Feasible separation regions for distillation I: Structure

A feasible separation region is determined for only four special combinations of a saturated vapor/liquid feed and total/partial condenser or reboiler. This work addresses the construction of a feasible separation region for a general case where the feed is a mixture of vapor and liquid in equilibrium and where the column is equipped with a partial/total condenser and reboiler. The analysis reveals that the product composition sets (which are defined for various reflux and reboil ratios and a fixed number of stages in each column section) are the main elements of the feasible separation region. The application of the geometric model of the column in combination with the shape of the distillation line led to the conclusion that the feasible separation region is the union of two product composition sets for both enriching and stripping columns both with an infinite number of stages. The boundary of the feasible separation region consists of several curves related to specific types of operating modes in the column. Some of these curves create a well‐known product composition multitude, whereas other curves form a generalized distillation limit. © 2017 American Institute of Chemical Engineers AIChE J, 2017     

Global optimization of multicomponent distillation configurations: 1. Need for a reliable global optimization algorithm

Nonazeotropic multicomponent mixtures are often separated into products by distillation configurations containing multiple distillation columns. One method of calculating the minimum vapor duty of a configuration is to sequentially calculate the minimum vapor duty of each mixture as it is split into two streams within a given column starting from the feed column. The other method simultaneously manipulates all the splits to yield the overall minimum vapor duty of the entire configuration. Of these two methods, the sequential minimization is attractive as it can be analytically solved. However, through extensive computations, we find that the sequential minimization method is not a valid substitute for the simultaneous minimization method. As the number of components in the feed increases, the fraction of the basic configurations for which sequential method yields a reasonable estimate decreases rapidly, thereby emphasizing the need for a more robust and reliable global optimization algorithm. © 2012 American Institute of Chemical Engineers AIChE J, 59: 971–981, 2013     

Liquid-holdup regions research of novel reactive distillation column for C5 fraction separation

Recent advances in technologies of reactive distillation (RD) offer various design concepts for chemical processes. For separation of cracking C5 fraction, one of the main challenges is improving the conversion of cyclopentadiene (CPD) and the recovery of isoprene (IP). In the current work, a novel reactive distillation column with several liquid-holdup regions was designed, since it allows long residence time and provides flexibility for narrowing the efficiency gap between reaction and distillation. By use of Aspen Plus, a corresponding mathematic model was established and verified to be accurate. Following that, comprehensive studies were carried out for the design of liquid-holdup regions position. Details and principles about the separation performance with the liquid-holdup regions were revealed and optimized parameters were determined with 100 theoretical plates, feed position of 35th plate, and four liquid-holdup regions at 25th, 60th, 75th and 90th plate. The designed RD column could wellmeet the technical requirement, and influence of other important factors including residence time, operating pressure and reflux ratio was further investigated.     

Attainable regions of reactive distillation. Part II: Single reactant azeotropic systems

In reactive distillation (RD) one can conveniently manipulate the concentration profiles on the reactive stages by exploiting the difference in volatility of the various components. This property of RD can be advantageously used to improve the selectivity toward the desired product in case of series or series parallel reactions, and obtain a performance superior to the network of conventional reactors. In the previous work [Agarwal, V., et al., 2008. Attainable regions of reactive distillation—Part I. Single reactant non-azeotropic systems. Chemical Engineering Science, submitted for publication], we introduced representative unit models of RD to obtain the attainable regions of RD for non-azeotropic systems. In this work, we extend the approach to a system involving single binary azeotrope. Design guidelines have been formulated based on the residue curve maps, to obtain the improved attainable region with the help of these representative RD models either alone or in the form of their network.     

一种通用的反应蒸馏塔综合与设计方法

反应精馏是反应过程和分离过程耦合为一体的单元操作,已成为当今研究的重要领域。然而,到目前为止并没有一套通用简便的方法去指导反应精馏过程的综合与设计,严重限制了它的广泛应用。本文在过程强化原理的基础上提出了一种反应蒸馏塔通用的综合与设计方法,并利用2种反应蒸馏系统来评价所提出的设计策略。结果表明,该综合设计方法可以简便高效地搜索出反应蒸馏塔的最优结构,适用于不同类型的反应蒸馏塔的综合与设计。     

