Diesel upgrading into a low emissions fuel

The revamp of existing diesel hydrotreating units using SHP technology was studied to improve the emission of the diesel engine. Gas and liquid-phase reactors were sequentially added to the actual trickle bed reactor. A special catalyst was employed. Micro-plant kinetic studies were performed and the results compared with those obtained with conventional trickle bed reactor operation. It was shown that using the gas and liquid-phase reactor, the hydrogenation, hydrogenolysis, and ring-opening reactions can be enhanced, so can be the sulfur and cetane number properties. The new scheme decreased the mono-aromatic content in the lighter part of the diesel that improve the NO_x and particulate emissions in exhaust gases of a diesel engine. A simplified kinetic model for gas and liquid-phase reactors was developed to optimize SHP reactors and to minimize investment.     

Modeling of monolithic and trickle-bed reactors for the hydrogenation of styrene

A kinetic study into the styrene hydrogenation over a palladium on alumina catalyst has been made. Styrene was used as a model component for pyrolysis gasoline. A kinetic rate expression has been derived and the inhibiting effect of sulfur components has been included. Using this kinetics and mass-transfer models compiled from literature, the performance of two types of reactors for the styrene (pyrolysis gasoline) hydrogenation has been evaluated. A structured reactor such as a monolith has large advantages over a conventional trickle-bed reactor. For the monolithic reactor a more than 3 times higher volumetric productivity is obtained with much less catalyst. The modeling results indicate that deactivation by gum formation should be significantly less due to much better hydrogen mass transfer in the reactor.     

苯乙炔选择性加氢滴流床反应器内的液相轴向返混特性

苯乙炔选择性加氢是从裂解汽油C₈馏分中回收苯乙烯的关键反应,本文采用滴流床反应器对该反应体系的液相轴向返混行为进行了研究。首先利用脉冲示踪法测得了不同操作条件下的液相停留时间分布密度;然后基于固定床轴向扩散模型,通过有限元正交配置法和Levenberg-Marquardt非线性最小二乘法,计算得到了Péclet数和液相平均停留时间;最后考察了主要操作条件对液相轴向返混的影响。研究结果表明,增大液体流量、气体流量、温度以及压力均可减小液相返混,而增大颗粒粒径会使液相返混加剧。     

Estimation of Kinetic Parameters for Hydrogenation Reactions Using a Genetic Algorithm

The kinetics of acetylene hydrogenation in a fixed‐bed reactor of a commercial Pd/Al₂O₃ catalyst has been studied. The hydrogenation reactor considered in this work is an essential part of a vinyl chloride monomer (VCM) plant. Three well‐known kinetic models were used to simulate the hydrogenation reactor under industrial operating conditions. Since none of the models provide appropriate prediction, the industrial data and calculated values were compared and optimum kinetic parameters were evaluated utilizing a genetic algorithm (GA) technique. The best kinetic parameters for the three models were determined under specified industrial operating conditions. The hydrogenation reactor was simulated using the estimated optimum kinetic parameters of the three models. Simulation results from the three models were compared to industrial data and the best kinetic model was found. This kinetic model with the evaluated optimum kinetic parameters can well predict the behavior of the industrial hydrogenation reactor to improve the performance of the process.     

Modeling of an industrial fixed bed reactor based on lumped kinetic models for hydrogenation of pyrolysis gasoline

In this work, a mathematical model of an industrial fixed bed reactor for the catalytic hydrogenation of pyrolysis gasoline produced from olefin production plant is developed based on a lumped kinetic model. A pseudo-homogeneous system for liquid and solid phases and three pseudo-components: diolefins, olefins, and parraffins, are taken into account in the development of the reactor model. Temperature profile and product distribution from real plant data on a gasoline hydrogenation reactor are used to estimate reaction kinetic parameters. The developed model is validated by comparing the results of simulation with those collected from the plant data. From simulation results, it is found that the prediction of significant state variables agrees well with the actual plant data for a wide range of operating conditions; the developed model adequately represents the fixed-bed reactor.     

Cumene Hydroperoxide Hydrogenation on a Pd/Al2O3 Catalyst in a Trickle Bed Reactor – Kinetics of Hydrogenation and Deactivation

Liquid‐phase hydrogenation using a Pd/Al₂O₃ catalyst provides a potential technique for the reduction of cumene hydroperoxide (CHP) to α‐cumyl alcohol (CA). In this paper, CHP hydrogenation was carried out in a cocurrent downflow trickle‐bed reactor over a wide range of reaction conditions to study the reaction and deactivation kinetics. The proposed intrinsic rate expression for CHP hydrogenation is based on an Eley‐Rideal mechanism that accounts for an irreversible surface reaction between the absorbed CHP with nonabsorbed hydrogen molecules. During CHP hydrogenation, an exponential decay in activity of the Pd/Al₂O₃ catalyst and the presence of residual activity were observed. A kinetic deactivation model with residual activity was developed. Based on reaction and deactivation kinetics, catalyst deactivation was attributed to oxidation of the catalyst surface by CHP. The presence of residual activity was due to the partial reduction of oxidized catalyst surface by hydrogen.     

Kinetics of the Selective Hydrogenation of Pyrolysis Gasoline

The kinetics of the selective hydrogenation of pyrolysis gasoline (pygas) over commercial Pd/Al₂O₃ catalyst particles were investigated using a stirred semi‐batch reactor in the absence of transport limitations. The effects of reaction temperature and pressure on the conversion of styrene, cyclopentadiene, cyclopentene and 1‐hexene were obtained over ranges of temperature (313–343 K) and total pressure (2–5 MPa). Competitive hydrogenation between monoolefins and diolefins was extensive, and the reaction rates of diolefins were much faster than those of the monoolefins. A Langmuir‐Hinshelwood type model was proposed and successfully fitted to the experimental data. The kinetic and adsorption parameters were estimated by using the fourth‐order Runge‐Kutta method together with the Levenberg‐Marquardt algorithm, which minimized the residual sum of squares between the experimental concentrations and the calculated values. The orders of the estimated activation energies and the adsorption parameters were consistent with the order of the reaction rates of monoolefins and diolefins.     

Parallel hydrogenation for the quantification of wetting efficiency and liquid–solid mass transfer in a trickle‐bed reactor

A novel method for the measurement of wetting efficiency in a trickle‐bed reactor under reaction conditions is introduced. The method exploits reaction rate differences of two first‐order liquid‐limited reactions occurring in parallel, to infer wetting efficiencies without any other knowledge of the reaction kinetics or external mass transfer characteristics. Using the hydrogenation of linear‐ and isooctenes, wetting efficiency is measured in a 50‐mm internal diameter, high‐pressure trickle‐bed reactor. Liquid–solid mass transfer coefficients are also estimated from the experimental conversion data. Measurements were performed for upflow operation and two literature‐defined boundaries of hydrodynamic multiplicity in trickle flow. Hydrodynamic multiplicity in trickle flow gave rise to as much as 10% variation in wetting efficiency, and 10–20% variation in the specific liquid–solid mass transfer coefficient. Conversions for upflow operation were significantly higher in trickle‐flow operation, because of complete wetting and better liquid–solid mass transfer characteristics. © 2010 American Institute of Chemical Engineers AIChE J, 2011.     

Simulating simultaneous fines deposition under catalytic hydrodesulfurization in hydrotreating trickle beds—does bed plugging affect HDS performance?

The deposition of fine particles under chemical reaction conditions in a high pressure/temperature trickle bed reactor was analyzed theoretically using a dynamic multiphase flow deep-bed filtration model coupled with heat and species balance equations in the liquid, gas and solid (catalyst+deposit) phases. The hydrodesulfurization process in the presence of sulfided Co-Mo/γ-Al₂O₃ catalyst was considered as a case study. The deep-bed filtration model incorporates the physical effects of porosity and effective specific surface area changes due to fines deposition/detachment, gas and suspension inertial effects, and coupling effects between the filtration parameters and the interfacial momentum exchange force terms. The detachment of the fine particles from the collector surface was assumed to be induced by the colloidal forces in the case of Brownian particles or by the hydrodynamic forces in the case of non-Brownian particles. The three-phase heterogeneous model developed to simulate the trickle bed performance incorporates the concentration gradients inside the catalyst particle and solid deposit. An important finding of the work is that fine particles deposition does not influence appreciably trickle bed reactor performance. Thus, the only undesirable effect of the fine particles deposition process is the bed plugging and the increase of the resistance to two-phase flow.     

