Everything you’ve wanted to know about co-processing (but were afraid to ask)

This article was first published by SAF Magazine (safmagazine.com) and is reproduced here with their kind permission.

Co-processing Essentials 

What is coprocessing in refinery terms?

Co-processing refers to the simultaneous processing of renewable and fossil feedstocks within existing refinery units, such as hydrotreaters or hydrocrackers.

In this approach, renewable materials including vegetable oils, animal fats or used cooking oils are blended with conventional petroleum streams and processed together.

This integration enables refineries to incrementally introduce renewable feedstock without building entirely new facilities, thus leveraging existing assets and infrastructure. These feedstocks are selected based on availability, cost and regulatory eligibility.

How does it differ from standalone renewable fuel production?

Standalone renewable fuel production usually involves constructing dedicated refinery facilities designed exclusively for 100% renewable feedstocks (or repurposing existing refinery units).

Co-processing utilizes existing refinery units with only minor modifications, allowing for a much faster and more cost-effective transition.

While standalone units can process a wider range of renewables at higher concentrations and volumes, co-processing is ideal for rapid deployment and incremental scaling.

What are the main advantages of co-processing for a conventional refinery?

Co-processing offers several interesting advantages for refineries. First, it enables rapid entry into the renewable fuels market with minimal capital investment, as existing refinery assets are utilized.

Second, it provides operational flexibility, allowing refineries to adjust renewable content in response to market demand or regulatory requirements.

Third, co-processing supports compliance with emerging mandates for renewable fuel blending, such as those for SAF, without the need for disruptive infrastructure overhauls.

Lastly, it reduces the carbon intensity of refinery products, enhances the sustainability profile of the operation and opens access to new revenue streams from renewable fuel credits and incentives.

What are the key challenges or limitations with co-processing?

Despite its advantages, co-processing will mean some technical and operational changes. Hydrogen demand will rise, as renewable feedstocks require more hydrogen for deoxygenation. The highly reactive oxygen molecules will also create very high exotherms that need to be handled in a clever way.

Renewable feedstocks will also increase water formation, which must be managed to avoid corrosion. Catalyst selection becomes critical, as some renewables can accelerate catalyst fouling or poisoning due to the presence of new contaminants like phosphorous.

There are also regulatory limits on the proportion of renewables that can be co-processed if the objective is to produce SAF capped at 5% by volume.

Maintaining product quality (especially for jet fuel, where freezing point and other specifications are stringent) requires careful process control and, in some cases, specialized catalysts for deep dewaxing.

Strategic Rationale and Market Positioning 

Why would a refinery choose co-processing over building a dedicated renewable unit or repurposing an existing unit?

Refineries often select co-processing as a pragmatic, lower-risk pathway to enter the renewable fuels market. The primary driver is the ability to leverage existing assets easily and quickly, minimizing capital expenditure and timelines.

Co-processing can be implemented with minor modifications, such as catalyst changes or small hardware upgrades, allowing for a rapid response to regulatory or market pressures.

Building a dedicated renewable unit is obviously more capital intensive and time consuming, and making these types of investments in an unstable market can be a challenge.

Repurposing existing infrastructure for renewable fuels and SAF can be a viable option and quite fast (we did this for Calumet’s Montana Renewables, where we helped convert idle hydrotreater capacity into SAF and renewable fuel production—not co-processing—in just 18 months).

But for many refineries, co-processing represents an optimal balance between cost, speed and compliance in the short term.

How does co-processing help meet regulatory mandates like SAF blending targets?

Co-processing is particularly effective in helping refineries meet regulatory mandates for SAF blending. By integrating renewable feedstocks into existing units, refineries can quickly produce SAF that meets international jet fuel standards, such as ASTM D1655.

This approach allows for incremental increases in SAF production, supporting compliance with both current and future blending mandates.

What are the current and emerging incentives for co-processing and SAF production in general?

