Pure Component Adsorption Isotherms Research Articles

Adsorption and thermodynamic studies of pure and binary CO2 and N2 gas components on nitrogen enriched nanostructured carbon adsorbents

Abstract Adsorption isotherms of pure components (CO2 and N2) on nitrogen enriched nanostructured carbon (UFZ-700) were evaluated at four different adsorption temperatures ranging from 303 to 373 K using a static volumetric analyzer. They were then correlated with the three pure component adsorption isotherm models namely Langmuir, Sips, and dual-site Langmuir (DSL) models. Binary components (CO2-N2) adsorption equilibria were then predicted by extending Sips and DSL equations empirically along with usage of ideal adsorbed solution theory. Further, it was compared with experimental data obtained from the breakthrough curves by various phase diagrams. Binary system breakthrough data were obtained at four different CO2 feed concentration and four adsorption temperatures (303–373 K) using a fixed-bed column. Sips and DSL adsorption isotherm models fitted well among three pure component adsorption isotherm models indicating energetically heterogeneous adsorbent surface. Because of the difference in adsorptive strengths of CO2 and N2 molecules, the models extended forms highly under-predicted the amount of CO2 adsorbed over the whole temperature and feed concentration range. Also, ideal adsorbed solution theory failed to describe the mixed-gas adsorption equilibria. With the increase in CO2 gas phase molar fraction, total adsorbed amounts were found to increase, deviation indicating positive from Raoult’s law with asymmetric x-y diagrams. Thermodynamic functions such as molar Gibbs free energy change, entropy change, and enthalpy change for the pure component system were numerically evaluated. They indicated the formation of more ordered configuration of CO2 molecules on the adsorbent surface and confirmed the feasibility of adsorption process.

Sustainable nanoporous carbon for CO2, CH4, N2, H2 adsorption and CO2/CH4 and CO2/N2 separation

The huge production of waste agricultural and biomass products has a negative impact on the environment, thus necessitating economic and environmental recycling of abundant bio-waste materials to useful materials. To recycle and convert bio-waste materials, a sustainable nanoporous carbon from bio-waste (peanut shell, gingko, and metasequoia leaves) is facilely synthesized via one-step carbonization. Carbonized samples contain a small quantity of metal and non-metal residues (including sulfur and phosphorus), resulting in naturally doped porous carbon. The porosity, morphology, and composition of the nanoporous carbons were investigated and compared with those of commercially available activated carbon. Pure component adsorption isotherms of CO2, CH4, and N2 were also measured at 40 °C up to1 bar for all samples. These data were used to estimate the separation selectivity for CO2/CH4 and CO2/N2 1:1 binary mixtures and pressures according to the ideal adsorbed solution theory (IAST) model. Carbonized gingko leaf had the lowest SSA and pore volume but the highest S and P contents, with the highest average selectivity of 506 and 54 for CO2/N2 and CO2/CH4, respectively. This implies that the composition of the prepared carbon materials plays a significant role in their CO2 adsorption and separation ability, rather than their textural properties.

Binary adsorption equilibrium and breakthrough of toluene and cyclohexane on macroporous and hypercrosslinked polymeric resins

Adsorption-based separation is one of the most widely used methods in treating gasoline vapor. For effective control of gasoline vapor emission, the total concentration of non-methane hydrocarbons (NMHC) and the specific component such as toluene must meet the emission limit values. In this study, hypercrosslinked polymeric resin (Hyper-resin) and macroporous polymeric resin (Macro-resin) were selected as adsorbents. Toluene and cyclohexane were chosen as the representative of alkanes and aromatic hydrocarbons components of gasoline vapor. Pure and binary component adsorption isotherms of toluene and cyclohexane on two resins were measured by head space analysis method. Breakthrough data for binary system were obtained at the different concentrations of toluene (12–46 mg/L) and cyclohexane (15 mg/L and 102 mg/L) using a fixed-bed reactor. The results indicate that adsorption equilibria of binary component can be predicted by ideal adsorbed solution theory (IAST) with the average relative error lower than 15% using the pure component adsorption isotherm data. Hyper-resin provides higher selectivity to toluene than Macro-resin in binary equilibrium and breakthrough system. Moreover, the breakthrough adsorption capacities of pure component (toluene and cyclohexane) and their mixture on Hyper-resin are higher than those on Macro-resin, suggesting Hyper-resin would be a promising adsorbent for treating gasoline vapor.

