CO2 Adsorption Uptake Research Articles

1,3-Diyne-Linked Conjugated Microporous Polymer for Selective CO2 Capture

In this work, we demonstrate that the introduction of pyrene and alkyne groups into a highly conjugated microporous polymer (LKK-CMP-1) can be achieved via oxidative homocoupling of 1,3,6,8-tetraethynylpyrene (L). The 1,3-diyne-linked conjugated microporous polymer not only has good thermal stability but also has small pore sizes. These small pores within LKK-CMP-1 facilitate the interactions between CO2 and its pore walls, evidenced by the high isosteric heats of adsorption of CO2 and also confirmed by ideal-adsorption-solution-theory (IAST) calculations based on single-component-isotherm data. Therefore, despite moderate CO2 adsorption uptake (9.78 wt %, 273 K, and 1 bar) and isosteric heat of adsorption (35.0 kJ mol–1) for CO2, LKK-CMP-1 still exhibits excellent selectivities of CO2/N2 (44.2) and CO2/CH4 (8.2) at molar ratios of 15:85 and 20:80 respectively. In addition, breakthrough experiments have also shown that LKK-CMP-1 is an effective material for CO2/N2 and CO2/CH4 separations under flowing con...

Experimental investigation on the CO2 separation performance from humid flue gas by TSA process

This work was aimed at removing CO2 from a fire power plant by using the thermal swing adsorption (TSA) process. It is well known that CO2 adsorption uptake is blocked by the coexistence of steam in the TSA process. In this paper, the influence of desorption temperature and relative humidity in the desorption process on the CO2 capture performance during the TSA process is kinetically investigated. Under conditions without water, the adsorption decreases by half; when the relative humidity is 1.1% at 393 K, adsorption decreases to 2.5 mg-CO2/ghoneycomb. The recovery ratio of the CO2 adsorption performance depends on the relative humidity, not the desorption temperature. Therefore, in the TSA process, it is expected that the influence of steam can be disregarded if a better steam desorption adsorbent is used. This has the added benefit of eliminating the need to remove steam during preprocessing.

Enhancement of CO2 adsorption and separation for non-porous Zn/Co azolate frameworks via ethanol-induced structural transformation

Non-porous zinc/cobalt azolate frameworks with diamond-type crystal structure (MAF–31/ZIF–D–CoM) have been synthesized in large scale with an acid-catalyzed process. Afterward, an ethanol exposure process was applied for 1, 7, and 14 days to transform MAF–31/ZIF–D–CoM into porous T–MAF–4/T–ZIF–67. Two porous zinc/cobalt azolate frameworks standards (MAF–4/ZIF–67) with sodalite-type crystal structures were prepared with a solvent-free method for comparison with T–MAF–4/T–ZIF–67. Effects of ethanol vapor exposure on structual transformation of MAF–31/ZIF–D–CoM were characterized throughly. Obvious structural transfomations between non-porous and porous zinc/cobalt azolate frameworks were found with X–ray diffraction (XRD), Field–emission scanning electron microscope (FE–SEM), and X–ray absorption near-edge structure/extended X–ray absorption fine structure (XANES/EXAFS) spectra. After the 14-day ethanol vapor exposure, the CO2 adsorption uptakes of MAF–31 and ZIF–D–CoM in low/high pressures were enhanced from 5.18 × 10−5/0.68 and 1.20 × 10−4/0.18 to 1.76 × 10−3/8.27 and 1.99 × 10−3/11.2 mmol/g, respectively. The CO2 selectivities of MAF–31/ZIF–D–CoM were also improved from 0.29/2.34 to 6.33/16.47. In addition, CO2 adsorption over zinc/cobalt azolate frameworks obeyed both Langmuir/Freundlich adsorption isotherm models with good agreements.

