In-situ CO2 capture in a pilot-scale fluidized-bed membrane reformer for ultra-pure hydrogen production

A novel pilot fluidized-bed membrane reformer (FBMR) with permselective palladium membranes was operated with a limestone sorbent to remove CO₂in-situ, thereby shifting the thermodynamic equilibrium to enhance pure hydrogen production. The reactor was fed with methane to fluidize a mixture of calcium oxide (CaO)/limestone (CaCO₃) and a Ni-alumina catalyst. Experimental tests investigated the influence of limestone loading, total membrane area and natural gas feed rates. Hydrogen-permeate to feed methane molar ratios in excess of 1.9 were measured. This value could increase further if additional membrane area were installed or by purifying the reformer off-gas given its high hydrogen content, especially during the carbonation stages. A maximum of 0.19 mol of CO₂ were adsorbed per mole of CaO during carbonation. For the conditions studied, the maximum carbon capture efficiency was 87%. The reformer operated for up to 30 min without releasing CO₂ and for up to 240 min with some degree of CO₂ capture. It was demonstrated that CO₂ adsorption can significantly improve the productivity of the reforming process. In-situ CO₂ capture enhanced the production of hydrogen whose purity exceeded 99.99%.     

Phase separation mechanism during membrane formation by dry‐cast process

Phase separation mechanisms during the membrane formation by dry‐cast process were investigated by light scattering in the cellulose acetate/dimethylformamide (DMF)/2‐methyl‐2,4‐pentanediol system. Phase separation occurred by spinodal decomposition (SD) when paths of the composition changes due to the evaporation of DMF were close to the critical point in the phase diagram. Characteristic properties of the early stage of SD such as an apparent diffusion coefficient and an interface periodic distance were obtained from the Cahn theory. Phase separation occurred by nucleation and growth (NG) when paths of the composition changes were far from the critical point. SEM observation confirmed that the membrane formed by the SD mechanism had interconnected structure, whereas that by the NG mechanism had the closed cell porous structure. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 776–782, 2000     

Study of flow instability in off design operation of a multistage centrifugal pump

In recent years, attempts have been made to make multistage centrifugal pumps smaller in size and more efficient. However, such designs are known to cause positive-slope phenomena in the Q-H curve, especially under low-flow conditions. These phenomena, which have thus far been studied experimentally and numerically, stem from flow instability in the pump. However, their mechanisms have not yet been clarified because it depends on various parameters. In this study, we focused on diffuser rotating stall, observed in positive Q-H characteristics. This study elucidates the mechanism of positive-slope generation through experimental results and two-dimensional numerical analysis.     

Effect of Inclusion Size on the Densification of ZnO–Zn7Sb2O12

Two-step densification curves, observed in the constant-rate heating of ZnO–Zn₇Sb₂O₁₂ composites, have been analyzed in correlation with the effect of inclusion particles (Zn₇Sb₂O₁₂). In the presence of these inclusion particles, the ZnO matrix is divided into two regions with different densification characteristics depending on the interaction with the particles. The linear shrinkage at the end of the first step depends on the inclusion size as well as on its volume fraction. The fractional volume of the region influenced by the inclusion particles has been estimated from the densification curve, and the size of the region influenced by an inclusion particle is found to increase with increasing inclusion size.     

Effect of MgO and SO3 on the Impurity Concentration in Alite in Portland Cement Clinker

MgO in clinker promotes the stable growth of alite in favor of the occurrence of M ₃. Mg ions go into solid solution in alite by simply replacing the Ca-sites in the structure. While the concentration of Mg in alite increases in proportion to the amount of MgO in the clinker, the concentration of Al, Fe, and Ti in alite remains constant. It is thus the Mg ions occupying the Ca-sites that give rise to the occurrence of M ₃ at ambient temperature. By contrast, SO₃ encourages the growth instability of alite. The concentration of impurity elements in alite tends to increase with increasing amount of SO₃ in clinker. This is most remarkable for Al and seems closely connected with the occurrence of M ₁ at ambient temperature. The presence of S was clearly recognized in alite.     

