Homogeneous Azeotropes Research Articles

Room Temperature Evaporation Behavior of Homogeneous Azeotropes Used in Art Conservation Cleaning Treatments

Cleaning painted surfaces of their grime, aged varnishes, and discolored overpaint is one of the most common interventive treatments for art conservators. Carefully concocted solvent mixtures navigate the solubility differences between the material removed and the original paint underneath. However, these solutions may be altered by differential evaporation rates of the component solvents (zeotropic behavior), potentially leading to ineffectively weak cleaning or conversely overly strong residual liquid capable of damaging the underlying paint. Azeotropic solvent blends, which maintain a constant composition during evaporation, offer a promising solution. These blends consist of two or more solvents combined at precise concentrations to function as a single solvent. Additionally, pressure-maximum azeotropes feature higher vapor pressure compared to other mixtures, further minimizing contact time and sorption of the solvents into artworks. This study examines azeotropes of isopropanol with n-hexane and 2-butanone in cyclohexane, which have been used previously in art conservation. The evaporation behavior at room temperature of these boiling point azeotropes was assessed using vapor pressure measurements, refractive index determinations, gravimetric analysis, and gas chromatography. Results showed changes in composition during evaporation and found that the actual room temperature azeotropic composition can vary between 1 and 10% v/v in concentration with those commonly reported at their boiling points. Art conservators should be cautious when using azeotropic blends reported at boiling points significantly higher than room temperature. To ensure the safety and efficacy of these mixtures, it is recommended to determine individual azeotropic cleaning blends experimentally before their use.

Design and control of fraction cutting for the separation of mixed alcohols from the Fischer–Tropsch aqueous by-products

Since the minimum-boiling azeotropes of C2–C8 alcohols with water and high-water content (up to 95% (mass)) in the Fischer–Tropsch aqueous by-products, the separation is energy-intensive and challenging. The energy-saving strategy for the complete separation of the Fischer–Tropsch aqueous by-products has received massive attention in recent decades. In this study, a stripper-sidestream decanter process is proposed by exploiting homogeneous azeotropes (C2–C3 alcohols–water) and heterogeneous azeotropes (C4–C8 alcohols–water). The introduction of the stripping column for pre-dehydration avoids the re-vaporization of the mixture, and energy carried by the overhead vapor is conserved instead of being removed in a condenser. The precise fraction cutting of C1–C3 alcohol–water mixture, C4–C8 alcohols, and water is realized by the sidestream distillation column. The C4–C8 alcohols rich mixture withdrawn from the sidestream flows into the decanter to break the distillation boundary, where the organic phase returns to the sidestream distillation column to obtain the dehydrated C4–C8 alcohols, and the aqueous phase enters the stripping column. Steady-state optimization based on total annual cost (TAC) minimization shows that the stripper-sidestream decanter process reduces TAC by 17.00% and saves energy by 21.27% compared with the conventional three-column distillation process. Further, a control structure of the process is established, and dynamic simulations show that the control structure combining a differential controller with a low-selector exhibits robust control. This study provides a novel design scheme and deepens the insights into the efficient separation of aqueous by-products of the Fischer–Tropsch synthesis.

Design and control of an energy-efficient triple-column pressure swing distillation configuration for separation of acetone-methanol-hexane mixture

Although several studies on the design of ternary mixtures with multiple binary azeotropes can be easily found in the existing literature, there are only a few recent design studies dealing with ternary mixtures including both binary and ternary azeotropes. In this study, two alternative triple-column pressure swing distillation (PSD) configurations are proposed for acetone-methanol-hexane mixture including three binary and one ternary minimum boiling homogeneous azeotropes. They are compared based on total annual cost by analyzing ternary maps at different pressures. Results show that methanol-acetone-hexane (M-A-H) separation sequence obtained by a column configuration operating at 0.5, 1 and 5 bar has a better economic performance compared to acetone-methanol-hexane (A-M-H) separation sequence. Moreover, the fully heat-integrated M-A-H configuration results in a further saving of 13.8%. Furthermore, the plantwide control structure of the heat-integrated M-A-H configuration including a pressure-compensated temperature controller shows a good performance against disturbances in feed flowrate and composition.

