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There are different factors and indices to characterize the performance of a pervaporation membrane, but none of them gives information about their capabilities in the area of liquid separation compared to the most convenient alternative, which is distillation. Membrane flash index (MFLI) can be considered the first and only one that shows if the membrane is more efficient or not than distillation and quantifies this feature too. Therefore, the MFLI helps select the best separation alternative in the case of process design. In this study, the evaluation and capabilities of membrane flash index are comprehensively investigated in the cases of six aqueous mixtures: methyl alcohol–water, ethyl alcohol–water, isobutyl alcohol–water, tetrahydrofuran–water, N-butyl alcohol–water, and isopropanol–water. It must be concluded that the separation capacity of organophilic type membranes is remarkably lower than hydrophilic membranes in all cases of separation. The study of the MFLI is extended with the consideration of other binary interaction parameters like separation factor, permeation flux, selectivity, and pervaporation separation index (PSI) in order to find a descriptive relationship between them. For the same membrane material type, descriptive function can be determined between feed concentration and MFLI and PSI and separation factor, which can be used to calculate each other’s value. On the basis of the indices and especially the MFLI, a significant help can be given to the process design engineer to select the right liquid separation alternative and, in the case of pervaporation, find the most appropriate membrane.

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

It can be stated that in the fine chemical industries, especially in the pharmaceutical industry, large amounts of liquid waste and industrial waste solvents are generated during the production technology. Addressing these is a key issue because their disposal often accounts for the largest proportion of the cost of the entire technology. There is need to develop regeneration processes that are financially beneficial to the plant and, if possible, reuse the liquid waste in the spirit of a circular economy, in a particular technology, or possibly elsewhere. The distillation technique proves to be a good solution in many cases, but in the case of mixtures with high water content and few volatile components, this process is often not cost-effective due to its high steam consumption, and in the case of azeotropic mixtures there are separation constraints. In the present work, the membrane process considered as an alternative, pervaporation is demonstrated through the treatment of low alcohol (methanol and ethanol) aqueous mixtures. Alcohol-containing process wastewaters were investigated in professional process simulator environment with user-added pervaporation modules. Eight different methods were built up in ChemCAD flowsheet simulator: organophilic pervaporation (OPV), hydrophilic pervaporation (HPV), hydrophilic pervaporation with recirculation (R-HPV), dynamic organophilic pervaporation (Dyn-OPV), dynamic hydronophilic pervaporation (Dyn-HPV), hybrid distillation-organophilic pervaporation (D + OPV), hybrid distillation-hydrophilic pervaporation (D + HPV), and finally hybrid distillation-hydrophilic pervaporation with recirculation (R-D + HPV). It can be stated the last solution in line was the most suitable in the terms of composition, however distillation of mixture with high water content has significant heat consumption. Furthermore, the pervaporation supplemented with dynamic tanks is not favourable due to the high recirculation rate in the case of tested mixtures and compositions.

Pervaporation is a separation method that is considered as green technology because of its low energy consumption. The mechanism of component separation in a liquid mixture by pervaporation is complex but it can be explained with the solution-diffusion mechanism. The work is motivated by an industrial separation problem, that is, ethyl acetate removal from aqueous mixture. To complete this goal hybrid organophilic/hydrophilic pervaporation of ethyl acetate/water mixture through commercially available Sulzer PERVAP™ 4060 and 1510 membranes are investigated to obtain information about the removal of ethyl acetate. Our experimental data are evaluated with the pervaporation model of our improvement (Valentinyi et al., 2013) and it is found that the model can be applied also for both cases. The hybrid separation process is rigorously modelled in professional flowsheet environment, and optimized with the dynamic programming optimization method. The objective function is product purity of 99.0, 99.5 m/m% in water and ethyl acetate content and the total annual cost is also determined. It can be determined, this hybrid separation should be become the alternative of distillation if the energy prices are too high.

The work is motivated by an industrial problem, which is alcohol removal from pharmaceutical process wastewater. The aim of the study was to develop a complete hybrid operation is investigated. Ethanol dehydration, in combination with distillation and hydrophilic pervaporation, is used to investigate about the extent of separation of the ethanol-water mixture. The aim of this research is to rigorously model and optimize this hybrid operation in professional flowsheet simulator environment. The number of minimal theoretical plates of distillation column and minimal effective membrane transfer area are determined. Cost estimation is also examined according to Douglas methodology. Considering our results it can be concluded that, the distillation and hydrophilic pervaporation processes are suitable for separation ethanol and water in 99.5 weight percent purity

Chemical process design is a creative step of engineers that should be supported by different computer-aided design tools. Such tools should be simple and easy to use because process synthesis often means the investigation of a huge number of alternatives. During the design of the separation of liquid mixtures, among many others, distillation and pervaporation are usually simultaneously considered because pervaporation is frequently considered as an alternative to distillation. To easily compare the efficiencies of continuous pervaporation and flash distillation, we propose a new and simple method, the so-called membrane flash index (MFLI). The comparison is based upon vapor–liquid equilibrium data and the permeation data of a pervaporation membrane and therefore can be plotted on a common chart in the case of binary mixtures. The permeation values of organophilic and hydrophilic pervaporations can be calculated with the help of known separation factors and feed concentrations. The MFLI is dimensionless a...

