abstract Aqueous solubility (Sw), 1-octanol/water partition coefficient (KOW), and vapor pressure of the nonionic form of 2,2,,6,6,-tetrabromo-4,4,-isopropylidenediphenol (tetrabromobisphenol A or TBBP-A) were measured. From this, enthalpies of solution and vaporization were estimated. Furthermore, enthalpy of fusion and melting point were measured to estimate subcooled liquid vapor pressure, the infinite dilution activity coefficient, and Henry's law constant. Since TBBP-A is expected to exit in both ionic and nonionic forms at near neutral pH, pH effects on physicochemical properties were also examined. Because of the ionization of TBBP-A, Sw increased by five orders of magnitude, while KOW decreased by eight orders of magnitude. Furthermore, an analytical model based on mass balance and dissociation of TBBP-A was applied to represent the pH dependence. [source] Vapor pressures and thermodynamics of oxygen-containing polycyclic aromatic hydrocarbons measured using knudsen effusion,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2008Jillian L. Goldfarb Abstract Polycyclic aromatic hydrocarbons (PAHs) and their oxygenated derivatives (OPAHs) are ubiquitous environmental pollutants resulting from the incomplete combustion of coal and fossil fuels. Their vapor pressures are key thermodynamic data essential for modeling fate and transport within the environment. The present study involved nine PAHs containing oxygen heteroatoms, including aldehyde, carboxyl, and nitro groups, specifically 2-nitrofluorene, 9-fluorenecarboxylic acid, 2-fluorenecarboxaldehyde, 2-anthracenecarboxylic acid, 9-anthracenecarboxylic acid, 9-anthraldehyde, 1-nitropyrene, 1-pyrenecarboxaldehyde, and 1-bromo-2-naphthoic acid. The vapor pressures of these compounds, with molecular weights ranging from 194 to 251 g/mol, were measured using the isothermal Knudsen effusion technique in the temperature range of 329 to 421 K. The corresponding enthalpies of sublimation, calculated via the Clausius-Clapeyron equation, are compared to parent, nonoxygenated PAH compound data to determine the effect of the addition of these oxygen-containing heteroatoms. As expected, the addition of ,CHO, ,COOH, and ,NO2 groups onto these PAHs increases the enthalpy of sublimation and decreases the vapor pressure as compared to the parent PAH; the position of substitution also plays a significant role in determining the vapor pressure of these OPAHs. [source] Modeling polycyclic aromatic hydrocarbon composition profiles of sources and receptors in the Pearl River Delta, China,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2008Chang Lang Abstract Changes in concentration profiles of polycyclic aromatic hydrocarbons (PAHs) from emission sources to various environmental media in the Pearl River Delta, China were investigated using fugacity modeling under steady state assumption. Both assumed evenly and observed unevenly distributed PAH moles emission profiles were applied. Applicability of the fugacity model was validated against the observed media PAH concentrations and profiles. At equal emission rates, the differences of media concentrations among various PAHS were as high as three (air) to seven (soil and sediment) orders of magnitude. Dramatic changes of PAH profiles from emission sources to various bulk environmental media also were demonstrated by using the actual emission rates. In general, the fractions of higher molecular weight PAHs in air and water were much lower than those at the emission sources, although the PAH profiles in soil and sediment were characterized by a significant reduction of lower molecular weight PAHs. It is likely that the field-measured median concentration profiles cannot be adopted directly for source apportionment without rectification. The most influential parameters affecting PAH profiles in the study area were emission rates, degradation rates, adsorption coefficient, Henry's law constant, PAH concentrations in upstream surface water, fugacity ratio, vapor pressure, and diffusion coefficient in air. [source] Vapor pressures and enthalpies of sublimation of 17 polychlorinated dibenzo- p -dioxins and five polychlorinated dibenzofuransENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2004Xian-Wei Li Abstract An apparatus for vapor pressure measurement with a very small cell by the mass-loss Knudsen effusion technique was tested with solid benzoic acid and anthracene. The vapor pressure and enthalpy of sublimation results of the two reference compounds were in good agreement with accepted literature data. The vapor pressures at different temperatures of 17 polychlorinated dibenzo- p -dioxins (including dibenzo- p -dioxin) and five polychlorinated dibenzofurans (including