Exact universal uniqueness criteria for the adiabatic tubular packed bed reactor

Exact, universal a priori bounds and regions of multiplicity for the entire tubular packed bed reactor are developed by application of a technique reported in Chang and Calo, Chem. Engng Sci. 1979 34 285 to a cascade two-phase cell model for an nth order chemical reaction with interphase resistance to mass and heat transport, Le ≠ 1 (or Le = 1) and either lumped parameter catalyst particles or with intraparticle concentration gradients with uniform temperature. Both the more common case of interphase heat transfer greater than interphase mass transfer rate and the inverse case of particle over-temperature have been considered. In all cases it has been shown that the reactor conservation equations can be decoupled at certain points along the bed determined by the Lewis number, and that questions of multiplicity and uniqueness reduce to consideration of a single algebraic equation which is actually a form of the two-phase adiabatic CSTR. Also as for the CSTR, the topology of the adiabatic packed bed reactor is shown to be the simple cusp catastrophe. The application of the resultant criteria is quite simple and represents a practical step in the design procedure for highly exothermic reactions in packed beds. A flow chart of a suggested procedure is included.     

Application of chitosan‐entrapped β‐galactosidase in a packed‐bed reactor system

The model enzyme β‐galactosidase was entrapped in chitosan gel beads and tested for hydrolytic activity and its potential for application in a packed‐bed reactor. The chitosan beads had an enzyme entrapment efficiency of 59% and retained 56% of the enzyme activity of the free enzyme. The Michaelis constant (K_m) was 0.0086 and 0.011 μmol/mL for the free and immobilized enzymes, respectively. The maximum velocity of the reaction (V_max) was 285.7 and 55.25 μmol mL^?1 min^?1 for the free and immobilized enzymes, respectively. In pH stability tests, the immobilized enzyme exhibited a greater range of pH stability and shifted to include a more acidic pH optimum, compared to that of the free enzyme. A 2.54 × 16.51‐cm tubular reactor was constructed to hold 300 mL of chitosan‐immobilized enzyme. A full‐factorial test design was implemented to test the effect of substrate flow (20 and 100 mL/min), concentration (0.0015 and 0.003M), and repeated use of the test bed on efficiency of the system. Parameters were analyzed using repeated‐measures analysis of variance. Flow (p < 0.05) and concentration (p < 0.05) significantly affected substrate conversion, as did the interaction progressing from Run 1 to Run 2 on a bed (p < 0.05). Reactor stability tests indicated that the packed‐bed reactor continued to convert substrate for more than 12 h with a minimal reduction in conversion efficiency. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1294–1299, 2004     

Comparative Study of Sterol Ester Synthesis using <Emphasis Type="Italic">Thermomyces Lanuginosus</Emphasis> Lipase in Stirred Tank and Packed-Bed Bioreactors

A comparative study was done on the production of different sterol esters using a stirred tank batch reactor (STBR) and packed bed reactor (PBR) using Thermomyces lanuginosus (Lipozyme TLIM) enzyme, a commercially immobilized lipase. Different oils were used as the sources of particular fatty acids, e.g., fish oil for n-3 polyunsaturated fatty acids (n-3 PUFA), linseed oil for alpha linolenic acid (ALnA) and mustard oil for erucic acid. Reaction parameters, such as substrate molar ratio, reaction temperature and enzyme concentration, were standardized in the STBR and maintained in the PBR. To provide equal time of residence between the substrate and enzyme in both the reactors for the same amount of substrates, the substrate flow rate in the PBR was maintained at 0.27 ml/min. Thin layer chromatography was used to monitor the reaction, and column chromatography was used to determine the product yields. Fatty acid compositions of the esters were determined by gas chromatography. The study showed that the packed bed bioreactor was more efficient than the batch reactor in sterol-ester synthesis with less migration of acyl groups.     

Modeling and stability of catalytic fixed bed reactors

The existence of a multiple or oscillatory condition in a packed bed reactor, with a strongly exothermic reaction, is reviewed. The following cases are discussed: simultaneous heat and mass transfer within and outside a catalyst particle, axial mixing in tubular reactors and a recycle reactor. It is shown that the condition describing multiplicity can be estimated solely on the basis of the CSTR analysis. A correspondence between stability and parametric sensitivity is presented.     

