摘要:

AbstractBimetallic Mo‐Fe and Mo‐Co sulfide clusters were anchored on Al2O3and used for CO hydrogenation. In addition to methane, significant amounts of dimethyl ether were produced. The reaction orders obtained from power rate laws for methanation indicated that the surfaces of the catalytic ensembles were not completely saturated by CO, in contrast to the observations for most conventional CO hydrogenation catalysts. A kinetic analysis and parameter estimation was performed to identify the rate‐determining step for methanation. A catalytic cycle was postulated that could account not only for the formation of methane and higher hydrocarbons, but also for dimethyl ether as a primary pr

ISSN:0001-1541    

DOI:10.1002/aic.690350112

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe homogeneous vapor phase cracking of newly formed wood pyrolysis tar was studied at low molar concentrations as a function of temperature (773–1,073 K), at residence times of 0.9–2.2 s. Tar conversions ranged from about 5 to 88%. The tars were generated by low heating rate (0.2 K/s) pyrolysis of ∼2 cm deep beds of sweet gum hardwood, and then rapidly conveyed to an adjacent reactor for controlled thermal treatment. Quantitative yields and kinetics were obtained for tar cracking and resulting products formation. The major tar conversion product was carbon monoxide, which accounted for over two‐thirds of the tar lost at high severities. Corresponding ethylene and methane yields were each about 10% of the converted tar. Coke formation was negligible and weight‐average tar molecular weight declined with increasing tar conversion. A first‐order distributed activation energy model more closely correlated tar conversion kinetics over a wider range of reaction conditions than did a single‐r

ISSN:0001-1541    

DOI:10.1002/aic.690350113

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractA study of the flow of viscous liquids contained in an open cavity driven by a moving wall has been undertaken as a first step toward understanding interphase heat and mass transport in polymer processing equipment where rolling pools of liquid are generated. Solutions to the equations of motion for creeping flow in cavities of different aspect ratios were obtained using a finite‐differences technique for circumstances when the wall moves in the same direction as the gravitational field.Experimental studies of the flow patterns in cavities of various aspect ratios were found to be in good agreement with the creeping flow predictions for cavity Reynolds numbersRe<50 and aspect ratiosa<1. The structure of the flow in this geometry was found to be similar to that in closed cavities of the same shape. The position and strength of the principal vortex were observed to be nearly independent of the existence of a free surface, and the gas‐liquid interface was found to significantly stabilize the rotational motion in shallow cavit

ISSN:0001-1541    

DOI:10.1002/aic.690350114

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractTheKnp≫ 1 gas‐kinetic approach of Waldmann (1959, 1961) is extended to predict the thermophoretic properties of nonspherical aerosolparticles, and massive nonspherical gasmolecules. Calculations are presented for sphero‐cylindrical particles (molecules) of arbitrary aspect ratio,L/R, predicting that in a local temperature gradientgrad Tthey will thermophoretically drift: (i) more rapidly when their major axis is aligned with −grad T; (ii) at a velocity different from that of a sphere of radiusRequal to the cylinder radius; (iii) at an angle with respect to −grad Twhen their major axis is not parallel to, nor perpendicular to, −grad T; and (iv)withouta net torque tending to orient the particle with respect to −grad T. Important corollaries are that nonspherical particles in a temperature gradient should also experience new thermophoretically‐induced coagulation mechanisms. We predict that the orientation‐averaged thermal diffusion factor αTshould increase approximately linearly with particle

ISSN:0001-1541    

DOI:10.1002/aic.690350115

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractA computer‐generated slim tube randomly packed with spheres of almost uniform size is used to model single‐phase flow in a packed tube with a small tube diameter to particle diameter ratio,R. To obtan a detailed description of its morphology, the slim packed tube is first tessellated into tetrahedra in the interior, and pentahedra near the walls of the tube. Then, the pore space is represented by a network of interconnected circular and triangular sinusoidal flow channels. The size and length of each channel, as well as their interconnectivity, are exactly known. In addition, porosity and solid surface area per unit volume of the porous medium are determined as a function of distance away from a wall. These data suggest that the presence of the walls has two counteracting effects on fluid flow. A higher porosity promotes flow along the walls but a higher surface area per unit volume hinders it. To confirm this prediction, experimental permeability data are obtained for tubes withRbetween 2.5 and 40. ForR>25, the permeability is the same as that of a large diameter tube,k∞. Between 8 and 25, the permeability can be larger or less thank∞. The way the tube is packed determines whether the higher porosity or surface area dominates in the wall region, and thus higher or lower permeability. BelowR= 8, the confining walls cause a marked increase in overall bed porosity and the permeability is always larger thank∞. Theoretical predictions of the permeability of such very slim tubes are in good agreement with experime

ISSN:0001-1541    

DOI:10.1002/aic.690350116

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

ISSN:0001-1541    

DOI:10.1002/aic.690350117

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

ISSN:0001-1541    

DOI:10.1002/aic.690350118

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

ISSN:0001-1541    

DOI:10.1002/aic.690350119

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

ISSN:0001-1541    

DOI:10.1002/aic.690350101

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY