Column Breakthrough Experiments Research Articles

Enhanced Separation of Butane Isomers via Defect Control in a Fumarate/Zirconium-Based Metal Organic Framework.

The discovery of appropriate synthetic reaction conditions for fabricating a stable zirconium-based molecular sieve (Zr-fum-fcu-MOF) with minimal defects and its utilization in the challenging separation of linear paraffins from branched paraffins is reported. The crystallinity and structural defects were modulated and adjusted at the molecular level by controlling the synthetic reaction conditions (i.e., amounts of modulators and ligands). The impact of molecular defects on the separation of n-butane from iso-butane was studied through the preparation, fine characterization, and performance evaluation of Zr-fum-fcu-MOFs with varying degrees of defects. Defect-rich Zr-fum-fcu-MOFs were found to have poor n-butane/iso-butane separation, mainly driven by thermodynamics, while Zr-fum-fcu-MOFs with fewer or minimal defects showed efficient separation, driven mainly by kinetics and full molecular exclusion mechanisms. The impact of intrinsic defects (i.e., missing organic or inorganic blocks) on the associated mechanisms involved in the separation of n-butane/iso-butane was evidenced through single-gas adsorption, mixed-gas column breakthrough experiments, and calorimetric studies. This investigation demonstrates, for the first time, the importance of controlling intrinsic defects to maintain the selective exclusion behavior of hydrocarbon isomers when using molecular sieves.

Protein adsorption to poly(ethylenimine)-modified sepharose FF: VII. Complicated effects of pH

Previously, we have studied protein adsorption behaviors on a series of poly(ethylenimine) (PEI)-grafted Sepharose FF, and a critical ionic capacity of PEI-grafted resins was observed, above which both protein adsorption capacity (q) and effective pore diffusivity (De) increased drastically. Moreover, reducing the charge density of the PEI-grafted resins from an ionic capacity of 740 mmol/L (FF-PEI-L740) to 440 mmol/L (FF-PEI-R440) by neutralization of the amino groups of PEI chains with sodium acetate brought out a three-fold increase of De value at pH 8. In this work, FF-PEI-L740 and FF-PEI-R440 were selected to investigate the complicated effects of pH on protein adsorption behavior using bovine serum albumin (BSA) as the model protein. It was found that, for FF-PEI-L740, both the q and De values decreased significantly when pH decreased from 9 to 5.5, and then increased dramatically at pH 5, and finally decreased remarkably at pH 4.5. The results were considered due to the following causes: The decrease of pH from 9 to 5.5 led to a greatly increased electrostatic repulsion between the PEI chains due to the increased dissociation degree of PEI, which caused the increase in steric hindrance effects and decrease in the bound protein transport by chain delivery. At pH 5, which was near the pI of BSA (∼4.9), the presence of few protein charges greatly decreased the electrostatic hindrance effect on protein transport and the high charge density of FF-PEI-L740 provided extensively accessible binding sites and facilitated the happening of chain delivery as well. At pH 4.5, the net charge of BSA shifted to positive, likely charged with PEI, so the overall electrostatic repulsion greatly hindered protein uptake. For FF-PEI-R440, whose charge density was much lower than FF-PEI-L740, its q and De values even increased mildly when pH decreased from 8 to 5.5, because its slightly-increased charge density did not cause much increased electrostatic and steric hindrance effects but provided more binding sites for protein adsorption. At pH 5, the few charges of BSA and the low charge density of FF-PEI-R440 could not afford enough electrostatic interaction for protein binding, resulting in significantly decreased q and De values. Besides, column breakthrough experiments revealed that FF-PEI-R440 kept high dynamic binding capacity (DBC) (>120 mg/mL) at pH 5.5–8, while FF-PEI-L740 offered high DBC (>80 mg/mL) at pH 5, 7 and 8 with a higher salt concentration (100 mmol/L NaCl). These findings demonstrated the excellence of FF-PEI-L740 and FF-PEI-R440 in different conditions, and would help in the design and selection of suitable resins for high-performance protein chromatography.