dibenzofuran) were measured with the apparatus, and the enthalpies of sublimation of the 22 dioxins and furans were derived from the temperature dependence of vapor pressure. The results were systematically compared with the literature data. [source] Concentrations of organochlorine pesticides and polychlorinated biphenyls in amphipods (Gammarus lacustris) along an elevation gradient in mountain lakes of western CanadaENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 11 2003Jules M. Blais Abstract Populations of the amphipod Gammarus lacustris were examined for their concentrations of organochlorine pesticides and polychlorinated biphenyls (PCBs) from seven lakes spanning a 1,300-m elevation gradient in Alberta, Canada. The concentrations of several of the semivolatile organochlorine compounds ([SVOCs], vapor pressure > 0.03 Pa at 20°C) increased at higher altitudes. This pattern was generally not observed among the less volatile organochlorines ([LVOCs], vapor pressure < 0.03 Pa at 20°C). These same SVOC compounds have been previously shown to increase at high latitudes as a result of their long-range transport and preferential deposition in cold climates. We also show that populations of G. lacustris at high elevations have slower growth rates and store more lipids than populations at lower elevations. To resolve the colinearity of independent variables, we used multiple regression to identify patterns of contaminant concentrations in this data set. Multiple regressions showed that the effect of elevation, lipid content, and temperature on contaminant concentrations was no longer significant once the growth rate of Gammarus was included as an independent variable. This study shows that enrichment of SVOCs occurs in Gammarus at high altitudes in Alberta, Canada, and that growth rate (biodilution) appears to be the primary influence. Because Gammarus is an important trophic link in aquatic foodwebs in these environments, enhanced concentrations of toxicants in prey may increase their biomagnification in top predators of high-altitude lakes. [source] A thermodynamics-based estimation model for adsorption of organic compounds by carbonaceous materials in environmental sorbentsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2003Paul C. M. van Noort Abstract A model was developed to estimate Langmuir affinities for adsorption of low-polarity organic compounds from either water or air by carbonaceous sorbents. Sorption enthalpies and entropies provided the basic information for the description of sorption affinities in terms of the entropy of melting and either solubility in water or vapor pressure. For m -xylene, polycyclic aromatic hydrocarbons (PAHs) and chlorobenzenes on 10 different sorbents, 80% of the measured sorption affinities fall within a factor of four of the model estimates. Equations for the limiting distribution coefficients in terms of either octanol,air (KOA) or octanol,water partition (Kow) coefficients were derived from regressions of calculated affinities combined with an estimated relation between experimental Langmuir sorption capacities and Kow. Estimated soot,water distribution coefficients were within a factor of three of measured data for polychlorobiphenyls (PCBs) and lower molecular weight PAHs on automotive soot samples and captured the dependence of PCB distribution coefficients on the extent of ortho substitution. For higher molecular weight PAHs, sorption was underestimated. For soot in sediment,water distribution coefficients of PAHs and PCBs, estimated values captured both the trend of measured data with Kow and the dependence on sorbate planarity. Tentative application to aerosol,air distribution explained the observed independence of distribution coefficient,KOA relations for PCBs on the extent of ortho substitution and suggested nonequilibrium conditions for PAHs in comparison with recent measurements. [source] Estimations of vapor pressure and activity coefficients in water and octanol for selected aromatic chemicals at 25°CENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 11 2000Sum Chi Lee Abstract A roupcontribution method is developed to estimate the supercooled liquid vapor pressure and the activity coefficients in water and octanol at 25°C of 98 selected monoaromatic compounds, many of which are or have been produced as chlorinated by-products in the manufacture of pulp and paper. The set includes alkylphenols, chlorinated phenols, anisoles, catechols, cymenes, guaiacols, syringols, and veratroles. The method can be used to estimate vapor pressures, solubilities in water, octanol-water partition coefficients, octanol-air partition coefficients, and Henry's law constants. It can also be used for predicting these partition