Different Adsorption Behaviors of Methane and Carbon Dioxide in the Isotypic Nanoporous Metal Terephthalates MIL-53 and MIL-47
A distinct step in the isotherm occurs during the adsorption of CO2 on MIL-53 at 304 K. Such behavior is neither observed during the adsorption of CH4 on MIL-53 nor during the adsorption on the isostructural MIL-47. This phenomenon seems to be due to a different mechanism than that of previous adsorption steps on MOF samples. It is suggested that a breathing behavior is induced in MIL-53 during CO2 adsorption.
Available from: Renju Zacharia
- "Due to its potential to purify CH 4 from CO 2 /CH 4 mixtures especially in small and medium industrial scales, PSA techniques are currently being extended to new areas like methane purification from biogas and landfill gas    . For zeolites  or activated carbon , which are the most commonly used adsorbent materials for PSA purification of biogas/landfill gas, the adsorbent regeneration is still difficult and energy consuming, leading to lower productivity and higher expenses  . "
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ABSTRACT: MIL-53(Al) aluminum terephthalate, a commercially available metal-organic framework material has been studied as a potential candidate for pressure swing adsorption (PSA) separation and purification of CO2/CH4 binary mixtures. Pure gas isotherms of CH4 and CO2 measured over 0–6 MPa and at room temperature are fitted with the Dubinin-Astakhov (D-A) model. The D-A model parameters are used in the Doong-Yang Multicomponent adsorption model (DYM) to predict the binary mixture isotherms. A one-dimensional multicomponent adsorption breakthrough model that accounts for the mass and heat transfer inside a column filled with MIL-53 is then used to perform a parametric study of the effect of adsorbent particle diameter (5, 20, 200, 300, 500 and 1000 µm), inlet pressures (0.2, 1 and 2.5 MPa), feed flow rates (10, 25 and 50 ml/min) and feed compositions (25%, 50% and 75% CO2) on the breakthrough performance. As-purchased MIL-53 has an average particle diameter of 20 µm which renders high flow tortuous; therefore they are less effective for separation. More effective separation within two minutes from the onset of flow can be achieved if MIL-53 monoliths of diameters above 200 µm are used. Faster separation is also possible by increasing the feed pressure from 0.2 to 2.5 MPa and also if the starting compositions are richer in CO2. As higher pressure gas stream mixture containing higher % of CO2 passes through the column, more heat is generated in the bed by the adsorption of larger quantities of CO2 as indicated by the temperature rise of up to 440 K, higher than the temperature generated when lower pressure gas stream is used. With the increasing CO2 content and the inlet pressure, larger amounts of adsorption heat is released into the bed. More CH4 is produced per cycle at higher feed pressures, but the shortened time at higher pressures can result in the reduction of the CH4 purity.
Available from: Qibin Xia
- "A comparison of Figs. 2 and 3 showed that the CO 2 adsorption capacities of MIL-101 were higher than those of MIL-100(Fe) due to the higher pore volume and surface area of MIL-101(Cr). The maximum CO 2 uptakes of MIL-100(Fe) and MIL-101(Cr) were separately up to 15.9 and 21.0 mmol/g at 298 K and 25 bar, which were much higher than those of many other adsorbents at the similar condition, such as zeolite NaX , activated carbon Norit R1  and MIL-53(Cr)  "
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ABSTRACT: It is well-known that water vapor is omnipresent. It always has strong influence on adsorption performances of various applied porous materials in realistic situations. Adsorption behaviors of CO2/N2 and CO2/CH4 binary mixtures over MIL-100(Fe) and MIL-101(Cr) were investigated in presence and absence of water vapor in feed stream by static adsorption, fixed bed experiments, CO2-TPD technique and in situ FTIR analysis. Interesting and unexpected results were obtained. It was found that the presence of water vapor significantly enhanced the CO2 working adsorption capacity and CO2/CH4 selectivity of MIL-100(Fe) due to formation of more adsorptive sites toward CO2, but it badly weakened those of MIL-101(Cr) due to H2O competitive adsorption. When relative humidity of feed stream increased from 0% to 50%, the CO2 capacity and CO2/CH4 selectivity of MIL-100(Fe) increased by 150% and 200%, respectively, and in contrast to that, those of MIL-101(Cr) decreased by 44% and 18% respectively. CO2-TPD curve of MIL-100(Fe) exhibited only one desorption peak in dry atmosphere, while two peaks in humid atmosphere, suggesting that new type of alkaline adsorptive sites were formed due to H2O dissociation on MIL-100(Fe), which was confirmed by in situ FTIR analysis. This water vapor-enhanced mechanism is interesting, and is worthy of further exploiting for obtaining novel adsorbents.
- "Nanoporous carbon of high surface area has contributed to environmental, energy, and chemical technologies     . This is because nanoporous carbons have distinguished merits such as high electrical and thermal conductivities  , excellent water resistivity , and considerably high chemical stability except for that in an oxidative atmosphere, although the tunability of pore width is not sufficiently established yet. "
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ABSTRACT: Graphene monoliths made from graphene oxide colloids by unidirectional freeze-drying method were activated by typical activation processes of CO2 activation, chemical activation using ZnCl2 or H3PO4, and KOH activation. The porosity development of graphene monolith markedly depends on the activation method. The monoliths with highest surface area are obtained by the KOH activation method; only the KOH activation is effective for production of the graphene monolith of which surface area is in the range of 1760–2150 m2 g−1. The mechanism of the porosity development by KOH activation method is proposed. This work provides a promising route for the bottom-up design of pore width-tunable nanoporous carbons.
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