Mauro M. Dal-Cin

Polymer nanosieve membranes for CO2-capture applications

Microporous organic polymers (MOPs) are of potential significance for gas storage, gas separation and low-dielectric applications. Among many approaches for obtaining such materials, solution-processable MOPs derived from rigid and contorted macromolecular structures are promising because of their excellent mass transport and mass exchange capability. Here we show a class of amorphous MOP, prepared by [2+3] cycloaddition modification of a polymer containing an aromatic nitrile group with an azide compound, showing super-permeable characteristics and outstanding CO(2) separation performance, even under polymer plasticization conditions such as CO(2)/light gas mixtures. This unprecedented result arises from the introduction of tetrazole groups into highly microporous polymeric frameworks, leading to more favourable CO(2) sorption with superior affinity in gas mixtures, and selective CO(2) transport by presorbed CO(2) molecules that limit access by other light gas molecules. This strategy provides a direction in the design of MOP membrane materials for economic CO(2) capture processes.

Advances in high permeability polymeric membrane materials for CO2 separations

Global CO2 emissions have increased steadily in tandem with the use of fossil fuels. A paradigm shift is needed in developing new ways by which energy is supplied and utilized, together with the mitigation of climate change through CO2 reduction technologies. There is an almost universal acceptance of the link between rising anthropogenic CO2 levels due to fossil fuel combustion and global warming accompanied by unpredictable climate change. Therefore, renewable energy, non-fossil fuels and CO2 capture and storage (CCS) must be deployed on a massive scale. CCS technologies provide a means for reducing greenhouse gas emissions, in addition to the current strategies of improving energy efficiency. Coal-fired power plants are among the main large-scale CO2 emitters, and capture of the CO2 emissions can be achieved with conventional technologies such as amine absorption. However, this energy-consuming process, calculated at approximately 30% of the power plant capacity, would result in unacceptable increases in power generation costs. Membrane processes offer a potentially viable energy-saving alternative for CO2 capture because they do not involve any phase transformation. However, typical gas separation membranes that are currently available have insufficiently high permeability to be able to process the massive volumes of flue gas, which would result in a high CO2 capture. Polymer membranes highly permeable to CO2 and having good selectivity should be developed for the membrane process to be viable. This perspective review summarizes recent noteworthy advances in polymeric materials having very high CO2 permeability and good CO2/N2 selectivity that largely surpass the separation performance of conventional polymer materials. Five important classes of polymer membrane materials are highlighted: polyimides, thermally rearranged polymers (TRs), substituted polyacetylenes, polymers with intrinsic microporosity (PIM) and polyethers, which provide insights into polymer designs suitable for CO2 separation from, for example, the post-combustion flue gases in coal-fired power plants.

Tangential flow streaming potential measurements: Hydrodynamic cell characterization and zeta potentials of carboxylated polysulfone membranes

Abstract Computational fluid dynamics calculations were carried out to ensure that a self-made tangential flow mode streaming potential measurement cell meets the hydrodynamic stipulations of laminar, steady and established electrolyte flow necessary for reproducible electrokinetic measurements. The calculations show that the cell design meets all of these conditions. Six carboxylated polysulfones with a range of different degrees of substitution (DS) from 0.26 to 1.74 carboxyl groups per polymer repeat unit were synthesized in a two-stage process of lithiation and carboxylation. Ultrafiltration membranes were made from both the unmodified polysulfone and these hydrophilic materials. The zeta potentials of these membrane surfaces were determined in 0.001xa0M KCl solution as a function of pH. The curves show the theoretically expected profiles for non-ionic and weakly acidic materials. The growing influence of the COOH dissociation on the surface charge formation is indicated by the flattening of the curves at low pH values. The magnitude of the negative zeta potentials plateau values ranged from −52 to −20xa0mV. While unmodified PSU has a plateau value of −52xa0mV this value decreases continuously with increasing DS to −20xa0mV for the PSU-COOH 1.74 material. It is suggested that this arises from a shift of the electrokinetic shear plane into the bulk electrolyte solution due to an extended swelling layer reflecting the enhanced hydrophilicity of these membrane surfaces.

Membrane performance with a pulp mill effluent: Relative contributions of fouling mechanisms

Abstract Severe flux decline was observed during ultrafiltration of a pulp mill effluent. Membrane fouling was the result of varying combinations of adsorption, pore plugging and concentration polarization or gel layer formation. A wide range of membrane materials and pore sizes were evaluated, showing the relationship between the membrane material, pore size and the relative contribution of the different fouling mechanisms. Individual resistances were evaluated for adsorption, R a , pore plugging, R pp , and concentration polarization, R cp , using a series resistance model. These were based on the pure water flux for (1) the new membrane, J i , (2) after static adsorption with the mill effluent, J a , (3) the product rate when ultrafiltering the effluent, J v , and (4) the pure water permeability with the fouled membrane, J f . These resistances were shown to be misleading in terms of the observed flux loss for cases with significant adsorptive fouling. Adsorptive fouling was underestimated and concentration polarization overestimated. An alternative method, which we shall call flux loss ratios, is proposed, which is based on the flux decline due to a particular mechanisms as a fraction of the overall flux decline. These new measures more accurately reflect the flux decline attributable to each fouling mechanism.

Polysulfone membranes. IV. Performance evaluation of Radel A/PVP membranes☆

Nuclear magnetic resonance (NMR) spectroscopic measurements were used to show that Radel A100 is a copolymer containing polyethersulfone and polyetherethersulfone repeat units. Membranes were cast from solutions of Radel A and polyvinylpyrrolidone (PVP) polymers dissolved in 1-methyl-2-pyrrolidinone (NMP). The variation in membrane pore size is related to the casting solution composition and viscosity. The performance of Radel A/PVP membranes is compared to those of commercially available polysulfone membranes.

