(Non-)Kolbe electrolysis in biomass valorization – a discussion of potential applications

Holzhäuser, F. Joschka; Mensah, Joel B.; Palkovits, Regina

doi:10.1039/c9gc03264a

Cited by 76 publications

(97 citation statements)

References 95 publications

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“…The electrolyte concentration in relation to the pH value of the solution on the other hand significantly influenced the reaction outcome. Although Harnisch and co‐workers recently showed an independence of the product composition on the initial pH values, [1c,19] other sources state that Kolbe reactions are preferred to be carried out in neutral to slightly acidic media, while for Non‐Kolbe electrolysis a slightly alkaline environment is preferable [1a,b] . The described reaction performs best, similar to Kolbe couplings, at a pH value of 5.7 with 65 % of product yield, corresponding to a triethylamine concentration of 0.8 M (Table 1, entry 6).…”

Section: Resultsmentioning

confidence: 99%

“…The disproportionation to dimerization ratio of the radical R⋅ may be higher than for most homogeneous reactions, nevertheless this olefin formation route plays only a subordinate role in Kolbe electrolysis [2b] . Alternative alkene or alkyne synthesis methods are, however, never being referenced as part of the portfolio of this well studied reaction class [1a,8] …”

Section: Introductionmentioning

confidence: 99%

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Intramolecular Biradical Recombination of Dicarboxylic Acids to Unsaturated Compounds: A New Approach to an Old Kolbe Reaction

et al. 2020

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The Kolbe or Non‐Kolbe electrolysis is one of the most studied electro‐organic reactions and a fundamental pillar of organic chemistry. In contrast to classical Kolbe dimerization of monocarboxylic acids, dicarboxylic acids are only scarcely subject for Kolbe electrolysis in the literature despite their vast natural abundance. Herein, we report on the intramolecular biradical recombination of dicarboxylic acids as a green way to prepare alkenes or alkynes over a newly proposed mechanistic route. Proceeding over a radical mechanism without dimerization, it clearly stands out from classical (Non‐)Kolbe electrolysis. In the presence of non‐toxic aqueous solvents, the desired products form in excellent yields (up to 83 %), which are the highest reported for this substrate class. Once feasibility had been shown for the electrolysis of methylsuccinic acid, we could demonstrate its application to a broad scope of different dicarboxylic acids.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Intramolecular Biradical Recombination of Dicarboxylic Acids to Unsaturated Compounds: A New Approach to an Old Kolbe Reaction

et al. 2020

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“…For instance, MCC-enriched waste-derived oil may be converted into less polluting biodiesels due to their potential lower unsaturation levels compared to conventional biodiesel [ 64 ]. LCC triglycerides in the enriched oil may be hydrolyzed to convert the resulting LCC and MCC salts into chemicals or aviation fuels through (non-)Kolbe electrolysis [ 65 ]. Sustainable aviation fuels (SAF) produced from waste oils and fats show high CO 2 savings (> 85%) compared to conventional aviation fuels [ 66 ] and ~ 7% of annual aviation fuel consumption could be replaced by SAF obtained from microbially produced MCC [ 6 ] in integrated (electro)biorefineries.…”

Section: Discussionmentioning

confidence: 99%

Reactor microbiome enriches vegetable oil with n-caproate and n-caprylate for potential functionalized feed additive production via extractive lactate-based chain elongation

Contreras-Dávila

Zuidema

Buisman

et al. 2021

Biotechnol Biofuels

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Background Biotechnological processes for efficient resource recovery from residual materials rely on complex conversions carried out by reactor microbiomes. Chain elongation microbiomes produce valuable medium-chain carboxylates (MCC) that can be used as biobased starting materials in the chemical, agriculture and food industry. In this study, sunflower oil is used as an application-compatible solvent to accumulate microbially produced MCC during extractive lactate-based chain elongation. The MCC-enriched solvent is harvested as a potential novel product for direct application without further MCC purification, e.g., direct use for animal nutrition. Sunflower oil biocompatibility, in situ extraction performance and effects on chain elongation were evaluated in batch and continuous experiments. Microbial community composition and dynamics of continuous experiments were analyzed based on 16S rRNA gene sequencing data. Potential applications of MCC-enriched solvents along with future research directions are discussed. Results Sunflower oil showed high MCC extraction specificity and similar biocompatibility to oleyl alcohol in batch extractive fermentation of lactate and food waste. Continuous chain elongation microbiomes produced the MCC n-caproate (nC6) and n-caprylate (nC8) from l-lactate and acetate at pH 5.0 standing high undissociated n-caproic acid concentrations (3 g L−1). Extractive chain elongation with sunflower oil relieved apparent toxicity of MCC and production rates and selectivities reached maximum values of 5.16 ± 0.41 g nC6 L−1 d−1 (MCC: 11.5 g COD L−1 d−1) and 84 ± 5% (e− eq MCC per e− eq products), respectively. MCC were selectively enriched in sunflower oil to concentrations up to 72 g nC6 L−1 and 3 g nC8 L−1, equivalent to 8.3 wt% in MCC-enriched sunflower oil. Fermentation at pH 7.0 produced propionate and n-butyrate instead of MCC. Sunflower oil showed stable linoleic and oleic acids composition during extractive chain elongation regardless of pH conditions. Reactor microbiomes showed reduced diversity at pH 5.0 with MCC production linked to Caproiciproducens co-occurring with Clostridiumtyrobutyricum, Clostridiumluticellarii and Lactobacillus species. Abundant taxa at pH 7.0 were Anaerotignum, Lachnospiraceae and Sporoanaerobacter. Conclusions Sunflower oil is a suitable biobased solvent to selectively concentrate MCC. Extractive reactor microbiomes produced MCC with improved selectivity and production rate, while downstream processing complexity was reduced. Potential applications of MCC-enriched solvents may include feed, food and biofuels purposes.

