Enhancement of ethanol production by novel morpholinium ionic liquids

Abstract

Two novel morpholinium ionic liquids, N-allyl-N-methylmorpholinium acetate ([AMMorph][Ac]) and morpholinium acetate ([Morph][Ac]), were synthesized and successfully used for pretreatment of rice straw. While imidazolium liquids are the most efficient solvents for the pretreatment of lignocelluloses, the main advantages of morpholinium liquids are their lower toxicity and price. Different concentrations of dimethyl sulfoxide (DMSO), as an inexpensive industrial co-solvent, were mixed with the synthesized ionic liquids to assist the pretreatment efficiency. The pretreatment was performed at 90, 100, and 120 °C for 2, 3, and 5 h. Then, the pretreated materials were subjected to enzymatic hydrolysis followed by fermentation. Moreover, the efficiency of the synthesized ionic liquids was compared with those of four widely used solvents, i.e., 85% N-methylmorpholine-N-oxide (NMMO), 1-butyl-3-methylimidazolium acetate ([Bmim][Ac]), 8% NaOH solution, and 85% H3PO4 solution. The pretreatment with [AMMorph][Ac] resulted in the significant improvement of enzymatic hydrolysis, which was as efficient as the best widely used pretreatments. The glucose yields of 98.4 ± 1.3% were achieved by pretreatment with mixtures of [AMMorph][Ac]-DMSO as well as NMMO, [Bmim][Ac], and NaOH. The highest ethanol yields of 90.8% and 94.8% were achieved through 70:30 (v/v) [AMMorph][Ac]-DMSO solution and NMMO, respectively. Moreover, using DMSO as a co-solvent could minimize the ionic liquids usage without lowering their performance and enhanced the pretreatment efficiency by viscosity reduction.