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Tube Reactor (tube + reactor)
Selected AbstractsPyrolysis of liquefied petroleum gas assisted by radicals desorbed from mesh catalyst surfaceINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 12 2003Eugene B. H. Quah The purpose of this study is to understand the reactions on the catalyst surface and in the gas phase during the catalytic pyrolysis of light hydrocarbons. To avoid the complexity of internal pore diffusion and heat transfer limitation, nickel mesh without pore structure was used as a catalyst for the catalytic pyrolysis of a commercial liquefied petroleum gas (LPG) sample in a quartz tube reactor and in a wire-mesh reactor over a temperature range of 600,850°C. With a Ni mesh catalyst, no catalyst deactivation associated with coke formation was observed at high gas flow rate. Our experimental results indicate that the desorption of radicals from the catalyst surface is an important process in the catalytic pyrolysis of LPG using the Ni mesh catalyst. The desorption of radicals across the gas,catalyst interface is greatly facilitated by increasing gas flow rate passing through the mesh. The desorbed radicals would initiate and/or enhance the gas-phase radical chain reactions and lead to improved reaction rates for the pyrolysis of LPG although the product selectivities remained unchanged. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 637,646, 2003 [source] Surviving Radicals: Promises of a Microwave Effect on Miniemulsion Polymerization for Technical ProcessesMACROMOLECULAR RAPID COMMUNICATIONS, Issue 4 2007Christian Holtze Abstract Rapid heating in a microwave oven has unexpected effects on free radical miniemulsion polymerization: After a temperature pulse of less than 20 s, ultra-high molecular weight polystyrene was yielded at a conversion larger than 40%. These results may be explained with the model of "surviving radicals" according to which single radicals remain active inside the confined reaction space of latex particles even after the emulsion has left the microwave oven. In the pure environment of a 100 nm droplet, they cannot terminate and will polymerize all the monomer within a droplet. In this contribution, we summarize the concept of "surviving radical polymerization" and present recent results on the effects of radical-active additives and the development of a tube reactor for continuous microwave-assisted processing. These investigations highlight the potential of this method for industrial applications. [source] Oxidative Coupling of Methane in a Negative DC Corona Reactor at Low TemperatureTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2003Faezeh Bagheri-Tar Abstract Oxidative coupling of methane (OCM) in the presence of DC corona is reported in a narrow glass tube reactor at atmospheric pressure and at temperatures below 200°C. The corona is created by applying 2200V between a tip and a plate electrode 1.5 mm apart. The C2 selectivity as well as the methane conversion are functions of methane-to-oxygen ratio, gas residence time, and electric current. At CH4/O2 ratio of 5 and the residence time of about 30 ms, a C2 yield of 23.1% has been achieved. The main products of this process are ethane, ethylene, acetylene as well as CO and CO2 with CO/CO2 ratios as high as 25. It is proposed that methane is activated by electrophilic oxygen species to form methyl radicals and C2 products are produced by a consecutive mechanism, whereas COx is formed during parallel reactions. On décrit le couplage oxydant du méthane (OCM) en présence d'une couronne CC dans un réacteur tubulaire étroit en verre à la pression atmosphérique et à des températures en dessous de 200°C. La couronne est créée en appliquant 2200 V entre une pointe et une électrode plate distantes de 1,5 mm. La sélectivité du C2 ainsi que la conversion du méthane sont des fonctions du rapport méthane-oxygène, du temps de séjour du gaz et du courant électrique. À un rapport de CH4/O2 de 5 et un temps de séjour d'environ 30 ms, un rendement de C2 de 23,1 % est obtenu. Les principaux produits de ce procédé sont l'éthane, l'éthylène, l'acétylène, ainsi que le CO et le CO2 avec des rapports de CO/CO2 aussi élevés que 25. On propose l'idée que le méthane est activé par des espèces d'oxygène électrophiles pour former des radicaux de méthyle et que les produits du C2 sont produits par un mécanisme consécutif, tandis que les COx se forment lors de réactions parallèles. [source] High-temperature sequestration of elemental mercury by noncarbon based sorbentsASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2010Sung Jun Lee Abstract This work is concerned with sequestration of elemental Hg at high temperatures (900,1100 °C) on a sorbent that is mineral based, rather than carbon based. This sorbent consists of an intimate mixture of CaO, CaCO3, and Al2O3,2SiO2, and is manufactured in industrially relevant quantities (metric