Analysis of elemental contaminants in renewable fuel feedstocks

Importance of topic

As global efforts intensify to reduce greenhouse gas emissions, biofuels derived from plant and animal feedstocks have emerged as critical renewable energy sources. Monitoring trace elemental contaminants in these feedstocks is essential to protect catalyst performance during hydrotreating, ensure product quality, minimize equipment fouling, and optimize process economics.

Study objectives and overview

This work presents an approach for quantifying trace metals in renewable fuel feedstocks from a major refinery. It evaluates inductively coupled plasma–optical emission spectroscopy (ICP-OES) and ICP–mass spectrometry (ICP-MS) techniques, focusing on method robustness, detection limits, sample throughput, and practical considerations for routine monitoring in a production environment.

Methodology and instrumentation

The hydrotreating process converts plant/animal oils into hydrocarbons using metal catalysts prone to deactivation by contaminants. To analyze trace impurities, two main platforms were applied:

• ICP-OES (Thermo Scientific iCAP PRO Series XPS Duo): full-range UV/Vis detection (iFR mode), Ultra Violet (eUV) mode, dual axial/radial torch, detection of elements from sub-μg·L⁻¹ to % levels in 1–5 min per sample.
• ICP-MS (Thermo Scientific iCAP Qnova Series TQ ICP-MS and iCAP RQ SQ ICP-MS): triple quadrupole mode with O₂ reaction gas for interference removal, single quadrupole mode with kinetic energy discrimination, 2–3 min analysis time, detection limits down to ppt/ppq.

The Teledyne CETAC ASX-7400 stirring autosampler with heated sample lines and organic-resistant tubing facilitated handling of high-viscosity feedstocks and reproducible dilution protocols using kerosene or PremiSOLV™ solvents.

Main results and discussion

ICP-OES limits of detection for key elements (As, P, K, Ca, Fe, Mg, etc.) reached low μg·kg⁻¹ levels in both axial and radial views. The eUV mode enhanced sensitivity for analytes in the 167–240 nm range (e.g., Hg, S, Pb).

ICP-MS performance yielded instrument detection limits (IDLs) and background equivalent concentrations (BECs) for selected isotopes:

• 31P¹⁶O⁺: IDL 0.308 μg·L⁻¹, BEC 11.3 μg·L⁻¹ (0–200 μg·L⁻¹ range, R² > 0.9999)
• 39K⁺: IDL 0.138 μg·L⁻¹, BEC 2.10 μg·L⁻¹ (R² = 0.9996)
• 75As¹⁶O⁺: IDL 0.006 μg·L⁻¹, BEC 0.05 μg·L⁻¹ (R² = 0.9999)

Spike-recovery experiments on soy feedstock (20 μg·L⁻¹ spike) demonstrated quantitative recoveries (P 106 %, K 90 %, As 108 %), confirming method accuracy.

Practical benefits and application

The combined ICP-OES/ICP-MS workflow offers rapid multi-element screening, broad dynamic range, low detection limits, and minimal sample preparation. Early detection of catalyst-poisoning metals enables targeted pretreatment, reduces downtime, and optimizes catalyst replacement schedules, delivering cost savings and process reliability.

Future trends and potential applications

Advances may include automated sample-handling integration, real-time monitoring of feedstock impurities, expanded speciation analysis, and miniaturized or portable ICP systems for on-line refinery control. Continued development of reaction-cell chemistries and high-throughput autosamplers will further enhance sensitivity and sample throughput.

Conclusion

Robust ICP-OES and ICP-MS methods enable accurate, sensitive, and rapid determination of trace metals in renewable fuel feedstocks. Implementing these techniques supports catalyst protection, product quality assurance, and cost-effective refinery operations in the biofuel industry.

Reference

Product Spotlight 44485: Thermo Scientific iCAP Qnova Series ICP-MS – PLUS Torch for improved ICP-MS analysis of challenging samples.