Oxidation Of Acetic Acid Research Articles

Experimental and numerical study of ethanol oxidation in sub-critical water

The oxidation rate of ethanol by oxygen in sub-critical water is investigated using a lab-scale, plug-flow reactor system at temperatures between 170 °C and 230 °C and a fixed pressure 23.5 MPa. The residence time ranges from 180 s to 580 s. Initial concentration of ethanol is set to 25 mmol/l and initial concentration of oxygen is changed from 50 mmol/l to 150 mmol/l, which corresponds to the variation of equivalence ratio from 0.5 to 1.5. A global oxidation rate including the dependence on oxygen concentration is derived from the complete set of experimental data using least-square method. The reaction orders for ethanol and oxygen are 0.86 ± 0.03 and 1.15 ± 0.05, respectively. The resulting activation energy and the pre-exponential factor are 61.1 ± 3.12 kJ/mol and 10 2.05 ± 0.24 , respectively. In order to confirm whether this obtained oxidation rate is applicable at the condition of higher ethanol concentration, numerical simulation of hydrothermal oxidation of ethanol in sub-critical water is conducted. Steady-state solutions are obtained by solving governing equations and the conversion of ethanol and the temperature increase are compared with the experimental results. The simulation results agree with the experimental results qualitatively. Thus, it is proved that the derived oxidation rate is generally applicable to hydrothermal oxidation of ethanol in sub-critical water. Quantitative difference is attributed to neglecting the further oxidation of acetic acid into carbon dioxide, which generates more heat.

Wet air oxidation of acetic acid over platinum catalysts supported on cerium-based materials: Influence of metal and oxide crystallite size

Platinum catalysts (2.5 wt%) prepared by impregnation on pure commercial ceria and on Zr 0.1(Ce 0.75Pr 0.25) 0.9O 2 sol–gel mixed oxide were synthesized and used for catalytic wet air oxidation (CWAO) of acetic acid. The influence of the platinum sintering (reducing treatment) was studied for both supports to modify the oxygen transfer from the gas phase onto the metallic active site of the catalyst and also to determine the effect of this treatment on the catalytic activity and stability. The catalysts were characterized by BET, TEM, XRD, FT-IR and hydrogen chemisorption before and after CWAO reaction, and oxygen storage capacity (OSC) was measured. The nature of the support [CeO 2 and Zr 0.1(Ce 0.75Pr 0.25) 0.9O 2 compounds] and the preparation conditions led to samples displaying a Pt dispersion ranging from 0.4 to 41%, and BET surface area varying from 4 to 45 m 2 g −1. The results demonstrate poisoning of the catalysts during the CWAO experiments due to the formation of carbonate species. This limits the performance of the mixed oxide-based catalysts displaying the highest OSC values. A correlation was established between the OSC of the catalysts and the formation of carbonate species. Nevertheless, there is no correlation between OSC and catalytic activity, with the ceria-based samples showing the highest reaction rate. An optimal platinum crystallite size is required to achieve the highest conversion of acetic acid in terms of turnover frequency values.

Incident light dependence for photocatalytic degradation of acetaldehyde and acetic acid on S-doped and N-doped TiO 2 photocatalysts

We have synthesized S (S 4+)-doped and N (N 3−)-doped TiO 2 photocatalysts. S-doped and N-doped TiO 2 loaded with Fe 2O 3 nanoparticles have also been prepared. These photocatalysts showed activity under a wide range of wavelengths of irradiation. Action spectra of photochemical reaction rate as a function of the incident light wavelength for oxidation of acetic acid on S-doped TiO 2 was studied.The photocatalytic activities of S-doped and N-doped TiO 2 photocatalysts loaded with Fe 2O 3 nanoparticles for oxidation of acetic acid in aqueous phase and acetaldehyde in gas phase are markedly improved compared to those of doped TiO 2 without loading of Fe 2O 3 nanoparticles under a wide range of incident light wavelengths. The optimum amount of Fe 2O 3 nanoparticles loaded on S-doped TiO 2 particles was different from that on N-doped TiO 2 for oxidation of organic compounds. The relationship between reaction rate of photocatalytic oxidation of acetaldehyde on doped TiO 2 loaded with Fe 2O 3 nanoparticles and amount of Fe 2O 3 nanoparticles is discussed.

