Reactive Dividing Wall Column Research Articles

Energy-Efficient Reactive Dividing Wall Column for Simultaneous Esterification of n-Amyl Alcohol and n-Hexanol

This study reports significant energy savings of combined reaction and distillation in a single reactive dividing wall column (RDWC) for the concurrent production of pure n-amyl and n-hexyl esters, which are the stable node (SN) in each phase diagram of the quaternary reaction system. The continuous removal of the byproduct, water, from the unstable node (UN) azeotrope by L-L decantation drives the two esterifications in the forward direction and enables the production of the pure ester products. A vapor recompression heat pump (VRHP) is introduced to the RDWC and the annual operating cost is reduced to 62.5% of the case without the VRHP. Implementing the multiple reactions with V-L-L separation in a single RDWC and its heat integration through the VRHP may provide chemical industries with enhanced economic feasibility.

Process control for energy efficient operation of reactive dividing wall columns

Process integration offers great potential, both economically as well as ecologically, mainly due to high possible energy savings. However, the design and operation of integrated processes is impeded by complex process dynamics introduced by the integration of multiple unit steps in one apparatus. A prime example, the reactive dividing wall column combines a reaction and several separation steps in one column shell. The high degree of integration results in an especially challenging operation of this apparatus. Reliable design methods and efficient control structures need to be provided in order to enable the industrial application of reactive dividing wall columns. A key challenge is to ensure an energy efficient operation in case of disturbances. This study aims at understanding the underlying dependencies of the most important variables, i.e. the liquid split, the energy demand and the component distribution, regarding energy efficient control. Based on these findings a straightforward decentralized control structure is presented and analysed. The structure utilizes the liquid split as manipulated variable in order to control the component composition on the top stage of the prefractionator. The evaluation of the structure regarding energy efficient process control is carried out by comparison to a structure with fixed liquid split.

Energy-saving investigation for diethyl carbonate synthesis through the reactive dividing wall column combining the vapor recompression heat pump or different pressure thermally coupled technique

The design of the diethyl carbonate (DEC) production process has received much attention due to its key role as the oxygenated gasoline additive with much fewer environmental and health issues than methyl tert-butyl ether. In this study, two configurations including vapor recompression heat pump (VRHP)-reactive dividing wall column (RDWC) with or without the splitting top stream are investigated for DEC production to screen out the best VRHP sequence. Furthermore, a novel alternative approach of different pressure thermally coupled-RDWC (DPTC-RDWC) is comparatively proposed to achieve less capital and energy cost. The effects of pressure within stripping section of the RDWC on total annualized cost (TAC) and the temperature difference between the condenser and reboiler are studied. The results illustrate that the proposed optimum process produces DEC production with the purity of 99.8 mol% and significant reduction of TAC is achieved by 20.52% with 10 years payback period. Apart from that, carbon dioxide emission of the process is decreased by 33.74% compared to that through conventional RDWC.

Process Development, Assessment, and Control of Reactive Dividing-Wall Column with Vapor Recompression for Producing n-Propyl Acetate

As a combination of the conventional reactive distillation (RD) and diving-wall column, reactive diving-wall column (RDWC) is the highly thermally integrated process that has the advantages of high...

Design, Optimization, and Retrofit of the Formic Acid Process II: Reactive Distillation and Reactive Dividing-Wall Column Retrofits

Formic acid (FA) is an important chemical with many applications in the industry. Nevertheless, its manufacturing process has not received much attention in the open literature. In Part I of this series (da Cunha et al., Ind. Eng. Chem. Res. 2018, 57, 9554–9570), FA process was simulated and optimized for the production of 98 wt % FA. Total annual cost (TAC) of the optimal base case process was 0.686 USD/kg. This process was then retrofitted via integration of two distillation columns into a dividing-wall column (DWC), but such retrofit was not profitable. Here, in Part II, FA process retrofit via reactive distillation (RD) and reactive dividing-wall column (RDWC) are investigated in detail. Results show that RD retrofit is not attractive as it increases TAC of the process. However, retrofit via RDWC is profitable, resulting in a thermal energy savings of 20.4% and a TAC savings of 0.020–0.042 USD/kg (by 3%–6%).

