Exothermal reaction heat

It is generally desirable to minimize the diameter of a tubular reactor, because the leak rate in case of a tube failure is proportional to its cross-sectional area. For exothermic reactions, heat transfer will also be more efficient with a smaller tubular reactor. However, these advantages must be balanced against the higher pressure drop due to flow through smaller reactor tubes. 

The reactor temperature can reach over 900°C in the secondary reformer due to the exothermic reaction heat. Typical analysis of the exit gas from the primary and the secondary reformers is shown in Table 5-1. 

Reaction conditions are generally mild, but they differ from one process to another. In the newer Unipol process (Eigure 12-1) used to produce both HDPE and LLDPE, the reaction occurs in the gas phase. Ethylene and the comonomers (propene, 1-butene, etc.) are fed to the reactor containing a fluidized bed of growing polymer particles. Operation temperature and pressure are approximately 100°C and 20 atmospheres. A single-stage centrifugal compressor circulates unreacted ethylene. The circulated gas fluidizes the bed and removes some of the exothermic reaction heat. The product from the reactor is mixed with additives and then pelletized. New modifications for gas-phase processes have been reviewed by Sinclair. ... 

Notice the progressively increasing exothermic reaction heat, moving downward in the series. 

Figure 1 illustrates the process in more detail. The inert liquid is pumped upflow through the reactor at a velocity sufficient to fluidize the catalyst and to remove the reaction heat. The low Btu feed gas is passed simultaneously up the reactor where it is catalytically converted to a high concentration methane stream. The exothermic reaction heat is taken up by the liquid mainly as sensible heat and partly by vaporization (depending on the volatility of the liquid). The overhead product gases are condensed to remove the product water and to recover any vaporized liquid for recycle. The main liquid flow is circulated through a heat... 

For exothermic reaction, heat is released and particles are hotter than the surrounding fluid, hence the nonisothermal rate is always higher than the isothermal rate as measured by the bulk stream conditions. However, for endothermic reactions the nonisothermal rate is lower than the isothermal rate because the particle is cooler than the surrounding fluid. 

Adding these ingredients will produce an exothermic reaction, heating the mixture to 125-140F. 

In the case of the nonisothermal first-order exothermic reaction heat is auto catalytic, for it raises the temperature and provokes an increase of reaction rate, yet is itself a product of the reaction. In the Gray-Scott scheme, B is plainly autocatalytic and its degeneration by the second reaction plays the role of the direct cooling in the non-isothermal case. This reaction appears in the chemical engineering literature in 1983,16 and is the keynote reaction in Gray and Scott s 1990 monograph on Chemical Oscillations and Instabilities.17 A justification of the autocatalytic mechanism in terms of successive bimolecular reactions is the subject of Chapter 12. 

For comparison to the isothermal conditions in the well, an adiabatic calculation with the same well geometry was executed. This time, all uncoated faces were set to be adiabatic while the coated channel faces obeyed the above-given boundary conditions. Figure 3.61 shows that there is a tremendous temperature increase if the exothermal reaction heat is not allowed to leave the control volume. 

A major difference to mass transfer is that now the real reaction rate can be higher than the apparent one. The concentration in the particle is always lower or equal to the concentration in the bulk fluid phase and therefore, from this perspective, the real rate is always lower or, at best, equal to the apparent rate. However, in strong exothermic reactions heat transfer cannot cope with the high rates of generation of reaction heat and the temperature in the catalyst particle can be much higher than in the fluid phase, resulting in a much higher reaction rate than the apparent one. 

Fig. 17 Schematic representation of the temperature gradient occurring during the exothermic curing reaction. Owing to the comparatively high thermal conductivity of the continuous metallic filler (e.g. wires consisting of copper), exothermic reaction heat Q is conducted away from the interface. By changing locally the thermal conditions of the curing reaction, the temperature gradient T(N) may influence the resulting network structure D (N) which in turn defines the elastic properties of the epoxy, e.g. its elastic modulus E(N). jw denotes the heat current density...