Adsorption characterization and CO2 breakthrough of MWCNT/Mg-MOF-74 and MWCNT/MIL-100(Fe) composites

Carbon capture using adsorption processes can significantly mitigate global warming. Mg-MOF-74 is a distinct reticular material amongst other adsorbents owing to its distinguished carbon dioxide adsorption capacity and selectivity under low-pressure applications, while MIL-100(Fe) has lower CO2 adsorption capacity, but extraordinary thermal and hydrostability in comparison to many classes of MOFs. In this paper, we present CO2 adsorption characteristics of new compounds formed by the incorporation of multi-walled carbon nanotubes (MWCNTs) into Mg-MOF-74 and MIL-100(Fe). This was done to improve the thermal diffusion properties of the base MOFs to enhance their adsorption capacities. The new composites have been characterized for degree of crystallinity, and the CO2 and N2 equilibrium uptake. The real adsorption separation has been investigated by dynamic breakthrough tests at 297 K and 101.325. The equilibrium isotherm results showed that Mg-MOF-74 and 0.25 wt% MWCNT/MIL-100(Fe) (MMC2) have the highest CO2 uptake in comparison to the other investigated composites. However, the interesting results obtained from breakthrough tests demonstrate that good improvements in the CO2 adsorption uptake and breakthrough breakpoint over pristine Mg-MOF-74 have been accomplished by adding 1.5 wt% MWCNT to Mg-MOF-74. The improvements of CO2 adsorption capacity and breakpoint were about 7.35 and 8.03%, respectively. Similarly, the CO2 adsorption uptake and breakthrough breakpoint over pristine MIL-100(Fe) are obtained by 0.1 wt% MWCNT/MIL-100(Fe) (MMC1) with improvements of 12.02 and 9.21%, respectively.

Structured emulsion-templated porous copolymer based on photopolymerization for carbon capture

Porous hydrogel copolymers of acrylamide (AAM) and acrylic acid (AAC) were structured in the form of monoliths and granules. AAM-co-AAC porous copolymer monoliths were synthesized using high internal phase emulsion (HIPE) as template and photopolymerization. For granulation, photopolymerization was used for the fabrication of the AAM-co-AAC hydrogel, which was subsequently freeze-granulated. The structural analysis (FTIR and XRD) confirmed the successful synthesis of hydrogel copolymers. The CO2 uptake capacity of structured AAM-co-AAC copolymers was evaluated through adsorption and absorption mechanisms by volumetric and gravimetric methods, respectively. The granules exhibited the CO2 adsorption uptake of 0.8mmolg−1 at 25kPa and 298K. The CO2 and N2 adsorption data demonstrated that the hydrogel copolymers were selective for CO2. Furthermore, the granules were capable of capturing CO2 in the presence of water. The results of absorption of CO2 on water-swollen granules demonstrated that CO2-uptake capacity increases with increasing water content up to 1.8mmolg−1.

Preparation of carbon molecular sieves and its impregnation with Co and Ni for CO2/N2 separation

The carbon molecular sieves (CMSs) prepared by carbonaceous materials as precursors are effective in CO2/N2 separation. However, selectivity of these materials is too low, since hydrocarbon cracking for developing the desired microporosity in carbonaceous materials has not been done effectively. Hence, in this study, cobalt and nickel impregnation on the precursor was conducted to introduce catalysts for hydrocarbon cracking. Cobalt and nickel impregnation, carbonization under N2 atmosphere, and chemical vapor deposition (CVD) by benzene were conducted on the extruded mixtures of activated carbon and coal tar pitch under different conditions to prepare CMSs. The best CMS prepared by carbon deposition on the cobalt-impregnated samples exhibited CO2 adsorption capacity of 54.79 mg/g and uptake ratio of 28.9 at 0 °C and 1 bar. In terms of CO2 adsorption capacity and uptake ratio, CMSs prepared by carbon deposition on non-impregnated and cobalt-impregnated samples presented the best results, respectively. As benzene concentration and CVD time increased, equilibrium adsorption capacity of CO2 decreased, and uptake ratio increased. Cobalt was found to be the best catalyst for benzene cracking in the CVD process.