Semiclassical SAFT-VR-2D modeling of adsorption selectivities for binary mixtures of hydrogen and methane adsorbed onto MOFs

Semiclassical versions of the statistical associating fluid theory for three- and two-dimensional chain molecules with attractive potentials of variable range (SAFT-VRQ) are applied to model selectivities and adsorption isotherms of mixtures containing hydrogen (H2) and methane (CH4) onto metal-organic frameworks (MOFs). The theoretical model for mixtures relies on eight molecular parameters and their corresponding combining rules. Six of the eight parameters are obtained from the bulk properties of pure components and only the other two, related to the energy depth of the surface-particle potential, εw, and the surface area S, are determined from fitting to experimental data of adsorption isotherms of pure components. The obtained S values are in agreement with reported BET surface areas. Satisfactory results are obtained for the prediction of adsorption isotherms for pure substances and mixtures containing hydrogen and methane compared with experimental data. This molecular thermodynamic model is also able to describe adsorption selectivities in mixtures and the relevance of the quantum description as the molar fraction of hydrogen is increased. Finally, we include detailed information about all the mathematical expressions used to describe the adsorption isotherms of mixtures.

Pure and Binary Gas Adsorption Equilibrium for CO2–N2 on Oxygen Enriched Nanostructured Carbon Adsorbents

Pure component (CO2 and N2) adsorption isotherms of oxygen enriched nanostructured carbon (RF-700) were evaluated using a static volumetric analyzer at four different adsorption temperatures ranging from 30 to 100 °C. Langmuir, Sips, and dual-site Langmuir (DSL) models were used to correlate pure component adsorption isotherms and it was found that Sips and DSL isotherm model fitted well with the experimental data, indicating the heterogeneous nature of the adsorbent surface. Fixed-bed column was used to obtain dynamic breakthrough data for binary system CO2–N2 at different adsorption temperatures (30–100 °C) and CO2 feed concentrations (5–12.5% by volume). Extended Sips, extended DSL, and IAST (ideal adsorbed solution theory) models using pure component adsorption isotherm data were used for the prediction of adsorption of binary system (CO2–N2). Predicted equilibria data was compared with experimental breakthrough curve data, and it was found that extended forms of the isotherm models (Sips and DSL) und...

Efficient simulation and equilibrium theory for adsorption processes with implicit adsorption isotherms – Ideal adsorbed solution theory

Recently an efficient method for the simulation of packed bed adsorbers with implicit adsorption isotherms was presented. It uses a method of lines approach and exploits standard software for the simultaneous solution of the resulting differential algebraic equations (DAEs). Application was demonstrated for stoichiometric ion exchange. In the present paper, the approach is extended to systems described by the adsorbed solution theory. For that purpose, the relation between the differential index of the DAE system and the spectral properties of the underlying adsorption equilibrium is established. In particular, it is shown that real and positive eigenvalues of the Jacobian of the underlying conservation equations will lead to a differential index of one. It is further shown that real and positive eigenvalues of the Jacobian related to the IAST can be guaranteed for binary mixtures with any type of pure component adsorption isotherm or for multicomponent mixtures with certain restricted types of pure component isotherms. The new method is illustrated for different explicit and implicit pure component adsorption isotherms belonging to this class. It is compared with alternative solution approaches using the modified FastIAS method by Do and Myers and semi-analytical solutions from equilibrium theory.

