Dehydration Of Acid Research Articles

Development and investigation of mixed-matrix PVA-fullerenol membranes for acetic acid dehydration by pervaporation

Abstract This study focuses on the development of a green pervaporation (PV) process for dehydrating a wide range of commercially significant mixtures such as concentrated (and corrosive) acetic acid blends using mixed-matrix membranes based on polyvinyl alcohol (PVA) cross-linked by low-hydroxylated fullerenol (C 60 (OH) 12 ). The effect of C 60 (OH) 12 and various conditions of physical cross-linking on the structure and internal morphology of composite membranes was investigated by X-ray diffraction and scanning electron microscopy, and the stability and transport properties of the developed membranes were investigated for acetic acid dehydration at a wide range of feed water contents (5–30 wt.%) and temperatures (25–60 °C). The supported mixed-matrix membranes exhibited high permeances and water selectivities, as well as good stability toward feed mixtures, with the best transport properties obtained for a C 60 (OH) 12 (5 wt.%)-PVA supported composite membrane thermally treated at 140 °C for 420 min.

Dynamics of the Interaction of Formic Acid with a Polycrystalline Pt Film Electrode: a Time-Resolved ATR-FTIR Spectroscopy Study at Low Potentials and Temperatures

Aiming at more insights into the interaction of formic acid with a Pt electrode, we have studied the dynamics of formic acid interaction with a polycrystalline Pt film electrode in the potential range around the onset of the reaction, from 0.0 to 0.4 V (reversible hydrogen electrode (RHE)), by a combination of electrochemical and in situ IR spectroscopy transient measurements. The measurements were performed under well-defined mass transport conditions; IR spectra were acquired in an attenuated total reflection (ATR) configuration with a time resolution of up to 25 ms (rapid scan mode). To slow down the reaction kinetics and thus stabilize short-living adsorbed intermediates, measurements were performed at ambient and low reaction temperatures (3 °C). Kinetic H/D isotope effects, introduced by using deuterated formic acid, were explored to learn more about the contribution of C–H bond splitting in the rate-determining step in formic acid dehydration (COad formation). Rapid scan ATR-FTIRS measurements show no measurable time delay between the appearance of the bands related to adsorbed bridge-bonded formate species and adsorbed CO at higher potentials (>0.1 V) and no detectable formate signals at low potentials (≤0.1 V), although COad is still formed even at 0.0 V. Adsorption of HCOOH species at low potentials (0.0–0.1 VRHE) is indicated by a band developing at around 1720 cm−1, which is isotope shifted upon deuteration of the C–H bond. Consequences of these and other observations, including the observation of a bell-shaped potential dependence of the initial rate for COad formation in the potential range 0.0–0.4 V or distinct kinetic H/D isotope effects in the rate constants for COad formation, on the mechanistic understanding of the formic acid–Pt interaction are discussed.

Novel Hybrid Catalyst for the Oxidation of Organic Acids: Pd Nanoparticles Supported on Mn‐N‐3D‐Graphene Nanosheets

AbstractThis paper reports the fabrication and electrochemical performance of a hybrid catalyst composed of Pd nanoparticles and atomically dispersed Mn active centers integrated into the nitrogen‐doped three‐dimensional graphene nanosheets (Pd/Mn−N‐3D‐GNS). Our results show that the synergistic integration of both Pd nanoparticles and atomically dispersed Mn can be used to enhance the activity toward the electrochemical oxidation of organic acids at biologically relevant pH values. The hybrid catalyst (Pd/Mn−N‐3D‐GNS) showed increased maximum currents toward the oxidation of oxalic acid when compared to its individual catalysts, namely, Pd/3D‐GNS and Mn−N‐3D‐GNS catalysts. The hybrid also showed a decreased onset potential for oxidation of mesoxalic acid as compared to Mn−N‐3D‐GNS and decreased onset potentials for the oxidation of glyoxalic acid when compared to both of its constituent catalysts. Oxidation of formic acid was also tested and the hybrid was shown to catalyze both dehydration and dehydrogenation mechanisms of formic acid electro‐oxidation. Using density functional theory calculations, it was elucidated that a two‐site catalysis most likely promotes dehydrogenation reaction for formic acid oxidation, which can explain the selectivity of Pd nanoparticles and atomically dispersed Mn towards the dehydrogenation/dehydration pathway.

