Selective removal of butanol from aqueous solution by pervaporation with a PIM-1 membrane and membrane aging

Crosslinking of Branched PIM-1 and PIM-Py Membranes for Recovery of Toluene from Dimethyl Sulfoxide by Pervaporation

Branched forms of the archetypal polymer of intrinsic microporosity PIM-1 and the pyridinecarbonitrile-containing PIM-Py may be crosslinked under ambient conditions by palladium(II) acetate. Branched PIM-1 can arise in polymerizations of 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobisindane with tetrafluoroterephthalonitrile conducted at a high set temperature (160 °C) under conditions, such as high dilution, that lead to a lower-temperature profile over the course of the reaction. Membranes of PIM-1 and PIM-Py crosslinked with palladium acetate are sufficiently stable in organic solvents for use in the recovery of toluene from its mixture with dimethyl sulfoxide (DMSO) by pervaporation at 65 °C. With both PIM-1 and PIM-Py membranes, pervaporation gives high toluene/DMSO separation factors (around 10 with a 77 vol % toluene feed). Detailed analysis shows that the membranes themselves are slightly selective for DMSO and it is the high driving force for toluene evaporation that drives the separation.

High-Flux Thin Film Composite PIM-1 Membranes for Butanol Recovery: Experimental Study and Process Simulations

Thin film composite (TFC) membranes of the prototypical polymer of intrinsic microporosity (PIM-1) have been prepared by dip-coating on a highly porous electrospun polyvinylidene fluoride (PVDF) nanofibrous support. Prior to coating, the support was impregnated in a non-solvent to avoid the penetration of PIM-1 inside the PVDF network. Different non-solvents were considered and the results were compared with those of the dry support. When applied for the separation of n-butanol/water mixtures by pervaporation (PV), the developed membranes exhibited very high permeate fluxes, in the range of 16.1-35.4 kg m^-2 h^-1, with an acceptable n-butanol/water separation factor of about 8. The PV separation index (PSI) of the prepared membranes is around 115, which is among the highest PSI values that have been reported so far. Hybrid PV-distillation systems have been designed and modeled in Aspen HYSYS using Aspen Custom Modeler for setting up the PIM-1 TFC and commercial PDMS membranes as a benchmark. The butanol recovery cost for the hybrid systems is compared with a conventional stand-alone distillation process used for n-butanol/water separation, and a 10% reduction in recovery cost was obtained.

A Review on Mixed Matrix Membranes for Solvent Dehydration and Recovery Process

Solvent separation and dehydration are important operations for industries and laboratories. Processes such as distillation and extraction are not always effective and are energy-consuming. An alternate approach is offered by pervaporation, based on the solution-diffusion transport mechanism. Polymer-based membranes such as those made of Polydimethylsiloxane (PDMS) have offered good pervaporation performance. Attempts have been made to improve their performance by incorporating inorganic fillers into the PDMS matrix, in which metal-organic frameworks (MOFs) have proven to be the most efficient. Among the MOFs, Zeolitic imidazolate framework (ZIF) based membranes have shown an excellent performance, with high values for flux and separation factors. Various studies have been conducted, employing ZIF-PDMS membranes for pervaporation separation of mixtures such as aqueous-alcoholic solutions. This paper presents an extensive review of the pervaporation performance of ZIF-based mixed matrix membranes (MMMs), novel synthesis methods, filler modifications, factors affecting membrane performance as well as studies based on polymers other than PDMS for the membrane matrix. Some suggestions for future studies have also been provided, such as the use of biopolymers and self-healing membranes.