Investigation of heavy metal adsorption in binary system by nanocrystalline cellulose – Bentonite nanocomposite: Improvement on extended Langmuir isotherm model

The preparation of NCC – bentonite nanocomposite using waste paper as the source of NCC was conducted in this study. The adsorption performance of the composite was tested for the removal of Pb(II) and Hg(II) from aqueous solution in single and binary systems. Langmuir and Freundlich adsorption isotherms were employed to correlate pure component adsorption isotherm. Langmuir equation can represent the experimental data better than Freundlich, the qm for lead is higher than mercury in both systems (single system qm = 0.44 mmol/g (Pb) and 0.23 mmol/g (Hg) for composite). All systems exhibit endothermic process, except for bentonite which shows the exothermic process. The modification of extended Langmuir model for a binary system with the inclusion of fractional loading and heat of adsorption was proposed in this study. The modified extended Langmuir model could represent the experimental data better than original extended Langmuir equation.

Modelling of adsorption isotherms of isomers using density functional theory

ABSTRACTFor the separation of components having very similar vapour pressures, adsorption may be a promising separation method leading to products with a high purity. Especially, the separation of alkanes having the same molecular mass, but differ in the molecule architecture is very challenging and very important in petroleum refining. The adsorption isotherms of pure components and binary mixtures are calculated with the density functional theory, in which the thermodynamic properties are expressed as functionals of the spatially varying density, in combination with an equation of state based on the lattice cluster theory (LCT-EOS), which is originally developed by Freed and co-workers. The LCT-EOS allows to take the branching of the molecules directly into account without any additional fitting parameter. This theoretical framework can be employed for the calculation of the density profiles of pure components and partial density profiles in the case of mixtures within the narrow pores. The integration of these profiles leads to the adsorption isotherm. The obtained adsorption isotherms show that adsorption can be a promising technology for the separation of isomers having very similar boiling point, however further optimisation is required.

Adsorption of propylene, propane, ethylene and ethane in an isoreticular series of MOF-74 structures

Alkene/alkane separation is the most expensive stage in the process of propylene or ethylene producing. Adsorptive separation with porous solid adsorbents is an alternative way to currently used cryogenic distillation process. In this work by GCMC simulation we investigate propane, propylene, ethane and ethylene adsorption in an isoreticular series of IRMOF-74-I (Mg-MOF-74) structures with different pore size. The adsorption isotherms of pure components as well as the selectivity of binary mixtures of propylene/propane and ethylene/ethane at the pressure fixed at 1 bar with variable composition are determined at 318 K. Also, the snapshots of guest adsorption are used to elucidate the adsorption mechanisms. At low pressure, ethane uptake is the same for all studied structures. IRMOF-74-I has the highest ethylene uptake at low pressure and also ethylene/ethane selectivity among studied MOFs. Open metal site is the first preferential site for adsorbing the guest in all structures. IRMOF-74-II, IRMOF-74-III and IRMOF-74-IV have additional site for adsorbing guest molecules. This additional adsorption site makes propylene and propane uptakes higher than that of IRMOF-74-I at low pressure. The second preferential site of IRMOF-74-II, IRMOF-74-III and IRMOF-74-IV, organic linker, interact with propane and propylene as the same and can’t separate them so IRMOF-74-II, IRMOF-74-III and IRMOF-74-IV have lesser selectivity than IRMOF-74-I. At high pressure, IRMOF-74-IV with largest pore size has the highest uptake for all studied hydrocarbons.

Prediction of Binary Gas Adsorption of CO2/N2 and Thermodynamic Studies on Nitrogen Enriched Nanostructured Carbon Adsorbents

Pure component adsorption isotherms for CO2 and N2 on the prepared nitrogen enriched carbon were evaluated using a static volumetric analyzer at four different adsorption temperatures ranging from 30–100 °C and were then correlated with three pure component adsorption isotherm models, namely, Langmuir, Sips, and dual-site Langmuir (DSL) models. Adsorption equilibria of binary CO2–N2 adsorption was then predicted by extending Sips and DSL equations empirically along with the usage of ideal adsorbed solution theory and was compared with experimental data obtained from the breakthrough curves through various phase diagrams. Breakthrough data for binary system were obtained at four different CO2 feed concentrations (5–12.5% by volume) and four adsorption temperatures (30–100 °C) using a fixed-bed reactor. Among three adsorption isotherms models used to investigate the equilibrium data of pure component system, Sips and DSL adsorption isotherm models fitted well, indicating energetically heterogeneous adsorben...

