Absolute Vapor Pressures Research Articles

Does the Oxygen Functionality Really Improve the Thermodynamics of Reversible Hydrogen Storage with Liquid Organic Hydrogen Carriers?

Liquid organic hydrogen carriers (LOHCs) are aromatic molecules that are being considered for the safe storage and release of hydrogen. The thermodynamic properties of a range of aromatic ethers were investigated using various experimental and theoretical methods to assess their suitability as LOHC materials. The absolute vapour pressures were measured for benzyl phenyl ether, dibenzyl ether and 2-methoxynaphthalene using the transpiration method. The standard molar enthalpies and entropies of vaporisation/sublimation were derived from the temperature dependence of the vapour pressures. The combustion energies of benzyl phenyl ether and dibenzyl ether were measured using high-precision combustion calorimetry, and their standard molar enthalpies of formation were derived from these data. High-level quantum chemical calculations were used to calculate the standard molar enthalpies of formation in the gas phase for benzyl phenyl ether, dibenzyl ether and 2-methoxynaphthalene. The latter values agreed very well with the experimental results obtained in this work. The thermodynamic properties of the hydrogenation/dehydrogenation reactions in liquid phase in LOHC systems based on methoxy–benzene, diphenyl ether, benzyl phenyl ether, dibenzyl ether and 2-methoxynaphthalene were derived and compared with the data for similarly structured hydrogen carriers based on benzene, diphenylmethane, 1,2-diphenylethane, 1,3-diphenylpropane and naphthalene. The influence of the oxygen functionality on the thermodynamic properties of the hydrogenation/dehydrogenation reactions was evaluated.

A new setup for measurements of absolute saturation vapor pressures using a dynamical method: Experimental concept and validation.

We describe a new experimental system for direct measurements of the absolute saturation vapor pressures of liquid or solid samples. The setup allows the isolation of the sample under steady conditions in an ultra-high vacuum chamber, where the measurement of the sample's vapor pressure as a function of its temperature can be performed in a range around room temperature and in a pressure range defined only by the applied absolute pressure sensor. We characterize the setup and illustrate its capability to measure saturation vapor pressures as well as enthalpies of evaporation around room temperature with explicit measurements on four liquid compounds (diethyl phthalate, 1-decanol, 1-heptanol, and 1-hexanol) for which accurate vapor pressures have previously been reported.

Thermodynamics of Reversible Hydrogen Storage: Are Methoxy-Substituted Biphenyls Better through Oxygen Functionality?

The reversible hydrogenation/dehydrogenation of aromatic molecules, known as liquid organic hydrogen carriers, is considered as an attractive option for the safe storage and release of elemental hydrogen. The recently reported efficient synthetic routes to obtain methoxy-biphenyls in high yield make them promising candidates for hydrogen storage. In this work, a series of methoxy-substituted biphenyls and their structural parent compounds were studied. The absolute vapour pressures were measured using the transpiration method and the enthalpies of vaporisation/sublimation were determined. We applied a step-by-step procedure including structure–property correlations and quantum chemical calculations to evaluate the quality of thermochemical data on the enthalpies of phase transitions and enthalpies of formation of the studied methoxy compounds. The data sets on thermodynamic properties were evaluated and recommended for calculations in chemical engineering. A thermodynamic analysis of chemical reactions based on methoxy-biphenyls in the context of hydrogen storage was carried out and the energetics of these reactions were compared with the energetics of reactions of common LOHCs. The influence of the position of the methoxy groups in the rings on the enthalpies of the reactions relevant for hydrogen storage was discussed.

Is hydrogen bonding the reason for differences in vapour pressure and vaporisation energetics of optically active and racemic compounds?

This work is a contribution to understanding of the thermodynamic properties of chiral compounds at the molecular level. The absolute vapour pressures of (RS)-2-amino-1-butanol, (S)-2-amino-1-butanol, (R)-2-amino-1-butanol, S-ethyl-lactate, and (RS)-1-methoxy-2-propylamine were measured by the transpiration method. The standard molar vaporisation enthalpies of these compounds were derived from vapour pressure–temperature dependences. The differences between vapour pressures and vaporisation enthalpies of racemates and enantiomerically pure isomers have been demonstrated and discussed. It was hypothesized that the intramolecular hydrogen bonds of the studied species in the gas phase are the reason for the observed differences.

