COSMO-RS Based Predictions for the Extraction of Cellulose and Hemicelluloses From Lignocellulosic Biomass Using Ionic Liquids: Effect of Cation and Anion Combination

Ionic liquids (ILs) constitute a new generation of solvents entirely composed of ions. Biotechnological applications involving the use of ILs are currently emerging. Ionic Liquids (ILs) provide an important alternative in removing lignin from lignocellulosic biomass to extract cellulose and hemicellulose. Lignocellulosic biomass constitutes mainly cellulose, hemicelluloses, lignin and it is a sustainable source to convert biomass into biofuels and bio-based products. A total of 34 cations belonging to 6 classes and 35 anions resulting in 1190 possible combinations were screened via COSMO-RS (Conductor Like Screening Model for Real Solvents). Infinite dilution activity coefficients (γ^∞) of cellulose, hemicelluloses and lignin in ionic liquids at room temperature (298.15 K) were predicted via COSMO-RS. Among the cations screened the triazolium based cation along with the halogenated anions gave the highest selectivity for cellulose. High values of selectivity (γ^∞,IL_lignin/γ^∞,IL_cellulose) at infinite dilution for cellulose for the ILs :[1-methyl-4-aminotriazolium][PF₆], [4-aminotriazolium] [BF₄], [4-aminotriazolium] [Cl] obtained were 26772, 3720.7 and 1029.6 respectively. The selectivity values for anions with the combination of cation 1-methyl-4-aminotriazolium decreases in the following order [PF₆] > [NO₃] > [Tfa] > [MAcA] > [BOB] > [B(CN)₄] > [Sal] > [CH₃SO₄] > [ThSal] > [C₂H₅SO₄] > [BMA] > [Tfi] > [MDEGSO₄]. Similarly, the selectivity value of cellulose for anions with the cation 4-aminotriazolium decreases in the order [BF₄] > [Cl] > [Tfo] > [OAc] > [Tfa] > [ThSal] > [Prop] > [ThPh] > [Sal] > [Ben] > [MDEGSO₄] > [DEP]. Similar values for hemicellulose were obtained with the IL: [4aminotriazolium] [BOB] (1186.8). The selectivity for the anions with 4aminotriazolium cation decreases in the order  [Cl] > [OAc] > [Tfa] > [Prop] > [ThPh] > [Sal] > [ThSal] > [Ben] > [DEP] > [DBP] .In the same manner, the selectivity values for anions with the combination of cation: 1methyl4aminotriazolium decreases in the following order [PF₆] > [NO₃] > [BOB] > [CH₃SO₄] > [Tfa] > [B(CN)₄] > [Tfo] > [C₂H₅SO₄] > [MAcA] > [BMA] > [ThPh]> [Sal] > [Tfi] > [ThSal] > [MDEGSO₄].

Nomenclature:

PF₆: Hexafluorophosphate, Tfa: Trifluoroacetate, MAcA: Methylsulfonylacetamide,

BOB: bis(oxalato)borate, Tfo: Trifluoromethansulfonate, BMA: bis(methylsulphonyl)amide

Tfi: bis(trifluormethylsulfonyl)imide, MDEGSO₄: 2-(2-methoxyethoxy)ethylsulfate