High Selective Composite Polyalkylmethylsiloxane Membranes for Pervaporative Removal of MTBE from Water: Effect of Polymer Side-chain

For the first time, the effect of the side-chain in polyalkylmethylsiloxane towards pervaporative removal of methyl tert-butyl ether (MTBE) from water was studied. The noticeable enhancement of separation factor during the pervaporation of 1 wt.% MTBE solution in water through the dense film (40–50 µm) can be achieved by substitution of a methyl group (separation factor 111) for heptyl (161), octyl (169) or decyl (180) one in polyalkylmethylsiloxane. Composite membrane with the selective layer (~8 µm) made of polydecylmethylsiloxane (M10) on top of microfiltration support (MFFK membrane) demonstrated MTBE/water separation factor of 310, which was 72% greater than for the dense film (180). A high separation factor together with an overall flux of 0.82 kg·m⁻²·h⁻¹ allowed this M10/MFFK composite membrane to outperform the commercial composite membranes. The analysis of the concentration polarization modulus and the boundary layer thickness revealed that the feed flow velocity should be gradually increased from 5 cm·s⁻¹ for an initial solution (1 wt.% of MTBE in water) to 13 cm·s⁻¹ for a depleted solution (0.2 wt.% of MTBE in water) to overcome the concentration polarization phenomena in case of composite membrane M10/MFFK (T_exp = 50 °C).

Development of novel hydrophilic ionic liquid membranes for the recovery of biobutanol through pervaporation

This paper aims to develop novel hydrophilic ionic liquid membranes using pervaporation for the recovery of biobutanol. Multiple polyvinyl alcohol (PVA) membranes based on three commercial ionic liquids with different loading were prepared for various experimental trials. The ionic liquids selected for the study include tributyl (tetradecyl) phosphonium chloride ([TBTDP][Cl]), tetrabutyl phosphonium bromide ([TBP][Br]) and tributyl methyl phosphonium methylsulphate ([TBMP][MS]). The synthesized membranes were characterized and tested in a custom-built pervaporation set-up. All ionic liquid membranes showed better results with total flux of 1.58 kg/m²h, 1.43 kg/m²h, 1.38 kg/m²h at 30% loading of [TBP][Br], [TBMP][MS] and [TBTDP][Cl] respectively. The comparison of ionic liquid membranes revealed that by incorporating [TBMP]MS to PVA matrix resulted in a maximum separation factor of 147 at 30 wt% loading combined with a relatively higher total flux of 1.43 kg/m²h. Density functional theory (DFT) calculations were also carried out to evaluate the experimental observations along with theoretical studies. The improved permeation properties make these phosphonium based ionic liquid a promising additive in PVA matrix for butanol-water separation under varying temperature conditions.

Transient and Steady Pervaporation of 1-Butanol-Water Mixtures through a Poly[1-(Trimethylsilyl)-1-Propyne] (PTMSP) Membrane

The transient and steady pervaporation of 1-butanol-water mixtures through a poly[1-(trimethylsilyl)-1-propyne] (PTMSP) membrane was studied to observe and elucidate the diffusion phenomena in this high-performing organophilic glassy polymer. Pervaporation was studied in a continuous sequence of experiments under conditions appropriate for the separation of bio-butanol from fermentation broths: feed concentrations of 1.5, 3.0 and 4.5 w/w % of 1-butanol in nutrient-containing (yeast extract) water, temperatures of 37, 50 and 63 °C, and a time period of 80 days. In addition, concentration polarization was assessed. As expected, the total flux and individual component permeabilities declined discernibly over the study period, while the separation factor (average β = 82) and selectivity towards 1-butanol (average α = 2.6) remained practically independent of the process conditions tested. Based on measurements of pervaporation transients, for which a new apparatus and model were developed, we found that the diffusivity of 1-butanol in PTMSP decreased over time due to aging and was comparable to that observed using microgravimetry in pure vapor in 1-butanol. Hence, despite the gradual loss of free volume of the aging polymer, the PTMSP membrane showed high and practically independent selectivity towards 1-butanol. Additionally, a new technique for the measurement and evaluation of pervaporation transients using Fourier transform infrared spectroscopy (FTIR) analysis of permeate was proposed and validated.