New Process Control Concepts for Energy Efficient Operation of Reactive Dividing Wall Columns

In this study a concentration control concept is employed for energy efficient operation of a reactive dividing wall column. The control concept takes into account the liquid split as a manipulated variable in order to manipulate the component flow in the column, while the heavy key reactant concentration on the top stage in the prefractionator serves as control variable. The dynamic performance as well as the ability to adjust energy minimal steady states after disturbances is analysed and evaluated by comparison of the proposed concept to one with a fixed liquid split.

Coproduction of Ethyl Acetate and n‐Butyl Acetate by Using a Reactive Dividing‐Wall Column

AbstractThe performance of the reactive distillation dividing‐wall column for coproduction of ethyl acetate and butyl acetate was experimentally studied. n‐Butanol and ethanol are raw reaction materials that react with acetic acid in the reaction zone to produce n‐butyl acetate and ethyl acetate, respectively. n‐Butyl acetate is not only a product, but also acts to remove water generated by the esterification reactions. The effects of various parameters, such as catalyst loading per stage, reflux ratio, liquid split and molar feed ratios, ethyl acetate/n‐butyl acetate purity, pressure drop, and total energy consumption, are investigated. Results show that ethanol could be completely converted and the products could be easily separated, which shows great industrial application potential in the coproduction of ethyl acetate and n‐butyl acetate.

Reactive dividing-wall column for the co-production of ethyl acetate and n-butyl acetate

Abstract Reactive dividing-wall column (RDWC) technology plays a critical role in the energy saving and high efficiency of chemical process. In this article, the process of co-producing ethyl acetate (EA) and n-butyl acetate (BA) with RDWC was studied. BA was not only the product, but also acted as entrainer to remove the water generated by the two esterification reactions. Experiments and simulations of the co-production process were carried out. It was found that the experimental results were in good agreement with the simulation results. Two kinds of RDWC structures (RDWC-FC and RDWC-RS) were proposed, and the co-production process operating parameters of the two types of RDWC were optimized by Aspen Plus respectively. The optimal operating parameters of the RDWC-FC were determined as follows: 0.6 of the reflux ratio of aqueous phase (RR), 0.66 of the vapor split (RV) and 0.51 of the liquid split (RL). And the optimal operating parameters of the RDWC-RS were shown as follows: RR was 0.295 and RV was 0.61. Furthermore, the energy saving analysis of the co-production process was based on the annual output of 10000 tons of EA, compared with the traditional reaction distillation (RD) to prepare EA and BA, the reboiler duty of the RDWC-FC column could save 20.4%, TAC saving 23.6%; RDWC-RS reboiler energy consumption could save 17.0%, TAC 22.2%.

Experimental and simulation of the reactive dividing wall column based on ethyl acetate synthesis

Abstract Reactive dividing wall column (RDWC) is a highly integrated unit which combines reaction distillation (RD) with dividing wall column separation technology into one shell, and it realized the chemical reaction and the separation of multiple product fractions simultaneously. In this paper, the reaction of esterification with acetic acid and ethanol to produce ethyl acetate was used as the research system, experiments and simulations of the RDWC were carried out. This system in the traditional process mostly used the homogeneous catalyst ( e.g. sulfuric acid). However, in view of the corrosion of the equipment caused by the acidity of the catalyst, we used the heterogeneous catalysts – iron exchange resins – Amberlyst15 and proposed a novel catalyst loading method. Firstly, the reliability of the model of the simulation was verified by the experimental study on the change of liquid split ratio and reflux ratio. After that, the four-column model was established in Aspen Plus to analyze the effects of the amount of azeotropic agent, reflux ratio and acetic acid concentration. Finally, for a fair comparison, the economic analysis was conducted between traditional RD column and RDWC. The results showed that RDWC can save 34.7% of total operating costs and 18.5% of TAC.

Controllability comparisons of a reactive dividing-wall column for transesterification of methyl acetate and isopropanol

Dynamic simulation has received researchers’ attention for its practical application in industry. In this work, five control structures are introduced to the reactive dividing-wall column process, with different control strategies of the internal liquid stream across the wall. Controllability of these control structures is investigated and compared. From the result, the control structure that the flowrate of the internal liquid stream is ratioed to the liquid flowrate of the tray of the column, has the best performance among the control structures studied in this work. Furthermore, the feed-flowrate ratio scheme shortens the time reaching a new steady state after the disturbances. The mole fractions of products are kept in acceptable values with acceptable settling times.

