Showing papers on "Wet oxidation published in 2009"

Evaluation of wet air oxidation as a pretreatment strategy for bioethanol production from rice husk and process optimization

Abstract: The pretreatment of rice husk by the wet air oxidation (WAO) technique was investigated by means of a statistically designed set of experiments. Reaction temperature, air pressure, and reaction time were the process parameters considered. WAO pretreatment of rice husk increased the cellulose content of the solid fraction by virtue of lignin removal and hemicellulose solubilization. The cellulose recovery was around 92%, while lignin recovery was in the tune of 8–20%, indicating oxidation of a bulk quantity of lignin. The liquid fraction was found to be rich in hexose and pentose sugars, which could be directly utilized as substrate for ethanol fermentation. The WAO process was optimized by multi-objective numerical optimization with the help of MINITAB 14 suite of statistical software, and an optimum WAO condition of 185 °C, 0.5 MPa, and 15 min was predicted and experimentally validated to give 67% (w/w) cellulose content in the solid fraction, along with 89% lignin removal, and 70% hemicellulose solubilization; 13.1 gl −1 glucose and 3.4 gl −1 xylose were detected in the liquid fraction. The high cellulose content and negligible residual lignin in the solid fraction would greatly facilitate subsequent enzymatic hydrolysis, and result in improved ethanol yields from rice husk.

Influence of substrate particle size and wet oxidation on physical surface structures and enzymatic hydrolysis of wheat straw

Abstract: In the worldwide quest for producing biofuels from lignocellulosic biomass, the importance of the substrate pretreatment is becoming increasingly apparent. This work examined the effects of reducing the substrate particle sizes of wheat straw by grinding prior to wet oxidation and enzymatic hydrolysis. The yields of glucose and xylose were assessed after treatments with a benchmark cellulase system consisting of Celluclast 1.5 L (Trichoderma reesei) and Novozym 188 β-glucosidase (Aspergillus niger). Both wet oxidized and not wet oxidized wheat straw particles gave increased glucose release with reduced particle size. After wet oxidation, the glucose release from the smallest particles (53–149 μm) reached 90% of the theoretical maximum after 24 h of enzyme treatment. The corresponding glucose release from the wet oxidized reference samples (2–4 cm) was ∼65% of the theoretical maximum. The xylose release only increased (by up to 39%) with particle size decrease for the straw particles that had not been wet oxidized. Wet oxidation pretreatment increased the enzymatic xylose release by 5.4 times and the glucose release by 1.8 times across all particle sizes. Comparison of scanning electron microscopy images of the straw particles revealed edged, nonspherical, porous particles with variable surface structures as a result of the grinding. Wet oxidation pretreatment tore up the surface structures of the particles to retain vascular bundles of xylem and phloem. The enzymatic hydrolysis left behind a significant amount of solid, apparently porous structures within all particles size groups of both the not wet oxidized and wet oxidized particles. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009

Activity and Stability of Perovskite-Type Oxide LaCoO3 Catalyst in Lignin Catalytic Wet Oxidation to Aromatic Aldehydes Process

Abstract: The perovskite-type oxide catalyst LaCoO3, prepared by the sol−gel method, was tested for catalytic wet oxidation (CWAO) of lignin to aromatic aldehydes. The lignin conversion and yield of each aromatic aldehyde were significantly enhanced by the catalytic process, compared to the noncatalytic process. A mechanism involving the reaction of lignin molecules with adsorbed oxygen surface sites, Co(surf)3+O2−, was proposed on the basis of experimental observations, yielding the cycle of Co(surf)3+ → Co(surf)2+ → Co(surf)3+O2− → Co(surf)3+. The formation rates of the intermediates quinonemethide and hydroperoxide were the rate-determining steps. The activity and perovskite-type structure of the LaCoO3 catalyst did not undergo any obvious changes after the five successive reactions.

Fe-zeolites as catalysts for chemical oxidation of MTBE in water with H2O2

Abstract: The heterogeneous catalytic wet oxidation of methyl tert-butyl ether (MTBE) with hydrogen peroxide, catalyzed by the iron-containing zeolites Fe-ZSM5 and Fe-Beta, was studied at ambient conditions and pH 7. The kinetics of MTBE degradation could be well-fitted to a pseudo-first-order model. Using Fe-ZSM5, the dependence of the reaction rate constant on hydrogen peroxide and catalyst concentration was determined. Furthermore, the formation and oxidation of tert-butyl alcohol and tert-butyl formate as intermediates of MTBE oxidation were studied. A comparison of the reaction rates of MTBE, trichloroethylene and diethyl ether in the Fe-ZSM5/H 2 O 2 system revealed that adsorption plays a positive role for the degradation reaction. Comparing the two types of Fe-containing zeolites applied in this study, Fe-Beta showed a lower catalytic activity for H 2 O 2 decomposition and also MTBE degradation. However, in terms of utilization of H 2 O 2 for MTBE degradation Fe-Beta is advantageous over Fe-ZSM5. This could be explained by the stronger adsorptive enrichment of MTBE on the Fe-Beta zeolite. This study shows that Fe-containing zeolites are promising catalysts for oxidative degradation of MTBE by H 2 O 2 .