Tailor-Made Microporous Metal-Organic Frameworks for the Full Separation of Propane from Propylene Through Selective Size Exclusion.

Adsorptive separation of olefin/paraffin mixtures by porous solids can greatly reduce the energy consumption associated with the currently employed cryogenic distillation technique. Here, the complete separation of propane and propylene by a designer microporous metal-organic framework material is reported. The compound, Y6 (OH)8 (abtc)3 (H2 O)6 (DMA)2 (Y-abtc, abtc = 3,3',5,5'-azobenzene-tetracarboxylates; DMA = dimethylammonium), is rationally designed through topology-guided replacement of inorganic building units. Y-abtc is both thermally and hydrothermally robust, and possesses optimal pore window size for propane/propylene separation. It adsorbs propylene with fast kinetics under ambient temperature and pressure, but fully excludes propane, as a result of selective size exclusion. Multicomponent column breakthrough experiments confirm that polymer-grade propylene (99.5%) can be obtained by this process, demonstrating its true potential as an alternative sorbent for efficient separation of propane/propylene mixtures.

Synthesis, crystal structure and adsorption property of a microporous Cd(II) metal–organic framework based on 1H-imidazo[4,5-f][1,10]phenanthroline

A microporous metal–organic framework (MOF), [Cd(IP)Cl]n (1, HIP = 1H-imidazo[4,5-f][1,10]phenanthroline), with 1D square channels along the c axis was constructed through the solvothermal method. Because of the polar nitrogen atoms and the π-electron-rich ligand, activated MOF 1a presents a strong interaction with CO2, showing selective capture of CO2 from a mixture of CO2/N2. Additionally, MOF 1a also shows significant selective capture of CO2 from CO2/CH4 and CO2/C2H4 mixtures due to the sieving effect of the 1D channels. The column breakthrough experiment results further confirmed that microporous MOF 1a could be used as a potential porous material for selective CO2 adsorption.

Enhanced Cr(VI) removal by polyethylenimine- and phosphorus-codoped hierarchical porous carbons

The amino- and phosphorus-codoped (N,P-codoped) porous carbons derived from oil-tea shells were facilely fabricated through a combination of phosphoric acid (H3PO4) activation and amino (polyethylenimine, PEI) modification method. The as-synthesized carbon adsorbents were systematically characterized and evaluated for Cr(VI) removal in aqueous solutions. The relationship between adsorbent properties and adsorption behaviors was illustrated. Moreover, the influences of contact time, initial Cr(VI) concentration, pH, coexisting anions and temperature were also investigated. The adsorption behavior of Cr(VI) could be perfectly described by the pseudo-second-order kinetic model and Sips adsorption model. The maximum adsorption capacity of Cr(VI) on the carbon adsorbents synthesized in this work was 355.0 mg/g, and this excellent Cr(VI) capacity could be sustained with other coexisting anions. In addition to high surface area and suitable pore size distribution, the high Cr(VI) removal capacity is induced by rich heteroatoms incorporation and the Cr(VI) removal mechanism was clearly illustrated. Furthermore, the continuous column breakthrough experiment on obtained N,P-codoped carbon was conducted and well fitted by the Thomas model. This work revealed that PEI modification and P-containing groups could significantly enhance Cr(VI) adsorption capacity and make these N,P-codoped biomass-derived carbons potent adsorbents in practical water treatment applications.

