Pervaporation performance and Transport phenomenon of PVA blend membranes for the separation of THF/water azeotropic mixtures

Summary Dense polymer membranes were made by mixing aqueous solutions of hydrophilic polymers poly(vinyl alcohol) (PVA) and polyethyleneimine (PEI) in different ratios for investigating the separation of Tetrahydrofuran (THF)/water azeotropic mixtures by pervaporation (PV). In order to gain a more detailed picture of the molecular transport phenomenon, we have performed sorption gravimetric experiments at 30 °C to compute diffusion, swelling, sorption and permeability coefficients of PVA/PEI membranes in the presence of THF and water. The membranes were found to have good potential for breaking the azeotrope of THF at 6% concentration of water. An increase in PVA content in the blend caused a reduction in the flux and an increase in selectivity. Among the blends tested in the study, the 5:1 PVA/PEI blend membrane showed the highest separation factor of 181.5, exhibited a flux of 1.28 kg/m²h for THF respectively at azeotropic feed composition.     

Preparation and characterization of CMCS/PVA blend membranes and its sorption and pervaporation performance (I)

Novel pervaporation (PV) membranes for ethanol dehydration were prepared by blend poly(vinyl alcohol) (PVA) and carboxymethyl chitosan (CMCS), followed by the crosslinking reaction with glutaraldehyde; the structure and miscibility of the blend membranes were characterized by Fourier transform infrared, X‐ray diffraction, and differential scanning calorimetry; the results indicated that the blends were miscible. The effect of feed concentration, operation temperature, crosslinking agent content, etc. on sorption performance and PV performance of the blend membrane is investigated. The membrane of CMCS/PVA blend ratio of 8 : 2 exhibited a high separation factor of 2959 with a reasonably high water flux value of 0.14 kg m^?2h^?1 at the azeotropic feed composition (95 wt % of ethanol) at a temperature of 45°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Energy-Efficient Process with a Decanter to Separate Toluene-Methanol-Water Ternary Azeotropic Mixtures

An extractive distillation process with two columns and a decanter was proposed to separate ternary toluene-methanol-water azeotropic mixtures in a previous study. Based on this process, six processes were established to explore further energy-efficient schemes to separate the ternary azeotropic system. The optimal parameters of the process were determined in terms of the minimum total annual cost (TAC). The processes with heat integration perform better than those with a side stream or thermal coupling in terms of energy savings and TAC reduction. A process in which both the feed stream of the extractive distillation column and the entrainer recovery column are preheated by the entrainer recycle stream can reduce energy consumption by up to 27.69 % and TAC by 21.36 %.     

Flowsheet synthesis for the extractive distillation of azeotropic mixtures in systems consisting of columns with partially coupled heat and material flows

The earlier proposed flowsheet synthesis methods for the distillation of zeotropic mixtures and the extractive distillation of ternary mixtures using two-product columns is used to develop a flowsheet synthesis method for the extractive distillation with partially coupled heat and material flows. The distillation of azeotropic mixtures with a complex liquid-vapor equilibrium diagram is used to illustrate the feasibility analysis of the flowsheets synthesized by the developed method.     

Control structure selection of increased-pressure extractive distillation process for DMC-MeOH azeotropic mixture

Producing dimethyl carbonate (DMC) as a green chemical with the desired purity is important in the industry. Although studies on the steady-state design of energy-efficient extractive distillation processes are important for the purification of DMC-methanol (DMC-MeOH) azeotropic mixtures, the dynamic controllability of these processes is also critical in the case of feed condition changes, and it should be investigated carefully. Results of the limited studies in the literature show that changing the operating pressures in extractive distillation processes might have different effects on the dynamic controllability of different systems. Thus, in this study, alternative control strategies are developed for a recently proposed increased-pressure extractive distillation process to separate DMC-MeOH mixture. All control structures are designed using inferential temperature controllers, which have a general acceptance in industrial applications. Effects of different ratio controllers are investigated by evaluating the dynamic responses of control structures for disturbances in feed flowrate and composition. Two metrics including integral absolute error and steady-state deviation of purities are used in the evaluation of alternatives. Results of dynamic simulations show that a control structure including reflux ratio controller is not a suitable strategy for this process. It is demonstrated that a control structure including reflux to feed ratio controller for both distillation columns is necessary for the robust and efficient control of a pressure-increased extractive distillation process. These efficient dynamic results support the economic advantage of increased-pressure extractive distillation process separating DMC-MeOH azeotropic mixtures.     

