Showing papers by "Robert Pfeffer published in 2007"

Effect of solvent strength and operating pressure on the formation of submicrometer polymer particles in supercritical microjets

Abstract: A supercritical antisolvent (SAS) process is described which utilizes a mixture of thermodynamically good and poor polymer solvents and micronozzles Experiments were conducted on polyvinylpyrrolidone (PVP) solutions in a mixture of dichloromethane (DCM) (a good solvent) and acetone (a poor solvent) Decreasing the nozzle diameter and the fluid velocity were shown to favor the disintegration of supercritical jets into drops Mass transport of CO2 into, and solvents out of, the falling supercritical drops, rather than mass transport during jet breakup, are found to control the particle formation Varying the acetone content of the solvent, the nozzle diameter and the jet velocity are demonstrated to provide an efficient method to decrease the particle diameter to several tens of nanometers and smooth their surface irregularities The proposed method is expected to be applicable to a wide variety of polymers

Inverse fluidization for purifying fluid streams

Abstract: A method for removing a contaminant from a fluid system comprises contacting the fluid system with an inversely fluidized material, for example a particulate aerogel, thereby removing at least a portion of the contaminant from the fluid system. The method can be used to remove oil or other organic materials from wastewater streams. It can be conducted in a fluidized bed, which includes nanoporous particles and a fluidizing medium, wherein the nanoporous particles have a density lower than that of the fluidizing medium.

Evaluation of Assisted Fluidization of Nanoagglomerates by Monitoring Moisture in the Gas Phase and the Influence of Gas Viscosity

Abstract: We have previously reported that the fluidization of nanoparticle agglomerates can be enhanced by the addition of external force fields such as vibration, acoustic waves, centrifugal force, and magnetic particles. The criteria usually used to evaluate the enhancement in fluidization quality are the fluidized bed expansion, pressure drop, and visual appearance of the fluidized bed to determine the presence of bubbles, large heavy agglomerates and/or channeling and spouting. Here we introduce a different approach based on measuring the rate of absorption/desorption of moisture (humidification/drying) of hydrophilic fluidized nanopowders. The fluidizing gas was humidified in a controlled manner, and the amount of moisture in the gas phase was measured before and after the fluidized bed by humidity sensors. The experiments show that the amount of moisture adsorbed or desorbed by the bed of powder is larger when the fluidized bed was assisted by vibration or moving magnetic particles than when the bed was conventionally fluidized. In addition, the effect of high temperature gas on the fluidization of nanopowders was studied by using neon as a fluidizing gas at room temperature. It is shown that due to the increase in gas viscosity, the minimum bubbling velocity is increased, bubbling is reduced and a smoother fluidization is obtained.