Adverse Effects of Inherent CaO in Coconut Shell-Derived Activated Carbon on Its Performance during Flue Gas Desulfurization.

Activated carbon has been used commercially to remove SO2 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.

Mechanistic Study of Selective Absorption of NO in Flue Gas Using EG-TBAB Deep Eutectic Solvents.

The selective absorption of NO in flue gas has been investigated using a series of deep eutectic solvents (DESs) as novel denitrifying agents. The EG-TBAB DESs used in this work are composed of a hydrogen donor ethylene glycol (EG) and a parent salt tetrabutylammonium bromide (TBAB). Effects of DES composition (EG:TBAB molar ratio), operation temperature, residence time, and O2 concentration in the flue gas on denitrification performances of EG-TBAB DESs have been investigated. The highest denitrification efficiency and capacity were achieved using EG to TBAB molar ratio of 50:1 at an operation temperature of 50 °C. The O2 partial pressure in the flue gas showed no noticeable effects on NO absorption in EG-TBAB DESs. EG-TBAB DESs maintain high denitrification stability after five absorption-desorption cycles. The calculated absorption equilibrium constant ( K0) and Henry's law constant ( H) showed that EG-TBAB DESs exhibited high absorption capacity for NO molecules, indicating that they are applicable in industrial denitrification processes. The kinetics analysis of NO absorption in EG-TBAB DESs indicated that EG-TBAB DESs could effectively absorb NO and the absorption of NO was strongly influenced by mass transfer.

Coal-based carbon nanosheets contained carbon microfibers modified with grown carbon nanotubes as efficient air electrode material for rechargeable zinc-air batteries.

Coal-based oxygen electrocatalysts hold immense promise for cost-effective applications in rechargeable Zn-air batteries (ZABs) and the value-added, clean utilization of traditional coal resources. Herein, an electrospun membrane electrode comprising coal-derived carbon nanosheets and directly grown carbon nanotubes (CNS/CMF@CNT) was successfully synthesized. The hierarchical porous structure of the electrode, composed of multiple components, significantly facilitates mass and ion transportation, resulting in exceptional electrochemical performance. Employing Fe as the catalyst for CNT growth, the CNS/CMF@CNT electrode exhibits a remarkable onset potential of 0.96 V and a half-wave potential of 0.87 V in the oxygen reduction reaction (ORR). In-situ surface-enhanced Raman spectroscopy reveals that hydroxyl radical desorption on the surface of CNS/CMF@CNT(Fe) is the rate-determining step of the ORR. Notably, the aqueous ZAB featuring the CNS/CMF@CNT(Fe) electrode achieved a peak power density of 216.0 mW cm-2 at a current density of 414 mA cm-2 and maintained a voltage efficiency of 65.1 % after 2000 charge/discharge cycles at 5 mA cm-2. Furthermore, the all-solid-state ZAB incorporating this electrode displayed an open-circuit voltage of 1.43 V, a peak power density of 70.1 mW cm-2 at a current density of 110 mA cm-2, and a voltage efficiency of 66.5 % after 150 charge/discharge cycles. The utilization of abundant coal as the raw material for electrode fabrication not only brings conceivable economic benefits in ZAB construction, but also commendably advances the effective application of traditional coal resources in a more sustainable manner.

S/N-codoped carbon nanotubes and reduced graphene oxide aerogel based supercapacitors working in a wide temperature range.

Among many supercapacitor electrode materials, carbon materials are widely used due to their large specific surface area, good electrical conductivity and high economic efficiency. However, carbon-based supercapacitors face the challenges of low energy density and limited operating environment. This work reports a facile self-assembled method to prepare three-dimensional carbon nanotubes/reduced graphene oxide (CNTs/rGO) aerogel material, which was applied as both positive and negative electrodes in a symmetric superacapacitor. The fabricated supercapacitor exhibited prominent capacitive performance not only at room temperature, but also at extreme temperatures (-20 âˆ¼ 80 °C). The specific capacitances of the symmetric supercapacitors based on CNTs/rGO at a weight ratio of 2:5 respectively reached 107.8 and 128.2 F g-1 at 25 °C and 80 °C with KOH as the electrolyte, and 80.0 and 144.6 F g-1 at -20 °C and 60 °C with deep eutectic solvent as the electrolyte. Notably, the capacitance retention and coulombic efficiency of the assembled supercapacitors remained almost unchanged after 20,000 cycles of charge/discharge test over a wide temperature range. The work uncovered a possibility for the development of high-performance supercapacitors flexibly operated at extreme temperatures.