Different research works demonstrate that the pervaporation can replace the distillation or deliver better solutions. It should be, however, accepted with criticism. In our case study, isobutanol-water separation is studied since it is increasingly important in the field of biofuels and process wastewater treatment. There are many options for the separation and they differ in their efficiency, economic features, robustness, development level and environmental impact. Five separation structures are investigated using distillation, both organophilic and hydrophilic pervaporations and hybrid separation units consisting of distillation and pervaporation including heat integrated solutions. The different alternatives are modelled in professional flowsheeting environment. Life cycle assessment, energy evaluation and Multi-Criteria Decision Analysis (MCDA) based on PEST (Political, Economic, Social, and Technological) analysis are completed to evaluate and compare the five alternatives. The feed stream to be separated has the composition of 7 wt% isobutanol 93 wt% water that corresponds to the mixture of the phase split due to the limited solubility. Two product purities are considered, 98.8 and 99.9 wt%. In case of distillation processes, heat integration is also considered, that is, the feed is preheated with its bottom flow. Heat integration significantly improves the efficiency of the distillation and makes it for practically a competitive alternative. The best efficiency can be obtained with heat integrated hybrid separation, that is, the combination of distillation and pervaporation. The pure pervaporation that is the combination of organophilic and hydrophilic pervaporation can be efficient only at sloppy product purities because of the modest separation factor of the organophilic pervaporation membranes. In case of sharp separations, the organophilic pervaporation can be an equally applicable solution as the azeotropic distillation for isobutanol-water separation.

This study continues our research about dividing-wall distillation columns (DWCs) with upper and lower partitions (Ind. Eng. Chem. Res. 2016, 56, 952). Thermodynamic efficiencies and heat demands are investigated to offer a more complex point of view about distillation technologies. Rigorous simulations of nine distillation systems are completed, and the results are evaluated. Among the separation systems there are conventional direct and indirect distillation systems and energy-integrated ones, that is, DWCs with upper and lower partition, columns with side stripper or side rectifier, the fully thermally coupled distillation column, the sloppy system, and a direct sequence with backward heat integration are examined using three different alcohol mixtures. Results are obtained from rigorous simulations using exergy analysis. Thermodynamic efficiencies are in agreement with the expectations based on previous researches. On the basis of the thermodynamic efficiencies and heat demands the direct sequence wit...

This study deals with the prediction of distillation trays’ efficiency in rectification columns, in case of low carbon content hydrocarbons (for example ethane-ethylene and propane-propylene) separation. During these technologies typically trayed columns are used, therefore the bubble cap and sieve trays were investigated in this paper. In the previous studies, we have assumed that the leaving vapour and liquid from each tray is in equilibrium. It assumed that the trays have 100% efficiency, however, in practice, this supposition is not true. It means that it is necessary to determine the actual efficiency of the trays because this value gives the actual trays’ number too. The studied methods are the O’Connell method and the AIChE method (Perry 1950). This study’s goal is to calculate and compare different trays’ efficiency because it has an effect of the tower height. In petrochemical industry the previously mentioned hydrocarbons have a high importance, these are the raw material of the plastic manufacturing. Generally, hydrocarbons are produced by distillation from higher carbon content materials, and this procedure has extremely high energy consumption. In case of higher plate efficiencies, the costs can be reduced.

The distillation based separation can be extremely complex if highly non-ideal mixtures are to be separated. In spite of different successfully applied unit operations there is always a possible way to improve the distillation technique and widen its toolbar. A novel improvement in this area is the development of the extractive heterogeneous-azeotropic distillation (EHAD). For the sake of the demonstration of the efficient use of EHAD in Dividing wall columns (DWC), two quaternary mixtures are selected for separation: Water – Ethanol – Ethyl acetate – Acetone and Water – Ethanol – Ethyl acetate – Ethylene glycol. There are real waste mixtures from pharmaceutical industry. It must be mentioned, extractive heterogeneous-azeotropic distillation method has never been investigated in dividing wall columns. Conventional distillation column sequences and dividing wall columns are selected for comparison. Rigorous steady-state simulations are carried out using ChemCAD flowsheet simulation software. Number of trays, heat duties and Total Annual Cost (TAC) of the systems are optimized. It can be concluded, the application of the EHAD in DWCs allows also the simplification of the separation schemes and the separation reduces the energy requirements of the distillation and opens new horizons for the separation of non-ideal mixtures saving energy, money and natural resources. Using DWCs the reboiler duties can be reduced with 20% and the appropriate separation can be reached with one less column.