A diverse and rapidly evolving set of incentives is driving the adoption of coprocessing and SAF production worldwide. In the European Union, ReFuelEU Aviation mandates a minimum share of SAF in the fuel mix, starting at 2% in 2025 and ramping up to 70% by 2050. The EU has also launched a delegated act on coprocessing that gives clear guidance on how to deploy this technology in refinery assets. Globally, the SAF regulatory landscape is highly dynamic. 

The United Kingdom and EU are at the forefront, employing a mix of incentives (“carrots”) and mandates (“sticks”), while also moving toward alignment on definitions and sustainability criteria, such as those outlined by CORSIA. Other regions, including Japan, India, Singapore, the United Arab Emirates and Brazil, are developing or have recently implemented SAF mandates, though some are still clarifying the details around obligations, penalties, incentives and GHG calculation methodologies.

In the United States, though co-processing does not qualify for 45Z credits under the Inflation Reduction Act, SAF producers can still benefit from renewable identification numbers (RINs) under the Renewable Fuel Standard, as well as credits from California’s Low Carbon Fuel Standard, depending on feedstock and process pathway. 

Some countries without domestic SAF mandates are positioning themselves as exporters to regulated markets.

What new revenue streams can co-processing unlock for a refinery?

Co-processing can open access to higher profit products due to regulatory mandates and voluntary commitments. Refineries can also generate and monetize carbon credits, RINs or other compliance instruments. Participation in these markets diversifies refinery income, reduces exposure to fossil fuel volatility and enhances the overall value proposition of the operation.

The payback period for co-processing projects is typically much shorter than for dedicated renewable units, due to the low capital investment required and the access to premium markets and incentives. Exact ROI depends on site-specific factors such as hydrogen availability, existing unit configuration, feedstock costs and local regulatory frameworks.

What are the projected trends in SAF demand over the next 5–10 years?

SAF demand is expected to grow exponentially over the next decade, driven by regulatory mandates, airline decarbonization commitments and increasing societal pressure to reduce aviation emissions. Coprocessing is poised to play a critical role in meeting this demand, especially in the early years, by enabling rapid, scalable SAF production within existing refinery infrastructure.

Unit Integration and Technical Feasibility 

Which refinery units are best suited for co-processing SAF?

As renewable feedstocks are scarce and expensive, the best-suited units for co-processing SAF are those that maximize the SAF yield.

Kerosene hydrotreaters and hydrocrackers are therefore the obvious choice. These units are designed to handle the molecular transformations required for jet fuel production and can be adapted to process renewable feedstocks with relatively minor modifications. Diesel hydrotreaters can also be used, but the yield of SAF may be significantly lower compared to dedicated kerosene units and the renewable feedstock will mostly end up as renewable diesel.

But ultimately, the choice of unit depends on refinery configuration, product slate and desired SAF output. Topsoe works closely with customers to ensure they choose the correct solutions for their operations, location and fuel requirements.

Can existing hydrotreaters or hydrocrackers be used with minimal upgrades?

Yes, in many cases, existing hydrotreaters or hydrocrackers can be adapted for co-processing with minimal upgrades.

The most common modifications involve changing catalysts to those optimized for renewable feedstocks, such as hydrodeoxygenation and dewaxing catalysts. Additional adjustments may include hydrogen management, water handling improvements and corrosion control measures. For blending ratios up to 5% renewable content, these changes are typically straightforward and do not require major capital investment.

What are the typical hardware or process modifications required?

Typical modifications include the installation of specialized catalysts, upgrades to hydrogen supply systems, enhancements to water separation and handling, and corrosion-resistant materials in areas exposed to increased water or organic acids.

Process control systems may also need to be updated to monitor and optimize the renewable feedstock blend. In some cases, additional reactor volume or catalyst beds may be required to maintain throughput and product quality for a reasonable cycle length.

What feedstock blending ratios are feasible and compliant?

Blending ratios that are approved in utilization as aviation fuel are fixed by the ASTM D1655.  

The current standard allows the following ratios:

• 5 vol% co-processing of mono-, di-, and triglycerides, free fatty acids, and fatty acid esters.

• 5 vol% co-processing of hydrocarbons derived from synthesis gas via the Fischer-Tropsch process using iron or cobalt catalyst.

