Nematic liquid crystalline polymer films for gas separation

The gas separation performances of free-standing planar aligned nematic LC polymer films were investigated for gas separations of He, CO2, CH4 and Xe. The films consist of derivatives of 1,4-phenylene bis(4-((6-(acryloyloxy)hexyl)oxy)benzoate)s with respective cyano, chloro, methyl and phenyl substituents on the central aromatic cores. Two new LC derivatives of 1,4-phenylene bis(4-((6-(acryloyloxy)hexyl)oxy)benzoate)s were successfully synthesised and fully characterised. Single gas permeation and sorption data show increasing gas permeabilities with increasing steric size of the substituents while the ideal gas selectivity of He over CH4 and He over CO2 decreases. The sorption coefficient of all films is independent of the LC substituents, while the subsequently extracted diffusion coefficient for the films with a phenyl substituent is three times higher compared to the films with a cyano substituent, demonstrating that the steric size of the LC substituents mainly affects the diffusion of gasses rather than the solubility of the gases. Irrespective of a methyl or a phenyl substituent, a larger kinetic diameter of Xe gives a 20 times lower diffusion coefficient compared to the smaller species (CO2).</p

Laparoscopic ileocolic resection versus infliximab treatment of distal ileitis in Crohn's disease: a randomized multicenter trial (LIR!C-trial)

Contains fulltext : 69534.pdf (publisher's version ) (Open Access)BACKGROUND: With the availability of infliximab, nowadays recurrent Crohn's disease, defined as disease refractory to immunomodulatory agents that has been treated with steroids, is generally treated with infliximab. Infliximab is an effective but expensive treatment and once started it is unclear when therapy can be discontinued. Surgical resection has been the golden standard in recurrent Crohn's disease. Laparoscopic ileocolic resection proved to be safe and is characterized by a quick symptom reduction.The objective of this study is to compare infliximab treatment with laparoscopic ileocolic resection in patients with recurrent Crohn's disease of the distal ileum with respect to quality of life and costs. METHODS/DESIGN: The study is designed as a multicenter randomized clinical trial including patients with Crohn's disease located in the terminal ileum that require infliximab treatment following recent consensus statements on inflammatory bowel disease treatment: moderate to severe disease activity in patients that fail to respond to steroid therapy or immunomodulatory therapy. Patients will be randomized to receive either infliximab or undergo a laparoscopic ileocolic resection. Primary outcomes are quality of life and costs. Secondary outcomes are hospital stay, early and late morbidity, sick leave and surgical recurrence. In order to detect an effect size of 0.5 on the Inflammatory Bowel Disease Questionnaire at a 5% two sided significance level with a power of 80%, a sample size of 65 patients per treatment group can be calculated. An economic evaluation will be performed by assessing the marginal direct medical, non-medical and time costs and the costs per Quality Adjusted Life Year (QALY) will be calculated. For both treatment strategies a cost-utility ratio will be calculated. Patients will be included from December 2007. DISCUSSION: The LIR!C-trial is a randomized multicenter trial that will provide evidence whether infliximab treatment or surgery is the best treatment for recurrent distal ileitis in Crohn's disease. TRIAL REGISTRATION: Nederlands Trial Register NTR1150

Plasticization behavior of crown-ether containing polyimide membranes for the separation of CO2

This paper describes the influence of crown-ether ring size and rigidity on the gas separation performance of CO2/N2 and plasticization behavior of crown-ether containing Matrimid® 5218 polyimide membranes. The crown-ethers provide the membrane material with good affinity for CO2 due to the polar ether segments. Three different crown-ethers were used that differ in ring size and in rigidity (DB21C7, DB18C6 and 18C6). The gas separation performance of the crown-ether containing membranes was evaluated using pure gas and mixed gas conditions at pressures up to 40 bar. Thermal analysis (TGA and DSC) shows that the incorporation of the crown-ethers in the polyimide matrix was successful and that the crown-ethers have good compatibility with the polymer matrix. Gas sorption in the crown-ether containing membranes shows an enhanced solubility selectivity due to the enhanced interaction with CO2 compared to the pristine Matrimid®. However, both solubility and permeability of CO2 and N2 are decreased in these crown-ether containing membranes over the whole pressure range. When the molecular size of the crown-ether decreases (DB21C7 > DB18C6 > 18C6) the permeability increases. In addition, the incorporation of the more rigid crown-ethers (DB18C6 and DB21C7) causes rigidification of the polymer matrix contributing to the lower permeability of DB18C6 and DB21C7-based membranes. Pure gas CO2 permeation measurements show a typical plasticization behavior for pristine Matrimid®, while for the crown-ether containing membranes the extent of plasticization is significantly reduced. Next to that the plasticization pressure is shifted to higher CO2 feed pressures. No plasticization was observed for the crown-ether containing membranes in the mixed gas conditions, as a result of the lower solubility of the crown-ether containing membranes and competition effects of CO2 and N2. The differences in size and rigidity of the different crown-ethers showed no significant influence on the plasticization resistance of crown-ether containing membranes. Altogether, the operating window of these crown-ether containing membranes is increased with respect to Matrimid® showing their potential to operate at higher CO2 partial pressure without compromising selectivity

