Influence of channel geometry on hydrodynamics and mass transfer in the monolith film flow reactor

The hydrodynamics and the gas–liquid mass transfer as a function of the channel geometry have been investigated for the monolith film flow reactor. For the hydrodynamic studies, the liquid distribution and the flooding boundaries have been experimentally determined. The liquid distribution improved with increasing liquid flow rate. The flooding limits are in the range of other commercial structured packings and allow operation under industrially relevant conditions. Larger channel sizes and lower surface tension expand the operating window, while viscosity seems to have a minor impact. The gas–liquid mass transfer is a strong function of the surface to volume ratio defined by the channel dimensions. Co- and counter-current flow operation result in similar performance. Furthermore, shorter monoliths, with larger contribution of the inlet section have significant higher mass transfer due to the development of the concentration profile. The obtained k_GLa_V values of around 0.01 s⁻¹ are in the range of other commercial packings in counter-current flow operation. A three-dimensional single channel model describing the hydrodynamic and diffusion phenomena in the monolith is in good agreement with the experimental results. The flexibility in channel size and dimension allows tailoring the monolith reactor to the specific needs of the individual application.     

Applying monolith reactors for hydrogenations in the production of specialty chemicals—process and economic considerations

Monolith catalysts, mainstays in gas-phase automotive and environmental process applications, have found new potential in replacing three-phase slurry reactors for the production of specialty chemicals, especially when their advantages are fully utilized in recirculation loop approaches. Many economic and logistical benefits for removing slurry catalysts drive the investment into monolith technology, both for new capacity and for retrofits onto existing stirred tank reactors. Benefits are most pronounced for fast reaction chemistries, where monolith catalysts can achieve volumetric activities several times higher than slurry reactors. This paper demonstrates how engineering design and scale-up can be performed using fundamental equations and literature correlations in combination with pilot plant measurements and presents an economic analysis emphasizing monolith catalyst life as a critical variable. Efforts to develop replacement catalysts must therefore integrate efficient catalyst fabrication and lab testing into the evaluation process.     

Influence of orientation upon the hydrodynamics of gas-liquid flow for square channels in monolith supports

Monoliths are being used increasingly as catalyst supports for two-phase gas-liquid reactions, yet substantial differences in the mass transfer performance between different configurations have not been thoroughly explained using either mass transfer or hydrodynamic arguments. In this paper, investigations of the differences in hydrodynamics between up-flow and down-flow have been made in a single channel using square glass capillaries of either 1.5 or 2 mm section. The fluids used were either water or 30%_v/v isopropanol/water mixture and air. Predictive flow maps are presented for down-flow: annular, Taylor (slug) flow, bubbly and churn flow were observed. In the Taylor flow regime, slug velocities and lengths measured using an optoelectronic technique were found to be in good agreement with the drift flux model [Zuber, N., Findlay, J.A., 1965. Average volumetric concentration in two-phase flow systems. Journal of Heat Transfer 87, 453-468]. Non-zero drift velocities were obtained. Particle image velocimetry (PIV) was used to investigate the velocity fields within the liquid slugs. For short slugs (slug length less than the tube hydraulic diameter), a flow is developed where the axial velocity component is only a function of position in the tube cross-section. The velocity profile is relatively flat, with the maximum observed velocity at the axis of the tube, V_max, being 0.8-1 times the bubble velocity, V_B. For long slugs, the axial velocity component depends on both the axial position and the position in the tube cross-section. Close to parabolic profiles are developed with V_max/V_B≈1.1-1.7. The location of the centre of the recirculation vortices produced in long slugs was found to be closer to the tube centre in down-flow compared with up-flow. Recirculation times in up-flow were 3 times faster: this has implications for the models used to predict rates of mass transfer and residence time distribution.     

Multiphase monolith reactors: Chemical reaction engineering of segmented flow in microchannels

The use of segmented flow in capillaries, also known as Taylor flow, for reaction engineering purposes has soared in recent years. On the one hand, Taylor flow has been used in honeycomb monolith catalyst supports. On the other hand, Taylor flow is the common flow pattern in multiphase microchannel reactors. This contribution reviews the fluid mechanical aspects of this flow pattern in quite general terms, with an emphasis on the underlying principles. From very simple analysis, design estimates for mass transfer, pressure drop and residence time distribution may be obtained with relative ease and—for multiphase reactors—surprising accuracy.     

Hydrogenation of 2‐ethylanthraquinone under Taylor flow in single square channel monolith reactors

The hydrogenation of 2‐ethylanthraquinone (EAQ) to 2‐ethylanthrahydroquinone (EAHQ) was carried out under Taylor flow in single square channel monolith reactors. The two opening ends of opaque reaction channel were connected with two circular transparent quartz‐glass capillaries, where Taylor flow hydrodynamics parameters were measured and further used to obtain practical flow state of reactants in square reaction channels. A carefully designed gas‐liquid inlet mixer was used to supply steady gas bubbles and liquid slugs with desired length. The effects of various operating parameters, involving superficial gas velocity, superficial liquid velocity, gas bubble length, liquid slug length, two‐phase velocity and temperature, on EAQ conversion were systematically researched. Based on EAQ conversion, experimental overall volumetric mass transfer coefficients were calculated, and also studied as functions of various parameters as mentioned earlier. The film model, penetration model, and existing semi‐empirical formula were used to predict gas‐solid, gas‐liquid, and liquid‐solid volumetric mass transfer coefficients in Taylor flow, respectively. The predicted overall volumetric mass transfer coefficients agreed well with the experimental ones. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

The selective hydrogenation of butyne-1,4-diol by supported palladiums: a comparative study on slurry, fixed bed, and monolith downflow bubble column reactors

The present study was carried out to asses performance of a Pd-monolith downflow bubble column (DBC) reactor, and compare it with that of the slurry and the fixed bed DBC. The selective hydrogenation of butyne-1,4-diol to cis-2-butene-1,4-diol over palladium catalyst was chosen as a model reaction. In principle, the monolith DBC allowed the reaction to take place under kinetic control regime. Comparison with DBC employing 5% Pd/C powder and 1% Pd-on-Raschig ring catalysts revealed a better performance of the monolith DBC (1% Pd loading) with advantage of smaller reaction volume and intensified reaction rate. In the monolith DBC, improved hydrogen transport was possible, as the interface between bubbles and the channel wall was very thin, thus, the length of the diffusion path was very short. In addition, the interfacial surface area at both gas–liquid and liquid–solid interface in the monolith was also very high. The reaction kinetics was well represented by the Langmuir–Hinshelwood mechanism. As an alternative to conventional three-phase reactors, the monolith DBC was simple due to its inherent characteristic operation and no specially designed device.     

多级串联等体积全混流反应器与平推流反应器等效性研究——以二级可逆反应为例

在多级串联全混流反应器中,在等温等容条件下给出了二级可逆反应第Ⅳ级反应器的出口浓度表达式.讨论了在相同操作条件下,达到平推流反应器的转化率所需要的等体积串联全混流反应器的级数Ⅳ;主要考察了正反应速率常数k1、平衡常数K、反应物初始浓度之比M、停留时间τ等因素对N的影响,得出了N与正反应速率常数k1、相平衡常数K以及停留...     

Continuous emulsion polymerization of styrene in a single Couette–Taylor vortex flow reactor

The effect of the geometrical and operational parameters on the mixing characteristics of a Couette–Taylor vortex flow reactor (CTVFR) were investigated and were correlated with the same parameters by using the tank‐in‐series model. Continuous emulsion polymerization of styrene was conducted at 50°C in a CTVFR to clarify the effects on kinetic behavior and reactor performance of operational parameters such as rotational speed of inner cylinder (Taylor number), reactor mean residence time, and emulsifier and initiator concentrations in the feed streams. It was found that steady‐state monomer conversion and particle number could be freely varied only by varying the Taylor number. In order to explain the observed kinetic behavior of this polymerization system, a mathematical model was developed by combining the empirical correlation of the mixing characteristics of a CTVFR and a previously proposed kinetic model for the continuous emulsion polymerization of styrene in continuous stirred tank reactors connected in series (CSTRs). On the basis of these experimental results, it was concluded that a CTVFR is suitable for the first reactor (prereactor) of a continuous emulsion polymerization reactor system. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1931–1942, 2001     

多级串联等体积全混流反应器与平推流反应器的等效性研究——以二级不可逆反应为例

在多级串联全混流反应器中针对二级不可逆反应,推导出第N级串级反应器的出口浓度表达式.为与平推流反应器进行比较,引人反应器的相对效率,在平推流反应器中一定的转化率条件下,考察反应速率常数和反应物初始摩尔比大于1的情况下对串联级数的影响.通过实例计算,得出随着相对效率的增大,串联反应器级数随之增大.而当串联级数达到5时,相...     

