Batch Distillation Column Research Articles

Separation of 2,2,2-trifluoroethanol – isopropanol azeotropic mixture by extractive distillation

On a laboratory scale, a complete technological extractive distillation cycle of an industrial azeotropic mixture of 2,2,2-trifluoroethanol (TFE) – isopropanol (IPA) of equimolar composition using N-methyl-2-pyrrolidone (NMP) as a separation agent (SA) was implemented. All technological stages (extractive distillation, target component separation and SA regeneration) were carried out in one apparatus – a batch distillation column. It was shown that this approach makes it possible to separate the TFE – IPA mixture into individual components, as well as to regenerate NMP. The proposed method is an alternative to traditional chemical methods and allows to eliminate the use of aggressive auxiliary reagents and the formation of by-products, to reduce the number of stages and apparatuses from 5 to 1.

Efficient dynamic sampling of batch processes through operation recipes

The complexity of dynamic phenomena present in chemical processes often results in high evaluation costs of accurate first-principles models. This limits their real-time applicability, e.g. for advanced process control. A common solution is the derivation of simpler but faster data-driven surrogate models trained on simulated time series generated from dynamic samplings of a mechanistic model. For batch processes, known non-adaptive dynamic sampling methods lead to unrealistic or even infeasible operation cycles, raising the cost of generating simulated datasets with sufficient information content to train accurate surrogate models. An alternative sampling strategy is developed and analyzed, where sampled input trajectories are constrained to process knowledge in the form of parametrized operation recipes. The proposed methodology is tested for the case studies of full batch cycles of a crystallizer and a batch distillation column, showing that it is more efficient in terms of convergent simulations compared to an established dynamic sampling strategy.

Spreadsheet to illustrate the application of relaxation methods for multicomponent distillation separations

Rigorous calculation methods to simulate multicomponent distillation processes involve large number of variables and equations that are difficult to solve by hand and require the use of specific software. With this purpose, commercial process simulators have been included for years as learning tools in the syllabus of Chemical Engineering degrees. Nevertheless, there is thus a possibility of using these packages as a black box and strategies to mitigate that risk have been developed, as the use of spreadsheets where students can follow and check the calculation algorithms and the details of such calculations. One alternative to solve multicomponent distillation problems is the use of relaxation methods, that find the steady-state solution of a continuous distillation column by solving unsteady-state equations from a specified initial condition, thus providing an analogy with the column startup. In this work, a novel spreadsheet to apply a relaxation method is proposed. Calculation begins with the simulation of a distillation column at total reflux, which is a common way to start up these processes. In order to facilitate the development of unsteady-state equations and operation, a batch distillation column is also simulated. Finally, the evolution of a continuous distillation column from a specified starting condition to steady-state is simulated.

Solution of the maximum distillate on a batch distillation column by a Pseudo-Newton method

This paper presents a new algorithm for the solution of the maximum distillate problem based on Pontryagin's maximum principle. Four cases of study were analyzed with the algorithm. The first case is a literature problem where the column uses twenty trays to distillate ten components, the second case is a binary mixture with no ideal behavior, the third case is a quaternary mixture, and the last case is a reactive mixture. In all cases, the desired purity was settled as a final constraint. The solution algorithm found the optimal control faster than results reported in literature concerning the CPU time.The batch distillation process is modeled by using a rigorous model with no constant volatility. The proposed algorithm uses the Hamiltonian function to reformulate the maximum distillate problem. Then, the optimal control is solved by a Broyden–Fletcher–Goldfarb–Shanno algorithm. The solution procedure of the indirect approach required the forward integration of the states, the integration of the co-state equations backward in time, and the control input is the distillate flow rate which is parameterized. The binary batch distillation column uses six stages, and the maximum recovery is 95% of the light component with a 95% mol percent on the accumulator. The multicomponent batch distillation column uses 17 stages, and the recovery of the lightest component in the product is 90% mol percent. The reactive case reached 80% conversion.

