Investigation of a rotating disc reactor for acetone stripping and asymmetric transfer hydrogenation: Modelling and experiments

Asymmetric transfer hydrogenation of acetophenone with isopropanol as hydrogen donor in the presence of a homogeneous catalyst was investigated in a rotating disc reactor. Initially, acetone stripping from binary mixtures acetone-isopropanol with nitrogen as inert gas was studied, since its removal is a key issue in improving reaction performance. The reactor consisted of a stainless steel disc mounted on a horizontal shaft, accommodated in a cylindrical shell. The disc was partially immersed in the liquid phase. Its rotation generated a thin liquid film on its upper part, which could be brought in contact with a gas phase used for stripping. A mathematical model was formulated to simulate the reactor and showed good agreement with experimental data for acetone stripping. It was observed that the efficiency of acetone removal from the liquid phase increased with the gas flowrate per initial liquid volume ratio. The effect of disk rotation was found to be small when the stripping gas was introduced in the liquid bulk. The reactor model agreed well with experimental data of the asymmetric transfer hydrogenation. An advantage of the rotating disk reactor is that the hydrodynamics of the phases can be decoupled and the gas flowrate can be increased without constraints in the liquid phase, unlike conventional agitated reactors that are limited by flooding. Simulations using high stripping gas flowrate per initial liquid volume, unachievable in stirred reactors, showed significant reduction of the residence time required to achieve >99% conversion.     

Modelling and control of a continuous distillation tower through fuzzy techniques

This paper presents a methodology for the design of a fuzzy controller applicable to continuous processes based on local fuzzy models and velocity linearizations. It has been applied to the implementation of a fuzzy controller for a continuous distillation tower. Continuous distillation towers can be subjected to variations in feed characteristics that cause loss of product quality or excessive energy consumption. Therefore, the use of a fuzzy controller is interesting to control process performance.A dynamic model for continuous distillation was implemented and used to obtain data to develop the fuzzy controller at different operating points. The fuzzy controller was built by integration of linear controllers obtained for each linearization of the system. Simulation of the model with controller was used to validate the controller effectiveness under different scenarios, including a study of the sensibility of some parameters to the control.The results showed that the fuzzy controller was able to keep the target output in the desired range for different inputs disturbances, changing smoothly from a predefined target output to another. The developed techniques are applicable to more complex distillation systems including more operating variables.     

Modelling a catalytic membrane reactor with plug flow pattern and a hypothetical equilibrium gas-phase reaction with Δn ≠ 0

The scope of this paper is to present a theoretical study of a catalytic polymeric dense membrane reactor (CPDMR) assuming isothermal conditions, plug flow pattern without pressure drop in both retentate and permeate sides, shell side feed and cocurrent operation. The conversion enhancement over the thermodynamic equilibrium value is studied for a gas-phase reaction of the type aAbB, considering two different stoichiometric ratios: Δn > 0 and Δn < 0, where Δn = b − a. For each of these cases, the influence of the relative sorption and diffusivity of the reaction species is studied. It is concluded that the conversion of a reversible reaction can be significantly enhanced when the diffusivity of the reaction products is higher than that of the reactants and/or the sorption is lower. It is also concluded that, even for equal sorption and diffusion coefficients, the conversion could also be improved for reactions with Δn ≠ 0. The extension of this enhancement depends on the reaction stoichiometry, the overall concentration inside the membrane, the Thiele modulus, and the contact time.     

Modelling hydrate formation kinetics of a hydrate promoter-water-natural gas system in a semi-batch spray reactor

Hydrate formation kinetic modelling studies reported so far mainly concentrates on pure water-gas systems in stirred-tank batch environments. This work proposes a model for gas hydrate formation kinetics of a hydrate promoter-water-natural gas system in a semi-batch reactor assuming steady-state, isothermal and isobaric conditions. The hydrate formation kinetics was modelled after extending the recent method proposed by Kashchiev and Firoozabadi (J. Crystral Growth 241 (2002a) 220; J. Crystal Growth 243 (2002b) 476; J. Crystal Growth 250 (2003) 499) for a single component gas-water system to a multi-component gas-water-additive system. The extended Kashchiev and Firoozabadi model was applied for a semi-batch spray reactor here for the first time. The hydrate formation experiments were carried out in a pilot plant spray reactor at three different pressure-temperature regimes to determine the actual hydrate formation kinetics in the spray reactor. The experiment results were then used to finetune the adjustable parameters to facilitate accurate model predictions.     

