n-Butyl acrylate production by esterification of acrylic acid with n-butanol combined with pervaporation

In this study, the esterification reaction of acrylic acid and n-butanol to produce n-butyl acrylate and water was studied using the pervaporation–esterification hybrid process to perform the separation and reaction simultaneously to increase the conversion of limiting reactant. A Pervap 2201 polymeric membrane was used to separate water and also to shift the equilibrium. The Pervap 2201 membrane showed high selectivity to water in the n-butanol, acrylic acid, n-butyl acrylate, and water reaction system. The effects of temperature, the initial molar ratio of n-butanol to acrylic acid, catalyst loading, and the ratio of membrane area to reaction volume (S/V) were studied. The maximum conversion of acrylic acid was calculated as 96.3% at a temperature of 358 K, a molar ratio of 8, with a catalyst loading of 10 g/L and an S/V ratio of 70 m⁻¹.     

A review on removal of sulfur components from gasoline by pervaporation

Desulfurization of gasoline has gained growing importance because of tighter limits of less than 10 ppm sulfur in gasoline in recent regulations. On the other hand, preserving octane rating in gasoline is the most concern subject of the manufacturers. This review focuses on the desulfurization of gasoline by means of pervaporation (PV) process. The process as a new technology has drawn increasing attention and provided an efficient approach for eco-friend sulfur removal in petrochemical industries due to its high selectivity, feasible economics, and safety. Theoretical aspects in selection of materials for the applied membranes and their modifications are investigated. The various parameters including the type and concentrations of sulfur and hydrocarbon species, feed temperature, feed flow rate, and permeate pressure, which influence the performance of PV are discussed.     

Manipulation of confined structure in alcohol-permselective pervaporation membranes

Alcohol-permselectivity pervaporation has been arousing increasingly more attention in bioalcohol production due to the advantages of environmental friendliness, lowenergy consumption and easy couplingwith fermentation process. With the intrinsic feature of larger molecules preferentially permeating and the consequent inferiority in selective diffusion, the development of alcohol-permselectivemembrane is relatively retarded compared with water-permselective membrane. This review presents the prevalent membrane materials utilized for alcohol-permselective pervaporation and emphatically expatiates the representative and important developments in the past five years fromthe aspect of tuning confined structure in membranes. In particular, the diverse structure tuningmethods are described with the classifications of physical structure and chemical structure. The corresponding structure-performance relationships in alcohol-permselective pervaporationmembranes are also analyzed to identify the objective of structure optimization. Furthermore, the tentative perspective on the possible future directions of alcohol-permselective pervaporation membrane is briefly presented.     

Plasticization of chitosan membrane for pervaporation of aqueous ethanol solution

The process of pervaporation in which two components diffuse through a nonporous polymer membrane was modelled when one of the penetrants can exert a plasticization action to the membrane material. Thereat a phenomenological model was employed for describing the plasticization effect on the diffusivities for penetrants in the membrane. The sorption equilibria and permeation fluxes for aqueous ethanol solutions in a chitosan membrane were measured, and the permeation fluxes for water were compared with those predicted by the proposed model. The concentration of sorbed water was linear with its weight fraction (x₄) in the feed solution, whereas the permeation flux of water was. affected by the plasticization action of sorbed water to the polymer. This plasticization effect on the diffusion process can be simulated in terms of the proposed phenomenological model.     

Development of polybenzoxazine membranes for ethanol–water separation via pervaporation

Polybenzoxazine membranes have been successfully synthesized from bisphenol-A, formaldehyde, and three different types of diamines: hexa-methylenediamine (hda), tetraethylenepentamine (tepa), and tetraethylenetriamine (teta) via a facile “quasi-solventless” method. To study the possibility of using polybenzoxazine membranes in a pervaporation system for ethanol–water separation, the sorption and swelling behaviors of these membranes were investigated. When hda was used as a reactant, the resulting polybenzoxazine membranes showed the best service time and interestingly only water permeated the membranes under the studied operation conditions. The total permeation flux was found to be 1.52 kg/m²h and the separation factor was higher than 10,000. Additionally, an increased permeation flux was achieved by raising the temperature of the feed solution and decreasing the membrane thickness. The optimum conditions for this study were 70 °C for the feed mixtures when a 200 μm thick was used.     

