CFD study on partial oxidation of methane in fixed-bed reactor

Partial oxidation of methane (POM) is a preferred method for synthesis gas, which usually occurs in fixed bed reactors. In this paper, the discrete element method (DEM) is used to reconstruct the structure of a reactor bed via simulating the process of filling the reactor with catalyst. The particle resolved CFD physical model with the detailed micro-kinetcis of the POM reaction was established to study the interaction among reactant flow, heat and mass transfer, and reaction in the fixed bed. The gas composition and temperature distribution in the reactor were obtained based on the simulation results. The effects of the space velocity and the reaction temperature on the CH₄ conversion, catalyst selectivity, and catalyst surface coke formation were analyzed. The simulation results show that the temperature hot spots of the catalyst in the bed occur at the inlet and the temperature increases further near the wall. With the increase in space velocity, the conversion rate of CH₄ decreases gradually, and the selectivity does not change significantly. As the temperature increases, the conversion rate of CH₄ gradually increases and the selectivity decreases. The risk of coke formation on the catalyst surface rises axially and the C species concentration is relatively higher near the outlet. Appropriately increasing the gas velocity and increasing the temperature helps to reduce the surface coke accumulation of the catalyst.     

Experimental and simulation study of the temperature distribution in a bench-scale fixed bed Fischer–Tropsch reactor

The temperature distribution in a bench-scale fixed bed Fischer–Tropsch reactor using Co-based catalyst was investigated under conditions of 2 MPa and 458 K at various syngas partial pressures and space velocities. The single-tube reactor had a diameter of 0.05 m, which is representative of the diameters used in industrial applications. With a special designed temperature measurement, the detailed temperature distribution in a bench-scale reactor was reported for the first time. The changes of maximum temperature in the bed and hot spot region were discussed at different N₂ flow rate and gas hourly space velocity. A 2D pseudo-homogeneous fixed bed reactor model was developed using ANSYS Fluent. A position-dependent heat-transfer coefficient, which considered more accurate in temperature prediction, was applied. The model was validated against both the reaction results and the measured temperatures. The inferred properties within the reactor were analyzed to give insight as to how to increase the reactor production capacity.     

Heterogeneous numerical modelling for the auto thermal reforming of crude glycerol in a fixed bed reactor

A mathematical model for the catalytic autothermal reforming (ATR) reaction of synthetic crude glycerol to hydrogen in a fixed bed tubular reactor (FBTR) and over an in-house developed metal oxide catalyst is presented in this work. The heterogeneous model equations account for a two-phase system of solid catalyst and bulk feed gas. Also, the ATR of crude glycerol reaction scheme and intrinsic kinetic rate model over an active, selective, and stable nickel-based catalyst were integrated in the developed model. Also, the model was validated using experimental data generated in our labs for the ATR of synthetic crude glycerol. The modelling results adequately described the detailed gas product composition and distribution, temperature profiles, and conversion propagation in the axial direction of the fixed bed reactor over a wide range of reaction temperature (773-923 K) and mass-time (12.71-158.23 g cat·min·(mol C)^-1). The crude glycerol conversion predicted with the model showing a close resemblance to those obtained experimentally with an average absolute deviation (AAD) of less than 8%. The maximum crude glycerol conversion and hydrogen yield were found to be 92% and 3 mol hydrogen/mol crude glycerol, respectively. Also, the gas product concentration profile in the reactor was adequately described (90%) accuracy with a hydrogen concentration of 39% (volume).     