Time-dependent plasticization behavior of polyimide membranes at supercritical conditions

The time-dependent CO2-induced plasticization behavior of glassy Matrimid® 5218 polymer membranes at supercritical conditions up to 120 bar was investigated. Glassy polyimide membranes were conditioned with both gaseous CO2 and liquid-like sc-CO2. The plasticization behavior during permeation and sorption was correlated with the intrinsic membrane properties and the CO2 fluid properties. In the gaseous region the CO2 concentration increased slightly over time, while in the liquid-like sc-CO2 region the CO2 concentration remained constant over time and showed no hysteresis, indicating an induced glass transition. Contrary to the CO2 sorption the CO2 permeability showed more pronounced time-dependent behavior which increases with feed pressure because of polymer membrane plasticization. Despite the strong time-dependency, the CO2 permeability was independent of the feed pressure in the liquid-like sc-CO2 region. This difference in time-dependent behavior between sorption and permeation is due to the presence of a concentration gradient during permeation experiments. In addition, the permeability showed significant hysteresis. Exposure to liquid-like sc-CO2 resulted in a highly plasticized membrane and changed the permeation behavior at all subsequent feed pressures, due to slow polymer chain relaxation rates. Clearly, these relationships proof that the permeation history is a critical aspect for time-dependent plasticization phenomena at high CO2 pressures

Structure and performance of clay composite membranes with improved sodium conductivity for salinity gradient batteries

Low-cost cation exchange membranes with improved ionic conductivity and permselectivity are needed for the deployment of efficient large-scale energy storage technologies or separation technologies such as electrodialysis. In this work, a series of montmorillonite (Mt) clays and sulfonated poly(ether ether ketone) (SPEEK) composite membranes with 1 to 20 weight percentage (wt%) additives are studied. Two types of clays are investigated, a generic K30 Mt and an aluminum pillared (Al-pil) Mt with larger interlayer spacing owing to the inorganic crosslinks between the clay platelets. The addition of inorganic clays with two-dimensional geometries enables the formation of percolating sodium diffusing pathways with reduced tortuosity. As a result, the conductivity of the membranes increases with an increasing clay loading fraction, reaching up to 1.4 times that of the pure SPEEK with 20 wt% K30 Mt. The permselectivity of the native SPEEK membrane also improves with the addition of set amounts of K30 Mt, while the Al-pil Mt composites suffer from a slightly reduced permselectivity due to their higher water uptake. The voltaic efficiency of a concentration gradient flow battery shows that the addition of 20 wt% K30 Mt clay to the SPEEK polymer matrix can improve the voltaic efficiency by up to 10%.</p

Magnetically aligned and enriched pathways of zeolitic imidazolate framework 8 in matrimid mixed matrix membranes for enhanced co2 permeability

Metal-organic frameworks (MOFs) as additives in mixed matrix membranes (MMMs) for gas separation have gained significant attention over the past decades. Many design parameters have been investigated for MOF based MMMs, but the spatial distribution of the MOF throughout MMMs lacks investigation. Therefore, magnetically aligned and enriched pathways of zeolitic imidazolate framework 8 (ZIF−8) in Matrimid MMMs were synthesized and investigated by means of their N2 and CO2 permeability. Magnetic ZIF−8 (m–ZIF−8) was synthesized by incorporating Fe3O4 in the ZIF−8 structure. The presence of Fe3O4 in m–ZIF−8 showed a decrease in surface area and N2 and CO2 uptake, with respect to pure ZIF−8. Alignment of m–ZIF−8 in Matrimid showed the presence of enriched pathways of m–ZIF−8 through the MMMs. At 10 wt.% m–ZIF−8 incorporation, no effect of alignment was observed for the N2 and CO2 permeability, which was ascribed anon-ideal tortuous alignment. However, alignment of 20 wt.% m–ZIF−8 in Matrimid showed to increase the CO2 diffusivity and permeability (19%) at 7 bar, while no loss in ideal selectivity was observed, with respect to homogeneously dispersed m–ZIF−8 membranes. Thus, the alignment of MOF particles throughout the matrix was shown to enhance the CO2 permeability at a certain weight content of MOF