Protein a resin lifetime study: Evaluation of protein a resin performance with a model-based approach in continuous capture

ABSTRACTA modified shrinking core model (MSCM) has been used to describe the mechanism for the degradation of Protein A resin particles taking place under continuous chromatographic operation. The model is based on the hypothetical shrinkage of the boundary layer of the resin particles, which house the active Protein A ligands within their pores. The caustic during the sanitization phase of chromatography has been determined to cause the Protein A ligand degradation. Protein A resins provided by manufacturers possess unique caustic stability, which has been used in MSCM to appraise the ligand degradation. The kinetic model utilized semiempirical parameters including diffusion constant, rate constant, stoichiometric factor, and reaction order. The parameters were estimated from column breakthrough experiments to simulate continuous Protein A chromatography for three distinct resins. The reaction order has been identified as the key parameter for predicting the degradation kinetics. The recorded reaction orders vary for three different resins with the resin B showing the highest reaction order of 4 and lowest being 1.65 for the resin C. The model can predict the effects of caustic on resin performance and displayed that minimal degradation of the resins A and B occurred, when exposed to 0.1 N and 0.2N NaOH, retaining up to 96% binding capacity after 240 cycles. The adsorption study conducted for the resin B demonstrated the dynamic physical and chemical changes transpiring through the life cycle of the resin, further supported the degradation model. The performance data demonstrate that the resin B exhibits the desirable performance, with higher reaction order indicating slower resin degradation, higher binding capacities, and increased sustenance of this binding capacity for extended duration. The degradation model can be extended to build effective cleaning strategies for continuous downstream processing.

Role of Immobile Kaolinite Colloids in the Transport of Heavy Metals.

Predicting the transport of contaminants in porous media is crucial to protecting public health and remediating contaminated soil and groundwater. However, the prediction of contaminant transport is challenging due to the presence of mobile and immobile colloids. The work performed in this experimental investigation quantified the role of immobile clay colloids on metal transport through sets of column breakthrough experiments under varying solution chemistry, clay content, and flow rate. Georgia kaolinite was chosen as the colloidal material, and Pb(II) was chosen as the dissolved contaminant. The silica sand used as the bed material was sized to ensure that the kaolinite colloids remained stationary during the column experiments. Results indicated that retardation of the Pb(II) breakthrough curve was observed as ionic strength decreased and kaolinite content and pH increased, while no significant variation of Pb(II) breakthrough was observed at any kaolinite content as flow rate decreased. This work demonstrated that, in the presence of immobile kaolinite colloids, Pb(II) breakthrough curves strongly depended on the pH and ionic strength, which controlled the charge on the surface functional groups and the surface availability of metal adsorption sites on immobile kaolinite colloids. In addition, the evaluation of unknown first-order coefficients in the continuum governing equation, bed efficiency, and Pb(II) saturation provided a quantitative description of Pb(II) breakthrough curves.

Pillar-Layered Metal-Organic Framework with Sieving Effect and Pore Space Partition for Effective Separation of Mixed Gas C2H2/C2H4.

The removal of acetylene from the industrial feed gas to purify the ethylene is an important and challenging issue. The adsorption-based separation is a more environmentally friendly and cost-effective method compared to the current removal approaches such as partial hydrogenation and solvent extraction, while facing the challenge of developing materials with high C2H2/C2H4 selectivity and C2H2 capacity. Herein, by expanding mixed-metal organic frameworks (M'MOFs) structure with high C2H2/C2H4 selectivity, we report a pillar-layered MOF, {[Cd5(MPCZ)2(BDC)3(NO3)2(H2O)4]·G}n (MECS-5), which not only inherits the sieving effects of M'MOF series but also develops its own characteristic-the 2D layer with expanding space and the plane pore-partition group to "cover" it. MECS-5 shows higher ideal adsorption solution theory C2H2/C2H4 selectivity than the most reported MOFs, especially more than 5 times higher than MOF-74 series while displaying great enhancement in the C2H2 capacity, more than 2 times higher compared to the M'MOF. The column breakthrough experiment further proves the possibility of MECS-5a for real industrial ethylene purification.