利用Fluent软件对N_2O催化分解反应器数值模拟

为了设计N_2O催化分解反应器,运用Fluent软件对整体式分子筛催化剂进行数值模拟,考察孔密度和操作条件对整体式分子筛催化剂转化率的影响。结果表明,在相同温度下,N_2O的转化率随着催化剂孔密度的减小而降低。在反应器轴向距离120 mm处,气体反应最快;提高入口温度、浓度或降低空速,均有利于在较短的轴向距离内达到较高的N_2O转化率。在固定床反应器中,比较棒状催化剂和整体式催化剂中床层温度、反应转化率及轴向压降的变化规律,为整体式分子筛催化剂工业化设计提供理论基础。     

Analysis and performance of a countercurrent moving-bed chromatographic reactor

A theoretical and experimental investigation of a countercurrent moving-bed chromatographic reactor is the subject of this paper. In this reactor a reversible heterogeneous reaction takes place on catalyst particles passing downward through an upcoming gas stream. The behaviour of an ideal reactor model was examined for different values of feed concentrations and reactor length. It is predicted that reaction and separation can be achieved simultaneously and that under appropriate operating conditions, a reactor fed at the bottom with the species more favoured by thermodynamic equilibrium can lead to 100% product purity with overall conversions lower than a conventional fixed bed reactor. The effect of nonidealities on the reactor performance is also discussed. Finite adsorption and axial dispersion have a generally deteriorating effect on overall conversion and product purity. An improved reactor configuration with a bottom stripping section is suggested. Its operating conditions can be tailored so that predicted performance exceeds that of a fixed bed both in yield and product purity. The hydrogenation of mesitylene with excess hydrogen over a Pt on alumina catalyst was used for an experimental investigation of the reactor. The experiments, performed in a 1/2″ i.d., 7′ long column, resulted in products of higher purity than the equilibrium prediction, and overall conversions comparable to a fixed bed reactor.     

Water Gas Shift Reaction in a Membrane Reactor Using a High Hydrogen Permselective Silica Membrane

A membrane reactor (MR) for the water gas shift (WGS) reaction was developed by integrating a highly hydrogen permselective silica membrane. The membrane was prepared using an extended counter-diffusion chemical vapor deposition (CVD) method. A tetramethylorthosilicate (TMOS) silica source was fed from one side of the membrane support and oxygen gas fed from the other. The dense silica film was deposited on a porous support by pressurizing the side that TMOS is supplied. A high hydrogen permselective silica membrane was obtained by this method. A commercial Pt catalyst was used in the WGS reaction. Efficacy of the silica membrane toward the WGS reaction was investigated as a function of temperature (523-623 K), steam/carbon monoxide (S/C) ratio (1-3), differential pressure (0-100 kPa), and gas hourly space velocity (GHSV; 1800-5400 h^?1). The CO conversion in the MR was higher than that for a fixed bed reactor (FBR) under all experimental conditions, and was also higher than the thermodynamic equilibrium conversion under almost all experimental conditions. This was due to the selective abstraction of hydrogen from the product stream by the silica membrane. At an S/C of 1.0, the CO conversion in the MR was superior to that in a FBR by 16.8%.     

Glycerol‐Reforming Kinetics Using a Pt/C Catalyst

Catalytic steam reforming of glycerol, a by‐product in biodiesel production, represents an attractive route to hydrogen. For the first time, the kinetics of the glycerol steam reforming reaction over a Pt/C catalyst was considered. Kinetic data, i.e., glycerol conversion vs. space time, were obtained experimentally by using a fixed‐bed reactor and were analyzed by the integral method of analysis. It was found that in the studied ranges of temperature from 623 to 673 K and space time from 0.39 to 1.56 g h/mol the investigated reaction is of the first‐order with respect to glycerol. The specific reaction rate constant at 673 K was determined to be 1.1·10⁵ cm³/g_cat h. The values of glycerol conversion predicted by the first‐order kinetic model were in good agreement with those obtained experimentally. The increase in temperature, space time, and initial water/glycerol ratio caused the expected increase in hydrogen yield.     

