Question

when would one purposely add an inert material to a feed stream ? illustrate this strategy with an example, and explain the advantages (and disadvantages) of doing this.

Answer 1

One can add inert matearial in feed stream (gas phase) that can affect the equilbrium, but only if the volume is allowed to change in a reversible reaction. Inert have no effect in irreversible reaction.

In industries addition of inert's has other advantages like when highly exothermic reactions need to be handled,deliberately we add inert's to the reactant stream so as to have better control of temperature of reactor and we can also shift the reaction equilibrium either in forward and in backward direction depending on number of moles.
1. One example is the addition of steam to a catalytic reaction using hydrocarbon feeds. In the styrene production process, superheated steam is added as a inert in feed stream to provide desired temperature for the endothermic reaction and to shift the equilibrium towards styrene product.

2. In another example, in production of acrylic acid steam is added to the feed of propylene and air to act as thermal ballast (absorb the heat of reaction and regulate the temperature), and staem also acts as an anti-coking agent - preventing undesired coking reactions that can deactivate the catalyst

Disadvantages

In some reaction adding an inert can dilute the reactant as a result reaction can be slow down .

3. This can be more understood by taking the example of fire extinguisher, CO2 dilutes the oxygen coming in contact with the combustible material to the point that combustion is no more possible. IN FIRE EXTINGUSHER THIS SLOW DOWN IS USEFUL BUT IN INDUTRY THAT CAN BE A DRAWBACK OF ADDING A INERT IN FEED STREAM.

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