Zeolite 4A-Incorporated Polymeric Membranes for Pervaporation Separation of Methanol–Methyl Acetate Mixtures

Zeolite 4A-incorporated poly(vinyl alcohol)/poly(vinyl pyrrolidone) (PVA/PVP) membranes were prepared for pervaporation separation of methanol/methyl acetate mixtures. These membranes were characterized by Infrared spectroscopy, X-ray diffraction and Scanning electron microscopy. The results showed that crystallinity of the membrane decreased with the increase of zeolite 4A content. The effect of zeolite loading, feed composition and temperature on the membrane separation performance were discussed in detail. With the increase of zeolite 4A content, permeation flux increased continuously, but separation factor first increased and then decreased. The addition of 2.5 wt% zeolite 4A in the polymer membrane improved the separation factor from 12.9 (for PVA/PVP membrane) to the maximum value of 34.4 for 20 wt% methanol in feed at 45 °C. The separation factor decreased with increasing feed temperature, however, the flux increased with increasing feed temperature. Zeolite 4A-incorporated PVA/PVP membranes provide an effective method for the separation of methanol/methyl acetate azeotropic mixtures.     

A selective organosilica membrane for ethyl acetate dehydration by pervaporation

Organosilica bis(triethoxysilyl) ethane (BTESE) membranes were explored for pervaporation dehydration of binary and ternary mixtures of ethyl acetate (EA) by undiluted sol coating combined with flash firing. Three BTESE membranes (M1, M2, and M3) were fabricated on macroporous supports by varying BTESE concentrations (0.5, 2.5, and 5 wt% BTESE, respectively) in polymer sols. The membranes were characterized by DLS, SEM, FTIR, XRD, contact angle, AFM, and pervaporation performance to discuss the effect of the BTESE contents in the polymer sol on the formation and dehydration performance of resulting organosilica membranes. It was found that 5 wt% loading of BTESE led to a highly selective membrane for dehydration of EA/H₂O mixture. Among the synthesized membranes, M3 delivered flux of 0.84 ± 0.05 kg.m⁻².h⁻¹ with a selectivity of >10,000 for EA/H₂O mixture (98/2 wt%) at 60°C. The time course of pervaporation dehydration for the EA/H₂O mixture (95/5 wt%) confirms the stability of BTESE membrane in the investigated time period of 120 h. Further, the membrane exhibited excellent selectivity larger than 10,000 for separation of ternary mixtures (90/2/8 wt%) of ethyl acetate/ethanol/water and n-propyl acetate/isopropanol/water respectively, the composition of which is similar to the top product of the distillation column used in the industrial esterification process. The best separation performance and excellent acid stability of BTESE membranes in this study suggest that the simple synthesis protocol of undiluted sol coating and flash firing will provide a cost-effective, quick, and efficient synthesis route for practical membrane based applications.     

