Energy Transfer During Exothermic Reaction

Ignition is dependent on various physicochemical parameters, such as the type of reactants, reaction rate, pressure, the heat transfer process from the external heat source to the reactants, and the size or mass of the reactants. The rate of heat production is dependent on the heats of formation of the reactants and products, the temperature, and the activation energy. As the process of ignition includes an external heating and an exothermic reaction of the reactants, there is a non-steady heat balance during these phases. 

An exothermal reaction is to be performed in the semi-batch mode at 80 °C in a 16 m3 water cooled stainless steel reactor with heat transfer coefficient U = 300 Wm"2 K . The reaction is known to be a bimolecular reaction of second order and follows the scheme A + B —> P. The industrial process intends to initially charge 15 000 kg of A into the reactor, which is heated to 80 °C. Then 3000 kg of B are fed at constant rate during 2 hours. This represents a stoichiometric excess of 10%.The reaction was performed under these conditions in a reaction calorimeter. The maximum heat release rate of 30Wkg 1 was reached after 45 minutes, then the measured power depleted to reach asymptotically zero after 8 hours. The reaction is exothermal with an energy of 250 kj kg-1 of final reaction mass. The specific heat capacity is 1.7kJ kg 1 K 1. After 1.8 hours the conversion is 62% and 65% at end of the feed time. The thermal stability of the final reaction mass imposes a maximum allowed temperature of 125 °C The boiling point of the reaction mass (MTT) is 180 °C, its freezing point is 50 °C. 

What kind of energy transfer occurs during the exothermic heat-pack reaction Heat produced by the reaction flows from the heat pack (the system) to yom cold hands (part of the surroundings). 

The rapid heat transfer allows nearly isothermal operation with a defined residence time. Therefore, undesired side reactions can be effectively suppressed. The formation of hot spots within the reactor and reactor runaway during fast, highly exothermic reactions can be avoided. As a consequence, higher operating temperatures are attainable, and the same conversion can be achieved with a smaller reactor volume and less catalyst. The smaller unit size in turn improves the energy efficiency, reducing the operational cost. 

The feasibility of electron transfer is dictated by the overall change of free energy (AG) during the process. Generally, an electron transfer reaction will be thermodynamically allowed when it is exothermic (AG < 0). It can be expressed by the simplified Rehn-Weller equation [17] ... 

Work is negative when energy is transferred out of the system and is positive when energy is transferred into the system. This is consistent with the signs associated with the heat of a reaction (q) during exothermic and endothermic processes. 

---