The preparation of X-ETS-4 by ion-exchanged method and adsorption performance of C3F8/N2

The development of new materials with high adsorption capacity and selectivity is becoming attractive for the applications of clean energy and environment pollution control. Metal-organic frameworks (MOFs) are promising adsorbents for gas storage and separation, such as H2 and CH4 storage, and CO2 capture, due to their extraordinarily high porosity, adjustable pore sizes, controllable surface functionality and potential scalability for industrial applications. This thesis focuses on developing novel MOFs for selective gas adsorption with large adsorption capacities and high selectivity, as well as good thermal and chemical stability. The studies include optimizing the activation conditions for uniform and empty pores with MOFs Cu-BTC taken as a case study, designing novel MOFs structure with desired functional groups for high selectivity of CO2 over other gases, fabricating MOFs contained composites with desired electrostatic force with ZIF-8/CNTs as an example, and evaluating the selective gas adsorption performance of all the prepared materials. This thesis aims to establish the relationship between the structure features of MOFs (pore size, metal centres, surface functional groups and electrostatic force) and gas adsorption performance of MOFs (including adsorption capacity and selectivity). The first part of experimental chapters focuses on the preparation and activation of copper-based MOFs Cu-BTC. The materials were synthesized by solvothermal method and activated by six different solvents (chloroform, dichloromethane, acetone, ethanol, methanol and water) in the activation process. The effects of different activation solvents on the thermal stability, porous structure and CO2 adsorption of Cu-BTC were investigated. The more DMF molecules were evacuated from the pores of Cu-BTC, the better adsorption performance was reflected in the material. The high crystalline and nearly solvent-free frameworks with highest BET surface area (2042 m2/g), largest pore volume (0.823 cm3/g) as well as highest CO2 loading (11.60 mmol/g at 0 dC and 132 kPa) can be achieved while using methanol as activation solvent. Then the selective adsorption of CO2/N2 and CO2/CH4 on Cu-BTC were examined through the experimental measurement of equilibrium adsorption capacities from pure fluids (CO2, CH4 and N2) and mixtures of CO2/N2 and CO2/CH4. Grand Canonical Monte Carlo (GCMC) model was performed to predict the adsorption capacities from pure fluids and binary mixtures. The GCMC model gives reasonable predictions of the measured adsorption capacities for pure gases at low pressures (l5 bar), but significantly over predicts that at pressures greater than 5 bar. The GCMC model fails to provide a satisfactory fit of the binary adsorption measurements across the entire pressure range studied. The Ideal Adsorbed Solution Theory (IAST) model using best-fit parameters for Langmuir isotherms of each pure fluid provides more satisfactory predictions of CO2/N2 and CO2/CH4 than the GCMC model. This combined experimental and modelling approach can provide criteria to screen MOFs for the separation of gas mixtures at industrially relevant compositions, temperatures and pressures. The second part of experimental chapters mainly focuses on synthesising MOFs with enhanced affinity for CO2 and selectivity of CO2 over other gases. Three novel amino-functionalized MOFs with both open metal sites (OMSs) and Levis basic sites (LBSs) were synthesized by solvothermal reactions. Single crystal structure analysis showed that Mg-ABDC and Co-ABDC were isostructural comprising two-dimensional layer structures, while Sr-ABDC contained a three-dimensional motif. These amino-functionalized MOFs were further characterized by powder X-ray diffraction, thermal gravimetric analysis and N2 ads-desorption. Adsorption isotherms of CO2 and N2 were obtained at various temperatures (0, 25 and 35 dC) and then the adsorption capacity and CO2/N2 selectivity for these MOFs were compared. Based on results, both Mg-ABDC and Co-ABDC decorated by the -NH2 groups and the open metal sites exhibit high heat of CO2 adsorption (g 30 kJ/mol) and excellent adsorption selectivity of CO2 over N2 (g375). In contrast, Sr-ABDC displays poor adsorption properties due to small pore size, low surface area and small pore volume. Introducing desired electrostatic force into MOF structures by the incorporation of carbon nanotubes (CNTs) into MOFs can obtain better crystals and enhance the properties of composite. A series of ZIF-8/CNTs composites were successfully synthesized by solvothermal method. The contents of ZIF-8 and CNTs in the composites were calculated from Thermogravimetric Analysis data. CO2 and N2 adsorption at 273 K on the composites were also investigated and compared. Results show that there are interactions (synergetic effect) between ZIF-8 crystals and CNTs in the composites, reflected in the change of crystallinity, morphology, thermal stability, and adsorption properties. The surface area and adsorption capacities of ZIF-8/CNTs composites can be controlled by adjusting the CNTs content in the composites. In optimal CNTs loading ratio, the ZIF-8/CNTs composite showed improved adsorption capacities and selectivity of CO2/N2, illustrating that the incorporation of CNTs into MOFs synthesis is a promising approach to enhance the adsorption performance of MOFs.