Pervaporation dehydration of ethyl acetate aqueous solution using the doubly modified polyvinyl alcohol (PVA) composite membrane

Polyvinyl alcohol–tetraethoxysilane–perfluorosulfonic acid (PVA–TEOS–PFSA) hybrid membrane was prepared by sol–gel method through PVA being modified doubly by PFSA and TEOS. With polyacrylonitrile (PAN) ultrafiltration membrane as a substrate membrane, PVA–TEOS–PFSA/PAN composite membrane was fabricated by dip-coating method for pervaporation (PV) dehydration of ethyl acetate (EAc) aqueous solution. The hybrid membrane was characterized by swelling degree, static contact angle, Fourier transform infrared spectra and scanning electron microscope. Effects of PFSA and TEOS contents in coating solution on PV performance of composite membrane were investigated, respectively. With increasing PFSA content, the permeation flux of composite membrane increased, while the separation factor decreased. Just the opposite, the increase of TEOS content resulted in the decrease in permeation flux and the increase in separation factor. In addition, the PV performances of composite membranes were also investigated at different feed temperatures and water concentrations in feed, respectively. The PVA–TEOS–PFSA/PAN composite membrane, which was prepared from coating with PVA/PFSA mass ratio of 80/20 and TEOS content of 20 wt%, exhibited the permeation flux of 347.9 g m^?2 h^?1 and the separation factor of 2218 for PV dehydration of 2 wt% water of EAc solution at 40 °C.     

Economic evaluation of energy saving alternatives in extractive distillation process

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

Separation of Acetic Acid/Water Mixtures by Pervaporation through Poly(Vinyl Alcohol)–Sodium Alginate Blend Membranes

Abstract

Dense pervaporation (PV) membranes were prepared by blending hydrophilic polymers, poly(vinyl alcohol) (PVA), and sodium alginate (SA), which were then crosslinked with glutaraldehyde (GA) for the separation of acetic acid/water mixtures. These membranes (PVA‐SA) were characterized for morphology, intermolecular interactions, thermal stability, and physico‐mechanical properties using XRD, FTIR, TGA and tensile testing respectively. The effect of experimental parameters such as feed composition and permeate pressure on separation performance of the crosslinked membranes was determined. Sorption studies and porosity measurement were carried out to evaluate the extent of interaction and degree of swelling of the polyion membranes, in acetic acid and water as well as in mixtures of acetic acid and water. Further the results were compared with the commercial membrane (Sulzer pervap 2205). The membrane appears to have a good potential for dehydrating 90 wt% acetic acid with a reasonably high selectivity of 21.5 and a substantial water flux of 0.24 kg/m²/h/10 µm. Separation factor was found to improve with decreasing feed water concentration whereas the corresponding flux decreased. Higher permeate pressures caused a reduction in both flux and selectivity.     

新型PVA/PA复合膜的运行工艺对渗透汽化性能的影响

研究了聚乙烯醇（PVA）/聚酰胺（PA）复合膜渗透汽化（PV）分离异丙醇（IPA）/水混合物时运行工艺的影响,模拟了渗透通量（J）预测方程。结果表明,PVA/PA复合膜在料液中w（IPA）%在0～95%范围内或在25℃～100℃的操作温度范围获得的渗透液中IPA含量[w′（IPA）]都小于1%,J随料液中w（IPA）%的下降或操作温度的提高而增加。分离性能预测方程的拟合结果与试验数据有良好一致性。在室温条件下,经过90 d的间歇运行或经过120 d的长期贮存后,PVA/PA复合膜的分离性能稳定,在IPA/水混合物的共沸温度80.4℃运行时的J为73.1 g/m^2·h,渗透液中的水含量[w′（H2O）]都大于99.5%,展示了其在食品、生物、制药和化学等工业中将具有良好的应用前景。     

Comparative behavior of PVA/PAN and PVA/PES composite pervaporation membranes in the pervaporative dehydration of caprolactam

