Levoglucosan cellulose pyrolysis

Cellulose pyrolysis kinetics, as measured by isothermal TGA mass loss, were statistically best fit using 1st- or 2nd-order for the untreated (control) samples and 2nd-order for the cellulose samples treated with three additives. Activation parameters obtained from the TGA data of the untreated samples suggest that the reaction mechanism proceeded through an ordered transition state. Sample crystallinity affected the rate constants, activation parameters, and char yields of the untreated cellulose samples. Various additives had different effects on the mass loss. For example, phosphoric acid and aluminum chloride probably increased the rate of dehydration, while boric acid may have inhibited levoglucosan... 

This reaction is supposed to have an E2 mechanism [32]. Further decomposition of the dehydrated cellulose results in an increased yield of water, char, gases and carbonyl compounds and a simultaneous decrease in levoglucosan formation as compared to pure cellulose pyrolysis. 

Normally hydroxyacetaldehyde, which is formed in competition with levoglucosan during cellulose pyrolysis (15), is catalyzed by the presence of cations such as alkali metal. Indeed, our results show that hychoxyacetaldehyde declines as levoglucosan increases in pyrolysate. However, hydroxyacetaldehyde remains a significant constituent of the pyrolysate from pretreated biomass, which suggests that some alkali remains in the feedstock even after pretreatment. 

Hydroxyacetaldehyde, which forms in competition with levoglucosan during pyrolysis of cellulose, remains a significant constituent of pyrolysate from pretreated biomass. Further tests are required to determine whether this is the result of residual alkali in the pretreated biomass. 

However, with the one-dimensional VBS there is an intrinsic problem compounds with similar volatility can be very different chemically. For example, two compounds with a (sub-cooled liquid) saturation concentration near 10 pg m are tricosane (C23H4g) and levoglucosan (CeHioOs). Each are important in the atmosphere - tricosane is a constituent of lubricating oil [9] while levoglucosan is an important tracer for wood burning because it is a cellulose pyrolysis product... 

Mayes HB, Nolte MW, Beckham GT, Shanks BH, Broadbelt LJ. The alpha-bet(a) of glucose pyrolysis computational and experimental investigations of 5-hydroxyme-thylfurfural and levoglucosan formation reveal impHcations for cellulose pyrolysis. 21CS Sustain Chem Eng. 2014 2 1461-1473. 

At higher temperatures, the intermediates, including levoglucosan and the condensation products further pyrolyze to give various products by fission of the carbohydrate units and rearrangement of the intermediate products. Table III shows the products obtained from the pyrolysis of cellulose and treated cellulose at 600° (8). The significant increase in the yields of water and char and decrease in the yield of tar in the acid treated cellulose verifies the previously mentioned promotion of dehydration and charring reactions by acidic additives. 

One important thermal degradation mechanism of cellulose fibres (cotton, rayon, linen, etc.) is the formation of the small depolymerisation product levoglucosan (Fig. 8.7). Levoglucosan and its volatile pyrolysis products are extremely flammable materials and are the main contributors to cellulose combustion. Compounds that are able to hinder levoglucosan formation are expected to function as flame retardants for cellulose. The crosslinking and the single type of esterification of... 

At temperatures above 250°, vacuum pyrolysis of cellulose provides, in addition to depolymerization and decomposition (with evolution of water, carbon dioxide, and carbon monoxide), a volatile tar which contains mainly levoglucosan and leaves a charred residue. Under these conditions, the oxidation reactions are eliminated or minimized, and the levoglucosan is removed from the heated area where it could undergo further decomposition. 

Formation of levoglucosan by the pyrolysis of cotton cellulose under vacuum was reported in 1918 by Pictet and Sarasin, who ob-... 

Detailed analysis of the tar fraction obtained from the vacuum pyrolysis of pure cellulose has shown that it contains mainly levoglucosan (80 % of the tar), " some carboxyl and carbonyl - decomposition products [including 5-(hydroxymethyl)-2-furaldehyde and 2-furyl hydroxymethyl ketone], and small proportions of 1,6-anhydro-... 

Vacuum pyrolysis results in rapid distillation of levoglucosan, and prevents further decomposition of this material. It has been shown that pyrolysis of cellulose in a nitrogen atmosphere proceeds at almost the same rate as pyrolysis under vacuum, but a lower yield of tar and a greater yield of the lighter fractions result, because of appreciable secondary reactions involving further decomposition of the intermediate fragments. ... 

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