Experimental investigation of column efficiency for two ternary systems in a three‐phase packed distillation column

In this work, the effect of vapor load and initial feed concentrations on column efficiency and liquid hold‐up in a two‐ and three‐phase packed distillation column at total reflux was investigated. Results for the two investigated mixtures (n‐heptane, n‐hexane, water) and (ethyl acetate, 1‐butanol, water) reveal that column efficiency remains almost constant for the former mixture but changes significantly for the latter. Specific liquid hold‐up and water to organic‐phase volumetric ratio within the column affect the column efficiency due to variations in initial feed concentrations. Influence of vapor load on separation efficiency and specific liquid hold‐up is also studied.     

Modeling and analysis of conventional and heat‐integrated distillation columns

A generic model that can cover diabatic and adiabatic distillation column configurations is presented, with the aim of providing a consistent basis for comparison of alternative distillation column technologies. Both a static and a dynamic formulation of the model, together with a model catalogue consisting of the conventional, the heat‐integrated and the mechanical vapor recompression distillation columns are presented. The solution procedure of the model is outlined and illustrated in three case studies. One case study being a benchmark study demonstrating the size of the model and the static properties of two different heat‐integrated distillation column (HIDiC) schemes and the mechanical vapor recompression column. The second case study exemplifies the difference between a HIDiC and a conventional distillation column in the composition profiles within a multicomponent separation, whereas the last case study demonstrates the difference in available dynamic models for the HIDiC and the proposed model. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4251–4263, 2015     

Separation of methanol‐tetrahydrofuran mixtures by heteroazeotropic distillation and pervaporation

The experimental investigation of the separation of tetrahydrofuran‐methanol by heteroazeotropic‐batch‐distillation and methanol‐hexane by pervaporation is presented. In particular for this last task, four different specialty commercial membranes were tested (varying feed concentration and temperature). The “pore filling” PolyAn membranes show methanol permeance values higher than 5100 GPU (Typ M2^®); separation factor of 19; and a selectivity of about 119 (Typ M1^®). From the results, a coupling phenomenon was observed. An assessment of the temperature effect in the pervaporation process corroborates the hypothesis of the presence of a coupling phenomenon. Finally, a discussion is made on two industrial scale units for the separation of the same mixture: a system of a distillation column integrated with a decanter and stand‐alone pervaporation unit. The energetic comparison shows that when using pervaporation a large reduction of the energetic consumption compared to a conventional distillation system (up to 29%) can be obtained. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2584–2595, 2014     

Pilot‐scale studies of process intensification by cyclic distillation

Process intensification in distillation systems receives much attention with the aim of increasing both energy and separation efficiency. Several technologies have been investigated and developed, as for example: dividing‐wall column, HiGee distillation, or internal heat‐integrated distillation. Cyclic distillation is a different method based on separate phase movement—achievable with specific internals and a periodic operation mode—that leads to key advantages: increased column throughput, reduced energy requirements, and better separation performance. This article is the first to report the performance of a pilot‐scale distillation column for ethanol‐water separation, operated in a cyclic mode. A comparative study is made between a pilot‐scale cyclic distillation column and an existing industrial beer column used to concentrate ethanol. Using specially designed trays that truly allow separate phase movement, the practical operation confirmed that 2.6 times fewer trays and energy savings of about 30% are possible as compared with classic distillation. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2581–2591, 2015     

Design and control of transesterification reactive distillation with thermal coupling

In the study, the design and control strategies of a reactive distillation process with partially thermal coupling for the production of methanol and n-butyl acetate by transesterification reaction of methyl acetate and n-butanol are investigated. Since methanol and methyl acetate formed an azeotrope, the products of a reactive distillation column include n-butyl acetate and the mixture of methanol and methyl acetate, which must be separated by an additional column. Partially thermal coupling can be used to eliminate the condenser of the second column. Not only energy reduction but also better operability and controllability can be obtained for the thermally coupled reactive distillation process. Proper selection and pairing of controlled and manipulated variables chosen for three control objectives were determined by using steady-state analysis. A simple control scheme with three temperature control loops is sufficient to maintain product purities and stoichiometric balance between the reactant feeds.     

Coproduction of Ethyl Acetate and n‐Butyl Acetate by Using a Reactive Dividing‐Wall Column

The performance of the reactive distillation dividing‐wall column for coproduction of ethyl acetate and butyl acetate was experimentally studied. n‐Butanol and ethanol are raw reaction materials that react with acetic acid in the reaction zone to produce n‐butyl acetate and ethyl acetate, respectively. n‐Butyl acetate is not only a product, but also acts to remove water generated by the esterification reactions. The effects of various parameters, such as catalyst loading per stage, reflux ratio, liquid split and molar feed ratios, ethyl acetate/n‐butyl acetate purity, pressure drop, and total energy consumption, are investigated. Results show that ethanol could be completely converted and the products could be easily separated, which shows great industrial application potential in the coproduction of ethyl acetate and n‐butyl acetate.     

