Neural Net Based Hybrid Modeling of the Methanol Synthesis Process

A Hybrid modeling approach, combining an analytical model with a radial basis function neural network is introduced in this paper. The modeling procedure is combined with genetic algorithm based feature selection designed to select informative variables from the set of available measurements. By only using informative inputs, the model's generalization ability can be enhanced. The approach proposed is applied to modeling of the liquid–phase methanol synthesis. It is shown that a hybrid modeling approach exploiting available a priori knowledge and experimental data can considerably outperform a purely analytical approach.     

Flow through packed bed reactors: 2. Two-phase concurrent downflow

A model for the prediction of pressure drop and liquid holdup for trickling flow in packed bed reactors has been developed, based on the relative permeability concept. The relative permeabilities for gas and liquid as functions of corresponding phase saturations have been studied with 1300 newly measured data pairs of pressure drop and liquid holdup obtained for a wide range of commercially relevant operating conditions (including pressures up to 50 bar) as well as types of packing (both in terms of size and shape). The relative permeabilities are found to be solely the functions of corresponding phase saturations and it is shown that the functional form of the correlations developed, which are otherwise purely empirical by nature, has its roots in the physics of flow at the microscale level. The proposed model requires no prior experimental knowledge about the packed bed and is able to predict liquid holdup and pressure drop to within 5% and 20%, respectively, regardless of the type of packing or operating range investigated.     

液相合成甲醇催化剂活性的研究

The effects of reduction procedure, reaction temperature and composition of feed gas on the activity of a CuO-ZnO-Al2O3 catalyst for liquid phase methanol synthesis were studied. An optimized procedure different from conventional ones was developed to obtain higher activity and better stability of the catalyst. Both CO and CO2 in the feed gas were found to be necessary to maintain the activity of catalyst in the synthesis process. Reaction temperature was limited up to 523K, otherwise the catalyst will be deactivated rapidly. Experimental results show that the catalyst deactivation is caused by sintering and fouling, and the effects of CO and CO2 on the catalyst activity are also investigated. The experimental results indicate that the formation of water in the methanol synthesis is negligible when the feed gas contains both CO and CO2. The mechanism for liquid-phase methanol synthesis was discussed and it differed slightly from that for gas-phase synthesis.     

THE STRING OF CATALYST SPHERES AS A TOOL FOR HEAT AND MASS TRANSFER STUDY IN A THREE-PHASE SYSTEM

A single vertical string of catalyst spheres with liquid film flowing over their surfaces was employed to model a three phase system. Simultaneous heat and mass transfer characteristics within a porous catalyst pellet and across the laminar liquid film was analyzed in terms of different values of reaction and transport parameters. It is shown that the liquid film thickness after the first three pellets reduces less than 10% even though a highly exothermic reaction is taking place within the pellets. It was also found that the mixing in pendular rings plays an important role in heat transfer from the pellets surface.     

Effect of structural and acidity/basicity changes of CuO–CeO2 catalysts on their activity for water–gas shift reaction

The objective of this work was to investigate the influence of CuO loading and catalyst pretreatment procedure to derive an optimal CuO–CeO₂ catalyst for the water–gas shift reaction (WGS), and to study in detail structure– and surface acidity–activity relationships. Catalyst samples prepared by coprecipitation and a 10, 15 and 20 mol% CuO content were examined by XRD, BET and TPR/TPD analyses and subjected to pulse WGS activity tests in the temperature range of 180–400 °C. Strong structure–activity dependence in the WGS reaction was observed for all catalyst samples. It was established that increasing CuO content has a positive effect on H₂ production during the WGS reaction, due to favored CeO₂ reduction. Increasing calcination temperature on the other hand reduces the BET surface area, induced by CuO sintering and agglomeration of CeO₂ particles, resulting in a negative effect on H₂ production. Distinctive WGS activity dependence on surface acidity was observed and investigated.     

Trickle-Bed Oxidation Reactors

For reactions necesitating a solid catalyst and which invoive both reisuvely volatile and nonvclarile reactants, three-phase reactirs are required. Equipment used to achieve intimate contacting of the three phases has been procominantly in the form of slurry reactors, analogous to the stirred-tank homogenous system, or fixed-bed reactors in which the two fluid phases flow through a stationary bed of catalyst particles. Trickle-bed reactors are a type ofthe second classification in which both gas and liquid flow downward through the catalyst bed. Such systems avoid the disadvantage of separating small catalyst particles from the fluid product streams associated with slurry reactors, and also avoid the limitation of flow rates uncountered with upflow or countercurrent flow through fixed beds.     

Hydrogenation of CO2 and CO in a high temperature gradient field between catalyst surface and opposite inert cool plate

Methanol synthesis was carried out at 25 bar in slit formed by two parallel plates 5 mm apart. Upper plate was covered by catalyst layer and heated up to 250°C, whereas lower one was kept at about 30°C. Reaction stream in laminar flow consisted of H_2, CO₂, and CO in concentration range usually encountered in industrial processes. Catalyst layer was prepared by spraying CuO/ZnO/Al₂O₃/V₂O₃ slurry on SS‐plate. Continuous removal of methanol and water by condensation on the cool surface shifted equilibrium toward products formation. At isothermal conditions with no temperature gradient in slit, total carbon conversion approached the thermodynamic equilibrium when residence time was long enough. Experiments with high temperature difference showed total carbon conversion much larger compared to the thermodynamic one calculated at plate‐catalyst temperature. Three‐dimensional model predicted total carbon conversion for both isothermal and high temperature gradient operation reasonably well. © 2013 American Institute of Chemical Engineers AIChE J 60: 613–622, 2014     

Catalytic syngas production from greenhouse gasses: Performance comparison of Ru-Al2O3 and Rh-CeO2 catalysts

In this work, 3% Ru-Al₂O₃ and 2% Rh-CeO₂ catalysts were synthesized and tested for CH₄-CO₂ reforming activity using either CO₂-rich or CO₂-lean model biogas feed. Low carbon deposition was observed on both catalysts, which negligibly influenced catalytic activity. Catalyst deactivation during temperature programmed reaction was observed only with Ru-Al₂O₃, which was caused by metallic cluster sintering. Both catalysts exhibited good stability during the 70 h exposure to undiluted equimolar CH₄/CO₂ gas stream at 750 °C. By varying residence time in the reactor during CH₄-CO₂ reforming, very similar quantities of H₂ were consumed for water formation. Reverse water-gas shift (RWGS) reaction occurred to a very similar extent either with low or high WHSV values over both catalysts, revealing that product gas mixture contained near RWGS equilibrium composition, confirming the dominance of WGS reaction and showing that shortening the contact time would actually decrease the H₂/CO ratio in the syngas produced by CH₄-CO₂ reforming, as long as RWGS is quasi equilibrated. H₂/CO molar ratio in the produced syngas can be increased either by operating at higher temperatures, or by using a feed stream with CH₄/CO₂ ratio well above 1.     

Trickle-Bed Oxidation Reactors

Abstract

For reactions necesitating a solid catalyst and which invoive both reisuvely volatile and nonvclarile reactants, three-phase reactirs are required. Equipment used to achieve intimate contacting of the three phases has been procominantly in the form of slurry reactors, analogous to the stirred-tank homogenous system, or fixed-bed reactors in which the two fluid phases flow through a stationary bed of catalyst particles. Trickle-bed reactors are a type ofthe second classification in which both gas and liquid flow downward through the catalyst bed. Such systems avoid the disadvantage of separating small catalyst particles from the fluid product streams associated with slurry reactors, and also avoid the limitation of flow rates uncountered with upflow or countercurrent flow through fixed beds.