Nov-2017

Operating in the jungle of renewables (ERTC)

In Europe, 10% of transport fuels should come from renewable sources by 2020. This will partially be achieved by hydroprocessing renewable feedstocks.

Kiki Larsen and Sylvain Verdier
Haldor Topsoe

Article Summary

However, compared to the processing of fossil fuels, the conversion of renewables to transport fuels poses new challenges. New types of contaminants, such as phosphorus, are introduced, large exotherms arise, and corrosion due to oxygenated compounds needs handling.

The key objective for each renewable processor is to find the optimal solution based on feed properties and the required product specifications. These parameters will impact the choice of technology and catalyst solution. This is best done by having a strong dialogue and collaboration with the technology and catalyst vendor, so that the introduced challenges specific to renewables are addressed to ensure the most optimal performance.

As with fossil fuels, variations in renewable types are many (vegetable oils, animal fats, used cooking oils and pyrolysis oils, residues from pulp mills). To successfully produce fuels from renewables, the feedstock needs to be evaluated with regard to:
- Fouling tendency and grading catalyst requirements: Which contaminants will affect the cycle and to what extent (deactivation, pressure drop)?
- Activity: Can the oxygenated compounds be easily hydrodeoxygenated (HDO)? Is organic nitrogen a concern due to its inhibiting effect on hydrotreating activity?
- Yield structure and product properties: The feedstock composition will have a huge influence on the end products and the end product properties. For example, some triglycerides may contain fatty acids with high carbon numbers that would produce molecules outside the desired fuel range.
- Deactivation: Phosphorous and silicon are known to deactivate the catalyst even at very low concentrations (a few ppm) and may deactivate the bulk HDO catalyst without a proper grading.
- Heat balance and hydrogen consumption: High oxygen content and unsaturated compounds will give rise to large exotherms and will also strongly affect the hydrogen consumption.
- Mechanical: The acid number and by-product of the feedstock will affect to 
which degree corrosion will be an issue for the unit.
- Unit operations: The handling of a wide operating window requires strong experience in layout, control, and handling of upset situations.

On top of the feedstock evaluation comes the fuel specifications. The three main fuel specifications are listed below:
•  EN-590 based mainly on 100% HDO and dewaxing for cloud point requirements.
•  MK-I, as EN-590, but the aromatic specifications are tightened to yield max 5% total and 200 ppm PHA. The T95 end point is also lower than the EN-590.
•  HVO-100, as MK-I, but the aromatic specifications are further tightened to max 1.1% total, and with lower density requirements.
To reach these specifications, a variety of solutions exists:
•  Graded beds for activity and guards against renewable impurities.
•  Combined isomerisation and cracking catalyst to improve cold flow properties and reduce heavy ends.
•  Isomerisation catalyst in sour mode for cloud point improvements with low yield loss. It can be combined with cracking catalyst if heavy end reduction is required.
•  Isomerisation catalyst in sweet mode for cloud point improvements and reduction in aromatic content. It can be combined with cracking catalyst if heavy end reduction 
is required.

To get the optimal performance of a renewable processing unit, feedstock, technology, and end product need to go hand in hand. This requires a close collaboration between the technology/catalyst vendor and the refinery.

Topsoe’s strengths as a technology and catalyst vendor include strong research and technology developments, plus extensive experience within design and field support. Table 1 lists the different renewable feedstocks, the main products 
derived from them, and Topsoe’s commercial experience.

Did you know: Topsoe just launched the TK-930 D-wax catalyst for diesel dewaxing without yield loss?

This short article originally appeared in the 2017 ERTC Newspaper, produced by PTQ / DigitalRefining.

For more information contact: kikl@topsoe.com