Global modelling of a gas-liquid-solid airlift reactor

This paper presents a global model of three phase flow (gas-liquid-solid) in an internal airlift reactor. The airlift is composed of four zones: a riser (on the aerated side on the internal wall), a downcomer (on the opposite side) and two turning zones above and below the internal wall. Tap water is the liquid continuous phase and the dispersed phases are air bubbles and polyethylene particles. The global modelling of the airlift involves mass and momentum equations for the three phases. The model enables phase velocities and phase volume fractions to be estimated, which can be compared to experimental data. Closure relations for the gas and solid drift velocities are based on the model proposed by Zuber and Findlay. The drift flux coefficients are derived from CFD numerical simulations of the airlift. Gas bubble and solid particle averaged slip velocities are deduced from momentum balances, including drag coefficient correlations. The link between Zuber and Findlay model and the two-fluid model is established. In the experiment as well as in the model, the gas flow rate is fixed. However, the liquid and solid flow rates are unknown. Two closure relations are needed to predict these flow rates: the first closure relation expresses that the volume of solid injected into the airlift remains constant; the second closure relation expresses a global balance between the difference of column height in the riser and the downcomer and the total pressure drop in the airlift. The main parameters of a three phase airlift reactor, like gas and solid volume fractions, are well predicted by the global model. With increasing solid filling rate (40%), the model starts to depart from the experimental values as soon as coalescence of bubbles appears.     

Analysis of packed distillation columns with a rate-based model

Multicomponent packed column distillation is simulated using a rate-based model and the simulation results are compared with the experimental results obtained from a 0.2 m diameter pilot-scale packed column. The simulation algorithm used is previously proposed by the authors, which based on an equation-tearing method for (6c+7) equations of one packing segment and the whole column is solved by an iterative segmentwise calculation with the overall normalized θ method for acceleration. The performance of two packings is examined by simulating the pilot-scale column experiments using the published correlations for estimating liquid and vapor phase mass transfer coefficients and an effective interfacial area.     

乙烯淤浆聚合反应器的模型与模拟

建立了乙烯淤浆聚合反应器的多相全混流模型,描述了包括乙烯共聚合反应动力学、气液和液固传质、反应器传热在内的物理化学过程。通过模拟计算分析了聚合过程的控制步骤,得到了反应器生产能力与有关操作变量之间的关系,对某工业反应器的模拟结果表明计算值与生产数据具有很好的一致性。     

Design of a fully thermally coupled distillation column based on dynamic simulations

A dynamic simulation of a fully thermally coupled distillation column is conducted for the design of a possible operation scheme, and its performance is examined with an example process of butanol isomer ternary system. The outcome of the dynamic simulation indicates that the column can be operated by using a 3 × 3 control structure. The structure consists of three controlled variables of the compositions of overhead, bottom and side products and three manipulated variables of the flow rates of reflux and steam and liquid split ratio between a main column and a prefractionator. This paper was presented at The 5th International Symposium on Separation Technology-Korea and Japan held at Seoul between August 19 and 21, 1999.     

The use of dilute acetic acid for butyl acetate production in a reactive distillation: Simulation and control studies

The recovery of dilute acetic acid, which is widely found as a by-product in many chemical and petrochemical industries, becomes an important issue due to economic and environmental awareness. In general, separation of acetic acid in aqueous solution by conventional distillation columns is difficult, requiring a column with many stages and high energy consumption. As a result, the primary concern of the present study is the application of reactive distillation as a potential alternative method to recover dilute acetic acid. The direct use of dilute acetic acid as reactant for esterification with butanol to produce butyl acetate in the reactive distillation is investigated. Simulation studies are performed in order to investigate effect of the concentration of dilute acetic acid and key process parameters on the performance of the reactive distillation in terms of acetic acid conversion and butyl acetate production. In addition, three alternative control strategies are studied for the closed loop control of the reactive distillation. The control objective is to maintain the butyl acetate in a bottom product stream at the desired purity of 99.5 wt%.     

A simple,reliable and fast algorithm for the simulation of multicomponent distillation columns

This work has developed a simple, reliable and fast algorithm for the simulation of multicomponent distillation columns, where any equilibrium stage can accept a feed-stream and/or a vapor-side-stream and/or liquid-side-stream. The new scheme considers internal molar overflows and constant relative volatilities to avoid the need of heat balances and vapor–liquid equilibrium calculations. The solution scheme is founded on a Newton-based formulation in block algebra, which relies in a simple, reliable and fast algorithm. Although the proposed calculation scheme can be classified as an approximate method, it is very useful when accurate phase equilibrium and enthalpy data are lacking. Numerical experimentations show good agreement with the results obtained with well-known rigorous simulation approaches.     

