Gas Phase Mixture Research Articles

Sulfuric acid-dimethylamine particle formation enhanced by functional organic acids: an integrated experimental and theoretical study.

Atmospheric new particle formation (NPF), which has been observed globally in clean and polluted environments, is an important source of boundary-layer aerosol particles and cloud condensation nuclei, but the fundamental mechanisms leading to multi-component aerosol formation have not been well understood. Here, we use experiments and quantum chemical calculations to better understand the involvement of carboxylic acids in initial NPF from gas phase mixtures of carboxylic acid, sulfuric acid (SA), dimethylamine, and water. A turbulent flow tube coupled to an ultrafine condensation particle counter with particle size magnifier has been set up to measure NPF. Experimental results show that pyruvic acid (PA), succinic acid (SUA), and malic acid (MA) can enhance sulfuric acid-dimethylamine nucleation in the order PA < SUA < MA with a greater enhancement observed at lower SA concentrations. Computational results indicate that the carboxylic and hydroxyl groups are related to the enhancement. This experiment-theory study shows the formation of multi-component aerosol particles and the role of the organic functional group, which may aid in understanding the role of organics in aerosol nucleation and growth in polluted areas, and help to choose organic molecules of specific structures for simulation.

Lee-Huang-Yang effects in the ultracold mixture of Na23 and Rb87 with attractive interspecies interactions

The beyond-mean-field Lee-Huang-Yang (LHY) correction is ubiquitous in dilute ultracold quantum gases. However, its effects are often elusive due to the typically much larger influence of the mean-field (MF) energy. In this work, we study an ultracold mixture of $^{23}\mathrm{Na}$ and $^{87}\mathrm{Rb}$ with tunable attractive interspecies interactions. The LHY effects manifest in the formation of self-bound quantum liquid droplets and the expansion dynamics of the gas-phase sample. A liquid-to-gas-phase diagram is obtained by measuring the critical atom numbers below which the self-bound behavior disappears. In stark contrast to trapped gas-phase condensates, the gas-phase mixture formed following the liquid-to-gas-phase transition shows an anomalous expansion featuring a larger release energy for increasing MF attractions.

Evaluation of Osmotic Virial Coefficients via Restricted Gibbs Ensemble Simulations, with Support from Gas-Phase Mixture Coefficients.

We present a method for computing osmotic virial coefficients in explicit solvent via simulation in a restricted Gibbs ensemble. Two equivalent phases are simulated at once, each in a separate box at constant volume and temperature and each in equilibrium with a solvent reservoir. For osmotic coefficient , a total of N solutes are individually exchanged back and forth between the boxes, and the average distribution of solute numbers between the boxes provides the key information needed to compute . Separately, expressions are developed for as a series in solvent reservoir density ρ1, with the coefficients of the series expressed in terms of the usual gas-phase mixture coefficients Bij. Normally, the Bij are defined for an infinite volume, but we suggest that the observed dependence of Bij on system size L can be used to estimate L dependence of the , allowing them to be computed accurately at L → ∞ while simulating much smaller system sizes than otherwise possible. The methods for N = 2 and 3 are demonstrated for two-component mixtures of size-asymmetric additive hard spheres. The proposed methods are demonstrated to have greater precision than established techniques, for a given amount of computational effort. The ρ1 series for when applied by itself is (for this noncondensing model) found to be the most efficient in computing accurate osmotic coefficients for the solvent densities considered here.

