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We are facing a high odor rating in Polypropylene. We have merox unit for sulfur removal from LPG & also PRUs. To further enhance sulfur removal (particularly for heavier mercaptans) we have installed Naphtha wash facility in Merox. Still we have odor issue. COS & heavier mercaptans, I think, are the main culprits. Can somebody advise how to improve Merox performance? Or suggest a new facility to cut down sulfur level further?
 
Answers
27/04/2011 A: Egbert van Hoorn, Hocon B V, Egbertvh@hotmail.com
Perhaps a bit late, but the LPG odour problems may also be related to the LPG and the amine treating unit. Is this LPG from a FCC unit?
Have you experienced problems with the amine treating unit?
14/02/2011 A: Lindsay McRae, Pall Corporation, Lindsay_McRae@pall.com
If you are having problems with gasolene rinse / disulphide oil carrying under with caustic solution in an extractive Merox unit, and then contaminating the LPG ( off spec for residue perhaps plus the odour which an indicator of this) then this may be caused by inadequate separation in settling drum.
The gasolene rinse / caustic solution can be a very stable emulsion, with the Infterfacial Tension(IFT) typically lower then 10 dynes/cm and often in the 1-5 dynes/cm range. Such low IFTs need a long residence time and if not sufficient, carryunder may occur. It should be noted that settling drum efficiency drops off dramatically where the IFT is <20 dynescm which if very often the case in caustic treaters.
Pall's high efficiency PhaseSep Liquid Liquid coalescers can remove gasolene rinse from caustic solution to <15 ppmv or can be used to remove water / casutic from LPG product which is widely done on caustic treaters including Merox units.
23/01/2011 A: Morgan Rodwell, Fluor Canada Limited, morgan.rodwell@fluor.com
Another option for COS removal is hydrolysis using a catalyst and water to convert the COS to H2S upstream of the Merox caustic treater.
19/01/2011 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
What process is being used for the COS removal? Here is an excerpt from my technology course manual:
"An extraction unit is typically preceded by a caustic wash step to remove H2S. COS is removed by an alumina based selective adsorbent if the COS is in the range of 2-50 wppm. For higher levels, hydrolysis of the COS to H2S occurs over a bed of activated alumina, followed by an amine or caustic wash. In some installations where the COS content is < 100 wppm, a 50-50 blend of MEA and caustic is used and discarded, as it is non-regenerable."