Showing papers on "Oxalic acid published in 2021"

Towards Sustainable Oxalic Acid from CO2 and Biomass.

Abstract: To quickly and drastically reduce CO2 emissions and meet our ambitions of a circular future, we need to develop carbon capture and storage (CCS) and carbon capture and utilization (CCU) to deal with the CO2 that we produce. While we have many alternatives to replace fossil feedstocks for energy generation, for materials such as plastics we need carbon. The ultimate circular carbon feedstock would be CO2 . A promising route is the electrochemical reduction of CO2 to formic acid derivatives that can subsequently be converted into oxalic acid. Oxalic acid is a potential new platform chemical for material production as useful monomers such as glycolic acid can be derived from it. This work is part of the European Horizon 2020 project "Ocean" in which all these steps are developed. This Review aims to highlight new developments in oxalic acid production processes with a focus on CO2 -based routes. All available processes are critically assessed and compared on criteria including overall process efficiency and triple bottom line sustainability.

Efficient cleavage of strong hydrogen bonds in sugarcane bagasse by ternary acidic deep eutectic solvent and ultrasonication to facile fabrication of cellulose nanofibers

Abstract: From the perspective of green chemistry, it is of great significance to produce cellulose nanofibers (CNFs) with more environmentally friendly and sustainable materials. This study investigated the efficient cleavage of strong hydrogen bonds occurred in sugarcane bagasse (SCB), ultrafast fabrication of CNFs through a 20 min microwave-assisted ternary carboxylic acid deep eutectic solvent (Mw-TCADES) deconstruction and sweep frequency ultrasonic (SFU) separation pretreatment. It also investigated the subsequent high-intensity ultrasonication (HIU) fibrillation process. After pretreating SCB with two different TCADES (choline chloride: oxalic acid: AlCl3·6H2O, and choline chloride: lactic acid: AlCl3·6H2O, molar ratio 1:1:0.2), the cellulose content of the SCB was 56.2 and 62.6%, respectively. The CNFs obtained after the two Mw-TCADES treatments contained 0.74 and 0.84 mmol/g carboxylic acid groups, and the crystallinity was 58.05 and 60.71%, respectively. Meanwhile, the CNFs obtained under the optimum treatment conditions (Mw-TCADES, 100 °C, 20 min and HIU) showed high thermal stability, which exhibited promising potential for further applications. Under the optimum conditions, the CNFs had a length of about 400–600 nm, width of around 15–17 nm, and a height of about 6–7 nm. The results showed that the TCADES can be used effectively as an alternative to the traditional acid–base pretreatment method and provide a green and efficient method for the utilization of lignocellulosic materials and the separation of CNFs.

Electrochemical Synthesis of Glycine from Oxalic Acid and Nitrate.

Abstract: In manufacturing C-N bond-containing compounds, it is important challenge to alternate the conventional methodologies that utilize reactive substrates, toxic reagents and organic solvents. In this study, we developed an electrochemical method to synthesize a C-N bond-containing molecule avoiding the use of cyanides and amines by harnessing nitrate (NO 3 - ) as a nitrogen source in an aqueous electrolyte. In addition, we utilized oxalic acid as a carbon source which can be obtained from electrochemical conversion of CO 2 , so that our approach can provide a route for the utilization of anthropogenic CO 2 and nitrate wastes which cause serious environmental problems including global warming and eutrophication. Interestingly, the coreduction of oxalic acid and nitrate generated reactive intermediates, which led to C-N bond formation followed by further reduction to an amino acid, namely, glycine. By carefully controlling this multireduction process with a fabricated Cu-Hg electrode, we demonstrated the efficient production of glycine with a faradaic efficiency (F.E.) of up to 43.1% at -1.4 V vs. Ag/AgCl (current density = ~90 mA cm -2 ).

Facilely Cross-Linking Polybenzimidazole with Polycarboxylic Acids to Improve H2/CO2 Separation Performance.

Abstract: Polybenzimidazole (PBI) with a strong size-sieving ability exhibits attractive H2/CO2 separation properties for blue H2 production and CO2 capture. Herein, we report that PBI can be facilely cross-linked with polycarboxylic acids, oxalic acid (OA), and trans-aconitic acid (TaA) to improve its separation performance. The acids react with the amines on the PBI chains, decreasing free volume and increasing size-sieving ability. The acid doping increases H2/CO2 selectivity from 12 to as high as 45 at 35 °C. The acid-doped samples demonstrate stable H2/CO2 separation performance when challenged with simulated syngas containing water vapor at 150 °C, which surpasses state-of-the-art polymers and Robeson's upper bound for H2/CO2 separation.

