Rapid gas chromatography – mass spectrometry profiling of small organic molecules in biomass pyrolysis: a simple and industry-ready approach for process optimisation

Abstract

Biomass pyrolysis is a sustainable process that converts organic matter into valuable products including biochar, bio-oil, and syngas. Depending on the type of biomass, its age, moisture content, and the process conditions, the composition of the resulting mixture can vary significantly. Quantifying compositional changes during pyrolysis is essential for improving product quality, ensuring process efficiency and recovering by-products for conversion into value-added products, thus enhancing sustainability. This study presents a novel gas chromatography-mass spectrometry (GC-MS) method to identify and quantify volatile organic compounds released during pyrolysis, namely formaldehyde, methanol, acetic acid, and formic acid. The method features simple sample preparation and achieves baseline separation of target analytes using a DB-WAX-UI column in under 15 minutes. Data acquisition was conducted in both selected ion monitoring (SIM) mode to obtain high sensitivity for targeted analytes and full scan mode to facilitate untargeted monitoring. Achieved instrumental LODs were 0.09, 0.04, 0.02, and 0.03 μg mL⁻¹ for formaldehyde, methanol, acetic acid, and formic acid, respectively. Intra- and inter-day repeatability was always better than 5% and 12%, respectively. The method was applied for the analysis of 141 samples collected from two sampling points at a local biomass pyrolysis facility over a period of 7 months, providing insights into the changes in the analyte profile during this period. The results demonstrate that this GC-MS method is a simple, fast, industry ready method, able to provide additional valuable insights into product quality for the purpose of process monitoring and optimisation.