Batch Reactive Distillation Research Articles

Dynamic modeling and optimal control of reactive batch distillation: An experimental case study

In the present study, dynamic modeling, optimal operation and control of a reactive batch distillation process is illustrated based on experimental and simulation studies using methyl acetate production case study. An equilibrium stage model, incorporating non-ideal VLE and start-up region of heating, is developed based on data generated on an experimental unit by identifying five input parameters representing uncertainties. The optimal control problem is solved using genetic algorithm, considering the objective function identified on the basis of trend analysis using the developed dynamic model, to find the optimal reflux ratio, heat input to the reboiler, and mole ratio of methanol to acetic acid in the initial reaction mixture. Open-loop and closed-loop implementations clearly illustrate the improved performance with respect to the quantity of methyl acetate in the distillate product with a reasonably high conversion and product purity within reasonably short batch duration, illustrating the successful optimal control implementation experimentally.

Modeling and Simulation of a Batch Reactive Distillation Process with Column Heating

AbstractA solid catalyzed esterification reaction in a batch reactive distillation (BRD) apparatus was carried out to evaluate the start‐up dynamics and steady‐state characteristics. As a novelty, the column was provided with a heating jacket. A wall heating of 50 °C of the column gave the highest purity of distillate for this system of producing methyl acetate from a catalytic reaction between acetic acid and methanol. Experiments were performed with constant heat supply rate to the reboiler. Temperature and concentration dynamics as well as purity of the top distillate were recorded. A modeling approach was developed to validate the experimental results. A simulation code for energy and material balance under reaction and distillation conditions was developed and the experimental distillate composition of the top product was validated with simulation results for various heat input rates.

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.

Local parameter identifiability of large-scale nonlinear models based on the output sensitivity covariance matrix

Abstract The use of first-principle models is motivated by the potential of detailed information available as well as their versatility. Therefore, it is important to keep these models up to date so the models represent accurate enough the processes at hand. However, most of these models are nonlinear with a large number of states and parameters but with a relatively low number of measured outputs. This lack of measurements hinders the possibility to estimate all of the parameters present in the model. In this work, parameter identifiability of large-scale nonlinear models is explored using the empirical output controllability covariance matrix approach. This empirical covariance matrix is used to extract the output sensitivity matrix of the model to assess parameter identifiability. The advantages of the proposed methods are discussed while different sensitivity indexes are evaluated to draw sound conclusions on the parameter ranking results. A large-scale reactive batch distillation process simulation is used as a demonstrator.

Experimental investigation of start-up dynamics for various heating effects in batch reactive distillation to produce methyl acetate

Abstract In this article the experimental results related to various wall heating conditions for a batch reactive distillation (BRD) are presented. A solid catalyzed esterification reaction between acetic acid and methanol to produce methyl acetate and water is chosen as the system for study. An experimental apparatus with reboiler and a rectification column along with top total condenser is used. As a novelty the rectification column is provided a jacket through which hot water can be circulated. The dynamics of temperature in the reboiler, the time for onset of distillate and the purity of product in the distillate were recorded. The wall temperature of rectification column is varied to study its effect. Another two sets of conditions with air filled jacket and insulated conditions were also studied. The reboiler is supplied a constant heat input rate at three different values. An objective function pertaining to high throughput of the desired product in distillate is defined to select the most suitable option among all the above mentioned operating conditions.

Modeling, analysis and multi-objective optimization of an industrial batch process for the production of tributyl citrate

This work describes the modeling and optimization of a trybutil citrate (TBC) production process at the industrial scale. The process comprises a batch reactive distillation for the esterification of citric acid with butanol. The dynamic model of the process was constructed based upon validated kinetic and thermodynamic models, implemented in gPROMSⓇ software, verified with industrial scale experiments, and used for further optimization to minimize batch time and energy consumption. Manipulated process variables were the molar ratio of butanol to citric acid, the alcohol loading policy, and the heat supply profile, and a Pareto front of optimal solutions was obtained. Depending on the main goal, the optimization process allowed to obtain energy savings up to 28%, and the corresponding processing times were reduced by 36%. Finally, multi-attribute utility theory (MAUT) approach was used as decision-making aid tool to select the preferred operating conditions for TBC production at the industrial scale.

