Table 5 Different selection parameters for organic solvents used in organosolv pretreatment and their significance
From: Organosolv pretreatment: an in-depth purview of mechanics of the system
Parameters | Constituents/definitions | Method of calculation | Significance | |
|---|---|---|---|---|
Combined severity factors (CSF) |  | Combination of reaction time, temperature, the addition of catalysts, pH, etc | \(\mathrm{Log}\left(R0\right)=\frac{\mathrm{Log }(t\mathrm{Exp}(T-T\mathrm{ref}))}{14.7}\) \(\mathrm{CSF}=\mathrm{Log} \left(R0\right)-\mathrm{pH}\) | • Log(R0) range of 0.5 to 0.7 was most suitable for pretreatment • A CSF value between1.0 to 2.5 is optimised for good cellulose recovery as well as improved enzymatic digestibility |
Solubility parameters | Hildebrand Solubility parameters (δ) | The solubility of a polymer is described as the square root of the cohesive energy density | \(\Delta =\sqrt{\frac{E}{\mathrm{Vm}}}\) | • Gives an idea about the action of solvents in the dissolution of lignin |
Hansen Solubility parameters (δ) | Measures solubility of polymers using the square root of the sum of the quadratics of the three interactions (δd, δp, δh) | Relative energy difference \(\mathrm{RED}= \frac{\mathrm{Ra}}{R0}\) | • RED ≤ 1 shows high solvent–solute affinity and can be used for pretreatment • RED˃1 shows a low affinity of the solvent with the solute | |
Conductor-like Screening Model for Real Solvents (COSMO-RS) | – | Combination of COSMOS with statistical thermodynamics | The σ-profile of the molecule is outlined from the histogram of the charge intensities around each molecule from the 3-D distribution of polarization charges | • Explains the affinity biomass–solvent interaction in a mixed state, other thermodynamic properties of the system • Employed for the selection of green solvents, ionic liquids, etc. For the dissolution of lignin |
Simulation models | Quantum chemical simulations | Investigates the underlying molecular interactions in the solute/solvent system | – | • Helps to predict the solvents’ ability to cause solute dissolution • Helps in the selection of ionic solvents for lignin extraction |
Molecular dynamics simulations | Provides snapshots of reaction mechanisms, studies the dynamic behavior of the molecular systems | – | • Helps to identify unique combinations of biomass–ionic solvent systems | |
Loss tangent (tan δ) | – | The ability of a solvent for the effective conversion of microwave into heat energy | The ratio of the dielectric loss factor to the dielectric constant of the solvents | • Solvents with high tan δ are known to perform well under microwave heating systems |