CARBON ISOTOPES IN WOOD COMBUSTION/PYROLYSIS PRODUCTS: EXPERIMENTAL AND MOLECULAR SIMULATION APPROACHES

A series of laboratory experiments was performed to determine the carbon stable isotopic composition of different combustion/pyrolysis (B/P) products. Variation in the delta C-13 values of the products was observed, up to 4%. The differences in the carbon isotopic compositions of the B/P products were dependent on temperature, time and wood type. Comparison of the results for fresh and fossil oak wood suggested that the delta C-13 differences were the effect of selective decomposition of some wood components during the fossilization process. The temperature dependence of the carbon isotopic composition was linked to variation in the carbon isotopic composition of the main wood components, which each had different levels of thermal stability. Isotopes exchange reactions in between different products can be also considered as possible source of variation of delta C-13 on temperature. Both these hypotheses were supported by molecular simulations of cellulose and lignin B/P. The results confirm that B/P should be treated as a continuous process, where the results depend on the degree of process development. Natural burning processes are dynamic and burning conditions change rapidly and it is necessary to take care when using combustion products as a paleoenviron-mental proxy or as an isotopic characteristic for the identification of source material.