Bio-Electrocatalytic Conversion of Food Waste to Ethylene via Succinic Acid as the Central Intermediate

Abstract

Ethylene is an important feedstock in the chemical industry, but currently requires production from fossil resources. The electrocatalytic oxidative decarboxylation of succinic acid offers in principle an environmentally friendly route to generate ethylene. Here, a detailed investigation of the role of different carbon electrode materials and characteristics revealed that a flat electrode surface and high ordering of the carbon material are conducive for the reaction. A range of electrochemical and spectroscopic approaches such as Koutecky−Levich analysis, rotating ring-disk electrode (RRDE) studies, and Tafel analysis as well as quantum chemical calculations, electron paramagnetic resonance (EPR), and in situ infrared (IR) spectroscopy generated further insights into the mechanism of the overall process. A distinct reaction intermediate was detected, and the decarboxylation onset potential was determined to be 2.2−2.3 V versus the reversible hydrogen electrode (RHE). Following the mechanistic studies and electrode optimization, a two-step bio-electrochemical process was established for ethylene production using succinic acid sourced from food waste. The initial step of this integrated process involves microbial hydrolysis/fermentation of food waste into aqueous solutions containing succinic acid (0.3 M; 3.75 mmol per g bakery waste). The second step is the electro-oxidation of the obtained intermediate succinic acid to ethylene using a flow setup at room temperature, with a productivity of 0.4−1 μmol ethylene cm electrode −2 h −1 . This approach provides an alternative strategy to produce ethylene from food waste under ambient conditions using renewable energy.

Photocatalytic production of ethylene and propionic acid from plastic waste by titania-supported atomically dispersed Pd species

“…As can be seen in Fig. 5C, the signals of carbon-centered alkyl radical (•CH 2 R) and hydroxyl radical (•OH) are observed for Pd 1 -TiO 2 (36,63). The alkyl radical is recognized as the key intermediate for Kolbe oxidations (15,64).…”

Electrocatalytic upcycling of plastic waste

“…11d and e). 87 The use of a graphite anode resulted in the highest FE of ethylene (27.5%) at 2.8 V vs. RHE in 0.08 M succinic acid aqueous solution ( pH 10). According to the DFT calculation and EPR spin-trapping experiment results, the ECDX of succinic acid undergoes sequential decarboxylation via monoalkyl-radical species; however, the formation of diradical species via direct 2e − oxidation cannot be neglected.…”

Alternatives to water oxidation in the photocatalytic water splitting reaction for solar hydrogen production

“…11 To this end, the photooxidation of food wastes and nonrecycled plastics has recently become an emerging topic in the field. 11,[37][38][39][40][41][42][43][44] The chemical composition of food waste varies greatly. Due to their hydrophobicity and typically chemically inert hydrocarbon chain, photoreforming fats in an aqueous solution is more difficult than photoreforming proteins composed of long chains of amino acid residues (Table 1).…”

“…Controlling the oxidation half-reaction is essential to produce high-value organic products instead of CO 2 . 21,41 In addition, pre-treatment, including physical pre-treatment (such as crushing, shredding, and grinding) and chemical pre-treatment (such as hydrolysis and solubilization under highly alkaline or acidic conditions), is one of the most critical barriers to the practical application of the current photocatalytic reforming systems, adding significant cost and time to the overall process. Recently, it was demonstrated that metal salt hydrate solutions allowed for the complete solubilization of biomass and could be used as a reaction medium for the photocatalytic reforming of lignocellulose to produce H 2 and organic products under more benign conditions than the typically required extremely alkaline aqueous solutions, though the photocatalysts suffered from partial deactivation due to metal salt hydrate adsorption, necessitating future development.…”