Low Relative Vapor Pressure Research Articles

Catalytic Decomposition of Nitrous Oxide for Use in Hybrid Rocket Motors

In recent years, there has been significantly increased interest in using nitrous oxide as an oxidizer in hybrid rocket motor systems. The attraction of nitrous oxide is its low relative toxicity and high vapor pressure, potentially enabling self-pressurizing systems. Its decomposition is highly exothermic with a large energy barrier, typically requiring high temperature (700°C) to achieve appreciable decomposition rates. One solution is to use a catalyst to enable decomposition at significantly lower temperatures. This Paper uses a commercially available rhodium-based catalyst in a custom test cell to decompose nitrous oxide at temperatures well below the uncatalyzed self-sustaining decomposition temperature. This Paper also demonstrates that decomposition using the tested catalyst is direct to and at all temperature ranges observed and is incomplete with residual present at lower temperatures. Further, this Paper couples our test cell with a counterflow burner to ignite and burn hydroxyl-terminated polybutadiene fuel with the decomposed nitrous oxide and evaluate performance via fuel regression rate at a variety of conditions. The fuel autoignites when the gas exit temperature reaches 750°C, and regression rate is shown to increase with both mass flux and temperature.

Low Pressure Hysteresis in Materials with Narrow Slit Pores

Humidity-dependent closing and reopening slit pores can produce hysteresis loops in sorption diagrams even at low relative vapor pressure. Pore closing is supported by adhesion of the slit wall surfaces. In a macroscopic model for sorption hysteresis in narrow slits, the adhesion energy jumps by a finite value when touching slit walls are separated from each other. We consider a more realistic adhesion model by introducing a smoothly-varying adhesion force, which depends on the distance between the slit walls. The range of the attraction between the slit walls is found to have a pronounced influence on the shape of hysteresis loops at low vapor pressure. A large interaction range avoids an extraordinarily small relative vapor pressure necessary for pore closing, which is a precondition for low pressure hysteresis. Our extended model allows us to describe a discontinuity, which can appear in the desorption branch of swelling/shrinkage diagrams for hardened cement paste.

Design of Porous Metal-Organic Frameworks for Adsorption Driven Thermal Batteries

ABSTRACTThermal batteries based on a reversible adsorption/desorption of a working fluid (water, methanol, ammonia) rather than the conventional vapor compression is a promising alternative to exploit waste thermal energy for heat reallocation. In this context, there is an increasing interest to find novel porous solids able to adsorb a high energy density of working fluid under low relative vapor pressure condition combined with an easy ability of regeneration (desorption) at low temperature, which are the major requirements for adsorption driven heat pumps and chillers. The porous crystalline hybrid materials named Metal–Organic Frameworks (MOF) represent a great source of inspiration for sorption based-applications owing to their tunable chemical and topological features associated with a large variability of pore sizes. Recently, we have designed a new MOF named MIL-160 (MIL stands for Materials of Institut Lavoisier), isostructural to CAU-10, built from the assembly of corner sharing aluminum chains octahedra AlO4(OH)2 with the 2,5-furandicarboxylic linker substituting the pristine organic linker, 1,4-benzenedicarboxylate. This ligand replacement strategy proved to enhance both the hydrophilicity of the MOF and its amount of water adsorbed at low p/p0. This designed solid was synthesized and its chemical stability/adsorption performances verified. Here, we have extended this study by incorporating other polar heterocyclic linkers and a comparative computational study of the water adsorption performances of these novel structures has been performed. To that purpose, the cell and geometry optimizations of all hypothetical frameworks were first performed at the density functional theory level and their water adsorption isotherms were further predicted by using force-field based Grand-Canonical Monte Carlo simulations. This study reveals the ease tunable water affinity of MOF for the desired application.

Dislocation model for sorption hysteresis in deformable solids

Adsorption and desorption branches of sorption isotherms for soft materials often differ from each other even at low relative vapor pressures of the adsorbate. This low vapor pressure hysteresis may result from elastic deformations produced by the capillary tension that condensates exert on pore walls. A dislocation model for materials with very narrow slit pores is proposed. The shape of adsorption/desorption isotherms of soft solids with slit pores depends on a dimensionless parameter, which is proportional to Young's modulus, the square of pore width, and inversely proportional to the adhesion energy of the solid. The model designed for soft solids can be modified to describe low vapor pressure hysteresis in more rigid materials such as hardened cement pastes.

