Adsorption Isotherms Of Ethane Research Articles

Adsorption of methane and ethane on HKUST-1 metal–organic framework and mesoporous silica composites

Composite materials HKUST-1@MCM-41 and HKUST-1@ BPS based on metal–organic framework HKUST-1 [Cu3(btc)2, btc = benzene-1,3,5-tricarboxylate] and silicas, i.e., mesoporous MCM-41 and biporous BPS with a bimodal mesopore size distribution, were prepared by one-step direct growth technique. Methane and ethane adsorption isotherms were measured for the HKUST-1@MCM-41 and HKUST-1@BPS composites in a wide pressure range for the first time. The silica porous structure significantly affects the content and location of HKUST-1 crystallites in these host matrices, and thereby the adsorption selectivities of the composites.

A Route to Understanding the Ethane Adsorption Selectivity of the Zeolitic Imidazolate Framework-8 in Ethane-Ethylene Mixtures.

Ethylene production has a negative environmental impact, with its separation step being one of the major contributors of pollution. This has encouraged the search for energy-efficient alternatives, among which the adsorptive separation of ethane and ethylene stands out. ZIF-8 is a molecular sieve that is potentially useful for this purpose. It is selective to ethane, an exceptional property that remains unexplained. Furthermore, the adsorption of ethane and ethylene above room temperature, such as at steam cracking process outlet temperatures, has not been addressed either. This work aims to fill this knowledge gap by combining experiments at very low volumetric fillings with density-functional theory modelling methods. Adsorption isotherms of ethane and ethylene on ZIF-8 at pressures below 0.3 bar and 311 K, 333 K, and 363 K were measured using zero-length column chromatography. The low-pressure domain of the isotherms contains information on the interactions between the adsorbate molecules and the adsorbent. This favors the understanding of their macroscopic behavior from simulations at the atomic level. The isosteric enthalpy of adsorption of ethane remained constant at approximately -10 kJ/mol. In contrast, the isosteric enthalpy of adsorption of ethylene decreased from -4 kJ/mol to values akin to those of ethane as temperature increased. ZIF-8 selectivity to ethane, estimated from ideal adsorbed solution theory, decreased from 2.8 to 2.0 with increasing pressure up to 0.19 bar. Quantum mechanical modelling suggested that ethylene had minimal interactions with ZIF-8, while ethane formed hydrogen bonds with nitrogen atoms within its structure. The findings of this research are a platform for designing new systems for the adsorptive separation of ethane and ethylene and thus, reducing the environmental impact of ethylene production.

C2/C3 Hydrocarbon Separation by Pressure Swing Adsorption on MIL-100(Fe)

The main objective of this work is the separation of 0.30/0.70 ethane/propane and 0.30/0.70 ethylene/propane by pressure swing adsorption (PSA) on MIL-100(Fe). The metal–organic framework MIL-100(Fe) was proposed as a potential adsorbent due to its high C2/C3 selectivity. Since adsorption equilibrium data are essential for the process design, the adsorption isotherms of ethane, ethylene, and propane were measured at 323, 373, and 423 K by a gravimetric method. Fixed-bed experiments were conducted at 0.5 SLPM, 323 K, and 150 kPa feed conditions on a bench-scale vacuum PSA (VPSA). Equilibrium and dynamic studies confirmed the preferential adsorption of propane over ethane and ethylene, with a high adsorption separation factor. Two five-step VPSA cycles with two different feed compositions, 0.30 ethane/0.70 propane, and 0.30 ethylene/0.70 propane, at 323 K and 150 kPa on MIL-100(Fe) were designed and performed experimentally. The performance parameters demonstrated the high viability of the proposed processes, since ethane purity of 99.5% was achieved, and with a high ethane recovery (86.7%). In the same cycle, 99.4% of propane was recovered with 97.0% purity. In cycle scheme 2, an ethylene purity of 100.0% was achieved. The propane was 100% recovered with a purity of 94.7%.