Development of a cost-effective CO2 adsorbent from petroleum coke via KOH activation

The capture of CO2 via adsorption is considered an effective technology for decreasing global warming issues; hence, adsorbents for CO2 capture have been actively developed. Taking into account cost-effectiveness and environmental concerns, the development of CO2 adsorbents from waste materials is attracting considerable attention. In this study, petroleum coke (PC), which is the carbon residue remaining after heavy oil upgrading, was used to produce high-value-added porous carbon for CO2 capture. Porous carbon materials were prepared by KOH activation using different weight ratios of KOH/PC (1:1, 2:1, 3:1, and 4:1) and activation temperatures (600, 700, and 800°C). The specific surface area and total pore volume of resulting porous carbon materials increased with KOH amount, reaching up to 2433m2/g and 1.11cm3/g, respectively. The sample prepared under moderate conditions with a KOH/PC weight ratio of 2:1 and activation temperature of 700°C exhibited the highest CO2 adsorption uptake of 3.68mmol/g at 25°C and 1bar. Interestingly, CO2 adsorption uptake was linearly correlated with the volume of micropores less than 0.8nm, indicating that narrow micropore volume is crucial for CO2 adsorption. The prepared porous carbon materials also exhibited good selectivity for CO2 over N2, rapid adsorption, facile regeneration, and stable adsorption–desorption cyclic performance, demonstrating potential as a candidate for CO2 capture.

Development of polyethylenimine-functionalized mesoporous Si-MCM-41 for CO2 adsorption

This work describes the functionalization of mesoporous Si-MCM-41 with different loadings of polyethylenimine (PEI), their characterization and detailed study of their CO2 adsorption performance. A series of Si-MCM-41 samples functionalized with 10–50wt% PEI was synthesized by wet impregnation method. The physicochemical properties such as pore structural ordering and textural properties of the samples were characterized by X-ray diffraction and N2 adsorption/desorption analysis, respectively. The XRD analysis of pristine Si-MCM-41 showed well-defined four diffraction peaks of (100), (110), (200) and (210) planes. Upon loading of 10–50wt% PEI, intensity of these diffraction peaks reduced gradually due to decrease in scattering contrast. Also, N2 adsorption/desorption analysis showed change in textural properties from porous to non-porous material as the loading of PEI increased from 10 to 50wt%. To optimize the loading of PEI for maximum CO2 adsorption, samples were screened at 25°C and 0–1 bar using a gravimetric method. The sample containing 50wt% PEI showed the highest CO2 uptake of 47.93 mg/g due to high content of CO2–affinity sites and was further used to investigate the effect of temperature ranging from 25 to 125°C on CO2 adsorption performance. The best CO2 adsorption (99.44 mg/g) was obtained at 100°C and 1 bar due to flexible behavior of PEI. At this optimized temperature, the Si-MCM-41 containing 50wt% PEI was used to evaluate the effect of pressure ranging from 0 to 20 bar where it showed increase in CO2 adsorption uptake of 156mg/g. Si-MCM-41 containing 50wt% PEI showed strong affinity for CO2 compared to N2 and H2. In a regeneration study, a gradual decline in CO2 uptake was observed as the number of adsorption/desorption cycles increased. Infrared spectroscopy revealed carbamates formation confirming the interaction of CO2 with the amino groups of PEI incorporated into Si-MCM-41 containing 50wt% PEI via chemisorption.

A flexible porous copper-based metal-organic cage for carbon dioxide adsorption

A metal-organic cage (termed FJI-C9) based on six square-shaped Cu2(CO2)4 paddle-wheel building units and eight flexible 1,3,5-trimethyl-2,4,6-tris(3-phenoxymethyl)benzoic acid (TTBA) linkers has been constructed. The porous FJI-C9 containing large cage of 1.5nm shows high CO2 adsorption uptake.

