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We integrate equilibrium and rate-based models to formulate a hybrid optimization scheme for designing an ionic liquid-based extractive distillation process for mixed-refrigerant separation. The equilibrium model assumes vapor–liquid equilibrium at each stage but challenges arise with low-volatility, high-viscosity solvents, which drive the system away from equilibrium. The rate-based approach considers mass and heat transfer rates, giving more accurate representation. We compare the two models for separating R-410A, an azeotropic mixture of R-32 and R-125, using [EMIM][SCN] ionic liquid as entrainer. Analyzing over 4300 simulations with various dimensionality reduction and topological analysis techniques, we find that predictions from the two models exhibit similar trends, but the overestimation in equilibrium-based purities sometimes leads to infeasible process designs. The proposed optimization algorithm thus combines the strengths of the two models to locate feasible and optimal designs. • Comparison of equilibrium and rate-based models for solvent-based gas separation. • Model similarity analysis using PCA, distance metrics, and Euler Characteristic. • Equilibrium models overestimate model predictions but capture trends of rate-based models. • Hybrid optimization using both models with new constraint refinement and update rules. [ABSTRACT FROM AUTHOR]

Surrogate modeling is used to replace computationally expensive simulations. Neural networks have been widely applied as surrogate models that enable efficient evaluations over complex physical systems. Despite this, neural networks are data-driven models and devoid of any physics. The incorporation of physics into neural networks can improve generalization and data efficiency. The physics-informed neural network (PINN) is an approach to leverage known physical constraints present in the data, but it cannot strictly satisfy them in the predictions. This work proposes a novel physics-informed neural network, KKT-hPINN, which rigorously guarantees hard linear equality constraints through projection layers derived from KKT conditions. Numerical experiments on Aspen models of a continuous stirred-tank reactor (CSTR) unit, an extractive distillation subsystem, and a chemical plant demonstrate that this model can further enhance the prediction accuracy. • PINN does not guarantee exact satisfaction of physical constraints. • A proposed architecture strictly guarantees linear equality constraints. • Hard constraints further improve surrogate model performance. [ABSTRACT FROM AUTHOR]

• A novel heterogeneous triple-column distillation (NHTCD) without solvent injection. • Simplification of previously established extractive distillation (ED) process. • Enhanced with heat integration (HI) and heat pump-vapor recompression (HP-VR). • HP-VR with HI NHTCD provides 87 %, 57 %, and 86 % lower energy, cost, and emission. • Conceptual design based on thermodynamic insights. The challenging separation of ethyl acetate (EtAC) and methanol (MeOH) from wastewater involves two azeotropes and a distillation boundary. Although extractive distillation (ED) has been explored, the heterogeneous region within the ternary azeotropic mixture has been overlooked, which suggests the possibility of using a decanter to cross the distillation boundary when the feed composition is present in the heterogeneous region. This study introduces a novel heterogeneous triple-column distillation (NHTCD) that eliminates the external solvent injection, simplifying the complex ED processes. The NHTCD process is developed via a systematic approach, comprising conceptual design based on thermodynamic insights and process optimization to determine the optimum configuration. Furthermore, heat integration (HI) and heat pump-vapor recompression (HP-VR) techniques were explored for energy conservation. Evaluation of energy, economic, and environmental (3E) aspects shows that the hybrid HP-VR with HI NHTCD process outperforms ED, achieving 87 %, 57 %, and 86 % reductions in energy, economic, and environmental emissions, respectively. [ABSTRACT FROM AUTHOR]

