Separability of SO2 from SO2/N2 mixture through sulfoxide-modified poly(vinyl alcohol) and cellulose membranes

Separability of SO₂ from mixtures of SO₂ and N₂ gases was studied for membranes of poly(vinyl alcohol) (PVA) and cellulose modified with methyl, ethyl, t-butyl, and phenyl vinyl sulfoxides. Of these sulfoxide-modified polymers, the phenyl vinyl sulfoxide-modified PVA membranes were found to give the best separation of SO₂. In the phenyl vinyl sulfoxide modified PVA membranes, the permeability coefficient of SO₂ increased with sulfoxide content while separability of SO₂ was maximum at a sulfoxide content of 23.5 mol %; the separation factor of SO₂ was about 170 at this sulfoxide content. © 1993 John Wiley & Sons, Inc.     

Microalgal cultivation in a solution recovered from the low-temperature catalytic gasification of the microalga

Microalgal cultivation in a solution recovered from the low-temperature catalytic gasification of the microalga itself was studied. The growth of Chlorella vulgaris in 75-300-fold diluted recovered solution containing phosphate, magnesium ions and micro-elements was comparable to that in the standard culture medium. It was suggested that C. vulgaris could use ammonium in the recovered solution as its nitrogen source and at the same time could provide a source of biomass which was recycled via gasification.     

Distinct element analysis for Class II behavior of rocks under uniaxial compression

In this study, the radial strain control method for uniaxial compression tests was introduced in the distinct element method (DEM) codes and the Class II behavior of rocks was simulated. The microscopic parameters used in the DEM models were determined based on laboratory uniaxial compression tests and Brazilian tests carried at Äspö Hard Rock Laboratory, Sweden. The numerical simulation results show good agreement with the complete stress–strain curves for Class II obtained from the laboratory experiments. These results suggest that the DEM can reproduce the Class II behavior of the rock successfully. The mechanism of the Class II behavior was also discussed in detail from the microscopic point of view. The loading condition and microscopic structure of rocks will play an important role for the Class II behavior.     

Direct room-temperature synthesis of a highly dispersed Pd nanoparticle catalyst and its electrical properties in a fuel cell

Highly dispersed palladium nanoparticles supported on bacterial cells were successfully prepared by a microbial method using the metal ion-reducing bacterium Shewanella oneidensis. Resting cells of S. oneidensis reduced soluble palladium(II) to insoluble palladium(0) at room temperature and neutral pH within 60 min when formate was provided as the electron donor. Transmission electron microscopy analysis of a thin section of S. oneidensis cells after exposure to a PdCl₂ solution revealed that palladium particles approximately 5–10 nm in size were deposited on the bacterial surface and in the periplasmic space. The initial concentrations of soluble palladium(II) and formate in the precursor solution strongly influenced the rate of palladium(II) reduction and the dispersity of biomass-supported palladium particles. The dried biomass-supported palladium was tested as an anode catalyst in a polymer electric membrane fuel cell for power production. The maximum power generation of the highly dispersed biomass-supported palladium particles was comparable to that of a commercial palladium catalyst.     

Hydrogen production from cellulose using a reduced nickel catalyst

Cellulose, a major component of biomass, was gasified in hot-compressed water using a reduced nickel catalyst at different reaction temperatures from 200°C to 350°C. The reaction mixture was separated to gases, oil, char and water-soluble products to discuss reaction mechanism based on the product distribution. The water-soluble products were considered as intermediates, and the obtained hydrogen was consumed by methanation reaction. The following simplified reaction scheme was proposed:

The effect of supports was also examined. Supports showed the strong effect on the gas yield, and the catalytic activity depended on the overall catalyst size rather than the surface area.     

