running an external minimizer including, as objective function, a whole plant (with columns etc.) can result very time expensive,
even the so called derivative free minimizers can call hundreds or thousands times the objective function,
which can result impractical for a complex plant (you can set bounds on each parameter and reduce ranges but still the task is very complex),
simulators include tools for sensibility analysis on different parameters, you may wish to use these tools (which call directly the simulator code) instead of external tools.
As said, to work with tools such as Excel, Mathcad or Matlab I prefer a library which is much more efficient (see similar threads for detailed discussions),
the limit of this approach is that optimization is limited to subsets of complex plants,
for example a column plus a very limited number of equips, also without recycles the task is hard,
to give you an example, in many cases solving a single column with Prode takes a second or less, still the optimization can require 30 minutes or more
for complex plants, probably the tools (sensivity analysis etc.) already included in your simulator are the best solution.