Reversed-flow Gas Chromatography Research Articles

Determination of Sulfur Dioxide Diffusion Coefficients in Hydrogen, Helium, and Nitrogen by Reversed-Flow Inverse Gas Chromatography

Diffusion coefficients of sulfur dioxide in hydrogen, helium, and nitrogen were determined by reversed-flow gas chromatography. Experiments were performed at temperatures ranging from 323.3 to 573.3 K and reduced at 101.3 kPa. The precision of the method is 96.6%, while its accuracy is 95.5%. Comparison with values predicted by Fuller–Schettler–Giddings and Huang equations indicates small deviations: the Chen–Otmer equation is successful only for the SO2–N2 system. The temperature exponents of SO2 diffusion are as follows: 1.77, 1.71, and 1.75 in H2, He, and N2, respectively. Comparisons with available experimental values for the SO2–H2 and SO2–N2 systems showed small average deviations: 5.7 and 1.3%, respectively.

Extending the study of mass transport across the gas-liquid interface by reversed-flow gas chromatography

The transfer of dichlorodifluoromethane to water was utilized as model system to provide better insight on the determination of mass transport parameters across the gas-liquid interface. Weak signals by reversed-flow gas chromatography were recorded at various temperatures, from 320.7 to 344.3 K, by digitizing and smoothing the output of the flame ionization detector. A flexible uncertainty analysis distinguished the main sources of error in the determined parameters, suggesting improvements on the utilized experimental setup. Liquid diffusivities decreased with rising temperature (4.39 to 1.01 × 10−10 m2 s-1), approaching literature values at lower temperatures. The estimated liquid film thicknesses similarly decreased (1.8 to 1.0 × 10-4 m) and were one order of magnitude larger than previous findings, due to the larger extent of evaporation permitted by the current experimental setup. A mass transfer coefficient was estimated, corresponding to the endothermic contribution of the reverse (liquid-to-gas) process, whose activation energy (43.4 ± 2.8 kJ mol-1) matched the vaporization enthalpy of water in the studied temperature range. Successful comparisons were made with literature distribution coefficients and Henry’s law constants. The dissolution of CFC-12 in water was found to be exothermic, slightly spontaneous at lower temperatures and approaching equilibrium at higher ones (indicated by the small negative molar Gibbs free energy values), with negative entropy change values [average: –(190.7 ± 6.9) J K-1 mol-1], as expected for a process of increased order.

Variation of linear alcohols’ activity coefficients, referred to aqueous solutions of methanol, ethanol and 1-propanol, in the presence of various types of surfactants, studied by reversed – Flow Gas Chromatography

The Reversed – Flow Gas Chromatography (R.F.G.C.) technique, a version of Inverse Gas Chromatography, was used to study the influence of the number of carbon atoms on the activity coefficients of the three linear alcohols methanol, ethanol and 1–propanol in their mixtures with water, in the presence of the surfactants CTAB (cationic), SDS (anionic) and TRITON X – 100 (non – ionic). The found activity coefficients, increase with increasing the alcohols' number of carbon atoms at constant temperature and pressure, as well as at constant alcohol's and surfactant's concentration and decrease with increasing the alcohol's molar fraction (at constant surfactant's concentration), as well as with increasing the number of the surfactant's films (at constant alcohol's concentration). The values of activity coefficients found for the three used alcohols, in the absence of surfactants, are in good agreement with those calculated theoretically or found in the literature. The precision of the Reversed – Flow Gas Chromatography for measuring activity coefficients of alcohols is approximately high (94.12% for methanol, 99.26% for ethanol and 94.35% for 1–propanol), showing that R.F.G.C. is a precise method not only for measuring activity coefficients of alcohols, but also for studying the influence of various parameters (molecular formula of linear alcohol, type of surfactant, as well as alcohol's and surfactant's concentration) on the measured activity coefficients.