The aim of this study is to compare the controllability properties of conventional distillation sequences and dividing-wall columns with upper and lower partitions (DWCs). The controllability analysis methodology uses the Control Design Interface (CDI) module of Aspen Dynamics to obtain the state space representation of the studied systems. The frequency dependent controllability indices are calculated by Matlab on the basis of the matrices of the transferred state space representation. The study includes the examination of the conventional direct and indirect sequences and two DWCs systematically generated from the corresponding conventional sequences. Case studies are completed using ternary alcohol mixtures with different eases of separation. Results show that conventional distillation sequences have more favorable controllability properties than those of the DWCs if direct separation and mixtures with symmetrical ease of separation are considered. In the cases of mixtures with nonsymmetrical ease of s...

The application of vapour-liquid equilibria-based separation alternatives can be extraordinarily complicated for the treatment of process wastewaters containing heterogeneous-azeotropic. Despite dissimilar successfully tested methods for separation, there is possibility to get better distillation method by enabling the separation of more and more specific process wastewater. Extractive heterogeneous-azeotropic distillation (EHAD) is a new advance in treatment of fine chemical wastewater showing special features to cope with the treatment of highly non-ideal mixtures. This method combines the worth of heterogeneous-azeotropic and extractive distillations in one apparatus without addition of any extra materials. The study of the separations of ternary component process wastewater from the fine chemical industry shows both in the modelled and experimental results that EHAD can be successfully applied. The measured and modelled compositions at extreme purities, that is, close to 0% or 100%, can be different because of the inaccuracies of the modelling. This highlights the paramount importance of the experiments if special extra-fine chemicals with almost no impurities, e.g. of pharmacopoeial quality are to be produced by special distillation technique. This study expands the application of EHAD technique, this new field is the separation of process wastewaters.

The work is motivated by an industrial separation problem, that is, isobutanol removal from aqueous mixture. To complete this goal a hybrid separation system of organophilic–hydrophilic pervaporation system is designed applying Sulzer PERVAP™ 4060 and 1510 membranes and investigated to obtain information about the separation of isobutanol–water mixture. The aim of research is to rigorously model and optimize this novel hybrid process. Permeation fluxes, permeances, selectivities and separation factors are experimentally determined for this hybrid system. The pervaporation separation index (PSI) and selectivity data are compared with those of other membranes published in the literature and it is found that PERVAP™ 4060 has the highest PSI value and its other parameters are also among the best. Our experimental data are evaluated with the pervaporation model of our improvement and it is found that the model can be applied also for both organophilic and hydrophilic pervaporations. The hybrid separation system is rigorously modelled with ChemCAD and optimized with the dynamic programming optimization method. The objective function of the hybrid system is the total annual cost but its energy consumption is also investigated. It can be determined that this hybrid process, that is, the combination of organophilic and hydrophilic pervaporations is capable for the separation of isobutanol and water and it can become the alternative of distillation based separation. Considering our results it can be assumed that the combination of the organophilic and hydrophilic pervaporations opens new horizons for the membrane processes.

The distillation based separation can be extremely complex if highly non-ideal mixtures are to be separated. In spite of different successfully applied unit operations there is still a possible way to improve the distillation technique and widen its toolbar. A new improvement in this area is the development of the extractive heterogeneous-azeotropic distillation (EHAD). This unit operation includes the merits of extractive- and heterogeneous-azeotropic distillations in one unit without extra material addition. Our work supports EHAD features with successful experiments compared with modelling and comparison with other separation structures proving that the application of EHAD makes the separation of extremely non-ideal mixtures possible on an easy, powerful, energy saving, and cost efficient way.

This work investigates the techniques used in evaluating distillation structures from lean manufacturing point of view. Oil & gas industry has already started adopting lean manufacturing principles in different types of processes from information flow to processing technologies. Generally, energy costs are the most important factors in processing hydrocarbons. Introducing flexibility desired by lean principles to the system may conflict energy efficiency of the system. However, this does not mean that the economic optimum is the energetic optimum. Therefore all possible changes due to temporarily stopped or not fully utilised plants have to be investigated, resulting in a large amount of cases that have to be evaluated. For evaluation exergy analysis can be used as it involves all energy types, and evaluation is straightforward. In this paper plain distillation structures are investigated, and the boundaries of the systems are set up according to the status of the site. Four component case studies are presented that show that the very same distillation structure can be more or less efficient depending on the status of the industrial site. It is also shown that exergy analysis used with different boundaries on the same system can show flexibility of the system and reveals potentials.