coefficients as well as solubilities and vapor pressures for these and structurally similar compounds. [source] Odor vapor pressure and quality modulate local field potential oscillatory patterns in the olfactory bulb of the anesthetized ratEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2008Tristan Cenier Abstract A central question in chemical senses is the way that odorant molecules are represented in the brain. To date, many studies, when taken together, suggest that structural features of the molecules are represented through a spatio-temporal pattern of activation in the olfactory bulb (OB), in both glomerular and mitral cell layers. Mitral/tufted cells interact with a large population of inhibitory interneurons resulting in a temporal patterning of bulbar local field potential (LFP) activity. We investigated the possibility that molecular features could determine the temporal pattern of LFP oscillatory activity in the OB. For this purpose, we recorded the LFPs in the OB of urethane-anesthetized, freely breathing rats in response to series of aliphatic odorants varying subtly in carbon-chain length or functional group. In concordance with our previous reports, we found that odors evoked oscillatory activity in the LFP signal in both the beta and gamma frequency bands. Analysis of LFP oscillations revealed that, although molecular features have almost no influence on the intrinsic characteristics of LFP oscillations, they influence the temporal patterning of bulbar oscillations. Alcohol family odors rarely evoke gamma oscillations, whereas ester family odors rather induce oscillatory patterns showing beta/gamma alternation. Moreover, for molecules with the same functional group, the probability of gamma occurrence is correlated to the vapor pressure of the odor. The significance of the relation between odorant features and oscillatory regimes along with their functional relevance are discussed. [source] An experimental and modeling study of Na-rich hydrothermal alterationGEOFLUIDS (ELECTRONIC), Issue 4 2005J. HARA Abstract Sodic alteration assemblages including clinoptilolite, mordenite, analcime and Na-montmorillonite were locally observed in sediments in the eastern part of the Hachimantai geothermal region, northeast Japan. This study investigated the mechanisms of sodic enrichment in the sediments during alteration. Kinetic results for water/rock interaction experiments are reported here. Batch-type experiments were conducted at 150,250°C under saturated vapor pressure. Pyroclastic rocks dissolved incongruently in these experiments, and the solubility and dissolution rates among elements varied as follows: the apparent steady-state concentrations of major elements are Si > Na , K > Ca > Al and the order of the dissolution rates is Si > Al > Na , K > Ca. Na had the highest steady-state concentration and fastest dissolution rate of the alkali and alkali earth metal ions. Based on surface analysis of plagioclase, dissolution was effected via a reaction layer of Na-montmorillonite on the mineral surface. Additionally, a reaction model constructed based on the experimentally observed reaction mechanism quantitatively explains the dissolution behavior. These results show that Na-montmorillonite can be precipitated by pyroclastic rock/meteoric water interactions without seawater involvement: the Na is derived from the host rocks. [source] New supplying evaporation precursor method with CVDHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 5 2009Motohiro Oshima Abstract We propose a novel system of chemical vapor deposition (CVD), i.e., flash boiling spray CVD (SF-CVD) to eliminate several kinds of problems, such as the decomposition of precursors in the supply line and evaporator. In this method, liquid precursors are supplied directly to the vacuum chamber through an injector, just like fuel for an automobile engine, without any vaporizers, so as to induce an unsteady and intermittent flash boiling spray in the chamber. However, it is necessary to keep the lowest ambient pressure possible because the saturated vapor pressure of the precursors is very low. Thus, this is very useful for modifying the saturated vapor pressure of the precursors. A technique of lowering the vaporization pressure is proposed by mixing a more saturated vapor-pressure organic solvent with a precursor. To determine the principles underlying FS-CVD, we first formed SiO2 film on the Si substrate. A mixed solution of tetraethylorthosilicate (TEOS) and n-pentane was used as the mixing solution. The film thickness distribution of SiO2 film on a 100-mm-diameter Si wafer was ±4% using this method. Furthermore, this method enabled us to control film with various thicknesses by optimizing the injection duration, cycle, and injection cycle per second. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20235 [source] Properties of 2,2,2-Trifluoroethanol/Water Mixtures: Acidity, Basicity, and DipolarityHELVETICA CHIMICA ACTA, Issue 2 2005Paz Sevilla, Sierra In this report, we focus our attention on the characterization of 2,2,2-trifluoroethanol(TFE)/H2O mixtures and describe their intrinsic parameters; i.e., solvent acidity (SA), solvent basicity (SB), and solvent dipolarity/polarizability (SPP), by the probe/homomorph-couple method for a range of mixtures from 0,100% (v/v) TFE. Variation of these parameters is not linear and has a singular and unpredictable behavior depending on the precise composition of the mixture. Based on these parameters, we describe the TFE-induced changes in some physical properties; i.e., viscosity (,), partial molar volume (V,), density (,), dielectric constant (,), vapor pressure (pv), and spectroscopic properties; i.e., NMR chemical shifts (,(1H)) of TFE Me group for all molar fractions studied. In addition, by means of CD studies, we report that formation of the secondary structure, as percentage of helical content, ,, of a polypeptide, poly(L -lysine), in several TFE/H2O mixtures is adequately described by these mixture parameters. SA, SB, and SPP of TFE/H2O mixtures provide an excellent tool for the interpretation of formation and stability of intramolecular H-bonds, and, thus, of secondary structures in polypeptides. [source] A convenient synthesis of N - t -butyl- N,-aminocarbonyl- N -(substituted)benzoyl-hydrazine containing , -aminoalkylphosphonate groups in a one-pot procedureHETEROATOM CHEMISTRY, Issue 2 2001Qingmin Wang A variety of novel N-t-butyl-N,-aminocarbonyl-N-(substituted)benzoylhydrazines containing ,-aminoalkylphosphonate groups were synthesized. Treatment of ,-aminoalkylphosphonates with triphosgene yielded ,-isocyanatoalkylphosphonates, and subsequent addition with N-t-butyl-N-substituted benzoylhydrazines provided the title compounds in a one-pot procedure with good yields. The triphosgene-mediated reaction for the synthesis of ,-isocyanatoalkylphosphonates enjoys a number of advantages: the reaction is carried out under mild condition in good yield, triphosgene is relatively safe to handle because of its low vapor pressure and high stability, and the experimental procedure is simple. This method can be applicable to the synthesis of other ,-isocyanatoalkyl-phosphonates and urylenediphosphonates. The structures of all of the products and by-products were confirmed by 1H NMR, 31P NMR, IR and mass spectroscopy, and elemental analysis. We also found that some of the compounds possess potential antitobacco mosaic virus (TMV) activities and anticancer activities. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:68,72, 2001 [source] Surrogate model-based strategy for cryogenic cavitation model validation and sensitivity evaluationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 9 2008Tushar Goel Abstract The study of cavitation dynamics in cryogenic environment has critical implications for the performance and safety of liquid rocket engines, but there is no established method to estimate cavitation-induced loads. To help develop such a computational capability, we employ a multiple-surrogate model-based approach to aid in the model validation and calibration process of a transport-based, homogeneous cryogenic cavitation model. We assess the role of empirical parameters in the cavitation model and uncertainties in material properties via global sensitivity analysis coupled with multiple surrogates including polynomial response surface, radial basis neural network, kriging, and a predicted residual sum of squares-based weighted average surrogate model. The global sensitivity analysis results indicate that the performance of cavitation model is more sensitive to the changes in model parameters than to uncertainties in material properties. Although the impact of uncertainty in temperature-dependent vapor pressure on the predictions seems significant, uncertainty in latent heat influences only temperature field. The influence of wall heat transfer on pressure load is insignificant. We find that slower onset of vapor condensation leads to deviation of the predictions from the experiments. The recalibrated model parameters rectify the importance of evaporation source terms, resulting in significant improvements in pressure predictions. The model parameters need to be adjusted for different fluids, but for a given fluid, they help capture the essential fluid physics with different geometry and operating conditions. Copyright © 2008 John Wiley & Sons, Ltd. [source] Polypropylene Fibers and their Effects on Processing