Adsorption isotherms and nucleation of methane and ethane on an analog of Titan’s photochemical aerosols

In planetary atmospheres, adsorption of volatile molecules occurs on aerosols prior to nucleation and condensation. Therefore, the way adsorption occurs affects the subsequent steps of cloud formation. In the classical theory of heterogeneous nucleation, several physical quantities are needed for gas condensing on a substrate like aerosols, such as the desorption energies of the condensing gases on the substrate and the wetting parameters of the condensed phases on the substrate. For most planetary atmospheres, the values of such quantities are poorly known. In cloud models, these values are often approximately defined from more or less similar cases or simply fixed to reproduce macroscopic observable quantities such as cloud opacities. In this work, we used the results of a laboratory experiment in which methane and ethane adsorption isotherms on tholin, an analog of photochemical aerosols, are determined. This experiment also permits determination of the critical saturation ratio of nucleation. With this information we then retrieved the desorption energies of methane and ethane, which are the quantitative functions describing the adsorption isotherms and wetting parameters of these two condensates on tholin. We find that adsorption of methane on tholin is well explained by a Langmuir isotherm and a desorption energy ΔFo = 1.519 ± 0.0715 × 10−20 J. Adsorption of ethane tholin can be represented by a Brunauer-Emmett-Teller isotherm of type III. The desorption energy of ethane on tholin that we retrieved is ΔFo = 2.35 ± 0.03 × 10−20 J. We also determine that the wetting coefficients of methane and ethane on tholin are m = 0.994 ± 0.001 and m = 0.966 ± 0.007, respectively. Although these results are obtained from experiments representative of the Titan case, they are also of general value in cases of photochemical aerosols in other planetary atmospheres.

Trace Adsorption of Ethane, Propane, and n-Butane on Microporous Activated Carbon and Zeolite 13X at Low Temperatures

Removing of trace-leveled light hydrocarbons from exhaust air or gas streams becomes an increasingly important issue in the field of process and environmental technology, e.g., storage and transport of liquefied natural gas. Adsorption processes at temperatures below 0 °C have great potential to meet process specifications or environmental regulatory limits. Designing of such adsorption processes requires a profound insight into the thermodynamics of adsorption at low temperatures, which is not available yet. Therefore, this work provides adsorption isotherms of ethane, propane, and n-butane on microporous activated carbon and zeolite 13X in a temperature range from −40 to +60 °C and at partial pressures from 5 to 1000 Pa. The influence of temperature on the adsorbed amount on activated carbon and zeolite 13X is discussed for each adsorptive considering isosteric heats of adsorption and specific interactions between the adsorptive and the adsorbent surface.

Effective Model for Olefin/Paraffin Separation using (Co, Fe, Mn, Ni)‐MOF‐74

AbstractAn increase in demand for energy efficient processes for the separation of saturated and unsaturated light hydrocarbons mixtures drives the need of noncryogenic processes. The adsorptive separation using Metal‐Organic Frameworks with coordinatively unsaturated metal sites may provide a cost‐effective alternative due to the strong binding of the metal cation with the unsaturated hydrocarbons. Since experiments on adsorption equilibrium of gas mixtures are challenging, we propose classical force field based simulations to analyse the ability of MOF‐74 with different metal substitutions for the separation of C2 and C3 olefin/paraffin binary mixtures. We parametrized the force field by fitting to available experimental single‐component adsorption isotherms of ethane, ethene, propane, and propene in M–MOF‐74 (M=Co, Fe, Mn, and Ni). The force field was validated for a variety of temperatures ranged from 273 K to 353 K. We then conducted Monte Carlo simulations in the Grand‐Canonical ensemble to elucidate the adsorption mechanisms of the saturated/unsaturated hydrocarbon mixtures, at 318 K and 353 K. We computed the adsorption isotherms, and from these the adsorption selectivity, and addressed the variations of MOF properties with different metal cations. Fe‐based MOF‐74 appears the best option for both ethane/ethene and propane/propene separation applications. This finding partly agrees with previous work based on the Ideal Adsorbed Solution Theory.

Ethane selective IRMOF-8 and its significance in ethane-ethylene separation by adsorption.

The separation of ethylene from ethane is one of the most energy-intensive single distillations practiced. This separation could be alternatively made by an adsorption process if the adsorbent would preferentially adsorb ethane over ethylene. Materials that exhibit this feature are scarce. Here, we report the case of a metal-organic framework, the IRMOF-8, for which the adsorption isotherms of ethane and ethylene were measured at 298 and 318 K up to pressures of 1000 kPa. Separation of ethane/ethylene mixtures was achieved in flow experiments using a IRMOF-8 filled column. The interaction of gas molecules with the surface of IRMOF-8 was explored using density functional theory (DFT) methods. We show both experimentally and computationally that, as a result of the difference in the interaction energies of ethane and ethylene in IRMOF-8, this material presents the preferential adsorption of ethane over ethylene. The results obtained in this study suggest that MOFs with ligands exhibiting high aromaticity character are prone to adsorb ethane preferably over ethylene.