Flat‐sheet composite membranes were developed by the traditional phase inversion technique using poly;(vinyl alcohol) (PVA). PVA composite pervaporation (PV) membranes were prepared with crosslinked PVA selective layer and porous polyacrylonitrile (PAN) and polyether sulfone (PES) substrate layer material as supports for separating heat sensitivity substance ε‐caprolactam (CPL) from CPL/water mixtures. Glutaraldehyde was used as crosslinking agent. The effect of the composition of glutaraldehyde on membrane stability and structure were investigated. The operating parameters, such as feed concentration and operating temperature, remarkably affected PV performance of the composite membranes. The composite membranes with PVA casted on PAN (PVA/PAN) showed superior PV performance than that casted on PES (PVA/PES). This study has also shown that the type of porous support plays an important role in the PV performance. As a result, this work has presented the information needed of the behavior of PV membranes for dehydration applications of industrial caprolactam. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 4005–4011, 2007     

碳酸二甲酯提纯方法的研究进展

综述了碳酸二甲酯提纯方法的最新研究进展,分别介绍了工业级和电池级碳酸二甲酯的提纯方法。在工业级碳酸二甲酯的提纯方法中,详细介绍了碳酸二甲酯-甲醇二元共沸物的分离方法,在各种分离方法中,膜分离和吸附分离能耗低、效率高,属于新型的分离方法;加压精馏、共沸精馏和萃取精馏具有投资较小、操作方便、产品纯度高等优势,具有较高的工业应用价值。在电池级碳酸二甲酯的提纯方法中,冷却结晶法具有设备简单、操作方便、节能的优点,比精馏法更具优势。     

乙酸乙酯的精制方法

介绍了几种乙酸乙酯的精制方法,并分析了它们的优缺点。分别介绍了用乙酸和乙醇酯化反应合成乙酸乙酯,通常可采用传统的四塔连续工艺过程;添加促进剂萃取精制过程;加饱和盐水萃取脱水工艺过程;加有机溶剂萃取分离过程;加恒沸剂共沸蒸馏和乙酸萃取反应精馏过程。乙醛缩合法生产乙酸乙酯的三塔连续精馏过程以及乙烯与乙酸气相催化反应的加水精制工艺过程。     

Synthesis of flowsheets for extractive distillation of azeotropic mixtures

An algorithm for synthesizing extractive distillation flowsheets for separation of complex ternary azeotropic mixtures with different vapor-liquid equilibrium patterns is proposed.Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 1, 2005, pp. 19–26.Original Russian Text Copyright © 2005 by Ivanova, Timoshenko, Timofeev.     

Effects of Ultrasonic Waves on Vapor-Liquid Equilibrium of an Azeotropic Mixture

Abstract

Azeotropic and extractive distillation techniques used to separate azeotropic mixtures are among the most challenging separation processes in the chemical industry. In this work, an innovative distillation technique which employed ultrasonic waves was proposed to intensify the conventional multi-column azeotropic distillation method into a single-column alternative. The effects of ultrasonic intensity on the vapor-liquid equilibrium (VLE) of methyl-tert-butyl-ether (MTBE)-methanol was investigated at 50, 100, 200, and 250 W/A·cm² and at a fixed frequency of 40 kHz. Studies were also done to examine the effects of ultrasonic frequency on the VLE data at 25 and 68 kHz frequencies. It was found that ultrasonic waves at 50 W/A·cm² intensity and 25 kHz frequency gave the highest relative volatility (α) at 2.654 and completely eliminated the MTBE-methanol azeotrope, thereby allowing highly pure MTBE to be recovered in just a single distillation column. The results revealed that ultrasonic waves had the potential to favorably manipulate α, and hence, the VLE of an azeotropic mixture.     

