Sunday, May 3, 2009
3-55
Mechanism of delignification in the ionic liquid tetradecyl(trihexyl)phosphonium chloride
Sai Keskar, William O. S. Doherty, and Les A. Edye. Queensland University of Technology, 2 George St, Brisbane, Australia
While dissolution and derivitization of cellulose in Ionic liquids (ILs) has been demonstrated at laboratory scale, the dissolution of lignocellulose is difficult due to the presence of inter-dispersed lignin in biomass matrix.Consequently dissolution of biomass in imidazolium ILs require longer reaction times and higher temperatures than for dissolution of pure cellulose.Some ILs that do not dissolve cellulose (e.g. tetradecyl(trihexyl)phosphonium chloride) are able to dissolve lignin rapidly at low temperatures.These ILs have potential as delignification solvents in biomass pretreatments.Tetradecyl(trihexyl)phosphonium chloride can effectively delignify sugarcane bagasse.It is found that the mechanism of delignification in the phosphonium IL is similar to an acid-organosolv pulping.This delignification reaction is studied over a range of temperatures and compared to acid-organosolv delignification.Phosphonium IL delignification is observed with very short reaction times and at atmospheric pressures.At high temperatures lignin recondensation reduces the effective delignification.However delignification in phosphonium ILs can be optimised to reduce the effect of unwanted condensation reactions.The results indicate that the ILs in the tetra alkyl phosphonium series are effective delignification or pulping solvents.