A complex treatment of process wastewaters (PWW) of the pharmaceutical industry has been elaborated, the objective was their common disposal and utilization. The biodegradability of polluting components is concentration dependent, the mixing of PWWs with domestic wastewater at WWTP is possible, if no toxic and/or non-biodegradable components are present. So the organic content can serve as carbon source in the denitrification step. The characterization and the proper treatment methods of PWWs have been developed. Only 20-30 % of PWWs required pretreatment. The majority can be mixed directly with the domestic wastewater and send to the WWTP. The characterization includes COD, TOC, BOD, AOX, volatile content, toxicity, metal ion content measurements. The pretreatment methods could be: distillation, WO or catalytic WO. After the activated sludge treatment the degradation of emergent pollutants and the disinfection can be performed by UV-Fenton or high energy irradiation. The design of a complex treatment plant attached to a WWTP of 100000 m3/day capacity and its life-cycle analysis to determine the environmental benefits were carried out also.

The distillation based separation can be extremely complex if highly non-ideal mixtures are to be separated. In spite of different successfully applied unit operations there is still possibility to improve distillation technique and widen its toolbar. A new improvement in this area is the introduction of the extractive heterogeneous-azeotropic distillation (EHAD). This unit operation includes the merits of the extractive and heterogeneous-azeotropic distillations in one unit without an extra material addition. In spite of the complexity of this unit operation it can be efficiently applied and complex separation technologies can be simplified with its application. The separations of ternary and quaternary mixtures from the fine chemical industry show both in the modelled and the experimental results that the extractive heterogeneous-azeotropic distillation is an efficient tool of this area. Demonstrating the accuracy of EHAD, the separation of methanol–ethyl-acetate–water and ethanol–ethyl-acetate–water mixtures are examined and the EHAD is compared with conventional distillation techniques. These separation processes are rigorously modelled and optimized with dynamic optimization method in professional flowsheeting environment. The objective function is the total annual cost but the energy consumption is also investigated. The modelling results are verified with laboratory experiments, too. It can be concluded that the extractive heterogeneous-distillation is a capable method for the separation of these highly non-ideal mixtures.

Distillation is an important and widely applied separation method. One of its major application areas is crude oil refining. We investigate and compare two different refinery technologies: (i) conventional, atmospheric and vacuum, AV-plant, and (ii) an alternative one, the so-called progressive distillation technology. For the sake of the comparison, simulation models of the two different distillation technologies are built in professional flowsheeting software environment. The investigation includes the study of crude oil fractionation on the examples of processing different types of crude oils. Both technologies are also evaluated with the tools of pinch technology. On the basis of the results of the pinch analysis, heat exchanger networks are also designed. The operating and capital costs are estimated for the energy integrated cases designed on the results of pinch technology. A comparison of the results shows that the progressive distillation plant proves to be both more energy efficient and economic...

In the engineering practice, there are two basic alternatives of physicochemical treatment for the removal of volatile compounds from process wastewaters: stripping with air or stripping with steam. In this work, these alternatives are investigated and compared in the case of a real industrial problem that is typical for the fine chemical industry and general conclusion is drawn. The removal of the organically bound halogens, called adsorbable organically bound halogens, is investigated. The two alternatives, air and steam stripping, are first modeled in the professional software environment of ASPEN Plus®. The model is validated on the data of an existing air stripper for the removal of organic halogens. Same organic halogens removal is applied for the design of a steam stripper. It is proved that the steam stripping shows better operability and economic performance than the air stripping; moreover, the volatile and/or adsorbable organically bound halogen compounds can be recovered in the distillate and they can be reused improving the sustainability.

In the case of process design a new graphical representation method is proposed on the basis of computer modelling of distillation and pervaporation. The new method relies on also vapour-liquid equilibrium data. The comparison can be performed on a common y-x equilibrium diagram of the mixture to be separated. In our work methanol-water, ethanol-water and isobutanol-water are the investigated systems. The alcohol permeate composition values are plotted over the feed composition. Permeate alcohol concentrations are calculated with the help of known separation factors and feed alcohol concentrations. The corresponding vapour-liquid equilibrium composition is also shown so that pervaporation and flash distillation could be compared. In the case of methanol and ethanol separation a lower separation capability of the different PDMS membrane is detected than a flash distillation. In the case of isobutanol-water mixture every calculated isobutanol permeate weight fractions of different organophilic membranes are above the equilibrium vapour concentration. The proposed graphical representation method visualizes the feasible operation ranges of distillation and pervaporation. It enables also the designing engineer for the proper selection of the separation method.