SrFe0.6Cu0.3Ti0.1O3-δ透氧膜反应器中甲烷部分氧化反应工艺及膜稳定性考察

采用SrFe_0.6Cu_0.3Ti_0.1O_3-δ混合导体透氧膜组装成膜催化反应器,进行甲烷部分氧化制合成气反应,考察了反应温度、空速、催化剂粒径等条件的影响,并分析了反应气氛引起的透氧膜结构变化情况。结果表明,在膜反应器内,催化反应与透氧过程存在相互制约和相互促进的关系。在膜反应器内进行甲烷部分氧化反应后,透氧膜的两侧表面均发生蚀刻现象,结晶度显著降低,反应侧蚀刻现象较为严重,膜表面形成了疏松的多孔层,反应气氛使膜表面晶体结构发生了较大改变,Sr容易从钙钛矿结构中析出并与CO₂结合形成SrCO₃,Sr的析出导致组成不平衡,促进了钙钛矿结构分解及其他物相的产生。     

Simulation of Secondary Reformer in Industrial Ammonia Plant

In order to develop a reactor design model for the secondary reformer in the industrial ammonia plant, the effectiveness factor and convection heat transfer coefficient between gas and catalyst surface have been studied. The temperature and composition of inlet gas to the catalyst bed are predicted using the kinetic equations of 32 radical reactions. The effect of oxygen content in air on the product synthesis gas composition and the ratio of synthesis gas to nitrogen have been studied. The effectiveness factor has been calculated with the assumption that the steam methane reforming reaction is first order in methane partial pressure. The catalyst shape is assumed to be spherical with an equivalent volumetric diameter. The temperature and composition profiles along the axial distance are predicted using a one‐dimensional heterogeneous catalytic reaction model. The temperatures of both gas and catalyst surface decreased with the axial distance from the top of the bed, while the reactions took place. The temperature difference between gas and catalyst surface also decreased along the axial distance. The predicted temperature and composition by the proposed simulation method have been verified with the data from the industrial plant.     

Computational fluid dynamics modeling of hydrogen production in an autothermal reactor: Effect of different thermal conditions

A numerical model was developed and validated to simulate and improve the reforming efficiency of methane to syngas (CO+H₂) in an autothermal reactor. This work was undertaken in a 0.8 cm diameter and 30 cm length quartz tubular reactor. The exhaust gas from combustion at the bottom of reactor was passed over a Ru/γ-Al₂O₃ catalyst bed. The Eddy Dissipation Concept (EDC) model for turbulence-chemistry interaction in combination with a modified standard k-? model for turbulence and a reaction mechanism with 23 species and 39 elementary reactions were considered in the combustion model. The pre-exponential factors and activation energy values for the catalyst (Ru) were obtained by using the experimental results. The percentage of difference between the predicted and measured mole fractions of the major species in the exhaust gas from combustion and catalyst bed zones was less than 5.02% and 7.73%, respectively. In addition, the results showed that the reforming efficiency, based on hydrogen yield, was increased with increase in catalyst bed’s thermal conductivity. Moreover, an enhancement of 4.34% in the reforming efficiency was obtained with increase in the catalyst bed wall heat flux from 0.5 to 2.0 kW/m².     

Machine learning-assisted multiscale modeling of an autothermal fixed-bed reactor for methanol to propylene process

The current commercial multistage reactor for methanol to propylene (MTP) process suffers from poor propylene selectivity and catalyst efficiency, mainly because of the low inlet methanol concentration and long residence time. In this work, we proposed an autothermal co-current flow reactor for MTP process, where the reaction heat is continuously removed through heat exchange with cold reactants, thus single-stage reactor can be used with higher methanol inlet concentration. The reactor feasibility was investigated by a three-dimensional multiscale model, in which the diffusion–reaction interaction inside catalyst particle was described by a neural network model trained by machine learning. With the feeding methanol fraction increasing to 30%, propylene selectivity reaches 82.27% while the space velocity approaches 2.68 g_MeOH g_cat⁻¹ h⁻¹ at 99.97% methanol conversion, about 1.4 and 3.8 times those of a commercial multibed reactor, respectively. With proper catalyst bed dilution, the reaction temperature is well controlled between 700 and 754 K.     

