Date of Award
Doctor of Philosophy (PhD)
Chemical and Biomolecular Engineering
Ionic liquids are novel solvents proposed as alternatives for the liquid phase catalysis of lignocellulosic biomass because these can molecularly dissolve lignocellulose to high concentrations. However, solvent effects caused by ionic liquids for this application, such as how they shift the kinetics and equilibrium of lignocellulose conversion relative to other solvents, as well as if these change the nature of catalysts used and inhibit catalytic activity or unfavorably alter catalytic selectivity have not been rigorously considered. Additionally, many issues associated with the use of ionic liquids as solvents in lignocellulose conversion arise. Firstly, most ionic liquids readily undergo liquid phase thermal degradation at moderately low temperatures relevant for catalysis. Secondly, solvothermal degradation of solid catalytic materials by ILs can occur and is something not widely evaluated. Furthermore, the catalytic nature of many commonly used catalysts is altered through ion exchange between ionizable surface groups and ionic liquid ions. To understand how hydrophilic imidazolium-based ionic liquids influence the hydrolysis of lignocellulose, I examine with the aid of spectroscopic ellipsometry, UV-Vis spectrophotometry, high performance liquid chromatography, reflectance-small angle x-ray scattering, and powder x-ray diffraction the: (1) thermal degradation of a 1,2,3-trialkylimidzaolium ionic liquid; (2) solvothermal stability of mesoporous silica and gamma-alumina catalytsts; (3) behavior of the hydrolysis reaction of a lignin model compound in 1,2,3-trialkylimidzaolium ionic liquid-water mixtures; and (4) this same reaction catalyzed by gamma-alumina. From my investigations, I discover that: (1) water is able to diminish the thermal degradation of imidazolium ionic liquids when its composition is above about 35 mol% in these mixtures, an effect I propose is from two different mechanisms; (2) mesoporous silica and gamma-alumina are solvothermally stable in 25 mol% ionic liquid-water mixtures and greater, which I suggest is due to IL cation adsorption based passivation; (3) hydrolysis of a lignin model compound in 40 mol% ionic liquid-water mixtures is not kinetically favorable and selectivity for this reaction is low; and (4) gamma-alumina is insufficient at significantly catalyzing the hydrolysis of this model compound in 40 mol% ionic liquid-water mixtures possibly due to active site blockage by IL cation adsorption or mass transfer limitations.
Prosser, Jacob Husted, "Solvent Effects by Ionic Liquid-Water Mixtures on the Heterogeneous Hydrolysis of Lignocellulosic Biomass With Solid Catalysts" (2015). Publicly Accessible Penn Dissertations. 1957.