Design Of Distillation Columns Research Articles

Synthesis and design of reactive distillation columns with two reactive sections

The synthesis and design of reactive distillation columns with two reactive sections (RDC–TRS) are attempted for the separations of reacting mixtures with somewhat unfavorable ranking of relative volatilities (RM–SURRV, i.e., two reactants are the light and heaviest components and two products the lightest and heavy ones). With the deliberate arrangement of the two reactive sections, the disadvantages by the unfavorable relative volatility can be substantially alleviated, facilitating consequently the reaction operation and separation operation involved. The separations of a hypothetical quaternary reaction, the esterification of acetic acid with methanol, and the transesterification of butyl acetate with ethanol are employed to evaluate the RDC–TRS. The process is found considerably superior to the reactive distillation column with a single reactive section and this demonstrates its feasibility and effectiveness in the separations of RM–SURRV. The RDC–TRS is found to present comparable or even improved performance in comparison with the reactive distillation column with an external recycle from bottom to reactive section and this corroborates it a potentially competitive alternative for the separations of the RM–SURRV. The RDC–TRS is also highlighted for the other kind of RM–SURRV (i.e., two reactants are the lightest and heavy components and two products the light and heaviest ones).

Simplified Conceptual Design Methodology for Double-Feed Extractive Distillation Processes

Shortcut methods have an important role in the conceptual design of distillation processes because they rapidly provide constraints for important design parameters such as minimum reflux ratio, number of stages, process feasibility, possible splits, and, specifically for extractive distillation, minimum solvent feed ratio and maximum reflux ratio. In this work, a simplified method using reversible distillation models has been applied to the conceptual design of double feed extractive distillation columns. This work uses continuation methods for calculating the curves that determine the feasibility region and all of the resulting design parameters. Combining continuation methods with the column equations yields a simple method for calculating the pinch curves that border the feasibility region. As previously found by other authors, we observed that these extractive distillation pinch curves, in addition to determining the feasibility region, are also useful for calculating an approximate minimum entrainer feed ratio independent of other parameters, as well as accurately pinpointing the minimum and maximum reflux ratios. Applications to example extractive distillation systems allow us to conclude that the method is reliable, fast, and much easier to implement than other methods presented previously in the literature. The systems acetone–methanol–water and ethanol–water–ethylene glycol were employed as case studies, allowing a graphical assessment of the method; however, it can be used in the analysis of systems with more than three components.

Rigorous design of distillation columns using surrogate models based on Kriging interpolation

The economic design of a distillation column or distillation sequences is a challenging problem that has been addressed by superstructure approaches. However, these methods have not been widely used because they lead to mixed‐integer nonlinear programs that are hard to solve, and require complex initialization procedures. In this article, we propose to address this challenging problem by substituting the distillation columns by Kriging‐based surrogate models generated via state of the art distillation models. We study different columns with increasing difficulty, and show that it is possible to get accurate Kriging‐based surrogate models. The optimization strategy ensures that convergence to a local optimum is guaranteed for numerical noise‐free models. For distillation columns (slightly noisy systems), Karush–Kuhn–Tucker optimality conditions cannot be tested directly on the actual model, but still we can guarantee a local minimum in a trust region of the surrogate model that contains the actual local minimum. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2169–2187, 2015

Design and operation of dividing-wall distillation columns. 2. Process dynamics and operation

In the first paper of this series, it was demonstrated that the black-hole problem of dividing-wall distillation columns (DWDCs) could effectively be diminished through over-design in terms of careful adjustment of the number of stages. Because the over-design serves to coordinate the relationship between the prefractionator and main distillation column involved, it yields frequently favorable effect to process dynamics and controllability and this represents essentially an additional advantage of such process modifications to diminish the black-hole problem. The three example systems studied in the first paper of this series are again employed to ascertain the anticipation. The DWDCs with and without the over-design are strictly compared in terms of open- and closed-loop controllability studies. It is found that the over-design helps to coordinate the interaction between the prefractionator and main distillation column involved and leads consequently to improved process dynamics and capabilities in disturbance rejection and set-point tracking. The outcome confirms again the necessity of diminishing the black-hole problem in the synthesis and design of the DWDCs. Though the interpretation is gained from the three example systems studied, it should be considered to be of general significance to the design and operation of the DWDCs.

