PERFORMANCE OF AN ANNULAR CATALYTIC THREE-PHASE REACTOR FOR A SECOND ORDER REACTION

A novel annular catalytic three-phase reactor is theoretically investigated for a second order hydrogenation reaction. The results indicate that the ratio of the gaseous reactant to the liquid reactant within the reaction zone of the annular reactor can be adjusted by changing the reactor dimensions and the concentration of the gaseous reactant in the feed. As a consequence, the annular reactor may have a significant advantage over the trickle-bed reactor with respect to the selectivities that may be achieved in the reactor.     

THE STRING OF CATALYST SPHERES AS A TOOL FOR HEAT AND MASS TRANSFER STUDY IN A THREE-PHASE SYSTEM

A single vertical string of catalyst spheres with liquid film flowing over their surfaces was employed to model a three phase system. Simultaneous heat and mass transfer characteristics within a porous catalyst pellet and across the laminar liquid film was analyzed in terms of different values of reaction and transport parameters. It is shown that the liquid film thickness after the first three pellets reduces less than 10% even though a highly exothermic reaction is taking place within the pellets. It was also found that the mixing in pendular rings plays an important role in heat transfer from the pellets surface.     

EXPERIMENTAL STUDY OF A COMPLEX CATALYTIC REACTION NETWORK IN A TRICKLE-BED REACTOR

In the present report a relatively complex reaction system including several side reactions to the desired main reaction has been studied in a trickle-bed reactor. In addition the experimental part—which showed very good reproducibility of the results—an attempt to a reasonable modelling of the reactor was tried. The starting point was the differential equation system describing the kinetics of the reactions as well as the corresponding kinetic parameters, which had been established earlier in a slurry-reactor. It was possible to demonstrate that the behaviour of a trickle-bed reactor can be simulated by a relatively simple approach containing the basic kinetic equations, the wetting efficiency of the catalyst particles and a one-dimensional, pseudohomogeneous reactor model, the cell model. The so calculated concentration curves of the different reactants and products fitted the experimental values very closely. For those reasons, and especially for the reasonable effort needed for very satisfactory modeling, the results and proceeding steps outlined here might be of particular interest for further applications of trickle-bed reactors.     

EFFECTS OF PARTICLE CHARACTERISTICS ON THE PERFORMANCE OF A FAST FLUIDIZED BED REACTOR

A heterogeneous model for the fast fluidized bed reactor which carries out a gas-solid non catalytic reaction is presented. The hydrodynamics of the fast fluidized bed is characterized by the model of Kwauk et al. (1985) which assumes the existence of two phases; a dense phase and a dilute pneumatic transport phase. For a given solid flowrate, the length of the reactor occupied by each phase depends on gas velocity, particle diameter and density and average voidage within the reactor. The gas-solid reaction is assumed to follow the shrinking core model. The solids are assumed to be completely backmixed in the dense phase and move in plug How in the dilute pneumatic transport phase. The gas phase is assumed to be in plug flow in both phases

For given gas and solid flowrates, the transition from the dense phase flow to the fast fluidized bed (containing two regions) as functions of particle size and density is determined using the model of Kwauk et al. (1985). The numerical solution of the governing mass balance equations show that for given solid and gas flowrates, (and average voidage) the gas phase conversion shows an unusual behavior with respect to particle diameter and density. Such behavior is resulted from the effects of particle diameter and density on the reactor volume occupied by each phase and the effect of particle diameter on the apparent reaction rate. The numerical results show that a fast fluidized bed gives the best conversion at large particle density and for the particle diameter which results the fast fluidized bed to be operated near the pure dense phase flow.     

A STUDY OF THE HIGH PRESSURE POLYETHYLENE TUBULAR REACTOR

As an example of the free radical polymerization reactor we have conducted a theoretical study of the high pressure polyethylene tubular reactor with cooling from the jacket. The plug flow model including the axial dispersion is considered with as well as without the steady state assumption for the active intermediates. We observe that the axial dispersion has negligible effect on the reactor performance and that the steady slate assumption is quite reasonable. The performance of the reactor is characterized by the exit monomer conversion, the peak temperature and the number and weight average degrees of polymerization, and the effects of various operating conditions are extensively investigated. Finally, an optimal temperature policy that would maximize the exit monomer conversion is determined by means of the Maximum Principle.     

STUDY ON THE PERFORMANCE OF VERTICAL TUBULAR LEACHING REACTOR

Hydrodynamics in vertical tubular leaching reactor was studied in this work. Based on the observation of particle saltation in curved and square return bends, the inclined return bend was developed and examined. For the narrow and wide size distribution particle system, the method for calculating the particle holdup in upflow and downflow tubes was derived on the basis of generalized fluidization equation. The model of unit pressure drop was given and examined by experiments.     