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“…shows the main mechanisms proposed for (non)-Kolbe electrolysis reactions. 14,16 Carboxylic acids (R-COOH) undergo a proton-coupled electron transfer Scheme 1. The reaction network for a) the overall Kolbe electrolysis of carboxylic acids (R-COOH) including the Kolbe reactions resulting in the formation of alkanes (highlighted in blue), and the Non-Kolbe reactions resulting in the formation of alkenes, esters and alcohols (Hofer-Moest product).…”

Section: Scheme 1(a)mentioning

confidence: 99%

“…With the electrochemical conversion of biomass derivatives as a potential means of green chemical production [1][2][3] , electro-organic synthesis is experiencing a revival [4][5][6][7][8][9][10] Compared to conventional catalytic (de)-hydrogenation reactions, electrocatalytic conversion schemes offer several advantages: a) they operate at ambient conditions, b) they can be powered by sustainable electricity from wind and solar energy, and c) they require only water as the proton source instead of expensive hydrogen feeds [11][12][13] . Kolbe electrolysis is a central reaction in electro-organic synthesis since it could be applied to produce longchained hydrocarbons [14][15][16] . The electrolysis of carboxylic acid was first observed by Faraday 17 , and Hermann Kolbe identified ethane and octane as the respective products of the electrolysis of acetic and valeric acid 18 .…”

Section: Introductionmentioning

confidence: 99%

Understanding the reaction mechanism of Kolbe electrolysis on Pt anodes

Liu

Govindarajan

Prats

et al. 2021

Preprint

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Kolbe electrolysis has been proposed an efficient electrooxidation process to synthesize (un)symmetrical dimers from biomass-based carboxylic acids. However, the reaction mechanism of Kolbe electrolysis remains controversial. In this work, we develop a DFT- based microkinetic model to study the reaction mechanism of Kolbe electrolysis of acetic acid (CH3COOH) on both pristine and partially oxidized Pt anodes. We show that the shift in the rate-determining step of oxygen evolution reaction (OER) on Pt(111)@α-PtO2 surface from OH* formation to H2O adsorption gives rise to the large Tafel slopes, i.e., the inflection zones, observed at high anodic potentials in experiments on Pt anodes. The activity passivation as a result of the inflection zone is further exacerbated in the presence of Kolbe species (i.e., CH3COO* and CH3*). Our simulations find the CH3COO* decarboxylation and CH3* dimerization steps determine the activity of Kolbe reaction during inflection zone. In contrast to the Pt(111)@α-PtO2 surface, Pt(111) shows no activity towards Kolbe products as the CH3COO* decarboxylation step is limiting throughout the considered potential range. This work resolves major controversies in the mechanistic analyses of Kolbe electrolysis on Pt anodes: the origin of the inflection zone, and the identity of the rate limiting step.

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(Non-)Kolbe electrolysis in biomass valorization – a discussion of potential applications

Abstract: The bio-availability of organic acids as platform chemicals and the potential of electrochemistry to directly integrate renewable energy into new value chains drive (Non-)Kolbe electrolysis to become an attractive tool in future electro-bio-refinery.

Cited by 76 publications

References 95 publications

Intramolecular Biradical Recombination of Dicarboxylic Acids to Unsaturated Compounds: A New Approach to an Old Kolbe Reaction

Intramolecular Biradical Recombination of Dicarboxylic Acids to Unsaturated Compounds: A New Approach to an Old Kolbe Reaction

Reactor microbiome enriches vegetable oil with n-caproate and n-caprylate for potential functionalized feed additive production via extractive lactate-based chain elongation

Understanding the reaction mechanism of Kolbe electrolysis on Pt anodes

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