Air-lift reactors in chemical and biological technology

The principle of the air-lift reactor is finding wide application in the fields of both chemical technology and biotechnology because it offers simple and effective mixing in three-phase processes involving gases, liquids and solids. The air-lift principle offers advantages of no moving parts, high gas absorption efficiency, good heat transfer characteristics and rapid mixing which are applicable in a range of industrial processes. This review considers specific aspects of air-lift reactors emphasizing their function and relevance to particular applications. The two main groups of air-lift reactor, baffled vessels and external loop reactors, have four main component parts in common, the riser, the downcomer, the base and the gas separator, all of which have distinct characteristics. The performance of these four components with respect to flow configurations, fluidization of suspended solids and mass transfer are discussed together with methods of evaluating mass transfer coefficients.     

A new approach to evaluate the energetic efficiency of batch‐jacketed reactors

This paper presents a new heat transfer configuration for exothermic batch‐jacketed reactors. The proposed design for the heat transfer scheme comprises an additional heat exchanger in the jacket‐cooling loop. A detailed comparison study considering the new concept and the conventional process is presented in terms of energetic efficiency (refrigerated fluid consumption per batch cycle) and process control (control of reaction temperature). The simulation results of the new heat transfer configuration show a substantial decrease in the total volume of refrigerated fluid injected in the cooling loop, whereas the process control performance was practically unaffected.     

Investigation of multiphase hydrogenation in a catalyst‐trap microreactor

BACKGROUND: Multiphase hydrogenation plays a critical role in the pharmaceutical industry. A significant portion of the reaction steps in a typical fine chemical synthesis are catalytic hydrogenations, generally limited by resistances to mass and heat transport. To this end, the small‐scale and large surface‐to‐volume ratios of microreactor technology would greatly benefit chemical processing in the pharmaceutical and other industries. A silicon microreactor has been developed to investigate mass transfer in a catalytic hydrogenation reaction. The reactor design is such that solid catalyst is suspended in the reaction channel by an arrangement of catalyst traps. The design supports the use of commercial catalyst and allows control of pressure drop across the bed by engineering the packing density. RESULTS: This paper discusses the design and operation of the reactor in the context of the liquid‐phase hydrogenation of o‐nitroanisole to o‐anisidine. A two‐phase ‘flow map’ is generated across a range of conditions depicting three flow regimes, termed gas‐dominated, liquid‐dominated, and transitional, all with distinctly different mass transfer behavior. Conversion is measured across the flow map and then reconciled against the mass transfer characteristics of the prevailing flow regime. The highest conversion is achieved in the transitional flow regime, where competition between phases induces the most favorable gas–liquid mass transfer. CONCLUSION: The results are used to associate a mass transfer coefficient with each flow regime to quantify differences in performance. This reactor architecture may be useful for catalyst evaluation through rapid screening, or in large numbers as an alternative to macro‐scale production reactors. Copyright © 2008 Society of Chemical Industry     

Novel Gas-Liquid-Solid Reactors

Multiphase reactors involving gas, liquid, and solid phases have several important applications in the chemical industry, particularly in catalytic processes. Some of the well-known examples are: hydrogenation and oxidation of organic compounds, hydro-processing coal-derived and petroleum oils, Fischer-Tropsch synthesis, and methanation reactions. Due to the presence of three phases, the problem of reactor design is often important to achieve effective mass and heat transfer as well as a mixing pattern favorable to the particular process. The reactors are mainly of two types: (a) solid catalyst is suspended either by mechanical agitation or gas-induced agitation and (b) solid catalyst is in a fixed bed with concurrent or countercurrent feed of gas and liquid re-actants. The reactor types conventionally used in industry are: (a) mechanically agitated or bubble column slurry reactors and (b) trickle-bed or packed-bed bubble reactor. The various design and modeling aspects of these reactors have been reviewed by Satterfield [1], Chaudhari and Ramachandran [2], Shah [3,4], Ramachandran and Chaudhari [5], Shah et al. [6], and Herskowitz and Smith [7]. In several industrial processes these reactor designs are modified to achieve a certain specific objective, such as better heat or mass transfer, higher catalyst efficiency, better reactor performance and selectivity, etc. Similarly, specially designed reactors are often used for laboratory kinetic studies or to understand a certain phenomenon. Thus, novel multiphase reactors are becoming important from both academic and industrial viewpoints. Some of the recently introduced novel gas-liquid-solid reactor types are: (a) loop recycle slurry reactors, (b) basket-type reactors, (c) ebullated-bed reactors, (d) internal or external recycle reactors, (e) multistage slurry or packed-bed reactors, (f) column reactors with sieve trays or multiple agitators, (g) gas-induced agitated reactors, and (h) horizontal-packed-bed reactors. are being used in several new commercial processes, and various design aspects, such as hydrodynamics and mass and heat transfer, have been the subject of investigations in the last few years. However, no attempt to review the scattered information on these novel gas-liquid-solid reactors has been made. Therefore, the main objective of this paper is to review important developments in novel gas-liquid-solid reactors. For each type of reactor, advantages, disadvantages, and applications are discussed. Further, the status of information on hydrodynamics and mass transfer parameters and scale-up considerations is reviewed. These novel reactor designs are being used in several new commercial processes, and various design aspects, such as hydrodynamics and mass and heat transfer, have been the subject of investigations in the last few years. However, no attempt to review the scattered information on these novel gas-liquid-solid reactors has been made. Therefore, the main objective of this paper is to review important developments in novel gas-liquid-solid reactors. For each type of reactor, advantages, disadvantages, and applications are discussed. Further, the status of information on hydrodynamics and mass transfer parameters and scale-up considerations is reviewed.     