Experimental study on physical properties and pervaporation performances of polyimide membranes

Five kinds of polyimide membranes have been synthesized from two dianhydrides (including pyromellitic dianhydride (PMDA) and 3, 3^′4, 4^′-benzophenonetetracarboxylic dianhydride (BTDA)) and three diamines (including 4,4^′-diaminodiphenylether (ODA), 4,4^′-diaminodiphenylmethane (MDA) and phenylenediamine (PDA)) via a two-step method, and the properties of polyimide membranes have been characterized by experimental techniques. The permeation experiments of water/ethanol mixtures through the polyimide membranes were carried out at 318, 328, 338 and 348 K. All polyimide membranes in this paper are water selectivity, and the flux of mixtures through MDA-based polyimide membranes is higher than that of solvents through PDA-based polyimide membranes with the same diahydrides, while the separation factor exhibits the opposite variation order at the same temperature. The total flux and the partial water flux through all the membranes increase with the operating temperature rising, and the relationships between the flux and temperature can be described by Arrhenius equation. According to the Arrhenius equation, the active energies of water/ethanol in PMDA-ODA, PMDA-MDA, BTDA-PDA, BTDA-ODA and BTDA-MDA membranes are 35.1, 52.6, 16.4, 19.8 and 27.1 kJ/mol, respectively, and those for partial water flux in PMDA-ODA, PMDA-MDA, BTDA-ODA and BTDA-MDA are 36.1, 46.8, 19.9 and 27.9 kJ/mol, respectively. The separation factors of mixtures in the polyimide membranes but no PMDA-MDA show the trend of increase with the operating temperature. The partial flux of ethanol increases while the separation factor of mixtures in PMDA-MDA decreases with the operating temperature, and the activation energy for partial ethanol flux in PMDA-MDA is 75.2 kJ/mol. In addition, pervaporation performances were attempted to correlate independently with the fractional free volume (FFV) and mean interchain distance (d-spacing) of polymers. It is shown that lnJ increases with d-spacing, while there is no clear relationship between the flux and FFV.     

Permselectivities of aromatic polyamide membranes for aqueous alcohol mixtures in pervaporation

The separation of water/alcohol mixtures was carried out using a series of fluorine-containing aromatic polyamide membranes. Aromatic polyamides were prepared by direct polycondensation of fluorine-containing diamine (2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, BAPPH) and various aromatic diacids. The separation factor toward water increased when the feed ethanol concentration was increased. The solubility of ethanol in aromatic polyamide membrane is higher than that of the water, but the diffusivity of water across the membrane is higher than that of alcohols. A separation factor of 83 and a permeation rate of 262 g/m²h with a 90 wt% feed ethanol concentration at 25 °C was obtained.     

Modelling of pervaporation: Parameter estimation and model development

Pervaporation is proved to be a commercially viable membrane separation process by this time. However, to become a widely applied process in the industry it is of crucial importance to develop membrane properties, process and module design as well as proper modelling in professional software environment. In this work a pervaporation model improvement of the basic solution–diffusion model (Rautenbach et al., 1990) is recommended and tested on experimental data. The reason behind this improvement is that the transport coefficient cannot be considered as constant assumed in the basic model in a wide concentration range. The change of the transport coefficient is considered as an exponential function of the composition of permeating compound. This exponential dependency is assumed by the authors after investigating the shape of the flux curves measured in a wider feed concentration range. The accuracy of this improved model is experimentally tested with the pervaporation of isobutanol–water, n-butanol–water, and ethanol–water mixtures on commercial hydrophilic composite membranes. This model improvement gives accurate and reliable data for a wide range of feed concentration proving that the assumption of practically constant transport coefficient cannot be applied. Therefore the use of this improved model in professional flowsheeting software packages is more reliable and reasonable than the application of the basic model for the design and operation of pervaporation, or a more effective hybrid separation system including pervaporation.     