Robust Trajectory Tracking in a Reactive Batch Distillation Process using Multirate Nonlinear Internal Model Control

Operating a reactive batch distillation (RBD) process in an optimal manner is of paramount importance for improving product quality and profitability in the face of changing market conditions. However, implementation of an open loop optimal control policy may lead to significant reduction in yield and amount of desired product produced when unmeasured disturbances occur during operation. In this work, an observer error feedback-based multirate nonlinear internal model control (NIMC) scheme is developed for optimal trajectory tracking in the face of unmeasured disturbances. In particular, mismatch in the initial conditions and process parameter variations that can occur during RBD operation are considered. To reduce the time required for online computations, a recently proposed reduced order RBD model [Reddy et al. Compt. Chem. Eng., 2017, 106, 40−56] is used for the controller synthesis. Because the thermodynamic model associated with the RBD process has discontinuities, a multirate version of unscented Kalman filter (UKF) has been developed on the basis of the reduced order model for solving the state estimation problem associated with the proposed NIMC formulation. The efficacy of the proposed approach has been demonstrated by simulating an optimal trajectory tracking problem in the RBD process involving production of butyl acetate. The proposed multirate NIMC formulation is found to be computationally efficient and work reasonably well when tested on the RBD process for solving the set point tracking problem in the presence of unmeasured disturbances. In particular, it is advantageous to operate the RBD process using the proposed UKF-NIMC scheme when the system is subjected to unmeasured disturbances.

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.

A novel split-reflux policy in batch reactive distillation for the optimum synthesis of a number of methyl esters

The production of a number of methyl esters such as methyl decanoate (MeDC), methyl salicylate (MeSC), and methyl benzoate (MeBZ) by esterification reactions of several carboxylic acids such as decanoic acid (DeC), salicylic acid (ScA), and benzoic acid (BeZ) with methanol, respectively, through a reactive distillation system (batch or continuous) is cost-intensive and operationally challenging operation. It is difficult to keep the reaction species together in the reaction section due to wide boiling point differences between the reactants. Methanol (in those esterification processes) having the lowest boiling temperature in the reaction mixture can separate easily from carboxylic acid as the distillation progresses, resulting in a severe drop in the reaction conversion ratio of the acid employing batch/continuous distillation system. In order to overcome this type of challenge and to increase the overall reaction conversion, a novel split-reflux conventional batch reactive distillation configuration (sr-BRD) is proposed/studied in detail in this investigation.The optimal performance of BRD/ sr-BRD column is determined in terms of maximum achievable conversion of acids, and highest concentration of the esters produced for each chemical reaction scheme. The results for given separation tasks are compared with those obtained using conventional batch distillation (BRD) process. The optimization results clearly show that the sr-BRD process significantly improves the process efficiency, the conversion ratio of acid, and the product purity of methyl esters compared to that obtained via the BRD process.

Batch Reactive Distillation in Bromodifluoroacetic Acid Synthesis Technology

A catalytic distillation process reacting in a column bottom was experimentally studied for the transesterification of methyl and ethyl esters of bromodifluoroacetic acid with trifluoroacetic acid. Sulfuric acid was used as a catalyst. Experiments were performed at different column bottom heat duties. As a result of the experiments, we had bromodifluoroacetic acid with a purity above 97.0 mol % at a product yield of 87.4%.

