Isothermal Oxidation of White Phosphorus Dispersed in Water in a Stirred-Tank Reactor

ABSTRACT

A global, first-order kinetic model was found to fit the data for the isothermal wet oxidation of elemental white phosphorus (P₄) in a batch, stirred-tank reactor. The initial concentration of white phosphorus solids was held constant at 1 g/L and an air flow of 2.0 standard liters per minute was used to supply the oxygen for the reaction. A CD6-like turbine and an A2 impeller were evaluated at speeds from 1000-2250 rpm. For the CD6-like turbine, mass transfer effects were assumed to be eliminated above 2000 rpm. Thus, the CD6-like turbine with a speed of 2250 rpm was selected for the isothermal studies. Particle size and temperature were varied. For the isothermal conditions, the first order kinetic constant varied from 0.022 min^-1 at 46 °C to 0.078 min^-1 at 80 °C. The apparent activation energy was 6.78 kcal/mol. Oxygen reacted with the suspended P₄ particles forming oxides of phosphorus, primarily phosphorus pentoxide (P₄0₁₀ or P₂ O₅). Some of the P₂O₅ reacted with the water to form PO₄ ^3- as the primary product of white phosphorus oxidation. The amount of phosphorus pentoxide absorbed in the water increased with temperature. The rate of phosphate formation followed zero order kinetics and was independent of particle size. As the temperature increased, the ratio of PO₄/ PO₃ increased. This observation and the apparently low activation energy suggest that diffusion effects may not have been eliminated completely.     

A comparative evaluation of the performance of full-scale high-rate methane biofilter (HMBF) systems and flow-through laboratory columns

Methane biofilter (MBF) technology, a cost effective method to control atmospheric emission of CH₄, is usually developed as a passively aerated system to control low-volume point-source emissions such as those from landfills with gas collection systems. Actively aerated high-rate methane biofilter (HMBF) systems are designed to overcome the shortcomings of passively aerated systems by ensuring the entire filter bed is utilized for CH₄ oxidation. Flow-through column experiments point to the fact that CH₄ oxidation rates of actively aerated systems could be several times higher than that of passively aerated systems. However, reports of the performance of field HMBF systems are not available in literature. Furthermore, there are no studies that demonstrate the possibility of using laboratory data in the design and operation of field systems. The current study was conducted to fill this research gap and involve a comparative study of the performance of laboratory columns to field performance of a HMBF system using solution gas produced at an oil battery site as the CH₄ source. The actively aerated column studies confirmed past results with high CH₄ oxidation rates; one column received air at two injection points and achieved an oxidation rate of 1417 g/m³/d, which is the highest reported value to date for compost-filled columns. Subsequent studies at a specially designed field HMBF filled with compost showed a higher oxidation rate of 1919 g/m³/d, indicating the possibility of exceeding the high CH₄ oxidation rates observed in the laboratory. The achievement of observed field oxidation rates being higher than those in the laboratory is attributed to the capability of maintaining higher temperatures in field HMBFs. Furthermore, results show that field HMBFs could operate at lower than stoichiometric air to CH₄ ratios, and lower retention times than that of laboratory columns. Results indicated that laboratory columns may not truly represent field behavior, and said results could only be used in the preliminary design of field HMBFs.     

Errors in representing regional acid deposition with spatially sparse monitoring: Case studies of the eastern US using model predictions

The current study uses case studies of model-predicted regional precipitation and wet ion deposition over 5-year periods to estimate errors in corresponding regional values derived from the means of site-specific values within regions of interest located in the eastern US. The mean of model-predicted site-specific values for sites within each region was found generally to overestimate the corresponding model-predicted regional wet ion deposition. On an annual basis across four regions in the eastern US, these overestimates of regional wet ion deposition were typically between 5 and 25% and may be more exaggerated for individual seasons. Corresponding overestimates of regional precipitation were typically <5%, but may be more exaggerated for individual seasons. Period-to-period relative changes determined from the mean of site-based model-predicted wet deposition for the current regional ensembles of sites generally estimated larger beneficial effects of pollutant emissions reductions in comparison to changes based on model-predicted regional wet deposition. On an annual basis site-based relative changes were generally biased low compared to regional relative changes: differences were typically <7%, but they may also be more exaggerated for individual seasons. Spatial heterogeneities of the wet ion deposition fields with respect to the sparse monitoring site locations prevented the monitoring sites considered in the current study from providing regionally representative results. Monitoring site locations considered in the current study over-represent the geographical areas subject to both high emissions and high wet ion deposition and under-represent the geographical areas subject to low emissions and low wet deposition. Since the current case studies consider only those eastern US site locations that have supported concurrent wet and dry deposition monitoring, similar errors may be expected for dry and total deposition using results from the same monitoring site locations. Current case study results illustrate the approximate range of potential errors and suggest caution when inferring regional acid deposition from a network of sparse monitoring sites.     