Understanding Competitive Adsorption of NTMP and Silica on Ferric Hydroxide

Abstract Ferric hydroxide adsorbents are commonly used to remove phosphonate antiscalants from membrane concentrate solutions. This research investigated competitive adsorption of nitrilotris(methylenephosphonic acid) (NTMP) and silica on ferric hydroxide. Equilibrium adsorption isotherms were measured and column breakthrough and regeneration experiments were performed for an NTMP adsorbate in simulated membrane concentrate solutions with and without dissolved orthosilicic acid. Quantum chemistry simulations using density functional theory (DFT) were used to evaluate the thermodynamic favorability of possible adsorption mechanisms for NTMP and silica. Column breakthrough experiments showed that 86 mg/L of dissolved silica decreased adsorption of NTMP by 36% after 3,685 bed volumes. DFT modeling indicated that NTMP and silica adsorption on ferric hydroxide may occur through both mono- and bidentate complex formation. NTMP adsorption through a bidentate binuclear complex was 12 kcal/mol more energetically f...

Transport of multi-walled carbon nanotubes stabilized by carboxymethyl cellulose and starch in saturated porous media: Influences of electrolyte, clay and humic acid

This study investigated the transport behaviors of carboxymethyl cellulose (CMC) and starch stabilized multi-walled carbon nanotubes (MWNTs) through a saturated quartz sand column in the presence of electrolytes, model clays, and natural organic matter (humic acid) through column breakthrough experiments and model simulations. Both stabilizers, CMC and starch, greatly enhanced the breakthrough of MWNTs, with a full breakthrough plateau (C/C0) ranging from 0.69 to 0.90 at ionic strength from 0.3 to 10mM. Between the two stabilizers, CMC was more effective in resisting particle deposition, and thus CMC-stabilized MWNTs were more transportable through the medium. While non-stabilized MWNTs were much less transportable and were vulnerable to electrolyte effects (especially Ca2+), the stabilized counterparts were much more resistant to the coagulation effects of electrolytes. The presence of colloidal clay particles showed contrasting effects on the transport of bare and stabilized MWNTs. The full breakthrough C/C0 of bare MWNTs was suppressed by kaolinite and montmorillonite particles from 0.33 to <0.15 with 5mg/L clay, indicating that the presence of both clays enhanced the aggregation and deposition of MWNTs. However, kaolinite particles facilitated the transport of stabilized-MWNTs, while montmorillonite weakened the breakthrough of stabilized MWNTs. Humic acid had less effect on the mobility of stabilized-MWNTs than that of bare MWNTs. The advection-dispersion transport model incorporated with the filtration theory was able to simulate the breakthrough curves and quantitatively interpret the particle deposition. The results can facilitate our understanding of fate and transport of stabilized carbon nanotubes in the environment.

A Fine-Tuned Fluorinated MOF Addresses the Needs for Trace CO2 Removal and Air Capture Using Physisorption.

The development of functional solid-state materials for carbon capture at low carbon dioxide (CO2) concentrations, namely, from confined spaces (<0.5%) and in particular from air (400 ppm), is of prime importance with respect to energy and environment sustainability. Herein, we report the deliberate construction of a hydrolytically stable fluorinated metal-organic framework (MOF), NbOFFIVE-1-Ni, with the appropriate pore system (size, shape, and functionality), ideal for the effective and energy-efficient removal of trace carbon dioxide. Markedly, the CO2-selective NbOFFIVE-1-Ni exhibits the highest CO2 gravimetric and volumetric uptake (ca. 1.3 mmol/g and 51.4 cm(3) (STP) cm(-3)) for a physical adsorbent at 400 ppm of CO2 and 298 K. Practically, NbOFFIVE-1-Ni offers the complete CO2 desorption at 328 K under vacuum with an associated moderate energy input of 54 kJ/mol, typical for the full CO2 desorption in conventional physical adsorbents but considerably lower than chemical sorbents. Noticeably, the contracted square-like channels, affording the close proximity of the fluorine centers, permitted the enhancement of the CO2-framework interactions and subsequently the attainment of an unprecedented CO2 selectivity at very low CO2 concentrations. The precise localization of the adsorbed CO2 at the vicinity of the periodically aligned fluorine centers, promoting the selective adsorption of CO2, is evidenced by the single-crystal X-ray diffraction study on NbOFFIVE-1-Ni hosting CO2 molecules. Cyclic CO2/N2 mixed-gas column breakthrough experiments under dry and humid conditions corroborate the excellent CO2 selectivity under practical carbon capture conditions. Pertinently, the notable hydrolytic stability positions NbOFFIVE-1-Ni as the new benchmark adsorbent for direct air capture and CO2 removal from confined spaces.