• A four-column extractive distillation system using natural gas liquid as heavy solvent is used to separate CO 2 –C 2 H 6 azeotrope. • Fixed reflux ratio and reflux/feed ratio control structure are used to investigate the controllability of four-column extractive distillation. • The reflux/feed ratio controller of four columns can adjust the reflux ratio in real time according to the disturbance of feed flow and composition, which greatly improves the stability of the top distillation products purity. The existence of heterogeneous azeotrope of CO 2 –C 2 H 6 makes it difficult to separate CO 2 from the hydrocarbons in the associated gas by cryogenic extractive distillation process. A four-column extractive distillation system using natural gas liquid as heavy solvent is used to separate CO 2 –C 2 H 6 azeotrope. Carbon dioxide, ethane, propane and butane are recovered from the top of the extractive distillation column, deethanizer, depropanizer and debutanizer respectively. The C3+ hydrocarbon mixture called natural gas liquid is recovered at the bottom of the debutanizer, one part of which is transported as NGL product and the other part is pumped back near the top of the extractive distillation column as solvent. The purpose of this paper is to develop an effective plant wide control structure for this four-column extractive distillation system. Fixed reflux ratio and reflux/feed ratio control structure are used to investigate the controllability of four-column extractive distillation. Results show that both control structures have successfully realize the dynamic simulation of the extractive distillation process. However, under the disturbance of feed flow rate and composition, the controllability of reflux/feed ratio control structure on purity of top distillation products is better than that of fixed reflux ratio control structure. The reflux/feed ratio controller of four columns can adjust the reflux ratio in real time according to the disturbance of feed flow and composition, which greatly improves the stability of the top distillation products purity. [ABSTRACT FROM AUTHOR]

Pressure in many distillation columns is set such that cooling water can be used in the condenser. Pressure selection is more involved in some columns such as reactive distillation in which there is a trade-off between temperatures favorable for reaction kinetics and temperatures favorable for vapor-liquid equilibrium. In azeotropic systems, pressure selection is critical in achieving the desired separation by consideration of distillation boundaries and isovolatility curves. A recent paper presented a striking example of pressure selection in extractive distillation. Operation at 1 atm required a solvent-to-feed (S/F) ratio of 3.52 while operating at 10 atm cut the S/F to only 0.717. The purpose of this paper is to explore the dynamic controllability of this low S/F extractive distillation system. Results show that the control structure must be modified from the conventional configuration used in most extractive distillation processes. [ABSTRACT FROM AUTHOR]

• A synthesis problem for separating ethanol-water mixtures using hybrid membrane distillation process structures was proposed. • A low aggregation superstructure was adopted in the synthesis problem. • The proposed process structures were superior in terms of utility cost and Total Annual cost savings compared with the pressure swing an extractive distillation processes. Conventional distillation is the most used unit operation to separate zeotropic mixtures. However, it is combined other unit operations to separate azeotropic mixtures. This work proposes a synthesis and intensification framework to obtain hybrid membrane distillation process structures. The synthesis problem was represented by a low aggregation superstructure comprised of functional modules. Then, the superstructure was reformulated as a Mixed Integer Linear Programming (MILP) problem to derive the optimal structure. The synthesis problem does not consider any pre-established process structure or connectivity; therefore, the optimal solution must be interpreted, simulated, and validated to generate a known process structure. Finally, the validated structure was post-optimized to fine-tune the detailed design of the process structure. The presented framework was applied to separating an ethanol/water mixture. The obtained solutions attained high energy and cost savings compared to the typical pressure swing and extractive distillation. [ABSTRACT FROM AUTHOR]

• A framework for green extractive solvent design with multi-index constraints is proposed. • A deep hierarchical molecular generative model is employed to navigate uncharted territories of the chemical space for green extractive solvent inverse design. • An improved deep learning-based predictive model is proposed to accurately and rapidly predict the V COSMO and σ -profile. • The 5-methyl furfural survived from 2726 generated molecules can be considered one of the best desirable green extractive solvents for separating cyclohexane and benzene by extraction distillation. Despite the popularity and efficiency of group contribution methods in computer-aided molecular design applications, their accuracy is sometimes limited due to the inability to discriminate some stereoisomers and complex compounds. One of the most urgent challenges in the chemical separation field is how to design desirable green solvents accurately and rapidly. In this contribution, a framework considering sustainability and techno-economic performance is proposed to purposively and effectively design green extractive solvents. First, a deep hierarchical molecular generative model is employed to navigate uncharted territories of the chemical space for extractive solvent inverse design. Then, the improved deep learning-based predictive models are proposed to accurately and rapidly predict the V COSMO and σ -profile, which are prerequisites for the COSMO-SAC model to calculate the infinite dilution activity coefficients of the generated molecules. Subsequently, the developed deep hierarchical molecular generative model and the improved deep learning-based predictive model are coupled with the computer-aided molecular design approach. The green extractive solvent design process is decomposed into three sub-problems with multi-index constraints. Finally, the developed framework for designing green extractive solvent is employed in an industrial case of cyclohexane/benzene mixtures separation. As a result, the 5-methyl furfural survives from 2726 generated molecules and could be considered one of the best desirable green extractive solvents for separating cyclohexane and benzene by extraction distillation. Furthermore, the proposed framework can also be applied to other separation processes, such as liquid-liquid extraction, gas absorption, and crystallization. [ABSTRACT FROM AUTHOR]

