Catalytic Dehalogenatin of Perchloroethylene in a Redox Environment

The catalytic dehalogenation of tetrachloroethylene (PCE) occurs via oxidation or reductive hydrodechlorination. Catalytic oxidation uses oxygen to dehalogenate PCE into CO₂ and Cl₂. This process requires higher temperatures >350°C then reductive hydrodechlorination and can produce undesirable toxic products, such as dioxins and furans. Hydrodechlorination uses a reductant to reduce PCE to ethane, and intermediate products such as less chlorinated hydrocarbons. Catalyst deactivation and associated loss of activity are commonly observed. Here, we examined a redox environment for the destruction of PCE on commercially available and laboratory made precious metal loaded catalysts. When a mixture of PCE, oxygen and hydrogen are passed over the catalyst, the PCE is converted to ethane, CO₂, water, and HCl as a function of temperature (ambient to 450°C) and hydrogen to oxygen ratio in the feed (0 to 5). In the laboratory experiments, high conversion of PCE was observed for relatively high H₂/O₂ ratios (84% conversion with H₂/O₂ = 2.15, 63% with H₂/O₂ = 1.18 at 350°C, for commercial catalyst) for retention time of ~ 1 s. The conversion of PCE generally increased with increasing temperature for all H₂/O₂ ratios. In the strictly oxidation environment (H₂/O₂ = 0), PCE conversion was lower than with hydrogen at any given temperature (380°C) CO₂ eluted from the reactor, suggesting that oxidation of reduction products or PCE occurs. Experiments were conducted by using a laboratory made catalyst. A mixture of three types of precious metals (Pt, Pd, and Rh) was impregnated onto a monolithic alumina support. These studies show no apparent performance difference between the two catalysts at high temperatures (>280°C). However, at low temperatures the laboratory catalyst outperforms the commercial catalyst. It was speculated that this difference due to high metal loading of the laboratory catalyst (38.61 mg versus 1.27 mg). A field scale study of the commercial catalyst was undertaken at the Superfund Park-Euclid site in Tucson, Arizona, where the soil is contaminated with PCE and other volatile hydrocarbons. Gases from a soil-vapor extraction unit were fed to the reactor, Even though the soil vapor contained high oxygen (>17%), high PCE conversion with and without hydrogen was observed. Due to the relatively high cost associated with the use of hydrogen, propane, methane, and diesel were investigated as replacement reductants. The results indicate that propane and diesel are promising replacements for hydrogen that deserve further investigation

Comparison of ultrasound and dorsal horizon radiographic view for the detection of dorsal screw penetration

WOS: 000422850300004PubMed ID: 29092760Objective: The aim of this study was to compare the efficiency of dorsal tangential fluoroscopy and ultrasonography in detecting dorsal screw penetration in distal radius volar locking plate applications. Methods: Ten cadaveric forearms were operated. The distal four screws were protruded 0, 1 and 2 mm into each of the second, third and fourth dorsal compartments of distal radius. Dorsal horizon views were taken using fluoroscopy. Each radiographic image was evaluated by two orthopedic surgeons who are blinded to procedure. Sonographic evaluations were performed by an orthopedic surgeon blinded to the procedure. Both dorsal horizon view and ultrasonography assessments were noted by the evaluators whether the tip of the screw penetrated or not the dorsal cortex for each compartment. Results: No significant difference was observed on correct detection of 0 mm, 1 mm and 2 mm screw penetrations at second and third compartments. In the fourth compartment, there was no difference with 0 mm and 2 mm penetrations but correct detection accuracy of 1 mm screw penetration was 87% in ultrasonography group and 71% in dorsal horizon view group. Conclusions: The accuracy of ultrasonography on 1 mm penetration at the fourth compartment is better than dorsal horizon view. However, dorsal horizon view and ultrasonography accuracy is similar for the other compartments and penetration levels. Ultrasonography is a reliable and effective procedure for detection of dorsal screw penetrations. (c) 2017 Turkish Association of Orthopaedics and Traumatology. Publishing services by Elsevier B.V

Catalytic Dechlorination of Gas-Phase Perchloroethylene Under Mixed Redox Conditions

The validity of a new method to destroy gas-phase perchloroethylene (PCE) is demonstrated at bench scale using a fixed-bed reactor that contains a Pt/Rh catalyst. Hydrogen and oxygen were simultaneously fed to the reactor together with PCE. The conversion efficiencies of PCE were sensitive to H2/O2 ratio and reactor temperature. When the temperature was ≥400 °C and H2/O2 was ≥2.15, PCE conversion efficiency was maintained at ≥90%. No catalyst deactivation was observed for over 2 years, using only mild, convenient regeneration procedures. It is likely that PCE reduction steps precede oxidation reactions and that the importance of oxidation lies in its elimination of intermediates that would otherwise lead to catalyst poisoning. In practice, this catalytic dechlorination method holds potential for low-cost, large-scale field operation