Higher Brønsted acidity of WOx/ZrO2 catalysts prepared using a high-surface-area zirconium oxyhydroxide

The precipitated zirconium oxyhydroxide, ZrOH(H), was used as a support for tungstate loading, where its specific surface area was 1.5-fold higher than that of the analogous sample obtained commercially, ZrOH(L). Due to this difference, crystalline WO3 and ZrO2 (tetragonal and monoclinic) were formed at a higher calcination temperature by 150K for WZrOH(H) than for WZrOH(L) when tungstate was loaded. For WOx/ZrO2 with different W surface densities produced by calcination at 723–1173K, pyridine-IR experiment and Raman spectroscopy revealed that more Brønsted acid sites were present for WZrOH(H) calcined at 1023 and 1073K than for WZrOH(L) calcined at 873K while distorted Zr-stabilized WO3 nanoparticles were found for these samples. Thus, the former samples showed the superior activity to the latter in the dehydration of formic acid. The linear relationship between the catalytic performance and Brønsted acidity was observed, explaining that WOx/ZrO2 with more Brønsted acid sites is more active in the dehydration reaction. Consequently, the enhanced Brønsted acidity and catalytic activity of WZrOH(H) resulted from the use of zirconium oxyhydroxide with a high surface area for tungstate loading.

Pervaporation dehydration of acetic acid using NH 2 -UiO-66/PEI mixed matrix membranes

Abstract Acetic acid dehydration is significant in chemical industry. Pervaporation has attracted increasing attention due to its low energy consumption and environmentally friendly process. However, there is still lack of efficient membrane materials for the pervaporation separation of acetic acid/water mixtures. Therefore, developing new material to prepare pervaporation membrane is currently the main task. In this study, an acid stable Zr-MOF NH2-UiO-66 was synthesized and incorporated into poly(ethyleneimine) (PEI) to form mixed matrix membranes (MMMs) for separating acetic acid/water mixtures. The NH2-UiO-66/PEI MMMs were deposited on the surface of NaA zeolite tubular substrate to form composite membranes using dip-coating method. The morphologies and structures of the particles and composite membranes were characterized by SEM, EDX, FTIR and contact angle. The effects of membrane preparation conditions on the separation performance were investigated. The results indicated that the NH2-UiO-66/PEI composite membranes showed good acetic acid dehydration behavior, because of the high porosity and hydrophilicity of the particles. Moreover, the particles had good compatibility with polymer and strong combination with substrate. Therefore, this study may provide a new material and facile strategy for preparing composite membrane in the separation of acetic acid/water mixtures.

Theoretical investigation of the selective dehydration and dehydrogenation of ethanol catalyzed by small molecules

Catalytic dehydration and dehydrogenation reactions of ethanol have been investigated systematically using the ab initio quantum chemistry methods The catalysts include water, hydrogen peroxide, formic acid, phosphoric acid, hydrogen fluoride, ammonia, and ethanol itself. Moreover, a few clusters of water and ethanol were considered to simulate the catalytic mechanisms in supercritical water and supercritical ethanol. The barriers for both dehydration and dehydrogenation can be reduced significantly in the presence of the catalysts. It is revealed that the selectivity of the catalytic dehydration and dehydrogenation depends on the acidity and basicity of the catalysts and the sizes of the clusters. The acidic catalyst prefers dehydration while the basic catalysts tend to promote dehydrogenation more effectively. The calculated water-dimer catalysis mechanism supports the experimental results of the selective oxidation of ethanol in the supercritical water. It is suggested that the solvent- and catalyst-free self-oxidation of the supercritical ethanol could be an important mechanism for the selective dehydrogenation of ethanol on the theoretical point of view.

