Catalytic Distillation Process Research Articles

High-Yield Synthesis of Dimethyl Carbonate from Urea and Methanol Using a Catalytic Distillation Process

Reaction equilibrium for the dimethyl carbonate (DMC) synthesis from urea and methanol was calculated based on the Benson method, and results showed that the reaction was thermodynamically unfavorable. In addition, urea methanolysis was conformed to be a consecutive reaction. Major side reactions in the DMC synthesis included the thermal decomposition of DMC and reaction between methyl carbamate (MC) and DMC, which reduced the DMC yield in the batch process. A catalytic distillation technique was proposed in this study to minimize the side reactions and unfavorable equilibrium for DMC synthesis. The DMC yield reached 60-70% in the catalytic distillation reactor over a Zn-based catalyst.

Production of n-Propyl Acetate by Reactive Distillation : Experimental and Theoretical Study

First steps of the development of a catalytic reactive distillation process for the production of n-propyl acetate based on experiments and simulations are proposed. The kinetics for homogeneously (sulphuric acid) and heterogeneously (Amberlyst 15) catalysed reaction were investigated and the constants for a pseudo-homogeneous model are presented. Pilot plant experiments were performed using a homogeneous strong acid catalyst in a packed column. A top-column decanter is used to withdraw the aqueous phase and to reflux the organic phase. Simulation results are in good agreement with experimental data. Thermodynamics non-idealities are taken into account using VLE and LLE NRTL interaction parameters. Alcohol conversion and n-propyl acetate purity may be dramatically increased just by adding to the pilot plant a stripping section in an additional column: six different configurations are identified to achieve such a production. The startup is studied in order to determine the best strategy to achieve steady-state conditions. The strong influence of the composition of the initial charging in the decanter can be seen and an initial charging of the two-phase top product leads to the fastest startup.

Combining Reaction with Distillation: Hydrodynamic and Mass Transfer Performance of Modular Catalytic Structured Packings

The combination of reaction with distillation is an elegant way to intensify a process. To fit the needs of catalytic distillation processes, modular arranged packings are developed to allow certain flexibility with regard to catalyst load in the column. The modular packing is built-up of alternating catalyst containing pockets with corrugated sheets. For design purposes the knowledge of hydrodynamics (dynamic liquid hold-up and pressure drop) and mass transfer efficiency characteristics (HETP) imposed by the internal configuration is vital and lacking in open literature. To overcome this, the geometry based Delft MCSP Model, a parallel column model, is developed to predict the hydrodynamics and mass transfer performance of modular catalytic structured packings (MCSP). The developed model is validated with pilot scale experiments carried out without reaction. This paper discusses the hydrodynamic performance of MCSP; the dynamic liquid hold-up is predicted within 10% and the pressure drop and capacity is well predicted. The HETP is predicted accurately around hydraulic loading of the packed bed.

TRENTA Facility for Trade-Off Studies between Combined Electrolysis Catalytic Exchange and Cryogenic Distillation Processes

One of the most used methods for tritium recovery from different sources of tritiated water is based on the combination between Combined Electrolysis Catalytic Exchange (CECE) and Cryogenic Distillation (CD) processes. The development, i.e. configuration, design and performance testing of critical components, of a tritium recovery system based on the combination CECE-CD is essential for both JET and ITER. For JET, a Water Detritiation System (WDS) is not only needed to process tritiated water which has already been accumulated from operation, but also for the tritiated water which will be generated during decommissioning. For ITER, the WDS is one of the key systems to control the tritium content in the effluents streams, to recover as much tritium as possible and consequently to minimize the impact on the environment. A cryogenic distillation facility with the aim to investigate the trade-off between CECE-CD, to validate different components and mathematical modelling software is current under development at Tritium Laboratory Karlsruhe (TLK) as an extension of the existing CECE facility.

A three-phase nonequilibrium dynamic model for catalytic distillation

A detailed three-phase nonequilibrium (NEQ) dynamic model for simulating batch and continuous catalytic distillation (CD) processes has been developed. In this model, both molar and energy holdups in liquid and vapour phases are taken into account. Multicomponent mass transfer and heat transfer between vapour and liquid phases as well as between liquid and solid (catalyst) phases are described by the Maxwell–Stefan equations. The resulting differential and algebra equations in this model are implemented in gPROMS and C++. The simulation results are in good agreement with the experimental data obtained from the batch and continuous CD processes for the production of diacetone alcohol (DAA) using Amberlite IRA-900 as a catalyst. Sensitivity analysis on the mass transfer and kinetics using the three-phase NEQ dynamic model indicates that the formation of DAA is controlled by solid–liquid mass transfer, whereas the formation of mesityl oxide is kinetically controlled under the simulation conditions.

