Synthesis of Tetraalkylammonium- and 1,3-Dialkylimidazolium-Based Ionic Liquids and Their Application for Lignocellulosic Feedstock Pretreatment(PPT)

摘要

Bioethanol produced from non-edible plant feedstock is the one of the most perspective alternative energy sources. Efficient methods of lignocellulose feedstock pretreatment are necessary to enhance economic efficiency of the bioethanol production. Ionic liquids (hereafter ILs) are quite novel, promising reagents for plant feedstock pretreatment. However, some disadvantages of the traditionally applied ILs, namely relatively high melting points and viscosities, decrease their cellulose solubilizing ability. Therefore the following subjects were within the focus of our investigation: the correlation between the properties of ILs and their structure, development of ILs synthesis technique, and application of the compounds obtained for lignocellulosic feedstock pretreatment. To accomplish this, we have investigated two main methods of ILs synthesis: the quaternization reaction and anion exchange (metathesis). A number of ILs based on tetraalkylammonium cations and 1,3-dialkylimidazolium was obtained. The synthesis of substituted imidazoles by Van Leusen (initial reagents for quaternization) was also conducted. The advantage of this method is the possibility of obtaining practically any 1,3- and 1,3,5-substituted imidazoles. The structures of the compounds obtained were confirmed by ~1H-NMR spectroscopy, the melting points of the majority of ILs were experimentally determined. The influence of the cations and anions structure on the ILs ability to dissolve cellulose was empirically established. As compared with the traditional ILs (alkyl-substituted imidazolium chlorides) ILs containing cations with hindered bulky radicals (benzyl) and/or iodide and acetate anions have reduced viscosities and melting points leading to the increasing cellulose solubility in those compounds. ILs containing hydroxyl groups or oxygen atoms as part of the radicals of imidazoilum ring don't have the ability to solve cellulose. The comparison of the pretreatment efficiency of the ILs obtained [BzMIm]CI and the most studied one [BMIm]Cl was conducted. The results showed the superiority of synthesized compound on a number of parameters, namely better solvent power in relation to cellulose and lower melting point.