Carbon Deposition from Benzene and Cyclohexane onto Active Carbon Fiber To Control Its Pore Size

Abstract

In this paper, we describe the investigation of chemical vapor deposition (CVD) of carbon from benzene and cyclohexane on a particular pitch-based active carbon fiber (ACF) at different deposition temperatures as a means of controlling the pore size of ACF in order to induce true molecular sieving capability and to discuss the mechanism of carbon deposition. This study showed that the specific temperature range 700−800 °C was very effective. In this range, deposition of amorphous carbon was restricted to the pore wall and became saturated at the level of 11% weight increase, as further deposition stopped. This treatment greatly enhanced the molecular sieve separation of CH4 from CO2. Reduction of pore size appeared to be limited by the thickness of the benzene plane, since no further carbon deposit took place when the pore could no longer accept benzene. Higher temperatures allowed deposition to occur on the outer surface of ACF, which plugged the pore completely on extended reaction time. Cyclohexane was found to be inferior to benzene as a carbon precursor, as it decomposed too rapidly in the gas phase at the temperature range used and precipitated the carbon plugging the pores. Thus, high molecular sieving selectivity was not obtained.

Carbon Molecular Sieves for Air Separation from Nomex Aramid Fibers

“…It has been predicted that CMSs with fibrous shapes can be the best adsorbents for pressure-swing adsorption application (9) because of their rapid adsorption/desorption rate and large adsorption capacity. Nevertheless, earlier efforts to modify the pore structure of activated carbon fibers (ACFs) to make them suitable for air separation have been only partially successful (9,10).…”

“…Commercial Takeda 3A CMS has been included for comparison; this material is designed for separation of air constituents. The selectivities for CO 2 /CH 4 and O 2 /N 2 separations have been defined here as the ratios of the uptakes for the corresponding gases at 2 min, and the capacities are given by the amounts of CO 2 and O 2 adsorbed in the same period of time, following the same criterion as Kawabuchi et al (9). The CO 2 /CH 4 pair has been included both because of the interest of this separation in itself (23) and as a way of following the process through which selectivity for the O 2 /N 2 separation is imparted.…”

Fine pore mouth structure of molecular sieve carbon with GCMC-assisted supercritical gas adsorption analysis

“…Ordinary a variety of molecular sieve carbons are produced by (1) carbonization of special materials at optimum conditions, (2) high temperature treatment of activated carbon, (3) carbon deposition at the pore mouth, (4) film coating of ultramicropore, (5) pore reopening after blocking micropores (Cabrera et al 1993;Kawabuchi et al 1996). The optimum method is adopted for each starting material using the selectivity test of gas separation.…”

Preparation of carbon molecular sieves from palm shell: effect of benzene deposition conditions

“…Several methods have been developed for CMS production such as pyrolysis (Braymer et al 1994), activation and carbon vapour deposition (CVD) (Vyas et al 1994;Nguyen and Do 1995;Villar-Rodil et al 2005;Freitas and Figueiredo 2001;Kawabuchi et al 1996). Among them, the CVD approach has been found particularly suitable and has received considerable attention.…”