Measurements of gas mixture adsorption equilibria at high pressures are important for assessing actual adsorbent selectivities but are often out of reach, given the challenging nature of the required experiments. Here, we report a high-pressure gravimetric binary gas adsorption equilibrium measurement system based on simultaneous gas density and mixture adsorption measurements in a single gas cell coupled to a magnetic-suspension balance. Compared to traditional techniques which rely on analytical measurements of gas composition, this approach does not require any sampling. Adsorption measurements of two gas mixtures (0.500 N2 + 0.500 CH4 and 0.400 N2 + 0.600 CO2, mole fraction) on a commercially available molecular sieve (NaY, sodium molecular sieve type Y) were carried out in the temperature range 282 to 325 K with a pressure up to 10 MPa. A prediction method for the gas mixture adsorption equilibria in a closed system using the ideal adsorbed solution theory (IAST) model was used to compare the experimental results. For binary mixtures of components with similar adsorption capacities (here N2 and CH4), the system can measure the adsorption equilibria at pressures higher than 1.0 MPa and the result agrees well with the IAST model prediction. For two gases with very different adsorption capacities, the uncertainty in the adsorption equilibrium measurement is much larger. The dominant uncertainty source is the gas density measurement, whose uncertainty could potentially be cut to half if the current titanium sinker is replaced with a sinker made of single-crystal silicon and with a larger volume.

Adsorption and separation of propane/propylene on various ZIF-8 polymorphs: Insights from GCMC simulations and the ideal adsorbed solution theory (IAST)

CO is a toxic gas discharged as a byproduct in tail gases from different industrial flue gases, which needs to be taken care of urgently. In this study, a CuCl/AC adsorbent was made by a facile route of physically mixing CuCl2 and Cu(HCOO)2 powder with activated carbon (AC), followed by heating at 533 K under vacuum. The samples were characterized by X-ray powder diffraction (XRD), inductively coupled plasma optical emission spectrometry (ICP-OES), N2 adsorption/desorption, and scanning electron microscopy (SEM). It was shown that Cu(II) can be completely reduced to Cu(I), and the monolayer dispersion threshold of CuCl on AC support is 4 mmol·g−1 AC. The adsorption isotherms of CO, CO2, CH4, and N2 on CuCl/AC adsorbents were measured by the volumetric method, and the CO/CO2, CO/CH4, and CO/N2 selectivities of the adsorbents were predicted using ideal adsorbed solution theory (IAST). The obtained adsorbent displayed a high CO adsorption capacity, high CO/N2, CO/CH4, and CO/CO2 selectivities, excellent ad/desorption cycle performance, rapid adsorption rate, and appropriate isosteric heat of adsorption, which made it a promising adsorbent for CO separation and purification.

An experimental and simulation study of binary adsorption in metal–organic frameworks

Effective CO2/N2 adsorptive separation by fluorinated CAG zeolitic imidazolate frameworks in humid environments

The presence of impurity in biogas like CO2, H2S and H2O reduce the efficiency and heating value of this renewable energy. While removal of H2S and H2O is relatively simple, effective purification is needed to remove CO2 which presence in biogas up to 45%. The separation of CO2 from CO2/CH4 mixture can be performed by carbon-based molecular sieves. Separation by molecular sieves is based on differences in the diffusivity of CO2 and CH4 passing through the pore of the carbon. This paper discusses a preparation of porous carbon from palm kernel shell as molecular sieves and its adsorption properties (equilibrium and kinetics) and separation performance for biogas purification. Porous carbon was synthesized by carbonization under steam activation at various temperature. The properties of porous carbon were characterized by N2-sorption analysis, scanning electron microscopy and proper adsorption study (equilibrium and kinetics). The results showed that the surface area of porous carbon increased with the increasing temperature of carbonization then decreased when the temperature raised to 1000 °C. The highest surface area of 803 m2 g−1 was obtained at a temperature of 800 °C and mesoporous structures increase with increasing temperatures but dropped at temperatures above 1000 °C. In the adsorption study at 1 atm and 30 °C, the results showed that the uptake capacities of CO2 (2.0 mmol g−1) was higher than that of CH4 (1.1 mmol g−1). based on ideal adsorption solution theory, adsorption of mixed CO2–CH4 showed an adsorption capacity of 1.3 mmol g−1. The adsorption kinetics test as well as breakthrough experiment showed that CO2 can be separated from mixture of CO2/CH4 using the carbon-based molecular sieve producing high purity of CH4 (> 95%).

Highly efficient separation of CO2/N2 and CO2/CH4 via metal-ion regulation in ultra-microporous metal-organic frameworks

Grand canonical Monte Carlo (GCMC) simulations have been performed to investigate the adsorption and separation behavior of ternary and quaternary gaseous mixtures of CO2, along with H2S, SO2, and N2, in bundles of aligned double-walled carbon nanotubes with a diameter of 3 nm and an intertube distance of 0.5 nm. All of the simulations are performed at 303 K and at pressures varying between 0 and 3 bar. The GCMC results are then compared to the ideal adsorbed solution theory (IAST) predictions. For the ternary mixture H2S–CO2–N2, the results show that CO2 has the highest adsorption among the three components. The IAST predictions agree reasonably well with the GCMC data for the ternary mixture, except for H2S. For the quaternary mixture H2S–SO2–CO2–N2, it is observed that initially CO2 has the highest adsorption up until around 2 bar, whereafter there is a crossover by SO2 to have the highest adsorption. IAST fails to predict the adsorption behavior of the quaternary mixture involving SO2.

