Einsatz der Elektrochemie zur Veredelung von biogenen Plattform-Chemikalien
- Use of electrochemistry to upgrade biogenic platform chemicals
Holzhäuser, Fabian Joschka; Palkovits, Regina (Thesis advisor); Waldvogel, Siegfried R. (Thesis advisor)
Aachen (2019, 2020)
Dissertation / PhD Thesis
Dissertation, RWTH Aachen University, 2019
This dissertation deals with the development of concepts for electrical energy storage by electrochemical conversion of renewable raw materials to industrially relevant fine chemicals and fuel additives. In this context, different reactions are investigated that could be used in an "electro"-bio-refinery. The Kolbe electrolysis of biogenic valeric acid into n-octane was investigated in an in situ NMR study. The electromagnetic environment of the low-field spectrometer led to a more efficient conversion of valeric acid to n-octane compared to experiments outside a NMR spectrometer. Most likely this is due to an improved mass transport of the substrate caused by the Lorentz force and a reduction of the charge transfer resistance. Furthermore, the most important transferable findings of the valeric acid Kolbe electrolysis were used in order to electrochemically convert other biomass obtainable acids. Various derivatives of succinic acid and methyl succinic acid were electrochemically cross-coupled or converted into fine chemicals via Non Kolbe electrolysis. In this regard, different alkanes or esters were obtained as products. Dimethyloctane and dimethyldecane could be produced in yields of 41% and 46% respectively. They possess promising properties to be considered as fuel alternatives. Using a real current profile from a wind turbine and Kolbe electrolysis, succinic acid mono-methyl ester could be converted into diethyl adipate (60%). After simple hydrolysis, diethyl adipate can be converted into the industrially relevant fine chemical adipic acid. In these experiments an alternative electrode to the conventionally used platinum electrode was investigated. The dimensionally stable RuxTi1-xO2 electrode was successfully utilized for both cross-coupling and mono-coupling. Acrylic acid, likewise industrially relevant, could be produced via Non-Kolbe electrolysis in its esterified precursor form (50%) from succinic acid mono-methyl ester. In addition to (Non)-Kolbe electrolysis, this dissertation also investigated the electrocatalytic hydrogenation of itaconic acid to methylsuccinic acid (96%). In this regard, various electrode catalysts were used and the optimal current potential was evaluated. Noteworthy, the efficient conversion of itaconic acid into methylsuccinic acid from untreated fermentation broth was achieved. The yield of methylsuccinic acid was only marginally different for both a pure solution and a fermentation broth of itaconic acid (64% to 60%). These results could not be achieved by a comparative thermocatalytic study using Ru/C or Raney nickel as hydrogenation catalyst. Lastly, the electrocatalytic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid was investigated. First, general reaction conditions, such as substrate concentration and pH value, were optimized and various electrocatalysts were tested in the following step. NiO in the CMK-1 structure showed the highest conversion (75%) and selectivity (93%) in the oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid. NiO/CMK-1 was also stable over at least five catalytic cycles despite a very high pH and oxidative potentials.