Production of H2 and medium heating value gas via steam gasification of lignins in fixed‐bed reactors

In this work, steam gasification of Alcell and Kraft lignins were carried out in a fixed‐bed reactor in order to produce H₂ and medium heating value gas. The conversion of lignins increased from a low of 64 wt% for Alceil lignin to a high of 88 wt% for Kraft lignin with increasing steam flow rate and temperature. Maximum H₂ production of 60.7 mol% was obtained at 800°C and at a steam flow rate of 15 g/h/g of Kraft lignin, whereas maximum heating value of 18000 kl/m³ of the product gas was obtained at 650°C and at 5 g/h/g of Alcell lignin. Also, the performance of a Ni‐based steam reforming catalyst for the production of H₂ was studied for both types of lignin in a dual fixed‐bed reaction system. A maximum H₂ production of 63 mol% was obtained at a catalyst bed temperature of 750°C and at a catalyst loading of 0.3 g for Alcell lignin. The sulfur present in Kraft lignin had detrimental effect on the catalyst performance.     

焦炉气催化部分氧化的数值模拟

利用F luent中标准κ-ε模型和多孔介质模型对焦炉气催化部分氧化转化炉进行模拟计算。整个反应床层分为氧化反应区和转化区,氧化反应区主要发生燃烧反应;转化区则装填催化剂,发生甲烷重整反应。通过模拟计算给出了转化炉内温度分布、压力分布、组分摩尔分数分布。转化炉出口的温度与气体摩尔分数与Aspen P lus软件模拟结果相吻合。表明CFD模拟结果是准确的,可用于焦炉气催化部分氧化转化炉的工艺和结构设计中。     

Catalytic conversion of palm oil to fuels and chemicals

The conversion of palm oil to hydrocarbons using a shape selective zeolite catalyst is reported in this work. Palm oil was passed over HZSM-5 catalyst in a fixed bed micro-reactor and the reactor was operated at atmospheric pressure, a temperature range of 360 to 420°C and weight hourly space velocity (WHSV) of 2 to 4 h^?1. The main objective was to study the effect of reaction temperature and oil space velocity on the conversion and selectivity of gasoline range hydrocarbons. The results show that 40 to 70wt% of the palm oil can be converted to aromatics and hydrocarbons in the gasoline, diesel and kerosene range, light gases, coke and water. The maximum gasoline range hydrocarbons yield of 40wt% of total product formed was obtained at 400°C and 2 h^?1 space velocity.     

Coupling non-isothermal trickle-bed reactor with catalyst pellet models to understand the reaction and diffusion in gas oil hydrodesulfurization

In this work, a trickle-bed reactor coupled with catalyst pellet model is employed to understand the effects of the temperature and catalyst pellet structures on the reaction–diffusion behaviors in gas oil hydrodesulfurization(HDS). The non-isothermal reactor model is determined to be reasonable due to non-negligible temperature variation caused by the reaction heat. The reaction rate along the reactor is mainly dominated by the temperature,and the sulfur concentration gradient in the catalyst pellet decreases gradually along the reactor, leading to the increased internal effectiveness factor. For the fixed catalyst bed volume, there exists a compromise between the catalyst reaction rate and effectiveness factor. Under commonly studied catalyst pellet size of 0.8–3 mm and porosity of 0.4–0.8, an optimization of the temperature and catalyst pellet structures is carried out, and the optimized outlet sulfur content decreases to 7.6 wppm better than the commercial level at 0.96 mm of the catalyst pellet size and 0.40 of the catalyst porosity.     

列管固定床反应器内CO氧化偶联制草酸二甲酯反应模拟及优化

针对列管式固定床反应器中的单根反应管,采用在接近工业条件下获得的CO氧化偶联制草酸二甲酯动力学方程,建立了一维、二维拟均相模型,并与单管实验结果进行了对比,结果表明一维拟均相反应器模型更能准确描述单管反应器内的CO偶联反应。进一步利用一维拟均相模型模拟计算了操作参数对床层热点温度、反应转化率、产物选择性及床层压降的影响,分析了反应器热点温度对操作参数的敏感性。计算结果表明：冷却介质温度对反应管热点温度、亚硝酸甲酯转化率有较大影响,是需要严格控制的工艺指标;较低的空速容易引起反应器飞温;反应器进口压力、原料气进料温度和反应物组成在计算范围内对反应器热点温度影响相对较小。为了提高偶联反应器的负荷和强化床层内的传热效果,可以将进料空速提高至4000 h^-1,同时,可以通过将反应器进口压力增大至500 kPa来降低压缩机能耗。研究结果可为现有列管式CO氧化偶联反应器的改进和工艺优化提供参考。     