Solar barometric distillation for seawater desalting Part II: Analyses of one-stage and two-stage distillation technologies

The report concerns design aspects for the recently proposed solar barometric distillation technology for seawater desalting (SW–SBD) with an underground barometric layout. Two types of SW–SBD desalting plants are analysed. The first plant utilizes a single-stage distillation process with one distillation heat exchanger (operative condensation temperature 50°C). The second plant utilizes a two-stage distillation process with two distillation heat exchangers connected in series (operative condensation temperatures 40 and 60°C). Vacuum solar collectors of simple design and construction, utilizing glass or suitable glass/polymer blends as transparent material, are proposed for the SW–SBD plants. The present analyses suggest that SW–SBD desalting technology may have a promising technico-economic potential. Field research on SW–SBD prototype plants is necessary to bring SW–SBD desalting technology to its full technological development.     

A generalized method for the synthesis and design of reactive distillation columns

Owing to the combination between the reaction operation and the separation operation involved, it is extremely difficult to determine in advance the optimum configuration of a reactive distillation column and this makes process synthesis and design a great challenging task. Currently, no easy-to-use and yet effective methods are available to guide process synthesis and design, restricting considerably the applications and therefore the impacts of reactive distillation columns to the chemical process industry. In this paper, a generalized method is proposed for the synthesis and design of reactive distillation columns in terms of the insights from process intensification. The method is initiated from a simple process design with all feeds of reactants at the middle of the process and all stages as reactive ones. In terms of an economical objective function, it can be evolved into the optimum process design via sequential structure adjustments, including reactive section arrangement, feed stage relocation, feed splitting, and catalyst redistribution. The generalized method proposed is characterized by great simplicity in principle, the capability to tap the full potentials of process intensification, and the high robustness to the initial guess of process configuration as well as the thermodynamic properties of the reacting mixtures separated. Four example systems are employed to evaluate the generalized method proposed and the obtained outcomes demonstrate its effectiveness and applicability to the synthesis and design of various reactive distillation columns.     

Molecular tracking: A concept for side-draw distillation column design

A simple approach is introduced to locate a side-draw tray for ternary and multi-component mixtures with middle boiling component(s) present in the system at trace levels. The concept is based on a probability function defined by the thermodynamic properties of the system. The advantage of this method over existing methods is the ability to quickly and efficiently provide a feasible configuration of the distillation unit without relying on rigorous optimization or trial and error approaches. Moreover, it provides an intuitive understanding of the movements of the middle boiling components in the column.     

A systematic method to synthesize all dividing wall columns for n‐component separation: Part II

We present a simple rule that, for the first time, enables exhaustive enumeration of dividing wall columns (DWCs) corresponding to any given thermally coupled distillation column‐configuration. With the successive application of our rule, every partition in a DWC can be extended all the way to the top and/or to the bottom of a column without losing thermodynamic equivalence to the original thermally coupled configuration. This leads to easy‐to‐operate DWCs with possible control/regulation of each and every vapor split by external means. As a result, we conclude that any given DWC can be transformed into a thermodynamically equivalent form that is easy‐to‐operate, and hence, there always exists at least one easy‐to‐operate DWC for any given thermally coupled distillation. Our method of enumerating and identifying easy‐to‐operate DWCs for an attractive thermally coupled configuration will contribute toward process intensification by providing ways to implement efficient and low‐cost multicomponent distillations. © 2017 American Institute of Chemical Engineers AIChE J, 64: 660–672, 2018     

Design of extractive distillation for the separation of close-boiling mixtures: Solvent selection and column optimization

A practical methodology for the design and optimization of extractive distillation is proposed in this work. The extractive distillation is generally applied to the separation of close-boiling mixtures, which by conventional distillation is difficult to separate. The design and optimization of extractive distillation is more complex than that of the conventional distillation when considering the selection of suitable solvent to enhance the separation. Currently, the solvent selection can be effectively handled by the assistance of the computer-aided molecular design (CAMD) approach. The selection result may however be inconclusive due to the lack of accurate or missing parameters in the property model. In this work, the experimental verification and the property parameter determination were proved to be necessary as an additional step to achieve a successful and reliable design. The overall design methodology was illustrated through an industrial separation of C8-Aromatics mixture.     

