Monolithic synthesis

FIGURE 12.5 Carbon monolith synthesis using resorcinol-crotonaldehyde polymer as carbon precursor. The polymerization took place in the pores of the large silica monoliths. Silver nanoparticles could also be dispersed in the silica template and transferred to the final templated carbon materials. The carbons retained the monolithic shape of the silica template and resisted chemical activation with potassium hydroxide (KOH). After activation, carbons exhibited microporous-mesoporous structures. (From Jaroniec, M. et al., Chemistry of Materials, 20, 1069, 2008. With permission.)... 

COE and a COE-based cross-linker, that is, tris(cyclooct-4-en-l-yloxy)methylsilane (TCOMS). This development was guided by the idea that the polymer backbone of poly (COE)-derived materials consists of sec-allylic carbons and, therefore, presents a viable alternative to NBE-based systems. However, compared to NBE-based monomers, COEs are characterized by a significantly reduced ring strain, which makes the use of a more active initiator than the commonly used first-generation Grubbs initiator inevitable. These changes in monomer, cross-linker, and initiator required a comprehensive redesign of monolith synthesis. As a direct consequence of... 

Synthesis of Monolithic Titania-Silica Aerogel for PCO Reactions... 

New developments in the field of ceramic foam monoliths could also potentially provide new catalytic process technology for the conversion of methane into synthesis gas. For example, workers at Minnesota University [9] have achieved high synthesis gas yields at both high temperatures and space velocities using rhodium supported on a ceramic foam. 

Concerning the reaction pathway, two routes have been proposed the sequence of total oxidation of methane, followed by reforming of the unconverted methane with CO2 and H2O (designated as indirect scheme), and the direct partial oxidation of methane to synthesis gas without the experience of CO2 and H2O as reaction intermediates. The results obtained by Schmidt and his co-workers [4, 5] indicate that the direct reaction scheme may be followed in a monolith reactor when an extremely short contact time is employed at temperatures in the neighborhood of 1000°C. However, the majority of previous studies over numerous types of catalysts show that the partial oxidation of methane follows the indirect reaction scheme, which is supported by the observation that a sharp temperature spike occurs near the entrance of the catalyst bed, and that essentially zero CO and H2 selectivity is obtained at low methane conversions (<25%) where oxygen is not fully consumed [2, 3]. A major problem encountered... 

Rieux, L., Niederlander, H., Verpoorte, E., Bischoff, R. (2005). Silica monolithic columns Synthesis, characterisation and applications to the analysis of biological molecules. J. Sep. Sci. 28, 1628-1641. 

The synthesis of the first polymer-supported chiral Mn-salen derivatives was reported independently by Sivaram171 and Minutolo.171-173 Different monomeric Jacobsen-type units, containing two polymerizable vinyl groups, were copolymerized with styrene and divinylbenzene to yield the corresponding cross-linked polymers as a monolithic compact block.174-176 The less mobile system (Figure 19) with no spacer between the aromatic ring and the polymer backbone is less enantioselective. 

Brandhuber, D., Torma, V., Raab, C., Peterlik, H., Kulak, A. and Husing, N. (2005) Glycol-modified silanes in the synthesis of mesoscopically organized silica monoliths with hierarchical porosity. Chemistry of Materials, 17, 4262 1271. 

In the specific case of silica nanoparticles-pH EMA hybrid materials, the synthesis relies on obtaining a fine dispersion of silica nanoparticles (with a mean diameter of 7nm) in HEMA monomers (liquid phase). When a homogeneous solution is obtained, a free radical initiator is added at a concentration based on the weight of the monomer mixture. After the initiator dissolution, the solution can be poured into molds or between two glass plates to obtain monoliths or uniform films, respectively, after being cured at temperatures around 60-85 °C for several hours. 

In a typical synthesis, the corresponding precursor and calcium methoxyethoxide are dissolved in ethanol in an acidic medium (commonly HC1, 1N) under an argon atmosphere. The critical factors in obtaining crack-free star gels monoliths are the temperature and processing times, as indicated in Table 12.2. 

A.-M. Hilmen, E. Bergene, O. A. Lindvag, D. Schanke, S. Eri and A. Holmen, Fischer-Tropsch synthesis using monolithic catalysts, Stud. Surf. Sci. Catal., 2000,130, 1163-1168. 

Keywords. Short monolithic columns, Monoliths, Chromatography, Separation, Purification, Proteins, DNA, Bioconversion, Solid-phase synthesis... 

Other fields using short monolithic units are solid phase synthesis and combinatorial chemistry. Hird et al. [102] predicted that having a single polymer particulate block of porous polymer or monolith would allow the optimization of automation in the field of solid phase (combinatorial) synthesis. They have developed a method for the preparation of monolithic rods, which were then cut into discs of 1.0 to 2.5 mm thickness and used for solid phase synthesis. They... 

Still, a lot needs to be done to develop large monolithic units, which would handle kilogram and larger production scales and guarantee to the process managers the stability of the support and its presence on the market over several decades. However it is realistic to expect that SMC will attract widespread use within a decade in a variety of applications, from chromatography to bioconversions, solid phase extractions and solid phase synthesis. 

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