Condensed Phase Reactions During Thermal Deconstruction

Heterodoxy in Fast Pyrolysis of Biomass

“…Improving selectivity of pyrolysis toward sugars would be an important contribution to the field. Despite advances in understanding thermal depolymerization, it is not clear how the rate of end-chain unzipping to produce anhydrosugars can be increased relative to ring fragmentation . A recent suggestion is that homolytic cleavage favoring levoglucosan formation can be promoted over concerted reactions through radical-generating non-thermal plasma pretreatment of cellulose .…”

“…In contrast, predicting product distribution in a non-equilibrium process requires detailed kinetic data on major reactants and intermediate products as well as models of the hydrodynamics of the reactor. , Progress has been hampered by the difficulty in interrogating the condensed phase reactions responsible for depolymerization of carbohydrate and lignin in biomass. Accounting for reactions responsible for the prominent intermediate and final pyrolysis products, which include light (permanent) gases, like carbon monoxide and low-molecular-weight hydrocarbons, light (condensable) oxygenates, such as alcohols, aldehydes, and carboxylic acids, and heavy organics consisting mostly of saccharides and phenolic compounds, is also daunting.…”

“…We propose thermal depolymerization of biomass, using heat instead of enzymes to break glycosidic bonds in plant polysaccharides, as an alternative pathway to cellulosic sugars . This pathway has been less explored than acid and enzymatic hydrolysis, likely because the low selectivity and unfavorable thermodynamics of high-temperature thermal processes would suggest poor prospects for thermal depolymerization.…”

“…46 We propose thermal depolymerization of biomass, using heat instead of enzymes to break glycosidic bonds in plant polysaccharides, as an alternative pathway to cellulosic sugars. 28 This pathway has been less explored than acid and enzymatic hydrolysis, likely because the low selectivity and unfavorable thermodynamics of high-temperature thermal processes would suggest poor prospects for thermal depolymerization. Indeed, pyrolysis of most lignocellulosic biomass yields very little sugar (see Figure 8), with yields that, at best, are only a small percent of the theoretical yields of hexose and pentose from cellulose and hemicellulose.…”

Increase in bio-oil quality from improvements on fast pyrolysis fluidized beds

“…However, removing or passivating the alkali and alkaline metal (AAEM) content of biomass can dramatically increase sugar yields [35], [36]. Thermal depolymerization of cellulose produces anhydrosugars instead of the more familiar monosaccharides from acid or enzymatic hydrolysis [37]. This suggests an alternative approach for producing cellulosic sugars that is much faster and potentially more economical than hydrolysis [38].…”