Application of kinetics and computational fluid dynamics in pinene isomerization

A reliable kinetic model to describe the effects of various factors on the reaction rate and selectivity of pinene isomerization is developed. Furthermore, computational fluid dynamics (CFD) is applied to simulate the solid- liquid dispersion in reactor. The catalyst TiM is obtained by improving the composition and structure of hydrated titanium dioxide. The kinetic equation of pinene isomerization is deduced based on reaction mechanism and catalyst deactivation model. The kinetic equation of pinene isomerization reaction is fitted, and the results show that the fitted equation is correlated with the experimental data. The rate and selectivity of pinene isomerization reaction are affected by the amount of catalyst, deactivation of catalyst, structure of catalyst, reaction temperature and water content of catalyst. The solid-liquid distribution of the reactor is calculated by computational fluid dynamics numerical simulation, and the solid-liquid dispersion in commercial scale reactor is more uniform than that in lab-scale reactor.     

Hydrotreated-LCO oxidation in a transport reactor-hydrocyclon system for a low-emission fuel oil production. II Catalyst deactivation and simulation model

The CuCr/IP (4-PVP) catalyst deactivation was studied using continuous stirred-tank reactor (CSTR) laboratory equipment at different temperatures during the oxidation of a tetralin- and fluorene-doped diesel. The concentration of naphtho-aromatics molecules was followed as a function of time on stream, and the catalyst properties analyzed at the beginning and end of run. A computational program was developed to simulate the operation of a continuous recirculation slurry-hydrocyclon-type reactor. The program uses a Runge Kutta Felberg numerical method to solve the mass and energy balance equations for gas, liquid, and solid. For this calculation, it uses a plug flow recycle reactor model for the riser and a plug flow for the downcomer, in agreement with previous fluid dynamic study. The deactivation results indicate a low catalyst deactivation that can be modeled by using an exponential function of the time on stream. The simulation results show that the most important operating variables affecting activity and selectivity are the gas/liquid ratio, the solid hold-up, and the initial temperature. The study confirms the effect of both fluid dynamics and kinetics model parameters in the diesel quality improvement     

Study on the pinene isomerization catalyzed by TiM

The isomerization reaction of pinene is one of the most important chemical reactions in the deep processing of pinene. The purpose of this study is to improve the performance of the metatitanic acid by composite. The composite metatitanic acid catalyst TiM was prepared by adding Mn elements in the preparation process. The catalytic performance of TiM was evaluated. Comparison of TiM and metatitanic acid catalyst (Ti-FGP), the reaction rate of TiM catalyst was faster, and after the reaction, the yield of camphene and tricyclene increased about 1%. The catalysts were characterized by an SEM, FT-IR and laser particle size analyzer. The results show that the pinene isomerization reaction requires the synergistic action of the Brönsted acid and Lewis acid. Brönsted acid has great influence on the activity of catalyst, and Lewis acid has a great influence on the selectivity of the catalyst. The structure and morphology of the catalyst have a certain effect on the selectivity of pinene isomerization reaction.     

Simulation of liquid and vapour phase xylene isomerization over deactivating H-Y-Zeolite

A steady-state simulation model for xylene isomerization over H-Y-Zeolite was developed. Liquid and vapour phase reactions were considered. The fixed bed catalytic reactor was simulated as a plug flow reactor that operates either isothermally or adiabatically. Four temperature levels were investigated taking into consideration catalyst deactivation. The main reactions considered in the model were the isomerization reactions and the disproportionation of xylenes to toluene and trimethylbenzene. The model predicts the concentration and temperature profiles for a given input of operating conditions. The simulation results revealed the similarity in the reactor behaviour if it operates either isothermally or adiabatically with respect to the distribution of the reaction products and catalyst deactivation. The study also indicated that performing the reaction in the liquid phase is more favourable than in the vapour phase due to better selectivity, relative productivity, efficiency and approach to equilibrium. © 1998 Society of Chemical Industry     

CFD analysis of hydrodynamic, heat transfer and reaction of three phase riser reactor

Catalytic cracking reaction and vaporization of gas oil droplets have significant effects on the gas solid mixture hydrodynamic and heat transfer phenomena in a fluid catalytic cracking (FCC) riser reactor. A three-dimensional computational fluid dynamic (CFD) model of the reactor has been developed considering three phase hydrodynamics, cracking reactions, heat and mass transfer as well as evaporation of the feed droplets into a gas solid flow. A hybrid Eulerian-Lagrangian method was applied to numerically simulate the vaporization of gas oil droplets and catalytic reactions in the gas-solid fluidized bed. The distributions of volume fraction of each phase, gas and catalyst velocities, gas and particle temperatures as well as gas oil vapor species were computed assuming six lump kinetic reactions in the gas phase. The developed model is capable of predicting coke formation and its effect on catalyst activity reduction. In this research, the catalyst deactivation coefficient was modeled as a function of catalyst particle residence time, in order to investigate the effects of catalyst deactivation on gas oil and gasoline concentrations along the reactor length. The simulation results showed that droplet vaporization and catalytic cracking reactions drastically impact riser hydrodynamics and heat transfer.     