A generalized CFD model for evaluating catalytic separation process in structured porous materials

A hybrid multiphase model is developed to simulate the simultaneous momentum, heat and mass transfer and heterogeneous catalyzed reaction in structured catalytic porous materials. The approach relies on the combination of the volume of fluid (VOF) and Eulerian–Eulerian models, and several plug-in field functions. The VOF method is used to capture the gas–liquid interface motion, and the Eulerian–Eulerian framework solves the temperature and chemical species concentration equations for each phase. The self-defined field functions utilize a single-domain approach to overcome convergence difficulty when applying the hybrid multiphase for a multi-domain problem. The method is then applied to investigate selective removal of specific species in multicomponent reactive evaporation process. The results show that the coupling of catalytic reaction and interface species mass transfer at the phase interface is conditional, and the coupling of catalytic reaction and momentum transfer across fluid–porous interface significantly affects the conversion rate of reactants. Based on the numerical results, a strategy is proposed for matching solid catalyst with operating condition in catalytic distillation application.     

Difference points in reactive and extractive cascades: IV—Feasible regions for multisection columns with kinetic reactions and side streams

The feasibility of three component distillation columns containing kinetically controlled chemical reactions and side streams is addressed through the use of difference points. We decompose complex columns into sections and identify feasible regions in composition space where each section operates. These regions enclose sectional profiles for the full range of operating parameters and are bounded by profiles constructed under extreme conditions. We efficiently determine the bounding profiles without computing interior compositions. We also develop a graphical feasibility test to connect sections and construct full columns using feasible regions. Finally, we present a technique to characterize the feasible regions and quantify how much reaction or side stream may be placed on any stage of a column section. The first three papers in this series [Hauan et al., 2000. Difference points in extractive and reactive cascades. I—Basic properties and analysis. Chemical Engineering Science 55 (16) 3145–3159; Lee et al., 2000. Difference points in extractive and reactive cascades. II—Generating design alternatives by the lever rule for reacting systems. Chemical Engineering Science 55 (16) 3161–3174; Hoffmaster and Hauan, 2004. Difference points in extractive and reactive cascades. III—Properties of column section profiles with arbitrary reaction distribution. Chemical Engineering Science 59 (17) 3671–3693] derive the fundamental properties of difference points, develop a lever rule to facilitate full column design, and analyze the properties of sectional profiles in reactive cascades. This fourth paper develops the necessary feasibility analysis tools for systematic identification of reactive distillation design alternatives.     

A note on an extended short-cut method for the design of multicomponent reactive distillation columns

Until now, few studies have proposed analytical short-cut methods for reliably designing multicomponent reactive distillation columns. Therefore, in this study we have improved and extended a design methodology for the design of RD columns of multicomponent systems. We have developed a graphical design method, based on distillation lines and tray-by-tray calculations defined in terms of reaction-invariant composition variables, to determine RD design parameters such as the number of theoretical stages, operating reflux ratio, the feed tray location and the top or bottom flow. In this note, we report our extended and improved method, which is analytical and useful for reliably determining the design parameters of multicomponent RD systems. We study the synthesis of TAME with inert components (with different feed thermal conditions) as case of study to show the effectiveness of the proposed strategy. Results obtained with our strategy show a significant agreement with those obtained using a rigorous model of commercial simulator AspenONE Aspen Plus^®.     

Development of enhanced three-dimensional printed packings for scale-up of distillation columns: A successful case study

This publication presents a general approach for the enhancement of packings regarding scalability, separation efficiency, and fluid dynamic properties using three-dimensional (3D) printing. The methodology is used to develop miniaturized, scalable packings for process development, and scale-up applications. For this purpose, a 3D printable computer-aided design version of the Rombopak 9M industrial packing (RP9M-3D), which is known for its positive scalability properties, was created. An initial characterization by means of computational fluid dynamics simulations and mass transfer measurements reveals positive but also negative design properties. These findings are used to create a more advanced, miniaturized packing structure, the XW-Pak. The evolved structure is compared to the RP9M-3D. The simulation and experimental results show that the enhanced packing, which is still in the early stages of development, exhibits higher separation efficiencies with improved scalability properties at the same void fraction and surface area than the RP9M-3D.     