EFFECT OF PARTIAL WETTING ON TRICKLE-BED REACTOR PERFORMANCE

Analysis of trickle-bed reactor data is almost always done by assuming that the catalyst particles are completely covered by a liquid film. The effect on reactor performance from violations of this assumption is demonstrated. The hydrodesulfurization of benzothiophene was simulated with the feed consisting of 10%, by weight, benzothiophene and 90% decalin. The temperature and pressure were held constant at 630 K and 68 atm. The results show that the exit conversion is strongly affected by the wetting efficiency.     

EFFECT OF PARTIAL WETTING ON TRICKLE-BED REACTOR PERFORMANCE

Analysis of trickle-bed reactor data is almost always done by assuming that the catalyst particles are completely covered by a liquid film. The effect on reactor performance from violations of this assumption is demonstrated. The hydrodesulfurization of benzothiophene was simulated with the feed consisting of 10%, by weight, benzothiophene and 90% decalin. The temperature and pressure were held constant at 630?K and 68?atm. The results show that the exit conversion is strongly affected by the wetting efficiency.     

用催化精馏技术水解乙酸甲酯的实验研究

用填料催化反应精馏塔对乙酸甲酯的水解过程进行了系统的研究,测定了不同条件下的水解转化率数据及沿塔各组分的浓度分布。与传统的固定床反应器的极限转化率相比,其水解转化率有了大幅度的提高。对所测数据的分析表明,进料组成中是否含有甲醇不影响催化精馏水解过程。     

MASS TRANSFER WITH A FIRST ORDER CATALYTIC REACTION IN A THREE-PHASE SYSTEM. TRICKLE FLOW ANALYSIS IN A PERIODICALLY CURVED CATALYTIC SOLID

The present work analyzes the process of mass transfer with chemical reaction in a system formed by a periodically curved catalytic wall, which is wetted by a descending film. Through the film a limiting gaseous reactant is transferred from the stagnant gas phase to the catalyst where the chemical reaction takes place.

The film hydrodynamics is first solved with the unknown free surface through a regular perturbation technique, by expanding the resulting equations in terms of a small parameter: the ratio between the film average thickness and the wave length of the curved solid wall. Assuming that the system is isothermal and at steady state, the mass transfer of the gas is afterwards incorporated. A first order kinetics whose limiting reactant is in the gas phase occurs in the solid phase.

Once the model is established and solved, the influence of the dimensionless parameters upon the effectiveness factor and the solid-liquid Biot number is then studied; important effects are found by changing the solid surface curvature at constant flow rate and catalyst volume. Besides, changes in the flow rate, the Peclet number and the ratio between the solid average width and the film average thickness, show significant effects on the net mass transfer process.     

三相生物流化床反应器处理生活污水的特性研究

运用三相生物流化床工艺对生活污水进行处理,以活性炭作生物载体,采用快速排泥挂膜法启动试验,在反应器的运行过程中逐渐改变容积负荷、进口浓度,水力停留时间、空气流量,考察这四种因素对COD及NH3-N去除率的影响.结果表明,当系统运行到第20天的时候COD及NH3-N去除率已经达到了一个较高水平,并趋于稳定,表明系统启动成功.在后30天COD去除率保持在80%以上,NH3-N去除率保持在60%以上,这说明此工艺对COD及NH3-N的去除效果较好.     

EXPERIMENTAL DETERMINATION AND MODELLING OF LIQUID-SOLID MASS TRANSFER COEFFICIENTS IN A THREE-PHASE REACTOR

Apparent mass transfer coefficients for solid dissolution in a liquid with and without a chemical reaction were experimentally determined in a fixed bed three phases reactor with downward cocurrent gas and liquid flows. The chemical system selected was benzoic acid, sodium hydroxide in aqueous solution, and atmospheric air. Continuous gas, pulse and dispersed bubble regimes were studied and the results were correlated obtaining apparent mass transfer coefficient as a function of liquid and fluid volumetric flow. It was found that gas flow effect on mass transfer coefficient was small over continuous gas and dispersed bubble regimes, but appreciable over pulse regime. Additionally, it was found that the mathematical model that best described the mass transfer process under pulse regime, by using the increment factor due to the instantaneous chemical reaction, is the film theory     

EFFECT OF VOLATILE LIQUID PHASE ON TRICKLE BED REACTOR PERFORMANCE

Many experimental trickle-bed reactors are operated at high temperatures and high pressures with volatile feedstocks which undergo partial vaporization of the liquid phase. The effect of this partial vaporization on the rate of reaction is demonstrated. The hydrodesulfurization of benzothiophene was simulated with the feed consisting of 5%, by weight, benzothiophene and 95% solvent. The pressure was held constant at 68 atm and temperature varied between 546 to 606 K employing isothermal simulations. The results show that the choice of solvent can significantly affect the rate of reaction.     