Dynamic process behavior and model validation of reactive dividing wall columns

Reactive dividing wall columns (RDWC) are a highly integrated column type. The coupling of a reactive distillation and a dividing wall column leads to complex interactions between vapor-liquid mass transfer, chemical kinetics and component split around the dividing wall. In simulation studies such interactions have been shown to lead to complex dynamics and the occurrence of multiple steady states. However, experimental investigations are still missing to verify the theoretical findings. In this work the first comprehensive experimental study of the dynamic behavior of RDWCs is presented. The reference system of enzymatic catalyzed butyl acetate transesterification with hexanol has been employed to investigate the start-up and open loop behavior under different operating conditions. Two different start-up strategies are tested and compared. The experiments demonstrate the reliable and secure start-up and stable operation of a RDWC. Additionally, a developed rigorous dynamic RDWC model is presented that considers the dynamic influence on the vapor distribution in the dividing wall section. A detailed model validation is carried out using the obtained experimental data. The comparison of simulation results and experimental values show good agreement over a wide range of operating conditions.

Optimal Design and Effective Control of the tert-Amyl Methyl Ether Production Process Using an Integrated Reactive Dividing Wall and Pressure Swing Columns

Design of the tert-amyl methyl ether (TAME) production process has received much attention because TAME is an important oxygenated gasoline additive with much fewer environmental and health issues than methyl tert-butyl ether. Although a reactive dividing wall column where reaction and separation take place in one vessel has been developed with less capital and operating cost, little work on its application to TAME production has been reported. In this paper, we propose a new overall procedure for optimal design of the TAME production process through an integrated reactive dividing wall and pressure swing columns, which includes screening of the best dividing wall configuration, thermodynamic feasible insight, and process simulation and optimization using the sensitivity analysis tool in Aspen Plus. The computational results demonstrate that the optimal design of the TAME production process through an integrated reactive dividing wall and pressure swing column is successfully obtained to achieve desired T...

Reactive Distillation in a Dividing‐Wall Column: Model Development, Simulation, and Error Analysis

AbstractA process model of a reactive dividing wall column process is developed and tested by comparing simulation results to data from pilot‐plant experiments. In general, the experimental data and the model prediction agree well in a simple comparison. By means of a sensitivity and error analysis both the influence of the choice of the model and the influence of uncertainties of the input parameters on the simulation results are studied. It is shown that the insight gained by such an enhanced analysis by far exceeds that from a simple comparison, and that such a simple comparison can easily lead to erroneous conclusions.

High Conversion of Methyl Acetate Hydrolysis in a Reactive Dividing Wall Column by Weakening the Self-Catalyzed Esterification Reaction

We show the superiority of reactive dividing wall column (RDWC) to the single reactive distillation (RD) column in improving the conversion of reactant, taking the hydrolysis of methyl acetate (MA) as example. It is difficult to achieve above 99% conversion for MA in a traditional reactive distillation column (TRDC) due to the existence of self-catalyzed methanol (MeOH)-acetic acid (HAc) esterification reaction in the column bottom. In this work, more than 99% conversion of MA hydrolysis was realized experimentally in an RDWC by separating MeOH from the hydrolysis mixture. The effects of several operation parameters on hydrolysis conversion were systematically investigated, including feedwater–MA mole ratio, heat duty, mole flow rate of feed MA, and vapor distribution. The simulation results by Aspen Plus showed that RDWC has several improvements in MA hydrolysis over TRDC, including lower energy consumption, lower water–MA mole ratio, and larger production capacity. With the increase in MA conversion, th...

Integrating a vapor recompression heat pump into a lower partitioned reactive dividing-wall column for better energy-saving performance

In this study, four integrated lower partitioned reactive dividing-wall columns (LRDWCs) with vapor recompression heat pump (VRHP) models are developed to reduce the energy consumption of a reactive dividing-wall column. Energy-saving, economic, and environmental performances of the integrated LRDWC with VRHP models are compared with the corresponding LRDWC. The results indicate that the integration of VRHP into the LRDWC significantly reduces the energy consumption and CO2 emissions associated with the process. The application of a preheater further improves the energy-saving and economic performance of the process. With the aid of a preheater, the integrated LRDWC with the VRHP model saves 49.86% energy consumption and 13.76% total annual cost with a payback period corresponding to five years, and reduces all CO2 emissions when compared with the corresponding LRDWC.