Pervaporation separation of binary and ternary mixtures with polydimethylsiloxane membranes

This study dealt with the separation of binary water–phenol and water–methanol mixtures and ternary water–phenol–methanol mixtures by pervaporation (PV) with polydimethylsiloxane (PDMS) membranes. The effects of the operating conditions (feed temperature, feed concentration, and feed flow rate) on the separation performance for binary mixtures were investigated. An increase in temperature or concentration increased the total permeation flux and decreased the organic separation factor. In other words, an increase in the temperature or feed organic concentration increased the water flux more significantly than the organic compound flux, which resulted in a separation factor reduction. Also, an increase in the feed flow rate increased the total flux and separation factor because the boundary layer effects diminished. The vapor–liquid equilibrium separation factor (α_VLE) and pervaporation separation factor (α_PV) values for the PDMS membrane were calculated, and this showed that α_PV for the water–phenol mixture was greater than α_VLE. This means that the membrane was highly efficient for the PV separation of phenol from dilute aqueous solutions relative to the separation of methanol. This was due to the fact that phenol has a higher solubility parameter than methanol in silicone membranes. To study the effect of a third component on membrane performance, PV experiments were also carried out with water–phenol–methanol mixtures. The results for total permeation flux and the phenol separation factor for PDMS membranes in contact with water–phenol–methanol ternary mixtures are similar to those in contact with water–phenol binary mixtures. The phenol separation factor of the membrane in contact with the ternary mixture was slightly lower than that in contact with the binary mixture. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Heterogeneous extractive batch distillation of chloroform-methanol-water: Feasibility and experiments

A novel heterogeneous extractive distillation process is considered for separating the azeotropic mixture chloroform-methanol in a batch rectifying column, including for the first time an experimental validation of the process. Heterogeneous heavy entrainer water is selected inducing an unstable ternary heteroazeotrope and a saddle binary heteroazeotrope with chloroform (ternary diagram class 2.1-2b). Unlike the well-known heterogeneous azeotropic distillation process and thanks to continuous water feeding at the column top, the saddle binary heteroazeotrope chloroform-water is obtained at the column top, condensed and further split into the liquid-liquid decanter where the chloroform-rich phase is drawn as distillate. First, feasibility analysis is carried out by using a simplified differential model in the extractive section for determining the proper range of the entrainer flowrate and the reflux ratio. The operating conditions and reflux policy are validated by rigorous simulation with ProSim Batch Column^® where technical features of a bench scale distillation column have been described. Six reproducible experiments are run in the bench scale column matching the simulated operating conditions with two sequentially increasing reflux ratio values. Simulation and experiments agree well. With an average molar purity higher than 99%, more than 85% of recovery yield was obtained for chloroform and methanol.     

A review of ternary azeotropic mixtures advanced separation strategies

In most multi-component systems, the predominant non-ideality occurs which lead to the occurrence of an azeotrope. The ternary systems classification and study are summarized in first part of this review. The next part covers thermodynamic knowledge of residue curve maps, univolatility and unidistribution curves. A feasibility criterion based on thermodynamic properties of ternary diagram is presented, they are considered as powerful tool for the flow-sheet development and conceptual design. Separation of azeotropic mixtures and close boiling mixtures require non-conventional distillation processes, among which the leading processes are pressure-swing distillation if the composition of the azeotrope changes significantly with pressure, azeotropic distillation, extractive distillation, reactive distillation, and salt-effect distillation. The final section provides an overview of concepts, history, and recent strategies in these non-conventional distillations.     

A polyvinyl alcohol-based mixed matrix membrane with uniformly distributed Schiff base network-1 for ethanol dehydration

In this study, Schiff base network (SNW)-1 nanoparticles with high hydrophilicity and large specific surface area were used to prepare polyvinyl alcohol (PVA)-based mixed matrix membranes (MMMs), which were evaluated for ethanol dehydration. Because of the low difference of density between SNW-1 and PVA, the as-prepared nanoparticles can be uniformly distributed into the PVA active layer. The effects of SNW-1 loading, feed temperature, and water concentration on pervaporation (PV) performance were further studied. The results showed the MMM with 10 wt% of SNW-1 loading exhibited a separation factor of 1,501 and a permeation flux of 187 g m⁻² h⁻¹ for feeding 95 wt% ethanol/water binary solution at 75°C. Overall, the SNW-1/PVA MMMs showed great prospect in ethanol dehydration via PV.