Jun-2021

Increasing profit in hydrocracking and diesel hydroprocessing

A drop-in catalyst for hydrocracking pretreat and distillate hydrotreating raises activity with heat management savings.

Keith Wilson, LOUIS BURNS, DEAN PARKER and PADMINI LINGARAJU, ExxonMobil
PIETER LUSSE, RENÉ SEVERENS and NATASJA BERG-SCHOUTEN, Albemarle

Article Summary

Increasing profitability is a key question addressed regularly by refiners, particularly in recent times. In hydroprocessing terms, and recognising that energy transition will mean limited scope for new build, increasing profitability will focus on a simple question: “How can we do more with the facilities we already have?” An answer to this question will certainly focus on selecting the right catalyst solutions for use in an existing refinery kit. Including Celestia catalyst in a catalyst system is a drop-in opportunity to improve unit profitability.

A refinery’s net profitability is determined from a balance of controlling opex in several dimensions: feed costs, energy use, and use of utilities. The goal is to drive to the highest margin for the amount of energy use. Older refineries may be processing feeds that are substantially different in quality from the original design. This can lead to units operating at lower utilisation, or at higher energy use to meet a sub-optimal product slate. The choice to include new capital to improve the operating efficiency is rarely justified, particularly in the current environment, thereby leaving the refinery margin also at sub-optimal levels. What if there is another way to unlock performance in existing equipment?

Celestia catalyst is a novel bulk-metal catalyst co-developed by Albemarle and ExxonMobil. The goal of the catalyst design was to drive catalyst activity to new heights to enable new use of existing equipment in ExxonMobil’s refineries. This continues a trend from 2000s with the Nebula bulk metal catalyst. Celestia catalyst was first commercialised in 2015 in a light feed hydrocracker and improved the unit profitability via a number of captured margin advantages. The catalyst has since been deployed in 15 process units in North America, Europe, and Asia Pacific, demonstrating outstanding hydroprocessing activity on light and heavy feeds, implemented across a range of hydroprocessing platforms, and providing in each case a clearly defined opportunity for increased profitability.

This article describes the Celestia catalyst, reviews three case studies where Celestia catalyst was deployed successfully, and illustrates how its applications can contribute to significantly improve economic outcomes from a hydroprocessing unit or hydrocracker. The case studies illustrate how application of Celestia technology in distillate hydrotreating, and light cycle oil (LCO) and vacuum gasoil (VGO) hydrocracker pretreat applications has yielded exceptional margin and operating expense returns.

Celestia catalyst
The catalyst’s performance is brought about by increased hydrodesulphurisation (HDS), hydrodenitrogenation (HDN) activity achieved through a unique design. The catalyst is a bulk-metal design synthesised almost entirely from the active metals needed for hydroprocessing activity. This enables much higher activity than conventional catalyst, more than twice the volumetric activity of leading NiMo catalysts. Moreover, Celestia catalyst’s advantage arises from strong hydrodearomatisation (HDA) activity that has been demonstrated at over 2.5 times the level expected from leading NiMo catalysts. Adding Celestia catalyst to a catalyst load brings a high degree of activity improvement and will improve performance significantly even where it forms less than 10% of the reactor volume.

Defining the opportunity
Profitability can have many dimensions, and examples where Celestia catalyst provides value include:
- Improve margin via feed basis change: increase feed rate, process less expensive and more refractory feed components.
- Improve margin via improved product quality and yield: lower product sulphur or nitrogen, lower product total aromatics, increase volume swell, improve cetane and cloud properties, and improve conversion.
- Reduce operating expense: stretch a unit cycle length, eliminate a unit shutdown to coordinate with refinery wide shutdown planning.
- Reduce energy consumption: change the reactor temperature profile to reduce inlet temperature, or/and increase outlet temperature, leading to reduced energy consumption.

Heat release management and energy sparing
Adding significant activity to the reactor does come with additional considerations. Hydroprocessing reactions are generally exothermic in nature and lead to temperature rises in the reactor catalyst beds. Celestia catalyst is certainly more exothermic than other catalysts and the catalyst temperature rise needs to be managed to ensure process and product quality control, and to minimise catalyst deactivation.

ExxonMobil has developed mitigation strategies to manage safely the operation of the catalyst. Mitigations used to control catalyst temperature rise include:
- Splitting the Celestia catalyst load between beds to limit the temperature rise per bed.
- Increasing inter-bed quench gases. Cold quench gases are introduced between catalyst beds and mix with the hot liquid and vapour exiting the bed above.
- Changing the reactor temperature control strategy to increase the ascending temperature rise axially in the reactor, accomplished by reducing the reactor inlet temperature, or increased outlet temperature, or both.
- Limiting the start-of-run operation to lower reactive feeds over one or two weeks during the catalyst line out period.

Placement of Celestia catalyst is a critical component to the catalyst stacking design, and typically it would be loaded in mid to lower catalyst beds. This strategy allows the catalyst to work efficiently, removing the more refractory sulphur and nitrogen species, and enhancing aromatic saturation.

A hydroprocessing unit configuration (hydrocracker or hydrotreater) and design will vary with core business purpose. While Celestia catalyst is an enabling influence to improve profitability, the extent of the gain in opportunity will depend on the unit configuration and facilities design.

Implementation pathways and case studies
Considering the above, the approach taken to achieve opportunities for profitability in 15 applications to date has broadly fallen into one of the two implementation pathways:
1. Optimising Celestia catalyst load to predefined equipment limitations: in this case, the catalyst load is maximised within the unit facilities capability and design. Improved outcomes created by Celestia catalyst will also be variable but generally complementary to the process unit’s economic targets, and also can generate value across the site’s business.
2. Optimising Celestia catalyst load to achieve a predefined process objective: in this case, the load is prioritised, determined to achieve process advantage and economic objectives. The application may require limited investment to fully mitigate heat release, heat integration, or hydraulics impacts.
Each of the value creation opportunities illustrated has been realised by incorporating Celestia catalyst into a reactor load. They are illustrated by the three following case studies.