Fuel Blend Analysis using the Cary 630 Spectrometer and 5 Bounce ZnSe ATR accessory

Importance of the Topic

Demand for sustainable energy sources has driven the integration of biofuels into conventional fuels. Higher alcohols such as 1-butanol offer advantages over ethanol, including lower hygroscopicity, higher energy density and compatibility with existing engines. Understanding blend composition and molecular interactions is essential to ensure fuel stability, engine performance and to prevent phase separation in storage.

Objectives and Study Overview

This study evaluates the capability of attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) to quantify and characterize blends of 1-butanol with a hydrocarbon surrogate (n-decane) and commercial diesel. Key aims are to:

• Establish spectroscopic signatures of pure components and blends across full concentration ranges.
• Investigate molecular mixing effects, particularly hydrogen-bonding interactions.
• Develop and validate a Partial Least Squares Regression (PLSR) model for accurate butanol quantification.

Methodology and Instrumentation

Samples of 1-butanol (99.5 %) were blended with n-decane and diesel in 10 % increments by mole or mass. Spectra were recorded on an Agilent Cary 630 FTIR spectrometer fitted with a 5-bounce ZnSe ATR accessory, covering 4000–650 cm⁻¹ at 2 cm⁻¹ resolution. The compact Cary 630 and Microlab software facilitated rapid background collection, automatic accessory recognition and user-guided analysis. Data processing included baseline correction and chemometric modelling via PLSR to correlate spectral features with butanol content.

Key Results and Discussion

Spectrum series of butanol/n-decane blends exhibited systematic shifts in the OH–stretch band (~3300 cm⁻¹). A pronounced blue-shift upon adding n-decane indicates strengthened OH bonds due to diminished hydrogen bonding among butanol molecules. Diesel blends revealed additional C=O stretching peaks at ~1750 cm⁻¹ (free ester) and ~1728 cm⁻¹ (hydrogen-bonded ester), reflecting dipole interactions with butanol. PLSR models achieved excellent linear correlation between predicted and actual butanol concentrations, demonstrating the method’s quantitative accuracy.

Benefits and Practical Applications

• Rapid measurement in seconds with no sample preparation or consumables.
• Non-destructive molecular fingerprinting enabling both qualitative and quantitative analysis.
• Minimal bench footprint and robust design suited for routine QA/QC and field deployment.
• High sensitivity via multi-bounce ATR, outperforming single-bounce systems.

Future Trends and Potential Applications

Advancements may include:

• Integration of inline ATR-FTIR sensors for on-board fuel monitoring.
• Extension to complex multi-component fuels, including biodiesel and alternative alcohols.
• Development of real-time chemometric algorithms embedded in portable instruments.
• Coupling with process simulators to predict blend stability and engine emissions.

Conclusion

The Agilent Cary 630 with a 5-bounce ZnSe ATR accessory and PLSR chemometrics provides a fast, reliable and non-destructive approach to quantify 1-butanol in hydrocarbon and diesel blends. Spectral shifts reveal fundamental mixing interactions, and the method meets industry requirements for precision and ease of use.

References

1. Lampe AI, Dittmar AK, Heyen C, Kiefer J. Butanol as potential biofuel: A spectroscopic study of its blends with n-decane and diesel. Fuel. 2018;222:312–318.