Solids activities

Active solids are widely used as adsorbents of gases and vapours, and the specific surface is the most important parameter for characterizing their... 

Another deep-bed spiral-activated solids-transport device is shown by Fig. ll-60e. The flights cany a heat-transfer medium as well as the jacket. A unique feature of this device which is purported to increase heat-transfer capability in a given equipment space and cost is the dense-phase fluidization of the deep bed that promotes agitation and moisture removal on drying operations. 

In contrast, there are fewer limitations from the chemical point of view. The preparation of large, well-defined, libraries that involve amino acid building blocks has been demonstrated many times. Carefully optimized reaction conditions for the preparation of other mixed libraries can also ensure that each desired compound is present in sufficient amount. However, the reaction rates of some individual selectors with the activated solid support may be lower than that of others. As a result, the more reactive selectors would occupy a majority of the sites within the beads. Since the most reactive selectors may not be the most selective, testing of a slightly larger number of specifically designed CSPs may be required to reduce the effect of falsenegative results. 

Liquid-solid chromatography (LSC). This process, often termed adsorption chromatography, is based on interactions between the solute and fixed active sites on a finely divided solid adsorbent used as the stationary phase. The adsorbent, which may be packed in a column or spread on a plate, is generally a high surface area, active solid such as alumina, charcoal or silica gel, the last... 

Magnetism and the Structure of Catalyt-ically Active Solids P. W. Selwoor... 

Herman Pines and Luke A. Schaap The Use of X-Ray K-Absorption Edges in the Study of Catalytically Active Solids Robert A. Van Nordstrand The Electron Theory of Catalysis on Semiconductors Th. Wolkenstein... 

C.G. Vayenas, S. Bebelis, I.V. Yentekakis, C. Karavasilis, and J. Yi, Non-Faradaic Electrochemical Modification of Catalytic Activity Solid Electrolytes as Active Catalyst Supports, Solid State Ionics 72, 321-327 (1994). 

Point defects were mentioned in a prior chapter. We now need to determine how they aiffect the structure auid chemical reactivity of the solid state. We will begin by identifying the various defects which can arise in solids and later will show how they can be manipulated to obtain desirable properties not found in naturally formed solids. Since we have already defined solids as either homogeneous and heterogeneous, let us look first at the homogeneous t5 e of solid. We will first restrict our discussion to solids which are stoichiometric, and later will examine solids which can be classified as "non-stoichiometric", or having an excess of one or another of one of the building blocks of the solid. These occur in semi-conductors as well as other types of electronically or optically active solids. 

The surface properties of three types of methanation catalysts obtained by oxidation of selected Intermetallics were examined In relation to their CO conversion activity. The first type (Ni Si, N1 A1 ) which corresponds to active phase-supporl iX the coXventionally prepared catalyst Is little affected by the oxidation treatment. The surface Nl is oxidized and relatively more abundant In the active solids. The second type (active phase-promoter ex Ni Th ) is extensively decomposed on oxidation. The transformation of these alloys Is accompanied by a surface enrichment in Nl. 

Y. Iwasawa, Chemical Design Surfaces for Active Solid Catalysts, (D.D. Eley, H. Pines, P.B. Weisz, Eds.), vol. 35, p. 187. Academic Press, New York, 1987. 

In Wilsonville Runs 143 and 147, thermal degradation of the coal-derived products greatly affected the SRC recovery on the Rerr-McGee CSD Unit. Both runs were made at identically the same operating conditions, except in Run 143, where presumably catalytically active solids were allowed to accumulate in the liquefaction reactor, whereas in Run 147 the solids were removed. The product yields exiting the reactor for both runs were very similar however, the thermal sensitivity of the... 