A UNIFIED COLLOCATION ALGORITHM FOR PACKED-BED CHEMICAL REACTOR SIMULATION

Mathematical models of packed-bed catalytic reactors are aimed to predict the conversions and temperature profiles in both fluid and solid phases within the reactor. Although very general models can be mathematically formulated, usually several simplifying hypothesis are introduced for the fluid phase and/or the solid phase, in order to overcome computational difficulties

We describe in this paper a computational algorithm based on Orthogonal Collocation Method on finite elements, with elimination of the knot unknown functions, coupled with an integration method for stiff ordinary differential equations. This has been used in the development of a computer code, which allows us to find the transient behavior of the reactor by solving the equation relative to the external field, coupled with those describing the transient behavior in the catalyst particles, for a wide class of reactor models. The most general examined model includes axial dispersion in the external fluid phase, interphase mass and heat transfer resistances, intraphase mass resistance and any given kinetic scheme with complex reaction rate expressions.     

Catalyst activity decay functions in liquid and vapour phase xylenes isomerization over H-Y zeolite

A kinetic comparison of the deactivation of a zeolite catalyst in vapour and liquid phase isomerization of xylenes has been made. Quantitative data confirm the more rapid deactivation in the vapour phase. The liquid phase deactivation was best expressed by an exponential function, while the vapour phase was best expressed by a power law. Both systems correlated best using time on stream as the variable. Changes in isomerization selectivity were shown to result from differing variation of deactivation parameters with temperature. The faster deactivation of mordenite compared with Y zeolite was confirmed, and is consistent with the structural characteristics of the two zeolites.     

Modeling and simulation of a small-scale trickle bed reactor for sugar hydrogenation

Laboratory-scale trickle bed reactor was modeled and simulated, taking into account axial dispersion, gas–liquid, liquid–solid and internal mass transfer as well as catalyst deactivation under isothermal conditions. For catalyst particles dynamic and steady state models were developed, including both mass and heat balances. Catalyst deactivation was included in the model by using the final activity concept for the catalyst particles. A well-working numerical algorithm (method of lines) was applied for solving the reactor model with Matlab 7.1 and the results followed experimental trends very well. The steady-state reactor model was based on simultaneous solution of mass balances. The aim was to illustrate how these parabolic partial differential equations could be solved with a step-by-step calculation for a selected geometry. The final model verification was done against experimental data from the hydrogenation of arabinose to arabitol on a ruthenium catalyst.     

Experimental investigation and CFD simulation of liquid–solid–solid dispersion in a stirred reactor

For understanding the monosodium aluminate hydrate crystallization from the supersaturated aluminate solution containing red mud as the leaching liquor of bauxite, the liquid–solid–solid dispersion of a simulant system, i.e. glycerite, red mud and sand, in a stirred reactor has been experimentally investigated as well as simulated using computational fluid dynamics model (CFD) for the first time. The computational model is based on the Eulerian multi-fluid model along with RNG k–ε turbulence model, where Syamlal–obrien-symmetric drag force model (Syamlal, 1987) of the inter-phase momentum transfer between two dispersed solid phases is taken into account. A good agreement is obtained between the experimental data of solid distributions and the simulation results in the flow fields of liquid–solid–solid as well as liquid–solid systems. The solid suspension qualities of both liquid–solid and liquid–solid–solid systems in the stirred reactors with and without draft tube were also studied in detail based on mixing time, the standard deviation of solid concentration proposed by Bohnet and Niesmak (1980), the flow pattern and power number. The influence of the interaction between two dispersed solid phases on the suspension of red mud is found significantly greater than that of sand. The holdup of sand below the impeller is considerably larger than that above the impeller and the red mud dispersion approaches homogeneous in the reactor. The mixing time of liquid–solid–solid suspension is longer than that of liquid–solid suspension under the same conditions, and the mixing times of both systems in the stirred reactor with draft tube are longer than that in the reactor without draft tube. Furthermore, the distributions of sand and red mud in the reactor with draft tube were found less homogeneous than those without draft tube in most cases.     

