Heterogeneous Modeling Approach for Gas‐Limited Reactions in an Inclined Rotating Fixed Bed Reactor

A heterogeneous modeling approach for an inclined rotating fixed bed reactor with concentric internal tube is introduced. The novel reactor is designed to intensify the mass transfer of gas‐limited heterogeneous catalyzed reactions by intermittent catalyst wetting, which is enabled exposing the packed bed to rotation and inclination. A simulation study for the hydrogenation of α‐methylstyrene is presented. In particular, the influence of period length and different wetting‐draining cycles on the space‐time yield of the reactor is analyzed.     

Synthesis Gas and Zinc Production in a Noncatalytic Packed‐Bed Reactor

A noncatalytic packed‐bed reactor has been constructed for management of the reduction of ZnO by methane, which leads to co‐production of synthesis gas and zinc. The reactor consisted of a simple vertical pipe filled with ZnO pellets. These pellets underwent reaction with a pure methane flow. Experimental tests were conducted in the temperature range 860–995 °C at atmospheric pressure in an electrically heated reactor. The results showed complete chemical conversion of methane to synthesis gas in the aforementioned temperature range. In addition, analysis of the product solids indicated that the collected solids in the outlet of the reactor were entirely zinc. The maximum methane flow rates (149–744 mL min^–1) were adjusted to ensure complete chemical conversion of methane. These adjustments were performed for different bed heights at various operating temperatures. Analysis of the product gases revealed high quality synthesis gas production without the influence of methane cracking or other undesired side reactions in the experimental tests. Finally, the governing partial differential equations of the reactor modeling were solved by the finite element method. Consequently, the gaseous profiles along the reactor and the breakthrough curves were predicted and compared with the experimental tests.     

乙烯氧氯化工业反应器的模型化

针对乙烯氧氯化反应过程所用的挡板流化床反应器的结构和操作特点，建立了一个比较完整和实用的能反映中、高气速下，较大开孔率挡板流化床的气固流动的多釜串联模型，并进行了模型的数学推导和求解。该模型能较好地模拟工业反应器内轴向的气体浓度分布和床层温度分布规律。研究结果表明，在本反应体系中，因乙烯和氧的过量，导致反应过程的后期ＨＣｌ转化率为相间传质控制，强化相间传质效果是保证ＨＣｌ高转化率的有效手段。     

Numerical Investigation of Resonance Behaviour of a Tubular Packed‐Bed Reactor with Non‐Uniform Activity

The effects of periodic temperature perturbations at the inlet of a packed‐bed catalytic reactor were investigated for a system of non‐uniform catalyst activity that could arise through catalyst deactivation. A simplified model consisting of zones of active catalyst and inert packing of similar thermal properties was assumed. Simulations showed that large amplification, expressed as gain, can occur. The largest gain is observed at a resonance frequency. Both gain and resonance frequency depend on the number of layers of active catalyst and inert packing, the depth of the inert packing and catalyst layers.     

Two‐Dimensional Model for Oxidative Coupling of Methane in a Packed‐Bed Membrane Reactor

A two‐dimensional (2D) model of a packed‐bed membrane reactor was developed to describe ethylene production by oxidative coupling of methane (OCM). The model covers all relevant energy and mass transport processes in the reactor and allows a more precise prediction of the temperature and conversion patterns. It is demonstrated that the fast OCM reaction leads to oxygen depletion in the vicinity of the membrane, causing strong radial concentration gradients in the bed. Further results indicate that the detailed 2D model can provide more accurate predictions of experimental data than the simplified one.     

Fixed‐Bed Multi‐Tubular Reactors for Oxidative Dehydrogenation in Ethylene Process

An industrial‐scale reactor for ethylene production was modeled using the oxidative dehydrogenation of ethane (ODHE) in a multi‐tubular reactor system, examining a variety of parameters affecting reactor performance. The model showed that a double‐bed multi‐tubular reactor with intermediate air injection scheme was superior to a single‐bed design, due to the increased ethylene selectivity while operating under lower oxygen partial pressures. The optimized reactor length for 100 % oxygen conversion was theoretically determined for both reactor designs. The use of a distributed oxygen feed with a limited number of injection points indicated a significant improvement on the reactor performance in terms of ethane conversion and ethylene selectivity. This concept also overcame the reactor runaway temperature problem and enabled operations over a wider range of conditions to obtain enhanced ethylene production.     

