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I have a question about light alkanes isomerization catalysts. UOP experts suggested that the silicon can poison hydrotreating and hydrocracking catalysts due to damaging the Al2O3 structure. I wonder if silicon can also poison the light alkane isomerization catalyst, such as chlorited Pt/Al2O3 catalyst, Pt/SO4 catalyst which contains Al2O3 as coagulant, and Pt/zeolite catalyst? Our partial feed for light naphtha isomerization unit is the raffinate from Benzene extraction unit, the raffinate is possible to have silicon due to using defoaming agent at top of benzene distillation extractor.
 
Answers
30/11/2017 A: Patrick Bullen, UOP, patrick.bullen@uop.com
While Silicon is detrimental to any isomerization catalyst at sufficient levels, it is a rare occurrence that it is measured on spent catalyst as it is atypical in light naphtha. If there is a risk potential of getting silicon from a source as described there are a couple of options. Once could run the raffinate back through the NHT upstream of the isomerization unit and allow the NHT catalyst or separate Silicon guard material adsorb it. The other option is to put in a dedicated Silicon guard bed for which there are a variety of vendors that can provide specific adsorbents.
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29/11/2017 A: Steve Mayo, Eurecat, smayo@eurecat.com
Silicon from anti-foam additives will non-selectively deposit on most catalyst surfaces. Deposition onto internal surface area of hydroprocessing catalysts is the most common, but any catalyst with surface area (alumina, zirconia, zeolite, etc.) is susceptible to silicon deposition if exposed to anti-foam additives. It would certainly be expected that isomerization catalyst activity could be negatively influenced by exposure to silicon. Silicon poisons by covering and restricting access to the active phase on the catalyst surface. As surface coverage by silicon increases, catalytic activity correspondingly decreases. Since Si deposition is non-selective, silicon may deposit on areas of the support without any active phase present. Thus it is difficult to know without experience to what extent catalyst activity is affected by silicon deposition.
27/11/2017 A: Sridhar Balakrishnan, Bharat Oman Refineries Limited , laksrid@yahoo.com
Almost all defoaming agent can contain silicon produced in market . Different types of defoamers available are Oil based defoamers, Power based defoamers, Water based defoamers ,EO /PO based defoamers, silicone based defoamers and Alkyl polyacrylates. Most of the defoamers may contain silicon in it. Always try to get details from manufacturer for the silicon content in defoaming agent which are used in plant.