Experimental investigation of the effect of temperature on ignition of modified kerosene

Kerosene based hydrocarbon fuels are preferred candidates for the source of energy due to its stable properties. Based on the requirement of the combustor and the growing concern over pollutant, kerosene based fuels are modified. The fuel under investigation is a modified form of kerosene with ultra-low sulphur content. The effect of temperature on modified kerosene is studied for viscosity, surface tension, specific heat, density and ignition delay. The time delay for ignition of gas-phase mixtures of modified kerosene/oxygen have been measured using a shock tube facility. The experiments are conducted in the temperature range of 1200–1877 K, pressure range of 4–12 atm and equivalence ratio of Ø = 1.5, 1 and 0.5. The ignition delay time measurements were carried out using piezoelectric pressure transducers, which records the pressure rise due to ignition and simultaneously recording the light emission during the process of ignition using a photodiode. The ignition delay is represented as τign = 0.168841 × P−1.49 × Ø0.72 × e(14310/T)

Verification of three-dimensional mathematical modeling when calculating the combustion of hydrocarbon fuel in an experimental cylindrical furnace enriched with a plasma fuel system

In this work, the operation of the boiler in traditional and plasma-activated conditions is investigated. To test the possibility of modeling the Cinar ICE program with an understanding of the physical mechanism of the processes of electrothermochemical fuel preparation (ETCF) and combustion, a study of coal combustion in an experimental furnace with a thermal power of 3 MW equipped with a plasma fuel system was carried out. To study the combustion process of an air mixture that had undergone preliminary plasma preparation for combustion, one-dimensional plasma-coal and three-dimensional computer programs Cinar ICE were used, which study in detail the mechanism of the kinetics of thermochemical exchange in a two-phase flow, where the plasma fuel source is located, and the exact geometry of the furnace, and the kinetics of the process сombustion of coal particles. As a result of calculations, the distribution of temperature, velocity of gas and particles in the process of ETCPT, the concentration of gas-phase mixtures, the concentration of carbon and the degree of gas contamination in the remainder of alloyed coal were determined. It was found that the plasma activation of combustion affects the thermal characteristics of the Torch, the mechanical non-combustible fuel residue and the concentration of nitrogen oxide at the outlet from the furnace. It has been proven that when simulating coal combustion, it is possible to achieve an effective description of the process using the Cinar ICE program.

A new high-pressure aerosol shock tube for the study of liquid fuels with low vapor pressures

A new shock-tube facility for studying gas-phase and condensed-phase mixtures has been developed for the investigation of various hydrocarbon species at the Qatar campus of Texas A&M University. At present, the facility is intended for studying combustion behaviors of long-chain hydrocarbon molecules and mixtures thereof under realistic engine conditions. Equipped with an aerosol generation and entrainment apparatus, the facility also possesses an enlarged driver section and double-diaphragm interface between the driver and driven sections. The driver section diameter is 19.37 cm with a configurable length of 1 m-6 m. Additionally, the stainless-steel driven section has an inner surface with a mirror finish and internal diameter of 15.24 cm. The driven section is also configurable in length up to approximately 5.2 m. As with most modern shock tubes, this shock tube is equipped for use with current methods of shock velocity detection, optical diagnostics, and other diagnostic techniques. In addition to the study of aerosolized liquids (fuels and non-fuels) related to combustion chemistry, reaction kinetics, evaporation studies, and particle-fluid interactions, among others, the facility is capable of investigating traditional gas-phase mixtures like those previously undertaken in a similar facility in the Petersen Group Laboratory at Texas A&M University. The operating limits of the title facility include temperatures and pressures up to 4000 K and 100 atm, respectively. The design and characterization of a novel aerosol introduction method is also presented, which yielded measured aerosol loading uniformities of 92%-97%. Finally, ignition delay time measurements of stoichiometric mixtures of decane in air are presented, which show excellent agreement with those recently recorded in heated shock tubes.

Non-catalytic gas phase NO oxidation in the presence of decane

Experiments without a catalyst revealed that NO was oxidized in a diesel exhaust gas phase mixture due to the presence of n-C10H22 (decane). This reaction was observed to occur following the low temperature oxidation catalyst test protocol (LTC-D) defined by U.S. DRIVE. The purpose of LTC-D conditions is to simulate an aftertreatment diesel combustion gas mixture in order to test candidate catalyst materials. 100% NO conversion was observed, without a catalyst, after beginning to react at 330 °C accompanied by consumption of decane. After experiments that isolated hydrocarbons, ethylene was also observed to facilitate NO oxidation to a lesser degree (>470 °C). Density functional theory (DFT) calculations were conducted to investigate thermodynamically-possible initiating elementary steps during n-C10H22 consumption and NO oxidation. Two feasible intermediate radicals to oxidize NO to NO2 are ·C10H21O2 and ·HO2.

Thermophysical, Acoustical, Spectral and DFT Study of Intermolecular Interactions of Terpinolene with Cresols

Densities and speed of sound were measured experimentally for binary mixtures of terpinolene with cresols (o-cresol, m-cresol, p-cresol) at three different temperatures 303.15, 308.15 and 313.15K at atmospheric pressure. From primary physical properties, some secondary properties like molar volume , excess molar volume , partial molar volume , excess partial molar volume , apparent molar volume , deviation in speed of sound , isentropic compressibility , deviation in isentropic compressibility , acoustical impedance , deviation in acoustical impedances , intermolecular free length , partial molar isentropic compression , excess partial molar isentropic compression and apparent molar isentropic compression were calculated. Infinite dilution apparent molar volume , infinite dilution apparent molar isentropic compression , empirical parameters , and , of the Redlich-Rosenberg-Mayer equation with the limiting apparent molar expansibility were also calculated. Some theoretical speed of sound calculating relations such as Nomoto relation , Ideal mixture relation , Junji relation and Free length theory relation were also calculated with their standard deviation . All the calculated values of excess/deviation properties were fitted with the fourth order Redlich-Kister polynomial equation and their standard deviation values were also calculated. FT-IR spectral analysis of binary mixtures at 4:1, 1:1 and 1:4 composition ratios were carried out at 298.15K. Computational calculations such as optimization of pure and binary mixtures in gas phase, bond length, Mulliken charges, theoretical vibrational frequencies and NBO calculations on basis of the DFT (Density Function Theory) were also carried out. The results were discussed in term of presence of intermolecular interactions, types, strength and behavior with change of temperatures and cresol components in binary mixtures.

Satellites of the resonance transitions of alkali atoms in mixtures with CF4

The absorption and luminescence excitation spectra of gas phase mixtures of alkali metals atoms A (A = K, Rb, Cs) with carbon tetrafluoride molecules CF4 are studied in the region of transitions from the ground state A(2S1/2) to the lowest resonance states A(2P1/2, 3/2). It is shown that these transitions have intense satellites corresponding to the simultaneous vibrational excitation of the carbon tetrafluoride molecule, A(2S1/2) + CF4(v3=0) + hv → A(2P1/2, 3/2) + CF4(v3=1), where v3 is the IR active mode of CF4 with a vibrational quantum energy of 1281 cm–1. The satellites are relatively narrow bands (FWHM ~ 30 cm–1) slightly (< 10 cm–1) shifted to the red from the energies corresponding to the asymptotes A(2PJ) + CF4(v3=1), J=1/2, 3/2. The spectral width and position of the satellites indicate that these transitions occur at relatively large atom-molecule distances. In contrast to the majority of the studied before pair excitation processes in the gas phase, the intensity borrowing mechanism responsible for the observed satellite bands cannot be explained by the dipole-dipole interaction. Possible alternative mechanisms are discussed. It is also established that mixtures with CF4 are chemically stable including at elevated temperatures up to at least 200°C and their optical excitation results in resonance luminescence of alkali atoms. As compared to Ar, collisions with CF4 provides a higher rate of the population transfer between the A(2P1/2) and A(2P3/2) states. These results indicate that CF4 may be used as a component of the active medium of diode pumped alkali lasers.

Macroporous silicon coated with M/TiO2 (M=Au,Pt) as a highly efficient photoreactor for hydrogen production

Macroporous silicon disks containing ordered channels of 2 μm side and 0.2 mm length (9 × 106 channels cm−2) have been functionalized with a thin layer of Au/TiO2 and Pt/TiO2 photocatalysts and tested in the photoproduction of hydrogen using UV light from water-ethanol mixtures in gas phase. An outstanding hydrogen production rate of 212 μmol h−1 cm−3reactor is demonstrated, which is three orders of magnitude higher than those achieved in conventional photoreactors. According to the simulation results, the fabulous hydrogen production rates obtained with the macroporous silicon photocatalytic structures are ascribed to an extraordinary high specific surface area per volume unit and to an enhanced light exploitation. This new microphotoreactor concept could boost the production of solar hydrogen for on-site and portable applications.