Catalytic wet air oxidation of dye pollutants by polyoxomolybdate nanotubes under room condition

Abstract: In order to develop a catalyst with high activity and stability for catalytic wet air oxidation of pollutant dyes at room condition, a new polyoxometalate Zn1.5PMo12O40 with nanotube structure was prepared using biological template. The structure and morphology were characterized using infrared (IR) spectra, UV–vis diffuse reflectance spectra (DR-UV–vis), elemental analyses, X-ray powder diffraction (XRD), and transmission electron microscopy (TEM). And the degradation of Safranin-T (ST), a hazardous textile dye, under air at room temperature and atmospheric pressure was studied as a model experiment to evaluate the catalytic activity of this polyoxomolybdate catalyst. The results show that the catalyst has an excellent catalytic activity in treatment of wastewater containing 10 mg/L ST, and 98% of color and 95% of chemical oxygen demand (COD) can be removed within 40 min. And the organic pollutant of ST was totally mineralized to simple inorganic species such as HCO3−, Cl− and NO3− during this time (total organic carbon (TOC) decreased 92%). The structure and morphology of the catalyst under different cycling runs show that the catalyst are stable under such operating conditions and the leaching tests show negligible leaching effect owning to the lesser dissolution. So this polyoxomolybdate nanotube is proved to be a heterogeneous catalyst in catalytic wet air oxidation of organic dye.

Pretreatment of reed by wet oxidation and subsequent utilization of the pretreated fibers for ethanol production.

Abstract: Common reed (Phragmites australis) is often recognized as a promising source of renewable energy. However, it is among the least characterized crops from the bioethanol perspective. Although one third of reed dry matter is cellulose, without pretreatment, it resists enzymatic hydrolysis like lignocelluloses usually do. In the present study, wet oxidation was investigated as the pretreatment method to enhance the enzymatic digestibility of reed cellulose to soluble sugars and thus improve the convertibility of reed to ethanol. The most effective treatment increased the digestibility of reed cellulose by cellulases more than three times compared to the untreated control. During this wet oxidation, 51.7% of the hemicellulose and 58.3% of the lignin were solubilized, whereas 87.1% of the cellulose remained in the solids. After enzymatic hydrolysis of pretreated fibers from the same treatment, the conversion of cellulose to glucose was 82.4%. Simultaneous saccharification and fermentation of pretreated solids resulted in a final ethanol concentration as high as 8.7 g/L, yielding 73% of the theoretical.

Removal of herbicide diuron and thermal degradation products under Catalytic Wet Air Oxidation conditions

Abstract: The Catalytic Wet Air Oxidation (CWAO) of diuron (N-(3,4-dichlorophenyl)-N,N-dimethylurea), a herbicide widely used in agriculture and belonging to the phenylurea family, has been investigated in aqueous solution in the presence of a Ru/TiO2 catalystat 140-180 degrees C and 5 MPa total air pressure. Diuron and Total Organic Carbon (TOC) have been analyzed. Some reaction products were identified by LC-ES/MS, and the amount of the inorganic ions and organic products generated during the process have been measured. Thermal degradation is the main initial process yielding mainly 3.4-dichloroaniline (DCA) and dimethylamine (DMA). Further oxidations lead to ring opening and smaller organic molecules from DCA, but the DMA fragment was more difficult to eliminate. Reactions between DCA and carboxylic acids conducted to the formation of condensation products. On the other hand, dechlorination was fast and complete. The work points out that CWAO over Ru supported catalysts may not a viable technique for degradation of diluted aqueous solutions of diuron. The mineralization is incomplete compared to other Advanced Oxidation Processes, and a possible leaching of the metal by the amines formed by thermal degradation of diuron may be critical. (C) 2009 Elsevier B.V. All rights reserved.

