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An infrared study has been conducted on CO 2 sorption into nanoporous CO 2 "molecular basket" sorbents prepared by loading polyethylenimine (PEI) into mesoporous molecular sieve SBA-15. IR results from DRIFTS showed that a part of loaded PEI is anchored on the surface of SBA-15 through the interaction between amine groups and isolated surface silanol groups. Raising the temperature from 25 to 75 °C increased the molecular flexibility of PEI loaded in the mesopore channels, which may partly contribute to the increase of CO 2 sorption capacity at higher temperatures. CO 2 sorption/desorption behavior studied by in situ transmission FTIR showed that CO 2 is sorbed on amine sites through the formation of alkylammonium carbamates and absorbed into the multiple layers of PEI located in mesopores of SBA-15. A new observation by in situ IR is that two broad IR bands emerged at 2450 and 2160 cm -1 with CO 2 flowing over PEI(50)/SBA-15, which could be attributed to chemically sorbed CO 2 species on PEI molecules inside the mesopores of SBA-15. The intensities of these two bands also increased with increasing CO 2 exposure time and with raising CO 2 sorption temperature. By comparison of the CO 2 sorption rate at 25 and 75 °C in terms of differential IR intensities, it was found that CO 2 sorption over molecular basket sorbent includes two rate regimes which suggest two distinct steps: rapid sorption on exposed outer surface layers of PEI (controlled by sorption affinity or thermodynamics) and the diffusion and sorption inside the bulk of multiple layers of PEI (controlled by diffusion). The sorption of CO 2 is reversible at 75 °C. Comparative IR examination of the CO 2 sorption/ desorption spectra on dry and prewetted PEI/SBA-15 sorbent revealed that presorbed water does not significantly affect the CO 2 -amine interaction patterns.

We investigate the dynamics of the near wake in turbulent flow past a circular cylinder up to ten cylinder diameters downstream. The very near wake (up to three diameters) is dominated by the shear layer dynamics and is very sensitive to disturbances and cylinder aspect ratio. We perform systematic spectral direct (DNS) and large-eddy simulations (LES) at Reynolds number (Re) between 500 and 5000 with resolution ranging from 200 000 to 100 000 000 degrees of freedom. In this paper, we analyse in detail results at Re = 3900 and compare them to several sets of experiments. Two converged states emerge that correspond to a U-shape and a V-shape mean velocity profile at about one diameter behind the cylinder. This finding is consistent with the experimental data and other published LES. Farther downstream, the flow is dominated by the vortex shedding dynamics and is not as sensitive to the aforementioned factors. We also examine the development of a turbulent state and the inertial subrange of the corresponding energy spectrum in the near wake. We find that an inertial range exists that spans more than half a decade of wavenumber, in agreement with the experimental results. In contrast, very low-resolution spectral simulation as well as other dissipative LES do not describe accurately the inertial range although they predict low-order statistics relatively accurately. This finding is analysed in the context of coherent structures using a phase averaging technique and a procedure to extract the most energetic (on the average) eigenmodes of the flow. The results suggest that a dynamical model would require of the order of twenty modes to describe the vortex shedding dynamics with reasonable accuracy.

In order to explore the adsorptive denitrogenation of liquid hydrocarbon streams for producing ultraclean fuels, the adsorption performance of seven representative activated carbon samples and three activated alumina samples was evaluated in a batch adsorption system and a fixed-bed flow adsorption system for removing quinoline and indole from a model diesel fuel in the coexistence of sulfur compounds and aromatics. Different adsorbents show quite different selectivity toward basic and nonbasic nitrogen compounds (quinoline and indole) and sulfur compounds (dibenzothiophene and 4,6-dimethyldibenzothiophene). The activated carbons generally show higher capacity than activated alumina samples for removing the nitrogen compounds. The adsorption capacity and selectivity of the activated carbons for nitrogen compounds were further correlated with their textural properties and oxygen content. It was found that (1) the microporous surface area and micropore volume are not a key factor for removal of the nitrogen compounds in the tested activated carbons; (2) the oxygen functionality of the activated carbons may play a more important role in determining the adsorption capacity for the nitrogen compounds since the adsorption capacity for nitrogen compounds increases with increase in the oxygen concentration of the activated carbons; and (3) the type of the oxygen-functional groups may be crucial in determining their selectivity for various nitrogen or sulfur compounds. In addition, regeneration of the saturated adsorbents was conducted by the toluene washing followed by the heating to remove the remained toluene. The results show that the spent activated carbons can be regenerated to completely recover the adsorption capacity. The high capacity and selectivity of carbon-based adsorbents for the nitrogen compounds, along with their good regenerability, indicate that the activated carbons may be promising adsorbents for deep denitrogenation of liquid hydrocarbon streams.

We investigate the stability and dynamics of three-dimensional limit-cycle states in flow past a circular cylinder using low-dimensional modelling. High-resolution direct numerical simulations are employed to obtain flow snapshots from which the most energetic modes are extracted using proper orthogonal decomposition. We show that the limit cycle is reproduced very accurately with only twenty three-dimensional modes. The addition of two-dimensional modes to the Karhunen–Loeve expansion basis improves the ability of the model to capture the three-dimensional bifurcation, including the discontinuity in the Strouhal number discovered experimentally.

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The present research is concerned with the question of why activated carbons that show good adsorption uptake for model diesel sulfur compounds are not effective for real diesel fuels. In this work, the effects of aromatics, O-containing fuel additives, nitrogen compounds, and moisture present in real diesel fuel on adsorption desulfurization (ADS) over a commercial activated carbon (AC-WPH) were investigated. Polyaromatics such as phenanthrene show a significant inhibiting effect on ADS, even at a concentration of less than 1.0 wt %, while monoaromatics such as butylbenzene, even up to 10 wt %, have a negligible effect. The adsorption of different sulfur compounds over AC-WPH can be attributed mainly to the interaction of their conjugated π electrons with the carbon surface, where the electron-donating methyl groups further enhance the interaction. Trace amounts of O-containing diesel additives, nitrogen compounds, and moisture all have inhibiting effects on adsorptive desulfurization over AC-WPH, which can be attributed partly to hydrogen-bonding interaction between polar groups.

Adsorptive desulfurization of model gasoline fuels and a real gasoline over a nickel-based adsorbent Ni−Al was conducted in a flowing adsorption system at a temperature range of 25−200 °C under ambient pressure without using H2 gas in order to evaluate the desulfurization performance of the adsorbent for producing ultra-low-sulfur gasoline for fuel cell applications. Adsorptive capacity and selectivity of the Ni−Al adsorbent for various sulfur compounds and the effects of coexisting olefin in gasoline as well as adsorptive conditions on the adsorptive performance were examined. It was found that the nickel-based adsorbent shows high capacity and selectivity for the adsorptive desulfurization of gasoline. Olefins in gasoline have a strong inhibiting effect on the desulfurization performance of the nickel-based adsorbent at room temperature. Increasing the temperature to 200 °C can significantly improve the desulfurization performance of the nickel-based adsorbent for real gasoline. The adsorption mechanism and selectivity are discussed on the basis of the experimental results and computational analysis. The adsorption of sulfur compounds on the nickel surface involves C−S bond cleavage, as evidenced by the formation of ethylbenzene from benzothiophene in the absence of H2 gas in the flow adsorption system.