Freeder, B. G. et al., J. Loss Prev. Process Ind., 1988, 1, 164-168 Accidental contamination of a 90 kg cylinder of ethylene oxide with a little sodium hydroxide solution led to explosive failure of the cylinder over 8 hours later [1], Based on later studies of the kinetics and heat release of the poly condensation reaction, it was estimated that after 8 hours and 1 min, some 12.7% of the oxide had condensed with an increase in temperature from 20 to 100°C. At this point the heat release rate was calculated to be 2.1 MJ/min, and 100 s later the temperature and heat release rate would be 160° and 1.67 MJ/s respectively, with 28% condensation. Complete reaction would have been attained some 16 s later at a temperature of 700°C [2], Precautions designed to prevent explosive polymerisation of ethylene oxide are discussed, including rigid exclusion of acids covalent halides, such as aluminium chloride, iron(III) chloride, tin(IV) chloride basic materials like alkali hydroxides, ammonia, amines, metallic potassium and catalytically active solids such as aluminium oxide, iron oxide, or rust [1] A comparative study of the runaway exothermic polymerisation of ethylene oxide and of propylene oxide by 10 wt% of solutions of sodium hydroxide of various concentrations has been done using ARC. Results below show onset temperatures/corrected adiabatic exotherm/maximum pressure attained and heat of polymerisation for the least (0.125 M) and most (1 M) concentrated alkali solutions used as catalysts. 

Mixtures of silica gel and the liquid difluoride sealed in tubes at 334 mbar exploded above -196°C, presence of moisture rendering the mixture shock-sensitive at this temperature [1], Reaction of oxygen difluoride with silica, alumina, molecular sieve or similar surface-active solids is exothermic, and under appropriate conditions may be explosive [2], A quartz fibre can be ignited in the difluoride [3],... 

Fig. 2. Type I hydrogen isotherms O, hydrogen activation A, oxygen activation (solid symbols denote desorption points). 

Herein, we consider the case when a porous conducting matrix with inclusion of active solid reagents represents the electrode. It is supposed, that both the reagent and the product are nonconductive. The conversion of the solid reagents is assumed to proceed via a liquid-phase mechanism in the following way dissolution - electrochemical reaction - crystallization. Figure 1 shows the structure of the electrode and its model. The model has been developed on the bases of several assumptions. 

Activated Solids Shallow Fluid Bed Heat Exchanger... 

Figure 31. Activated Solids Shallow fluid-bed heat exchanger. (Liu, Liu, Li, and Kwauk, 1986.)...

The OH groups present on the surface of activated solids may be distinguished by v(OH) vibration bands ranging from 3800 to 3300 cm 1 (figure 3). Three different groups of v(OH) vibrations are visible ... 

The amount of heat actually taken up by the particles was an important quantity, as tubes operate under heat transfer limited conditions near the tube inlet. Fig. 30 shows a plot of Q against r, where Q was the total energy flow into the solid particles, for the entire segment. For inlet conditions, Q varied strongly at lower r, but was almost constant at higher values. As rcut/rp decreased from 0.95 to 0.0 and the effectiveness factor increased from nearly zero to one, the active solid volume increased by a factor of 7. If the solid temperature had remained the same, the heat sink would also have had to increase sevenfold. This could not be sustained by the heat transfer rate to the particles, so the particle temperature had to decrease. This reduced the heat sink and increased the driving force for heat transfer until a balance was found, which is represented by the curve for the inlet in Fig. 30. 

Fig. 28.1. Results (symbols) and simulations (lines) of an experiment at 25 °C by Liger et al. (1999 their Fig. 6) in which uranyl was oxidized by ferrous iron in the presence of nanoparticulate hematite, which served as a catalyst. Vertical axis is amount of NaHCCE-extractable uranyl, which includes uranyl present in solution as well as that sorbed to the nanoparticles in the experiment, nearly all the uranyl was sorbed. Broken line shows results of a simulation assuming uranyl forms a single surface complex, >Fe0U020H, which is catalytically active solid line shows simulation in which a non-catalytic site of this stoichiometry is also present. Inset is an expanded view of the first few hours of reaction.

Benters, R. Niemeyer, C. M. Wohrle, D., Dendrimer activated solid supports for nucleic acid and protein microarrays, Chembiochem. 2001, 2, 686 694... 

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