Evaporation rates and vapor pressures of the even-numbered C8-C18 monocarboxylic acids

Temperature-dependent vapor pressures of the even-numbered alkanoic monoacids from C8-C18 were measured using temperature-programmed desorption (TPD). In TPD, the evaporation rates from the samples are directly measured and the vapor pressures are subsequently determined from the Hertz-Knudsen equation. Our measurements indicate that the vapor pressures of the solid even-numbered alkanoic acids decrease monotonically with increasing carbon number by more than 6 orders of magnitude going from C8 to C18. The enthalpies of sublimation increase monotonically with carbon number, from approximately 110 to 205 kJ/mol. The liquid-phase vapor pressure was measured for oleic acid, a C18 alkenoic acid. Comparison to the estimated liquid-phase vapor pressure for the corresponding C18 alkanoic acid indicates that the liquid-phase vapor pressures of these two compounds are identical. Our measured solid-phase vapor pressures for the C14 and larger alkanoic acids are lower than in previous studies. We attribute these differences to the influence of residual solvent molecules on the previous measurements, which cause the measured vapor pressures to be too large.     

Adipic and malonic acid aqueous solutions: surface tensions and saturation vapor pressures

The surface tension of adipic aqueous solutions was measured as a function of temperature (T=278-313 K) and adipic acid mole fraction (X=0.000-0.003) using the Wilhelmy plate method. A parametrization fitted to these data is presented. The evaporation rates of binary water-malonic and water-adipic acid droplets were measured with a TDMA technique at different temperatures (T=293-300 K) and relative humidities (58-80%), and the saturation vapor pressures of subcooled liquid malonic and adipic acids were derived from the data using a binary evaporation model. The temperature dependence of the vapor pressures was obtained as least-squares fits to the derived vapor pressures: ln(Psat,l) (Pa)=220.2389-22634.96/T (K)-26.66767 ln T (K) for malonic acid and ln(Psat,l) (Pa)=140.6704-18230.97/T (K)-15.48011 ln T (K) for adipic acid.     

Single aerosol particle studies

This paper surveys the research carried out on single aerosol particles in the micron and submicron size range with emphasis on the work performed by the authors. The principles and design of the electrodynamic and electrostatic balances are reviewed, and experimental data for evaporating droplets in a stagnant gas at various total pressures and various temperature are compared with theoretical results for Knudsen aerosol evaporation and are used to determine Lennard-Jones interaction parameters, diffusivities and vapor pressures for relatively nonvolatile compounds. The use of the electrodynamic balance or “picoblance” developed to study aerosol particles of the order of a piogram is illustrated for diffusion-controlled droplet evaporation measurements, and new data and an analysis for binary dorplet evaporation are presented.     

Measurement of vapor pressures and heats of sublimation of dicarboxylic acids using atmospheric solids analysis probe mass spectrometry

Vapor pressures of low volatility compounds are important parameters in several atmospheric processes, including the formation of new particles and the partitioning of compounds between the gas phase and particles. Understanding these processes is critical for elucidating the impacts of aerosols on climate, visibility, and human health. Dicarboxylic acids are an important class of compounds in the atmosphere for which reported vapor pressures often vary by more than an order of magnitude. In this study, atmospheric solids analysis probe mass spectrometry (ASAP-MS), a relatively new atmospheric pressure ionization technique, is applied for the first time to the measurement of vapor pressures and heats of sublimation of a series of dicarboxylic acids. Pyrene was also studied because its vapor pressures and heat of sublimation are relatively well-known. The heats of sublimation measured using ASAP-MS were in good agreement with published values. The vapor pressures, assuming an evaporation coefficient of unity, were typically within a factor of ～3 lower than published values made at similar temperatures for most of the acids. The underestimation may be due to diffusional constraints resulting from evaporation at atmospheric pressure. However, this study establishes that ASAP-MS is a promising new technique for such measurements.     