Gasification reaction kinetics on biomass char obtained as a by-product of gasification in an entrained-flow gasifier with steam and oxygen at 900-1000 °C

The purpose of this study was to investigate the gasification kinetics of biomass char, such as the wood portion of Japanese cedar char (JC), Japanese cedar bark char (JB), a mixture of hardwood char (MH) and Japanese lawngrass char (JL), each of which was obtained as a by-product of gasification in an entrained-flow type gasifier with steam and oxygen at 900-1000 °C. Biomass char was gasified in a drop tube furnace (DTF), in which gasification conditions such as temperature (T_g), gasifying agent (CO₂ or H₂O), and its partial pressure (P_g) were controlled over a wide range, with accompanying measurement of gasification properties such as gasification reaction ratio (X), gasification reaction rate (R_g), change of particle size and change of surface area. Surfaces were also observed with a scanning electric microscope (SEM). By analyzing various relationships, we concluded that the random pore model was the most suitable for the biomass char gasification reaction because of surface porosity, constant particle size and specific surface area profile, as well as the coincidence of R_g, as experimentally obtained from Arrhenius expression, and the value is calculated using the random pore model. The order of R_g was from 10⁻² to 10⁻¹ s⁻¹, when T_g = 1000 °C and P_g = 0.05 MPa, and was proportional to the power of P_g in the range of 0.2-0.22 regardless of gasifying agent. Reactivity order was MH > JC > (JB, JL) and was roughly dependent on the concentration of alkali metals in biomass feedstock ash and the O/C (the molar ratio of oxygen to carbon) in biomass char.     

Ultrasonic Noise Relaxation for Evaluating Thermal Aging Embrittlement of Duplex Stainless Steels

A noncontact ultrasonic method is presented to evaluate the thermal aging embrittlement of the cast duplex stainless steels, which uses the shear-wave backscattering noise detected by an electromagnetic acoustic transducer (EMAT). Duplex stainless steel is a highly damping material, and the pulse-echo measurement for the velocity and attenuation is unavailable. High damping comes from the scattering at boundaries between the austenitic and ferritic phases. But, since little energy is absorbed in the material, the elastic waves impinged by an EMAT last in the sample for a long period (in the order of 10 ms) and are received by the same EMAT as a slowly decaying backscattering noise. The relaxation time coefficient is calculated by integrating the digitized noise signal and is correlated with the aging time. It clearly discriminates four duplex stainless steels aged for 0, 300, 1000, and 3000 h at 673K. The noise decays in a shorter time as the aging period increases. The difference of the noise relaxation rate is interpreted by the phase decomposition of ferrite into Cr-rich α' phase and Fe-rich α phase as supported by transmission electron microscopy (TEM).     

Droplet Generation and Nanoparticle Formation in Low-Pressure Spray Pyrolysis

In the present study, we found that pressure-dependent droplet-to-particle formation is important for the control of both droplet and particle characteristics during the production of particles with enhanced properties. Using experimental and simulation approaches, the present study investigated the droplet-to-particle formation of zinc oxide as a model material that was synthesized via low-pressure spray pyrolysis. The size distributions of both the droplets generated under low-pressure and the synthesized particles were measured and compared. The effects of operating conditions, i.e., operating pressure, carrier gas-, and liquid-flow rates, reactor temperature, and precursor concentration, on the characteristics of the generated droplets and synthesized zinc oxide particles were systematically investigated. We found that broad and bimodal droplet size distributions shifted to narrow and monodispersed distributions as chamber pressures were reduced. The low-pressure-synthesized zinc oxide nanoparticles were highly crystallized with unimodal distributions and sizes of approximately 8 nm. Droplet temperature decreased with decreasing chamber pressure, which confirmed both the evaporative cooling of droplets and the formation of smaller droplet sizes. The chamber temperature and droplet size simulation results were in accordance with the experimental results. In conclusion, we found that the chamber pressure is the primary determinant of monodispersity with respect to droplet size distribution and to the size and morphology of the synthesized particles.     

A constitutive model for fcc crystals with application to polycrystalline OFHC copper

Based on the results of a series of experiments on commercially pure OFHC copper (an fcc polycrystal), a physically based, rate- and temperature-dependent constitutive model is proposed for fcc single crystals. Using this constitutive model and the Taylor averaging method, numerical calculations are performed to simulate the experimental results for polycrystalline OFHC copper. The model calculation is based on a new efficient algorithm which has been successfully used to simulate the flow stress of polycrystalline tantalum over broad ranges of temperature, strain rate, and strain (Nemat-Nasser, S., Okinaka, T., Ni, L., 1998. J. Mech. Phys. Solids 46, 1009). The model effectively simulates a large body of experimental data, over a broad range of strain rates (0.001–8000 s⁻¹), and temperatures (77–1096 K), with strains close to 100%. Few adjustable constitutive parameters of the model are fixed at the outset for a given material. All other involved constitutive parameters are estimated based on the crystal structure and the physics of the plastic flow.