Characterizations of platinum catalysts supported on Ce, Zr, Pr-oxides and formation of carbonate species in catalytic wet air oxidation of acetic acid

Catalytic wet air oxidation (CWAO) of aqueous solution of acetic acid (78 mmol L −1) was carried out with pure oxygen (2 MPa) at 200 °C in a stirred batch reactor on platinum supported oxide catalysts (Pt/oxide, oxide = CeO 2, Zr 0.1Ce 0.9O 2, Zr 0.1(Ce 0.75Pr 0.25) 0.9O 2 and ZrO 2). Platinum was loaded on oxides by impregnation (5 wt%), and then the catalysts were reduced under H 2. Homogenous dispersions of 2–3 nm metal crystallites were obtained. The catalytic activity depended on the ability of the support to resist to the formation of carbonates. Ce(CO 3)OH species, determined by FT-IR and XRD, were rapidly formed during the CWAO reaction especially on mixed oxides. These carbonates were responsible to a drastic drop in catalytic performances. Amounts of carbonate species increase with the ability of the catalyst to transfer oxygen.

Synthesis and thermolysis rate constants of diastereomeric oxadiazoline sources of acetoxy(methoxy)carbene — Reaction of acetoxy(methoxy)carbene with isocyanates

Oxidation of the methoxycarbonylhydrazone of p-methoxyacetophenone affords both the cis- and trans-2-acetoxy-2-methoxy-5-(p-methoxyphenyl)-5-methyl-Δ3-1,3,4-oxadiazolines (also known as corresponding 2,5-dihydro-1,3,4-oxadiazoles) as well as methyl 1-acetoxy-1-(p-methoxyphenylethyl)diazenecarboxylate. The three isomers were separated and identified by spectroscopic means. Methyl 1-acetoxy-1-(p-methoxyphenylethyl)diazenecarboxylate is the major product from oxidation in dichloromethane. Oxidation in acetic acid did not afford the oxadiazolines but gave the diazenecarboxylate and, in addition, 1-(p-methoxyphenyl)ethyl acetate. Attempts to isomerize the diazenecar boxylate to the oxadiazolines by acid catalysis were not successful. Thermolysis of the oxadiazolines at 50.4 °C occurred with approximately the same rate constant (ca. 3.6 × 10–5 s–1) to afford acetoxy(methoxy)carbene, which rearranges to methyl pyruvate by acetyl transfer. The carbene, which reacts with relatively unhindered isocyanates to transfer the methoxy carbonyl group to carbon and the acetyl group to nitrogen, can be considered an acyl anion equivalent in that reaction.Key words: acetoxy(methoxy)carbene, diazene, oxadiazoline, isocyanate, (acetylamino)oxoacetate.

Use of cw-CRDS for studying the atmospheric oxidation of acetic acid in a simulation chamber

The coupling between cavity ring-down spectroscopy (CRDS) and an environmental chamber in the investigation of photo-induced reaction mechanisms is demonstrated for the first time.

Atmospheric Oxidation Pathways of Acetic Acid

One of the most abundant carboxylic acids measured in the atmosphere is acetic acid (CH(3)C(O)OH), present in rural, urban, and remote marine environments in the low-ppb range. Acetic acid concentrations are not well reproduced in global 3-D atmospheric models because of the poor inventory of sources and sinks to model its global distribution. To understand the complete oxidation of acetic acid in the atmosphere initiated by OH radicals, ab initio calculations are performed to describe in detail the energetics of the reaction potential energy surface (PES). The proposed reaction mechanism suggests that the CH(3)C(O)OH + OH reaction takes place via three pathways: the addition of OH to the central carbon, the abstraction of a methyl hydrogen, and the abstraction of an acidic hydrogen. The PES is characterized by prereactive H-complexes, transition states, and more interestingly unique radical-mediated isomerization reactions. From the analysis of the energetics, acetic acid atmospheric oxidation will proceed mainly via the abstraction of the acidic hydrogen, consistent with previous experimental and theoretical studies. The major byproducts from each pathway are identified. Glyoxylic acid is suggested to be a major byproduct of the atmospheric oxidation of acetic acid. The atmospheric fate of glyoxylic acid is discussed.