Perfusion calorimetry in the characterization of solvates forming isomorphic desolvates

In this study, the potential of perfusion calorimetry in the characterization of solvates forming isomorphic desolvates was investigated. Perfusion calorimetry was used to expose different hydrates forming isomorphic desolvates (emodepside hydrates II–IV, erythromycin A dihydrate and spirapril hydrochloride monohydrate) to stepwise increasing relative vapour pressures (RVP) of water and methanol, respectively, while measuring thermal activity. Furthermore, the suitability of perfusion calorimetry to distinguish the transformation of a desolvate into an isomorphic solvate from the adsorption of solvent molecules to crystal surfaces as well as from solvate formation that is accompanied by structural rearrangement was investigated. Changes in the samples were confirmed using FT-Raman and FT-IR spectroscopy. Perfusion calorimetry indicates the transformation of a desolvate into an isomorphic solvate by a substantial exothermic, peak-shaped heat flow curve at low RVP which reflects the rapid incorporation of solvent molecules by the desolvate to fill the structural voids in the lattice. In contrast, adsorption of solvent molecules to crystal surfaces is associated with distinctly smaller heat changes whereas solvate formation accompanied by structural changes is characterized by an elongated heat flow. Hence, perfusion calorimetry is a valuable tool in the characterization of solvates forming isomorphic desolvates which represents a new field of application for the method.

SORPTION OF WATER VAPOUR AND SURFACE ACTIVITY OF GHATTI GUM.

Abstract The sorption of water vapour by three fractions of sodium ghattate has been studied at 25° and 40°. The results were fitted by Brunauer, Emmett & Teller plots at low relative vapour pressures. Calculations of the differential heats and entropies of sorption gave initially exothermic ΔH̄ values and negative ΔS̄ values. As the sorption proceeded the signs of the thermodynamic properties became positive The mechanism of sorption onto different parts of the macromolecules was discussed. The surface tension of one sodium ghattate fraction was measured in water, 0.05 and 0.5 N sodium chloride solution, as a function of concentration, using the sessile drop method. The presence of salt enhanced the surface activity. A structure for the adsorbed film is suggested.

Effect of relative vapor pressure on separation of nanoscale contact in atomic force microscope

The separation of nanoscale contact junction is investigated in an atomic force microscope at various relative vapor pressure conditions. Gradual increase in adhesion force is observed as the relative vapor pressure increases. However, the force-deformation behaviors of the water-mediated nanoscale contacts vary extensively with the relative vapor pressure conditions. At low relative vapor pressure (p/ps<0.06), water molecules play a role as a weak glue contributing solid extension. In contrast, at high relative vapor pressure (p/ps=0.8), the highest adhesion force is observed without indication of the solid extension. The meniscus collapses and forms a water column after solids separates at an intermediate relative vapor pressure condition (p/ps=0.4). The detailed analysis revealed the transition of adhesion mechanism from the solid-dominant adhesion to liquid-dominant adhesion as the relative vapor pressure increases.

Adsorption, Capillary Condensation and Friction

Frictional behaviors between mica surfaces have been investigated with the Surface Force Apparatus under various relative vapor pressures (RVP) of both water and cyclohexane. The dependence of frictional forces on RVP, particularly in the low RVP range, has been studied because the embryo of liquefaction and layering of molecules occurs in these conditions. The results of the measurements of kinetic shear stress as a function of sliding velocity at different RVP reveal the role of liquid condensed around the contact zone. A mechanism based on capillary condensation is proposed to explain the role of RVP on friction by adsorption of liquid layers on free mica surfaces and at contact.

Nonenzymatic Browning Kinetics in Low-moisture Food Systems as Affected by Matrix Composition and Crystallization

ABSTRACT: Nonenzymatic browning (NEB) in lactose, trehalose, and lactose/trehalose food model systems containing L-lysine and D-xylose (5% w/w) as reactants was studied at 4 different relative vapor pressure (RVP) (33.2%, 44.1%, 54.5%, 65.6%) environments at room temperature. Sorption isotherms of model systems were determined gravimetrically, and data were modeled using the Brunauer-Emmett-Teller (BET) and Guggenheim-Anderson-deBoer (GAB) models. Glass transition, Tg, was measured by differential scanning calorimetry (DSC). NEB was followed spectrophotometrically. Although the 3 model systems showed similar glass transition behavior, different crystallization properties were observed from loss of sorbed water. Mixtures of trehalose and lactose showed delayed crystallization of component sugars. The NEB rate was affected by sugar composition. At a low RVP (33.1%) environment, the NEB rate in trehalose system was higher than in the lactose/trehalose system, and the NEB rate in lactose system was the lowest. The NEB rate in different models seemed to be affected by component crystallization. The highest extent of browning in the trehalose matrix system seemed to be related to the formation of trehalose crystals in the system after crystallization at high RVP. The results indicated that the composition of the carbohydrate-based low-moisture real food systems should be considered in controlling NEB reaction.

