Catalytic Distillation Process Research Articles

Simulation of Methyl Tertiary Butyl Ether Production in Catalytic Distillation

The software of the catalytic distillation process of methyl tertiary butyl ether was developed by using Process Simulation System Platform. The isobutylene conversion rate was calculated by using the catalytic distillation software. The relative error of isobutylene conversion rate between the simulation results and the design data from the China Petroleum Hohhot Petrochemical Co. was less than 5%. The relative error satisfies industrial design requirements. At present, enterprise workers use this software to learn how to operate the catalytic distillation process. The catalytic distillation software is further used to study the influence of reaction temperature and reflux ratio on the isobutylene conversion rate which can be used for future empirical model development and control studies.

Economics-based NMPC strategies for the operation and control of a continuous catalytic distillation process

Process profitability is an yes or no criterion for the successful long-term operation of industrial processes. This article describes the use of dynamic online economic process optimization to improve the performance of chemical processes. Different model-predictive control techniques have progressively been applied to coupled multivariable control problems and in many cases, especially in the petrochemical industry, the reference values are adjusted infrequently by stationary optimization based upon a rigorous nonlinear stationary plant model (real-time optimization, RTO). In between these optimizations, however, the process may be operated suboptimally due to the presence of disturbances. Nonlinear dynamic model-based optimization has been proposed recently to combine optimal operation and feedback control. In this paper, a model of the complex dynamics of a pilot-scale continuous catalytic distillation process is used to explore the potential benefits of online economics optimizing control strategies. We compare the direct economic optimization scheme with a compromise scheme, the economics-oriented tracking controller. The outcome of this work indicates that by using direct economics optimizing NMPC the plant economics can be handled better while guaranteeing the product specifications which are formulated as explicit constraints.

Pressure Drop Models of Seepage Catalytic Packing Internal for Catalytic Distillation Column

A seepage catalytic packing internal (SCPI) consisting of catalyst containers with avert-overflow baffles and corrugated metal sheets was developed for a catalytic distillation column. By changing the width ratio (Rcc/cms) of the catalyst containers (CC) relative to corrugated metal sheets (CMS), the SCPI developed in this work can be suitable to various reaction and separation zones in different catalytic distillation processes. The influence of the Rcc/cms, a significant factor influencing the pressure drop, also was studied. The flooding behaviors and pressure drop were evaluated using cold model experiments in the column (600 mm in diameter × 1500 mm height); the results were compared with that of the catalytic packing typically used in catalytic distillation. A model for predicting the pressure drop of SCPI was developed and compared with experimental results. Results show that the pressure drop was decreased with decreases of Rcc/cms. The results from this work are valuable in the design and scale-up of SCPI in catalytic distillation columns.

Synthesis of High‐Purity Methylal via Extractive Catalytic Distillation

AbstractAn integrated continuous process, which combines catalytic distillation and extractive distillation in one column, is investigated for the synthesis of high‐purity methylal from methanol and formalin in the presence of a cation‐exchange resin catalyst. A feed with methanol:formaldehyde 2:1 molar ratio is chosen to evaluate the effects of operating parameters, such as extractant feeding position, ratio of extractant to feed, reflux ratio, and reboiler temperature, on the continuous synthesis of methylal. Under the optimum operating conditions and with water as extractant, the extractive catalytic distillation process operated continuously, producing a methylal purity of 98.7 % (H2O: < 1.30 %) with 98.0 % formaldehyde conversion.

Optimal LQ-Control of a PDAE Model of a Catalytic Distillation Process

In this contribution a linear quadratic (LQ) control design for a partial differential and algebraic equation (PDAE) system which represents a catalytic distillation process, is presented. The model involves a set of coupled partial differential equations (PDEs), ordinary differential equations (ODEs), and algebraic equations (AEs). The design is based on an infinite-dimensional state-space representation of the system in a Hilbert space and the well-known operator Riccati equation (ORE) method. The underlying PDE-ODE-AE system is converted to one containing coupled PDEs-ODEs, in which the PDE part involves a hyperbolic operator with a space-varying and non-symmetric velocity matrix whose eigenvalues are not necessarily negative through of the domain. Moreover, in the resulting PDE-ODE system, the control variable acts through the ODE part on the boundaries of the PDE section. Using the boundary control transformation method, the PDE-ODE system is represented in an infinite-dimensional state-space with a homogeneous boundary condition. The stabilizability and the detectability properties of the resulting system are explored, which provide guarantees of the existence and uniqueness of the solution to the resulting ORE. The ORE is solved by converting it to a set of equivalent matrix Riccati equations. The designed LQ controller is implemented on the process and its performance is evaluated.

An investigation of Economics-Driven NMPC-Formulations for a Continuous Catalytic Distillation System

For continuously operated processes, even a small increase in the efficiency pays important dividends in terms of energy savings and profit. Therefore, tighter and more efficient control of chemical plants is becoming a strategic objective. In this work, we demonstrate the use of dynamic process optimization to improve the business performance of chemical processes. Model predictive control techniques are widely applied to coupled multivariable control problems. The reference values in these problems are usually adjusted by infrequent optimizations based upon a static rigorous nonlinear model of the plant. In between these optimizations, however, the process may undergo sub-optimality of operation due to the presence of disturbances. In this paper, nonlinear model-based optimization with different schemes is proposed to combine optimal operation and feedback control. The work demonstrates the feasibility and the potential of using optimizing as well as economics-oriented tracking control techniques for a challenging example, a catalytic distillation process. The performances of the proposed controllers are investigated and compared. This work points out that by using direct optimizing NMPC, the plant economics can be handled better while guaranteeing the product specifications.

Sulfated zirconia as a robust superacid catalyst for multiproduct fatty acid esterification

Sulfated zirconia catalysts obtained by employing chlorosulfuric acid show significantly higher activity in the esterification of fatty acids with different alcohols compared with catalysts made using sulfuric acid. The superior performance results from higher sulfur content, larger pores and stronger acid sites. These catalysts are robust and do not leach out sulfonic groups. Catalyst performance depends strongly on the sulfation reagent and the calcination conditions of the intermediate zirconium hydroxide. A series of kinetic experiments was carried out with lauric acid and various alcohols (methanol, 2-ethylhexanol, propanols and butanols). The new catalysts are ca. five times faster when using primary alcohols independent of the alcohol chain length. When using secondary and tertiary alcohols the reaction rate drops considerably. This is explained by a linear free energy relationship of substituent reactivity. The kinetic investigation shows that chlorosulfated zirconia is suitable as a multiproduct catalyst for manufacturing fatty esters, by employing a catalytic reactive distillation process.

The Prediction of Tritium Level Reduction of NPP Cernavoda Using CTRF

The National Research and Development Institute for Cryogenics and Isotopic Technologies (ICIT Rm. Valcea) was established in 1970 as a research focused Industrial Pilot Plant with the main goal of developing a heavy water production technology.Within ICIT there is an experimental pilot plant for tritium and deuterium separation, which has as main purpose the development of tritium separation technique from heavy water used as moderator in CANDU-like nuclear reactors as those existent at CNE Cernavoda.The CNE Cernavoda detritiation installation (CTRF) was designed primarily to reduce the level of tritium from the reactor moderator 1 of the nuclear power plant, from 54 Ci/kg - an estimated value to be achieved in 15 years of continuous operation, up to a threshold of maximum 0.54 Ci/kg.Under a contractual agreement ICIT Rm.Valcea and AECL are to jointly produce both a pre-feasibility and feasibility study for the project. The pre-feasibility study completed in August 2006, provided the rationale for choosing the Liquid Phase Catalytic Exchange-Cryogenic Distillation process for the Cernavoda TRF.After reaching the planned threshold in the water of moderator 1, the CTRF can alternatively provide the reduction in heavy water activity from the moderator of reactor 1 and 2 respectively.

Development of a Novel Catalytic Distillation Process for Cyclohexanol Production: Mini Plant Experiments and Complementary Process Simulations

A new, two-step process concept for the production of cyclohexanol by indirect hydration of cyclohexene using formic acid as a reactive entrainer is suggested, and its principle technical feasibility is demonstrated. The first step of this process is based on an ester formation reaction of cyclohexene with formic acid. This reaction was carried out in a mini plant stainless steel catalytic distillation column of 2.35 m height. The column was packed with noncatalytic structured packings (SULZER-DX) and catalytic structured packings (KATAPAK-S). The experiments were conducted under low-pressure conditions (<0.6 bar) to avoid formic acid decomposition. Concentration and temperature profiles were obtained under steady-state conditions. Up to 98.3% conversion of cyclohexene and 75.5 mol % ester concentration in the bottom product of the column was obtained. In a similar manner, the second step of the process, i.e. the hydrolysis of the cyclohexyl formate formed in the first step, was investigated experimentall...

Kinetics for the Esterification Reaction of n-Butanol with Acetic Acid Catalyzed by Noncorrosive Brønsted Acidic Ionic Liquids

It is very attractive that noncorrosive Brønsted acidic ionic liquids (BAILs) are used as catalysts in liquid catalyst-based reactive distillation columns, which avoids the technical difficulties raised from solid catalysts or corrosive mineral acids. The kinetics for the esterification of n-butanol with acetic acid using noncorrosive BAILs as catalysts was therefore studied systemically, to explore the possibility of BAIL-based catalytic distillation processes. The effects of various parameters such as temperature, catalyst loading, and molar ratio of the reactants on the kinetics were examined in detail, and a pseudohomogeneous (PH) kinetic model was used successfully to correlate the experimental data. The kinetic data are for the first time used to interpret clearly the synergistic effect resulted from the acidity and hydrophilicity of BAILs. It is also validated from the comparison of esterification kinetics between noncorrosive BAILs and Amberlyst-15 resin (a commonly used solid catalyst of strong acidity) that noncorrosive BAILs are talented and prospective substitutes for the establishment of liquid catalyst-based reactive distillation processes.

Coupled Reaction/Distillation Process for Hydrolysis of Methyl Acetate

A process composed of a fixed-bed and a distillation column with a side withdraw, mainly methanol, is developed to hydrolyze methyl acetate (MA) as a typical byproduct in polyvinyl alcohol (PVA) and pure terephthalic acid (PTA) factory. The process is simulated by employing the equilibrium stage model RadFrac and plug flow model Rplug in Aspen Plus. Experiments are also carried out in a lab-scale to evaluate the process. The results show that at the molar ratio of water to methyl acetate about 4.0-5.0 in the feed stream and the volume ratio of distillate to feed MA above a critical value, the side product contains more than 80% (by mass) (MeOH) and less than 2% (by mass) MA, while the bottom contains more than 46% (by mass) acetic acid (HAc) and less than 0.5% (by mass) methanol with almost complete conversion of MA. Compared with the old catalytic distillation process we proposed before, this process can cut down 47.6% energy consumption and a distillation column.

Hydrolysis of methyl acetate via catalytic distillation: Simulation and design of new technological process

An equilibrium stage model was developed for the simulation of the catalytic distillation process of methyl acetate (MeOAc) hydrolysis. In the model, the influences of the reactive kinetics, residence-time, liquid holdup, and separation efficiency of the catalytic packing were considered. The model predicted the conversion of MeOAc and the mass ratio of acetic acid to water in the hydrolysis mixture. The predictions were in good agreement with experimental data. A novel process was designed based on the results of theoretic analysis and the simulation research. This new process had a higher conversion of MeOAc compared with the results in previous research and was found to be energy efficient. Optimal effect parameters and design factors of new technology on energy consumption and conversion were also determined and summarized as the following: the position of side draw is 18th to 19th stages, the catalytic distillation (CD) column pressure is at 350kPa, the volume ratio of reflux to feed is 6–8, mole ratio of feed water to MeOAc is 3.5–4.5, and the mass ratio of side withdrawal to feed is 0.32–0.34.

Catalytic reactive distillation process development for 1,1 diethoxy butane production from renewable sources

Some acetals can be produced from renewable resources (bioalcohols) and seem to be good candidates for different applications such as oxygenated diesel additives. In the present case the production of 1,1 diethoxy butane from bioethanol and butanal is presented. Butanal can be obtained from biobutanol following a partial oxidation or a dehydrogenation process. In this paper innovative process development about the synthesis of the mentioned acetal including catalytic reactive distillation experimental and simulation results will be presented and discussed. Katapak SP modules containing Amberlyst 47 resin were used as structured catalytic packings. This reactive system allowed reaching higher conversions than the equilibrium ones at the same temperatures. All the experimental data gathered allowed to tune a simulation model for the reactive distillation operation which showed a fairly good behavior in order to perform initial 1,1 diethoxy butane production process design studies.

Coating of polymeric substrate catalysts on metallic surfaces

This article presents results of a study on coating of a polymeric substrate catalyst on metallic surface. Stability of coating on metallic surfaces is a proper specification. Sol-gel technology was used to synthesize adhesion promoters of poly-silane compounds that act as a mediator. The intermediate layer was coated by synthesized sulfonated polystyrene-divinylbenzene as a catalyst for production of MTBE in catalytic distillation process. Swelling of catalyst and its separation from the metal surface was improved by (i) increasing the quantity of divinylbenzene in resin?s production process, and (ii) applying adhesion promoters based on the sol-gel process. The rate of ethyl silicate hydrolysis was intensified by increasing the concentration of utilized acid while the condensation polymerization was enhanced in presence of OH-. Sol was formed at pH=2, while the pH should be 8 for formation of gel. By setting ratio of initial concentrations of water to ethyl silicate to 8, the gel formation time was minimized.

Experimental study and process simulation of n-butyl acetate produced by transesterification in a catalytic distillation column

The production of n-butyl acetate by transesterification of methyl acetate with n-butanol, catalyzed by acidic ion-exchange resin NKC-9, was experimentally investigated in a homemade catalytic distillation column with a diameter of 80 mm. A non-equilibrium stage model for describing the catalytic distillation process was established and solved with Newton-Homotopy method. The effect of feeding mode, reflux ratio, material molar ratio and number of reactive sections on the conversion of methyl acetate was investigated. The experimental results agree well with those obtained by the theoretical simulation calculations, indicating the accuracy and reliability of the non-equilibrium model. It can be concluded that the non-equilibrium model established in this paper can provide theoretical guidance for the further process design and optimization.

Catalytic distillation for simultaneous hydrolysis of methyl acetate and etherification of methanol

A catalytic distillation process was developed for the treatment of a methyl acetate/methanol byproduct stream typically encountered in polyvinyl alcohol manufacture. A two-step reaction scheme (hydrolysis + etherification) with separation is modeled in a catalytic distillation column to produce dimethyl ether (DME) and acetic acid. Simulations are performed using Aspen Plus ® and assume both physical and reaction equilibrium. A batch catalytic distillation test with only methyl acetate and methanol as feed, showed DME to be the sole distillate product, whereas, the bottoms product contained acetic acid, water, methanol, and DME. Simulation results show that this “self-feeding” reaction sequence can be used to produce a high purity DME product with complete conversion of water and methanol. The effect of pressure, water, molar feed ratio of methyl acetate/methanol, and feed location were examined. Even with no additional water fed, the hydrolysis reaction proceeds to completion and is only dependent on the molar feed ratio of methyl acetate/methanol. All possible azeotropes (methyl acetate/water, methyl acetate/methanol) are eliminated by completely reacting away water and methanol.

A three-phase nonequilibrium model for catalytic distillation

AbstractNonequilibrium model for steady state simulation of catalytic distillation is presented. Mathematical model takes into account both mass and heat transfers across the gas liquid interface and through the liquid-solid (catalyst) interface. Equations describing the mentioned phenomena are based on the effective diffusivity approach. The resulting system of nonlinear algebraic equations was implemented in the FORTRAN programming language and solved by the BUNLSI (Ferraris &amp; Tronconi, 1986) solver. The described model was verified using the experimental data obtained from a continuous distillation column equipped with catalytic packing. As an experimental model system, synthesis of propyl propionate from propan-1-ol and propionic acid was chosen. Comparison of experimental and simulation data is presented, and appropriateness of the developed model for other types of catalytic distillation processes is discussed.

Transesterification of dimethyl oxalate with phenol over TiO2/SiO2: Catalyst screening and reaction optimization

AbstractPhysicochemical properties of silica‐supported titanium oxide catalysts as well as their performances for transesterification of dimethyl oxalate (DMO) with phenol to methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO) have been investigated systematically. Various wt % of TiO2 were loaded on SiO2 by a two‐step wet impregnation method. The surface properties of TiO2/SiO2 catalysts were explored by various characterization techniques (BET, SEM, ICP, XPS, XRD, FTIR of pyridine adsorption, and NH3‐TPD). Catalytic performances of TiO2/SiO2 catalysts were found to be strongly dependent on TiO2 dispersion and surface acidity. Monolayer dispersion capacity of TiO2 on silica was estimated to be about 4.0 TiO2 molecules per nm2 (SiO2) and no crystalline TiO2 was detected at TiO2 loading less than 12 wt %. FTIR and TPD analysis suggested that weak Lewis acid sites on the surface of TiO2/SiO2 were responsible for their unique selectivity to the target products, MPO and DPO. An optimization of reaction conditions for the transesterification of DMO with phenol was performed over 12 wt % TiO2/SiO2 calcined at 550°C. In addition, we studied the disproportionation reaction from MPO to DPO via a catalytic distillation process, which is highly efficient to promote formation of the desired DPO. © 2008 American Institute of Chemical Engineers AIChE J, 2008

Non-equilibrium model for catalytic distillation process

A new improved tri-diagonal method was developed for the non-equilibrium stage model of the catalytic distillation by coupling consumptive reaction coefficient. The reactions in the distillation column were divided into generative reaction and consumptive reaction. The non-equilibrium stage model was introduced for the catalytic distillation process of the dimethyl carbonate (DMC) synthesis by urea methanolysis over solid based catalyst, and the improved tri-diagonal method was used to solve the model equations. Comparison of predicted results with experiment data shows that the mean relative error of the yield of DMC was 3.78% under different conditions such as different operating pressures and reaction temperatures. The improved tri-diagonal matrix method could avoid the negative values of the liquid compositions during the calculations and restrain the fluctuation of compositions by slowing down the variations of the values in the iteration. The modeling results show that the improved tri-diagonal method was appropriate for system containing a wide range of boiling point components and a different rate of reactions.

Modeling of the Catalytic Distillation Process for the Synthesis of Dimethyl Carbonate by Urea Methanolysis Method

A nonequilibrium model of the catalytic distillation was developed for the process of DMC synthesis by a urea methanolysis method over a solid base catalyst at the bench scale, and the Wilson model was used to account for the nonideality of the liquid phase. The superiority of the catalytic distillation on the removal of the products to restrain the reverse reaction was illustrated in the present work. Furthermore, the influence of total pressure and the reaction temperature on DMC yield and the sensitivity analysis to the reaction kinetics were discussed in detail. The results revealed that the catalytic distillation was appropriate for the process of DMC synthesis.