Tools and techniques for solvent selection: green solvent selection guides

Driven by legislation and evolving attitudes towards environmental issues, establishing green solvents for extractions, separations, formulations and reaction chemistry has become an increasingly important area of research. Several general purpose solvent selection guides have now been published with the aim to reduce use of the most hazardous solvents. This review serves the purpose of explaining the role of these guides, highlighting their similarities and differences. How they can be used most effectively to enhance the greenness of chemical processes, particularly in laboratory organic synthesis and the pharmaceutical industry, is addressed in detail

Compositional optimization of polyimide-based SEPPI membranes using a genetic algorithm and high-throughput techniques.

Asymmetric, nanosized zeolite-filled solvent resistant nanofiltration (SRNF) membranes, prepared from emulsified polyimide (PI) solutions via the earlier reported solidification of emulsified polymer solutions via phase inversion (SEPPI) method, were optimized for their performance in the separation of rose bengal (RB) from 2-propanol (IPA). All membranes were prepared and tested in a parallellized, miniaturized, and automated manner using laboratory-developed high-throughput experimentation techniques. Nine different synthesis parameters related to the composition of the casting solutions were thus optimized. In a first, “conventional” approach, a preliminary systematic screening was carried out, in which only four constituents were used, that is, Matrimid PI, NMP as solvent, THF as volatile cosolvent, and an NMP-based zeolite precursor sol as emulsifying agent. A combinatorial strategy, based on a genetic algorithm and a self-adaptive evolutionary strategy, was then applied to optimize the SRNF performance of PI-based SEPPI membranes. This directed approach allowed the screening of an extended, 9-dimensional parameter space, comprising two extra solvents, the two corresponding nanosized zeolite suspensions, as well as another cosolvent. Coupling with high-throughput techniques allowed the preparation of three generations of casting solutions, 176 compositions in total, resulting in 125 testable membranes. With IPA permeances up to 3.3 L.m−2 h−1 bar−1 and RB rejections around 98%, the combinatorially optimized membranes scored significantly better with respect to fluxes and selectivities than the best membranes obtained in the systematic screening. The best SEPPI membranes also showed much higher IPA permeances than two commercial SRNF membranes at similar or slightly lower RB rejections

Effect of benzoic acid content on aging of 6FDA copolyimides based thin film composite (TFC) membranes in CO2/CH4 environment

© 2018 Elsevier B.V. 6FDA based polyimides possess outstanding properties, with a high free volume fraction entailing in high permselectivity properties for gas separation processes. However, they are very sensitive to aging process. Copolyimdes 6FDA–DAM:DABA were synthesized using different ratios of diamines: (9:1), (3:1) and (2:1) and the homopolyimide 6FDA–DAM. Thin Film Composite membranes were prepared and thermally annealed at 300 °C for 1 h to improve CO2 induced plasticization resistance. For exploring the future applications of these polymers, long–term performance studies of TFC membranes are absolutely needed. For this purpose, TFC membranes were tested for 180 h at 35 °C using a 50/50 vol./vol. CO2/CH4 feed composition at 8 bars of transmembrane pressure and aging was done under similar conditions. As a result, a more accurate behavior of long–term performance under working conditions can be disclosed. Overall, the drop of performance of all TFC membranes was minor, if it is compared with other studies of aging under ambient conditions. It is explained because polymeric materials experience certain swelling under continuous working conditions due to the presence CO2 and they cannot rearrange themselves as fast as under ambient conditions. 6FDA based polyimides are optimal candidates for industrial applications without losing their properties over extended period of time.status: publishe

Silica filled poly(4-methyl-2-pentyne) nanocomposite membranes: Similarities and differences with poly(1-trimethylsilyl-1-propyne)-silica systems

The performance of poly(4-methyl-2-pentyne) (PMP)/silica nanocomposites was studied for membranes with a filler content between 10 and 40 wt%. An increase in permeability and a constant vapor selectivity were measured with increasing filler content. The constant selectivity was in contrast to earlier published results for silica filled poly(l-trimethylsilyl-l-propyne) (PTSMP) membranes. Therefore, a comparison between both materials was made. Free volume sizes and interstitial mesopore sizes were determined by use of positron annihilation lifetime spectroscopy (PALS) and image analysis was performed on transmission electron microscopy (TEM) pictures of both materials. Although both materials possessed interstitial mesopores, a difference in membrane structure was noticed, explaining the difference in membrane performance. (c) 2008 Elsevier B.V. All rights reserved