Chemical reaction engineering adiabatic reactors

Techniques for approaching optimum temperature profiles for exothermic reaction, (a) Adiabatic operation of reactors with interstage cooling, (b) Countercurrent heat exchange. (Adapted from Chemical Reaction Engineering, Second Edition, by O. Levenspiel. Copyright 1972. Reprinted by permission of John Wiley and Sons, Inc.)... 

A major breakthrough with regard to the understanding of this phenomenon in the field of chemical reaction engineering was achieved by Ray and co-workers (Uppal et ai, 1974, 1976) when in one stroke they uncovered a large variety of possible bifurcation behaviours in non-adiabatic continuous stirred tank reactors. In addition to the usual hysteresis type bifurcation, Uppal et al. (1976) uncovered different types of bifurcation diagrams, the most important of which is the isola which is a closed curve disconnected from the rest of the continuum of steady states. 

These are systems that exchange neither energy nor matter with the environment. The simplest chemical reaction engineering example is an adiabatic batch reactor. These systems tend towards their thermodynamic equilibrium which is characterized by maximum entropy (highest degree of disorder). 

Purely adiabatic fixed-bed reactors are used mainly for reactions with a small heat of reaction. Such reactions are primarily involved in gas purification, in which small amounts of noxious components are converted. The chambers used to remove NO, from power station flue gases, with a catalyst volume of more than 1000 m3, are the largest industrial adiabatic reactors, and the exhaust catalyst for internal combustion engines, with a catalyst volume of ca. 1 L, the smallest. Typical applications in the chemical industry include the methanation of traces of CO and CO2 in NH3 synthesis gas, as well as the hydrogenation of small amounts of unsaturated compounds in hydrocarbon streams. The latter case requires accurate monitoring and regulation when hydrogen is in excess, in order to prevent complete methanation due to an uncontrolled temperature runaway. 

Figure 4.31 Measured hystersis for reaction of sodium thiophosphate and hydrogen peroxide in an adiabatic CSTR. In this experiment reactor temperature was measured as a function of holding time. [After S.A. Vejtassa and R.A. Schmitz, Amer. Inst. Chem. Engrs. JL, 16, 410, with permission of the American Institute of Chemical Engineers, (1970).]...

Hanika, J., Lange, R., Dynamic aspects of adiabatic trickle-bed reactor control near the boiling point of reaction mixture. Chemical Engineering Science, 1996, 51(11), 3145-3150... 

---