Calculating Collection Efficiencies for Electrostatic Precipitators

The body of information presented In this paper is directed to those Individuals involved In research on, or the design of, electrostatic precipitators. A model for calculating collection efficiencies— one based solely on physical principles and, as a result, one requiring no prior Information from pilot plant or field testing—has been employed to generate performance curves for twelve Industries presently using electrostatic precipitators. These industries Include the electric power, cement, pulp and paper, steel, chemical, and petroleum industries. The performance curves describe the predicted collection efficiency as a function of preclpltator length, plate-to-plate spacing and average field strength, and are presented In graphical, tabular, and equation form. Wherever literature values for a particular Industry are available, comparisons are made between the collection efficiencies generated by the new model and those based on actual preclpltator performance. The two are generally found to be In reasonable agreement.

The use of the Deufsch-Anderson model for preclpltator design Is also discussed. Results from the new model demonstrate that collection efficiency Is sensitive to particle size distribution, a complication that cannot be easily treated In the Deutsch-Ander-son equation which, In Its unmodified form, requires the use of a single representative particle size. It is concluded that the new model Is potentially a more realistic and viable approach to the prediction of collection efficiencies and as such should prove to be a valuable aid in electrostatic preclpltator design.     

Quantitative Determination of Gaseous Nitrogen Dioxide Concentrations over Long Path Lengths by Selective Absorption of Argon Ion Laser Emission

An argon ion laser emits several laser lines In the visible region of the optical spectrum. The absorption coefficients of N0₂ at these laser emissions were measured in a multiple pass absorption cell. A differential technique, in which the ratio of the transmitted intensities of the argon laser emissions is measured, is described to determine the concentration of N0₂ in a polluted atmosphere over path lengths of several kilometers. Measurement of ratios eliminates interferences from particle scattering and thermal index gradients. Evaluation of the data taken in the 48 meter multipass cell indicates that concentrations of N0₂ less than one part per million could be determined in a 1 km optical path.     

Effects of arsenic on nitrate metabolism in arsenic hyperaccumulating and non-hyperaccumulating ferns

This study investigated the effects of arsenic on the in vitro activities of the enzymes (nitrate reductase and nitrite reductase) involved in nitrate metabolism in the roots, rhizomes, and fronds of four-month old Pteris vittata (arsenic – hyperaccumulator) and Pteris ensiformis (non-arsenic--hyperaccumulator) plants. The arsenic treatments (0, 150, and 300 μM as sodium arsenate) in hydroponics had adverse effects on the root and frond dry weights, and this effect was more evident in P. ensiformis than in P. vittata. Nitrate reductase and nitrite reductase activities of arsenate-treated plants were reduced more in P. ensiformis than in P. vittata. This effect was accompanied by similar decreases in tissue NO₃^? concentrations. Therefore, this decrease is interpreted as being indirect, i.e., the consequence of the reduced NO₃^? uptake and translocation in the plants. The study shows the difference in the tolerance level of the two Pteris species with varying sensitivity to arsenic.     

Hydrothermal carbonization of food waste and associated packaging materials for energy source generation

Hydrothermal carbonization (HTC) is a thermal conversion technique that converts food wastes and associated packaging materials to a valuable, energy-rich resource. Food waste collected from local restaurants was carbonized over time at different temperatures (225, 250 and 275 °C) and solids concentrations to determine how process conditions influence carbonization product properties and composition. Experiments were also conducted to determine the influence of packaging material on food waste carbonization. Results indicate the majority of initial carbon remains integrated within the solid-phase at the solids concentrations and reaction temperatures evaluated. Initial solids concentration influences carbon distribution because of increased compound solubilization, while changes in reaction temperature imparted little change on carbon distribution. The presence of packaging materials significantly influences the energy content of the recovered solids. As the proportion of packaging materials increase, the energy content of recovered solids decreases because of the low energetic retention associated with the packaging materials. HTC results in net positive energy balances at all conditions, except at a 5% (dry wt.) solids concentration. Carbonization of food waste and associated packaging materials also results in net positive balances, but energy needs for solids post-processing are significant. Advantages associated with carbonization are not fully realized when only evaluating process energetics. A more detailed life cycle assessment is needed for a more complete comparison of processes.