| Dipolar aprotic solvents (DASs) were used as co-solvents to reduce the viscosityof ionic liquids (ILs), and improve the dispersion and dissolubility of solute in the ILs.Therefore, ILs/DASs pretreatment of lignocellulosic biomass has been widely used inbiorefineries. Because of the cost for producing or purchasing the expensive ILs andthe potential environmental pollution, ILs recycling is of great significance to thepromotion of industrialization process for ILs.In this study, lignocellulosic biomass was pretreated by ILs/DASs. Effects of theIL structure, pretreatment time, pretreatment temperature and particle size onlignocellulosic composition, structural change, biogas production and sugar yieldswere evaluated. Moreover, IL-based aqueous biphasic systems (ABSs) in the presenceof DAS were formed to recycle and reuse the ILs along with the DASs. After thepretreatment of water hyacinth, rice straw, mango leaves and spruce with chloride([C4mim]Cl)/dimethyl sulfoxide (DMSO) under120℃for2h, the surface area ofregenerated samples was increased, the extracted lignin contents were49.2%,38.2%,23.7%and48.0%, crystallinity (CrI) values were decreased by10.5%,6.60%,2.81%and8.57%, and accumulated CH4productions were increased by97.6%,70.4%,65.4and65.9%, respectively. Moreover, after the pretreatment of water hyacinth, rice huskand rice straw with1-N-ethyl-3-methyimidazolium alaninate ([C2mim]Ala)/DMSOunder120℃for2h, the lignin could be remove by48.5%,47.4%and31.3%, CrIvalues were decreased by5.1%,5.6%and6.3%, and sugar yields were increased by232.5%,135.0%and139.5%, respectively, as compared with unpretreated samples. Inaddition, the ILs and DASs used in the study were recovered and reused by formingABSs with salt, and the recovery rates were all over90%.To evaluate the effects of ILs, salts, DASs and temperatures on the ABSscomposed with ILs and salts in the presence of DAS, the solvation parameters of ILsand DASs, the hydration Gibbs free energy of salt anions, and the standard molarthermodynamic functions of the transfer for DASs were investigated, and phase diagrams, tie-line lengths, partition coefficients of DAS, IL recovery efficiencies (RIL)and physicochemical properties were also studied. The results were summarized asfollows:(1) DAS preferentially dissolves in the IL-rich phase, adding DASs is able toaffect the hydrophobicity of ILs, and a large range of DASs are able to produce theABSs composed of hydrophilic ILs ([C4mim]Cl, etc) and inorganic salts, while theability of hydrophobic ILs (1-N-butyl-3-methyimidazolium tetrafluoroborate,[C4mim]BF4, etc) to form ABSs with organic salts was decreased with the increasingconcentration of DASs;(2) The hydrophobic IL with hydrogen bond basicity (β)ranging between0.38and0.60can form ABS with organic salts, and the lower βvalues of hydrophilic ILs results in greater RIL;(3) Increasing the length of thealiphatic chain from C2to C6alkyl chains increases the ability of ILs to form ABS,but the ability to form ABS for the ILs with longer cation side chain decreases;(4)Salting-out effect is in accordance with Hofmeister Series, and is increased with thevalence and the ΔhydG value of the salt anions;(5) IL-based ABSs preferentially formsat lower temperatures;(6) The RILvalues increase with the density differencesbetween the two phases and the surface tension of the top phase.Toxicity studies on aquatic organisms suggest the potential environmental risk ofILs. To avoid the release of the ILs into the environment through wastewaters, a novelmethod of degrading ILs using plasma electrolysis (PE) was proposed. Resultsindicated that ILs with initial concentrations of1.0~4.0g/100mL readily decomposedto inorganic molecules by the oxidation and cleavage of active radicals under anapplied boltage of600V within2h. |
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