Changes in crushing strength of hydrocarbon steam-reforming catalyst along the reactor tube under operating conditions

The catalytic hydrocarbon steam reforming process for the production of synthesis gas is accomplished using a nickel-based catalyst. The catalyst is designed to suit fixed-bed continuous-flow tubular reactor operation. It is manufactured in cylindrical form and possesses a relatively high crushing strength. The nickel active ingredient is homogeneously dispersed on the carrier surface in its oxide form. The currently applied reformers are vertical continuous-flow reactors consisting of several hundred tubes in which the reactants—hydrocarbon and steam—are introduced at the top of the reactor tubes and the reformed gaseous products are collected at their bottom ends. Performance and long-term uninterrupted operation of hydrocarbon steam reformers are severely affected by the alteration of the crushing strength of catalyst pellets. Changes in the crushing strength of the catalyst along the reformer tube under actual operating conditions were investigated and the results are presented here. The usefulness of the crushing strength as a diagnostic test for catalysts is discussed. This test has direct bearing on the selection of prospective catalyst charge, the reuse of partially used catalyst charge, and the investigation of catalyst failures.     

精对苯二甲酸装置氧化反应器操作新模式探讨

介绍了国内某PTA装置的氧化反应器操作情况,重点介绍了氧化反应器的原理、影响氧化反应的工艺因素,依据化学工程理论和专利商提供的数据以及生产实践积累的数据,寻找降低酸耗和提高装置负荷的方法,并在实践中得到验证,即氧化反应器采用低压、低溶剂比、高催化剂浓度的操作模式,可以在不增加装置投资的情况下,使操作负荷增加25%,酸耗降低10%。     

Influence of geometry on gas holdups in a reversed flow jet loop reactor

The effects of ratio of draft tube to reactor diameter (D_d/D), liquid nozzle diameter (d_N), aeration tube diameter (d_G) and immersion height of the two-fluid nozzle into the draft tube (H_N) on overall and annulus gas holdups for the air-water system were evaluated experimentally in a reversed flow jet loop reactor over wide ranges of gas and liquid flow rates. Both the gas holdups increased with increasing gas and liquid flow rates and with decreasing d_N and H_N. The influence of d_G on gas holdups is found to vary with gas flow rates. Correlations are proposed to predict gas holdups.     

Similar effect of carbon and silica catalyst support on the hydrogenation reaction rate in organic slurry reactors

This paper investigates the influence of the catalyst support type on mass transport and reaction rate for the case of hydrogenation of α-methylstyrene to cumene in a gas inducing stirred slurry reactor and in a slurry bubble column. The reaction is carried out in the presence of 3% Pd/carbon and 3% Pd/silica catalyst particles. The lyophobicity of the two catalyst supports in the cumene slurry is found to be similar. The overall rate of the hydrogenation reaction is described by the classical transport and reaction resistances-in-series model. The rate of gas-to-liquid mass transfer is somewhat larger during reaction than without reaction. This enhanced mass transfer points to particle-to-bubble adhesion as a result of the relative affinity of both catalyst supports to the gas phase. The observed reaction enhancements are similar for both Pd/carbon and Pd/silica catalyst/cumene slurries.     

Dehydration of ortho-boric acid in a three-phase bubble column reactor operating at low pressure

This study investigates the applicability of the bubble column as a reactor to perform the dehydration of ortho-boric acid efficiently and economically. The effects of operating conditions such as reaction time, temperature, gas flow rate, particle size and solid content in the slurry phase on the fractional conversion of the reaction have been determined, and the performance of the three-phase bubble column reactor operating at low pressure (92 kPa) has been discussed. It can be noted from this study that the reaction time has been reduced and the particle size and solid content which are required in the slurry phase for favourable fractional conversion have been increased in the bubble column reactor in comparison with those in the continuous stirred tank reactor. The reaction could be described by means of a fluid–solid heterogeneous reaction model.     

