Batch Reactive Distillation Column Research Articles

Optimisation of semi-batch reactive distillation column for the synthesis of methyl palmitate

Synthesis of methyl palmitate (MP) has not been considered in the past using a reactive distillation process (continuous or batch) due to the challenge of keeping the reactants palmitic acid (PA) and methanol (MeOH) together in the reactive zone. MeOH, being the lightest in the reaction mixture, travels up the distillation column as distillation proceeds and will be removed from the system via the distillate in a conventional batch reactive distillation (CBRD) column and thus will limit the conversion of PA. Therefore, in this work semi-batch reactive distillation (SBRD) column is proposed where additional methanol will be fed at the bottom of the column in a continuous mode allowing the chemical reaction to continue. However, as water (H2O) is one of the reaction products and is the second lightest component in the mixture, it will travel up the column next and will be removed in the distillate tank. Also due to wide difference in the boiling points of the reaction products and due to diminishing amount of water in the reboiler, the backward reaction will not be a dominating factor and therefore ignored in this work. With this backdrop, optimal performance of the SBRD column is evaluated in terms of conversion of PA to MP and energy consumption via minimization of the operating batch time for a wide range on MP purity.

Porous polymer microsphere functionalized with benzimidazolium based ionic liquids as effective solid catalysts for esterification

Abstract To prepare polymer supported ionic liquids (PSILs) as effective catalysts for esterification, the free radical suspension copolymerization of vinylbenzyl chloride (VBC, monomer), styrene (St, monomer) and divinylbenzene (DVB, crosslinker) with the addition of n-heptane (porogen) was carried out for the fabrication of the porous polymer (PVD) microsphere as support, followed by the immobilization of sulfonic acid-functionalized ionic liquids by the successive treatment of benzimidazole (BIm), 1,3-propane sultone and sulfuric acid (H2SO4) or trifluoromethanesulfonic acid (CF3SO3H). The effects of the compositions of DVB and n-heptane on the internal structure of the polymer supports were investigated, and it was found that the support with 40 wt% DVB and 60 wt% n-heptane (with relative to the monomer) could endow the final PSILs with the relatively optimal catalytic performance. The preliminary experiment in the batch reactor indicated that PSILs herein exhibited higher catalytic activities than commercial Amberlyst 46 resin for the esterification of propanoic acid (PROAc) with n-propanol (PROOH). Consequently, the optimal PSILs catalyst, PVD-[Bim-SO3H]HSO4, was selected for further study in the batch reactive distillation column because of low cost and its ease of preparation. The yield of propyl ropionate (PROPRO) could reach up to 97.78% at the optimized conditions of PROOH/PROAc molar ratio (2:1) and catalyst dosage (2.0 wt%). The investigation of the reaction kinetic manifested that the calculated results of second order pseudo-homogeneous kinetic model were in good agreement with experimental values. The pre-exponential factor and activation energy were 4.12 × 107 L·mol−1·min−1 and 60.57 kJ·mol−1, respectively. It is worth noting that the PSILs catalyst could be simply recovered and reused with relatively satisfactory decrease in the catalytic activity, which made it an environmental friendly and promising catalyst in the industrial application.

Investigation about Profitability Improvement for Synthesis of Benzyl Acetate in Different Types of Batch Distillation Columns

In this work, for the first time, the synthesis of benzyl acetate via the esterification of acetic acid and benzyl alcohol is investigated in the reactive distillation system using a middle vessel (MVD), inverted (IBD), and conventional batch reactive distillation columns. The measurement of the performance of these column schemes is determined in terms of profitability through minimization of the batch time for a defined separation task. The control variables (reboil ratio for MVD, IBD columns) and (reflux ratio in case of CBD column) are considered as piecewise constants over batch time. The optimization results obviously indicate that the CBD system is a more attractive process in terms of batch time reduction, and maximum achievable yearly profit as compared to the MVD, and IBD operations.

Feasibility of novel integrated dividing-wall batch reactive distillation processes for the synthesis of methyl decanoate

Abstract The production of methyl decanoate (MeDC) through esterification of decanoic acid (DeC) with methanol by reactive distillation is operationally challenging and energy-intensive due to the complicated behaviour of the reaction system and the difficulty of retaining the reactants together in the reaction region. Methanol being the lightest component in the mixture can separate itself from the reactant DeC as the distillation proceeds which will cause a massive reduction in the conversion of DeC utilizing either a batch or continuous distillation process. Aiming to overcome this type of the potential problem, novel integrated divided-wall batch reactive distillation configuration (i-DWBD) with recycling from the distillate tank is established in this study and is examined in detail. This study has clearly demonstrated that the integrated divided-wall batch reactive distillation column (i-DWBD) is superior to the traditional conventional batch distillation (CBD) and both the divided-wall (DWBD), and split reflux divided-wall (sr-DWBD) batch reactive distillation configurations in terms of maximum achievable purity of MeDC and higher conversion of DeC into MeDC. In addition, significant batch time and energy savings are possible when the i-DWBD is operated in multi-reflux mode.

