Mechanistic Study and Development of a Catalyst for Glycerol Conversion to Acrolein : 글리세롤 탈수반응의 반응기작 연구와 안정적인 촉매 개발

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공과대학 화학생물공학부
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서울대학교 대학원
Glycerol dehydrationacroleina sustainable catalystreaction mechanism
학위논문 (박사)-- 서울대학교 대학원 : 화학생물공학부, 2017. 2. 이종협.
Since the demand for a clean and green technology has increased, countless efforts have been made to replace conventional petrochemical processing. Biomass could be a solution to satisfy the needs of the times because it has a potential for producing fine chemicals or building blocks without increasing greenhouse gas emissions. Therefore, various studies concerning the production of value-added chemicals from biobased compounds have been reported in recent years. In particular, the conversion of glycerol to acrolein has attracted a considerable amount of attention as an alternative route to the production of acrolein from petroleum-based propylene. Furthermore, an increasing cost ratio of acrolein to glycerol in recent years makes the conversion also economically viable. In this thesis, catalytic mechanism for glycerol dehydration via Brønsted acid site is studied, and a sustainable catalyst for acrolein production is developed.
At first, the catalytic mechanism of glycerol dehydration on Brønsted acidic amorphous aluminosilicate is explored via first principle calculation. Si-(OH)-Al groups of amorphous aluminosilicate have been known to play important roles in acid catalyzed reactions. However, there is a lack of theoretical understanding on the catalytic function of the acid sites and reaction mechanisms on the amorphous aluminosilicate surface. Here, the preferred glycerol dehydration mechanism on Si-(OH)-Al sites was investigated. It was found that when the primary OH group of glycerol is adsorbed on Brønsted proton (Si-(OH)-Al sites), the adsorption strength is too strong to convert to acetol. On the other hand, the secondary OH group of glycerol is adsorbed with a relatively moderate strength at the acid site, which then leads to favorable production of 3-hydroxypropionaldehyde (3-HPA). Consequently, the 3-HPA is readily dehydrated into acrolein and water due to its reactive properties. Therefore, glycerol is preferentially converted into acrolein on amorphous aluminosilicate during dehydration. In order to verify the preferential formation of acrolein, catalytic activity test was experimentally conducted. The amorphous aluminosilicate catalyst exhibited remarkable selectivity for acrolein (39.8%), which supported our theoretical approach. In addition, the adsorbed and polymerized glycerol on the used catalyst surface was identified via 13C NMR. This suggests that when glycerol is too strongly adsorbed, it can be transformed into coke during dehydration. Combining our theoretical and experimental observations, it was concluded that strongly adsorbed glycerol gives rise to not only a lower level of conversion to acetol, but also coke deposition on the amorphous aluminosilicate surface.
Then, a catalyst for the sustainable conversion of glycerol to acrolein is designed and investigated. Developing a catalyst to resolve deactivation caused from coke is a primary challenge in the dehydration of glycerol to acrolein. An open-macropore-structured and Brønsted-acidic catalyst (Marigold-like silica functionalized with sulfonic acid groups, MS-FS) was synthesized for the stable and selective production of acrolein from glycerol. A high acrolein yield of 73% was achieved and maintained for 50 h in the presence of the MS-FS catalyst. The hierarchical structure of the catalyst with macropores was found to have an important effect on the stability of the catalyst because coke polymerization and pore blocking caused by coke deposition were inhibited. In addition, the behavior of 3-hydroxypropionaldehyde (3-HPA) during the sequential dehydration was studied using density functional theory (DFT) calculations because 3-HPA conversion is one of the main causes for coke formation. We found that the easily reproducible Brønsted acid sites in MS-FS permit the selective and stable production of acrolein. This is because the reactive intermediate (3-HPA) is readily adsorbed on the regenerated acid sites, which is essential for the selective production of acrolein during the sequential dehydration. The regeneration ability of the acid sites is related not only to the selective production of acrolein but also to the retardation of catalyst deactivation by suppressing the formation of coke precursors originating from 3-HPA degradation.
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College of Engineering/Engineering Practice School (공과대학/대학원)Dept. of Chemical and Biological Engineering (화학생물공학부)Theses (Ph.D. / Sc.D._화학생물공학부)
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