Model of simultaneous denitrification and methanogenesis in an Upflow Packed‐Bed Biofilm Reactor: Nitrogen compounds' inhibition and pseudo two‐dimensional biofilm model

BACKGROUND: The modelling of simultaneous denitrification and methanogenesis (DM) in upflow packed‐bed biofilm reactors (UPBR) and the effect of inhibition by nitrogen compounds on methanogenesis has received little attention. This study evaluated the effect using a model that incorporates a pseudo‐two‐dimensional biofilm model. RESULTS: The model was validated through comparison with experimental data, and achieved deviations below 5% for the liquid and gas phases. The model indicated that biomass stratification exists throughout the reactor and within the biofilm interior. At C/N ratios close to the stoichiometric C/N ratio, the process achieves efficiencies greater than 70% for nitrogen load rate (NLR) < 270 mg NO₃^?‐N dm^?3 h^?1. At high C/N ratios (50 mg total organic carbon (TOC) mg^?1 NO₃^?‐N), the process achieves efficiencies greater than 70% for organic load rate (OLR) < 83 mg TOC dm^?3 h^?1. CONCLUSION: The inclusion of the inhibition of methanogenesis by nitrogen compounds did not improve the predictions. Indeed, mass transfer in the biofilm was the phenomenon that most influenced the process. At C/N ratios close to the stoichiometric C/N ratio, process efficiency depends on the NLR; while at high C/N ratios, process efficiency depends on the OLR. Copyright © 2008 Society of Chemical Industry     

Controlled Air Oxidation of Plastic and Biomass in a Packed‐Bed Reactor

A packed‐bed reactor was established to study the effect of polypropylene (PP) content on the controlled air oxidation performance of a mixture of PP and sawdust (SD) at a fixed feed gas flow rate. Attention was focused on product yields, evolutionary behavior of the gas flow rate, and gas compositions. A higher PP content led to increased gas yield, lower solid yield, and substantially reduced liquid yield. The PP content significantly affected the gas composition and rate of gas production. Mixtures of plastic and biomass can be radically converted to gaseous and liquid products under controlled air oxidation conditions.     

Amplification of Periodic Temperature Disturbances in a Packed‐Bed Reactor: CO Oxidation over a CuO/Al2O3 Catalyst

Amplification of periodic variations of input temperature in a product‐inhibited reaction — CO oxidation over CuO‐γ‐Al₂O₃ — was investigated experimentally in an insulated packed‐bed reactor. At steady state the temperature profile was elongated compared with that of a reactant‐inhibited CO oxidation over Pt/Al₂O₃, studied elsewhere. Under periodic operation, amplitudes of the resulting travelling temperature waves, monitored downstream from the reaction front, were amplified to a greater extent than those in the reactant‐inhibited CO oxidation over Pt/Al₂O₃. The magnitude of the amplification depended on the perturbation frequency and showed resonance behaviour. The magnitude decreased monotonically with increasing perturbation amplitude.     

A Combined Packed‐Bed Friction Factor Equation: Extension to Higher Reynolds Number with Wall Effects

A unique combination of classic packed bed friction factor equations and newly refit correlation constants is proposed which produces a new friction factor correlation which significantly improves predictions in high turbulence regimes, high porosity regimes, and high wall effect regimes.     

Characterization and Modeling of Oxygen Transfer in a Spouted‐Bed Reactor with Auxiliary Aeration

A draft‐tube spouted‐bed (DTSB) reactor was equipped with an auxiliary aeration device to provide air into the annular region and thereby improve the oxygen transfer efficiency. The effects of the total air flow rate and its distribution between spout and annulus, the liquid phase viscosity (water and carboxymethyl cellulose solutions), and the solid holdup (glass and cyclodextrin polymer beads) on the oxygen transfer efficiency were discussed. The oxygen transfer coefficient increased with the air flow rate and the ratio of air flowing through the annulus, whereas it decreased with increasing viscosity and solid holdup. A correlation was proposed to predict the transfer coefficient in DTSB reactors with primary and auxiliary aeration. A good fitting was achieved between the experimental data and those estimated with the model.     

Effect of Temperature on Controlled Air Oxidation of Plastic and Biomass in a Packed‐Bed Reactor

A packed‐bed reactor was established to study the effect of temperature on the controlled air oxidation (CAO) performance of a mixture of polypropylene and sawdust at a fixed feed gas flow rate. The reactor temperature was varied from 400 to 800 °C. Attention was focused on product distribution, compositions of liquid and gas products, and technical parameters. The chemical composition of the liquid products was analyzed by gas chromatography/mass spectrometry. The results indicated an obvious impact of the temperature on the described parameters. The increase in temperature led to the decrease in solid fraction and a convex shape curve for the gas yield as well as to a decrease of alkanes and alkenes, and favored the generation of oxygen‐containing hydrocarbons. According to criteria of CAO conversion, the optimum temperature in the primary chamber was found to be 700 °C.     

