Liquid–Liquid Equilibrium Data and Continuous Process Concept for the Electrosynthesis of Valeric Acid from Levulinic Acid

Abstract

Aiming toward a scalable continuous electrochemical production of valeric acid, the mutual insolubility of valeric acid with the aqueous reaction medium of levulinic acid and the aqueous electrolyte are investigated in order to assess the possibility for an integrated product separation based on the liquid-liquid equilibrium of the system. The influence of the electrolyte concentration in the mixture and the mixture temperature on the liquid-liquid equilibrium is studied. Based on these results, the possibility for a batch and a continuous product separation process is developed and discussed.

Electroreductive upgradation of biomass into high-value chemicals and energy-intensive biofuels

“…Compared to the traditional reduction pathways, ECH is more suitable for biomass upgrading, whether from an operational or economic point of view. [43][44][45][46] Along this direction, three prevalent catalytic models have been established. 46 Direct utilization of inert electrodes (e.g., Pt, Pb, and carbon electrodes) is the most well-studied catalytic method, but is not efficient enough (Fig.…”

“…57 A catalyst or electrode with high surface area, high chemical stability, and suitable coordination numbers of the active sites are generally able to deliver better activity. 43,58 The optimized catalyst in an acidic medium exhibited poor activity and stability in a basic medium, imply-ing that a negative cathodic potential is required to offer rational current densities to reduce the substrate. For specific electrodes and substrates, even at the same potential, a change of electrolyte pH will lead to different products, giving a hint that the catalytic mechanism may be distinguishing in different electrolytes, as detailed in section 3.…”

Electrochemical Depolymerization of Lignin in a Biomass‐based Solvent**

“…Here, we explored a one-step approach for the reductive catalytic fractionation (RCF) of lignin, which consisted in its solubilization/depolymerization in levulinic acid, selectively forming aromatic monomers. As levulinic acid can be also reduced via different methods, [38][39][40] including electrochemical routes, [41][42][43][44][45] the 5.17 m aqueous solution of levulinic acid, with and without kraft lignin, was tested in a linear sweep voltammetry (LSV) experiment (Figure 2). Potentials over À 1.5 V exhibited different current densities, with the highest value for the solution containing lignin.…”

Closing the Gap: Towards a Fully Continuous and Self‐Regulated Kolbe Electrosynthesis

“…Thus, the products of electrochemical transformations (e. g., hydrogenations, hydrodeoxygenations, decarboxylations) of polar biogenic compounds are often significantly less polar than their precursors, leading to a reduced solubility and therefore the option to achieve a separation of the insoluble product phase (liquid or solid) from the electrolyte phase. [8,[12][13][14] Kolbe reactions are generally performed at slightly acidic pH values. [15] This pH range can be understood as a compromise between the necessary acidic reaction conditions to avoid the Hofer-Moest-reaction [16] (see Scheme 1) on the one hand and the required deprotonation of the carboxylic group for a sufficiently high carboxylate concentration.…”

“…Using aqueous electrolyte solutions also offers an elegant product separation opportunity. Thus, the products of electrochemical transformations (e. g., hydrogenations, hydrodeoxygenations, decarboxylations) of polar biogenic compounds are often significantly less polar than their precursors, leading to a reduced solubility and therefore the option to achieve a separation of the insoluble product phase (liquid or solid) from the electrolyte phase [8,12–14] . Kolbe reactions are generally performed at slightly acidic pH values [15] .…”