Process design and intensification for the clean separation of ternary multi-azeotropes system via special distillation coupled with reaction

A ternary mixture of diisopropyl ether, isopropanol and water exists in the production process of isopropanol. Ensuring the clean separation of this mixture is of great significance for the clean production of isopropanol from both economy and environment. However, there are three binary and one ternary minimum boiling point homogeneous azeotropes in this system, which complicate the clean production of isopropanol. In this study, with the aid of the hydration reaction of ethylene oxide, clean separation of a ternary mixture of diisopropyl ether–isopropanol–water was realized. Three separation processes—reaction–pressure swing distillation, reaction–extractive distillation and reaction–dividing wall extractive distillation—were proposed. These processes were optimized based on the sequential iterative algorithm, with the minimum total annual cost as the objective. Reaction-pressure swing distillation had the best economic performance, reaction-extractive distillation followed, and reaction-dividing wall extractive distillation performed the worst. The carbon dioxide, sulfur dioxide, and nitrogen oxide emissions of the three processes were calculated based on the optimization results. Reaction-pressure swing distillation had the lowest emissions, followed by reaction-dividing wall extractive distillation. However, reaction-extractive distillation had the highest emissions. The exergy analysis of distillation units and exchanger was performed, and the results showed that reaction-pressure swing distillation had the best exergy performance. Reaction-pressure swing distillation was better than reaction-extractive distillation and reaction-dividing wall extractive distillation in terms of economy, environment, and thermodynamic efficiency. This study provides an original idea for the clean separation of diisopropyl ether-isopropanol-water azeotropes.

VLLE of binary aqueous systems containing 2-butanol, isobutanol, or tert-amyl alcohol

Isothermal vapor-liquid-liquid equilibrium (VLLE) data were measured for water + 2-butanol, water + isobutanol, and water + tert-amyl alcohol at temperatures from 323.12 K to 373.16 K. A modified static-type apparatus equipped with a visual cell was used in the present study. The experimental results confirm that homogeneous azeotrope forms in water + 2-butanol and heterogeneous azeotrope forms in water + isobutanol and in water + tert-amyl alcohol. The VLLE data of the investigated binary systems were correlated well with the NRTL and the UNIQUAC models.

Novel energy-saving methods to improve the three-column extractive distillation process for separating ethyl acetate and ethanol using furfural

• Eight energy-saving processes based on the features of the system and the flowsheet. • A novel way of partial condensation saves 8.6% TAC compared with the normal way. • A novel vapor–liquid coupling process saves 48.6% TAC compared with the base case. • Using a compressor for vapor–liquid coupling process can further save TAC by 12.8%. A mixture of ethyl acetate and ethanol is difficult to separate because of a minimum-boiling homogeneous azeotrope. The characteristics of the ethyl acetate/ethanol system are analyzed. The energy-saving potential of a three-column extractive distillation process to separate the system is explored. The effects of the distillate composition of pre-concentrator, the temperature of solvent feed and operating pressures are studied. Energy-saving processes including heat pump distillation, heat integration and partial condensation are proposed. A novel way of partial condensation is proposed and compared with the conventional way. An innovative method of vapor–liquid coupling between the per-concentrator and the extractive column is then proposed. It is more economical and energy-efficient than the above processes. Besides, based on the vapor–liquid coupling process, two further improvements are proposed through heat integration and through compressors. All processes are optimized using the sequential iterative optimization procedure with the minimum total annual cost as the target. Compared with the conventional process operated at 101.3 kPa, the two improved processes can reduce total annual cost by more than 52%, reduce energy consumption by more than 60%, and reduce CO 2 emissions by more than 61%.