Interactions between substituents in the benzene ring. Experimental and theoretical study of methoxy substituted acetophenones

The mutual interaction of substituents in the aromatic ring is one of the fundamentals of organic chemistry. Acetyl and methoxy substituted benzenes are abundant in value added lignin valorisation products. Using the transpiration method, the absolute vapor pressures of methoxy-acetophenones were measured and used to calculate the standard molar enthalpies of vaporisation. The new thermodynamic results and those available in the literature were evaluated in this work using structure–property correlations. The gas-phase standard molar enthalpies formation of methoxy-acetophenones were estimated using a high-level quantum chemical method G4. The pair-wise interactions of acetyl and methoxy substituents were derived in the frame of a “centerpiece” group-contribution approach. It was shown that in the case of agglomeration of up to three substituents in the benzene ring, no additional interactions are generally required for a reliable prediction of the thermodynamic properties of value-added compounds from lignin utilization processes.

Reversible storage and release of hydrogen with LOHC: Evaluation of thermochemical data for methyl-quinolines with complementary experimental and computational methods

The liquid organic hydrogen carriers (LOHC) are aromatic molecules, which can be considered as an attractive option for the storage and transport of hydrogen. A considerable amount of hydrogen can be loaded and unloaded with a reversible chemical reaction. Methyl-substituted quinolines are available from petroleum, coal processing, wood preservation or they can be synthesized from aniline. Quinolines can be considered as potential LOHC systems, provided they have favorable thermodynamic properties, which were the focus of this current study. The absolute vapor pressures of methyl-quinolines were measured using the transpiration method. The standard molar enthalpies of vaporization of methyl-quinolines were derived from the vapor pressure temperature dependences. Thermodynamic data on vaporization and formation enthalpies available in the literature were collected, evaluated, and combined with own experimental results. The theoretical standard molar gas-phase enthalpies of formation of methyl-quinolines, calculated using the quantum chemical G3MP2 and G4 methods, agreed well with the evaluated experimental data. The hydrogenation/dehydrogenation reaction enthalpies of methyl-quinolines were calculated and compared with the data for other potential liquid organic hydrogen carriers. The comparatively low enthalpies of reaction make these heteroaromatics a seminal LOHC systems.

Vaporization Thermodynamics of Pyrrolidinium, Pyridinium, and Imidazolium-Based Ionic Liquids Bearing the Bis(fluorosulfonyl)imide [FSI] and the Bis(trifluoromethylsulfonyl)imide [NTf2] Anions

New experimental vapor pressures in the range 407 K to 460 K and vaporization enthalpy of the ionic liquids (IL) N-alkyl-N-methyl-pyrrolidinium bis(fluorosulfonyl)imide ionic liquids have been measured using quartz crystal microbalance. The absolute vapor pressures and vaporization enthalpies were compared with analogous pyrrolidinium-based ILs with the bis(trifluoromethanesulfonyl)imide anion. The evaluated difference in vaporization enthalpy of ILs with bis(fluorosulfonyl)imide and bis(trifluoromethanesulfonyl)imide anions allowed for estimation of corresponding property for a wide set of ILs with bis(fluorosulfonyl)imide anion. The results are relevant to chemical engineering calculations of processes involving ILs as reaction and separation media.

Prediction of thermodynamic properties: centerpiece approach—how do we avoid confusion and get reliable results?

The absolute vapor pressures of three amino-alcohols were measured using the transpiration method. The consistent set of standard molar enthalpies of vaporization for eighteen amino-alcohols was evaluated using empirical and structure–property correlations. The averaged values of vaporization enthalpies were recommended as reliable benchmark properties for the heat management of CO2 capture technologies. Centerpiece approach based on the group-additivity principles was developed toward amino-alcohols.Graphic abstract

Hydrogen Storage: Thermodynamic Analysis of Alkyl-Quinolines and Alkyl-Pyridines as Potential Liquid Organic Hydrogen Carriers (LOHC)

