Reactive Dividing Wall Column Research Articles

Enhanced Dimethyl Ether Synthesis by Reactive Distillation in a Dividing-wall Column

Abstract The high market demand for dimethyl ether (DME) requires innovative solutions able to overcome the drawback of energy intensive distillation steps, and to reduce the large scale production costs of the current process. This study proposes a novel DME process based on methanol dehydration, taking place in a reactive dividing-wall column (DWC) that effectively integrates in one shell a reactive distillation (RD) unit and an ordinary distillation column. The novel process alternatives based on RD and R-DWC, were optimized using the state of the art sequential quadratic programming (SQP) method and compared with the conventional DME process. The results of the rigorous simulations performed in AspenTech Aspen Plus clearly show that significant energy savings of 12-58% are possi blefor the novel process intensification alternative based on R-DWC, while using less equipment units.

Towards FAME and Fortune by Reactive DWC

This work proposes a novel biodiesel process based on a reactive dividing-wall column (R-DWC) that allows the use of only ∼15% excess of methanol to completely convert the fatty acids feedstock. Fatty acid methyl esters (FAME) are produced as pure bottom product, water as side stream, while the methanol excess is recovered as top distillate and recycled. The optimal configuration was established by using simulated annealing (SA) as optimization method implemented in Mathworks Matlab, and coupled via Microsoft Excel with rigorous simulations carried out in AspenTech Aspen Plus. The generated improved design alternatives allow a fortune to be saved by having lower investment costs and up to 25% energy savings, while also ensuring a smaller plant footprint.

Innovative dimethyl ether synthesis in a reactive dividing-wall column

Dimethyl ether (DME) is of great industrial interest due to its use as clean fuel for diesel engines or in combustion cells, as a precursor to other organic compounds, as well as a green aerosol propellant that can effectively replace chloro-fluoro-carbons. Conventionally, high purity DME is synthesized by dehydration of methanol produced from syngas, in a process involving a catalytic fixed-bed reactor and a direct sequence of two distillation columns.The key problem of this classic process is the high investment costs for several units that require a large overall plant footprint, as well as the associated high energy requirements. To solve these problems, we propose in this work an innovative DME process based on a reactive dividing-wall column (R-DWC) that effectively integrates in one shell a reactive distillation (RD) unit with the DWC technology. The double integrated system allows the production of high-purity DME in only one unit, with minimal footprint and significantly lower costs.This study also makes a fair comparison between the reported conventional DME process and the optimally designed process alternatives based on RD and R-DWC, respectively. All processes are optimized in terms of minimal energy requirements, using the state of the art sequential quadratic programming (SQP) method implemented in AspenTech Aspen Plus. The results clearly demonstrate that the R-DWC process has superior performances as compared to the conventional or RD process: significant energy savings of 12–58%, up to 60% reduced CO2 emissions, as well as up to 30% lower capital investment costs.

젖산회수를 위한 분리벽형 반응증류탑의 제어

젖산(lactic acid)은 식품, 의약품, 화학약품 등의 원료로서 많이 사용되고 있으며, 생분해성 고분자(biodegradable polymer)인 폴리젖산(polylactic acid)의 원료로서 최근 사용량이 증가하고 있다. 하지만 고비점 물질의 존재와 젖산의 비휘발성은 젖산 분리 및 정제를 어렵게 만든다. 이를 극복하기 위해 분리벽형 반응 증류를 이용하여 비휘발성 물질인 젖산을 에스테르화 반응에 의하여 휘발성이 있는 물질로 전환시킨 후 분리하고 가수분해반응을 이용하여 다시 젖산으로 전환하여, 회수하는 공정을 제안하였다. 제안된 연속적인 젖산회수 분리벽형 반응증류공정의 동특성을 조사하여, 이를 바탕으로 제어계들을 구성하였고 각 제어계들의 성능을 비교하였다. Lactic acid is widely used in the food, chemical and pharmaceutical industries, and there is an increasing demand for lactic acid as the raw material of polylactic acid, which is a biodegradable polymer. The presence of high boilers and non volatility of lactic acid makes the separation of lactic acid very difficult job. Esterification of lactic acid with methanol followed by hydrolysis of the separated methyl lactate was employed for the recovery of lactic acid. Reactive dividing wall column was proposed for the simultaneous reaction and separation. The intensified process poses a challenging control problem. Dynamic characteristics of the proposed process were examined and control systems were proposed to get a stable control performance for a disturbance in feed. Control performances of the proposed control systems were compared.

