Breaking Azeotropes by Azeotropic and Extractive Distillation in a Dividing-Wall Column

Energy-saving exploration and optimization of methyl alcohol – Methyl ethyl ketone – Tertbutyl alcohol separation by extractive dividing-wall distillation with ionic liquid as extractant

Tetrahydrofuran (THF) is widely used in many processes as solvent or chemical intermediate. It is necessary to separate mixture of THF-water, because in most commercial production processes, THF is produced from its water mixture. However, the above mixture cannot be separated with ordinary distillation, since THF and water can form azeotrope. Instead, extractive distillation (ED) and pressure-swing distillation (PSD) have been widely applied for commercial separation of mixture of THF-water. In this paper, Aspen Plus simulator is used to simulate extractive distillation and pressure-swing distillation process for separation of mixture of THF-water. Economic analysis is carried out by Aspen Process Economic Analyzer (APEA) for the two processes. The conclusion obtained based on the above process simulation and analysis is that the total annualized cost of the extractive distillation is slightly lower than that of pressure-swing distillation. The results obtained provide useful references for commercial separation of mixture of THF and water.

The mixture of toluene-methanol-water is difficult to separate because of the formation of toluene-methanol and toluene-water azeotropes. Extractive distillation process with two-column decanter (EDTCD) was improved to separate the system. The process was optimized by the software named Extractive Distillation Optimization Software (EDOS) which based on the minimum total annual cost (TAC). A comparison of the EDTCD and the traditional extractive distillation with triple-column (TEDT) indicated that the former was much more economical. In this comparison, n-methyl-2-pyrrolidone (NMP) and diethylene glycol (DEG) was used as a heavy entrainer in EDTCD and TEDT. The choice of thermodynamic model was discussed in this paper, and the model of UNIQUAC was used in the two processes. The results show that high purity of toluene, methanol and water can be obtained from the process of EDTCD, and it can save 34 % TAC than the process of TEDT.

Spherical silica nanoparticles with average particle size of 10 nm were synthesized using sodium silicate extracted from oil shale ash as silica source.The results showed that the addition of poly(ethylene glycol)(PEG) could effectively prevent the aggregation of silica nanoparticles and tune the particle size,the optimal PEG concentration was found to be 3.0%.Ultrasonication is a key factor to the formation of small,uniform nanoparticles and an optimized hydrolysis-condensation period for ultrasonication is 0.5 h.The azeotropic distillation evidently suppresses agglomeration and a possible mechanism of azeotropic distillation was also proposed.

Design and Optimization of Pressure Swing Distillation using a Stochastic Algorithm based in the Boltzmann Distribution

Heterogeneous azeotropic distillation is one of many method for breaking azeotrope. Azeotropic distillation is an energy intensive process, with high operating cost. Development of process intensification results in dividing wall column for combining two sequential distillation column into one column. Application of dividing wall column for azeotropic distillation is therefore a prospective process. Process control for azeotropic distillation with dividing wall column is studied to determine its controllability and feasibility for industrial applications. Systems studied in this paper includes isopropanol-water mixture with cyclohexane as entrainer. Product composition, as control objective, is controlled via tray temperature control, with reboiler duty and liquid split ratio as manipulated variables. Internal Model Control (IMC) and Ziegler-Nichols tuning method are also studied and compared. Simulation results with ASPEN Plus Dynamic shows that IMC and Ziegler-Nichols method are equally effective in achieving good process control. However, Ziegler-Nichols is concluded to be simpler for practical application, if compared to IMC.