Optimization of a microcontroller for the simultaneous logging of temperature and reversed-flow inverse gas chromatography measurements

ABSTRACTThe utilization of a microcontroller board, optimized for the simultaneous data logging of chromatographic information, the oven temperature, and remote transfer to a personal computer, is investigated, with the goal to extend the capabilities of a gas chromatograph (Shimadzu GC-14A) which does not include a built-in data logging module. An initial comparison of the chromatographic peaks obtained from solute injections, collected both by a dedicated analog-to-digital expansion card and the microcontroller board, demonstrated the latter’s ability to perform accurate analog signal digitization. Afterward, the evaporation of three organic liquids (methanol, acetone, and n-pentane) was studied by reversed-flow inverse gas chromatography. From the temperature variation of the experimentally determined rates, the respective thermodynamic functions of enthalpy and entropy changes of acetone and methanol evaporation were determined. The small deviations from the theoretical values indicate the reliability of the proposed methodology. More importantly, it was made apparent that by utilizing automatic data logging instead of the carrier gas flow reversal procedure, the monitoring of rapid physicochemical phenomena was performed with better accuracy, while the duration of the experiments was decreased with the reduced consumption of gas chromatographic consumables.

Study of the influence of surfactants on the activity coefficients and mass transfer coefficients of methanol in aqueous mixtures by reversed-flow gas chromatography

This work focuses on the influences of surfactants on the activity coefficients, γ, of methanol in binary mixtures with water, as well as on the mass transfer coefficients, kc, for the evaporation of methanol, which is a ubiquitous component in the troposphere, from mixtures of methanol with water at various surfactant’s and methanol’s concentrations.The technique used is the Reversed-Flow Gas Chromatography (R.F.G.C.), a version of Inverse Gas Chromatography, which allows determining both parameters by performing only one experiment for the kc parameter and two experiments for the γ parameter. The kc and γ values decrease in the presence of the three surfactants used (CTAB, SDS, TRITON X-100) at all methanol’s and surfactant’s concentrations. The decrease in the methanol’s molar fraction, at constant number of surfactant films leads to a decrease in the kc and γ values, while the decrease in the surfactant’s concentration, at constant methanol’s molar fraction leads to an increase in both the kc and γ parameters.Mass transfer coefficients for the evaporation of methanol at the surfactant films, are also calculated which are approximately between 4 and 5 orders of magnitude larger than the corresponding mass transfer coefficients at the liquid films.Finally, thicknesses of the boundary layer of methanol in the mixtures of methanol with water were determined.The quantities found are compared with those given in the literature or calculated theoretically using various empirical equations. The precision of the R.F.G.C. method for measuring γ and kc parameters is approximately high (94.3–98.0%), showing that R.F.G.C. can be used with success not only for the thermodynamic study of solutions, but also for the interphase transport.

The reversed–flow gas chromatography technique as a tool for the study of the evaporation retardation of SO2 and (CH3)2S from water by soluble surfactants

In the present work the evaporation retardation of SO2 and (CH3)2S (=DMS) from water by soluble surfactants was studied by the Reversed–Flow Gas Chromatography (R.F.G.C.) technique. Using suitable mathematical analysis, rate coefficients, kc, for the transfer of SO2 and DMS from pure or artificial sea water to the atmospheric environment were determined in the presence or the absence of surfactants. The efficiency of the three surfactants used (CTAB, TRITON X-100 and SDS) to retard the evaporation rate of SO2 and DMS from water was estimated by the decrease of the kc values in the presence of the three surfactants, compared to those in the absence of surfactants. The more efficient surfactant for the retardation evaporation of SO2 from both the pure and the artificial sea water was found to be the cationic CTAB surfactant, as the maximum decreases of the kc values were found to be 4.61×10−3cms−1 (number of films, n=1) and 3.07×10−3cms−1 (n=3), respectively. On the other hand, more efficient surfactant for the retardation evaporation of DMS from pure water was found to be the non-ionic TRITON X-100, in which the decrease of the kc value was estimated to be 18.20×10−3cms−1 (n=3) and from artificial sea water the cationic CTAB surfactant in which the decrease of the kc value was found to be 8.24×10−3cms−1 (n=3). Finally, the precision of the R.F.G.C. method in studying the retardation effect of various surfactants in the transfer of SO2 and DMS from the water body to the atmosphere is estimated (mean value 96.69%), and the experimental values of kc are compared with those given in the literature.

Theory and Experiment of Binary Diffusion Coefficient of n-Alkanes in Dilute Gases.

