Extraction and electrochemical valorization of lignin in novel electrolytes
Aachen (2019) [Book, Dissertation / PhD Thesis]
Page(s): 1 Online-Ressource (x, 157 Seiten) : Illustrationen, Diagramme
Lignin is one of the most abundant sources of natural aromatics. Pulp and paper industry currently produces 130 million tonnes per year which are almost exclusively utilized for energy production, via combustion. The production of valuable aromatic compounds from lignin could potentially substitute or complement the utilization of fossil resources for compounds as vanillin, an important phenolic flavouring agent, or guaiacol, a fundamental chemical precursor in the polymer industry. Until now, research has been mainly concentrating on traditional routes to valorize lignin. Among others, hydrothermal and catalytic processes have been widely explored with the aim of generating high value products from lignin. However, drawbacks such as high process costs, expensive noble metal catalysts, high pressure and temperature conditions, hindered the application of these valorization processes in the industry. Therefore, alternative strategies should be taken into account to overcome these limitations. Electrochemical processes represents a feasible alternative to substitute traditional valorization processes, due to the possibility to work at room temperature and pressure and often with no need for expensive catalysts. In this thesis, electrochemical processes are applied to valorize lignin, with a particular focus on the role of the electrolyte. The influence of aqueous and non aqueous electrolytes on the depolymerization of lignin and the products´ yield has been thoroughly investigated. More specifically, innovative deep eutectic solvents were utilized as cheapnon-aqueoues electrolytes for the electrochemical depolymerization. Additionally, their potential for wood fractionation and their influence on electrode corrosion was evaluated. Beside the non aqueous electrolytes, water based hydrotropic solution and standard alkaline electrolyte were used to depolymerize lignin by means of the Fenton reaction and of an electrochemical swiss-roll reactor. Main results regarded the successful depolymerization in the deep eutectic solvent and the formation of aromatic compounds with a high selectivity for guaiacol and vanillin. Further, deep eutectic solvents were successfully used to extract lignin from beechwood. The wood pretreatment extracted a lignin with high content of ether bonds. Additionally, the stability of many electrodes in deep eutectic solvents was investigated and titanium proved to be a stable electrode. Fenton process in hydrotropic solutions and electrochemistry in alkaline electrolyte yielded high amount of carboxylic acids. The implementation of a sustainable and feasible process in several electrolytes represents a key point for bridging the pulp and paper industry and the innovative lignin valorization research. Theoretically, the lignin valorization strategies developed in this thesis, could be used to implement a larger integrated biorefinery concept.
Di Marino, Davide