流化催化裂化反应器的技术进展

介绍并讨论了近期开发的流化催化裂化反应器,包括两段串联反应器、双提升管反应器、下行式反应器、多段进料反应器以及新型提升管反应器端口结构技术。以新型反应器为核心技术的各种催化裂化新工艺可以有效地提高催化裂化反应的转化率和选择性,减少非理想产品产率,也可以改善产品质量,生产环境友好的清洁燃料油品。此外新型提升管反应器端口结构还可以抑制设备结焦,延长流化催化裂化(FCC)装置的开工周期。     

Theoretical analysis of reactant dosing concepts to perform parallel-series reactions

The possibility of enhancing selectivities and yields in networks of parallel and series reactions is investigated theoretically. Isothermal tubular reactors are considered where reactants can be introduced at the entrance and also over the wall. The latter way of dosing could be realised, e.g., in a membrane reactor where one or several reactants can be dosed through a porous reactor wall. Besides numerical solutions of the underlying mass balance equations of simplified reactor models, instructive analytical solutions were derived which are valid under certain constraints. Using these solutions an optimisation of the reactor performance could be performed. As objective function the molar fraction of a desired intermediate product at the reactor outlet was maximised. The impact of influencing via the dosing strategy applied the local composition (and thus the local reaction rates) and the component residence time distributions is elucidated.     

Nonisothermal design of fluid segments for precise temperature control in microreactors

The present paper discusses the effects of the fluid segment size on reaction temperature as well as mixing performance in microreactors under nonisothermal conditions. In the reactors, exothermic parallel-series reaction systems having different ratio of activation energy proceeds with the cooling through walls of a fixed temperature. Reactant fluids are fed in the form of fluid segments. The width of fluid segment determines the diffusive mixing rate, and the height of fluid segment affects the cooling rate of reactant fluids. When the activation energy of the reaction producing the desired product is higher than that of the by-product, an optimum height to maximize the yield of the desired product exists with a fixed fluid segment width. This result indicates that the fluid segment size can be determined from the mixing rate and cooling rate. From the results on the reactor where reactants are mixed from the reactor inlet, even in a channel the scale of which is in the sub-millimeter range, suppressing hot spot is difficult when mixing and reaction are rapid and heats of reactions are large. For such reaction systems, mixing based on fluid segments is effective for controlling mixing and reaction rate.     

Hydrodeoxygenation of HMF over Pt/C in a continuous flow reactor

The three‐phase hydrodeoxygenation reaction of 5‐hydroxymethylfurfural (HMF) with H₂ was studied over a 10 wt % Pt/C catalyst using both batch and flow reactors, with ethanol, 1‐propanol, and toluene solvents. The reaction is shown to be sequential, with HMF reacting first to furfuryl ethers and other partially hydrogenated products. These intermediate products then form dimethyl furan (DMF), which in turn reacts further to undesired products. Furfuryl ethers were found to react to DMF much faster than HMF, explaining the higher reactivity of HMF when alcohol solvents were used. With the optimal residence time, it was possible to achieve yields approaching 70% in the flow reactor with the Pt/C catalyst. Much higher selectivities and yields were obtained in the flow reactor than in the batch reactor because side products are formed sequentially, rather than in parallel, demonstrating the importance of choosing the correct type of reactor in catalyst screening. © 2014 American Institute of Chemical Engineers AIChE J, 61: 590–597, 2015     

固定床催化反应器中平行反应的飞温现象Ⅰ冷却介质温度恒定

对在固定床催化反应器中冷却介质温度恒定时平行反应的飞温现象做了详尽的理论分析，推导出该系统安全操作所允许的温度上限和临界初始条件。研究结果表明简单反应的飞温理论适用于平行反应，在相同条件下平行反应和简单反应飞温区域之间的差异与主副反应的反应速率和热效应大小有关。对于平行反应系统，判断副反应的取舍，不应只从副反应速率本身的大小来考虑，还应该考虑副反应的热效应。     