This work presents a process design methodology that evaluates the distillation systems based on exergetic, economic, and greenhouse gas (GHG) emission aspects. The aim of the methodology is to determine how these three features should be applied in process design to obtain information about the accuracy of the design alternatives. The methodology is tested and demonstrated on three different energy-integrated distillation systems: the direct sequence with backward heat-integration (DQB), fully thermally coupled distillation column (FTCDC), and sloppy distillation system with forward heat-integration (SQF). The average relative emission saving is the highest for the DQB scheme and this sequence shows the most flexible range of use. The case studies prove the accuracy of our evaluation methodology. On the other hand, it highlights and demonstrates that the exergy analysis can predict the results of the economic study and the environmental evaluation to make the decisions, associated with process design, much simpler. © 2009 American Institute of Chemical Engineers AIChE J, 2010

A simulation tool is developed in order to support the operation of an industrial scale hybrid distillation–pervaporation system that is used to regenerate isopropanol. Laboratory-scale experiments were carried out to determine the parameters of a semi-empirical solution–diffusion membrane transport model that is used for the modelling of the pervaporation transport. Isotherm experiments were made at three different temperatures (60, 80, 90°C) using a hydrophilic flat sheet membrane (PERVAP 2210, Sulzer Chemtech). The permeate fluxes and compositions were measured at different constant feed compositions. The parameters of the applied transport model were fitted to the experimental data. For simulating the pervaporation apparatus, an earlier developed user added pervaporation module within the ChemCad software package was applied. The user added module and the fitted transport model parameters were used for the simulation of our measured laboratory-scale data. Simulation of the industrial scale distillation pervaporation hybrid system was also carried out. The simulated and measured data were compared.

Hybrid separation processes are becoming more and more important in the practice if membrane technologies are also involved. In this work, a systematic investigation is completed for three sequence alternatives of distillation and pervaporation. These are the following: pervaporation followed with distillation (PV+D), distillation followed with pervaporation (D+PV), two distillation columns and a pervaporation unit between them (D+PV+D). The hybrid separation process alternatives are evaluated with rigorous modelling tools, but first, a rigorous simulation algorithm is determined for the pervaporation. The three hybrid separation processes are rigorously modelled with CHEMCAD, and optimized with the dynamic programming optimization method for the case of the separation of ethanol-water mixture. The objective function is the total annual cost (TAC). The energy consumption is also investigated. The selection of the ethanol-water mixture has two motivations: (i) it is quite often studied and well known, and (ii) to make biofuel (ethanol) production more economical, membrane technologies might also be applied. The results are compared with each other and with the classical separation completed with heteroazeotropic distillation. The optimized TAC shows that the distillation column followed with pervaporation is the most economical hybrid separation process alternative. Its TAC is about 66% of that of the classical separation.

Design of novel hybrid processes is performed for the industrial recovery of tetrahydrofuran (THF) from two different highly non-ideal mixtures. The novel hybrid processes combine the advantages of batch and/or continuous distillations, extractive distillation, and pervaporation for efficient separation of highly non-ideal mixtures. Pervaporation, used for the final dewatering of the THF, is the last step in the separation technologies and carried out with available industrial technology (Sulzer Chemtech GmbH, Batch pervaporation BP models, PERVAP ® 2210 membrane type). It is necessary, however, to design a proper pre-separation process of the mixture to be pervaporated and coordinate its operation with the pervaporation unit. Since methanol is also present in one of the mixtures, its behaviour during pervaporation is also investigated. It shows that since the methanol is able to permeate the membrane, it should be separated in the pre-separation process. The vapour–liquid equilibrium data indicate that with extractive distillation it becomes possible to break the THF—methanol azeotrope and the appropriate application of pervaporation makes the further reduction of the recovery costs possible. The total annual costs of the novel hybrid separation processes range between 10.3 and 54% of that of the old technology based on chemical dewatering. The THF loss decreases to the 7.5 and 17% of that of the old technology and shows that pervaporation is also a powerful tool for the application of the principles of the sustainable development and consumption.

Energy consumption of distillation needs high portion of the total energy demand of the fuel- grade bioethanol production. Pervaporation, being a membrane separation process, is a promising alternative process to distillation. A detailed analysis was performed considering the energy demand of concentration of ethanol solution obtained during fermentation up to the fuel-grade quality applying both hydrophilic and hydrophobic membranes. It was also discussed how the specific energy demand of the process varies during the pervaporation process and how energy consumption can be reduced applying pervaporation process with different operating modes. It was stated that standalone pervaporation process can provide fuel-grade quality biofuel at very high separation coefficient, only, using consecutively switched hydrophobic and hydrophilic membranes. Three- stage pervaporation process is needed at separation coefficient of 50, and two-stage one at separation coefficient of 100 to achieve the desired quality. Application of a hybrid process with lower membrane separation coefficient can give the desired quality by lower energy than that the distillation alone. Thus, the hybrid process can provide saving of essential amount of energy comparing it with the energy demand of distillation. However, the commercially available membrane, at present, has not the desired selectivity for replacing, at least partly, the distillation.