Amine-functionalized microporous covalent organic polymers for adsorptive removal of a gaseous aliphatic aldehyde mixture

To pursue effective removal of gaseous volatile organic compounds (VOCs), adsorptive removal of a six-component aliphatic aldehyde gas phase mixture was investigated using two amine-functionalized microporous covalent organic polymers (COPs).

Laminar Flame Speed Experiments of Alternative Liquid Fuels

Abstract New laminar flame speed experiments have been collected for two alternative liquid fuels. Understanding the combustion characteristics of these synthetic fuels is an important step in developing new chemical kinetics mechanisms that can be applied to real fuels. Included in this study are two synthetic Jet fuels: Syntroleum S-8 and Shell GTL. The precise composition of these fuels is known to change from sample to sample. Since these are low-vapor pressure fuels, there are additional uncertainties in their introduction into gas-phase mixtures, leading to uncertainty in the mixture equivalence ratio. An in-situ laser absorption technique was implemented to verify the procedure for filling the vessel and to minimize and quantify the uncertainty in the experimental equivalence ratio. The diagnostic utilized a 3.39-μm HeNe laser in conjunction with Beer's law. The resulting spherically expanding, laminar flame experiments were conducted over a range of equivalence ratios from φ = 0.7 to φ = 1.5 at initial conditions of 1 atm and 403 K in the high-temperature, high-pressure (HTHP) constant-volume vessel at Texas A&amp;M University. The experimental results show that both fuels have similar flame speeds with a peak value just under 60 cm/s. However, it is shown that when comparing the results from different datasets for these real fuels, equivalence ratio may not be the best parameter to use. Fuel mole fraction may be a better parameter to use as it is independent of the average fuel molecule or fuel surrogate used to calculate equivalence ratio in these real fuel/air mixtures.

Enantiospecific equilibrium adsorption and chemistry of d-/l-proline mixtures on chiral and achiral Cu surfaces.

A fundamental understanding of the enantiospecific interactions between chiral adsorbates and understanding of their interactions with chiral surfaces is key to unlocking the origins of enantiospecific surface chemistry. Herein, the adsorption and decomposition of the amino acid proline (Pro) have been studied on the achiral Cu(110) and Cu(111) surfaces and on the chiral Cu(643)R&S surfaces. Isotopically labelled 1-13 C-l-Pro has been used to probe the Pro decomposition mechanism and to allow mass spectrometric discrimination of d-Pro and 1-13 C-l-Pro when adsorbed as mixtures. On the Cu(111) surface, X-ray photoelectron spectroscopy reveals that Pro adsorbs as an anionic species in the monolayer. On the chiral Cu(643)R&S surface, adsorbed Pro enantiomers decompose with non-enantiospecific kinetics. However, the decomposition kinetics were found to be different on the terraces versus the kinked steps. Exposure of the chiral Cu(643)R&S surfaces to a racemic gas phase mixture of d-Pro and 1-13 C-l-Pro resulted in the adsorption of a racemic mixture; i.e., adsorption is not enantiospecific. However, exposure to non-racemic mixtures of d-Pro and 1-13 C-l-Pro resulted in amplification of enantiomeric excess on the surface, indicative of homochiral aggregation of adsorbed Pro. During co-adsorption, this amplification is observed even at very low coverages, quite distinct from the behavior of other amino acids, which begin to exhibit homochiral aggregation only after reaching monolayer coverages. The equilibrium adsorption of d-Pro and 1-13 C-l-Pro mixtures on achiral Cu(110) did not display any aggregation, consistent with prior scanning tunneling microscopy (STM) observations of dl-Pro/Cu(110). This demonstrates convergence between findings from equilibrium adsorption methods and STM experiments and corroborates formation of a 2D random solid solution.