In the present work, extractive and pressure-swing distillation methods are analyzed in detail through steady state ASPEN Plus simulations to propose the most economic method for separation of equimolar mixture of THF-Water. Various solvents were evaluated and DMSO was identified as the most appropriate solvent, as it gave minimum Total Annual Cost (TAC) for desired purity. In case of pressure swing distillation, various pressure ranges were explored to achieve minimum TAC. Configurations for extractive and pressure swing distillation with heat integration were also worked out. The optimum designs of extractive and pressure swing distillation with and without heat integration were compared on a common basis of feed conditions and purity constraints. Results indicate that TAC of extractive distillation with heat integration is 5.2% less than that of PSD with partial heat integration. [ABSTRACT FROM AUTHOR]

A novel extractive distillation system is presented. The proposed separation system evolves from an extractive thermally coupled system with a side rectifier. Specifically, the modification involves substituting the thermal coupling, i.e., the vapor-liquid interconnection, by a liquid side stream fed to a modified second column of the arrangement. The design procedure and performance on energy consumption and CO 2 emissions of the proposed structure is illustrated with three case studies, which involve bioethanol dehydration and the separation of acetone-methanol and heptane-toluene mixtures. The results show that the proposed system can be more energy efficient and provide a more sustainable option when compared to conventional extractive distillation or thermally coupled sequences. We also show how the implementation of heat integration between columns of the proposed structure can be considered for additional savings on energy and CO 2 emissions. [ABSTRACT FROM AUTHOR]

Ethanol and toluene are important organic solvents in chemical industry. Ethanol, toluene and water present a ternary minimum-boiling azeotrope and three binary azeotropes. In this article, two methods are studied to separate the ternary azeotrope: heterogeneous azeotropic distillation using the toluene, which is in the system itself, as entrainer and extractive distillation with glycerol as the only one solvent. In the heterogeneous azeotropic distillation, the pressures of the three columns are changed respectively to achieve heat integration. In the extractive distillation, only one solvent and two columns are used to separate the ternary mixture. Experiment shows that the partially heat-integrated heterogeneous azeotropic distillation reduces the energy cost and total annual cost by 27.7% and 13.4% respectively compared with the conventional heterogeneous azeotropic distillation. Unexpectedly, the extractive distillation can save 18.8% and 39.3% in the energy cost and total annual cost respectively compared with the partially heat-integrated heterogeneous azeotropic distillation. [ABSTRACT FROM AUTHOR]

• A new alternative technology is proposed that side-stream pressure swing distillation (PSD) processes to separate azeotropic mixtures of acetone and cyclohexane. • Based on the SIAE values and TACs of the side-stream PSD process and the ED process, the dynamic performance and economy of both processes is compared. • The products purities in the side-stream PSD process is well controlled, as evident by the small SIAE values (0.018). Dynamic controls of a side-stream pressure swing distillation (PSD) and extractive distillation (ED) process for cyclohexane and acetone separation are investigated. The processes operating parameters are optimized with a sequential iterative procedure based on the total annual cost (TAC). The dynamic result shows that for the side-stream PSD process, a modified control structure 2 (CS2) with the composition controller (CC) cascaded with the temperature controller 2 (TC2) can efficiently handle the feed disturbances, with the output signal being the ratio of reboiler duty to feed flow rate (Q R /F). For the ED process, a modified control structure 4 (CS4) with the acetone product composition controller as the characteristic control loop can efficiently handle the disturbances which is controlled by the ratio of solvent flow to feed flow rate (S/F). A comparison of the side-stream PSD process and the ED process shows the former has decent dynamic performance. [ABSTRACT FROM AUTHOR]

Until now, there has not been consensus about the superiority of thermally coupled sequence over the conventional sequence in the extractive distillation process. In this sense, the main goal of this paper is to analyze three approaches for saving energy in the extractive distillation process: optimization, thermal integration and thermal coupling. Three azeotropic mixtures were investigated: ethanol and water (M1); tetrahydrofuran and water (M2); and acetone and methanol (M3). The solvents were ethylene glycol for M1 and M2, and water for M3. The results are shown in terms of the total annual cost (TAC) and specific energy consumption (SEC), and revealed that a thermally coupled extractive distillation sequence with a side rectifier did not always present the best results. Taking the case studies from literature as a starting point (without thermal integration), the optimization procedure used in this work found that TACs are always lower. The inclusion of thermal integration in configurations led to reducing TAC for all mixtures under investigation when compared to the sequences without this integration. When comparing two modifications in the layout of extractive distillation, it can be seen that it is more advantageous to use the preheating of the azeotropic feed with the recycle stream from the recovery column of the conventional sequence than using a thermally coupled sequence. [ABSTRACT FROM AUTHOR]

• Energy-efficient extractive distillation process for formic acid-water separation developed. • Optimization for series separation processes conducted with genetic algorithm. • Operational issues with respect to intensified process investigated by advanced control scheme. • Model-based control scheme shows its superiority for efficient extractive distillation process. It is urgent to develop sustainable chemical process through process intensification, especially for the energy-intensive distillation process. Formic acid-water forms maximum azeotrope which is purified by pressure-swing distillation in Kemira–Leonard (K-L) process and extraction plus distillation in BASF route. However, either process for this maximum azeotrope separation is energy-intensive. In the present work, by selecting the effective heavy entrainer, extractive distillation and extractive dividing wall column was firstly synthesized and optimized with genetic algorithm for formic acid-water separation. Based on optimal design, the energy consumption and CO 2 emission among these proposed and existent processes were compared, and extractive distillation shows its strength for achieving high efficiency and sustainability. Then multi-loop PI control scheme and linear model predictive control based on temperature and temperature difference were developed, respectively. Dynamic response validates the control performance superiority of advanced controllers, especially for controlled variables with large overshoot, oscillations and settling time. [ABSTRACT FROM AUTHOR]

We provide insights for the development of a fast, dynamic, and adaptive way of modeling and optimizing chemical processes. We investigate two data-driven methodologies to optimize the energy cost of an extractive distillation process using an Aspen simulator. The first method uses surrogate-based optimization to explore two model-building techniques: Automated Learning of Algebraic Models's (ALAMO) generalized linear models and neuron network models with rectifier (ReLU) activation function. We compare the accuracy and performance of these models when embedded into mathematical programming models. The second approach uses black-box optimization (BBO) to optimize problems directly using simulation results. We compare four BBO solvers and three different penalty functions to address constraints. We find that ALAMO performs well for a less complex system, whereas the ReLU network performs better for a more complex one. BBO with a smooth penalty function for constraints is the more effective approach for problems considered in this study. • Black-box solvers have advantages over surrogate modeling for low-dimensional optimization. • Modeling with generalized linear models requires fewer data measurements than neural network. • Smooth penalty functions outperform non-smooth ones for black-box optimization. [ABSTRACT FROM AUTHOR]