• Co-processing (including cofractionation) of hydrocarbons derived from hydroprocessed mono-, di-, and triglycerides, free fatty acids, and fatty acid esters. The maximum allowable volume is 24% of the feed and 10% of the product.

SAF-Specific Considerations 

How much SAF can be produced via coprocessing?

Even when the maximum blending ratios are fixed in the ASTM D-1655, not all refinery hydroprocessing units can reach these co-processing amounts.

Some refineries will be better suited to reach high levels of coprocessing while others will require more important investments. In those cases, refineries may consider a stand-alone facility to boost SAF production capacity.    

What is the expected quality of co-processed SAF compared to HEFA SAF?

Co-processed SAF needs to fulfill slightly less stringent specifications compared to HEFA (hydroprocessed esters and fatty acids) SAF, as the blending amounts are much lower. Co-processed SAF specifications are defined in ASTM- D1655, while HEFA-SPK is covered in ASTM-D7566 as a blending component for jet fuel. It should be noted that HEFA-SPK can be blended with fossil jet fuel at up to 50% in an airplane.

How is traceability of biogenic carbon ensured in co-processed SAF?

Physical separation of renewable and fossil molecules is not possible in co-processing. However, it's important to note that the sustainability characteristics of each fraction are preserved in bookkeeping or mass balance systems. These systems track the amount and sustainability attributes of the renewable feedstock through the supply chain, ensuring that the environmental benefits of the renewable component are accurately represented and credited.

There are several methodologies available to track the biogenic content in products, including mass balance, energy content, yield and carbon dating. The EU accepts the first three methodologies but requires regular verification using 14C monitoring.

Catalysts and Process Chemistry 

Do I need different catalysts for co-processing?

Absolutely. Co-processing requires specialized catalysts, particularly for hydrodeoxygenation and deep dewaxing.

These catalysts are essential to efficiently remove oxygen and contaminants from renewable feedstocks. But most importantly, there is a need to transform n-paraffin into i-paraffins to ensure the final product meets jet fuel specifications, including freezing point requirements.

This dewaxing catalyst should be designed in a way that allows it to perform deep dewaxing while keeping the renewable molecules in the liquid jet. Topsoe has a best-in-class dewaxing catalyst for this purpose, the TK-930 D-wax, which has shown optimal results in our pilot-scale demo and is being deployed industrially in various sites.

How does co-processing affect catalyst life and performance?

Renewable feedstocks often contain higher levels of contaminants, such as metals, which can accelerate catalyst deactivation. Added to that, the replacement of some of the catalyst volume for dewaxing catalyst will impact the original cycle length of the unit.

As a result, catalyst life may be shorter and more frequent regeneration or replacement may be required. Careful feedstock selection, pretreatment and process monitoring are essential to optimize catalyst performance.

Are process conditions such as temperature and pressure significantly different?

Process conditions may need to be adjusted; higher temperatures, increased hydrogen-to-oil ratio and modified liquid hourly space velocity are often required to ensure complete deoxygenation and maintain throughput. The exact parameters depend on feedstock composition, desired product yield and unit configuration.

Execution and Scalability 

How scalable is co-processing for larger SAF mandates?

Co-processing is highly scalable for initial SAF production and is ideal for meeting early-stage blending mandates.

However, scalability is ultimately limited by regulatory blending caps and the capacity of existing refinery units. For higher SAF penetration, refineries may need to expand co-processing across multiple units or consider hybrid approaches that combine co-processing with dedicated renewable units.

Co-processing remains the fastest and most cost-effective route to scale SAF production in the near term.

What support does Topsoe provide during co-processing implementation?

Topsoe provides end-to-end support for co-processing projects, including feasibility studies, process design, catalyst selection, unit optimization and ongoing technical assistance. This collaborative approach ensures that refineries can confidently and efficiently transition to renewable fuel production.

Since 2004, Topsoe has been helping refiners to produce renewable fuels. One-third of SAF globally is produced with Topsoe solutions, with its HydroFlex technology having more than 70 commercial references worldwide.