A versatile noninvasive method for adsorber quantification in batch and column chromatography based on the ionic capacity.

Within the Quality by Design (QbD) framework proposed by the International Conference on Harmonisation (ICH), high-throughput process development (HTPD) and mechanistic modeling are of outstanding importance for future biopharmaceutical chromatography process development. In order to compare the data derived from different column scales or batch chromatographies, the amount of adsorber has to be quantified with the same noninvasive method. Similarly, an important requirement for the implementation of mechanistic modeling is the reliable determination of column characteristics such as the ionic capacity Λ for ion-exchange chromatography with the same method at all scales and formats. We developed a method to determine the ionic capacity in column and batch chromatography, based on the adsorption/desorption of the natural, uv-detectable amino acid histidine. In column chromatography, this method produces results comparable to those of classical acid-base titration. In contrast to acid-base titration, this method can be adapted to robotic batch chromatographic experiments. We are able to convert the adsorber volumes in batch chromatography to the equivalent volume of a compressed column. In a case study, we demonstrate that this method increases the quality of SMA parameters fitted to batch adsorption isotherms, and the capability to predict column breakthrough experiments. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:666-677, 2016.

Transport of stabilized iron nanoparticles in porous media: Effects of surface and solution chemistry and role of adsorption

Carboxymethyl cellulose (CMC) stabilized zero-valent iron (ZVI) (CMC-ZVI) nanoparticles have been extensively tested for remediation of soil and groundwater. This study investigated effects of iron oxide and aluminum oxide on retention and transport of CMC-ZVI nanoparticles, which have a mean hydrodynamic diameter of 155nm. Column breakthrough experiments showed that the metal oxides coatings on quartz sand greatly enhanced particle retention. A mechanistically sounder transport model was proposed by incorporating a Langmuir-type adsorption rate law into the classic convection–dispersion equation with the adsorption parameters derived from independent experiments. The model allows for a quantitative evaluation of the role of adsorption. While filtration is the primary mechanism for particle retention at lower pore velocities, adsorption becomes more significant at elevated velocities. The presence of 40–80mg-CL−1 of natural organic matter and high ionic strength (up to 200mM CaCl2) had negligible effect on the breakthrough profiles of the nanoparticles. Starch, a neutral polysugar stabilizer, was also tested as a stabilizer. Starch-stabilized ZVI nanoparticles, with a mean hydrodynamic diameter of 303nm, displayed a higher particle retention than CMC-ZVI. The information and modeling approach can facilitate our understanding of fate and transport of stabilized ZVI nanoparticles under various geochemical conditions.

A Hierarchically Porous Metal‐Organic Framework from Semirigid Ligand for Gas Adsorption

AbstractHierarchically porous materials play an important role in facilitating mass transport and improving efficiency of adsorption and separation processes. In this paper, a new strategy is proposed to realize a hierarchically porous metal‐organic framework ([Cu2(OH)(L)]·(DMF)0.8 (FJU‐11, H3L=3,5‐(4‐carboxybenzyloxy)benzoic acid, DMF=N,N‐dimethylformamide) via using semi‐rigid multi‐carboxylic acids. Interestingly, FJU‐11 possesses the large adsorption capacities and small isosteric heats toward CO2. The column breakthrough experiment for FJU‐11 highlights its potential application in the separation of the flue gas.

A straightforward methodology for designing continuous monoclonal antibody capture multi-column chromatography processes

A simple process development strategy for continuous capture multi-column chromatography (MCC) is described. The approach involves a few single column breakthrough experiments, based on several simplifying observations that enable users to rapidly convert batch processes into well-designed multi-column processes. The method was validated using a BioSMB® (Pall Life Sciences) lab scale multi-column system and a mAb capture process employing Protein A resin. The approach enables users to optimize MCC processes based on their internal preferences and constraints without requiring any mathematical modeling expertise.

Uranium transport in a crushed granodiorite: Experiments and reactive transport modeling

The primary objective of this study was to develop and demonstrate an experimental method to refine and better parameterize process models for reactive contaminant transport in aqueous subsurface environments and to reduce conservatism in such models without attempting to fully describe the geochemical system. Uranium was used as an example of a moderately adsorbing contaminant because of its relevance in geologic disposal of spent nuclear fuel. A fractured granodiorite from the Grimsel Test Site (GTS) in Switzerland was selected because this system has been studied extensively and field experiments have been conducted with radionuclides including uranium. We evaluated the role of pH, porous media size fraction, and flow interruptions on uranium transport. Rock cores drilled from the GTS were shipped to Los Alamos National Laboratory, characterized by x-ray diffraction and optical microscopy, and used in uranium batch sorption and column breakthrough experiments. A synthetic water was prepared that represented the porewater that would be present after groundwater interacts with bentonite backfill material near a nuclear waste package. Uranium was conservatively transported at pH8.8. Significant adsorption and subsequent desorption was observed at pH ~7, with long desorption tails resulting after switching the column injection solution to uranium-free groundwater. Our experiments were designed to better interrogate this slow desorption behavior. A three-site model predicted sorption rate constants for a pH7.2 solution with a 75–150μm granodiorite fraction to be 3.5, 0.012, and 0.012mL/g-h for the forward reactions and 0.49, 0.0025, and 0.001h−1 for the reverse reactions. Surface site densities were 1.3, 0.042, and 0.042μmol/g for the first, second, and third sites, respectively. 10-year simulations show that including a slow binding site increases the arrival time of a uranium pulse by ~70%.

Ionized Zr-MOFs for highly efficient post-combustion CO2 capture

In this study, a previously reported Zr-MOF UiO-66(Zr)-(COOH)2 with optimal features for CO2 capture was ionized by neutralization with aqueous MOH solutions (M=Li+, Na+, K+). This post-synthetic modification route has endowed some of the resulting MOFs with higher CO2 uptake capacity. The CO2/N2 selectivity of UiO-66(Zr)-(COOK)2 calculated by Ideal Adsorption Solution Theory (IAST) demonstrates a significant enhancement of 83% compared with the pristine MOF. In addition, dynamic column breakthrough experiments were performed using a binary CO2/N2 mixed gas with a molar ratio of 15:85 to mimic the flue gas composition. The CO2/N2 selectivity of UiO-66(Zr)-(COONa)2 calculated based on breakthrough data is 99.6, which is among the highest CO2/N2 selectivities obtained experimentally using binary mixed gas breakthrough/co-adsorption experiments. Our results strongly confirm that ionization is an effective way of introducing strong CO2 adsorption sites into MOFs for higher CO2-MOF interactions and better CO2 separation performance.

Fabrication of Liquid and Vapor Protective Cotton Fabrics

Through microwave-assisted techniques, cotton textiles treated with heptadecafluoro-1,1,2,2-tetrahydrodecyltrimethoxysilane in the presence of high surface area silica nanoparticles create a material capable of repelling bulk liquid challenges while simultaneously adsorbing organic vapors from bulk liquid droplets. Characterizing the contradictory behavior of adsorption of vapors and repellency of liquids is the primary focus of this article. These procedures reveal a quick and simple method for a one-step deposition of a vapor-sorptive, liquid-repellent, Cassie-Baxter surface onto textiles. Packed column breakthrough and single swatch permeation experiments showed that treated materials possess a high affinity for 3-hepten-2-one vapor, while goniometry revealed contact angles in excess of 120° for surface-deposited, 5 μL droplets of several test liquids. Scanning electron micrograph images confirm a lotus-like, nanorough surface, while ATR-FTIR spectra confirm surface fluorocarbon moieties. The performance of so-treated materials lends itself to the application of chemical protective apparel, while the simplicity of the treatment bodes well for potential commercialization.