Thermal coupled extractive distillation sequences with three entrainers for the separation of azeotrope isopropyl alcohol + diisopropyl ether

AbstractBACKGROUNDDuring the synthesis of isopropyl alcohol (IPA) by hydration of propylene, diisopropyl ether (DIPE) is usually produced as a by‐product. Because IPA and DIPE can form a binary homogeneous azeotrope with the minimum boiling temperature at atmospheric pressure, it is difficult to separate the binary mixture by simple distillation.RESULTFor separating the azeotrope IPA + DIPE, side‐stream extractive distillation column (SSED) and extractive dividing wall column (EDWC) processes with three entrainers [2‐methoxyethanol (2‐MEA), 2‐ethoxyethanol and propylene glycol ethyl ether (PGEE)] were simulated and optimized based on the minimal total annual cost (TAC). Moreover, CO2 emissions of the six sequences were calculated and the impact on the environment evaluated.CONCLUSIONSThe sequence of SSED with PGEE as entrainer can reduce TAC by ≤34.48%, but EDWC with PGEE can offer TAC reduction of ≤52.46%. The results demonstrate that the EDWC sequence with PGEE as entrainer is favourable for separating the binary azeotrope IPA + DIPE. © 2020 Society of Chemical Industry

Enhanced separation of maximum boiling azeotropic mixtures with extractive heterogeneous-azeotropic distillation

In the separation industry the extractive heterogeneous-azeotropic distillation (EHAD) is a new and powerful innovation, that is capable of making the separation of highly non-ideal mixtures feasible and economical. In the last years there has been much attention paid to the separation of the minimum boiling homogeneous azeotropes. Although maximum boiling azeotropes are fewer in numbers than the minimum boiling ones but their separation is more complicated but it could be solved with the EHAD, too. Since EHAD is not limited to the separation of minimum boiling azeotropes, the separation of the maximum boiling azeotropes is studied in this work. Our work is motivated by industrial problems because there are such maximum boiling azeotropes in the liquid wastes of the fine chemical industry. The separation of highly non-ideal Water–Acetone–Chloroform–Methanol and Water–Ethyl Acetate–Chloroform–Ethanol quaternary mixtures are investigated and optimized in professional flowsheet simulator environment. Total Annual Costs are also determined. The purity requirement is 99.5 m/m% for Chloroform and the bottom product should be as clear as possible in water so that less liquid organic waste has to be incinerated. It is also an important merit of the EHAD that the chemicals in the distillate can be usually reused supporting sustainability. Different solutions for the separations supplemented with heat integration are examined. On the basis of the computer simulations and the experimental verification it can be concluded, the first time on the literature, that the separation efficiency of EHAD is superior also for the separation of the maximum boiling azeotrope mixtures.

Synthesis, Design, and Control of an Azeotropic Distillation System for Methanol–Isopropyl Acetate Separation

The existence of a minimum boiling homogeneous azeotrope precludes the separation of a methanol–isopropyl acetate (MeOH–IPAc) binary mixture into its constituent pure components using simple distil...

Production of Commercial Naphthalene by Coal-Tar Processing

The derivation of commercial naphthalene by rectification is a possible approach in coal-tar processing. Naphthalene is widely used in chemical synthesis for the production of phthalic anhydride, superplasticizers, and intermediate products such as Cleve’s acids in dye production. The quality of the naphthalene derived from petroleum is markedly higher than that of coal-tar naphthalene, primarily in terms of the thionaphthene content, since the thionaphthene content in the initial petroleum fractions is much less than in the naphthalene fraction of coal tar. Simulation of the vapor–liquid equilibrium of binary and ternary mixtures of the components in coal tar by means of the NRTL activity model, at different pressures, indicates that 2,3-xylenol–naphthalene, naphthalene–thionaphthene, and 3-xylenol–naphthalene–thionaphthene mixtures are characterized by positive homogeneous azeotropes. The composition and boiling points of the azeotropes are determined. The presence of the azeotropes significantly complicates the derivation of naphthalene from the naphthalene fraction of coal tar, in which the naphthalene content exceeds 97%. Analysis of the composition of the initial mixture and the azeotropes suggests a design for a three-column system for the distillation of commercial naphthalene, with the preliminary separation of water without the need for special separating agents or chemical extraction of impurities. Optimization of the proposed equipment by means of HYSYS software indicates high technological flexibility of the process and the production of naphthalene from coal tar that matches the quality of the naphthalene derived from petroleum. The naphthalene content in the commercial product derived from coal tar by the proposed method is 99.99 wt %. The yield of naphthalene is 90.5 wt %. The energy consumption in the basic three-column system is 0.92 Gcal/t of commercial naphthalene (of purity 99.99 wt %). If heat is recycled in the three-column system, the energy consumption is reduced to 0.6 Gkal/t of product (with the same degree of purity). That is comparable with the energy consumption in a two-column system, and the commercial naphthalene produced is characterized by greater yield and purity.

