Comparison of gas and kerosene oils chemical composition before and after hydrotreating using comprehensive two-dimensional gas chromatography

Význam tématu

In the global push for cleaner fuels and tighter environmental standards, understanding the detailed chemical makeup of diesel precursors is critical. Gas oil and kerosene streams contain a complex mixture of hydrocarbons and sulfur species that directly influence the efficiency of hydrotreating processes, catalyst performance, fuel quality, and exhaust emissions. By mapping these components before and after treatment, refineries can optimize conditions, minimize catalyst poisoning, and ensure compliance with ever-stricter sulfur limits.

Cíle a přehled studie

This work set out to characterize two gas oil and two kerosene samples, each before and after hydrotreating, from four commercial refinery units. The main objectives were:

• To quantify changes in hydrocarbon classes (paraffins, cycloparaffins, aromatics) induced by hydrotreating.
• To identify and measure individual sulfur compounds, with a focus on refractory dibenzothiophenes.
• To compare performance of different unit configurations, catalysts (NiMo vs. CoMo), and operating pressures.

Použitá instrumentace

The analytical platform combined three complementary techniques:

• GC×GC–FID (Agilent 8890 GC with LECO QuadJet thermal modulator) for detailed group-type hydrocarbon quantitation.
• GC×GC–SCD (Agilent 7890B GC with sulfur chemiluminescence detector) for speciated sulfur analysis.
• Monochromatic wavelength-dispersive X-ray fluorescence (Sindie + CI) for total sulfur screening.

Použitá metodika

Samples were injected in split mode and separated using dual columns with orthogonal stationary phases, employing a cryogenic thermal modulator to achieve two-dimensional separation. GC×GC–FID data were processed to assign weight percentages of n-paraffins, iso-paraffins, mono-, di- and tri-cycloparaffins, alkylbenzenes, cycloaromatics, alkylnaphthalenes, and biphenyls across carbon numbers C5–C27. GC×GC–SCD classification was validated with 42 sulfur standards and roof-tile elution patterns, enabling quantification of thiophenes, benzothiophenes, dibenzothiophenes, and higher sulfur aromatics.

Hlavní výsledky a diskuse

Hydrotreating led to:

• Complete saturation of alkenes to alkanes and reduction of mono- and diaromatics, with the most pronounced hydrogenation observed in the NiMo catalyst unit at 6 MPa.
• Removal of > 99.8 % total sulfur in gas oils and nearly 100 % in kerosenes, as confirmed by XRF.
• Persistence of hindered dibenzothiophenes—especially 4,6-dimethyl and mixed-alkyl isomers—after treatment, highlighting steric limitations in desulfurization under current conditions.

The composition of feedstocks (light cycle oil, visbreaking gas oil, straight gas oil, straight kerosene) influenced the dibenzothiophene load, with straight gas oil and light cycle oil contributing most to refractory sulfur content.

Přínosy a praktické využití metody

Comprehensive GC×GC analysis provides refinery engineers and catalyst developers with:

• Fine-grained hydrocarbon profiles to tailor hydrogenation severity and avoid over-processing or coking.
• Speciation of residual sulfur compounds for targeted catalyst improvements and process adjustments (temperature, pressure, LHSV).
• Data to support compliance with ultra-low-sulfur diesel regulations and minimize particulate or SOx emissions.

Budoucí trendy a možnosti využití

Anticipated developments include:

• Design of next-generation catalyst formulations or supports (e.g., mixed-metal sulfides, meso-microporous structures) optimized for 4,6-disubstituted dibenzothiophenes.
• Integration of real-time GC×GC monitoring in process control loops for dynamic adjustment of hydrotreating parameters.
• Exploration of complementary deep desulfurization routes (adsorptive, oxidative) to achieve near-zero sulfur levels.
• Extension of the approach to bio-derived middle distillates and alternative fuels blending.

Závěr

Comprehensive two-dimensional GC with dual FID and sulfur-selective detection delivers unparalleled insight into the fate of hydrocarbons and sulfur species during hydrotreating. The method pinpoints both the broad hydrocarbon transformations and the stubborn sulfur aromatics that evade full removal. Such detailed compositional knowledge underpins process optimization, catalyst innovation, and compliance with tightening fuel standards.