Molecular insights into organic particulate formation

Carboxylic acids have been detected in particles collected in various regions of the world. Here, we use experiments and Born–Oppenheimer molecular dynamics simulations to better understand the mechanism of particle formation from gas phase mixtures of formic acid (HCOOH), (CH3)3N, and water vapor. A flow reaction cell coupled to two scanning mobility particle sizers has been used to measure particle size, absolute number of particles and kinetics of particle formation. Experimental results show that the addition of (CH3)3N to a mixture of HCOOH and water vapor results in a dramatic increase in particle formation. Simulation results indicate that the ion-pair formation on the water surface involves direct proton transfer between HCOOH and (CH3)3N. The HCOO—··(CH3)3NH+ ion-pair remains at the air–water interface due to hydrogen bonding and the interfacial hydration shell. This experiment-theory study shows the formation of aerosol particles from the organic acid-amine interactions, which may aid in understanding the role of organics in haze and cloud droplet formation and nanoparticle growth.

Composition Determination of Low-Pressure Gas-Phase Mixtures by 1H NMR Spectroscopy.

1H NMR spectroscopy was used to analyze gas-phase mixtures of methane and propane at pressures near 0.1 MPa. The mixtures were prepared gravimetrically and had low uncertainty in their composition. The primary mixture used for this work had a methane mole fraction of xmethane,grav = (0.506875 ± 0.00019) and a propane mole fraction of xpropane,grav = (0.493125 ± 0.00019). NMR samples were prepared in two types of commercially available sample tubes that seal with a PTFE piston. Sample pressures ranged from 0.02 to 0.5 MPa. An analysis of measurement uncertainty for the NMR method resulted in combined standard uncertainties that decreased from 0.0082 x to 0.0010 x, as the pressure increased from 0.02 to 0.5 MPa. The larger uncertainties at lower pressures were primarily caused by uncertainties associated with phasing and baseline correction. A key difficulty in working with gas-phase samples, especially at lower pressures, is that the spectral peaks are inherently broad. Consequently, peak overlap was problematic, and it was not always possible to integrate a high percentage of a peak's intensity. However, with corrections to the integrated areas, based on the assumption of ideal Lorentzian peak shapes, excellent agreement between the NMR analyses and the gravimetric composition was observed across the entire pressure range. These experiments demonstrate the potential of 1H NMR for quantitative composition determinations of low-pressure gas-phase mixtures.

Multiplexed characterization of complex gas-phase mixtures combining chirped-pulse Fourier transform microwave spectroscopy and VUV photoionization time-of-flight mass spectrometry.

We report details of the design and operation of a single apparatus that combines Chirped-Pulse Fourier Transform Microwave (CP-FTMW) spectroscopy with vacuum ultraviolet (VUV) photoionization Time-of-Flight Mass Spectrometry (TOFMS). The supersonic expansion used for cooling samples is interrogated first by passing through the region between two microwave horns capable of broadband excitation and detection in the 2-18 GHz frequency region of the microwave. After passing through this region, the expansion is skimmed to form a molecular beam, before being probed with 118 nm (10.5 eV) single-photon VUV photoionization in a linear time-of-flight mass spectrometer. The two detection schemes are powerfully complementary to one another. CP-FTMW detects all components with significant permanent dipole moments. Rotational transitions provide high-resolution structural data. VUV TOFMS provides a gentle and general method for ionizing all components of a gas phase mixture with ionization thresholds below 10.5 eV, providing their molecular formulae. The advantages, complementarity, and limitations of the combined methods are illustrated through results on two gas-phase mixtures made up of (i) three furanic compounds, two of which are structural isomers of one another, and (ii) the effluent from a flash pyrolysis source with o-guaiacol as the precursor.