Pre-treatment and ethanol fermentation potential of olive pulp at different dry matter concentrations

Abstract: Renewable energy sources have received increased interest from the international community with biomass being one of the oldest and the most promising ones. In the concept of exploitation of agro-industrial residues, the present study investigates the pre-treatment and ethanol fermentation potential of the olive pulp, which is the semi solid residue generated from the two-phase processing of the olives for olive oil production. Wet oxidation and enzymatic hydrolysis have been applied aiming at the enhancement of carbohydrates' bioavailability. Different concentrations of enzymes and enzymatic durations have been tested. Both wet oxidation and enzymic treatment were evaluated based on the ethanol obtained in a subsequent fermentation step by Saccharomyces cerevisiae and Thermoanaerobacter mathranii. It was found that a four-day hydrolysis time was adequate for a satisfactory release of glucose and xylose. The combination of wet oxidation and enzymatic hydrolysis resulted in the glucose and xylose concentration increase of 138 and 444%, respectively, compared to 33 and 15% with only enzymes added. However, the highest ethanol production was obtained when only enzymic pre-treatment was applied, implying that wet oxidation is not a recommended pre-treatment process for olive pulp at the conditions tested. It was also showed that increased dry matter concentration did not have a negative effect on the release of sugars, indicating that the cellulose and xylan content of the olive pulp is relatively easily available. The results of the experiments in batch processes clearly emphasize that the simultaneous saccharification and fermentation (SSF) mode is advantageous in comparison with the separate hydrolysis and fermentation (SHF) mode concerning process contamination.

Fe-MCM-41 with highly ordered mesoporous structure and high Fe content: synthesis and application in heterogeneous catalytic wet oxidation of phenol

Abstract: Iron-substituted MCM-41 materials (Fe-MCM-41) have been synthesized via a hydrothermal method with in situ incorporation of Fe(III) oxalate complex under various basic conditions. The resulting Fe-MCM-41 samples were characterized by X-ray diffraction, N2 adsorption measurement, and UV–Vis spectrometry. By controlling initial synthesized pH, the Fe-MCM-41 with highly ordered hexagonal mesoporous structures and high iron content (Si/Fe = 20) could be obtained. The iron species in Fe-MCM-41 samples mainly coexisted in isolated iron and highly dispersed iron oxide nanoclusters. Activity and stability of the obtained catalyst were evaluated on the wet peroxide oxidation of phenol under mild reaction conditions (<80 °C, ambient pressure). The Fe-MCM-41 with highly ordered mesoporous structure and high Fe content appeared to be the most interesting catalysts for phenol degradation owing to its high organic mineralization, low sensitivity to leaching Fe out and good oxidant efficiency.

Wet air oxidation with tubular ceramic membranes modified with polyelectrolyte/Pt nanoparticle films

Abstract: Gas–liquid reactions with membrane-supported catalysts often use the interfacial contactor configuration in which the reaction occurs at the gas–liquid-catalyst interface within the membrane. Thus, control over the catalyst location in the membrane is crucial for making efficient use of expensive materials such as noble metal nanoparticles. Layer-by-layer (LBL) adsorption of polyelectrolyte/metal nanoparticle films in tubular ceramic membranes allows deposition of the catalytic nanoparticles only near the interior of the tube, where the gas–liquid interface is typically located. In wet air oxidation of formic acid, tubular membranes modified by LBL deposition of polyelectrolyte/Pt nanoparticle films show 2 to 3 times higher specific activities than similar membranes modified by traditional methods such as anionic impregnation/reduction and evaporation/recrystallization/reduction. In acetic acid and phenol oxidations, the LBL method gives order of magnitude increases in specific activity relative to the traditional membrane modification methods. The enhanced activity with LBL-modified membranes is likely due to the controlled deposition of the Pt in the catalytic inner layer of the tubes, as only the LBL method gives tubular membranes that show higher activity than pulverized membranes in stirred tank reactors.

Thermo-chemical preparation of the process water of a hydrothermal carbonisation

Abstract: The method comprises feeding a process water (10) after a retention time of maximum 12 hours, in a carbonization reactor to a thermo-chemical process such as wet oxidation in the presence of a catalyst. The pressure level of the thermo-chemical process through wet oxidation lies between the pressure level of the hydrothermal carbonization and atmospheric pressure. A mechanical dewatering of the mixture of solid material product and process water is carried out after a hydrothermal carbonization process on the pressure level of the hydrothermal carbonization. The method comprises feeding process water (10) after a retention time of maximum 12 hours, in a carbonization reactor to a thermo-chemical process such as wet oxidation in the presence of a catalyst. The pressure level of the thermo-chemical process through wet oxidation lies between the pressure level of the hydrothermal carbonization and atmospheric pressure. A mechanical dewatering of the mixture of solid material product and process water is carried out after a hydrothermal carbonization process on the pressure level of the hydrothermal carbonization or on the pressure level of the thermo-chemical process through wet-oxidation.

