Feedstock focus

Chelsea Grimes, global strategic marketing manager at Grace, outlines how the company has been supporting the biofuels industry.

Can you outline Grace’s solutions for biofuels and SAF?
Let me start by saying that Grace is one of the leading global suppliers of speciality chemicals and solutions that enable industries to enhance modern life. To that end, we have been supporting the biofuels sector for over 60 years, helping to innovate new and improved renewable production processes. Today, we offer a range of biofuel and SAF solutions — from silica adsorbents for feedstock pretreatment to molecular sieves for ethanol dehydration and hydroprocessing catalysts. One of our flagship products, TRISYL®, is a synthetic amorphous silica adsorbent that helps refiners reduce impurities in a variety of feedstocks down to trace levels during pretreatment. It is used for renewable diesel, sustainable aviation fuel, and first-generation biodiesel, and its specially engineered structure helps it adsorb polar contaminants and prolong catalyst life. TRISYL® silica may reduce solid waste from pretreatment by up to 85%, while improving productivity and reducing the overall cost of pretreatment. TRISYL® is a synthetic hydrogel, containing roughly 60% moisture and 40% pure amorphous SiO₂. Due to its chemical and physical properties, polar contaminants in the feedstock have a higher affinity to TRISYL®, and the risk of metals leaching back into the feedstock is reduced compared to bleaching earth (BE) adsorbents. Another advantage is that it does not contain detectable levels of crystalline silica, unlike BE, making it a safer alternative for material handling purposes. We have also been manufacturing molecular sieves for ethanol dehydration since the 1970s. Today, our SYLOBEAD® molecular sieves dry ethanol produced from edible feedstocks, cellulosic feedstocks, and synthetically produced ethanol. One of our newer innovations is EnRich® catalysts from Advanced Refining Technologies (ART), a Chevron and Grace joint venture, which acts as a “drop in” solution for hydrotreating feedstocks into renewable fuels.

What are some of the challenges when it comes to producing SAF? Is there enough feedstock to go around?
Producing SAF comes with its challenges, especially when it comes to feedstocks. Right now, there are limited amounts of lipid-based feedstocks available to turn into fuel making it difficult to source enough oils, fats and grease to consistently feed your refinery. This can be resolved either by uncovering new feedstock sources, or by retaining more feedstock during the refining process. That’s where our TRISYL® silica adsorbent comes in. It helps refiners achieve the same level of feedstock purity with a lower adsorbent dosage than alternative methods by introducing fewer solids and generating less filter cake waste — so less oil is lost in the process. Feedstock flexibility is another issue. The quality and source of feedstock can change daily, but that shouldn’t impact the refining processes if you have a pretreatment process that is compatible with a range of feedstock sources. Depending on the oil and fat used, contaminant levels can also vary widely – a highly efficient pretreatment process should be able to remove impurities without leaching any back into the feedstock. Most pretreatment technologies have been adapted from the edible oil industry and often use BE adsorbents, which often result in a large amount of solid waste. Managing the logistics of purchasing large amounts of clay and disposing of the resulting mounds of solid waste can be a challenge. As colour is not a specification for non-edible oils, BE is not necessary to use as an adsorbent for renewable fuels. TRISYL® silica’s larger surface area of roughly 700 m2/g and higher adsorption capacity mean refiners can achieve the same pretreatment performance as with traditional clays, but with much less adsorbent.

What types of feedstocks are compatible with TRISYL® silica adsorbents?
TRISYL® silica adsorbents have been utilised globally in the refining of plant oils and fats for the past 40 years. They can remove polar and ionic contaminants, such as some phosphorus- and metal based species, down to trace levels, and can be used in all HEFA pretreatment units utilising lipid-based feedstocks such as used waste oils, cover crops and other novel oils. When introduced into a non-polar environment such as triglycerides, partial glycerides, and fatty acids, TRISYL® silica’s hydrogel composition and hydrophilic surface area of over 700 m²/g creates a strong affinity for polar compounds, efficiently adsorbing impurities and improving the feedstock’s suitability for SAF production.

Do you think that the cost of producing SAF can come down and, if yes, how?
I do. The cost of producing SAF is expected to decrease over time as production technologies develop at scale and mature, regardless of the pathway used. Of the four main pathways — hydroprocessing esters and fatty acids (HEFA), alcohol-to-jet (AtJ), biomass-to-liquids (BtL), and power-to-liquids (PtL) — I believe HEFA will likely remain the most cost-competitive route to SAF until 2050, with most production costs linked to lipid-based feedstocks. Choosing the right adsorbent for feedstock pretreatment can also help contribute to a lower total cost of ownership for the refinery. For instance, TRISYL® silica adsorbents help retain more feedstock in the refining process, lowering feedstock costs. TRISYL® silica’s adsorption capacity is not hindered by feedstock qualities such as free fatty acids, enabling refiners to use a variety of feedstocks, including waste streams and cover crops that natural silica adsorbents cannot purify.

Can you describe your feedstock pretreatment processes for SAF?
Pretreatment is especially critical for renewable fuels like renewable diesel and sustainable aviation fuel. Compared to traditional crude oil, lipid-based feedstocks often contain elevated concentrations of uncommon impurities, such as phosphorus and metals, which must be removed to prevent impacts on the refinery’s catalyst and downstream operations. Pretreatment also ensures a variety of feedstocks can be used, regardless of their source and initial contaminant level.
It is a multi-step process, similar to how the edible oil industry has been refining oils for decades:
• Feedstock blending: Feedstocks are blended depending on supply availability. This often includes two or three different sources, but blends can involve up to eight or more.
• Straining: Depending on the source, feedstocks may contain plastics, bone fragments, or other particulates, which are removed through a series of strainers.
• Acid conditioning: The feedstock blend is conditioned with a mild acid, usually citric acid, to chelate metals and phospholipids, causing them to precipitate out of the matrix.
• Caustic treatment/water washing: This optional step, depending on contamination levels, can remove up to 75% of phosphorus and metals after water washing — though additional treatment is needed to protect downstream processes.
• Impurity adsorption: The critical step for removing remaining phosphorus and metals down to trace levels (3 ppm and 7 ppm, respectively). In a slurry tank, an adsorbent material such as TRISYL® silica is added to adsorb residual impurities. Its high functional moisture content, large surface area and high purity enable efficient attraction of polar contaminants without leaching metal oxides back into the feedstock.
• Vacuum and filtration: A vacuum removes moisture from the adsorbent/feedstock mixture, after which solids and contaminants are filtered out. TRISYL®’s mass shrinks to about 40% of its original amount during drying, introducing fewer solids into the filter and minimising feedstock loss. This extends filter cycles and increases renewable diesel and SAF yields. Hydroprocessing catalyst technology licensors set strict specifications for phosphorus and various metals. The adsorbent must be capable of treating a wide range of contaminants. If feedstock is not sufficiently pretreated, catalyst licensors may not guarantee performance. There is no one-size-fits all solution for pretreatment — it depends on the specific refinery setup, production capacities, feedstock sources and impurity levels. We work closely with customers to collect and analyse feedstock samples to determine optimal adsorbent dosage levels.

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