I’ve added some material to the web site – solving equations for Continuous Stirred Tank Reactors (CSTR) using Comsol. There are some things you have to be careful of when the parameters lead to multiple solutions or to no steady solutions at all. This material repeats, using Comsol, what is in the book on pages 161-168: steady CSTRs, transient CSTRs, and ones with weird oscillations. In the latter case one must adjust tolerances in the numerical integration, and the writeup shows how to do that. Here is one of the graphs that indicates a problem.
Comsol 4.1 hints