Design of thermally coupled reactive distillation schemes for triethyl citrate production using economic and controllability criteria

This work describes a systematic process design for triethyl citrate production by direct esterification of citric acid with ethanol via simultaneous reaction-separation technologies. The design methodology includes simultaneous optimization of controllability and profitability criteria. With a novel approach, the conceptual feasibility analysis of the intensified processes was carried out by extending the reactive residue curve maps (RRCM) to mixtures with six components by implementing a substitution degree parameter. The RRCM have been also extended to the conceptual design of dividing wall columns. The configuration of both, traditional and dividing wall reactive distillation columns, were obtained from the conceptual analysis. The processes were simulated using experimentally validated models, and further optimized using a nature inspired multi-objective algorithm. A triethyl citrate production capacity of 10kTon/yr was used as process specification. Final designs evidenced citric acid conversions above 99.9%, energy consumption from 3-5MJ/kg, and a TEC production costs of c.a 1.5USD/kg. Controllability assessment was performed by evaluating the condition number of the proposed operating schemes. Pareto diagrams indicate that the minimization of total annual costs and controllability are conflicting goals in both production schemes. Nevertheless, both alternatives withstand large perturbations over the main process variables. The reactive dividing wall column scheme results in large energy and cost savings over a traditional reactive distillation process.

Investigation about Energy Saving for Synthesis of Isobutyl Acetate in the Reactive Dividing-Wall Column

The reaction kinetic and chemical equilibrium for the production of isobutyl acetate via transesterification between methyl acetate and isobutanol is investigated as the presence of catalyst Amberlyst-15. The experimental kinetic parameters are obtained by the application of the Arrhenius equation. The novel reactive dividing-wall distillation process for production of isobutyl acetate via transesterification is proposed on the basis of a conventional reactive distillation process. The reactive dividing-wall distillation process is simulated and investigated for saving more energy and reducing the total annual cost (TAC) of the process. The energy consumption and the TAC of the reactive dividing-wall distillation process can be reduced by 26.40% and 18.25%, respectively, in comparison with the conventional RD process.

Reducing energy requirements for ETBE synthesis using reactive dividing wall distillation column

Production of ETBE is one of most important industrial processes. It is used both as biofuel and bio additive in gasoline. The motivation behind its use is that, its blend with gasoline reduces greenhouse gas emissions. Present work focuses on the synthesis of ethyl tertiary butyl ether (ETBE) by using Reactive dividing wall column (RDWC) and a comparative assessment with three other process alternatives as-reactor followed by distillation sequence, reactor plus reactive distillation (RD), and RD. The comparison was done in terms of energy requirements, CO2 emissions, total annual costs (TAC), total investment costs (TIC) and total operating costs (TOC). RDWC proved its forte in saving energy therefore cutting CO2 emissions and handling the reactions limited by chemical equilibrium. RDWC was found to be the most promising alternative out of the four process alternatives. It gave highest purity of the product ETBE 99.999% (mol.), the CO2 emissions were reduced by 74% and 43% as compared to conventional sequence and RD respectively, and also the energy requirements were very less as compared to the conventional sequence and RD. TIC reduction as high as 68% was observed, this also established RDWC as a lucrative option for the synthesis of ETBE.

Decentralized Process Control of Reactive Dividing Wall Columns

In this work a decentralized control structure for the reactive dividing wall column (RDWC) is proposed. Based on sensitivity analyses with a steady state model the optimal pairing of controlled and manipulated variables is shown. For the first time an experimental study about a RDWC control structure is conducted. Therefore, an enzymatic catalysed reactive dividing wall column in pilot scale is employed. Several experiments are carried out systematically in order to examine the dynamic performance under the influence of disturbances. In this paper the results of disturbances in heat duty and set point changes are shown and discussed.

Enzymatic catalyzed reactive dividing wall column: Experiments and model validation

A novel process for the integration of chemical reaction and product separation is proposed: the enzymatic catalyzed reactive dividing wall column (eRDWC). The eRDWC combines the highly integrated and complex reactive dividing wall column (RDWC) with the use of a very selective enzymatic catalyst. This apparatus enables the simultaneous production and separation of up to 4 pure product streams. Comprehensive experiments with the reference system of a hexanol and butyl acetate transesterification in a DN 65 pilot scale column show the feasibility of stable steady state operations for this process. A rigorous model for the plant design of an eRDWC wall column is developed. The reaction kinetics and vapor‐liquid‐equilibria for the reference system are measured and implemented in the model. The model is successfully validated using the acquired experimental data. The application of enzymes in continuous reactive distillation processes has the potential to increase the selectivity at milder process conditions. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2198–2211, 2017