Bubble-size distributions and interfacial areas in a jetloop reactor for multiphase catalysis

Jetloop reactors show specific properties, such as intensive mixing and effective gas dispersion, which make them an interesting alternative for conventional reactor concepts in homogeneous multiphase catalysis. This contribution investigates the effect of specific power input and common additives in multiphase catalysis on bubble-size distributions in the draft tube and riser section of a miniplant-scale jetloop reactor and elucidates the coalescence during circulation. Finally interfacial areas are calculated and compared to standard reactors.     

THE DEVELOPMENT OF HIGH INTENSITY GAS-LIQUID JET REACTORS

A novel type of gas-liquid contactor was researched and developed to enhance phase mixing. These high velocity impinging stream reactors are characterised by small reactor volumes supplied with nozzles, which are directed towards each other. The gas and liquid feed streams are jetted through the nozzles into the reactor volume, resulting in a highly turbulent mixture of the phases. Under these enhanced mixing conditions, mass transfer rates are increased dramatically. A mechanism for bubble formation and breakup in gas —liquid jet reactors. operated in the bubble mode, is proposed and a design philosophy of such reactors is also formulated.     

Reactors for hydrogenation of edible oils

Due to the characteristics of the hydrogenation of edible oil, by far the most common type of reactor has been the batch-type shurry hardener. Although continuous reactors offer several advantages compared to batch reactors, they are seldom used in the industry. This review paper describes the most commonly used full-scale reactors, both batch and continuous. Several different laboratory reactors are also described. The experimental results obtained from those reactors indicate that it is possible to achieve selectivites and reaction rates in a continuous reactor as high as in a slurry batch reactor.     

CHALLENGES AND INNOVATIONS IN REACTION ENGINEERING

The importance of reaction engineering in generating a myriad of products on which developed societies depend is outlined. The challenges of a political, economic, and technical nature that need to be addressed in rendering conversion of raw materials into desired products that are more environmentally friendly and sustainable are briefly discussed. It is shown that multiphase reactors are prevalent in all applications, and improvements in the reactor material and energy efficiencies lead to more environmentally benign processes. This requires, in addition to the selection of green process chemistry, systematic implementation of the multi-scale reaction engineering methodology to accomplish proper reactor type selection and scaleup for commercial applications. It is also illustrated that recent innovations in multiphase reaction engineering basically utilize two key concepts: process intensification (e.g., enhancement in mass and heat transfer rates) and simultaneous reaction and separation. Examples of these are discussed, such as micro-reactors, reactive distillation, etc. It is also shown that commercialization of bench-scale discoveries requires either scaleup in parallel or vertical scaleup. New tools for visualization of opaque multiphase flows and development of appropriate rational phenomenological multiphase reactor models for scaleup and design are also briefly discussed.     

Optimal temperature profiles for tubular reactors implemented through a flow reversal strategy

Optimal steady-state reactor temperature profiles in classic jacketed tubular reactors often exhibit a (nearly) trapezoidal shape along the reactor, i.e., in a first part the temperature is raised, then a constant temperature interval follows, and (possibly) the temperature is lowered towards the outlet. The practical realisation of these optimal reactor temperature profiles is, however, complex because of the spatially varying jacket fluid temperature profile that is required for the constant reactor temperature part. Since similar trapezoidal temperature profiles are encountered in reverse flow configurations, this reactor type may be an alternative to implement the optimal profiles in practice. This article conceptually proves the feasibility of this concept and provides an optimisation procedure for its design and operation.     

A novel approach to the design and operation scheduling of heterogeneous catalytic reactors

A number of studies have been conducted to reduce the overall level of catalyst deactivation in heterogeneous catalytic reactors, and improve the performance of reactors, such as yield, conversion or selectivity. The methodology generally includes optimization of the following: (1) operating conditions of the reaction system, such as feed temperature, normal operating temperature, pressure, and composition of feed streams; (2) reactor design parameters, such as dimension of the reactor, side stream distribution along the axis of the reactor beds, the mixing ratio of inert catalyst at each bed; and (3) catalyst design parameters, such as the pore size distribution across the pellet, active material distribution, size and shape of the catalyst, etc. Few studies have examined optimization of the overall catalyst reactor performance throughout the catalyst lifetime, considering catalyst deactivation. Furthermore, little attention has been given to the impact of various configurations of reactor networks and scheduling of the reactor operation (i.e., online and offline-regeneration) on the overall reactor performance throughout the catalyst lifetime. Therefore, we developed a range of feasible sequences of reactors and scheduling of reactors for operation and regeneration, and compared the overall reactor performance of multiple cases. Furthermore, a superstructure of reactor networks was developed and optimized to determine the optimum reactor network that shows the maximum overall reactor performance. The operating schedule of each reactor in the network was considered further. Lastly, the methodology was illustrated using a case study of the MTO (methanol to olefin) process.     

