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Producing ultra low sulphur gasoline with octane retention

A drop-in catalyst enabled refiners to meet ultra low sulphur gasoline requirements with more severe feedstocks while retaining octane barrels.

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Article Summary
Over the past decade, the refining industry has taken major steps toward accommodating the increasingly stricter regulatory requirements that aim for a low sulphur world. Europe has generally been the front runner on regulations for low sulphur, ‘clean’ transportation fuels, but the rest of the world is also gearing up to accommodate changes in maximum sulphur limits in gasoline over the next few years. While reducing emissions from existing vehicles, the lower gasoline sulphur limits will also enable more stringent vehicle emission standards and make emission control systems more effective.

There are several operational and performance unknowns associated with reducing the average sulphur content of gasoline to ≤10 ppmw. To address this challenge and meet regulatory requirements, refiners are carrying out extensive technical and economic studies of the various catalyst drop-in solutions available in the market to assess which would provide maximum profitability and performance for their refineries.

The processing of FCC naphtha takes on an even more important role in meeting the new regulatory changes. Table 1 shows typical gasoline pool blending components before treating.

Although the gasoline pool comes from various sources in the refinery, full range FCC naphtha typically accounts for 30-50% of the overall gasoline blend and is the biggest contributor to sulphur. Operating selective hydrodesulphurisation (HDS) gasoline units to process FCC naphtha effectively generally entails lower investment and operating costs compared with the alternatives available for meeting the regulatory changes.

Although process configurations and operating constraints vary between refineries, the choice of catalyst has a tremendous impact on the level of HDS activity and selectivity for octane retention. Refiners judge that they can achieve maximum refinery economic benefits by increasing operating severity and the yields of higher octane products. Robust catalyst stability, improved performance with ageing and the ability to cope with significant variations in feed components are all important catalyst parameters for reliably producing ≤10 ppmw ultra low sulphur gasoline while maximising octane barrels and profitability.

Owing to strong gasoline margins, some refiners are focusing on developing a strategy to maximise gasoline production while preparing for the upcoming regulatory changes.

Octane demand and refiner profitability
Demand for octane remains high

Although changes in gasoline regulations generally focus on product sulphur, they also concern octane quality. Gasoline with a higher octane number enables greater engine efficiency and performance. The US gasoline octane market has varied over the years and has typically been affected by changes in gasoline grade demand, crude oil quality, crude and gasoline prices, gasoline specifications and octane enhancers.

To better track pricing and historical demand for octane, Albemarle has developed a correlation for octane barrel value that combines market data from the US Energy Information Administration with commercial customer data over the last two decades. Figure 1 summarises the trend in the value of the road octane number, which is the average of the research octane number (RON) and motor octane number (MON).

The data show that octane values rose between 2004 and 2006 when the market was also seeing an expansion in refinery gasoline production. Crude and product prices were rising and methyl tertiary butyl ether was being phased out of the gasoline pool owing to 
concerns over its solubility in water and consequent contamination of water resources. From 2007 to 2011, there was a slowdown in octane demand because of the increased use of ethanol as an octane booster and lower refinery octane targets. The timeframe also coincides with severe economic recessions in the global market.

However, the octane barrel value, which fluctuated periodically from 2012 to 2015 and increased to historic highs, has now plateaued. Some non-traditional drivers leading to the increased octane value include high compression engines, premium share increase, ethanol growth decline and processing more light tight oils.

The high cost of octane is expected to continue, as regulations for lower sulphur levels are already in effect. Added costs will come in the form of new refining equipment or higher severity hydrotreating of gasoline. Additionally, the lower sulphur requirements will cause refiners to blend less light naphtha into the gasoline pool owing to its low sulphur and octane values. As refiners look for new ways to improve octane quality while meeting sulphur regulations, catalyst drop-in solutions for existing selective HDS gasoline units are effective ways for them to capitalise on the market changes without large capital investments.

Profitability: octane is still the name of the game

With demand for octane remaining high, refiners have an opportunity to capitalise on profit margins by maximising octane barrels while producing ultra low sulphur gasoline. Figure 2 captures the impact of better octane retention from an existing selective HDS gasoline unit. Using data from the gasoline octane market and Albemarle’s correlation for octane barrel, the plot uses an estimated value of $1 per octane barrel for the valuation. However, the cost of octane will vary for each refiner based on the octane target, among other factors relating to refinery operations.
For example, if a refiner has a single stage unit that is processing 30000 b/d from a selective HDS gasoline unit, an improvement of 0.5 in RON for the product could lead to approximately $5 million/y in additional profits. However, a two stage unit processing the same feed rate could expect to achieve a RON improvement greater than 1, which would lead to correspondingly larger profits for the refinery (upwards of $10 million/y).

Catalytic solutions
Conventional hydrotreating to reduce sulphur in gasoline has the unfortunate side effect of saturating olefins and consequently reducing octane. In preparation for more stringent regulation and performance optimisation, some refiners have carried out an extensive study of the various catalyst drop-in solutions available in the market for their selective HDS gasoline units. Outside the general catalyst performance characteristics a refiner typically looks for when selecting a catalyst system, the refiners wanted to challenge the status quo and strive for a solution that offered:
• Improved selectivity to save additional octane
• Increased HDS activity to handle more severe feedstocks with higher sulphur levels
• Improved carbon monoxide tolerance to prevent octane loss.
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