Date of Award

Summer 7-18-2014

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

First Advisor

John W. Daily

Second Advisor

G. Barney Ellison

Third Advisor

Veronica M. Bierbaum

Abstract

Limited fossil fuel resources and climate impacts due to carbon dioxide emissions have made it critical that we use renewable, carbon-neutral fuels. Biomass, in the form of crop waste or the inedible portion of plants, has the potential to be a renewable and economical source of energy. Recent developments in the conversion of lignocellulosic biomass have sparked an interest in the production of biofuels and valuable platform chemicals, synthesizing molecules such as alkylated furans, furanic ethers, and various lactones. Early studies indicate that many of these potential furanic and lactonic fuels have similar properties to gasoline or diesel, however, little is known about their pyrolytic and combustion behavior.

In order to establish a molecular picture of the first thermal products formed from the pyrolysis and oxidation of furanic biofuels, a microtubular flow reactor was used to thermally decompose furan, 2-methoxyfuran, and select lactones. Dilute samples of these molecules were entrained in He or Ar and thermally cracked in a heated silicon carbide microreactor. Products, including radicals and metastables formed at early pyrolysis times (50−200 μs), were detected by 118.2 nm (10.487 eV) photoionization mass spectrometry (PIMS), tunable synchrotron vacuum ultraviolet PIMS and Ar matrix infrared spectroscopy. As most initiation rates need to be calculated because they are too difficult to measure, the experimental results presented in this thesis demonstrate progress towards validating these calculations, aiding in the development of accurate initiation chemistry for kinetic mechanisms.

The published mechanism for pyrolysis of furan (C4H4O), the parent compound of the more complicated furans described above, involves decomposition via a pair of carbenes. The product branching ratio of this reaction was measured over a range of temperatures and compared to predictions of three published furan kinetic mechanisms. A higher-energy radical channel that produces propargyl radical (HCCCH2) and H-atom was also detected and quantified.

The unimolecular and low-pressure bimolecular decomposition mechanisms of the simplest furanic ether, 2-methoxyfuran, were also studied. Recent electronic structure calculations indicate this substituted furan has an unusually weak O−CH3 bond, which results in bond scission and the production of CH3 and 2-furanyloxy radicals. The final products detected from the ring opening of 2-furanyloxy radical include 2 CO, HCCH and H. Secondary products resulting from H or CH3 addition to the parent and radical reactions with 2-furanyloxy were also detected and include CH2=CH-CHO, CH3-CH=CH-CHO, CH3-COCH= CH2 and furanones. In addition to detection and quantification of the primary pyrolysis products, this work also includes the first experimental characterization of 2-furanyloxy radical by the assignment of several vibrational bands in an Ar matrix and a low-resolution estimate of the ionization threshold of this allylic lactone. Finally, the pyrolysis products of the lactones 2(5H)-furanone, 2(3H)-furanone and _-angelica lactone (5-methyl-2(3H)-furanone) were identified by 118.2 nm PIMS and Ar matrix IR spectroscopy as these species were also shown to be relevant to the decomposition of 2-methoxyfuran.

Furans and lactones are among a variety of molecules derived from non-edible biomass that offer a renewable path to biofuels. Since the pyrolytic behavior of these oxygenated fuels are not well-known this work contributes to the field by identifying the first thermal products, helping to elucidate possible chemical mechanisms for emission formation from these biofuels.

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