Olefin/Paraffin Separation Potential of ZIF‐9 and ZIF‐71: A Combined Experimental and Theoretical Study

Two zeolitic imidazolate frameworks, ZIF‐9 and ZIF‐71, are evaluated by adsorption experiments and molecular simulations with respect to their potential towards olefin/paraffin separation. Pure component adsorption isotherms are measured and compared to grand‐canonical Monte–Carlo (GCMC) simulations. The experiments show that the adsorption of the paraffin is favorable over the olefin in both structures. Whereas the isotherms are predicted well by simulations for ZIF‐71, in case of ZIF‐9 only the saturation loading could be computed accurately because the latter material seems to undergo a so‐called gate‐opening effect upon adsorption of guest molecules; ZIF‐71 does not show this effect. Both structures show promising results with respect to olefin/paraffin separation.

Nanoporous chalcogenides for adsorption and gas separation.

The adsorption and gas separation properties of amorphous porous chalcogenides such as GeS2 are investigated using statistical mechanics molecular simulation. Using a realistic molecular model of such amorphous adsorbents, we show that they can be used efficiently to separate different gases relevant to environmental and energy applications (H2, CO2, CH4, N2). In addition to shedding light on the microscopic adsorption mechanisms, we show that coadsorption in this novel class of porous materials can be described using the ideal adsorbed solution theory (IAST). Such a simple thermodynamic model, which allows avoiding complex coadsorption measurements, describes the adsorption of mixture from pure component adsorption isotherms. Our results, which are found to be in good agreement with available experimental data, paves the way for the design of gas separation membranes using the large family of porous chalcogenides.

PyIAST: Ideal adsorbed solution theory (IAST) Python package

Ideal adsorbed solution theory (IAST) is a widely-used thermodynamic framework to readily predict mixed-gas adsorption isotherms from a set of pure-component adsorption isotherms. We present an open-source, user-friendly Python package, pyIAST, to perform IAST calculations for an arbitrary number of components. pyIAST supports several common analytical models to characterize the pure-component isotherms from experimental or simulated data. Alternatively, pyIAST can use numerical quadrature to compute the spreading pressure for IAST calculations by interpolating the pure-component isotherm data. pyIAST can also perform reverse IAST calculations, where one seeks the required gas phase composition to yield a desired adsorbed phase composition.Source code: https://github.com/CorySimon/pyIASTDocumentation: http://pyiast.readthedocs.org/en/latest/ Program summaryProgram title: pyIASTCatalogue identifier: AEZA_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEZA_v1_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: MITNo. of lines in distributed program, including test data, etc.: 38478No. of bytes in distributed program, including test data, etc.: 1918879Distribution format: tar.gzProgramming language: Python.Operating system: Linux, Mac, Windows.Classification: 23.External routines: Pandas, Numpy, ScipyNature of problem: Using ideal adsorbed solution theory (IAST) to predict mixed gas adsorption isotherms from pure-component adsorption isotherm data.Solution method: Characterize the pure-component adsorption isotherm from experimental or simulated data by fitting a model or using linear interpolation; solve the nonlinear system of equations of IAST.Running time: Less than a second.

