| The biomass pretreatment is one of the most important steps in the process of manufacturing biofuels from biomass. While the modern technology is not that efficient and still waiting for big break. In this paper, to develop the ionic liquids pretreatment process, we have developed the molecular thermodynamic model for chain-like fluid system and studied the phase equilibrium for systems containing ionic liquids and its application in the biomass pretreatment process. These previous exploration has provided fundamental information and necessary molecular thermodynamic models for optimizing ionic liquids pretreatment process.Mainly, the theory work includes the following three parts:(1) A new molecular thermodynamic model of mixing Helmholtz energy for random copolymer solutions based on close-packed lattice has been developed. The model contains three contributions:the contribution from athermal mixing of polymer chain and solvent, the Helmoltz energy of mixing in a multi-component Ising lattice, and the contribution from dissociation of polymer and association of monomers. The Guggenheim model is used to calculate the athermal mixing entropy, Yang et al.’s multicomponent Ising lattice model is used to calculate the mixing Helmholtz energy of multi-component Ising lattice and the statistical association theory of Cummings, Zhou and Stell is used to calculate the Helmholtz energy due to dissociation of polymer and association of monomers, respectively. It is shown that comparisons between show that the agreement between Monte Carlo (MC) simulated coexistence curves and that predicted by this model is nearly perfect. The model can be satisfactorily used to correlate the liquid-liquid equilibrium of practical random copolymer solutions.(2) Based on previous model, we have generally extended it to the multicomponent chain-like fluid mixtures by considering all the long-range interactions in each single chain. The liquid-liquid phase equilibrium of ternary chain-like mixtures predicted by this model are in good agreement with MC simulation results and much better than that calculated by Flory Huggins theory (FHT) and Revised Freed theory (RFT) obviously. This model can describe types 1-3 phase separations of Treybal classification satisfactorily. Meanwhile, model parameters correlated from the binary system can be further used to predict the corresponding liquid-liquid equilibrium of ternary mixtures, including systems containng ionic liquids or chain-like polymers.(3) Since the closed-packed lattice model can’t describe the effect of pressure on the phase equilibrium, we have developed a revised Percus-Yevick-van der Waals equation of state. Pure-component parameters a and b in the equation are estimated from the enthalpy of vaporization and liquid-density data of pure-component. The only adjustable binary parameter a12 can be obtained from Henry’s constant for the nonelectrolyte. Calculated total pressures of ionic liquid solutions are in good agreement with experimental data although in a few systems observed total pressures are slightly higher than those calculated in the region where the ionic liquid is dilute. The results of correlating a few binary systems with a miscibility gap are also quite satisfying.For the application of ionic liquids in biomass pretreatment process, we have done the following three experimental works:(1) At 22℃, we have measured the ternary liquid-liquid equilibrium data for aqueous biphasic systems containing [C2mim][Ac] or [C4mim][Ac]. The results show that using the potassium phosphate solution (K3PO4) is able to recycle at least 95.0% ionic liquids. Meanwhile, to better understand the phase separation mechanism of these systems, we have used our model to calculate and correlate the experimental data.(2) We have studied the solubility of biomass in different ionic liquids and chose 1-ethyl-3-methylimidazole acetate ([C2mim][Ac]) as the candidate solvent to dissolve Miscanthus. The results show that the K3PO4 solution is able to be used as an anti-solvent to precipitate biomass and an aqueous biphasic system of IL phase and salt phase is formed. After separating the liquids and solid, the solid phase has been washed by water twice before an enzymatic hydrolysis step carrying out to convert cellulose to glucose at 50℃. The results of this new process show that it is a very potential pretreatment method for Miscanthus, which gives a pellet with relative low content of lignin and hemicellulose and has obtained a high rate and high yield of glucose conversion from cellulose. The yield of 85.0% was obtained in 12h and nearly 100% after 24h. Meanwhile, the [C2mim][Ac] and K3PO4 solutions were recycled and reused after simple treatment. The two re-runs have also given a pretty good result,70.0% yield in 12h.(3) To solve the accumulation problem of lignin in IL-rich phase, we have studied three organic solvents:ethyl acetate (EtOAc),1,4-dioxane and tetrahydrofuran (THF) to extract and separate different kinds of lignin from [C2mim][Ac] aqueous solution. The results show that the smaller the molecular weight of lignin, the easier be extracted to the organic phase. THF has turned out to be the best solvent among these three. Lower pH is able to increase the partition coefficients. |
