Conversion (chemistry)

For continuous processes the two are the same, for batch and semi-batch there are important differences.

In semi-batch polymerisation, the instantaneous conversion is defined as the total mass of polymer divided by the total mass of monomer fed:[1][2] Total conversion of the formulation: Total conversion of the fed reactants: Yield in general refers to the amount of a specific product (p in 1..m) formed per mole of reactant consumed (Definition 1[3]).

If not all of the limiting reactant has reacted, the two definitions contradict each other.

Combining those two also means that stoichiometry needs to be taken into account and that yield has to be based on the limiting reactant (k in 1..n): The version normally found in the literature: Instantaneous selectivity is the production rate of one component per production rate of another component.

For overall selectivity the same problem of the conflicting definitions exists.

Generally, it is defined as the number of moles of desired product per the number of moles of undesired product (Definition 1[3]).

However, the definitions of the total amount of reactant to form a product per total amount of reactant consumed is used (Definition 2) as well as the total amount of desired product formed per total amount of limiting reactant consumed (Definition 3).

The version normally found in the literature: The version normally found in the literature: For batch and continuous reactors (semi-batch needs to be checked more carefully) and the definitions marked as the ones generally found in the literature, the three concepts can be combined: For a process with the only reaction this mean that S=1 and Y=X.

For the following abstract example and the amounts depicted on the right, the following calculation can be performed with the above definitions, either in batch or a continuous reactor.