Fabrication of graphene oxide composite membranes and their application for pervaporation dehydration of butanol

As a new kind of 2D nanomaterials, graphene oxide (GO) with 2–4 layers was fabricated via a modified Hummers method and used for the preparation of pervaporation (PV) membranes. Such GO membranes were prepared via a facile vacuum-assisted method on anodic aluminium oxide disks and applied for the dehydration of butanol. To obtain GO membranes with high performance, effects of pre-treatments, including high-speed centrifugal treat-ment of GO dispersion and thermal treatment of GO membranes, were investigated. In addition, effects of oper-ation conditions on the performance of GO membranes in the PV process and the stability of GO membranes were also studied. It is of benefit to improve the selectivity of GO membrane by pre-treatment that centrifuges the GO dispersion with 10000 r·min?1 for 40 min, which could purify the GO dispersion by removing the large size GO sheets. As prepared GO membrane showed high separation performance for the butanol/water system. The separation factor was 230, and the permeability was as high as 3.1 kg·m?2·h?1 when the PV temperature was 50 °C and the water content in feed was 10%(by mass). Meanwhile, the membrane still showed good stabil-ity for the dehydration of butanol after running for 1800 min in the PV process. GO membranes are suitable candidates for butanol dehydration via PV process.     

A characterization of pdms pervaporation membranes for the removal of trace organic from water

A new silicone pervaporation membrane for the removal of one of trace organies, 1,2-dichloroethane from water has been developed using polydimethylsiloxane (PDMS) and oligomeric silylstyrene as a crosslinking agent of PDMS. Optimal conditions for fabricating the best membrane were determined from swelling measurements ard pervaporation experiments and then the membrane was characterized at different membrane thickness and operating conditions. In the pervaporation separation of 55–70 ppm of l,2-dichlorocthanc aqueous mixtures, the developed membrane has flux of 2.5–330 g/(m².h) and selectivity of 230–1750 depending on membrane thickness, permeate pressure and operating Temperature. Water permeation through thin membrane was found to be subjected to significant desorption resistance, while the desorption resistance and thermodynamic factors as well as the concentration polarization of the organic at the boundary layer in feed can affect the organic permeation, depending on membrane thickness. Selectivity change with permcaic pressure depends on membrane thickness: at small membrane thickness range, selectivity increases with permeate pressure and at large thickness region it decreases. From the Arrhenius plots of each component fluxes, the permeation activation energies were determined. Through an analysis of the permeation activation energies of each components, the desorption resistance as well as the effects of the thermodynamic factors on permeation was qualitatively characterized.     

Membrane materials in the pervaporation separation of aromatic/aliphatic hydrocarbon mixtures—A review

The separation of aromatic/aliphatic hydrocarbon mixtures is a significant process in chemical industry,but challenged in some cases.Compared with conventional separation technologies,pervaporation is quite promising in terms of its economical,energy-saving,and eco-ffiendly advantages.However,this technique has not been used in industry for separating aromatic/aliphatic mixtures yet.One of the main reasons is that the separation performance of existed pervaporation membranes is unsatisfactory.Membrane material is an important factor that affects the separation performance.This review provides an overview on the advances in studying membrane materials for the pervaporation separation of aromatic/aliphatic mixtures over the past decade.Explored pristine polymers and their hybrid materials (as hybrid membranes) are summarized to highlight their nature and separation performance.We anticipate that this review could provide some guidance in the development of new materials for the aromatic/aliphatic pervaporation separation.     