Importance of Dimer Quantification for Accurate Catalytic Evaluation of Lactic Acid Dehydration to Acrylic Acid

Catalytic dehydration of lactic acid in the presence of water is a potentially green, synthetic approach for the production of acrylic acid, and development of a highly selective catalyst is a primary challenge, leading to a resurgence in catalyst exploration and discovery. However, because the complexity in the analytical assessment of the efficiency of catalysts stemming from the possible presence of dimers in lactic acid feedstocks has often been neglected in the literature, we demonstrate, without consideration of the dimer during catalyst evaluation, that they can have a substantial influence on the determination of conversion of lactic acid and selectivity to acrylic acid in aqueous solution. In one example of a modified zeolite catalyst, a true acrylic acid of selectivity of 64% was overestimated to be 80% if the dimers in the feed solution were neglected in the analytical analysis. A survey of the literature demonstrated very few researchers account for the possible presence of lactic acid dimers ...

Simultaneously fabrication of free and solidified N, S-doped graphene quantum dots via a facile solvent-free synthesis route for fluorescent detection

A facile one-step solvent-free synthesis approach is proposed for the simultaneous fabrication of free and solidified N, S-doped graphene quantum dots (N, S-GQDs) by using citric acid as precursor and L-cysteine as dopant. Graphene nucleus is firstly formed via the intermolecular dehydration of citric acid. N and S are then incorporated into the graphene structure by attacking the margin of graphene nucleus. The cross-linking among the graphene nucleus via the intermolecular condensation leads to the generation of free N, S-GQDs, while the intermolecular amidation between L-cysteine molecules and graphene nucleuses contributes to the solid-state fluorescence graphene quantum dots (SSF-GQDs). The free N, S-GQDs exhibit favorable photoluminescence behaviors such as high fluorescent quantum yield of 74.5%, stable photoluminescence within a wide range of pH and high tolerance to external ionic strength of up to 1.0molL−1 NaCl, making it excellent fluorescence probe for the sensitive detection of Fe3+ with a linear range of 0.01–3μM and a detection limit of 3.3nM. The solidification of GQDs prevents the aggregation of GQDs efficiently and offers the solidified N, S-GQDs yellow-green fluorescence, with a fluorescence quantum yield of 10.6%. This proposed protocol provides a novel avenue to fabricate diverse fluorescent graphene materials for different practical applications.

Preparation and catalytic properties of cobalt salts of Keggin type heteropolyacids supported on mesoporous silica

Some heteropoly salts – mesoporous silica composites were prepared from Co salt of molybdophosphoric acid CoHPMo12O40 (CoHPM) by supporting on mesoporous silica in different concentrations (20–40wt% CoHPM) of active phase. The acidity of composites was studied by the adsorption of ammonia and its temperature programmed desorption – TPD using thermogravimetry. The evolved gases during the adsorption–desorption of ammonia on CoPM-silica composites were identified by online mass spectrometry coupled with thermal gravimetry technique. The elemental concentrations based on the relative area of XPS spectra components for Co 2p, Mo 3d, Si 2p and O 1s were obtained for the surface of CoHPM/silica. The dehydration of ethanol was used to probe the catalytic properties of the CoHPM samples incorporated on the silica matrix. The main reaction products obtained on acid (dehydration) catalytic centres were ethylene and diethyl ether, besides acetaldehyde which was obtained on redox (dehydrogenation) catalytic centres. It is shown that silica – supported catalysts, appeared to be more active than bulk CoHPM catalyst in dehydration and dehydrogenation reactions. The higher values of dehydration and reaction products formation are obtained with the lowest loading (20wt% CoHPM) and as a consequence the highest dispersion of active phase. The ethanol conversion and the carbon selectivity to the primary compounds were investigated during time on stream in order to study the stability and regenerability of supported catalysts.

Synthesis of lactide from lactic acid and its esters in the presence of rare-earth compounds

A procedure is described for the synthesis of lactide by dehydration of L-lactic acid and subsequent depolymerization of its oligomer mixture in the presence of yttrium(III) and praseodymium(III) oxides, as well as of cerium(III) chloride heptahydrate. The catalytic activity of yttrium and praseodymium sesquioxides was determined at different temperatures at the oligomerization and deoligomerization stages. Ethyl lactate was prepared in the presence of Purolite C100 MB cation exchange resin and subjected to oligomerization followed by thermal decomposition of oligoester and oligolactic acid mixture in the presence of yttrium(III) and praseodymium(III) oxides and aqueous cerium(III) chloride.