Hydrogen production via catalytic steam reforming of fast pyrolysis bio-oil in a two-stage fixed bed reactor system

Hydrogen production was prepared via catalytic steam reforming of fast pyrolysis bio-oil in a two-stage fixed bed reactor system. Low-cost catalyst dolomite was chosen for the primary steam reforming of bio-oil in consideration of the unavoidable deactivation caused by direct contact of metal catalyst and bio-oil itself. Nickel-based catalyst Ni/MgO was used in the second stage to increase the purity and the yield of desirable gas product further. Influential parameters such as temperature, steam to carbon ratio (S/C, S/CH₄), and material space velocity (W_BHSV, GHSV) both for the first and the second reaction stages on gas product yield, carbon selectivity of gas product, CH₄ conversion as well as purity of desirable gas product were investigated. High temperature (> 850 °C) and high S/C (> 12) are necessary for efficient conversion of bio-oil to desirable gas product in the first steam reforming stage. Low W_BHSV favors the increase of any gas product yield at any selected temperature and the overall conversion of bio-oil to gas product increases accordingly. Nickel-based catalyst Ni/MgO is effective in purification stage and 100% conversion of CH₄ can be obtained under the conditions of S/CH₄ no less than 2 and temperature no less than 800 °C. Low GHSV favors the CH₄ conversion and the maximum CH₄ conversion 100%, desirable gas product purity 100%, and potential hydrogen yield 81.1% can be obtained at 800 °C provided that GHSV is no more than 3600 h^− 1. Carbon deposition behaviors in one-stage reactor prove that the steam reforming of crude bio-oil in a two-stage fixed bed reaction system is necessary and significant.     

Dynamic modelling of a gas phase catalytic fixed-bed reactor—I: Experimental apparatus and determination of reaction kinetics

A large scale fixed bed pilot reactor for performing dynamic experiments is described. The reactor system is especially designed to suppress secondary dispersion effects not characteristic for the packed bed itself.As a model reaction the reaction between oxygen (<1%) and hydrogen on a platinum catalyst supported by alumina has been used.Differential reactor experiments disclosed a hysteresis phenomenon in the catalyst activity. The catalyst is generally more active when going from high to low temperatures than vice versa.A global first order reaction rate expression with Arrhenius temperature dependency fits the fixed-bed reactor profiles well but the static gains badly. However by simultaneous estimation of frequency factor and activation energy in several axial segments a much better approximation to the static gains was obtained. This result indicates that the reaction kinetics is more complicated than first assumed. However for dynamic modelling the exact reaction mechanism is not needed.     

Combined experimental and kinetic modeling studies for the conversion of gasoline range hydrocarbons from methanol over modified HZSM-5 catalyst

The reaction was carried out in fixed bed reactor. The effect of process variables on the activity of oxalic acid treated 0.5 wt% ZnO/7 wt% CuO/HZSM5 catalyst for the conversion of methanol to gasoline range hydrocarbons was studied. The catalyst was prepared by incipient wetness impregnation method. After impregnation the catalyst was treated with oxalic acid. The validity of kinetic model proposed for the methanol to gasoline range hydrocarbon process at zero time on stream was studied, from the experimental results obtained in a wide range of operating conditions. The kinetic parameters for various models were calculated by solving the equation of mass conservation in the reactor for the lumps of the kinetic models. The kinetic model fitted well for simulating the operation in the fixed bed reactor in the range of 635 to 673 K, with regression coefficient (R²) higher than 0.96.