Differences in soot produced from rapid pyrolysis of xylan, cellulose and lignin under pulverized-fuel conditions

Abstract

This study reports the properties of size-segregated soot from rapid pyrolysis of three biomass model compounds (i.e., xylan, cellulose and lignin) in a drop-tube furnace under pulverized fuel conditions in argon at 1300 °C. Lignin (100.7 mg/g) yields much more soot than xylan and cellulose (7.0 and 11.6 mg/g, respectively) during pyrolysis. All soot samples have a unimodal size distribution but lignin soot has a considerably larger mode diameter (0.246 µm) than soot from xylan and cellulose (0.043 and 0.077 µm, respectively), attributing to enhanced agglomeration of soot formed from lignin pyrolysis. The fringe of soot from lignin pyrolysis is longer and straighter than that of xylan soot or cellulose soot. Additionally, soot from cellulose pyrolysis contains little inorganic species as cellulose contains little ash. However, for xylan and lignin that contain abundant inorganic species, considerable Na, K, Cl and S are present in the soot samples. Even though the yield of inorganic species in carbonaceous material with aerodynamic diameter <1 µm (CM1) from xylan pyrolysis is lower than that from lignin pyrolysis, xylan soot has higher contents of inorganic species than lignin soot. The presence of Na and K in soot is attributed to the incorporation of these inorganic species in soot through organic bound and/or condensation. K is more likely to incorporate with soot than Na. More Na and K are incorporated with soot from xylan pyrolysis compared to those with soot from lignin pyrolysis. Non-mature soot contains higher contents of Na and K than mature soot does.