Modelling and simulation of trickle‐bed reactors using computational fluid dynamics: A state‐of‐the‐art review

Trickle‐bed reactors (TBRs), which accommodate the flow of gas and liquid phases through packed beds of catalysts, host a variety of gas–liquid–solid catalytic reactions, particularly in the petroleum/petrochemical industry. The multiphase flow hydrodynamics in TBRs are complex and directly affect the overall reactor performance in terms of reactant conversion and product yield and selectivity. Non‐ideal flow behaviours, such as flow maldistribution, channelling or partial catalyst wetting may significantly reduce the effectiveness of the reactor. However, conventional TBR modelling approaches cannot properly account for these non‐ideal behaviours owing to the complex coupling between fluid dynamics and chemical kinetics. Recent advances in the application of computational fluid dynamics (CFD) to three‐phase TBR systems have shown promise of achieving a deeper understanding of the interactions between multiphase fluid dynamics and chemical reactions. This study is intended to give a state‐of‐the‐art overview of the progress achieved in the field of CFD simulation of TBRs over the past two decades. The fundamental modelling framework of multiphase flow in TBRs, advances in important constitutive models, and the application of CFD models are discussed in detail. Directions for future research are suggested.     

n-Pentane isomerization in different phase regions near the critical temperature

The isomerization reaction of n-pentane over porous solid acid catalyst was investigated at 198.0 °C, which is slightly higher than the critical temperature of n-pentane. The pressure of the reactant in the reactor was controlled so that the reaction fluid was in gas, near critical, and supercritical (SC) states. The results showed that the conversion of n-pentane increased sharply with increasing pressure near the critical point. The amount of coke deposition depends strongly on the pressure of the reaction fluid. The main reason for the deactivation of the catalyst was coke deposition on the catalyst. Deactivation of catalyst was repressed at the higher pressure because more coke precursors produced in the reaction was dissolved into the fluid, which increases the stability of the catalyst. UV–vis, IR, thermogravimetric analysis and ¹H NMR studies indicated that there were at least two kinds of coke precursors on catalyst surface. The effect of pressure on the properties of the coke was not considerable, although it influences the quantity of the coke deposition on the catalyst significantly. The loss of sulfur can be neglected at reaction temperature and the state of sulfur remains unchanged after reaction. It is advantageous to conduct the isomerization reaction at SC condition.     

固体超强酸催化异构桃金娘烯醛合成紫苏醛

以桃金娘烯醛为原料,以低温浸渍法制备的SZT-15固体超强酸为新型催化剂,在裂解反应装置中进行催化异构桃金娘烯醛合成紫苏醛反应。考察了异构反应条件对反应转化率和选择性的影响规律,并对催化剂的酸度和晶体结构表征。结果表明：在浸渍浓度1.0 mol/L,焙烧温度550 ℃,进样速度1.0 mL/min,反应温度400 ℃条件下,转化率达87.51%,选择性可达40.56%。催化剂的酸度H0可达?16.0,出现了较强的锐钛矿晶相衍射峰。     

Kinetics of liquid phase xylene isomerization over H-mordenite

A study of the kinetics for the liquid phase isomerization of ortho-xylene over H-mordenite has been made at 505°K, 2.76 × 10⁵ N/m², and 23 mole % toluene diluent. This is the first known study reporting kinetic data for the liquid phase isomerization of xylene over a zeolite catalyst. High activity is indicated by the 80% achievement of para-xylene equilibrium at 505°K, 2.76 × 10⁵ N/m², and 0.767 × 10⁻³ kg/s/kg. Although high selectivity has previously been reported for a specifically prepared zeolite catalyst, the 99+% selectivity of the isomerization reaction with H-mordenite as indicated by no C₉+ aromatics and less than 0.5 mole % benzene in the product is most significant. Catalyst deactivation was also significant. Reaction rate constants are reported for a first-order reversible triangular model among the xylene isomers with catalyst deactivation incorporated into the model.     

基于超临界流体密度的烷基化内扩散影响动力学

利用烷基化反应实验数据和超临界流体密度计算数据,开展了考虑内扩散影响的烷基化反应动力学研究,采用优化计算方法进行模型参数估值,确定了烷基化反应速率常数、有效扩散系数、催化剂失活速率常数.研究结果表明,基于PengRobinsn(PR)方程计算流体密度的动力学模型在显著性水平α=0.01下有较高的实验数据拟合精度和模型可信度,说明该方法是计算超临界流体密度的较好方法.从有效因子大小可以看出,烷基化反应总体上处于中孔扩散阻力区.     

