Excess Isotherms Research Articles

Evolution of adsorption isotherm and isosteric heat from sub-triple to super-critical points

We carried out a comprehensive molecular simulation to investigate the evolution of the excess isotherms and the isosteric heat with respect to temperature for argon adsorption on strong and weak substrates. The temperature ranges from well below the bulk triple point temperature to above the bulk critical temperature to show the first- (second-) order transitions and the state of the system at the bulk coexistence pressure P0, whether it is non-wetting, partial wetting or complete wetting (preceded by pre-wetting). It is found that the key parameter that affects the dependence of the transitions on temperature and the state of the system at P0 is the relative difference between the isosteric heat and the heat of sublimation (or condensation). For strong substrates, the state of the system changes from partial wetting to complete wetting when the temperature crosses the bulk triple point temperature, and for temperatures well below the bulk triple point the 2D-condensation occurs in the first and second (and possible higher) layers. For weak substrates, the state of the system changes from non-wetting to complete wetting when the temperature crosses the wetting temperature TW, which is specific to the substrate. For temperatures greater than TW, complete wetting in weak substrates only occurs at pressures close to the bulk coexistence pressure P0 via the initial stage of clustering (unfavourable adsorption), followed by a pre-wetting (known as thin-to-thick transition), and this is reflected in the increase of the isosteric heat from a value less than the heat of condensation λ and approaching λ as the pressure tends to P0.

Determination of CH4, C2H6 and CO2 adsorption in shale kerogens coupling sorption-induced swelling

Gas adsorption can induce kerogen swelling with changes in pore volumes. In this study, hybrid Grand Canonical Monte Carlo/Molecular Dynamics simulations are conducted to investigate gas adsorption in kerogen and the corresponding sorption-induced swelling. A unified relationship between volumetric strain and an absolute adsorption amount is developed for different adsorbates. A theoretical model for calculating excess adsorption isotherms coupling swelling is proposed. Results show that (i) steep increases in C2H6 and CO2 adsorption isotherms at lower pressure indicate stronger affinities of C2H6 and CO2 than CH4; however, a larger size of C2H6 results in smaller accessible pore volumes and smaller maximum absolute adsorption amounts than CH4 and CO2. (ii) A linear relationship between volumetric strain and an adsorption amount is shown for CH4, C2H6 and CO2, separately. The volumetric strain caused by per unit of the absolute adsorption amount for C2H6 is the greatest because C2H6 with greater diameters has larger contact areas with pore walls for the same adsorbed amount. The maximum swelling upon CO2 adsorption is the largest (CO2 > CH4 > C2H6) due to its greatest absolute adsorption amount. (iii) Excess adsorption isotherms generated by our model are consistent with excess adsorption data calculated by variable pore volumes, which shows a large discrepancy compared to that determined using constant volumes, especially at high pressures. The difference between the fraction of free CH4 in our model and that calculated by using a constant volume is up to 23.2% at 323 K, 40 MPa. Therefore, this theoretical model can accurately determine free and adsorbed gas amounts in shale, further influencing prediction of hydrocarbon production and CO2 sequestration.

Effect of adsorbed phase density on the correction of methane excess adsorption to absolute adsorption in shale

In order to evaluate the accuracy of different methods for the methane excess adsorption correction, the Polanyi adsorption potential theory was introduced to analyze the absolute methane adsorption amount obtained by correction. One shale sample from the Lower Silurian Longmaxi Formation in the southern Sichuan Basin, China was selected to conduct high-pressure methane adsorption experiments at 40.6 °C, 60.6 °C, 75.6 °C, and 95.6 °C at pressures up to 52 MPa. Based on the experimental results at different temperatures, four densities (the liquid density of methane at boiling temperature and ambient pressure, the van der Waals density, the adsorbed phase density based on the falling segment fitting of excess adsorption isotherm, and the adsorbed phase density obtained by fitting excess adsorption isotherm using modified Langmuir equation) were used for the correction of excess adsorption to absolute adsorption. At the same time, in order to enhance the reliability and accuracy of the conclusions in this study, the results of methane adsorption experiments on shale in the reference were used for a comparative study to further support our conclusions. The results indicate that the greater the constant adsorbed phase density used for the excess adsorption correction, the lower the degree of overlap of the adsorption characteristic curves at different temperatures. The adsorbed phase density used for methane excess adsorption correction may be in the vicinity of 0.30 g/cm3 to 0.40 g/cm3. Particularly, it should not be greater than the liquid density of methane at boiling temperature and ambient pressure, which is 0.421 g/cm3. Although the adsorbed phase density differs across different temperatures and pressures, the current results show that 0.373 g/cm3 can be used as the adsorbed phase density for the excess adsorption correction, which may be a convenient method and can yield results close to the actual adsorption.

