More from the barrel
An alumina-supported catalyst for ULSD production or hydrocracking pretreat provides longer catalyst cycles, higher throughput, and better product qualities.
SERGIO A ROBLEDO and PER ZEUTHEN
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The current pandemic has introduced complications which refiners must contend with. Lower jet demand due to less air travel, along with overall less consumption of transportation fuels due to lower mobility indices, results in less than favourable refining margins. In addition, the move towards green fuels will undoubtedly put additional pressure on the refining industry in the years to come. However, whether demand is high or low, the market still calls for high quality fuels. These tough market conditions mean refiners are trying to squeeze as much value as possible from every molecule processed.
In order to fare well, refiners must have all eventualities covered when managing the molecules. The market will dictate how much each molecule of crude, or hydrocarbon feedstock, costs and how many molecules of product are needed and what their respective value is. Refiners need to have the flexibility to respond to these market changes and produce different products by either processing more barrels of a specific stream, increasing the boiling range of the feed, and/or maximising the barrels produced of a given product. The right hydroprocessing catalyst can provide this flexibility by having maximum activity and providing the highest volume swell.
Low natural gas prices, observed particularly in the US, result in low production costs for hydrogen gas. This low-cost hydrogen, when catalytically added to middle distillate fractions, becomes very profitable by increasing the liquid volume swell, which results in higher volumetric yields of valuable products. As a result, a catalyst that can maximise hydrogen uptake into hydrocarbon streams becomes desirable and, generally speaking, NiMo catalyst has high activity for such a mechanism. Therefore, it is no surprise that worldwide market demand for higher activity NiMo hydrotreating catalysts is extraordinary. Despite the tremendous improvements in catalyst technology over the past 20-30 years, refiners are still looking for the absolute best NiMo catalyst for their ULSD or hydrocracker pretreat reactors.
To avoid setbacks, refiners continuously need better, more cost- efficient, alumina based catalysts with the highest possible activity, in order to obtain the desired boost in performance and hydrogen consumption. In addition, alumina based hydrotreating catalysts will help minimise the operating cost when targeting volume swell by comparison with higher cost bulk-metal catalyst formulations. This article will present the industrial performance of TK-6001 HySwell.
Haldor Topsoe has for decades been at the forefront of important technological breakthroughs in the hydroprocessing industry. In the 1970s, Topsoe discovered the active CoMoS phase present in hydrotreating catalysts. In the 1980s, Topsoe’s researchers, led by Dr Henrik Topsøe, discovered the difference between Type I and Type II hydrotreating catalysts and coined these names, which are known throughout the industry today. In the early 2000s, Topsoe’s commitment to fundamental research in surface science paid off again, and a new activity site was discovered: the brim site. Using scanning tunnelling electron microscopes, researchers took pictures of these new activity sites (see Figure 1) which they named brim sites. With this finding, Topsoe developed the BRIM technology which fuelled the company’s growth through a leading catalyst portfolio.
For years, BRIM and HyBRIM catalysts have been relied upon by refiners facing challenges brought about by clean fuels legislation, maximising volume swell to reap increased profits from lower cost hydrogen, or processing cheaper, more difficult feeds. Building on the experience from more than 500 industrial applications of these catalysts, a new catalyst has been developed, TK-6001 HySwell.
Topsoe’s latest catalyst technology, HySwell, involves an improved production technique for NiMo hydrotreating catalysts. It combines the BRIM and HyBRIM technologies with a proprietary catalyst preparation step. Merging previous technologies with novel, atomic-level insights enabled Topsoe to design a metal slab structure characterised by an optimal interaction between the active metal structures with even higher concentrations supported on the catalyst carrier. The activity of the Type II sites is positively influenced by this interaction between the metal slab and the carrier. HySwell technology exploits this combination of higher concentration of active metals and optimised interaction, substantially increasing the activity of both direct and hydrogenation sites, without compromising catalyst stability.
Topsoe’s current NiMo catalysts have more than 500% higher activity than the catalysts produced in the mid-1980s. Figure 2 illustrates the progression in activity over generations of catalysts for hydrocracking pretreatment applications. The increased activity corresponds to improvements in the required operating temperature. Topsoe’s scientists utilised tools such as electron microscopes, in-situ monitoring, and high-throughput screening in their research programmes to make progress in the development of hydrotreating and hydrocracking catalysts. HySwell technology is a direct outcome of this approach.
Case study 1
A US Midwest refiner operates a single-stage recycle hydrocracker processing 17000 b/d of vacuum gas oil and light cycle oil (LCO). As part of the refiner’s catalyst selection process when considering replacing the incumbent catalyst, Haldor Topsoe conducted a pilot plant study using the reactor scheme shown in Figure 3.
The feed properties for the pilot plant are listed in Table 1. The pilot plant tested the performance of a combination of hydrocracking, dewaxing, and post-treat catalysts in R-2, and TK-609 HyBRIM in R-1. The scheme chosen allowed the refiner to see the individual performance and impact of the pretreat catalyst, and to measure nitrogen slip versus required WABT and its impact on the hydrocracking catalyst. This is key information because pretreat catalysts play a crucial role in determining final hydrocracker product properties. The pilot plant’s operating conditions are listed in Table 2.
Based on these results, the refiner ordered Haldor Topsoe’s catalyst for the next cycle. In the period after completion of the pilot plant and the loading of the reactor, Haldor Topsoe launched its second generation NiMo HyBRIM, TK-611 HyBRIM. As a result of pilot plant validation work, the launch of the new catalyst, and the pilot plant work for the unit, the refiner chose to order TK-611 HyBRIM instead. The new catalyst performed in the unit as expected, even when the feed was heavier than feed tested in the pilot plant (see Figure 4) and still maintained a low deactivation rate of ~1.0°F (0.5°C)/month (see Figure 5).
Case study 2
An Indian refiner operates a single-stage hydrocracker processing 39000 b/d of vacuum gasoils. In the 2015 cycle loaded with Topsoe’s hydrocracking and TK-609 HyBRIM pretreat catalyst, the unit performed quite well. For the 2019 cycle, the refiner aimed to lower sulphur and nitrogen in the UCO and diesel products.
Haldor Topsoe performed a unit analysis and concluded that, for the 2019 cycle only, the pretreatment catalyst needed to be replaced as the highly active hydrocracking catalyst still had plenty of activity left. The target cycle length for the 2019 load was 36 months, while lowering product sulphur and nitrogen to new levels. Topsoe recommended the installation of a split load of TK-611 HyBRIM and TK-6001 HySwell in the pretreatment reactor, which achieved unit targets while reducing catalyst costs. Due to market conditions in the pandemic, the unit has been operating with varying feed rates, while meeting all unit margin objectives with significant savings for the refinery. Feed and operating parameters are shown in Table 3.
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