Fenton’s chemistry in biorefineries

  • Fenton-Prozesse in Bioraffinerien

Keller, Robert Gregor; Wessling, Matthias (Thesis advisor); Goetheer, Earl (Thesis advisor)

Aachen : RWTH Aachen University (2021)
Book, Dissertation / PhD Thesis

In: Aachener Verfahrenstechnik Series 14 (2021)
Page(s)/Article-Nr.: 1 Online-Ressource : Illustrationen, Diagramme

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2021

Abstract

Today, the energy, industrial, and transport sectors rely heavily on fossil resources as energy and carbon source. An economy based on fossil carbon leads to high emissions of green house gases, such as carbon dioxide, which cause the anthropogenic climate change. In order to prevent a further increase in the average global temperature and combat the adverse impacts it entails, power-to-x technologies and biorefineries are on the rise. Until now, the technological breakthrough of biorefineries is hampered by numerous barriers: For example, harsh chemical pretreatment conditions with the use of harmful solvents for biomass fractionation lead to high investment costs and high complexity due to non-integrated processes. This thesis presents integrated biorefinery processes based on green solvents, lignin-first conceptualization, and the coupling of electrochemical processes to cellulose depolymerization. Lignin was extracted from beech wood chips by employing hydrotropic and deep eutectic solvents. Subsequently, lignin was depolymerized via Fenton’s chemistry in the hydrotropic solvent and coupled with an in situ extraction. Fenton’s chemistry was additionally investigated for the depolymerization of cellulose that was studied using the model compound cellobiose. The process was electrified as electro-Fenton and coupled with an in situ membrane separation. Lignin was extracted with up to 80% yield with deep eutectic and hydrotropic solvents. The highest yields were obtained with high pretreatment temperatures of 120 and 200 °C, respectively, and small wood chip sizes. The lignin that was extracted in a hydrotropic solution was depolymerized to aromatics in the solvent itself. Even though the depolymerization was successful and an in situ extractionwas employed, only low amounts of value-added aromatics were obtained. Organic acids were found to be the main product of the depolymerization with a yield of up to 30% based on the initial lignin concentration. Glucose was successfully formed by the depolymerization of cellobiose using Fenton’s reagent. However, the selectivity was limited to values below 30% for all parameters tested in this work. With increasing reaction time, the selectivity decreased continuously due to the oxidation of glucose by Fenton’s reagent. Thus, a nanofiltration separation stage was coupled to the (electro-)Fenton process. Experimental and simulation results demonstrated that the separation prevents overoxidation of glucose while simultaneously retaining the reactant cellobiose and the catalyst iron in the Fenton reactor. This thesis emphasizes the need for integrated processes in biorefineries. Electrochemical processes provide the opportunity to drive reactions by an electrical potential that is powered by renewable electricity. When using Fenton’s chemistry for the formation of value-added compounds a strong focus must be laid on in situ separation techniques to prevent degradation of the target products.

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