Extractive Distillation of Acetone – Methanol Mixture using 1-Ethyl-3-methylimidazolium Trifluoromethanesulfonate

Acetone and methanol are organic solvents widely used in industry. Acetone with methanol forms a homogeneous minimum-boiling azeotrope which is not separable by conventional distillation processes. A common method for its separation is the extractive distillation in the presence of a selective solvent (such as water). In this paper, the use of an ionic liquid (1-ethyl-3-methylimidazolium trifluoro methanesulfonate [Emim][triflate]) for acetone–methanol separation by extractive distillation was designed. The aim of the design calculation was to obtain acetone with the purity of 99.5 mol % and methanol with the purity of above 99.0 mol %. Calculations were carried out in a proprietary program constructed in Matlab® by solving a set of material balances at individual theoretical stages of the distillation column combined with the vapor–liquid equilibrium (VLE) of the ternary system acetone–methanol–[Emim][triflate]. For the description of VLE of the above mentioned system, the NRTL equation was used. Several optimization cycles were done resulting in optimal parameters of the extractive distillation column (number of theoretical stages, solvent consumption, reflux ratio and position of the feed stage) in regard to the required purity of products (acetone and methanol). Regeneration of ionic liquid was provided by evaporation at the low pressure of 20 kPa. The heat and cooling consumption duties of the designed separation process were analyzed. Regeneration of the ionic liquid is energy-demanding compared to the separation of acetone–methanol in an extractive distillation column. The heat consumption is only 11 % of the heat used up by the whole separation process.

STRUCTURAL OPTIMIZATION OF THE NAPHTHALINE DISTILLATION SCHEME BASED ON PHASE EQUILIBRIUM ANALYSIS

The research main aim is to analyze the presence, composition and naphthalene azeotropes type with impurities in the naphthalene fractions obtained by the distillation of coal tar. The presence of mentioned impurities significantly complicates the process of obtaining a pure product – naphthalene. The most difficult problem is the separation of naphthalene-thionaphthene mixture.Based on the simulations of the vapor-liquid equilibrium of the these mixtures components at different pressures, which were carried out in the HYSYS simulation environment using the UNIFAC method and the NRTL activity model, it has been shown that there are positive homogeneous azeotropes of 2,3-xylenol – naphthalene and naphthalene – thionaphthene. Azeotrope of xylenol – naphthalene – thionaphthene existence in the mixture was predicted. At atmospheric pressure, the azeotrope composition is presented: xylenol - 43 mass %, naphthalene - 5 mass % and thionaphthenes - 52 mass %. The boiling point is 201°C.Based on the analysis of phase equilibria, a unified energy efficient naphthalene separation method was proposed. Scheme consist of two columns, which operate under different pressures: the first column at a residual pressure of 100 mm Hg, the second at atmospheric pressure. The required regimes and efficiency of the columns were determined, ensuring the production of a commercial product with a main substance content of more than 99 % from naphthalene fractions with different composition with minimal loss of naphthalene.The conditions for the formation of the power-energy unit were determined in order to use the upper product condensation heat in the second column to heat the column operating under vacuum. This principal reduces the energy costs of obtaining the pure naphthalene (99 mass %) by 35 % in comparison with the design scheme without linking the heat fluxes.