Thermodynamic interpretation of the drift and noise of gradient baselines in reversed-phase liquid chromatography using mobile phase additives

The drift and noise of acetonitrile-water gradient baselines (5-95%, v/v, 5 min linear gradient) in reversed phase liquid chromatography (RPLC) are recorded at a wavelength of 215 nm using 0.1% trifluoroacetic acid (TFA) as the mobile phase additive, a 4.6 mm × 150 mm 5 μm Symmetry-C18 RPLC column, and an Arc system (low-pressure gradient proportioning valve or GPV, pump with a stroke volume of either 66 or 132 μL, no mixer) as the LC instrument. These observations are predicted from solid-liquid adsorption thermodynamics which requires the measurement of the excess adsorption isotherm of acetonitrile from water onto the RPLC column and of the variation of the Henry’s constant of TFA as a function of the volume fraction of acetonitrile in the bulk mobile phase. The incomplete mixing of the acetonitrile and water packets delivered by the low-pressure GPV is represented by a sinusoidal perturbation of the programmed volume fraction of acetonitrile during the entire gradient. The variation of the TFA absorbance at 215 nm with increasing acetonitrile concentration is measured in order to transform TFA concentration into the observable absorbance unit. The drift and noise of the gradient baseline are calculated by solving numerically (Rouchon method) the equilibrium-dispersive (ED) mass balance equations of acetonitrile and TFA.The agreement between the calculated and observed gradient baselines is very good as the proposed model of chromatography accurately accounts for the displacement of TFA between stationary and mobile phases (early excess and late deficit of TFA concentration relative to 0.1%) and for the frequency (equal to the ratio of the applied flow rate to the stroke volume) and the amplitude of the periodic noise recorded during the gradient. From a practical viewpoint, the drift of the gradient baseline can be minimized by maximizing the ratio of the gradient volume to the hold-up volume ( > 10) and/or by minimizing the retention factor of the mobile phase additive in the water-rich eluent (k < 0.2). The reduction of the noise amplitude below 0.1 mAU as requested by the pharmaceutical industry imposes the ratio of the flow rate to the stroke volume of the pump to be larger than 1 Hz. This opens avenues towards the development of new GPV, pump, and mixers in order to mix efficiently the solvent packets delivered by conventional LC instrument.

Characterization of structural and chemical modifications during the steam activation of activated carbons

An anthracite-based material of low porosity was activated in a nitrogen stream enriched with water vapor to produce four activated carbons, which differ systematically in their structural and chemical properties. Characterization of the structural properties of the base and the activated materials was carried out by volumetric measurements and mercury porosimetry. A general classification of chemical composition was done by ultimate analysis. The surface chemistry was analyzed by Boehm titration. The adsorption performance was investigated by measuring excess isotherms and load-dependent adsorption enthalpies of selected probe molecules: acetone (polar), n-heptane (non-polar) and toluene (aromatic). Assuming distribution rules for selective adsorption, the molar ratios of the surface groups were estimated from the excess isotherms. The combination of these methods enables the observation and differentiation of structural and surface chemical changes of the carbons during activation. For example, it could be shown that the broader pore width distribution with an increasing proportion of mesopores occurring in the course of activation leads to a more pronounced energetic heterogeneity. It was also found that an increase in surface area with increasing activation time is accompanied by an increase in aromatic surface groups and a reduction of polar and non-polar surface groups. Especially the adsorption of the polar probe molecule acetone revealed the heterogeneity of the surface chemistry, which together with the heterogeneous structural composition resulted in a distinct decrease of the adsorption enthalpy with increasing loading.

