Carbon-based monoliths

Recently, there has been a growing interest in the use of monohthic structures for (bio)chemical conversion and adsorption processes. A very versatile type of monolith is based on carbon. The combined properties of carbon and monolithic structures create a support with great potential. In this chapter we describe recent developments in the field of carbon-based monolithic structures with respect to preparation, support properties, and application in catalytic processes. Furthermore, two examples are used to demonstrate the approach and possible pitfalls when using carbon (coated) monoliths in catalysis. 

Carbon-based monoliths can be of the integral or coated type [5,6]. For practical applications, several requirements are set to monolithic structures. For a coated type of monolithic support, the mechanical properties are adopted from the ceramic or metallic monoliths. It is, however, important that the coating adhere well to the monolith to prevent flaking and subsequent loss of active... 

Table 11.2 Applications of Carbon-Based Monoliths in Catalysis...

In this study, the influence of dispersion and distribution of the active phase (rnthenium) and the accessibility and performance of the carbon-based monolithic strnctures have been evaluated in the hydrogenation of D-glucose. Special attention has been paid to the stabihty of the catalysts in successive hydrogenation rnns. Especially, fixed-bed catalysts (e.g., monoliths) require a maintained activity for long periods of time for successful application in industry. The performance of the monolithic reactor has been compared with slurry-phase operation. 

Because the application of carbon-based monoliths forms an emerging field in (bio)chemical engineering, new applications and process developments can be expected in the future. One might think of applications of monoUth-CNF combinations in water-air filter systems [66], carbon precnrsors with tailored porons texture for production of integral/coated monoliths, ultrathin coatings on ACM monoliths for higher mass-transfer rates, and carbon monoliths in adsorption processes or as high-surface-area electrodes. 

Chapter 11 provides a short review of carbon-based monoliths, their preparation, and applications in varions liqnid-phase processes, inclnding bioconversions. 

Carbon-based monolithic structures are only occasionally a topic in scientific literature. However, there are several patents that describe a variety of preparation procedures for these materials [58]. 

It has been published that hydrophobic-activated carbons can be suitable supports for noble metal species active for total oxidation. The catalytic behaviour of platinum and palladium supported on carbon-based monoUths was studied in the low temperature catalytic combustion of benzene, toluene and m-xylene, and compared with the corresponding behaviour of Pt-supported on y-Al203 coated monoliths. Carbon-based monoliths showed much better catalytic performance, which was ascribed to the fact that the carbon surface is more hydrophobic than the y-Al203, and the poisoning effect of water molecules produced during the combustion was... 

Perez-Cadenas, A., Morales-Torres, S., Maldonado-Hodar, F.,etal. (2009). Carbon-based Monoliths for the Catalytic Elimination of Benzene, Toluene and m-Xylene, Appl Catal. A Gen., 366, pp. 282-287. 

Burchell, T.D., Judkins, R.R. and Rogers, M.R., A carbon fiber based monolithic adsorbent for gas separation. In Proc. 23rd Biennial Con/, on Carbon, American Carbon Society, 1997, pp. 158 159. 

Phenyl (Cohesive Technologies), the polymer-based Oasis HLB (Waters), the Cyclone (Cohesive Technologies), and the porous graphitized carbon-based Hypercarb (ThermoHypersil, Cheshire, UK) Cohesive s 2300 system was the HTLC component. Merck s monolithic reversed-phased Chromolith Speed ROD (RP-C18 (50 x 4.6 mm) served as the analytical column. The Oasis HLB, Cyclone TFC, and Hypercarb yielded the best retention capacity and good elution efficiency and volume. Recovery was 42 to 94% with a sample volume of 10 mL. Run time was 14 min. LODs were 0.4 to 13 ng/L for most compounds. 

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. 

Different carbon monoliths were prepared from a sucrose coating [8,43], a polyfurfuryl coating [9], a furan coating [44] via the dipcoating method, and from methane [14,35] via the CVD method over deposited Ni. Ruthenium was loaded on furan-based monoliths by impregnation from [RuCls H20] in diluted hydrochloric acid, and lipase was loaded on the other monoliths by physical adsorption from a phosphate buffer (pH 7). 

The REZKLAD epoxy-based system consists of a Concrete Primer and Flooring Compound, plus an Expansion Joint Compound and Surface Sealer available for use where necessary. The CLADKOTE Flooring Compound is a modified polyester, resin-based monolithic overlay for concrete. The composite of resins and siliceous reinforcing material cures to a tough, chemical resistant topping. CLADKOTE C utilizes a 100% carbon filler specifically designed for service in hydrofluoric acid and fluoride salts. 

The catalytic converter on a car uses a precious-metal-based, solid catalyst, usually in the form of a monolith, to convert unburned hydrocarbons and carbon monoxide to carbon dioxide. Many different reactants are converted to two products CO2 and water. 

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