Design and control of fully heat-integrated pressure swing distillation with a side withdrawal for separating the methanol/methyl acetate/acetaldehyde ternary mixture

In the industrial manufacturing process of polyvinyl alcohol, there is inevitably a small amount of acetaldehyde in the alcoholysis solution (methyl acetate/methanol mixture), the accumulation of which may decrease the purity of product. The effect of acetaldehyde on the separation of homogeneous azeotrope of methyl acetate and methanol via fully heat-integrated pressure swing distillation (FHI-PSD) is investigated. A PSD process with a side withdrawal is proposed and proved to avoid the accumulation of acetaldehyde in the system effectively. The optimum separation configuration conditions are based on the minimum total annual cost (TAC) analysis. In the steady-state design, the simulation reveals that the process has the minimal TAC when operating pressure of the HPC is 10atm. A conventional pressure-compensated temperature control (CS3) and a new temperature difference control (CS4) are compared in Aspen Dynamics. Both of them can eliminate the influence of pressure fluctuation on bubble points at the sensitive plates and perform well even for large feed disturbances. However, it is easier to design CS4 as CS4 doesn’t require complex bubble point temperature calculation compared with CS3. Therefore, CS4 is suggested to be another favorable and viable control scheme for PSD process, which may show superiority in industrial application.

Experimental studies and thermodynamic analysis of isobaric vapor-liquid-liquid equilibria of 2-propanol + water system using n-propyl acetate and isopropyl acetate as entrainers

Heterogeneous azeotropic distillation is a widely used technique in chemical industries for the purification of alcohols from their aqueous mixtures. This study aims at exploring the possibility of using n-propyl acetate and isopropyl acetate as entrainers for heterogeneous azeotropic distillation to effect the separation of 2-propanol + water azeotropic mixture. A novel yet simple still was constructed to measure the vapor-liquid equilibrium (VLE) and vapor-liquid-liquid equilibrium (VLLE) data for the binary and ternary systems. The isobaric VLE data for the binary systems 2-propanol + water, 2-propanol + n-propyl acetate and 2-propanol + isopropyl acetate and isobaric VLLE data for the ternary systems 2-propanol + water + n-propyl acetate and 2-propanol + water + isopropyl acetate were measured at atmospheric pressure. Subsequently, the experimental data was compared with predictions by thermodynamic models such as UNIFAC, UNIQUAC and NRTL. The feasibility of the entrainers n-propyl acetate and isopropyl acetate in separating the azeotropic mixture 2-propanol + water was studied using the Residue Curve Map (RCM). The experimental data showed the existence of a ternary homogeneous azeotrope in the 2-propanol + water + n-propyl acetate system and a heterogeneous ternary azeotrope in the 2-propanol + water + isopropyl acetate system. Since the heterogeneous azeotropic distillation process depends on the presence of ternary heterogeneous azeotrope, n-propyl acetate is not considered a suitable entrainer for the separation of 2-propanol + water mixture. Finally, a separation sequence for the heterogeneous azeotropic distillation of 2-propanol + water system using isopropyl acetate as entrainer has been proposed.

Comparison of alternative distillation processes for the maximum-boiling ethylenediamine dehydration system

An investigation and comparative analysis on the design and control of the maximum-boiling ethylenediamine (EDA) dehydration system is made in this work. Extractive distillation (ED) and heterogeneous azeotropic distillation (HAD) are used to separate EDA/water mixture that forms a maximum-boiling homogeneous azeotrope. 1,4-butanediol (BDO) and n-propyl acetate (NPAC) are selected as the suitable heavy/light entrainer from three candidate ones for each distillation process respectively. Savings of 17.80% in energy consumption and reduction of 26.26% in minimal total annual cost (TAC) can be obtained by comparing optimum design of ED process to that of HAD process for this system. Moreover, an initial control structure (CS) and an improved one are established for each distillation process. Finally, the comparison of dynamic responses indicates that the HAD process represents an alternative at the stand point of dynamic control for this system.

