Effects of CO2 on submicronic carbon particulate (soot) formed during coal pyrolysis in a drop tube reactor.

In oxycombustion and gasification processes coal pyrolysis occurs in CO 2 -rich atmospheres. The present work investigates the effect of such conditions on the quantity and quality of the submicronic carbon particulate produced. Pyrolysis experiments were carried out in either N 2 or CO 2 atmospheres in a laminar drop tube reactor, with wall temperatures of 1573 K, heating rates of 10 4 –10 5 K/s and residence times below 130 ms, so as to reproduce pyrolysis conditions comparable to those of pulverized coal-fired boilers. The carbon particulate sampled in the reactor was found to have bimodal distribution in the micronic and submicronic ranges. A method based on solvent extraction was applied to carbon particulate for separating the two modes and determining the relative mass contribution of micronic and submicronic fractions. In CO 2 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 N 2 experiments. 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 CO 2 environment in respect to N 2 environment were observed by means of a large array of techniques including thermogravimetry, microscopy (SEM+EDX), FT-IR, UV–visible and Raman spectroscopy along with XRD and XPS techniques. [ABSTRACT FROM AUTHOR]