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Biofuel is an important alternative to the limited resources of fossil fuels for use in power generation. Currently, regular alcohol is used as a feedstock; however, it is known to be toxic. Hence, in this paper, we demonstrate that anhydrous alcohol obtained from palm wine is a potential alternative as the main feedstock for biofuel production. In this study, the aim was to improve the anhydrous alcohol obtained from palm wine based on storage conditions. Although this type of anhydrous alcohol has been previously produced, it is demonstrated that the current method is more efficient than the previous one. The processes implemented in this study were fractionation and extractive distillation. Two numerical simulations were carried out using extractive distillation processes to evaluate of an ethanol and water mixture, that is, ethylene glycol or glyceride. The palm wine was characterized based on the determination of the alcohol content, pH, acidity and the content of free SO2. The alcohol produced was characterized through the determination of its concentration, viscosity and density and infrared spectroscopy analysis. The results illustrate that it is possible to obtain excellent quality anhydrous alcohol suitable for small biofuel production, which is increasingly in demand in rural villages in Sub-Saharan Africa. Keywords: Biodiesel, Palm wine, Anhydrous alcohol feedstock

Methyl ethyl ketone (MEK) is a widely used chemical in the industry. Most of the MEK uses are directly related to industrial application; however, recent studies suggest the use of MEK as a possible fuel for spark-ignition engines. The industrial process to produce MEK is performed through the hydration of butylene and the dehydration of that alcohol. Butylene is produced from oil cuts. However, petroleum is a recognized finite resource and is pointed out as a major cause of environmental issues. An alternative to improve a process is process intensification (PI). In this work, an intensified alternative to produce MEK from 2,3- Butanediol is proposed. 2,3-Butanediol might be produced by a fermentation process based on renewable biomass. The intensified alternatives consist of a reactive distillation column, an extractive distillation column, and three conventional distillation columns. The novel alternatives produce and purify MEK, 1,2-BD, 2MPL, and water, from 2,3-BD using calcium phosphate as catalyst were modelled in Aspen Plus. To evaluate the intensified alternative, it was considered the energy requirements per kilogram of MEK, conversion, selectivity as well as an environmental impact index, the greenhouse gas emissions. The RD column resuzlted in a conversion of 99.86 % and a selectivity for MEK of 44 %. After evaluation, the direct scheme resulted as the most promising one, with energy requirements of 2790 kcal/kgMEK (11.6 MJ kg/MEK). Regarding the environmental impact, the direct scheme reported 7.07 tCO2/h of greenhouse gas emissions.

The distillation technique plays a key role in a separation and purification of multicomponent mixtures. Several alternative designs using conventional distillation for purifying cyclopentane with high purity have been done using Pro/II Process Engineering Software. Using conventional distillation process for purifying cyclopentane from close boiling point mixture is uneconomic and impractical. The distillation technique is also applied in the cyclopentane production. However feed mixture contains multicomponent of hydrocarbons including cyclopentane and 2, 2-dimethylbutane forming azeotrope. Only 80-85%wt cyclopentane purity can be achieved from the conventional distillation. Therefore, a widely used technology, extractive distillation is applied for purifying cyclopentane with 95%wt purity. High-purity cyclopentane gains higher benefit from a larger cyclopentane market.

Hexamethylene diisocyanate (HDI) is an important chemical building block in the production of high value-added polyurethane because of its some excellent properties. Traditionally, the HDI synthesis route involves extremely toxic phosgene as an industrial scale reagent. Recently, thermal decomposition of hexamethylene-1,6-dicarbamate (HDC) has been considered as the most attractive non-phosgene process for the HDI synthesis because HDC can be synthesized by reacting 1,6-hexamethylene diamine (HDA) with a green compound, dimethyl carbonate (DMC), instead of toxic phosgene. Therefore, the intermediate HDC synthesis is crucial to the whole process. In the study, design of two plant-wide processes is explored for green HDC synthesis. In the first process, HDC is produced in two reactive distillation (RD) columns in series. Complete conversion of HDA is designed and excess DMC reactant is used to increase the reaction conversion. The mixture of un-reacted DMC and by-product methanol from RD column tops is separated by a series of conventional distillation columns containing a pre-concentrator column and an extractive distillation system comprising an extractive distillation column and a solvent recovery column. In the second process, RD is enhanced by vapor recompression (VR) to reduce energy consumption. The key cost saving from VR is attributed to fully take advantage of small temperature difference between RD column bottom and top, and higher RD column top temperature rendering condenser duty totally utilized by RD column bottom. Furthermore, additional latent heat of RD overhead vapor is released to the extractive distillation system by external heat integration, which can then achieve significant saving in the operation cost of this system. Compared to the RD intensified process, total annual cost of the RD + VR intensified process can be reduced by 35%.