Binary diffusion coefficients were measured for n-pentane, n-hexane, and n-octane in helium and of n-pentane in nitrogen over the temperature range of 300 to 600 K, using reversed-flow gas chromatography. A generalized, analytical theory is proposed for the binary diffusion coefficients of long-chain molecules in simple diluent gases, taking advantage of a recently developed gas-kinetic theory of the transport properties of nanoslender bodies in dilute free-molecular flows. The theory addresses the long-standing question about the applicability of the Chapman-Enskog theory in describing the transport properties of nonspherical molecular structures, or equivalently, the use of isotropic potentials of interaction for a roughly cylindrical molecular structure such as large normal alkanes. An approximate potential energy function is proposed for the intermolecular interaction of long-chain n-alkane with typical bath gases. Using this potential and the analytical theory for nanoslender bodies, we show that the diffusion coefficients of n-alkanes in typical bath gases can be treated by the resulting analytical model accurately, especially for compounds larger than n-butane.

English

Spillage of water polluting substances via industrial disaster may cause pollution to our environment. Thus, reversed-flow gas chromatography (RF-GC) technique, which applies flow perturbation gas chromatography, was used to investigate the evaporation and estimate the diffusion coefficients of liquid pollutants. Selected alcohols (99.9% purity) and its mixtures were used as samples. The evaporating liquids (stationary phase) were carried out by carrier gas-nitrogen, 99.9% purity (mobile phase) to the detector. The findings of this work showed the physicochemical measurements may vary depending on the composition of water and alcohol mixtures, temperature of the mixtures, as well as the types of alcohol used. This study implies that there is a variation in the results based on the concentration, types and temperature of the liquids that may contribute in the references for future research in the area of environmental pollution analysis.

Influence of Temperature and pH on the Transfer of SO2 from Water to Air by Inverse Gas Chromatography

Reversed-flow gas chromatography, a version of inverse gas chromatography, was applied for the study of the transfer of sulfur dioxide from pure and artificial sea water to the atmospheric environment. Using suitable mathematical equation rate coefficients, the transfer of SO2 from water to air (k c) as well as diffusion coefficients of SO2 vapors into nitrogen (D g) was determined. The rate coefficients increase with increasing temperature and decrease with increasing pH of the liquid phase. Moreover, they depend on the water environment, being bigger for the transfer of SO2 from pure water than those from artificial sea water. Finally, the values of D g and k c are compared with those given in the literature or calculated theoretically.

Comparative study of the kinetic approach on the alcoholic fermentation procedure conducted in laboratory and scale-up systems by inverse gas chromatography

Summary The major objective of the present work was to compare the kinetic study of alcoholic fermentations conducted in the presence of wheat supported biocatalysts in laboratory scale and in a scale-up system of 80 L and to compare these results with those reported in literature. The kinetic study of fermentation processes was accomplished with the technique of reversed flow gas chromatography (RFGC), which is a version of inverse gas chromatography. The wine yeast species used was Saccharomyces cerevisiae AXAZ-1, and fermentations were conducted between 20 and 2°C. At low temperatures, maximal ethanol productivity and fermentation rate were reduced. The rate constants, determined through a mathematical model obtained from RFGC, were higher in the laboratory scale comparing to the scale-up system at the temperatures of 20 and 15°C. However, with the reduction of temperature, both systems presented almost similar values proving the great fermentative ability of immobilized cells even at extremely low tem...

Transport Phenomena and Evaporation on Interface of Gas-Liquid by Reversed-Flow Gas Chromatography

Transport Phenomena and Evaporation on Interface of Gas-Liquid by Reversed-Flow Gas Chromatography

Characterization of Polymeric Coatings in Terms of Their Ability to Protect Marbles and Clays against Corrosion from Sulfur Dioxide by Inverse Gas Chromatography

The protective performance of polymeric coatings was tested on marble and clays against their corrosion from sulfur dioxide. The method used was reversed-flow gas chromatography, which allowed us to determine deposition velocities (V d ), total effective diffusion coefficients (D y ), and local adsorbed equilibrium concentrations of SO2 on marbles and clays both in the presence and in the absence of the coating. The protective efficiency of a model polymeric coating, namely the acrylic copolymer Paraloid B-72, on marbles and clays against corrosion from SO2 was estimated in terms of the parameters Vd, Dy, and .