The liquid organic hydrogen carriers (LOHC) are aromatic molecules, which can be considered as an attractive option for the storage and transport of hydrogen. A considerable amount of hydrogen up to 7–8% wt. can be loaded and unloaded with a reversible chemical reaction. Substituted quinolines and pyridines are available from petroleum, coal processing, and wood preservation, or they can be synthesized from aniline. Quinolines and pyridines can be considered as potential LOHC systems, provided they have favorable thermodynamic properties, which were the focus of this current study. The absolute vapor pressures of methyl-quinolines were measured using the transpiration method. The standard molar enthalpies of vaporization of alkyl-substituted quinolines and pyridines were derived from the vapor pressure temperature dependencies. Thermodynamic data on vaporization and formation enthalpies available in the literature were collected, evaluated, and combined with our own experimental results. The theoretical standard molar gas-phase enthalpies of formation of quinolines and pyridines, calculated using the quantum-chemical G4 methods, agreed well with the evaluated experimental data. Reliable standard molar enthalpies of formation in the liquid phase were derived by combining high-level quantum chemistry values of gas-phase enthalpies of formation with experimentally determined enthalpies of vaporization. The liquid-phase hydrogenation/dehydrogenation reaction enthalpies of alkyl-substituted pyridines and quinolines were calculated and compared with the data for other potential liquid organic hydrogen carriers. The comparatively low enthalpies of reaction make these heteroaromatics a seminal LOHC system.

KELEMBABAN UDARA DENGAN ALAT HUMYDIMETER PADA LAHAN SAWAH DI KELURAHAN TANAH MERAH

Humidity is the concentration of water vapor in the air. In agriculture, air humidity is associated with increased productivity and development of cultivated plants, humidity in the environment where it grows can determine the selection of appropriate plant species, the purpose of this study was to determine air humidity in paddy fields between April, May , and June, changes in air humidity at any time describe the water vapor content in the air can be expressed as absolute humidity, relative or vapor pressure deficit, relative humidity compares the actual water vapor content/pressure with its saturation state or the air's capacity to accommodate water vapor. The relationship between air humidity in paddy fields in Tanah Merah Village is relatively low, this is the impact of changes in temperature, quantity and quality of radiation, wind movement, air pressure, vegetation, and availability of water and productivity of irrigated ricefields

Hydrogen storage technologies: Methyl-substituted biphenyls as an auspicious alternative to conventional liquid organic hydrogen carriers (LOHC)

Derivatives of biphenyls, namely mono-, di- and tert- methyl substituted biphenyls, can be considered as promising hydrogen carriers. The absolute vapour pressures of nine methyl-substituted biphenyls were measured using the transpiration method. The vapour pressures available in the literature for methylbiphenyls were collected and analyzed. The standard molar enthalpies of vaporization/sublimation of methyl substituted biphenyls were derived from the temperature dependencies of the vapour pressures. The experimental enthalpies of vaporization were validated using Kovats’s indices. The enthalpies of fusion of four methylbiphenyls were measured by DSC. The standard molar enthalpy of formation of the liquid 3,3′-dimethylbiphenyl was determined using high precision combustion calorimeter. The enthalpies of formation of methylbiphenyls available in the literature were collected and combined with the evaluated enthalpies of vaporization/sublimation to obtain their gas-phase enthalpies of formation. High-level G3MP2 and G4 quantum-chemical methods were used to establish consistency of the experimental and theoretical results. The enthalpies of the reversible hydrogenation/dehydrogenation reactions of the biphenyls were calculated and compared with conventional liquid organic hydrogen carriers.

Paving the way to the sustainable hydrogen storage: Thermochemistry of amino-alcohols as precursors for liquid organic hydrogen carriers

The absolute vapour pressures of four amino-alcohols were measured using the transpiration method. A consistent set of standard molar enthalpies of vaporization for eighteen amino-alcohols was evaluated using empirical and structure–property correlations. The averaged values of vaporization enthalpies are recommended as reliable benchmark properties for thermochemical calculations of the energetics of chemical reactions including synthesis of alkyl-substituted pyrazines, compounds considered as seminal liquid organic hydrogen carriers (LOHC)

Evaluation of vaporization thermodynamics of pure amino-alcohols

The absolute vapour pressures of three amino-alcohols were measured using the transpiration method. The consistent set of standard molar enthalpies of vaporization for eighteen amino-alcohols was evaluated using empirical and structure–property correlations. Correlation of vaporization enthalpies with normal boiling temperatures was established. Vaporization enthalpies of amino-alcohols obey the group-additivity rules. The averaged values of vaporization enthalpies were recommended as reliable benchmark properties for the heat management of CO2 capture technologies.

