Radical cation Diels–Alder
reactions by titanium dioxide
(TiO2) photocatalysis in lithium perchlorate/nitromethane
solution are described. TiO2 photocatalysis promotes reactions
between electron-rich dienes and dienophiles, which would otherwise
be difficult to accomplish due to electronic mismatching. The reactions
are triggered by hole oxidation of the dienophile and are completed
by the excited electron reduction of the radical cation intermediate
at the dispersed surface in the absence of any sacrificial substrate.
In
pulverized coal combustion plants, low-grade sub-bituminous
coal is known to cause adhesion of fly ash and its growth on the surface
of the super heater, heat exchanger, and furnace walls, even when
cocombusted with high-grade bituminous coal. In this study, six different
fly ash samples collected from commercial pulverized coal combustion
plants were investigated to find if the porosity and the liquid phase
would have a significant impact on the tensile strength of the ash
powder beds. Herein, we demonstrate that the use of alumina (Al2O3) nanoparticles as an additive is highly effective
in preventing such troublesome events, which would be a great aid
to facilitate stable and long-term operation of coal combustion plants.
The function of Al2O3 nanoparticles is found
to be 2-fold: retaining the porosity and perturbing the chemical composition
of the ash samples. This is rationally supported by experimental and
theoretical results. The key to our study is a split-type tensile
strength tester that can directly measure the tensile strength of
a powder bed being studied at various temperatures.
In
sewage sludge incineration plants, fly ash can adhere to the
surfaces of both the incinerator and dust filter and then accumulate
over time. Since this grown layer can potentially block the gas flow
and damage the filter, thus preventing stable and long-term operation
of incineration plants, fly ash adhesion must be monitored carefully
and suppressed as much as possible. Herein, we used three different
fly ash samples to demonstrate that the merger of experimental and
theoretical approaches enabled a rational choice of additive that
could suppress fly ash adhesion. The tensile strength of ash powder
beds provided a benchmark for the adhesive properties, which were
further studied by thermodynamic calculations. Experimental and theoretical
results suggest that the use of alumina nanoparticles is a promising
approach to suppress the adhesion of fly ash containing a relatively
high concentration of phosphorus components.
During sewage treatment, phosphorus (P) is concentrated in sewage sludge, and the sludge is incinerated to produce P-concentrated ash particles. The P-containing ash particles possess high adhesiveness at high temperatures, which can cause problems for the incineration plants. Phosphorus is considered a key element for inducing ash particles adhesiveness; however, the mechanistic details remain unclear. The present study clarified the role of P in particle adhesion at high temperatures using synthetic ashes, which consist of P and Si. The tensile strength of synthetic ash powder beds was quantified using a specially developed device that could estimate adhesiveness of particles at high temperatures. Since synthetic ash has few components compared to incineration ashes collected from commercial incineration plants, evaluating the role of P is easier. Iron (Fe)-containing chemical species are used for water treatment as chemical conditioners, and Fe also is concentrated with P in the sludge-incinerated ashes. To determine the interactions between Fe and P, iron oxide nanoparticles were added to P-containing synthetic ashes and their adhesiveness was evaluated. A small addition of iron oxide nanoparticles significantly decreased the adhesiveness of P-containing synthetic ashes at high temperatures, information that can help to control adhesiveness of sewage sludge-incinerated ashes.
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