• The separation of pressure-insensitive azeotrope is investigated. • THF and DMSO are used as pressure sensitive entrainer and solvent, respectively. • Heat integration is considered for pressure-swing distillation (PSD) schemes. • Schemes proposed is optimized using multi-objective genetic algorithm. • Economic cost of extractive distillation is at least 51.80% lower than that of PSD. Pressure-insensitive azeotropes are often encountered in chemical production. Entrainer-assisted pressure-swing distillation (EAPSD) is a special pressure-swing distillation showing promising performance in separating pressure-insensitive azeotropes. However, few studies have been reported on this method. In this work, the comparison between the EAPSD with tetrahydrofuran as pressure-sensitive entrainer and extractive distillation (ED) with dimethyl sulfoxide as solvent in separating water/isopropanol azeotrope is performed to explore the performance of EAPSD. Different EAPSD sequences, low-high sequence (LHS) and high-low sequence (HLS), are designed with different product sequences. A strategy considering the possibility of both partial and full heat integration is used to reduce capital cost and energy consumption. Multi-objective genetic algorithm is applied to achieve the optimal performance. The results show that the heat-integrated HLS sequence has lower total annual cost (TAC) by 7.04% and lower CO 2 emission (CDE) by 4.27% than LHS, while ED process has lower TAC and CDE by 51.80% and 36.96% than the optimal EAPSD process. [ABSTRACT FROM AUTHOR]

· σ-profiles based COSMO-SAC theory is adopted to screen DESs entrainers for acetonitrile dehydration. · The selected DESs are further studied by the thermodynamic topological analysis. · For extractive distillation, EG and GC3:1 are evaluated economically. · The control structure of GC3:1 extractive distillation process is studied. Deep Eutectic Solvents (DESs) show properties that make them effective as environmental-friendly entrainers for extractive distillation. However, the technical and economic evaluation via process simulation and the method of screening a suitable DES for a given azeotropic system are less studied. In this work, the extractive distillation process for acetonitrile dehydration with glycolic acid/choline chloride 3:1 (GC3:1) as entrainer is studied. Firstly, the σ-profiles based on the COSMO-SAC model are employed to select an appropriate DES entrainer. Then, the feasibilities of GC3:1 and ethylene glycol (EG) as entrainer are further studied by the analysis of residue curve maps. Finally, the design and optimization of the extractive distillation process for acetonitrile dehydration with GC3:1 and EG are conducted. The results demonstrate that the conventional extractive distillation process with GC3:1 entrainer gives 13.40% and 9.64% reduction in TAC over the conventional and heat-integrated extractive distillation processes with EG as entrainer, respectively. The TAC of the GC3:1 process is further reduced by 3.14% after heat integration. In addition, the control scheme of the extractive distillation process with GC3:1 entrainer is studied by Aspen Dynamics, and the proposed control structure is effective in managing operational stability. [ABSTRACT FROM AUTHOR]

Despite the economic benefits of flowsheet optimization, many commercial tools suffer from long computational times, limited problem formulation flexibility and numerical instabilities. In this study, we address these challenges and present a framework for efficient large scale flowsheet optimization. This framework couples advanced process optimization formulations with state-of-the-art algorithms, and includes several notable features such as (1) an optimization-friendly formulation of cubic equation of state thermodynamic models; (2) a new model for distillation column optimization based on rigorous mass, equilibrium, summation and heat (MESH) equations with a variable number of trays that avoids integer variables; (3) improvements on the Duran–Grossmann formulation for simultaneous heat integration and flowsheet optimization; and (4) a systematic initialization procedure based on model refinements and a tailored multi-start algorithm to improve feasibility and identify high quality local solutions. Capabilities of the framework are demonstrated on a cryogenic air separation unit synthesis study, including two thermally coupled distillation columns and accompanying multistream heat exchangers. A superstructure is formulated that includes several common ASU configurations in literature. As part of the optimization problem the solver selects the best topology in addition to operating conditions (temperatures, flowrates, etc.) for coal oxycombustion applications. The optimization problem includes up to 16,000 variables and 500 degrees of freedom, and predicts specific energy requirement of 0.18 to 0.25 kWh/kg of O 2 depending on design assumptions. These results are compared to literature and plans to extend the framework to an entire coal oxycombustion power plant optimization study are discussed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The relatively high viscosities of ionic liquids could reduce the mass transfer efficiency of the extractive distillation process. The rate-based model was adopted to analyze this phenomenon since it predicted the performance of an extractive distillation pilot plant using ionic liquids as solvent. For the water–ethanol separation, three ionic liquids: 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium acetate and 1-ethyl-3-methylimidazolium dicyanamide and the organic solvent ethylene glycol were used for the analysis. Simulations were conducted for sieve trays and Mellapak ® 250Y. The results indicate that relatively high viscosities affect the mass transfer efficiency. However, the improvements in relative volatilities obtained from the ionic liquids help to overcome this effect. However, with high solvent viscosities (>65 mPa s at T = 353.15 K) it was not possible to overcome the reductions. Additionally, at higher distillate rates high relative volatilities yielded negative effects on mass transfer efficiency because of a decrease in vapor velocity. [ABSTRACT FROM AUTHOR]

