Biomass-derived Carboxylic Acids Research Articles

An innovative catalytic pathway for the synthesis of acyl furans: the cross-ketonization of methyl 2-furoate with carboxylic acids

Continuous-flow, gas-phase cross-ketonization of alkyl 2-furoates with bio-based acids toward an alternative, selective production of valuable acyl furan intermediates.

Understanding the reaction mechanism of Kolbe electrolysis on Pt anodes

Kolbe electrolysis has been proposed as an efficient electro-oxidation process to synthesize (un)symmetrical dimers from biomass-based carboxylic acids, but its mechanism remains controversial. In this work, we develop a microkinetic model based on density functional theory to study the reaction mechanism of Kolbe electrolysis of acetic acid (CH 3 COOH) on both pristine and partially oxidized Pt anodes. We show that the shift in the rate-determining step of the oxygen evolution reaction (OER) on a Pt(111)@α-PtO 2 surface from OH ∗ formation to H 2 O adsorption gives rise to large Tafel slopes, i.e., the inflection zones observed experimentally at high anodic potentials on Pt. Our simulations find that the CH 3 COO ∗ decarboxylation and CH 3 ∗ dimerization steps determine the activity of the Kolbe reaction. This work resolves major controversies in the mechanism of Kolbe electrolysis on Pt anodes: the origin of the inflection zone and the identity of the rate-limiting step. • A microkinetics model for Kolbe electrolysis of acetic acid on Pt anodes is developed • Oxidation of the Pt surface dramatically weakens the adsorption strength of Kolbe species • Suppressed activity of oxygen evolution reaction leads to the inflection zone • Decarboxylation and/or dimerization steps determine activity of Kolbe products Organic electrosynthesis has, in recent years, been revived as a promising pathway for the sustainable production of important chemicals. The advantages of electrosynthesis include mild reaction conditions, the use of green electricity, and the tunability of activity and selectivity with the applied potential. The Kolbe reaction converts biomass-derived carboxylic acids to high-value products through decarboxylation and dimerization. However, the mechanism of this reaction is not fully understood, which limits further optimization of the reaction systems. Building on previous mechanistic studies, this work identifies the key steps involved in Kolbe electrolysis of acetic acid. The mechanistic insights obtained suggest that tuning the relative adsorption strength of carboxylic species versus water in aqueous systems could promote Kolbe products. Electroorganic synthesis from biomass-derived chemicals has been revived in recent years, but reaction mechanisms remain to be established. Liu et al. perform a detailed mechanistic study of Kolbe electrolysis on oxidized platinum by developing a microkinetics model based on density functional theory calculations.

Highly selective and stable ZnO-supported bimetallic RuSn catalyst for the hydrogenation of octanoic acid to octanol

• Octanoic acid was converted over RuSn supported on ZnO. • High conversion (99.4 %) and selectivity to octanol (93.0 %) were achieved. • Ru 3 Sn 7 alloy phase was responsible for the high hydrogenation activity. • Esterification was suppressed by optimizing the reaction condition. • RuSn/ZnO was exceptionally robust over 1000 h. The chemoselective hydrogenation of biomass-derived carboxylic acids is promising for the development of biorefineries. Herein, the selective conversion of octanoic acid to octanol over bimetallic RuSn/ZnO in a fixed-bed continuous reactor system, is reported. Almost complete conversion (99.4 %) of octanoic acid was achieved, with a remarkably high selectivity to octanol (93.0 %), when using specific reaction conditions (300°C, a weight hourly space velocity (WHSV) of 2 h −1 , and 30 atm H 2 ). Characterizations of the catalysts by BET, CO pulse chemisorption, ICP-AES, XRD, XPS and STEM-EDS revealed that the addition of Sn to Ru/ZnO resulted in the formation of a Ru 3 Sn 7 alloy phase as well as SnO x . Comparison with Ru/ZnO catalyst gives an insight that the presence of Ru 3 Sn 7 alloy was most likely the active site and it significantly improved the hydrogenation activity and selectivity to octanol. The SnO x and ZnO favored the formation of octyl octanoate by esterification of the formed octanol and octanoic acid, although it was successfully suppressed by optimizing the reaction conditions. Long-term stability tests revealed that RuSn/ZnO retained its activity for 1000 h with no coke formation. This study reveals the potential of RuSn/ZnO for the valorization of medium-chain fatty acids into value-added chemicals.

