Insights on the role of secondary tar reactions in soot inception dur-ing fast pyrolysis of coal

Coal pyrolysis has been studied extensively for more than a century. However, due to complexity of the chemistry and of transportation phenomena involved, no general mechanism is universally accepted, nor all observations can be accounted for by any single model [1]. Recent work from a collaboration of Bochum and Naples addressed the influence of environment gas atmosphere (N2 and CO2) on the early products of fast pyrolysis in a DTR at 1573 K of a high volatile bituminous coal [2]. As regards the char, it was found that the CO2-char exhibited a lower reactivity compared to the N2-char. Moreover, in CO2 atmosphere the amount of submicronic fraction of carbon particulate, referred to as soot, was found to be up to four times as much as upon N2 experiments [3]. Beside the larger formation of soot, relevant differences in terms of combustion reactivity, size distribution and chemical structure of the residual carbon particulate produced in CO2 environment with respect to N2 environment were observed [2]. The present paper reports data on the tar produced in the fast pyrolysis of the same coal in a DTR and also in a heated strip reactor (HSR). In the DTR particles heat up and pyrolyze in a hot gas environment. Differently, in the HSR the particles heat up on a hot carbon foil, the surrounding gaseous environment being at nearly ambient temperature. As a consequence, volatile pyrolysis products are released in a hot environment in the DTR and in a cold environment in the HSR, determining different paths of volatile matter evolution