Since the time of the industrial revolution, the atmospheric CO2 concentration has risen by nearly 35 % to its current level of 383 ppm. The increased carbon dioxide concentration in the atmosphere ...has been suggested to be a leading contributor to global climate change. To slow the increase, reductions in anthropogenic CO2 emissions are necessary. Large emission point sources, such as fossil‐fuel‐based power generation facilities, are the first targets for these reductions. A benchmark, mature technology for the separation of dilute CO2 from gas streams is via absorption with aqueous amines. However, the use of solid adsorbents is now being widely considered as an alternative, potentially less‐energy‐intensive separation technology. This Review describes the CO2 adsorption behavior of several different classes of solid carbon dioxide adsorbents, including zeolites, activated carbons, calcium oxides, hydrotalcites, organic–inorganic hybrids, and metal‐organic frameworks. These adsorbents are evaluated in terms of their equilibrium CO2 capacities as well as other important parameters such as adsorption–desorption kinetics, operating windows, stability, and regenerability. The scope of currently available CO2 adsorbents and their critical properties that will ultimately affect their incorporation into large‐scale separation processes is presented.
Getting the point: As concern over the rise in atmospheric CO2 concentration has increased, recent research efforts have focused on capturing CO2 from large anthropogenic point sources. Many solid adsorbent classes, including zeolites, activated carbons, calcium oxides, hydrotalcites, organic–inorganic hybrids, and MOFs, have been considered as alternatives to the current benchmark aqueous amine absorption technology for CO2 capture.
Computer-assisted surgical (CAS) navigation has been developed with the aim of improving the accuracy and precision of total knee arthroplasty (TKA) component positioning and therefore overall limb ...alignment. The historical goal of knee arthroplasty has been to restore the mechanical alignment of the lower limb by aligning the femoral and tibial components perpendicular to the mechanical axis of the femur and tibia. Despite over 4 decades of TKA component development and nearly 2 decades of interest in CAS, the fundamental question remains; does the alignment goal and/or the method of achieving that goal affect the outcome of the TKA in terms of patient-reported outcome measures and/or overall survivorship? The quest for reliable and reproducible achievement of the intraoperative alignment goal has been the primary motivator for the introduction, development, and refinement of CAS navigation. Numerous proprietary systems now exist, and rapid technological advancements in computer processing power are stimulating further development of robotic surgical systems. Three categories of CAS can be defined: image-based large-console navigation; imageless large-console navigation, and more recently, accelerometer-based handheld navigation systems have been developed.
A review of the current literature demonstrates that there are enough well-designed studies to conclude that both large-console CAS and handheld navigation systems improve the accuracy and precision of component alignment in TKA. However, missing from the evidence base, other than the subgroup analysis provided by the Australian Orthopaedic Association National Joint Replacement Registry, are any conclusive demonstrations of a clinical superiority in terms of improved patient-reported outcome measures and/or decreased cumulative revision rates in the long term. Few authors would argue that accuracy of alignment is a goal to ignore; therefore, in the absence of clinical evidence, many of the arguments against the use of large-console CAS navigation center on the prohibitive cost of the systems. The utilization of low-cost, handheld CAS navigation systems may therefore bridge this important gap, and over time, further clinical evidence may emerge.
Oxide supports functionalized with amine moieties have been used for decades as catalysts and chromatographic media. Owing to the recognized impact of atmospheric CO2 on global climate change, the ...study of the use of amine-oxide hybrid materials as CO2 sorbents has exploded in the past decade. While the majority of the work has concerned separation of CO2 from dilute mixtures such as flue gas from coal-fired power plants, it has been recognized by us and others that such supported amine materials are also perhaps uniquely suited to extract CO2 from ultradilute gas mixtures, such as ambient air. As unique, low temperature chemisorbents, they can operate under ambient conditions, spontaneously extracting CO2 from ambient air, while being regenerated under mild conditions using heat or the combination of heat and vacuum. This Account describes the evolution of our activities on the design of amine-functionalized silica materials for catalysis to the design, characterization, and utilization of these materials in CO2 separations. New materials developed in our laboratory, such as hyperbranched aminosilica materials, and previously known amine-oxide hybrid compositions, have been extensively studied for CO2 extraction from simulated ambient air (400 ppm of CO2). The role of amine type and structure (molecular, polymeric), support type and structure, the stability of the various compositions under simulated operating conditions, and the nature of the adsorbed CO2 have been investigated in detail. The requirements for an effective, practical air capture process have been outlined and the ability of amine–oxide hybrid materials to meet these needs has been discussed. Ultimately, the practicality of such a “direct air capture” process is predicated not only on the physicochemical properties of the sorbent, but also how the sorbent operates in a practical process that offers a scalable gas–solid contacting strategy. In this regard, the utility of low pressure drop monolith contactors is suggested to offer a practical mode of amine sorbent/air contacting for direct air capture.