Refractory CastablesINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 6 2007Rafael Salomão Polymeric fibers are efficient drying additives for refractory castables as they can reduce the risks of explosion during the first heat-up. When fibers are melted, they increase permeability, enhancing the drying rate and reducing vapor pressure. Despite these benefits, adding fibers can induce mixing and pumping difficulties due to particle entanglement. In the present work, an analysis involving rheology, dynamic permeability, drying and explosion likelihood of polypropylene fiber containing castables is presented. An optimized condition (fiber content and geometry) to maximize the performance of fibers as drying additives and to prevent mixing drawbacks is also highlighted. [source] Snow disappearance in Eastern Siberia and its relationship to atmospheric influencesINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 2 2007Yoshihiro Iijima Abstract In the present study, we examine the climatological features and interannual variations in snow disappearance within the Lena River Basin, Eastern Siberia, during a recent 15-year period (1986,2000), and the relationship of snow disappearance to atmospheric conditions. According to the climatology of the day of the year on which snow disappears, the boundary of snow disappearance within the Lena River Basin migrates rapidly northward from mid-April until early June, with minimum interannual variation occurring in the middle part of the basin. In addition, the preceding snow disappearance is apparent in the central Lena River Basin. Melting of snow within the Lena River Basin commonly occurs within 30 days of complete snow disappearance under certain atmospheric conditions: daily mean air temperature in excess of , 10 °C, greater than 2 hPa of water vapor pressure, and, hence, more than 170 W m,2 of downward longwave radiation under clear sky conditions. Composite analysis using a reanalysis dataset demonstrates that the increase in air temperature and water vapor that accompanies snow melting is due to wet (and warm) air advection in conjunction with enhanced water vapor convergence over the central Lena River Basin during the 30-day period prior to snow disappearance. Copyright © 2006 Royal Meteorological Society. [source] A new technique for foaming submicron size poly(methyl methacrylate) particlesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2007Hiroyuki Ogawa Abstract About 0.7,2 ,m diameter poly (methyl methacrylate) (PMMA) foamed particles were prepared via thermally induced phase separation (TIPS) from a PMMA/ethanol mixture and vacuum dried. It was found that ethanol, known to be a poor solvent to PMMA, could dissolve PMMA when the temperature was over 60°C. The solubility of PMMA (Mw = 15,000 and Mw = 120,000) in ethanol was measured and was found to increase as the temperature increased. PMMA particles on the scale of submicron and single micron diameter could be precipitated from the PMMA/ethanol solution by temperature quenching. Then, since the precipitated particles contained a certain amount of ethanol, the precipitated particles could be foamed using the ethanol as a foaming agent in a vacuum drying process. Vacuum drying at temperatures slightly below the glass transition temperature of the polymer could make the particles foam. The effects of foaming temperature and the molecular weight of the polymer on the size of foamed particles were investigated. The experimental results showed that the vapor pressure and the molecular weight of the polymer are key factors determining the expandability of the micro particles. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] EXPERIMENTAL VACUUM SPRAY DRYING OF PROBIOTIC FOODS INCLUDED WITH LACTIC ACID BACTERIAJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 6 2009YUTAKA KITAMURA ABSTRACT This research aims to develop a vacuum spray dryer (VSD) that performs spray drying in a vacuumed drying tower at a lower temperature than the conventional spray drying. The VSD operational drying temperatures for the probiotic foods containing lactic acid bacteria were determined by the relationships between the temperature and the vapor pressure, and were correlated by Clapeyron's equation. The drying of the fermented milk starter at 35C drying tower was experimentally possible; however, powder from the lactic fermenting beverage was not obtained even at 50C, which resulted from the lower glass transition temperature of the material. Compared with ATP concentration of the fermented milk starter before and after the VSD drying, the lower the drying temperature, the higher the microbial activity is retained. The ATP ratio as 30% of the raw materials shows the high feasibility