Mercaptans removal

[jlmtl]

Does any one know if there are any technologies that have higher selectivity for mercaptans removal over H2S? For example, in the natural gas containing both H2S and mercaptans, I prefer to remove mercaptans first, then remove H2S later. But so far, I could not find a technology with no or minimum coabsorption of H2S. Thanks for sharing.

 

[moltenmetal]

Activated carbon- H2S will rapidly saturate and go right through. Mercaptans will be more strongly retained, with retention increasing with molecular weight.

 

[jlmtl]

Hi moltenmetal,
Your idea may eventually work, if just a little of H2S is captured by AC, it should be acceptable. Did you have any practical operating experience of capturing mercaptans with min. coadsorption of H2S?

 

[georgeverghese]

Dont know of a process that enables this. H2S is more acidic than RSH so H2S tends to get absorbed or adsorbed more easily than RSH in most processes commonly known.

May we know why you wish to remove RSH, and then only H2S ?

 

[jlmtl]

@georgeverghese
I could only partially share some reasons. We are evaluating a technology for H2S removal; however, with high RSH, the equipment cost would be higher. If there is a technology could help reduce the RSH to lower level, overall,it might help to save the total cost.

 

[georgeverghese]

So you're getting no consolation on the process simulation for this even after you've MAXed out on the piperazine content in activated MDEA at the current circulation rate?

Presume you're not considering MEA due to corrosion / degradation concerns.

Other options may be to optimise the column operation by using options such as intercooling, increasing circulation rate, but these would lead to higher cost as you say.

 

[georgeverghese]

Documentation with me indicates the Shell Sulfinol X mixed solvent may be suitable for this ( MDEA - piperazine - sulfolane - water) for RSH and H2S removal, if the activated MDEA option ( MDEA - piperazine - water only blend) doesnt cut the cake. If heavy hydrocarbons co absorption is an issue with sulfolane, switch out sulfolane with Selexol. The Sulfinol X process is proprietory to Shell.

Obviously, if you could chill or cool this gas somewhat before the absorber, that will help to knock out the heavier RSH components and the heavy hydrocarbons too, and reduce the heavy HC co absorption associated with sulfolane.

Obviously, a split feed of lean solvent to the absorber may be another option to investigate with any of the solvent options mentioned.

 

[jlmtl]

@georgeverghese
Thanks. Sulfinol-X should remove H2S first; then RSH. We want the other way around.