#### Multiple Reactions and Selectivity: Interactive Simulations

These simulations should run on your browser. For these simulations, screencasts are provided to explain how to use them.

##### Simulation: Selectivity in a Semibatch reactor

The parallel reactions A + B → D and A + B → U are carried out in an isothermal semibatch reactor. Both reactions are first-order in A. The desired reaction to form the product D is second-order in B, whereas the undesired reaction to form product U is first-order in B. Both reactions are irreversible. This Demonstration compares two scenarios: (1) pure A is fed to a reactor that initially contains only B, and (2) pure B is fed to a reactor that initially contains only A. For either scenario, the addition of the second reactant stops after 10 minutes, when the amount of the reactant added equals the amount of the other reactant initially in the reactor. Use sliders to vary the activation energy of each reaction and the isothermal reactor temperature to determine how selectivity and moles of products and reactants change with time.

Try to answer these questions before determining the answer with the simulation. We suggest that you write down the reasons for your answers.

These two reactions are carried out in an isothermal semibatch reactor:
A + B → D    $$r_D = k_DC_AC_B^2$$
A + B → U    $$r_U = k_UC_AC_B$$

1. Which scenario yields the highest selectivity to the desired product D?
a. feed A to a reactor that initially contains only B
b. feed B to a reactor that initially contains only A
c. feed a mixture of A and B to the reactor

2. For which scenario(s) does the selectivity decrease with time?
a. feed A to a reactor that initially contains only B
b. feed B to a reactor that initially contains only A
c. feed a mixture of A and B to the reactor

1.
##### Simulation: Series Reaction in a Batch Reactor
Two first-order, liquid-phase, irreversible reactions A → B → C take place in an isothermal batch reactor. The reactor initially contains only A at a concentration of 2 mol/L. The activation energy of the second reaction is higher than the activation energy of the first reaction. Vary the temperature of the reaction with a slider. Select Display: “selectivity” to plot selectivity (CB/CC) versus time.
Try to answer this question before determining the answer with the simulation. We suggest that you write down the reason for your answer.

1. Is selectivity to product B favored at high or low temperature if the activation energy for the second reaction (to form C) is higher than the activation energy for the first reaction (to form B)?