Effective Absorption Mechanism of SO2 and NO2 in the Flue Gas by Ammonium-Bromide-Based Deep Eutectic Solvents.

Simultaneous capture of SO2 and NO x from flue gas is critical for coal-fired power generation. In this study, environmentally friendly and high-performance deep eutectic solvents based on ethylene glycol and ammonium bromide were designed to capture SO2 and NO2 simultaneously. The SO2 and NO2 absorption performances and absorption mechanisms were systematically investigated by 1H NMR and Fourier transform infrared (FT-IR) spectroscopy in combination with ab initio calculations using Gaussian software. The results showed that EG-TBAB DESs can absorb low concentrations of SO2 and NO2 from the flue gas simultaneously at low temperatures (≤50 °C). 1H NMR, FT-IR, and simulation results indicate that SO2 and NO2 are absorbed by forming EG-TBAB-SO2-NO2 complexes, Br- is the main active site for NO2 absorption, and NO2 is more active in an EG-TBAB-NO2-SO2 complex than SO2. EG-TBAB DESs exhibit outstanding regeneration capability, and absorption capacities remain unchanged after five absorption-desorption cycles. The fundamental understanding of simultaneous capture of SO2 and NO2 from this study enables DES structures to be rationally designed for efficient and low-cost desulfurization and denitrification reagents.

Desulfurization Performance and Kinetics of Potassium Hydroxide-Impregnated Char Sorbents for SO2 Removal from Simulated Flue Gas.

Potassium hydroxide-impregnated char sorbents (KOH/char) prepared via an ultrasonic-assisted method were used for SO2 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 SO2 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 O2 present in the solvent could improve the SO2 removal efficiency of the sorbent. The analyzed XRD patterns showed that K2SO4 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 SO2 adsorption by KOH/char sorbent of 20.25 kJ/mol.

Mechanistic Study on the Removal of NO2 from Flue Gas Using Novel Ethylene Glycol-tetrabutylammonium Bromide Deep Eutectic Solvents.

The removal of NO x (approximately 90% of which is NO) from flue gas is a crucial process for clean power generation from coal combustion. Oxidation of NO to NO2 followed by NO2 absorption using sorbents is considered to be a promising technology alternative to selective catalytic reduction (SCR). This study investigated the absorption of NO2 in flue gas by ethylene glycol (EG)-tetrabutylammonium bromide (TBAB) deep eutectic solvents (DESs) under a range of experimental conditions. The effects of experimental conditions including molar ratio of EG to TBAB, operating temperature, residence time, and the O2 and steam partial pressure in the flue gas on the denitrification performance of EG-TBAB DESs were systematically analyzed. The concentrations of NO2 in the inlet and outlet were evaluated using a flue gas analyzer. The chemical structure changes of DESs after denitrification were characterized using Fourier transform infrared (FT-IR) spectroscopy. The obtained analysis signified that maximum denitrification efficiency and capacity were achieved at a EG/TBAB molar ratio of 5:1, 50 °C, and 6 s residence time. EG-TBAB DESs were able to maintain a stable denitrification performance after five absorption-desorption cycles. The results of quantum chemical calculation and 1H NMR spectra of EG-TBAB DES show that bromide anions in the EG-TBAB DES maintained strong interactions with NO2 via hydrogen bonding, leading to increased NO2 adsorption. The presence of O2 and steam in the flue gas improved the absorption of NO2 in EG-TBAB DESs due to chemical reactions and formation of nitrate.

Combustion characteristics and air pollutant formation during oxy-fuel co-combustion of microalgae and lignite.

Oxy-fuel combustion of solid fuels is seen as one of the key technologies for carbon capture to reduce greenhouse gas emissions. The combustion characteristics of lignite coal, Chlorella vulgaris microalgae, and their blends under O2/N2 and O2/CO2 conditions were studied using a Thermogravimetric Analyzer-Mass Spectroscopy (TG-MS). During co-combustion of blends, three distinct peaks were observed and were attributed to C. vulgaris volatiles combustion, combustion of lignite, and combustion of microalgae char. Activation energy during combustion was calculated using iso-conventional method. Increasing the microalgae content in the blend resulted in an increase in activation energy for the blends combustion. The emissions of S- and N-species during blend fuel combustion were also investigated. The addition of microalgae to lignite during air combustion resulted in lower CO2, CO, and NO2 yields but enhanced NO, COS, and SO2 formation. During oxy-fuel co-combustion, the addition of microalgae to lignite enhanced the formation of gaseous species.