The High Yield Synthesis of Benzaldehydes from Benzylic Alcohols using Homogeneously Catalyzed Aerobic Oxidation in Acetic Acid

AbstractThe kinetics and yields for the formation of benzaldehydes from benzylic alcohols via aerobic oxidation using homogeneous catalysts in acetic acid are reported. For compounds of the type X‐C6H4CH2OH where X=H, 4‐CH3, 4‐OCH3, 4‐Cl, 4‐COOH the observed yields were 84, 78, 57, 88 and 52 mol %, respectively. These yields are comparable to those reported for the stoichiometric Co(III)/Br oxidation of these same benzylic alcohols. These results are limited to benzylic alcohols. The high yields are possible for two reasons: 1) the rate of reaction exhibits two maxima in which the benzaldehyde is predominately being generated in the first phase and the carboxylic acid in the second and 2) the competing esterification of the benzylic alcohol with the acetic acid solvent is an order of magnitude slower. A variety of other catalysts were also evaluated which give lower yields mainly because they are less active and the competing esterification reaction becomes more important. Water addition to the acetic acid increased the rate of acetylation of the alcohol, contrary to expectation. The oxidation of the benzaldehyde appears to be inhibited by the presence of the benzylic alcohol. Even though the rate of oxidation of the benzaldehyde, by itself, is equally reactive as the benzylic alcohol, the benzaldehyde does not significantly react until the benzylic alcohol concentration is very low. Two possible reasons, using a free‐radical chain mechanism, are suggested to explain this behavior. A mechanism demonstrating why the stoichiometric and catalytic reactions give similar yields is given.

Phenol oxidation in supercritical water in a well-stirred continuous reactor

A well-stirred reactor for phenol and acetic acid oxidation in supercritical water is considered. A mathematical model of an adiabatic reactor is formulated. A numerical algorithm for solving the model equations using the homotopy method is developed. The model takes into account specific features of processes under supercritical conditions, namely, the changes in the thermodynamic properties (enthalpy, heat capacity, and critical parameters) of mixtures with a change in pressure and temperature. The thermodynamic properties are calculated by methods of nonideal thermodynamics. It is shown that there is a multiplicity of steady-state solutions at various reactor performances. The results of numerical analysis of the effect of the inlet flow temperature, the amount of methanol (fuel) fed, and the total pressure on the reactor performance are presented.

Mo(VI)-catalysis of perborate oxidation in acetic acid: Oxidation of dimethyl and dibenzyl sulfoxides

Molybdenum(VI) effectively catalyzes sodium perborate oxidation of dimethyl and dibenzyl sulfoxides to sulfones in glacial acetic acid and the yields are 70% and 85%, respectively. The catalyzed oxidations are zero-order with respect to the oxidant and first-order with respect to Mo(VI) and the sulfoxides. Trichloroacetic acid enhances the oxidations. Glacial acetic acid is the suitable solvent; methanol, ethylene glycol or water suppresses the reactions. The kinetic results reveal dioxoperoxomolybdenum(VI) as the reactive oxidant.

The surface properties and the activities in catalytic wet air oxidation over CeO 2–TiO 2 catalysts

No-noble metal CeO 2–TiO 2 catalysts prepared by sol–gel method were developed and examined for catalytic wet air oxidation (CWAO) of acetic acid. The structure of the catalysts was measured by BET, SEM, XRD, XPS and DTA-TG. We investigated the effect of the interactions of Ce and Ti on the structure of CeO 2–TiO 2 catalysts. The mechanisms of the relationships between the different content of Ti and the activity of CeO 2–TiO 2 catalysts were discussed. The results showed that the average crystal size of CeO 2 decreased and the surface areas increased; the low valence of Ce 3+ increase, and the chemisorbed oxygen slightly decreased with the increase of Ti content on the surface of CeO 2–TiO 2 catalysts. The order of the activity in CWAO of acetic acid followed: Ce/Ti 1/1 > Ce/Ti 3/1 > Ce/Ti 1/3 > Ce/Ti 5/1 > CeO 2 > TiO 2 > no catalyst. In CWAO of acetic acid, the optimal atomic ratio of Ce and Ti was 1, and the highest COD removal was over 64% at 230 °C, 5 MPa and 180 min reaction time over Ce/Ti 1/1 catalyst. The excellent activity and stability of CeO 2–TiO 2 catalysts was observed in our study.