分布孔大小对环流反应器内流动影响数值模拟

采用k-ε二方程模型和欧拉多相流模型,对一种气升式环流反应器内的湍流气液二相流进行了全尺寸的数值模拟研究,考察了采用具有不同大小分布孔气体分布器时反应器内气含率和流速分布的细节。模拟结果表明采用小分布孔的反应器内的平均气含率较高,气液二相接触效果较好,对于反应过程有利。计算所得的整体气含率与实测的整体气含率进行了对比,吻合较好。     

微通道反应器中二氯丙醇环化反应研究

研究了微通道反应器内二氯丙醇的环化制备环氧氯丙烷的反应,考察了反应温度、原料配比、停留时间等单因素对环氧氯丙烷收率的影响。实验确定了较优的工艺参数组合:环化反应温度50℃,二氯丙醇与氢氧化钠的摩尔比1∶1.2,停留时间45 s,NaOH质量分数20%时,ECH的收率达到95.2%。在微通道反应的时空转化率要比常规反应高出2个数量级。与传统的工艺方法相比,微通道反应中环氧氯丙烷的收率提高了10%,降低了过程的能耗,废水排放量减少了45%。     

Effect of recycling the unconverted residue on a hydrocracking catalyst operating in an ebullated bed reactor

The effect of recycling the unconverted bottom on catalyst deactivation as a way to improve the hydrocracking conversion of heavy oil was analyzed using the experimental information obtained in a steady-state ebullated bed reactor. The recycle contained different amounts of partially converted (aged) material. Four sets of experiments were performed to demonstrate that after five passes through the reactor, the reactivity of the unconverted material decreased by 15% and its impact on catalyst deactivation increased by 30%. The results indicated that the higher the conversion, the lower is the reactivity and the higher is the catalyst deactivation. The production of an insoluble and refractory to convert material imposes a limit on the recycling benefit.     

Effect of external mass transfer in a packed bed reactor system for a reversible enzyme reaction

A mathematical model was developed to describe the effect of external mass transfer for a packed-bed enzyme reactor in which a reversible, one-substrate, two-intermediate enzyme reaction took place. The model equation was applied to the analysis of an immobilized glucose isomerase reactor system. A Colburn-type mass transfer correlation was obtained from the Colburn j-factor versus Reynolds number plot: i.e., j_D = 0.045N_Re^−0.48. The values of mass transfer coefficient for the system under study ranged from 0.01 to 0.1 cm h⁻¹ depending on the substrate flow rate. Very good agreements were observed between the computer simulation using a plug flow reactor model with the derived mass transfer correlation and the experimental results obtained from the packed-bed reactor operation.     

Influence of the operating conditions on yield and selectivity for the partial oxidation of ethane in a catalytic membrane reactor

In this study, simulation results are presented for the partial oxidation of ethane to ethylene in a Catalytic Membrane Reactor (CMR) under isothermal and non-isothermal conditions. Considering the importance of the transport processes, a 2D model was developed and implemented in FLUENT^® using self-designed program modules for reaction kinetics, transport properties and post-processing. An analysis of significance of the influencing variables is carried out on the basis of a reference case. The number of parameters were minimized by the dimensionless formulation of the model. One of the most important variables is the oxygen dosage through the membrane. Both velocity and oxygen concentration of the trans-membrane stream were varied with the aim of attaining maximum ethylene yield. The results of the different simulations clearly show the advantages of the CMR compared to the Catalytic Wall Reactor (CWR). The numerical simulations are essential in order to reduce the experimental costs and to evaluate different reactor concepts.     

浆态反应器中苯氯化反应的宏观动力学

采用自行设计的三相鼓泡浆态实验反应器 ,在半连续操作条件下 ,通过改变催化剂粒度 ,消除了内扩散的影响 ;测定了不同催化剂浓度、通氯量以及苯回流量条件下的苯氯化反应的宏观动力学数据。建立了宏观动力学模型 ,并由实验数据估计出模型参数 ,模型计算值和实验值吻合较好