Identification of the fractions responsible for morphology conservation in lignocellulosic pyrolysis: Visualization studies of sugarcane bagasse and its pseudo-components

Abstract

Pyrolysis of lignocellulosic materials typically form carbonaceous residues (chars) with structures similar to the starting material. However, previous studies reported in the literature have shown that fast pyrolysis of cellulose and lignin form a molten intermediate liquid resulting in chars with smooth surfaces and evidences of intense bubbling. The fraction responsible for morphology conservation during pyrolysis is not known. In this article, pyrolysis visualization studies were carried out with a fast camera on cellulose, xylan, Organosolv lignin (OL), milled wood lignin (MWL), and lignocellulosic sugarcane bagasse to identify the component responsible for morphological conservation. The materials were heated using a modified Pyroprobe with measured sample heating rates close to 100°C/s. Our studies confirm that cellulose, lignin, and deashed xylan are completely transformed into an intermediate liquid; the intensity of bubbling for lignin was far superior that of cellulose. Xylan as received, however, only forms a small amount of intermediate liquid; it does not fully melt and maintains its general shape during pyrolysis. These results suggest that the presence of mineral matter is critical for lignocellulosic materials to retain their original morphology. We repeated the studies on raw bagasse and acid washed bagasse. The raw bagasse retains its morphology; the acid washed bagasse shrank dramatically, but was not completely converted into a liquid. Our results suggest that in addition to hemicellulose with the presence of ash, other biomass fractions or the different temperatures at which the different fractions melt and solidify could also be contributing to maintain the structure of the lignocellulosic material during pyrolysis.