Experimental and Theoretical Studies on Hydrogenation in Multiphase Fixed‐Bed Reactors

Multiphase fixed‐bed reactors have complex hydrodynamic and mass transfer characteristics. The modeling and scale‐up are therefore difficult. The present work focuses on the role of mass transfer on the effective reaction rate. The catalytic 1‐octene hydrogenation was taken as a model reaction. The reaction rate in the trickle‐bed reactor is by a factor of 20 smaller than (theoretically) in the absence of any mass transfer limitations. For high octene concentrations (> 10 %), the effective reaction rate is limited by the H₂ consumption, above all by the gas/liquid and liquid/solid mass transfer. For lower octene concentrations the reaction is zero order with respect to H₂ and only depends on the octene consumption, i.e., on the interplay of chemical reaction, L/S and intraparticle mass transfer of octene.     

HYDROGENATION OF 1,5-CYCLOOCTADIENE IN A TRICKLE BED REACTOR ACCOMPANIED BY PHASE TRANSITION

This paper examined the evaporation and condensation of the reaction mixture within the trickle bed reactor during 1,5-cyclooctadiene hydrogenation. The aim of study has been to formulate a mathematical model of heat and mass transfer influenced the exothermic reaction of a volatile reaction mixture apt to evaporation by the reaction heat in the system which is often accompanied by a hot spot temperature formation in the reactor followed by the enhancement of undesirable side reactions and/or catalyst deactivation. The numerical solution of the proposed model agreed quite well with the experimental temperature profiles in the trickle bed reactor.     

Gas‐Liquid Mass Transfer in a Bench‐Scale Trickle Bed Reactor used for Benzene Hydrogenation

The gas‐liquid mass transfer coefficients (MTCs) of a trickle bed reactor used for the study of benzene hydrogenation were investigated. The Ni/Al₂O₃ catalyst bed was diluted with a coarse‐grained inert carborundum (SiC) particle catalyst. Gas‐liquid mass transfer coefficients were estimated by using a heterogeneous model for reactor simulation, incorporating reaction kinetics, vapor‐liquid equilibrium, and catalyst particle internal mass transfer apart from gas‐liquid interface mass transfer. The effects of liquid axial dispersion and the catalyst wetting efficiency are shown to be negligible. Partial external mass transfer coefficients are correlated with gas superficial velocity, and comparison between them and those obtained from experiments conducted on a bed diluted with fine particles is also presented. On both sides of the gas‐liquid interface the hydrogen mass transfer coefficient is higher than the corresponding benzene one and both increase significantly with gas velocity. The gas‐side mass transfer limitations appear to be higher in the case of dilution with fine particles. On the liquid side, the mass transfer resistances are higher in the case of dilution with coarse inerts for gas velocities up to 3 · 10^–2 cm/sec, while for higher gas velocities this was inversed and higher mass transfer limitations were obtained for the beds diluted with fine inerts.     

Selective Hydrogenation of 1‐Butene Rich Cuts: the Impact of the Intraparticle Diffusion Limitations on the Selectivity

The impact of intraparticle diffusion limitations on the selectivity of an industrial reactor for selective hydrogenation of 1‐butyne and 1,3‐butadiene contained in 1‐butene rich cuts was evaluated. To this end, a simple model of a trickle‐bed reactor was employed and actual process operating conditions were chosen. A kinetic model was chosen whose parameters correspond to a commercial catalyst. These parameters were calculated from experiments conducted under industrial operating conditions. The complex diffusion and reaction phenomena occurring inside catalyst pellets placed at different depths of the reactor are comprehensively described. 1‐Butene losses in the range 20–30 %, which are usual in commercial plants, were predicted. It was concluded that the operating pressure is crucial for enhancing process selectivity.     

QUALITATIVE OBSERVATIONS OF HEAT AND MASS TRANSFER EFFECTS ON THE BEHAVIOUR OF A TRICKLE BED REACTOR

This paper examines the effect of simultaneous heat and mass transfer on the hydrogenation of cyclohexene in a trickle bed reactor with particular attention given to the problem of liquid phase evaporation and transition to the gas-phase regime of operation. The reaction rates are obtained as a function of temperature and hydrogen flow rate; the concentration of the substrate in the feed displays considerable hysteresis due to an abrupt increase of the reaction rate arising from temperature gradients within the bed and in the gas film surrounding the catalyst pellet, during the transition from the liquid to the gas-phase regime. The transition is accompanied by the change of apparent kinetics of the model reaction as well as by a change of regime and operation of the pellet. In the liquid phase a pellet originally showing inter-phase and intra-particle diffusion resistances changes into the gas-phase regime with a large resistance due to inter-phase diffusion.     

