Surface treated reactors

Two different polyacrylonitrile precursor carbon fibers, an A fiber of low tensile modulus and an HM fiber of intermediate tensile modulus were characterized both as to their surface chemical and morphological composition as well as to their behavior in an epoxy matrix under interfacial shear loading conditions. The fiber surfaces were in two conditions. Untreated fibers were used as they were obtained from the reactors and surface treated fibers had a surface oxidative treatment applied to them. Quantitative differences in surface chemistry as well as interfacial shear strength were measur-ed. 

An assumption involving heat losses from the reactor is made in most treatments. The effect of heat transfer on the maximum reaction rates of a homogeneous reactor has been treated by DeZubay and Woodward (14). It was found that a lowering of the reactor surface temperature appreciably lowered the chemical reaction rates. Longwell and Weiss (43) found, for example, a loss equal to 5% of the maximum adiabatic heat liberated reduces the maximum heat release rate by more than 30%, while a 20% heat loss reduces the rate about 85%. One should not assume an adiabatic system without some definite knowledge of the magnitude of the heat losses. 

For this purpose, conjugated dehydrogenation of some alkylbenzenes was executed in reactors treated by various inorganic compounds [48], The experimental results indicate that in all cases the reaction proceeding is highly sensitive to the reactor surface type. For example, target product yields decreased in the following sequence with respect to salt selected for treatment of the reactor ... 

In order to create glow discharge in the basket, it is necessary to insert the hot electrode coaxially placed in the center of the basket and ground the reactor and the tumbler basket as the counterelectrodes. Without the hot center electrode, glow discharge will develop between the reactor wall and the metal basket, i.e., in the volume (Fi — F2) outside of the basket, and develop the same situation for the secondary plasma discussed in Chapter 18, which could be good for surface treating... 

TCE isotherms were also measured in 250-ml well-mixed batch reactors (amber bottles sealed with teflon septa). Aliquots of TCE stock solution (4,000 mg/L in methanol) were added to reactors containing 10 to 15 mg of either as-received or surface treated carbons to yield initial TCE concentrations ranging from 0.030 to 8 mg/L. The solution phase consisted... 

Water Chemistry of Nuclear Reactor Systems, Bournemouth, UK, 1992, Vol. 2, p. 49—60 Lister, D. H., Anderson, P. G., Barry, B. J., Lavoie, R. G. Deposition of cobalt on surface-treated stainless steel under PWR conditions. Report EPRI NP-6528 (1989)... 

Reactor surfaces which are treated with oxygen produced strong surface effects. However, the level of activity of the oxidized surface as compared to that of the untreated surface depends largely on the type of metal or alloy. The initial activity of 304 stainless steel, incoloy, and inconel increased after oxygen-treatment of the surface. 

The results for a run in the stainless steel reactor that had been oxidized (and then reduced) 15 times demonstrate the nature of the above reaction. In this particular run, the oxidized reactor was treated with carbon monoxide until no further reactions occurred. Calculation Indicated that 8800 millimoles of carbon were deposited per sg. meter of surface. When hydrogen was passed at a flow rate of 60 cc/min through the reactor, the exit gas stream was found to contain up to 9.5% methane and the remainder hydrogen trace amounts of water were noted just after the hydrogen flow was started. Carbon equivalent to 8100 millimoles/ sq. meter was removed as methane during 38 hours of hydrogen treatment. In this time period, the methane concentration in the exit stream decreased to less than 0.1%. 

Where there are large volumes of contaminated water under a small site, it is sometimes most convenient to treat the contaminant in a biological reactor at the surface. Considerable research has gone into reactor optimization for different situations and a variety of stirred reactors, fluidized-bed reactors, and trickling filters have been developed. Such reactors are usually much more efficient than in situ treatments, although correspondingly more expensive. 

Pentachlorophenol is readily degraded in biofHm reactors (53), so bioremediation is a promising option for the treatment of contaminated groundwater brought to the surface as part of a pump-and-treat operation. 

Catalytic methanation processes include (/) fixed or fluidized catalyst-bed reactors where temperature rise is controlled by heat exchange or by direct cooling using product gas recycle (2) through wall-cooled reactor where temperature is controlled by heat removal through the walls of catalyst-filled tubes (J) tube-wall reactors where a nickel—aluminum alloy is flame-sprayed and treated to form a Raney-nickel catalyst bonded to the reactor tube heat-exchange surface and (4) slurry or Hquid-phase (oil) methanation. 

Qua.driva.Ient, Zirconium tetrafluoride is prepared by fluorination of zirconium metal, but this is hampered by the low volatility of the tetrafluoride which coats the surface of the metal. An effective method is the halogen exchange between flowing hydrogen fluoride gas and zirconium tetrachloride at 300°C. Large volumes are produced by the addition of concentrated hydrofluoric acid to a concentrated nitric acid solution of zirconium zirconium tetrafluoride monohydrate [14956-11-3] precipitates (69). The recovered crystals ate dried and treated with hydrogen fluoride gas at 450°C in a fluid-bed reactor. The thermal dissociation of fluorozirconates also yields zirconium tetrafluoride. 

New reactors should also be treated in air as mentioned above, before they are first used. After the treatment the light yellowish hue indicates the presence of the chromoxide layer on the surface. 

Chapter 10 begins a more detailed treatment of heterogeneous reactors. This chapter continues the use of pseudohomogeneous models for steady-state, packed-bed reactors, but derives expressions for the reaction rate that reflect the underlying kinetics of surface-catalyzed reactions. The kinetic models are site-competition models that apply to a variety of catalytic systems, including the enzymatic reactions treated in Chapter 12. Here in Chapter 10, the example system is a solid-catalyzed gas reaction that is typical of the traditional chemical industry. A few important examples are listed here ... 

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