Highlights: [•] Two distillation processes for methanol–chloroform separation are explored. [•] Pressure-swing distillation is more economical than extractive distillation. [•] Pressure-swing distillation is easily controlled using a basic control structure. [•] Heat-integrated process requires pressure-compensated temperature control structure. [Copyright &y& Elsevier]

Abstract: The separation of acetone from chloroform is difficult because the highly nonideal vapor–liquid equilibrium produces a maximum-boiling azeotrope. An earlier paper (Luyben, W. L. (2008). Control of the maximum-boiling acetone/chloroform azeotropic distillation system. Industrial & Engineering Chemistry Research, 47, 6140–6149) discussed the use of extractive distillation for making this separation. This paper studies the use of pressure-swing distillation for making the same separation. Results show that the extractive distillation process is much more attractive from the standpoint of both capital investment and energy consumption. But pressure-swing distillation avoids the potential problem of product contamination by the extractive solvent that must be added to the binary system. [Copyright &y& Elsevier]

Abstract: In this paper, an investigation of the design and control of an extractive distillation process to produce anhydrous ethanol using glycerol as entrainer is reported. The extractive distillation process receives the azeotropic mixture ethanol–water that is fed into a dehydration column in one of the intermediate stages while at the same time glycerol is fed into one of the top stages. As overhead product high purity ethanol is withdrawn and in the bottom stream a mixture of water/glycerol is sent to a recovery column. The effects of the entrainer to feed molar ratio, reflux ratio, feed stage, feed entrainer stage and entrainer feed temperature were studied to obtain the best design with minimal energy requirements. A control scheme is developed in order to maintain stable operation for large feed disturbances. Dynamic simulations show that is possible to use only one temperature control to hold the purity specifications. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: In the study, reactive distillation is designed to produce dimethyl carbonate and ethylene glycol by the transesterification of ethylene carbonate and methanol. The products of the reactive distillation column include ethylene glycol and a dimethyl carbonate/methanol mixture, close to azeotropic composition. The azeotrope is separated in the study by pressure-swing distillation and extractive distillation using phenol as an extractive agent. The extractive distillation is found to be much more economical than the pressure-swing distillation. Thermal coupling technology is also implemented between the two columns of the extractive distillation. Thermally coupled extractive distillation provides the best energy efficiency. Proper selection and pairing of controlled and manipulated variables are determined by using steady-state analysis. A simple temperature control scheme is sufficient to maintain stoichiometric balance between the reactant feeds and product purities at or around their designed values for the plant-wide process of reactive distillation+thermally coupled extractive distillation. [Copyright &y& Elsevier]

Abstract: Off-cut production and recycling played an important role in efficient separation of binary and multicomponent mixtures using batch distillation. However, the research in this area is handful and all the investigations until to date were concerned with only operation optimisation in terms of minimisation of batch time or maximisation of productivity (amount of main products per unit time). No consideration was given to market demand of the products; therefore these operation policies would result in under and over production of the products leading to potential revenue losses. In this work, for the first time we considered both design (number of stages, vapour load) and operation (reflux ratio, batch time) optimisation for fixed market demand of the products while maximising a profit function reflecting product revenues, operating cost, storage cost and annualised capital cost. The effect of off-cut production and recycling on the design, operation and profitability are evaluated using an easy and a difficult binary separation problem and off-cut recycling is found to be more beneficial for difficult separation. Design and operation policies are also found to be different for different amount of off-cut. Finally, the storage cost can be a deciding factor for the production and recycling of off-cut. [Copyright &y& Elsevier]