The spurring increase in bio-diesel production produces a large amount of glycerol as side product, which causes its over-supply. Hence, converting glycerol (GLY) into other value added chemicals would be a promising solution. In this work, the design and optimization of a plant-wide glycerol carbonate (GC) production processes of GLY and dimethyl carbonate (DMC) is firstly proposed, which is consisted of a reactive distillation section and an extractive distillation-based separation section. The research scope includes regressing the thermodynamic parameters suitable for representing both vapour-liquid and liquid-liquid equilibrium, correcting the kinetic parameters, developing process flowsheets, and optimization.

Solvent-based separation processes, such as extractive distillation, show large potential for the separation of azeotropic mixtures. However, these processes are rather complex to design and optimize since the overall process performance depends strongly on the choice and amount of solvent and can only be evaluated for a process flowsheet with closed recycles. It is important to note that the potential for heat integration also depends strongly on the solvent choice. Consequently, a successive selection of a suitable solvent followed by process design and optimization and finally energy integration likely results in suboptimal choices. In order to allow for direct optimization of an extractive distillation process, including solvent selection and different means for energy integration, the current study proposes the use of a hybrid evolutionary-deterministic algorithm. The application is demonstrated for the separation of an azeotropic acetone-methanol mixture, considering six solvent candidates and up to four alternative means for energy integration. The results illustrate the existence of a multitude of suboptimal local solutions and demonstrate the capability of the proposed method to effectively overcome these limitations.

This work provides a short review of extractive distillation (ED) technology, covering all relevant topics: concept and working principles, residue curve maps, solvent design, screening and selection, types of mass separating agents, influence on VLE, solvent-to-feed ratio, process design, advanced ED in dividing-wall columns, and a list of applications.

In this work have been designed and optimized simultaneously three different process separations for purify furfural, using Differential Evolution with Tabu List Algorithm. The study cases are a conventional Quaker Oats process, a thermally coupled process and liquid-liquid extraction process. The objective of this work is select the best alternative to purify furfural taken into consideration economic, environmental and safety issues. The results show which the thermally coupled process has several improvements and reductions on the risk, similar cost and environmental impact compared with Quaker Oats process. While the liquid-liquid extraction process does not have any improvement in the objective function, these results are associated with the use of entrainer in this sequence with respect to Quaker Oats Process. Therefore, due to the important improvements in safety issues the TCP process is choosing as the best alternative.

This work focuses on the exergy analysis of an extractive distillation column in the second-generation bioethanol production process. The study of the exergy performance of the separation and purification section is relevant from a thermodynamic point view due to the large amount of the energy consumed by their unit operations. A sensitivity analyses of the separation section, the location of the feeding stages for the solvent and the ethanol-water azeotropic mixture, the reflux ratio and solvent/feed ratio were performed for obtaining the minimum energy consumption in the column reboiler. Finally, the profiles of exergy components, irreversibilities and the exergy efficiency for the base case and enhanced case were compared. The results show a 29.21 % decrease on the irreversibilities and a corresponding increase of 22.82 % in the exergy efficiency for the separation section. The simulation as well as the sensitivity analyses were done using a connection between the process simulator Aspen Plus v 8.8 and Excel.

The separation of azeotropic mixtures is of particular importance for bio-based processes in the chemical industry. Extractive and heteroazeotropic distillation are oftentimes the favored solution for medium to large scale processes due to their proven robustness and the economics of scale. The feasibility as well as economic efficiency of these processes depends strongly on the selection of a suitable mass separating agent (MSA). Furthermore, energy integration can increase the energy and economic efficiency of these thermal processes. Since, MSA selection, process design and energy integration are usually performed as consecutive steps in process design, potential synergies are easily missed, resulting in sub-optimal choices. In order to determine an optimal process design, including solvent selection and energy integration, an efficient optimization-based approach for the design of extractive distillation processes is proposed. The application of the method is illustrated for the separation of the azeotropic mixture of acetone and methanol. The results highlight that the optimal MSA choice under consideration of energy integration differs from the selection without energy integration.

