A Highly Exothermic Reaction

In cases where a large reactor operates similarly to a CSTR, fluid dynamics sometimes can be estabflshed in a smaller reactor by external recycle of product. For example, the extent of soflds back-mixing and Hquid recirculation increases with reactor diameter in a gas—Hquid—soflds reactor. Consequently, if gas and Hquid velocities are maintained constant when scaling and the same space velocities are used, then the smaller pilot unit should be of the same overall height. The net result is that the large-diameter reactor is well mixed and no temperature gradients occur even with a highly exothermic reaction. 

When catalysts are used in a highly exothermic reaction, an active phase may be diluted with an inert material to help dissipate heat and moderate the reaction. This technique is practiced in the commercial oxychlorination of ethylene to dichloroethane, where an alumina-supported copper haUde catalyst is mixed with a low surface area inert diluent. 

An important effect in the design of a tubular flow reactor is the development of a radial temperature gradient in a highly exothermic reaction with wall cooling. The temperatures near the tube axis are... 

Older methods use a liquid phase process (Figure 10-11). ° New gas-phase processes operate at higher temperatures with noble metal catalysts. Using high temperatures accelerates the reaction (faster rate). The hydrogenation of benzene to cyclohexane is characterized by a highly exothermic reaction and a significant decrease in the product volume... 

Polymerizing ethylene is a highly exothermic reaction. Eor each gram of ethylene consumed, approximately 3.5 KJ (850 cal) are released ... 

The oxidative propane dehydrogenation is well investigated and also a highly exothermic reaction. In a fixed-bed reactor, steep temperature gradients are ob-servableandtheconversionofpropaneandselectivityofthereactionarestrongly determinedbytemperatureandtotalflowrate[133]. 

Dinitrogen tetroxide has a highly exothermic reaction with boron trichloride. 

Aluminium can detonate when mixed with ammonium nitrate. It has a highly exothermic reaction with metal nitrates if it is heated at 70-135°C when water traces are present. 

When one considers the potential high-energy release on rupture of a carborane unit, together with the thermodynamic stability of combustion products, it is hardly surprising that there is a body of literature that reports on the use of carbo-ranes within propellant compositions. Their use in energetic applications is to be expected when the enthalpy of formation (AH/) data for the products of combustion for boron are compared to those of carbon. Thermodynamic data for the enthalpy of formation of o-carborane and of typical boron and carbon combustion products is shown in Table 4. Measurements of the standard enthalpy of combustion32 for crystalline samples of ortho-carborane show that complete combustion is a highly exothermic reaction, AH = — 8994 KJmol. ... 

Addition of the aluminate (0.5 g) to pyridine (50 ml) must be effected very slowly with cooling. Addition of 1 g portions may cause a highly exothermic reaction. 

The formation enthalpies of a few acids and parent hydrocarbons are given in Table 1.6. The oxidation of the methyl group of hydrocarbon to carboxyl group is a highly exothermic reaction. The enthalpy of the reaction... 

Some experimental studies (1-7) have demonstrated the possibility of improving the performance of a catalytic reactor through cyclic operation. Eenken et al. (4) reported an improvement of 70% in conversion of ethylene to ethane under periodic operation. In a later article (2), they concluded that periodic operations can be used to eliminate an excessively high local temperature inside the catalytic reactor for a highly exothermic reaction. In our laboratory, Unni et al. (5) showed that under certain conditions of frequency and amplitude associated with the forced concentration cycling of reactants, the rate of oxidation of SC>2 over catalyst can be increased by as much as 30%. Re-... 

Use of Ac20 as solvent and H2S04 as catalyst permits a highly exothermic reaction that results in vic-acetoxy alcohols. 

Hydrogenation of coal is a highly exothermic reaction corresponding to a heat evolution of about 15 kilojoules per cubic metre of hydrogen reacted. Means must be provided to remove this heat from the reaction zone so that the reaction temperature can be maintained in the optimum range. This is usually accomplished by injecting coal liquid as quench into various sections of the reac tor. 