tons) from residues produced in paper recycling processes. In contrast to activated carbon (AC), this noncarbon based sorbent has special advantages in that, it can actually enhance fly ash utilization for cement manufacture, rather than diminish it, as is the case for AC. Disperse phase experiments have been conducted, using an externally heated quartz tube reactor, with sorbent feeding rates ranging from 1 to 6 g/h. Preliminary results indicate that Hg removal efficiency is sensitive to sorbent feed rates and to furnace temperature. The Hg removal percentage increased with both these variables. Two mechanisms come into play: an in-flight Hg sorption mechanism, and an Hg sorption mechanism related to sorbent deposits on the reactor wall. A maximum total (in-flight plus deposit-related) Hg removal efficiency of 83,90% was obtained at temperatures of 900,1100 °C. There was negligible sorption by either mechanism at temperatures below 600 °C. Results for the in-flight mechanism alone showed a maximum sorption efficiency at ,900 °C, whereas that on the reactor surface increased monotonically with temperature. This suggests that sorbent deactivation can occur in-flight at high temperatures, which is in agreement with other fixed bed results obtained in this laboratory. Deactivation was not apparent for the sorbent-related substance formed on the reactor wall. Raw and spent sorbents were analyzed by X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive spectrophotometer (SEM-EDS) to identify the sorbent mineral transitions that seem to activate the process. The in-flight mechanisms appear to involve (1) activation of the sorbent, caused most probably by an internal solid,solid reaction, followed by (2) Hg sorption, and (3) possible deactivation, if the temperatures are too high for longer period. Reactor surface mechanisms still remain to be elucidated. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Online assessment of biofilm development, sloughing and forced detachment in tube reactor by means of magnetic resonance microscopyBIOTECHNOLOGY & BIOENGINEERING, Issue 1 2010Michael Wagner Abstract Magnetic resonance microscopy (MRM) was successfully applied for non-invasive online monitoring of biofilm development, sloughing, and forced detachment. Biofilm cultivation was performed in a tube reactor directly placed in the MRM scanner. Based on the differences in relaxation time of free and bound protons, the distributed water signal was allocated to the bulk and the biofilm phase. The velocity of the flowing water in the tube reactor was measured in all three directions (x, y, and z) at spatial resolutions of 78,µm. From the velocity data, maps of flow gradients (shear rates) were derived. The experiments showed that a more compact biofilm structure is sloughed off in total with nearly no biomass left on the substratum. Continued biofilm cultivation resulted in filamentous biofilm structures, which did not show any sloughing. Experiments at higher Reynolds numbers were performed in order to force biofilm detachment. Continuous measuring of proton velocity and biomass was used to characterize the different stages of biofilm development. The measurements revealed that biofilms are able to resist extremely high local shear stress being raised up to factor of 20 compared to the mean local shear stress acting on the complete biofilm surface. The maximum local shear stress of single biofilm structures exposed to flow was found to be on average seven times higher compared to the mean local shear stress of the entire biofilm surface. MRM was able to visualize and quantify the development of biofilms and interaction of biofilms with the surrounding fluid at the meso-scale. It is suggested that detachment and sloughing depends on both internal and external structural parameters. Biotechnol. Bioeng. 2010;107: 172,181. © 2010 Wiley Periodicals, Inc. [source] Static Magnetic Fields Enhancement of Saccharomyces cerevisae Ethanolic FermentationBIOTECHNOLOGY PROGRESS, Issue 1 2004Mauricy Alves da Motta Magnetic effects induced in ethanolic fermentation by Saccharomycescerevisiae strain DAUFPE-1012 were studied during a 24 h exposure to 220 mT steady magnetic fields (SMF) at 23 ± 1 °C, produced by NdFeB rod magnets. The magnets were attached diametrically opposed (N to S) to a cylindrical tube reactor. The biomass growth in the reactor culture media (yeast extract + glucose 2%) during 24 h was monitored by measurements of optical density, which was correlated to cell dry weight. Ethanol concentration and glucose level were measured every 2 h. The pH of the culture media was maintained between 4 and 5. As a result, biomass (g/L) increased 2.5-fold and ethanol concentration 3.4-fold in magnetized cultures ( n = 8) as compared with SMF nonexposed cultures ( n = 8). Glucose consumption was higher in magnetized cultures, which correlated to the ethanol yield. [source] | |||||||||||||