BATCH AND SEMIBATCH REACTORS MODELLING AND VALIDATION BASED ON ON-LINE pH MEASUREMENT

Based on on-line pH measurement, a comparative study between batch and semibalch reactors performance has been carried out in a glass-jacketed reactor of 51 provided with the measuring, data acquiring and controlling system. The reaction system chosen was an acid-base reaction, the concentrations of the species in the reactor were obtained simply by measuring the pH of reaction solution. Based on the conductivity profiles of the solution at different temperatures, the kinetic equation of this acid-base reaction was established. The thermal behaviors of batch reactor were investigated by heating and cooling water in the reactor. The dynamic behavior of batch reaction could be described by a set of differential equations resulting from the mass and energy balance of the reaction mixture, the energy balance of the jacket wall and the circulating fluid inside the jacket. This model has been validated with experimental results, and could be applied to the complex control situations.     

A review on computational fluid dynamic simulation for rotating packed beds

A rotating packed bed (RPB) is one of the cutting-edge process intensification technologies due to its high mass transfer and mixing efficiency. Nevertheless, owing to the complex structure and hydrodynamic characteristics of RPBs, valuable data inside the reactor is hard to obtain by conventional experimental methods. Computational fluid dynamics (CFD) owing to its unique advantages of low cost, completeness of data and ability to simulate real and ideal conditions, has been adopted by many researchers to carry out fundamental research and practical application of RPBs in recent years. This paper therefore elaborates on the research progress on CFD simulation of RPBs. The building of a physical model of these reactors as well as selection of mathematical models are described, then applicability and accuracy of these models are compared and discussed. Simulation results for gas and multiphase flow in reactors are also presented. Additionally, the application of CFD to mixing and mass transfer between phases and processes in rotating packed beds is introduced. Optimum designs of reactors by the CFD method are also described. Finally, problems remaining with CFD simulation of rotating packed beds and future development directions are discussed. © 2018 Society of Chemical Industry     

多相搅拌槽内宏观混合研究进展

多相搅拌槽反应器广泛应用于化工、冶金等过程工业中,而多相混合状态对于多相搅拌槽反应器的设计、优化和放大具有重要意义.混合时间是表征其宏观混合过程的一个重要参数.文中从实验和数值模拟二方面对多相搅拌槽反应器的液相混合时间研究进行综述,对气液、液固、液液、气液固4种体系的多相搅拌槽进行了分类总结,讨论了分散相、桨型、转速、...     

下行床内提高颗粒浓度及改善颗粒分布研究进展

重质油高效转化和优化利用是国民经济发展的重大需求,具有十分重要的现实意义和战略意义。提升管催化裂化一直是重油轻质化的重要手段,但提升管的不均匀环核结构及气固返混特性降低了重油转化率和产品选择性。相对于提升管,下行床具有近平推流流型及气固短停留时间的优点,处理重油具有潜在优势。但下行床内颗粒浓度过低且气固初始接触较差限制其推广及应用。本文综述了提高下行床颗粒浓度及改善颗粒初始分布的相关文章,指出了深入研究下行床的颗粒增浓机制及气固初始混合可以丰富下行床的基础研究并推动其工业应用。     

Development of a multi-scale simulation method for design of novel multiphase reactors

In this paper a multi-scale simulation method for modelling dispersions in a novel multiphase reactor is presented. This novel reactor is a continuous reactor which consists of repeated identical small mixing elements. The reactor is excellent for studying the effect of turbulence on drop size distributions since turbulence is continuously produced and dissipated along the reactor. Furthermore the energy dissipation within each element is very homogeneous. In addition it allows optical access at all positions along the reactor.Simulations were performed for a wide range of turbulence intensities for different dispersed phase hold-up. Each simulation was validated with measurements of the size distribution along the reactor. Good quantitative agreement was obtained at low hold-up in terms of prediction of the breakage rates and prediction of the size distributions. At higher hold-up the model gave reasonable predictions at low turbulence intensity however too large drops were predicted at high turbulence intensity. This can be a result of turbulence modulation and shows that reliable turbulence models for multiphase flows are necessary in this simulation method. The results show that physical models describing breakup and coalescence combined with CFD provide a good tool for efficient development and optimisation of novel multiphase reactors.     