Water Sorption and Plasticization Behavior of Spray‐dried Lactose/Protein Mixtures

ABSTRACT: Water sorption properties, effects of proteins on glass transition temperature, and time‐dependent lactose crystallization of spray‐dried lactose and lactose in lactose/WPI (3:1), lactose/Na‐caseinate (3:1), lactose/albumin (3:1), and lactose/gelatin (3:1) mixtures were investigated. Brunauer‐Emmett‐Teller (BET) and Guggenheim‐Anderson‐de Boer (GAB) models were used to model water sorption. Lactose/protein mixtures sorbed high amounts of water at low relative vapor pressure (RVP) up to 23.1%. Above 23.1% RVP levels, water sorbed by pure lactose was higher, up to 44.1% RVP, except in the case of the lactose/gelatin mixture. Lactose/ gelatin also sorbed a high amount of water at 33.2% RVP. Loss of sorbed water resulting from crystallization of amorphous lactose was observed. Crystallization of pure lactose and lactose crystallization in lactose/protein mixtures occurred at RVP ≥ 44.1% within 24 h. After crystallization at RVP ≥ 54.5%, water contents remained higher for lactose/protein mixtures than for pure lactose. The rate of lactose crystallization was less in all lactose/protein mixtures than was observed for pure lactose. WPI had the lowest effect on lactose crystallization. Crystallization occurred most slowly in lactose/gelatin mixtures. Both GAB and BET models fitted to water sorption data up to 0.441 aw. It seems that different proteins interact with lactose differently. Water sorption and time‐dependent lactose crystallization of lactose/protein mixtures have important consequences to processing and storage behavior of lactose‐protein based products.

Predicting Volatile Organic Vapor Sorption from Soil Specific Surface Area and Texture

AbstractVapor sorption of a volatile organic chemical (VOC) to soil minerals at low water contents can increase the total VOC sorption capacity of the soil by several orders of magnitude. Vapor sorption can subsequently cause high VOC fluxes out of the soil during periods with fluctuating low soil water contents. Models for predicting VOC sorption, including vapor sorption, as a function of soil water content are therefore valuable for evaluating contaminant volatilization and exposure risk at polluted sites. A model for estimating trichloroethylene (TCE) surption parameters at low relative vapor pressure from ethylene glycol monoethyl ether (EGME)‐measured soil specific surface area (SA) and soil clay and organic carbon content was developed based on TCE sorption data from 26 different porous media. Significant improvement in prediction accuracy compared with a previous model was achieved. Based on data for 13 soils, an organic carbon partitioning coefficient of Koc, = 0.60 foc cm3 g−1 (R2 = 0.97) for TCE is recommended for use in the new TCE sorption model. In case SA is not available, an expression for predicting SA from soil clay content is proposed. The clay‐based TCE surption model was tested against independent data for two Japanese soils (a sand and a clay loam) measured in this study by a gas chromatography‐based soil microcolumn method. The sorption model accurately predicted TCE retardation (sorption) as a function of soil water content for both soils. Model calibration to sorption data for three different VOC's (benzene, TCE, and toluene) implies that the sorption model may also be applied to chemicals other than TCE. However, sorption measurements for more chemicals and soils at varying water contents are necessary to further generalize the VOC sorption model.

Prediction of Sorption by Soils of Volatile Hydrocarbon Mixtures.

