In commercial chemical reaction the exact path taken by the substances in changing from reactants to products are sometimes out of the way.On slight variation of pressure, composition and temperature there may be a dangerous path of the reaction which is difficult to control.Such reactions are known as runaway reactions.Temperature is the most important cause of divergence from the normal reaction path.
Characteristics of chemical reactions:
1.There are collisions among reactant molecules.
2.The reactant molecules have sufficient energy to penetrate each other’s electron field.The amount of energy required to cause chemical reaction is called activation energy.
3.Rate of chemical reaction depends on number of collisions per unit time and the fraction which posseses sufficient energy to make the collisions.
4.Catalysts reduce the activation energy.
Reasons of runaway reactions:
1.Impurities present in the commercial chemicals.
2.Radial temperature gradient
3.Longer processing time.
4 Catalytic effect of byproducts,metals etc.
5.Formation of free radicals.
Types of reactions prone to runaway reactions: Nitration,oxidation,halogenations,polymerization etc.
Control of runaway reaction:
6.Deluge with water.
7.Purge with inert gas like nitrogen.
9.Reduce inside pressure.
10.Adopt flareing(burning of gas),neutralization,water scrubbing etc.as mitigation strategy.