Sep-2016

Developments in hydrotreating catalyst

How a second generation hydrotreating catalyst was developed for high pressure ultra-low sulphur diesel units and hydrocracker pretreaters.

MICHAEL T SCHMIDT
Haldor Topsoe

Article Summary

The worldwide market demand for more active NiMo hydrotreating catalysts is extraordinary. Despite tremendous improvements in catalyst technology for the past 20-30 years, ultra-low sulphur fuel legislation and the shift towards VGO hydrocracking to maximise diesel production are more than ever forcing refiners to search for the absolute top tier NiMo catalyst for their ultra-low sulphur diesel (ULSD) or hydrocracker pretreat reactor.

The dramatic drop in natural gas prices observed particularly in the US has resulted in a low production cost for hydrogen. The low cost of hydrogen makes it very profitable to add hydrogen catalytically to middle distillate fractions, thereby increasing the liquid volume swell, resulting in higher yields of valuable diesel.

To address these requirements, refineries continuously need better, yet cost-efficient, alumina based catalysts with the highest possible activity in order to obtain the desired boost in performance 
and hydrogen consumption. Furthermore, alumina based hydrotreating catalysts will help minimise the operating cost when targeting volume swell in comparison with higher cost unsupported catalyst formulations.

Continuously improving alumina based catalysts
Topsoe has been at the forefront of important technological breakthroughs in the hydroprocessing industry for decades and continuously explores the possibilities within this area. In the 1970s, Topsoe discovered the active CoMoS phase in hydrotreating catalyst, which revolutionised the catalyst world by applying fundamental research in the catalyst development approach. In the 1980s, Topsoe researchers, headed by Dr Henrik Topsøe, discovered the difference between Type I and Type II hydrotreating catalysts and gave them the names that are known throughout the industry today. With this breakthrough, the hydroprocessing catalyst development entered the nanotechnology era, and the Type II hydrotreating catalysts became the industry standard for high-activity catalysts. In the early 2000s, Topsoe’s research in surface science paid off again, and a new activity site was discovered: the BRIM site. With this finding, Topsoe developed BRIM technology within both the CoMo and NiMo type catalysts, which fuelled Topsoe’s unparalleled growth in market share globally due to a top tier catalyst portfolio.

From BRIM to HyBRIM
Topsoe’s latest catalyst technology, HyBRlM, involves an improved production technique for both NiMo and CoNiMo hydrotreating catalysts. It combines the BRlM technology with a proprietary catalyst preparation step. The synergistic effect of merging the two technologies has enabled Topsoe to design an advanced metal slab structure that is characterised by an optimal interaction between the active metal structures and the catalyst carrier. The activity of the Type II sites is positively influenced to a high degree by this interaction between the metal slab and the carrier. HyBRIM technology exploits this interaction and substantially increases the activity of both the direct sites and the hydrogenation sites without compromising the catalyst stability.

Topsoe’s NiMo catalysts that are developed today are around three times more active than the catalysts produced in the 1990s. Figure 1 illustrates the development of the company’s many catalyst generations. Since Topsoe’s scientists employed tools such as electron microscopes, in situ monitoring, and high throughput screening in their research programmes, we have made considerable progress within hydrotreating and hydrocracking catalyst development. The BRIM and HyBRIM catalyst technologies are the direct outcomes of this scientific approach.

HyBRIM technology was originally introduced with Topsoe’s TK-609 HyBRIM in 2013 and has since been extended to include several different hydrotreating catalysts covering medium to high pressure refinery applications. As mentioned above, the need for ULSD production from low quality crudes and higher severity hydrocracking is creating a need for even better catalysts.

During the past three years, HyBRIM technology has been broadly recognised by the industry to be at the forefront of what is possible within hydrotreating. In addition, more than 100 hydrotreating units around the globe have a HyBRIM catalyst installed right now. However, Topsoe’s researchers recently discovered even more potential within the HyBRIM method – a potential utilising the active metals to an even higher extent and securing a dispersion of active sites to a level never seen before. Therefore, Topsoe is launching the second generation of HyBRIM technology – the TK-611 HyBRIM catalyst with 25% higher activity for both sulphur and nitrogen removal. 

Higher activity, same stability
When applying the TK-611 HyBRIM catalyst in either ULSD or hydrocracker pretreatment service, the improved activity can be exploited in several ways. Obviously, a higher activity is often used to operate the unit as in previous cycles, only at a lower reactor temperature, which then yields longer cycle lengths. However, the new high activity can also be utilised in terms of increasing unit throughput or, in the case of a hydrocracker, to lower the nitrogen slip from the pretreat section to the cracking section, resulting in higher conversion and better yields. In addition, TK-611 HyBRIM will increase the volume swell due to better hydrogenation functionality. Refiners also benefit from purchasing more opportunity crudes or processing more LCO and they will have a stronger and robust catalyst candidate to handle these more challenging feedstocks. In any case, TK-611 HyBRIM will significantly improve the profitability of refinery assets.

Figure 3 shows ULSD pilot plant testing and compares TK-611 HyBRIM with TK-609 HyBRIM side-by-side. It is seen that if the two catalysts are operated at exactly the same conditions and at a reactor temperature giving 10 wt ppm product sulphur for TK-611 HyBRIM, then TK-609 HyBRIM will simultaneously deliver a product with 32 wt ppm sulphur. Hence the activity advantage of TK-611 HyBRIM corresponds to a delta product sulphur of 22 wt ppm at ULSD conditions, which is a remarkable step-change in activity.

The same type of experiment is illustrated in Figure 4 for vacuum gas oil (VGO) at hydrocracker pretreatment conditions. While 62 wt ppm product nitrogen slip is achieved with TK-609 HyBRIM, TK-611 HyBRIM, at exactly the same conditions, is able to deliver a product nitrogen slip of only 26 wt ppm. Such a difference is a substantial improvement for a hydrocracker pretreating unit.

High start-of-run activity is obviously important; however, activity has no real meaning unless it is accompanied by high catalytic stability, ensuring that improved performance is maintained over the projected cycle. Some catalyst formulations on the market display an impressive fresh activity; however, due to the nature of these catalysts, there is an initial line-out deactivation caused by the nitrogen species present in the feed passivating the most active sites. When these types of catalysts are installed, they will typically have lost their activity benefits after four to six weeks on-stream.

During the development of BRIM and subsequent HyBRIM technologies, Topsoe has successfully been able to modify the alumina structure and catalytic surface. By employing scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques, Topsoe’s researchers have observed how the catalyst preparation steps influence the catalyst functions. This knowledge has led to an improved alumina pore structure and an optimised interaction with the alumina support, providing very active and stable CoMoS/NiMoS catalyst formulations. The data shown in Figure 5 compares the stability of the new TK-611 HyBRIM with TK-609 HyBRIM in VGO hydrocracker pretreat service at the same operating conditions. The testing reveals that even though TK-611 HyBRIM is operated at higher sulphur and nitrogen conversion levels, due to its higher activity, the two catalysts exhibit exactly the same performance stability.