The distillation-based separation of ideal liquid mixtures has been comprehensively studied. The optimization of the different separation structures has allowed the development of general heuristic rules to aid the designers in finding good solutions quickly for the type of problem at hand. The separation of nonideal mixtures is also an exhaustively studied area, but because of the complexity of the vapor-liquid-liquid behavior of such mixtures, it is more difficult to suggest guidelines for synthesis in separation sequences. On the other hand, recently several special so-called hybrid separation tools have also been involved in that kind of synthesis task, complicating further the synthesis problem. To obtain some general conclusions for the separation structure synthesis of such mixtures, in this study the separation of two nonideal quaternary mixtures containing one nonazeotropic-forming component (most volatile or least volatile) is studied based on optimization of the separation structures. The separation schemes involve the so-called extractive heterogeneous azeotropic distillation, which is a novel hybrid separation process. The economic optimization of the different separation structures results in the conclusion that the heuristic rule for ideal mixtures, that is, easy separation first should be done and the complicated one should be made last, is valid also for such nonideal mixtures.

The solvent recovery is often the separation of highly non-ideal mixtures. The separation and recovery of quaternary solvent mixtures coming from printing and medicine factories are investigated. The components of the six quaternary mixtures studied in form of heterogeneous and homogeneous azeotropes of minimum boiling point. The mixtures can be categorised into three groups according to their VLLE behaviours. After studying their behaviours, three novel hybrid separation processes based on the extractive heterogeneous-azeotropic distillation, a special kind of new distillation, are developed and recommended for each group of solvents. In the novel processes, beside the extractive heterogeneous-azeotropic distillation, ordinary distillations and phase separation units are also used utilising the fact that the combination of such units, the hybrid processes, offer a higher variety of the possibilities for the separation of highly non-ideal mixtures. The separation processes are verified experimentally and the agreements between the simulated and measured data prove to be rather favourable. A strategy is recommended for the use of the novel hybrid processes developed according to the VLLE behaviour of the non-ideal quaternary mixtures.

Direct separation sequence without, with forward, and with backward energy integration, indirect separation sequence without, with forward, and with backward energy integration, sloppy separation sequence without (preflash system), with forward, with backward, and with double energy integration, and thermally coupled sloppy separation sequence (Petlyuk system) are compared with short-cut and rigorous modelling. Based on theoretical considerations and economically evaluated rigorous case studies for ternary mixtures it is demonstrated that in the most cases the Petlyuk system is not superior to the energy integrated configurations even in energy savings. According to the energy consumption of sharp separation determined by short-cut methodology, all the sloppy sequence structures are equivalent. According to the energy losses determined by short-cut methodology, derived here, the energy-integrated structures win almost everywhere in the studied conditions that include a range of relative volatility ratios and the whole feed composition triangle. According to rigorously simulated and optimised results, together with controllability studies, the advantageous application of the thermally coupled (Petlyuk) systems is constrained to a very small range of relative volatility ratio, feed composition, and price structure. This small range is situated somewhere around balanced relative volatility ratio A/B to B/C, small amount of the middle component B, balanced presence of the two swing components A and C in the feed, and high energy costs to investment costs ratio or slow depreciation rate.

Separation of a ternary mixture by different distillation schemes was simulated rigorously at steady state. Conventional schemes, heat integrated schemes, and the fully thermally coupled structure (Petlyuk system) have been optimized over total annual cost including two different regional utility price systems (high and low utility prices): The results show that price ratios have considerable effect on the savings and consequently on the optimal schemes. Using low utility price the number of actual trays is reduced and the reflux ratios will be increased. At extreme high utility prices the Petlyuk system can be justified as one of the best schemes in savings, but not against the sloppy forward heat integrated scheme. The maximum savings in total annual cost in both cases are about 28%.

Two energy integrated distillation schemes for the separation of three different ternary mixtures of four typical feed compositions have been rigorously investigated and compared to the best conventional two-column distillation scheme. The two energy integrated schemes are: the heat integrated two column system and the fully thermally coupled distillation column (FTCDC), also known as Petlyuk column. The comparison of the energy savings and the total costs of the investigated schemes show that the heat integrated two column scheme is economically always better than the conventional scheme. The FTCDC shows considerable energy savings in several cases, however, it can be competitive with the heat integrated two column system only in those rare cases where the concentration of the middle component is high, the split between the first and second components is harder than the split between the second and third components, and the separation is not too sharp (Annakou and Mizsey, 1996). The rigorous economic study is supported by controllability studies for the two energy integrated distillation schemes. Degrees of freedom analysis and steady-state multivariable control structure synthesis tools show that both investigated schemes can be controlled by conventional decentralised control structures, however, in the case of the heat integrated two column scheme heuristics and also the steady-state control indices show that the interaction among the control loops is less than in the case of the FTCDC. The dynamic simulations of the two energy integrated schemes without and with the most promising control structures support the steady-state analysis. They also demonstrate that in the case of the control of the FTCDC due to the significant interaction among the control loops detuning of the controllers is necessary. Higher overshoots, longer settling time and more sluggish behaviour are expected compared to the heat integrated two column system.

