(145e) Improving Glucose Yield By Fractionation of Biomass With Non-Cl? Ionic Liquids

Lignocellulosic biomass is a sustainable, available energy resource that is mostly carbon-neutral. To convert it to liquid fuels by biochemical means, however, requires pretreatment of biomass to remove lignin to enhance the availability of cellulose. Most standard lignin removal processes use either high temperatures and pressures, hazardous acids or alkalis, or some combination of these steps.

Ionic liquids are molten salts with melting points below 100 ºC, some of which have been shown to dissolve lignin. However, many such ionic liquids frequently contain Clˉ ions, which can interfere with downstream processing, e.g., enzymatic hydrolysis.  Ionic liquids, with their low vapor pressures and potential for recycling, are a green alternative for lignin removal at low temperatures. 

In this study, the effects of non- Clˉ containing ionic liquids 1-ethyl-3- methylimidazolium acetate (EMIM Ac), 1-ethyl-3- methylimidazolium formate (EMIM Formate), and 1-ethyl-3-methylimidazolium lactate (EMIM Lactate) were examined.  The biomass studied were rice hulls, corn stover, switchgrass, loblolly pine, and poplar. The experiments used a 10% (w/w) loading of biomass in ionic liquid, a temperature of 110ºC, and a fractionation time of 3 hours. The effects of biomass type and ionic liquid type were investigated by performing enzymatic hydrolysis on raw and pretreated biomass types.   The non- Clˉ containing ionic liquids removed  up to 98% of the lignin from biomass, which would be expected to make cellulose more available for further processing. However, EMIM lactate was less effective than  EMIM Ac and EMIM Formate for each biomass type. When enzymatic hydrolysis was performed, only biomass pretreated with EMIM Ac and EMIM Formate showed greatly improved glucose yield compared to the raw biomass.

This pretreatment step using environmentally-friendly,  non- Clˉ ionic liquids to remove lignin enables a  green  pathway from lignocellulosic biomass through enzymatic hydrolysis and fermentation to biofuels.  This pretreatment step might permit more cost effective cellulosic biofuels.