Fast and Exothermic Reactions

Tetrachlorosilane was added to aqueous ethanol (the presence of water was accidental). There was no proper stirring during this operation, which led to the formation of two liquid layers of compounds that did not react. The very fast and exothermic reaction of the alcoholysis-hydrolysis of chlorosilane started violently and the large compoundion of hydrogen chloride caused the reactor to detonate. 

Combustion processes are fast and exothermic reactions that proceed by free-radical chain reactions. Combustion processes release large amounts of energy, and they have many applications in the production of power and heat and in incineration. These processes combine many of the complexities of the previous chapters complex kinetics, mass transfer control, and large temperature variations. They also frequently involve multiple phases because the oxidant is usually air while fuels are frequently liquids or solids such as coal, wood, and oil drops. 

In conclusion, a fast and exothermal reaction such as this cannot be performed in a batch reactor. This reaction will also be studied in other reactor types in the following chapters. 

If the feed is stopped immediately in the case of malfunction, the CSTR is uncritical the non-converted reactant is only 1%, resulting in a ATai of ca. 1 °C only. This result enhances the strength of the CSTR in its behavior after cooling failure. The CSTR is a practicable and elegant solution for the industrial performance of this fast and exothermal reaction. Since the technique is based on a stirred tank, it does not require high investment for it to be realized in a traditional multipurpose plant. 

The situation is most critical at the entrance of the reactor where the reaction will continue under quasi adiabatic conditions, even if the feed has been stopped. The temperature increase can be limited by adequate construction, such as increase of the heat capacity of the reactor itself. The PFR represents another practicable solution to achieve safe performance of this fast and exothermal reaction at industrial scale. The small volume of 42 liters compared to 900 liters for the CSTR and 5 m3 for the SBR make protecting the reactor against overpressure easy and economical. 

This expression was established for zero-order reactions, but can also be used for other reactions, if the influence of concentration on reaction rate can be neglected. This approximation is particularly valid for fast and exothermic reactions (see Section 2.4.3). 

The BMIs are prepared according to a two-step process based on the reaction of a diamine with maleic anhydride. The first reaction is usually performed at room temperature in an aromatic, or chlorinated, or aprotic solvent. This fast and exothermic reaction leads to the monoamide (so called maleamic acid) of maleic acid. However formation of the monoamide of fumaric acid (trans-isomer) was observed [6] and the formation of the trans-isomer which does not cy-clize, has to be minimized by working at low temperature. 

Haber, J., Kashid, M.N., Borhani, N., Thome, J., Krtschil, U., Renken, A., and Kiwi-Minsker, L. (2013) Infrared imaging of temperature profiles in microreactors for fast and exothermic reactions. Chem. Eng. J, 214, 97-105. 

Kumar, A. (2012) Characterization of Hot Spots in Microstructured Reactors for Fast and Exothermic Reactions in Mixing Regime, Ecole Polytechnique Federale de Lausanne, EPFL, Lausanne. 

The global heat transfer coefficient comprises all transfer resistances as shown in Equation 5.8. In general, a minimum volumetric heat transfer coefficient of U, >1 MW m is required for fast and exothermic reactions [16]. 

The influence of the inlet temperature on the axial temperature profile in the microchannel reactor is illustrated in Figure 5.18. All other reaction conditions are kept constant. The initial temperature difference between the cooling fluid and the reaction mixture at the inlet is in all cases identical To-T = 10K). At the reactor outlet the temperature reaches nearly the cooling temperature for all inlet conditions. But, the maximum temperature increases drastically with an increase of Tq. The important increase of the maximum temperature because of a small change of the inlet conditions is called parametric sensitivity and can be observed for fast and exothermic reactions in tubular reactor. In the domain of high parametric sensitivity the reactor is difficult to control and important temperature excursions carmot be avoided. High local temperatures may lead to important... 

As discussed above, the volumetric heat transfer coefficient is inversely proportional to the square of chatmel diameter. If fast and exothermic reactions are considered, the reactors with internal dimensions in the submillimeter range are required being suitable for low tormage production. However, to increase the throughput, higher reactor volumes are required. As a traditional scale-up of such reactors would eliminate their main advantages, one has to scale-out or number-up. ... 

In the petrochemical industry close to 80% of reactions are oxidations and hydrogenations, and consequently very exothermic. In addition, profitability requires fast and selective reactions. Fortunately these can be studied nowadays in gradientless reactors. The slightly exothermic reactions and many endothermic processes of the petroleum industry still can use various tubular reactors, as will be shown later. 

With PI, traditional proeess design criteria (particularly those focused around stirred batch reactors) are thrown out and the equipment is designed to mateh the chemistry. It is not unexpected, therefore, to find that PI has been successfully applied to reactions that are very fast and exothermic, where the process is being limited by poor design. Traditionally these proeesses have been handled either by the use of large amounts... 

Phosgeneisanintermediateutilizedinthechemicalandpharmaceuticalindus-triesfortheproductionofisocyanatesformakingpolyurethanefoamsandforthe synthesis ofpharmaceuticals and pesticides (see original citations in [79]). Phosgene is extremely toxic and is an aggressive reactant. The reaction is moderately fast and exothermic (-26kcalmol Phosgene formation demands specialized... 

We will next consider the additional complexities of combustion, which are caused by the fact that combustion reactions are chain reactions, which are extremely fast and exothermic, and therefore, once the reaction is ignited, the process proceeds very quickly and becomes very nonisothermal. 

An explosion can be defined as a fast, transient, exothermic reaction. It needs exothermicity to generate energy and must be fast to generate this energy very quickly in a transient pulse. We can also distinguish between events in which the reaction propagates at subsonic velocity as an explosion and one in which the reaction propagates with sonic or supersonic velocity as a detonation. 

The key factor in the development of a commerical hot-gas desulfurization process is the regeneration of the spent sorbent Two methods are discussed here regeneration with a air-S02 mixture and regeneration with a steam-air mixture The reaction of iron sulfide with air is very fast and exothermic, and forms Fe203 and S02 as the only products Consequently the reaction rate is largely controlled by the pore diffusion mechanism Reactions of iron sulfide with SO2 and with steam are relatively much slower, and form F63O4 and elemental sulfur The overall rate in these cases is largely controlled by the intrinsic chemical reaction. 

The reaction in Eq. (11.3) is fast and exothermic and essentially goes to completion under the high pressure reaction conditions that are used industrially. The reaction in Eq. (11.4) is slower and is endothermic. It does not go to completion. The conversion (on a C02) basis is usually 50% to 80%. The conversion increases with increasing temperature and NH3/CO2 ratio. It decreases with increasing H20/C02 ratio110. 

Based on experience with endothermic and exothermic reactions in FAB/CFB calciners and combustors, the fast fluidized bed has been used in the gasification of biomass (wood chips, bark, etc.) and coals with low and high ash contents. The major advantages of FAB gasification are ... 

Polymerizations were carried out in three necked fladcs equipped with mechanical stirrer, and thermometer. The flask was placed in a thermostatically controlled bath filled with n-pentane and cooled by liquid nitrc en (IS). Initiator solutions were precooled and added throu a cold jacketed addition futmel to the stirred charges. Reactions were fast and exothermic. 

The reaction between an aromatic diamine and an aromatic dianhydride such as pyromellitic dianhydride is fast and exothermic. It is usually carried out in a solvent for the polyamic acid, which is, of course, a polyamide. Both meta- and para-diamide units are formed... 

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