Reliable adsorption equilibrium data and theoretical models for their accurate representation are crucial to the design of any adsorption based separation. The adsorption equilibria of carbon dioxide, methane and nitrogen are particularly important to the development of industrial pressure swing adsorption processes intended to separate CO2 and N2 from a variety of conventional as well as unconventional natural gas sources. The adsorption equilibrium capacities of gas mixtures needed for process design and simulation are often predicted from pure component adsorption data using various models including the ideal adsorbed solution theory (IAST). In this work, we present the adsorption equilibrium capacity data for a ternary gas mixture of CO2, CH4 and N2 as well as pure and binary gas mixtures of the same components on a commercial zeolite 13X, measured at temperatures of (273, 303 and 333 K) and pressures from (25 to 900 kPa) using a dynamic column breakthrough (DCB) apparatus. Although previous adsorption studies have reported the adsorption equilibria of pure and to a lesser degree binary gas mixtures on zeolite 13X, no experimental data are available in the literature for a ternary gas mixture of CO2, CH4 and N2 on zeolite 13X APG-III, a promising adsorbent for carbon capture and natural gas separation. The measured pure component adsorption capacities were regressed to a Toth isotherm model and the obtained Toth parameters were used to implement an IAST model for binary and ternary adsorption predictions. The IAST predictions of mixture gas adsorption represented the binary and ternary adsorption equilibria well with their corresponding maximum deviations being 0.055 and 0.3 mmol/g, respectively. This indicates the IAST can be applied successfully to these adsorption systems even though they involve molecules with different adsorption affinity and adsorbents with heterogeneous surfaces.

Separation of propane/propylene mixture using MIL-101(Cr) loaded with cuprous oxide nanoparticles: Adsorption equilibria and kinetics study

Electrically heated catalyst device

The efficient separation of light gaseous hydrocarbons, particularly the extraction of propane (C3H8) from natural gas, is critical for optimizing petroleum refining processes and reducing energy consumption. In this study, we demonstrate the synthesis of cost-effective porous carbon adsorbents derived from waste distiller's grains using an alkali-ion activation approach. By tuning the activating agent-to-precursor ratio, we systematically controlled the pore structure of the resulting materials, leading to a proportional increase in the specific surface area with higher activating agent concentrations. The optimized adsorbent, designated AC-3-800, exhibited exceptional performance at 273 K and 1 bar, achieving adsorption capacities of 14.87 mmol g-1 for C3H8 and 9.55 mmol g-1 for ethane (C2H6). Ideal adsorbed solution theory (IAST) calculations further validated its high selectivity, with predicted values of 79.6 for C3H8/CH4 and 14.9 for C2H6/CH4 separations. Breakthrough experiments confirmed the practical viability of AC-3-800, demonstrating complete separation of a 15/85 C3H8/CH4 mixture at 298 K and excellent cyclic stability over multiple adsorption/desorption cycles. These findings highlight AC-3-800 as a scalable and sustainable adsorbent for light hydrocarbon separations, offering a compelling balance of low cost, high adsorption capacity, and superior C3H8/CH4 selectivity. Its performance positions it as a promising candidate for industrial-scale natural gas upgrading and petrochemical applications.

Pyrazine functionalized large-pore metal-organic framework for efficient separation of acetylene/carbon dioxide and ethane/ethylene.

The objective of this work is to develop CuCl@AC adsorbent with high CO capacity and selectivity from CO/N2 binary gas mixture. A series of CuCl@AC adsorbents were prepared by a solid-state auto dispersion method, and then characterized by N2 adsorption test, XRD and XPS. CO and N2 adsorption isotherms on the adsorbents were measured by a volumetric method. The adsorption isotherms and selectivities of CuCl@AC adsorbents for CO/N2 binary mixture were estimated on the basis of ideal adsorbed solution theory (IAST). Results showed that (a) CO uptakes of CuCl@AC increased with CuCl loading in the loading range of 0–1.2 g/g. The maximal CO adsorption capacity of the CuCl@AC with CuCl loading of 1.2 g/g reached 38 cc/g at the P/P0 of 0.40, around 8 times of that over the original AC; (b) calcination time for the preparation of Cu(I)@AC had significantly impact on CO adsorption of the adsorbents due to valence change of Cu species on carbon surfaces. XPS analysis indicated that when the calcination time was optimized to be 1 h at 350 °C under argon, the prepared Cu(I)@AC had the highest percentage of Cu+ species on its surfaces, and consequently it had the highest CO capacity among the adsorbents since adsorptive species responsible for CO adsorption is Cu+; (c) The IAST-predicted CO/N2 adsorption selectivities of 1.2CuCl/AC decreased with pressure. Its CO/N2 selectivity was up to 100–450 at low pressure range of 0–10 kPa, and it remained in the range of 50–100 at higher pressure range of 20–100 kPa. The high adsorption capacity and selectivity of Cu(I)@AC adsorbents made it a promising adsorbent for CO/N2 mixture separation.