5 replies to this topic

[Steve90]

Hi guys ,

 

actually our professor said that to remove CO2 from natural gas using chemical absorption each one of MEA and MDEA has advantges and disadvantages that's why we mix them to obtain better results. someone can explain why because the carachteristics don't change in mixture. i'm confused . she didn't convince me

 

thanks

[Art Montemayor]

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.

[Pilesar]

I have used a mixture of MEA and MDEA for CO2 removal. This used to be common in the 'proprietary recipes' from the solution vendors. My application was in a system designed for MEA but plagued with corrosion problems. The prominent vendor's 'top secret recipe' caused less corrosion and allowed similar performance with little equipment modification at the expense of spending more money to replace solution losses. Amine solutions are mixed with water so the concentration is also a variable. The idea is to absorb all the acid gas required but also to use as little energy as possible to release the acid gas from the solution. Metal corrosion, solution costs, solution durability are also factors. The circulating amine solution can get contaminated with heat stable salts which affect performance and cost money to reclaim or replace. Different solutions perform differently, but there is no one perfect amine to fit all needs. Advantages and disadvantages for each result in different solutions being selected for very similar applications.

[RockDock]

I have seen this use before, too. MDEA is used as the bulk solvent, with MEA as an additive. It allows you to run your system at a higher rich loading and higher amine concentration, allowing you to reduce your reboiler duty. It also take advantage of the lower heat of reaction for regenerating MDEA, which also lowers the reboiler duty.

 

Recent developments have largely replaced MEA as the additive with chemicals like DEA or piperazine. These are much more stable additives that help avoid the problems Pilesar and Art correctly outlined.

[SSK22]

Hi,

I'm a student and I'm working on design of CO2 removal section in Monoethylene glycol plant. I'm using potassium carbonate to absorb CO2 from a gas stream (mixture of ethylene, ethylene oxide, CO2, oxygen, water, and methane). I am suppose to do hand calculation solving the mass and energy balance of this CO2 removal system which consist of absorber, stripper and flash tanks.

 

Howver, to start with the absorber, since there is chemical absorption taking place, can I do the mass balance around the absorber the normal way as we do for physical absorption? If not, how do I do the mass balance (hand calculation). Is there a book or any other resources that I can refer to? Please guide.

 

Thanks.

[Bobby Strain]

As to mixing MEA and MDEA, BASF has a proprietary amine which people pay to use. MEA is a part of the BASF recipe. This is straight from the horse's mouth.

 

Bobby