A model for the rate of hydrodesulfurization of thiophene in a continuous catalytic fixed bed reactor

Hydrodesulfurization of thiophene in n-heptane, using a mixture of cobalt and molybdenum oxides as catalyst, has been studied in a fixed bed integral reactor, 200 mm long, 30 mm outer diameter and 20 mm inner diameter. It has been shown that, under experimental conditions employed in this study, neither external nor internal diffusion had been effective in the process and isothermal conditions prevailed in both gas and solid phases. A three step mechanism has been proposed for the hydrodesulfurization of thiophene. According to such a mechanism the diluent (n-heptane) acts as an inhibitor by occupying free active sites. In further steps, thiophene is adsorbed on the catalyst surface and then undergoes reaction with hydrogen gas. Based on this scheme a rate model has been derived and verified by experimental results.     

Methanol steam-reforming in a catalytic fixed bed reactor

Designing an appropriate methanol steam reformer requires detailed knowledge about the processes within such a reactor. Thus, the axial temperature and concentration gradients and catalyst ageing were investigated. It was found that for a fresh catalyst load, the catalyst located in the reactor entrance was most active during the experiment. The activity of this part of the catalyst bed decreased after some time of operation due to ageing. With further operation, the most active zone moved through the catalyst bed. From the results concerning hydrogen production and catalyst degradation, the necessary amount of catalyst for a mobile PEMFC-system can be estimated.     

Temperature profile in a two-stage fixed bed reactor for catalytic partial oxidation of methane to syngas

Detailed axial temperature distribution has been studied in a two-stage process for catalytic partial oxidation of methane to syngas, which consists of two consecutive fixed bed reactors with oxygen or air separately introduced. The first stage of the reactor, packed with a combustion catalyst, is used for catalytic combustion of methane at low initial temperature. While the second stage, filled with a partial oxidation catalyst, is used for the partial oxidation of methane to syngas. A pilot-scale reactor packed with up to 80 g combustion catalyst and 80 g partial oxidation catalyst was employed. The effects of oxygen distribution in the two sections, and gas hourly space velocity (GHSV) on the catalyst bed temperature profile, as well as conversion of methane and selectivities to syngas were investigated under atmospheric pressure. It is found that both oxygen splitting ratio and GHSV have significant influence on the temperature profile in the reactor, which can be explained by the synergetic effects of the fast exothermic oxidation reactions and the slow endothermic (steam and CO₂) reforming reactions. Almost no change in activity and selectivity was observed after a stability experiment for 300 h.     

Cooling exothermic catalytic fixed bed reactors: Co-current versus countercurrent operation in a methanol conversion reactor

A comparison between two possible designs of exothermic catalytic fixed bed reactors, fully co-current and fully countercurrent flow, was performed for the process of methanol transformation into hydrocarbons. The fully co-current operation proved more appropriate, yielding, under low parametric sensitivity, higher productivities and allowing higher inlet methanol partial pressures. The co-current design showed, in a wide range of operating conditions, the Pseudoadiabatic Regime, a useful mode of operation. The countercurrent design did not allow Pseudoadiabatic Operation and had drawbacks such as multiple steady states and reactor ignition.     

Effect of particle shape on methanol partial oxidation in a fixed bed using CFD reactor modeling

Particle shape is one of the most important parameters in the design and optimization of fixed-bed processes. To address the impact of particle shape on methanol partial oxidation to formaldehyde over molybdate catalyst, packings of spheres, cylinders, rings, and trilobes are numerically generated. The generated packings are used to carry out resolved particle Computational Fluid Dynamics (CFD) simulations under industrial conditions. Pressure drop, voidage and velocity profiles, radial heat transfer, and local and overall conversion and selectivity results are presented. Despite their lower particle surface area, lower particle effectiveness and more uneven flow distribution than trilobes, and lower overall heat transfer coefficient than cylinders, rings had the best conversion and selectivity due to their balance between the factors. Three longer tubes of rings, rings and cylinders, and rings and trilobes are simulated and show a small gain in selectivity for the rings and trilobes.     

甲醇制汽油固定流化床试验装置的设计

根据甲醇制汽油反应的工艺要求和影响流化床反应器性能的主要特性参数,设计研制了固定流化床反应器,使其作为前期催化剂实验室研发的一个评价装置,并取得了较佳的效果。     

Air oxidation of aqueous cyanides in a countercurrent fixed bed reactor

This study was conducted to discuss the removal of cyanides from water by air oxidation. Experiments were carried out in a countercurrent fixed bed reactor for three different values of temperature, concentration, gas and liquid flow rates. It was operated at pH 12 by using delrin (formaldehyde polymer) as packing material. Effects of some operating parameters on the conversion were studied, and it was observed that the conversion percent increased by increasing temperature and decreasing gas and liquid flow rates. Effect of concentration was not steady. A conversion of 89% was achieved under optimum conditions while it ranges from 44 to 79% at room temperature.     

