Improving Renewable Diesel Pretreatment Filtration with High-Permeability Silica-Gel Adsorbents

Miguel Monsanto and Arnold Wong
1 hour ago
3 min read

Figure 1: Filtration rate comparison for Sorbsil® R60F vs. ABE in laboratory testing. (Source: PQ Corp.)

High solids loading and rising differential pressure can make bleaching filtration the throughput-limiting step in renewable diesel pretreatment. Sorbsil® R60F improves filtration rate while maintaining phosphorus and total-metals control vs. activated bleaching earth, with measurable yield benefits from lower spent-cake oil retention.

Feedstock pretreatment is a critical step in renewable diesel production, using degumming and bleaching to remove catalyst poisons from crude fats, oils and greases before hydrotreating. During bleaching, adsorbents reduce metals, phosphorus and other trace contaminants via adsorption and filtration to meet hydrotreater-catalyst specifications. Silica-gel adsorbents such as Sorbsil® are selected where operators need both consistent contaminant control and strong filterability.

Filtration as the Bottleneck

In renewable diesel pretreatment, filtration capacity is often the practical bottleneck: rising differential pressure, frequent cake discharge and short cycle times can limit throughput while increasing labor and waste-handling costs. Sorbsil® R60F is a high-permeability silica-gel adsorbent engineered to maintain contaminant-removal performance while enabling higher filtration rates and longer filter cycles.

In laboratory testing vs. activated bleaching earth (ABE), Sorbsil® R60F delivered a 35 percent higher filtrate rate (Figure 1). At the same time, the data presented below show that equivalent phosphorus and total-metals reduction can be achieved at a lower dosage rate, reducing catalyst-poison carryover to downstream hydrotreating.

Figures 2a-2b: Phosphorus removal and total-metals removal vs. dosage rate for Sorbsil® R60F compared with ABE in RTB oil. (Source: PQ Corp.)

Performance Data: Phosphorus, Metals Control at Lower Dosage Rate

In ready-to-bleach (RTB) oils, performance data indicate that Sorbsil® R60F achieved contaminant reduction comparable to ABE at a lower dosage rate: 0.8 percent for Sorbsil® R60F vs. 1.2 percent for ABE for both phosphorus and total metals (Figures 2a and 2b). The following is a summary of the test conditions:

Feed: RTB oil.

Adsorbents compared: Sorbsil® R60F vs. ABE.

Dosage rates highlighted: 0.8 percent (Sorbsil® R60F) vs. 1.2 percent (ABE).

Reaching equivalent endpoints at lower dosage can reduce solids loading to the filter and improve filtration stability.

Yield, Waste Implications: Spent-Cake Oil Retention

In addition to throughput, spent-cake oil retention is a direct yield lever. Under the dosage conditions shown, Sorbsil® R60F exhibited approximately 1.5 kilograms (kg) of oil loss per metric ton (MT) of oil produced, compared with approximately 4 kg/MT for ABE. Lower oil retained in the cake reduces product loss and lessens the volume burden associated with disposal.

Operational Takeaways

For operating teams, the decision typically comes down to how an adsorbent affects filtration capacity, yield, waste generation and downstream catalyst protection. Practical takeaways associated with high-permeability silica-gel adsorbents such as Sorbsil® R60F include:

Higher permeability supports longer filter cycles and higher effective filtration capacity, reducing interruptions for cake discharge.

Comparable phosphorus and total-metals removal at lower dosage rates vs. ABE, helping protect downstream hydrotreating catalysts.

Lower solids addition can reduce filter-cake generation, decreasing waste handling and disposal costs.

Lower oil retention in spent cake helps improve overall yield and reduces value loss to waste.

In many applications, operation without body feed is possible, simplifying dosing and improving filterability.

Reduced catalyst poisons in pretreated oil can extend catalyst run length and stabilize unit performance in renewable diesel service.

Conclusion

For renewable diesel pretreatment trains constrained by filtration capacity, high-permeability silica gel offers a practical lever to increase run time and stabilize operations without trading off contaminant control. In RTB oils, Sorbsil® R60F demonstrated phosphorus and total-metals reduction comparable to ABE at a lower dosage rate (0.8 percent vs. 1.2 percent) while also reducing spent-cake oil retention (approximately 1.5 kg/MT vs. 4 kg/MT). Taken together, these outcomes indicate a pathway for higher effective throughput, improved yield and a lower waste-handling burden—supporting longer and more consistent hydrotreating-catalyst performance. In practice, the best fit is confirmed through a short plant trial that tracks filter differential pressure and cycle time alongside dosage rate, cake generation/oil retention, and outlet phosphorus/metals vs. catalyst-performance targets.

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