Microbial oxidation/amidation of benzhydrylsulfanyl acetic acid. Synthesis of (+)-modafinil

A highly enantioselective oxidation of benzhydrylsulfanyl acetic acid to the corresponding ( S)-sulfinyl carboxylic acid was achieved employing the fungus Beauveria bassiana in very good yield. This product was amidated using the bacteria Bacillus subtilis to afford ( S)-modafinil in good yield.

Multi-Phase Chemistry of C2 and C3 Organic Compounds in the Marine Atmosphere

A box model is used to explore the detailed chemistry of C2 and C3 organic compounds in the marine troposphere by tracing the individual reaction paths resulting from the oxidation of ethane, ethene, acetylene, propane, propene and acetic acid. The mechanisms include chemical reactions in the gas phase and in the aqueous phase of clouds and aerosol particles at cloud level under conditions resembling those in the northern hemisphere. Organic hydroperoxides are found to be important intermediate products, with subsequent reactions leading partly to the formation of mixed hydroxy or carbonyl hydroperoxides that are readily absorbed into cloud water, where they contribute significantly to the formation of multifunctional organic compounds and organic acids. Organic hydroperoxides add little to the oxidation of sulfur dioxide dissolved in the aqueous phase, which is dominated by H2O2. Next to acetaldehyde and acetone, glycol aldehyde, glyoxal, methyl glyoxal and hydroxy propanone are prominent oxidation products in the gas and the aqueous phase. Acetaldehyde is not efficiently converted to acetic acid in clouds; the major local sources of acetic acid are gas-phase reactions. Other acids produced include hydroperoxy acetic, glycolic, glyoxylic, oxalic, pyruvic, and lactic acid. The mechanism of Schuchmann et al. (1985), which derives glycolic and glyoxylic acid from the oxidation of acetate, is found unimportant in the marine atmosphere. The principal precursors of glyoxylic acid are glyoxal and glycolic acid. The former derives mainly from acetylene and ethene, the latter from glycolaldehyde, also an oxidation product of ethene. The oxidation of glyoxylic acid leads to oxalic acid, which accumulates and is predicted to reach steady state concentrations in the range 30–90 ng m−3. This is greater, yet of the same magnitude, than the concentrations observed over the remote Pacific Ocean.

Ethane to acetic acid oxidation over supported heteropoly acids

Molybdo(vanado)phosphoric heteropoly acids of Keggin structure supported on oxide supports (SiO 2, TiO 2, Al 2O 3) were used as catalysts for ethane to acetic acid oxidation in the range of reaction temperature from 250 to 400 °C. Vanadium atoms introduced into Keggin structure enhanced oxidative activity of catalytic system, while vanadyl groups exchanged into cationic position diminished ethane conversion. Nature of support (acidic or base centres on the surface) influenced both ethane conversion and distribution of products. Ethane oxidation over silica- and titania-supported HPMoV x was due to the presence of regular or defected Keggin structure while low catalytic performance on alumina-supported samples was attributed to mixed Mo–V–P oxides formed as a result of HPMoV x decomposition. Presence of water vapours in the reaction mixture was indispensable both for catalysts surface modification and for acetic acid desorption.

The Sonochemical Insertion of Nanomaterials into Mesostructures

Ultrasound radiation has been recently used for the synthesis of mesoporous materials (MSPM). The main advantages are manifested in the short preparation time and thicker walls leading to a more hydrothermally stable structure.1 This preparation method has already been reviewed.2 The discovery of MSP materials led immediately to the development of many experimental methods for the deposition of materials, especially catalytic materials, into the mesopores. Impregnation, thermal spreading, ion adsorption, and the most recent method3 in which colloidal gold solution is premixed with the precursors for the preparation of the MSPM, are among the methods used for the insertion of materials into the mesopores. Sonochemistry was also employed for this purpose. We will outline in this article the use of the sonochemical processes for the insertion of nanomaterials into the pores of MSPM. We will explain how this process is conducted, to what extent the materials are deposited in the pores and what is the mechanism for the insertion. An example will be given for the preparation of Ru/MSP TiO2 and its application as a catalyst in the wet air oxidation of succinic acid and acetic acid, which often appear as the ultimate intermediates in oxidation of many organic pollutants.