Parametric Study of Pt/C-Catalysed Hydrothermal Decarboxylation of Butyric Acid as a Potential Route for Biopropane Production

Sustainable fuel-range hydrocarbons can be produced via the catalytic decarboxylation of biomass-derived carboxylic acids without the need for hydrogen addition. In this present study, 5 wt% platinum on carbon (Pt/C) has been found to be an effective catalyst for hydrothermally decarboxylating butyric acid in order to produce mainly propane and carbon dioxide. However, optimisation of the reaction conditions is required to minimise secondary reactions and increase hydrocarbon selectivity towards propane. To do this, reactions using the catalyst with varying parameters such as reaction temperatures, residence times, feedstock loading and bulk catalyst loading were carried out in a batch reactor. The highest yield of propane obtained was 47 wt% (close to the theoretical decarboxylation yield of 50 wt% on butyric acid basis), corresponding to a 96% hydrocarbon selectivity towards propane. The results showed that the optimum parameters to produce the highest yield of propane, from the range investigated, were 0.5 g butyric acid (0.57 M aqueous solution), 1.0 g Pt/C (50 mg Pt content) at 300 °C for 1 h. The reusability of the catalyst was also investigated, which showed little or no loss of catalytic activity after four cycles. This work has shown that Pt/C is a suitable and potentially hydrothermally stable heterogeneous catalyst for making biopropane, a major component of bioLPG, from aqueous butyric acid solutions, which can be sourced from bio-derived feedstocks via acetone-butanol-ethanol (ABE) fermentation.

The mechanism of hydrogen donation by bio-acids over metal supported on nitrogen-doped carbon nanotubes

Biomass-derived carboxylic acids (e.g. acetic acid AcOH and formic acid FA) are a green and low-cost hydrogen source to replace hazardous H2 gas in in-situ hydrogenation processes. To date, bio-acids dehydrogenation has been mainly conducted using noble metal catalysts which would negatively impact the process economy, thus development of efficient non-noble metal catalysts for this purpose is highly desirable. In this study, the performance of transition metals supported on nitrogen doped carbon nanotubes was thoroughly evaluated by computational modelling based on Density Functional Theory (DFT). Results revealed that, out of the 10 selected transition metal candidates, molybdenum (Mo) was most active for binding AcOH and a combination of Mo and nitrogen doping significantly enhanced binding to the carboxylic acid molecules compared to pristine carbon nanotubes (CNTs). The newly designed Mo/N-CNT catalysts considerably facilitated the bio-acids decomposition compared to the non-catalytic scenarios by lowering energy barriers. FA distinctly outperformed AcOH in hydrogen donation over Mo/N-CNT catalysts, through its spontaneous cleavage leading to facile hydrogen donation.

Halloysite-Catalyzed Esterification of Bio-Mass Derived Acids.

Halloysite, a natural clay with a hollow tubular structure, was studied as a catalyst for the esterification of biomass-derived carboxylic acids (levulinic acid, fumaric acid, maleic acid, and succinic acid) with four different alcohols (MeOH, EtOH, n-PrOH, and n-BuOH). Reaction conditions were optimized (10 mol % halloysite, 170 °C, 24 h) and gave high yields of the corresponding esters and diesters (>90%). The halloysite was easily recovered and recycled after washing and drying.

Copolymerization of Biomass-Derived Carboxylic Acids for Biobased Acrylic Emulsions

The production of biobased copolymers such as poly(styrene-co-butyl acrylate-co-methacrylic acid) for paints and coating applications is indispensable for the establishment of sustainable biorefine...

Core–Shell Pt@Ir Nanothorns on Carbon Fiber Paper Electrodes for Carboxylic Acid Valorization via Kolbe Electrolysis

Valorization of biomass-derived carboxylic acids into drop-in fuels with the input of renewably sourced electricity is promising for a clean and sustainable energy future. Herein, self-supporting core–shell Pt@Ir nanothorns on 3D porous carbon fiber paper anodes have been employed for the electrocatalytic upgrading of carboxylic acids into fuel-range hydrocarbons. The core–shell anode is synthesized by electrodepositing Pt nanothorns on carbon fiber paper followed by galvanic deposition of a thin layer of Ir nanothorns on the surface. Pt@Ir exhibited a remarkably higher yield (49.5%) and Faraday efficiency (62.3%) for hydrocarbon production as compared to that of benchmark commercial Pt/C. The anode also has good recyclability with little activity loss after five successive runs.

Selective catalytic decarboxylation of biomass-derived carboxylic acids to bio-based methacrylic acid over hexaaluminate catalysts

Methacrylic acid (MAA) is a polymer molecular constituent in related plastics industry, presently produced from supplied fossil-based resources. This scientific paper reports an environmentally-benign catalytic process for the production of MAA via the decarboxylation of carboxylic groups. Various hexaaluminate catalysts were synthetized examined and tested to achieve the maximum amount yield of MAA from biomass derived carboxylic acids. Active phases on catalyst surfaces were characterized with numerous microscopic, spectroscopic and chemi-/physi-sorption techniques. Among hexaaluminate catalysts, the highest selectivity towards MAA (50%) was accomplished over barium hexa-aluminate at relatively mild reaction conditions (3 h, 250 °C and 20 bar). In addition, the catalyst could be reused four times without the loss of activity. A plausible pathway mechanism was also hypothesized. The high catalytic activity of BHA catalyst compared to the other tested catalysts believed to be associated with its peculiar layered structure, surface defect sites, moderate basicity and high surface area. The newly developed catalyst and corresponding process avoid the use of expensive noble or transition metals and corrosive alkalis. Overall, the development of catalysis presents a step forward in the synthesis of a sustainable structural constituent.