BTXs (benzene, toluene and xylenes), used widely as basic chemical intermediates, are separated generally from petroleum naphtha, coking naphtha, and pyrolysis gasoline. These oil fractions contain aromatic and non-aromatic hydrocarbons between C5 to C8 in which certain components have approximate boiling points and form azeotropes. Extractive distillation (ED) is one of the most attractive approaches for separating azeotropic mixtures with approximate boiling points. The aromatic ED technique aided by sulfolane used widely in recent years because of its simple process flowsheet, small equipment investment and high energy efficiency. The solvent and operating parameters are the cores of ED process in the economical design. Some results were published to rapidly screen the solvents as well as process parameter optimization for ED separating process, but few contributions have been reported to optimize an extractive distillation from the view of simultaneous optimization of the solvent composition and operation parameters for process economics. In this work, we propose a systematic optimization approach for energy saving of sulfolane aromatic ED processes based on process simulation and genetic algorithm (GA) optimization. The NRTL property method and rigorous unit models in Aspen Plus are used to simulate the ED processes. In particular, considering multi-variable and their interaction, a coordinating strategy is proposed to optimize the solvent composition and significant operating parameters for the ED processes by combining Aspen Plus with MATLAB. Under given separation specifications, the energy consumption and separation efficiency are investigated and optimized by GA optimization. The results show that the through the above optimization, the minimum heating utility of the ED process is significantly reduced by 29.2%.

A pressure-swing distillation process for the separation of n-hexane and ethyl acetate, which form a minimum boiling azeotrope, is proposed and optimized using simulated annealing and simulation-optimization. The design variables considered are the two column pressures, the feed stages and total number of stages of both columns. The optimal process design is somewhat more expensive than the optimal extractive distillation process (designed separately) but the pressure-swing process benefits from the fact that no additional component is introduced.

International audience; A distinctive strategy for entrainer recycling is proposed in this work for acetic acid (AA) dehydration by extractive distillation by using N methyl acetamide (NMA). The use of standard entrainers such as DMF or DMSO has the main drawback of forming an azeotrope with acetic acid. However, the vapour liquid equilibrium AA – NMA exhibits a tangential pinch point at NMA end composition. The new strategy rises from the thermodynamic analysis of the ternary diagram that which involves no azeotrope. As a result, acetic acid with high purity can be obtained by the recycling of the entrainer with a relaxed constraint in its purity. Optimization studies are discussed by using two approaches: two-step optimization method with Sequential Quadratic Programming (TSOM case) and the multi-objective genetic algorithm. The multi-objective genetic algorithm allowed the computation of the optimal acetic acid dehydration with an impurity of 3% in the recycled entrainer. Significant cost savings are achieved thanks to the optimization of both columns together. Energy consumption is reduced by 12.8% and 56.9% whereas TAC is saved by 28.4% and 56.3% compared with optimal case TSOM (impurity content 1%) and a published “Case Ref” (impurity content 0.01%), respectively.

Solvent mixtures are typical byproducts of many chemical processes. In the chemical industry, distillation is still the most commonly used separation technique for separating solvent mixtures to enable efficient recycling. Some mixtures contain azeotropes that require the use of entrainers, or mass-separating agents, for extractive distillation. Ionic liquids (ILs) possess unique properties that make them suitable for use as entrainers in extractive distillation, thereby leading to a more environmentally friendly operation, reduces exposure of chemicals to workers, increases ease of reuse and recycling by striping evaporation or drying, and consequently reducing total operating costs. This chapter discusses the use of ILs for extractive and azeotropic distillation.

Two batch extractive distillation (BED) separation of two minimum boiling azeotropic mixtures (acetone − methanol + water as entrainer, isopropyl alcohol − water + DMSO) are simulated and optimized with GA. Production series consist of three consecutive batches. Both off-cuts are recycled to the next charge. The entrainer regenerated is also reused in the next batch. The objective function to be maximized is the profit of the whole production series. The optimization variables are the reflux ratios of all steps (main cuts, intermediate and after-cut), duration of the heating-up and the intermediate cut withdrawal and location and flow rate of entrainer feeding.

Bioethanol is one of the most promising alternatives among sustainable biofuels. Methods such as extractive distillation columns are used for the production of bioethanol, because the binary azeotrope of ethanol-water mixture limits the ethanol purity achievable with conventional separation techniques. Since these methods comprise several disadvantages in terms of solvents usage, capital and energy costs, alternative methods are investigated in the industry. This study focuses on the steady-state design and dynamic controllability of a new configuration including a pre-concentrator column and a reactive distillation column to overcome these problems. Steady-state process is simulated using Aspen Plus and Aspen Dynamics is used for dynamic simulations. This configuration is capable to produce ethylene glycol with 99.4 mole% purity as a second product besides bioethanol with 99.7 mole% purity. Dynamic results show that a stable base-level regulatory control is possible for this configuration. Both product purities are held at their design specification against disturbances such as change in production rate handle and feed composition.

