Specific heat Fast Chemical Reactions

As fast liquid-phase chemical reactions usually occur in the diffusion area, a macrokinetic approach should be used to reveal their aspects and specificity, as it describes reactions with consideration of the heat and mass transfer [47, 48]. This approach to the modelling of fast polymerisation processes, such as the cationic polymerisation of isobutylene [27-30,38,39,49], has revealed aspects of its behaviour. Many problems of fast chemical reactions were solved via the creation of sufficiently high turbulence in a reaction zone within small-scale tubular turbulent devices. 

The necessity to implement new conditions for carrying out heat and mass exchange processes directly in the reaction zone of fast chemical reactions, resulted in unprecedented designs of tubular reactors with the hydrodynamic flow mode of a reaction mixture as a key parameter [33-35]. These devices are characterised by high specific productivity and make it possible to achieve a quasi-plug flow mode in a reaction zone, providing heat and mass exchange processes with duration comparable to that of a chemical reaction. 

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. 

Quasi-equilibrium plasma-chemical processes canbe subdivided into two phases. In the first phase, reagents are heated to the high temperatures required to shift chemical equilibrium in the direction of products. In the second phase, which is called quenching, the temperature decreases fast enough to protect the products produced on the first high-temperature phase from reverse reactions. Three specific quenching modes can be introduced to analyze efficiency of the quasi-equilibrium plasma-chemical processes. 

Selection of reactor for sulfation of a-olefmes caused significant complications due to specificity of chemical process proceeding. Reaction proceeds fast enough (characteristic reaction time according with [276] is lower than 30 sec) and is high-exothermal. In particular, heat of sulfation is equal to q 502,MO kJ per 1 m of a-olefines [277]. As a consequence temperature rise in reaction zone is about 190 5°C. We should also note that due to significant difference in values of viscosity (n)... 

Introduced only recently in the literature (Haugwitz et al., 2007), the open plate reactor (OPR) is based upon the well-known Alfa Laval Plate Heat Exchanger (see Chapter 4). The OPR is specifically designed to handle highly exo- or endothermic and fast reactions. The aim is to safely produce the chemicals using highly concentrated reactant solutions. The main new features of the OPR, needed to reach this objective, are the improved heat transfer capacity and the micro-mixing conditions inside the reactor. It consists of reactor plates, inside which the reactants mix and... 

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