Modeling of the Oxidation of Organic Compounds in Supercritical Water

A system for oxidation of organic impurities in supercritical water is proposed. Models are formulated and calculations are performed to determine the characteristics of the main apparatuses of the system, namely, heat exchangers, a chemical reactor, and a separator. The models take into account specific features of processes under supercritical conditions, specifically, the changes in the thermodynamic properties (enthalpy, specific heat, critical parameters) of the reaction mixtures with changes in pressure and temperature, and also the variations of the compositions of the mixtures along the lengths of the apparatuses. The thermodynamic properties are calculated by methods of nonequilibrium thermodynamics. A numerical analysis is performed of one of the variants of a system for acetic acid oxidation by oxygen in supercritical water, which can be a prototype of a pilot plant. The fuel is chosen to be an aqueous methanol solution, and the oxidant is taken to be hydrogen peroxide. Replacement of the reactant, the fuel, or the oxidant does not fundamentally change the methods for calculating the characteristics of the apparatuses and the entire system.

A comparative study of the effects of chloride, sulfate and nitrate ions on the rates of decomposition of H 2O 2 and organic compounds by Fe(II)/H 2O 2 and Fe(III)/H 2O 2

The effects of chloride, nitrate, perchlorate and sulfate ions on the rates of the decomposition of hydrogen peroxide and the oxidation of organic compounds by the Fenton’s process have been investigated. Experiments were conducted in a batch reactor, in the dark at pH ⩽ 3.0 and at 25 °C. Data obtained from Fe(II)/H 2O 2 experiments with [Fe(II)] 0/[H 2O 2] 0 ⩾ 2 mol mol −1, showed that the rates of reaction between Fe(II) and H 2O 2 followed the order SO 4 2− > ClO 4 −NO 3 −Cl −. For the Fe(III)/H 2O 2 process, identical rates were obtained in the presence of nitrate and perchlorate, whereas the presence of sulfate or chloride markedly decreased the rates of decomposition of H 2O 2 by Fe(III) and the rates of oxidation of atrazine ([atrazine] 0=0.83 μM), 4-nitrophenol ([4-NP] 0=1 mM) and acetic acid ([acetic acid] 0=2 mM). These inhibitory effects have been attributed to a decrease of the rate of generation of hydroxyl radicals resulting from the formation of Fe(III) complexes and the formation of less reactive (SO 4 − ) or much less reactive (Cl 2 − ) inorganic radicals.

The effect of micro-morphology of Bi2O3on catalytic properties of Co/Bi catalyst for wet air oxidation of acetic acid

Two catalysts that consist of cobalt-bismuth complex oxides were prepared by different methods. These two catalysts, which exhibited different catalytic properties for wet oxidation of acetic acid, were investigated by XRD, TEM, ESR and XPS, and the interaction between Co and Bi was studied. It has been found that this kind of interaction was reinforced due to a close contact of the nanometer-sized Bi2O3 with Co3O4 and the catalytic activity of Co-Bi catalyst was greatly improved by this kind of interaction. The mechanism of the wet oxidation of acetic acid over Co-Bi catalyst is also discussed in this paper.

Computational Multiple Steady States in Heterogeneous Catalysis of Wet Oxidation of Acetic Acid in an Isothermal CFSTR

A family of chemical reaction networks, involving heterogeneous catalysis of wet oxidation of acetic acid in an isothermal continuous flow stirred tank reactor (CFSTR), is determined to have the capacity to exhibit steady state multiplicity by implementation of the Deficiency One Algorithm and the Subnetwork Analysis. A set of rate constants and two corresponding steady states are constructed for each case. The phenomena of bistability, hysteresis and bifurcation are discussed. Two sets of signatures of multiple steady states are provided, which can be used to identify the reaction mechanisms as steady states of some species are measured.

State of Ru on CeO2 and its catalytic activity in the wet oxidation of acetic acid

The relationship between the state of Ru on CeO2 and catalytic activity in the wet oxidation of acetic acid was investigated for Ru/CeO2 catalysts prepared by different methods. The temperature programmed reduction (TPR) experiments of Ru/CeO2 showed that the oxygen species of RuO2 was reduced at different temperatures depending upon the methods of preparation. Ru species reduced at low temperatures could not be observed by TEM and XRD. It was concluded that RuOCe bonds in the well-dispersed Ru species are highly fragile and its mobile oxygen is the active species in the wet oxidation.