Numerical Investigation of the Reactive Dividing Wall Column Exemplified by Methyl Acetate Hydrolysis

AbstractReaktive Trennwandkolonnen bieten eine Möglichkeit, die Vorzüge der Trennwandkolonnen und der Reaktivrektifikation in einem Apparat zu kombinieren. Aufgrund der Neuartigkeit dieses komplexen Verfahrens sind ausgiebige, numerische Untersuchungen unabdingbar. Zu diesem Zweck wurde ein auf dem rigorosen Stoffaustauschmodell basiertes Simulationstool entwickelt. Die erfolgreiche Validierung des Modells und des Simulationstools anhand von Experimenten wird vorgestellt.

Reactive Dividing-Wall Columns - Defying Equilibrium Restrictions

This work presents an integrated reactive-distillation design based on a dividing-wall column (DWC) applied to an industrial case study within AkzoNobel. Remarkably, it is among the first industrial applications of a reactive DWC reported in literature. The benefits of this novel integrated design are the ability to overcome VLE and chemical equilibrium limitations, as well as to separate the main product as high purity side-stream. To solve the problem of a production shift required by market demand changes, we propose an innovative integrated design that combines reaction and separations into one reactive DWC that allows significant savings in capital and operating costs – up to 35% and 15%, respectively. Two scenarios are analyzed and the results of the rigorous AspenPlus simulations are provided.

REACTIVE DIVIDING-WALL COLUMNS—HOW TO GET MORE WITH LESS RESOURCES?

This work presents a novel integrated reactive-separation design based on a dividing-wall column (DWC) applied to an industrial case study within AkzoNobel Chemicals. To the best of our knowledge this is one of the first reported industrial applications of a reactive DWC. Due to changing market conditions, one of the by-products in a plant became more economically attractive than the main product. However, the design of the existing plant does not allow an increase of the by-product production rate at the cost of the main product. To solve this problem we developed a novel integrated design that combines reaction and separation into a feasible reactive DWC that allows 35% savings in capital and 15% savings in energy costs. This article describes the novel reactive DWC design, presents the rigorous simulation results, and makes a comparison with the base case alternative.

Thermodynamic analysis and hydrodynamic behavior of a reactive dividing wall distillation column

A complete thermodynamic analysis of a reactive dividing wall distillation column and an equilibrium reactor followed by a dividing wall distillation column was conducted for several equilibrium reactions using data of a real pilot plant for the distillation column. In addition, several aspects related to the hydrodynamic behavior of the implemented reactive dividing wall distillation column were analyzed in order to prevent operation problems with regard to hydraulics. Results indicate that the reactive dividing wall column presented both higher thermodynamic efficiencies and lower exergy losses than those obtained in the classical configurations of a reactor plus a distillation column. The reactive dividing wall distillation column also required lower energy consumption compared to that required by classical processes. These facts confirm the higher energy efficiency of reactive dividing wall designs. Results also indicate that the reactive dividing wall column meets process intensification goals: i) it requires lower energy consumption, which can be translated into lower carbon dioxide emissions, and ii) the reduction in energy consumption can be associated with lower traffic of liquid in the column and reduction in column diameter (miniaturization). Finally, it was observed that proper collection of the liquid in a side tank and an adequate split to both sides of the dividing wall play an important role in hydraulics. The manipulation of this split enables minimum energy consumption and high thermodynamic efficiency.

