Double-shot pyrolysis of the non-hydrolysable organic fraction isolated from a sandy forest soil (Landes de Gascogne, South-West France). Comparison with classical Curie point pyrolysis

Abstract

Double-shot pyrolysis was performed on the insoluble, non-hydrolysable, macromolecular material isolated from a sandy forest soil of Cestas (Landes de Gascogne, France). Analysis of the pyrolysates showed conspicuous differences between the first and the second shot regarding the nature and/or the distribution of the numerous products generated. The non-hydrolysable material thus appears to exhibit a complex, heterogeneous, composition, including various types of tightly trapped compounds not released by extraction (n-alkanes, n-alkenes, n-alkanones and, probably, some fatty acids) and of biomacromolecules (cellulose, lignin, cutans/suberans and condensed tannins). Some moieties (chlorophyll-derived isoprenoid moieties, esterified fatty acids and other lipids) are also covalently linked to the macromolecular structures. Most of these components originate from higher plants and exhibit low to moderate alteration owing to the efficient steric protection provided by the macromolecular network. Important differences in thermal stability were also observed between the components of the non-hydrolysable material and some of these components (lignin, cellulose, isoprenoid moieties and esterified fatty acids) are thermolabile. Double-shot pyrolysis thus afforded important additional information, on the composition, origin and nature of the hydrolysis-resistant fraction of the Cestas soil, compared to classical Curie point pyrolysis.