The hydrogenation of isophorone to trimethyl cyclohexanone using the downflow single capillary reactor

Despite many innovations in the intensification of catalytic multiphase reactors for the small and medium scale manufacture of chemicals, there have as yet been relatively few commercial successes. One reason for this might be that many of these developments inherently incorporate a fixed catalyst, which may not suit an industry that is based on principles of batch manufacture and multi-product plant. This study evaluates an intensified reactor that encompasses the opportunities demonstrated from structured flows and thin channels, together with a mobile, slurry catalyst, namely a capillary reactor with gas/liquid/suspended catalyst flow. A downflow single capillary reactor (SCR) was designed, built and evaluated for the selective hydrogenation of isophorone to trimethyl cyclohexanone using commercial Pd- and Rh-based catalysts. Using the single capillary arrangement, the reaction was shown to be operating under kinetic control.

Comparison of the rate of hydrogenation with autoclave showed a significant increase of the reaction rate when capillary reactor was used. The temperature of reaction is a crucial factor in tuning the reaction towards different products. The constant relative reaction rate obtained for different catalyst loading as well as the calculated value of the apparent activation energy show that the reaction of hydrogenation of isophorone is not mass transfer limited in the single capillary reactor.     

Optimal operation policies in batch reactors

Optimal operation policies in batch reactors are obtained using dynamic optimisation technique. Two different types of optimisation problems, namely, maximum conversion and minimum time problems are formulated and solved and optimal operation policies in terms of reactor temperature or coolant flow rate are obtained. A path constraint on the reactor temperature is imposed for safe reactor operation and an endpoint constraint on undesired waste production (by-product) is imposed to minimise environmental impact.Two different types of models are considered within the optimisation framework. The shortcut model allows determination of optimal reactor temperature profile to be used for detailed design of the reactor. The detailed model allows optimising operating conditions for an already designed batch reactors.     

A comparative study of residence time distribution and selectivity in a monolith CDC reactor and a trickle bed reactor

A comparative study of the performance of a trickle bed reactor (TBR) and a monolith cocurrent downflow contactor (CDC) reactor in terms of selectivity and residence time distribution was conducted for the hydrogenation of 2-butyne-1,4-diol (B). Selectivity (S) towards 2-butene-1,4-diol was investigated with the solvent 2-propanol and a 30% (v/v) 2-propanol/water mixture (M) in batch recycle mode. Liquid residence time distribution (RTD) curves were obtained for both reactors. Although both reactors presented almost identical hydrodynamic behaviour, i.e. RTD, significant differences regarding selectivity towards the alkene were observed in both solvents. The use of 2-propanol gave lower selectivities in both reactors, but even then the monolith reactor was superior. In the monolith CDC, the liquid RTD curve was also obtained at different radial positions. RTD profiles across the monolith showed that from the centre to the column wall there is possibly an increased retention of material and despite this, overall selectivity does not appear to be considerably depressed by the backmixing that the above result implies in 2-propanol/water where the selectivity was found to be 100% towards the intermediate (C).

Modelling of the monolith CDC reactor was also conducted to predict RTD. The models tested were tanks-in-series, piston exchange and piston dispersion exchange; from which, piston exchange model was found to best predict and fit the experimental data.     

