Conversion of Carbon Dioxide and Crude Glycerine into Value-Added Products
Creators: Rodriguez Herrero, Yanet
Publisher: name: University of Alberta Library
Year: 2023

<p>Modern civilization has become dependent on fossil fuels as a source of energy and chemicals. As a result, the rapid industrial development and growing energy demand are pushing toward two imminent problems, the depletion of fossil fuel reserves and the negative impact on global climate. Subsequently, the lookout for renewable alternatives as energy sources and chemical feedstock has mobilized the academic community and the industry to adapt existing technologies and develop new methodologies. Biomass is currently the most widespread alternative feedstock due to its availability and relatively short regeneration cycle, yet its valorization has to deal with the waste that results from biomass processing. For instance, the biodiesel industry, the second larger biofuel manufacturer, generates approximately 10 wt.% of crude glycerol from the transesterification of vegetable oil, and 0.71 kg of CO2 is released into the atmosphere per liter of biodiesel combusted as vehicle fuel.<br><br>
Thus, this thesis focuses on valorization routes for the major by-products from the biodiesel industry. We investigated the catalytic conversion of carbon dioxide (CO2) to methanol, and a microwave-assisted metal-free catalytic route for glycerol transformation to allyl monomers and polymers. The general background is presented in the literature review, and the results are discussed in three data chapters as follows: <br>
In the first study, CO2 was reduced to methanol in mini-batch reactors using a Cu/ZnO as an active phase supported in a novel hydrophobic material, phenyl polyhedral oligomeric silsesquioxane (POSS). Two types of POSS nanoparticles, octaphenyl POSS (O-POSS) and dodecaphenyl POSS (D-POSS) were compared to evaluate the influence of the cage size and the number of ligands in the CO2 conversion and methanol yield. The nanoparticles had an average size of 7 nm (CuO/ZnO/O-POSS) and 15 nm (CuO/ZnO/D-POSS). The structural characterization of the as-synthetized materials revealed that CuO/ZnO were electron withdrawers from POSS. Furthermore, the increased number of phenyls attached to the siloxane cage augmented the catalytic system&#39;s hydrophobic character, resulting in higher CO2 conversion and methanol yield under the conditions studied. <br>
Furthermore, we identified that the hydrophobic nature of the supports plays a decisive role in driving the reaction to completion. These conclusions emerged after comparing the results with Cu/ZnO supported on reduced graphene oxide (RGO). Although RGO had a higher surface area due to its hydrophilic character but yielded 0% of methanol under the conditions studied. Finally, the thermal gravimetric analysis in a nitrogen atmosphere revealed the thermal stability of the new catalytic systems under the interest temperature range (200 °C – 270 °C).<br>
The second study deepened the thermal stability of the catalytic system CuO/ZnO/POSS. We identified irreversible thermal events with low transition energy associated with the supports&#39; molecular relaxation and crystalline arrangements. The impregnation, followed by mild calcination of the metal oxides CuO/ZnO, did not interfere with the thermal stability of supports until about 450 °C. Nevertheless, as temperature increased above 450 °C, the metal oxides accelerated the support degradation rate. <br>
In the third study, glycerol was converted to allyl alcohol through a formic acid-mediated metal-free deoxydehydration reaction under microwaves. The produced allyl alcohol was also converted to allyl formate and allyl phthalate. The synthesized monomers (allyl alcohol, allyl formate, and allyl phthalate) were polymerized using microwave-assisted polymerizations. The microwave-assisted method resulted in faster conversions and higher energy efficiency (&gt;16 times less energy consumption) compared to the conventional heating method to produce allyl alcohol. Furthermore, a three-factor, three-level Box-Behnken response surface design was performed to investigate the influence of time, temperature, and molar ratio on the yield of allyl alcohol and allyl formate. The results showed that temperature and molar ratio between formic acid to glycerol had a more significant effect on the reaction, whereas the reaction time did not impact the yield of allyl alcohol. <br>
In summary, this thesis developed two approaches for utilizing two waste-biomass resources to value-added products using friendly technologies such as microwaves, which helped to reduce reaction time and minimize energy consumption. Overall, this research would benefit the biodiesel industry to utilize glycerol and petrochemical industries to deepen the know-how to improve CO2 catalytic conversion.</p>