CO2adsorption and separation in covalent organic frameworks with interlayer slipping

In layered COFs, slipping results in non-monotonous variation in CO2adsorption and higher uptakes were found near a slipping distance of 10 Å.

Metal‐Organic Frameworks for Carbon Dioxide Capture and Methane Storage

In the global transition to a sustainable low‐carbon economy, CO2 capture and storage technology still plays a critical role for deep emission reduction, particularly for the stationary sources in power generation and industry. However, for small and mobile emission sources in transportation, CO2 capture is not suitable and it is more practical to use relatively clean energy, such as natural gas. In these two low‐carbon energy technologies, designing highly selective sorbents is one of the key and most challenging steps. Toward this end, metal‐organic frameworks (MOFs) have received continuously intensive attention in the past decades for their highly porous and diversified structures. In this review, the recent progress in developing MOFs for selective CO2 capture from post‐combustion flue gas and CH4 storage for vehicle applications are summarized. For CO2 capture, several promising strategies being used to improve CO2 adsorption uptake at low pressures are highlighted and compared. In addition, the conventional and novel regeneration techniques for MOFs are also discussed. In the case of CH4 storage, the flexible and rigid MOFs, whose CH4 storage capacity is close to the target set by U.S. Department of Energy are particularly emphasized. Finally, the challenge of using MOFs for CH4 storage is discussed.

Hierarchical porous nitrogen-doped carbon materials derived from one-step carbonization of polyimide for efficient CO2 adsorption and separation

Hierarchical porous nitrogen-doped carbon (HPNC) materials are synthesized through one-step carbonization of polyimide using triblock copolymer P123 as mesoporous template. The microstructure, chemical composition and CO2 adsorption behaviors are investigated in detail. The results show that HPNC materials have hierarchical micro-/mesopore structures, high specific surface area of 579 m2/g, large pore volume of 0.34 cm3/g, and nitrogen functional groups (5.2 %). HPNC materials exhibit high CO2 uptake of 5.56 mmol/g at 25 °C and 1 bar, which is higher than those of previously reported nitrogen-doped porous carbon materials. After 5 cycles the value of CO2 adsorption uptakes is 5.28 mmol/g, which is approximately 95 % of the original adsorption capacity. The estimated CO2/N2 selectivity of HPNC materials is 17, revealing great promise for practical CO2 adsorption and separation applications. The efficient CO2 uptake and enhanced CO2/N2 selectivity are due to the combination of nitrogen-doped and hierarchical porous structures of HPNC materials.

CO2 Capture in the Sustainable Wheat-Derived Activated Microporous Carbon Compartments.

Microporous carbon compartments (MCCs) were developed via controlled carbonization of wheat flour producing large cavities that allow CO2 gas molecules to access micropores and adsorb effectively. KOH activation of MCCs was conducted at 700 °C with varying mass ratios of KOH/C ranging from 1 to 5, and the effects of activation conditions on the prepared carbon materials in terms of the characteristics and behavior of CO2 adsorption were investigated. Textural properties, such as specific surface area and total pore volume, linearly increased with the KOH/C ratio, attributed to the development of pores and enlargement of pores within carbon. The highest CO2 adsorption capacities of 5.70 mol kg−1 at 0 °C and 3.48 mol kg−1 at 25 °C were obtained for MCC activated with a KOH/C ratio of 3 (MCC-K3). In addition, CO2 adsorption uptake was significantly dependent on the volume of narrow micropores with a pore size of less than 0.8 nm rather than the volume of larger pores or surface area. MCC-K3 also exhibited excellent cyclic stability, facile regeneration, and rapid adsorption kinetics. As compared to the pseudo-first-order model, the pseudo-second-order kinetic model described the experimental adsorption data methodically.