A heterogeneous one-dimensional model for non-adiabatic fixed bed catalytic reactors

A heterogeneous one dimensional model which takes separately into account the heat transfer through the solid and fluid phases is introduced. The response of this model is compared with that of the heterogeneous two-dimensional model, and a very good agreement, especially at mild conditions, is obtained. Its performance is better than previous one dimensional models and the deviations are explained in tenns of the operative conditions and of the value of dimensionless groups. Conditions at which the different one and two-dimensional models are recommended to be used are presented.     

数学模型在固定床反应器中的应用

化学反应器是整个化工生产过程的核心装置，其中固定床反应器是应用较为广泛的反应设备，建立能准确描述其特性的数学模型，不但可以给反应器设计和最优化操作提供理论依据，更减少了工作量。实现其优化操作，具有重要意义。主要介绍了固定床反应器中各种吸附过程数学模型的建立及其相应解法。     

Variable-gas-density fluidized bed reactor model for catalytic processes

A generalized fluidized bed reactor model which covers the three fluidization flow regimes most commonly encountered in industry (bubbling, turbulent and fast fluidization) is proposed. The model is based on probabilistic averaging shown previously (Thompson, Bi, & Grace, Chem. Eng. Sci. 54 (1999) 2175; Grace, Abba, Bi, & Thompson, Can. J. Chem. Eng. 77 (1999) 305) to be applicable over a range of superficial gas velocities. In this paper, we extend the model to cases where the volumetric gas flow changes appreciably due to variations in molar flow, pressure and temperature. For the air-based oxy-chlorination process as a case study, it is shown that the volume change affects both the hydrodynamics and the reactor performance. Because the reactions are rapid, almost complete conversion of ethylene is attained immediately above the distributor resulting in an ∼25% reduction in volumetric flowrate. Using the probabilistic averaging technique, the model tracks the probability of being in the bubbling, turbulent and fast fluidization regimes along the reactor height. The impacts of temperature and pressure variations are also examined. The variable density model gives predictions which compare well with commercial data; ignoring density variations leads to significant underprediction.     

A novel continuous reactor for catalytic reduction of NOx—fixed bed simulations

A novel dual‐zone fluidized bed reactor was proposed for the continuous adsorption and reduction of NO_x from combustion flue gases. The adsorption and reaction behaviour of such a reactor has been simulated in a fixed bed reactor using Fe/ZSM‐5 catalyst and propylene reductant with model flue gases. Fe/ZSM‐5 exhibited acceptable activity at T = 350°C and GHSV = 5000 h^?1 when O₂ concentration was controlled at levels lower than 1% with a HC to NO molar ratio of about 2:1. XPS and BET surface area measurement revealed the nature of the deactivation of the catalyst. Those performance data demonstrated the feasibility of a continuous dual‐zone fluidized bed reactor for catalytic reduction of NO_x under lean operating conditions.     

Analysis of a model for a nonisothermal continuous fluidized bed catalytic reactor

A three-phase model, consisting of a dilute or bubble phase, an interstitial gas phase and a solids phase, has been developed for a non-isothermal gas fluidized-bed catalytic reactor with continuous circulation of catalyst particles. The dilute phase is assumed to be in plug flow, the interstitial gas is considered to be either perfectly mixed or in plug flow, and the particles are assumed to be perfectly mixed.It is shown that the conversion in a reactor and steady state temperature and concentration profiles are the same irrespectively of the assumed flow pattern in the interstitial gas.The numerical computations were done for the case of a single irreversible reaction with or without catalyst decay and for the case of two consecutive irreversible reactions. In the case of an adiabatic reactor and ordinary exothermic reactions, or in the case of a cooled reactor with a highly exothermic reaction, multiple steady states may occur.     

Modelling of the reversed flow fixed bed reactor for catalytic decontamination of waste gases

Catalytic decontamination of waste gases in a fixed bed reactor, operating at non-steady state conditions achieved by periodic gas flow reversal, is simulated on the basis of a mathematical model. The opportunity to utilize a significant part of the reaction heat is discussed and the effect of catalyst inactivation upon reactor performance is analyzed. Stable temperature regime and conversion exceeding 99.5% could be ensured by a more than eightfold reduction of catalyst activity.     

Parametric sensitivity of a fixed bed catalytic reactor: Cooling fluid flow influence

Temperature variation in a cocurrent cooling medium and its influence on the operation of a fixed bed catalytic reactor of the type used for orthoxylen oxydation is examined. Two characteristic regimes are found: a first regime where temperature shows a maximum at a finite axial reactor position (MFARP and a second regime where temperature is always increasing with the axial reactor coordinate: pseudoakiabatic operation (PO). The relative importance o ach operating mode may be observed by modifying the cooling flow. Two equations are derived from these findings. One of them estimates the limiting condition between MFARP temperature curves and PO curves. The other equation establishes an a prioi run away criterion for hot spot operation, being an extension of a previous formula derived by Van Welsenaere and Froment.     