Simultaneous optimal design and operation of a diabatic extractive distillation column based on exergy analysis

The concept of diabatic distillation is applied to an extractive distillation system of ethanol, which uses glycerol as entrainer, to study the influence of heat flows in optimal design, operation, and thermodynamic efficiency of such systems via exergy analysis. First, optimal operating conditions for minimum exergy losses are computed for a diabatic column with fixed feed locations and number of trays. Then, optimal design (feed locations, number of trays, and heat flows along the column) and operation of the system is calculated as a mixed integer nonlinear programming (MINLP) problem, for an economic and economic-exergetic objective functions for two different entrainer molar flows. It was found that the entrainer molar flow has remarkable influence in the reduction of the exergy losses of the system.

Adopting feed splitting in design of reactive distillation columns with two reactive sections

For the separations of reacting mixtures featuring the heaviest and lightest reactants and intermediate products, although feeding the heaviest/lightest reactant to condenser/reboiler of reactive distillation columns with two reactive sections (RDCs-TRS) at top/bottom favors the reaction operation involved, it poses a detrimental effect to the separation operation involved because the reactants tend to move through the stage for withdrawing the intermediate product and increase consequently separation difficulties. A performance index is derived for the RDC-TRS and feed splitting is adopted to suppress the drawback. The separations of an ideal quaternary reaction, the esterification of lactic acid with methanol, and the esterification of palmitic acid with isopropanol, are employed to evaluate the proposed design philosophy. The resultant design is found considerably superior to the RDC-TRS and exhibits better or at least comparable performance with the reactive distillation column with a top–bottom external recycle. These outcomes indicate that feed splitting is especially effective for enhancing internal mass and energy integration between the reaction operation and separation operation involved. Despite the existence of adverse internal energy integration in case of reactions with thermal effect, the reinforced internal mass integration could still facilitate the resultant design a potentially competitive alternative.

Direct-contact Condensation of Hydrocarbon Mixtures in a Structured Packing Bed

This article deals with experimental research of the direct-contact condensation in column with structured packing. Lots of experiments have been performed in a column of 257 mm inner diameter with Topic 125 Y structured packing using hydrocarbon mixtures. The influences of the vapor and liquid flow rate as well as liquid temperature at vacuum pressure have been investigated. A new empirical correlation was developed to predict the heat transfer coefficient for structured packings, which can be applied to both design and simulation of distillation columns in petroleum refinery.

ANALYSIS OF THE CONNECTING ZONE BETWEEN CONSECUTIVE SECTIONS IN DISTILLATION COLUMNS COVERING MULTIPLE FEEDS, PRODUCTS AND HEAT TRANSFER STAGES

In the present work, we provide a systematic analysis about all the streams involved in the zone connecting two consecutive sections for the design of distillation columns with different thermal feed conditions, product extractions and heat additions or withdrawals. This analysis allows a better understanding of what happens on a feed or side draw (of mass or energy) stage, what compositions are or are not in equilibrium, and the impact on internal liquid and vapor flows.

Applied Research on the Resource Recovery of Formaldehyde in Pesticide Wastewater

Applied research on the technology of resource recovery of formaldehyde in pesticide wastewater through compression distillation was accomplished intensively in this study. Vapor–liquid equilibrium data of the low-molar fraction formaldehyde aqueous solution were measured accurately in experiments. The results were in high accordance with the theoretical values through data association. It filled in a gap in data at the zone of low formaldehyde molar fraction (particularly below 0.006) and also provided theoretical basis for the distillation column design for recycling formaldehyde. Systematic experimental research investigated the recovery of formaldehyde in pesticide wastewater by compression distillation. The distillation column was operated under a top pressure of 0.2 to 0.4 MPa and with feed formaldehyde molar fraction range of approximately 0.006 to 0.03. The formaldehyde molar fractions at the top and bottom of column were 0.15 and 0.00072, respectively. Therefore, concentrated formaldehyde solutio...

