Adsorption behaviors of VOCs under coal-combustion flue gas environment using activated carbon injection coupled with bag filtering system

Enhanced mitigation of inhalable particles and fine particle-bound PAHs from a novel hazardous waste-power plant candidate

Emissions of the inhalable particle (dp < 10 μm, PM10) and their harmful compositions from combustion sources have high potential on health risk with nearly no regulation. This study investigates the particle size distribution (PSD), as well as the removal mechanism of PM10 and fine particle (FP)-bound polycyclic aromatic hydrocarbons (PAHs) from the flue gas of a hazardous waste thermal treatment system. It has ultralow regulated emission and becomes a candidate of power generation module. A series of the advanced scrubbers, cyclonic demister, and baghouse was equipped for multi-pollutant control. The moderate or intense low oxygen dilution (MILD) combustion effectively inhibited the PM2.5 generation by volumetric oxidation. Advanced scrubbers removed PM1, PM2.5, and PM10 by 85.24, 68.68, and 97.60%, respectively, which achieved by local supersaturation, heterogeneous condensation of water vapor, and the growth of fine PM. Moreover, the scrubbers effectively scavenged the course PM10 containing the high-molecular-weight PAH homologs onto the water phase but promoted the condensation and absorption of the lighter homologs onto the fine particle surface (dp ∼5.3 μm). The size window (dp = 0.3-1.0 μm) of the minimum efficiency reporting value of a BH filtration led to the peak of FP-PAH mass and BaP equivalent (BaPeq) toxicity at dp = 0.1-0.4 and 0.1-0.8 μm, respectively. Consequently, the synergy of MILD combustion and the SCB-CYC-BH system effectively inhibited the PM2.5, PM10, PM2.5-PAHs, and FP-PAH levels from a waste thermal treatment process and further mitigated the potential health risk.

Conversion mechanism of selenium on activated carbon surface: Experimental and density functional theory study

The mechanism of SeO2 capture by activated carbon (AC) was explored via combining experiments with density functional theory (DFT). Adsorption experiments confirmed that after mass loss coefficient correction of AC, the selenium capture capacity of AC reached 7.76 mg/g at 350 °C. AC reached a saturated selenium removal capacity of 9.93 mg/g at 50 min. The weight loss curve recorded the temperature window of selenium desorption on AC surface at about 305 °C. The XPS spectrum revealed that the decomposition and reduction behavior of SeO2 on the AC surface promoted the existence of selenium in the form of Se0. DFT calculations showed that SeO2 was chemically adsorbed on the typical Armchair and Zigzag surfaces of AC, and the adsorption energies of the most stable structures were - 89.77 and - 235.12 kcal/mol, respectively. The effect of temperature on selenium capture via AC was studied by thermodynamic and kinetic analysis. Temperature increase promoted the decomposition and reduction of SeO2 on the AC surface. Kinetic analysis further confirmed that the transformation of Se4+→Se0 was more dominated by decomposition behavior. A part of SeO2 in the gas phase was reduced to Se0 by CO and enriched on AC as elemental selenium.

Technological solutions for NOx, SOx, and VOC abatement: recent breakthroughs and future directions

NOx, SOx, and carbonaceous volatile organic compounds (VOCs) are extremely harmful to the environment, and their concentrations must be within the limits prescribed by the region-specific pollution control boards. Thus, NOx, SOx, and VOC abatement is essential to safeguard the environment. Considering the importance of NOx, SOx, and VOC abatement, the discussion on selective catalytic reduction, oxidation, redox methods, and adsorption using noble metal and non-noble metal-based catalytic approaches were elaborated. This article covers different thermal treatment techniques, category of materials as catalysts, and its structure-property insights along with the advanced oxidation processes and adsorption. The defect engineered catalysts with lattice oxygen vacancies, bi- and tri-metallic noble metal catalysts and non-noble metal catalysts, modified metal organic frameworks, mixed-metal oxide supports, and their mechanisms have been thoroughly reviewed. The main hurdles and potential achievements in developing novel simultaneous NOx, SOx, and VOC removal technologies are critically discussed to envisage the future directions. This review highlights the removal of NOx, SOx, and VOC through material selection, properties, and mechanisms to further improve the existing abatement methods in an efficient way.

Biomass Derived, Hierarchically Porous, Activated Starbons® as Adsorbents for Volatile Organic Compounds

The use of potassium hydroxide activated Starbons® derived from starch and alginic acid as adsorbents for 29 volatile organic compounds (VOCs) was investigated. In every case, the alginic acid derived Starbon (A800K2) was found to be the optimal adsorbent, significantly outperforming both commercial activated carbon and starch derived, activated Starbon (S800K2). The saturated adsorption capacity of A800K2 depends on both the size of the VOC and the functional groups it contains. The highest saturated adsorption capacities were obtained with small VOCs. For VOC's of similar size, the presence of polarizable electrons in lone pairs or π-bonds within non-polar VOCs was beneficial. Analysis of porosimetry data suggests that the VOC's are being adsorbed within the pore structure of A800K2 rather than just on its surface. The adsorption was completely reversible by thermal treatment of the saturated Starbon under vacuum.

Adsorption of multicomponent VOCs on various biomass-derived hierarchical porous carbon: A study on adsorption mechanism and competitive effect

Biomass-derived porous carbon materials are potential adsorbents for VOCs. In this work, biomass-derived nitrogen-doped hierarchical porous carbons (NHPCs) were synthesized by a one-step pyrolysis activation combined with nitrogen doping method from several biomass wastes (corn straw, wheat stalk, bamboo, pine, and corncob). NHPCs have a hierarchical porous structure with micro-meso-macropores distribution, nitrogen doping, large specific surface area, and pore volume. The corncob derived carbon (NHPC-CC) has the best activation result as analyses showed that a lower ash content and higher total cellulose composition content of the biomass result in a better pore activation effect. Single and multi-component dynamic adsorption tests of typical VOCs (benzene, toluene, and chlorobenzene) were conducted on NHPCs in laboratory conditions (∼500 ppm). Promising VOC adsorption capacity and great adsorption kinetics with low mass transfer resistance were found on NHPCs. Correlation analysis showed that the high VOC adsorption capacity and great adsorption kinetics can be attributed to the large surface area of micro-mesopores and the mass transfer channels provided by meso-macropores respectively. The competitive dynamic adsorption tests revealed that the VOC with lower saturated vapor pressure has more adsorption sites on the surface of micro-mesopores and stronger adsorption force, which results in the higher adsorption capacity and desorption caused by substitution reaction in VOCs competitive adsorption process. In detail, the process of toluene and chlorobenzene competitive adsorption was described. Besides, well recyclability of NHPC-CC was revealed as the VOCs adsorption capacity reductions were less than 10% after four adsorption-desorption cycles. All studies showed that the NHPC-CC could be potential adsorbent for VOCs in industrial process.