There are various methods in the industry that can be used for separating azeotrope mixture. Wise choice of effective separation method is very important in saving energy and reducing total annualized cost of such separation processes. In this chapter, methods for separating azeotrope via distillation will be reviewed. Industrial applications are used to demonstrate that large savings of energy can be made by selecting the most effective separation method. Several analytical tools can be used to aid the decision-making process. Rigorous process simulation is demonstrated for the two industrial examples. To further explore energy-saving potential for the azeotropic separation processes, several feasible heat-integration schemes are also explained. These include feed–effluent heat exchanger, multieffect distillation, and two kinds of thermally coupled distillation systems, i.e., extractive distillation and heterogeneous azeotropic distillation systems.

Bioethanol dehydration can be achieved in a highly-integrated process comprising of a dividing wall column, combining extractive distillation and vapour recompression technology. Compared to conventional processes, this integrated design allows 40% energy savings and reduces the energy requirements to only 4.45 MJ/kg ethanol. This work addresses the challenges related to process dynamics and control, which are just as important as the economic improvements. A dynamic simulation model, built in Aspen Plus Dynamics, is used to identify the control difficulties. Small design modifications are introduced to stabilize the system. A control structure is proposed, where the main element is temperature control of pre-fractionator side, achieved by a combined manipulation of the side reboiler external duty and recompressed vapour by-pass. Several concentration controllers ensure product quality. Dynamic simulations show that rather large feed flow rate and composition disturbances can be effectively rejected.

The separation of aromatic compounds from naphtha (mainly aliphatics) has a great interest for the petrochemical industry. This separation is commonly carried out by liquid- liquid extraction using different solvents which entails very high energy cost during the solvent recovery steps. Recently, ionic liquids (ILs) have been proposed as entrainers for the separation of this mixtures. In this paper we present a multiobjective optimization to select of ILs. One objective is minimize the toxicity of the mixture of ionic liquids used as entrainer in the separation of aromatics and aliphatics mixtures. The second target is to improve the separation performance in the extractive distillation process. The estimation of the toxicity has been carried out by training an artificial neural network (ANN) from structure information and toxicity values of ionic liquids. Results show a high correlation between the presence of heteroatoms and toxicity. The separation of aromatic and aliphatic hydrocarbons was evaluated through rigorous simulation of an extractive distillation process as detailed in Diaz et al. (2016). The evaluation of objectives was carried out in MATLAB connecting Aspen Plus simulations of the single stage extractive distillation process (vapor-liquid-liquid equilibria)through COM objects and evaluating the trained ANN for the ILs mixtures evaluated in each iteration. The multiobjective optimization of the problem was performed using a derivative free algorithm (genetic algorithm). Results show that 1-ethyl-3-methylimidazolium dicyanamide ([EMIM][DCA]) is a promising solvent in terms of separation performance and low toxicity.

International audience; We show how reducing pressure can improve the design of a 1.0-1a mixture homogeneous extractive distillation process and we use extractive efficiency indicators to compare the optimality of different designs. The case study concerns the separation of the diisopropyl ether (DIPE)–isopropyl alcohol (IPA) minimum boiling azeotrope with heavy entrainer 2-methoxyethanol. We first explain that the unexpected energy cost OF decrease following an increase of the distillate outputs is due to the interrelation of the two distillate flow rates and purities and the entrainer recycling through mass balance when considering both the extractive distillation column and the entrainer regeneration column. Then, we find that for the studied case a lower pressure reduces the usage of entrainer and increases the relative volatility of DIPE–IPA for the same entrainer content in the extractive column. A 0.4 atm operating pressure is selected to enable the use of cheap cooling water in the condenser. We run an optimization of the entrainer flow rate, both columns reflux ratios, distillates and feed locations by minimizing the total energy consumption per product unit. Double digit savings in energy consumption are achieved while TAC is reduced significantly. An extractive efficiency indicator that describes the ability of the extractive section to discriminate the desired product between the top and the bottom of the extractive section of the extractive section is calculated for comparing and explaining the benefit of lowering pressure on the basis of thermodynamic insight.

Knowing the importance and necessity of the existence of a control system in chemical processes, this paper aims to investigate the control performance of an extractive column with thermal integration facing common process disturbances. The dehydration of ethanol using ethylene glycol as a solvent was used as a case study. The extractive column was simulated in steady and dynamic states using the commercial software Aspen Plus® and Aspen Plus Dynamics®, in which it was used a more rigorous model with decoupled condenser and reflux vessel. The technique of control by inference was adopted to control the overhead product composition. The results showed that it is possible to maintain the composition of ethanol near specification using a simple control structure, although the thermal integration lead to deviations in the solvent feed temperature of about 5 degrees, when disturbances in the azeotropic mixture feed flow rate are applied.

