Monolithic processes

In the design of optimal catalytic gas-Hquid reactors, hydrodynamics deserves special attention. Different flow regimes have been observed in co- and countercurrent operation. Segmented flow (often referred to as Taylor flow) with the gas bubbles having a diameter close to the tube diameter appeared to be the most advantageous as far as mass transfer and residence time distribution (RTD) is concerned. Many reviews on three-phase monolithic processes have been pubhshed [37-40]. 

There are three main fields of (potential) applications of monolithic catalysts/reactors hydrogenations, oxidations, and bioprocesses. Pioneers in studying monolithic processes... 

Irandoust and Andersson [22] studied hydrogenation of 2-ethyIhexenal in a monolith. Slurry experiments with powdered monolithic catalyst were also performed. The reaction was investigated at 413-433 K and 0.4-0.98 MPa and at velocities of both phases of 0.023-0.085 m sec". The monolithic process proceeded much faster, as is shown in Fig. 3. This large difference might be due to deactivation of the catalyst during grinding. 

Kobe Steel Co. [42] has patented a monolithic process for oxidation of Fe to Fe in acidic aqueous solutions using monolith made of carbon. The monoliths were prepared by mixing active carbon with a binder, extrusion, and thermal treatment. Slices 150 mm in diameter of cell density 20-60 cells/cm were tested. Monolithic slices 30 mm thick were stacked and separated one from another with turbulizers. The reactor was operated in the countercurrent mode with the gas flowing upward. The liquid was recirculated. The liquid flow rate was varied from 250 to 333 cm sec and the gas flow rate ranged from 83 to 250 cm sec . Pressure was up to 0.31 MPa. The oxidation efficiency was 34-80% at circulation time of 1800 sec, and rose to 89-93% at 3600 sec. 

Uses monolithic column technology Smaller i.d. monolithic Process development... 

The two main approaches to explain nanotechnology to the general public have been oversimplified and have become known as the top-down approach and the bottom-up approach. The top-down approach involves fabrication of device structures via monolithic processing on the nanoscale. This approach has been used with spectacular success in the semiconductor devices used in consumer electronics. The bottom-up approach involves the fabrication of device structures via systematic assembly of atoms, molecules or other basic units of matter. This is the approach... 

Morrow A.B., Gay I.D. Infrared and NMR characterization of the silica surface. In Adsorption on Silica Surfaces. Papirer E. Marcel, ed. New York Dekker, 2000, p. 26 Nikolic L. J., et al. Effect of drying control chemical additives in sol-gel-glass monolith processing. Ceram. Int. 1994 20(5) 309... 

Figure 23.8 An SEM image of a microcellular PS-PFS monolith processed at 60 °C and 30 MPa and depressurized at 25 °C at a rate of 0.5 MPa/min. The bar indicates 200 nm. (Reprinted with permission from H. Yokoyama and K. Sugiyama, Nanocellular structures in block copolymers with C02-philic blocks using CO2 as a blowing agent Crossover from nicro- to nanocellular structures with depressurization temperature, Macromolecules, 38, 10516-10522, 2005. 2005 American Chemical Society.)...

The seven processing steps shown schematically in Figure 1 are involved to various degrees in making sol—gel-derived siUca monoliths by methods 1, 2, and 3. The emphasis herein is primarily on net-shape sol—gel-derived siUca monoliths made by the alkoxide process (method 3) prepared under ambient pressures. 

The sol—gel process can be utilized to yield products within a wide range of appHcations. Some of these appHcations include production of nanocomposites, films, fibers, porous and dense monoliths, and biomaterials. 

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