Filled poly(2,6-dimethyl-1,4-phenylene oxide) dense membranes by silica and silane modified silica nanoparticles: characterization and application in pervaporation

The effects of silica and silane modified silica fillers on the pervaporation properties of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) dense membranes have been studied. Crystallinity, thermal and mechanical properties of unfilled and filled PPO membranes with silica and silane modified silica nanoparticles were investigated. The surface energy together with the solubility parameters of the membranes and the nanoparticles were determined. Pervaporation separation of methanol/methyl tert butyl ether (MTBE) mixtures over the entire range of concentration were carried out using both filled and unfilled membranes. The results are discussed in terms of the solubility and the diffusivity of each liquid component in the membranes. Flory-Huggins theory was used to predict the sorption methanol selectivity. Compared to the unfilled PPO membrane, the filled PPO membranes exhibit higher methanol selectivity and lower permeability. For methanol concentration in liquid feed mixture lower than 50 wt%, methanol selectivity of the filled PPO membranes with silane modified silica is better than that of the silica filled and unfilled PPO membranes.     

A study on the effect of cross-linkers on pervaporation performance of room temperature vulcanised silicone rubber membranes for butanol recovery

As a rising membrane separation technology, pervaporation (PV) has been regarded as one of the most promising separation technology applied in separation of azeotropic mixtures due to its high selectivity and low energy consumption. In a PV process, separation process mainly occurs in the PV membrane, so it is of significance to develop a membrane with high performance. Room temperature vulcanised (RTV) silicone rubber is a kind of membrane material possessing good hydrophobicity and low glass transition temperature. It is widely used in the recovery of organic compounds from their dilute aqueous solutions. In this paper, RTV silicone rubber membranes were fabricated by a typical one-pot method and characterised by Fourier transform infrared spectroscopy, thermal gravimetric analysis, water contacting angle, differential scanning calorimetry, scanning electron microscopy and swelling experiment. The membranes were used in PV recovery of n-butanol from its dilute aqueous solution (about 1?wt-%). The influences of temperature and cross-linkers on the performance of PV were discussed at the same time. In conclusion, RTV silicone rubber membrane cross-linked by vinyltrimethoxysilane (WD-21), which obtained membrane selectivity of 82.9 with butanol permeability of 1.1_?×_?10⁶ Barrer at 50°C, got the best performance.     

Unsteady-state absorption of CO2 into w/o emulsion with aqueous alkaline liquid droplets

Unsteady-state absorption of CO₂ into w/o emulsion was studied by experimental measurements and prediction from mathematical modeling. Absorption experiments were performed by using a stirred vessel with a flat gas-liquid interface under 0.101 MPa and 25 °C. Continuous phase was benzene that has larger solubility than water. Dispersed phase was an aqueous solution of NaOH and AMP. The effects of reactant concentration, size of emulsified droplets, volume fraction of continuous phase and stirring speed on the absorption rate of CO₂ were investigated. In the mathematical model, the mechanism of CO₂ absorption into the continuous phase through a gas-liquid interface was described on the basis of the penetration model, while the subsequent absorption/reaction in the dispersed aqueous droplets was modeled by the film model.     

Dehydration of ethanol through blend membranes of chitosan and sodium alginate by pervaporation

Polyion complex membranes made by blending 84% deacetylated chitosan and sodium alginate biopolymers followed by crosslinking with glutaraldehyde were tested for the separation of ethanol–water mixtures. The membranes were characterized by FTIR to verify the formation of the polyion complex, X-ray diffraction (XRD) to observe the effects of blending on crystallinity, DSC, and TGA to investigate the thermal stability, and tensile testing to assess their mechanical stability. The effect of experimental parameters such as feed composition, membrane thickness and permeate pressure on separation performance of the crosslinked membranes was determined. Sorption studies were carried out to evaluate the extent of interaction and degree of swelling of the blend membranes, in pure as well as mixtures of the two liquids. Crosslinked blend membranes were found to have good potential for breaking the azeotrope of 0.135 mol fraction of water and a high selectivity of 436 was observed at a reasonable flux of 0.22 kg/(m² 10 μm h). Membrane selectivities were found to improve with decreasing membrane pressure but remained relatively constant for variable membrane thickness. Increasing membrane thickness decreased the flux and higher permeate pressure caused a reduction in both flux and selectivity.     

