Schematic representation of a section of typical hardwood lignin, with monolignol units, p-hydroxyphenyl (H), syringyl (S) and guaiacyl (G), highlighted in green, blue, and red, respectively. Credit: Bridget Tang et al.
Researchers at Aston University have demonstrated that benchtop NMR spectrometers can analyze pyrolysis bio-oils as accurately as their significantly more expensive high-field counterparts. Benchtop spectrometers will make analysis cheaper and more accessible to a range of new users.
Bio-oils that result from the pyrolysis of agricultural or industrial byproducts are often seen as a potential alternative to fossil fuels. However, their stability and treatment depend on their composition, something that can be costly to analyze given that they are often made up of hundreds of different compounds.
“The composition of any pyrolysis bio-oil is absolutely key to future use,” said Dr Robert Evans, Senior Lecturer in Physical Chemistry at Aston University. “For example if there are oxygen-containing chemicals in the oil, that will make the oil more corrosive and it will be more unstable. So in particular we need to know if carbonyl groups are present - where oxygen and carbon atoms are bonded together - as these can have a major impact.”
Current analysis methods include high-field NMR spectroscopy. High-field NMR provides excellent results, however, these instruments can cost anywhere from $650,000 to $ 10 million. High-field NMR also requires a constant supply of cryogens and solvents which increase their operational costs. Due to the costs, high-field NMR instruments are typically only found at the largest research facilities around the world.
In the study, published in ChemSusChem, the researchers set out to evaluate benchtop NMR spectrometers as an alternative source for bio-oil analysis by comparing their data to that of the high-field models. Benchtop NMR spectrometers are significantly cheaper and do not require cryogenic cooling which further reduces the operational cost of the instruments at the cost of lower sensitivity and resolution.
The researchers found that the benchtop models not only compared favorably to titration analysis for carbonyl content but also to high-field spectrometers for specific identification of carbonyl groups.
“Despite the known limitations of benchtop spectrometers, a very similar quality of NMR data could be obtained for these samples, enough to accurately estimate concentrations of different classes of carbonyl-containing species,” said Dr Evans. “Using benchtop spectrometers will make NMR analysis of pyrolysis oils much simpler, cheaper, and more accessible to a wider range of different users.”