Adsorption of alkaloids on ordered mesoporous carbon

An ordered mesoporous carbon (OMC) adsorbent was synthesized, characterized, and evaluated for effective separation and purification of alkaloid compounds from aqueous solutions. The OMC adsorbent has a large BET specific surface area (1532.2m2/g), large pore volume (2.13cm3/g), and narrow pore diameter distribution with a median pore diameter of 4.21nm. Berberine hydrochloride, colchicine, and matrine were selected as the model compounds for evaluating the adsorption properties of the OMC adsorbent for alkaloid purification. Batch adsorption experiments of pure components in water were carried out to measure both adsorption equilibria and kinetics, and column breakthrough and desorption experiments were performed to validate the separation and regeneration efficacy of the OMC adsorbent. The adsorption equilibrium capacities of berberine hydrochloride, colchicine, and matrine on the OMC adsorbent at 0.100mg/L and 298K are 450, 600, and 480mg/g, respectively, which are more than double the adsorption capacities of these compounds on two commonly used commercial resins (HPD300 and HPD100B) at similar conditions. Adsorption equilibrium of all three alkaloids could be obtained within 120min at 298K. The dynamic adsorption capacities determined from the breakthrough experiments are within 12% of the estimated equilibrium capacities from the Langmuir isotherms; and 74.3–92.8% of the adsorbed amounts could be recovered by desorbing with a 70% alcohol solution. The adsorption isotherms are analyzed with both Langmuir and Freundlich models, the adsorption kinetic data with the pseudo-first-order and pseudo-second-order models, and the breakthrough curves with four breakthrough models. The large adsorption capacity, fast adsorption rate, and easy regeneration make the ordered mesoporous carbon a promising adsorbent for adsorption and purification of alkaloid compounds from the extracts of herbal plants.

Post-combustion CO2 capture with the HKUST-1 and MIL-101(Cr) metal–organic frameworks: Adsorption, separation and regeneration investigations

CO2 sequestration from combustion of fossil fuels, particularly coal, is an essential component of any serious plan to avoid catastrophic impacts of human-induced climate change. In this work, we describe a comparative investigation of post-combustion CO2 capture by using two representative metal–organic frameworks (MOFs), i.e. MIL-101(Cr) and [Cu3(BTC)2]n (HKUST-1, BTC=benzene-1,3,5-tricarboxylate). Adsorption of CO2 was investigated over a wide range of adsorption conditions (30–200°C, 0–10bar) on these MOFs. The results reveal that CO2 adsorption capacity of the MOFs investigated increases with increasing CO2 pressure while decreases with increasing the adsorption temperature. The CO2 capacities for MIL-101(Cr) and HKUST-1 were determined to be 8.07 and 7.19mmolg−1, respectively, at 30°C and 10bar. Particularly, dynamic column-breakthrough experiments for CO2 separation in a binary CO2/N2 mixture with a composition typical of flue gas were investigated in a single-bed adsorption unit. Temperature swing adsorption (TSA) experiments were further investigated for regeneration of HKUST-1 and MIL-101(Cr). The results reveal that HKUST-1 has a higher CO2 adsorption capacity (1.82mmolg−1) than MIL-101(Cr) (1.17mmolg−1) under similar conditions, suggesting the HKUST-1 is more promise for separating CO2 in comparison with MIL-101(Cr). Furthermore, both TSA and vacuum swing adsorption (VSA) investigations were conducted for HKUST-1 regeneration, clearly indicating that TSA shows high efficiency for the MOF regeneration. However, VSA strategy was inefficient for regeneration of HKUST-1, which is due to the existence of coordinatively unsaturated metal active sites in the framework.