Partial Validation of Cross Flow Ultrafiltration by Atomic Force Microscopy

Atomic force microscopy was used to evaluate a cross flow ultrafiltration (CFUF) system. The CFUF system was used for the size fractionation of natural colloidal material from freshwaters. Analysis of the images of bulk water, permeates, and retentates shows the primary materials observed were near-spherical structures with height dimensions up to ∼12 nm. The number of colloidal particles (per unit area) on the mica surfaces derived from the retentates increased by a factor of 2 between a concentration factor (cf) of 1 and of 20. Colloidal densities of nanoparticles were ∼2 orders of magnitude lower in the permeate compared to the retentate, indicating a good size fractionation. As the cf value increased from 1 to 20, the percentage of <1-nm material decreased substantially and the percentage of >1-nm material increased substantially in the retentates. Line transects along a surface and surface roughness values show good agreement with the above results. Results suggest the size fractionation is good but not perfect and high cf values produce a better size fractionation, although some retention of small material is always observed. High cf values are recommended

Validation of cross-flow ultrafiltration for sampling of colloidal particles from aquatic systems

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Carrier-sensing range model.

<p>Carrier-sensing range model.</p

Elucidating the Zeolite Particle Size Effect on Butene/Isobutane Alkylation

In this study, X zeolites with average particle sizes of 0.9, 3.2, and 15.0 μm (labeled as NaX-0.9 μm, NaX-3.2 μm, and NaX-15.0 μm) were prepared. The latter two samples were single crystals, while NaX-0.9 μm was an aggregate composed of nanosized crystals. After being transferred to their La forms, the alkylation performances of the zeolites were examined in a continuous-flow slurry reactor. Contrary to the general belief that reducing the particle size can effectively enhance catalyst stability, the results showed that LaX-3.2 μm exhibited better stability than the other two samples. This phenomenon was explained by the balance between acidity and diffusion resistance. Although LaX-15.0 μm possessed very similar acidities to LaX-3.2 μm, its active sites cannot be fully utilized due to the diffusion limitations associated with the larger particle size. As for LaX-0.9 μm, although it was theoretically favorable for product diffusion, it also suffered from more significant dealumination because of the high structural defect concentrations. As a result, LaX-0.9 μm yielded lower Brønsted acidity, higher Lewis acidity, and weaker acid strength, all of which were disadvantageous for alkylation. Given the tradeoff effect between diffusion resistance and acidity, there is speculated to be an optimal particle size for LaX zeolites when used in a slurry reactor for alkylation. Furthermore, suggestions on catalyst design for isobutane alkylation were provided based on our results

The throughput under different carrier-sensing threshold <i>γ</i>.

<p>The throughput under different carrier-sensing threshold <i>γ</i>.</p

PPP model (Red dots represent the CNs while the green dots represent the TNs).

<p>PPP model (Red dots represent the CNs while the green dots represent the TNs).</p

The throughput of HCPP model with guard zone.

<p>The throughput of HCPP model with guard zone.</p

System Parameters.

<p>System Parameters.</p

The success probability under different carrier-sensing threshold <i>γ</i>.

<p>The success probability under different carrier-sensing threshold <i>γ</i>.</p

The success probability with the guard zone.

<p>The success probability with the guard zone.</p