连续多级串联完全混合槽中固体颗粒反应产率计算方法

本文针对级内颗粒完全混合一级间无颗粒返混的多级反应器,探讨了按停留时间分布计算固体颗粒反应率的方法。首先分析了用δ（0）函数示踪法与多元独立随机变量和的分布密度函数法求颗粒停留时间分布的特点;应用后一种方法推得了计算颗粒反应产率的一般公式。从固体颗粒固相反应物浓度分布密度函数也可以推得此公式。在此基础上对一类特殊的反应速度方程,解析求出了直接计算任何一级反应产率的通式;对求解计算通式困难的反应速度方程,论证了两种逐级计算方法:以反应时间作计算参量及以颗粒固相反应物浓度作计算参量。     

工业聚合反应装置 Ⅳ．乳液聚合反应器（上）

比较了乳液聚合用间歇聚合釜和连续搅拌釜式反应器操作中的反应工程特性，并根据这些特性介绍了间歇式和连续式乳液聚合反应器，除釜式外还有环管式和脉冲填料塔等新型反应器，同时还相应讨论了乳液聚合过程反应热的撤除以及传热设备。     

Numerical investigation and experimental validation of the performance of a tubular packed bed reactor for hydrogenation of diene‐based polymers

A process which comprised a tubular reactor (that can be packed with different internal structures) has been modeled and theoretically analyzed for conducting the hydrogenation of nitrile butadiene rubber (NBR). The dynamics of the tubular reactor and the intrinsic hydrogenation kinetics are coupled, and detailed numerical simulations are performed under isothermal and isobaric conditions. The proposed model thus obtained involves coupled, nonlinear, partial differential equations (distributed parameter system). The effect of different reactor design parameters such as Peclet number, carbon–carbon double bond loading, mass transfer to reaction resistance, and solubility of hydrogen with respect to hydrogenation of the NBR has been investigated numerically. The conversions predicted using the proposed model for tubular packed bed reactor are compared with those possible in conventional plug flow reactor and continuous stirred tank reactor models. The optimal parameters and operating conditions for efficient production of hydrogenated NBR are suggested. Finally, the validity of the proposed model is confirmed by comparing the predicted and the experimental degree of hydrogenation obtained in a tubular reactor packed with Intalox saddles. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

二氧化硫强制动态氧化过程的模型化(Ⅱ)——模型模拟与参数分析

建立了充填国产S101钒催化剂的、单段流向变换周期操作固定床反应器的非均相动态模型。藉助模型所做的数值分析,证实了低浓度SO_2自热氧化的可行性,研究了参数对反应器性能的影响,证明存在着适宜的气速。计算结果还表明,转化率等性能指标对原料气浓度、流量的变化较敏感,对于气源浓度、流量可能大幅度变化的情况,在设计时必需采取相应的措施。     

Reactant dynamics in catalytic fluidized bed reactors with flow reversal of gas in the emulsion phaset

In the present study both the steady-state and transient behavior of reactant gas in a bubbling fluidized bed reactor are analytically investigated with the occurrence of flow reversal of emulsion phase gas. The model developed contains no adjustable constants and no major two-phase theory assumptions. In addition, the concept of local flow reversal of emulsion phase gas and emulsion phase de-gassing coefficients are introduced. The transient behavior of reactant gas as a function of the extent of flow reversal of gas, rate constant and reaction order, and operating superficial gas velocity is discussed. Finally, model predictions are shown to compare favorably to various reported experimental results including the division of gas flow analysis, steady-state axial concentration profiles, overall conversions, and cumulative residence time distributions.     