High Pressure Adsorption Studies of Ethane and Ethylene on Clay-Based Adsorbent Materials

Bentonite clay is tailored in three different ways to produce porous materials viz. PCH1, PCH2, and PILC, where PCH1 and PCH2 are two different clay heterostructures and PILC is a Zr-oxide pillared clay. Surface characterization materials shows that both of PCHs have a higher surface area than PILC, and have micro and mesoporosity, where PILC is basically a microporous. DRIFT and X-ray techniques were used to investigate the surface-groups and height of micropores in PCHs and PILC, respectively. Adsorption isotherms of ethane and ethylene were measured on these materials up to high pressure (1000 kPa) under different temperatures, and by processing the obtained data these materials were evaluated for their aptness for ethane ethylene separation. Isosteric heats of adsorption were observed higher for ethylene than ethane during initial surface coverage for each material-gas system. Interaction in each material-gas system with gradual increase in pressure was elucidated with the help of isosteric heat curves. Adsorption performances of these materials were compared with already studied materials (reported by other workers for ethane/ethane separation). Comparison was based on selectivity and working capacity, which are the two decisive parameters for screening suitability of any adsorbent material (for PSA application).

Adsorption of carbon dioxide, ethane, and methane on titanosilicate type molecular sieves

The separation of carbon dioxide from light hydrocarbons is a vital step in multiple industrial processes that could be achieved by pressure swing adsorption (PSA), if appropriate adsorbents could be identified. To compare candidate PSA adsorbents, carbon dioxide, methane, and ethane adsorption isotherms were measured for cation exchanged forms of the titanosilicate molecular sieves ETS-10, ETS-4, and RPZ. Mixed cation forms, such as Ba/H-ETS-10, may offer appropriate stability, selectivity, and swing capacity to be utilized as adsorbents in CO 2/CH 4 PSA processes. Certain cation exchanged forms of ETS-4 were found to partially or completely exclude ethane by size, and equivalent RPZ materials were observed to exclude both methane and ethane, while allowing carbon dioxide to be substantially adsorbed. Adsorbents such as Ca/H-ETS-4 and Ca/H-RPZ are strong candidates for use in PSA separation processes for both CO 2/C 2H 6 and CO 2/CH 4, potentially replacing current amine scrubber systems.

Adsorption of ethane and ethylene on modified ETS-10

Ethylene and ethane adsorption isotherms were measured for Engelhard Titanosilicate (ETS-10) both as made in the sodium form and ion exchanged with different mono-, di-, and trivalent cations. Isotherms for Na-, K-, and Ag-ETS-10 were found to be nearly rectangular indicating very strong adsorption. In contrast, isotherms for Li-, Ba-, and Cu-ETS-10 show substantial curvature. Isotherms for some mixed cation forms (such as Ba/H and La/H) demonstrate the weakest adsorption with substantial adsorption swing capacity between 1 and 200 kPa. Using the ideal adsorption solution theory (IAST), it was determined that ethylene/ethane adsorption selectivity decreases in the order Na > K > Li > Cu ≈ Ba > Ba / H > La / H , while the adsorption swing capacity (from 1 to 200 kPa) shows an exactly reversed trend. It is thus probable to find the right balance between selectivity and swing capacity in order to design appropriate pressure swing adsorption (PSA) processes for the separation of ethylene and ethane under a wide range of conditions.

Molecular simulation of adsorption of alkanes in sodium MOR-type zeolites using a new force field

The applicability of a recently proposed force field of Calero et al. (J. Am. Chem. Soc., 2004, 126, 11377) to Na-MOR zeolites is evaluated. The Henry law coefficients of ethane and C(5)-C(9) as well as the adsorption isotherms of ethane, propane, butane, and hexane in various Na-MOR zeolites are computed and compared with experimental values. These comparisons show that the new force field is suitable for Na-MOR zeolites. Furthermore, this force field is used to study the effects of sodium cations on the adsorption behavior of larger alkanes, such as C(4)-C(7), in MOR-type zeolites. These simulations give a better understanding of the underlying mechanisms of the cations' position and density influence on adsorption. In addition, a characteristic pressure named "reversal pressure" is introduced which characterizes the efficiency of the presence of cations in zeolites.

