Monolithic carbons

One such monolithic carbon has been produced by Sutcliffe Speakman Carbons and is described by Tamainot-Telto and Critoph [17]. Powdered activated carbon is mixed with a polymeric binder, compressed in a die and fired to produce a monolith of the desired shape, with a density of 713 kg/m and conductivity of 0.33 W/mK. A heat transfer coefficient of 200 W/m K has been measured between the blocks and aluminium fins. 

Monolithic carbons may also be manufactured in finished form fi om PVDC as has been done by Quinn [18]. The porosity and density compare favourably with those of conventional granular carbons and the Sutcliffe Speakmann monoliths but the manufacturing process is not easy to scale up from the laboratory to commercial levels. The properties, (including K and n from the D-A equation) are compared in Table 3 below, taken from Critoph [4]. 

Tamainot-Telto, Z. and Critoph R.E, Adsorption refrigeration using monolithic carbon - ammonia pair. International Journal of Refrigeration, 1997, 20(2), 146 155. 

Tamainot-Telto, Z., and R.E. Critoph, 2001. Monolithic carbon for sorption refrigeration and heat pump applications, Appl. Thermal Eng., 21 (1), 37-52. 

Taguchi et al. [97] and Liang et al. [98,99] reported on the preparation of monolithic carbon columns, which exhibit a hierarchical, fully interconnected porosity. Silica particles (10 pm) have been suspended in an aqueous solution, containing ethanol, FeClj, resorcinol, and formaldehyde. After polymerization, the solid rod was dried, cured, and carbonized by raising temperature to 800°C and finally up to 1250°C. Finally, concentrated FIF was used to remove silica and iron chloride. Even if carbon have been shown to possess a high specihc surface area (up to lllSmVg), their chromatographic efficiency is moderate (FIETP of 72 pm). 

Syntactic materials based on polybenzimidazole and glass or phenolic microspheres (y = 40-500 kg/m3) have been described in the literature109 nl). They have been used as ablation materials that consist of two layers, one of which is a monolithic carbon plastic. Carbon fiber was added to the polyimide binder to improve the mechanical properties of the material. 

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],... 

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

An obvious solution to the surface area limitation is to distribute the selected metal over a high surface area support. However, as metal is consumed in the process, a conventional metal support system would require frequent replacement. A more attractive proposition is offered by the availability of permeable monolithic carbon fiber composites, which were discussed earlier in this chapter. The ability to make these composites electrically conducting allows metals to be... 

Fuertes, A.B., Marban, G., and Nevskaia, D.M. (2003). Adsorption of volatile organic compounds by means of activated carbon fibre-based monoliths. Carbon, 41, 87-96. 

S.E. Voltz and D. Liederman, "Thermal Deactivation of a Platinum Monolithic Carbon Monoxide/Hydrocarbon Oxidation Catalyst", Ind. Eng. Chem. Prod. Res. Dev.. 1974,1314). 243-250. 

An important feature of these materials is that metal-doped monolithic carbon gels can readily be prepared (see below). These are emergent materials in the field of heterogeneous catalysis, and their use will grow in the near future, due... 

On the other hand, the mechanical properties of monolithic carbon gels are of importance when they are to be used as adsorbents and catalyst supports in fixed-bed reactors, since they must resist the weight of the bed and the stress produced by its vibrations or movements. A few smdies have been published on the mechanical properties of resorcinol-formaldehyde carbon gels under compression [7,36,37]. The compressive stress-strain curves of carbon aerogels are typical of brittle materials. The elastic modulus and compressive strength depend largely on the network connectivity and therefore on the bulk density, which in turn depends on the porosity, mainly the meso- and macroporosity. These mechanical properties show a power-law density dependence with an exponent close to 2, which is typical of open-cell foams. 

In other Pt-doped monolithic carbon aerogels, prepared by adding the Pt pre-cnrsor to the initial R/F mixture [41], the Pt particle size determined by H2 chemisorption was mnch higher than that determined by high-resolution transmission electron microscopy (HRTEM). This indicates that some Pt particles were encapsnlated by the carbon matrix and were consequently inaccessible to H2. This can be the main problem of this preparation method when the metal-doped carbon gel is to be used as catalyst, because part of the metal will not be accessible to the reactant molecules. 

Studies on the behavior of chromium, molybdenum and tungsten oxide-doped monolithic carbon aerogels in the isomerization of 1-butene have been carried out by the group of Moreno-Castilla [38]. Samples were prepared by polymerization of a resorcinol-formaldehyde mixture which contained metallic salts of the elements and then the polymer was carbonized at both 500 and 1000 °C. The catalyhc performance of the samples was studied at temperatures ranging from 50 to 425 °C. 

Monolithic carbons are easier to handle than powdered materials. Direct shaping of monolithic mesoporous carbons during their preparation is highly desirable. Mesoporous carbon monoliths may be fabricated by using mesoporous silica monoliths as template. Carbon monoliths with well-developed and accessible porosity have been produced using silica monoliths with a hierarchical structure containing macropores and meso-pores as templates and furfuryl alcohol or sucrose as a carbon precur-... 

---