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I am have two diesel hydrotreaters in my refinery. One (35bar) is producing Euro III diesel with a sulfur specification of 350 ppm maximum and other (100bar) producing Euro IV diesel with a specification of 50 ppm sulfur. Now I would like to know what type of catalyst to be used. Co-Mo catalyst or Ni-Mo? Moreover kindly explain the basis for choosing the Catalyst-type.
 
Answers
22/11/2011 A: Randy Alexander, EURECAT, randy.alexander@eurecat.com
As Mr. Angadi points out, a full analysis of your feed and operating conditions is required to accurately answer that question. Note that a combination of NiMo and CoMo may be the best solution. In addition, different catalysts companies may have much different catalyst recommendations based on the performance of their products under the conditions you specify.
11/11/2011 A: Virendra Kapoor, Petroleum Refining Consultants, vkkapoor9@yahoo.com
May I put up following points for your kind consideration:
1-As Co is costly than Ni, it is observed that Co-Mo may be costlier than Ni-Mo, though at lower pressure of 35 bar both may function almost similarly in activity.
2- At pressure of about 35 bar, Co-Mo finds itself difficult to hydrodesulfurise feeds having higher nitrogen and alkyl substituted dibenzothiophenes such as DMDBT to get 5o ppm sulfur diesel product. Co-Mo have low sensitivity to pressure, have low flexibility and consume minimum hydrogen.
3- Ni- Mo catalysts are less sensitive to refractory feeds, have high flexibility, better activity to DMDBT removal. They have higher hydrogen consumption, require higher pressure to work effectively for refractory feeds, better hydrogenation activity than Co-Mo. Sometimes beds having Ni- Mo and Co- Mo catalysts both are used appropriately.
4 For 50 ppm diesel sulfur, at 100 bar, Ni- Mo may be better. It may saturate aromatics, enhance cetane.
10/11/2011 A: Satish Angadi, Haldor topsoe, satish.angadi@gmail.com
The catalyst choice will be based on feed details(Nitrogen, aromatics, etc.) and desired product properties like cetane number/poly-aromatics, catalyst cycle length. Point is that it involves thorough consideration besides feed and product sulfur.
In most of times both catalyst can work for the same objective!
What determines is what WABT temperature(s) are allowed in the HDS reactor and other hardwares (recycle gas compressor capacity).
So, I recommend that you get in touch with catalyst supplier with detailed information, and I know of one unit that is capable of producing 10 ppm product sulfur at 35 bar cold separator operating pressure!