Determination of process parameters and modelling of lipase-catalyzed transesterification in a fixed bed reactor

Chemical transesterification is of major importance to the edible oil industry. While alkali catalysts randomize all the fatty acids in a triglyceride mixture, the use of a 1,3 specific lipase causes a more selective exchange of fatty acid residues. Basic process parameters for the development of a continuous solvent-free process in a fixed bed reactor have been determined. The kinetics of the transesterfication reaction and the influence of particle diameter, substrate and water concentration on the effective reaction rate were examined in batchwise experiments. Residence time distribution and parameters of inter- and intraparticle mass transfer were determined by modelling of experiments carried out in a fixed bed reactor under transient conditions. Fixed bed reactors with side stream analysis were used for continuous transesterification. A kinetic model was developed for the enzyme catalyzed reaction, thereby showing the analogy between heterogeneous catalytic and enzyme catalyzed reactions. A one-dimensional heterogeneous reactor model was formulated on the basis of the kinetic equation and different process parameters. For numerical calculations, an exponential enzyme distribution inside the carrier was assumed. The simulation of experimental results indicates that they are well described by the developed model. Water concentration and presence of other substances strongly influence the stability of the immobilized enzyme.     

A numerical study on the effects of acidic catalyst on the polymerization of nylon-6

The effects of acetic acid on the polymerization characteristics of nylon-6 are investigated in a reactor model that consists of a continuous flow stirred tank reactor (CSTR) and a tubular reactor connected in series. Mathematical models for the CSTR and the tubular reactor have been established and solved by numerical methods. In the CSTR, the monomer conversion and the molecular weights are increased as the feed acetic acid concentration is increased. In the tubular reactor, the acid acts as both a catalyst and a modifier for the polymerization reaction. The effects of the feed acetic acid content on the zeroth, first and second moments and the polydispersity index of the polymer have been discussed.     

管式填料床反应器内的湍流微观混合研究

采用碘化物-碘酸盐平行竞争反应体系研究了管式填料床反应器内的湍流微观混合.通过沿程取样分析来考察离集指数(Xs)沿反应器轴向位置的分布.实验结果表明,反应物在管式填料床反应器内的离集主要发生在反应物开始相遇的区域且随着流速的增加离集状况得到明显改善.在实验基础上,采用团聚(Incorporation)模型计算得到管式填料床反应器的微观混合时间tm在1×10-3s到4×10-3s之间,明显小于搅拌槽反应器内的微观混合时间.相对于搅拌槽反应器,管式填料床反应器更适合于快速反应.同时研究表明,丝网填料的加入能提高微观混合效率.     

A Novel Radial‐Flow,Spherical‐Bed Reactor Concept for Methanol Synthesis in the Presence of Catalyst Deactivation

A radial‐flow, spherical‐bed reactor concept for methanol synthesis in the presence of catalyst deactivation, has been proposed. This reactor configuration visualizes the concentration and temperature distribution inside a radial‐flow packed bed with a novel design for improving reactor performance with lower pressure drop. The dynamic simulation of spherical multi‐stage reactors has been studied in the presence of long‐term catalyst deactivation. Model equations were solved by the orthogonal collocation method. The performance of the spherical multi‐stage reactors was compared with a conventional single‐type tubular reactor. The results show that for this case study and with similar reactor specifications and operating conditions, the two‐stage spherical reactor is better than other alternatives such as single‐stage spherical, three‐stage spherical and conventional tubular reactors. By increasing the number of stages of a spherical reactor, one increases the quality of production and decreases the quantity of production.     

Study of unsteady-state catalytic oxidation of sulfur dioxide by periodic flow reversal

A systematic study of catalytic oxidation of sulfur dioxide in a fixed bed reactor operated in flow reversal mode was made. A heterogeneous transient model of the reactor was developed. The global rate equations and the heat transfer parameter correlation were obtained, based on a series of previous experiments. The experiments of unsteady-state oxidation of low concentration SO₂ were conducted in a bench-scale fixed bed reactor, packed with a domestic commercial catalyst. The model can successfully predict the transient concentration and temperature profiles when a correction factor is introduced to the global rate equations.     