Effects of an adsorbent accessible volume on methane adsorption on shale

An adsorbed gas amount obtained from excess adsorption isotherms is of great importance to an estimation of reservoir reserves and prediction of gas production in shale reservoirs. Generally, excess adsorption amounts are calculated by a void volume of an adsorbent measured by helium expansion tests. However, helium atoms can closely approach a pore wall and get into small pores due to their small size. Therefore, a helium-based volume is always larger than the accessible volume for a specific adsorbate. In this work, we use GCMC (Grand Canonical Monte Carlo) simulation to investigate methane adsorption on shale with pore sizes of 10, 20 and 30 Å at a temperature of 323 K. Five void volumes, including an apparent volume determined by helium expansion tests, a helium-probed volume, a simulated methane-based volume, an analytical methane-based volume, and a physical volume, are recognized. Use of a physical volume and a helium-based volume leads to negative excess adsorption at high pressure, which is not consistent with local density profiles at such pressure. It is thus necessary to calibrate a physical volume or use a methane-based volume as a theoretical value for calculating excess isotherms. Excess isotherms determined by a calibrated volume or methane-based volume are more accurate and keep positive even at high pressure. Appropriate calculations of excess isotherms also influence an estimation of proportions of excess adsorbed and free gas amounts in shale gas reservoirs, further having a great impact on the determination of a development strategy.

Effect of supercritical CO2 saturation pressures and temperatures on the methane adsorption behaviours of Longmaxi shale

Abstract To investigate the effects of supercritical CO2 (SC–CO2) saturation pressures and temperatures on the methane adsorption capacity of shale, total organic carbon (TOC) analysis, X-ray diffraction (XRD) analysis, scanning electron microscope and energy dispersive spectrometer (SEM/EDS) analysis, low-pressure N2 adsorption (LP-NA), and high-pressure methane adsorption (HP-MA) were conducted on raw and SC–CO2–saturated (8, 12, 16 MPa; 40, 60, 80 °C) shale collected from the Sichuan Basin. Results indicate that the excess adsorption isotherm of shale to methane clearly exhibited excess adsorption characteristics with increasing adsorption pressures. This excess methane adsorption capacity decreased after SC-CO2 saturation and is mainly attributable to decreases in the TOC content, clay minerals and specific surface area (SSA) in the SC–CO2–saturated shale. The density of adsorbed phase methane was considered at different adsorption models, and the results suggest that the Langmuir-Freundlich (LF) and Dubinin-Astakhov (DA) models better describe methane adsorption behaviours than the Langmuir and Ono-kondo models. The methane adsorption capacity of shale is closely related to the solubility of SC-CO2, which decreased significantly with increasing SC-CO2 saturation time and pressure, while the influence of SC-CO2 saturation temperatures was not evident at low-pressure (8 MPa). This study provides a theoretical reference for CO2 enhanced shale gas recovery.

On the pressure and temperature dependence of adsorption densities and other thermodynamic properties in gas shales

Black shale source rocks have become a key natural gas resource in the US and China. Unlike in conventional hydrocarbon reservoirs, a significant fraction of the gas in shales is adsorbed onto the inordinate specific surface areas (SSA) of micropores inside organic matter with densities exceeding those of bulk gas by an order of magnitude. Yet, the distribution of adsorbed versus bulk gas remains poorly understood. Experiments measure excess adsorption isotherms, which are corrected to absolute adsorption amounts by a factor that involves the density, ρabs, of the adsorption layer(s). Constant values of ρabs are widely used in the literature but, we argue, are inconsistent with the pressure- and temperature-dependence of adsorption behavior. In this work, we propose a more reliable approach that assumes a constant volume of each adsorption layer that can be determined from the SSA of the substrate.We measure nine high-pressure methane excess adsorption isotherms up to 15 MPa for three shale samples from China and Germany at temperatures of 65, 75, and 95 °C, and low-pressure carbon dioxide and nitrogen isotherms to estimate the SSA. We also investigate another 24 isotherms at 35, 50, and 65 °C for 8 Chinese shale samples and 3 isotherms at 60, 90, and 120 °C for an Argentinian shale sample from the literature. A new variation of the multi-layer Ono-Kondo lattice model is introduced to derive the temperature and pressure dependent adsorption layer densities, which are subsequently used to obtain the absolute adsorption isotherms of interest. This practical methodology has the potential to significantly improve our estimates of shale gas-in-place resources, and adsorption modeling more broadly.

