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Nov-2018

Advanced catalyst characterisation for improved hydrocracking performance

Advanced analytical techniques delivered new insights into catalyst structure and manufacturing leading to improved performance material.

MAUREEN L BRICKER, SARIKA GOEL, MARJORIE MIRANDA and TONY VRANJES
Honeywell UOP
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Article Summary
When choosing a hydrocracking catalyst, refiners base their selection upon desired product properties and yield profile. Some refineries desire a heavier product slate and hydrocracking catalysts that produce high distillate yield. Other refiners want the ability to use unconverted oil (UCO) to produce higher value lubricants. Having a catalyst that hydrogenates across the entire product slate to improve quality is important. The catalyst manufacturer now has the ability to produce hydrocracking catalysts to deliver this functionality. The refiner may obtain the desired product slate by selecting an individual catalyst or combining appropriate performance aspects by staging multiple catalysts.

The use of improved advanced analytical techniques has helped explain phenomena that lead to performance properties of catalysts. Of particular value is the Titan 80-300 keV Super-X aberration-corrected electron microscope. This instrument produces a surface level representation of the catalyst at a resolution that was not previously possible. The application of characterisation techniques to hydrocracking catalysts gives scientists a better understanding of interactions between the active metal and the catalyst support. This information sheds light on the effects manufacturing processes and activation procedures have on catalyst performance.

This article presents the results of an advanced characterisation study comparing two commercially successful Honeywell UOP hydrocracking catalysts. The goal was to explain, on a molecular level, the reasons for differences in performance.

UOP HC-410 LT, a commercially proven hydrocracking catalyst known for high yield, high activity and high viscosity index of the UCO, was chosen for the study. HC-410 has been accepted globally by base oil producers, with high performance demonstrated in seven units. This article describes how it met the performance targets of a particular Asian refiner.

The study compares HC-410 to a commercially proven reference hydrocracking catalyst, HC-115 LT. It was widely used in the same segment for 10 years, before the 2015 introduction of HC-410.

Knowledge obtained from the catalyst comparison study was applied in the development of Honeywell UOP’s newest hydrocracking distillate catalyst, HC-620 LT. This has improved hydrogenation function resulting from better metals utilisation and improves upon the performance of Honeywell UOP’s DHC-32 LT, a proven, previous generation hydrocracking catalyst. HC-620 exhibits higher yield, better activity and more hydrogen consumption. Volume swell for hydrocracking of vacuum gas oils is thereby increased. HC-620 is commercially available and has been sold into three commercial units in 2018.

This article also discusses performance benefits that may be realised from the increased hydrogenation function of HC-620 when used in combination with other hydrocracking catalysts. This benefit was demonstrated in pilot screening studies of HC-620 stacked with HC-410. This option would be beneficial in applications processing difficult feeds.

Advanced characterisation study
The characterisation study compares Honeywell UOP Unity Portfolio hydrocracking catalyst HC-410 and a previous generation catalyst HC-115, used as a reference. Both catalysts are commercially proven and are used in the lubes segment. HC-410 exhibits improved yield (see Figure 1).
 
Background
HC-115, the reference catalyst, has been successfully used for hydrocracking in the commercial lubes segment for over 10 years. HC-410 was introduced in 2016 as a new generation hydrocracking catalyst for both UCO for base oil plant feed and distillate for fuels production. The finely tuned hydrogenation function of this catalyst delivers a higher dewaxed viscosity index than prior generations, enabling production of higher grade lube base oils. This catalyst also offers proven higher activity and diesel yields. HC-410 delivers better metals utilisation for improved hydrogenation and provides high distillate yield.

Refiners require well-demonstrated improvements to risk changing to a new catalyst. HC-410 has received global acceptance by both fuels and base oil producers and has been loaded in nine refineries in Asia Pacific, North American, and European regions.

The following example demonstrates successful performance by HC-410 in meeting the performance targets of one particular Asian refiner. In 2017, HC-410 replaced a catalyst from a different vendor in this refiner’s hydrocracking unit. The prior catalyst system required operation at higher than desired conversion to meet the waxy VI target of greater than 134, lowering UCO yield. The refiner conducted its own pilot plant performance testing to evaluate other catalyst vendors and selected HC-410.

HC-410 met the waxy VI target at lower conversion, increasing the yield of UCO, the desired product, and maximising profitability for the refiner. Commercial operation confirmed the predicted conversion at which the UCO VI specification would be met with HC-410 (see Figure 2). The sulphur and nitrogen values were low in the UCO and met specifications. HC-410 continues to meet the refiner’s expectations, consistent with predicted performance. Net conversion is at target with higher middle distillate yields than predicted.
 
Catalyst characterisations to determine surface phenomena
HC-410, a NiW catalyst, is prepared using methods that differ from the reference catalyst HC-115, resulting in superior total distillate yields. Advanced analytical techniques were used to characterise these catalysts with the aim of determining the phenomena responsible for performance improvements.

The Titan 80-300 keV Super-X aberration-corrected scanning transmission electron microscope (AC STEM) uses atomic level imaging to show catalyst surface morphology not previously visible with traditional transmission electron microscopy. In addition, spherical aberrations are reduced. Energy dispersive X-ray (EDX) imaging maps from the microscope showing HC-410 and HC-115 revealed new information on catalyst support, metal-metal interactions and interactions between the support and metals.

The maps of HC-410 showed localised areas of alumina, amorphous silica alumina, and zeolite (see Figure 3). Individual metals tended to locate preferentially in selected localised zones of a particular base material, and to avoid others. The micrograph shows the localisation of elements. Some metal species migrate to edges of stacks. Alumina rich regions underlie the stacks (nanostructures). The bulk metal sulphide stacking stoichiometry was thus determined.

Figure 4 shows high angle annular dark-field scanning transmission microscopy (HAADF-STEM) images displaying the differences in catalyst structure observed with different preparation methods. HC-410 has shorter length flakes and less layer stacking of the sulphided metal particles.

Discoveries made during this work about the inter-relationships of these phenomena led to new methods of catalyst preparation and activation that optimise activity and yield.
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