Solid state 13C and 1H NMR studies of the evolution of the chemical structure of coal char and tar during devolatilization

Abstract

Solid-state 13 C and 1 H nuclear magnetic resonance (NMR) spectroscopy techniques are used to investigate the chemical structure of char particles and condensed tar vapors produced as pyrolysis products from an Illinois #6 coal at rapid heating conditions (≈10 4 K/s) at two gas conditions (maximum gas temperatures of 1250 K and 1050 K). The temperature history of particles in the flow reactor is determined using a unique infrared sizing-pyrometry system. The 13 C NMR analyses of the coal chars indicate that significant amounts of aliphatic material are released from the coal during devolatilization, with little change to the aromatic cluster size or number of attachments per cluster. At long residence times, and at higher temperatures, small increases in the cluster size in the char are observed. The 1 H NMR analyses indicate that thermal decomposition of tar vapor occurs at the 1250 K gas conditions, as evidenced by increases in the aromaticity and decreases in the peripheral aliphatic groups, such as methyl groups and aliphatic bridge material.