Coupling mechanism of activated carbon mixed with dust for flue gas desulfurization and denitrification

Oxidative and Extractive Desulfurization of Fuel Oils Catalyzed by N-Carboxymethyl Pyridinium Acetate and N-Carboxyethyl Pyridinium Acetate Acidic Ionic Liquids: Experimental and Computational DFT Study

This study reports on the synthesis, characterization, and application of two acidic ionic liquids, namely, N-carboxymethylpyridinium acetate ([HO2CCH2Py][CH3CO2] or AIL1) and N-carboxyethylpyridinium acetate ([HO2C(CH2)2Py][CH3CO2] or AIL2), as both extractants and catalysts for the oxidative and extractive desulfurization (OEDS) of model fuel oils containing heteroaromatic sulfur compounds. The structural properties of the synthesized acidic ionic liquids (ILs) were confirmed by 1H NMR, 13C NMR, and FT-IR spectroscopic analysis. To optimize the performance of the acidic AILs in the desulfurization process, the effects of different parameters, such as H2O2 dosage, reaction time, and temperatures, were investigated. The experimental results showed that AIL1 has exceptionally high desulfurization-extraction rates, with values of 99.8%, 97.8%, and 95.4%, for DBT, BT, and 4,6-DMDBT, respectively, under the optimum conditions established. Under the same conditions, the desulfurization-extraction rates using AIL2 reached 91.6%, 87.3%, and 82.4%, respectively, for DBT, 4, 6-DMDBT, and BT. Both ionic liquids can be recycled up to 9 times without a significant decrease in their sulfur removal efficiencies. Furthermore, density functional theory (DFT) calculations were conducted to evaluate the electronic interaction energies (ΔIE) between the AILs with each of the sulfur-containing compounds and their putative oxidized products. The computational findings strongly supported the experimental outcomes.

Performance on desulfurization and denitrification of one-step produced activated carbon for purification of sintering flue gas

An innovative one-step process for activated carbon production from low-rank coal is proposed in this research by applying oxidized pellets as activator. The new process can realize synchronous production of the activated carbon and direct reduction iron through combination of carbonization and activation of low-rank coal in one step while no solid wastes were discharged. The desulfurization and denitrification performance of the obtained activated carbon was also evaluated on the simulative sintering flue gas in comparison with one type of commercial activated carbon. The results indicated that a superior activated carbon with high specific surface area of 370.42 m² g^-1, iodine sorption value of 695.13 mg g^-1, compressive strength of 315 N·per^-1and abrasive resistance of 96.61%, can be prepared under suitable conditions of activation temperature at 850 °C for 140 min with C/Fe mass ratio of 2.5. Meanwhile, the direct reduction iron has a metallization ratio of 88.31%. The activated carbon has a preferable desulfurization performance with the breakthrough sulfur capacity of 5.463 mg/g and breakthrough time of 46.33 min, and single denitrification performance with the breakthrough nitric capacity of 1.935 mg/g and breakthrough time of 90.17 min at flue gas temperature of 80 °C, airspeed ratio of 8370 h^-1, gas flow of 1.8 m³/h, and oxygen concentration of 16%. The denitrification of activated carbon in the simultaneous desulfurization and denitrification process can be improved by catalytic reduction via the transformation from NO to N₂. The good results show that this process has a bright future with high technical and economic feasibility.

Effect of Na2CO3, HF, and CO2 Treatment on the Regeneration of Exhausted Activated Carbon Used in Sintering Flue Gas