Bubble point measurement and high pressure distillation column design for the environmentally benign separation of zirconium from hafnium for nuclear power reactor

We examined the feasible separation of ZrCl4 and HfCl4 through high pressure distillation as environmentally benign separation for structural material of nuclear power reactor. The bubble point pressures of ZrCl4 and HfCl4 mixtures were determined experimentally by using an invariable volume equilibrium cell at high pressure and temperature condition range of 2.3–5.6 MPa and 440–490 °C. The experimental bubble point pressure data were correlated with Peng-Robinson equation of state with a good agreement. Based on the vapor-liquid equilibrium properties evaluated from the experimental data, the feasibility of high pressure distillation process for the separation of ZrCl4 and HfCl4 was investigated with its main design condition through rigorous simulation using a commercial process simulator, ASPEN Hysys. An enhanced distillation configuration was also proposed to improve energy efficiency in the distillation process. The result showed that a heat-pump assisted distillation with a partial bottom flash could be a promising option for commercial separation of ZrCl4 and HfCl4 by taking into account of both energy and environmental advantages.

A combined method for the design and optimization of intensified distillation systems

The sequential design method (SDM) is a recently introduced distillation column design method based on the correspondence between the simple column and the alternative sequences design parameters. It can be defined as a method that combines the alternatives generation step with the design procedure. The Multi-Objective Differential Evolution (MODE) algorithm instead, is based on the minimization or maximization of a defined objective function; it is a strong method that allows the evaluation of a large number of alternatives.The SDM is characterized by a poor control of the error propagation among the sequences, the MODE algorithm by a high computational time. It was obtained that a proper combination of the methods allows the compensation of the drawbacks of the stand-alone procedures. For the case study considered, when the MODE algorithm is initialized with the SDM, a 39% reduction of the computational time was observed. If the combination between the methods is realised at the beginning of the design procedure, the reduction of the computational time was of about 28%. The time reduction was due to a narrower initialization of the MODE algorithm with the parameters obtained applying the SDM. Moreover, when some overestimated design values where used to initialize the MODE algorithm, it is still possible to identify a configuration very close to the optimum.

Liquid Flow Behavior of a Seepage Catalytic Packing Internal for Catalytic Distillation Column

A seepage catalyst packing internal (SCPI) as a good alternative for catalytic distillation internals was investigated in this work. The seepage flow behavior and liquid holdup characteristics of the SCPI have a significant influence on the performance and industrial design of a catalytic distillation column with SCPI, and the present study focused on this issue. Measurements of the seepage flow and liquid holdup of the SCPI were achieved using a 100-mm-diameter plexiglas tube and a 600-mm-diameter Perspex column, respectively. The experimental results were used to develop a series of correlations to predict the liquid holdup of the SCPI. Again, a comparison to the experimental data showed good agreement. It was concluded that the model represents the real process with satisfactory accuracy, although some deviations were observed. Furthermore, compared with two classical catalytic packings, the experimental results show that the SCPI has a much larger liquid holdup, which is advantageous for the reaction....

Kinetics Studies on Esterification Reaction of Acetic acid with Iso-amyl Alcohol over Ion Exchange Resin as Catalysts

In this work, the esterification of acetic acid with iso-amyl alcohol catalyzed by acidic ion-exchange resins (TULSION R T-62, T-63 and T-66 MP) has been investigated in a batch reactor to determine the intrinsic reaction kinetics. Iso-amyl acetate is synthesized in this reaction, has the fragrance of strong odor (similar to both banana and pear). The effects of various parameters on the rate of reaction (such as temperature, mole ratio, catalyst loading, and stirrer speed) are studied. The solid- liquid external mass transfer resistance as observed using various stirring speeds is absent and the rate of reaction depends on temperature. Further pseudo-homogenous model is developed for an intrinsically kinetically controlled reaction, which is free from either intra-particle diffusion or external mass transfer resistance. The rate expression developed in this work would be useful in the simulation and design of reactive distillation column for the production of iso-amyl acetate. The resultant kinetic model fitted the experimental data well. The activation energy is found to be 41.88 kJ/kmol for the formation of iso-amyl acetate.

