Model 3 (General)

For our third model, we will again consider a non-isobaric reactor with changing total molar flow rate. However, we will also include heat effects. In general, it is important to consider the temperature in a reactor, since highly endothermic reactions can be explosive. Ignoring a significant temperature increase could be a potentially dangerous assumption.

As the reaction proceeds through the channel, heat is released or absorbed, depending on whether it is an exothermic or endothermic reaction, respectively. This change in heat is related to the amount that the species reacts. Since the flow rate of each species changes along the length of the reactor, the temperature also changes also along the reactor. The temperature change affects the flow rate by increasing the rate constant, which in turn increases the conversion rate of the desired product.

The reaction we are considering is exothermic; consequently, the temperature will increase in the microreactor as the reaction proceeds. For the first case, we will set the inlet temperature to 673 K. Two graphs will be compared, the first has is for a non-isothermal reactor; the second is for the isothermal reactor we examined in the first model.
 

  Graph 3.1: Non-isothermal Reactor with Inlet temperature = 673K

Graph 3.2 : Isothermal Reactor

We can see that with the temperature effects added, more NH3 converts into NO. Also the flow rates level earlier down the channel of the microreactor. This is a result of the reaction achieving equilibrium more quickly because of the increased temperature.

Now we will compare the two results for an inlet temperature of 873K. The graphs are for the non-isothermal and isothermal cases, respectively.

Graph 3.3 : Non-isothermal reactor with inlet temperature = 873 K

Graph 3.4: Isothrmal reactor at 873K

Once again, comparing the non-isothermal and isothermal cases, we see that there is more desired product produced when temperature effects are considered. However, it should also be noted that there is little difference between the amount of NO produced for either of the non-isothermal cases. This is because, in both cases, the reaction reaches equilibrium in the microreactor. After this equilibrium point is reached, no more of the desired product can be produced, regardless of the temperature. Therefore, there is less of a need to run the reaction at the elevated temperature.

Want to find out more? Click on the Expert Model 3 page.
 
    Previous Pageglossary Next Page