Peter M. Budd

High-Performance Membranes from Polyimides with Intrinsic Microporosity†

Membranes with high permeability to gases are formed from polyimides with rigid backbones that incorporate a spiro-centre. A route to this new range of high-free-volume polyimides is demonstrated, and exceptional performance is obtained for a polymer containing a dimethyl binaphthyl unit.

Nanoporous Organic Polymer/Cage Composite Membranes

Organic?organic composite membranes are prepared by in?situ crystallization of cage molecules in a polymer of intrinsic microporosity. This allows a direct one-step route to mixed-matrix membranes, starting with a homogeneous molecular solution. Extremely high gas permeabilities are achieved, even after ageing for more than a year, coupled with good selectivity for applications such as CO2 recovery.

Characterization ofAnacardiumoccidentale exudate polysaccharide

The composition, structure and molar mass distribution of Anacardium occidentale exudate polysaccharide of Brazilian origin was investigated. The composition from gas–liquid chromatography (GLC) and 13C NMR was 72% β-D-galactopyranose, 14% α-D-glucopyranose, 4·6% α-L-arabinofuranose, 3·2% α-L-rhamnopyranose and 4·5% β-D-glucuronic acid. A thorough analysis of high resolution 13C NMR spectra from intact, partially hydrolysed and Smith-degraded polysaccharide enabled reliable chemical shift assignments to be made, and indicated the presence of three types of unit within the branched galactan core: linked at C-1 and C-3, at C-1 and C-6, and at C-1, C-3 and C-6. The polysaccharide was fractionated with respect to molar mass using water/ethanol as a solvent/non-solvent system. The polysaccharide and fractions were characterized by gel permeation chromatography (GPC), intensity light scattering, dilute solution viscometry and sedimentation velocity. The intrinsic viscosity in 0·1M aqueous NaCl at 25°C was found to depend on molar mass according to: [η]/(cm3g-1)=0·052M0·42. The molar mass distribution for the whole polysaccharide, determined by GPC using a universal calibration, exhibited two main peaks at 28000 and 67000gmol-1, together with traces of much higher molar mass material.

Separation of alcohol/water mixtures by pervaporation through zeolite A membranes

Abstract Zeolite NaA membranes were prepared from homogeneous solution on macroporous zirconia composite supports in sheet and tube form. Zeolite KA membranes were obtained by ion exchange from the sodium form. The membranes were tested for the removal of water from isopropanol/water mixtures by pervaporation. Feed and permeate compositions and flux were measured for pervaporation at 25 and 70°C. Both the Na and K forms of zeolite A membranes were highly selective, separation factors in excess of 10 4 being achieved at low concentrations of water in the feed. Membrane performance was not affected by heat treatments to 150°C.

Enhancement of esterification reaction yield using zeolite A vapour permeation membrane

Abstract A tubular zeolite NaA membrane, prepared on a carbon/zirconia support, was tested for the removal of water from water/isopropanol and water/ethanol mixtures, in both pervaporation and vapour permeation modes, and shown to give high selectivity. The esterification of lactic acid with ethanol to give ethyl lactate was studied in a batch reactor, without catalyst and with p -toluene sulphonic acid as catalyst. The use of a zeolite A vapour permeation membrane to remove water generated by the reaction gave substantially enhanced yields of product, compared to control experiments carried out without the membrane and with the membrane but without vacuum being applied.

