Equilibrium concentrations of species and gas loading in aqueous solutions of alkanolamine loaded with CO2 are being compared with predicted profiles obtained from the Deshmukh-Mather Model. A new technique is being proposed based on titration using a base, NaOH, to determine the concentrations of the different species at equilibrium. The technique is reliable and easy to perform to give reproducible results. Experimental and predicted concentrations of species are in good agreement over a range of gas loading between 0.4 and 1.0 for aqueous AMP solutions. For DEA, the predicted and measured values complement each other at high loading typically above 0.6. At low loading, there is a significant difference between the sets of values for carbamate and bicarbonate. These differences are likely due to the value of the equilibrium constant for the carbamate formation, which is taken as an adjustable parameter in the model, to give the best fit to the experimental data of either CO2 partial pressure or gas loading.
Fundamentals and computer-aided methods of practice for the calculation and checking of azeotropes, and for the qualitative and rigorous determination of separating spaces for closed distillation are presented, which are valid for non-ideal multicomponent systems. Separating spaces can occur in azeotropic systems only and are decisive for the separability of a system, if distillation is the separation technique. As a prerequisite, a rigorous mathematical model of the vapour-liquid equilibrium is required. The eigenvalues and eigenvectors of the Jacobian matrix of the equilibrium concentrations are the key ingredients of several methods: the eigenvalues describe the asymptotic behaviour of closed distillation profiles, which indicates the order according to which components can be separated; the eigenvalues enter a topological equation for checking the thermodynamic consistency of the azeotropes of a system; the eigenvectors initiate paths connecting azeotropes and pure substances, from the network of which separating spaces can be deduced qualitatively; and eigenvectors are essential to initiate the rigorous profiles of separating spaces.
Equilibrium and kinetic parameters for methane and nitrogen on a new, high specific area active carbon Maxsorb are reported. Volumetric and chromatographic methods are used to measure the pure component adsorption isotherm and the effective mass transfer coefficient for each gas. The adsorption isotherms at 300 K, measured up to a pressure of 550 kPa, are approximately linear for both methane and nitrogen on Maxsorb. The equilibrium separation factor is 3.0 in favor of methane. The mass transfer resistance is observed to be very low for each sorbate. The equilibrium and kinetic parameters are input in the mathematical model of binary breakthrough experiments using an axial dispersion model. The theoretical and experimental breakthrough curves are observed to be in excellent agreement.
Dynamic liquid hold-up was measured with an air/aqueous sodium citrate buffer solution at 20–40 °C, and an air/water system at 23 °C, in a 0.1 m diameter/1 m high glass column covered by a heat-isolating vacuum jacket and packed with 0.012 m nominal size ceramic Raschig rings. The superficial gas velocity range was extended to 1.2 m s−1. Experimental results of this work were compared with literature data, with different correlations and with a general equation. All expressions were found to be unacceptable for the air/buffer system and useable for the air/water system. In the case of the air/buffer solution a new correlation is recommended on the basis of our measured data and literature values.
Ethylene recovery was carried out from the gas product of oxidative coupling of methane by the temperature swing adsorption (TSA) method on NaA zeolites modified by Ca2+. The maximum concentration of ethylene was 98 vol.% in the output mixture. The results were obtained for zeolite containing 6.62% by weight of CaO. The adsorption was carried out at room temperature and the desorption by inert gas was performed at 200 °C.
The separation of air for the production of nitrogen by pressure swing adsorption over a carbon molecular sieve is kinetically based. The basic steps involved in a cycle are typically pressurization, high pressure adsorption, countercurrent blowdown and vent. Simulations studies with DAPS (Dynamic Adsorption Process Simulator) were performed to analyze the effect of the pressurization rate and bed length on the performance of a single bed nitrogen pressure swing adsorption unit in the high purity region. Both specific product and yield improve with the bed length due to the reduction in the axial dispersion effect. A comparison between the predictions of the theoretical model and experimental results was carried out.
The performance of a pilot test for biogas upgrading has been tested under different process conditions to produce oxygen-enriched air for aqueous media application. The selectivity of the polysulfone hollow fibres for N2O2 permeation allows the production of an oxygen-enriched air stream in the 30–50% range and an inert gas (nitrogen between 82–98%) by operating the pilot unit at different stage-cut values in a single pass mode. Membrane area requirements for a medium size plant of 100 Nm3 h−1 are discussed according to a simple perfect mixing model for gas permeation.