Vapour pressures of methoxy substituted benzaldehydes

Absolute vapour pressures of 4‑hydroxy‑3-methoxybenzaldehyde (vanillin), 2‑hydroxy‑3-methoxybenzaldehyde (ortho-vanillin), 2‑hydroxy‑5-methoxybenzaldehyde, and 3,5-dimethoxy-benzaldehyde were measured by using transpiration method. Standard molar enthalpies of sublimation and vaporization were derived from vapour pressures temperature dependences. Available primary experimental results on vapour pressures were collected from the literature and evaluated. The consistent set of thermodynamic data can be recommended to optimize the lignin valorisation technologies.

Long-chain linear alcohols: Reconciliation of phase transition enthalpies

Thermodynamics of phase transitions of long-chain linear alcohols were revised by means of complementary experimental techniques: transpiration, differential scanning calorimetry (DSC), fast scanning calorimetry (FSC), and solution calorimetry (SC). Absolute vapor pressure temperature dependencies for heptadecanol-1 and octadecanol-1 were measured by the transpiration and FSC methods. The validity and accuracy of the FSC experimental setup towards reliable vapor pressure measurement was established. It was shown that vaporization enthalpies for heptadecanol-1 and octadecanol-1 obtained by FSC and transpiration method are in good agreement. The SC approach was used for estimation of sublimation/vaporization enthalpies of linear alcohols. Energetics of the phase transitions found with the SC-approach agree well with that from conventional methods and they are consistent with each other.

The Error Analysis for the Remote Sensing of Water Vapor Data by Ground Based GPS in Tengchong, Yunnan Province

Due to its special observation principle, GPS remote sensing atmospheric precipitation has the advantages of high time resolution and no weather conditions, and has been widely used in the research field of atmospheric precipitation. Using ground-based GPS precipitate water vapor data (GPS-PWV) and radiosonde-precipitate water vapor data (RS-PWV) that integrated by Radiosonde data, the error between GPS-PWV and RS-PWV in Tengchong is analyzed on its distribution of wet and dry seasons, also the difference between 00:00 UTC and 12:00 UTC. Results show that the RMSE of GPS-PWV and RS-PWV on both 00:00 UTC and 12:00 UTC are less than 5 mm, they correspond with each other well and their correlation coefficient is above 0.95, additionally, GPS-PWV value is stable than RS-PWV value. On the whole, the value of GPS-PWV is slightly larger than RS-PWV. And the mean absolute error between them has higher values, 4.5 mm in 2011 and 4.7 mm in 2012 from May to October (local rainy season) and lower values, 2.8 mm in 2011 and 3.1 mm in 2012 in November to April (local dry season). Besides, the mean absolute error in the morning seems has a difference with its component in the evening. Specifically, it is bigger on 12:00 UTC than on 00:00 UTC and the mean absolute errors on 12:00 UTC of two years are 27% and 11% larger than errors on 00:00 UTC respectively. The correlation of mean absolute error and surface vapor pressure, surface air temperature is examined in this study as well. We achieved that the correlation coefficient between mean absolute error and surface vapor pressure, surface air temperature equals 0.32, 0.37 separately. Diverse characters of mean absolute error under different precipitation conditions are also discussed. The outcome is that the mean absolute error has a higher value on rainy days and a lower value on clear days. However, during the precipitation periods, it appears that the mean absolute error and the rainfall situation don’t agree with each other well, it is likely to change randomly.

Volatility of Amorphous Solid Water.