In situ biobutanol recovery from clostridial fermentations: a critical review

Butanol is a precursor of many industrial chemicals, and a fuel that is more energetic, safer and easier to handle than ethanol. Fermentative biobutanol can be produced using renewable carbon sources such as agro-industrial residues and lignocellulosic biomass. Solventogenic clostridia are known as the most preeminent biobutanol producers. However, until now, solvent production through the fermentative routes is still not economically competitive compared to the petrochemical approaches, because the butanol is toxic to their own producer bacteria, and thus, the production capability is limited by the butanol tolerance of producing cells. In order to relieve butanol toxicity to the cells and improve the butanol production, many recovery strategies (either in situ or downstream of the fermentation) have been attempted by many researchers and varied success has been achieved. In this article, we summarize in situ recovery techniques that have been applied to butanol production through Clostridium fermentation, including liquid-liquid extraction, perstraction, reactive extraction, adsorption, pervaporation, vacuum fermentation, flash fermentation and gas stripping. We offer a prospective and an opinion about the past, present and the future of these techniques, such as the application of advanced membrane technology and use of recent extractants, including polymer solutions and ionic liquids, as well as the application of these techniques to assist the in situ synthesis of butanol derivatives.

How Do Organic Vapors Swell Ultrathin Films of Polymer of Intrinsic Microporosity PIM-1?

Dynamic sorption of ethanol and toluene vapor into ultrathin supported films of polymer of intrinsic microporosity PIM-1 down to a thickness of 6 nm are studied with a combination of in situ spectroscopic ellipsometry and in situ X-ray reflectivity. Both ethanol and toluene significantly swell the PIM-1 matrix and, at the same time, induce persistent structural relaxations of the frozen-in glassy PIM-1 morphology. For ethanol below 20 nm, three effects were identified. First, the swelling magnitude at high vapor pressures is reduced by about 30% as compared to that of thicker films. Second, at low penetrant activities (below 0.3p/p₀), films below 20 nm are able to absorb slightly more penetrant as compared with thicker films despite a similar swelling magnitude. Third, for the ultrathin films, the onset of the dynamic penetrant-induced glass transition P_g has been found to shift to higher values, indicating higher resistance to plasticization. All of these effects are consistent with a view where immobilization of the superglassy PIM-1 at the substrate surface leads to an arrested, even more rigid, and plasticization-resistant, yet still very open, microporous structure. PIM-1 in contact with the larger and more condensable toluene shows very complex, heterogeneous swelling dynamics, and two distinct penetrant-induced relaxation phenomena, probably associated with the film outer surface and the bulk, are detected. Following the direction of the penetrant's diffusion, the surface seems to plasticize earlier than the bulk, and the two relaxations remain well separated down to 6 nm film thickness, where they remarkably merge to form just a single relaxation.

Hybrid and Mixed Matrix Membranes for Separations from Fermentations

Fermentations provide an alternative to fossil fuels for accessing a number of biofuel and chemical products from a variety of renewable and waste substrates. The recovery of these dilute fermentation products from the broth, however, can be incredibly energy intensive as a distillation process is generally involved and creates a barrier to commercialization. Membrane processes can provide a low energy aid/alternative for recovering these dilute fermentation products and reduce production costs. For these types of separations many current polymeric and inorganic membranes suffer from poor selectivity and high cost respectively. This paper reviews work in the production of novel mixed-matrix membranes (MMMs) for fermentative separations and those applicable to these separations. These membranes combine a trade-off of low-cost and processability of polymer membranes with the high selectivity of inorganic membranes. Work within the fields of nanofiltration, reverse osmosis and pervaporation has been discussed. The review shows that MMMs are currently providing some of the most high-performing membranes for these separations, with three areas for improvement identified: Further characterization and optimization of inorganic phase(s), Greater understanding of the compatibility between the polymer and inorganic phase(s), Improved methods for homogeneously dispersing the inorganic phase.