of VSD for dairy processing. PRACTICAL APPLICATIONS During the spray drying of liquid or slurry food, the heat-sensitive functional ingredients such as vitamin, enzyme or bacteria are usually degraded or lost because of the contact with hot air between 120 and 180C. Markets need food powder that involves a lot of functional materials and a long shelf life for the expansion of healthy food. The experimental vacuum spray dryer (VSD) showed a potential to dry probiotic foods involving lactic acid bacteria without their inactivation. Although the lactic acid bacteria contained in the powder at 35C,VSD was 30% of the raw material, it is more economical than using the liquid type fermented milk starter. With some mechanical or operational modifications for the high moisture content and low recovery ratio of the powder, VSD is applicable for dairy processing factories. [source] Crystallization Kinetics and X-ray Diffraction of Crystals Formed in Amorphous Lactose, Trehalose, and Lactose/Trehalose MixturesJOURNAL OF FOOD SCIENCE, Issue 5 2005Song Miao ABSTRACT: Effects of storage time and relative humidity on crystallization kinetics and crystal forms produced from freeze-dried amorphous lactose, trehalose, and a lactose/trehalose mixture were compared. Samples were exposed to 4 different relative water vapor pressure (RVP) (44.1%, 54.5%, 65.6%, 76.1%) environments at room temperature. Crystallization was observed from time-dependent loss of sorbed water and increasing intensities of peaks in X-ray diffraction patterns. The rate of crystallization increased with increasing storage humidity. Lactose crystallized as ,-lactose monohydrate, ,-anhydrous, and anhydrous forms of ,- and ,-lactose in molar ratios of 5:3 and 4:1 in lactose and lactose/trehalose systems. Trehalose seemed to crystallize as a mixture of trehalose dihydrate and anhydrate in trehalose and lactose/trehalose systems. The crystal forms in a mixture of lactose and trehalose did not seem to be affected by the component sugars, but crystallization of the component sugars was delayed. Time-dependent crystallization of lactose and trehalose in the lactose-trehalose mixture could be modeled using the Avrami equation. The results indicated that crystallization data are important in modeling of crystallization phenomena and predicting stability of lactose and trehalose-containing food and pharmaceutical materials. Keywords: crystallization, lactose, trehalose, crystal form, X-ray diffraction [source] Water Vapor Transmission Rates and Sorption Behavior of Chitosan FilmsJOURNAL OF FOOD SCIENCE, Issue 7 2000J.L. Wiles ABSTRACT: This study measured the water vapor transmission rates (WVTR) and moisture sorption of chitosan films over a range of water vapor pressures at 25 °C. Films of a constant thickness were made using chitosan with 3 levels of deacetylation. Films were tested at test relative humidity (RH) difference between RH values of 84%, 75%, 69%, 53%, 43%, 33%, 23%, 11%, and 0 at 25 °C using ASTM F1249-90 or ASTM E 96-80. The equilibrium moisture content in the films ranged from 3.7% to 31.8% (dry basis) corresponding to 11% to 84% RH. WVTRs of films increased with increase in water vapor pressure. The mean WVTR ranged from 6.7 to 1146 (g/m2/d) over the range of water vapor pressure from 2.68 (11% RH) to 19.9 mmHg (84% RH). The percentage of deacetylation of chitosan films and the viscosity of the cast solution did not have an effect on the WVTR properties of chitosan films. [source] Comparative study of hydrogen, argon, and xenon uptake into a propane hydrateAICHE JOURNAL, Issue 10 2010Joanne A. Abbondondola Abstract The rate of absorption of hydrogen, argon, and xenon into a Type II propane clathrate hydrate has been studied. The propane hydrate is synthesized from 250-,m ice grains, is estimated to have a porosity of 65% and has roughly the consistency of chalk. Hydrogen is rapidly absorbed by the hydrate sample and approaches the equilibrium vapor pressure in an hour before a very slow residual absorption process ensues. For an initial hydrogen pressure of 1.5 MPa, about 4.5% of the available 512 cages are occupied by hydrogen after 1 h, and 4.9% after 18 h. In contrast, for both argon and xenon significantly more gas is absorbed by the hydrate but at a much slower rate: about 5% as fast for xenon and 1% as fast for argon. We conclude that hydrogen readily diffuses through the propane hydrate microcrystal structure, while argon and xenon are probably absorbed by growing new double hydrate while consuming the propane hydrate. Although considerably higher pressures would be required to store significant quantities of hydrogen in propane hydrate, it appears that the crystal can be loaded and emptied in relatively short times. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Transferable intermolecular potentials for carboxylic acids and their phase behaviorAICHE JOURNAL, Issue 2 2010Amir Vahid Abstract Transferable step potentials are characterized for 39 carboxylic acids. The reference potential is treated with discontinuous molecular dynamics, including detailed molecular structure. Thermodynamic perturbation theory is used to interpret the simulation results and to provide an efficient basis for molecular modeling and characterization of the attractive forces. Four steps are used for representation of the attractive forces with only the first and last steps varied independently. The two middle steps are interpolated such that each site type is characterized by three parameters: the diameter, ,, the depth of the inner well, ,1, and the depth of the outer well, ,4. The depths of the attractive wells are optimized to fit experimental vapor pressure and liquid density data. Generally, the vapor pressure is correlated to an overall 43% average absolute deviation (% AAD) and the liquid density to 5% AAD. The deviations tend to be largest for the higher molecular weight acids. These deviations are larger than the errors previously encountered in characterizing organic compounds, but carboxylic acids present exceptional challenges owing to their peculiar dimerization behavior. Simultaneous correlation of vapor pressure, vapor compressibility factor, and phase equilibria of water + carboxylic acids place several constraints on the nature of the potential model, with the parameters of the present model representing a reasonable tradeoff. In other words, our model represents minimal deviations for vapor pressure, vapor compressibility factor, and phase equilibria of all acids simultaneously while varying the parameters ,, ,1, ,4, ,CC(dimerizing site bonding energy), ,AD(acceptor-donor bonding energy), and KHB(hydrogen bonding volume) for the acid O and OH site types. The present model is characterized by one acceptor and one dimerizing site on the carbonyl oxygen and one acceptor and one donor site on the hydroxyl oxygen. The acceptor and donor are capable of interacting with water while the dimerizing site is not. With this model, the saturated vapor compressibility factor of acids with seven or fewer carbons is near 0.5 while higher carbon ratios lead to a compressibility factor approaching 1.0. To compensate for the high vapor pressure deviations of the transferable potential model, a correction is introduced to customize the molecule-molecule self interaction energy. This adaptation results in deviations of 3.1% for vapor pressure of the pure acid database. To validate the behavior of the model for carboxylic acids in mixtures, 33 binary solutions were considered. Acids in this database ranged from formic to hexadecanoic. The average absolute deviation in bubble pressure for aqueous acid systems is 4.4%, 10.5% for acid + acid systems, and 4.7% for acid + n-alkane systems without a customized interaction correction. When applying the correction, deviations were 2.4% for aqueous systems, 2% for acid systems, and 2.8% for acid + n-alkane systems. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Determination of cubic equation of state parameters for pure fluids from first principle solvation calculationsAICHE JOURNAL, Issue 8 2008Chieh-Ming Hsieh Abstract A new method for estimation of parameters in cubic equations of state from ab initio solvation calculations is presented. In this method, the temperature-dependent interaction parameter a(T) is determined from the attractive component of solvation free energy, whereas the volume parameter b is assumed to be that of solvation cavity. This method requires only element-specific parameters, i.e., atomic radius and dispersion coefficient, and nine universal parameters for electrostatic and hydrogen-bonding interactions. The equations of state (EOS) parameters so determined allow the description of the complete fluid phase diagram, including the critical point. We have examined this method using the Peng,Robinson EOS for 392 compounds and achieved an accuracy of 43% in vapor pressure, 17% in liquid density, 5.4% in critical temperature, 11% in critical pressure, and 4% in critical volume. This method is, in principle, applicable to any chemical species and is especially useful for those whose experimental data are not available. © 2008 American Institute of Chemical Engineers AIChE J, 2008 [source] Distributed midpoint chain scission in ultrasonic degradation of polymersAICHE JOURNAL, Issue 9 2004G. Sivalingam Abstract The ultrasonic degradation of poly(bisphenol A carbonate), poly(,-caprolactone), and poly(vinyl acetate) was