Control of mesoporous structure of organic and carbon aerogels

Resorcinol-formaldehyde (RF) aerogels were synthesized via the sol-gel polycondensation of resorcinol with formaldehyde in a slightly basic aqueous solution and followed by supercritical drying with carbon dioxide. Mesoporous carbon aerogels were then obtained by pyrolyzing the RF aerogels in an inert atmosphere. The control of mesoporous structure of the aerogels was studied by changing the amount of resorcinol (R), formaldehyde (F), distilled water (W) and sodium carbonate (basic catalyst) (C) used in the polycondensation. As a result of characterization by nitrogen adsorption, the mesopore radius of the RF aerogel was controlled in the range of 2.5–9.2 nm by changing the mole ratio of resorcinol to sodium carbonate (R/C) and the ratio of resorcinol to water used as diluent (R/W). Although the aerogels shrank by 1–4 nm during pyrolysis, the shape of pore size distribution of the RF aerogel was kept. It was found that the mesopore radius of carbon aerogel ranged from 2.0 to 6.1 nm. As the pyrolysis temperature increased, the peak radius of pore size distribution was kept the same despite the fact that the pore volume decreased because of shrinkage. Adsorption isotherms of ethane and ethylene were measured on the aerogels prepared. As the pyrolysis temperature increased, the amounts of ethane adsorbed became larger than those of ethylene adsorbed on the aerogels. The aerogels pyrolyzed at 1000°C had the same adsorption characteristics of ethane and ethylene as the activated carbons did.

Control of Mesoporous Structure of Silica Aerogel Prepared from TMOS

Silica aerogels were synthesized via the sol–gel polymerization of tetramethylorthosilicate (TMOS) under basic conditions and followed by supercritical drying with carbon dioxide. As a result of characterization by nitrogen adsorption, the aerogels were mesoporous materials with high surface areas and had few micropores. The experimental results suggested that the surface area and the pore radius of the aerogel were controlled by changing the mole ratios of ammonia (NH3) to TMOS in the sol–gel polymerization. On the other hand, the mesopore volume of the aerogel was independent of the [NH3]/[TMOS] ratio. Adsorption isotherms of ethane, ethylene, propane, and propylene were measured on the aerogels. It was found that the [NH3]/[TMOS] ratio influenced the adsorption isotherms.

Preparation and Characterization of Silica–Titania and Silica–Alumina Aerogels

Silica–titania and silica–alumina aerogels were prepared by the two-step hydrolysis of metal alkoxides, the sol–gel polymerization and the supercritical drying with carbon dioxide. As a result of characterization by nitrogen adsorption, the aerogels were mesoporous materials with high surface areas and had few micropores. The experimental results suggested that the surface area, the mesopore volume, and the pore radius of the aerogel depended on the titanium (Ti) or aluminum (Al) content. Adsorption isotherms of ethane, ethylene, propane, and propylene were measured on the aerogels prepared. It was found that the adsorption capacities for these hydrocarbons were changed by mixing Ti or Al to the silica aerogel. In the ethane–ethylene or propane–propylene system, the adsorption selectivity of ethylene or propylene on the silica–titania aerogel was lower than that on the silica aerogel. On the other hand, the selectivity on the silica–alumina aerogel was higher than that on the silica aerogel. Hence, the silica–alumina aerogel was useful for separating ethylene from ethane or propylene from propane.

Monte Carlo Simulations of pVT Relations and Adsorption Equilibria of Ethane Under Sub- and Supercritical Conditions.

Adsorption isotherms of ethane in slit pores of a single-plane wall model at 298 K and 323 K, from low to high pressures, are calculated by use of the Gibbs ensemble MC method. The two-site Lennard-Jones model (SS model) was used in the calculations by slightly adjusting the parameters of Jorgensen et al. (1984) to fit the experimental and calculated values of both vapor pressure and saturation liquid density of ethane near the critical point. The adsorption isotherms calculated from the SS model and those from the spherical LJ model, are found to be almost the same in shape and magnitude though slight differences are observed. That is, the maximum adsorption capacity of the SS model is slightly larger than that of the LJ model while the LJ model gives higher adsorption in the low-pressure region. The local density and orientational ordering of the dumbbell molecule of the SS model in slit pores are calculated. The molecular orientation to the surface is suggested to be sensitive to the ratio of the slit width and the site diameter.

