rosity has been incorporated to increase zeolitic contact with reactants and result in fewer secondary reactions owing to faster disengagement. Overall, Denali cata- lysts deliver improved yields, especially improved coke selectivity and more selective cracking of larger mole- cules to assist in bottoms cracking. Q What steps can we take in our mild hydrocracking operations to improve FCC conversion performance? A Per Zeuthen, Senior Director, Haldor Topsoe, pz@topsoe. com Aromatic compounds are not converted in FCC units, so steps to improve FCC conversion will be minimising feed monoaromatic and polyaromatic compounds the most. A mild hydrocracker is typically a single-stage reac- tor unit loaded with various hydroprocessing catalysts, including hydrotreating and hydrocracking catalysts. To improve FCC conversion, the following should be considered: • Increase hydrogen partial pressure the most; this will increase aromatic saturation, lower aromatic com- pounds in the FCC feed, and increase conversion by increasing the total pressure or the hydrogen purity in the make-up hydrogen supply. • Increase aromatic saturation activity of the loaded catalysts and ensure that the most HDA active catalysts are used. This is important also for the conversion cata- lyst if this is included in the catalyst load. Topsoe has a number of catalysts (hydrotreating and hydrocracking) with improved aromatic saturation activity. • Use the latest generation of reactor internals; this will ensure that all loaded catalyst is utilised and exposed to hydrogen – a very important step that is often overseen. Again, Topsoe holds an extensive reference list and industrial feedback for such improvements. Finally, mild hydrocrackers are typically being oper- ated at relatively high temperatures, particularly during the second half of the cycle. This ensures the right product sulphur and nitrogen level in the FCC feed and sulphur specks in the FCC products. However, high temperatures, higher than 390°C, at the outlet of the mild hydrocracker are unfavourable for the saturation of the polyaromatic compounds. Thus, for thermody- namic reasons, there are no catalytic ways to lower the product aromatics in the FCC feed at such conditions. A minor revamp of the unit, for example, with Topsoe’s Aroshift layout, by installing a small high LHSV with- out fractionation, being operated at a lower tempera- ture with a proprietary catalyst, will lower the FCC feed polyaromatics by typically 25% and thus show a great positive impact to the FCC conversion and yield structure. A Rainer Rakoczy, Technology Advisor Fuel, andMaximilian Dochnahl, Head of Modelling & On-site Technology, Clariant Catalysts Besides asphaltic species, the level viscosity of the desired FCC feed can be key to improving and optimis-
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