Polymerisation of methyl methacrylate in a pilot-scale tubular reactor: modelling and experimental studies

A pilot-scale tubular reactor fitted with in-line static mixers is experimentally and theoretically evaluated for the polymerisation of methyl methacrylate (MMA). A non-isothermal and non-adiabatic axially dispersed plug-flow model is used to describe the flow characteristics of the reactor. The model is applied to the polymerisation of a concentrated MMA solution (up to 72% (v/v)). Key model parameters were attained through independent bench and pilot-scale experiments. Measured monomer conversions and polymer molecular weight were accurately predicted by model simulation. The presence of static mixers is shown to give near-ideal plug-flow operation for the experimental conditions of this study. Furthermore, an approximately four-fold increase in overall heat transfer coefficient is indicated due to the radial mixing incited by the mixers. Studies also demonstrated the importance of inhibitor kinetics on the dynamic and steady-state performance of the reactor.     

Three-dimensional numerical simulation of a circulating fluidized bed reactor for multi-pollutant control

Circulating fluidized bed adsorber (CFBA) technology is regarded as a potentially effective method for simultaneously controlling emissions of sulfur dioxide, fine particulate matter, and trace heavy metals, such as mercury vapor. In order to analyze CFBA systems in detail, a gas mixture/solids mixture model based on the three-dimensional Navier-Stokes equations is developed for particle flow, agglomeration, physical and chemical adsorption in a circulating fluidized bed. The solids mixture consists of two solids, one with components of CaO and CaSO₄, and the other being an activated carbon. The gas mixture is composed of fine particulate matter (PM), sulfur dioxide, mercury vapor, oxygen and inert gas. Source terms representing fine particulate matter agglomeration onto sorbent particles, sulfur dioxide removal through chemical adsorption onto calcined lime, and mercury vapor removal through physical adsorption onto activated carbon are formulated and included into the model. The governing equations are solved using high-resolution upwind-differencing methods, combined with a time-derivative preconditioning method for efficient time-integration. Numerical simulations of bench-scale operation of a prototype CFBA reactor for multi-pollutant control are described.     

Economic evaluation of seawater desalination for a nuclear heating reactor with multi-effect distillation

Seawater desalination for low temperature nuclear heat reactor (NHR) has been studied for many years in China and other countries in the world, such as Morocco, and five countries in North Africa. Now, the feasibility studies of nuclear desalination demonstration plants are being performed using NHR with 200 MW thermal coupling to a multi-effect distillation (MED) plant, with a production of 160,000 m³/d (NHR-200) in Yintai City, Shandong province and Tianjin City on the coastal area in eastern China. This paper presents the economic assessment of the NHR-200 in Tianjin City, and reviews the economics of the different power sizes of NHR coupling to the MED, e.g. NHR-10, NHR-200, double NHR-200 in North Africa, the Middle East, the Red Sea and the Arabian Gulf. It is very suitable to satisfy the site of no great electric grid, drought and scarce of freshwater for the characteristics of NHR with safe, clean and low total investment.     

合成气一步法5000t/a二甲醚管式反应器设计

应用实验所得动力学数据,建立管式固定床反应器的一维数学模型。通过计算典型工况下5000t/a二甲醚反应器,得到了反应器的工艺与设备设计参数。     

微通道反应器中二氯丙醇环化反应

研究了微通道反应器内二氯丙醇的环化制备环氧氯丙烷的反应,考察了反应温度、原料配比、停留时间等单因素对环氧氯丙烷收率的影响。实验确定了较优的工艺参数组合:环化反应温度50℃,二氯丙醇与氢氧化钠的摩尔比1∶1.2,停留时间45 s,NaOH质量分数20%时ECH的收率达到95.2%。在微通道反应的时空转化率要比常规反应高出两个数量级。与传统的工艺方法相比,微通道反应中环氧氯丙烷的收率提高了10%,降低了过程的能耗,废水排放量减少了45%。     

New developments for modelling and simulation of activated anionic polymerization of lauryllactam

This work deals with the development of a predictive model for the anionic polymerization of lauryllactam activated by a particularly efficient catalytic system composed of aluminium hydride as catalyst and 4,4^′-diphenylmethane diisocyanate urea as activator. This model takes into account important side reactions occurring during the process, i.e. branching reactions and Claisen's condensations giving rise to macromolecules with several functional end-groups. Its main key parameters are identified on the basis of batch experimental data which describe the complete sketch of polymerization. They allow to predict with a good precision the monomer conversion under different operating conditions. The model is then used to simulate the concentrations of the different functional end-groups as well as the number of condensation bonds per unit volume resulting from Claisen's condensations.     

Simulation and analysis of extractive distillation process in a valve tray column using the rate based model

Valve trays are becoming popular in the chemical process industries owing to their flexibility to handle a wide range of vapor throughputs. Using the rigorous rate based model, the importance of the non-equilibrium approach is demonstrated for a typical extractive distillation process in a Glitsch V-1 valve tray column. Simulation results based on an in-house developed code indicated that the rate based model predictions for a valve tray column operation showed significant differences relative to the equilibrium model. Even small errors in product purities translated into nonoptimal feed stage locations and inaccurate number of stages required. The counter-intuitive effect of high reflux ratio on separation is explained.