Carbon monolith

In addition to the particulate adsorbents listed in Table 16-5, some adsorbents are available in structured form for specific applications. Monoliths, papers, and paint formulations have been developed for zeolites, with these driven by the development of wheels (Fig. 16-60), adsorptive refrigeration, etc. Carbon monoliths are also available as are activated carbon fibers, created from polymeric materials, and sold in the forms of fabrics, mats, felts, and papers for use in various applications including in pleated form in filters. Zeolitic and carbon membranes are also available, with the latter developed for separation by selective surface flow [Rao and Sircar, J. Membrane Sci., 85, 253 (1993)]. 

A wide variety of carbon materials has been used in this study, including multi-wall carbon nanotubes (sample MWNT) chemically activated multi-wall carbon nanotubes (sample A-MWNT)16, commercially available vapor grown carbon nanofibers (sample NF) sample NF after chemical activation with K.OH (sample A-NF) commercially pitch-based carbon fiber from Kureha Company (sample CF) commercially available activated carbons AX-21 from Anderson Carbon Co., Maxsorb from Kansai Coke and Chemicals and commercial activated carbon fibers from Osaka Gas Co. (A20) a series of activated carbons prepared from a Spanish anthracite (samples named K.UA) and Subituminous coal (Samples H) by chemical activation with KOH as described by D. Lozano-Castello et al.17 18 activated carbon monoliths (ACM) prepared from different starting powder activated carbons by using a proprietry polymeric binder from Waterlink Sutcliffe Carbons, following the experimental process described in the previous paper13. 

Details about the porous texture properties of the studied materials can by found in our previous papers 4 18. In general, all activated carbons, activated carbon fibers and activated carbon monoliths are essentially microporous materials with a negligible contribution of meso- and macroporosity. 

Figure 5. Amount of hydrogen adsorbed at 77 K and 4 MPa for powder activated carbons (0) and activated carbon monoliths (ACM) ( ) in gravimetric basis (right hand y-axis) and in volumetric basis (left hand y-axis) for powder activated carbons (c) and ACM ( ).

Figure 6. Total hydrogen storage capacity on the basis of a 1 I container, (a) at 298 K for the activated carbon KUA5 (b) at 77 K for an activated carbon monolith.

M. Jorda-Beneyto, D. Lozano-Castello, F. Suarez-Garcia, D. Cazorla-Amoros, and A. Linares-Solano, Advanced activated carbon monoliths and activated carbons for hydrogen storage, Microporous Mesoporous Mater., (2007), doi 10.l016/j.micromeso.2007.09.034. 

Hydrogen storage in carbon has been considered during the last few years on account of the existence of new carbon nanomaterials, such as fullerenes, superactivated carbons, carbon monoliths, carbon nanotubes, and carbon nanohoms [147,166,176-179], distinguished by their high adsorption capacities, hydrophobic nature, and high adsorption/desorption rates [170],... 

Figure 3.5.14 Carbon monolith with hierarchical porosity. Reprinted from [69] with permission, copyright 2007 Wiley-VCH.

Hu YS, Adelhelm P, Smarsly B, Hore S, Antonietti M, Maier J. Synthesis of hierarchically porous carbon monoliths with highly ordered microstructure and their application in rechargeable lithium batteries with high-rate capability. Adv Funct Mater. 2007 17(12) 1873-8. 

The preparation of carbon monoliths has challenged many researchers. Integral carbon monoliths are prepared by extrusion of the carbon precursor, mixed with additives to make the resin extrudable. 

Table 3 shows the textural characteristics of three carbon monoliths, two of which were produced by dipcoating a cordierite monolith with a solution of sucrose or PFA and one of which was produced by a CVD process resulting in a CNF coating. These are referred to as Cord-SUC, Cord-PFA, and Cord-CNF, respectively. From a texture analysis, it was concluded that the sucrose-derived carbon is highly porous, with pore diameters in a favorable range (t)q5ically, 11 nm). The PFA-derived carbon was microporous and, as a consequence, not suitable for adsorption of large species, such as enzymes. 

Figure 32 includes results illustrating the performance of lipase/car-bon monolith systems in an acylation reaction. For comparison, the free lipase and a commercial immobilized lipase (Novozyme) were also tested. As expected, in all cases the specific activity of immobilized lipase was foimd to be lower than that of the free enzyme. Such a difference is usually ascribed to conformational changes of the enzyme, steric effects, or denaturation. For the monolithic biocatalysts, the activity of the immobilized catalyst relative to that of the pure enzyme was found to be 30-35%, and for the Novozyme catalyst about 80% in the first rim. However, the Novozyme catalyst underwent significant deactivation, in contrast to the carbon monolith-supported catalysts. The deactivation of the Novozyme catalyst in consecutive runs is probably a consequence of the instability of the support matrix under reaction conditions (101,102). 

FIGURE 32 Initial rates of reaction in catalysis by free lipase and immobilized lipase (Novozyme, and catalyst supported on 200 cpsi carbon monolith) in the acylation of butanol with vinyl acetate in an organic medium at 300 K. 

Carbon monolith Carbon loading (wt%) Lipase adsorption (mg/gcarbon) Enzyme activity (mmol/s/genzyrne) Overall activity of monolith (pmol/gmonolith )... 

It is concluded that carbon/monolith systems, especially those incorporating CNFs, offer good potential value for catalysis involving liquid-phase reactants and for biocatalysis, as a consequence of the excellent accessibility of the active phase, which is present at the outside of the fibers, without any microporosity to offer a resistance interfering with the reaction. 

Ga.s S5mthesis and application of carbon monoliths Environmental Reduction of NO with NH3 Low-temperature de-NO realistic conditions Vanadium oxide/ carbon-coated monohth (164)... 

Liquid S5mthesis and application of carbon monoliths Biocatalysis... 

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