Uncertainties in the simulation of catalytic distillation process: A systematic grid refinement study

Computational fluid dynamics (CFD) methods are gradually finding applications in the simulation of distillation processes. In the discretization of the governing differential equations for the mass- and the energy-balance, finite volume method (FVM) is commonly employed. Upwind differencing scheme (UDS) and central differencing scheme (CDS) are most commonly employed in FVM to approximate the values of the variables on the control volume faces. The problems that arise while using these approximation methods are discussed here. These may be overcome by using a bounded linear deferred correction scheme (LDC). When solutions on more than one grid sizes are available, and the order of the numerical scheme is known, the exact solution may be predicted by using Richardson extrapolation technique. If the order is unknown, then the order of the scheme may be determined from grid refinement studies. However, for the determined order of the scheme to be meaningful, sufficiently fine grids must be used for these studies.

Comparison of a Pseudo-homogeneous Nonequilibrium Dynamic Model and a Three-phase Nonequilibrium Dynamic Model for Catalytic Distillation

A comparison of a pseudo-homogeneous nonequilibrium (NEQ) dynamic model and a three-phase NEQ dynamic model was studied for the simulation of both a batch catalytic distillation (CD) process and a continuous CD process for the aldol condensation of acetone. The models were implemented in gPROMS and C++. The simulation results show that most of the dynamic responses of both the batch and continuous CD columns are either close to zero order or first order; however, the responses of temperatures in and below the reaction zone of the batch CD column predicted by the pseudo-homogeneous NEQ dynamic model are highly nonlinear. The formation rate of diacetone alcohol (DAA) and the liquid phase temperatures predicted by the pseudo-homogeneous NEQ dynamic model were found to be much higher than those predicted by the three-phase NEQ dynamic model for both the CD columns. Through a comparison with the experimental data, it was found that the three-phase NEQ dynamic model can adequately describe this CD process, while the simpler pseudo-homogeneous NEQ dynamic model overly predicts the formation rate of DAA and the liquid phase temperatures because the mass- and heat-transfer resistances between the liquid and solid phases are ignored. Since the computation time for the two NEQ dynamic models is very similar, it is recommended that the three-phase NEQ dynamic model should be used in the simulation of the CD process unless it is known a priori that the CD process is kinetically controlled.

05/00045 A catalytic distillation process for light gas oil hydrodesulfurization: Vargas-Villamil, F. D. et al. Chemical Engineering and Processing, 2004, 43, (10), 1309–1316

05/00045 A catalytic distillation process for light gas oil hydrodesulfurization: Vargas-Villamil, F. D. et al. Chemical Engineering and Processing, 2004, 43, (10), 1309–1316

Dynamic tracer study of column packings for catalytic distillation

The combination of heterogeneously catalysed chemical reactions and distillation in a catalytic distillation process provides several advantages. However, designing catalytic distillation columns remains a challenge. Different models of the process as well as new structured catalytic column internals have been developed. However, a lack of experimental investigation of packing properties makes it more difficult to model the process accurately. One of the important properties is the residence time distribution (RTD) affecting both reaction and separation performance. This paper presents selected results from the experimental programme of the EU project ‘Intelligent column internals for reactive separations (INTINT)’. Two types of structured catalytic packings, KATAPAK ®-S from Sulzer and MULTIPAK ® from Montz, each of them in two different constructions, are the subjects of the investigations presented here. RTD was studied experimentally using a tracer technique in 55 mm i.d. test column. Liquid hold-up and axial dispersion coefficients have been derived from RTD curves recorded during experiments and can be used for modelling the catalytic distillation process. The derived conclusions allow an evaluation of the column internals and facilitate an improved design with respect to the investigated properties.

Dehydration of Methanol to Dimethyl Ether by Catalytic Distillation

AbstractThe kinetics of liquid catalytic dehydration of methanol over an ion exchange resin (Amberlyst 35) has been determined for the temperature range 343 to 403 K using a batch reactor. The experimental data are described well by an Eley‐Rideal type kinetic expression, for which the surface reaction is the rate‐determining step. A catalytic distillation process for methanol dehydration to dimethyl ether (DME) has been modeled using the experimentally determined kinetic data. The results were incorporated into the rate‐controlled reaction mode for RadFrac, a part of the commercial simulation program Aspen Plus. It was shown that synthesis of high purity DME can be achieved using a single catalytic distillation column. Thus there is significant potential for reduction of overall capital cost for a plant for methanol dehydration to DME when compared to conventional production facilities that involve separate reaction and distillation processes.

