Jan Bilek

Date of Award

January 2017

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemistry

First Advisor

Alena Kubatova

Second Advisor

Evguenii Kozliak

Abstract

A novel analysis method of lignin and its degradation products was developed based primarily on thermal desorption and pyrolysis coupled with carbon quantification and speciation. Gas chromatography-mass spectrometry (GC-MS) is a traditional method for characterization of the volatile product fraction, however the volatile (thermal desorption) fraction usually contributes less than 10%wt. of the overall product yield. The unique properties of thermal carbon analysis (TCA) allow not only for the analysis of the thermal desorption fraction (200–300 у), which may further be compared to the GC-MS results, but also for the analysis of higher molecular weight oligomers evolving at pyrolytic temperatures (400–890 у). In addition, using an oxygenation step (550–890 у in the presence of oxygen) as the final step, it is possible to evolve the rigid cross-linked oligomers, inorganic carbon and other remaining carbon forms and close the mass balance. The key TCA parameters, drying and purging time, were evaluated in different solvent systems in order to ensure a near-100% recovery of all the lignin degradation products. Furthermore, other factors potentially affecting the TCA profile, such as sample loading, interactions with the sampling surface and initial step temperature, were evaluated.

In the second main part of this study, the lignin hydrotreatment reactions performed in a lab scale, static batch reactor were evaluated using both TCA and GC-MS. The effect of the reaction temperature and the presence of a catalyst, particularly different nickel based catalysts, zeolites, activated carbon and silica-alumina, were studied. The overall yield of monomeric and dimeric degradation products increased with temperature. A promising result was obtained at reactions conducted at 300 у in the presence of LaO doped activated carbon and zeolite catalysts, where the total yield of volatiles was 5.3 and 6.3%wt., respectively. In addition, a significant amount of dimers over 1.0%wt. was produced. A good agreement between the GC-MS and thermal desorption fraction of TCA was obtained. Combining the overall TCA yield of carbon with gravimetric data of unreacted lignin lead to a successful mass balance closure.

Ultimately, a complete mass balance closure was also obtained for the solid alkali lignin analyzed by TCA with the newly developed protocol and the results were compared with TGA, proving the excellent TCA analytical performance and selectivity towards the carbon containing species. Another parallel comparison was made using Pyrolysis-GC-MS in order to identify the lignin degradation products contributing to the carbon evolved in each temperature fraction.

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