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• What hydrocracking reactor catalysts are demonstrating optimal mid-distillate selectivity, better yield structures, and more efficient use of hydrogen? In combination, which of these catalyst systems seems to be the most flexible in adjusting to feed quality variations and heavy feeds such as DAO and HVGO molecules?

  Mar-2023

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Answers

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• Andrew Layton, KBC (A Yokogawa Company), Andrew.layton@kbc.global

  Typically, hydrocracking catalyst systems are a combination of catalyst types based on feed type, feed contamination, selectivity, conversion, and unit design. The unit designs vary, depending on the combination of 1-3 stages with or without bottom product recycling. The hydrocracking catalyst selection can target different products such as naphtha, distillate, lubes, or some level of aromatic saturation.

  Stage 1 reactors generally use varying levels of metal contaminant removal catalyst based on feed metal concentration levels. If necessary, they also use antifoulant grading catalyst/inerts that have high metal adsorption potentials, different grading sizes, and high surface areas. The next catalyst bed typically consists of varying amounts of NiMo or NiCoMo catalyst.

  The NiMo catalyst is designed to sufficiently remove N2 to avoid impacting the performance of hydrocracking catalysts downstream. NiMo also improves aromatic saturation with HDS following more the ring saturation route. Units which require /prefer higher aromatic saturation sometimes used NiW but now also have a choice to use varying quantities of massive metal catalysts, which some vendors carry. These catalysts also require a minimum concentration of H2 pp to be effective and consume more H2.

  Stage 2 reactors, or downstream beds, contain most of the cracking catalyst. The number of stages is determined both by feed type and necessary conversion level. High conversions tipping 75% and requiring high N2 feeds are likely to appear in Stage 2, at the very least.

  Two types of cracking catalyst exist: amorphous silica alumina and alumina silica crystalline zeolites. Amorphous silica alumina shows lower cracking activity and targets more kero/diesel production. In comparison, alumina silica crystalline zeolites achieve higher activity and target more naphtha production. Thus, amorphous catalyst may predominate diesel maximisation as limited by achieving adequate activity.

  The heavier feeds will always favour some type of NiMo catalysts in the lead beds, and a larger percentage of this ‘pretreat’ catalyst will be required as the feed gets heavier and higher in N2. If feeds are heavier than DAO/HVGO, both catalyst particle and pore size may increase, making fixed bed units unsuitable. After the interstage H2S/NH3 removal, a noble metal catalyst may be used for high-conversion naphtha production units during the downstream stage.

  Several catalyst vendors offer a tailored combination of catalysts to meet conversion, selectivity, HDS, HDN, and Arosat needs while taking equipment design, H2 availability, and cycle length into account.

  To differentiate between vendors and confirm their proposals, comparative data for catalyst systems can be requested. For example, H2 consumption data can vary widely. Alternately, pilot plant data compared to a reference catalyst may also be available if requested early enough.

  Mar-2023