微通道中环己酮氧化合成ε-己内酯的连续流工艺

在微通道反应器中,由H2O2、乙酸酐反应连续合成过氧乙酸氧化剂,再与环己酮经Baeyer-Villiger氧化连续合成ε-己内酯。先后考察了过氧乙酸氧化剂合成中乙酸酐与H2O2摩尔比、反应温度、停留时间等因素的影响,环己酮氧化反应中原料摩尔配比、反应温度、停留时间等因素对ε-己内酯合成的影响,优化了工艺条件。结果表明,当n(乙酸酐)∶n(H2O2)=1.2∶1、反应温度为70℃、停留时间为115s时,H2O2转化率达88.9%,过氧乙酸收率达86.7%;当n(过氧乙酸)∶n(环己酮)=1.1∶1、反应温度为90℃、停留时间为90s时,环己酮转化率达96.2%,ε-己内酯的收率达80.9%。与传统间歇釜式反应工艺相比,微通道反应工艺提高了ε-己内酯的收率和选择性,缩短了反应时间,减少了原料消耗,实现了连续化操作,提高了生产安全性。     

Performance Enhancement by Unsteady‐State Reactor Operation: Theoretical Analysis for Two‐Sites Kinetic Model

Theoretical analysis of the reactor performance under unsteady‐state conditions was carried out. The reactions are described by two kinetic models, which involve the participation in catalytic reaction of two types of active sites. The kinetic model I assumes the blocking of one of the active sites by a reactant, and the kinetic model II suggests a transformation of active sites of one type into another under the influence of the reaction temperature. The unsteady‐state conditions on the catalyst surface are supposed to be created (i) by forced oscillations of temperature and concentration in the reactor inlet (periodic operation of reactor) and (ii) by catalyst circulation between two reactors in a dual‐reactor system (spatial regulation). The influence of various parameters like concentration of reactant, cycle split, length of period of forced oscillations, temperatures and the ratio of catalyst volumes in the dual‐reactor was investigated with respect to the yield of the desired product. It is shown that for both cases of unsteady‐state conditions (periodic reactor operation as well as in a dual‐reactor system), a mean reaction rate predicted by the kinetic model I was up to two times higher than the steady‐state value. The kinetic model II shows a 20 % increase of the selectivity towards the desired product.     

Selective Oxidation of Hydrocarbons on Composite Oxides

A catalyst for the selective oxidation of hydrocarbons to unsaturated aldehydes, acids, acid anhydrides, divinyls, or styrenes has to perform several functions. First, it must supply a limited amount of oxygen to the reactant, sufficient to allow the formation of the desired product but not enough to allow complete oxidation. Further, it must provide appropriate sites for the adsorption of the hydrocarbons in deformed, reactive states. Last, the catalyst should be capable of transferring electrons from and to the reactants. These three demanding characteristics of an active catalyst impose severe limitations on the systems that can effectively perform selective oxidation reactions. Therefore catalyst selectivity, normally measured by the rate of formation of the specific product relative to that of undesired products, is sensitive to reaction conditions (temperature, feed rate, feed composition, and reactor design) and is very dependent on the details of the structure of the catalyst itself, its carriers, and promoters.     

Reactive mass transfer at gas-liquid interfaces: impact of micro-scale fluid dynamics on yield and selectivity of liquid-phase cyclohexane oxidation

The impact of single-bubble wake dynamics on the reaction-enhanced mass transfer and on the yield and selectivity of the cyclohexane oxidation reaction was studied using a two-dimensional CFD-reaction model that was developed by our group. Temperature and the concentrations of the (desired) intermediate and (undesired) final products of this autocatalytic reaction were the parameters of this study. Two bubble types were studied: (a) a circular bubble with closed wake, and (b) an elliptical bubble with an unsteady, vortex-shedding wake. The main results of our work are: (1) Film theory over-predicts reaction-enhanced mass transfer since the assumption of an average film thickness is not justified. In order to study fast reaction systems on a reactor scale using coarse-grid CFD codes, a full bubble model, or correlations based on it, should be incorporated as a sub-grid micro model. (2) The bubble wake does not contribute to mass transfer in systems where reaction rates are low. For fast reactions, the local mass transfer rate in the wake can increase by several thousand percent. (3) Vortex shedding causes qualitatively different mixing since patches rich in the dissolved gas are quickly convected away from the bubble. Bubbles that cause vortex shedding will lead to a significantly higher conversion per volume than spherical bubbles. (4) Parallel-consecutive reactions with a high liquid-phase reactant concentration and with reaction rates that depend in an identical way on the dissolved gas concentration, are not micro-mixing sensitive in terms of selectivity. Since bubble shapes and sizes can be controlled by changing operating and design parameters, the yield of this reaction can be controlled.     

