Using reactivated hydroprocessing catalysts in TGTUs for financial and sustainability rewards (ERTC)

For over 40 years, the global petroleum refining industry has successfully been reusing hydroprocessing catalysts through ex situ reactivation, to capitalise on the economic and environmental benefits such technologies deliver.

Brian Visioli

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Article Summary

The process provides more cost-effective catalyst configurations whilst continuing to deliver performance levels equivalent to fresh catalysts. However, these gains have been exclusive to refinery hydroprocessing units – that is, until now.

Following the successful installation and operation of reactivated hydroprocessing catalysts in the tail gas treating units at two US refineries, this is now changing. This fresh approach is already producing several benefits, namely: lower replacement catalyst costs, increased circularity, and increased activity levels (which has resulted in reduced SO₂ and CO₂ emissions), and less spent catalyst hazardous waste.

Moreover, it has demonstrated a reduced dependence on fresh cobalt and molybdenum metals. Consequently, refiners can reap the double benefit of decreasing their carbon footprint and enhancing circularity without any adverse effect on performance levels.

The extension of this technology to tail gas treating has been made possible thanks to Evonik’s unique experience in both hydroprocessing catalyst recovery and sulphur recovery catalysis. Patent coverage is held by the company for the use of reactivated hydroprocessing catalysts in tail gas treating units, consolidating its reputation for industry-leading innovation.

Manufacturing catalysts
Until recently, tail gas treating catalysts have been produced from basic raw material building blocks, including alumina, cobalt, and molybdenum. Each of these catalyst precursors is derived from a naturally occurring ore. The ‘upstream’ processes of mining, ore processing, and ore purification each require a significant energy input. These processes also have significant environmental and societal impacts, which though more difficult to quantify, should not be ignored.

Four decades ago, the majority of hydroprocessing catalysts also came from similar raw materials. Since then, we have seen significant advances in the technologies and methods involved in catalyst reactivation, which is why the use of reactivated hydroprocessing catalysts has become a central part of many oil refinery operating companies’ strategies today.

Catalyst reactivation (regeneration and rejuvenation)
Eventually, hydroprocessing catalysts will reach the end of their active life. This could be caused by several factors, such as:
• Loss of catalytic activity/selectivity due to process upset
• Operating limit of reactor feed heater
• Operating limit of other reactor control parameter
• Catalyst bed fouling
• Equipment failure
• Coordinating timing with other operating units at the refinery

At the end of its life cycle, the catalyst is removed from the reactor, with the spent catalyst then classified as hazardous.
A spent hydroprocessing catalyst can be disposed of in one of three main ways:
- Disposal in a hazardous waste landfill However, this is the least desirable method for several reasons: the refiner loses the value inherent in the spent catalyst and an additional fee must be paid for the spent catalyst to be disposed of in landfill. The fact that this places environmentally hazardous materials into a landfill must also be factored into considerations.

Processing for metal reclamation, where oxidation removes much of the carbon and sulphur compounds in preparation for recovery of valuable metal components (e.g. molybdenum). This approach is an improvement upon disposal in landfill, as the refiner is typically credited for a fraction of the value of certain components reclaimed from the spent catalyst. This method still requires a thermal treatment and leaves a final waste stream containing the less-valuable components of the catalyst particles (e.g. alumina), which must be disposed of in turn.

Both these options, however, involve a processing cost and neither leverages the value of the technology inherent in the catalyst particle for the refiner’s benefit. Which brings us to the third option:
- Reactivation for reuse This involves oxidation under controlled conditions to remove carbon and sulphur compounds but preserve catalyst qualities for certain applications. An additional chemical treatment (commonly referred to as ‘rejuvenation’) may also be employed. This is the superior of the three options for dealing with spent hydroprocessing catalysts, as it allows the refiner to leverage the maximum value of their spent catalyst, avoids disposal to landfill, and gives the active metal components which comprise a hydroprocessing catalyst a ‘fresh start’. And crucially, regenerating and reusing the catalyst in this way reduces the refining industry’s dependence on freshly mined metals.

From hydroprocessing to tail gas treating
There are several similarities between tail gas treating catalysts and hydroprocessing catalysts. Both applications commonly employ metals such as cobalt and molybdenum, supported on a carrier containing aluminum, silicon, zeolites, or combinations thereof.

Both need to be converted to a metal-sulphide state for activity toward the desired reactions, and both consume hydrogen as a reactant in the desired reactions. In both applications, extruded catalysts are quite common, although spherical tail gas treating catalysts have been introduced to provide lower pressure drop.

That said, there are also important differences between the two types of catalysts. For example, the quantity of active metal applied to hydroprocessing catalysts is commonly much greater than that on tail gas treating catalysts, and hydroprocessing catalysts do not typically come in contact with species containing oxygen atoms when processing fossil fuels. Moreover, the operating pressure is significantly greater in hydroprocessing (up to 2000+ psig/140+ bar) compared to tail gas treating.

Case Study: Catalyst in Context
EcoMax™ TG catalyst was selected by a US Gulf Coast refinery for installation in its tail gas treating unit. The subject unit is a conventional temperature TGTU which processes Claus tail gas from one upstream SRU. The catalyst was sulphided in situ and operated for four months prior to performance testing.

Performance testing was completed by a well-known SRU/TGU performance testing company. Gas samples were taken at the inlet and outlet of the tail gas reactor at a variety of conditions and analysed by gas chromatography. Reactor bed temperatures ranged from the baseline of 271°C to as low as 254°C, corresponding to reactor inlet temperatures from 263°C to as low as 248°C. The gas chromatography analysis indicated that no SO₂ was present at the tail gas reactor outlet throughout the testing, and conditions in the quench water system confirmed that complete SO₂ conversion was taking place in the tail gas reactor.

The operating conditions were challenging. Very high levels of CS₂ were observed at the reactor inlet, ranging from 8,000 to 25,000 ppmv. Throughout the testing, zero CS₂ was observed in the tail gas reactor effluent, indicating complete conversion over the catalyst at all conditions tested.

Unlocking potential
It would be prudent for operators in the sulphur recovery industry to investigate using our patented reactivated hydroprocessing catalysts in their tail gas treating units, given the raft of potential benefits – both financial and environmental – that these technologies can provide. References available on request.

This short article originally appeared in the 2022 ERTC Newspapers, which you can view HERE

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