New Approaches to the Kinetic Study of Alcoholic Fermentation by Chromatographic Techniques

The kinetics of the fermentation process has gained increasing interest, not only in the scientific community, but in the industrial world as well. Information concerning the improvement of batch fermentation performance may potentially be valuable for the designing of scale-up processes. Intensive studies have been conducted with the use of various chromatographic techniques, such as conventional gas chromatography, reversed-flow gas chromatography (RFGC), high-performance liquid chromatography, field-flow fractionation and others. In the present study, specific focus is placed on the employment of RFGC, a method that can successfully be applied for the determination of physicochemical quantities, such as reaction rate constants and activation energies, at each phase of the alcoholic fermentation. In contrast to conventional chromatographic techniques, RFGC can lead to substantial information referring to the evaluation of fermentation kinetics at any time of the process. Moreover, gravitational field-flow fractionation, a sub-technique of field-flow fractionation, presents the ability to monitor the proliferation of Saccharomyces cerevisiae cells through their elution profiles that can be related to the different cell growth stages. The combination of the two techniques can provide important information for kinetic study and the distinction of the growth phases of yeast cell proliferation during alcoholic fermentations conducted under different environmental conditions.

Study the Effect of Imposing Surfactants toward the Evaporation of Low Molecular Weight Alcohol

In this paper, Reversed-Flow Gas Chromatography (RF-GC) is utilized to investigate the evaporation of low molecular weight alcohol. Evaporation rates as well as the diffusion rates of methanol are determined with a surfactant monolayer on the surface of the liquid; while nitrogen acts as carrier gas, at 313 K. The precision (>99.9%) and accuracy of this investigation demonstrates the potential of current methodologies for environmental impact studies; this is further verified when the results are compared with the available literature. The varying evaporation rates of methanol in the presence of varying amounts of Triton X-100 reflects that application of surfactants do damper the evaporation rates of liquid pollutants; without interference with the former's diffusion coefficients. High amounts of Triton X-100 are required for retardation of evaporation rates, suggesting the formation of a densely packed surface monolayer or the formation of an insoluble monolayer.

THE STUDY OF THE INFLUENCE OF TEMPERATURE AND INITIAL GLUCOSE CONCENTRATION ON THE FERMENTATION PROCESS IN THE PRESENCE OF Saccharomyces cerevisiae YEAST STRAIN IMMOBILIZED ON STARCH GELS BY REVERSED-FLOW GAS CHROMATOGRAPHY

The technique of reversed-flow gas chromatography (RFGC) was employed for the determination of the alcoholic fermentation phases and of kinetic parameters for free and immobilized cell systems, at different initial glucose concentrations and temperature values. In addition to this, due to its considerable advantages over other techniques, RFGC was used for the characterization of a new biocatalyst, yeast cells immobilized on starch gel, and especially wheat starch gel. Immobilization of wine yeast Saccharomyces cerevisiae AXAZ-1 was accomplished on wheat and corn starch gels in order to prepare new biocatalysts with great interest for the fermentation industry. The RFGC led with great accuracy, resulting from a literature review, to the determination of reaction rate constants and activation energies at each phase of the fermentation processes. A maximum value of rate constants was observed at initial glucose concentration of 205 g/L, where a higher number of yeast cells was observed. The increase of glucose concentrations had a negative influence on the growth of AXAZ-1 cells and rate constants were decreased. The decrease of fermentation temperature caused a substantial reduction in the viability of immobilized cells as well as in rate constant values. Activation energies of corn starch gel presented lower values than those of wheat starch gel. However, the two supports showed higher catalytic efficiency than free cell systems, proving that starch gels may act as a promoter of the catalytic activity of the yeast cells involved in the fermentation process.

Hydrocarbon binary diffusion coefficient measurements for use in combustion modeling

Recent studies have identified uncertainties in fuel diffusion coefficients as a source of significant uncertainty in combustion modeling. This paper presents accurate binary diffusion coefficients of linear hydrocarbons in helium and nitrogen at temperatures from 300K to 723K. Diffusion coefficients are determined using a reversed-flow gas chromatography (RF-GC) system. Earlier work in our laboratory has established the validity of this methodology for noble gases and methane under these elevated-temperature conditions, and we utilize the methodology to measure diffusion coefficients for longer chain systems of interest in combustion modeling: ethane, propane, and n-butane. For propane and n-butane in nitrogen, the present results show dramatically different (up to 16.9% deviation at the highest common temperature) diffusion coefficients than previous work in addition to extending the available temperature range. The effects of decomposition of the analyte at higher temperatures and adhesion of the analyte on the diffusion column at lower temperatures during the measurements are briefly considered but have only a small impact on the present systems.