Pore Size Dependence of Adsorption and Separation of Thiophene/Benzene Mixtures in Zeolites

Grand canonical ensemble Monte Carlo simulations were applied to study the adsorption and separation of thiophene from binary and ternary mixtures of benzene and n-alkanes in nine types of zeolites. Adsorption of thiophene is important for removing sulfur from gasoline. The computed pure component adsorption isotherms are in good agreement with experimental results for FAU zeolites. The calculated Qst for thiophene in FAU were found to be 33–46 kJ/mol depending on uptake, in good agreement with the experimental data. The adsorption heats as a function of zeolite pore diameter suggest high thiophene affinity when the pore diameter is between 4.6 and 5 A. Binary mixture simulations at two different compositions show that FER is very selective toward thiophene over benzene at 373 K. The thiophene selectivity shows a significant dependence on pore size in binary mixtures, and the smaller thiophene molecule can replace benzene at elevated pressures due to size entropy effects for some zeolites. For ternary mix...

Porous aromatic frameworks impregnated with fullerenes for enhanced methanol/water separation.

Molecular simulation techniques have revealed that the incorporation of fullerenes within porous aromatic frameworks (PAFs) remarkably enhances methanol uptake while inhibiting water uptake. The highest selectivity of methanol over water is found to be 1540 at low pressure (1 kPa) and decreases gradually with increasing pressure. The adsorption of water is very small compared to methanol, a useful material property for membrane and adsorbent-based separations. Grand canonical Monte Carlo (GCMC) simulations are utilized to calculate the pure component and mixture adsorption isotherms. The water and methanol mixture simulations show that water uptake is further inhibited above the pure component results because of the dominant methanol adsorption. Molecular dynamics (MD) simulations confirm that water diffusivity is also inhibited by strong methanol adsorption in the mixture. Overall, this study reveals profound hydrophobicity in C60@PAF materials and recommends C60@PAFs as suitable applicants for adsorbent and membrane-based separations of methanol/water mixtures and other alcohol/water separation applications.

Post-combustion CO2 capture using mesoporous TiO2/graphene oxide nanocomposites

The development of robust adsorbents with high adsorption capacity and high selectivity to separate CO2 from flue gas streams, a major greenhouse gas contributing to global warming, is a topic of current global interest. In this study, a series of mesoporous titanium dioxide/graphene oxide (TiO2/GO) nanocomposites, with different GO to TiO2 mass ratios, were synthesized using a simple colloidal blending process and systematically investigated for the first time as potential CO2 adsorbent materials. The synthesized composites were characterized by diffraction, spectroscopy, and microscopy techniques. Pure component adsorption isotherms of CO2 were measured at 0, 25, and 50°C and pressures up to 100kPa. Analysis of adsorption results showed that the CO2 adsorption isotherms could be well fitted to the temperature dependent Toth model. The adsorption kinetic data were well-represented by the Avrami model. TiO2/GO exhibited a CO2 uptake capacity of 1.88mmolg−1 at room temperature, which is much higher than many other commonly used adsorbents. Moreover, TiO2/GO also demonstrated a low heat of adsorption and remarkably high CO2/N2 selectivity and hence merits further consideration for capturing CO2 from dry flue gas.

A DIH-based equation for separation of CO2–CH4 in metal–organic frameworks and covalent–organic materials

We develop a new S(DIH) equation based on the difference of isosteric heats (DIH) to calculate the selectivity for CO2 over CH4 in metal–organic frameworks (MOFs) and covalent–organic materials. Using the S(DIH) equation to predict the selectivity requires only the adsorption isotherms of pure components and the DIH of the two components. By comprehensive comparison with the GCMC data in different types of porous materials, including MOFs, ZIFs, COFs and PAFs, it is found that the new S(DIH) equation can predict with high accuracy the selectivity of different types of porous materials for CO2 over CH4 at the low pressure of p = 0–1 bar. Therefore, the new S(DIH) can serve as an efficient tool for the selectivity predictions of porous materials for CO2 over CH4 at p = 0–1 bar, especially for the cases in which experiments can measure the adsorption isotherms and adsorption heats of pure components (such as CO2, CH4, N2 and H2) because the new S(DIH) requires only the adsorption isotherms and adsorption heats of pure components as inputs. In short, the new S(DIH) equation can be considered as a valuable screening tool for obtaining an estimation about the selectivity of a porous material for a certain component of the gas mixture.

