What water should be used to prepare desulfurization MDEA?
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For the newly installed amine solution regeneration units, what type of water is used for preparing the amine solution? One option is to use demineralized water ； Another option is to use deoxygenated water. The difference between the two cases lies in the impact of the dissolved oxygen level in water on the amine solution. Deoxygenated water has a lower oxygen content, which is certainly beneficial for the amine solution; however, since the temperature of deoxygenated water is relatively high, around 110°C, consideration must be given to the effects of such high-temperature water on the tanks and foundations when preparing the solution for the first time after the system is put into operation. When preparing the mixture on a regular basis, the amount used is relatively small, so it may have little impact. Speaking of which, the dissolved oxygen level in demineralized water is generally around 3–5 mg/L. How much impact does such a level have on the amine solution? Please share your approaches on your own setups and express your opinions.
I recommend that you use deoxygenated water; it brings more benefits to the solvent than drawbacks, and the price difference is not significant. It’s also great for the device to operate over long periods of time!
Our initial design used deoxygenated water, but currently both deoxygenated water and demineralized water can be used.
Deoxygenated water is recommended. The deionized water does have a low oxygen content, but it still contains oxygen, and the presence of oxygen can cause amine solutions to degrade into carboxylic acids. Although this reaction is slow, it still occurs ； Moreover, if CH3OH and HCN are present in the gas—these two gases can also be present—the rate of this degradation reaction will increase.
Using demineralized water is sufficient. The reaction of MDEA with oxygen is something well-known to everyone; the choice between deionized water and deoxygenated water should be made based on overall considerations. Free oxygen in demineralized water does have a certain impact on MDEA, but what is more important to consider is whether these impacts are on the same order of magnitude as those exerted by the process gas on MDEA during operation of the plant. The degradation of MDEA is inevitable and ongoing; aside from the impact caused by the use of desalinated water, it is negligible compared to the degradation rate during normal production. Therefore, there is no need to worry that the use of desalinated water will have irreversible effects.
Amine solutions must not come into contact with oxygen; deoxygenated water is generally used for preparation