Rongkai Chen

Date of Award

5-2012

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Chemical Engineering

Advisor

M. Clayton Wheeler

Second Committee Member

William J. DeSisto

Third Committee Member

Brian G. Frederick

Abstract

The continuously rising price and non-renewable characteristic of fossil fuel make it urgent to develop alternative energy sources. Plant biomass is a potentially sustainable carbon source for liquid transportation fuels and chemicals. As an abundant and inexpensive resource, lignocellulosic biomass can be converted into liquid fuels through several primary routes such as gasification, pyrolysis, hydrolysis in addition to biological and biochemical routes. Fast pyrolysis can produce a high yield of liquid products called bio-oil. The bio-oil has many unfavorable properties including lower energy content, high acidity, high viscosity and poor thermal stability due to the high oxygen contents. Hydrodeoxygenation (HDO) using heterogeneous catalysts has been studied by researchers in our group as a method to upgrade bio-oils. The classes of catalysts which have been studied including noble metals, metal sulfides, metal oxides and metal nitrides. Reducible metal oxides, as a new class of HDO catalysts, have demonstrated their abilities of selectively breaking carbon-oxygen bonds. Therefore, it is of interest to investigate the characteristics of these catalysts for HDO. Evidence has shown that the active phase of metal oxides is a hydrogen bronze whose formation is similar to the Mars-van Krevelen cycle. Micro-calorimetry can be useful for studying catalytic reactions because micro-calorimeters can be rapidly heated and cooled, (τ ~5 ms) This allows development of dynamic temperature operation at rates which are characteristic of surface reaction processes. Also, the short heating/cooling cycle promises potential for screening HDO catalysts compared to traditional reactor screening methods. The nano-calorimeters which were used in this work were fabricated in the clean room facilities of the University of Maine's Laboratory for Surface Science and Technology. An analog circuit was designed for feedback control of the temperature of the nano-calorimeter. Using the measured response characteristics of the nano-calorimeter and controller, a model was built to predict the of the nano-calorimeter response to reactions for a variety of experiment protocols. The experiment models were then used to estimate the sensitivity of the experiment measurements for typical material properties and reaction rate parameters. Tungsten oxide film was chosen as model oxide because of its relatively high heat of reaction during redox reactions and readily available deposition technology in our group. The behavior of the circuit was predicted under several conditions including different thickness and temperature programs. With the WO3 film being 1 (μm thick, the power of reaction was detectable under a mild temperature program (200 K/s). But if the film thickness was reduced to 0.1 (μm, the circuit needed more aggressive temperature programs to be able to detect the reaction power. Experiments were planned using the nano-calorimeters to explore hydrogen bronze formation of WO3 which had previously been characterized using thermogravimetry. Two metal oxides were deposited as thin films on the nano-calorimeter using both chemical vapor deposition and physical vapor deposition. Scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to characterize the thin films. Unfortunately, the nano-calorimeters failed during reaction testing, and it was unfeasible to reproduce the devices as part of this thesis.

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