Observer-based extended generic model control of a reactive batch distillation

In this communication, a nonlinear observer based control system is developed and illustrated by a reactive batch distillation column (RBDC) producing ethyl acetate. This ethyl acetate is the product of the esterification reaction between acetic acid and ethanol. Being the lightest component, ethyl acetate comes out first as distillate from the top of the column. With the aim to achieve a constant product purity, a nonlinear control scheme is developed, consisting of an extended generic model controller (EGMC) and an observer for the estimation of states required for controller simulation. Here two nonlinear state observers, namely neuro extended Kalman filter (NEKF) and neuro high gain observer (NHGO) are devised. Both the NHGO and NEKF are basically coupled with an artificial neural network (ANN) model, which aims to infer the product composition based on the measured tray temperature required for the closed-loop high gain observer (HGO) and nonlinear extended Kalman filter (EKF), respectively. Through open-loop simulation study, performance of these two state observers is evaluated. Although both the state observers are good enough to track the process output, the NEKF proves its superiority over the NHGO. In the subsequent closed-loop constant composition control investigation, a comparison is made between the EGMC-NHGO and EGMC-NEKF with respect to a traditional proportional integral (PI) controller. In this closed-loop comparative study, it is observed that the performance of the EGMC-NEKF is better than the EGMC-NHGO and the conventional PI.

Feasibility of integrated batch reactive distillation columns for the optimal synthesis of ethyl benzoate

The synthesis of ethyl benzoate (EtBZ) via esterification of benzoic acid (BeZ) with ethanol in a reactive distillation is challenging due to complex thermodynamic behaviour of the chemical reaction and the difficulty of keeping the reactants together in the reaction zone (ethanol having the lowest boiling point can separate from the BeZ as the distillation proceeds) causing a significant decrease in the conversion of BeZ in a conventional reactive distillation column (batch or continuous). This might be the reason of not reporting the use of reactive distillation for EtBZ synthesis although the study of BeZ esterification reaction is available in the public literature. Our recently developed Integrated Conventional Batch Distillation (i-CBD) column offers the prospect of revisiting such reactions for the synthesis of EtBZ, which is the focus of this work. Clearly, i-CBD column outperforms the Conventional Batch Distillation (CBD) column in terms of product amount, purity and conversion of BeZ and eliminates the requirement of excess use of ethanol. For example, compared with CBD column, the i-CBD operation can yield EtBZ at a much higher purity (0.925 compared to 0.730) and can convert more benzoic acid (93.57% as opposed to only 74.38%).

Feasibility Study of Reactive Distillation for the Production of Propylene Glycol Monomethyl Ether Acetate through Transesterification

This paper aims to present the feasibility of conducting the transesterification of propylene glycol ether (PM) with methyl acetate (MeAc) in a reactive distillation (RD) column to improve the reaction conversion. The essential thermodynamic and reaction kinetic data of the reaction system were measured for the feasibility study. There is only one azeotrope, MeAc–MeOH, in the reaction system, and the NRTL model could describe well the thermodynamic behavior of this system. The transesterification of PM with MeAc is an endothermic reaction with activation energy E = 55.704 kJ·mol–1. The feasibility was analyzed by residue curve maps (RCM), showing that full conversion of PM could be realized by RD with a mole ratio of MeAc–PM larger than 2.882. The intensification effect was experimentally verified in a batch RD column. Finally, some important parameters are given through the conceptual design to develop a continuous RD column for the transesterification of PM with MeAc.

In Situ Separation of the Chiral Target Compound (S)-2-Pentanol in Biocatalytic Reactive Distillation

In situ separation of a chiral target compound is realized for the first time as distillate on top of an integrated biocatalytic batch reactive distillation column. The applied reaction system is the racemic resolution of (R/S)-2-pentanol in a transesterification with propyl butyrate, which is catalyzed by immobilized Candida antarctica lipase B (Novozym435). Biocatalyst integration is realized in baskets of wire gauze catalytic packings as column internals. The equilibrium limited reaction is shifted to the product side by fractional distillation of low boiling propanol and the target compound (S)-2-pentanol. Increased molar fractions up to x(S)-2-PeOH = 65 ± 4% with an enantiomeric excess of 90 ± 4% and 51 ± 3% overall conversion are reached for (S)-2-pentanol. Feasibility of the reaction system is investigated in our preselection tool. This tool is developed to evaluate predefined operation conditions in the column setup for transesterification reactions based on criteria regarding biocatalyst stabilit...

