Novel CO₂‑Selective Cross-Linked Poly(vinyl alcohol)/Poly­vinyl­pyrrolidone Blend Membrane Containing Amine Carrier for CO₂–N₂ Separation: Synthesis, Characterization, and Gas Permeation Study

This article reports structural characterizations and gas permeation properties of novel CO₂-selective cross-linked thin-film composite poly­(vinyl alcohol) (PVA)/polyvinylpyrrolidone (PVP) blend membranes doped with suitable amine carriers. The characterization of the active layer was carried out by thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, and X-ray diffraction. Gas streams containing 20% CO₂ and 80% N₂ by volume were used to study the transport properties of CO₂ (CO₂ and N₂ flux, CO₂ permeability, and CO₂/N₂ selectivity) across the membrane. The effects of active layer thickness (34–87 μm), feed absolute pressure (1.7–6.2 atm), temperature (90–125 °C), and sweep side water flow rate (0.02–0.075 cm³/min) on CO₂ transport properties across the membrane were analyzed. The maximum CO₂/N₂ selectivity of 370 and a CO₂ permeability of 1396 barrer were obtained for the composite membrane with 40 μm active layer thickness at 2.8 atm feed side absolute pressure and 100 °C

Measurement and Correlation of the Physicochemical Properties of Novel Aqueous Bis(3-aminopropyl)amine and Its Blend with <i>N</i>‑Methyldiethanolamine for CO₂ Capture

Physicochemical properties such as density and viscosity of aqueous novel bis­(3-aminopropyl)­amine (APA) and an aqueous novel blend of <i>N</i>-methyldiethanolamine (MDEA) and APA solutions as well as solubility and diffusivity of N₂O into these binary and ternary solutions were measured from temperature <i>T</i> = 298 to 323 K at atmospheric pressure. In this study, experiments cover the molality range for APA = 0–1.291 mol·kg^–1 and MDEA = 2.915–4.416 mol·kg^–1. The diffusivity and solubility experiments were conducted with a wetted wall column absorber and Corning glass equilibrium cell, respectively. The experimental binary and ternary density data as well as binary viscosity data were correlated by Redlich–Kister equation whereas ternary viscosity data were correlated by the Grunberg and Nissan model. On the other hand, solubility and diffusivity were correlated with different models. All of the correlations based on the different model performed are capable of adequately predicting experimental physicochemical data

Adsorption Characteristics of Metal–Organic Frameworks Containing Coordinatively Unsaturated Metal Sites: Effect of Metal Cations and Adsorbate Properties

Metal–organic frameworks in the M/DOBDC series are known to contain a large number of coordinatively unsaturated metal (M) sites. In this work, we study the influence of various metal cations (M = Mg, Mn, Co, and Ni) in the framework on its gas adsorption characteristics. The probe gases (viz. CO₂, CO, CH₄, C₂H₆, N₂, and Ar) were carefully chosen to cover a wider range of polarity and polarizability. While a significant impact of metal atom in the framework is observed on adsorption of polar gases such as CO₂ and CO, it has a negligible effect on adsorption of other relatively nonpolar gases. On one hand, Henry’s constant of CO₂ for Mg/DOBDC is about 4–10 times higher than that for other frameworks; on the other, Henry’s constant for CO on Ni/DOBDC is about 100 times larger than that on Mn/DOBDC. The pore volume of the framework governs adsorption capacity at higher pressures. Each of the frameworks exhibits widely different adsorption enthalpies for polar gases such as CO₂ and CO. At pressures below 15 bar, the Ideal Adsorbed Solution Theory predicts very good selectivity for CO over all other studied gases on Ni and Co/DOBDC frameworks, while Mg and Mn/DOBDC frameworks exhibit preferential selectivity for CO₂

Adsorption and Separation of Carbon Dioxide Using MIL-53(Al) Metal-Organic Framework

In this work, we report adsorption isotherms of various industrially important gases, viz. CO₂, CO, CH₄, and N₂ on MIL-53­(Al) metal organic framework (MOF). The isotherms were measured in the range of 0–25 bar over a wide temperature range (294–350 K). The structural transformation of the adsorbent and the resulting breathing phenomenon were observed only in the case of CO₂ adsorption at 294 and 314 K. Adsorption of CO (another polar gas), N₂ and CH₄ did not induce any structural transformation in this adsorbent for the experimental conditions considered in this work. Since the CO₂ isotherms at 294 and 314 K involve structural transformation and show a distinct step, a conventional isotherm model cannot be used to describe such behavior. In order to model these isotherms, a dual-site Langmuir-type equation (one site each for the two structural forms, i.e., large pore phase and narrow pore phase) that includes a normal distribution function to account for structural transformation is proposed. This model successfully mimics the Type-IV isotherm behavior of CO₂ on MIL-53­(Al). Henry’s constants and adsorption enthalpies of CO₂ on the two structural forms were calculated using this model. The Ideal Adsorbed Solution Theory (IAST) was used to predict the selectivity of CO₂ at 350 K over other gases studied in this work

Effect of Adsorbent History on Adsorption Characteristics of MIL-53(Al) Metal Organic Framework

Structural transformation of MIL-53­(Al) metal organic framework from large pore to narrow pore form (lp → np) or vice versa is known to occur by adsorption of certain guest molecules, by temperature change or by applying mechanical pressure. In this work, we perform a systematic investigation to demonstrate that adsorbent history also plays a decisive role in the structural transitions of this material (and hence on its adsorption characteristics). By changing the adsorbent history, parent MIL-53­(Al) is tuned into its np domain at ambient temperature such that it not only exhibits a significant increase in CO₂ capacity, but also shows negligible uptake for CH₄, N₂, CO, and O₂ at subatmospheric pressure. In addition, for the high pressure region (1–8 bar), we propose a method to retain the lp form of the sample to enhance its CO₂ uptake

Measurement and Modeling of Adsorption of Lower Hydrocarbons on Activated Carbon

This work reports adsorption isotherms for C₁ to C₆ hydrocarbons on activated carbon at three different temperatures (293 K, 318 K, and 358 K) over a wide range of pressure (0 bar to 100 bar). The isotherms were measured using a standard gravimetric method. The experimental data were correlated and compared using Toth, modified virial, and potential theory models. On the basis of the adsorption potential, characteristic curves were also generated for methane, ethane, propane, isobutane, <i>n</i>-pentane, and <i>n</i>-hexane on activated carbon over broad ranges of pressure and temperatures. The micropore volume of the activated carbon predicted from potential theory was in good agreement with those obtained using a N₂ isotherm measured at 77 K. The enthalpy of adsorption at zero loading was found to increase linearly with the carbon number