Prediction of phase transitions by investigating CO2 adsorption on 1% lithium doped MIL-101 (Cr) MOF with anomalous type isosteric heat of adsorption

The amount of adsorbate uptakes and heats of adsorption (Qst) for CO2 + 1% Li doped MIL-101 (Cr) metal organic framework (MOF) system are measured at wide ranges of pressures and temperatures. Some data are reported for the regions below the triple point (200 K–216.5 K). The multilayer CO2 adsorption uptakes in a series of discontinuous jump are found in the sub-triple region. Various types and shapes of Qst are observed and the unexpected differences in Qst at sub-triple, sub-critical and super critical regions are explained. At sub-triple zone, two sharp spikes of Qst against uptakes are found for identifying the transitions of adsorbate layer from the gaseous phase to the solid phase. The gas – liquid transition is also observed from the uptake dependence Qst data at 220 K and 240 K. A monotonic decrease in Qst is found at higher temperatures.

Characterization on trace carbon monoxide leakage in high purity hydrogen in sorption enhanced water gas shifting process

The sorption-enhanced water–gas shift (SEWGS) reaction based on elevated-temperature CO2 adsorbent and water–gas shift (WGS) catalyst has the potential to produce fuel cell levels of H2 from syngas directly. However, more than 20 ppm of CO could poison the Pt electrode in a proton exchange membrane fuel cell. In this paper, the outlet CO concentration of SEWGS was investigated in a fixed bed at 350–450 °C at 1–3 MPa. The reactor was filled with K2CO3-promoted Mg–Al hydrotalcite and high-temperature Fe–Cr WGS catalyst with a volume ratio of 5. The ratio of CO and CO2 breakthrough time τk was first proposed to characterize the utilization ratio of CO2 adsorbent quantitatively. Various working conditions of SEWGS, including inlet CO concentration (5–20 Vol%), balanced gas (Ar, H2), cycle index (1–4), and S/G ratio (1.25–5), are studied. The experimental results show that CO concentration can be less than 10 ppm when the inlet gas consists of 5%–20% CO and balanced Ar. If 95% H2 is added, a range of 147.5–205.0 ppm of CO concentration is achieved. τ20 is between 0.34 and 0.81 in the tested conditions. The breakthrough time of CO is maintained relatively stable by changing the CO inlet concentration. There is an optimal S/G ratio owing to the WGS thermodynamic balance and the competitive adsorption of H2O. The CO2 adsorption uptake before the breakthrough of CO increases with increasing total pressure, and the performance of SEWGS declines at temperatures above 400 °C.

Direct Carbonization of Cyanopyridinium Crystalline Dicationic Salts into Nitrogen-Enriched Ultra-Microporous Carbons toward Excellent CO2 Adsorption.

A family of nitrogen-enriched ultramicroporous carbon materials was prepared by direct carbonization of task-specifically designed molecular carbon precursors of cyanopyridinium-based crystalline dicationic salts (CISs). Varying the molecular structure of CISs, large surface area (918 m(2) g(-1)), high N content (20.10 wt %), and narrow distributed ultramicropores (0.59 nm) can be simultaneously achieved on the sample PCN-14 derived from methyl-linked 4-cyanopyridinium D[4-CNPyMe]Tf2N. It therefore exhibited exceptional performance in greenhouse gas CO2 capture, i.e., simultaneously possessing (1) high CO2 adsorption uptakes: 5.33 mmol g(-1) at 273 K, and 3.68 mmol g(-1) at 298 K (both at 1.0 bar); (2) unprecedented selectivity of CO2 versus N2: 156; and (3) a high adsorption ratio of CO2 to N2: 148 (at 1.0 bar). This is the first time such a high selectivity and adsorption ratio over carbon materials has been achieved, which is among the highest values over solid adsorbents.

