ABSTRACT
A series of binary oxide catalysts (ceria-ZnO) were prepared and doped with different amounts of palladium in the range of 0.5%-1.5%. The prepared catalysts were characterized by SEM, TEM, XRD and XPS, as well as by N2 sorptiometry study. The XPS results confirmed the structure of the Pd CeO2-x-ZnO. The photocatalytic activity of these catalysts was evaluated for degradation of MTBE in water. These photocatalyst efficiently degrade a 100ppm aqueous solution of MTBE upon UV irradiation for 5h in the presence of 100mg of each of these photocatalysts. The removal of 99.6% of the MTBE was achieved with the ceria-ZnO catalyst doped with 1% Pd. In addition to the Pd loading, the N2 sorptiometry study introduced other factors that might affect the catalytic efficiency is the catalyst average pore sizes. The photoreaction was determined to be a first order reaction.
Subject(s)
Environmental Pollutants/chemistry , Methyl Ethers/chemistry , Nanocomposites/chemistry , Palladium/chemistry , Zinc Oxide/chemistry , Environmental Pollutants/radiation effects , Methyl Ethers/radiation effects , Microscopy, Electron , Nitrogen , Photoelectron Spectroscopy , Photolysis , X-Ray DiffractionABSTRACT
An experimental study of methyl tert-butyl ether (MTBE) pyrolysis (3.72% MTBE in argon) has been performed at low pressure (267 Pa) within the temperature range from 700 to 1420 K. The pyrolysis process was detected with the tunable synchrotron vacuum ultraviolet (VUV) photoionization and molecular-beam mass spectrometry (MBMS). About thirty intermediates are identified from near-threshold measurements of photoionization mass spectrum and photoionization efficiency spectrum. Among them, H2, CO, CH4, CH3OH and C4H8 are the major pyrolysis products. The radicals such as methyl, methoxy, propargyl, allyl, C4H5 and C4H7 are detected. The isomers of pyrolysis products are identified as well, i.e., propyne and allene, 1,2,3-butatriene and vinylacetylene, isobutene and 1-butene, propanal and acetone. Furthermore, the mole fractions of the pyrolysis products have been evaluated under various temperatures. Meanwhile, the initial formation temperatures of different pyrolysis products can be obtained. This work is anticipated to present a new experimental method for pyrolysis study and help understand the pyrolysis and combustion chemistry of MTBE and other oxygenated fuels.
Subject(s)
Mass Spectrometry/methods , Methyl Ethers/chemistry , Methyl Ethers/radiation effects , Synchrotrons , Ultraviolet Rays , Mass Spectrometry/instrumentation , Photochemistry , Pressure , Temperature , VacuumABSTRACT
Two UV-based advanced oxidation processes (AOPs), UV/H2O2 and UV/TiO2, were tested in batch reactor systems to evaluate the removal efficiencies and optimal conditions for the photodegradation of methyl tert-butyl ether (MTBE). The optimal conditions at an initial MTBE concentration of 1 mM ([MTBE]0=1 mM) were acidic and 15 mM H2O2 in UV/H2O2 system, and pH 3.0 and 2.0 g/l TiO2 in UV/TiO2 suspended slurries system under 254-nm UV irradiation. Under the optimal conditions, MTBE photodegradation during the initial period of 60 min in UV/H2O2 and UV/TiO2 systems reached 98 and 80%, respectively. In both systems, MTBE photodegradation decreased with increasing [MTBE]0. While MTBE photodegradation rates increased with increasing dosage of H2O2 (5-15 mM) and TiO2 (0.5-3 g/l), further increase in the dosage of H2O2 (20 mM) or TiO2 (4 g/l) adversely reduced the MTBE photodegradation. Pseudo first-order kinetics with regard to [MTBE] can be used to describe the MTBE photodegradation in both systems. The pseudo first-order rate constants linearly increased with the increase in the molar ratio of [H2O2]0 to [MTBE]0 in UV/H2O2 system and linearly increased with the decrease in [MTBE]0 in UV/TiO2 system.
