The objective of the work presented here is to develop a nanoporous solid adsorbent which can serve as a "molecular basket" for CO 2 in the condensed form. Polyethylenimine (PEI)-modified mesoporous molecular sieve of MCM-41 type (MCM-41-PEI) has been prepared and tested as a CO 2 adsorbent. The physical properties of the adsorbents were characterized by X-ray powder diffraction (XRD), N 2 adsorption/desorption, and thermogravimetric analysis (TGA). The characterizations indicated that the structure of the MCM-41 was preserved after loading the PEI, and the PEI was uniformly dispersed into the channels of the molecular sieve. The CO 2 adsorption/desorption performance was tested in a flow system using a microbalance to track the weight change. The mesoporous molecular sieve had a synergetic effect on the adsorption of CO 2 by PEI. A CO 2 adsorption capacity as high as 215 mg-CO 2 /g-PEI was obtained with MCM-41-PEI-50 at 75 °C, which is 24 times higher than that of the MCM-41 and is even 2 times that of the pure PEI. With an increase in the CO 2 concentration in the CO 2 /N 2 gas mixture, the CO 2 adsorption capacity increased. The cyclic adsorption/desorption operation indicated that the performance of the adsorbent was stable.

No abstract

No abstract

No abstract

The formation of pyrolytic solid deposit, or coke, in the fuel line can be detrimental to the operation of high-speed aircraft. Yet, the formation of coke from the fuel has not been well characterized. The present study has investigated the relationship between the formation of aromatic compounds and solid deposition for three candidates for high-thermal-stability jet fuels at 482 °C (900 °F) with stressing periods up to 2 h. The fuels include one coal-derived (JP-8C), one paraffinic petroleum-derived (JP-8P), and one naphthenic petroleum-derived (DA/HT LCO). The DA/HT LCO, an extensively hydrotreated light cycle oil where virtually all aromatics have been hydrogenated to cycloalkanes, suppressed the solid deposition to a greater extent than that of the more paraffinic petroleum-derived JP-8P and showed a comparable low solid deposition to that of the coal-derived fuel JP-8C. Both GC/MS and solution-state 13 C NMR analysis on the stressed fuels confirmed that the paraffinic content is most likely to crack under thermal stress, while cycloalkane structures are more thermally stable. Solution-state 13 C NMR and HPLC investigations of the overall structure of the stressed liquids indicate that the solid deposition is a function of the rise in the aromatic content and also the amount and rate of development of the nonprotonated aromatic carbons, giving mostly 2 to 4 rings aromatics. Furthermore, solid-state 13 C NMR was used to follow the development of the aromatic structure in the corresponding solid deposit as a function of the buildup of aromatic compounds in the stressed liquid fuel.

High-temperature in-situ 1H NMR with a probe operating at a frequency of 100 MHz has been used to quantify the effects of particle size, mild oxidation, and different heating regimes on plasticity development for a low-volatile Australian bituminous coal in terms of the proportions of rigid and fluid material present. At the temperature of maximum fluidity, the fluid phase accounts for 35% of the hydrogen remaining, with both its concentration and mobility increasing up to this temperature. Reducing the particle size below ca. 150 μm suppresses plasticity through a reduction in the mobility of the fluid phase with the concentration of rigid material remaining constant. This effect is considerably more pronounced with slow heating than it is with fast heating (3−4 cf. 30 °C min-1). In contrast, suppressing the fluidity by mild oxidation reduces primarily the concentration of the fluid phase. Isothermal treatments give rise to a loss of fluidity due to reductions in both the proportion and mobility of the fluid component. The in-situ measurements have confirmed that plasticity development is a reversible phenomenon provided that relatively fast quenching rates (ca. 75 °C min-1) are used. These results are discussed in relation to estimating the contribution to fluidity development from the non-solvent-extractable material in coals. Heating coking coal in a tube furnace to the temperature of maximum fluidity followed by fairly rapid cooling is shown to be a simple procedure for recovering relatively large amounts of partially carbonized coal with the structural features responsible for maximum fluidity preserved.

No abstract

No abstract