This question contains chemistry, but the main focus is DOE design--hence posting on the engineering stack exchange.
The problem is a chemical reaction:
- A + B -> Product
- Product + B -> Impurity
The goals are
- to minimize the impurity.
- to minimize leftover A.
Reacting the mixture for a long time will get rid of A but increase the Impurity.
Reducing B will decrease the Impurity but increase leftover A.
To optimize the reaction, I'm planning a DOE with temperature, reagent amounts, and reaction time as variables.
I used software to generate a central composite design. However, the reaction time inputs for each experiment aren't physically reasonable. Look at some of the experiments:
+-------------+---------------+-------------------+ | Temperature | Reaction time | Amount of B | +-------------+---------------+-------------------+ | 20 C | 4 hrs | 1 mole equivalent | +-------------+---------------+-------------------+ | 50 C | 4 hrs | 1 mole equivalent | +-------------+---------------+-------------------+
At 20C, I think the reaction will proceed slowly enough that it won't be done after 4 hours. However, at 50C, I think the reaction will be done in less than an hour. The reaction output at 4 hours will be useless--all the B will have been long reacted (i.e. the maximum amount of impurity for that temperature/B input will have formed).
How can I handle the fact that reaction time inputs cannot be assigned randomly?