Preparation of porous carbons based on polyvinylidene fluoride for CO2 adsorption: A combined experimental and computational study

Microporous carbons were developed for CO2 capture from polyvinylidene fluoride (PVDF) via a simple carbonization method. The carbonization was carried out in the temperature range of 400–800 °C, and the effects of the carbonization temperature on the characteristics and CO2 adsorption behavior of the prepared carbon materials were investigated by both experiments and density functional theory studies. The textural characteristics of the carbon materials were highly dependent on the carbonization temperature, and narrow micropores (<0.7 nm) were predominantly generated from the decomposition of PVDF giving off fluorine during carbonization. The specific surface area and pore volume increased up to 1011 m2 g−1 and 0.416 cm3 g−1, respectively, and the highest CO2 adsorption capacity of 3.59 mol kg−1 was obtained at 25 °C and ∼1 bar in PVDF carbonized at 800 °C. The carbonized PVDFs also exhibited highly stable CO2 adsorption uptake and rapid kinetics through repeated adsorption–desorption cycles, showing that carbonized PVDFs are promising adsorbents for CO2 capture. The density functional theory calculation suggested that stable configuration with favorable adsorption energy can be introduced by the removal of fluorine from PVDF, which results in the reduction of repulsive interactions between electronegative fluorine in PVDF and oxygen in CO2 molecule.

Chromium-based metal–organic framework/mesoporous carbon composite: synthesis, characterization and CO2 adsorption

New composites of a water-stable chromium-based metal organic framework MIL-101 and mesoporous carbon CMK-3 were in situ synthesized with different ratios of MIL-101 and CMK-3 using the hydrothermal method. The composites as well as the parent materials were characterized by X-ray diffraction, thermo gravimetric analysis, scanning electron microscope, transmission electron microscope and nitrogen/carbon dioxide adsorption isotherms. The hybrid material possesses the same crystal structure and morphology as its parent MIL-101, and exhibits an enhancement in CO2 adsorption uptakes when compared to MIL-101 and CMK-3. The increase in CO2 uptakes was attributed to the combined effect of the formation of additional micropores, the enhancement of micropore volume and the activation of unsaturated metal sites by CMK-3 incorporation.

Development of porous carbon nanofibers from electrospun polyvinylidene fluoride for CO2capture

Highly porous carbon nanofibers (CNFs) are successfully prepared for CO2 capture from the carbonization of electrospun polyvinylidene fluoride (PVDF). In the CNF preparation, different temperatures in the range 300–1000 °C are applied for carbonization, and the effect of temperature is investigated. Well-developed porosities and enhanced CO2 adsorption uptakes are achieved by applying a large degree of carbonization at temperatures of 400 °C or above. In the carbonization at high temperatures, narrow micropores (<0.7 nm) are predominantly developed in the PVDF-based CNFs, contributing to an increase of specific surface area and pore volume up to 1065 m2 g−1 and 0.61 cm3 g−1, respectively. The highest CO2 adsorption uptake of 3.1 mol kg−1 is measured at 30 °C and ∼1 atm for PVDF-based CNF carbonized at 1000 °C. PVDF-based CNFs also display excellent recyclability and rapid adsorption–desorption kinetics, which make PVDF-based CNFs promising adsorbents for CO2 capture.

Solvent-assisted amine modification of graphite oxide for CO2adsorption

Amine-modified graphite oxides (GAs) for CO2 adsorption were prepared using 3-aminopropyl-triethoxysilane. Graphite was first oxidized using highly concentrated acid, and then modified with the amine using a solvent-assisted method. Ethanol and water were used as the solvents, and the solvent effects were investigated. The morphological changes, functionalities, and compositions of the GAs were characterized by scanning electron microscopy, Fourier-transform infrared and X-ray photoelectron spectroscopies, and elemental analysis. The CO2 adsorption behavior was evaluated by thermogravimetric analysis at 30 °C under atmospheric pressure. The GA prepared in water (GA-W) had a higher CO2 adsorption uptake (1.64 mol kg−1) than did the GA prepared in ethanol (1.31 mol kg−1). The amine loading was predominantly influenced by the solvent, and water was an effective solvent for amine modification. GA-W also showed good regenerability in repeated adsorption–desorption cycles with high adsorption/desorption rates.