May-Britt Hägg

Influence of TiO2 on the Chemical, Mechanical, and Gas Separation Properties of Polyvinyl Alcohol-Titanium Dioxide (PVA-TiO2) Nanocomposite Membranes

PVA/TiO2 nanocomposite membranes developed were investigated for chemical, mechanical, and gas separation properties. PVA/TiO2 dispersion offers good optical property and less aggregation, as shown by UV-vis photospectroscopy. FT-IR spectra suggest strong interaction between PVA and TiO2. Mechanical properties of the composite membranes were enhanced by the addition of TiO2. Permeation results show that the addition of TiO2 up to 20 wt.% increased the selectivity of gas pairs O2/N2, H2/N2, H2/CO2, and CO2/N2 by 60%, 55%, 23%, and 26% respectively, with a corresponding decrease in the permeability. At higher loading of TiO2, a reverse trend was observed.

Carbon Molecular Sieve Membranes

Abstract: Carbon molecular sieve (CMS) membranes (hollow fibers) have been studied for application as possible separation units for selected industrial gas streams. Gas streams at petrochemical plants (polypropene and polyethene) and upgrading of biogas to fuel specifications have been in focus. Gases present in biogas (N2, CO2, H2Ovap, and CH4) and gas streams at polyolefin plants (C2H4, C3H6, and C3H8) have been measured; both as pure gases and in mixtures. Aging of the CMS‐membranes as a function of humidity and pore blocking is discussed; likewise, possible regeneration methods when flux decrease is experienced. Transport mechanisms depending on pore size and molecular properties are also discussed. Excellent separation properties were documented for these applications, but also the need for frequent regeneration of the membrane in order to maintain permeability flux. The mixed gas experiments documented clearly the need for careful pore tailoring in order to optimize selectivity when the membranes were used for alkane‐alkene separation.

Membranes for Environmentally Friendly Energy Processes

Membrane separation systems require no or very little chemicals compared to standard unit operations. They are also easy to scale up, energy efficient, and already widely used in various gas and liquid separation processes. Different types of membranes such as common polymers, microporous organic polymers, fixed-site-carrier membranes, mixed matrix membranes, carbon membranes as well as inorganic membranes have been investigated for CO2 capture/removal and other energy processes in the last two decades. The aim of this work is to review the membrane systems applied in different energy processes, such as post-combustion, pre-combustion, oxyfuel combustion, natural gas sweetening, biogas upgrading, hydrogen production, volatile organic compounds (VOC) recovery and pressure retarded osmosis for power generation. Although different membranes could probably be used in a specific separation process, choosing a suitable membrane material will mainly depend on the membrane permeance and selectivity, process conditions (e.g., operating pressure, temperature) and the impurities in a gas stream (such as SO2, NOx, H2S, etc.). Moreover, process design and the challenges relevant to a membrane system are also being discussed to illustrate the membrane process feasibility for a specific application based on process simulation and economic cost estimation.

Development of nanocomposite membranes containing modified Si nanoparticles in PEBAX-2533 as a block copolymer and 6FDA-durene diamine as a glassy polymer.

Nanocomposite membranes of modified Si nanoparticles as inorganic filler in two different polymers from two different categories were developed. Synthesized 6FDA-durene diamine as a glassy polymer and PEBAX-2533 as a block copolymer were used as the polymer matrix to develop the nanocomposite membranes of modified Si nanoparticles in polymer matrix. The scanning transmission electron microscopy (STEM) results showed nice nano size dispersion of inorganic nanofillers in the polymer matrix in both cases. Pure gas permeation for the gases CO2, CH4, N2, and O2 and mixed gas of CO2-N2 was carried out at 2 and 6 bar for single gas and 2.6 bar for mixed gas using the developed nanocomposite membranes. The loading of inorganic fillers in the PEBAX-2533 polymer matrix resulted in a dramatic increase in gas permeability for all tested gases, while a decrease was observed for CO2/N2 and CO2/CH4 selectivities with small amounts of loading of filler. With higher loading of inorganic filler, the selectivity did not change, which is probably due to the formation of nanogap around the nanoparticles in the polymer matrix. The dispersion of the nanoparticle inorganic fillers in 6FDA-durene polymer matrix caused an increase on the fractional free volume of the polymer matrix due to the disruption of the polymer chain in the presence of the inorganic fillers. Hence, this disruption resulted in an increase of gas permeability for both single and mixed gases, also with an increase in CO2/N2 and CO2/CH4 selectivities.