Direct Capture of CO2 from Ambient Air Sanz-Pérez, Eloy S; Murdock, Christopher R; Didas, Stephanie A ...
Chemical reviews,
10/2016, Letnik:
116, Številka:
19
Journal Article
Recenzirano
Odprti dostop
The increase in the global atmospheric CO2 concentration resulting from over a century of combustion of fossil fuels has been associated with significant global climate change. With the global ...population increase driving continued increases in fossil fuel use, humanity’s primary reliance on fossil energy for the next several decades is assured. Traditional modes of carbon capture such as precombustion and postcombustion CO2 capture from large point sources can help slow the rate of increase of the atmospheric CO2 concentration, but only the direct removal of CO2 from the air, or “direct air capture” (DAC), can actually reduce the global atmospheric CO2 concentration. The past decade has seen a steep rise in the use of chemical sorbents that are cycled through sorption and desorption cycles for CO2 removal from ultradilute gases such as air. This Review provides a historical overview of the field of DAC, along with an exhaustive description of the use of chemical sorbents targeted at this application. Solvents and solid sorbents that interact strongly with CO2 are described, including basic solvents, supported amine and ammonium materials, and metal–organic frameworks (MOFs), as the primary classes of chemical sorbents. Hypothetical processes for the deployment of such sorbents are discussed, as well as the limited array of technoeconomic analyses published on DAC. Overall, it is concluded that there are many new materials that could play a role in emerging DAC technologies. However, these materials need to be further investigated and developed with a practical sorbent–air contacting process in mind if society is to make rapid progress in deploying DAC as a means of mitigating climate change.
Composites of poly(ethylenimine) (PEI) and mesoporous silica are effective, reversible adsorbents for CO2, both from flue gas and in direct air-capture applications. The morphology of the PEI within ...the silica can strongly impact the overall carbon capture efficiency and rate of saturation. Here, we directly probe the spatial distribution of the supported polymer through small-angle neutron scattering (SANS). Combined with textural characterization from physisorption analysis, the data indicate that PEI first forms a thin conformal coating on the pore walls, but all additional polymer aggregates into plug(s) that grow along the pore axis. This model is consistent with observed trends in amine-efficiency (CO2/N binding ratio) and pore size distributions, and points to a trade-off between achieving high chemical accessibility of the amine binding sites, which are inaccessible when they strongly interact with the silica, and high accessibility for mass transport, which can be hampered by diffusion through PEI plugs. We illustrate this design principle by demonstrating higher CO2 capacity and uptake rate for PEI supported in a hydrophobically modified silica, which exhibits repulsive interactions with the PEI, freeing up binding sites.
Molecular sieving metal-organic framework (MOF) membranes have great potential for energy-efficient chemical separations, but a major hurdle is the lack of a scalable and inexpensive membrane ...fabrication mechanism. We describe a route for processing MOF membranes in polymeric hollow fibers, combining a two-solvent interfacial approach for positional control over membrane formation (at inner and outer surfaces, or in the bulk, of the fibers), a microfluidic approach to replenishment or recycling of reactants, and an in situ module for membrane fabrication and permeation. We fabricated continuous molecular sieving ZIF-8 membranes in single and multiple poly(amide-imide) hollow fibers, with H2/C3H8 and C3H6/C3H8 separation factors as high as 370 and 12, respectively. We also demonstrate positional control of the ZIF-8 films and characterize the contributions of membrane defects and lumen bypass.
High‐quality 2D MFI nanosheet coatings were prepared on α‐alumina hollow fiber supports by vacuum filtration and then transformed into molecular sieving membranes by two sequential hydrothermal ...treatments. This processing method eliminates the need for specially engineered silica‐based support materials that have so far been necessary to allow the formation of functional membranes from 2D MFI nanosheets. The sequential steps enhance adhesion of the membrane on the fiber support, fill in nanoscale gaps between the 2D nanosheets, and preserve the desirable (0k0) out‐of‐plane orientation without the need of any support engineering or modification. The membrane exhibits high performance for separation of n‐butane from i‐butane, and for other technologically important hydrocarbon separations. The present findings have strong implications on strategies for obtaining thin, highly selective zeolite membranes from 2D zeolites in a technologically scalable manner.
Thin highly (0k0)‐oriented zeolite MFI membranes were prepared on ceramic hollow fibers, starting from 2D MFI nanosheet coatings and followed by secondary and tertiary hydrothermal treatments. These membranes show excellent separation of butane isomers and natural gas liquid (NGL) components from methane.
Incorporating bio-inspired acid-base cooperative design features into heterogeneous catalysts by understanding how to select acid-base pairs and to control the distance between acid-base pairs. ...Display omitted
•Controlling acid–base interactions is important in design of cooperative catalysts.•Homogeneous and heterogeneous results show weaker acids are beneficial.•Amine–silanol cooperativity tuned by adjusting the linker length and pore size.•Nitroaldol condensation is very sensitive to changes in amine–silanol cooperativity.
