Which metal is used for sulphur guard for naphtha services? What are the available options?
Answers
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15/07/2019
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Peter Marsh, XBP Refining Consultants Ltd, peter.marsh@xbprefining.co.uk
There are 2 types of sulphur guard bed (SGB); liquid phase and vapour phase. The liquid phase SGB is positioned upstream of the catalytic reformer in the naphtha feed system and typically operates at temperatures in the range 120 – 175 Deg.C (248 – 347 Deg.F). Liquid phase SGBs are very effective at mopping up any hydrogen sulphide and light mercaptans in catalytic reformer feed. The vapour phase SGB is positioned in the catalytic reformer recycle gas loop downstream of the Combined Feed Exchangers and typically operates at temperatures in the range 370 – 425 Deg.C (698 – 797 Deg.C). Vapour phase SGBs are effective at removing residual mercaptans and thiophenes in the reformer feed (ie. sulphur compounds which escape on the first pass through the liquid phase SGB) as they are converted to hydrogen sulphide in the reforming reactors and are easily removed on the second pass. However the vapour phase SGB imposes additional pressure drop in the recycle loop and increases the load on the recycle gas compressor. Active metals used on the absorbents include copper oxide, zinc oxide, manganese oxide or nickel oxide (either individually or combined). Extra care is required when nickel-based adsorbents are used because of potential nickel carbonyl formation which is highly toxic.
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15/07/2019
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A:
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Robert Stults, Eurecat US, bstults@eurecat.com
For feed that can contain heavier sulfur components, heavier than light mercaptans, a high nickel guard material is optimum. Eurecat's EUS-175 is a high Ni catalyst (>50%) with excellent sulfur capacity. EUS-175 will remove heavier sulfur molecules including disulfides and thiophenes, which are the sulfur components that are most likely to slip through the naphtha hydrotreater. Other guard material such as Cu or CuZn have little or no adsorption capacities for these species. The typical operating temperature for EUS-175 would be 375 F.
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