Fast and catalytic pyrolysis of pistacia khinjuk seed in a well-swept fixed bed reactor

The pyrolysis of pistacia khinjuk seed was investigated with the aim to study the product distribution and their chemical compositions and to identify optimum process conditions for maximizing the bio-oil yield. Fast and catalytic pyrolysis of biomass sample with two selected commercial catalyst, namely BP 3189 and Criterion-424 have been conducted in a well-swept resistively heated fixed bed reactor under nitrogen atmosphere. The maximum bio-oil yield of 66.5% with the use of Criterion-424 and 69.2% with the use of BP 3189 were obtained at the catalytic pyrolysis conditions, while it was only 57.6% without catalyst. The bio-oils were investigated, using chromatographic and spectroscopic techniques.     

Electro-oxidation of benzene in a fixed bed reactor

A fixed bed electrochemical reactor was used in the laboratory to oxidize benzene to quinone. The reactor consisted of a 3 mm thick bed of 1 mm lead shot, 0.5 m long by 0.05 m wide, sandwiched between a lead feeder plate and an asbestos diaphragm which was compressed against a stainless steel cathode plate. A dispersion of benzene in aqueous sulphuric acid was passed through the reactor and the rates of production of quinone, hydroquinone, carbon dioxide, oxygen and hydrogen, together with the cell voltage and pressure drop, were obtained for a range of operating conditions.Concentrations of quinone in the benzene product varied from 0.04 to 0.31 M and current efficiencies for quinone were in the range 22 to 55%. In a single pass of 1 M acid and benzene through the reactor at 25° C the quinone efficiency fell from 53% to 39% as the average superficial current density increased from 0.4 to 2.0 kA m^–2. At an average superficial current density of 2.0 kA m^–2 the quinone efficiency decreased with an increase in process temperature (25 to 50° C), but increased with increases in acid concentration (1 to 4 M), acid flow (0.5 to 1.0 cm³ s^–1), benzene flow (0.05 to 10 cm³ s^–1) and co-current nitrogen gas flow (0 to 32 cm³ s^–1 at STP). Recycling the 4 M sulphuric acid at 25° C raised the concentration of quinone in the product benzene but decreased the net current efficiency for quinone. Corresponding changes were observed in the cell voltage and in the current efficiencies for hydroquinone, carbon dioxide and oxygen. The results are discussed in terms of the process stoichiometry, electrode kinetics and mass transfer for three-phase flow in a fixed bed reactor.Nomenclature A Acid flow - a ₁ Liquid/liquid specific interfacial area - a _s Liquid/solid specific interfacial area - B Benzene flow - d ₃₂ Sauter mean drop diameter - d _P Particle diameter - E Current efficiency - F Faraday number - I Total current - i _l Superficial transfer-limited current density - K Liquid/liquid distribution coefficient - k _c Liquid/liquid mass transfer coefficient in continuous phase - k _s Liquid/solid mass transfer coefficient - L _c Superficial liquid load — continuous phase - L _d Superficial liquid load — disperse phase - Q _A Quinone concentration in aqueous phase - V ⁰ Standard electrode potential - z Number of electrons per equivalent     

Production of pharmaceuticals: Amines from alcohols in a continuous flow fixed bed catalytic reactor

This paper reports the use of an immobilised ruthenium complex in a continuous flow process for the N-alkylation of morpholine with benzyl alcohol. The ruthenium-based catalyst was supported on a phosphine bound polymer. Screening experiments were first performed in a batch reactor, with a 16 vol% mixture of morpholine and benzyl alcohol (stoichiometric molar ratio of 1:1) in toluene as the solvent. Operating at 110 °C for 24 h, it was shown that high conversions (>99%) into the desired tertiary amine could be achieved. This reaction was then shown to be viable in a continuous flow reactor, where the catalytic polymer beads were retained in the bed. Operating at 150 °C and using p-xylene as a solvent, the conversion into the desired tertiary amine was shown to be as high as 98%. This approach is clearly very promising, as it provides a greener and more atom efficient route for the production of secondary and tertiary amines in the pharmaceutical industry.     

A two-phase compartments model for the selective oxidation of n-butane in a circulating fluidized bed reactor

A phenomenological model for the partial oxidation of n-butane to maleic anhydride (MAN) in a gas–solid riser reactor is proposed. The model captures the main transport–kinetic interactions at both the particle and reactor scale. Two different kinetic models from the literature that either include or neglect the role of solid-state diffusion of oxygen in the catalyst bulk are compared in terms of their impact on overall reactor performance. The use of computational fluid dynamics (CFD) as a means of defining a macroscopic cell-type model for describing the flow patterns in an industrial-scale gas–solids riser is also described. Predictions for the conversion of n-butane and yield of MAN are presented as a function of selected operating variables, and the impact of the variable model parameters on the predictions is briefly assessed. It is shown that the predictions are particularly sensitive to the kinetic model. The relative importance of the interactions between the chemical kinetics and the hydrodynamics is also highlighted.