Maximising cycle duration of hydroprocessing units has always been important to refiners, but what other step-out gains can we see from catalyst developments in terms of volume swell, PNA saturation, and HDN activity while achieving high HDS performance?Mar-2023
Peter Andreas Nymann, Topsoe, PAN@topsoe.com
Higher activity catalysts like HyBRIM and HySWELL not only improve HDS activity but also improve the removal of nitrogen-containing hydrocarbons and the saturation of aromatic components.* The higher HDN and HDA activity leads to lower product density (higher API), which leads to better cetane index and greater volume yields. The higher degree of aromatic saturation also provides additional end-point reduction, enabling the processing of higher boiling material in diesel hydrotreaters while still meeting the T95 specifications. Higher activity may also facilitate the upgrading of lower-value streams like LCO and CGO in hydrotreaters to produce high-quality diesel. Higher saturation of aromatics and removal of nitrogen in FCC feed pretreaters improve FCC yields and product quality or alternatively enable co-feeding of lower quality feeds in the FCC.
*Note: HyBRIM and HySWELL are marks of Topsoe.
Andrew Layton, KBC (A Yokogawa Company), firstname.lastname@example.org
CoMo catalyst was the typical distillate catalyst with high HDS but has improved in terms of available active sites and better surface areas contacting through Type II and equivalent catalyst active area changes. In many cases, these catalyst types also minimise H2 consumption. To process feeds high in N2 and boost cetane and cloud point, different catalysts became more important.
NiMo catalysts improve Arosat (aromatics saturation) and HDN (most important in high N2), cracked and heavier feeds with additional Type II metals/base interaction. NiMo HDS/HDN reactions occur more through ring saturation than CoMo catalysts. Sometimes NiCoMo catalysts are a better fit.
Improvements in catalyst ex-situ regeneration have enabled better catalyst re-use without sacrificing activity, even for Type II catalysts.
While massive metal catalysts for high Arosat and HDS have a higher cost and higher H2 consumption, these catalysts deliver a large increase in potential activity and aromatic saturation capability. This type of catalyst can be considered when a sufficiently high partial pressure of hydrogen is available and for some lubes operations.
Providing the reactor design is flexible enough to control bed temperatures adequately, isomerisation catalysts are now used in the bottoms beds to improve cold flow properties. The cloud reduction/isomerisation catalysts are also improving to reduce yield loss resulting from cracking reactions.
Most vendors offer tailored solutions, though massive metal catalysts currently have limited suppliers.
Each round of development affects the relative catalyst ranking. Thus, the catalyst selection should not be based on one vendor for too long without comparing catalysts from multiple vendors.
Note that maximising cycle length may now conflict with minimising energy use and carbon emissions as longer run length can mean more fouling, require high-pressure operations, and increase compression costs. Thus, optimum cycle length should be re-evaluated for both new and existing units.
Steve DeLude, Becht, email@example.com
Catalyst activity improvements over the years have allowed operators to pursue various options to improve profitability and operating flexibility. While increasing cycle length and reducing the annualised shutdown cost can be significant, most refiners find that increasing throughput (debottlenecking), processing more difficult feedstocks, changing feed fraction cutpoints (yield optimisation), modifying operation to improve blending flexibility (improved product quality through higher hydrogenation), and/or higher volume yields offer better overall value than simply pursuing a long cycle length strategy.
Catalyst vendors have pursued multi-catalyst systems and new modelling techniques to tailor catalyst loads to specific refinery objectives. This situation makes it very important for the refiner to discuss in detail with potential catalyst suppliers their preferred operating strategy, feed options, and product quality improvement opportunities when considering their next reactor catalyst load.
Brian Watkins, Advanced Refining Technologies LLC (ART), firstname.lastname@example.org
ART’s DX catalyst series has been used in ULSD applications for over 16 years, while ART’s 425DX catalyst continues to be used worldwide for middle distillates. The recent addition of 430DX to this line of catalysts allows refiners to process tougher feeds, meet tighter specifications, improve product quality, and expand capacity with no additional capital costs.
The 430DX catalyst is built on recent advancements in alumina technologies. Innovations in surface chemistry and new pore structures significantly boost HDS, HDN, and HDA activity, with improvements exceeding 15% in some applications. 430DX exhibits an optimised bimodal pore size distribution for high activity and sustained performance.
430DX offers improvement opportunities to every diesel hydrotreating unit. Its benefits have been demonstrated on both straight-run and cracked stocks and at low and high operating pressures. Figure 1 compares 430DX to its predecessor 425DX in an ULSD protocol using a feed containing 15% cracked stocks. 430DX shows a clear activity gain in the low-pressure ULSD test and further extends its advantage in the higher-pressure test. This increased activity enables the refiner to exploit the additional activity by processing more opportunity feedstocks as well as increasing the relative cycle length of the hydrotreater.
Researchers have previously identified surface acidity as a key property for improved catalytic performance. It is generally accepted that there is a strong relationship between the role of increased surface acidity, increased pore volume and surface area to improve the reaction rate for reactions controlled through ring saturation, such as nitrogen and hard sulphur removal.
Changes in surface acidity have also been shown to affect the interaction of active metals with the alumina surface during impregnation. This phenomenon has been exploited in the design of 430DX, as seen by the significant increase in HDN activity and by utilising the ART hydrocracker pretreat support tailored to ULSD service. This catalyst improves upon the legacy impregnation technology leveraged in 425DX, whereby a chelate is used to bind to the cobalt ions in the impregnation solution and reduce interactions with the alumina support. The chelate/ion complex stays intact on the catalyst, which allows the molybdenum to sulphide at a lower temperature, promoting the formation of Type II active sites. 430DX features an optimised loading of cobalt and tuned chelation to further enhance activity compared to 425DX.
Combining a modified alumina carrier with improved surface acidity and a larger pore diameter gives a catalyst that is custom tailored for demanding service at low and medium pressures. While the acid sites give 430DX better performance for both HDS and HDN activity, they are not strong enough to initiate any cracking reactions under typical hydrotreating conditions.
Figure 2 compares the line of ULSD catalysts from ART Hydroprocessing.
430DX can be coupled with the new 550DX (NiMo) catalyst within the proprietary SmART Catalyst System. This method fully utilises existing assets within a refinery’s individual constraints. Figure 3 shows how catalyst selection and placement can be tailored to provide the optimum balance of maximum HDS and hydrogen consumption.