Adaptation of Dynamic Data‐Driven Models for Real‐Time Applications: From Simulated to Real Batch Distillation Trajectories by Transfer Learning

AbstractIn the absence of knowledge about challenging dynamic phenomena involved in batch distillation processes, e.g., complex flow regimes or appearing and vanishing phases, generation of accurate mechanistic models is limited. Real plant data containing this missing information is scarce, also limiting the use of data‐driven models. To exploit the information contained in measurement data and a related but inaccurate first‐principles model, transfer learning from simulated to real plant data is analyzed. For the use case of a batch distillation column, the adapted model provides more accurate predictions than a data‐driven model trained exclusively on scarce real plant data or simulated data. Its enhanced convergence and lower computational cost make it suitable for optimization in real‐time.

Data Driven Linear Quadratic Gaussian Control Design

The implementation of the Linear Quadratic Gaussian (LQG) scheme is often considered problematic as it requires a dynamic model of the system as a whole. The challenges come from state variables without a physical representation and the interference factors that affect the reading process. This paper presents and assesses a combination of methods to adapt the LQG scheme to a discrete-time linear system. The method KalmanNet constructed by the Long-Short Term Memory architecture (LSTM) is employed to replace the role of Kalman Filter (KF). The Value Iteration (VI) algorithm supersedes the role of the Linear Quadratic Regulator (LQR) controller in solving quadratic regulation issues. The assessment of the proposed algorithm on a cart-pole system and batch distillation column with a disturbance factor in uncorrelated Gaussian white noise is carried out in a simulated way under a discrete-time linear system. The result indicates that the solving of regulation problems through the conventional LQG method is not conclusive as the output response oscillation is still in progress. The combination of the KalmanNet and VI algorithm, as aforementioned, provides better results as it proves to solve the regulation problem as well as to compel the system output to converge.

Batch distillation for separating the acetone and n-heptane binary azeotrope mixture: Optimization and simulation

A batch distillation column is one of several approaches that have been developed to improve the distillation process's performance. Batch and specialty chemical industries require quick and reliable process simulations to predict the extent of separation of mixtures such as volatile natural compounds. Acetone and n-Heptane found in wastewater are usually associated with solvents from the pharmaceutical industry. At 329.11 K, acetone and n-Heptane easily combine to form an azeotropic mixture. The different distillation and separation techniques were used to separate the azeotropic mixture which requires several plates and columns. In the current work, batch distillation was used to study the separation of the azeotropic mixture (Acetone and n-Heptane).It was observed that the desired separation was not possible for the Acetone and n-Heptane system. To overcome this, a third component such as Butyl propionate or Benzene is added to the mixture of Acetone and n-Heptane system. This system was simulated using Equinox Software and Services Pvt. Ltd. licensed Multi Batch Distillation Software (MBDS™).Different thermodynamic models have been studied for the azeotropic mixtures, such as NRTL, UNIFAC I, UNIFAC II, and UNIFAC III. The batch distillation system for separating the Acetone and n-Heptane was optimized. Various operating factors such as the number of plates, reflux ratio, batch times, and distillate rates were investigated. Based on simulation studies, the optimal parameters were determined to be a reflux ratio of 2.2, 19 number of plates, and a total time of 1 h to separate >99 wt % Acetone purity from the azeotropic mixture.

Self-optimising Control, a Batch Distillation Simulation Study

A dynamic mathematical model of batch distillation columns is formulated using four basic assumptions: binary separation, negligible vapour holdup, constant pressure and constant molar flows. Simulations performed in the modelling tool MATLAB, proved that the model gives satisfactory description of the process behaviour. Simulations studies were then used to apply the theory of self-optimising control to batch distillation columns, in order to provide a systematic procedure for the selection of controlled variables based on operational economics. It was found that the distillate and boilup flows have good self-optimising properties. The study has also shown the unsuitability of the reflux ratio (Rin) and reflux return (LT) to self-optimising control due to their sensitivity to disturbances in batch distillation of the system.

