Abstract

Energy usage is continually on the rise and significant efforts are being extended to provide more renewable energy. One area of exploration is the development of fuel cells, which includes biofuel cells that can extract energy from carbohydrates obtained from biomass. Recently, viologen catalysts have been shown to enhance reaction rates of energy extraction and improve carbohydrate conversion efficiencies. However, characterizing the effects of process parameters such as pH, reactant concentrations, and carbohydrate exposure time to buffer solutions with a rigorous model is lacking. This thesis characterizes the homogeneous reaction between carbohydrates and a methyl viologen catalyst to provide insights on ways to enhance the reaction rates to produce more energy. Specifically, the rate of formation of reduced methyl viologen (MV+) in the presence of carbohydrates was measured based on changes in the MV2+ concentration, carbohydrate concentration, pH, and carbohydrate exposure time. A rigorous mechanistic model of the reaction rate was developed and showed a first-order dependence on OH- concentration, a zero-order dependence when the MV2+ concentration was >> 0.5 mM, and a 3-fold increase in the reaction rate when glucose was pre-incubated in a pH 12 buffer solution for 100 minutes. The pre-incubation effect had a strong dependence on pH. The mechanistic model agreed well with experimental data. This thesis also addresses the decomposition of viologen catalysts. MV2+ decomposition experiments showed a trend seen previously in literature that the rate of decomposition increases with an increase in MV2+ concentration, OH- concentration, and temperature. The data and mechanistic model suggest second order dependence of both MV2+ and OH- concentrations under conditions in this thesis (MV2+ concentrations of 100-300 mM and OH- concentrations of 0.001 M and 0.01 M). An activation energy was found from MV2+ decomposition to be 145 kJ/mol. MMV+ decomposition was shown to decompose anywhere from 6.2 – 16.1 times slower than MV2+. Therefore, MMV+ decomposes slower and is more stable than MV2+. It was also found that MV2+ is more stable than IPV-Cl and IPV-Br. An analysis was performed to find the recommended operating range for MV2+/glucose biofuel cells under different conditions while ensuring that at least a viable amount of energy could be produced.

Degree

MS

College and Department

Ira A. Fulton College of Engineering and Technology; Chemical Engineering

Rights

http://lib.byu.edu/about/copyright/

Date Submitted

2018-07-01

Document Type

Thesis

Handle

http://hdl.lib.byu.edu/1877/etd10310

Keywords

fuel cell, viologen, kinetics, model, carbohydrate

Language

english

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