Biofuels have taken importance on the last years, due to the concern on the environmental impact of the transport sector. One of the most known liquid biofuels is biodiesel. The use of supercritical alcohols to produce biodiesel has been studied recently because of its advantages over the methods with homogeneous catalysts. Nevertheless, due to the high pressure and temperature conditions under which the supercritical process operates, the energy demand is considerable high. In addition, glycerol is produced as by-product, and it is expected that the price of glycerol falls; because of its high production on the biodiesel processes reducing the incomes for its commercialization. On the other hand, bioethanol is other well-known biofuel. To overcome the azeotrope between water and ethanol and produce high-purity bioethanol, extractive distillation is usually employed, where glycerol may be used as entrainer. Therefore, in this work it is proposed the mass and energy integration between supercritical biodiesel production process and bioethanol purification train. For the energy integration, a pinch analysis will be used to integrate the two processes, aiming to reduce the external energy demand by using the energy released by the chemical reactions. By this approach, reductions on the total annual costs can be obtained if compared with the individual processes. Also, since the energetic requirements are partially satisfied by the energy delivered in the processes, global environmental impact is reduced as well.

Just a few papers have addressed the study of start-up operating policies for extractive distillation. For this reason, this paper deals with the design of start-up procedure and the influence of solvent feeding time. The start-up procedure developed is based on total reflux policy. To evaluate the spent time three cases is studied: the solvent feed being introduced at the same time of azeotropic mixture feed, the solvent feed being started thirty minutes and an hour after the azeotropic mixture feed was started. The results showed that the shortest time required to reach the steady state was achieved when both feed streams were feeding at the same time, the startup period was 2.86 hours.

The present paper proposes a flexible modular linear model of decision-making for the selection of processes and unit operations for lignocellulosic bioethanol production. The methodology begins by suppressing the commonly accepted bilinear restrictions for flows and compositions, and there after allows building the identity of the synthesis problem by easing the introduction of components, interconnection specifications or block characteristics and performance. A case study in second generation ethanol production using biomass from sugarcane bagasse as raw material is presented to test the developed process synthesis tool, using GAMS. Results show that the diluted acid pretreatment, the SSCF configuration for hydrolysis and fermentation, and the extractive distillation as the selected blocks. The methodology demonstrated a low computational cost and a simplified management of the problem complexity. These approach is suitable for process screening when missing or restricted data from the process alternatives is available.

Most of the energy consumed in the chemical industry is due to distillation units. This unit operation is very mature but any improvement in its efficiency leads to important savings. The goal of the present study is to show that the feed impurities, which usually are disregarded in calculation for sake of simplicity, could be useful to enhance the distillation efficiency. Enhanced distillation is only considered when it is required to break an azeotrope or in the presence of a pinch zone, but it could be also used to improve distillation efficiency. The most common enhanced distillation operation is the extractive distillation and the heterogeneous azeotropic distillation. In this case, a third heavy boiling compound (extractive agent) or a compound that forms a light heterogeneous azeotrope respectively (entrainer) is added. The novel method is applied to a case study: the dehydration of the acetic acid from the terephtalic acid production. The results show that methyl acetate and p-xylene would both increase the distillation efficiency and none of them would require an entrainer make up without using any second column for entrainer recovery. The effect of the decanter feed stream flow rate and the column feed stage are evaluated by rigorous simulation using Aspen Plus® v8.6.

In this work, a process for the production of bioethanol from lignocellulosic materials is proposed and analyzed using the process simulator Aspen Plus. The stream leaving the reactive section, which has a bioethanol composition of around 5.7 wt%, enters to a stripping column where water and by-products are separated from ethanol. From that column, a side stream is withdrawn, containing mainly ethanol and water in an approximately equimolar mixture, with traces of by-products. For that stream, three alternatives of separation trains are studied, aiming to obtain anhydrous bioethanol: a distillation column to reach the azeotropic composition, followed by vapour permeation membranes; a distillation column followed by an extractive distillation column; and a liquid-liquid extraction column followed by an extractive distillation columns. All the alternatives are compared in terms of energy consumption and total annual cost.

Isoamyl acetate (iAAc) - isoamyl alcohol (iAA) mixture has not been widely studied or reported in the open literature and a complete topological description is still lacking: e.g., its vapor-liquid equilibrium (VLE) data and its azeotropy. VLE experimental data of the mixture was measured in our laboratory at pressures of 50.00, 101.31, 250.00 and 350.00 kPa in a dynamic recirculation cell Fischer Labodest® model 602. It was determined the existence of an azeotrope of minimum boiling point. The data was regressed in order to obtain the adjusted aij parameters for the NTRL model at each system pressure. For the design of the separation strategy of this mixture two different arrangements were proposed: the first corresponds to a pressure swing distillation system that uses two columns, and the second is an extractive distillation system. These two arrangements were simulated in Aspen Plus® platform and an economic assessment of the process through a total annual cost (TAC) and the market price of the iAAc and the iAA were taken into account for the comparison of the two alternatives. It was found that the PSD distillation has better results in terms of TAC than the extractive distillation process.

