(165d) Biomass Pyrolysis: Aerosol Generation by Reactive Boiling Ejection of Molten Cellulose

Pyrolysis of lignocellulosic biomass presents a complex physical and chemical conversion process that occurs during forest fires, cigarette smoking and the combustion, fast pyrolysis and gasification of biomass for bio-fuels [1]. In these processes, a significant fraction (up to 30 wt. % [2]) of the original biomass is converted to aerosols which are entrained in the vapor phase. These micro-scale particles are known to alter atmospheric chemistry, contribute to tar inhalation from cigarette smoke and lead to a nonvolatile fraction in condensed bio-oils from fast pyrolysis. Despite the importance of aerosols on pyrolysis, the mechanism for aerosol generation is unknown. Recently, it has been proposed that the non-volatile fraction observed in condensed pyrolysis oils is derived from the secondary polymerization of the highly reactive oil species [3, 4]. However, this mechanism does not account for intact β-1,4 linkages observed in the heavy components of the bio-oil, indicating preferential selectivity to the native linkages found in the parent biopolymers [1]. In this work, primary aerosols are directly observed physically ejecting from molten cellulose intermediate by utilizing an ablative pyrolysis surface and high speed photography apparatus (1000 fps). By measuring the ejection velocity distribution, we were able to estimate the surface tension of the cellulose intermediate to be 10^-6 < γ < 10^-5N/m. The liquid intermediate is observed to undergo vigorous internal bubbling followed by surface jetting, fragmentation, and aerosol ejection. The phenomenon is further explored by coupling experimental measurements with computational fluid dynamics that confirm the bubble collapse mechanism for aerosol generation and further corroborate the bulk fluid properties for the reactive cellulose intermediate.

1. Teixeira, A.R., et al., Aerosol generation by reactive boiling ejection of molten cellulose. Energy & Environmental Science, 2011. 4(10): p. 4306-4321.

2. Piskorz, J., P. Maherski, and D. Radlein, Pyrolysis of Biomass - Aerosol Generation: Properties, Applications, and Significance for Process Engineers, in Biomass, A Growth Opportunity in Green Energy and Value-Added Products: proceedings of the 4th Biomass Conference of the Americas, R.P. Overend and E. Chornet, Editors. 1999, Elsevier Science: Amsterdam. p. 1153-1159.

3.  Shafizadeh, F. and Y.L. Fu, Pyrolysis of cellulose. Carbohydrate Research, 1973. 29(1): p. 113-122.

4.  Patwardhan, P.R., et al., Distinguishing primary and secondary reactions of cellulose pyrolysis. Bioresource Technology, 2011. 102(8): p. 5265-5269.