Modeling of reactive batch distillation processes for control

Reactive batch distillation (RBD) is a preferred process intensification technology to carry out equilibrium-limited reactions. It is a multicomponent, multiphase system. Appropriate process description requires dynamic modeling of coupled thermodynamics and transport phenomena including the chemical reactions. Such models are barely applicable to online model based operation technology such as model predictive control, real-time optimization and online process monitoring. Therefore, in this paper, the rigorous dynamic model of an RBD is transformed into a set of decoupled ordinary differential equations using linear transformation matrices, called extent transformation, that preserve the physical meaning of the transformed variables. The resulting model has a state space representation with a diagonal state matrix. This representation is suitable for control purposes and can be considered as a linear parameter varying system. Based on the final structure of the model, controllability conditions are stated, and model reduction scenarios are proposed. Finally, the model based on extent transformations is compared with the rigorous nonlinear model via the simulation of a polyesterification process.

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.

Integrated reaction and separation in a continuous middle vessel column for enhancing indirect hydration of cyclohexene to cyclohexanol

This study introduced economically-viable continuous reactive distillation (RD) design alternatives for cyclohexanol production through the indirect hydration of cyclohexene. The feasibility concept of batch RD was employed for generating the new design alternatives. The first alternative process utilized a continuous stripper for recovering the stable node product of cyclohexyl formate in the esterification reaction and then employed a continuous middle vessel column (MVC) for recovering the stable and unstable node products of cyclohexanol and formic acid in the hydrolysis reaction. The second design had a single MVC-type column having the reactive rectifying zone and the middle vessel reactor for the two respective reactions. The simulation results showed the two alternative sequences required less energy duty than the previously proposed RD process. However, compared to the prior RD process, the life cycle cost (LCC) of the first alternative design increased about 30% due to high equipment costs and the LCC of the second process decreased nearly 40% because of low equipment costs and energy requirements.

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.

Multi-objective optimization of a reactive batch distillation process using reduced order model

Reactive batch distillation (RBD) processes are highly nonlinear in nature and use of first principles model into the optimization problem demands high computational time. Therefore, a reduced order model for RBD process is proposed which is based on selection of states of prime importance, identification of input state variables, definition of reference trajectories for nominal case, and definition of additional variable transformation to facilitate adaptation of the model to variations in operating conditions. Further, the work focuses on development of a multi-objective optimization formulation for arriving at an optimal operation policy for RBD, and a modified version of Non-dominated sorting Genetic algorithm (NSGA-II) is developed for its solution. The proposed approach is evaluated by application to a simulation case study for production of butyl acetate. The optimization results obtained using the reduced order model are comparable to those obtained with first principles model, while requiring only 1/20th of the time.

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...

Synthesis of Methyl Decanoate Using Different Types of Batch Reactive Distillation Systems

Methyl decanoate (MeDC) is a fatty acid methyl ester (FAME) and is an important chemical compound with global production of 31 million tons per year. However, synthesis of methyl decanoate (MeDC) via esterification of decanoic acid (DeC) with methanol by reactive distillation is operationally challenging due to the difficulty of keeping the reactants together in the reaction zone; methanol being the lightest component in the mixture can separate itself easily from the other reactant deteriorating significantly the conversion of DeC using either a conventional batch or continuous distillation column. This is probably the main reason for not applying the conventional route to MeDC synthesis. Whether a semibatch distillation column (SBD) and the recently developed integrated conventional batch distillation column (i-CBD) offer the possibility of revisiting such chemical reactions for the synthesis of MeDC is the focus of this paper. The minimum energy consumption (Qtot) as the performance measure is used to evaluate the performances of each of these reactive column configurations for different ranges of methyl decanoate purity and the amount of product. It is observed that the use of i-CBD column provides much better performance than the SBD column in terms of the production time and the maximum energy savings when excess methanol is used in the feed. However, the SBD column is found to perform better than the i-CBD column when both reactants in the feed are in equal amounts. Also, the optimization results for a given separation task show that the performance of a two-reflux-interval strategy is superior to the single-reflux interval in terms of operating batch time, and energy usage rate in the SBD process at equimolar ratio.