Carbon isotopes in wood combustion/pyrolysis products: experimental and molecular simulation approaches

Abstract

A series of laboratory experiments was performed to determine the carbon stable isotopic composition of different combustion/pyrolysis (B/P) products. Variation in the δ13C 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 δ13C 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 δ13C 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 paleoenvironmental proxy or as an isotopic characteristic for the identification of source material.

Chronostratigraphy of Jerzmanowician. New data from Koziarnia Cave, Poland

“…Another explanation for the observed discrepancy between the dates achieved from bones and at least some dates achieved from charcoal, includes the altered 14 C content in charcoal fragments. From recent study [70] we know that carbon in wood during the high temperature processing (such as burning) is a subject to kinetic fractionation of isotopes. Namely, charcoal from coniferous wood burned in low temperatures is enriched in heavy carbon and oppositely, burned in higher temperature (400-600 °C) is depleted in heavy carbon in relation to the original wood.…”