Effects of helium adsorption in carbon nanopores on apparent void volumes and excess methane adsorption isotherms

A void volume, which is measured by helium expansion tests and used in the calculation of methane adsorption amounts, is always overestimated due to helium adsorption. In this study, by comparing void volumes of carbon nanopores determined under different temperatures and pressures using GCMC (Grand Canonical Monte Carlo) simulation, suitable experimental conditions for helium expansion tests are obtained. Five volumes, including one apparent volume Vapp, three referred volumes Vref and one physical volume Vphy, are recognized. The apparent volume Vapp corresponds to the volume directly determined under traditional experimental conditions, while three referred volumes are determined at 500 K with different pressure ranges (low, moderate, high). The physical volume is calculated by multiplying a pore width and a surface area. Besides, a volume determined by using a helium probe is named an accessible volume Vacc and used as a criterion for a determined volume through mass balance. It is found that use of a void volume determined under traditional experimental conditions or a physical volume leads to negative adsorption amounts at high pressures. Considering an economic effect and measurement accuracy, determining a void volume by helium expansion tests within a moderate pressure range at 500 K is suggested. Excess isotherms of methane calculated by the suggested volume are more appropriate and of great physical meanings for further investigation of adsorption mechanisms.

Comparison of the Absolute Adsorption of CH4, n-C4H10, and CO2 on Shale

Comprehensive knowledge of absolute adsorption of light hydrocarbons and CO2 is significant for shale reservoir assessment and CO2 stimulation optimization. In this work, excess adsorption isotherm...

Gas Adsorption onto an MN-270 Polymer Adsorbent within a Supercritical Range of Temperatures and Pressures

The adsorption of nitrogen, argon, and methane onto MN-270 polymer adsorbent was studied within a pressure range of 0.1–40 MPa at temperatures of 303, 323, 343, and 363 K. The excess adsorption isotherms were measured for these adsorption systems, the adsorption volumes were determined, the total content adsorption isotherms, characteristic energies of adsorption, and differential, integral, and average isosteric heats of adsorption were calculated. The last two heats of adsorption were also calculated via the characteristic energies.

Supercritical Methane Adsorption on Shale over Wide Pressure and Temperature Ranges: Implications for Gas-in-Place Estimation

Methane adsorption experiments over wide ranges of pressure (up to 30 MPa) and temperature (30-120 °C) were performed using a gravimetric method on the Longmaxi shale collected from the northeast boundary of Sichuan Basin, China. Organic geochemical analyses, shale composition determination, and porosity tests were also conducted. The experimental supercritical methane excess adsorption isotherms at different temperatures initially increase and then decrease with increasing pressure, giving a maximum excess adsorption capacity (Gexm = 1.86-2.87 cm/g) at a certain pressure P (6.71-12.90 MPa). The excess adsorption capacity decreases with increasing temperature below 28 MPa, while this effect reversed above 28 MPa. However, the absolute adsorption capacity decreases as the temperature increases over the full pressure range. Supercritical methane adsorption on shale is of temperature dependence because it is a physical exothermic process supported by calculated thermodynamic parameters. P is positively correlated with the temperature, while the decline rates (0.021-0.058 cm g MPa) in excess adsorption negatively correlate with the temperature. Meanwhile, Langmuir volume G (3.07-4.04 cm/g) decreases while Langmuir pressure P (1.44-4.31 MPa) increases with temperature elevation. In comparison to the actual adsorbed gas (absolute adsorption), an underestimation exists in the excess adsorption calculation, which increases with increasing depth. The conventional method, without subtracting the volume occupied by adsorbed gas, overestimates the actual free gas content, especially for the deep shale reservoirs. In situ adsorbed gas is simultaneously controlled by the positive effect of the reservoir pressure and the adverse effect of the reservoir temperature. Nevertheless, in situ free gas is dominated by the positive effect of the reservoir pressure. Lowerature overpressure reservoirs are favorable for shale gas enrichment. Geological application of gas-in-place estimation shows that, with increasing depth, the adsorbed gas content increases rapidly and then declines slowly, whereas the free gas content increases continuously. There was an equivalence point at which the contents of adsorbed and free gas are equal, and the equivalence point moved to the deep areas with increasing water saturation. Moreover, the adsorbed gas and free gas distribution are characterized by the dominant depth zones, providing the reference for shale gas exploration and development.

Calculating the absolute adsorption of high-pressure methane on shale by a new method

Currently, many adsorption experiments of methane on shale have been done to understand adsorption characteristics of methane on shale, but those experiments’ pressure and temperature are far less than reservoir pressure and temperature; therefore, we carried out the experiments of methane adsorption on shale at 75.6°C and 95.6°C with 0–50 MPa pressure range to study the adsorption characteristics of shale under reservoir condition. We also build a new method to calculate the real (absolute) adsorption of methane on shale. Results present that the characteristics of excess adsorption isotherm under high pressure is different from the characteristics of excess isotherm under low pressure; adsorption obtained by adsorption experiment increases with pressure going up until reaching a peak and then declines with further increase in pressure. We build a new method to calculate the absolute adsorption by assuming that the adsorption phase volume approximately equals to the total volume occupied by adsorbed molecule, and the results calculated by our method show this method is reasonable and effective.