The odor is detectable at 8 ppm. Mixing with acids results in polymerization, a highly exothermic reaction that may result in explosions. ... 

An example of a highly exothermic reaction carried out in this manner is provided by the manufacture of dodecylbenzene sulphonic acid. The reactor is charged with dodecylbenzene and 20% oleum is fed in continuously at a rate which is regulated to give a uniform temperature during the sulphonation reaction. The conversion is thus effectively controlled by the rate of oleum addition rather than the rate of the chemical reaction. 

The high reaction rate with low water levels is associated with a highly exothermic reaction pattern. The reactor is actually, in part, an energy source for the rest of the plant... 

BP, BLYP, EDFl and B3LYP density functional models all lead to significant improvements over both Hartree-Fock and local density models, at least in terms of mean absolute deviations. While most reactions are better described, there are exceptions. Most notable among these is the bond separation reaction for tetrachloromethane. All four models show a highly exothermic reaction in contrast with both G3 and experimental results which show a nearly thermoneutral reaction. Similar, but somewhat smaller, effects are seen for isobutane and trimethylamine. As was the case with Hartree-Fock calculations. 

The isobutene oligomerization is a highly exothermic reaction, carried out via the carbenium ion mechanism, which is thermodynamically favoured at low temperature. The kind of products obtained as well as the conversion and stability at constant temperature and pressure will depend on the reaction GHSV, which determine the intermediate carbenio ion formed during the first steps. 

Most carbenes are relatively easily generated by photolysis of nitrogeneous precursors such as diazo compoundsor diazirines. The reaction is clean, as nitrogen is the only byproduct and it is also very efficient as nitrogen evolution is a highly exothermic reaction. Therefore carbenes can be easily generated even under very inert conditions, such as in a noble gas matrix at very low temperatures. 

Reaction of Carbon Atoms with Alcohols and Ethers. The electro-philicity of atomic carbon and the exothermicity of carbon monoxide formation in its reactions facilitates attack on, and removal of oxygen by C atoms. Deoxygenation of ethers, alcohols, and carbonyl compounds has been reported. This process is generally a highly exothermic reaction, which is likely to generate products with excess energy. 

To a solution of methylenecyclopropane (5.4 g, 0.10 mol) in CH2C12 (50 mL) cooled to — 80 °C was added 4-nitroperoxybenzoic acid (18.3 g, 0.10 mol) and the mixture was warmed with stirring. At about 0°C, a highly exothermic reaction occurred and occasional euoling in an ice-waicr bath was necessary. The mixture was stirred at rt overnight, filtered, and the filtrate was distilled under reduced pressure (15 Torr) at rt. The residue (ca. 5 g) was 4-nitrobenzoic acid. The distillate was a solution of oxaspiropentane in CH2C12 which was concentrated by distillation under ordinary pressure. 

In the process jointly developed by Bayer and Hoechst,933-935 a palladium-gold-on-silica or alumina catalyst impregnated with KOAc is used. A mixture of ethylene, acetic acid, and oxygen is converted at 150-170°C and about 5-10 atm to produce vinyl acetate with about 91-92% selectivity at about 10% conversion in a highly exothermic reaction. The only major byproduct is C02. KOAc requires continuous replenishment. A similar process was independently developed by U.S.I. Chemicals.932 936... 

Fig. 1. A new process (Urea Technologies) developed for the Tennessee Valley Authority operates at considerable energy savings. Urea is produced in an overall exothermic reaction of ammonia and carbon dioxide at elevated pressure and temperature. In a highly exothermic reaction, ammonium carbamate is first formed as an intermediate compound, followed by its dehydration to urea and water, which is a slightly endothermic reaction. The conversion of CO2 and NH3 to urea depends oil the ammonia-to-caibon dioxide ratio, temperature, and water-to-carbon dioxide ratio, among other factors. The new process makes maximum use of the heat created in the initial reaction, including heat recycling. 1 Urea Technologies and Tennessee Valley Authority)...

---