When threatened, the bombardier beetle mixes hydroquinone and H202 with enzymes. Peroxide oxidizes hydroquinone to quinone, and the strongly exothermic reaction heats the solution to boiling. The hot, irritating liquid sprays from the tip of the insect s abdomen. 

In the case of bulk polymerization, the initiator is dissolved in the monomer and the viscosity of the system increases with progressing polymerization from liquid, through the state of gel ("gel-effect") to solid polymer. This polymerization technique has many disadvantages, among others the transfer of exothermic reaction heat from the system is very complicated. The reaction heat reaches values as high as 85 kj/ mol, and because polymers are poor heat conductors, this may cause the temperature of the system to reach the boiling point of monomer and consequently the polymer is foamed by vapours of monomer. 

Description Anhydrous liquid ammonia, recycled amines and methanol are continuously vaporized (1), superheated (3) and fed to a catalyst-packed converter (2). The converter utilizing a high-activity, low-byproduct amination catalyst simultaneously produces MMA, DMA and TMA. Product ratios can be varied to maximize MMA, DMA, or TMA production. The correct selection of the N/C ratio and recycling of amines produces the desired product mix. Most of the exothermic reaction heat is recovered in feed preheating (3). 

Temperature is commonly the most dominant variable in reactor systems. Since many chemical reactors are exothermic, controlling the dominant variable in these systems amounts to removing the exothermic reaction heat through temperature control. We gave many examples of how that is done. In cases where temperature is not the most dominant variable, compositions typically dominate. In this case unit control is not localized to the reactor since composition control is affected by other parts of the plant. 

The simple model of a thermal explosion which we examined in the last section was based on the view that, for an exothermic reaction, heat played the role of an autocatalytic product. It is now interesting to ask if it is possible for chemical species produced as intermediates, or even final... 

The reduction of double bonds is an exothermic reaction. Heat control is important during hydrogenation to avoid damage to the product and the equipment. Also, the capture of heat and its reuse to bring subsequent hydrogenation runs up to reaction temperatures is a significant aspect in overall process economics. 

Although the preparation of continuous beds on a small scale is easy, the preparation of large-size monoliths is quite difficult. The unstirred nature of the polymerization within the mold leads to a low capacity to effectively dissipate the exothermic reaction heat. The appearance of radial temperature gradient across the reaction mixture also results in the formation of inhomogeneities in the pore structure of the obtained monolith. This is the reason why most of the work reported in the last decades focused on the apphcation of smaU-size monoliths in chromatographic processes. 

Industrially, a continuously operating overflow tank is generally used. About twice the stoichiometric quantity of water is added to the calcium oxide in a premixer and the mixture transported to the reaction tank, in which the heat from the exothermic reaction heats up the reaction mixture to 100° C. The evaporating excess water entrains the very small lime hydrate particles and carries them upwards, where they are separated by an overflow from the coarse particles. The hydration process is then completed. The calcium hydroxide obtained contains less than 1 % water. 

In an endothermic reaction, heat is treated as a reactant. In an exothermic reaction, heat is treated as a product. 

To eliminate errors resulting from mixing or due to the exothermic reaction heat, so-called 1C adhesives were developed. These EP resins are only single-component adhesives in a procedural sense Chemically they are stiU two-component or multiple-component adhesives. These resins frequently contain additional catalysts that influence the course and kinetics of the reaction. 

The A5 sun is defined as the quantity of heat exchanged per K temperature in the course of a specific chemical or physical change. For an exothermic reaction, heat is released and the value of AH is a negative number. Therefore,... 

The reactor temperature can reach over 900 C in the secondary reformer due to the exothermic reaction heat. The second step after secondary reforming is removing carbon monoxide, which poisons the catalyst used for ammonia synthesis. This is done in three further steps, shift conversion, carbon dioxide removal, and methanation of the remaining CO and C02. Every stage involved in ammonia synthesis is environmentally important. Any emission or mishandling would represent not only a short-term disastrous threat to human health, but also a long-term environmental problem of grave consequences. 

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