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Gas-phase Reactor (gas-phase + reactor)

Distribution by Scientific Domains

Polymers and Materials Science	50%

Selected Abstracts

Encapsulation of nanoparticles by polymerization compounding in a gas/solid fluidized bed reactor

AICHE JOURNAL, Issue 9 2009
Babak Esmaeili
Abstract For the first time, a fluidized bed reactor was used for encapsulating nanoparticles by the polymerization compounding approach using Ziegler,Natta catalysts. The polymerization reaction was carried out using a solvent-free process in a gas-phase reactor. This direct gas,solid reaction greatly simplified collecting the particles of interest after polymerization because none of the extra steps often found in encapsulation processes, such as filtering and drying, were performed in this work. The grafting of the catalyst to the original surface of particles was confirmed by X-ray photoelectron spectroscopy. Micrographs obtained by transmission electron microscopy confirmed the presence of a thin layer of polymer, in the order of a few nanometers, around the particles. The thickness of this coating was affected by the operating conditions of the process. The characterization of the modified particles with electron microscopy also revealed that zirconia nanoparticles tend to be coated in an agglomerated state, whereas aluminum particles were mostly individually encapsulated by the polymer. In addition, the effects of temperature and pressure were studied on the encapsulation process and a kinetic analysis was presented based on the available models in the literature. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

Optimization of Enzymatic Gas-Phase Reactions by Increasing the Long-Term Stability of the Catalyst

BIOTECHNOLOGY PROGRESS, Issue 3 2004
Clara Ferloni
Enzymatic gas-phase reactions are usually performed in continuous reactors, and thus very stable and active catalysts are required to perform such transformations on cost-effective levels. The present work is concerned with the reduction of gaseous acetophenone to enantiomerically pure ( R)-1-phenylethanol catalyzed by solid alcohol dehydrogenase from Lactobacillus brevis (LBADH), immobilized onto glass beads. Initially, the catalyst preparation displayed a half-life of 1 day under reaction conditions at 40 °C and at a water activity of 0.5. It was shown that the observed decrease in activity is due to a degradation of the enzyme itself (LBADH) and not of the co-immobilized cofactor NADP. By the addition of sucrose to the cell extract before immobilization of the enzyme, the half-life of the catalyst preparation (at 40 °C) was increased 40 times. The stabilized catalyst preparation was employed in a continuous gas-phase reactor at different temperatures (25,60 °C). At 50 °C, a space-time yield of 107 g/L/d was achieved within the first 80 h of continuous reaction. [source]

A Simplified Model for Prediction of Molecular Weight Distributions in Ethylene-Hexene Copolymerization Using Ziegler-Natta Catalysts

MACROMOLECULAR REACTION ENGINEERING, Issue 5 2007
Duncan E. Thompson
Abstract A simplified steady-state model has been developed to predict molecular weight distributions and average compositions of ethylene-hexene copolymers produced using heterogeneous Ziegler-Natta catalysts in gas-phase reactors. The model uses a simplified reaction scheme to limit the number of parameters that must be estimated. The number of parameters is further reduced by assuming that different types of active sites share common rate constants for some reactions. Estimates of kinetic parameters are obtained using deconvolution analysis of industrial copolymer samples produced using a variety of isothermal steady-state operating conditions. The parameter estimates should prove useful as initial guesses for future parameter estimation in a non-isothermal model. [source]

Gas-Phase Polymerization with Transition Metal Catalysts Supported on Montmorillonite , A Particle Morphological Study

MACROMOLECULAR SYMPOSIA, Issue 1 2009
Sang-Young A. Shin
Abstract This investigation focuses on the mechanism of particle fragmentation and growth when clay-supported metallocene catalysts are used to polymerize ethylene in gas-phase reactors. We supported bis(cyclopentadienyl)-zirconium dichloride (Cp2ZrCl2) on montmorillonite (MMT) pretreated with triisobutylaluminum and 10-undecence-1-ol to produce in-situ polyethylene-clay nanocomposites. During gas phase polymerization, the MMT layers were exfoliated by the growing polymer chains, starting from the openings of the clay galleries. After microtoming, the cross-section of the fragmented MMT particles showed bundles of distorted silicate layer stacks, proving that exfoliation took place during polymerization, producing an in-situ polyethylene-clay nanocomposite. Calculations of d-spacing by transmission electron microscopy (TEM) matched those measured by X-ray diffraction (XRD) analysis. [source]