This paper presents results of a rigorous study and comparison of conventional and energy-integrated distillation schemes for the separation of ternary mixtures. The major part of this work is devoted to the design and simulation of the fully thermally coupled distillation column (Petlyuk or Kaibel column) with particular emphasis on the question of the fractional recovery of the middle component in the prefractionator and as a consequence the internal recycle streams. A comparative economic parametric study is carried out for three different distillation schemes: conventional sequences, heat-integrated columns, and the fully thermally coupled distillation column. The heat-integrated columns show the best economic features over the other two schemes except the few cases when the concentration of the middle component in the feed is high and the A/B split is more difficult than the B/C split. In such rare cases the fully thermally coupled distillation column proves to be the cheapest solution. In the cases...

The effects of the recycle of mass or energy on the control of chemical processes are studied. The recycle can be considered analogous to a feedback and significantly changes the characteristics of the process. The study on simple transfer function models indicates that the recycle loop gain strongly and time constant of the recycle unit somewhat less strongly influence the behaviour and the controllability of the process. Higher time constants of the recycle, the use of large surge tanks, and the control of the recycle unit of smaller time constants improves the range of stability. Two case studies, the distillation train of the manufacture of styrene and a simple reactor-distillation column system, demonstrate that chemical processes with internal recycle can usually be controlled with decentralised control structure with individually tuned controllers. The case studies also show that in the case of the control structure design the connections of the different units should be considered and the control of the recycle unit is also important.

In this work a propylene-propane splitter assisted by a heat pump of the vapour recompression type is investigated by rigorous methods. Two schemes, a single compressor scheme and a double compressor scheme in parallel arrangement, are scrutinised and compared to the conventional stand alone column. The investigation includes parametric study, operability assessment and an estimation of the role of heat pump in minimising flue gas emissions. The parametric study of the influences of the column top pressure and the pressure lift of the heat pump on the economics shows, for both schemes at the optimal conditions, practically the same annual total cost, which is about 37% cheaper than the conventional stand alone column. The operability of the system is investigated by degrees of freedom analysis and steady state controllability parameters. The operability considerations show that in the case of the double compressor scheme, the column pressure can be independent of the threshold temperature of the condenser. Thus the column pressure can be determined to satisfy the optimum separation parameters. Due to this operability reason, the double compressor scheme is preferred to the single compressor scheme. The heat pump share in reducing flue gas emissions is estimated. It is found that about 60% of the flue gas emissions can be minimised when using a heat pump.

The task of synthesizing optimal total flowsheets with energy integration usually represents a large combinatorial problem. In order to reduce the search space, an efficient bounding strategy is presented for synthesizing energy integrated total flowsheets with distillation-based liquid separation systems. The strategy utilizes a predictor-based ordered search technique and can be attached to the conceptual design of chemical processes. The strategy is based on computing lower bounds of the utility and investment costs for the feasible process alternatives. Beside optimizing the column matches the integration of heat pumps with separation system is also considered. The outlined procedure exploits the advantages of both major approaches, i.e. the hierarchical and algorithmic design.

A comprehensive process investigation/design methodology is presented that combines economic, control, and environmental features. The methodology is presented on the case study of energy integrated distillation columns separating ternary hydrocarbon mixtures of different ease of separations. The economic features involve capital and operating costs; the controllability investigations are based on the evaluation of frequency dependent features and dynamic simulations; the environmental evaluation counts for the CO2 emissions. The results show that the heat integrated scheme is practically the best selection from every point of view.

In printing companies often different four-component-mixtures (mixture 1: ethanol, ethyl acetate, isopropyl acetate, and water, mixture 2: ethanol, ethyl acetate, methyl-ethyl-ketone, and water) arise as waste. The recovery of the individual components is complicated by the highly nonideal feature of the mixtures, namely several binary and ternary azeotropes are formed by the components. Based on the synthesis procedure proposed by Rev et al. (1994) and Mizsey et al. (1997), new separation processes using hybrid separation techniques are developed followed up the vapour-liquid-liquid equilibrium behavior of the mixtures. The first process (ternary-cut-system) splits mixture 1 into two ternary mixtures which are separated later in subsequent units into components of the prescribed purity (∼95%). This technology needs, however, seven distillation columns and two extractors. The second separation process is based on two coupled columns and a three-phase-flash (two-column-system) which can cope with the separation of both mixtures into binary mixtures and the binaries can be easily separated further with conventional methods. Both processes are using extra water addition for the necessary separation. These processes are experimentally also verified (Mizsey et al., 1997, Raab, 2001). A third integrated separation process is developed with evolutionary steps merging the extractor and distillation units, designed for the ternary-cut-system, into integrated extractive distillationprocess using water as extractive agent (integrated-system). The integrated-system can separate both mixtures into components of the prescribed purity and consists of only four distillation columns. Beside the simpler separation structure the energy consumption is also investigated and compared with the other two processes. The use of this innovative solvent recovery process makes the reduction of the number of processing units possible and operating costs can be significantly reduced compared to the other non-integrated separation technologies.