The degradation of aqueous diethanolamine (DEA) solutions by carbon disulfide (CS2) was investigated using a batch reactor at temperatures ranging from 120 to 190 °C, DEA concentrations of 2 to 6 M and CS2DEA mole ratios of 0.05 to 0.23. Reaction products identified by gas chromatography (GC), gas chromatography/mass spectrometry (GC/MS), melting point determination, elemental analysis and infrared analysis include monoethanolamine, bis(hydroxyethyl)-ethylenediamine, bis(hydroxyethyl)-piperazine, hydroxyethyl-oxazolidone, hydroxyethyl-imidazolidone, tris(hydroxyethyl)-ethylenediamine, bis(hydroxyethyl)-imidazolidone and an insoluble, sulfur-rich, linear, polymeric solid. The formation of the products increased with temperature, DEA concentration and CS2DEA mole ratio. A mechanism for the formation of the products is presented, and the experimental data are consistent with a first-order overall reaction with respect to DEA.
The zero length column (ZLC) technique has been successfully used to measure diffusivities in zeolite crystals. However, in industrial applications pellets with bidisperse structure, containing macropores and micropores (crystals), are commonly used as zeolites. In this paper, a model of ZLC desorption curves for bidisperse porous materials is developed. Model equations are analytically solved for linear systems. A numerical solution of model equations using orthogonal collocation is also used. The various regions of control (macropore diffusion, micropore diffusion) are identified. Simulations allow the choice of operating conditions for the ZLC technique. Procedures for the analysis of ZLC experiments are reported.
There is an emergent need to reduce the emissions of toxic volatile organic compounds (VOCs) to the atmosphere. One strategy to reduce the emissions of VOCs from point sources is to use air pollution control devices on the sources' discharge streams. This paper describes the development of a new activated carbon cloth (ACC) adsorption system that is integrated with cryogenic vapor recovery to reduce the amount of VOCs emitted to the atmosphere from point sources and provide for reuse of the VOCs that are recovered. Electrical current is used to regenerate the ACC. ACC adsorption followed by electrothermal regeneration results in formation of a concentrated organic vapor which is cryogenically condensed from the gas phase. Electrothermal desorption allows for careful control of the desorption time and the concentration profile of the desorbed VOC to allow minimal use of cryogen. Adsorption, followed by cryogenic treatment enables VOC sources to meet air quality control regulations while providing a high quality liquid VOC product for reuse.
A simple model has been created for predicting acid gas vapor-liquid equilibrium (VLE) in alkanolamines. The model is simple enough to use in a hand held calculator, but its structure is derived from theory. Model parameters were obtained by regression of experimental VLE data. The model is valid for total gas loadings from 0.003 to 0.8 and over a wide range of temperatures and amine concentrations. Partial pressure predictions are shown to agree with a more complex model over seven orders of magnitude in pressure. Heat of absorption values derived from the model are also shown to agree with literature sources. Parameters are given for the MDEA-H2O-H2S-CO2 and DEA-H2O-H2S systems.
Natural gas storage for natural gas vehicles and the separation and removal of gaseous contaminants from gas streams represent two emerging applications for carbon adsorbents. A possible precursor for such adsorbents is waste tires. In this study, activated carbon has been developed from waste tires and tested for its methane storage capacity and S02 removal from a simulated flue-gas. Tire-derived carbons exhibit methane adsorption capacities (g/g) within 10% of a relatively expensive commercial activated carbon; however, their methane storage capacities (VmVs) are almost 60% lower. The unactivated tire char exhibits SO2 adsorption kinetics similar to a commercial carbon used for flue-gas clean-up.
In the present work the water gas shift reaction is considered as a particular application of a catalytic membrane reactor. Three different methods to deposit a thin film of palladium on a porous ceramic tubular membrane have been studied: the magnetron sputtering technique, the physical vapour deposition technique, and the co-condensation technique or solvated metal atom deposition method. For each composite membrane, characterization in terms of pore distribution, thickness of the film, percentage of Pd deposited along the thickness of the membrane and CO conversion versus feed flow rate and versus different H2OCO molar ratio are presented.
In this experimental study the water gas shift (WGS) reaction is considered as a particular application of a catalytic membrane reactor (CMR). Experiments on the WGS reaction were carried out using a composite palladium membrane obtained by coating an ultrathin double-layer palladium film on the inner surface of the support of a commercial tubular ceramic membrane by a so-called co-condensation technique. The best operating conditions were determined at various H2OCO molar ratios, temperature, PIumen, gas feed flow, and with and without nitrogen sweep gas. For a non-porous stainless steel tube and for the commercial ceramic membrane having the same geometrical dimensions, the conversion results are always lower than the equilibrium value. For the composite palladium membrane, the conversion also depends on the flow of the sweep gas utilized. For example, using a nitrogen sweep gas flow of 28.2 cm3/min, the maximum conversion value reaches 99.89%. The study of the effect of temperature on conversion of carbon monoxide in the WGS reaction shows that at higher reaction temperature, the thermodynamic equilibrium conversion of CO decreases. In contrast for the CMR considered in this work, there is a maximum conversion value around 600 K. This value is a compromise between the kinetic rate of the reaction (which increases with increasing temperature) and thermodynamic considerations for the WGS reaction. The effect of the time factor (WF) on conversion of CO, with and without sweep gas at three different temperatures (595, 615 and 633 K) shows that at greater WF there are correspondingly higher values of the CO conversion for each temperature considered. For each temperature there is a slight effect of the sweep gas, and this is higher at 595 K. The good performance of the composite ceramic-palladium membrane is confirmed by a comparison with experimental results recently presented in the literature for the same reaction. Reaction tests have been carried out for a feed mixture also. In this case, however, the resulting values are always below the equilibrium ones.
