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.

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The chemical vapor deposition (CVD) of some heterocyclic compounds was examined to control the porosity and surface functionality of the active carbon fiber (ACF). The deposition took place only on the pore wall of the ACF, when the heterocyclic compound as the precursor and the deposition temperature were selected carefully to be thermally stable and around 700 °C, respectively. Moderately activated ACFs modified with pyridine, pyrrole, and thiophene demonstrated molecular sieving activity for selective adsorptions of CO 2/CH4 and O2/N2 through selective CVD. In contrast, furan decomposed at this temperature, failing to provide molecular sieving activity. The thermal stability of the depositing molecules is a key factor to obtain the molecular sieving performance after CVD. Pyridine, pyrrole, and thiophene produced amorphous carbon within the pore which appears to implant the nitrogen and sulfur atoms over the surface of the ACF, respectively.

The liquefaction of Wyoming coal (subbituminous coal) was investigated with an autoclave of 50 mL capacity, using Ketjen Black (KB)-supported NiMo catalyst, which has higher hydrogenation activity of 1-methylnaphtalene than a commercial NiMo/Al2O3. KB-supported NiMo catalyst gave the oil and oil plus asphaltene yield of 54 and 69% under reaction conditions of 440 °C, 60 min, and 13 MPa. These yields were much higher than those of a commercial NiMo/Al2O3 and synthesized FeS2 catalysts. The KB-supported NiMo catalyst was found to be recovered from the solid products using polar solvents such as THF because it is highly dispersed in liquid products due to its low specific gravity and the hydrophobic property of its surface. It was also found that KB-supported NiMo catalyst suffered the least deactivation by coke formation and mineral matter deposition because the recovered catalyst as THFI residue appeared to regenerate the activity to a level similar to the fresh catalyst.

Single- and two-stage liquefaction processes of Yallourn (YLC), South Banko (SBC), and Tanitoharum (THC) coals were performed in an autoclave of 50-mL capacity at variable solvent (tetralin)/coal ratios from 0 to 1.5 under the reaction hydrogen pressure of 15 MPa, using NiMo sulfide supported on carbon nanoparticles or commercial NiMo/alumina and synthetic pyrite catalysts. Although the oil yield decreased very much with all the catalysts by reducing the amount of solvent to zero, the NiMo/carbon catalyst gave much higher oil yields of 52 and 64%, respectively, in the single-stage (450 °C, 60 min) and two-stage (360 °C, 60 min; 450 °C, 60 min) liquefaction under the solvent-free conditions compared with the yield of around 40% by the other two catalysts in both single- and two-stage liquefaction under the same conditions. The oil yield depended on the coal species under the solvent-free conditions, being in the order of SBC > YLC > THC regardless of the reaction conditions. SBC provided the highest oil yields of 60 and 68% in the single- and two-stage liquefaction, respectively, reflecting its higher reactivity and lower gas yield. THC gave the lowest oil yields among the coals examined, although the oil yield reached 60% by the two-stage liquefaction even under the solvent-free conditions. The oil produced with NiMo/carbon catalyst carried lighter fractions in the boiling range 100−300 °C than those with the other catalysts regardless of the reaction conditions and coal species. Such excellent performance of the NiMo/carbon catalyst reflects its higher hydrogenation activity as well as the high dispersion on the coal surface at the initial stage of coal liquefaction, suppressing the retrogressive reactions. It is confirmed that the major portion of solid coal was solubilized during the heating and the initial stage to work as the self-producing solvent under the solvent-free reaction conditions. The design of coal liquefaction with the least use of solvent is discussed for the higher productivity.