Modified method to improve the design of Petlyuk distillation columns

BackgroundA response surface analysis was performed to study the effect of the composition and feeding thermal conditions of ternary mixtures on the number of theoretical stages and the energy consumption of Petlyuk columns. A modification of the pre-design algorithm was necessary for this purpose.ResultsThe modified algorithm provided feasible results in 100% of the studied cases, compared with only 8.89% for the current algorithm. The proposed algorithm allowed us to attain the desired separations, despite the type of mixture and the operating conditions in the feed stream, something that was not possible with the traditional pre-design method. The results showed that the type of mixture had great influence on the number of stages and on energy consumption. A higher number of stages and a lower consumption of energy were attained with mixtures rich in the light component, while higher energy consumption occurred when the mixture was rich in the heavy component.ConclusionsThe proposed strategy expands the search of an optimal design of Petlyuk columns within a feasible region, which allow us to find a feasible design that meets output specifications and low thermal loads.

Optimal design of cryogenic distillation columns with side heat pumps for the propylene/propane separation

Propylene is one of the most important products in the petrochemical industry, which is used as raw material for a wide variety of products. The propylene/propane separation is a very energy-intensive process because their boiling points are quite similar. In addition, at atmospheric conditions, their boiling points are −47.6°C and −42.1°C, respectively. To separate this mixture conventional columns which operate at high pressure and cryogenic distillation columns which operate at low pressure have been used, however, this approaches are still energy-intensive. This work presents energy-efficient and intensified distillation columns which are adiabatic such as the vapor recompression column (VRC) or diabatic such as columns with heat-integrated stages. A design and optimization procedure, which minimizes the energy consumption in the propylene/propane separation is presented. Conceptual design, superstructure representation, rigorous simulations and mathematical programming techniques are effectively combined to assess all the candidate distillation structures, refrigeration cycles, and heat integration possibilities simultaneously. Results showed that VRC and diabatic distillation columns with heat-integrated stages can reduce the energy consumption between 58 and 75% when compared with conventional distillation at high pressure. Furthermore, the proposed synthesis procedure derived simplified optimal distillation structures with few heat-integrated stages and still attained important energy savings.

Control analysis of an extractive dividing-wall column used for ethanol dehydration

This paper deals with design and control of an extractive dividing-wall distillation column (EDWC) for ethanol dehydration using ethylene glycol as entrainer. An initial design, based on a section analogy procedure for a conventional extractive distillation sequence, was obtained and then used in an optimization process to minimize the total annual cost. It was shown that the EDWC can result in significant savings over the conventional process. As these savings sometimes go along with a decrease in the control properties, an investigation of two control structures for the EDWC and one for the conventional column configuration was performed next.It was observed in closed-loop simulations that the EDWC with an appropriate structure exhibited good control properties and that its closed-loop responses were similar to those obtained for the operation of a conventional extractive distillation system.

Logic hybrid simulation-optimization algorithm for distillation design

In this paper, we propose a novel algorithm for the rigorous design of distillation columns that integrates a process simulator in a generalized disjunctive programming formulation. The optimal distillation column, or column sequence, is obtained by selecting, for each column section, among a set of column sections with different number of theoretical trays. The selection of thermodynamic models, properties estimation, etc. is all in the simulation environment. All the numerical issues related to the convergence of distillation columns (or column sections) are also maintained in the simulation environment. The model is formulated as a Generalized Disjunctive Programming (GDP) problem and solved using the logic based outer approximation algorithm without MINLP reformulation. Some examples involving from a single column to thermally coupled sequence or extractive distillation shows the performance of the new algorithm.