Combined experiments to measure low sublimation pressures and diffusion coefficients of organometallic compounds

Vapor pressures and sublimation pressures of organometallic (metalorganic) compounds are needed in several processes like chemical vapor deposition (CVD). Thermobalances at ambient pressures are often used to study the evaporation of such compounds. At least three strategies are found in the literature to evaluate the results using different theoretical approaches. In some of the frequently used approaches the diffusion out of a crucible is neglected. We present a simple theoretical approach which describes the interrelation between the observed mass transfer rate and the physical variables of typical TGA set-ups. It turns out that the mass transfer rate at a given total pressure and temperature is mainly a function of the diffusion coefficient and the vapor pressure of the sublimating substance. The vapor pressures may be determined from an independent measurement using the Knudsen cell and combined with the TGA to obtain the diffusion coefficients. Experiments have been performed with two well studied substances naphthalene and phenanthrene to check the present strategy. Further measurements were then performed for the metal organic CVD relevant compounds: ferrocene and Tris(2,2,6,6-tetramethyl-3,5-heptanedianato)cobalt III [Co(tmhd)₃].     

Evaporation of ethanol/water droplets: examining the temporal evolution of droplet size, composition and temperature

The evolving size, composition, and temperature of evaporating ethanol/water aerosol droplets 25-57 microm in radius are probed by cavity enhanced Raman scattering (CERS) and laser induced fluorescence. This represents the first study in which the evolving composition of volatile droplets has been probed with spatial selectivity on the millisecond time scale, providing a new strategy for exploring mass and heat transfer in aerosols. The Raman scattering intensity is shown to depend exponentially on species concentration due to the stimulated nature of the CERS technique, providing a sensitive measure of the concentration of the volatile ethanol component. The accuracy with which we can determine droplet size, composition, and temperature is discussed. We demonstrate that the CERS measurements of evolving size and composition of droplets falling in a train can be used to characterize, and thus avoid, droplet coagulation. By varying the surrounding gas pressure (7-77 kPa), we investigate the dependence of the rate of evaporation on the rate of gas diffusion, and behavior consistent with gas diffusion-limited evaporation is observed. We suggest that such measurements can allow the determination of the vapor pressures of components within the droplet and can allow the determination of activity coefficients of volatile species.     

CRTA for the thermoanalytical screening of volatile compounds

Quasi-equilibrium thermogravimetry (variant of CRTA) is utilized as a thermoanalytical screening method for volatile compounds, standard Q-derivatograph sample holders (platelike holder, open crucible, crucible with lid, and conical holder) were calibrated against the partial pressures of metal β-diketonate vapor (in sublimation and evaporation processes) in the range 0.0006–0.11 atm. The mathematical relationship between the vapor partial pressure, the holder construction, the vapor molecular mass, and the mutual diffusion coefficient of the gas was derived and considered. It is possible to obtain a roughp-T relationship for volatile compounds by using stabilized temperatures of sublimation (evaporation) processes in four pressure-calibrated sample holders.     

Determination of Thermodynamic Parameters from Evaporation of Binary Microdroplets of Volatile Constituents

An experimental technique based on a modified vibrating orifice aerosol generator has been employed to study unsteady evaporation of linear streams of highly monodisperse binary microdroplets of volatile constituents over short time periods (i.e., <1 ms), such that the droplet composition remains nearly constant. The droplet size and temperature (i.e., refractive index) have been determined with high temporal resolution from the resonances observed in the simultaneous elastic and Raman light scattering spectra obtained by varying the droplet size through modulation of droplet generation frequency. By using this technique we show that thermodynamic parameters of binary systems, such as activity coefficients as well as vapor pressures of the constituents as functions of temperature, can be determined. We have applied the procedure to study unsteady evaporation rates of pure ethanol and methanol droplets as well as binary droplets containing various ratios of ethanol and methanol. We have obtained vapor pressures of ethanol and methanol as functions of temperature as well as activity coefficients of ethanol and methanol as functions of composition, and the results show excellent agreements with the values reported in the literature. The technique presented in this paper is applicable to any binary system containing at least one volatile constituent. Copyright 2000 Academic Press.     

