Sep-2021

Discovering hydrocracking units potential with pretreat and tailored hydrocracking catalysts

A refiner uses pretreat and hydrocracking catalyst to maximise heavy naphtha, kerosene, and diesel production with improved product properties.

XAVIER RUIZ MALDONADO and RAHUL SINGH, Haldor Topsoe
PABLO DOSDÁ MANZANO, Cepsa

Article Summary

Hydrocracking pretreatment and zeolitic hydrocracking catalysts are widely used in refining to produce valuable finished products. Selecting the right combination of both catalyst systems is imperative to maximise feed conversion while maintaining the desired selectivity towards the preferred product fractions. Refiners will select catalysts which generate maximum profits for their hydrocrackers.

The primary objectives of hydrocracker pretreat catalysts are to remove organic nitrogen and sulphur, particularly basic nitrogen compounds, and to saturate aromatics. Nitrogen compounds have a significant negative impact on the activity of hydrocracking catalysts and, consequently, on the performance of the hydrocracker. In addition, aromatic compounds are difficult to crack and, by saturating them with the pretreatment catalyst, the resulting naphthenes are much more easily cracked over the hydrocracking catalyst. The saturation of these aromatic compounds also provides a higher volume swell which increases unit profitability.

Optimal catalyst performance does not depend on just one parameter, such as metals content or porosity, but also on characteristics of the support itself, the interaction between support and active metals, and the structure, acidity, porosity, and surface conformation of the zeolite.

TK-611 HyBRIM is one of Haldor Topsoe’s latest HyBRIM catalysts. Data from industrial operation in the hydrocracker (NK) at the La Rábida refinery of Compañia Española de Petróleos, S.A. (Cepsa), shows that TK-611 HyBRIM is 7ºC/13ºF more active than TK-609 HyBRIM. In addition, both catalysts showed the same deactivation rate.

Along with discussing its performance in the Cepsa hydrocracking unit, this article describes how Haldor Topsoe’s research has played a key role in enhancing the performance of hydrocrackers in the refining industry. A case story is presented to show the flexibility that Topsoe’s hydrocracking catalyst portfolio provides refiners with an opportunity of adjusting product yields to meet market demand and maximise unit profitability.

The desired performance of Topsoe catalysts is a result of the company’s product development and manufacturing techniques. As a part of its technical support, Topsoe uses customer feedback to guide catalyst development which addresses the objectives of various hydrocrackers, supporting continuous product improvement to meet the industry requirements.
 

In 1984, Topsoe’s researchers published results showing that there was a modified Co-Mo-S structure with substantially higher activity per active site than traditional Co-Mo-S structures. The two structures were called Type I and Type II sites. In 2000, the company discovered another type of active site using scanning tunnelling microscopy (STM), which the researchers named “BRIM” sites. These BRIM sites are responsible for initial hydrogenation reactions, a key pathway to removing the most sterically hindered sulphur compounds, and are located on top of the Co-Mo-S (or Ni-Mo-S) slabs.

As Figure 1 shows, the BRIM sites are located close to the edges, where their pi-electron clouds interact with the pi-electron clouds of organo-sulphur reactants. This interaction draws the most difficult sulphur molecules in for the initial hydrogenation step, enhancing their ability to interact with the nearby Type II sulphur vacancies.

Topsoe’s latest catalyst technology HyBRlM was commercialised in 2013. It includes an improved production technique in which the BRlM technology is combined with a proprietary catalyst preparation step. The technique ensures better dispersion of active components on the surface of the support along with optimised metal-support interactions. Together, they facilitate the formation of more active Type II sites and maximise the nickel promotion of the molybdenum slabs (see Figure 2). This ultimately increases both hydrodesulphurisation (HDS) and hydrodenitrogenation (HDN) activity. The first application of this technology was TK-609 HyBRIM. During the last few years, HyBRIM technology has been further improved and introduced to the market with second generation HyBRIM catalysts. Topsoe is now offering two new catalysts: premium high activity TK-611 HyBRIM and ultra-high activity TK-6001 HySwell for maximising volume swell.

The relative volume activity of various NiMo catalysts is shown in Figure 3. From the 1980s until today, Topsoe’s NiMo catalysts have increased in activity by 500%, meaning that the amount of catalyst required to meet a given objective now is five times lower now than it was in the 1980s.
Moreover, to fulfill refineries’ needs and provide flexible solutions for all types of feedstock, the company has extensively researched the synergy between hydrocracking pretreatment catalysts and hydrocracking catalysts.

Topsoe manufactures its own zeolites, which allows full control of the entire manufacturing process. The performance of hydrocracking catalysts depends on several factors, including zeolite types, zeolite porosity, zeolite acidity, and acid site proximity. The company also controls the production of aluminas, alumina-silicas, metals, and metal/support relationships. Coupled with tight quality control in manufacturing, this enables Topsoe to achieve the desired catalyst performance. This understanding is further enhanced by use of advanced pilot plants and analytical tools.

As Figure 4 shows, Topsoe’s base metal hydrocracking portfolio offers three main types of catalysts. The red series offers maximum hydrogenation to enhance volume well, maximise naphtha and kerosene yields, and upgrade unconverted oil (UCO) for base oil services. The blue series offers a balanced high yield of middle distillates and optimised diesel cold flow properties. The D-sel series offers the maximum yield of middle distillates in both kerosene and diesel ranges.

Commercial experience
Topsoe has worked for several cycles with Cepsa. This relationship includes close collaboration with both Cepsa Research Center and La Rábida refinery, with the aim of achieving maximum refinery profits. La Rábida refinery is located in Huelva, Andalucía, and has an annual capacity of 9.5 million tonnes. Together with the company’s Gibraltar San Roque and Tenerife facilities, this provides a total refining capacity of nearly 500000 b/d.The NK unit at La Rábida site operates in a single stage recycle (SSREC) manner. A partial layout and process description of the hydrocracker unit is shown in Figure 5.

The hydrocracker unit was originally designed to process 5800 t/d of vacuum gasoil (VGO) but now operates at 33% higher capacity. The VGO feed comes either from tanks and/or directly from two vacuum distillation units (VDU).