摘要:

AbstractIn order to illustrate the use of CFD in providing an understanding of mixing processes, three examples, mixing in a pipe, homogenization with a static mixer and flow in a mixing vessel with a Rushton turbine, are discussed and compared with experimental results. Special attention is focussed on the resultant concentration distribution, which is closely linked to turbulent properties. A semi‐empirical model is presented for a quantitative prediction of the initial turbulent conditions. Using special numerical techniques a mixing vessel with wall‐separated baffles, which represents a problem generally regarded as beyond the capabilities of numerical analysis, can be simula

ISSN:0930-7516    

DOI:10.1002/ceat.270170302

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractSeveral kinds of diesel soot filters and filter materials of high melting points with eleven different catalytic coatings were prepared. They were calcined at a maximum temperature of 1000°C. The reaction rate and the kinetic parameters of the combustion of diesel soot were determined in a closed loop laboratory reactor. A packed bed of alumina particulates was the most active filter in soot combustion. Catalytic coatings with oxides of vanadium, copper or cerium accelerated the reaction. In each case the effect of the coating was dependent on specific interactions between the catalyst and the filter material. The manner of filtration and the nature of the soot filter are found to be more important for the overall result than the nature of the catalytic coating

ISSN:0930-7516    

DOI:10.1002/ceat.270170303

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractCombined XPS and SIMS measurements, partly supplemented by XRD investigations, were utilized to detect precious metal/support interactions on catalysts containing various precious metals. The Klemm‐Bronger reaction between Pt and α‐Al2O3on methane/ammonia catalysts was used as a standard reference. Evidence was found for different stages of Pt/Al interactions and changing electronic properties of Pt on the surfaces of these Pt/α‐Al2O3catalysts by means of XPS and SIMS, and in the bulk material by XRD. The SIMS investigations on Pt and Rh on γ‐Al2O3showed that, even at temperatures around 500 °C, Rh/Al interactions can appear to a small extent in the topmost atomic layers, whereas the Pt/γ‐Al2O3specimens did not show any measurable effects. After on‐road operation, enhanced SIMS cluster‐ion signals as well as anomalous XPS signal contributions were measured on the surfaces of used three‐way automotive emission control catalysts. These signals did not appear for the fresh catalysts. By analogy with the related results reported on the methane/ammonia catalysts, the ion signals were used as qualitative surface probes indicating the presence of precious metal/support interactions, especial

ISSN:0930-7516    

DOI:10.1002/ceat.270170304

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractThe catalytic oxidation of fluorene to 9‐fluorenone in a fluidized‐bed reactor was investigated by modeling of the reactor and simulation of its performance. The “Bubble Assemblage Model” of Kato and Wen, the “Bubbling Bed Model” of Kunii and Levenspiel and the “Countercurrent Backmixing Model” of Potter were applied. From a comparison of simulation results obtained by the various fluidized‐bed models and a fixed‐bed model conclusions were drawn about the influence of interphase mass transfer and gas backmixing on the conversion of fluorene and slectivity of 9‐fluorenone formation. Furthermore, the dependence of conversion and selectivity on temperature and hydrodynamic conditions was investigated. In particular, the implications of a change of hydrodynamic conditions for scale‐up were analysed. The highest yield of 9‐fluorenone predicted for a bench‐scale fluidized bed amounted to 88% (XF= 97%,SNON= 91%). This yield was lower than in a fixed‐bed reactor (YNON= 92%,XF= 99%,SNON= 93%). A further drop of the yield was predicted when scaling‐up from a bench‐scale reactor to a commercial size u

ISSN:0930-7516    

DOI:10.1002/ceat.270170305

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractThe conversion of ethanol over H‐ZSM‐5 was studied as a function of ethanol partial pressure, reaction temperature, weight hourly space velocity and Si/Al ratio. The results obtained were in qualitative agreement with most of those in the literature. Combination with all published results to give a significant regression model was not possible due to the large scatter of the data from various scientific groups. In mechanistic investigations, temperature programmed reaction measurements of ethanol, diethyl ether and ethene were performed. The formation of ethene from ethanol via direct elimination or from diethyl ether as intermediate could be confirmed. In the conversion of ethanol/water mixtures, the product distribution did not change significantly up to a water content of 60 wt%. Then, a pronounced increase of ethene formation and a considerable decrease of the yields of aromatics was observed. When several reaction mixtures from syngas conversion to ethanol were converted over H‐ZSM‐5, the coking rate depended on the product distribution in the feed. Product mixtures from processes with higher amounts of compounds having an unfavourable C/H ratio led to rapid deactivation of the

ISSN:0930-7516    

DOI:10.1002/ceat.270170306

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractThe formation of verbenol, verbenone and acids during liquid phase ozone‐initiated oxidation of α‐pinene has been investigated; temperature, ozone partial pressure and ozone initiation time were the variables studied. While increasing temperature promotes the formation of secondary products, the other two variables affect mainly the selectivity. Thus, an ozone partial pressure and ozone initiation time of 1014 Pa and 10 min, respectively, lead to the highest selectivities. Kinetic expressions for the formation of verbenol and verbenone, which are consistent with experimental data, have also been developed from a free radical mecha

ISSN:0930-7516    

DOI:10.1002/ceat.270170307

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractShock tube pyrolysis of propane at temperatures between 1300 K and 2700 K at reflected shock pressures of 500 to 1500 kN/m2has been investigated. The reaction is of 1st order with a rate constantK= 1.79 × 108exp (‐176.2 kJ/RT) s−1. The major reaction products were acetylene, ethylene and methane, while traces of propylene and ethane were only detected at temperatures below 1500 K. At higher temperatures, propane conversion to acetylene increased at the expense of the other products. Optimum conversions to ethylene and methane, in contrast to that to acetylene, were more sensitive to changes in temperature than to variations in reaction time. However, at reaction pressures above 550 kN/m2, extension of reaction time beyond 0.5 ms did not favour the formation of acetylene. A simple kinetic model which confirmed the experimental optimum product selectivity conditions is put for

ISSN:0930-7516    

DOI:10.1002/ceat.270170308

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractThis contribution presents a chemical reactor model of a circulating fluidized bed (CFB) which takes into account adsorption effects and provides a description of the vertical profiles of gas concentration in the riser. The oxidation of NO is used as an example of a heterogeneous catalytic reaction. Mass transfer between the gas phase and solid particles in the CFB was investigated at various temperatures and solids mass flow rates. The measurements show that the mass transfer coefficient decreases with increasing solids mass flux and that the CFB resembles a bubbling fluidized bed as regards gas‐solid contactin

ISSN:0930-7516    

DOI:10.1002/ceat.270170309

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractThe kinetics of the pseudohomogeneous liquid phase synthesis of a high molecular weight ester in a stirred tank reactor using cobalt chloride as catalyst has been studied at various temperatures, catalyst concentrations, and acid/alcohol molar ratios. A kinetic model has been determined that predicts the experimental results quite well.

ISSN:0930-7516    

DOI:10.1002/ceat.270170310

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

ISSN:0930-7516    

DOI:10.1002/ceat.270170301

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY