Batch Reactive Distillation Research Articles

Design and optimization of batch reactive distillation processes with off-cut

Although off-cut is commonly applied in non-reactive batch distillation, reports of the application of off-cut for batch reactive distillation (BREAD) are quite rare. In order to systematically investigate the use of off-cut in BREAD systems, we develop the optimal BREAD process design with and without off-cut for a canonical set of hypothetical reaction systems and a process for the hydration of methyl lactate. The results show that using off-cut can significantly improve performance, especially when both reactants have boiling points between those of the two products (for a quaternary system), when the product purity specification is high, and when the reaction equilibrium constant is low. The optimal batch recipe including off-cut can also be understood based on the normal boiling point ranking of the reactants and products.

An ideal internally heat integrated batch distillation with a jacketed still with application to a reactive system

Batch distillation is an irreversible process and consumes many times the theoretical minimum energy requirement. The present work focuses on the development of an internally heat integrated batch distillation with a jacketed still (IHIBDJS) aiming to reduce the degree of irreversibility towards zero. The IHIBDJS scheme consists of a rectifying tower equipped with an overhead condenser and a still pot or reboiler that surrounds the tower concentrically. For improving the energy efficiency by the reduction of external energy input, the rectifier is operated at an elevated pressure so that a thermal driving force should exist between the rectifying tower and the concentric still. For this purpose, an isentropic compression system is mounted in the reboiled vapor line. Aiming to reduce further the degree of process irreversibility, we propose an additional thermal arrangement into the IHIBDJS configuration that couples the overhead vapor with the reboiler liquid, thereby reducing further the external heat consumption. It is investigated for a reactive batch distillation column that the effective use of internal heat sources would make the heat integrated column an independent scheme of external heat source.

A novel combination of internal and external heat integrations in batch distillation: Application to a reactive system

Studies on the thermal integration of batch rectifier have received almost no attention, although it is well-known for continuous distillation since the 1960s. In this contribution, we aim to develop an energy integration approach for batch distillation columns by thermally coupling the rectification tower with the concentric reboiler that surrounds the tower as a jackted. In this internally heat integrated batch distillation with a jacketed reboiler (IHIBDJR), the vapor produced in the concentric reboiler is compressed and then it enters the bottom of the rectifier. With the judicious use of internal heat source, the proposed IHIBDJR shows its attractiveness in terms of energy savings and payback time of excess capital. The pressure elevation from the jacketed reboiler to rectifying section generates a possibility of further intensification through the introduction of direct vapor recompression mechanism in the IHIBDJR. This novel combination of internal and external heat integrations can utilize the latent heat, an additional internal source, released by the compressed overhead vapor in vaporizing the reboiler liquid. After deriving the general form of this combined heat integrated structure, the mechanism is finally illustrated by a batch reactive distillation. This hybrid configuration shows promising energetic and economic potential over the IHIBDJR and its conventional counterpart.

Model reduction and optimization of a reactive dividing wall batch distillation column inspired by response surface methodology and differential evolution

Carrying out reaction and separation simultaneously in a reactive dividing wall batch distillation column batch RDWC in the case of ethyl acetate synthesis provides the possibility of separating both products and increasing the equilibrium reaction conversion. Overcoming the known azeotrope conditions, high purity for ethyl acetate and decreasing the batch time compared to simple reactive batch distillation are the advantages of this configuration. The corresponding dynamic simulation is carried out by simultaneously solving the model-associated system of differential and algebraic equations. In this study, the optimal values of the vapour and liquid split ratios are considered as the decision variables in order to maximize the amount of ethyl acetate accumulated during batch time. The optimization strategy is implemented inspired by response surface methodology in which an optimal surface is fitted to the collected data set using differential evolution (DE). The optimal surface relevant algebraic equation is then considered as the reduced form of the complex model and the optimal values are obtained using the DE method.

Neural Network MIMO Model for Production of Isopropyl Myristate in a Semibatch Reactive Distillation Column

Batch reactive distillation is an integrated unit of batch reactor and distillation. It provides benefits of having higher conversion and yield by continuous removal of side product. The aim of this paper is to develop an artificial neural network (ANN) based model for production of isopropyl myristate in an industrial scaled semibatch reactive distillation. Two cases of the MIMO model were developed. Case 1 does not consider historical data as inputs while case 2 does. The trained ANN for both cases was validated with independent validation data and the best architecture was optimized. Case 1 resulted to 8 inputs, 14 hidden nodes and 2 outputs [8-14-2] ANN while Case 2 resulted to [12-13-2] ANN. The results show that both ANN models have ability to predict the unknown validation and testing data very well. However, the [8-14-2] ANN model produce higher accuracy than [12-13-2] ANN model with MSE of 0.00094 and 0.0013, respectively.

Intensified thermal integration in batch reactive distillation

Published work on the heat integration of batch distillation is scare and mainly focuses on the continuous flow columns. This paper introduces a novel thermally integrated batch reactive distillation, in which, the rectification tower runs as usual at atmospheric pressure and the concentric reboiler operates under vacuum. It is inspected that the proposed thermally integrated batch reactive distillation with a concentric vacuum reboiler secures positive savings of energy and better economic figures than the conventional batch reactive distillation. Importantly, this scheme has the potential to enhance the product purity at steady state by the improvement of reaction conversion. For boosting both the energetic and economic performance of the proposed thermally integrated batch distillation scheme, in this contribution, we introduce further intensification by coupling the overhead vapor and the reboiler liquid.

Integration of Enzymatic Catalysts in a Reactive Distillation Column with Structured Packings

The integrated process setup of reaction and separation in reactive distillation can be favorable for enzyme-catalyzed reactions that are often equilibrium-limited and/or inhibited by the product of the reaction. However, until now, no appropriate way has described the implementation of the enzymes into distillation columns. In this work, a special type of biocatalytic coating for commercially available structured packings was developed to enable enzymatic reactions in reactive distillation columns. Lipase CALB was immobilized within the silica-gel based coating and showed high long-term stability, i.e., the coatings can be stored for at least 50 days at room temperature without any significant loss of enzyme activity. In addition, the silica-gel coatings were stable in organic media and at increased temperatures. Reactive distillation experiments were carried out in a batch reactive distillation setup comprising of structured A3-500 packings from Montz (Hilden, Germany) coated with the catalytic silica gel. Stepwise removal of the low boiling point product from the distillate shifted the equilibrium to the product side and increased the conversion of the reactants from 60% to 98%, in comparison with the corresponding setup in a standard batch reactor. The stability of the silica-gel coating and loss of the enzyme was investigated during the distillation runs. Overall, the integration of an enzymatic reaction into a reactive distillation column offers new possibilities for the application of biocatalysts in organic synthesis.

Mapas de Curvas Residuales para Procesos de Destilación Reactiva Multicomponente

The present work presents a novel theoretical model that allows visualizing the chemical reactions evolution in a specific multicomponent reactive distillation process. Math provides tools to represent real processes for analysis, and with the basic elements of linear algebra chemical species and chemical reactions could be represented by linear combinations of natural elements and homogeneous equations systems, respectively. A subset of an L-dimensional space is required for the graphical representation of these mathematical objects. A reactive diagram is drawn as a study case. This diagram allows locating the involved chemical species as well as their temporary evolution through a batch reactive distillation process. Furthermore, in this triangular diagram, the behavior of that system can be visualized.

Enabling integrated biorefineries through high-yield conversion of fractionated pentosans into furfural

Dilute aqueous solutions of furfural were produced in high yield from biomass hydrolysates using an acid-catalyzed batch reactive distillation process that separated the vapor phase from the aqueous reactant medium. Hot water hydrolysates from hybrid poplar, miscanthus, switchgrass and corn stover were dehydrated using sulfuric acid. The vapor fraction from the reactor was condensed to produce furfural in excess of 85% of the theoretical yield based on total pentose. Using xylose as the model compound, and temperature and acid concentration as the variables, the process conditions were optimized by the construction of a three-level statistical model. Hot water hydrolysis of biomass provided with a cellulose-rich solid fraction which has potential for conversion into pulp or cellulosic ethanol, while the liquid fraction, rich in hemicellulose sugars, was converted into furfural. Fractionating the biomass allows for exploration of the concept of the integrated biorefinery where the hemicellulose sugars are not underutilized or encountered as potential inhibitors during microbial conversions of the solid stream, but are converted into furfural, a valuable chemical precursor. The availability of the cellulose fraction for further conversion into pulp or ethanol gives the current process a major advantage over the conventional batch process used in industry, where theoretical yields do not exceed 45–50% with the conspicuous absence of a usable cellulose stream.

Input reconstruction for statistical‐based fault detection and isolation

AbstractIn this work, an input reconstruction scheme for detecting and isolating sensor, actuator, and process faults is proposed. The scheme uses model‐based and statistical‐based FDI methods, which yields an improved analysis of abnormal operation conditions in chemical processes. The main advantage of the proposed approach over existing works lies in the reconstruction of system inputs and the subsequent estimation of fault signatures. This advantage is demonstrated through simulation examples and the analysis of recorded process data from a reactive batch distillation column. © 2011 American Institute of Chemical Engineers AIChE J, 2012

Semi-Continuous Reactive Batch Distillation for Production of Methyl Formate

Reaction kinetics of the esterification of Methyl Formate (MF) is studied in a batch reactor at different temperatures and the reliability of the estimated parameters is analyzed with Matlab using a fourth order Runge-Kutta method in the paper. Kinetic constants were experimentally examined and used to calculate the optimal operation parameters of semi-continuous reactive distillation for production of MF in order to minimize the amount of unconverted Formic Acid (FA) remained in the bottom. The results show that the optimal condition is obtained at the formic acid/methanol mole ratio of 0.5:1 and the mass fraction of formic acid at the bottom is 2% which is very close to the calculated value. Simulation work was carried out with Matlab and the results showed good agreement with the experimental data.

Optimal operation of different types of batch reactive distillation columns used for hydrolysis of methyl lactate to lactic acid

Hydrolysis of methyl lactate to lactic acid in a reactive distillation column is widely used in the purification of lactic acid. In this work, optimal operations of conventional and inverted batch reactive distillation columns undergoing the hydrolysis reaction are presented. Minimum time optimisation problem is formulated incorporating a process model within gPROMS software and is solved for different range of lactic acid purity and the amount of product using both columns. For a given column type and configuration the minimum operation time is obtained by optimising the reflux ratio profile. For conventional column, the lactic acid being the heaviest in the reaction mixture, reflux ratio policy plays an important role in removing the light product methanol from the top of the column while ensuring the presence of both reactants in the reaction zone to maximise the conversion to lactic acid. For inverted column, reboil ratio policy plays an important role in removing the lactic acid from the bottom of the column while ensuring the presence of both reactants in the reaction zone to maximise the conversion to lactic acid. For some cases (although limited) it is observed that for low lactic acid product purity the conventional column outperforms the inverted column while for high product purity the inverted column outperforms the conventional column in terms of batch time.

Neural network-based controller design of a batch reactive distillation column under uncertainty

This paper presents the use of neural network-based model predictive control (NNMPC) incorporated with a neural network (NN) estimator for handling the predefined optimal policy tracking of a batch reactive distillation. The predefined optimal policy has been determined by dynamic optimization strategy. Then, the NNMPC incorporated with the NN estimator has been implemented to provide tracking of the obtained optimal policy. The NN model in the MPC algorithm gives as a one-step-ahead prediction of states, and it is therefore used in every iteration over a prediction horizon. Thus, the measured distillate composition at current time, needed as one of NN model inputs, is needed. However, the composition measurement is rarely available online in practice. Hence, an NN estimator is developed to estimate the current composition from the available measured composition with delay of 10 min. Both NNs are trained based on Levenberg–Marquardt algorithm. It has been found that the NNMPC provides satisfactory control performance for set point tracking problems. The robustness of the NNMPC is investigated with respect to parametric plant uncertainties and temperature measurement noise. Comparisons are made with a proportional integral derivative (PID) controller incorporated with the NN estimator. The results show that the NNMPC provides better control performance than the PID controller in all cases. © 2011 Curtin University of Technology and John Wiley & Sons, Ltd.

Neuro-estimator based GMC control of a batch reactive distillation

In this paper, an artificial neural network (ANN)-based nonlinear control algorithm is proposed for a simulated batch reactive distillation (RD) column. In the homogeneously catalyzed reactive process, an esterification reaction takes place for the production of ethyl acetate. The fundamental model has been derived incorporating the reaction term in the model structure of the nonreactive distillation process. The process operation is simulated at the startup phase under total reflux conditions. The open-loop process dynamics is also addressed running the batch process at the production phase under partial reflux conditions. In this study, a neuro-estimator based generic model controller (GMC), which consists of an ANN-based state predictor and the GMC law, has been synthesized. Finally, this proposed control law has been tested on the representative batch reactive distillation comparing with a gain-scheduled proportional integral (GSPI) controller and with its ideal performance (ideal GMC).

Feasibility of Batch Reactive Distillation with Equilibrium‐Limited Consecutive Reactions in Rectifier, Stripper, or Middle‐Vessel Column

A general overall feasibility methodology of batch reactive distillation of multireaction systems is developed to study all the possible configurations of batch reactive distillation. The general model equations are derived for multireaction system with any number of chemical equilibrium‐limited reactions and for any number of components. The present methodology is demonstrated with the detailed study of the transesterification of dimethyl carbonate in two reversible cascade reactions in batch reactive distillation process. Pure methanol is produced as distillate, and pure diethyl carbonate is produced at the bottom simultaneously in middle‐vessel column; in each section, continuous feeding of ethanol is necessary. The results of feasibility study are successfully validated by rigorous simulations.

Significant thermal energy reduction in lactic acid production process

Lactic acid is widely used as a raw material for the production of biodegradable polymers and in food, chemical and pharmaceutical industries. The global market for lactic acid is expected to reach 259 thousand metric tons by the year 2012. For batch production of lactic acid, the traditional process includes the following steps: (i) esterification of impure lactic acid with methanol in a batch reactor to obtain methyl lactate (ester), (ii) separation of the ester in a batch distillation, (iii) hydrolysis of the ester with water in a batch reactor to produce lactic acid and (iv) separation of lactic acid (in high purity) in a batch distillation. Batch reactive distillation combines the benefit of both batch reactor and batch distillation and enhances conversion and productivity (Taylor and Krishna, 2000 [1]; Mujtaba and Macchietto, 1997 [2]). Therefore, the first and the last two steps of the lactic acid production process can be combined together in batch reactive distillation (Fig. 1) processes. However, distillation (batch or continuous) is an energy intensive process and consumes large amount of thermal energy (via steam). This paper highlights how significant (over 50%) reduction in thermal energy consumption can be achieved for lactic acid production process by carefully controlling the reflux ratio but without compromising the product specification. In this paper, only the simultaneous hydrolysis of methyl lactate ester and the separation of lactic acid using batch reactive distillation is considered.

Operating Parameters and Selectivity in Batch Reactive Distillation

This Article provides new predictions for selectivity in batch reactive distillation, identifying the reflux or reboil ratio and a Damkohler number (Da) as the key operating parameters. The dimensionless Da incorporates the influence of liquid holdup, vapor rate, and rate of reaction. Example results for a system of serial isomerization reactions and for the synthesis of ethylene glycol are provided. The results show that selectivity improvements in BRD are limited for high values of Da or for high values of the reflux or reboil ratio and that selectivity is enhanced as Da or reflux or reboil ratio is decreased. However, decreasing Da can cause conversion loss, which can be mitigated by increasing the reflux (or reboil) ratio at the expense of selectivity. Consequently, there is an optimum value of reflux or reboil ratio that gives a maximum yield for systems operated at low or moderate Da. For the isomerization in a BRD, the heat released by reaction can improve selectivity at the expense of conversion. ...

Semibatch Reactive Distillation for Isopropyl Acetate Synthesis

Batch reactive distillation, which combines the flexibility of batch process with the advantages of reactive distillation, can be an effective alternative to conventional batch processing. For instance, acetate esters such as n-butyl acetate and amyl acetate can be produced using batch reactive distillation. Previous studies have shown that isopropyl acetate can also be produced in batch reactive distillation with the addition of chloroform as an entrainer and using a large reflux ratio and number of stages. This paper compares the vapor−liquid and liquid−liquid features of these acetate ester systems, and shows the similarities and differences among them. We show why the isopropyl system is more difficult than the others and how semibatch reactive distillation without an additional entrainer can result in a feasible and more efficient process for the production of isopropyl acetate than has been previously known. In a semibatch reactive distillation, the loss of isopropyl alcohol can be substantially dec...

Composition Estimation of Reactive Batch Distillation by Using Adaptive Neuro-Fuzzy Inference System

Composition estimation plays very important role in plant operation and control. Extended Kalman filter (EKF) is one of the most common estimators, which has been used in composition estimation of reactive batch distillation, but its performance is heavily dependent on the thermodynamic modeling of vapor-liquid equilibrium, which is difficult to initialize and tune. In this paper an inferential state estimation scheme based on adaptive neuro-fuzzy inference system (ANFIS), which is a model base estimator, is employed for composition estimation by using temperature measurements in multicomponent reactive batch distillation. The state estimator is supported by data from a complete dynamic model that includes component and energy balance equations accompanied with thermodynamic relations and reaction kinetics. The mathematical model is verified by pilot plant data. The simulation results show that the ANFIS estimator provides reliable and accurate estimation for component concentrations in reactive batch distillation. The estimated states form a basis for improving the performance of reactive batch distillation either through decision making of an operator or through an automatic closed-loop control scheme.

Model reduction and optimization of reactive batch distillation based on the adaptive neuro-fuzzy inference system and differential evolution

This paper considers the application of the adaptive neuro-fuzzy inference system (ANFIS) instead of the highly nonlinear model of a reactive batch distillation column for optimization. The architecture has been developed for fuzzy modeling that learns information from a data set, in order to compute the membership function and rule base in accordance with the given input–output data. In this work, the differential evolution algorithm has been employed for optimization of operation policy of reactive batch distillation for producing ethyl acetate. In optimization, minimal batch time and high purity of product are considered, and reflux ratio and final batch time are taken as decision parameters. The results show that the reduced model (ANFIS) is able to properly create a robust model of the reactive batch distillation, and CPU use is reduced to 1/18,000 of that of a real mathematical model. The highest yield and mole fraction of ethyl acetate were achieved through the use of the obtained optimization policy.