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.