A steady-state equilibrium-stage model based on normalized MESH equations is proposed to simulate saline extractive distillation columns and applied to the production of absolute ethanol, using CaCl2 to break the ethanol–water azeotrope. Among the activity coefficient models available for mixed solvent/salt systems, the NRTL-E model (with refitted parameters), is shown to be the most accurate to correlate the experimental vapor–liquid equilibrium (VLE) data available for the ethanol/water/CaCl2 system. A model is proposed and implemented to calculate the salt contribution to the liquid phase enthalpy by combining calorimetric quantities of the solute such as its relative apparent enthalpy and the infinite dilution values of its integral heat of solution and partial isobaric heat capacity. The column model is solved by use of the Newton–Raphson method with a damping factor found by minimizing the Euclidean norm of the vector of discrepancy functions associated with the MESH equations. [Copyright &y& Elsevier]

This paper reports the work to find the best additives added to acetonitrile (ACN) for improving the separation of C4 mixtures with the help of computer-aided molecular design (CAMD). CAMD is programmed to provide necessary information for our search of the additives. The two types of additives we seek, liquid solvents and salts, are designed by CAMD. The selected additives are then tested by experiments. It is found that the addition of salt is more efficient than the addition of liquid solvents (including water) for improving the separation ability of ACN. After taking implicit properties into consideration, salts NaSCN and KSCN, are the best candidates to improve ACN. As a strong tool, CAMD greatly reduces experimental working in separating C4 by extractive distillation with ACN. [Copyright &y& Elsevier]

• A systematic framework is presented for the design of a sustainable extractive distillation configuration. • The composite sustainability index is constructed considering the economic, environmental and social dimensions. • The self-adaptive mesh direct search algorithm optimization is used in evaluating the single composite objective. • The heat-pump technique can be used in extractive distillation to save energy. In order to achieve the sustainable separation design of azeotropic mixtures, this study proposed a systematic framework for distillation process optimization and intensification based on a composite sustainability index. Binary minimum azeotropic mixture ethanol-ethyl propionate was studied as an illustrative example. Specifically, three extractive distillation configurations were firstly applied on the separation and the sustainability of distillation processes were evaluated comprehensively. The composite sustainability index was constructed with the indicators of the economic, environmental, technical and social dimensions, and fuzzy weighting method was used to determine the weight of each indicator. Then, the process can be optimized with the objective of the composite sustainability index by the mesh adaptive direct search algorithm. After that, the heat-pump is further implemented to make full use of the latent heat of vapor stream in the distillation system. The T-H diagram of two upgraded processes clearly demonstrates the heat recovery while considering the specified minimum heat-transfer temperature difference. [Display omitted] [ABSTRACT FROM AUTHOR]

• Evaluation of two advanced hybrid optimization methods for MINLP problems. • Global optimization for simple column design verified by comparison with BARON. • EA-based hybrid algorithm more efficient than MSGS-based hybrid algorithm. • Optimization-based design of energy-integrated process and solvent selection. • Illustration for extractive distillation process for acetone-methanol separation. While the need for more efficient and integrated processes for the separation of non-ideal and azeotropic mixtures mandates model-based design methods, the resulting mixed-integer problems are highly nonlinear and particularly hard to solve without proper initialization. In order to handle such complex design problems, two hybrid optimization methods are presented in the current contribution. Both methods rely on a nested approach, which integrates a polylithic modeling and solution strategy, based on the solution of successively refined nonlinear programming problems, with an upper level metaheuristic for the initialization and optimization of discrete design decisions. Both methods are evaluated for two case studies. The optimization of a simple column design problem allows for the direct comparison with an available global deterministic optimization solver for identifying the global optimal solution. The optimization of an extractive distillation process with simultaneous solvent selection and energy integration illustrates the potential complexity that can be handled effectively. [ABSTRACT FROM AUTHOR]