Novel Gas-Liquid-Solid Reactors

Multiphase reactors involving gas, liquid, and solid phases have several important applications in the chemical industry, particularly in catalytic processes. Some of the well-known examples are: hydrogenation and oxidation of organic compounds, hydro-processing coal-derived and petroleum oils, Fischer-Tropsch synthesis, and methanation reactions. Due to the presence of three phases, the problem of reactor design is often important to achieve effective mass and heat transfer as well as a mixing pattern favorable to the particular process. The reactors are mainly of two types: (a) solid catalyst is suspended either by mechanical agitation or gas-induced agitation and (b) solid catalyst is in a fixed bed with concurrent or countercurrent feed of gas and liquid re-actants. The reactor types conventionally used in industry are: (a) mechanically agitated or bubble column slurry reactors and (b) trickle-bed or packed-bed bubble reactor. The various design and modeling aspects of these reactors have been reviewed by Satterfield [1], Chaudhari and Ramachandran [2], Shah [3,4], Ramachandran and Chaudhari [5], Shah et al. [6], and Herskowitz and Smith [7]. In several industrial processes these reactor designs are modified to achieve a certain specific objective, such as better heat or mass transfer, higher catalyst efficiency, better reactor performance and selectivity, etc. Similarly, specially designed reactors are often used for laboratory kinetic studies or to understand a certain phenomenon. Thus, novel multiphase reactors are becoming important from both academic and industrial viewpoints. Some of the recently introduced novel gas-liquid-solid reactor types are: (a) loop recycle slurry reactors, (b) basket-type reactors, (c) ebullated-bed reactors, (d) internal or external recycle reactors, (e) multistage slurry or packed-bed reactors, (f) column reactors with sieve trays or multiple agitators, (g) gas-induced agitated reactors, and (h) horizontal-packed-bed reactors. are being used in several new commercial processes, and various design aspects, such as hydrodynamics and mass and heat transfer, have been the subject of investigations in the last few years. However, no attempt to review the scattered information on these novel gas-liquid-solid reactors has been made. Therefore, the main objective of this paper is to review important developments in novel gas-liquid-solid reactors. For each type of reactor, advantages, disadvantages, and applications are discussed. Further, the status of information on hydrodynamics and mass transfer parameters and scale-up considerations is reviewed. These novel reactor designs are being used in several new commercial processes, and various design aspects, such as hydrodynamics and mass and heat transfer, have been the subject of investigations in the last few years. However, no attempt to review the scattered information on these novel gas-liquid-solid reactors has been made. Therefore, the main objective of this paper is to review important developments in novel gas-liquid-solid reactors. For each type of reactor, advantages, disadvantages, and applications are discussed. Further, the status of information on hydrodynamics and mass transfer parameters and scale-up considerations is reviewed.     

