Monoliths as supports

Extensive investigations were performed to determine the potential of carbon-coated monoliths as supports for enzymes. The enzymes were adsorbed on the functionalized supports under ambient conditions, in a recycle reactor in which the liquid was recycled over the support under upflow conditions. A 50 mM phosphate buffer with pH 7 was used as a medium. The protein concentration was determined by using UV-VIS... 

Josic, Dj. Buchacher, A. Application of monoliths as supports for affinity chromatography and fast enzymatic conversion. J. Biochem. Biophys. Methods 2001, 49, 153-174. 

Whereas in packed bed chromatography, mass transfer rates and pressure drop may be limiting, in monoliths surface interactions determine the overall reaction rate . The feasibility of using ceramic monoliths as support in affinity chromatography has been clearly establishedt ... 

J. Howitt, Thin Wall Ceramics as Monolithic Catalyst Supports, SAE 910611, Society of Automotive Engineers, Warrendale, Pa., 1991. 

The following section focuses specifically on those design strategies that produce either monoliths or supported films that may then serve as a solid but textured platform in the first design step toward a 3-D battery architecture. 

Methacrylate monoliths have been fabricated by free radical polymerization of a number of different methacrylate monomers and cross-linkers [107,141-163], whose combination allowed the creation of monolithic columns with different chemical properties (RP [149-154], HIC [158], and HILIC [163]) and functionalities (lEX [141-153,161,162], IMAC [143], and bioreactors [159,160]). Unlike the fabrication of styrene monoliths, the copolymerization of methacrylate building blocks can be accomplished by thermal [141-148], photochemical [149-151,155,156], as well as chemical [154] initiation. In addition to HPLC, monolithic methacrylate supports have been subjected to numerous CEC applications [146-148,151]. Acrylate monoliths have been prepared by free radical polymerization of various acrylate monomers and cross-linkers [164-172]. Comparable to monolithic methacrylate supports, chemical [170], photochemical [164,169], as well as thermal [165-168,171,172] initiation techniques have been employed for fabrication. The application of acrylate polymer columns, however, is more focused on CEC than HPLC. 

Acrylamide monoliths as well as methacrylamide monoliths [106,173-179] have been introduced as hydrophilic column support materials for CEC [175,176] of small molecules, as NPC [179]... 

A wide range of polymeric materials can be prepared from HIPEs. Polymerisation of the continuous phase yields highly porous cellular polymers with a monolithic structure. These are known as PolyHIPE polymers, and possess a number of unique properties including, in most cases, an interconnected cellular structure and a very low dry-bulk density. Their very high porosity favours their use as supports for catalytic species, precursors for porous carbons and inert matrices for the immobilisation of enzymes and micro-organisms. 

Catalysts. The properties of the two catalysts used in this study are given in Table II. The Monolith catalyst was prepared in the laboratory at OSU by impregnating Co and Mo on the Monolith alumina support received from the Coming Glass Company. The Nalcomo 474 catalyst was received from the Nalco Chemical Company and is a commercial preparation used as a reference catalyst in this study. 

Alternatively it may take the form of a ceramic or metallic monolith, of which a variety of physical shapes is available monoliths are now widely used as supports for the active catalyst, which lines the channels which permeate the structure. They find particular application for the control of exhaust from vehicles powered by internal combustion or diesel engines. If the catalyst particles are small enough, a fast flow of reactants causes the bed to expand and the particles to move about like molecules in a liquid. We then have a fluidised bed reactor, which affords a more uniform temperature profile than is possible in fixed bed reactors, and is therefore more apposite to strongly exothermic reactions. 

Aluminas are used in various catalytic applications, a-, y-, and -aluminas are all used as support materials, the first one in applications where low surface areas are desired, as in partial oxidation reactions. The latter two, and especially y-alumina, in applications where high surface areas and high thermal and mechanical stability are required. One of the most prominent applications of y-alumina as support is the catalytic converter for pollution control, where an alumina washcoat covers a monolithic support. The washcoat is impregnated with the catalytically active noble metals. Another major application area of high-surface aluminas as support is in the petrochemical industry in hydrotreating plants. Alumina-supported catalysts with Co, Ni, and/or Mo are used for this purpose. Also, all noble metals are available as supported catalysts based on aluminas. Such catalysts are used for hydrogenation reactions or sometimes oxidation reactions. If high... 

Multi-channel ceramic monoliths (Fig. 7.4) are now the primary choice as support structures to carry the active catalytic species for cleaning emissions from various sources of pollution.5 Figure 7.4 shows the shapes used for both automotive and stationary pollution abatement applications. 

It is truly remarkable that catalysts can function so well in the exhaust of the modem highspeed vehicle. This fact has raised confidence in industry to use different monolithic (ceramic and metal) structures as supports for catalysts for other environmental applications such as diesel exhausts, power and chemical plants, restaurants, and even on widebody aircraft. 

In the last 15 years, the use of monoliths has been extended to include applications for performing multiphase reactions. Particular interest has been focused on the application of monolith reactors in three-phase catalytic reactions, such as hydrogenations, oxidations, and bioreactions. There is also growing interest in the chemical industries to find new applications for monoliths as catalyst support in three-phase catalytic reactions. 

M. R. Benoit and J.T. Kohler, An evaluation of a ceramic monolith as an enzyme support material, BiotechnoL Bioeng. 77 1617 (1975). 

In addition to porous ceramic and stainless steel plates and tubes commonly employed as supports of zeolite membranes and films, a wide variety of alternative supports have been used. Among these are steel [250], ceramic [251,252] monoliths... 

Zeolite monoliths have been useful for such apphcations as rotatory adsorbers for use as dehumidifiers and desiccant cooling processes [253] or in VOC treatment systems [269]. Alumina-coated sUicon carbide monoliths have also been employed as supports for B-ZSM-5 membranes [270] providing a larger surface area per unit volume, compared to traditional membrane supports. With these membranes, these authors have reported n/f-butane and H2/f-butane separation selectivities of 35 and 77, respectively [85]. Also, silicalite-1 membranes supported on stainless steel grids (Figure 10.29) have shown a good performance in the separation of n/f-butane mixtures, with separation factors as high as 53 at 63°C [255]. 

Recent developments in LM module design, including rotational, vibrational membrane devices, pulsed-flow fluid management for polarization control, use of low-cost refractory monoliths as membrane supports, and use of electric potentials to minimize macrosolute polarization and fouling, may permit practical and economic application of membrane processes to liquid and gaseous streams which today are untreatable by such methods. 

The introduction of automobile exhaust catalysts in the United States and elsewhere has produced a major market for platinum-type oxidation and reduction systems. An innovative consequence of this industry has been the development of ceramic honeycombed monoliths as catalyst supports. These structures contain long, parallel channels of less than 0.1 mm in diameter, with about SO channels per square centimeter. The monolith is composed of cordierite (2MgO - 2AI2O) SSiOj) and is manufactured by extrusion. A wash coat of stabilized alumina is administered prior to deposition of the active metal, either by adsorption or impregnation methods. 

Deluca, J. P., and Campbell, L. L., Thin Vail Ceramics as Monolithic Catalyst Supports Advanced Materials in Catalysis, Academic Press, Inc., 1977 Chapter 10. 

Howitt, J. S., Ceramic Industry 1975, 104, 19 Thin Vail Ceramics as Monolithic Catalyst Supports SAE Tech Paper No. 800082 (1980). 

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