Dispersed phase back transport during ultrafiltration of cutting oil emulsions with a spinning membrane disc geometry

Abstract A commercial centrifugal rotary membrane module was used for the ultrafiltration of oil–water emulsions (droplet radius 50–3000xa0nm). This configuration can achieve high shear rates (>10 5 xa0s −1 ) which are decoupled from the bulk recirculation rate. Fluxes were in the pressure controlled regime above 600xa0rpm with transmembrane pressures up to 345xa0kPa. The pressure dependent flux behaviour suggests that concentration polarization or gel formation was minimal. The dominant back transport mechanism was determined by comparing various back transport mechanisms to the permeation drag force. Back transport mechanisms included Brownian diffusion, shear induced diffusion, lateral migration, viscous drag, centrifugal and DLVO forces. The effect of the membrane surface porosity and Sherwoods correction for Stokess law on the permeation drag were also studied. Viscous drag was the dominant force on droplet sizes between 50–1000xa0nm and was the only mechanism which could overcome the permeation drag force. Lateral migration was significant for droplets between 1000–3000xa0nm which were present in small quantities.

A surface spectroscopic study of membranes fouled by pulp mill effluent

Abstract Infrared internal reflection spectroscopy (IR-IRS) and flux decline has been used to examine the build-up of adsorbed foulants on the surfaces of membranes during the treatment of the plug screw feed pressate (PSFP) from the sulfite digestion of wood chips. Of the four commercial membranes studied, hydrophillic cellulose and thin film composite membranes resisted fouling as shown by no drop in flux during in-plant trials and absence of foulants by IR-IRS. In contrast both hydrophobic polyvinylidene fluoride (PVdF) and polysulfone membranes showed rapid flux decline and were found by IR-IRS to be coated with essentially all of the pressate constituents after exposure to the mill effluent. PVdF membranes were examined in detail by IR-IRS to monitor membrane fouling as a function of exposure time in a laboratory permeation test cell and exposure to PSFP in a static contact test. Hydrated lignin sulfonates, as free acid or salts, were found to be the initially absorbed species, with cellulosic oligomers depositing later on the initial foulant layer.

CFD-assisted thin channel membrane characterization module design

Abstract This project involved the design of a thin channel cross-flow module for the characterization of flat ceramic membranes. A primary objective of this work was to ensure that the flow characteristics over the permeating area were uniform. To house these membranes, a thin channel module with a long rectangular base was envisioned. The module feed is supplied by a multi-inlet tube-type plenum meant to provide a uniform flow distribution through pressure equilibration attained in its volume. The design criteria for the module were minimization of both the flow non-uniformity and the pressure drop across the permeating area which was a central rectangular portion of a larger slab-style cell. The flow non-uniformity was taken as the normalized standard deviation of the velocity field above the permeating area. The pressure drops considered were those across the inlet plenum and across the permeating area normalized with respect to the outlet pressure. The computational fluid dynamics (CFD) scheme which calculated the above module characteristics was a k - e based turbulent transport model which used the finite difference method. Design variables considered were: the plenum diameter, module width, height and length, and the diameters, distribution and number of the inlets on the plenum. The distribution of the inlet diameters was determined by two variables: either a linear or parabolic profile of variable slope and model coefficient. The operating variables were the cross-flow velocity and the plenum inlet pressure. A two-level factorial design was used to screen the design variables. A refined three-level factorial design was used with a reduced set of design variables to optimize the module and study the response surface. The final module design parameters were chosen such that the design criteria of flow uniformity and low pressure drop were met under a preset range of operating conditions. The local gradients of the response surface were used to verify that the design criteria were not overly sensitive to the selected module design parameters.

Membrane performance with plug screw feeder pressate : operating conditions and membrane properties

Abstract Membrane performance can be significantly affected by operating conditions. The effects of transmembrane pressure and cross flow velocity are discussed for various membranes during ultrafiltration of a pulp mill effluent. The effluent contained suspended solids, colloidal particles such as resin and fatty acids and materials with a wide molecular weight distribution. This effluent had severe membrane fouling characteristics, the nature of which complicated interpretation of the results. A variety of commerically available membranes made with different polymers and pore sizes were evaluated. Permeation experiments were performed using thin-channel, flat sheet, test cells. Cross-flow velocities varied from 0.4 to 1.2 m/s and the transmembrane pressure from 345 to 1,035 kPa. Flux decline occurred by several mechanisms and the selection of the membrane material, pore size and the operating conditions determined the relative contribution of these mechanisms. A modified series resistance model using flux loss ratios qualitatively explained changes in membrane performance under different operating conditions.

An Apparatus for Automated Cross Flow Solute Permeation Characterization of Membranes

Abstract An apparatus is described for the automated characterization of ultrafiltration membranes using solute permeation in cross flow mode. The automated characterization approach described in this work lends itself well for the purpose of increased productivity and reducing operator fatigue/error. The operational, control, and data acquisition aspects of an automated membrane cross flow test unit, which are accomplished using LabVIEW 5.0™ are described. The interpretation of the flux and separation data is independent of the apparatus and depends on the filtration regime and various theoretical models available. The apparatus can be used for reverse osmosis, nanofiltration, or ultrafiltration experiments, with appropriate selection of test cells and pumps. Issued as NRCC No. 47871.