Separation of ethyl tert-butyl ether-ethanol by combined pervaporation and distillation

A cellulose derivative membrane (30 wt.% cellulose acetate butyrate (CAB) combined with 70 wt.% cellulose acetate propionate (CAP)) was prepared, and its properties were evaluated by the pervaporation separation of mixtures of ethyl tert-butyl ether (ETBE) and ethanol. The experimental results showed that the selectivity and permeability of the membrane were dependent on the blend composition, the processed feed and the experimental temperature. With respect to the temperature, the fluxes obeyed the Arrhenius equation. On the basis of these results, a separation process for the production of ETBE was developed by combining pervaporation and distillation. The distillation column was designed with the software ASPEN PLUS, and the liquid-vapour equilibria were predicted by the UNIFAC method. The area of the membrane was calculated according to the production capacity. It may be concluded that the combined process for the separation of mixtures of ETBE and ethanol is simple with high recovery of the ETBE product.     

甲醛－水渗透蒸发膜分离

制备了乙烯共聚醋酸乙烯酯复合膜和聚酰亚胺均相致密膜，研究了这两种膜与全氟磺酸型离子交换膜的渗透蒸发分离性能。实验测得最大分离系数α＝２７４，并发现料液的甲醛浓度增加，膜的分离系数提高。     

Experimental and modeling study on CO<Subscript>2</Subscript> absorption in a cyclone scrubber by phenomenological model and neural networks

Experimental and modeling studies have been conducted on CO₂ absorption in a cyclone scrubber operated at room temperature. The effects of parameters such as the initial concentration of alkali in the solution and the liquid - gas ratio on the CO₂ absorbed flux were experimentally and theoretically investigated. A phenomenological model and three-layer feed-forward neural networks have been applied to estimate the CO₂ absorbed flux in the cyclone scrubber. It was shown that the neural networks’ values agreed well with the experimental data, while the values by phenomenological model partly agreed with the experimental data around the initial concentration of alkali in the solution, C_Bo≤0.001 kmol/m³ (pH≤11).     

The potential of pervaporation for biofuel recovery from fermentation:An energy consumption point of view

Recovering alcohols from dilute fermentation broth is an emergent task in bio-fuel production process. Since they are primary planned for fuels, energy required to separate these alcohols should be considered in evaluating the potential of a separation technology. A membrane-based process, pervaporation, is of special interest because of its environmental friendliness and easy integrating character. This review probes into the fundamentals of pervaporation especially in terms of the heat required for evaporation. Meanwhile, the separation data of the most representative alcohol-selective pervaporation membranes reported in the literatures are collected and compared with the vapor–liquid equilibrium curve, which represents the distillation selectivity. They include:inorganic membranes, silicon rubber based membranes, Mixed Matrix Membranes and some other special materials. By doing so, the status of alcohol recovery via pervaporation would be more clear for researchers.For ethanol recovery, it is selectivity rather than flux that is in urgent need of solution. While for butanol recovery,membranes with satisfactory selectivity have been developed, increasing the separation capacity would be more pressing.     

Synthesis,characterization and application of PVA/ionic liquid mixed matrix membranes for pervaporation dehydration of isopropanol

In this study,polyvinyl alcohol (PVA)-ionic liquid (IL) membranes were prepared for the separation of isopropylalcohol (IPA)-water azeotropic mixtures by pervaporation.PVA-IL composite membranes were prepared by simple solvent evaporation method using four ILs,viz.,1-n-butyl-3-methylimidazolium chloride (BMIMCl),1-hexyl-3-methylimidazolium chloride (HMIMCl),1-hexyl-3-methylimidazolium tetrafluoroborate (HMIMBF4)and 1-octyl-3-methylimidazolium chloride (OMIMCl).Three ILs were used to study the effect of alkyl chain on the pervaporation performance.The study had focused on the effect feed water concentration from 10％-40％and effect of feed temperature from 50-80 ℃.Physiochemical properties of all the membranes were studied using Fourier transform infrared spectroscopy (FTIR),scanning electron microscopy (SEM) and contact angle measurement.The Arrhenius activation energies for permeation were estimated to be in the range 4-12 kJ.mol-1 from the temperature dependent permeation values.