Adsorption of gases on a polymer adsorbent MN-200 in the region of supercritical temperatures and pressures

Adsorption of nitrogen, argon, and methane in a polymer adsorbent MN-200 was studied in the pressure range of 0.1–40 MPa at temperatures of 303, 323, 343, and 363 K. The excess adsorption isotherms were measured, the adsorption volumes were determined, the adsorption isotherms of total content and the characteristic adsorption energies were calculated. Isosteric, integral, and average heats of adsorption were determined.

Isotherms, thermodynamics and kinetics of methane-shale adsorption pair under supercritical condition: Implications for understanding the nature of shale gas adsorption process

This research article selects supercritical methane and organic-rich shale as adsorbate-adsorbent pair to investigate methane adsorption behavior and enrich our understanding of the nature of shale gas adsorption process. The isotherms and kinetics of methane-shale adsorption pair are measured at temperatures of 303 K, 323 K, 343 K and 363 K by using a volumetric experimental setup. Then, the Langmuir-based (Langmuir, Langmuir + k, Langmuir + Henry), BET-based (BET, BET + k, BET + Henry) and DA-based (DA, DA + k and DA + Henry) excess models are used to interpret measured excess isotherms, and the Unipore Diffusion (UD), Bidisperse Diffusion (BD) and Two Combined First-Order Rate (TCFOR) models are used to interpret the adsorption kinetics data. Instead of using the coefficient of determination (R2), this work used the corrected Akaike’s Information Criterion (AICc) for model selection. It is found that the DA + Henry model is more suitable for excess adsorption isotherms, and the TCFOR model is more appropriate for adsorption kinetics study. Additionally, for methane-shale adsorption under supercritical condition, the fugacity is of great significance in evaluating thermodynamic properties including isosteric heat of adsorption (qst), enthalpy change (ΔH), entropy change (ΔS) and Gibbs free energy change (ΔG). These properties show strong dependence on adsorption amount and temperature, and suggest that supercritical methane adsorption on organic-rich shale is a process of physisorption, exothermic and spontaneous. Further, the kinetics parameters extracted from kinetics curves suggest that the methane adsorption at each pressure step is a two-stage process, with a fast macropore diffusion process at early time, followed by a slow micropore diffusion process at later time. Additionally, the fast macropore diffusion dominates the two-stage adsorption process at lower pressures, while at higher pressures slow micropore diffusion dominates.

On the Negative Excess Isotherms for Methane Adsorption at High Pressure: Modeling and Experiment

Summary An excess adsorption amount obtained in experiments is always determined by mass balance with a void volume measured by helium (He) –expansion tests. However, He, with a small kinetic diameter, can penetrate into narrow pores in porous media that are inaccessible to adsorbate gases [e.g., methane (CH4)]. Thus, the actual accessible volume for a specific adsorbate is always overestimated by an He–based void volume; such overestimation directly leads to errors in the determination of excess isotherms in the laboratory, such as “negative isotherms” for gas adsorption at high pressures, which further affects an accurate description of total gas in place (GIP) for shale–gas reservoirs. In this work, the mass balance for determining the adsorbed amount is rewritten, and two particular concepts, an “apparent excess adsorption” and an “actual excess adsorption,” are considered. Apparent adsorption is directly determined by an He–based volume, corresponding to the traditional treatment in experimental conditions, whereas actual adsorption is determined by an adsorbate–accessible volume, where pore–wall potential is always nonpositive (i.e., an attractive molecule/pore–wall interaction). Results show the following: The apparent excess isotherm determined by the He–based volume gradually becomes negative at high pressures, but the actual one determined by the adsorbate–accessible volume always remains positive.The negative adsorption phenomenon in the apparent excess isotherm is a result of the overestimation in the adsorbate–accessible volume, and a larger overestimation leads to an earlier appearance of this negative adsorption.The positive amount in the actual excess isotherm indicates that the adsorbed phase is always denser than the bulk gas because of the molecule/pore–wall attraction aiding the compression of the adsorbed molecules. Practically, an overestimation in pore volume (PV) is only 3.74% for our studied sample, but it leads to an underestimation reaching up to 22.1% in the actual excess amount at geologic conditions (i.e., approximately 47 MPa and approximately 384 K). Such an overestimation in PV also underestimates the proportions of the adsorbed–gas amount to the free–gas amount and to the total GIP. Therefore, our present work underlines the importance of a void volume in the determination of adsorption isotherms; moreover, we establish a path for a more–accurate evaluation of gas storage in geologic shale reservoirs with high pressure.