Development of chitosan membrane using non-toxic crosslinkers for potential wound dressing applications

Abstract: There is a myriad of ways to crosslink hydrogel wound dressings; however, they require additional steps to remove the residue of the crosslinking agents, or their byproducts in biological environments are toxic. In this study, we studied and characterized the crosslinking of the chitosan hydrogels by various dicarboxylic acids, including oxalic acid, adipic acid, and sebacic acid under vacuum at 90 °C. The concentrations of the crosslinkers in the crosslinked hydrogels are tolerable for the cells, and the membranes can be used after crosslinking without complicated additional steps to remove the unreacted residues. The molar ratio of the crosslinkers was calculated based on the stoichiometry of the chitosan amine groups. Attenuated total reflectance Fourier transform infrared spectroscopy revealed amide linkage formation between amine groups of the chitosan and carboxyl groups of the dicarboxylic acids at 90 °C. The results showed that the chitosan membranes crosslinked with oxalic acid had higher Young's modulus (~ 1042 N/mm2) and ultimate tensile strength (~ 75 N/mm2) in comparison with the other dicarboxylic acids. Moreover, the membranes crosslinked with oxalic acid showed a weight loss of ~ 5.4% after 24 h at double-distilled water, which was drastically lower than that of the others. Thus, oxalic acid was selected as the most effective crosslinker. Cell viability assay, using mouse fibroblast (L929) cells, was conducted on the mechanically optimized membranes. The fibroblast cells successfully attached and spread well on the surface of the membranes. In conclusion, the obtained results suggested oxalic acid as an effective and non-toxic crosslinker for chitosan-based membranes for wound dressing applications.

Production of Formate via Oxidation of Glyoxal Promoted by Particulate Nitrate Photolysis

Abstract: Particulate nitrate photolysis can produce oxidants (i.e., OH, NO2, and NO2-/HNO2) in aqueous droplets and may play a potential role in increased atmospheric oxidative capacity. Our earlier works have reported on the SO2 oxidation promoted by nitrate photolysis to produce sulfate. Here, we used glyoxal as a model precursor to examine the role of particulate nitrate photolysis in the formation of secondary organic aerosol (SOA) from particle-phase oxidation of glyoxal by OH radicals. Particles containing sodium nitrate and glyoxal were irradiated at 300 nm. Interestingly, typical oxidation products of oxalic acid, glyoxylic acid, and higher-molecular-weight products reported in the literature were not found in the photooxidation process of glyoxal during nitrate photolysis in the particle phase. Instead, formic acid/formate production was found as the main oxidation product. At glyoxal concentration higher than 3 M, we found that the formic acid/formate production rate increases significantly with increasing glyoxal concentration. Such results suggest that oxidation of glyoxal at high concentrations by OH radicals produced from nitrate photolysis in aqueous particles may not contribute significantly to SOA formation since formic acid is a volatile species. Furthermore, recent predictions of formic acid/formate concentration from the most advanced chemical models are lower than ambient observations at both the ground level and high altitude. The present study reveals a new insight into the production of formic acid/formate as well as a sink of glyoxal in the atmosphere, which may partially narrow the gap between model predictions and field measurements in both species.

Selective recovery of vanadium from red mud by leaching with using oxalic acid and sodium sulfite

Abstract: Selective leaching of vanadium and separation of iron from red mud by using oxalic acid and sodium sulfite were put forward. The main influencing factors of selective leaching were studied and the leaching mechanism was analyzed with XRD, SEM-EDS, thermodynamic theory and leaching kinetics. The results show that more than 90% of vanadium could be selectively leached into the acid solution with less than 10% of iron under the suitable leaching conditions. The acid leaching of vanadium is controlled by boundary layer diffusion with R2 more than 0.98. The acid leaching of iron is controlled by surface chemical reaction with R2 more than 0.99 under different oxalic acid concentrations. The apparent activation energy of vanadium and iron was 8.21 kJ/mol and 13.57 kJ/mol, respectively. H2C2O4 could selectively destroy the minerals of red mud resulted in the high recovery of vanadium. H2C2O4 reacted with Fe2+ to generate the precipitation of FeC2O4 in the leaching residue caused by the p-π conjugation of O--C--O of C2O42-. The stable VO(C2O4)22- complex was present in the leaching solution due to the conjugated system of π-π with O--C--O of C2O42- and V˭O of VO2+.