Mixtures of hydrocarbon vapors evaporating from petroleum spills are often transported through the unsaturated zone. To predict the course of evaporation the sorption isotherm of each component, and how this is affected by the other components, must be known. The sorption of m-xylene and n-dodecane vapors sorbed on air- and ovendry soil was studied. Mixtures of m-xylene and n-dodecane containing 0, 20, 40, 60, 80, and 100% n-dodecane by volume were prepared. The pure compounds and each mixture were diluted with nonvolatile paraffin to contain 5, 10, 20, 50, 80, and 100% of the pure compound or mixture of m-xylene and n-dodecane, thus providing a wide range of vapor composition. Samples of Evesham clay (Orthic Grumaquert) were suspended over each of the vapors, and the amounts sorbed by the soil were determined by gas chromatography after extraction of the soil with CCl4 . On oven-dry soil at low relative vapor pressures the two gases competed for sorption sites. At higher relative vapor pressures the increased sorption due to formation of multilayers more than compensated for competition by the other gas, so that addition of the second component increased sorption of the first. On air-dry soil the addition of a second component always increased sorption of the first at all relative vapor pressures. Empirical isotherms of the pure components give no information about their influences on each other's sorption. Hill's theory of multilayer multicomponent sorption allows one to predict such influences from parameters derived solely from the isotherms of the pure components. The Hill equation is shown to be more successful in predicting the sorption from mixtures of m-xylene and n-dodecane vapors than an empirical equation based on the isotherms of the pure components.

Characteristics of Water in Copoly(methyl methacrylate–N-vinylpyrrolidone) Membranes

The characteristics of water in methyl methacrylate–N-vinylpyrrolidone (MMA/NVP) copolymer membranes were studied. The sorption and permeation behavior and differential scanning calorimetric behavior of MMA/NVP copolymer-water systems contained two types of water in the copolymer membranes at relative vapor pressures up to ca. 0.9: water directly bound to polar NVP residues at low relative vapor pressures, i.e., the “tightly bound” water, and water associated in the vicinity of hydrophobic MMA residues forming multimolecular clusters at higher relative vapor pressures, i.e., “hydrophobic hydration” water. The latter was characterized by a rigid structure resulting in an increase in the shear modulus of the copolymer membrane at relative vapor pressure higher than 0.5. It is concluded that the cluster size or clustering tendency in MMA/NVP membranes, i.e., the amount of hydrophobic hydration water in the copolymer, is enhanced by the presence of the proper amount of NVP residues in the copolymers via enhancement of water uptake by the membranes.

Surface area and swellability of coal

Sorption data have been obtained for a range of vapours on a Kentucky No.12 coal. The data at high relative vapour pressures ( P/ P 0 > 0.3) are interpreted in terms of coal swelling. The sorption data at low relative vapour pressures ( P/ P 0 < 0.3) are used to obtain information on surface area. The results indicate that surface areas obtained in this way are influenced by vapour-induced swelling effects.

(METHYL GLUTAMATE-GLUTAMIC ACID) COPOLYMER AND SURFACE SAPONIFIED POLY (METHYL GLUTAMATE) FIBERS

Preparing of polypeptide fibers having the excellent characteristics of both poly(methyl glutamate) (PMG) and poly(glutamic acid) (PGA) fibers was examined, and the following results were obtained.(1) By uniformly saponifying PMG fiber, a uniform (methyl glutamate-glutamic acid) copolymer fiber was obtained, and the water-sorptive capacity and the dyeability were improved without serious deterioration of mechanical properties. By surface saponifying PMG fiber, which yielded a continuous composite fiber of copolymer of surface part and PMG of core part, especially the wet strength and the wet modulus were much improved.(2) The tensile strength of polypeptide fibers depended more on the content of β-form structure than on the degree of molecular orientation.(3) The water vapor sorption of fiber was higher than that of membrane, because of the β-form structure of fiber.(4) The water sorption process in the β-form structure may be described as follows: water molecules are sorbed on free polar groups of main chain at low relative vapor pressure, and hydrogen bonds between polar groups in the main chain are in some extent broken at the higher relative vapor pressure for water molecules to be absorbed on those parts.

Water vapor sorption and desorption behavior of some keratins

Sorption and desorption isotherms of water vapor in a number of keratin substrates including excised human stratum corneum, guinea pig and neonatal rat corneum and human hair have been obtained and the data compared to the information available on wool. An attempt was made to analyze the data according to the BET and D'Arcy-Watt equations, Flory-Huggins polymer solution theory and Zimm's clustering function. The results suggest strong binding between the sorbate and keratins in the low relative vapor pressure range, reflecting a sorption process on primary reactive sites (Langmuir) which proceeds up to 0.2-0.3 relative vapor pressure. More confirmation is obtained from isosteric heat of sorption measurements. Extensive clustering and multilayer formation occur in the higher relative vapor pressure range.

