A theoretical explanation of solvent effects in zeolite catalysis

In a previous study of solid acid catalysis (Nature (1998) 389, 832) we showed that the catalytic activity of zeolites could be increased by the coadsorption of “solvent” molecules, such as nitromethane. These coadsorbates do not participate directly in the reaction, but alter the environment within the zeolite such that reactivity is increased. In this work we provide further theoretical explanation of the increased reactivity observed upon coadsorption. We first use density functional theory (DFT) to study the proton affinity of acetone, and complexes of acetone with propane, bromomethane, nitromethane, nitroethane, nitropropane, and acetonitrile. We find that the proton affinity of acetone in the complexes is much higher than for acetone alone. Optimizations and frequency calculations at the B3LYP/6–311++G** level predict proton affinity increases that range from 0.9 kcal/mol for the acetone/propane complex to 12.8 kcal/mol for the acetone/acetonitrile complex. The increase in proton affinity due to the coadsorbed molecules is one of the causes of the increased reactivity observed experimentally. We also used DFT (B3LYP/DZVP2) to optimize the geometry of acetone and the acetone–nitromethane complex in contact with a cluster model of HZSM-5. There is greater proton transfer from the zeolite to acetone when nitromethane is present, as is reflected in the shorter distance between the acidic zeolite proton and the carbonyl carbon of acetone. Predictions of ¹H and ¹³C NMR isotropic chemical shifts also indicate increased proton transfer to acetone in the presence of nitromethane. This further demonstrates how coadsorbates promote reactivity. This revised version was published online in June 2006 with corrections to the Cover Date.     

Free Radical Chemistry. Part 9.1 Approaches to Fluorinated Polyethers—Model Compound Studies

Using peroxide, γ-, and UV-irradiation, free radical addition reactions of hexafluoropropene to diethers and to 18-crown-6 have been investigated and mono-, di-, and poly-adducts have been obtained. Factors influencing these additions, especially polar characteristics of intermediate radicals, have been elucidated. Adducts of 18-crown-6 retain a capacity to complex to alkali-metal ions.     

A parametric study of a horizontal rotating fluidized bed using slotted and sintered metal cylindrical gas distributors

The pressure drop in a horizontal rotating fluidized bed was measured using slotted and sintered metal cylindrical gas distributors as a function of rotating speed, gas velocity and bed thickness. Experiments were conducted using polydisperse alumina particles and nearly monodisperse glass beads. The pressure drop for the slotted distributor exhibited a much larger pressure overshoot at incipient fluidization than the sintered metal distributor. This behavior was also studied using high-resolution photography. Physically consistent explanations are presented for the observed phenomena. The experimental results are compared to theoretical models available in the literature.     

Response to Comment on “Development of a High-Pressure Aerodynamic Lens for Focusing Large Particles (4–10 μm) into the Aerosol Time-of-Flight Mass Spectrometer”

Copyright 2015 American Association for Aerosol Research     

Airborne Dust Capture and Induced Airflow of Various Spray Nozzle Designs

Water spray characteristics, including droplet size and velocity, airborne dust capture potential, and induced airflow quantity for various spray nozzle designs were evaluated to provide basic information for improving spray applications. Water droplet size and velocity characteristics were initially measured by a Phase Doppler Particle Analyzer (PDPA) for hollow cone, full cone, flat fan, and air atomized spray nozzles at similar operating parameters. Airflow inducement and dust capture experiments were also conducted under the same operating parameters to examine any salient features of the spray nozzle type, droplet characteristics, induced airflow, and airborne dust capture.

Test results indicate that there are trade offs between airflow inducement and dust capture efficiency. A spray nozzle with a wider discharge angle was observed to induce more airflow, but at reduced dust capture efficiencies. Increasing spray nozzle fluid pressure(s) generally reduced water droplet sizes with concurrent increases in droplet velocity, airflow inducement, and airborne dust capture. Placing a three-sided barrier around the spray nozzles normally reduced spray air induction and increased dust capture efficiency. A direct relationship between airborne dust capture efficiency and spray input power normalized per unit of airflow induced was observed. This information can be utilized to improve the performance of water sprays for reducing airborne dust levels.     

A Cough Aerosol Simulator for the Study of Disease Transmission by Human Cough-Generated Aerosols

Aerosol particles expelled during human coughs are a potential pathway for infectious disease transmission. However, the importance of airborne transmission is unclear for many diseases. To better understand the role of cough aerosol particles in the spread of disease and the efficacy of different types of protective measures, we constructed a cough aerosol simulator that produces a human-like cough in a controlled environment. The simulated cough has a 4.2 l volume and is based on coughs recorded from influenza patients. In one configuration, the simulator produces a cough aerosol containing particles from 0.1 to 100 μm in diameter with a volume median diameter (VMD) of 8.5 μm and a geometric standard deviation (GSD) of 2.9. In a second configuration, the cough aerosol has a size range of 0.1–30 μm, a VMD of 3.4 μm, and a GSD of 2.3. The total aerosol volume expelled during each cough is 68 μl. By generating a controlled and reproducible artificial cough, the simulator allows us to test different ventilation, disinfection, and personal protection scenarios. The system can be used with live pathogens, including influenza virus, which allows isolation precautions used in the healthcare field to be tested without risk of exposure for workers or patients. The information gained from tests with the simulator will help to better understand the transmission of infectious diseases, develop improved techniques for infection control, and improve safety for healthcare workers and patients.

Copyright 2013 American Association for Aerosol Research