Diffusion‐enhanced hierarchically macro‐mesoporous catalyst for selective hydrogenation of pyrolysis gasoline

A novel Pd/Al₂O₃ catalyst with the hierarchically macro‐mesoporous structure was prepared and applied to the selective hydrogenation of pyrolysis gasoline. The alumina support possessed a unique structure of hierarchical mesopores and macropores. The as‐prepared and calcined alumina were characterized by X‐ray diffraction, N₂ adsorption‐desorption, and scanning electron microscopy. It showed that the hierarchically porous structure of the alumina was well preserved after calcination at 1073 K, indicating high thermal stability. The 1073 K calcined alumina was impregnated with palladium metal and compared with a commercial catalyst without macrochannels. Both the catalytic activity and the hydrogenation selectivity of the novel Pd/Al₂O₃ catalyst were higher than those of the commercial Pd/Al₂O₃ catalyst. In addition, apparent reaction activation energies obtained with the novel catalyst for model pyrolysis gasoline were 46–81% higher than those with the commercial catalyst. The results adequately demonstrated the enhanced mass transfer characteristics of the novel macro‐mesostructured catalyst. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

An NMR Imaging Study of Steady-State and Periodic Operation Modes of a Trickle Bed Reactor

NMR imaging has been applied to study the steady-state and the periodic operations of a functioning trickle bed reactor. It has been revealed that under conditions of the continuous supply of a liquid reagent to the catalyst bed, the bed was mostly filled with the liquid phase and was characterized by the uniform and stationary distribution of a liquid phase, whereas under conditions of the periodic supply of a liquid reagent to the catalyst bed with the same liquid flow velocity the bed was mostly dry and was characterized by a non-stationary distribution of the liquid phase. The oscillations of the liquid phase content within the bed, corresponding to the modulated liquid flow, have been observed. It has been shown that performing the hydrogenation reaction in a trickle bed reactor under conditions of the periodic supply of a liquid reagent to the catalyst bed leads to the intensification of the hydrogenation process. It becomes apparent in the significant increase of the temperature of the catalyst bed as well as in the increase of the conversion degree in the regimes under forced time-varying liquid flow rates in comparison to the steady-state regime of the reactor operation.     

裂解汽油中混合烯烃选择性加氢反应动力学

采用高压搅拌釜式反应器,在消除催化剂外扩散影响的基础上,对裂解汽油选择性加氢反应动力学进行了研究。以反应组分环戊二烯、苯乙烯、1-己烯与溶剂正庚烷的混合物为模型化合物,考察了反应温度和压力的影响。结果表明,环戊二烯、苯乙烯、1-己烯和环戊烯在催化剂表面为竞争加氢,双烯的反应速率远大于单烯。采用Langmuir-Hinshelwood反应机理,导出了反应动力学模型,并采用非线性最小二乘法对动力学模型参数进行估值。实验结果验证了动力学模型的合理性。     

A fluidized bed kinetic model for the fluorination of dissociated zircon

A reaction kinetic model for the fluorination of plasma dissociated zircon (PDZ, or ZrO₂.SiO₂) with hydrogen fluoride was developed. The model uses reaction as rate‐limiting step, with a shrinking core of PDZ in a porous matrix of zirconia (ZrO₂). This model was used to develop models for a multi‐stage fluidized bed reactor. These models facilitated the determination and design of an optimally configured multi‐stage fluidized bed reactor for the fluorination of PDZ. It was shown that a combination cross‐/countercurrent multi‐stage fluidized bed reactor could yield significant improvement over the conventional countercur‐rent multi‐stage fluidized bed reactor for certain reaction kinetic conditions.     

环戊二烯及双环戊二烯对裂解汽油全馏分加氢装置运行的影响

介绍了裂解汽油全馏分加氢过程中发生的环戊二烯热二聚及双环戊二烯热分解反应。该转化反应导致了二段加氢反应器双烯值高于一段出料的双烯值,并缩短了二段加氢反应催化剂的运行周期,提出了降低影响的措施。     

Liquid phase hydrogenation of aniline in a trickle bed reactor

A rate equation is developed for the liquid phase hydrogenation of aniline over cylindrical catalyst pellets of 30% nickel deposited on clay in a trickle bed reactor. The equation takes into account external and internal diffusional limitations, and describes the experimental data adequately. The hydrogenation reaction is first order with respect to hydrogen and zero order with respect to aniline. Effectiveness factors are in the range 0.003–0.03. Apparent activation energy of the reaction is 12.7 kcal/mol and true activation energy is 39.6 kcal/mol.