Feasible separation regions for distillation I: Structure

A feasible separation region is determined for only four special combinations of a saturated vapor/liquid feed and total/partial condenser or reboiler. This work addresses the construction of a feasible separation region for a general case where the feed is a mixture of vapor and liquid in equilibrium and where the column is equipped with a partial/total condenser and reboiler. The analysis reveals that the product composition sets (which are defined for various reflux and reboil ratios and a fixed number of stages in each column section) are the main elements of the feasible separation region. The application of the geometric model of the column in combination with the shape of the distillation line led to the conclusion that the feasible separation region is the union of two product composition sets for both enriching and stripping columns both with an infinite number of stages. The boundary of the feasible separation region consists of several curves related to specific types of operating modes in the column. Some of these curves create a well‐known product composition multitude, whereas other curves form a generalized distillation limit. © 2017 American Institute of Chemical Engineers AIChE J, 2017     

Thermal coupling links to liquid‐only transfer streams: An enumeration method for new FTC dividing wall columns

Novel dividing wall columns (DWCs) can be obtained by converting thermal couplings to liquid‐only transfer streams. Here, we develop a simple four‐step method to generate a complete set of DWCs containing n ? 2 dividing walls, for a given n‐component fully thermally coupled (FTC) distillation. Among the novel DWCs, some easy‐to‐operate DWCs possess the property that the vapor flow in every section of the DWC can be controlled during operation by means that are external to the column. We develop a simple method to enumerate all such easy‐to‐operate DWCs. We expect that the easy‐to‐operate DWCs can be operated close‐to‐optimality; leading to a successful industrial implementation of the n‐component (n ≥ 3) FTC distillation in the form of a DWC. As an illustration, we show figures of all easy‐to‐operate DWCs with two dividing walls for the four‐component FTC distillation. © 2015 American Institute of Chemical Engineers AIChE J, 62: 1200–1211, 2016     

Multiple Analysis in a Reactive Distillation Column for the Synthesis of tert‐Amyl Methyl Ether

tert‐Amyl methyl ether (TAME) is produced via reactive distillation. A simulation is set up and controlled on Aspen HYSYS v 8.0 for generating the highest purity of TAME. This simulation includes a plug‐flow reactor and a reactive distillation column. Emphasis was put on finding the optimal operating conditions of the reactive distillation column in order to get the maximum purity of TAME. The operational parameters were reflux ratio, number of reactive stages in the distillation column, and condenser pressure. The results indicated the optimal reflux ratio and condenser pressure which could be adapted to industrial scale.     

Three‐phase fluidized distillation

Separation efficiency in distillation operations can be improved by modifying the characteristics of the dispersions formed on the trays. The present work reports on the hydrodynamic and mass transfer characteristics of liquid‐solid‐vapour dispersions formed on sieve trays without downcomers of a distillation column operating under total reflux conditions. Murphree efficiency and the operating limits of distillation using the ethanol‐n‐butanol system are analyzed for a large range of vapour velocities and liquid mixture compositions, utilising wettable PVC particles and non‐wettable silicone, PE, and Teflonr? particles. It was verified that wettable particles show a drastic reduction in the upper operating limit of vapour velocity, but this does not occur for non‐wettable particles. Tray efficiency can be increased when non‐wettable particles are used, mainly for high vapour velocity operations.     

Design and Control of Ionic Liquid‐Catalyzed Reactive Distillation for n‐Butyl Acetate Production

A simulation study of n‐butyl acetate production with the [Hpy][HSO₄] ionic liquid catalyst was performed. Due to the lack of phase equilibrium data, the binary interaction parameters of the NRTL model for ionic liquid and reactive species were calculated by the COSMO‐RS technique. A reactive distillation process with recycled ionic liquid stream was proposed, and the column configuration was optimized by minimization of the total annual capital. The novel process is considerably efficient and economic compared to the traditional reactive distillation process of nonionic liquids. With the steady‐state parameters, a plant‐wide control structure was further developed to evaluate the robustness of the control system by exerting the disturbances of feed flow rate and feed composition. Dynamic simulation results suggest that the control scheme with a composition controller is timely and effective.     