Tray efficiency in the air-water-solid system without reaction and its application

This work deals with the investigation of tray effi ciency with the gas-liquid-solid three phases and its application in the suspension catalytic distillation (SCD) process. The experimental data of tray efficiency under dif- ferent conditions were measured by utilizing the desorption of oxygen dissolved in water by air. A method of estimation of tray efficiency for the gas-liquid-solid three phases was put forward and its suitability was also verified. This method was developed on the basis of the AIChE method for gas-liquid two phases. As an application example of this modified AIChE method, the SCD process for synthesizing cumene, based on equilibrium stage (EQ) model incorporating tray efficiency, was simulated.

Steady-State Rate-Based Simulation of Packed Reactive Distillation: Spatial Discretization

This paper investigates issues related to the numerical simulation of rate-based models for catalytic distillation processes. Special emphasis is placed on spatial discretization in the solution of steady-state models describing packed reactive distillation columns. A general rate-based model for packed reactive distillation is briefly presented, along with its underlying assumptions. This mathematical model is then discretized along its spatial dimensions using different finite-difference schemes. In this paper, steady-state simulations are considered to assess various properties of the different discretization methods. Using a tert-amyl methyl ether (TAME) packed reactive distillation as a case study, we show that a cell-based approach, similarly to a first-order finite-difference approximation, is inefficient in converging to the solution of the mathematical model. To address this problem, a higher-order discretization scheme is used, and its advantages are illustrated. This latter method is of interes...

A catalytic distillation process for light gas oil hydrodesulfurization

A light gas oil hydrodesulfurization process via catalytic distillation is developed and compared to a conventional process. By integrating the separation and reaction into a single unit, the catalytic distillation may produce a diesel with low concentration of sulfur compounds at a lower cost than the traditional reaction/separation process. The process proposed in this work is compared to an optimized conventional hydrodesulfurization unit which represents fairly well a plant that belongs to the National System of Refineries. During the optimization of the conventional process, a compromise is established among the production of diesel and naphtha and the operating costs. The results show that the light gas oil hydrodesulfurization via catalytic distillation is as or more efficient than the conventional process. However, the removal of the sulfur compounds is carried out under less rigorous conditions. This design reduces the fix and operational costs.

Model-based design, control and optimisation of catalytic distillation processes

In this contribution, the benefits of using dynamic models of different complexity and size for process design, optimal operation and control of catalytic distillation (CD) processes are discussed for the case study of the heterogeneously catalysed reactive distillation (RD) of methyl acetate. Dynamic reactive distillation experiments at pilot plant scale were performed using the catalytic structured packing MULTIPAK. A dynamic rate-based model were developed which contains hydrodynamic effects as liquid holdup, liquid backmixing and pressure drop as well as reaction kinetics and which describes the process behaviour accurately. For offline and online optimisation and control, reduced order and simplified models were applied. A systematic control structure selection and controller design studies for the experimental column were conducted. The linear controller shows good performance over a wide range of operating conditions.

Suspension catalytic distillation of simultaneous alkylation and transalkylation for producing cumene

This work deals with the improvement of the suspension catalytic distillation (SCD) process. An improved process that alkylation and transalkylation reactions for producing cumene are carried out simultaneously in a SCD column, was put forward. The kinetic data of alkylation of benzene with propylene over a modified β-zeolite catalyst, YSBH-01, were determined in a fixed-bed laboratory micro-reactor. On this basis, the equilibrium stage (EQ) model (MESHR equations) is established to simulate the SCD column. The performance of the SCD column is discussed. The innovation present in this work for the SCD process is also suitable for the fixed-bed catalytic distillation (FCD) process for producing cumene.

Modeling of the Catalytic Distillation Process for the Synthesis of Ethyl Cellosolve Using A Three-Phase Nonequilibrium Model

The catalytic distillation (CD) process for the synthesis of ethyl cellosolve from ethanol and ethylene oxide on molecular sieve catalyst NKC-01 in a 200 mm CD pilot column was simulated using the three-phase nonequilibrium model which was developed in our laboratory. The main feature of this model is that the actual rates for transport and reaction are used and the stage efficiency or HETP (height equivalent to a theoretical plate) is not required. The effect of multicomponent mass and heat transfer between vapor and liquid phases as well as between liquid and solid (catalyst) phases was taken into account according to the Maxwell-Stefan equations. The Newton-Raphson method was used to solve the model equations. The simulation profiles of the temperature and composition along the column are in good agreement with the pilot CD plant data obtained for the synthesis of ethyl cellosolve. Good agreement between model predictions and experimental data is also obtained for the yield and selectivity of the ethyl cellosolve. This model could be extended to simulate other CD processes and commercial scale CD plants.