Reactive dividing wall distillation columns: Simulation and implementation in a pilot plant

We performed steady state and dynamic simulations of a reactive Petlyuk column through an equivalent reactive dividing wall column (RDWDC). In the case of the reaction between ethanol and acetic acid catalyzed by sulfuric acid to produce ethyl acetate and water, we have found that the reactive Petlyuk column can achieve set point changes in two control loops of temperature. Also, for load rejection, the control loops can eliminate the effect of the disturbances in the feed composition. These results and previous knowledge reported about thermally coupled distillation columns and reactive distillation were considered to design and implement a RDWDC.

Rate-based analysis of reactive distillation sequences with different degrees of integration

In this work, reactive distillation sequences with different degrees of integration are investigated with the aim to identify the optimal configuration. Such integration includes the combination of both unit operations, reaction and distillation, as well as the combination of distillation columns within one unit. For rapid determination of required design parameters, a special two-step approach based on the decomposition method is developed. As a test system, the transesterification of carbonates is chosen, and three promising configurations with increasing integration degree are identified. These configurations comprise two different combinations of single non-reactive and reactive distillation columns as well as a highly integrated reactive dividing wall column. Their analysis shows that the unit integration leads to significant savings in energy consumption and production costs.

Reactive Distillation in a Dividing Wall Column: Rate-Based Modeling and Simulation

In this paper, a novel rate-based description of nonreactive and reactive dividing wall columns is presented. These highly integrated units promise advantages in the context of process intensification. Until now, published studies have been focused on the nonreactive columns, based on equilibrium stage models, whereas the modeling of both dividing wall columns and reactive dividing wall columns, using the rate-based approach, has not been done yet. In the presented model, special attention is given to phenomena that have not been considered in previous publications (e.g., heat transfer through the dividing wall). The model has been applied to a nonreactive, ternary alcohol mixture and successfully validated. The transesterification of carbonates has been identified as an interesting system for the reactive dividing wall column. This reaction system is equilibrium limited and characterized by high conversion, yet low selectivity. Initial simulation studies demonstrate that the selectivity can be significan...

Methyl Acetate Hydrolysis in a Reactive Divided Wall Column

The combination of reactive distillation and a divided wall column leads to a reactive divided wall column. The first use of such a reactive divided wall column for the hydrolysis of methyl acetate is presented here. For the development of this system, kinetic data for the involved reactions was determined at the University of Stuttgart, mini plant experiments were performed at BASF and an industrial scale column with an inner diameter of 220 mm was run at Sulzer Chemtech. Results of one mini plant experiment and of one experiment in an industrial scale are shown.

Water and chemicals recovery in the German automotive industry

A reactive dividing-wall column (RDWC) is developed for the production of methyl acetate (MeAc) in this work. Both design and control of the RDWC are investigated by using commercial chemical simulator Aspen Plus and Aspen Dynamics. The optimum RDWC design in terms of total annual costs (TAC) is screened based on the proposed optimization procedure. The results show that about 7.7% savings in energy consumption, 8.3% reduction in operating cost and 15.5% decrease in capital investment can be achieved by the RDWC design compared to the corresponding two-column design. Two control structures (i.e., basic control structure and improved control structure) for the RDWC are presented. The results indicate that the improved control structure can handle disturbances in ±20% feed flow rate and −5 wt% feed composition effectively.

95/00231 Liquefaction of density separated coal fractions

This contribution aims to present a methodology to model and simulate the reactive dividing wall column (RDWC) using commercial software. Feasibility of separation scheme was established with ASPEN DISTIL™. Simulation of flowsheet configuration was performed with ASPEN HYSYS™, using the two columns model. The reactive zone hosted by the prefractionator was modelled and simulated as backward flow CSTR series. Proposed solution is attractive from industrial point of view. As case study isoamylenes (contained in fluid catalytic cracking-FCC-C5-fraction) etherification with ethanol (EtOH), to obtain tert-AmylEthylEther (TAEE) in RDWC with structured packing was illustrated. Operation of such arrangement involves very careful solution of the model. Composition profiles demonstrated feasibility of proposed flowsheet.