Hardened slag–cement pastes of various porosities. III. Surface area in relation to pore structure

AbstractThe total surface areas, total pore volumes, and the distribution of pore surface and pore volume in pores of different sizes were determined on the hardened slag‐cement pastes. Adsorption isotherms of four different adsorbates, namely water, methanol, nitrogen and cyclohexane, were used for surface area and pore structure determinations. The results obtained indicated that water can penetrate into the total pore system, namely both the micropores and the wide pores; whereas methanol can measure wide pores and some of the micropores; moreover, nitrogen and cyclohexane molecules tend to measure only wider groups of pores. The indication gained from this result is that the molecular sieve property plays the most significant role in surface area and pore structure determinations of the hardened cement pastes. The polarity of the molecules seems to be important at low relative vapour pressures, and at high pressures it causes expansion of the pastes.

The-brown coal/water system: Part 2. Water sorption isotherms on bed-moist Yallourn brown coal

The high moisture content of Victorian brown coals is the major obstacle to their economic utilization. Some insight into the bonding of this water in the coals can be obtained from the water sorption isotherms reported in this investigation. The isotherms (30–60 °C) are typically sigmoid with a marked desorption/adsorption hysteresis extending to low relative vapour pressures. The BET monolayer capacity of the coal for water, calculated from the isotherms, correlates with the number of hydrophilic functional groups on the coal rather than the extent of its surface. Isosteric heats of sorption determined from the isotherms increase from the latent heat of vaporization (10.4 kcal/mol ∗) in the bulk water or saturated end of the isotherm to 14 kcal/mol in the monolayer region. This increase can be explained by enhanced hydrogen bonding of the water to functional groups on the coal surface. A mechanism for the hysteresis effect has been proposed, based on differences between the desorption and adsorption data.

The behavior of cotton cellulose and beech wood in ammonia atmosphere

AbstractIn order to learn more about the plasticization of wood, sorption measurements on cellulose rich specimen, cotton fibers, and bending tests on beech wood were performed in ammonia atmosphere. The results showed that the sorption of NH3 on cotton was substantially hindered at low relative vapor pressure, presumably due to interaction of NH3 with hydrate water. Near the saturation pressure a reduction of the sorption capacity was observed because of developing collapse in the capillary system. In the middle relative vapor pressure range the equilibria were retarded while the active surface area was extended to more than double. Observations at different temperatures‐15, 25, 35°C, revealed that the extension of the sorptive area took place consistently at the same ammonia content of the specimen. The other mentioned diverging sorption features, however, were intensified variously by raising the temperature. No difference was found between the ammonia sorption properties of cellulose I and III.Bending tests on beech wood laths in ammonia environment displayed a dynamic progression of the plasticization. At the beginning of the exposition to ammonia the bending ability of the specimen was increasingly enhanced. When in course of the plasticization the modulus of elasticity of the laths dropped below 1/3 of the starting value, bendability changed by levelling off progressively. The conclusion thereof that the plasticization of wood can be forced only to given limits was confirmed by destructive bending tests and by porosimetric measurements. To reach a sufficiently softened state of the beech laths with dimensions 25×1×0.6 cm, 15 min appeared to be enough while further alterations could be observed even on the smallest specimen size for considerably longer periods.

On the Interaction of Water Molecules and Montmorillonite Surfaces

AbstractThe adsorption of water was studied on monoionic montmorillonite saturated with Cs, Rb, Li, Na, NH4, and Ca ions. These ions vary in their influence on the structure of water in solution. Thus the effect on the adsorbed water by exchange ions could be compared with the effect of these ions in solution. Heats of wetting of the montmorillonite samples were determined as a function of the equilibrium relative vapor pressure. Entropy values were calculated from the heats of wetting combined with values of the surface potential from adsorption isotherms using the Gibbs surface excess equation. The decrease in heats of wetting with increasing relative vapor pressure was discontinuous near p/po = 0.1. This was interpreted as indicating a change at the surface of the clay mineral probably related with ion hydration effects. Consequently the obtained entropy changes could not be assigned entirely to the adsorbed water molecules. At low relative vapor pressures the entropy values strongly reflected the influence of the exchange ion which was found to be similar to that exerted by these ions in solution. At higher relative vapor pressures the entropy of the system was about 4 e.u. below that of liquid water which was nearly the same as the likely value for the silicate sheet itself obtained in earlier studies.