Endothermic chemical processes

In order to exemplify the potential of micro-channel reactors for thermal control, consider the oxidation of citraconic anhydride, which, for a specific catalyst material, has a pseudo-homogeneous reaction rate of 1.62 s at a temperature of 300 °C, corresponding to a reaction time-scale of 0.61 s. In a micro channel of 300 pm diameter filled with a mixture composed of N2/02/anhydride (79.9 20 0.1), the characteristic time-scale for heat exchange is 1.4 lO" s. In spite of an adiabatic temperature rise of 60 K related to such a reaction, the temperature increases by less than 0.5 K in the micro channel. Examples such as this show that micro reactors allow one to define temperature conditions very precisely due to fast removal and, in the case of endothermic reactions, addition of heat. On the one hand, this results in an increase in process safety, as discussed above. On the other hand, it allows a better definition of reaction conditions than with macroscopic equipment, thus allowing for a higher selectivity in chemical processes. 

The minimum design temperature should be the lowest temperature to which the tank will be subjected, taking into consideration the minimum temperature of material entering the tank, the minimum temperature to which the material may be autorefrigerated by rapid evaporation of low-boiling liquids or mechanically refrigerated, the minimum ambient temperature of the area where the tank is located, and any possible temperature reduction by endothermic physical processes or chemical reactions involving the stored material. API 620 provides for installations in areas where the lowest recorded 1-day mean temperature is 50°F (10°C). 

Temperature increase can cause various physical and chemical processes for the adsorbed TNT molecules, including melting, vaporization, and decomposition. All these reactions are endothermic except deflagration. Since the resonance frequency of the cantilever returns to its original value after deflagration, it can be assumed that all the adsorbed TNT desorbed from the surface. 

The disadvantage of the elementary reaction (5.39) is its relatively high endothermicity (the heat effect equals -79.6kJ/mol), which makes the implementation of this reaction mechanism ambiguous. However, chemical induction provides products of the induced reaction with the ability to form in concentrations exceeding thermodynamically equilibrium concentrations. This allows implementation of chemical processes with the equilibrium essentially shifted towards the initial substances [27],... 

Figure 12 indicates a possibility of such a case, which is comparable to the existence of endothermic chemical compounds. Once formed, such an endothermic surface molecule may have a certain time of existence before dissociating. This time may be long enough to enable it to react with other molecules. In many catalytic processes the intermediate role... 

Production of H2 of 1 mol needs an enthalpy of 242 kJ/mol-CO. Reduction of C02 into CO with H2 is endothermic reaction required heat input of 41 kJ/mol-CO. Because CO has higher energy density than H2, CO is one of the most popular media in chemical processes. 

The application refers to the production of fine chemicals [67]. A10 m3 batch vessel was used to perform the two-step chemical process. The first strongly exothermic reaction step needed cooling because of the volatility of one of the starting materials. The reaction was finished when all of the volatile reactant had reacted. The second step was endothermic and the batch vessel had to be heated for some hours to complete the reaction. It took several hours to perform these two steps and a throughput of about 1800 kg/h was achieved. 

A chemical reaction that gives out heat, e.g. when a fuel bums in air. The opposite of this process is when a chemical reaction needs heat to react at all, this is called an endothermic chemical reaction. 

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