Efficient production of acrylic acid by dehydration of lactic acid over BaSO4with crystal defects

Crystal defects in BaSO4catalyst provide acid sites that catalyze the dehydration of lactic acid to acrylic acid.

Ammonia promoted barium sulfate catalyst for dehydration of lactic acid to acrylic acid

Defects were formed in a BaSO4catalyst by controlling its synthesis and it offered excellent activity for the dehydration of lactic acid to acrylic acid.

Thermal effects of carbonated hydroxyapatite modified by glycine and albumin

In this work calcium phosphate powders were obtained by precipitation method from simulated solutions of synovial fluid containing glycine and albumin. X-ray diffraction and IR spectroscopy determined that all samples are single-phase and are presented by carbonate containing hydroxyapatite (CHA). The thermograms of solid phases of CHA were obtained and analyzed; five stages of transformation in the temperature range of 25-1000°C were marked. It is shown that in this temperature range dehydration, decarboxylation and thermal degradation of amino acid and protein connected to the surface of solid phase occur. The tendency of temperature lowering of the decomposition of powders synthesized from a medium containing organic substances was determined. Results demonstrate a direct dependence between the concentration of the amino acid in a model solution and its content in the solid phase.

Thermal effects of carbonated hydroxyapatite modified by glycine and albumin

In this work calcium phosphate powders were obtained by precipitation method from simulated solutions of synovial fluid containing glycine and albumin. X-ray diffraction and IR spectroscopy determined that all samples are single-phase and are presented by carbonate containing hydroxyapatite (CHA). The thermograms of solid phases of CHA were obtained and analyzed; five stages of transformation in the temperature range of 25-1000°C were marked. It is shown that in this temperature range dehydration, decarboxylation and thermal degradation of amino acid and protein connected to the surface of solid phase occur. The tendency of temperature lowering of the decomposition of powders synthesized from a medium containing organic substances was determined. Results demonstrate a direct dependence between the concentration of the amino acid in a model solution and its content in the solid phase.

Highly selective one-step dehydration, decarboxylation and hydrogenation of citric acid to methylsuccinic acid.

The one-step dehydration, decarboxylation and hydrogenation of the bio-based and widely available citric acid is presented. This reaction sequence yields methylsuccinic acid with yields of up to 89%. Optimal balances between the reaction rates of the different steps were found by varying the hydrogenation catalyst and the reaction parameters (H2 pressure, pH, temperature, time and catalyst-to-substrate ratio).

Simultaneous construction of two linkages for the on-surface synthesis of imine-boroxine hybrid covalent organic frameworks.

The orthogonality between the Schiff base reaction and the boronic acid dehydration reaction is explored during the on-surface synthesis process. By activating the above two reactions in one-step and employing asymmetrical substituted monomers and the 3-fold symmetric monomer 1,3,5-tris(4-aminophenyl)benzene (TAPB), highly ordered imine-boroxine hybrid single-layered covalent organic frameworks (sCOFs) have been successfully constructed on HOPG by a gas-solid interface reaction method and characterized by scanning tunnelling microscopy (STM). In particular, the reaction between the meta-substituted monomer and TAPB generates sCOFB with a windmill structure, which is the first sCOF with surface chirality so far reported. The demonstration of the one-step synthesis of multiple linkages to form sCOFs can further enlarge the sCOF family and expand the design routes for functional 2D organic nanomaterials.

