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

Abstract

a b s t r a c tPyrolysis 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.

The catalytic effect of inherent and adsorbed metals on the fast/flash pyrolysis of biomass: A review

“…Lignin liquefies more readily and over a greater temperature range than xylan, while cellulose is far more refractory. It is the elasticity of the crystalline cellulose, in combination with the mineral skeleton, which maintains the structural integrity of the cell [15]. This collapse of cell structures and the consequent fluidity of the mass should facilitate contact between metal and substrate.…”

“…It is more resistant to decomposition than the other components of biomass because of the presence of high-energy carbon-carbon bonds between lignin units, such as 5-5' links [51]. Dehydration reactions are initiated around 200 C, and between 200 and 400 C cleavage of a-and b-aryl-alkyl-ether linkages (b-O-4 and a-O-4 bonds) occurs [15]. Around 300 C, aliphatic side chains start splitting off from the aromatic ring, resulting in the production of light hydrocarbons as well as small oxygenated compounds.…”

Progress in understanding the four dominant intra-particle phenomena of lignocellulose pyrolysis: chemical reactions, heat transfer, mass transfer, and phase change

“…Recent work has showed the corollary result that materials that still have mineral content tend to maintain their original tissue structure after pyrolysis. 82…”

“…Using a fast speed camera the formation of intermediate liquid phase was observed in 3 stages: complete lignin melting, foaming and swelling of liquid phase by bubbles, and shrinking by evaporation and bubble collapse. Pecha et al 52,82,206 published a series of manuscripts in 2017 detailing experiments which studied the effect of vacuum on pyrolysis of cellulose, lignin, and xylan. These works illustrated, through high speed photography and pyrolysis product analysis, that the liquid intermediate is made up of partially pyrolyzed oligomers which will either break down into monomers or turn into char at atmospheric pressure.…”

“…Recent research actually indicates that metal ("ash") content plays a role in preserving the structural porous backbone. 82 It is possible that the ash catalyzes char formation reactions and since the ash is solid and less mobile than liquids, it acts as a template on which polycyclic rings form. Note that stars represent sugars like cellobiosan.…”