Sunday, May 4, 2008
3-23

Ammonia Phase Equilibrium in Vapor-Water-Biomass Pretreatment Systems

Timothy J. Campbell and Farzaneh Teymouri. MBI International, 3900 Collins Road, Lansing, MI 48910-8396

Pretreatment of lignocellulosic biomass materials with ammonia has been shown to increase yields of fermentable sugars and ethanol in enzymatic hydrolysis and Simultaneous Saccharification and Fermentation (SSF) processes.  Yields from many types of biomass, including corn stover, corn husk, corn fiber, bagasse, and switchgrass, have been shown to increase significantly after ammonia treatment.  Ammonia pretreatment processes are currently being scaled up to provide industrially-significant quantities of treated biomass for subsequent production of sugars, alcohols, organic acids, and other products.  However, engineering calculations for design of large-scale ammonia pretreatment plants are hindered by lack of detailed thermodynamic data on ammonia-water-biomass mixtures.  While ammonia speciation and vapor-liquid equilibria in ammonia-water systems have been described in detail, the effect of the presence of biomass on ammonia phase equilibrium in vapor-water systems has not been carefully studied.  Ammonia sorption on biomass is a significant ecological phenomenon that impacts nitrogen distributions in natural soils, but the sorbed and aqueous concentrations found in nature are low.  Ammonia sorption on biomass has not been quantified at the high concentrations, temperatures, and pressures used in pretreatment processes.  In this study, the effect of biomass on equilibrium vapor pressure in closed ammonia-water systems is measured, and the extent of sorption of aqueous ammonia species on biomass solids is estimated.  The implications of the observed ammonia sorption for design of large-scale ammonia pretreatment plants are discussed. 

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