Economic trade-offs in acrylic acid reactor design

The acrylic acid process using air oxidation of propylene presents many interesting design trade-offs, particularly in the design of the reactor. The desired and undesired reactions are highly exothermic and very temperature dependent (large activation energies), so a large flowrate of inert water is also fed to the reactor to act as a thermal sink. Propylene conversion increases with temperature and reactor size, but acrylic acid yield decreases with increasing temperature. The heat of reaction is removed by generaing steam, and the steam pressure is an important design optimization variable since it sets low limits on reactor temperature. Using low-pressure steam gives high acrylic acid yield and lower carbon dioxide generation but requires large reactors. Larger air flowrates increase reactor oxygen concentrations, which reduce reactor volume but increase air compression costs.This paper explores the effects of the many design trade-offs on capital investment, energy cost and product selectivity.     

Kinetic-transport models and the design of catalysts and reactors for the oxidative coupling of methane

The design of catalytic pellets and reactors using detailed kinetic-transport models is illustrated for the oxidative coupling of methane to form ethane and ethylene. Oxygen sieving within diffusion-limited pellets and staged oxygen injection reactors increase C₂ selectivity by inhibiting full oxidation homogeneous pathways that lead to CO and CO₂ products. Our simulations suggest that high densities of surface sites with kinetics that depend weakly on oxygen concentration are required to benefit from oxygen-sieving catalyst and reactor schemes. These sites favor beneficial surface activation processes even at the low oxygen concentrations present within staged injection reactors and diffusion-limited pellets. Controlled introduction of stoichiometric oxygen reactants leads to C₂ yields as high as 50%; the reactions, however, occur at much slower rates and require much greater reactor volumes than in conventional cofeed reactors.     

Casson流体层流反应器中连串反应的产品分布

引　言目前化工流体力学涉及的范围已由传统的牛顿流体发展到非牛顿流体 .常见的非牛顿流体包括幂律流体、Bingham流体和Casson流体 .有许多高聚物反应物系和生化反应物系属于非牛顿流体 .特别是某些生化反应系统 ,所处理的物系常由各种天然物质组成 ,因而表现出典型的非牛顿流     

Understanding and optimization of chemical reactor performance for bimodal reaction sequences

The relative contributions of heterogeneously catalyzed and homogeneous bulk phase reactions in bimodal reaction sequences have been assessed via 1D reactor simulations. Starting from a reaction network only comprising two parallel, irreversible heterogeneously catalyzed and homogeneous bulk phase steps, complementary consecutive steps were included with the option of being reversible. The final product formed after a minimum number of homogeneous bulk phase reactions is obtained with high yields in continuous flow fixed bed reactors. The products obtained after a higher number of homogeneous bulk phase reactions generally dominate in slurry reactors. Yields of the latter may exhibit an optimum as a function of the catalyst amount in the reactor. The adsorption enthalpies of the intermediates in the reaction network critically determine the position and shape of this maximum. The reversibility of the homogeneous bulk phase steps provides specific opportunities to tune the product yields in bimodal reaction sequences. © 2016 American Institute of Chemical Engineers AIChE J, 63: 111–119, 2017     

Selective Oxidation of Hydrocarbons on Composite Oxides

Abstract

A catalyst for the selective oxidation of hydrocarbons to unsaturated aldehydes, acids, acid anhydrides, divinyls, or styrenes has to perform several functions. First, it must supply a limited amount of oxygen to the reactant, sufficient to allow the formation of the desired product but not enough to allow complete oxidation. Further, it must provide appropriate sites for the adsorption of the hydrocarbons in deformed, reactive states. Last, the catalyst should be capable of transferring electrons from and to the reactants. These three demanding characteristics of an active catalyst impose severe limitations on the systems that can effectively perform selective oxidation reactions. Therefore catalyst selectivity, normally measured by the rate of formation of the specific product relative to that of undesired products, is sensitive to reaction conditions (temperature, feed rate, feed composition, and reactor design) and is very dependent on the details of the structure of the catalyst itself, its carriers, and promoters.     

