Electrochemical Synthesis of Tailor-Made Hydrocarbons from Organic Solvent Free Aqueous Fatty Acid Mixtures in a Micro Flow Reactor

Abstract

The process described in the current paper is an alternative route that allows running the Kolbe electrolysis under economically attractive conditions and thus bringing it closer to an industrial application through novel process conditions, novel reactor technology, and the utilization of low-cost excess renewable electricity. The process allows the conversion of fatty acids into hydrocarbons in aqueous electrolytes without applying organic solvents. Important process parameters such as electrode material costs, surface area, and energy requirements of an electrochemical reactor in MW scale have been calculated. Depending on the fatty acid mixtures chosen, tailor-made product equivalents of jet oil, lamp oil, and diesel fuels can be achieved at high Faraday efficiency and high conversion, yields, and selectivities.

Scalable Microreactor Concept for the Continuous Kolbe Electrolysis of Carboxylic Acids Using Aqueous Electrolyte

“…Hence, at very high current densities, higher flow rates should be applied, increasing the mass transfer and improving the removal of gas bubbles to maintain high Kolbe selectivity. In addition, it was also shown that high hydroxide ion concentrations (high pH value) do not necessarily implicate in the formation of non‐Kolbe products like alcohols (aldehydes) or esters, which has been also shown in one of our previous works [22] and had been studied in detail by Harnisch et al [18] . Despite the discussed results, we could reach a very high selectivity for Kolbe products (>91 %) in the investigated current density range, and the detected differences where only small.…”

“…In addition, phase separation allows a direct recycling of the aqueous phase in a continuous operation where reactant is constantly added. [ 20 , 21 , 22 ]…”

“…In addition, phase separation allows a direct recycling of the aqueous phase in a continuous operation where reactant is constantly added. [20][21][22] Considering such a continuous process, a proper electrochemical flow cell, for example realized by a thin gap between (microstructured) electrodes where the electrolyte is pumped through, is required. Flow cells have advantages over conventional batch cells, namely higher selectivity due to the defined residence time control, good heat transfer and high space-time yields achieved by high surface-to-volume ratios and a lowered potential drop between the electrodes because of the diminished distance.…”

Enhancing the selectivity of hydrocarbons during the Kolbe electrolysis of biomass-derived short-chain carboxylic acids by anionic surfactants

“…G. Yuan et al 14 demonstrated that the selective production of hydrocarbons with different chain lengths could be achieved by designing 3D nanoscale Pt anodes with preferred orientations, for the biomass-derived n -octatonic acids in aqueous media via Kolbe electrolysis. Depending on the fatty acid mixtures (C 5 –C 9 ) chosen, A. Ziogas et al 15 obtained the tailor-made products of hydrocarbons through Kolbe electrolysis in aqueous electrolytes without organic solvents by using the microstructured reactors. Recently, D. Klüh et al 16 proposed the basic engineering design on a continuously working process for three different feedstocks (acetic acid, valeric acid and lauric acid), and it was confirmed that the long-chain fatty acids are favorable as feedstock, concerning the best carbon yield and lowest product-specific charge.…”

3D Printed Microreactors for the Continuous Non‐Kolbe Electrolysis

“…These olefins include important monomers like propylene [12,13] or ethyl acrylate [3], whereas oxygenated products show promising applications in fuel design [4] or fine chemical industry [6]. While the general reaction con-ditions of (Non-)Kolbe electrolysis were thoroughly studied [7,8], current research focuses on the substrate scope [14,15], economical and ecologically improved anodes [3,16], and sophisticated reaction engineering like in situ product separation [3,9,10] or continuous processes [10,17,18]. The Non-Kolbe electrolysis of monomethyl succinic acid enables a sustainable pathway to methyl acrylate, which is used in textile industry.…”