Preparation of porous poly(oxymethylene) membrane with high durability against solvents by a thermally induced phase‐separation method

Porous poly(oxymethylene) membranes were prepared as new solvent‐resistant membranes by a thermally induced phase‐separation method. Porous structures were formed by solid–liquid phase separation (polymer crystallization) rather than liquid–liquid phase separation. The pores existed in the intraspherulitic and interspherulitic regions. The effects of the polymer weight percentage and cooling rate on toluene permeance and solute rejection were investigated. The solvent resistance of the membranes was tested by the immersion of the membranes in organic solvents for 1 month, and high durability against the solvents was confirmed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1993–1999, 2002     

Hydride Anion Substitution Boosts Thermoelectric Performance of Polycrystalline SrTiO3 via Simultaneous Realization of Reduced Thermal Conductivity and High Electronic Conductivity

The development of environmentally benign thermoelectric materials with high energy conversion efficiency (ZT) continues to be a long-standing challenge. So far, high ZT has been achieved using heavy elements to reduce lattice thermal conductivity (κ_lat). However, it is not preferred to use such elements because of their environmental load and high material cost. Here a new approach utilizing hydride anion (H⁻) substitution to oxide ion is proposed for ZT enhancement in thermoelectric oxide SrTiO₃ bulk polycrystals. Light element H⁻ substitution largely reduces κ_lat from 8.2 W/(mK) of SrTiO₃ to 3.5 W/(mK) for SrTiO_3−xH_x with x = 0.216. The mass difference effect on phonon scattering is small in the SrTiO_3−xH_x, while local structure distortion arising from the distributed Ti−(O,H) bond lengths strongly enhances phonon scattering. The polycrystalline SrTiO_3−xH_x shows high electronic conductivity comparable to La-doped SrTiO₃ single crystal because the H⁻ substitution does not form a grain boundary potential barrier and thus suppresses electron scattering. As a consequence, SrTiO_3−xH_x bulk exhibits maximum ZT = 0.11 at room temperature and the ZT value increases continuously up to 0.22 at T = 657 K. The H⁻ substitution idea offers a new approach for ZT enhancement in thermoelectric materials without utilizing heavy elements.     

Effects of emulsifiers on the oxidative stability of soybean oil TAG in emulsions

The effects of two types of commercial emulsifiers, sucrose FA esters and polyglycerol FA esters, on the oxidation of soybean oil TAG-in-water emulsions were studied. Both emulsifiers influenced the oxidative stability of soybean oil TAG in the emulsion, but they had little effect on the oxidation of TAG in bulk phase. When the TAG were dispersed with sucrose esters having the same FA composition, the oxidative stability increased as their hydrophilic-lipophilic balance (HLB) increased. On the other hand, when the HLB was the same, the oxidative stability increased with increasing acyl chain length of the FA esterified on sucrose ester. However, the effect of the polyglycerol ester could not be explained by the relationship with HLB or the acyl composition. When the stability of TAG in emulsion was compared under the same concentrations of TAG, emulsifier, and oxidation inducer, the TAG dispersed with sucrose esters were oxidatively less stable than with polyglycerol esters. Analysis of the emulsion droplet size suggested that the lower oxidative stability of TAG dispersed with sucrose esters was partly due to their relatively smaller droplet sizes.     

Phase Stability Study on the Remelting Reaction in Ca2SiO4 Solid Solutions

A pseudobinary phase equilibrium diagram has been established for the P₂O₅-bearing Ca₂SiO₄-CaFe₄O₇ system to confirm the occurrence of remelting reaction in α-Ca₂SiO₄ solid solutions (C₂S(ss)). The reaction started at 1290°C immediately after the α-to-α'_H transition and finished at 1145°C. The reaction products were made up of about 1 wt% of liquid and 99 wt% of solid α'_H-C₂S(ss). The liquid exsolved at 1290°C was rich in Fe₂O₃, consisting of about 30 wt% of Ca₂SiO₄ and 70 wt% of CaFe₄O₇. The liquid coexisting with α-C₂S(ss) precipitated new α'-phase crystals in association with the remelting reaction.