Enzymatic catalyzed reactive dividing wall column: Experiments and model validation

A novel process for the integration of chemical reaction and product separation is proposed: the enzymatic catalyzed reactive dividing wall column (eRDWC). The eRDWC combines the highly integrated and complex reactive dividing wall column (RDWC) with the use of a very selective enzymatic catalyst. This apparatus enables the simultaneous production and separation of up to 4 pure product streams. Comprehensive experiments with the reference system of a hexanol and butyl acetate transesterification in a DN 65 pilot scale column show the feasibility of stable steady state operations for this process. A rigorous model for the plant design of an eRDWC wall column is developed. The reaction kinetics and vapor‐liquid‐equilibria for the reference system are measured and implemented in the model. The model is successfully validated using the acquired experimental data. The application of enzymes in continuous reactive distillation processes has the potential to increase the selectivity at milder process conditions. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2198–2211, 2017     

Systematic design of an extractive distillation for maximum‐boiling azeotropes with heavy entrainers

Extractive distillation is one of the most attractive approaches for separating azeotropic mixtures. Few contributions have been reported to design an extractive distillation for separating maximum‐boiling azeotropes and no systematic approaches for entrainer screening have been presented. A systematic approach to design of two‐column extractive distillation for separating azeotropes with heavy entrainers has been proposed. A thermodynamic feasibility analysis for azeotropes with potential heavy entrainers was first conducted. Then, five important properties are selected for entrainer evaluation. Fuzzy logic and develop membership functions to calculate attribute values of selected properties have been used. An overall indicator for entrainer evaluation is proposed and a ranking list is generated. Finally, the top five entrainers from the ranking list have been selected and use process optimization techniques to further evaluate selected entrainers and generate an optimal design. The capability of the proposed method is illustrated using the separation of acetone–chloroform azeotropes with five potential entrainers. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3898–3910, 2015     

Experimental validation of hybrid distillation‐vapor permeation process for energy efficient ethanol–water separation

BACKGROUND: The energy demand of distillation‐based systems for ethanol recovery and dehydration can be significant, particularly for dilute solutions. An alternative separation process integrating vapor stripping with a vapor compression step and a vapor permeation membrane separation step, termed membrane assisted vapor stripping (MAVS), has been proposed. The hydrophilic membrane separates the ethanol–water vapor into water‐rich permeate and ethanol‐enriched retentate vapor streams from which latent and sensible heat can be recovered. The objective of this work was to demonstrate experimentally the performance of a MAVS system and to compare the observed performance with chemical process simulation results using a 5 wt% ethanol aqueous feed stream as the benchmark. RESULTS: Performance of the steam stripping column alone was consistent with chemical process simulations of a stripping tower with six stages of vapor liquid equilibria (VLE). The overhead vapor from the stripper contained about 40 wt% ethanol and required 6.0 MJ of fuel‐equivalent energy per kg of ethanol recovered in the concentrate. Introduction of the vapor compressor and membrane separation unit and recovery of heat from both membrane permeate and retentate streams resulted in a retentate ethanol concentrate containing ca 80 wt% ethanol, but requiring only 2.2 MJ fuel kg^?1 ethanol, significantly less than steam stripping alone. CONCLUSION: Performance of the experimental unit with a 5 wt% ethanol feed liquid corroborated chemical process simulation predictions for the energy requirement of the MAVS system, demonstrating a 63% reduction in the fuel‐equivalent energy requirement for MAVS compared with conventional steam stripping or distillation. Published 2009 by John Wiley & Sons, Ltd.     

Feasible separation regions for distillation II: A generalized distillation limit

The boundary of the feasible separation region consists of several curves that are related to specific types of operating modes of the column. Some of these curves create a well‐known product composition multitude, whereas other curves form a generalized distillation limit. The generalized distillation limit demarcates the sloppy splits (i.e., separations in which the composition of at least one product lies inside the composition space) from regions not accessible by distillation and depends on the thermodynamic state of the feed (a mixture of vapor and liquid in equilibrium or saturated vapor/liquid) and column equipment (total/partial condenser and total/partial reboiler). The mathematical equations describing the generalized distillation limit are obtained based on the relationships between the curves (which form the generalized distillation limit) and specific types of operating modes of the column as well as the material balances for the enriching and stripping columns. Furthermore, the vapor and liquid pinch‐point curves, which go through the feed composition point, are not dependent on the thermodynamic state of the feed and column equipment. In addition, an algorithm for determining the generalized distillation limit is obtained. © 2017 American Institute of Chemical Engineers AIChE J, 2017     

Concentration of Natural Vitamin E Using a Continuous Countercurrent Supercritical CO2 Extraction‐Distillation Dual Column

A continuous countercurrent supercritical CO₂ extraction‐distillation dual‐column process was developed to extract and concentrate natural vitamin E (VE) from soybean oil deodorizer distillate (SODD). The experimental results demonstrated that process parameters such as extraction pressure, temperature, and solvent‐to‐feed ratio significantly impacted on the extraction efficiency of natural VE. A new five‐parameter mass transfer model for the continuous countercurrent supercritical CO₂ extraction‐distillation dual‐column process was presented based on the Penetration and Double‐Film theories. The calculated values of the mathematical model agreed well with the experimental data, with absolute average relative deviation values of less than 25 %.     

