Yuji Kawabuchi

High catalytic activity of pitch-based activated carbon fibres of moderate surface area for oxidation of NO to NO2 at room temperature

Catalytic oxidation of NO (380 ppmv) to NO2 over activated carbon fibres of moderate surface area (∼800 m2 g−1) at room temperature was carried out, to develop oxidative removal of NO from flue gas. The heat treatment of pitch-based activated carbon fibres of moderate surface area markedly increased the conversion of NO to 87% in dry air, 62% in air of 80% relative humidity and 24% in wet air (100% r.h.) at 25°C and a ratio of fibre mass to gas flow rate of 1.0 × 10−2g min mL−1. The strong inhibiting effect of humidity on the activity of the as-received fibres was moderated by heat treatment of the fibres at 850°C. A lower concentration of 10 ppmv NO markedly reduced the oxidation, the conversions being 24 and 5% in dry and wet (100% r.h.) air respectively. The catalytic activities of other pitch-based fibres of different surface area were also much inferior in moist air above 60% r.h.

The modification of pore size in activated carbon fibers by chemical vapor deposition and its effects on molecular sieve selectivity

Abstract Pore size control of a series of activated carbon fibers was attempted by chemical vapor deposition (CVD) of benzene to clarify the influence of the pore distribution on the development of molecular sieving ability. Weight increase by CVD was found to saturate at a certain level respective to the fiber, reflecting their surface areas. However, when saturation was obtained, the molecular sieving selectivity between CO2 and CH4 was induced only in the smaller surface area fibers, whereas the fibers with larger surface areas lost the adsorption activity for both gases. Straight micropores developed from the surface can be controlled in their slit size, by carbon deposition selectively onto their wall, if benzene molecules can get into the pore. In contrast, the size of micropores developed on the walls of mesopores in the fibers with large surface area are difficult to control since the carbon deposition continues until the whole wall of the mesopore is covered by the deposited carbon, which plugs the micropores.

Molecular sieving selectivity of active carbons and active carbon fibers improved by chemical vapour deposition of benzene

Abstract Modification of the pore size of several types of carbon adsorbents by chemical vapour deposition of carbon from benzene at 1000 K was examined. The carbons included commercial molecular sieve carbon (MSC), pitch based active carbon fiber (ACF), super and commercial active carbon (S-AC, AC). Greatly improved selectivity for the separation of CO2 and CH4 was achieved by this method for MSC and ACF. ACF is expected to exhibit rapid adsorption and desorption rates during molecular sieving separations. Carbon adsorbents which contain micropores of uniform size appear to have the highest potential for improvement in selectivity by CVD. Saturation of benzene CVD was observed in such carbons, indicating the deposition in the pore. In contrast, carbons which contain micropores in combination with large concentrations of mesopores lose adsorption capacity by filling of the mesopores with deposited carbon. The concentration of benzene and deposition temperature are key factors in achieving homogeneous carbon deposition on the pore wall but not on the outer surface which leads to improved selectivity.

Influence of heat-treatment on the selective adsorption of CO2 in a model natural gas over molecular sieve carbons

The kinetically selective adsorption of CO2 in CH4 was studied using three commercially available molecular sieve carbons. All as-received carbons examined in this study exhibited poor kinetic selectivity. However, heat-treatment at around 1273 K significantly improved the kinetic selectivity of one carbon (K-MSC) with the least decrease of adsorptive capacity of CO2. No improvement was obtained with other two carbons. The heat-treatment at 1273 K removed oxygen functional groups on the surface of K-MSC and significantly increased the degree of graphitization. The extent of graphitization of the other carbons remained unchanged by heat-treatment. The increasing degree of graphitization caused shrinkage of K-MSC and controlled the slit width of the pores. Higher temperature of the heat-treatment further increased the kinetic selectivity but markedly reduced the adsorptive capacity because of too much shrinkage, owing to excess graphitization. Heat-treatment at 1273 K enhanced the hydrophobicity of the carbon surface and reduced the inhibition of CO2 adsorption by water in the relative humidity range of 0–50%. At higher humidity, the effect was minimal as condensation on the pore wall occurred. Removal of oxygen functional groups by heat-treatment appears favorable for improving this kind of selectivity.