Integration of aprotic CO2 reduction to oxalate at a Pb catalyst into a GDE flow cell configuration

Abstract: Electrochemical CO2 reduction to oxalic acid in aprotic solvents could be a potential pathway to produce carbon-neutral oxalic acid. One of the challenges in aprotic CO2 reduction are the limited achievable current densities under standard conditions, despite the increased CO2 solubility compared to aqueous applications. The application of aprotic solvents can reduce CO2 rather selectively to oxalate, and faradaic efficiencies (FEs) of up to 80% were achieved in this study with a Pb catalyst in acetonitrile, the FE being mainly dictated by the local CO2 concentration at the electrode. This process was integrated into a flow cell employing a two-layered carbon-free lead (Pb) gas diffusion electrode (GDE) and a sacrificial zinc (Zn) anode. With the application of this GDE the applicable current densities could be improved up to a current density of j = 80 mA cm−2 at a FE(oxalate) = 53%, which is within the range of the highest j reported in the literature. In addition, we provide an explanation for the deactivation mechanism of metal catalysts observed in the aprotic CO2 reduction literature. The deactivation is not related to a mass transport limitation but to cathodic corrosion observed at highly negative potential when employing quaternary ammonium supporting electrolyte cations, promoting catalyst leaching.

Monomers from CO 2 : Superbases as Catalysts for Formate-to-Oxalate Coupling.

Abstract: An interesting contribution to solving the climate crisis involves the use of CO 2 as a feedstock for monomers to produce sustainable plastics. In the European Horizon 2020 project "OCEAN" we develop a continuous multistep process from CO 2 to oxalic acid and derivatives, starting with the electrochemical reduction of CO 2 to potassium formate. The subsequent formate to oxalate coupling is a reaction that has been studied and commercially used for over 150 years. With the introduction of super-bases as catalysts under moisture free conditions we now show unprecedented improvements for the formate coupling reaction. With isotopic labelling experiments we prove the presence of carbonite as an intermediate during the reaction and with a unique operando set-up we studied the kinetics. Ultimately, we were able to drop the required reaction temperature from 400 °C to below 200 °C, reduce the reaction time from 10 minutes to 1 minute whilst achieving 99% oxalate yield.

Colonization and bioweathering of monazite by Aspergillus niger: solubilization and precipitation of rare earth elements.

Abstract: Geoactive fungi play a significant role in bioweathering of rock and mineral substrates. Monazite is a phosphate mineral containing the rare earth elements (REE) cerium, lanthanum and neodymium. Little is known about geomicrobial transformations of REE-bearing minerals which are also relevant to REE biorecovery from terrestrial and extra-terrestrial reserves. The geoactive soil fungus Aspergillus niger colonized monazite in solid and liquid growth media without any apparent growth inhibition. In a glucose-minerals salts medium, monazite enhanced growth and mycelium extensively covered rock particle surfaces, probably due to the provision of phosphate and essential trace metals. Teeth-like and pagoda-like etching patterns indicated monazite dissolution, with extensive precipitation of secondary oxalate minerals. Biomechanical forces ensued causing aggressive bioweathering effects by tunnelling, penetration and splitting of the ore particles. High amounts of oxalic acid (~46 mM) and moderate amounts of citric acid (~5 mM) were produced in liquid media containing 2% (wt./vol.) monazite, and REE and phosphate were released. Correlation analysis suggested that citric acid was more effective than oxalic acid in REE mobilization, although the higher concentration of oxalic acid also implied complexant activity, as well as the prime role in REE-oxalate precipitation.

Catalytic production of 5-hydroxymethylfurfural from sucrose and molasses by aluminum chloride in green aqueous γ-valerolactone system

Abstract: 5-Hydroxymethylfurfural (HMF) is a promising platform chemical for production of value-added chemicals and fuels. Conversion of abundantly available and cheap sucrose for HMF synthesis was systematically investigated in the present study. Results showed that Lewis acid AlCl3 is effective in catalytic transformation of sucrose. Combining AlCl3 with different Bronsted acids, no matter whether they were inorganic acids (HCl, H2SO4, and H3PO4) or organic acids (malic acid, succinic acid, and oxalic acid), or variation of ratio of Lewis acid/Bronsted acid represented by AlCl3/HCl, did not change the obtained maximum HMF yields compared with AlCl3 alone, but shortened the time required to reach the maximum HMF yield. Sucrose conversion in a green reaction media of aqueous γ-valerolactone (GVL) solvent resulted into comparable HMF yields with dimethyl sulfoxide (DSMO)-water system. Addition of monovalent salt NaCl and divalent salt Na2SO4 produced opposite effect with Cl− promoting while SO42− inhibiting HMF production. Furthermore, HMF synthesis from constituent monosaccharides of sucrose and molasses, a by-product from sugar manufacturing process, was also carried out and it was found that an equivmole mixture of glucose and fructose gave rise to almost identical HMF yield to the same mole of sucrose. Molasses, even after chemical pretreatment for removal of certain amount of inorganic salts and color substances, was significantly inferior to synthetic molasses in terms of HMF formation, indicating the complexity and difficulty in chemical valorization of molasses for production of platform molecules.