Activated carbon has been used commercially to remove SO 2 from coal combustion flue gas. However, the role of inherent CaO in activated carbon is uncertain. In this study, the adverse effects of inherent CaO in the activated carbon derived from coconut shell (CSAC) on its desulfurization performance were systematically studied at the temperature range of 60−100 °C in a fixed-bed reactor. The solid sorbent samples were analyzed using scanning electron microscopy, X-ray diffraction, X-ray fluorescence, Fourier transform infrared spectroscopy, and Brunauer−Emmett−Teller analysis. The flue gas compositions were analyzed by using an online flue gas analyzer. The experimental results showed that the inherent CaO had a profoundly adverse influence on the desulfurization capacity and efficiency of CSAC at all of the temperatures studied. This adverse influence was clearly identified by a comparison of the desulfurization performance of the raw CSAC to those of the acid-washed CSAC samples. It was found that the removal of the inherent CaO from CSAC using a pretreatment of HCl aqueous solution led to an increase in the desulfurization capacity of 41.7%. The adverse effects were attributed to the conversion of CaO into dihydrate calcium sulfate whiskers which formed solid crystals that blocked the micropores of the CSAC particles.
Potassium hydroxide-impregnated char
sorbents (KOH/char) prepared
via an ultrasonic-assisted method were used for SO
2
removal
from flue gas. The desulfurization experiment was analyzed using a
fixed-bed reactor under 40–150 °C temperature range, using
simulated flue gas. X-ray diffraction (XRD), Fourier-transform infrared
spectroscopy, and scanning electron microscopy/energy-dispersive X-ray
spectroscopy (SEM/EDS) were used to analyze both the chemical and
physical characteristics of the sorbents. The analyzed results exposed
that the complete elimination of SO
2
from flue gas was
achieved when using the char/KOH sorbent with a mass ratio of char
to KOH of 11:1. It was noted that temperature had a substantial influence
on the desulfurization performance with sulfur capacity maximized
at 100 °C. Experimental results also revealed that a small amount
of O
2
present in the solvent could improve the SO
2
removal efficiency of the sorbent. The analyzed XRD patterns showed
that K
2
SO
4
was the main desulfurization product,
which was consistent with the SEM/EDS analysis. The experimental results
were well-described with the Lagergren first-order adsorption kinetics
model with the activation energy (
E
a
)
of the SO
2
adsorption by KOH/char sorbent of 20.25 kJ/mol.
A series of Mn0.15Fe0.05/fly-ash catalysts have been synthesized by the co-precipitation method using coal fly ash (FA) as the catalyst carrier. The catalyst showed high catalytic activity for low-temperature selective catalytic reduction (LTSCR) of NO with NH3. The catalytic reaction experiments were carried out using a lab-scale fixed-bed reactor. De-NOx experimental results showed the use of optimum weight ratio of Mn/FA and Fe/FA, resulted in high NH3-SCR (selective catalytic reduction) activity with a broad operating temperature range (130–300 °C) under 50000 h−1. Various characterization methods were used to understand the role of the physicochemical structure of the synthesized catalysts on their De-NOx capability. The scanning electron microscopy, physical adsorption-desorption, and X-ray photoelectron spectroscopy showed the interaction among the MnOx, FeOx, and the substrate increased the surface area, the amount of high valence metal state (Mn4+, Mn3+, and Fe3+), and the surface adsorbed oxygen. Hence, redox cycles (Fe3+ + Mn2+ ↔ Mn3+ + Fe2+; Fe2+ + Mn4+ ↔ Mn3+ + Fe3+) were co-promoted over the catalyst. The balance between the adsorption ability of the reactants and the redox ability can promote the excellent NOx conversion ability of the catalyst at low temperatures. Furthermore, NH3/NO temperature-programmed desorption, NH3/NO- thermo gravimetric-mass spectrometry (NH3/NO-TG-MS), and in-situ DRIFTs (Diffuse Reflectance Infrared Fourier Transform Spectroscopy) results showed the Mn0.15Fe0.05/FA has relatively high adsorption capacity and activation capability of reactants (NO, O2, and NH3) at low temperatures. These results also showed that the Langmuir–Hinshelwood (L–H) reaction mechanism is the main reaction mechanism through which NH3-SCR reactions took place. This work is important for synthesizing an efficient and environmentally-friendly catalyst and demonstrates a promising waste-utilization strategy.
Thermal diffusion (TD) salt bath chromizing of cold working dies was studied. Firstly, it obtained an ideal salt bath formula by comparing with a variety of formulas, and then obtained the influence rule of coating thickness based on studying of some process parameters. The microstructure morphologies and phase structures of the TD chromizing coating were investigated by X-ray diffraction (XRD), energy-dispersive spectrometry (EDS) and other modern analysis methods. Meanwhile, it carried out a system of testing and analysis of coating, such as hardness, wear resistance, etc.
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