MEROX sweeting or exstraction 1

[Milutin]

Hi All,

We use sweeting type merox unit to treat light FCCU naphtha. In this way sulfur content in light naphtha is unchanged.
Does anybody use extraction merox unit to treat FCCU light naphtha, to decrease sulfur content? What are main factors to decide which merox type to use for one product?

Regards,

Milutin

 

[25362]

It is widely recognized that sweetening reduces mercaptans but doesn't markedly change the total sulfur content. Pay a visit to

http://www.uop.com/objects/21 Gasoline Desulf.pdf

for more information.

 

[Milutin]

Hi 25362,

It is clear, from licensor brochure, that sweeting unit is proposed for this case. Suppose desulfurisation will depend on mercaptan content in untreated naphtha , do you have experience what is efficiency in mercaptan removal?

Regards,

 

[Milutin]

Sorry, instead "sweeting" it should be "extraction", in my previous post.

 

[mbeychok]

Milutin:

It really doesn't matter whether you call it mercaptan sweetening or extraction. Look at the process diagrams in the Wikipedia article at

http://en.wikipedia.org/wiki/Merox

and you will note that there are two versions of the Merox process. One is for treating LPG and one is for treating jet fuels or kerosenes. In both versions, the first step is a caustic wash to remove hydrogen sulfide followed by the process to remove mercaptans.

I speculate that if your licensor is talking about reducing some of the total sulfur content as well removing mercaptans, he is simply talking about the removal of hydrogen sulfide (in the caustic prewash) plus mercaptans.

If there are any other sulfur compounds in your FCC light naphtha, then hydrodesulfurization should be considered.

Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[25362]

Sweetening is exclusively dedicated to the removal of objectionable odours. For an FCC gasoline (40-200 Celsius range) derived from Middle East feedstocks, the total sulfur content may be as high as 0.2% w/w.
As for mercaptan removal I've seen a report showing a reduction from ~140 ppm w/w down to 2 ppm w/w.

 

[rgrokkam]

The type of merox to be used depends on the product specification. for eg, in our country LPG spec is 150ppm total Sulfur. So we use merox based on extraction. the disulfide oils have to be separated.
However aviation fuel spec is 30ppm RSH and 0.3wt% total sulfur. So we just have to change RSH to disulfide oils. The disulfide oils are insoluble in caustic and can be retained in the aviation fuel. Hence we use merox based only on sweetening to achieve the same.

 

[CJKruger]

Milutin,

Regardig your original question.

Extraction merox cannot be used for heavier hydrocarbon streams due to the low solubility of these mercaptans in caustic.

But, I suspect light FCC gasoline is a borderline case. Extraction may or may not be feasible. Best is to ask UOP, they will gladly design you one if it is possible.

 

[sievers]

Can Methyl Mercaptan be converted to DMDS before it gets to the Extractor?