PVA/PVAm Blend FSC Membrane for Natural Gas Sweetening

Abstract Polyvinylamine/polyvinylalcohol (PVAm/PVA) blend membranes with fixed amino groups as CO 2 transport carriers were developed. PVAm offers a high amount of primary amino groups while the entanglement of PVAm with a mechanically robust polymer, PVA, enhances polymeric network with good membrane forming properties. The reversible reactions of CO 2 with amino carriers in PVAm facilitate the CO 2 transport, resulting in both high CO 2 permeability and CO 2 /CH 4 selectivity. The defect-free ultra thin PVAm/PVA blend membranes cast on porous polysulfone (PSf) supports were prepared and evaluated. The selectivity of CO 2 /CH 4 up to 45 and CO 2 permeance up to 0.3m 3 (STP)/m 2 .h.bar were documented at 2bar. Selectivity up to 40 for CO 2 /CH 4 was also recorded at 15bar. The blend membrane showed good reproducibility and stable performance. Keywords : Natural gas, Blend membrane, Facilitated transport, Polyvinyl amine, polyvinyl alcohol. 1. Introduction CO 2 in natural gas must be removed (natural gas sweetening) to meet specifications in order to increase heating value (Wobbe index) and reduce corrosion of pipelines. The most widely used technology for natural gas sweetening is amine absorption; a technology with high capital cost, high energy consumption for absorbent regeneration and potentially environmental pollution. Being low-cost, energy-saving and environment-friendly, optimized membrane technology has the potential of becoming a very good alternative for natural gas sweetening. Commercial membranes for this separation are in general conventional polymeric membranes based on solution-diffusion mechanism, which exhibit relatively low selectivity and flux compared with the facilitated transport membranes. For example, Cellulose acetate (CA) membranes, the most commonly used commercial CO

Selectivity and self-diffusion of CO2 and H2 in a mixture on a graphite surface

We performed classical molecular dynamics (MD) simulations to understand the mechanism of adsorption from a gas mixture of CO2 and H2 (mole fraction of CO2 = 0.30) and diffusion along a graphite surface, with the aim to help enrich industrial off-gases in CO2, separating out H2. The temperature of the system in the simulation covered typical industrial conditions for off-gas treatment (250–550 K). The interaction energy of single molecules CO2 or H2 on graphite surface was calculated with classical force fields (FFs) and with Density Functional Theory (DFT). The results were in good agreement. The binding energy of CO2 on graphite surface is three times larger than that of H2. At lower temperatures, the selectivity of CO2 over H2 is five times larger than at higher temperatures. The position of the dividing surface was used to explain how the adsorption varies with pore size. In the temperature range studied, the self-diffusion coefficient of CO2 is always smaller than of H2. The temperature variation of the selectivities and the self-diffusion coefficient imply that the carbon molecular sieve membrane can be used for gas enrichment of CO2.

Crosslinking High Free Volume Polymers - Effect on Gas Separation Properties

Crosslinkable nanoparticle-filled poly(4-methyl-2-pentyne) [PMP] membranes were cast from carbon tetrachloride solutions containing PMP, hydrophobic fumed silica, and 4,4i¯-(hexafluoroisopropylidene)diphenyl azide [HFBAA]. The composite membranes were crosslinked by UV irradiation at room temperature. Low levels of the bis azide were effective in rendering the membranes insoluble in cyclohexane and carbon tetrachloride, both good solvents for PMP. The process is simple and effective, and thus PMP can be easily converted to mechanically stable membranes. Compared to the pure PMP membrane, the permeability of the crosslinked membrane is initially reduced for all tested gases due to the crosslinking. By adding nanoparticles, the permeability is again increased, crosslinking is successful in maintaining the permeability and selectivity of PMP over time.

CO2 Separation in Nanocomposite Membranes by the Addition of Amidine and Lactamide Functionalized POSS® Nanoparticles into a PVA Layer

In this article, we studied two different types of polyhedral oligomeric silsesquioxanes (POSS®) functionalized nanoparticles as additives for nanocomposite membranes for CO2 separation. One with amidine functionalization (Amidino POSS®) and the second with amine and lactamide groups functionalization (Lactamide POSS®). Composite membranes were produced by casting a polyvinyl alcohol (PVA) layer, containing either amidine or lactamide functionalized POSS® nanoparticles, on a polysulfone (PSf) porous support. FTIR characterization shows a good compatibility between the nanoparticles and the polymer. Differential scanning calorimetry (DSC) and the dynamic mechanical analysis (DMA) show an increment of the crystalline regions. Both the degree of crystallinity (Xc) and the alpha star transition, associated with the slippage between crystallites, increase with the content of nanoparticles in the PVA selective layer. These crystalline regions were affected by the conformation of the polymer chains, decreasing the gas separation performance. Moreover, lactamide POSS® shows a higher interaction with PVA, inducing lower values in the CO2 flux. We have concluded that the interaction of the POSS® nanoparticles increased the crystallinity of the composite membranes, thereby playing an important role in the gas separation performance. Moreover, these nanocomposite membranes did not show separation according to a facilitated transport mechanism as expected, based on their functionalized amino-groups, thus, solution-diffusion was the main mechanism responsible for the transport phenomena.