The recovery of methanol from an industrial waste solvent mixture (acetone (A) – methanol (B) – THF (C) –water (D) – toluene (E)) by batch (BD) and batch extractive distillation (BED) is optimised. A production cycle consists of six consecutive batches. The 1st fore-cut is incinerated; 2nd fore-cut, after-cut and hold-up are recycled to the next batch. Both processes are studied for constant and varying fresh feed compositions. The optimization of the batches was performed consecutively by a genetic algorithm (GA) with a professional flow-sheet simulator for the dynamic simulation. Objective function is the profit of the actual batch. Optimization variables are reflux ratios of all steps, duration of fore-cut withdrawals and for the BED flow rate and duration of entrainer (water) feeding. The effects of the variation of fresh feed composition on the optimal values of parameters are studied. The results of BD and BED processes are compared.

A thermodynamic model was developed to describe the vapour–liquid equilibria encountered in the reactive extractive distillation of 1-hexene mixed with n-hexane and 2-methyl-1-pentene, used to represent a Fischer–Tropsch stream. Experimentally it is determined that the feed mixture behaves nearly ideal in the absence of any solvent and that the obtained selectivities are near unity. A non-reactive solvent (D2EHPA) increases the activity coefficients but does not significantly improve the selectivity. The selectivity can only be increased by enriching the solvent with a metal-ion (Ag). The model uses the Wilson equation to describe the activity coefficients and can represent the vapour–liquid equilibria accurately as function of composition, pressure and temperature. To produce 1-hexene with a 99% recovery and at 99.5% purity, the solvent-to-feed ratio should be around 5 (at 0.2 bar, T = 311 K). Under these conditions the selectivity is 1.34 (2-methyl-1-pentene/1-hexene) and 1.55 (n-hexane/1-hexene) and the minimum number of equilibrium trays approximately 42.

Production of anhydrous ethanol in large scale has been made by extractive distillation using solvents such as ethylene-glycol or glycerol. In this work, azeotropic distillation is studied to dehydrate bioethanol using n-octane as entrainer. We use a procedure to account for risk and safety, in addition to economic evaluations, in the process design. A probabilistic methodology is applied for the evaluation of a distance likely to cause death as a risk index. The safety assessment combines a frequency and consequence analysis to calculate process total risk. The approach is applied to the design of ethanol dehydration processes, for which azeotropic and extractive distillation systems are compared. The properties of the solvents affect the inherent process safety. The comparison between the two alternatives is done in terms of individual risk, CO 2 emissions and total annual cost. The results show that the azeotropic distillation using n-octane as entrainer presents lower total energy consumption and risk compared to the purification process with extractive distillation using ethylene glycol. The product of the proposed separation scheme is a dehydrated mixture of ethanol and n-octane with 81% mol (61% vol) ethanol, which can be used to produce gasohol.

Biofuels are an attractive source of renewable energy as they can easily replace liquid fuels used in transportation and other machinery. The present study considers typical feed of ethanol-water-CO 2 from which ethanol is recovered and purified using two popular techniques: pressure swing adsorption with molecular sieves and extractive distillation using ethylene glycol. Heat integration in both processes is performed to ensure a fair basis for evaluation. Optimal separation cost is found to be US$0.1394/kg and US$0.1185/kg for the extractive distillation and pressure swing adsorption process, respectively. Hence, fuel-grade ethanol production via pressure swing adsorption with 15% lower separation cost is better than extractive distillation using ethylene glycol.

The recovery of methanol by batch extractive distillation using water as entrainer from an azeotropic waste solvent mixture (acetone(A)-methanol(B)-THF(C)-water(D)-toluene(E)) is optimised by a genetic algorithm (GA) coupled with a professional flowsheet simulator performing the dynamic simulation. Optimization variables are the reflux ratios of the different operation steps, the location, the flow rate and duration of entrainer (water) feeding. The objective function to be maximized is the profit. The effect of changing the charge concentration of methanol and the two main organic impurities (THF and toluene) on the profit and optimal values of the operational variables was studied.

This paper arose from a new approach to evaluating separation and energy consumption of extractive distillation columns using as primary analysis parameter the solvent content throughout the column. This new approach allows to find a range of possible solutions that contemplates the global optimal point of operation. In view of this, the objective of this paper is to investigate the influence of the solvent content throughout the column and the size (number of stages) of the column on controllability. The results showed that the columns with smaller number of stages operating with lower solvent content have a better controllability when applied disturbances in the composition of the azeotropic mixture that feeds the column. The production of anhydrous ethanol by extractive distillation using ethylene glycol as solvent was used as a case study for this work.