Characterization of Activated Carbon Adsorbents – State of the Art and Novel Approaches

AbstractActivated carbons are widely used as commercial adsorbents. Thermal or chemical activation creates a pore system and functional groups on the inner surface which may significantly change adsorption properties. Therefore, in addition to knowledge of the structural properties, a sound understanding of surface chemistry is indispensable. This paper summarizes the state of art as well as new developments in both fields. Standardized methods for characterizing structural properties are volumetric measurements and mercury porosimetry. To get a more detailed insight into the region of micropores, a probe molecule method was developed. For characterization of surface chemistry, methods such as IR spectroscopy, temperature‐programmed desorption, and Boehm titration are subject of research. Novel methods were developed such as measuring of excess isotherms and calorimetric measurement of heat of adsorption, which are presented and discussed in greater detail in this paper. As each single method can only provide limited information, a better description of surface chemistry requires combination and careful interpretation of complementary information from different methods.

Simplified local density model for gas adsorption in cylindrical carbon pores

Abstract Carbon materials, coal-bed methane and shale gas reservoirs contain various carbon pore geometries like slit and cylinder. Simplified local density (SLD) model is a beneficial and widely recognized method for gas adsorption in slit-like carbon pore, and hasn't been completely extended from slit-like carbon pore to cylindrical carbon pore, which restricts its actual application. Herein, a SLD-cylinder model is established by obtaining the key parameters (i.e. attractive parameter and co-volume parameter in adsorbed phase) with the introduction of dummy attractive potential and the validation with clean energy gas (i.e. H2 and CH4) computational adsorption results. Meanwhile, for this model, the effect of carbon layers and the sphere of application are fully discussed here. Furthermore, based on SLD-cylinder model, isobars and isotherms of H2 and CH4 at a temperature ranging from 213 to 413 K and a pressure ranging from 1 to 10 MPa are investigated in 2.7 nm and 1.35 nm cylindrical pores. We find that carbon layer number is an essential factor for gas adsorption calculation in a cylindrical pore. Also, the SLD-cylinder model is applicable for the pressure higher than ambient one and the pore size larger than 1 nm. Moreover, owing to the significant effect of bulk fluid density (BFD) on excess adsorption, for CH4 especially, the shapes of isobar and excess isotherm vary mightily with pressure and temperature, respectively. This understanding could be applied to the storage of clean energy gas and the recovering of coal-bed methane (CBM) and shale gas. Therefore, the new developed SLD-cylinder model is as useful as the original SLD-slit model in the applications of gas storage, unconventional gas reservoirs recovering and pore structure characterization.

The Effect of Thermal Treatment on the Hydrogen-Storage Properties of PIM-1.

There has been recent interest in polymers of intrinsic microporosity (PIMs) for solid-state hydrogen-storage materials; however, the gas-sorption properties and conditions for hydrogen uptake are relatively unexplored. PIM-1 has been synthesised using the condensation reaction between 3,3,3,3-tetramethyl-1,1-spirobisindane-5,5,6,6-tetraol and 2,3,5,6-tetrafluorophthalonitrile as precursors. The synthesised PIM-1 was annealed at different temperatures for varying times and then characterised for hydrogen uptake at both ambient and cryogenic temperatures. The excess hydrogen PCT isotherms have been measured to high pressure (320 bar) for the first time and the effect of different annealing conditions on the hydrogen capacity is reported.

Excess and Absolute Adsorption from Binary Liquid Solution by Microporous Crystalline Adsorbents: Cumene + n-Octane/Zeolite NaX

The excess adsorption isotherms of cumene from solutions in n-octane in zeolite NaX have been measured at 303.15, 338.15 and 363.15 K using the conventional static method. The absolute (limiting) adsorption values of the pure components have been measured by the pycnometric method. The absolute adsorption isotherms for the system have been calculated using a non-fitting three parameter equation, based on the modified Dubinin–Radushkevich one. The detailed derivation of the formulas for these calculations is given. The absolute adsorption data are then used for estimation of average adsorbate density and other characteristics of the adsorbed phase.