Finding a more efficient way to derive fuel from cellulosic material has been a priority in chemical research for decades. Hydrolyzing the ether bond, the glycosidic linkage in biomass, is the limiting factor in producing fuels from cellulosic biomass due to the high cost of enzymes required for this step. Recently, focus has shifted to ionic liquids (ILs) as a potential alternative solvent to enhance product yield of the breakdown of cellulosic biomass. By choosing the anion/cation combination, ILs can be uniquely engineered for specific applications based on preferred physiochemical properties such as density, viscosity, hydrophobicity, and solubility, and are more environmentally sustainable than traditional organic solvents. However, atomistic details not well understood to explain how ILs affect the enzymatic reaction mechanism to improve yield. Given this information, the most efficient ion combination can be chosen, improving the efficiency of the reaction for each unique system.<br/><br/>Dimethyl ether (DME) offers a simplified representation of the ether bond in cellulose so the system can be modeled at the atomic level. Using <i>ab initio </i>molecular dynamics and Density Functional Theory (DFT) we investigated how ILs affect energetic and geometric features of DME hydrolysis at the atomic level to gain insight into how reaction yield is improved. DFT was performed with Gaussian 09 in vacuum and water to obtain minimum energy geometries for the reactants and products and to find the relevant transition state steps for both the catalyzed and uncatalyzed reactions. The transition state step occurs during the proton transfer from water to the DME oxygen, agreeing with previous findings. DME hydrolysis was modeled in vacuum, water, and IL mixtures with parameters used in a study by Liang, et al. that modeled catalyzed DME hydrolysis in water with CPMD enhanced with metadynamics. Results show the solvent significantly affects the geometric features, specifically the torsional angle and bond lengths. The energy surface also indicates direct dependence on solvent atoms. By constructing free energy surfaces corresponding to specific geometric features, we can match exactly which steps of the hydrolysis reaction are made more favorable by ILs and why. Details learned will assist in designing optimal reaction conditions for biomass breakdown with solvents to enhance enzyme degradation during processing, making biofuels a more economic alternative form of energy.

Molecular simulation of hydrolysis reactions to engineer more efficient biomass conversion

249th National Meeting (2015)

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