Adsorption isotherms of ethane, ethylene, and carbon dioxide on activated carbon fiber at elevated pressures.

Adsorption isotherms of ethane, ethylene, and carbon dioxide on activated carbon fiber at elevated pressures.

ADSORPTION OF LIGHT HYDROCARBONS ON SPENT SHALE PRODUCED IN A COMBUSTION RETORT

Adsorption isotherms of ethane, propane, and n-butane on two different retorted oil shales were determined gravimetrically at 284.3, 293.7, and 303.2 K. The equilibrium data for these hydrocarbons were correlated with the Langmuir isotherm equation. The equilibrium adsorption data for all the hydrocarbons studied were also correlated by the modified Polanyi potential theory. A single generalized characteristic curve which correlates the equilibrium adsorption data for all three hydrocarbons was obtained by using the ratio of characteristic free energies.

Adsorption of ethane and ethylene by zeolites MgNaX and CaNaX with different degrees of ion exchange

Zeolites MgNaX and CaNaX with varying concentrations of Na+, Mg2+ and Ca2+ were prepared from zeolite NaX. Adsorption isotherms of ethane and ethylene were measured on these zeolites at different temperatures, and the dependence of differential heats of adsorption, qv, on the amount of adsorption, ns, was determined. The adsorption properties of zeolites MgNaX and CaNaX are similar to those of zeolite NaX up to a degree of exchange β of ∼40–50%. With a further rise in the concentration of Me2+ cations in the zeolite the ns and qv values for ethane and especially for ethylene become much higher and the values of qv are practically inveriable over a certain interval of ns rising with β. The amount of adsorbed ethylene molecules, Δns, corresponding to the range of ns over which the values of qv are still high is approximately equal to the amount of Me2+ cations situated in the supercage on the sites II. These results are interpreted on the basis of the nature of the distribution of Me2+ cations in dehydrated zeolites assuming that these cations are situated preferentially on sites inside the sodalite units and hexagonal prisms, inaccessible to hydrocarbons. Only after occupying these sites did Me2+ cations appear in the supercages, giving rise to a sharp increase in the specific adsorption of ethylene.

Symposium on application of pulse techniques to kinetic measurements: Une nouvelle formulation dynamique des interactions fluide solide — Application à des mesures de diffusivités intraparticulaires et de constantes d'équilibre d'adsorption

AbstractA general model of the dynamics of linear chromatographic interactions between a fluid and a solid is proposed, according to the following steps: Analysis of the processes occurring at the particle level. Transfer function relating the mean concentration in the particle to the surface concentration. Contribution of external and internal mass transfer. Approximation by a first order system. Transfer function of a mixing cell containing solid particles. Approximation by two coupled first order systems. Generalization to any kind of flow. Association of mixing cells in series: model of a chromatographic column. Mean and variance of the impulse response. Two experimental examples are given: Measurement of the internal tortuosity and ethane adsorption isotherms in microporous alumina pellets using a spontaneously jet stirred gas solid reactor. Determination of the effective diffusivity of argon in porous alumina beads using the so called “two measurements chromatographic method”.

The influence of size, charge and concentration of exchange cations on the adsorption of ethane and ethylene by zeolites

Adsorption isotherms of ethane and ethylene on zeolites NaY, CaNaX, and SrNaX were measured at different temperatures and the isosteric heats of adsorption at various surface coverages were determined. The amount of the adsorption a and heat of adsorption Q of ethylene on all zeolites are greater than the corresponding values of a and Q for ethane, due to the specific interaction of the π-bonds of ethylene with the cations of the zeolites. The energy of this interaction with doubly charged cations is much greater than with singly charged cations, and decreases with increasing cation radius. The nature of the dependence on surface coverage of the heat of adsorption of ethane, and particularly of ethylene, on zeolites CaNaX and SrNaX is related to the number of cations Ca 2+, Sr 2+, and Na +, situated on sites accessible for adsorption in a large cavity. The adsorption and heat of adsorption of ethane and ethylene on zeolite NaY are less than on zeolite NaX on account of the lower concentration of cations in zeolite NaY. The virial coefficients and their temperature dependence were found from the corresponding experimental adsorption isotherms. This permits the calculation of a at different pressures and temperatures over a wide range of temperature and surface coverage up to 50–70% and also the value of Q at different values of a.