Fluid Phase Topology of Benzene + Cyclohexane + 1-Propanol at 101.3 kPa

Isobaric vapor–liquid equilibria for the benzene + cyclohexane + 1-propanol ternary mixture were experimentally investigated at atmospheric pressure. Data were tested and considered thermodynamically consistent by means of the McDermott and Ellis method. The experimental results showed that this ternary mixture is completely miscible and exhibits three binary minimum homogeneous azeotropes and a ternary minimum azeotrope at the studied conditions. Satisfactory results were obtained for correlation of equilibrium compositions with the UNIQUAC equation and also for prediction with the UNIFAC method. In both cases, low root-mean-square deviations of the vapor mole fraction and temperature were calculated. The capability of 1-propanol as a modified distillation agent at atmospheric conditions is discussed in terms of thermodynamic topological analysis. However, because of the complex topology of the ternary mixture, it leads to a distillation scheme with two columns specifying ternary azeotrope recycling and difficult operation. Thus, this compound is not recommended as a separation agent for the binary benzene + cyclohexane azeotrope.

Control of a Heat-Integrated Pressure-Swing Distillation Process for the Separation of a Maximum-Boiling Azeotrope

Methanol and trimethoxysilane form a maximum-boiling homogeneous azeotrope whose composition changes fairly significantly with pressure, so separation into high-purity products is viable using pressure-swing distillation. Heat integration of the two columns can be used to reduce energy costs since they operate at different temperatures. The pressure in the high-pressure column is not controlled but “floats” depending on conditions in the base of the low-pressure column. An auxiliary reboiler is required to balance the heat duty in the low-pressure column. Since pressure affects the composition of the azeotropic, this variable pressure increases the complexity of the required control structure. The purpose of this paper is to develop a control scheme that can effectively handle large disturbances in feed flow rate and feed composition.

Comparison of Pressure-Swing Distillation and Extractive Distillation Methods for Isopropyl Alcohol/Diisopropyl Ether Separation

In the production of isopropyl alcohol, diisopropyl ether appears as a byproduct. Diisopropyl ether and isopropyl alcohol form a binary minimum-boiling homogeneous azeotrope. In this paper, two methods are explored to achieve the separation of this binary azeotrope: fully heat-integrated pressure-swing distillation and extractive distillation with 2-methoxyethanol as an entrainer. The optimal design and dynamic control of the two processes are investigated, respectively. It is revealed that the fully heat-integrated pressure-swing distillation system offers 5.75% reduction in the total annual cost and 7.97% saving in energy consumption as compared to the extractive distillation system. Moreover, control configurations of both processes performed nicely in maintaining the two products’ quality when feed flow rate and composition disturbances are introduced. From the standpoint of dynamic control stability, both processes can be used for DIPE/IPA separation.

Methanol/Trimethoxysilane Azeotrope Separation Using Pressure-Swing Distillation

The process to produce trimethoxysilane involving the reaction of methanol with silicon produces a mixture of unreacted methanol and trimethoxysilane that requires separation so that the methanol can be recycled back to the reaction section. This binary mixture forms a maximum-boiling homogeneous azeotrope of 28.65 mol % methanol at 1 bar and 87.94 °C. The composition of the azeotrope changes fairly significantly with pressure, so separation into high-purity component streams is viable using pressure-swing distillation. The purpose of this paper is to design a pressure -swing distillation process for this separation that uses heat integration of the two columns, which operate at different pressures and different temperatures. One of the unique features of this system is the use of a vacuum column in which tray pressure drop has a significant effect on the optimum selection of design parameters such as the number of trays. The specifications for the bottoms compositions must be adjusted as pressures are changed so as to not get too close to or too far away from the azeotropic compositions. The economic optimum design has two columns operating at 7 and 0.25 bar with an auxiliary reboiler used on the low-pressure column. Feed composition strongly impacts the economics but not the basic process topology and operating conditions.

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.