• The pervaporation-distillation hybrid process considering economy and ecology is proposed. • The models of flux and permeability are regressed based on experimental data. • The hybrid process can reduce the energy consumption by 45.91% under the condition of ecological. • LCA is used to analyze the environmental impact of processes. Isopropanol and acetonitrile are important chemical raw materials that are widely used in the chemical industry. However, mixtures of acetonitrile, isopropanol, and water are difficult to separate as these compounds form azeotropes. The solvents were screened based on their relative volatility and toxicity. To reduce the energy consumption, a heat pump-assisted extractive distillation process was proposed. Furthermore, the pervaporation–distillation hybrid process was studied. Life cycle assessment was used to evaluate the environmental impact of the processes. The total annual cost and energy consumption of the hybrid process were 21.11% and 45.91% lower, respectively, than those of the basic process. The values of global warming potential and acid potential of the hybrid process are 810.57 and 1.45, respectively, which are the smallest among those of processes studied. It is concluded that the hybrid process can not only reduce energy consumption, but is also more environmentally friendly than the other processes. [ABSTRACT FROM AUTHOR]

• Dynamic control analysis of eco-efficient double side-stream ternary extractive distillation process is studied. • A newly robust control scheme is developed that handles the large step disturbances. • Dynamic control performance is improved by using the composition control loops. • Good product compositions controls are achieved without any product offsets. The novel contribution of this paper is to implement the dynamic control investigation for the energy-saving double side-stream ternary extractive distillation configuration with constructing the practical and workable plumbing arrangement taking the representative example of separating a ternary benzene/isopropanol/water mixture. The new proposed control scheme achieves the stable regulatory control at rejecting the large disturbances of throughput and feed composition, wherein the particularly key control loops are controlling the product isopropanol composition by adjusting the extractant flow rate into extractive column C 2 with simultaneously regulating the reflux ratio in extractive column C 1 to abate the solvent dilution effect through composition cascade temperature control loops. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The side-stream extractive distillation (SSED) system is attracting widespread attention due to its high eco-efficiency. In the article, three double-column SSED (DC-SSED) sequences and two single-column SSED (SC-SSED) sequences with different side-stream extraction locations are proposed for separating the methanol-toluene azeotrope with intermediate boiling entrainer triethylamine, which are compared with two conventional extractive distillation (CED) processes including direct and indirect CED sequences. The genetic algorithm is employed to optimize seven extractive distillation sequences to minimize the total annual costs (TAC). CO 2 emissions and thermodynamic efficiency of the optimized processes are quantified as well as TAC to calculate the Eco-efficiency Comparison (ECI) Index for eco-efficiency analysis. The results illustrate that two DC-SSED sequences demonstrate the eco-efficiency superiority compared to the optimal CED process (direct CED), and their side-streams are located in the rectifying section and extractive section of the side extractive distillation column, while their ECI indexes reach 97.38% and 97.60%. [ABSTRACT FROM AUTHOR]

• Optimization-based design of extractive and heteroazeotropic distillation processes. • Automatic initialization and polylithic modeling and solution approach. • Evaluation of heat integration, vapor recompression and dividing wall columns. • Integration of solvent selection and energy integration. • Efficient comparison of competing process options in three complex case studies. The separation of azeotropic mixtures is frequently performed by extractive or heteroazeotropic distillation processes. The design of these processes requires careful selection of a suitable solvent and is specifically challenging since feasibility and optimality of the processes require consideration of the closed loop design including solvent recovery. Consideration of energy integration further complicates the design task and is usually conducted as post-evaluation step. The current publication proposes an efficient optimization-based design approach, which allows for the direct evaluation of several energy-integrated process concepts, while significantly reducing manual effort and computational time through a polylithic modeling and solution approach. The developed approach allows for a simultaneous evaluation of solvent selection and energy integration and is illustrated for different case studies, including the evaluation extractive and heteroazeotropic distillation for the dehydration of ethanol, as well as the evaluation of multiple solvent candidates for the extractive distillation of acetone and methanol. [ABSTRACT FROM AUTHOR]