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...     

PERIODIC OPERATION OF ISOTHERMAL PLUG-FLOW REACTORS FOR AUTOCATALYTIC REACTIONS

The performance of isothermal plug-flow tubular reactors under periodic inlet concentration is theoretically analyzed for improvement in yield for liquid phase, homogeneous, autocatalytic reactions of both quadratic and cubic forms. The system of two hyperbolic partial differential equations describing the reactor is solved by the topological method suggested by Bailey (1977). The negligible yield of product obtained at steady-state operation is enhanced to 100 percent yield under periodic operation. The performance of the periodically forced reactor with autocatalytic reactions is compared with that of ordinary simple reactions. The improvement in the yield is much more (at least five times) than that of ordinary simple reactions. The effect of decay of autocatalyst to stable product and the effect of reversibility of reactions on the performance of the periodically forced reactor are evaluated. For irreversible reaction with decay, the yield shows a resonance with inlet pulse width. This is due to complete conversion of the reactant and further only the decay of the autocatalyst.     

RESIDENCE TIME DISTRIBUTION IN AN OPEN REACTOR:EFFECT OF BACKGROUND REACTANT ON TRACER DISPERSION

A new approach is presented for deriving the residence time distribution(RTD)in open-type reactors with exclusion of residence in the fore section.Inasmuch as failure to predict the con-version of chemical reactions has been evidenced in many occasions,numerical solution of tracerdispersion in the presence of background concentration gradient of reactant is given to demonstratethe strong effect of background reactant on the true RTD a reactant molecule experiences.Withinthe error of computation,the conversion of a first-order chemical reaction under steady state is shownto be equal in both closed and open reactors,despite difference in relevant RTDs     

Performance of a cascade of imperfectly mixed reactors for simple isothermal and exothermic reactions ag

The behaviour of the model of imperfectly mixed reactors in series has been studied for simple isothermal and exothermic reactions. The effect of the three parameters p, m and n and that of some kinetic parameters on the performance of the cascade of reactors is presented.In the case of isothermal reactions, the study involved both unsteady and steady-state operating conditions. For the latter condition, the cascade of reactors always gave an inferior performance, for a given reaction, when compared to that of an ideal tubular reactor.For exothermic reactions, the accent was placed on steady-state adiabatic conditions. At a residence time below a certain value, the conversion obtained in the model is higher than that achieved in a tubular reactor.Optimization of reactor performance is also discussed; it is shown that the same general condition for optimizing MT reactors applies to the optimum design of imperfect CSTR's with feed-channeling, either when maximizing the conversion for a given residence time or when minimizing the residence time for a given conversion.     

Membrane Reactor/Separator: A Design for Bimolecular Reactant Addition

Abstract

A membrane reactor (MBR) is used to investigate the effect of selective reactant addition on series-parallel reaction networks, such as the oxidative dehydrogenation of ethane to ethylene. Ethylene is favored in an oxygen-lean environment, while excess oxygen favors the formation of combustion products. Control of the reactant ratio (ethane to oxygen) is crucial to both the overall selectivity and the hydrocarbon conversion. Traditional reactor designs co-feed the bimolecular reactants at the top of the reactor at some preset feed ratio. The MBR uses a tube (porous alumina membrane) and shell configuration. One reactant is fed at the top of a catalyst bed packed within the membrane core. The other reactant permeates into the tube along the length of the reactor via an imposed pressure drop. The reactant ratio is large at the top of the MBR, which leads to high selectivities; as the oxygen is consumed, it is replenished via downstream permeation to improve the ethane conversion. The MBR and a plug flow reactor (PFR) are evaluated at 600 [ddot]C, with identical space velocities, and using a magnesium oxide catalyst doped with samarium oxide. At low to moderate reactant feed ratios, the ethylene yield in the MBR exceeds the PFR by a factor of three, under some conditions. At higher feed ratios, the performance of the PFR nears or exceeds the performance of the MBR.