Analysis and theory of gas transport in microporous sol-gel derived ceramic membranes

Sol-gel modification of mesoporous alumina membranes is a very successful technique to improve gas separation performance. Due to the formed microporous top layer, the membranes show activated transport and molecular sieve-like separation factors. This paper concentrates on the mechanism of activated transport (also often referred to as micropore diffusion or molecular sieving). Based on a theoretical analysis, results from permeation and separation experiments with H2, CO2, O2, N2, CH4 and iso-C4H10 on microporous sol-gel modified supported ceramic membranes are integrated with sorption data.\ud \ud Gas permeation through these membranes is activated, and for defect-free membranes the activation energies are in the order of 13¿15 kJ.mol¿1 and 5¿6 kJ.mol¿1 for H2 and CO2 respectively. Representative permeation values are in the order of 6×10¿7 mol.m¿2.s¿1.Pa¿1 and 20×10¿7 mol.m¿2.s¿1.Pa¿1 for H2 at 25°C and 200°C, respectively. Separation factors for H2/CH4 and H2/iso-butane are in the order of 30 and 200 at 200°C, respectively, for high quality membranes.\ud \ud Processes which strongly determine gas transport through microporous materials are sorption and micropore diffusion. Consequently, the activation energy for permeation is an apparent one, consisting of a contribution from the isosteric heat of adsorption and the activation energy for micropore diffusion. An extensive model is given to analyse these contributions.\ud \ud For the experimental conditions studied, the analysis of the gas transport mechanism shows that interface processes are not rate determining. The calculated activation energies for micropore diffusion are 21 kJ.mol¿1 and 32 kJ.mol¿1 for H2 and CO2, respectively. Comparison with zeolite diffusion data shows that these activation energies are higher than for zeolite 4A (dpore=4Å), indicating that the average pore size of the sol-gel derived membranes is probably smaller

Book Review: Water delivery: Public or private?

Teaching/Communication/Extension/Profession,

History of vertical displacement of Kerepehi Fault at Kopouatai bog, Hauraki Lowlands, New Zealand, since c. 10 700 years ago

Thirteen tephra layers interbedded with peat, and a basal peathorizon, in four pairs of cores provide radiocarbon-dated reference horizons that indicate vertical displacement on the Kerepehi Fault at Kopouatai bog, Hauraki Lowlands. Progressive offset of the horizons with time shows that vertical fault movement, downthrown to the west, has been occurring for the past c. 10 700 radiocarbon years at an approximately uniform rate of c. 0.13 mm/yr. Step functions indicate faulting events earthquakes at c. 1400, c. 5600, c. 6800, and C. 9000 years ago, a mean recurrence interval of c. 2500 years. These findings support geophysical and geological evidence that the Hauraki Depression is an active rift, and show that active faulting occurs along the northern as well as southern extensions of the Kerepehi Fault. If such earthquakes occur randomly in time, and based on the return period of 2500 years, there are 2%, 18%, and 33% probabilities of a major earthquake affecting the Kerepehi Fault at Kopouatai bog in the next 50, 500, and 1000 years, respectively

Energy production and use in Dutch agriculture

Energy relationschips in the agriculture of one of the most densely populated areas of the world, the Nether lands, are described. The Netherlands appear selfsupporting in food energy. However, if one takes account of energy consumption in horticulture, the direct and indirect fossil energy cost exceeds the food energy produced in agriculture. An input-output analysis to estimate the indirect energy is applied on Japanese data. It appears that in Japanese agriculture for every unit energy used directly, two units are used indirectly. Energy relationships are different for the main agricultural sectors. In the primary production sector more energy is produced than consumed (9 : 1), while in the secondary production sector and in the horticulture the oppositie holds (1 : 7). The energy input of the secondary production sector, however, is mainly of plant origin. Energy balances of an arable farm at present and around 1800 are given to show in more detail in which way food energy is and was produced. Possible ways to diminish the fossil energy input of the modern farm are discussed

Explicit correlation and intermolecular interactions: Investigating carbon dioxide complexes with the CCSD(T)-F12 method