Modeling of Ethylene Glycol Production from Glucose in a Semi-Continuous Reactor

A numerical study describes the catalytic conversion of glucose into ethylene glycol (EG) in a semi-batch reactor. This analysis couples a set of power law models (homogeneous reactions) and Langmuir-Hinshelwood-Hougen-Watson (LHHW) equations (hydrogenations). For this purpose, the kinetic parameters of the LHHW expressions are estimated for the reaction conditions. Then, the kinetic model evaluates the influence of the H₂ pressure and the catalyst concentrations on the selectivity. The results indicate that the EG yield is increased by setting the temperature and the H₂ pressure. In this manner, the process reduces the hexitols and methane production and increases the EG yield. The originality of the work is based on the influence of the H₂ pressure and the catalyst concentrations in the model.     

环氧乙烷非均相催化水合动力学及均温反应器热稳定性分析

采用碳纳米管增强复合材料催化剂,在等温积分反应器中获得环氧乙烷非均相催化水合宏观反应动力学实验数据,建立了幂函数型宏观反应动力学方程,采用Levenberg-Marquardt法对动力学模型参数进行估算,并以该动力学模型为基础,分析了均温反应器的热稳定性。结果表明,生成乙二醇主反应的表观活化能为71.7 k J/mol,与两个典型的串联副反应的活化能接近。模型参数统计检验结果表明,该宏观动力学方程参数是适定的,可用于工业反应器的设计。给出的反应器关键参数的计算方法,可为乙二醇合成反应器的模拟计算和设计开发提供必要的依据。     

Estimations of Gas Flow Maldistribution in Packed‐Bed Columns

A review of research articles dealing with estimation of the rate of gas flow maldistribution in packed‐bed columns is presented. The proposed relations for determination of the maldistribution factor are given along with the conditions at which they are obtained. It is shown that the indices of maldistribution are usually based on particular terms, i.e., variation coefficient, dispersion or standard deviation. However, they cannot be regarded as a single indicator of gas maldistribution if the gas flow irregularities are not homogeneously distributed over the cross‐section. There is no unified methodology for measuring the gas flow velocity profile. Schemes for measuring the velocity profiles, as well as equations for calculating the maldistribution factor are recommended.     

Stability Study on Ethylene Oxide Industrial Reaction from the Management of Critical Process Variables

The performance of an ethylene oxide process is measured by the selectivity reaction. A production unit was studied in order to maximize selectivity by developing a strategy to manage key process variables. A statistical analysis of data indicated that four variables account for the influence over selectivity. Regression models were developed in order to represent the process selectivity as a function of these variables. The model proposed was statistically and phenomenologically validated, demonstrating consistency with the current data process. The model was deployed in subsets, representing possible operational conditions. Surface responses were evaluated for each model deployed and provided to identify the optimum operational conditions.     

One‐Dimensional Pseudo‐Homogeneous Packed‐Bed Reactor Modeling: I. Chemical Species Equation and Effective Diffusivity

Packed‐bed reactor experimentation is a key tool used in order to formulate chemical kinetics. The chemical species equation and overall methodology are described for a one‐dimensional pseudo‐homogeneous packed‐bed reactor model useful for experimental calibration of chemical kinetics. Over the history of simulation development for this equation there exist numerous different effective diffusivity correlations. The included historical review and parametric study of these correlations help to determine the correct choice based on numerical simplicity and model outcomes. A subsequent review paper describes the energy equation and effective thermal conductivity correlations while coming to a generalized conclusion regarding modeling efforts.     

Heterogeneous Catalytic Epoxidation: High Limonene Oxide Yields by Surface Silylation of Ti‐MCM‐41

Limonene oxide is an intermediate getting growing attention in industrial chemistry. A series of Ti‐MCM‐41 heterogeneous catalysts with different hydrophilic/hydrophobic character, prepared by post‐synthesis silylation with hexamethyldisilazane (HMDS), were studied in the liquid‐phase epoxidation of limonene with tert‐butylhydroperoxide (TBHP). A maximum yield of 84 % in limonene oxide was obtained over a partially silylated catalyst with a surface coverage of 55 %.     

Modeling of Multi‐Tubular Reactors for Fischer‐Tropsch Synthesis

The results of the simulation of multi‐tubular Fischer‐Tropsch reactors based on a two‐dimensional pseudo‐homogeneous model are presented. The model takes into account the intrinsic kinetics of two commercial iron and cobalt catalysts, intraparticle mass transfer limitations, and the radial heat transfer within the fixed bed and to the cooling medium (boiling water). The effective rate with Co is slightly higher than with Fe. Hence, a temperature level can be used for Co that is 20 °C lower compared to Fe. The conversion and product selectivies are then almost the same and the reactor can be operated safely without a temperature runaway. The results of the simulations are consistent with literature data and show that there is still room for improvement of fixed bed FT reactors, e.g., by an enhanced heat transfer.