The Etherification of Methanol and Isobutene in a Catalytic Distillation Column Packed with Zeolite-Beta-Coated Catalytic Packings

Zeolite-beta-coated catalytic packings were used to improve the etherification of methanol and isobutene in a catalytic distillation column. The steady-state composition profiles and the characteristics of the reaction in the catalytic distillation column were investigated. The zeolite-beta-coated packing has better characteristics and an activity that is comparable to that of the conventional resin catalyst in both catalysis and the separation of reactants from products. The optimal operating conditions for the catalytic distillation process are a pressure of 0.7 MPa, a methanol/isobutene feed molar ratio of 1, and a reflux ratio of more than 3. The effect of the strong nonlinearity in the vapor−liquid equilibrium of the reactive system on the conversion of isobutene was analyzed on the basis of the experimental results for both catalytic distillation and conventional distillation. There is a valley in the boiling-point temperature surface of the ternary mixture of methanol/isobutene/MTBE. This valley, a...

Reactive separation of isobutene from C4 crack fractions by catalytic distillation processes

Reactive distillation is a hybrid process where chemical reaction and distillative separation are performed in a single equipment. Even though reactive distillation could increase the selectivity of the desired product by the selective reaction this is not always true as shown in this work. A study on the MTBE reaction system using two coupled reactive distillation columns to separate a C4 crack mixture is carried out, where methanol acts as reactive entrainer and MTBE is the intermediate product. In the first column, isobutene and methanol react to form MTBE hence separating the inert C4 component, while in the second column MTBE splits back to methanol and isobutene. Methanol is recycled back to the MTBE formation column and isobutene is obtained as a product. This coupled process with direct recycle of methanol is possible only if no side reactions occur. When the side reactions are taken into account, byproducts such as diisobutene, dimethyl ether and water will be produced so that higher purity methanol can not be obtained at the bottom of the splitting column. The outlet of the splitting column must be firstly separated rather than being recycled directly to the formation column. Moreover, an attempt has been made to show how the selectivity of the desired product isobutene can be critically influenced by the operating parameters such as the reflux ratio. If the reflux ratio increases, a high quantity of diisobutene and dimethyl ether will be obtained which seriously affects the selectivity of isobutene. The influence of operating parameters is investigated by using a continuation method, which shows that bifurcation behavior can appear in both MTBE formation and decomposition process.

Development of a novel catalytic distillation column

A new type of catalytic distillation column has been developed for catalytic distillation processes. The catalysts are loaded loosely in the downcomer of the new column, so that they can be replaced easily. A new type of column plate structure has also been proposed to accommodate the new distillation column. Experimental results show that the new column and plate structure have much improved performance, with high plate efficiency, low pressure drops across the plate and very good operation flexibility. The novel catalytic distillation columns could be employed to many catalytic distillation processes.

Catalytic Distillation: A Three-Phase Nonequilibrium Model for the Simulation of the Aldol Condensation of Acetone

A nonequilibrium model (MECRES equations) for the simulation of catalytic distillation (CD) processes developed by Huang et al. (Chem. Eng. Sci. 1998, 53, 3489; 2000, 55, 5919) was improved so as to provide a more generalized three-phase model for the simulation and optimal design of a CD process. Instead of using the overall mass transfer coefficients for the reaction zone determined for the column, the vapor and liquid mass transfer equations in the MECRES model were modified to take into account the effect of multicomponent mass transfer according to multicomponent mass transfer theory. In addition, temperature gradients among the vapor, liquid, and solid (catalyst) phases were considered. The heat transfer rates in the heat balances were calculated according to multicomponent heat transfer theory. The CD process for the aldol condensation of acetone to diacetone alcohol was simulated using this improved model. The model predictions for the product yield and selectivity are in excellent agreement with experimental CD data. The simulation profiles of the temperature along the column and the composition in the reboiler are in better agreement with the experimental data than those simulated by the MECRES model. This improved model is more generalized and will be used to simulate the new CD process for the oligomerization of butenes.