A novel application of wet oxidation to retrieve carbonates from large organic-rich samples for ocean-climate research

Abstract: [1] For ocean-climate research, carbonates are extracted from large organic-rich bulk sediments for specific geochemical analyses. This is conventionally achieved by time-consuming dry oxidation or nonoxidative preprocessing. To significantly shorten sample preparation time we designed and evaluated a rapid technique that uses sequential wet oxidization of bulk samples in a hot alkaline 18% H2O2 solution. We successfully tested this wet oxidation technique on multiple bulk aliquots from two sediment trap samples and a core top sediment that were also processed by dry oxidation and without oxidation. From all aliquots four calcitic foraminifera species and an aragonitic juvenile bivalve from the 250–315 μm fraction were analyzed for size-normalized weight (SNW), δ18O, δ13C, Mg/Ca, and Sr/Ca. In addition, these proxies were determined on powdered bulk aliquots from the 150–250 μm fraction processed by wet oxidation, dry oxidation, and without oxidation. At an initial pH of 8 and temperature of 70°C the alkaline H2O2 solution appeared to be most stable and reactive. Carbonate dissolution did not occur as no reduction was observed in SNW of the four foraminifera species G. ruber, G. trilobus, N. dutertrei, G. bulloides, and the aragonitic bivalve shells. For sediment traps the δ18O and δ13C between the three cleaning methods only deviated between 0.05 and 0.3‰ compared to 0.1 and 0.6‰ in sediments, with equally small variation in Mg/Ca and Sr/Ca ratios (0.1–0.4 mmol/mol). Lowest Ba/Ca ratios show that wet oxidation successfully removed organic matter along with residual salts. No significant systematic differences between samples or methods were found, but a residual scatter remained, particularly in the nonoxidized sediment because of intraspecies and intrashell inhomogeneity. Given proper preprocessing all three techniques performed well, with the proposed wet oxidation method emerging as a fast technique for extracting carbonate shells from wet, gram-sized bulk samples. Within 3 h wet oxidation produced clean, dry residues of unaltered calcareous shells from batches of four wet bulk samples without time-consuming intermediate steps. For Mg/Ca thermometry on time series sediment trap samples, wet oxidation results approached those obtained using the Barker et al. (2003) protocol with improved sample recovery. Consequently, the proposed wet oxidation offers a rapid alternative to conventional extraction techniques for carbonate geochemistry.

Oxidation Behavior of Pure Copper in Oxygen and/or Water Vapor at Intermediate Temperature

Abstract: The oxidation of pure copper in oxygen with and without water vapor was investigated as a function of temperature, oxygen pressure, and water vapor pressure using thermogravimetric analysis. The rate of the oxidation was increased with increasing temperature from 500 to 700°C and followed by the parabolic rate law regardless of the presence of water vapor. The activation energy for the oxidation was 90.67 kJ/mol in dry oxygen and 95.86 kJ/mol in oxygen with water vapor. The change of oxygen pressure without water vapor does not affect the oxidation rate at given temperatures. However, increasing water vapor pressure from 0.39 to 0.58 atm resulted in higher oxidation rate due to the increase of copper vacancies. CuO whiskers were observed and their growth seems to be enhanced by the presence of water vapor.

Total catalytic wet oxidation of phenol and its chlorinated derivates with MnO2/CeO2 catalyst in a slurry

Abstract: In the present work, a synthetic effluent of phenol was treated by means of a total oxidation process-Catalyzed Wet Oxidation (CWO). A mixed oxide of Mn-Ce (7:3), the catalyst, was synthesized by co-precipitation from an aqueous solution of MnCl2 and CeCl3 in a basic medium. The mixed oxide, MnO2/CeO2, was characterized and used in the oxidation of phenol in a slurry reactor in the temperature range of 80-130oC and pressure of 2.04-4.76 MPa. A phenol solution containing 2.4-dichlorophenol and 2.4-dichlorophenoxyacetic acid was also degraded with good results. A lumped kinetic model, with two parallel reaction steps, fits precisely with the integrated equation and the experimental data. The kinetic parameters obtained are in agreement with the Arrhenius equation. The activation energies were determined to be 38.4 for the total oxidation and 53.4 kJ/mol for the organic acids formed.

Wet Oxidation of Thiocyanate under Different pH Conditions: Kinetics and Mechanistic Analysis

Abstract: The wet oxidation of thiocyanate has been investigated in a 1-L semibatch reactor at temperatures in the range of 438.15−468.15 K and total pressures between 2.0 × 103 kPa and 8.1 × 103 kPa. The initial pH value of the reaction media was varied between pH 2 and pH 12 and was found to be a key parameter in the rate of thiocyanate degradation. The evolution of concentration of substrate and products (sulfate and ammonium) were analyzed. Based on the experimental data and bibliography information, a kinetic model was obtained and, here, possible pathways, depending on the initial pH of the media, are suggested for thiocyanate oxidation.