Calibration of complex mixtures in one sweep

The calibration of extremely complex humid gas-phase mixtures – often required in ion mobility spectrometry applications – is challenging, even when high-performance calibration gas generators such as HovaCAL® are applied. Here, we describe an approach to develop and apply mixtures of VOCs in one channel of such a calibration gas generator for a complex calibration in one sweep. As an example, a mixture of so-called “Signs of Life” – compounds available in the exhaled breath and/or in the sweat of everybody was used. The procedure of developing the appropriate mixture and the results of a successful calibration of a GC-ion mobility spectrometer are presented.

Data interpretation in GC-ion mobility spectrometry: Pecunia non Olet?

The analysis of multi-component gas-phase mixtures by ion mobility spectrometry with gas-chromatographic pre-separation obtains complex data. In particular, numerous compound specific signals make data interpretation challenging. Here we describe the procedure of data treatment and processing to facilitate the interpretation of such data. In detail, after data pre-processing (smoothing, baseline correction, alignment of ion mobility and retention time) and after specifying threshold values for each one of the detected signals to reduce information from signal intensities down to only presence or absence of the signals, a kind of barcode for each sample will remain. Using this “barcode” as sample description, it is possible to differentiate between different samples immediately after data acquisition. We exemplarily applied this approach for the differentiation of various banknotes of different values and from different currencies as well as of real from counterfeit money successfully.

Fast and Simple Microwave Synthesis of TiO2/Au Nanoparticles for Gas-Phase Photocatalytic Hydrogen Generation.

The fabrication of small anatase titanium dioxide (TiO2) nanoparticles (NPs) attached to larger anisotropic gold (Au) morphologies by a very fast and simple two-step microwave-assisted synthesis is presented. The TiO2/Au NPs are synthesized using polyvinylpyrrolidone (PVP) as reducing, capping and stabilizing agent through a polyol approach. To optimize the contact between the titania and the gold and facilitate electron transfer, the PVP is removed by calcination at mild temperatures. The nanocatalysts activity is then evaluated in the photocatalytic production of hydrogen from water/ethanol mixtures in gas-phase at ambient temperature. A maximum value of 5.3 mmol·h−1 (7.4 mmol·h−1) of hydrogen is recorded for the system with larger gold particles at an optimum calcination temperature of 450°C. Herein we demonstrate that TiO2-based photocatalysts with high Au loading and large Au particle size (≈50 nm) NPs have photocatalytic activity.

Naphtha vs. dieseline – The effect of fuel properties on combustion homogeneity in transition from CI combustion towards HCCI

The scope of this research study pertains to compare the combustion and emission behavior between naphtha and dieseline at different combustion modes. In this study, US dieseline (50% US diesel + 50% RON 91 gasoline) and EU dieseline (45% EU diesel + 55% RON 97 gasoline) with derived cetane number (DCN) of 36 are selected for experimentation in an optical engine. Besides naphtha and dieseline, PRF60 is also tested as a surrogate fuel for naphtha. For the reported fuel with same RON = 60, the effect of physical properties on combustion homogeneity when moving from homogenized charge compression ignition (HCCI) to compression ignition (CI) combustion is studied.The combustion phasing of naphtha at an intake air temperature of 95 °C is taken as the baseline data. The engine experimental results show that higher and lower intake air temperature is required for dieseline mixtures to have same combustion phasing as that of naphtha at HCCI and CI conditions due to the difference in the physical properties. Especially at HCCI mode, due to wider distillation range of dieseline, the evaporation of the fuel is affected so that the gas phase mixture becomes too lean to auto-ignite. However, at partially premixed combustion (PPC) conditions, all test fuels required almost same intake air temperature to match up with the combustion phasing of baseline naphtha. From the rate of heat release and combustion images, it was found that naphtha and PRF60 showed improved premixed combustion when compared dieseline mixtures. The stratification analysis shows that combustion is more stratified for dieseline whereas it is premixed for naphtha and PRF60. The level of stratification linked with soot emission showed that soot concentration is higher at stratified CI combustion whereas near zero soot emissions were noted at PPC mode.