Effective separation of aromatic hydrocarbons by pyridine‐based deep eutectic solvents

Many promising qualities of deep‐eutectic solvents made them suitable solvents in separation process. In this work, the pyridine‐based deep eutectic solvents were designed and synthesized with N‐ethylpyridinium bromide and two HBDs (N‐formyl morpholine and levulinic acid). Two ternary systems, benzene + cyclohexane + DES and toluene + n‐heptane + DES, were studied by the liquid‐liquid extraction. The effect of different HBDs, extraction time, volume ratio of DES to system solution, and the initial concentration of aromatic were studied. The DES with N‐formyl morpholine showed better separation performance than that with levulinic acid. The liquid‐liquid extraction equilibrium could be obtained in 10 minutes. The volume ratio of DES to system solution was set as 1:1. Both DESs showed their best separation performance at low temperatures (20°C) and low aromatic concentration system. For the benzene + cyclohexane system, the distribution coefficient of benzene was 1.733 and the selectivity was 23.8 at 20°C. For the toluene + n‐heptane system, the distribution coefficient of toluene was 0.853 and the selectivity was 40.7. Tie‐lines for two ternary systems were obtained, and the Othmer‐Tobias correlation was used to check the reliability of the obtained liquid‐liquid extraction experimental data. The experimental LLE data were correlated using the NRTL model and the calculated data correlated significantly with the experimental data.     

Distillation technology – still young and full of breakthrough opportunities

Throughout history, distillation has been the most widespread separation method. However, despite its simplicity and flexibility, distillation still remains very energy inefficient. Novel distillation concepts based on process intensification, can deliver major benefits, not just in terms of significantly lower energy use, but also in reducing capital investment and improving eco‐efficiency. While very likely to remain the separation technology of choice for the next decades, there is no doubt that distillation technology needs to make radical changes in order to meet the demands of the energy‐conscious modern society. This article aims to show that in spite of its long age, distillation technology is still young and full of breakthrough opportunities. Moreover, it provides a broad overview of the recent developments in distillation based on process intensification principles, for example heat pump assisted distillation (e.g. vapor compression or compression–resorption), heat‐integrated distillation column, membrane distillation, HiGee distillation, cyclic distillation, thermally coupled distillation systems (Petlyuk), dividing‐wall column, and reactive distillation. These developments as well as the future perspectives of distillation are discussed in the context of changes towards a more energy efficient and sustainable chemical process industry. Several key examples are also included to illustrate the astonishing potential of these new distillation concepts to significantly reduce the capital and operating cost at industrial scale. © 2013 Society of Chemical Industry     

Molecular Simulation‐Assisted Solvent Selection for Separation of 1,2,4‐Trimethylbenzene

Extractive distillation is an alternative for processes where normal distillation is difficult, such as separation of close‐boiling mixtures, but solvent selection for distillation is laborious, and its selection pool is narrow. An innovative selection process using molecular simulation is proposed, and the performance of the selected solvent, 1,2,4‐trichlorobenzene, for the separation of 1,2,4‐trimethylbenzene from a C9 mixture is reviewed. The proposed process requires less investment and leads to lower operating expenses than the conventional two‐column process. The computed vapor‐liquid equilibrium determined from the molecular simulation is close to the HYSYS estimation in two ternary systems.     

Investigation of flow parameters and efficiency of mixture separation on a structured packing

Results of experimental study of the effect of initial maldistribution of structured packing irrigation on efficiency of binary mixture separation are presented in this article. The studies were carried out in the experimental distillation column with the diameter of 0.9 m using the R114 and R21 freon mixture. Experiments were performed on the structured Mellapak 350.Y packing of stainless steel 316L, containing 19 layers with the total height of 4.016 m at the ratio of mole liquid and vapor flow rates L/V = 1 and 1.7, respectively, and the pressure in the upper part of the column p_top = 3 bars. Nonuniformity at the packing inlet was generated via the blocking of some holes in the liquid distributor. Here, we present some results on efficiency of mixture separation, pressure drop on the packing, distribution of local liquid flow rate under the packing over the cross‐section and on the column wall within the range of vapor loading factor (0.69 < F_v < 1.61 Pa^0.5), as well as experimental data on distribution of local concentration of the low‐boiling component over the cross‐section and along the height of the structured packing. It is found out that significant maldistribution of mixture concentration and liquid flow rate over the cross‐section slightly changes along the height in the lower part of the column at a change in the degree of packing irrigation nonuniformity at the inlet. It is shown that efficiency of mixture separation depends considerably on the value of parameter L/V, vapor flow factor F_v, and size of the zone underirrigated by liquid at the inlet. In the studied range of liquid and vapor flow rates, the relative pressure drop on the packing does not depend on the ratio of liquid and vapor flow rates L/V and degree of irrigation maldistribution. © 2013 American Institute of Chemical Engineers AIChE J 60: 690–705, 2014