The TRISYL® Silica Advantage for Renewable Feedstock Pretreatment
Transportation—including cars, airplanes, and everything in between—accounts for approximately 21% of global carbon emissions. To help meet carbon neutrality and Net Zero targets established by the United Nations, many refiners are exploring the production of biomass-based diesel fuels, such as biodiesel, renewable diesel, and sustainable aviation fuel (SAF).
Typically made from lipid-based waste like animal fats, used cooking oil, and distillers' corn oil, renewable diesel and SAF offer a sustainable, drop-in alternative to petrochemical-based fuels. This is particularly important in aviation where, unlike with land-based transportation, electric-powered commercial alternatives are not yet a viable option to avoid CO2 emissions.
Removing Feedstock Impurities with Pretreatment
But there is a catch: these lipid-based feedstocks can contain elevated concentrations of untraditional impurities, such as phosphorus and specific metals, that can diminish a refinery’s productivity. "In petroleum feedstocks, these contaminants are typically low," says Chelsea Grimes, global strategic marketing manager at Grace. "But now that we are looking at bio-based feedstocks, the range and variability of impurities from one feedstock source to the next is significant.”
If left alone, these impurities can severely impact the refinery’s operations. For example:
Phosphorous compounds can polymerize inside reactors at high temperatures, which can lead to problems with clogging, fouling, and pressure drops.
Calcium can precipitate, leading to a buildup of scale in reactors and piping.
Magnesium, sodium and other reactive metals can poison the catalyst and hinder active sites needed to convert bio-based oils into renewable fuels.
Together, these impurities can significantly reduce the lifespan of hydroprocessing catalysts and increase the amount of maintenance needed for a continuous operation. “If you think your catalyst is supposed to last two years, it might only last six months or one year if there is insufficient pretreatment,” Grimes explains. Replacing the catalyst is expensive—not just because of costs for the catalyst itself but because replacement typically requires a pause in refining operations and specialized utilities.
Hydroprocessing catalyst technology licensors understand the nuances of processing bio-based oils and therefore have set feedstock specifications for phosphorus and various metals components. If a refiner does not pretreat the feedstock sufficiently, the catalyst technology licensor might not guarantee the performance.
To assure optimal performance of hydroprocessing catalysts used in renewable fuel production, feedstock pretreatment is essential. Traditionally, renewable diesel and SAF producers add activated clay (also known as activated bleaching earth) to the feedstock to adsorb impurities. The mixture is then filtered to remove the clay particles, and the purified oil proceeds downstream to the hydroprocessing catalytic reactors to convert the oil to fuel.
Activated clay typically has a surface area around 300 m2/g, requiring dosages up to 2.5 w/w% to control impurity levels and meet catalyst technology licensor specifications. The logistics of purchasing large amounts of clay and managing the resulting mounds of solid waste can pose a great burden to renewable diesel and SAF producers.
TRISYL® Silica Adsorbents: An Alternative for Reducing Pretreatment Waste
Recognizing the disadvantages to pretreating feedstock with activated clay, the scientists and engineers at Grace developed TRISYL® silica adsorbents for biomass-based diesel pretreatment. In commercial use across numerous renewable fuel refineries around the world, TRISYL® silica has been shown to reduce solid waste generated (and therefore the cost and effort of disposal) during pretreatment by up to 85% while improving productivity and reducing the overall cost of pretreament.
TRISYL® synthetic amorphous silica does not contain hazardous crystalline silica, unlike activated clays which may contain detectable amounts. TRISYL® silica contains approximately 40% silica and 60% functional moisture, which makes it superb at adsorbing hydrophilic contaminants such as phosphorous- and metal-based species. Due to TRISYL® silica’s larger surface area of roughly 700 m2/g and thus higher adsorption capacity, refiners can achieve the same pretreatment performance as with traditional clays – but with much less adsorbent. Once TRISYL® silica adsorbs the contaminants, a vacuum dryer removes the moisture from silica, leaving behind only the solid silica portion with the impurities trapped within the particle’s porous structure.
Many renewable fuel producers are able to reduce solid waste by switching from clay adsorbents to Grace’s TRISYL® silica for pretreatment because it is an adsorbent with a lower solids content and is utilized at an overall lower dosage. As total waste is reduced, so is the environmental impact of renewable fuel production which may ultimately decrease the fuel’s carbon intensity (CI) score. With a lower CI, biofuel producers may be entitled to tax incentives or other financial benefits, depending on local regulations and programs.
Reducing solid waste also decreases the amount of oil lost during pretreatment. "When using an adsorbent, all spent filter cake waste will have residual feedstock attached to it," Grimes says. "With TRISYL®, there is less feedstock lost during pretreatment because there is significantly less solid waste generated than with activated clay." Retaining more feedstock in the fuel refining process allows refiners to increase yields of renewable diesel and SAF without the need to secure additional feedstock.
As renewable diesel and SAF become primary sources of fuel for road and aviation transportation across the globe, renewable fuel producers can count on Grace’s TRISYL® silica to help minimize their environmental footprint, enhance material handling safety, and improve overall productivity and efficiencies.