Biogas mixtures include methane (which is useful), carbon dioxide, and hydrogen sulfide (which can be a nuisance). To remove hydrogen sulfide from biogas, we conducted separation experiments using tetra-n-butyl ammonium bromide semi-clathrate hydrate (hereafter referenced as TBAB hydrate). TBAB hydrate is stable under atmospheric pressure and can cage gas molecules in their empty small cage. A solution of 10 wt % TBAB was enclosed in a pressure vessel with a gas mixture containing hydrogen sulfide, and then TBAB hydrate was formed in the solution by cooling. Because of the selective incorporation of hydrogen sulfide into TBAB hydrate, >90% of the hydrogen sulfide in the vapor phase was removed during the hydrate growth. We also determined that the removal efficiency of hydrogen sulfide was not dependent on the initial pressure or the cooling rate. The results showed that TBAB hydrate was an effective material for desulfurization.

The contact area between the platinum paste electrode and the zirconia electrolyte was estimated on the basis of a linear relationship between the peak area of linear sweep voltammetry and the actual contact area. The latter area was measured by microscopic observation of the contact area from one side of a transparent zirconia single-crystal disk on the other side of which the platinum paste had been sintered. Applying the peak area vs. contact area relationship obtained to the same platinum electrode sintered on polycrysta]line zirconia disks, the contact area was estimated from the voltammogram peak. The electrode performance increased monotonically with increasing contact area, but there was a small deviation from the proportional relationship. This deviation was corrected by using the length of the three-phase boundary, instead of the contact area, as a morphological parameter.The electrode used for solid oxide fuel cells (SOFC) is a porous electrode which is usually prepared by sintering powder material onto a solid electrolyte. The electrode performance therefore is strongly affected by the morphology of the electrode as well as the properties of the material used. To compare different electrode materials on an equal basis, the effect of morphology must be eliminated. Singlepoint contact electrodes have been used to approach this problem. 1 For porous electrodes, however, no direct measurements of the morphological parameters have been made.To evaluate the effect of morphology, the capacitance of the electrode has been measured from the ac impedance or potential response to the pulsed currentY This method is based on the doubled-layer model having parallel plates of area S and spacing d. The double-layer capacity Cdt is expressed by Cdt = eS/d, where 9 is the dielectric constant of the space between parallel plates. Inserting 9 = 8.85 ~F 9 A/cm 2 (permittivity of free space), S = 1 cm 2 and d = 1 A (an approximate closest approach of O 2-ion), we obtain Cdl = 8.85 ~F/cm 2. However, the experimental values obtained for SOFC electrodes are one order of magnitude or more greater than expected above. 7 This discrepancy has been explained as being due to the pseudocapacitance arising from the faradaic process of adsorbed oxygen, s'8 or due to the adsorption of large polarizable ions in the electrolyte to the electrode-electrolyte interface. 8 The latter interpretation was supported experimentally for AgI and AgBr electrolytes, 9 but this is less likely for the more compact 02-ion having an adsorption behavior far from that of such large halide ions.If the capacitance is associated with any faradaic process, the meaning of the plate area is indefinite, depending on the location of the rate-determining reaction, e.g., the dissociation of O2 gas on the three-phase boundary (TPB), the charge transfer of O~ over the whole interface area between electrode and electrolyte, and various intermediates between these two extremes. At the present time, the interpretation of capacitance remains ambiguous and controversial, a...

The influence of lignin and inorganic salts on the catalytic activity was studied in the hydrolytic hydrogenation of real biomass by a supported Pt catalyst. The direct conversion of raw silver grass by Pt/carbon catalyst under H 2 pressure produced small amounts of sorbitol (2.8 wt%), xylitol (7.3 wt%), and other sugar alcohols. It has been suggested that lignin reduces the reactivity of cellulose, as lignin exists together with cellulose in the biomass and both compounds are insoluble in water.Moreover, even weak bases drastically change the product distribution with more by-products such as EG and PG. Bases enhance the decomposition of sugar intermediates and sorbitol. The removal of lignin and inorganic salts by alkali-explosion and neutralization raises the contents of cellulose and hemicellulose, thus increasing the yields of sorbitol (13 wt%) and xylitol (14 wt%) in the hydrolytic hydrogenation reactions.

The transient depolarization curves of Pt/ZrO2 high temperature air cathodes have been measured and compared with theoretical curves calculated by assuming a diffusion mechanism of atomic oxygen. The decay equation used involves the limiting current density, time constant for the decay rate and effective reaction area, as parameters to be determined. These parameter values were obtained by curve fitting. The polarization loss was found to decrease with increasing O2 pressure at the rate expected from the diffusion mechanism. The performance of the electrodes was enhanced as the sintering temperature rose. This trend was reflected on an increase in the parameter of effective reaction area. The performance was improved by loading an excess current. This effect was explained as being due to an increase in the diffusivity of Oa.

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