• Energy Research

Gas-phase photocatalytic oxidation (PCO) and thermal catalytic oxidation (TCO) of dimethylamine (DMA) on titanium dioxide was studied in a continuous flow simple tubular reactor. Volatile PCO products of DMA included ammonia, formamide, carbon dioxide, and water. Ammonia was further oxidized in minor amounts to nitrous oxide and nitrogen dioxide. Effective at 573 K, TCO resulted in the formation of ammonia, hydrogen cyanide, carbon monoxide, carbon dioxide, and water. The PCO kinetic data fit well to the monomolecular Langmuir-Hinshelwood model, whereas TCO kinetic behaviour matched the first-order process. No deactivation of the photocatalyst during the multiple long-run experiments was observed.

The global energy industry works towards an increased use of carbon-neutral biomass. Nutshell represents a regional bio-waste, i.e., a bio-energy resource. Pyrolysis is a common method for processing biomass into valuable energy products. The heat demand, however, limits pyrolysis applications. Yet, such demand may be addressed via exothermic pyrolysis reactions under selected operation conditions. Making the pyrolysis of Siberian pine nutshell autothermic comprised the objective of the study. The study involved analytical methods together with a pyrolysis experiment. The analytical methods included a thermogravimetric analysis combined with differential scanning calorimetry and an integrated gas analyzer. Thermophysical characterization was executed using a thermal diffusivity analyzer with the laser flash method. At 650 °C, pyrolytic heat was released in the amount of 1224.6 kJ/kg, exceeding the heat demand of 1179.5 kJ/kg. Pyrolysis at a lower temperature of 550 °C remained endothermic, although the combusted gas product provided 847.7 kJ/kg of heat, which, together with exothermic release, covered the required heat demand for the pyrolysis process.

Antibiotics are the most frequently detected pharmaceuticals in the environment creating conditions for the development of resistant genes in bacteria. Degradation and mineralization of glycopeptide antibiotic vancomycin (VMN) were examined by UV photolysis, pulsed corona discharge (PCD), and their combinations with extrinsic oxidants, hydrogen peroxide (HP), peroxydisulfate (PDS), and peroxymonosulfate (PMS). Both combinations were effective in VMN degradation and faster at pH 11 than in acidic or neutral media. Combined with the UV photolysis, HP showed a higher oxidation rate than other oxidants, whereas PMS and PDS proved to be more efficient in combinations with PCD. In contrast to low-to-moderate mineralization of VMN in the UV/oxidant combinations, PCD and PCD/oxidant combinations appeared to be more effective, reaching up to 90% of TOC removal in acidic/neutral solutions. Application of extrinsic oxidants resulted in an energy efficiency of VMN 90% oxidation improved from 36 to 61 g kW−1 h−1 in HP-assisted photolysis, and from 195 to 250 g kW−1 h−1 in PCD with additions of HP and PDS, thus showing the promising character of the combined treatment.

The photocatalytic oxidation (PCO) of the steroid estrogens (SEs),β-estradiol, and 17α-ethynylestradiol, competitive with some constituent compounds of the sanitary fraction of domestic sewage, was studied. The copollutants, urea, and saccharose, present in concentrations exceeding those of the SEs by a factor of a hundred to thousands, appeared to exert a weaker influence to the photocatalytic degradation of the SEs than was expected. The removal of the SEs from diluted urine proceeded, selectively, demonstrating the potential of PCO in the treatment of the separate sanitary fraction of domestic sewage.

Photocatalytic oxidation (PCO) of methylamine (MA) on titanium dioxide in aqueous and gaseous phases was studied. A simple batch glass reactor for aqueous PCO and an annular continuous flow reactor for the gas-phase PCO were used. Maximum aqueous PCO efficiency was achieved in alkaline media. Two mechanisms of aqueous PCO—decomposition to formate and ammonia, and oxidation of organic nitrogen directly to nitrite—lead ultimately toCO2, water, ammonia, and nitrate: formate and nitrite were observed as intermediates. A part of the ammonia formed in the reaction was oxidized to nitrite and nitrate. Volatile PCO products of MA included ammonia, nitrogen dioxide(NO2), nitrous oxide(N2O), carbon dioxide, and water. Thermal catalytic oxidation (TCO) resulted in the formation of ammonia, hydrogen cyanide, carbon monoxide, carbon dioxide, and water. The gas-phase PCO kinetics is described by the monomolecular Langmuir-Hinshelwood model. No deactivation ofTiO2catalyst was observed.

The photocatalytic oxidation (PCO) of UV‐irradiated aqueous solutions containing humic acids and lignin was studied. The photocatalyst TiO2 was attached to buoyant hollow glass microspheres and glass plates. A maximum oxidation efficiency as low as 1.1 and 2.54 mg W−1h−1 for humic acids and lignin, respectively, was achieved in neutral and alkaline media with 25 gm−2 of the buoyant catalyst. In acidic media, efficiency was even lower. The photocatalytic efficiency with the photocatalyst attached to glass plates was about 3 to 4 times higher than that for the buoyant catalyst. Ferrous ions added to acidic solutions did not increase the rate of PCO of humic acids. However the addition of Fe2+ ions, up to 0.05 mM, to the lignin solution leads to a dramatic increase, about 25%, in PCO efficiency. A further increase in ferrous ion concentration results in a decrease in the PCO efficiency of lignin. Proceeding most likely by a radical mechanism, the efficiency of PCO of humic acids did not benefit from an excessive presence of hydroxyl radical promoters, such as hydrogen peroxide, although the reaction rate increased. However, PCO of lignin in the acidic medium, where OH.‐radical formation is suppressed, benefited from the introduction of hydrogen peroxide due to promoted radical formation.

An experimental research into aqueous photocatalytic oxidation (PCO) of the deicing compounds, 2-ethoxyethanol (2-EE), diethylene glycol monomethyl ether (DEGMME), and ethylene glycol (EG) was undertaken. The addition of iron ions to the acidic aqueous solutions to be treated displayed complex influence on the oxidation efficiency of the above mentioned substances, resulting in a sharp increase of the PCO efficiency at smaller concentrations of iron ions followed by a drastic decrease with the increasing iron ion concentrations. The phenomena observed can be explained by the electron scavenging effect of the iron ions and the competitive adsorption of iron ions and the oxidized substances on titanium dioxide surface. The carbonic acids determined as the PCO by-products allow outlining some reaction pathways for the substances under consideration.

The complex influence of ferrous ions on the efficiency of aqueous photocatalytic oxidation (PCO) of 2‐ethoxyethanol (2‐EE) was examined. A drastic efficiency increase at lower concentrations of ferrous ions was observed to change to a sharp decrease at higher concentrations. An explanation was proposed for the observed phenomena based on the low sensitivity of the pollutant towards radical‐oxidation reactions and the competitive adsorption of metallic ions and 2‐EE on the TiO2 surface.