Surface reaction vessel

Imagine a closed reaction vessel in which an exothermic reaction proceeds at room temperature at a finite rate. Although the temperature in the reaction vessel is initially the same as room temperature, it rises gradually until the rate of heat generation due to the exothermic chemical reaction is equal to the rate of heat escape from the reaction vessel surface. However, if a thermal balance is not established for such a chemical reaction, the reaction rate is accelerated by self-heating as the temperature rises, leading to thermal runaway. The temperature change in a reaction vessel is represented by Eq. (1),... 

While claiming no finality for their mechanism, the authors pointed out that it accounted satisfactorily for the zero-order dependence on NC13 concentration, the intensity exponent of unity and many other characteristics of the reaction. However, a serious defect lies in the apparent absence of any effect of pressure on the rate of diffusion of NC14 to the reaction vessel surface. Such an effect would be expected under their conditions and it would yield a dependence of the reaction rate on total pressure opposite to that observed. 

This opened the possibility of ascertaining quantitative characteristics in the numerous individual reactions comprising the complex mechanism of oxidative chain reactions. Thus, rate constants have been determined for reactions with respect to their initiation and the branching, extension, and chain rupture, establishing specific details concerning the influence of solvents, reaction vessel surfaces, and other factors on the mechanism of individual reactions. Results of these investigations have... 

Data on alkyl radical oxidation between 300° and 800°K. have been studied to establish which of the many elementary reactions proposed for systems containing alkyl radicals and oxygen remain valid when considered in a broad framework, and the rate constants of the most likely major reactions have been estimated. It now seems that olefin formation in autocatalytic oxidations at about 600°K. occurs largely by decomposition of peroxy radicals rather than by direct abstraction of H from an alkyl radical by oxygen. This unimolecular decomposition apparently competes with H abstraction by peroxy radicals and mutual reaction of peroxy radicals. The position regarding other peroxy radical isomerization and decomposition reactions remains obscured by the uncertain effects of reaction vessel surface in oxidations of higher alkanes at 500°-600°K. 

If S is the reaction vessel surface area, and h is the over-all heat transfer coefficient for... 

The 20 % minor products were a complex mixture of oxygenates and propene, the composition of which varied with the nature of the reaction vessel surface as shown in Fig. 6. In contrast, however, the ratio of major/minor products was little affected by surface conditions. It was... 

At 330 °C using an HF-washed pyrex vessel the products found by Hoare and Ting-Man Li [32] were similar, but methanol was an early product (in the other study it appeared only at the time of maximum rate) and no methyl hydroperoxide was detected. Possible causes of this discrepancy include the different reaction vessel surfaces employed (although Barnard and Honeyman [30] found the low temperature reaction to be remarkably insensitive to reactor surface) and the rather higher temperature employed by Hoare and Ting-Man Li. Increasing temperature displaces the equilibrium... 

This simple interpretation of the second-limit mechanism is appropriate provided the reaction vessel surface is efficient with respect to removal of the species HO2. This situation arises with many salt-coated vessels, with KCl being widely exploited. Provided this is arranged, the rate determining part of the termination process is the gas-phase step (5) and the... 

As a general rule addition of molten CHDI directly to a liquid polyol is not recommended. In some instances this technique may cause CHDI to partially evaporate and recrystallize on exposed reaction-vessel surfaces. This problem can be minimized by first dissolving CHDI flakes into a molten polyol before the reaction temperature is raised above the melting point of CHDI diisocyanate. CHDI will form an opaque solution in many polyols at 60 C. 

To minimize the effects of this difficulty, an initiator is frequentiy employed. Among the numerous suggestions in the Hterature, the most satisfactory industrial procedure is to retain a portion of the Grignard from the preceding batch and to add this portion to the initial ether charge. The purpose of this procedure is to eliminate residual water and to clean the magnesium surface. Once this initiator has been added, the hahde is added at a rate deterrnined by the temperature and the pressure in the reaction vessel. 

Since finely divided lithium floats on the surface of the solvent and will be in contact with the atmosphere in the reaction vessel, an argon atmosphere, rather than a nitrogen atmosphere, should be used to avoid formation of the insoluble reddish-brown lithium nitride. 

Electrochemical corrosion protection of the internal surfaces of reaction vessels, tanks, pipes and conveyor equipment in the chemical, power and petroleum industries is usually carried out in the presence of strongly corrosive media. The range stretches from drinking water through more or less contaminated river, brackish and seawater frequently used for cooling, to reactive solutions such as caustic soda, acids and salt solutions. 

The contents of a reaction vessel are heated by means of steam at 393 K supplied to a heating coil which is totally immersed in the liquid. When the vessel has a layer of lagging 50 mm thick on its outer surfaces, it takes one hour to heat the liquid from 293 to 373 K. How long will it take if the thickness of lagging is doubled ... 

A reaction vessel is heated by steam at 393 K supplied to a coil immersed in the liquid in the tank. It takes. 1800 s to heat the contents from 293 K to 373 K when the outside temperature is 293 K. When the outside and initial temperatures are only 278 K, it takes 2700 s to heat the contents to 373 K. The area of the steam coil is 2.5 rn2 and of the external surface is 40 m2. If the overall heat transfer coefficient from the coil to the liquid in the vessel is 400 W/m2 K, show that the overall coefficient for transfer from the vessel to the surroundings is about 5 W/m2 K. 

A stainless steel cannula with a 2-mm. inside diameter and both ends sharpened is inserted through the septum into the receiving flask above the surface of the liquid, and a stream of nitrogen is passed briefly through the stopcock and out the cannula to remove air. The other end of the cannula is then inserted through the septum on the reaction vessel, the end of the cannula in the receiver is pushed below the surface of the liquid, and the solvent is forced into the reaction vessel with nitrogen pressure. 

When the product of a reaction is purified and isolated, some of it is inevitably lost during the collection process. Gases may escape while being pumped out of a reactor. Liquids adhere to glass surfaces, making it impossible to transfer every drop of a liquid product. Likewise, it is impossible to scrape every trace of a solid material from a reaction vessel. 

The rate coefficients k and k at 25 °C (/r = 1.2 M) have values and corresponding activation parameters of 1.10x10" l. mole . sec 17.6 kcal. mole S —22 cal.deg . mole and 6.45 x 10 mole.P. sec , 36.8 kcal.mole 32 cal.deg mole S respectively. Some surface catalysis was found the above results relate to teflon reaction vessels. The processes suggested by these authors were, for the path associated with k, ... 

Dark Decay of UDMH in Air, UDMH was observed to undergo a gradual dark decay in the 30,000-liter Teflon chamber at a rate which depended on humidity. Specifically, at 41 C and 4% RH the observed UDMH half-life was " 9 hours (initial UDMH 4.4 ppm) and at 40 C and 15% RH, the half-life was -6 hours (initial UDMH 2.5 ppm). The only observed product of the UDMH dark decay was NH3, which accounted for only -5-10% of the UDMH lost. In particular, no nitrosamine, nitramine, or hydrazone were observed. Formaldehyde dimethyIhydrazone was observed in previous studies which employed higher UDMH concentrations and reaction vessels with relatively high surface/volume ratios (, ) ... 

The additivity principle was well obeyed on adding the voltammograms of the two redox couples involved even though the initially reduced platinum surface had become covered by a small number of underpotential-deposited mercury monolayers. With an initially anodized platinum disk the catalytic rates were much smaller, although the decrease was less if the Hg(I) solution had been added to the reaction vessel before the Ce(lV) solution. The reason was partial reduction by Hg(l) of the ox-ide/hydroxide layer, so partly converting the surface to the reduced state on which catalysis was greater. 

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