Why is ammonia used instead of alkanolamines for H2S removal? !
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Today, I was reading the Chemical Engineering Handbook, which states that the reaction between alcohols and amines and H2S is reversible, allowing it to be reused! Logically, then, alkanolamines should be used to remove H2S in engineering applications! But in reality, I rarely see it used this way; ammonia is used far more often! Such as PDS, 888, and other methods! Why is it like this? ! Which veteran driver can explain this? ! Thank you! !
The refining and chemical processing projects we work on basically use alcohol amines, which are recyclable and have low corrosivity
We remove H2S from gas; we’ve never seen alcohol amines being used for that! Ammonia is used in all of them!
The choice of desulfurization solvent is determined based on factors such as the process, medium, materials, and operating conditions; it’s not a simple matter of saying which one is better or worse. If it were that simple, why go through all those studies and improvements in processes and design? For desulfurization of light hydrocarbons in the petrochemical industry, as well as for desulfurization of materials and fluids under high pressure and temperature conditions, a higher proportion of alcohol amines is used ； For many non-condensable gases (permanent gases) and devices with low pressure and temperature, ammonia is more commonly used. This takes into account factors such as mass transfer, evaporation equilibrium, and absorption equilibrium.
Alkylamine desulfurization is only the first step in desulfurization; regeneration and the Claus process follow. It is suitable for large-scale sulfur recovery units, but currently low-temperature methanol washing is the method most commonly used. PDS, 888 – the sulfur recovery method based on glue coating is a wet desulfurization process that directly converts hydrogen sulfide into sulfur. It is economical for desulfurizing materials with low total sulfur content; however, when the scale of operation becomes large and the amount of desulfurizer that needs to be recycled is high, this method becomes uneconomical. In my opinion, it is mainly determined by scale.
Alcohol-ammonia can be used for desulfurization and decarbonization. In situations like this, factors such as the cost and performance of the materials are taken into consideration; it’s not simply a matter of whether a reaction can take place. In my book on gas purification, I state that alcohol-ammonia can be utilized for desulfurization. Moreover, when industrial applications require the same outcomes, there are many different processes available
PDS and 888 are both catalysts. . .
There are many processes, but alcohols and amines can be regenerated on their own, whereas ammonia requires a catalyst to be regenerated!
If you are interested, you can learn more about alcohol amine regeneration: hydrogen sulfide is desorbed, and further treatment is required afterward, namely the Claus sulfur recovery process and alkali solution regeneration. In fact, hydrogen sulfide is oxidized to sulfur paste in the liquid phase, followed by solid-liquid separation; these are all regeneration processes with different principles. Once you understand the processes and principles, it will become clear why some methods use alcohol amines or low-temperature methanol for desulfurization, while others use alkali solutions