Methane storage

Zhao and Yan studied the CH4 adsorption capacities of modified COFs, and found that the excess methane uptakes of COF-102-X (X = I, Br, Cl, or NH2) are 156, 153, 148, and 143 V(STP)/V, respectively. The adsorbents can be considered as promising adsorbents for methane uptake. Rabbani et al. 

FIGURE 3.6 The crystal stmcture of the PCN-14 MOF. (a) Squashed cuboctahedral cage and (b) nanoscopic cage with 18 vertices, 30 edges, and 20 faces. Color scheme C, gray Cu, turquoise and O, red [39]. (Reproduced from Ma, S.Q. et al., J Am Ghent Soc 130, 1012-1016 (2008), with permission). 

Industrial Catalysis and Separations Innovations for Process Intensification 

FIGURES.7 Experimental COj uptake in different MOFs at 0.1 bar. Data were obtained at 293-298 K [42]. (Reproduced from Yazaydin, A.O. et al., Chem Soc 131, 18198 (2009), with permission). 

Instead of the surface area or the free volume, the authors found that MOFs such as Mg/DOBDC and Ni/DOBDC with a high density of open metal sites are promising candidates for CO capture from flue gas in, which CO partial pressure is about 0.1 atm. Caskey et al. [43] found that metal substitution in the DOBDC series can significantly impact their CO capacities in the low-pressure region. The metal substitution effect m be caused by the differences in the ionic character of the metal-oxygen bonds in the DOBDC-series MOFs. Liu et al. found that Ni/DOBDC has a higher CO capacity than NaX and 5A zeolites at 0.1 atm, and 25° C. In addition, water does not affect CO adsorption in the Ni/DOBDC as much as in NaX and 5A zeolites, and it is much easier to remove water from Ni/DOBDC by heat regeneration [44]. Therefore, the Ni/DOBDC can adsorb more CO than traditional zeolites under the same moist conditions. 

Most flue gas is composed of N, so it is important to have a MOF that can selectively adsorb CO over N. Motkuri et al. showed that Prussian blue 

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AJcafiiz-Monge, J., de la Casa-Lillo, M. A., Cazorla-Amoros, D. and Linarcs-Solano, A., Methane storage in activated carbon fibres. Carbon, 1997, 35(2), 291 297. 

Adsorption of supercritical gases takes place predominantly in pores which are less than four or five molecular diameters in width. As the pore width increases, the forces responsible for the adsorption process decrease rapidly such that the equilibrium adsorption diminishes to that of a plane surface. Thus, any pores with widths greater than 2 nm (meso- and macropores) are not useful for enhancement of methane storage, but may be necessary for transport into and out of the adsorbent micropores. To maximize adsorption storage of methane, it is necessary to maximize the fractional volume of the micropores (<2 nm pore wall separation) per unit volume of adsorbent. Macropore volume and void volume in a storage system (adsorbent packed storage vessel) should be minimized [18, 19]. 

Thus, while models may suggest optimal pore spuctures to maximize methane storage, they give no indication or suggestion as to how such a material might be produced. On the other hand, simple measurement of methane uptake from variously prepared adsorbents is not sufficient to elucidate the difference in the pore structure of adsorbents. Sosin and Quinn s method of determining a PSD directly from the supercritical methane isotherm provides an important and valuable link between theoretical models and the practical production of carbon adsorbents... 

Nitric acid treatment lowered the methane uptake by about ten percent. This could be due to oxygen occupying sites within pores, but may be the result of weaker interaction between methane and an oxide surface as is observed for silica. Reduction of these treated carbons with hydrogen restored their original methane uptake. Clearly for methane storage, there is no advantage in modifying the carbon surface by nitric acid treatment. 

From the above data, it would appear that methane densities in pores with carbon surfaces are higher than those of other materials. In the previous section it was pointed out that to maximize natural gas or methane storage, it is necessary to maximize micropore volume, not per unit mass of adsorbent, but per unit volume of storage vessel. Moreover, a porous carbon filled vessel will store and deliver more methane than a vessel filled wnth a siliea based or polymer adsorbent which has an equivalent micropore volume fraction of the storage vessel. 

Tabic 3. Some Studies on Methane Storage using Amoco Type KOH Activated Carbon Adsorbents... 

D. Lozano-Castello, J. Alcaiiiz-Monge, M. A. Casa-Lillo, D. Cazorla-Amoros, and A. Linares-Solano, Advances in the study of methane storage in porous carbonaceous materials, Fuel, 81, 1777-1803 (2002). 

D. Lozano-Castello, D. Cazorla-Amoros, A. Linares-Solano, and D. F. Quinn, Influence of pore size distribution on methane storage at relatively low pressure preparation of activated carbon with optimum pore size, Carbon, 40,989-1002 (2002). 

M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. Wachter, M. O Keefe, and O. M. Yaghi, Systematic design of pore size and functionality in isoteticular MOFs and their application in methane storage, Science, 295,469-472 (2002). 

The authority behind this reference book is the I DECAT Network of Excellence and it is dearly divided into four parts covering fuel cells, hydrogen and methane storage, hydrogen and hydrogen vectors production and industrial catalysis for sustainable energy. 

A second workshop, Catalysis for Sustainable Energy Production , was held in Sesto Fiorentino (Florence, Italy) from 29 November to 1 December 2006. The structure and approach of this workshop were similar to those of the first, but the focus was on (i) fuel cells, (ii) hydrogen and methane storage and (iii) H2 production from old to new processes, including those using renewable energy sources. The present book is based on this second workshop and reports a series of invited contributions which provide both the state-of-the-art and frontier research in the field. Many contributions are from industry, but authors were also asked to focus their description on the identification of priority topics and problems. The active discussions during the workshop are reflected in the various chapters of this book. 

Hydrate structure Methane storage in hydrate [m3/m3] Hydrate stability condition ... 

S. Biloe, V. Goetz, S. Mauran, Characterisation of adsorbent composite blocks for methane storage, Carbon 39 (2001) 1653-1662. 

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