The purification of bioethanol fuel requires an energy demanding separation process to concentrate the diluted streams obtained in the fermentation stage and to overcome the azeotropic behaviour of ethanol-water mixture. The classic separation sequence consists of three distillation columns that carry out several energy demanding tasks: pre-concentration of ethanol, extractive distillation and solvent recovery. To solve this problem, we propose a novel heat pump assisted extractive distillation process taking place in a dividing-wall column (DWC). In this configuration, the ethanol top vapour stream of the extractive DWC is recompressed from atmospheric pressure to over 3.1 bar (thus to a higher temperature) and used to drive the side reboiler of the DWC, which is responsible for the water vaporization. The results show that the specific energy requirements drop from 2.07 kWh/kg (classic sequence) to only 1.24 kWh/kg ethanol (VRC assisted extractive DWC), thus energy savings of over 40 % and 24 % reduced total annual costs are possible, as compared to the conventional process.

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., are 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. Spanish Ministry of Science and Innovation (CTQ2012-37039-C02-02).

The design and synthesis of extractive distillation rely upon the knowledge of residue curve map topology and the calculation of univolatility curves to analyze the volatility order of the mixture. Contrary to common belief, light, intermediate, heavy, and heterogeneous entrainers can be used to separate minimum- or maximum-boiling azeotropes and low-relative-volatility mixtures. After a preliminary selection of candidate entrainers based on selectivity and entrainer capacity, a general feasibility criterion enables one to find attainable products and suitable process configurations with the entrainer fed at a different location than the main mixture to be separated, inducing an extractive section within the column. It shows that the most or the least volatile component is recovered from a direct or an indirect split-column configuration in the distillate or in the bottom stream, respectively. Batch and continuous operations are governed by the same entrainer selection rules, but the operating parameter value ranges for the entrainer-feed flow rate ratio and the reflux ratio are different.

The separation of CO2 and/or H2S from the natural gas processing is focused on preventing some undesired effects, as decreasing the heat capacity in the natural gas, and so on. Moreover, the carbon dioxide removal has an extensive interest in other application fields, like mitigating CO2 emissions, being an entrainer in EOR (Enhanced Oil Recovery), among others. One novelty alternative to deal with CO2 separation consists in the use of cryogenic extractive distillation by utilizing as entrainer the liquid hydrocarbon fraction obtained in the process. This process has some advantages, such as that the entrainer is CO2 selective, noncorrosive, and waterless by-product, effective for high CO2 concentration feedstock. In this work, the Aspen Plus One 7.0 process simulator was used to model the CO2 - ethane azeotrope for different extractive distillation sequences and distinct entrainers, considering a rate based model. The study included the formal design and optimization (minimizing the Total Annual Cost (TAC) and maximizing the acid gas removal) to finally compare the alternative configurations with the conventional chemical absorption system used in the industrial field. Complementary studies regarding the controllability, thermodynamic efficiency and greenhouse gases generation were conducted. The proposed cryogenic extractive distillation sequences showed, in terms of costs and CO2 emissions, better performance than the conventional chemical absorption configuration. Even more, the extractive thermally coupled distillation structures reached the best energy savings with appropriate dynamic behavior, making these alternatives competitive and environmentally friendly.

The large-scale production of bioethanol fuel requires energy demanding distillation steps to concentrate the diluted streams from the fermentation step and to overcome the presence of the ethanol-water azeotrope. The conventional separation sequence consists of three distillation columns performing several tasks with high energy penalties: preconcentration distillation (PDC), extractive distillation (EDC) and solvent recovery (SRC) columns. Remarkable, almost all papers on this topic focus on the azeotropic separation only, while neglecting the pre-concentration step. Usually, the ethanol concentration in the first distillate stream is arbitrarily considered close to the azeotropic composition. While the energy usage in the PDC increases as the distillate composition gets closer to the azeotrope, the energy requirements in the EDC-SRC units decreases as the feed to EDC becomes richer in ethanol – and the other way around. This paper addresses this key trade-off of the distillate composition – a fundamental issue that was not studied before. Aspen Plus simulations were used to investigate how this parameter affects the energy usage and investment costs of the complete system. This issue applies in any other methods using a pre-concentration column (e.g. extractive and azeotropic distillation). The optimal economics is reached at a distillate concentration of 91.0 %wt ethanol, where the specific energy use is only 2.11 kWh (7,596 kJ) per kg ethanol.