喷射环流三相流化床反应器轴向液速分布的研究

在喷射环流三相流化床反应器中，应用本文所开发的内热式热膜流体速率探头，获得了带有沉降分离区的夹套式环流反应器在不同压力、气量、流量条件下，不同轴向位置的液体速率分布规律。对于本文所述这类反应器，喷射区流体运动速率最大；自喷口向上，速率先是随距离的增大易急骤下降，然后逐渐向一渐近点逼近；当进入环隙转折口处时，由于气体的逸出及流道的变化液速急骤下降；凝固相进入环隙时，液速随距离的变化也存在渐近点。当采用变径结构时，流道面积突变处的液速变化率仅次于喷射入口区。在环流反应器中，液速主要取决于喷射动能及气提推动力，受液体进料量及压力的影响较小。     

甲烷磺酸铝催化合成氯乙酸酯的性能研究

合成了甲烷磺酸铝,用热重和红外对其进行表征。并以甲烷磺酸铝为催化剂,研究其催化氯乙酸与异丙醇酯化反应中各种因素对酯化率的影响。反应条件为:醇酸摩尔比1.2∶1,催化剂摩尔分数1.0%(以酸的摩尔数计),反应时间2.5h,反应温度80～85℃,环己烷5mL作为带水剂,酯化率可达96.8%,反应后催化剂经过简单的相分离就可重复使用。与AlCl3·6H2O、Al2(SO4)3·18H2O及其它Lewis酸进行比较,甲烷磺酸铝的催化活性最好。用甲烷磺酸铝作催化剂合成其它氯乙酸酯,酯化率均在96.0%以上。     

ABR反应器处理有机废水的运行特性研究

以重庆啤酒厂废水处理工程厌氧池内的厌氧消化污泥作为接种污泥,经培养成熟后用以处理屠宰废水,研究在室温(30～42℃)的条件下ABR反应器处理屠宰废水的运行特性,分析影响ABR反应器对屠宰废水去除效果的因素.结果表明,ABR反应器处理的屠宰废水出水相对稳定,反应器对进水水质的变化具有一定的缓冲能力,在COD容积负荷2.2～4.7kg·m-3·d-,HRT在15～17.5 h之间时,COD去出率在65%以上,反应器运行效果最佳.     

EFFECT OF EQUATION OF STATE ON PREDICTION OF TRICKLE BED REACTOR MODEL PERFORMANCE

Trickle bed reactors are widely employed in hydrotreating pocesses that operate at conditions where a significant portion of the liquid phase will flash. This partial vaporization of the feed affects the reactor performance. In order to determine the extent of liquid flashing and its effect on reactor performance, an equation of state is needed. In this study we used seven cubic equations of state to determine their effect in predicting reactor performance as well as parameter estimation

Two important variables that are calculated from the equation of state are the vapor liquid equilibrium and the molar density of the liquid phase. It was observed that although the distribution coefficients calculated by each equation of state are significantly different from each other, they do not affect the reactor model appreciably. However, molar density determination has a large effect both on modelling of reactor performance and the parameter estimation.     

EFFECT OF INTERACTION AND MOBILITY ON FIXED-BED REACTOR PERFORMANCE

The roles of interaction and mobility in determining surface rates and hence reactor performance, as reflected in the space time values required for achieving a desired conversion or selectivity, are demonstrated. It is shown that localized adsorption models predict larger space times in comparison to the mobile models. Further, repulsive forces lead to higher space times in comparison to attractive forces, and the divergence between models is most marked for localized adsorption.     

THE EFFECT OF OPERATING VARIABLES ON THE DYNAMICS OF CATALYTIC CRACKING PROCESSES

The dynamic Characteristics of a Fluidized Catalytic Cracking Process are examined over a wide range of operating conditions. A novel Order of Magnitude Approach is introduced to successfully provide physical insight into the cause and effect relationship between operating conditions and dynamic characteristics. It is shown that the original five-dimensional dynamic model is characterized by three fast time constants and two slow ones that dominate the dynamic responses. The two most important time constants are expressed as explicit functions of the operating conditions. These formulas correctly indicate in which parameter regions the open loop response is oscillatory (underdamped) or nonoscillatory (overdamped). Extensive process variables, that are either flow or capacity, related are defined in order to provide an approximate physical meaning for the dynamic modes of the system. It is shown that the two slow modes of the process are related to the enthalpy content of the regenerator and the sensible heat content of the catalyst phase in both the reactor and regenerator.