Decarboxylative Olefination of Activated Aliphatic Acids Enabled by Dual Organophotoredox/Copper Catalysis

Herein, we demonstrate a dual organophotoredox/copper catalytic strategy toward challenging decarboxylative olefination processes proceeding in high yields and selectivities. This operationally simple method uses photoactive organic molecules and Cu(II)-complexes as catalysts to provide rapid access to a wide variety of olefins from inexpensive synthetic and biomass-derived carboxylic acids under mild light-mediated conditions. Mechanistic investigations suggest that the reaction rate for this process is controlled solely by the incident photon flux.

Novel Strategies for the Production of Fuels, Lubricants, and Chemicals from Biomass.

Growing concern with the environmental impact of CO2 emissions produced by combustion of fuels derived from fossil-based carbon resources has stimulated the search for renewable sources of carbon. Much of this focus has been on the development of methods for producing transportation fuels, the major source of CO2 emissions today, and to a lesser extent on the production of lubricants and chemicals. First-generation biofuels such as bioethanol, produced by the fermentation of sugar cane- or corn-based sugars, and biodiesel, produced by the transesterification reaction of triglycerides with alcohols to form a mixture of long-chain fatty esters, can be blended with traditional fuels in limited amounts and also arise in food versus fuel debates. Producing molecules that can be drop-in solutions for fossil-derived products used in the transportation sector allows for efficient use of the existing infrastructure and is therefore particularly interesting. In this context, the most viable source of renewable carbon is abundantly available lignocellulosic biomass, a complex mixture of lignin, hemicellulose, and cellulose. Conversion of the carbohydrate portion of biomass (hemicellulose and cellulose) to fuels requires considerable chemical restructuring of the component sugars in order to achieve the energy density and combustion properties required for transportation fuels-gasoline, diesel, and jet. A different set of constraints must be met for the conversion of biomass-sourced sugars to lubricants and chemicals. This Account describes strategies developed by us to utilize aldehydes, ketones, alcohols, furfurals, and carboxylic acids derived from C5 and C6 sugars, acetone-butanol-ethanol (ABE) fermentation mixtures, and various biomass-derived carboxylic acids and fatty acids to produce fuels, lubricants, and chemicals. Oxygen removal from these synthons is achieved by dehydration, decarboxylation, hydrogenolysis, and hydrodeoxygenation, whereas reactions such as aldol condensation, etherification, alkylation, and ketonization are used to build up the number of carbon atoms in the final product. We show that our strategies lead to high-octane components that can be blended into gasoline, C9-C22 compounds that possess energy densities and properties required for diesel and jet fuels, and lubricants that are equivalent or superior to current synthetic lubricants. Replacing a fraction of the crude-oil-derived products with such renewable sources can mitigate the negative impact of the transportation sector on overall anthropogenic greenhouse gas (GHG) emissions and climate change potential. While ethanol is a well-known fuel additive, there is significant interest in using ethanol as a platform molecule to manufacture a variety of valuable chemicals. We show that bioethanol can be converted with high selectivity to butanol or 1,3-butadiene, providing interesting alternatives to the current production from petroleum. Finally, we report that several of the strategies developed have the potential to reduce GHG emissions by 55-80% relative to those for petroleum-based processes.

Integrated catalytic sequences for catalytic upgrading of bio-derived carboxylic acids to fuels, lubricants and chemical feedstocks

We describe catalytic sequences for converting biomass-derived carboxylic acids, to fuels and lubricants that are compatible with the existing energy infrastructure.

Research Progress in Ketonization of Biomass-derived Carboxylic Acids over Metal Oxides

Research Progress in Ketonization of Biomass-derived Carboxylic Acids over Metal Oxides

Kinetic and Thermodynamic Parameters for Uncatalyzed Esterification of Carboxylic Acid