Anchored Wilkinson Catalyst: Hydrogenation of β Pinene

The hydrogenation of β pinene over homogeneous and anchored Wilkinson’s catalysts was studied. Phosphotungstic acid was used to anchor the Wilkinson catalyst to an alumina support by an interaction between the heteropoly acid and the rhodium atom of the complex. The hydrogenation of β pinene over the anchored catalyst was accompanied by some isomerization to α-pinene which was subsequently hydrogenated along with the β pinene to the pinanes with selectivities to the cis (endo) pinane in the 85–88 % range at near 100 % conversion. With the homogeneous Wilkinson catalyst an 88 % selectivity to cis pinane was also observed but only at 82 % conversion. The use of a 1 % Rh/Al₂O₃ catalyst for this hydrogenation gave some unexpected results. There was a facile isomerization to α pinene which was not hydrogenated further. The reaction stopped at about 30 % conversion at which time the cis and trans pinanes were present in near equal amounts in about 16–18 % yields.     

Anchored Wilkinson Catalyst: Hydrogenation of β Pinene

The hydrogenation of β pinene over homogeneous and anchored Wilkinson’s catalysts was studied. Phosphotungstic acid was used to anchor the Wilkinson catalyst to an alumina support by an interaction between the heteropoly acid and the rhodium atom of the complex. The hydrogenation of β pinene over the anchored catalyst was accompanied by some isomerization to α-pinene which was subsequently hydrogenated along with the β pinene to the pinanes with selectivities to the cis (endo) pinane in the 85–88 % range at near 100 % conversion. With the homogeneous Wilkinson catalyst an 88 % selectivity to cis pinane was also observed but only at 82 % conversion. The use of a 1 % Rh/Al₂O₃ catalyst for this hydrogenation gave some unexpected results. There was a facile isomerization to α pinene which was not hydrogenated further. The reaction stopped at about 30 % conversion at which time the cis and trans pinanes were present in near equal amounts in about 16–18 % yields.

     

Mathematical modeling of the partial hydrogenation of vegetable oil in a monolithic stirrer reactor

Experimental and theoretical studies on the partial hydrogenation of vegetable oil in a monolithic stirrer reactor are reported. A complete mathematical model of the reactor was developed, including hydrogenation and isomerization kinetics, catalyst deactivation, external gas–liquid and liquid–solid as well as internal mass transfer. The experimental studies were carried out in a Pd/Al₂O₃/Al monolithic stirrer reactor, at a wide range of temperatures (353–373 K), pressures (414–552 kPa), and catalyst loadings (0.00084–0.00527 kg_Pd,exp m^?3). Based on this model, simulated data can be used to evaluate the catalyst (Pd/Al₂O₃/Al) and the hydrogenation process in consecutive catalytic tests under different operating conditions. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3524–3533, 2014     

Polytrope Kinetikmessung zur Bewertung von Ionenaustauscherharzen für die Veresterung von Acrylsäure mit n‐Butanol

A catalyst screening for the esterification of acrylic acid with n‐butanol is presented. The kinetics was investigated in the temperature range of 70 – 100 °C and the selectivity was determined. The kinetic data fitted well with the Langmuir‐Hinshelwood‐Hougen‐Watson approach. The model was applied for the design of a reactive distillation column. Due to the similar fluid dynamics and the fast data generation a temperature scanning plug flow reactor was used.     

固载化离子液体催化环氧乙烷和二氧化碳合成碳酸乙烯酯

用溴化1-羟乙基-3-乙烯基咪唑、甲基丙烯酸钠、丙烯酸羟乙酯、苯乙烯4种单体共聚合成了高分子离子液体催化剂,表征了其结构. 将该催化剂固载到分子筛上制成固体颗粒催化剂,催化环氧乙烷(EO)与CO2合成碳酸乙烯酯(EC)的反应,考察了反应时间、温度、压力、催化剂用量对EO转化率及生成EC选择性的影响. 结果表明,在反应时间4 h、温度403.15 K、压力2.5 MPa、催化剂与环氧乙烷质量比9%的条件下,EO转化率为95%, EC选择性为98%,催化剂在循环使用10次后,EO转化率无明显下降,EC选择性接近100%. 该反应为一级反应,动力学方程为r=-dCEO/dt=9.872×104e-52.00/(RT)CEO.