CALCULATION OF VAPOR PRESSURES FROM MODEL FRAGRANCE EMULSIONS DURING EVAPORATION

The vapor pressure data from previous publications of a model fragrance emulsion system consisting of water, an aromatic fragrance phenethyl alcohol, an aliphatic one limonene, and a nonionic surfactant Laureth 4, were used to calculate the variation in vapor pressures of both fragrances and water during free evaporation. The evaporation path in a three-dimensional four-component phase diagram was estimated from the vapor pressures.

The results showed as expected that the high note fragrance compound evaporates first followed by water and the low note one. Unexpectedly, it was found that vapor pressure of low note fragrance, phenethyl alcohol, is significantly increased during evaporation.     

Saturated vapor pressures and enthalpies of evaporation of esters of glycerol and lower carboxylic acids

Saturated vapor pressures and enthalpies of evaporation of trisubstituted esters of glycerol and carboxylic acids C₁–C₅ with normal and branched structure were determined by the transpiration method in the temperature range of 300–371 K. Dependences of enthalpies of evaporation on the number of carbon atoms in a molecule and on the retention indices are established. Prognostic possibilities of existing calculation schemes are analyzed for compounds with three carboxyl groups in a molecule.     

The effect of a polymeric additive on the evaporation of organic aerocolloidal droplets

 The evaporation of single triethyl phosphate (TEP) micro-droplets containing a high molecular weight polymer, poly(methyl methacrylate) (PMAA), was inves-tigated using an electrodynamic trap and light scattering measurements to explore the suppression of evaporation by the additive. Pure-component evaporation rates were measured to determine the vapor pressure over a range of temperatures, and the polymer was found to significantly decrease the evaporation rate. A numerical solution of the problem of simultaneous solvent evaporation and polymer diffusion within the droplet indicated a rapid build-up of PMMA at the surface of the drop, but vapor/liquid thermodynamic considerations alone do not account for the observed reduction in the evaporation rate for the droplets containing PMMA. After significant evaporation of TEP occurred, the ultra-low evaporation rate was measured using changes in the Raman spectra associated with morphology-dependent resonances. The evaporation in this regime appears to be controlled by the rate of solvent molecules diffusing through the polymer matrix. Received: 17 June 1997 Accepted: 24 October 1997     

Comparative study between a CMS membrane and a CMS adsorbent: Part II. Water vapor adsorption and surface chemistry

The adsorption/desorption equilibria of water vapor in a carbon molecular sieve (CMS) membrane and a commercial CMS adsorbent were determined, exhibiting S-shaped, type V isotherms. The fits of several models found in the literature to the experimental data were evaluated. The results obtained led to the development of a new model accounting for both adsorption and desorption and essentially based on the work of Lagorsse et al. (2005) [15]. Furthermore, the adsorption kinetics was also assessed for both materials and well described by a linear driving force model. The existence of hydrophilic groups responsible for water vapor adsorption in such carbonaceous materials has been related to the surface chemistry by means of X-ray microanalysis and by thermogravimetry. It was concluded from X-ray microanalyses that the carbon membrane presents a lower C/O ratio and is thus more sensitive towards water vapor exposure, as evidenced by the measured water adsorption at lower relative pressures. It was also observed that the diffusion rates are higher for the CMS membrane than for the CMS adsorbent.     

Calibration system and analytical considerations for quantitative sesquiterpene measurements in air