A reactive distillation column with double reactive sections for the separations of two-stage consecutive reversible reactions

In this paper, a novel reactive distillation column with double reactive sections (RDC-DRS) is proposed for the separations of two-stage consecutive reversible reactions. The arrangement of two reactive sections not only allows the careful coordination of the two reaction operations involved, but also provides additional degrees of freedom for the reinforcement of internal mass integration and/or internal energy integration between the reaction operations and the separation operation involved, which could facilitate the RDC-DRS to be more advantageous than the conventional reactive distillation column with a single reactive section (RDC-SRS) in operating cost and capital investment. A representative hypothetical and real two-stage consecutive reversible reactions are chosen to evaluate the steady-state performance of the RDC-DRS. With the constraints of the same total number of stages and the same total number of reactive stages, the RDC-DRS is demonstrated to require less utility consumption than the RDC-SRS and this outcome indicates that the former could be a competitive alternative to the latter in the separations of the two-stage consecutive reversible reactions. The number of reactive sections should therefore be viewed as an important decision variable for the synthesis and design of reactive distillation columns especially in the separations of complicated reacting mixtures involving multiple reversible reactions.

Application of the Firefly and Luus–Jaakola algorithms in the calculation of a double reactive azeotrope

The calculation of reactive azeotropes is an important task in the preliminary design and simulation of reactive distillation columns. Classically, homogeneous nonreactive azeotropes are vapor–liquid coexistence conditions where phase compositions are equal. For homogeneous reactive azeotropes, simultaneous phase and chemical equilibria occur concomitantly with equality of compositions (in the Ung–Doherty transformed space). The modeling of reactive azeotrope calculation is represented by a nonlinear algebraic system with phase equilibrium, chemical equilibrium and azeotropy equations. This nonlinear system can exhibit more than one solution, corresponding to a double reactive azeotrope. In a previous paper (Platt et al 2013 J. Phys.: Conf. Ser. 410 012020), we investigated some numerical aspects of the calculation of reactive azeotropes in the isobutene + methanol + methyl-tert-butyl-ether (with two reactive azeotropes) system using two metaheuristics: the Luus–Jaakola adaptive random search and the Firefly algorithm. Here, we use a hybrid structure (stochastic + deterministic) in order to produce accurate results for both azeotropes. After identifying the neighborhood of the reactive azeotrope, the nonlinear algebraic system is solved using Newton's method. The results indicate that using metaheuristics and some techniques devoted to the calculation of multiple minima allows both azeotropic coordinates in this reactive system to be obtains. In this sense, we provide a comprehensive analysis of a useful framework devoted to solving nonlinear systems, particularly in phase equilibrium problems.

Vapor–Liquid Equilibria for Water + Propylene Glycols Binary Systems: Experimental Data and Regression

The vapor–liquid equilibria (VLE) data are essential for the design of distillation columns to separate propylene glycols mixtures, obtained via the hydrolysis of 1,2-epoxy propane. In this study there are reported data for four binary systems involved, such as water + propylene glycols. VLE data have been measured in the temperature range (295.15 to 460.15) K and pressure up to 34.529 kPa for the following binary systems: water +1,2-propanediol (monopropylene glycol, MPG), water +1-(2-hydroxypropoxy)propan-2-ol (dipropylene glycol, DPG), water +2-[2-(2-hydroxypropoxy)propoxy]propan-1-ol (tripropylene glycol, TPG), and water +2-(2-[2-(2-hydroxypropoxy)propoxy]propoxy)propan-1-ol (tetrapropylene glycol, TePG). The equipment used was a static apparatus built in our laboratory. The only literature data available for these systems were for the water + MPG binary system. The experimental data obtained were correlated with the NRTL model. The results showed a fairly good agreement between the model and the experimental data with a maximum deviation in composition terms of 3%.