A hybrid batch distillation/membrane process for high purification part 2: Removing of heavy impurities from xenon extracted from natural gas

High-purity xenon of 6 N purity grade and higher is widely used in electronics, space, and medicine. A hybrid distillation/membrane process for the purification of xenon extracted from natural gas by gas hydrate crystallization is studied experimentally and via simulations. Membrane gas separation data for xenon-containing mixtures is measured for polysulfone membrane and polyetherimide/polyimide blend membrane. Parametric analysis and process optimization are performed in Aspen Plus Dynamics™ for a middle-vessel batch distillation column with an integrated hollow fiber membrane unit implemented via Aspen Custom Modeler™. Removal of higher- and lower-boiling impurities such as ethane, carbon dioxide, propane, methane, and krypton is considered to achieve 6 N and 9 N target purity grades. Hybrid distillation/membrane process flowsheets built with a multi-stream passive heat exchanger with either retentate or permeate being returned to the column are analysed. It is shown that the operating conditions and the configuration of the hybrid process with a membrane separation treatment of heavy impurities fraction can be tailored to achieve up to 30% increase in batch productivity for the considered case studies and improve xenon recovery reaching above 99.8% as compared to standalone batch distillation, which is especially critical for higher purity grades.

Optimal control of a rate-based modelled batch distillation column: Initialization strategy

Batch distillation columns are dynamic processes represented by a system of differential and algebraic equations (DAE). Their optimal control problem can be solved through orthogonal collocation, which is an effective discretization method with accurate approximations to the behavior of state and control variables. Convergence of such technique is greatly improved by providing good initial values and bounds of the variables. Thus, this work proposes a strategy to estimate the initial values for a sieve trays batch distillation column modeled with a rate-based approach. During the initialization procedure, the modeling equations are solved under a steady state assumption by using the GAMS modeling environment. An experimental pilot scale batch distillation column was used as the case-study to evaluate the proposed initialization algorithm. This column was used to separate a mixture of methanol and ethanol. The initialization results for the state profiles show good agreement with the experimental results.

Reproducibility of Fruit Spirit Distillation Processes

Fruit spirit distillations processes are based on physical principles of heat and mass transfer. These principles are decisive for the separation of desired and undesired aroma compounds, which affect the quality of the distilled product. It is mandatory to control heat and mass transfer parameters to be able to perform fruit spirit distillation processes in a reproducible manner and to achieve equal products with similar volatile compound compositions repeatedly. Up to now, only limited information is available on the magnitude of reproducibility errors since fruit spirit distillation columns are typically not equipped with a suitable control or monitoring technique. We upgraded a batch distillation column with digitized instrumentation and a control technique to be able to control crucial parameters such as thermal energy inputs and reflux rates. This study aimed to identify whether control over two distillation parameters has the potential to enable us to perform distillation processes repeatedly. This study analyzed the magnitude of reproducibility errors for (i) six monitored distillation process parameters and (ii) 13 quantified volatile compounds in the product between duplicated distillation runs performed with equal setups. A total of eight different distillations were performed in duplicate (n = 16), while the six distillation parameters were monitored and logged every ten seconds. The produced distillates were equally subsampled into 20 fractions and each fraction analyzed for 13 volatile compound concentrations. Based on a dataset of 28,600 monitored duplicate distillation process data points, this study showed that process parameters can indeed be replicated with a median relative standard deviation (RSD) of <0.1% to 7% when two crucial process parameters are controlled. The comparison of 1540 volatile compound concentrations in the product fractions showed a reproducibility error with an average median RSD of 9 ± 8%. This illustrated that by gaining control over thermal energy input and reflux rates, the reproducibility of fruit spirit distillation processes and their associated products can largely be met. It is advisable to equip distillation columns with a suitable control technique to be able to reproduce the performance of fruit spirit distillations.

Reclamation of Halon 1301 using industrial-scale heat-pump-assisted batch distillation: Design, simulation, and experiment

In this study, the reclamation of Halon 1301 from an industrial waste gas mixture using an existing heat-pump-assisted batch distillation system was investigated. A cold water circuit and a hot water circuit are added to the conventional vapor compression heat pump for easy operation. To design and optimize the separation, where several design variables and constraints must be verified and satisfied, a modification of the design methodology proposed by Long et al. (2020) was used. Following design using Aspen Hysys software in the simulation of the shortcut column and heat pump system and Aspen Batch Modeler in the simulation of batch distillation, experimental operation of the existing heat-pump-assisted batch distillation system was performed to purify Halon 1301. The experimental performance matched well with that in the simulation. The purification of Halon 1301 with purity of 99.9% was accomplished after 22 h under the designed and optimized operating conditions. The results show that the reboiler duty and operating costs of the existing industrial system can be saved by as much as 100.0% and 36.5%, respectively, compared with a conventional batch distillation column. In addition, the total CO2 emission was reduced by as much as 43.7% compared with that of the conventional process. Moreover, the proposed design is convenient and gives reliable performance. This study demonstrated that the use of an advanced distillation configuration in industrial applications is practically viable and economical.

