Advanced analytical techniques for bio‐oil characterization

Abstract

Bio-oil (pyrolysis oil) is the liquid product of biomass thermochemical conversion. It is a dark, viscous liquid that contains the depolymerization products of hemicellulose, cellulose, and lignin. The physicochemical properties of bio-oils are determined by employing the conventional methods for fuels analysis with proper adaptations. However, the detailed composition of bio-oils in terms of analytes as well as their concentration remains ambiguous and is a challenging task for analytical chemistry. The compounds in the bio-oil range from nonpolar (e.g., hydrocarbons) to highly polar (e.g., phenolics) and from volatile (e.g., organic acids) to nonvolatile (e.g., sugar derivatives), covering a molecular weight (MW) range of about 50-2000 Da. Hence a combination of analytical techniques such as high pressure liquid chromatography, gas chromatography (GC), gel permeation chromatography (GPC), nuclear magnetic resonance spectroscopy (NMR), and Fourier transform infrared spectroscopy (FTIR) are required to determine the bio-oil's composition. Despite the significant breakthroughs of these techniques, they face limitations regarding the sample pretreatment, the incomplete separation and determination of components, and the need of multiple analyses with each method for more complete results. The development of sophisticated, comprehensive, and hyphenated chromatographic and spectrometric techniques such as GC × GC, LC × LC, high-resolution mass spectrometry (HRMS), and 2D-NMR has brought actual advancement in the field of bio-oil analysis. GC × GC and LC × LC have allowed the development of qualitative and quantitative methods for the individual determination of lower MW compounds. However, HRMS and 2D-NMR have facilitated the elucidation of the structure of the higher MW components, offering insight in the effect of pyrolysis conditions on biomass depolymerization and the possibilities for further upgrading of bio-oils.

Combination of electrospray ionization, atmospheric pressure photoionization and laser desorption ionization Fourier transform ion cyclotronic resonance mass spectrometry for the investigation of complex mixtures – Application to the petroleomic analysis of bio-oils

“…It appeared that formulae were specific to ESI, and to LDI in the best conditions. Finally, as (−) ESI has been the only ionization method in most bio-oil analyses [22], it is clearly demonstrated here that this strategy nearly highlights 1250/4500 elemental formulae corresponding to less than 28% of the total bio-oil components.…”

“…Indeed, pyrolysis bio-oil components are too oxygenated to allow their direct use as a fuel and require catalytic treatment to remove the main part of the oxygen atoms. Exhaustive and accurate characterization is required to improve, the pyrolysis process itself and the catalytic treatment efficiency [21][22][23][24]. This can be achieved through application of the petroleomic non-targeted approach with FT-ICR MS [25][26][27] or FT-Orbitrap MS [28,29], whereby a part of the total composition of bio-oil can be elucidated.…”

Measuring biomass fast pyrolysis kinetics: State of the art

“…A common problem in biomass pyrolysis is the complexity of product spectra. The two‐dimensional chromatographic techniques, such as GC × GC and LC × LC (LC: liquid chromatography), have improved chromatographic resolution when compared to their single‐dimensional counterparts (Bahng et al, ; Carpenter et al, ; Kanaujia et al, ; Michailof et al, ; Negahdar et al, ; Toraman et al, , Toraman, Franz, et al ). For example, a simple GC system can separate the bio‐oil components based on either their boiling point or polarity depending on the stationary phase of the column used.…”

Recent research progress on bio‐oil conversion into bio‐fuels and raw chemicals: a review

“…An appropriate quantification requires other techniques, such as liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FTIR), and more accurate techniques (e.g. GCxGC, LCxLC, high‐resolution mass spectrometry (HRMS) and 2D‐NMR) …”