This paper models the performance of a membrane reactor. The membrane, a composite alumina-based one, is packed with a catalyst and allows low molecular weight gases to diffuse through it at a faster rate than gases with a higher molecular weight. This allows a greater conversion to be achieved in one pass through the reactor. The reaction that is specifically considered in this paper is the dehydrogenation of methyl-cyclohexane to toluene with the production of hydrogen. This latter species is preferentially removed by the membrane. Data for the performance of the membrane have been estimated from previous experiments using single gases and the mechanisms considered are Knudsen and bulk flow. Surface flow is not considered in the model as it is possibly not important as the endothermic reaction is carried out at a high temperature. A standard kinetic model is also incorporated in the calculations. The correlations of maximum effective length of membrane reactors and maximum percentage conversion as functions of the feed velocity and the membrane diameter are demonstrated in this paper. This paper also considers the behaviour of a compound reactor in which the first section is a straightforward ‘plug flow’ reactor where the catalyst is confined in an impermeable tube with the same internal diameter as the membrane. This is followed by a section containing the membrane. The reason for considering this configuration is to avoid unnecessary leakage of methyl-cyclohexane feed in the initial stages of the reaction. This innovation leads to predicted increases in the overall conversion of the process.
A scheme is presented for the calculation of the UNIFAC activity coefficient and its analytical derivatives with respect to mole fractions and with respect to temperature. A numerical example is also given.
A mathematical model has been developed to predict the rates of gas absorption in turbulent falling liquid films with and without the first order homogeneous reaction and external gas phase mass transfer resistance. The eddy viscosity model used to describe the flow distribution is the van Driest model, modified in the outer region of the film by the use of an eddy diffusivity deduced from gas absorption measurements. The results are given for special cases to illustrate the effects of turbulence, reaction rate and gas phase resistances on the concentration profiles and the rates of gas absorption.
Conventionally, high purity O2 has been separated and recovered from air by cryogenic air separation plants. Recently, PSA (pressure swing adsorption) technology has improved and a new process is proposed to produce high purity O2 by PSA. In this technology, the removal of Ar (argon) by CMS (carbon molecular sieves) and the removal of N2 from O2 and N2 mixtures by zeolite is the key technology for the production of high purity O2. Concerning this technology, several patents for the production of high purity O2 have been issued. We have conducted a series of experiments to optimize the high purity O2 PSA process and have found an interesting result. In this paper, various factors that affect the economics of the high purity O2 generator are discussed.
Adsorption of pure methane, ethane and ethylene on molecular sieve zeolites was examined via the gas chromatographic method to determine the potential for the separation of ethylene from light hydrocarbons. The molecular sieves chosen for the study were H-mordenite and 13X, CaX, 4A and 5A zeolites. Henry's law constants were determined over a variety of temperature ranges between 233 and 473 K. van't Hoff plots are presented for all three gases on 4A and 5A zeolites and for methane and ethylene on the CaX and 13X zeolites and H-mordenite. Equilibrium separation factors for the ethylene/methane system are provided for all zeolites (except clinoptilolite) over various temperature ranges. Separation is most promising with CaX zeolite, which yielded separation factors ranging from 1100 at 100 °C to 100 at 200 °C. Separation seems possible in 5A and CaX zeolites at very high temperatures due to the strong affinity of their divalent cations for the ethylene π-bond.
Experimental data demonstrate that mixing of absorbents gives the possibility to increase gas solubility. This effect may be predicted using a simplified theory of solution. Solution theory predicts that increasing solubility is possible in mixtures with positive deviations from Raul's law and when some other conditions exist. This effect is greatest near lamination of solvent mixture. Gas solubility in regular solution may increase not more than 1.6 times. A similar effect may arise when mixing chemisorbents. This effect is very large. When an equal saturation degree of solution by gas is fixed, the equilibrium pressure of gas above solution may decrease by 10–50 times as compared with the pressure above the solution of one of the chemisorbents. Theory and experiment demonstrate that the positive effect is greatest when the saturation degree is small, and this effect becomes negative when the saturation degree is great. These results give a new explanation for the effect of chemisorbent mixing in industrial processes such as the Benfield process.
