LARTC 2025 Conference Newspaper

LARTC 2025

Optimising renewable fuel feedstock pretreatment

Chelsea Grimes W. R. Grace & Co

Pretreatment is a Key to Refinery Success Policymakers worldwide are implementing stricter regulations on the transportation sector to achieve carbon neutrality and build energy security. The biofuels industry faces significant challenges as refineries look to lipid-based feedstocks to produce renewable diesel (RD) and sustainable avi- ation fuel (SAF). RD, produced by hydroprocessing fats, oils, and greases, is chemically identical to petroleum-based diesel, making it a drop- in replacement up to 100%. SAF, pro- duced in a similar manner, requires further processing to meet the stringent specifica- tions necessary for jet engine operations, and can only be a drop-in replacement for up to 50% of aviation fuel. With low carbon intensities, high blend- ing limits, and clean emissions, RD and SAF are highly attractive options to help consumers and businesses reach sustain- ability targets today. Feedstock contaminants, such as met- als and phospholipids, can affect a refin- ery’s efficiency and profitability and must be removed to ensure full utilisation of equipment and catalysts. The presence of these impurities can lead to fouling, corrosion, and catalyst poi- soning, ultimately reducing productivity and increasing operational expenses. With a flexible and efficient pretreatment pro- cess, renewable fuel producers can utilise a wide range of feedstocks based on what is readily available. Not All Adsorbents are Created Equal Feedstock cost is often the largest expense for producing RD and SAF, causing refin- eries to look at all avenues to reduce the overall cost of production, especially in their pretreatment units (PTU). In a typical pretreatment process ( Figures 1 and 2 ), the feedstocks are first blended and homogenised, followed by a series of strain- ers to remove large particulates. During ‘dry degumming,’ mixing the feedstock blend with a mild acid chelates metal contaminants prior to the adsorption step. If ‘wet degumming’ is preferred, a water washing step follows to physically remove most contaminants prior to the adsorption process. During impurity adsorption, the feedstock is sent to a slurry tank, then an adsorbent is added to remove remaining contaminants down to trace levels. The majority of catalyst technology licensors set a limit of 3 ppm for phospho- rus and 7 ppm for metals before the feed- stock can be sent to the renewable diesel unit (RDU). While SAF and RD production often begins with using activated bleaching earth (ABE), colour correction specifica- tions are not required as they are with edible oils. Additionally, phosphorus and metal specifications for pretreated feed-

Typical properties of Trisyl Silica, Trisyl 300 Silica, and ABE

Acid conditioning

Impurity adsorption

Blend feedstock

RDU

Strainers

Trisyl

ABE

300

Total volatile @ 954˚C (wt%) 65

Figure 1 Typical sequence of operations in a PTU with dry degumming

4.5

2.5

3.6-4.5

Average particle size ( µ m) Bulk density packed (g/cm 3 )

0.48

0.56 300

Surface area (m 2 /g)

700

Chemical analysis

Blend feedstock

Impurity adsorption

Acid conditioning

Strainers

Wash water

RDU

SiO 2

99.6 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

98.8 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

70.0

Na 2 O

0.3 7.9 2.4 10.1 1.6 4.2

SO 4

Figure 2 Typical sequence of operations in a PTU with wet degumming

Fe 2 O 3 Al 2 O 3 MgO CaO

10 20 30 40 50 60 70

resulting in fewer contaminants removed from the feedstock. In extreme cases, met- als from the adsorbent can leach back into the feedstock. Unlike ABE, Grace’s Trisyl ® silica is com- posed of highly pure SiO₂ with no detect- able levels of metal oxides present ( Table 1 ). Additionally, this silica has a signifi- DID you know? Switching from activated bleaching earth to Grace’s Trisyl silica adsorbent for the pretreatment of renewable feedstocks can help reduce solid waste up to 85%

Table 1

cantly larger surface area and moisture content, resulting in a much higher capac- ity to adsorb polar and ionic impurities ( Figure 3 ). Although soft vegetable oils are techni- cally adequate for RD and SAF, produc- ers are challenged with sourcing inedible waste feedstocks and creating fuels with a lower carbon intensity (CI) score. Even in severely contaminated feedstock blends, Trisyl 300 silica maintains a higher adsorp- tion capacity for contaminants than ABE, while avoiding any potential of introduc- ing metal contaminants into the feedstock ( Figure 4 ). Adsorbent dosages are much lower com- pared to ABE because of the silica’s larger adsorption capacity in both wet and dry degumming. Using less adsorbent with a lower solids content results in less solid waste generation and potentially lowers emissions related to waste disposal trans- portation. In addition, there is less feed- stock lost during the pretreatment process ( Figure 5 ), allowing for increased produc- tivity at the refinery and a reduction in environmental footprint. TRISYL Silica: Optimised Process-of-Use When used as an adsorbent for renewa- ble feedstock pretreatment, it is recom- mended to add Trisyl silica to the slurry tank under atmospheric pressure once the oil contains <0.5% moisture. If the feed- stock contains more moisture, the adsorp- tion equilibrium could be hindered, and a vacuum dryer should be installed. Once Trisyl silica is added, mix the slurry for approximately 15-30 minutes between 60 and 70ºC to allow the mix- ture to reach equilibrium and maximise the silica’s capacity to remove contaminants ( Figure 6 ). The moisture in the pores enhances adsorption by attracting polar and ionic contaminants to the surface of the hydro- philic particles.

Phosphorus remaining (ppm) 10 T risyl 300 T risyl ABE 20 30

40 50

Figure 3 Adsorption capacity of Trisyl silica, Trisyl 300 silica, and ABE in soybean oil where:

stocks are much lower for RD/SAF produc- tion than in edible oil. Notably, non-food competing feedstocks usually come at the expense of high free fatty acids (FFA) or metal contaminants. If the adsorbent introduced contains metals, the adsorption equilibrium is hin- dered, reducing the adsorption capacity,

Blend 1 with w et d egumming

Blend 2 with w et d egumming

100 120 140

T risyl 300 ABE

20 40 60 80

T risyl 300 ABE

Contaminants remaining in feedstock (ppm)

Figure 4 Adsorption capacity in various feedstock blends. Blend 1 = 30% soybean oil and 70% tallow. Blend 2 = 30% soybean oil, 30% used cooking oil, and 40% tallow