We have optimized the lowest energy structures and calculated interaction energies for the CO₂–Ar, CO₂–N₂, CO₂–CO, CO₂–H₂O, and CO₂–NH₃ dimers with the recently developed explicitly correlated coupled cluster singles doubles and perturbative triples [CCSD(T)]-F12 methods and the associated VXZ-F12 (where X = D,T,Q) basis sets. For a given cardinal number, we find that results obtained with the CCSD(T)-F12 methods are much closer to the CCSD(T) complete basis set limit than the conventional CCSD(T) results. The relatively modest increase in the computational cost between explicit and conventional CCSD(T) is more than compensated for by the impressive accuracy of the CCSD(T)-F12 method. We recommend use of the CCSD(T)-F12 methods in combination with the VXZ-F12 basis sets for the accurate determination of equilibrium geometries and interaction energies of weakly bound electron donor acceptor complexes

The development of a treadle pump: Lessons from the South African experience

Manual pumps / Design / South Africa

Influence of intensity distribution on the meltpool and clad shape for laser cladding

The influence of the optical system on the laser cladding process is studied, in particular with respect to the burn-in shape: the penetration of the meltpool into the substrate. The beam caustic and intensity profiles for the commonly used out-of-focus laser clad operation are presented and discussed. To avoid the disadvantages of the out-of-focus operation, a novel telezoom optical system is developed, which allows in-focus operation with a sufficiently large focus with a uniform intensity distribution and a spot diameter ranging from 3 up to over 6 mm. Different typical burn-in shapes are indicated, as they can be found in cross sections of experimental clads. The influence of the intensity distribution on the occurring burn-in shapes is discussed, as well as other phenomena that can play a role, such as flow recirculation cells in the meltpool

Quantifying cooperative intermolecular interactions for improved carbon dioxide capture materials

We have optimized the geometry and calculated interaction energies for over 100 different complexes of CO₂ with various combinations of electron accepting (Lewis acid) and electron donating (Lewis base) molecules. We have used the recently developed explicitly correlated coupled cluster singles doubles and perturbative triples [CCSD(T)-F12] methods and the associated VXZ-F12 (where X = D,T,Q) basis sets. We observe only modest changes in the geometric parameters of CO₂ upon complexation, which suggests that the geometry of CO₂ adsorbed in a nanoporous material should be similar to that of CO₂ in gas phase. When CO₂ forms a complex with two Lewis acids via the two electron rich terminal oxygen atoms, the interaction energy is less than twice what would be expected for the same complex involving a single Lewis acid. We consider a series of complexes that exhibit simultaneous CO₂-Lewis acid and CO₂-Lewis base intermolecular interactions, with total interaction energies spanning 14.1–105.9 kJ mol⁻¹. For these cooperative complexes, we find that the total interaction energy is greater than the sum of the interaction energies of the constituent complexes. Furthermore, the intermolecular distances of the cooperative complexes are contracted as compared to the constituent complexes. We suggest that metal-organic-framework or similar nanoporous materials could be designed with adsorption sites specifically tailored for CO₂ to allow cooperative intermolecular interactions, facilitating enhanced CO₂ adsorption

Surface anchoring on liquid crystalline polymer brushes

We present a Monte Carlo study of the surface anchoring of a nematic fluid on swollen layers of grafted liquid crystalline chain molecules. The liquid crystalline particles are modeled by soft repulsive ellipsoids, and the chains are made of the same particles. An appropriately modified version of the configurational bias Monte Carlo algorithm is introduced, which removes and redistributes chain bonds rather than whole monomers. With this algorithm, a wide range of grafting densities could be studied. The substrate is chosen such that it favors a planar orientation (parallel to the surface). Depending on the grafting density, we find three anchoring regimes: planar, tilted, and perpendicular alignment. At low grafting densities, the alignment is mainly driven by the substrate. At high grafting densities, the substrate gradually loses its influence and the alignment is determined by the structure of the interface between the brush and the pure solvent instead.Comment: Computer Physics Communications, in press. Invited talk at the CCP 200