Improving energy efficiency and cost-effectiveness of batch distillation for separating wide boiling constituents. II: Internal versus external heat integration

In the first paper of this series, we developed a vapor recompressed batch distillation (VRBD) scheme by means of external heat integration. This contribution aims at devising an internally heat integrated batch distillation with a concentric reboiler (IHIBDCR) configuration, in which the rectifying tower is surrounded by a jacket. The operating cost can be reduced with the improvement of energy savings substantially through seeking further external heat integration under the framework of vapor recompression mechanism in the IHIBDCR structure between the overhead vapor and the reboiling liquid. The features of both the IHIBDCR system and its hybrid form that combines the vapor recompression column (VRC) and the IHIBDCR scheme are illustrated by a binary mixture having wide boiling constituents, with special emphasis focused on the comparative performance study between the externally integrated VRBD presented in Part 1 of the current work, the internally integrated IHIBDCR arrangement and the hybrid structure.     

A novel type of equipment for reactive distillation: Model development,simulation, sensitivity and error analysis

A simulation study of heterogeneously catalyzed reactive distillation experiments carried out with the D + R tray, a novel type of laboratory equipment, is presented. One advantage of the D + R tray is that reaction and distillation are alternating stage‐wise, in a well‐defined way that can be modeled straightforwardly. An equilibrium stage model is used to describe the distillation and a plug flow reactor model to describe the catalyst bed reactors. The model parameters are derived from a systematic experimental characterization of the D + R tray both as a reactor and as a distillation unit. A validated physicochemical fluid property model is used. The primary experimental data are reconciled. Results from the predictive simulations are in good agreement with the experimental results. The influence of errors in the input parameters on the simulation results is investigated by means of a sensitivity and error analysis. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1533–1543, 2013     

Reactive Separations for In Situ Product Removal of Enzymatic Reactions: A Review

The topic of integrating enzymatic reactions with in situ product removal is addressed. Different integrated reactive separations structured accordingly to the corresponding unit operations, i.e., reactive distillation, reactive chromatography, reactive crystallization, and extractive biocatalysis, are discussed. Special attention is given to their realization with homogenous and heterogeneous biocatalysis. Various enzyme immobilization techniques are presented and distinct strategies for installation of heterogeneous catalysts into process equipment are discussed.     

Alkanol removal from the apolar phase of a two-liquid phase bioconversion system. Part 1: Comparison of a less volatile and a more volatile in-situ extraction solvent for the separation of 1-octanol by distillation

Biocatalytic systems can be used for the regio- and stereospecific synthesis of oxidized alkanes and aromatic compounds, such as aliphatic and aromatic alcohols, aldehydes and epoxides. These reactions are typically carried out in two-liquid phase media. The biocatalyst is usually a natural microorganism, often a Pseudomonas, or a genetically altered host, a Pseudomonas or E. coli recombinant typically, which grows in the aqueous phase, while the substrate and product are present in an organic bulk phase. Oxidation products formed in these systems must be purified after separation of the two liquid phases. We have evaluated the performance of distillation for the separation of the product 1-octanol by examining a more volatile (octane) and a less volatile (hexadecene) in-situ extraction system. The separation performance of the two systems has been compared based on recovery efficiency, energy cost and number of required process units. Results showed that a less volatile extractant compared favorably in terms of number of product separation unit steps, decreased operating and energy cost to the use of a more volatile extraction solvent. In addition, a major disadvantage of the more volatile in-situ extraction process was the coloring of the bottom product of the first distillation step, in which the product is contained in this case. Such modifications can be implemented into an upstream and downstream process of bioconversions to improve the overall system and to reduce downstream processing cost. © 1998 SCI     

A Reynolds mass flux model for gas separation process simulation:II. Application to adsorption on activated carbon in a packed column☆

Simulations of adsorption process using the Reynolds mass flux model described in Part I of these serial articles are presented. The object of the simulation is the methylene chloride adsorption in a packed column (0.041 m id, packed with spherical activated carbon up to a length of 0.2 m). With the Reynolds mass flux model, breakthrough/regeneration curves, concentration and temperature as well as the velocity distributions can be obtained. The simulated results are compared with the experimental data reported in the literature and satisfactory agreement is found both in breakthrough/regeneration curves and temperature curves. Moreover, the anisotropic turbulent mass diffusion is characterized and discussed.