Refolding of proteins in a CSTR

A model to predict refolding of proteins in a continuous stirred tank reactor (CSTR) was developed and compared to a batch refolding process with simple dilution of the protein in a stirred tank reactor. For experimental verification of the model a continuous refolding of a model protein (α-lactalbumin) was performed in a CSTR. The refolding process of denatured and fully reduced α-lactalbumin could be accurately predicted by a set of differential equations assuming a first order reaction rate for folding and a second order reaction rate for aggregation. The system composed of a CSTR with an additional diafiltration circuit for removal of denaturing agents from the feed solution and to maintain constant refolding conditions. Based on the folding kinetic the dynamic behavior of such a continuous refolding reactor was simulated under different operating conditions. It was shown that the refolding efficiency was higher compared to batch dilution under certain conditions, namely high residence times. The yield of refolded protein could further increased by recycling the outlet stream containing unfolded protein to the reactor entrance.     

共轭双烯聚合物选择性加氢反应器技术进展

对以橡胶、弹性体为代表的含共轭双烯聚合物进行烯属双键的选择性加氢,可显著提高聚合物的稳定性;加氢反应器和反应工艺是制约加氢度和产率的关键技术之一。该文综述了目前共轭双烯聚合物选择性加氢反应器的技术进展,包括以机械搅拌反应器、鼓泡反应器、外循环反应器为代表的全混流型反应器;以填料塔和静态混合管式反应器为代表的平推流型反应器;以及各种反应器的组合技术、特殊操作方式。结合加氢体系的流体力学特征和反应动力学特征,分析了制约加氢度和产率的关键问题,总结了进一步提高加氢度和产率、降低能耗物耗的潜在途径。     

Estimation of heating time in tubular supercritical water reactors

Reactor efficiency and product distribution in supercritical water (SCW) reactors is greatly influenced by the design of the heating section of these reactors. However, little experimental or theoretical work is available to estimate the rate of heat transfer in such systems. In the present study, CFD modeling of the heat transfer in tubular SCW reactors has been performed. Effects of various operating parameters; i.e. reactor temperature and pressure, flow rate, reactor diameter, and the external heating mechanism, on the heating time constant, the temperature profile along the reactor, and reactor residence time are investigated. Based on numerical simulations, a semi-theoretical model is proposed to estimate the heating time constant as a function of reactor operating conditions. Results of this study provide useful insights for designing continuous supercritical water reactors as well as for the analysis of experimental data obtained from such systems.     

酶解反应与膜分离耦合连续制备酪蛋白磷酸肽

采用酶解反应与膜分离耦合新工艺连续水解全酪蛋白制备酪蛋白磷酸肽(CPPs)。考察了超滤膜对胰蛋白酶及底物溶液的截留效果;研究了初始底物质量浓度、初始酶质量浓度、反应体积、膜渗透通量等参数对反应器性能和反应转化率的影响规律;利用高效凝胶排阻色谱系统(HPSEC)对酶解产物进行检测分析;建立了酶膜反应器连续水解动力学模型,并对间歇与连续酶解过程进行比较分析,证明反应-分离耦合技术可使酶解效率及蛋白酶利用率大幅提高,并使产物得到调控与富集,为CPPs的酶法制备提供了一种更为有效的方法。     

Revisiting the maximum conversion of substrate in an enzymatic cstr with micromixing considerations

The balance equations pertaining to an enzyme undergoing first order thermal deactivation and a substrate undergoing enzyme-catalyzed transformation following Michaelis-Menten kinetics in a CSTR are solved for the two limits of micromixing. The maximum conversions of substrate are obtained under the assumption that the space time of the reactor is infinite. The range of the maximum conversion of substrate is wider at intermediate values for the dimensionless Michaelis-Menten constant and becomes narrower as the ratio of the time scales of the enzyme-catalyzed reaction and the enzyme deactivation increases.     

动态膜分离式酶反应器连续操作运行方式评价与研究

应用动态膜分离技术开发研制的新型多功能酶反应器,实现了在进行酶解反应过程中同时分离产物的耦联操作。在该反应器上完成了使用菊粉酶、糖化酶等单基质酶不同操作形式的水解实验,考察了不同操作方式下反应器内流体流动的特性,并分别导出了停留时间分布函数式,从而对连续酶解过程的不同运行方式进行了对比性评价研究。