Towards Bio-upgrading of Biogas: Biomass Waste-based Adsorbents

The choice of an appropriate adsorbent for CO2 separation by pressure swing adsorption remains a field of intense research and it would be of great help to rely on a parameter that could be used to quickly evaluate the performance of those materials. In this work, two activated carbons prepared in our laboratory from biomass wastes (olive and cherry stones) are studied for the separation of CO2 from mixtures of CO2 and CH4. CO2 and CH4 adsorption isotherms at room temperature and up to 10 bar were determined in a high pressure magnetic suspension balance. Breakthrough adsorption experiments with simulated biogas binary mixtures were conducted in a fixed-bed lab-pilot adsorption unit. The performance of the tested carbons was assessed in terms of a dimensionless sorbent selection parameter (S), which is based on the selectivity but incorporates the nature of the adsorption isotherm under PSA operating conditions. A commercial activated carbon Calgon BPL was also tested and used as reference material for the separation process. Experimental results show that the performance of the different adsorbents, based on the calculated S parameter, may be very different depending on whether data is derived from pure component adsorption isotherms or from breakthrough adsorption experiments. Under dynamic flow conditions, activated carbons produced in this study show a great potential to be applied to a CO2/CH4 separation for biogas upgrading purposes. Further research is envisioned in order to define a PSA process that maximizes the purity and recovery of CH4.

Maxwell–Stefan Modeling of Ethanol and Water Unary Pervaporation through a High-Silica MFI Zeolite Membrane

The pervaporative mass transfer of pure ethanol and water through a thin (0.5 μm) supported high-silica MFI membrane was studied experimentally at 30–70 °C, and modeled on the basis of the Maxwell–Stefan formalism. The temperature dependency of adsorption was described with the temperature dependency of pure component saturated vapor pressure. Two scenarios of coverage dependency, i.e., coverage-dependent and coverage-independent Maxwell–Stefan diffusivity, were applied in the modeling of the mass transfer through the zeolite film. In addition, the mass-transfer resistance of the support layers was taken into account. The derived unary models provided good representations of ethanol and water pervaporation flux. The study illustrates that pure component steady-state pervaporation flux measurements at different conditions offer a feasible basis for determining diffusion coefficients. Basically, pure component adsorption isotherms and derived diffusivities can be used in the modeling of pervaporative mass transfer of mixtures using zeolite membranes.

Adsorption of CO2, CH4, and N2 on Ordered Mesoporous Carbon: Approach for Greenhouse Gases Capture and Biogas Upgrading

Separation of CO₂ and N₂ from CH₄ is significantly important in natural gas upgrading, and capture/removal of CO₂, CH₄ from air (N₂) is essential to greenhouse gas emission control. Adsorption equilibrium and kinetics of CO₂, CH₄, and N₂ on an ordered mesoporous carbon (OMC) sample were systematically investigated to evaluate its capability in the above two applications. The OMC was synthesized and characterized with TEM, TGA, small-angle XRD, and nitrogen adsorption/desorption measurements. Pure component adsorption isotherms of CO₂, CH₄, and N₂ were measured at 278, 298, and 318 K and pressures up to 100 kPa, and correlated with the Langmuir model. These data were used to estimate the separation selectivities for CO₂/CH₄, CH₄/N₂, and CO₂/N₂ binary mixtures at different compositions and pressures according to the ideal adsorbed solution theory (IAST) model. At 278 K and 100 kPa, the predicted selectivities for equimolar CO₂/CH₄, CH4/N₂, and CO₂/N₂ are 3.4, 3.7, and 12.8, respectively; and the adsorption capacities for CH₄ and CO₂ are 1.3 and 3.0 mmol/g, respectively. This is the first report of a versatile mesoporous material that displays both high selectivities and large adsorption capacities for separating CO₂/CH₄, CH₄/N₂, and CO₂/N₂ mixtures.