This chapter introduces the choice and usage of new separating agents (i.e. entrainers) in distillation processes. Such substances are preferentially used for the separation of narrow boiling and azeotropic mixtures using extractive distillation. The chapter focuses on ionic liquids and hyperbranched polymers. Because of their customizable properties, these two solvent classes can be used as entrainers for various separation problems. The regeneration of the entrainer is easy because the vapor pressures of both solvent classes are infinitely small. The thermodynamic choice of the best-suited entrainer can be done by solubility experiments (e.g. with headspace gas chromatography), by using a structure-interpolating method such as UNIFAC, or by an a priori predictive method (e.g. the Conductor-like Screening Model for Real Solvents) to calculate the solubility.

This chapter introduces the major types of azeotropic distillation processes and describes a systematic framework for their conceptual design. The framework is based on a three-step approach consisting of (1) variant generation, (2) screening of all variants based on shortcut methods, and (3) the final detailed design by means of rigorous optimization. Different approaches for the generation of distillation flowsheets and the analysis of inherent limitations are presented and compared in the context of a qualitative and quantitative assessment of split feasibility. An elaborate overview on different shortcut methods for the evaluation of distillation process performance is given, and their applicability to the design of azeotropic distillation processes is discussed. Since rigorous optimization should always follow shortcut-based design and evaluation steps, recent advances in this field with a focus on azeotropic distillation are highlighted. The chapter closes with the presentation of a few example case studies for the conceptual design of different types of azeotropic distillation processes.

The separation of a multicomponent azeotropic industrial waste solvent mixture by batch distillation (BD) and batch extractive distillation (BED) is studied. From a mixture methanol-THF-water-toluene methanol must be recovered in high purity. The optimization of both processes is performed by a genetic algorithm (GA) coupled with a professional flow-sheet simulator performing the dynamic simulation. The optimization variables are the reflux ratios of the operation steps, the location, flow rate and duration of entrainer (water) feeding. The objective function to be maximized is the profit.

The optimal design of an extractive distillation column and entrainer regeneration column sequence is studied with a MINLP method. The objective function minimizes the energy consumption per product flow rate under purity and recovery constraints. Total annual cost (TAC) for the process is calculated. A trade-off between the two columns variables is found and optimal parameters with lower energy consumption and TAC than literature results are found. A case study is provided with the extractive distillation separation of acetone-methanol with entrainer water (class 1.0–1a).

Dividing wall columns have found wide application in chemical industry. Compared to conventional distillation columns, they offer considerable advantages with respect to energy requirements and investment costs. The field of application extends from simple separations with moderate purity requirements to the highest electronic-grade product specifications. When thermally sensitive products have to be separated, lower thermal degradation tendency and better product qualities can be expected due to the shorter residence time in column sections with high temperatures. Dividing wall columns are also used in the field of extractive distillation. Additionally, applications in reactive distillation have been investigated and found feasible as they offer considerable potential to simplify the process and reduce equipment cost. Industrial applications of such reactive distillations have not been reported so far.

Distillation is one of the oldest and most used separation processes that exist in chemical industries worldwide. In cases of azeotropic mixtures, simple distillation is unable to perform separation at a certain composition, so they are separated using azeotropic distillation. Traditionally, there are two different configurations used to produce anhydrous ethanol by azeotropic distillation. One of them is the heterogeneous azeotropic distillation and the other one is the homogeneous azeotropic distillation. In both configurations, it is necessary to add a third component (solvent) to promote separation and it is also necessary to use a second distillation column in order to recover the solvent. This paper deals with homogeneous azeotropic distillation (also called extractive distillation) and the process of obtaining anhydrous ethanol was chosen as a case study. For this case, the solvent used to break the azeotrope was ethylene glycol. The purpose of this work is to determine the optimal conditions of a new configuration of extractive distillation process for producing anhydrous ethanol using only one column with a sidestream withdrawal, using the process simulator Aspen Plus®. After optimization, it was possible to achieve a reduction of 18.53 % in the reboiler heat duty. A comparison, in terms of energy consumption of the reboilers, between the traditional extractive configuration and the new configuration, was also assessed.

A feasibility evaluation procedure for reactive extractive distillation is proposed on the basis of the graphical analysis in the composition space. To do this, the feasible direction of the composition trajectory is defined and its profile is traced in composition space. Thermodynamic constraints from reaction/phase equilibria and operational constraints from material balances are also determined and plotted in the composition space. If the composition trajectory goes toward the desired direction while circumventing phase equilibrium limitations, the complete reaction conversion and recovery of pure products are possible through reactive extractive distillation. To confirm validity of this graphical evaluation method, the feasibility for the reactive extractive distillation of isopropyl acetate esterification is evaluated to understand how an external entrainer can lead to the full reaction conversion and the recovery of pure products.