Mustapha:
In my opinion you are doing the correct thing for your self and your learning by challenging your prof. I don't mean to criticize your use of English, and to make the query express what I think you mean to write, I'll edit it as follows. Correct me if I missed your point:
"Our professor has said that to remove CO2 from natural gas using chemical absorption, both MEA and MDEA have advantges and disadvantages that's why we mix them in order to obtain better results in the CO2 removal. Can someone on this Forum explain why the characteristics of each don't change when mixed together? I'm confused and she hasn't convinced me."
If the above is a correct interpretation of what you mean, then my response is:
I've never heard of anyone (individual or an engineering company) mixing MEA and MDEA. I don't see any advantages in the resulting mixture that would be better than either of each one being applied on its own merits. MEA is attractive only from its affinity for CO2 and the very low levels of CO2 it can produce in the treated gas. MDEA can, with some additives (which are proprietary) come very close to the same results (I am told). Although MEA can produce a very pure gas product, it has its classical drawback: degradation produced by contaminants and high heat spots. This degradation produces a very corrosive solution if left untreated. MDEA was developed to avoid to a large extent this effect of corrosion and solution degradation and it has led to further improvements. In my experience with both, I would take sides with you and would never mix the two. You can't have your cake and eat it also. It's either or.