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In the deactivation of commercial catalysts by coke formation, complete deactivation of the catalyst is seldom observed and frequently a certain lower activity level is maintained. In the present work, several kinetic models that predict partial catalyst deactivation have been analysed. The presence of active sites with different strengths on the catalyst surface and reversible coke formation have...
In the deactivation of commercial catalysts by coke formation, complete deactivation of the catalyst is seldom observed and frequently a certain lower activity level is maintained. In the present work, several kinetic models that predict partial catalyst deactivation have been analysed. The presence of active sites with different strengths on the catalyst surface and reversible coke formation have...
Plasma deposition processes involve complex phenomena which render the design and optimization of industrial equipment difficult to perform. In the particular case of silane plasmas used to produce amorphous silicon, two flow arrangements were studied by numerical modeling of mass transport. The modeling of the first geometry, using inlet slit gas feed, showed a decrease of both silane concentration...
Mo-catalysed hydrogenation processes of four coals, ranked between lignite B and high volatile bituminous coals, are studied. Ammonium heptamolybdate was used as a catalyst precursor. Hydrogenations were carried out at 300, 350 and 400 o C at a hydrogen pressure of 10 MPa, with reaction times ranging from 5 to 30 min. The maximum rate of the process, related to the textural characteristics...
The present study concerns the separation of fine liquid-liquid dispersions having mean droplet diameters between 20 and 100 μm by phase inversion. A theoretical model based on gravity separation is proposed. Two modes of operation of the settling device are studied: without and with bed formation. The results are compared with the theoretical predictions. As can be seen, good operating conditions...
Mo-catalysed hydrogenation processes of four coals, ranked between lignite B and high volatile bituminous coals, are studied. Ammonium heptamolybdate was used as a catalyst precursor. Hydrogenations were carried out at 300, 350 and 400°C at a hydrogen pressure of 10 MPa, with reaction times ranging from 5 to 30 min. The maximum rate of the process, related to the textural characteristics of the coal,...
Fixed bed reactors for exothermic catalytic reaction offer special challenges given the problems of safe operation and hot spot development. These problems can be considered in the context of so-called pseudoadiabatic operation (PO), with the highest temperature occurring at the reactor exit. This study deals with the derivation of analytical equations for finding the limiting PO and POAT (pseudoadiabatic...
Fixed bed reactors for exothermic catalytic reaction offer special challenges given the problems of safe operation and hot spot development. These problems can be considered in the context of so-called pseudoadiabatic operation (PO), with the highest temperature occurring at the reactor exit.This study deals with the derivation of analytical equations for finding the limiting PO and POAT (pseudoadiabatic...
Off-gas from anaerobic digestion and landfills has significant potential as an alternative energy source. Current technologies to purify off-gas and increase its caloric value have been primarily limited to physicochemical methods. An alternative biological method has been proposed that increases the methane content. Through the use of a chemo-autotrophic methanogen (Methanobacterium thermoautotrophicum),...
This paper presents the results of studies on self-aspirating impellers, i.e. those in which air flows through a hollow shaft into the impeller and then enters the liquid being mixed. The initial conditions of the gas sucking, mixing power, mass transfer coefficients and gas flow rate were determined.
The present study concerns the separation of fine liquid-liquid dispersions having mean droplet diameters between 20 and 100 μm by phase inversion. A theoretical model based on gravity separation is proposed. Two modes of operation of the settling device are studied: without and with bed formation. The results are compared with the theoretical predictions. As can be seen, good operating conditions...
Spherical polymeric microbeads were produced by suspension cross-linking of hydroxyl-terminated polydimethylsiloxane prepolymers. Dimethylsiloxane-ethyleneoxide copolymer, dibutyltin dilaurate and methyltriethoxysilane were used as surfactant, catalyst and cross-linker, respectively. The surfaces of the microbeads were further modified by exposure of 3-amino-propyltriethoxysilane plasma in a glow-discharge...
When the impeller Reynolds number is sufficiently high, so that the turbulence in a stirred tank is fully developed, the macroscopic flow characteristics, e.g. velocity distribution, power consumption and bulk blending time, are independent of viscosity. However, the fine-scale characteristics, near the Kolmogorov microscale, are influenced by viscosity and an effect on micromixing must be expected...
Starting from analysis of the behaviour of peak retention time vs. the adsorption constant and vs. the mass transfer coefficient, we propose a simple macroscopic model describing adsorption in molecular sieves at high Peclet numbers and at low temperatures. The model is based on the hypothesis that adsorption kinetics evolve through the superposition of an instantaneous adsorption step and a slower...
Plasma deposition processes involve complex phenomena which render the design and optimization of industrial equipment difficult to perform. In the particular case of silane plasmas used to produce amorphous silicon, two flow arrangements were studied by numerical modeling of mass transport. The modeling of the first geometry, using inlet slit gas feed, showed a decrease of both silane concentration...
When the impeller Reynolds number is sufficiently high, so that the turbulence in a stirred tank is fully developed, the macroscopic flow characteristics, e.g. velocity distribution, power consumption and bulk blending time, are independent of viscosity. However, the fine-scale characteristics, near the Kolmogorov microscale, are influenced by viscosity and an effect on micromixing must be expected...
Starting from analysis of the behaviour of peak retention time vs. the adsorption constant and vs. the mass transfer coefficient, we propose a simple macroscopic model describing adsorption in molecular sieves at high Peclet numbers and at low temperatures. The model is based on the hypothesis that adsorption kinetics evolve through the superposition of an instantaneous adsorption step and a slower...
The effect of micromixing on parallel reactions was studied experimentally and interpreted theoretically using closure models. A solution of soduim hydroxide was contacted with a pre-mixture of hydrochloric acid and ethyl chloroacetate solutions in a tubular reactor equipped with an impingement mix-head. Two different impingement mix-heads were applied: the first was T. shaped with two feeding nozzles;...
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