喷射式气-液反应器的型式及应用

气体和液体以喷射形式进料 ,是喷射式气液反应器的显著特征 ;喷射式气液反应器是一种多相反应器 ,具有较好的传热、传质和混合特性。对喷射式气—液反应器的型式及应用作了概要介绍     

自由基聚合反应器中多尺度流场的模拟进展

自由基聚合过程中,由于混合、传递及聚合反应的相互作用使得反应器内部存在复杂的多尺度流场,例如宏观尺度的速度、浓度、温度分布,介观尺度的液滴粒径分布,微观尺度的聚合反应速率、聚合物分子量和多分散性指数分布。这些复杂的多尺度流场分布使得聚合反应器的模型化研究成为难题。本文较为系统地介绍了自由基聚合反应器中存在的多尺度现象;简述了微观尺度聚合物性质流场分布的模型化与模拟研究方法;从悬浮聚合和乳液聚合两个方面介绍了介观尺度液滴粒径分布的模拟研究进展;从非理想混合的角度阐述了宏观尺度多相流流场分布的研究进展。最后,本文分析了多尺度模型的耦合求解方法。本综述也有本文作者对这个领域的初步观点,可为聚合反应器的设计、优化和放大提供参考。     

Economic feasibility of silica and palladium composite membranes for industrial dehydrogenation reactions

This article addresses the economic feasibility of silica and palladium composite membranes for gaseous dehydrogenation reaction schemes. Unlike other methodologies addressed so far, this work presents the economic assessment of dehydrogenation reaction schemes using a conceptual design based simulation methodology for the comparative economic assessment of membrane reactors with conventional reactors. The suggested methodology is applied to two industrially prominent reaction schemes namely styrene (from ethylbenzene) and propylene (from propane) production using silica and palladium composite membrane reactors. Various sub-cases studied in this work include the influence of membrane area per reaction zone volume, reaction zone temperature, reaction and permeation zone pressure, membrane thickness and sweep gas flow rate on process economics. Based on this work, the propylene production scheme is evaluated to provide 60–70% excess profits using membrane reactors when compared with the conventional reactor based technology. However, the gross profit profiles for both conventional reactor and membrane reactor configurations have been found to be similar for styrene production case. For all cases, the cost contribution of membranes and other auxiliary equipment is estimated not to exceed 20% of the total costs. In addition, similar economic performance has been observed for both silica and palladium membranes. Based on these studies, it has been concluded that the industrial applicability of membrane reactors is economically suitable for those dehydrogenation reactions that enable significant conversion enhancement with respect to the conventional reactor technologies.     

MICROMIXING EFFECTS ON BARIUM SULFATE PRECIPITATION IN AN MSMPR REACTOR

The Effects of non-ideal and nonhomogeneous mixing on barium sulfate precipitation in an MSMPR reactor were observed experimentally and analyzed theoretically. To generate nonhomogeneous mixing the unmixed feed streams were fed to the reactor at the same location (joint feeding mode) or a plug flow reactor was connected to the MSMPR reactor. These nonhomogeneous mixing conditions resulted in significant reductions in particle size and increases in particle numbers. These non ideal mixing effects were dependent on the impeller speed, feed stream velocity and residence time in the connected plug flow reactor and are believed to result from elevated supersaturation levels in a premixing zone which are controlled by turbulent micromixing

To model the effect of nonhomogeneous mixing (premixing) in the MSM PR reactor a plug flow-stirred lank reactor series model was developed. The plug flow reactor represents the premixing region of the MSMPR reactor in which turbulent micromixing is important, and the stirred tank reactor describes the homogeneous mixing region of the MSMPR reactor where particle growth is important. The model predicts that the premixing effect is strongly dependent on micromixing of the feeds in the premixing region, and thus, as the turbulent mixing intensity in this region is increased, the particle size in the product suspension is reduced and the particle population is increased. These predictions of the model arc in good agreement with the experimental data. An interesting prediction of the model is that as the impeller speed increases, the precipitation of barium sulfate in an MSMPR reactor deviates increasingly from the precipitation in a perfectly mixed (ideal) reactor.     

Advancements in droplet reactor systems represent new opportunities in chemical reactor engineering: A perspective

Traditional chemical reactors, such as batch reactors, continuous reactors, and semi-batch reactors, have been extensively studied and frequently act as central components of modern chemical plants. Recently, various advances in reaction times, surface-to-volume ratios, required amounts of reagents, and throughput have led to new directions in the design of miniaturized chemical reactors. In this Perspective, we provide an overview of the progress from traditional to miniaturized chemical reactors by summarizing the characteristics and applications of different types of reactors. Furthermore, we compare classical chemical reactors and miniaturized droplet reactors to highlight advancements in the design of droplet reactor systems based on open functional surfaces. Finally, we provide an outlook on the research directions of miniaturized droplet reactors.