Systematic investigation of methods to suppress membrane plasticization during CO2 permeation at supercritical conditions

The suppression of CO2-induced plasticization in polyimide membranes at supercritical conditions up to 120 bar is investigated. Three approaches (polymer blending, thermal treatments and chemical crosslinking) known from relatively low-pressure applications are applied and their effectiveness to suppress membrane plasticization at high CO2 pressures and under supercritical conditions is systematically identified. CO2 sorption measurements reveal that especially Henry sorption promotes plasticization and that the corresponding Henry sorption parameter (kD) correlates with the d-spacing and Tg of the membranes. A lower d-spacing and higher Tg results in a reduced kD parameter and thus a higher resistance to plasticization. A high interchain rigidity is required to suppress plasticization at the highly plasticizing liquid-like CO2 densities. Chemical and thermo-oxidative crosslinking results in the largest decrease in interchain mobility and therefore shows the highest resistance to plasticization, but also a significantly lower permeability. Thermally treating the membranes in N2 retains a high permeability, while still displaying significant plasticization resistance. Polymer blending does increase the plasticization resistance, but strongly reduces the permeability. All three methods manage to suppress plasticization at supercritical conditions, but crosslinking offers superior plasticization resistance. However, proper tailoring strategies are required to combine a high plasticization resistance with a high permeability

Corrigendum to “Supercritical CO2 permeation in glassy polyimide membranes” [J. Membr. Sci. 620 (2021) 118922] (Journal of Membrane Science (2021) 620, (S0376738820314964), (10.1016/j.memsci.2020.118922))

The authors regret that the printed version of the above article contained an error with respect to the experimental membrane area reported. This however does not affect the content, the discussions nor the conclusion of the paper as only trends are discussed, and these remain unchanged. Absolute values did change though. The correct data are given below. The authors apologize for any inconvenience caused. 1) Experimental section 3.4, second sentence: The correct membrane area is 78.8 cm2 instead of 47.9 cm2. 2) Following this change in membrane area, Figs. 4, 6 and 9 are updated and the correct figures are shown below: [Fiure presented] [Fiure presented] [Fiure presented

Supercritical CO2 permeation in glassy polyimide membranes

The high-pressure permeation and sorption behavior of supercritical carbon dioxide (sc-CO2) in glassy Matrimid® 5218 polymer membranes were extensively investigated. The effect of pressure (0–120 bar) and temperature (25–55 °C) was examined. The observations were related to the intrinsic membrane properties, plasticization phenomena and the CO2 fluid properties. The phase transition from gaseous (-like sc) CO2 to liquid (-like sc) CO2 has the largest influence on the CO2 fluid properties and therefore was found to have the most influence on the CO2 sorption and CO2 permeability. The CO2 sorption was directly dependent on the CO2 density in the liquid (-like sc) regime. The CO2 permeability of Matrimid® 5218 showed typical CO2-induced plasticization behavior in the gaseous (-like sc) CO2 regime. When entering the liquid (-like sc) CO2 regime, the extent of plasticization was found to be independent of the applied feed pressure in this regime. The membranes showed strong hysteresis with pressure. The permeation history of the membrane thus has a large influence on the time-dependent permeability behavior. Clearly, the CO2 permeability behavior at these high pressures in glassy Matrimid® 5218 is determined by a combination of the CO2 fluid density and plasticization phenomena

Tuning the Gas Separation Performances of Smectic Liquid Crystalline Polymer Membranes by Molecular Engineering

The effect of layer spacing and halogenation on the gas separation performances of free-standing smectic LC polymer membranes is being investigated by molecular engineering. LC membranes with various layer spacings and halogenated LCs were fabricated while having a planar aligned smectic morphology. Single permeation and sorption data show a correlation between gas diffusion and layer spacing, which results in increasing gas permeabilities with increasing layer spacing while the ideal gas selectivity of He over CO2 or He over N2 decreases. The calculated diffusion coefficients show a 6-fold increase when going from membranes with a layer spacing of 31.9 Å to membranes with a layer spacing of 45.2 Å, demonstrating that the layer spacing in smectic LC membranes mainly affects the diffusion of gasses rather than their solubility. A comparison of gas sorption and permeation performances of smectic LC membranes with and without halogenated LCs shows only a limited effect of LC halogenation by a slight increase in both solubility and diffusion coefficients for the membranes with halogenated LCs, resulting in a slightly higher gas permeation and increased ideal gas selectivities towards CO2. These results show that layer spacing plays an important role in the gas separation performances of smectic LC polymer membranes