The gas–liquid contacting effect on the operation of small scale upflow hydrotreaters

The effect of reactor geometry and bed dilution on the extent of gas oil hydrodesulfurization was tested by conducting hydrodesulfurization experiments in two laboratory reactors of different scale with non-diluted and diluted beds in ascending flow. The superficial gas and liquid velocities and the catalyst bed height were kept constant while the main difference between the two reactor scales was the reactor diameter. The diluted bed of the mini-reactor showed the best performance and its results were identical in upflow and downflow mode. The differences between the performance of the mini- and the bench-scale reactor operating in upflow mode have been investigated. Reactor performance simulation was attempted by a mathematical model that takes into account axial dispersion of the liquid phase and gas–liquid mass transfer. Bench-scale reactor operation was characterized by lower mass transfer rates than the corresponding mini-scale one. Combining model predictions and mock up operation it is concluded that the stronger mass transfer resistances calculated for the bench-scale reactor are associated with poorer gas distribution through the catalyst bed. Reduction of the bed diameter results in better gas–liquid contact by forcing the gas bubbles to distribute more effectively into the liquid phase.     

Gas–liquid and liquid–liquid mass transfer in microstructured reactors

This article is a comprehensive overview of gas–liquid and liquid–liquid mass transfer in microstructured reactors (MSR). MSR are known to offer high heat and mass transfer rates for two phase systems due to high surface to volume ratio as compared to conventional reactors. The reactions with fast kinetics controlled by mass transfer have been successfully intensified using MSR. The first part of the review deals with the methods of mass transfer characterization. Further, different dimensionless parameters used to analyze mass transfer in MSR are discussed. The literature data with different flow regimes and proposed empirical correlations for both gas–liquid and liquid–liquid systems is also presented. The conventional mass transfer models such as penetration and film theory are analyzed. Finally, the important issues of mass transfer in MSR are summed up.     

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.     

湍流气固两相流动状况的数值模拟

应用已建立的提升管反应器固两相流动反应模型,对工业催化裂化提升管反应器内在有传热及裂化反应时的湍流气固两相流动进行了数值模拟,得到了气固两相湍充动状况的详细信息,揭示了提升管内部有反应和传热时气固两相湍流流动的基本特征。模拟结果表明,在轴向,径向和圆周方向都存在着流动,湍能与率剂颗粒浓度的不均匀分布,进料段内的流动是整个反应器最复杂的部分。工业提升管反应器内这一复杂的气固两相湍流流动必将对传热和裂     

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.     

Experimental investigation of fast-mode liquid modulation in a trickle-bed reactor

Unsteady-state operation of trickle-bed reactors (TBRs) is a promising technique to improve reactor performances especially when mass transfer phenomena are rate controlling. Among the different techniques, fast-mode modulation of the liquid flow rate seems to be one of the most successful. In fact cycling the liquid flow rate at very low frequencies can induce the reactor to work at the high-interaction regime where mass and heat transfer phenomena are strongly enhanced. Fast-mode periodic operation, then, can be considered an extension of the natural high-interaction regime at a mean range of gas and liquid flow rate normally associated with trickling regime in steady-state conditions.Experimental tests have been performed in a TBR employing α-methyl styrene hydrogenation on Pd/C catalyst in unsteady-state conditions by “on-off” fast-mode liquid modulation. Results have been compared with the steady-state experiments at the corresponding average liquid flow rate, revealing a conversion rate improvement up to 60%. All experiments have been performed in isothermal conditions, so conversion improvement can be ascribed only to mass transfer increase and not to thermal effects. The variation of gas and liquid flow rates and liquid cycle parameters presented several important implications about the optimal working conditions.     

气固流化床外取热器内流动和换热特性分析

外取热器是维持催化裂化反应-再生系统热平衡和保持装置平稳运行的关键设备之一。外取热器的优化设计和合理调控,要求深入理解外取热器内的流动特性、换热特性及两者之间关系。在一套大型冷模热态实验装置上,分别考察了表观气速、颗粒质量流率对换热管附近的局部固含率和气泡频率、床层与换热管间传热系数的影响。结果表明:增加表观气速可以降低局部固含率、增加局部气泡频率、强化床层与换热管间换热;随着颗粒质量流率增加,局部固含率和局部气泡频率均增加;在较低表观气速下,增加颗粒质量流率不利于换热,而在较高表观气速下,传热系数随颗粒质量流率逐渐增加。不同流型下,气固流动特性对换热特性的影响不同。在鼓泡床流型下,过高的局部固含率不利于颗粒在换热表面的更新,增加换热管附近的局部气泡频率可以明显强化换热;而在湍流床流型下,换热管附近的局部固含率和气泡频率的增加,均使传热系数逐渐增大。建立了针对不同流型的换热经验关联式,预测值与实验值的平均相对偏差分别为6.9%和1.3%。     

HYDRODYNAMIC MODELLING IN AN AIR-LIFT LOOP REACTOR

A simple hydrodynamic model is proposed for use in the design, scale-up and characterization of external loop air-lift reactors. The approach is based upon a momentum balance for the flow loop coupled with a drift-flux equation for the reactor riser and establishes a rational basis for a predictive model relating gas throughput to induced liquid flow and gas hold-up in a range of air-lift reactors. The effective resistance of the reactor, k, defined in terms of the total loss coefficients of the reactor and the aerated height of the two-phase riser, was identified to allow for the quantification of the influence of reactor design on the hydrodynamic variables. An extensive body of data for the air-water system, collected on two reactors with active volumes of 0·055 m³ and 0·3 m³, is presented and used, in conjunction with literature data encompassing a wide range of reactor geometries and flow conditions, to define a unique relationship between flow behaviour and reactor configuration. The model, which accounts for the prevailing flow regime in the reactor, provides a direct method of predicting hydrodynamic behaviour in relatively non-viscous systems.     

整装反应器起燃阶段传热的数学模拟

整装反应器已经广泛地应用于催化领域,其暂态传热特性对反应器的起燃有重要作用。本文研究了整装反应器在反应点火前起燃阶段的传热,通过对绝热反应器建立的简单一维传热数学模型的求解,分析了固相轴向导热、气流性质、催化剂性质及反应器设计参数对传热的影响,比较了用金属体和陶瓷体时基体热响应的不同。     

Sparged loop reactors

Circulating bubble columns or loop reactors form one of the important classes of modified bubble columns. The present paper analyses the performance of external loop air lift reactors (EL-ALR). The EL-ALR has many advantageous features especially at large scale. These arise from its feature of having controlled liquid circulation which is the key parameter for the design and operation of EL-ALR contactors. Therefore, a reliable and generalised circulation model has been presented. The reliability of the model depends on the accuracy of the predictive methods for the gas hold-up and the two-phase fractional pressure drop. Detailed analysis of these fundamental parameters of gas-liquid flows has been presented. The effects of design (area ratio of riser to downcomer, height to diameter ratio and volume of reactor) and operating (gas flow rates and sparging locations) parameters on the performance of the EL-ALR have been analysed in detail. A rational basis has been developed for the estimation of pressure drop, mixing time and mass transfer coefficient. An optimum combination of design and operating parameters has been suggested and a criterion has been developed for the optimum location of spargers. An attempt has been made to provide critical analysis of the published information and to construct a coherent picture of EL-ALR.     

Periodic Operation of Three — Phase Catalytic Reactors

Periodic operation of three phase reactors has been explored for more than two decades. This type of forcing changes selectivity and can increase either conversion or throughput. Experiments and simulation demonstrate periodic flow interruption or variation enhances reaction rates for concurrent trickle beds provided reactants are in the gas phase or can be volatilized under bed operating conditions. Temperature excursions in trickle beds can be controlled by either flow variation or switching the feed between an inert and a reactant. Several approaches to increasing rate through faster mass transfer using flow pulsing have been studied. Pulsing flow can be induced by low amplitude modulation. Periodic switching of flow direction in airlift reactors increases gas hold up and thereby the mass transfer rate. Periodic operation of three phase reactors, thus, appears to be a fertile area for engineering research.     

气升式环流反应器内传质行为的分析与测量

1 INTRODUCTION Airlift loop reactors have emerged as one of the most promising devices in chemical, biochemical and environmental engineering operations. Its main ad-vantages over conventional reactors include excellent contact among different phases, ease of removal or replenishment of particles, and high heat and mass transfer rates[1]. High gas-liquid contacting area and favorable flow pattern are the attractive features of this type of three-phase contactors. Typical processes that ca…     

Investigation of the local specific energy dissipation rates in a jet‐zone loop reactor for halogenation of ketones

Within the framework of process intensification there is a growing demand for novel reactor technologies. For the improvement of halogenation of ketones a jet‐zone loop reactor (JZR) is used, which leads to an enormous increase in yield and selectivity compared to stirred vessels (Kutschera et al., 2008 ). This JZR is a special jet loop reactor with high specific mass transfer performance and good macromixing behaviour. It is obvious that there is direct relation between the reaction and the hydrodynamics in the reactor. Despite several aspects of hydrodynamics in jet loop reactors have been investigated, the essential flow characteristics behind a two‐component jet are not sufficiently understood. In these investigations, the flow field in the jet zone of the JZR was analysed by 2D particle image velocimetry (PIV) and the kinetic energy dissipation rate ε was determined from the spatial gradients of the fluctuating velocity.