Catalysts incorporating acid and base cooperative interactions can more efficiently catalyze the aldol and nitroaldol reactions than single component catalysts since cooperative interactions enable activation of both reaction partners. Both homogeneous and heterogeneous catalysis studies demonstrate that limiting acid–base interactions is important and can be achieved by using weak acids (including surface silanols of heterogeneous catalysts) or using a rigid backbone between the acid and base. For heterogeneous catalysts, cooperativity between amines and silanols can be tuned by controlling the alkyl linker length of the aminosilane and controlling the silica support pore size. The nitroaldol condensation is more sensitive to these parameters than the aldol condensation, resulting in an order of magnitude difference in reaction rates when varying these two parameters. While knowledge of the amine–silanol cooperativity is still limited, these findings demonstrate useful structure–property trends that can be used to design more efficient bio-inspired catalysts.
Behavioral health risks are among the most serious and difficult to mitigate risks of confinement in space craft during long-duration space exploration missions. We report on behavioral and ...psychological reactions of a multinational crew of 6 healthy males confined in a 550 m(3) chamber for 520 days during the first Earth-based, high-fidelity simulated mission to Mars. Rest-activity of crewmembers was objectively measured throughout the mission with wrist-worn actigraphs. Once weekly throughout the mission crewmembers completed the Beck Depression Inventory-II (BDI-II), Profile of Moods State short form (POMS), conflict questionnaire, the Psychomotor Vigilance Test (PVT-B), and series of visual analogue scales on stress and fatigue. We observed substantial inter-individual differences in the behavioral responses of crewmembers to the prolonged mission confinement and isolation. The crewmember with the highest average POMS total mood disturbance score throughout the mission also reported symptoms of depression in 93% of mission weeks, which reached mild-to-moderate levels in >10% of mission weeks. Conflicts with mission control were reported five times more often than conflicts among crewmembers. Two crewmembers who had the highest ratings of stress and physical exhaustion accounted for 85% of the perceived conflicts. One of them developed a persistent sleep onset insomnia with ratings of poor sleep quality, which resulted in chronic partial sleep deprivation, elevated ratings of daytime tiredness, and frequent deficits in behavioral alertness. Sleep-wake timing was altered in two other crewmembers, beginning in the first few months of the mission and persisting throughout. Two crewmembers showed neither behavioral disturbances nor reports of psychological distress during the 17-month period of mission confinement. These results highlight the importance of identifying behavioral, psychological, and biological markers of characteristics that predispose prospective crewmembers to both effective and ineffective behavioral reactions during the confinement of prolonged spaceflight, to inform crew selection, training, and individualized countermeasures.
Flue gases from coal-fired power plants typically contain not only CO2 but other acid-gas impurities such as SO x and NO x that can dramatically influence the CO2 capture efficiency. Whereas ...postcombustion CO2 capture by aminosilica materials has been extensively studied over the past few years because of their high equilibrium CO2 capacities, the performance of these materials under realistic conditions (in the presence of SO x , NO x , and O2) remains relatively unexplored. In this study, the degree of irreversible binding of SO2, NO, and NO2 to four supported amine adsorbents is evaluated to assess the SO2, NO, and NO2 adsorption capacities of aminosilica sorbents and their effects on the CO2 adsorption capacities. Adsorbents constructed using poly(ethyleneimine) and three different silane coupling agents (based on propyltrimethoxysilane linkers) with primary, secondary, and tertiary amines are evaluated. Under the experimental conditions used in this investigation, it is found that primary amines with high amine loadings displayed more affinity toward NO than their secondary and tertiary amine counterparts. However, overall, NO adsorption on the aminosilica adsorbents is low, and therefore, the CO2 capacities of the adsorbent materials exposed to NO remained almost unchanged after the exposure. In contrast, all materials showed a very high nitrogen dioxide adsorption capacity upon exposure to NO2. As a result, all adsorbents treated with NO2 exhibited a dramatic reduction in CO2 capacity, which corresponds to the deactivation of amine groups due to the irreversible binding of NO2. In addition, our results indicate that SO2 adsorbed significantly on supported amine adsorbents, resulting in a dramatic loss in CO2 capacity during CO2 capture from flue gas. With similar amine loadings, although secondary amines exhibited higher affinity to SO2, their CO2 capacity loss after exposure to SO2 is lower than that of primary amines, indicating that these materials are more stable in the presence of SO2, which implies that more SO2 desorbs from secondary amines during the desorption step. These results suggest that for silica-supported amine materials to be useful in practical CO2 capture applications, it is necessary to significantly reduce the SO2 and NO2 concentrations of the flue gas prior to the CO2 capture process. On the other hand, the capture efficiency of these materials does not change significantly in the presence of NO. This suggests that such materials might be promising for postcombustion CO2 capture from flue gas streams derived from natural gas combustion, as these streams typically contain reduced SO2 concentrations but can still have significant NO x concentrations.
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