The method of continuous treatment with Na₂CO₃ solution, HF solution, and CO₂ was proposed for the regeneration of the exhausted activated carbon (EAC) produced in the sintering flue gas purification process. In order to obtain the optimal operation conditions, the effect of key parameters such as Na₂CO₃ solution concentration, HF solution concentration, and CO₂ activation temperature on the sulfur conversion rate and regeneration efficiency was analyzed. Also, the N₂ adsorption, Brunauer-Emmett-Teller analysis, scanning electron microscopy-energy dispersive spectrometry, X-ray diffraction, X-ray fluorescence, and Fourier transform infrared spectroscopy were adopted to investigate the deactivation reason and the change of the physical-chemical properties. The results showed that the deactivated EAC was mainly due to the deposition of inorganic compounds such as CaSO₄, SiO₂, and KCl to block the pores. Continuous treatment with Na₂CO₃ solution and HF solution could remove the inorganic compounds effectively. CO₂ activation treatment further developed the blocked porosity and decreased the surface acidity. The optimal conditions for the regeneration of EAC were a Na₂CO₃ concentration of 0.5 mol/L, an HF concentration of 0.8 mol/L, and a CO₂ activation temperature of 1073 K with the activation time of 1 h, corresponding to the specific surface area of 607.91m²/g. In the fourth regeneration cycle, the adsorption performance during the successive adsorption-regeneration process could still maintain a high level and the regeneration efficiency was 95.31%.

Study on the Flow Characteristics of Desulfurization Ash Fine Particles in a Circulating Fluidized Bed

In view of the current status of catalytic cracking flue gas treatment, it is necessary to study the flow environment of desulfurization ash particles, which are a type of Geldart C particle, in a circulating fluidized bed (CFB) for semi-dry flue gas desulphurization using CFB technology. This study investigated the flow characteristics of desulphurization ash particles in a riser with an inner diameter of 70 mm and a height of 12.6 m, at a gas velocity of 4–7 m/s and a solids circulation rate of 15–45 kg/m2·s. The solids holdup in the axial distribution is relatively high near the bottom of the riser, and gradually decreases as the riser height increases, with a stable value from the middle to the top of the riser. In the radial distribution, the solids holdup of desulfurization ash particles is low in the center and high in the wall region. Within the above operating conditions, the solids holdup ranges from 0.008 to 0.025. The particle-based Archimedes number has a linear relationship with the solids holdup at all operating conditions.

New Insights on Competitive Adsorption of NO/SO2 on TiO2 Anatase for Photocatalytic NO Oxidation

Here, we investigate competitive adsorption and photocatalytic reaction over TiO₂@SiO₂: NO conversion efficiency decreases by 29.1%, and the adsorption capacity decreases from 0.125 to 0.095 mmol/g due to the influence of SO₂. According to identification and comparative analysis of the IR signal, SO₂ has little effect on the NO conversion route and intermediates (adsorbed NO → nitrite → nitrate), but accelerates the deactivation of catalysts. The electronic interaction scheme from density functional theory (DFT) confirms that surface hydroxyls create an unsaturated coordination of neighboring Ti or O atoms, which is favorable for NO/SO₂ adsorption on anatase (101). In addition, the lone pair electrons of N or S atoms prefer to be delocalized and form covalent bonds with active surface-O on the (101) facet with terminal hydroxyls. However, preadsorbed SO₂ could offset the increase of hydroxyls and strongly inhibit NO adsorption, which is consistent with the result performance evaluation. A possible reaction mechanism characterized by oxygen vacancies and·O₂^- is proposed, while the essential reason of catalyst deactivation and regeneration is theoretically analyzed based on the experimental and DFT calculation.

O3 oxidation combined with semi-dry method for simultaneous desulfurization and denitrification of sintering/pelletizing flue gas

With the vigorous development of China's iron and steel industry and the introduction of ultra-low emission policies, the emission of pollutants such as SO₂ and NO_x has received unprecedented attention. Considering the increase of the proportion of semi-dry desulfurization technology in the desulfurization process, several semi-dry desulphurization technologies such as flue gas circulating fluidized bed (CFB), dense flow absorber (DFA) and spray drying absorption (SDA) are briefly summarized. Moreover, a method for simultaneous treatment of SO₂ and NO_x in sintering/pelletizing flue gas by O₃ oxidation combined with semi-dry method is introduced. Meantime, the effects of key parameters such as O₃/NO molar ratio, CaSO₃, SO₂, reaction temperature, Ca/(S+2N) molar ratio, droplet size and approach to adiabatic saturation temperature (AAST) on denitrification and desulfurization are analyzed. Furthermore, the reaction mechanism of denitrification and desulfurization is further elucidated. Finally, the advantages and development prospects of the new technology are proposed.