Energy-efficient extractive distillation combined with heat-integrated and intermediate reboilers for separating acetonitrile/isopropanol/water mixture

Steady state gain analysis for azeotropic distillation

Analysis of control properties of intensified distillation sequences: Reactive and extractive cases

Design and control of an energy-efficient alternative process for separation of Dichloromethane-Methanol binary azeotropic mixture

The ease of separation index (ESI) that is defined by the ratio of the relative volatility between the light and middle components to that between the middle and heavy components has been adopted in the literature for the selection of optimum distillation configuration for ternary separation. The present work showed that the separation requirements (the products’ purity) have a significant impact on the economic performance of distillation systems. Then we proposed a new index, generalized ease of separation index (GESI), to include the separation requirement into consideration for the selection of the optimum ternary distillation configuration. Simple column sequences with or without heat-integration, side-rectifier, side-stripper column, and dividing wall column (DWC) were evaluated as the candidates. Triangle map of ternary mixture composition was used to show the dependence of the optimal selection on feed compositions. We showed by numerical simulation that, for a given ESI, a profound change of the partition on the triangle map occurred with the change in GESI, and on the other hand, for a given GESI, slight changes of the partition on the map could be found with the change in ESI, showing stronger dependence of the economical behaviours of the ternary distillation configurations on the proposed GESI than on the ESI. Then, the dependence of the map partition on the GESI was investigated, and we found that with the increase in GESI, the area in triangle map where DWC was the optimal configuration shrunk, while the area of direct sequence with backward heat integration (DB) expanded. We concluded that the use of the newly defined index GESI can be conductive to the optimal selection of non-azeotropic ternary distillation configuration.

This paper presents simulation and analysis of multiple steady states (MSS) in dividing wall column (DWC). First steady state simulation of benzene–toluene–xylene (BTX) separation in DWC is run to obtain its four different solutions using Aspen Plus software, and then detailed comparisons and analysis of these solutions are carried out. From simulation results, it can be concluded that MSS inevitably exists in DWC, which is important for its design, operation and control but has not been declared in open literature up to now. In addition, obvious grouping feature is found among the four solutions of BTX DWC case, and light component benzene and heavy component xylene have, respectively, two different recoveries at the top of the side column among the four solutions. The grouping feature is interesting and important for DWC, which may be explained by the existence of impurities in side product stream and their different flow paths from the feed to the side product stream, that is, above or under the dividing wall. © 2014 Curtin University of Technology and John Wiley & Sons, Ltd.

In chemical processes, beside main products, significant quantities of by-products are often produced due to thermodynamics. Therefore, separation techniques and methods play such an important role, in chemical technologies, as reactor systems. Rectification is one of the most frequently used fluid separation process, which usually involves significant energy consumption. The production of hot and cold energy causes notable environmental load (CO2 emission, dust pollution, etc.). Hence, from environmental point of view, research on energy saving in separation processes, for instance analysing divided wall columns (DWC), is exceedingly important. This article focuses on how to find more efficient structures with minimal energy consumption. The DWC system is a promising energy-saving alternative for separating multi-component mixtures (Chem Eng Process 38: 549–562, 1999; Chem Eng Process 49: 825–835, 2010). The innovation of this equipment is a wall which divides the inner space of the tower separating the feed and the side stream-product zones. The side stream and the feed stream are prevented from mixing by this wall. The DWC possesses greater efficiency than common column sequences. Conventional columns with side stream can be converted to DWC. In this article, several constructions of DWC are investigated with simulation experiments. The structure of the column is implemented in Aspen Plus in: 2006 Reference Guide, AspenTech Inc., Cambridge, 2006 simulator using the Radfrac unit of the software. The effects of the split ratio, the height and the vertical position of the wall, as the main parameters of DWC, are analysed.

Sensitivity of Thermodynamic Model Parameter to the Design of Heterogeneous Reactive Distillation: Amyl Acetate Esterification

Currently, process intensification using dividing-wall columns (DWCs) is one of the most promising alternatives for reducing the costs of the distillation process. However, for extractive distillation, there are still questions regarding whether the DWC is a more economical option than the conventional sequence (CS). Normally, extractive DWCs are simulated with two thermally coupled columns (TCSs), and their designs are usually obtained by setting the TCSs in different ways that do not necessarily constitute an optimum design. Thus, this work proposes a systematic procedure based on stage equilibrium for obtaining an optimized DWC configuration, in terms of operability and design. A strict comparison between the DWC configuration and the CS (also optimized) was performed, and the best results in terms of the total annual cost (TAC) were obtained for columns with a distinct number of stages in each section of the wall; however, these columns did not outperform the optimized conventional systems.