Process Simulation Study Of Biofuel Preparation From Lignocellulosic Biomass

The rapid consumption of fossil fuels,the negative impact on the environment,and concerns about oil reserves have prompted researchers to search for a renewable fuel alternative.The preparation process of bioethanol based on sustainable lignocellulosic biomass is a current research hotspot.In this paper,Aspen Plus software is used to establish the whole process simulation of fuel ethanol from lignocellulosic biomass under two pretreatment processes,namely sodium hydroxide pretreatment process and deep eutectic solvent pretreatment process.The results show that the annual treatment of corn stover is 67.3thousand tons;and the amount of bioethanol obtained by the deep eutectic solvent pretreatment with choline chloride/urea（1:2）is 1931.04 kg/h,while the bioethanol yield by the sodium hydroxide pretreatment is 1777.08 kg/h.In the subsequent bioethanol refining procedure,choline chloride/urea（1:2）as an entrainer is proved to be suitable for the bioethanol-water system separation,yielding the bioethanol product with a purity of 99.5%.Molecular dynamics is used to study the extraction mechanism of the deep eutectic solvent at the microscopic level,and the results show that choline chloride/urea（1:2）has a hige interaction with water and a low one with bioethanol,and that the hydrogen bond acceptor plays a dominant role during the extraction process.Finally,the economics is evaluated using the net present value method,and the results indicate that both deep eutectic solvent pretreatment and sodium hydroxide pretreatment are economically feasible,with minimum sales prices of 3.8￥/L and 4.0￥/L for the products,respectively.Density fuctional theory is used to study the structure,physicochemical properties and internal hydrogen bonding network of the deep eutectic solvent.Based on the Reax FF force field,a model of lignin-carbohydrate complexes is established to investigate the mechanism of the pretreatment of choline chloride-based deep eutectic solvents by reaction molecular dynamics simulation.The results show that theβ-O-4ether and glycosidic bonds are broken in the model,and the chloride ions and free protons increase the cleavage rate and efficiency,respectively.The best pretreatment solvent is choline chloride/lactic acid（1:2）,in which 40%of PG-LCC compounds are decomposed in 100 ps,and a total of 22 phenolic and carbohydrate molecules are finally obtained.Subsequently,the hydrogen bond donors are investigated in detail.Acidic hydrogen bonding donors generally have high lignin removal rates.In the choline chloride/lactic acid deep eutectic solvent,there is a tendency for the delignification effect to decrease with increasing lactic acid content.The delignification effect of monocarboxylic acid hydrogen bond donors reduces with increasing molecular chain length,while the opposite is true for dicarboxylic acid hydrogen bond donors.The reason is that decreasing the monocarboxylic acid alkyl chain length will enhance the ability of deep eutectic solvents to contribute protons in solvent-solute interactions.In addition,the weak hydrogen bond network in deep eutectic solvent reduces the binding of hydrogen bond accepters for better dissolved product molecules.Molecular dynamics simulation is used to investigate the solubilization effect of green solvents on hemicellulose systems and to probe the solubilization mechanism.The three xylan models constructed are all soluble in the selected ionic liquids[CH][CH₃COO],[Bmim][CH₃COO]and[Bmim][Cl].Xylan with glucuronic aldehyde residues is easier to be dissolved,and ionic liquids with acetate anions have the better dissolution effect.The anion plays a leading role in the solubilization of the system,and the mechanism of action is the formation of strong hydrogen bonds between the anion and the hydroxyl group on the xylan model.The three deep eutectic solvents choline chloride/lactic acid（1:2）,choline chloride/glycerol（1:2）,and choline chloride/urea（1:2）also have the ability to solubilize hemicellulose,which is soluble up to 15 wt%and the xylan of gluconate aldehyde residues has the highest solubility in choline chloride/urea（1:2）.The dominant role in the dissolution process is taken by the hydrogen-bonded acceptor with chloride ions.In addition,choline chloride/urea（1:2）is selected to evaluate the effect of molar ratio and water content on the dissolution process.The results suggest that the hydrogen bonding network and its strength of the system both increase with the increase of urea content in the solvent,especially for the xylan model with gluconate aldehyde residues.Meanwhile,the hydrogen bonding strength within the deep eutectic solvent is affected by the addition of water.Excessive water will significantly reduce the hydrogen bonding strength of the deep eutectic solvent-hemicellulose system,but a new deep eutectic solvent-water hydrogen bonding network will be formed,which in turn will enhance the interaction between hemicellulose and the deep eutectic solvent then promote the dissolution of the two substances.