Extending reversed-flow chromatographic methods for the measurement of diffusion coefficients to higher temperatures

A reversed-flow gas-chromatography (RF-GC) apparatus for the measurement of binary diffusion coefficients is described and utilized to measure the binary diffusion coefficients for several systems at temperatures from (300 to 723) K. Hydrocarbons are detected using flame ionization detection, and inert species can be detected by thermal conductivity. The present apparatus has been utilized to measure diffusion coefficients at substantially higher temperatures than previous RF-GC work. Characterization of the new apparatus was accomplished by comparing measured binary diffusion coefficients of dilute argon in helium to established reference values. Further diffusion coefficient measurements for dilute helium in argon and dilute nitrogen in helium (using thermal conductivity detection) and dilute methane in helium (using flame ionization detection) were performed and found to be in excellent agreement with literature values. The measurement of these well-established diffusion coefficients has shown that specific experimental conditions are required for accurate diffusion measurements using this technique, particularly at higher temperatures. Numerical simulations of the diffusion experiments are presented to demonstrate that artifacts of the analysis procedure must be specifically identified to ensure accuracy, particularly at higher temperatures.

Analysis of Diffusion Coefficient using Reversed-Flow Gas Chromatography-A Review

Problem statement: Since the earliest publication on the technique, Reversed-Flow Gas Chromatography (RF-GC) has been used to determine physicochemical properties by measuring the value of one in the presence of another. The method is precise, accurate and simple compared to other conventional techniques. Approach: The experimental setup consists of a small modification of a commercial gas chromatograph, so that it includes a four- or six-port gas sampling valve and a simple cell placed inside the chromatographic oven. Results: This cell suppresses the effects of the carrier gas flow on the physicochemical occurrence taking place in the stationary phase. These phenomena pertain to rate coefficients and diffusion coefficients. Conclusion: The RF-GC methodologies can be considered as a wise instrumental approach to study the physicochemical phenomenon of liquid pollutants. It can be used to determine the rate coefficients and diffusion coefficients values of samples at various temperatures for the studies of environmental science and physical chemistry research areas. However, the methodologies are not restricted to the current fields of research. It is also relevant in the area of food chemistry, geochemistry, material science, nanotechnology, biological science and chemical technology.

Determination of Diffusion Coefficients of Selected Long Chain Hydrocarbons using Reversed‐ Flow Gas Chromatographic Technique

The reversed‐flow gas chromatography (RF‐GC) technique was used to study the evaporation rate and estimating the diffusion coefficient of samples. The RF‐GC system comprises of six‐port valve, sampling and diffusion column, detector and modified commercial gas chromatography machine. Selected long chain of hydrocarbons (99.99% purity) was used as samples. The solute (stationary phase) were carried out by carrier gas (mobile phase) to the detector. The data obtained from the RF‐GC analysis were analysed by deriving the elution curve of the sample peaks using mathematical expression to find the diffusion coefficients values of respective liquids. The values obtained were compared with theoretical values to ensure the accuracy of readings. The interesting findings of the research showed the theoretical values of equilibrium at liquid‐gas interphase lead to profound an agreement with the experimental evidence, which contributes for the references of future studies.

Kinetic Study of the Alcoholic Fermentation Process, in the Presence of Free and Immobilized Saccharomyces Cerevisiae Cells, at Different Initial Glucose Concentrations by Reversed Flow GC

Reversed flow gas chromatography (RFGC) was applied for the kinetic study of the alcoholic fermentation processes conducted with cells of the alcohol-resistant and psychrophilic Saccharomyces cerevisiae AXAZ-1 yeast strain, either free or immobilized on wheat, barley and corn grains as well as on potato pieces. Repeated alcoholic fermentations with must of varying initial glucose concentrations were performed in order to estimate the catalytic efficiency of the biocatalysts used in the present study. With the RFGC method, the distinction of the duration of alcoholic fermentation phases was achieved, which may be correlated to the phases of AXAZ-1 cells growth cycle. The rate constants of ethanol production for each phase of the alcoholic fermentations, conducted with free and immobilized cells, were also determined with the aid of RFGC, confirming the predominance of the immobilized against free cells in the fermentation process. Comparing the supports used for immobilization, wheat and barley grains seemed to be more efficient than corn grains and potato pieces, as they provided a higher number of immobilized cells and rate constant values.