CO2 Adsorption by para-Nitroaniline Sulfuric Acid-Derived Porous Carbon Foam

The expansion product from the sulfuric acid dehydration of para-nitroaniline has been characterized and studied for CO2 adsorption. The X-ray photoelectron spectroscopy (XPS) characterization of the foam indicates that both N and S contents (15 and 9 wt%, respectively) are comparable to those separately reported for nitrogen- or sulfur-containing porous carbon materials. The analysis of the XPS signals of C1s, O1s, N1s, and S2p reveals the presence of a large number of functional groups and chemical species. The CO2 adsorption capacity of the foam is 7.9 wt% (1.79 mmol/g) at 24.5 °C and 1 atm in 30 min, while the integral molar heat of adsorption is 113.6 kJ/mol, indicative of the fact that chemical reactions characteristic of amine sorbents are observed for this type of carbon foam. The kinetics of adsorption is of pseudo-first-order with an extrapolated activation energy of 18.3 kJ/mol comparable to that of amine-modified nanocarbons. The richness in functionalities of H2SO4-expanded foams represents a valuable and further pursuable approach to porous carbons alternative to KOH-derived activated carbons.

Potassium-Ion-Exchanged Zeolites for Sustainable Production of Acrylic Acid by Gas-Phase Dehydration of Lactic Acid

Development of high-performance solid acid catalysts for chemicals and materials production from bioresourced feedstock has become an important research topic in heterogeneous catalysis for renewable energy and green chemistry. We provide herein a comprehensive study on the catalytic performance of various K+-exchanged zeolites (KxNa1-xZ_y, x = 0.90–0.98) with similar molar K/Al ratios for acrylic acid (AA) production by gas-phase dehydration of lactic acid (LA) and discuss the effects of zeolite type (Z = ZSM-22, ZSM-35, MCM-22, ZSM-11, ZSM-5, ZSM-5/ZSM-11, and β) and SiO2/Al2O3 ratio (y). ZSM-5 and β are found more efficient than the other zeolites for this LA-to-AA reaction. Variation of y in the zeolite (β and ZSM-5) is shown to significantly affect the catalytic performance: not only higher AA selectivity and yield but also better catalytic stability is achieved by lowering y. A K0.97Na0.03ZSM-5_27 is then identified as the best-performing catalyst, offering very high AA selectivity (80–81 mol%) and ...

Synthesis of Organic Molecules, R Ribose and S Amino Acids by Adsorption on Carbon at The Birth of Life on The Earth

Reasons for appearance of optically active organic molecules in nature have not been ascertained up to the present, but clarification of conditions on the Earth during the period of their appearance can contribute to this. H2 and gases, containing H2, were oxidized by CO2 with allocation of carbon and H2O or CH2O and СНO(OН) in volcanic gas and in the early atmosphere. During adsorption on carbon CH2O dissolved in water could be the synthesis only of R (rectus, Latin) ribose, and with NH3 and СНO(OН) synthesis of glycine and only of S (sinister) serine, and on its bases of other S amino acids. Adsorption on the carbon ensured in complex: concentration of initial components, hydrophobic-hydrophilic properties, optical purity, protection from hydration, decay and racemization. It is shown the possibility of the early Archean reactions: dehydration of phosphoric acid, of phosphoester bonds connection formation in nucleotides, with CH2O fatty acids and nitrogenous bases.

Layer-by-layer self-assembly for carbon dots/chitosan-based multilayer: Morphology, thickness and molecular interactions

Oxidized Carbon dots, prepared from the acid dehydration of cellulose, were used in the preparation of self-assembled films with the biopolymer chitosan. The morphology, thickness and molecular interactions of the films were characterized with a variety of techniques including AFM, FTIR, UV–Vis and Surface Plasmon Resonance (SPR) spectroscopy. We noticed an increase in the thickness of the bilayers with increasing ionic strength and pH provided by the increase of the amount of CD and chitosan deposited in each cycle. This increase was mainly due to higher flexibility of the biopolymer on these conditions and to the formation of agglommerates of carbon dots in high ionic strength. On the other hand, the greater flexibility together with the higher adsorption have generated films with smoother morphology due to the higher coating on the spherical particles. The results described here suggest that the structure of the film, i.e., morphology and thickness can be easily controlled and reproduced, by controlling the conditions of the biopolymer and CD solutions, in addition to the traditional number of dips. Finally, the prepared films have potential application in the development of imunosensors, functional coatings, surface photoactive and UV protection films.