Amorphous solid water is probably the most abundant form of solid water in the universe. Its saturation vapor pressure and thermodynamic properties, however, are not well known. We have investigated the saturation vapor pressure over vapor-deposited amorphous ice at temperatures between 133 and 147 K using a novel experimental method. The new method determines the absolute vapor pressures and the sublimation rates by measuring the mass growth rates of ice-covered nanoparticles under supersaturated water vapor conditions. We find that the vapor pressure of amorphous solid water is up to a factor of 3 higher than that predicted by current parameterizations, which are based in part on calorimetric measurements. We demonstrate that the calorimetric measurements can be reconciled with our data by acknowledging the formation of nanocrystalline ice as an intermediate ice phase during the crystallization of amorphous ice. As a result, we propose a new value for the enthalpy of crystallization of amorphous solid water of Δ H = 2312 ± 227 J/mol, which is about 1000 J/mol higher than the current consensus. Our results shine a new light on the abundance of water ice clouds on Mars and mesospheric clouds on Earth and may alter our understanding of ice formation in the stratosphere.

Thermochemistry of drugs: experimental and theoretical study of analgesics

Acetanilides are broadly used in the pharmaceutical industry. Thermochemical data on vapor pressures, solid-gas, liquid-gas, and solid-liquid phase transitions, as well as on enthalpies of formation of substituted acetanilides have been collected and evaluated with help of additional experimental measurements. Absolute vapor pressures of meta- and para-substituted acetanilides were studied by using transpiration method. Significant disagreement of available literature data on isomeric hydroxyacetanilides was detected and resolved. A quick estimation scheme of vaporization enthalpies of substituted acetanilides at 298.15 K was developed based on “structure-property” relationships. Quantum-chemical methods were applied for calculation of theoretical gas-phase enthalpies of formation of substituted acetanilides. Theoretical values together with results from “structure-property” analysis allowed for validation of the experimental crystalline state enthalpies of formation and prediction of these values based on quantum-chemical calculations.

Thermodynamics of Imidazolium‐Based Ionic Liquids Containing the Trifluoromethanesulfonate Anion

AbstractA thermochemical investigation of the series of 1‐alkyl‐3‐methylimidazolium ionic liquids (ILs) with the trifluromethanesulfonate CF3SO3− anion is presented. Absolute vapor pressures and vaporization enthalpies were measured by using a quartz crystal microbalance (QCM). The enthalpies of solutions were determined by solution calorimetry. Gas‐phase enthalpies of the formation of ILs were calculated by applying the high‐level quantum‐chemical method G3MP2. From a combination of experimental and theoretical results, the enthalpy of formation of aqueous CF3SO3− anion was derived for the first time.

Contact skin temperature measurements and associated effects of obstructing local sweat evaporation during mild exercise-induced heat stress

Objective: Locally increasing evaporative resistance is one mechanism by which contact skin temperature (Tsk) sensors and their attachments may disturb the temperature of the skin site being measured. We aimed to determine the extent to which an obstruction of evaporation affects local Tsk during exercise-induced sweating and how this compares to the Tsk measured using a conventional contact Tsk sensor. Approach: Twelve adult males each completed one experimental session (~24 °C, ~46% relative humidity) involving seated rest and exercise (cycle ergometer). Air velocity was ~0.5 m · s−1 during rest and ~1 m · s−1 during exercise. Tsk of the right posterolateral forearm was measured using fine-wire thermocouples (0.125 mm diameter; chosen for minimal sensor-related disturbance) under two concurrent experimental conditions: uncovered or directly covered by a moisture-impermeable matte-black aluminium foil (thickness 0.08 mm, area 15 mm × 22 mm). The adjacent Tsk was also measured using an iButton attached with a nonwoven medical tape. Changes in next-to-skin absolute vapour pressure were used to estimate the onset of sweating. Main results: During exercise, covered thermocouple temperatures were consistently warmer than those uncovered. These differences were small before the onset of sweating (0.1 °C, p = 0.16), but increased thereafter (0.6 and 1.0 °C by minutes 15 and 30 of exercise, respectively; p ⩽ 0.03). For change scores from baseline rest, the iButton-measured Tsk was as much as 0.7 °C warmer than uncovered and −0.4 °C cooler than covered thermocouples during sweating, but differences were not statistically supported and with wide 95% limits of agreement (up to ±3.1 °C). Significance: When delineated, a small obstruction of evaporation itself caused an overestimation of Tsk during exercise although, while demonstrable, these effects were less clear in the context of using a conventional contact Tsk sensor and attachment.