Sesquiterpenes (C15H24, SQT) are semi-volatile organic compounds emitted from vegetation and are of interest for air quality considerations because of their suspected contribution to the formation of secondary aerosol. This article investigates the application of a capillary diffusion method for the generation of standard atmospheres of 16 SQT and four other related semi-volatile compounds. This instrument subsequently has been used in the testing of analytical materials, protocols and calibration of air sampling methods. SQT DB-1 retention indices, vapor pressures at 25 and 75 degrees C, and diffusion coefficients were determined. A quantitative, on-line GC method yielded improved results (median relative standard deviation of 5.0-6.1%) for the diffusion rate determination in comparison to a gravimetric approach (median relative standard deviation 18%). The GC method also allowed identifying errors in the gravimetric method stemming from residual solvent evaporation, impurities, and chemical analyte losses. Stainless steel, glass, nickel and PTFE tubing that were tested for transfer lines and a sampling loop had to be kept at temperatures in excess of approximately 110 degrees C in order to prevent significant analytical errors from the stickiness of SQT to these materials. In addition to SQT analysis, results from this research provide general guidelines for gas-phase analysis of related compounds in the C14-C16 volatility range.     

Thermodynamic study on the sublimation of diphenyl and triphenyl substituted acetic and propanoic acids

Knudsen mass-loss effusion technique was used for measuring the vapor pressures at different temperatures of the following crystalline compounds: diphenylacetic acid, between 357.27 and 379.08 K; triphenylacetic acid, between 418.98 and 436.97 K; 2,2-diphenylpropanoic acid, between 366.08 and 386.00 K; 3,3-diphenylpropanoic acid, between 366.09 and 386.03 K; 3,3,3-triphenylpropanoic acid, between 402.17 and 420.10 K. From the temperature dependence of the vapor pressure of each crystalline compound, the standard (p ⁰ = 10⁵ Pa) molar enthalpies and Gibbs energies of sublimation, at T = 298.15 K, were derived. The measured thermodynamic properties are compared with literature results for phenylacetic and phenylpropanoic acids and correlations for estimation of the vapor pressures from the enthalpy of sublimation and the temperature of fusion of these and other compounds are presented.     

A comparative study of the mass and heat transfer dynamics of evaporating ethanol/water, methanol/water, and 1-propanol/water aerosol droplets

The mass and heat transfer dynamics of evaporating multicomponent alcohol/water droplets have been probed experimentally by examining changes in the near surface droplet composition and average droplet temperature using cavity-enhanced Raman scattering (CERS) and laser-induced fluorescence (LIF). The CERS technique provides a sensitive measure of the concentration of the volatile alcohol component in the outer shell of the droplet, due to the exponential relationship between CERS intensity and species concentration. Such volatile droplets, which are probed on a millisecond time scale, evaporate nonisothermally, resulting in both temperature and concentration gradients, as confirmed by comparisons between experimental measurements and quasi-steady state model calculations. An excellent agreement between the experimental evaporation trends and quasi-steady state model predictions is observed. An unexpectedly slow evaporation rate is observed for the evaporation of 1-propanol from a multicomponent droplet when compared to the model; possible explanations for this observation are discussed. In addition, the propagation depth of the CERS signal, and, therefore, the region of the droplet from which compositional measurements are made, can be estimated. Such measurements, when considered in conjunction with quasi-steady state theory, can allow droplet temperature gradients to be measured and vapor pressures and activity coefficients of components within the droplet to be determined.     

Improved quasi-unary nucleation model for binary H2SO4-H2O homogeneous nucleation

Aerosol nucleation events have been observed at a variety of locations worldwide, and may have significant climatic and health implications. Binary homogeneous nucleation (BHN) of H2SO4 and H2O is the foundation of recently proposed nucleation mechanisms involving additional species such as ammonia, ions, and organic compounds, and it may dominate atmospheric nucleation under certain conditions. We have shown in previous work that H2SO4-H2O BHN can be treated as a quasi-unary nucleation (QUN) process involving H2SO4 in equilibrium with H2O vapor, and we have developed a self-consistent kinetic model for H2SO4-H2O nucleation. Here, the QUN approach is improved, and an analytical expression yielding H2SO4-H2O QUN rates is derived. Two independent measurements related to monomer hydration are used to constrain the equilibrium constants for this process, which reduces a major source of uncertainty. It is also shown that the capillarity approximation may lead to a large error in the calculated Gibbs free energy change for the evaporation of H2SO4 molecules from small H2SO4-H2O clusters, which affects the accuracy of predicted BHN nucleation rates. The improved QUN model-taking into account the recently measured energetics of small clusters-is thermodynamically more robust. Moreover, predicted QUN nucleation rates are in better agreement with available experimental data than rates calculated using classical H2SO4-H2O BHN theory.     