Subject(s)
Hydrogen Peroxide/chemistry , Methyl Ethers , Oxidants/chemistry , Titanium/chemistry , Ultraviolet Rays , Water Pollutants, Chemical , Hydrogen-Ion Concentration , Kinetics , Methyl Ethers/chemistry , Methyl Ethers/radiation effects , Photochemistry , Water Pollutants, Chemical/chemistry , Water Pollutants, Chemical/radiation effects , Water Purification/methodsABSTRACT
Hexavalent chromium and methyl tert-butyl ether (MTBE) are two important environmental pollutants. Simultaneous decontamination of Cr(VI) and MTBE was studied by UV/TiO2 process. The influences of pH and the concentrations of pollutants on the kinetics of the photocatalytic reactions were evaluated. Dark adsorption tests showed that the acidic pH favored the adsorption of Cr(VI) while neutral pH favored the adsorption of MTBE. Under UV irradiation, Cr(VI) reduction was observed in Cr(VI)/TiO2 system, and MTBE oxidation was observed in MTBE/TiO2 system. The system containing Cr(VI) and MTBE by UV/TiO2 process demonstrated the synergistic effect between oxidation of MTBE and reduction of Cr(VI). The results demonstrated that two pollutants Cr(VI) and MTBE could be eliminated simultaneously by UV/TiO2 process. tert-Butyl formate, tert-butyl alcohol and acetone were identified as primary degradation products of MTBE by gas chromatography-mass spectrometry in the degradation of MTBE by UV/TiO2 process.
Subject(s)
Chromium/chemistry , Chromium/radiation effects , Methyl Ethers/chemistry , Methyl Ethers/radiation effects , Titanium/chemistry , Ultraviolet Rays , Adsorption , Catalysis , Oxidation-Reduction , Photochemistry , Waste Disposal, Fluid , Water Pollutants, Chemical/radiation effects , Water Purification/methodsABSTRACT
W values of tissue-equivalent gases based on propane and butane were measured for protons in the energy range 1-100 keV and compared with those of dimethylether and water vapour. The experimental values of the tissue-equivalent gas mixtures were compared with data calculated from the W values of the mixture components using five existing additivity models and two new models derived within the scope of the present work. Apart from one model--the simplest one--all models show a good agreement with the experimental data.
Subject(s)
Algorithms , Alkanes/radiation effects , Linear Energy Transfer , Methyl Ethers/radiation effects , Models, Chemical , Protons , Radiometry/methods , Alkanes/chemistry , Body Burden , Computer Simulation , Gases/chemistry , Gases/radiation effects , Methyl Ethers/chemistry , Neutrons , Radiation Dosage , Radiation Protection/methods , Radioisotopes/analysis , Radioisotopes/chemistry , Relative Biological EffectivenessABSTRACT
An aqueous deoxygenated dilute PVME solution (cP = 0.5 mass %) was irradiated with gamma-rays at different radiation doses (D = 0.2-10 kGy). At these concentrations and doses contracted molecules are formed but no macroscopic networks. For the analysis of the structural changes, the irradiated samples were analyzed by size exclusion chromatography (SEC) with a triple detector system, static light scattering, and viscometry. SEC measurements necessitate for the application of the universal calibration principle the knowledge of the Kuhn-Mark-Houwink (KMH) parameters. To obtain these parameters commercially available poly(vinyl methyl ether) was fractionated and analyzed by the same means. We found at 30 degrees C a KMH relationship to [eta] = 0.0226 (mL/g) x Mw(0.67) in THF. We observed an increase in molar masses without any significant structural changing for D < 0.5 kGy. With increasing radiation dose, the intramolecular cross-linking reaction becomes more and more important. The results of viscosity measurements show a slight increase in contraction for 1.0 kGy. For irradiation dose higher than D > 1.5 kGy, a strong contraction occurs. For D > 5.0 kGy, the favored intramolecular reactions lead to the formation of microgels.