Simultaneous separation of ternary mixture using modified dual compression middle vessel batch distillation column: Control and dynamic optimization

BackgroundMultivessel batch distillation has been found to be an effective method for the separation of multi-component mixtures. In this article, an effort has been made to devise a fast middle vessel batch distillation column (MVBDC) for the ternary separation of an Ethanol/Propanol/Butanol mixture by the means of inducing vapor compression in the system. MethodsASPEN PLUS V12 has been used to generate the initial steady-state flowsheet of the process for equipment sizing. In contrast, ASPEN Dynamics was used to evaluate the performance of the batch distillation with various control structures and to perform a dynamic optimization on the proposed batch distillation column. MATLAB was used to identify single-input single-output transfer functions for more effective PID controller tuning. Significant FindingsThe proposed Middle vessel batch distillation was found to separate each component of the mixture to a purity of 99 mol% in 22 h (for the cascade control structures) and 21.73 h (for the temperature control structure). This was found to be significantly lesser than the batch time of a conventional batch distillation column (28.12 h), while the energy consumed by the proposed column was 3.4 MMkcal lesser than the energy consumed by the conventional column. Dynamic optimization further reduced the batch time by 14.4% while simultaneously reducing the energy consumed by 20.3%.

Optimal Operation of Vapor-recompressed Batch Distillation Column under Total Reflux

This article addresses optimal operation of a vapor recompressed batch distillation (VRBD) column under total reflux. This system allows us to obtain high purity top and bottom products simultaneously, which is usually not possible in a VRBD system with product removal. In this paper, we propose a novel approach wherein trajectory optimization is combined with model-based control to achieve optimal operation. Specifically, key performance indices are defined to characterize operation and assess the trade-off between production and energy efficiency. Subsequently, one of these indices is maximized, in closed-loop, using a model predictive controller. The effectiveness and robustness of this approach is demonstrated using a simulation case study of benzene/toluene separation.

Constant distillate composition of batch distillation column with variable reflux mode based on still pot concentration

The objective of this work is to control the constant distillate composition of batch distillation column xD. A new correlation developed involved the instant reflux ratio value R with a composition of the remaining mixture in the bottom pot (boiler) xB. Also adding the dynamic time as ahead time (+dt) to the control algorithm to increase the R to anticipate the changes in xD. +dt was calculated using an electroconductive tracer that was injected both in the bottom pot and in the top tray to estimate the upward and the downward dynamic time. The proposed correlation was successfully applied as a control strategy on a glass batch distillation pilot plant that has 5 cm diameter, 1 m long, eight sieve trays, and Methanol–Water mixture as a system. The real-time experimental runs of the suggested control algorithm applied by manipulating the reflux stream that affects the changes that happened in the top composition product to keep it constant. The proposed procedure shows a quick and stable response for distillate product composition during the operating time that minimizes and saves the energy supplied to the boiler. Moreover, the system gives a straight, smooth linear constant distillate product even in case of disturbing the system.

Experimentation and dynamic modeling of batch packed distillation for star anise essential oil purification

ABSTRACT This study focused on dynamic modeling of the essential oil purification process using a batch distillation column and verified with experimental data. Anethole is the main component in the star anise essential oil with an average content of 80–90 wt.%. The effects of feed, pressure, number of theoretical stages, pot liquid holdup, and reflux ratio to product purity were investigated. The results showed that there are agreements between experimental and simulated data of top and bottom temperatures and anethole composition. The higher purity of anethole is obtained when increasing the number of theoretical stages and the reflux ratio and/or decreasing the pot liquid holdup and the condenser pressure. Star anise essential oils from China and Vietnam could be purified up to 98.4 wt.% and 96.4 wt.% of anethole with recovery efficiencies of 95.8% and 87.1%, respectively. The method combining experimental works and modeling could be applied to scale up the production of not only star anise oil but also other essential oils.

