Selective facilitated fixed-site carrier transport of methanol through sulfonated copolyimide pervaporation membranes for the separation of methanol/toluene mixtures

Dehydration of Organic Solvents from Ternary Mixtures Containing Toluene/Methanol/Water by Pervaporation

The separation of a toluene/methanol/water ternary mixture is a difficult task due to the toluene/water and toluene/methanol azeotropes. In this article, low-energy pervaporation is proposed for the separation of the ternary azeotrope toluene-methanol-water. This work investigates the effects of feed temperature, feed flow rate, and vacuum on pervaporation and compares the energy consumption of pervaporation with that of distillation. The results showed that at the optimized flow rate of 50 L/h and a permeate side vacuum of 60 kPa at 50 °C, the water and methanol content in the permeate was about 63.2 wt.% and 36.8 wt.%, respectively, the water/ methanol separation factor was 24.04, the permeate flux was 510.7 g/m2·h, the water content in the feed out was reduced from 2.5 wt.% to less than 0.66 wt.%, and the dehydration of toluene methanol could be realized. Without taking into account the energy consumption of pumps and other power equipment, pervaporation requires an energy consumption of 43.53 kW·h to treat 1 ton of raw material, while the energy consumption of distillation to treat 1 ton of raw material is about 261.5 kW·h. Compared to the existing distillation process, the pervaporation process consumes much less energy (about one-sixth of the energy consumption of distillation). There is almost no effect on the surface morphology and chemical composition of the membrane before and after use. The method provides an effective reference for the dehydration of organic solvents from ternary mixtures containing toluene/methanol/water.

Effect of Hydroxyl-Containing Fragments on the Structure and Properties of Membrane-Forming Polyamide-Imides

The structural features and thermophysical and transport properties of dense nonporous membranes of the casting type from (co)polyamide-imides synthesized by the polycondensation of the diacid chloride of 2-(4-carboxyphenyl)-1,3-dioxoisoindoline-5-carboxylic acid and diamines 5,5'-methylene-bis (2-aminophenol) (DADHyDPhM) and 4,4'-methylenebis(benzeneamine) (DADPhM), taken in molar ratios of 7:3, 1:1, and 3:7, have been studied. The effect of hydroxyl-containing modifying fragments of dihydroxy diphenylmethane introduced in various amounts into the main polymer chain on the pervaporation properties of the formed films is discussed. It has been shown that the presence of the residual solvent N-methyl-2-pyrrolidone in the films not only has a plasticizing effect on the characteristics of film membranes but also promotes the preferential transmembrane transport of polar liquids, primarily methanol (permeation rate over 2 kg for a copolymer with a ratio of DADHyDPhM:DADPhM = 7:3). The removal of the residual solvent from the polymer film, both thermally (heating to 200 °C) and by displacement with another solvent as a result of sequential pervaporation, led to a significant decrease in the rate of transfer of polar liquids and a decrease in the selectivity of the membrane. However, the dehydrocyclization reaction resulted in more brittle films with low permeability to penetrants of different polarities. The results of our comprehensive study made it possible to assume the decisive influence of structural changes in membranes occurring in connection with the competitive formation of intra- and intermolecular hydrogen bonds.

PyVaporation: A Python Package for Studying and Modelling Pervaporation Processes

PyVaporation-a freely available Python package with an open-source code for modelling and studying pervaporation processes-is introduced. The theoretical background of the solution, its applicability and limitations are discussed. The usability of the package is evaluated using various examples of working with and modelling experimental data. A general equation for the representation of a component's permeance as a function of feed composition, temperature and initial feed composition is proposed and implemented in the developed package. The suggested general permeance equation may be used for the description of an extremal character of permeance as a function of process temperature and feed composition, allowing the description of processes with a high degree of non-ideality. The application of the package allowed modelling experimental points of various sets of hydrophilic pervaporation data and data on membrane performance from independent sources with a relative root mean square deviation of not more than 9% for flux and not more than 5% for a separated mixture concentration. The application of the facilitated parameter approach allowed the prediction of the components' permeance as a function of feed concentration at various initial feed concentrations with a relative root mean square error of 3-26%. The package was proven useful for modelling isothermal and adiabatic time and length-dependent pervaporation processes. The comparison of the models obtained with PyVaporation with models provided in the literature indicated similar accuracy of the obtained results, thereby proving the applicability of the developed package.

New polyimide ionomers derived from 4,4′-diamino-[1,1′-biphenyl]-2,2′-disulfonic acid for fuel cell applications

The set of important properties of polymers necessary for their use as fuel cell membranes, such as film-forming properties, stability in acidic aqueous media, thermal stability, proton conductivity, is determined by their chemical structure, which provides not only basic and fragmentary mobility of the polymer chain but also complex supramolecular structural features (in particular, phase separation). The effect of the chemical structure of aromatic polyimide sulfonic acids, containing a fragment of 4,4′-diamino[1,1′-biphenyl]-2,2′-disulfonic acid (BDSA), on their membrane-forming properties is discussed, as well as the membrane stability under the conditions of a hydrogen-air fuel cell. The research is aimed at investigating sulfonated polyimides based on the commercially available rigid monomer - BDSA and flexible dianhydrides with an electron donor in their structure. As a model for this study, two aromatic anhydrides with flexible -O- bonds were chosen for investigating the potential of corresponding polyimide films in application to proton exchange membranes. The synthesized sulfonic acid polyimide BDSA-SPI-4(H) is of interest as a proton-conducting membrane polymer for direct energy conversion electrochemical devices and has shown to be a promising material for this group of devices. It is suggested that the presence of the flexible electron donor bonds in the structure of dianhydride should increase the stability of the membranes prepared from BDSA. The properties of polyimide sulfonic acids from the aforementioned diamine and dianhydrides of different fragmentary flexibility implemented in this work could help the understanding of the connection between chemical structure and properties of the material in application to proton exchange membranes development.