A nanoporous network polymer derived from hexaazatrinaphthylene with potential as an adsorbent and catalyst support

The synthesis and properties of a nanoporous network polymer incorporating 5,6,11,12,17,18-hexaazatrinapthylene (Hatn) as the rigid functional unit is described. This material is readily prepared from the efficient dibenzodioxane forming reaction between 2,3,8,9,14,15-hexachloro-5,6,11,12,17,18-hexaazatrinaphthylene and 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobisindane and exhibits a high BET surface area (775 m2 g−1) similar to that obtained from related nanoporous networks based on phthalocyanine and porphyrin macrocycles. The ability of the Hatn unit to bind to metal ions was shown by the sequential binding of three palladium(II) dichloride moieties to a soluble model Hatn compound using a 1H NMR titration experiment. When exposed to an excess of palladium(II) dichloride in chloroform solution, the Hatn nanoporous network is shown to adsorb 3.9 mmol g−1 of the metal complex. The resulting material retains porosity (BET surface area = 347 m2 g−1) and should be useful as a heterogeneous catalyst. The Hatn network polymer is also shown to be effective for the adsorption of phenol from aqueous solution with a maximum adsorption of 5 mmol g−1, which is a significant improvement over the performance of activated carbon reported in similar studies.

Sustainable wastewater treatment and recycling in membrane manufacturing

It is widely accepted that membrane technology is a green and sustainable process; however, it is not well known that the membrane fabrication process itself is quite far from green, with more than 50 billion liters of wastewater being generated every year contaminated with toxic solvents such as DMF and NMP. This urgent challenge is often overlooked and recent attempts to improve the sustainability of membrane fabrication have been limited to the replacement of toxic solvents with greener alternatives. Our recent survey from membrane industries indicates that such wastewater contributes to more than 95% of the total waste generated during the membrane fabrication process, and their disposal is considered cumbersome. Hence, recycling wastewater in the membrane industry is a pressing challenge to be resolved to augment the rapidly growing membrane market. In this work, a continuous wastewater treatment process is proposed and the quality of the recycled water was validated through membrane fabrication and performance tests. Seven different classes of adsorbents—graphene, polymers with intrinsic microporosity, imprinted polymers, zeolites, metal organic frameworks, activated carbon, and resins—were evaluated. The isotherm and kinetic behaviors of the best adsorbents have been fully characterized and the adsorbent regenerability without any performance loss has been confirmed for up to 10 wastewater treatment cycles. It has been demonstrated that over 99% of the organic impurities in the wastewater can be successfully removed and the recycled water can be reused without adverse effects on the final membrane performance. The proposed wastewater treatment technique can reduce the process mass intensity (PMI) of membrane fabrication by 99.9% per m2 of the membrane produced. The required energy duty for different regeneration methods and wastewater treatment methods revealed that the adsorption technology is the most effective method, with the lowest energy requirement of about 1200 kJ per m2 of the membrane produced.

Novel spirobisindanes for use as precursors to polymers of intrinsic microporosity

The synthesis of novel spirobisindane-based monomers for the preparation of polymers of intrinsic microporosity (PIMs) with bulky, rigid substituents is described. Polymers derived from monomers containing spiro-linked fluorene substituents display enhanced solubility and microporosity due to additional frustration of packing in the solid state.

Enhancement of CO2 Affinity in a Polymer of Intrinsic Microporosity by Amine Modification.

Nitrile groups in the polymer of intrinsic microporosity PIM-1 were reduced to primary amines using borane complexes. In adsorption experiments, the novel amine–PIM-1 showed higher CO2 uptake and higher CO2/N2 sorption selectivity than the parent polymer, with very evident dual-mode sorption behavior. In gas permeation with six light gases, the individual contributions of solubility and diffusion to the overall permeability was determined via time-lag analysis. The high CO2 affinity drastically restricts diffusion at low pressures and lowers CO2 permeability compared to the parent PIM-1. Furthermore, the size-sieving properties of the polymer are increased, which can be attributed to a higher stiffness of the system arising from hydrogen bonding of the amine groups. Thus, for the H2/CO2 gas pair, whereas PIM-1 favors CO2, amine–PIM-1 shows permselectivity toward H2, breaking the Robeson 2008 upper bound.

Materials chemistry communications. Synthesis of a zeolite NaA membrane

A self-supporting zeolite NaA membrane has been synthesized from an initially homogeneous hydrothermal solution. Membranes ca. 7 µm thick were formed successfully on polyethylene, glass and poly(tetrafluoroethylene) substrates.