Comparative analysis of pyrolysate from herbaceous and woody energy crops by Py-GC with atomic emission and mass spectrometric detection

On-line pyrolysis-gas chromatography combined with mass spectrometric (Py-GC-MS) and atomic emission detection (Py-GC-AED) were applied to study the pyrolytic behaviour of different biomass proposed as feedstock in biofuel production (poplar, sweet sorghum, corn stover and switchgrass). Results were reported in terms of carbon yields of organic fractions (Py-GC-AED) and individual pyrolysis products (Py-GC-MS). Global carbon yields of gas and semi/volatile compounds were determined from the chromatograms of Py-GC-AED. The relatively non-volatile fraction eluding GC elution and the solid residue left after pyrolysis (char) were determined by weighting the quartz tube after each Py-GC-AED experiment. The semi-volatile fraction and non-volatile matter were assumed to compose the final bio-oil. The yield of semi-volatile ranged from 26% (poplar) to 19% (corn stover), while gas yields were similar for all biomass types (10-11% on carbon basis). Py-GC-MS was conducted in the presence of an internal standard (o-isoeugenol) in order to quantify principal lignin phenols along with hemi/cellulose degradation products. Acetic acid and hydroxyacetone were the main pyrolysis products with similar yields for all tested biomass. Herbaceous biomass provided 4-vinylphenol and 4-vinylguaiacol as most intense lignin monomers, while sorghum pyrolysate was featured by high yields of 5-hydroxymethyl-2-furaldehyde. In comparison to herbaceous biomass, poplar was predicted to produce high yield of organic bio-oil rich in lignin monomers and with a lower content of non-volatile matter. Among herbaceous biomass, switchgrass was characterised by the lowest ash and nitrogen content and a highest production of bio-oil.