14-05: Use of a twin-screw extruder as a mixing tool to promote sugarcane bagasse pretreatment with ionic liquids at high solid contents

Ionic liquids (ILs) have been successfully reported for the pretreatment of cellulose and lignocellulosic materials as they bring about a noticeable increase in enzymatic digestibility in comparison to other well-known pretreatment procedures. The usual reported biomass:IL ratio for ILs pretreatment of biomass often falls in the range of 1:10 - 1:20 (wt %), which hinders its application due to a large amount of IL consumption. Moreover, standard mixing systems of continuous stirred-tank reactors are not able to effectively mix biomass:ILs mixtures with ratios under 1:5 (i.e, over 20% solids content). Considering that an effective mixing is necessary to improve the interaction of IL with the biomass and decrease the biomass:IL ratio,  this work has evaluated the use of a twin-screw extruder to promote an efficient mixing of bagasse with the IL 1-ethyl-3-methylimidazolioum acetate within 1:1–1:8 ratios, at 140 ºC.  Besides the application as a mixing tool, the use of extruder allows the continuous pretreatment of large amounts of biomass, which is advantageous in comparison to batch procedures. Results showed that the use of the twin-screw extruder as a mixing tool allowed the effective pretreatment of a bagasse:IL ratio of 1:3 (33% solids content). Under this condition, a glucose yield over 90% was obtained within 24h enzymatic saccharification, which was comparable to that observed using 1:20 biomass:IL ratio (5% solids content) in a stirring reactor for 2h. To the best of our knowledge this is the first report showing the possibility to decrease IL load without impairing the pretreatment performance.