investigated with various solvents such as benzene, monochlorobenzene, and dichlorobenzene. The time evolution of molecular weight was determined using gel permeation chromatography. A limiting molecular weight was observed for all the systems and was a function of solvent properties. The degradation rates increased with increase in viscosity and decrease in vapor pressure. The polydispersity reached a maximum before reaching a constant value at longer times. The experimental data indicate that the breakage of the polymer is around midpoint, with a distribution rather than an ideal midpoint scission. A continuous distribution model with a stoichiometric kernel based on Lorentzian probability distribution function was developed to satisfactorily model the experimental data. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2258,2265, 2004 [source] Novel pervaporation technology using absorption refrigeration for vapor removalAICHE JOURNAL, Issue 11 2002Alaa Fahmy A novel process configuration for pervaporation and vapor permeation realizes the permeation driving force by absorbing the permeate vapor into a suitable solution with a very low vapor pressure. Although the suggested process design lacks an experimental demonstration, by using two well-established technologies,the separation by pervaporation and the absorption refrigeration,it can achieve technical and economic advantages over the conventional condensation technology. Vacuum pressures as low as 8 mbar can be obtained at ambient temperatures without refrigeration, as well as low vacuum ranges that are not possible by condensation without freezing. Process simulations and feasibility investigations for the suggested process are discussed. [source] Synthesis, pharmacology, crystal properties, and quantitative solvation studies from a drug transport perspective for three new 1,2,4-thiadiazolesJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2010German L. Perlovich Abstract A novel 1,2,4-thiadiazoles were synthesized. Crystal structures of these compounds were solved by X-ray diffraction experiments and comparative analysis of molecular conformational states, packing architecture, and hydrogen bonds networks were carried out. Thermodynamic aspects of sublimation processes of studied compounds were determined using temperature dependencies of vapor pressure. Thermophysical characteristics of the molecular crystals were obtained and compared with the sublimation and structural parameters. Solubility and solvation processes of 1,2,4-thiadiazoles in buffer, n -hexane and n -octanol were studied within the wide range of temperature intervals and thermodynamic functions were calculated. Specific and nonspecific interactions of molecules resolved in crystals and solvents were estimated and compared. Distribution processes of compounds in buffer/n -octanol and buffer/n -hexane systems (describing different types of membranes) were investigated. Analysis of transfer processes of studied molecules from the buffer to n -octanol/n -hexane phases was carried out by the diagram method with evaluation of the enthalpic and entropic terms. This approach allows us to design drug molecules with optimal passive transport properties. Calcium-blocking properties of the substances were evaluated. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:3754,3768, 2010 [source] Limitations of amorphous content quantification by isothermal calorimetry using saturated salt solutions to control relative humidity: Alternative methodsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 4 2010Nawel Khalef Abstract Despite the high sensitivity of isothermal calorimetry (IC), reported measurements of amorphous content by this technique show significant variability even for the same compound. An investigation into the reasons behind such variability is presented using amorphous lactose and salbutamol sulfate as model compounds. An analysis was carried out on the heat evolved as a result of the exchange of water vapor between the solid sample during crystallization and the saline solution reservoir. The use of saturated salt solutions as means of control of the vapor pressure of water within sealed ampoules bears inherent limitations that lead in turn to the variability associated with the IC technique. We present an alternative IC method, based on an open cell configuration that effectively addresses the limitations encountered with the sealed ampoule system. The proposed approach yields an integral whose value is proportional to the amorphous content in the sample, thus enabling reliable and consistent quantifications. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99: 2080,2089, 2010 [source]
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