Detection of Polycyclic Aromatic Compounds at Jungfraujoch High-Alpine Research Station using Two-Step Laser Mass Spectrometry

Jungfraujoch (JFJ) is considered to be a location for background free troposphere measurements. Aerosol particles collected at JFJ are analyzed to characterize adsorbed polycyclic aromatic compounds (PACs). Aerosol samples were collected from March 21 to 25, 2000 and from August 1 to 9, 2000. Samples were then analyzed by two-step laser mass spectrometry (L2MS). The mass spectra show higher relative concentrations of PACs present on samples collected during the August sampling period versus the March sampling period. L2MS data from March indicates good correlation with black carbon aerosol data measured in parallel. This suggests that long range transport of aerosol from combustion is responsible for the majority of PACs observed. Data from August unexpectedly showed markers indicative of environmental tobacco smoke (ETS). The contribution to total aerosol may be small, but the relative signal of ETS markers correlates well with the number of visitors coming daily to JFJ, pointing to a local source of ETS.     

Polyamides with pendant 1,3,4-oxadiazole and pyridine moieties

A novel aromatic diamine,2-（5-（3,5-diaminophenyl）-l,3,4-oxadiazole-2-yl）pyridine（POBD）,containing a pyridine ring and a 1,3,4-oxadiazole moiety,was synthesized.It was used in a polycondensation with various aromatic and aliphatic diacid chlorides to generate a series of new aromatic polyamides with pendant 1,3,4-oxadiazole groups.The prepared polyamides were characterized by IR,elemental analysis and through the synthesis of model compounds.Thermophysical properties of the synthesized polyamides have been studied by DSC,TGA and inherent viscosity measurements. Relatively high inherent viscosity values（0.76-1.62 dL/g,in 0.125%H₂SO₄ at 25℃） were observed for these compounds. Number average molecular weight（M_n） of the polymers was measured by vapor phase osmometry（VPO）.The introduction of bulky side chains in the structure of aromatic polyamides led to increased solubility of these polymers in common polar and aprotic solvents,such as DMF,DMSO,NMP and DMAc,which allowed thin films to be cast from polymer solutions. The highest molecular weight（M_n = 51190） was observed for polymer（DC）,which was prepared from pyridine-2,6-dichlorocarbonyl.     

Features of sulfur hexafluoride adsorption on carbon adsorbents

The isotherms describing excess adsorption of SF₆ and N₆I₆ on carbon adsorbents with different pore structures were measured at pressures of 0.001—2.4 and 0.0001—0.1 MPa, respectively, and temperatures of 298—408 E. A linear dependence of Henry"s constant on temperature in the lnK—10³/O coordinates was found for all the samples. The specific surface areas of the samples determined by the BET method from the SF₆ adsorption are lower than those derived from benzene adsorption. The most pronounced difference was found for the grafitized carbon black. When SF₆ was adsorbed on supermicroporous carbon AC-71 and on microporous carbons PAC and CMS, a hysteresis was found, which, unlike that on mesoporous carbon adsorbents, is observed in the initial region of the equilibrium pressures.     

Vapor—liquid equilibrium studies for the carbon dioxide—methanol system

Experimental vapor—liquid equilibrium measurements of carbon dioxide and methanol have been conducted from 230 K (−43.15°C) to 330 K (56.85°C) at pressures to the very vicinity of the critical states. The consistency of the data sets are examined and compared to literature values.Unlike the methane—methanol system, which exhibits two liquid phases at low temperatures, the carbon dioxide—methanol system exhibits complete liquid phase miscibility. Accordingly, the effects of critical behavior on the vapor liquid equilibria behavior begin to manifest themselves at much lower pressures.