A fundamental study on uncatalyzed esterification of various biomass-derived aliphatic carboxylic acids with stoichiometric amount of ethanol has been investigated in an isothermal batch reactor, with the objective to convert carboxylic acids to corresponding ethyl esters and to determine both the kinetic and thermodynamic parameters. The effects of temperature on the conversion of carboxylic acid, kinetic and thermodynamic parameters have been investigated. Temperature was found to have significant effect on the rate of reaction and conversion of carboxylic acid. A simple second order reversible kinetic model was developed to determine the kinetic and thermodynamic parameters. The thermodynamic and kinetic parameters varied for uncatalyzed esterification reaction of both short-chain and long-chain carboxylic acids considered. The predicted data from the kinetic model were correlated with experimental data and the two sets of data agreed reasonably well for the uncatalyzed esterification systems. It was observed that the Van't Hoff plot for uncatalyzed esterification of linoleic acid was non-linear curve, whereas for the Arrhenius and Eyring plots, they were linear. Additional experiments to assess the catalytic and corrosion effects of several metallic substances revealed Inconel 625 alloy, nickel wire and stainless steel materials were susceptible to corrosion problem with uncatalyzed esterification reaction at elevated reaction temperatures. However, tantalum and grade-5 titanium materials were corrosion resistance metals, suitable for similar reaction conditions and this can encourage the design of a flow reactor system. Although, uncatalyzed esterification of carboxylic acids at elevated reaction temperature is still at laboratory scale. It is our hope that the estimated kinetic and thermodynamic parameters would be the guiding tools for reactor scale-up, thus providing a new perspective into the conversion of biomass-derived carboxylic acids into value-added ester products under uncatalyzed esterification reaction system.

CeMOx-Promoted Ketonization of Biomass-Derived Carboxylic Acids in the Condensed Phase

Ketonization of the model bio-oil compound acetic acid was performed in a toluene-solvent condensed phase using five different CeMOx catalysts. The catalysts were characterized using a number of different techniques both before and after reaction testing to gain understanding of how material traits influence their catalytic performance. A number of potentially important catalytic properties were found to be of little importance for the respective reaction. For instance, it was discovered that there was no direct correlation between prereaction surface area with activity for ketonization at high or at low temperatures. Furthermore, better reducibility of the oxide did not appear to correlate with improved ketonization rates. XRD of postreaction materials used at different temperatures demonstrated the reaction temperature regime influenced whether the crystal structure of the fresh mixed oxide was disrupted. The precise temperature regimes were different, depending on composition of the catalytic material....

Catalytic decarbonylation of biomass-derived carboxylic acids as efficient route to commodity monomers

The palladium-catalyzed decarbonylation of bio-derived carboxylic acids to alkyl acrylates, styrene, and acrylonitrile is reported. The olefins were isolated by continuous distillation in yields up to 87% by heating a neat, equimolar mixture of pivalic anhydride with the appropriate carboxylic acid to 190 °C in the presence of a Pd-phosphine catalyst.

Selective sequestration of carboxylic acids from biomass fermentation by surface-functionalized mesoporous silica nanoparticles

Carboxylic acids produced by acid fermentation have attracted much attention recently as promising chemical feedstock. The feasibility of the acid fermentation as a high-value added bioconversion process depends on the selective separation of carboxylic acids from the bulk solution. The authors synthesized an aminopropyl-functionalized mesoporous silica nanoparticle (MSN) material with the MCM-41 type, parallel channel porous structure via a co-condensation method. The adsorption isotherms were analyzed with an extended Langmuir model using an overloading term. The highest acid adsorption capacity was 3.38 mol kg−1 for 1 : 1 complexation at an amine density of 3.14 mol N kg−1. Positive isosteric heat showed the reaction was exothermic and favored at low temperature. Desorption/regeneration by increasing the pH to 10.5 was completed within 1 min, and the regenerated MSN showed an adsorption capacity equivalent to the original. MSN had a high selectivity for carboxylic acid over ethanol, glucose, and protein. The pseudo-second-order rate constant for acetic acid adsorption on MSN was 0.41 kg mol−1 min, significantly higher than those of an anion exchange resin (0.14 kg mol−1 min) and activated carbon (0.06 kg mol−1 min). We envision that the MSN material could serve as an efficient adsorbent for selective sequestration of biomass-derived carboxylic acids for various applications.

Catalytic Conversion of Renewable Biomass Resources to Fuels and Chemicals

Lignocellulosic biomass is renewable and cheap, and it has the potential to displace fossil fuels in the production of fuels and chemicals. Biomass-derived carboxylic acids are important compounds that can be used as platform molecules for the production of a variety of important chemicals on a large scale. Lactic acid, a prototypical biomass derivative, and levulinic acid, an important chemical feedstock produced by hydrolysis of waste cellulosic materials, can be upgraded using bifunctional catalysts (those containing metal and acid sites), which allows the integration of several transformations (e.g., oxygen removal and C-C coupling) in a single catalyst bed. This coupling between active sites is beneficial in that it reduces the complexity and cost of the biomass conversion processes. Deoxygenation of biomass derivatives is a requisite step for the production of fuels and chemicals, and strategies are proposed to minimize the consumption of hydrogen from an external source during this process.