Experimental study on essential anise star oil purification in vacuum batch distillation

Vietnam is one of the world’s largest annual anise harvest countries. However, products from anise are mainly in the form of dried anise fruit and crude star anise essential oil with low economic value. The main component of the star anise essential oil is trans-anethole which needs to be purified to produce higher-value products. This study focused on building an experimental system for purifying star anise essential oil by a batch distillation column working at vacuum pressure. The products obtained during the purification process were analysed by gas chromatography-mass spectrometry (GC-MS). Analytical results were used to evaluate the ability to separate volatile impurities in the crude star anise essential oil. Results showed that the bottom temperature of the tower below 150oC, corresponding to a vacuum pressure of less than 0.1 bar, can reduce the thermal decomposition of essential oils. The volatile components, such as α-pinene, β-phellandrene, limonene, and linalool, were thoroughly separated at the top of the tower. The purified star anise essential oil was from the bottom of the distillation and had the anethole composition of over 88% of mass fraction (wt.%). Anethole recovery efficiency was 98.5 and 88.8% at a pressure of 0.1 and 0.08 bar, respectively. The bottom product can have a higher anethole composition if increasing the column height, the reflux ratio, and decreasing the pressure and the quality of impurities removed at the top is increased.The experimental results are helpful for the calculation, design, manufacture, and operation of an industrial-scale essential oil purification system.

Control and dynamic optimization of middle vessel batch distillation column for the separation of ethanol/propanol/butanol mixture

The middle vessel batch distillation column is an alternative to the regular batch distillation column. This configuration allows simultaneous separation of the light fraction (accumulated at top), heavy fraction (accumulated at bottom) and the intermediate fraction (accumulated in the middle vessel) in a single column. The objective of this article is to extensively analyse and discuss different control systems for the middle vessel batch distillation column (MVBDC) and dynamically optimize the column. Three control structures such as composition level cascade, composition temperature cascade, and temperature control system, have been tested and evaluated. Further, a dynamic optimization study has been performed on the control system providing the fastest separation. The optimizer is set to minimize the total energy consumed during the process. This resulted in a decrease in batch time from 26.8 to 25.2h and a 13.5% decrease in overall energy usage. The presented dynamic optimization technique and control system design is useful for improving the performance of the MVBDC.

Novel use of dividing wall columns for intensification multicomponent batch distillations

While the dividing wall columns for continuous distillations have become quite popular, we present the first detailed analysis of a dividing wall column for batch distillation. For a dividing wall side stripper batch distillation column, we present an operating sequence and its associated mathematical model. Since there are many operating parameter combinations possible for this column, selecting the right operating parameters according to product specifications is presented as an optimization problem. This new configuration's performance is compared with the conventional batch rectifier and the middle vessel columns using two case studies related to the separation of a ternary mixture. The new batch dividing wall column performance is significantly better than the rectifier or the middle vessel column. As the purity specifications increase, the percentage improvement in profit due to the batch dividing wall column compared to the rectifier and the middle vessel columns increases.

Energy saving in batch distillation for separation of ternary zeotropic mixture integrated with vapor recompression scheme: dynamics and control

Abstract In this work, tight composition control and in parallel the operation is integrated with vapor recompression scheme (VRC) is proposed to achieve energy savings and maximum product at a specified high purity for the separation of ternary zeotropic mixture in batch distillation. Firstly, the model representing a ternary system of hexanol/octanol/decanol has been simulated to analyze the open-loop and close-loop dynamics of the process. Secondly, the open-loop and closed-loop operations are integrated with single stage VRC scheme to achieve energy savings. Single stage VRC is operated at very high compression ratio (CR) due to the large temperature difference of the top and bottom streams in batch distillation column. To further improve the thermodynamic efficiency of single stage VRC, double stage compression without intercoolers between the stages of VRC is proposed. Two control schemes have been implemented for constant composition, namely proportional integral (PI) controller and nonlinear gain scheduling proportional integral (GSPI) with and without VRC in closed-loop. The results shows that double stage VRC with GSPI algorithm provides better performance than conventional in terms of energy, product amount and Integral Square Error (ISE).