The industrial application of pervaporation as a membrane separation technology is increasing caused by the numerous advantages of this method. However, to complete engineering design, like in the cases of distillation, azeotropic distillation and absorption, reliable and adequate modelling of the process in flowsheeting environment is indispensable. A proper model is especially needed if the more complicated but more economical and environmentally sound hybrid separation methods are designed or investigated.In this study two pervaporation models, the solution-diffusion model of Rautenbach [1] and its developed form [2], are compared and evaluated with computer simulation on the dehydration processes of isobutanol-water and ethanol-water mixtures. Simulations of a hybrid separation method containing pervaporation for the separation of these mixtures are performed, thus proving the importance of using a proper pervaporation model regarding the discrepancies caused by the application of a false model.

In this paper exergy analysis is applied to select the most efficient rectification structures for separation of quaternary hydrocarbon mixtures. The basis and usage of exergy analysis is shown, as well as the benefits of its application. Exergy loss and thermodynamic efficiency is calculated from basic equations of thermodynamics. The ranking, even based on exergy analysis, highly depends on the product purification prescription. Finally it is shown that heat integration of distillation columns is exergetically beneficial in a wide product purity range.

This work provides physicochemical solutions for the treatment of process wastewaters of fine chemical industries, that is, pharmaceutical industry. Economical methods are recommended for practical use, which can reduce the disposal ratio of the process wastewaters with higher values of chemical oxygen demand (COD) and Adsorbable Organically Bound Halogens (AOX) than the corresponding emission limits. Such treatment alternatives are also the part of environmental sustainability. The work reviews the theoretical background of the problem and gives options for using the waste management hierarchy chart. Then the general features of pharmaceutical process wastewaters and the treatment methods are summarized. In the algorithm developed for process wastewater treatment, the distillation is the core of the physicochemical treatment alternatives. In the case of the real industrial case studies, the distillation and membrane filtration laboratory experiments and cost calculations prove the efficiency of the selected physicochemical treatment options.

The pharmaceutical industry produces carbon-rich liquid wastes which have been generally qualified as hazardous. A significant proportion of these carbon-rich wastes are currently sent for incineration, although they could be utilised. It was found that the majority of the liquid wastes investigated in this study could be used in biological N-removal as carbon sources for denitrification in domestic wastewater treatment, or for anaerobic biogas production. The volatile content could be separated and the solvents re-utilised, the residual toxic organic compounds could be decomposed by wet oxidation and subsequently sent for biological treatment.

The protection of our environment is an actual and global problem in our time and the wastewater treatment is its important part. It is based on biological treatment. In certain cases, however, due to special regulations, the biological tools are not allowed and other options should be considered and selected. The incineration is an alternative but impact assessment studies show that it can make a serious burden upon the environment as well as it might be an expensive solution. Physico-chemical tools can mean a realistic alternative in such cases. In case of wastewater containing organic solvents (ethanol, ethyl-acetate, toluene, halogenated solvents, etc.), that is typical for wastewaters of medicine and fine chemical industries, the distillation is a powerful tool to remove the volatile polluting compounds. These volatile organic compounds (VOC) can contribute significantly to the chemical oxygen demand (COD) of the wastewater. This contribution we call VOC-COD. The Adsorbable Organically Bound Halogens (AO X) can be removed also with distillation. Industrial case studies show that the distillation offers a realistic alternative and the recovered solvents can be also utilised. The COD can be reduced in certain cases below the emission limit (1000 mg/lit) and the AOX, after the physico-chemical treatment, is less than 8 mg/lit.

This work presents the retrofit design of an industrial N, N-dimethylformamid (DMF)-water separation system originally consisting of three heat-integrated distillation columns. Our task was to examine how the capacity of the separation system could be increased by 42.8%. If necessary an unused on-site extra distillation column was available for the project. The performance of the existing distillation system and of various increased-capacity structures have been studied using rigorous process simulation. Our study shows that the required capacity increase can be attained by adding the extra distillation column only when replacing the column internals of the original columns and when installing a new structured packing also into the available extra column. Replacing the column internals is expected to result in better controllability, too.

In this case-study the effects of the recycles in an ethylbenzene producing system are investigated, simulated and analysed. The studied steady-state technology contains of two recycle streams, hence serves as a good model system for our study. Recirculation is often used in chemical technologies, especially in separating techniques. Being a positive feedback, it is expected that the application of recycle streams may result in controllability problems. In this study composition control is dealt with, exclusively. Based on our simulation calculations, it is shown that applying recirculation in the studied technology can effectively lead to instability if no appropriate process control system is installed. A method is shown that enables the selection of the appropriate process control structure, which ensures constant product purity. The example systems behaviour is studied with and without recirculation in both steady-state and dynamic domains. All the reasonable composition control structures are simulated a nd compared. Based on the steady-state results, controllability indices are calculated for the distillation columns and the best control structures are predicted. The steady-state investigations are confirmed later by dynamic simulations, and finally the best composition control scheme is selected for the entire system - based on the controllability indices.