Integrated batch reactive distillation column configurations for optimal synthesis of methyl lactate

Although batch reactive distillation process outperforms traditional reactor-distillation processes due to simultaneous reaction and separation of products for many reaction systems, synthesis of Methyl lactate (ML) through esterification of lactic acid (LA) with methanol in such process is very challenging due to difficulty of keeping the reactants together when one of the reactants (in this case methanol) has the lowest boiling point than the reaction products. To overcome this challenge, two novel reactive distillation column configurations are proposed in this work and are investigated in detail. These are: (1) integrated conventional batch distillation column (i-CBD) with recycled methanol and (2) integrated semi-batch and conventional batch distillation columns (i-SBD) with methanol recovery and recycle.Performances of each of these configurations are evaluated in terms of profitability for a defined separation task. In i-SBD column, an additional constraint is included to avoid overflow of the reboiler due to continuous feeding of methanol into the reboiler as the reboiler is initially charged to its maximum capacity. This study clearly indicates that both integrated column configurations outperform the traditional column configurations (batch or semi-batch) in terms of batch time, energy consumption, conversion of LA to ML, and the achievable profit.

Rigorous modeling, simulation and optimization of a conventional and nonconventional batch reactive distillation column: A comparative study of dynamic optimization approaches

In this paper we address the optimization of two batch distillation columns: a conventional batch distillation column (BDC) and a nonconventional dividing wall batch distillation column (DWBDC) with and without chemical reaction. The simultaneous solution of these systems of differential and algebraic equations is performed using two different approaches: pure equation oriented approach (EOA) based on orthogonal collocation over finite elements implemented in GAMS (24.2.2), and control vector parameterization (CVP) as implemented in gPROMS (3.7.1). In order to accomplish this objective, we describe and propose for the nonconventional batch configuration, two dynamic models that involve stage-by-stage calculations for the time varying column profiles. Case studies with and without reaction are presented in order to compare the two discretization approaches and to demonstrate possible benefits of dividing wall columns in batch separations.

Synthesis of Methacrylic Anhydride by Batch Reactive Distillation: Reaction Kinetics and Process

The reaction kinetic of the synthesis of methacrylic anhydride was investigated with a batch stirred-tank reactor at atmospheric pressure using methacrylic acid and acetic anhydride as raw materials. The reactions were conducted at several temperatures between 343.15 and 363.15 K and at various starting reactant compositions. A homogeneous reversible reaction of the second order was described. A batch reactive distillation column was employed to obtain methacrylic anhydride. The influence of feed molar ratio, reflux ratio, and entrainer on the reaction was investigated, and a suitable operating parameter was obtained. Under these conditions, the conversion of methacrylic acid was 99.95%, and the yield of methacrylic anhydride was 86.99%.

Comparison of Conventional and Middle Vessel Batch Reactive Distillation Column: Application to Hydrolysis of Methyl Lactate to Lactic Acid

Comparison of Conventional and Middle Vessel Batch Reactive Distillation Column: Application to Hydrolysis of Methyl Lactate to Lactic Acid

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.

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

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).

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.

State estimation and inferential control for a reactive batch distillation column

An optimal reflux ratio profile is obtained for a reactive batch distillation system utilizing the capacity factor as the objective function in a nonlinear optimization problem. Then, an Artificial Neural Network (ANN) estimator system, which utilizes the use of several ANN estimators, is designed to predict the product composition values of the distillation column from temperature measurements inferentially. The network used is an Elman network with two hidden layers. The designed estimator system is used in the feedback inferential control algorithm, where the estimated compositions and the reflux ratio information are given as inputs to the controller to see the performance of the ANN. In the control law, a scheduling policy is used and the optimal reflux ratio profile is considered as pre-defined set-points. It is found that, it is possible to control the compositions in this dynamically complex system by using the designed ANN estimator system with error refinement whenever necessary.

Nonlinear state estimation and control of a batch reactive distillation

This paper deals with the advanced adaptive control of a batch reactive distillation (RD) column for the production of ethyl acetate. The nonlinear adaptive control law consists of the generic model controller (GMC) and an adaptive state estimator (ASE). In the first part of the present work, the design approach of the ASE scheme in two different forms, namely ASE1 and ASE2, has been addressed for a batch reactive rectifier. The predictor model of both the ASE estimators includes only a component mole balance equation around the condenser-reflux drum system and an extra state equation having no dynamics, and therefore, there is a large process/predictor mismatch. In presence of this structural discrepancy, the adaptive estimation schemes compute the imprecisely known parameters quite accurately based on the measured distillate composition under initialization error, disturbance and uncertainty. In the subsequent part, the adaptive GMC–ASE1 control structure has been formulated for the sample reactive column. This nonlinear control strategy shows comparatively better closed-loop performance than the gain-scheduled proportional integral (GSPI) controller due to the exponential error convergence capability of the estimation scheme and the high-quality control of the GMC law.