PM Removal Research Articles

An Advanced Dual‐Function MnO2‐Fabric Air Filter Combining Catalytic Oxidation of Formaldehyde and High‐Efficiency Fine Particulate Matter Removal

AbstractComprehensive treatment of indoor contaminants such as volatile organic compounds (VOCs) and fine particulate matter (PM2.5) using transition metal oxide catalysts or functional fibrous filters has gained substantial attention recently. However, coupling VOC oxidation catalysts into high‐performance filter systems remains a challenge. Herein, an overall solution to strongly bind manganese dioxide (MnO2) nanocrystals onto polypropylene (PP) nonwoven fabrics is provided. For the first time, uniform heterogeneous nucleation and growth of MnO2 onto PP nonwoven fabrics using intermediate inorganic nucleation films, including Al2O3, TiO2, and ZnO, formed conformally on the fabrics via atomic layer deposition (ALD) are demonstrated. How different ALD thin films influence the crystallinity, morphology, surface area, and surface oxygen species of the MnO2 grown ALD‐coated PP fibers is further investigated. In addition to uniformity and integrity, ZnO thin films give rise to MnO2 crystals with the largest fraction of available surface oxygen, enabling 99.5% catalytic oxidation of formaldehyde within 60 min. Moreover, the metal oxide filters provide excellent PM removal efficiencies (ePM), achieving ePM2.5 90% and ePM10 98%, respectively, making the approach an outstanding method to produce fully dual‐functional filtration media.

Copper//terbium dual metal organic frameworks incorporated side-by-side electrospun nanofibrous membrane: A novel tactics for an efficient adsorption of particulate matter and luminescence property

Particulate matters with different sizes (PM2.5 and PM10) in the air have become a supreme environmental concern to human health globally. Herein, the magnetic-luminescent Cu//Tb dual metal-organic frameworks (MOFs) incorporated side-by-side nanofibrous (SBS-NFs) membrane has been successfully fabricated via the electrospinning technique with the self-designed nozzle for the first time. The fabricated SBS-NFs membrane was composed of Cu-MOF/PAN at one side and Tb-MOF/PAN at another side with their individual characteristics. The Cu-MOF was used to improve the filtration efficiency and reduced the pressure drop by enhancing the electrostatic interaction, whereas, Tb-MOF was incorporated to investigate the PM adsorption process through the changes in luminescence intensity. Compared to polyacrylonitrile nanofibers (PAN NFs), Cu//Tb dual MOFs incorporated SBS-NFs membrane showed an enhanced filtration efficiency (90.2%) and a reduced pressure drop (60.7 Pa) when sodium chloride (NaCl) aerosols with particle size less than 300 nm were used for testing. As a result of the filter test using car exhaust, Cu//Tb SBS-NFs membrane still maintained >91% PM removal efficiency for >30 h. In addition, it was confirmed that the luminescence intensity over the PM adsorption time was linearly weakened. Therefore, Cu//Tb dual MOFs incorporated SBS-NFs membrane can be used for a variety of applications.

Research on removal of NOX, SO2 and PM from flue gas of coal-fired boilers and engineering application

Removal of NOX and SO2 from flue gas by Ozone (O3) oxidation and NaOH absorption was carried out in practical engineering. The effects of the liquid to gas ratio (L/G), the molar ratio of O3 dosage and initial content of NOX (O3/NOX), pH and NaOH concentrations on the removal efficiencies of NOx and SO2 were investigated. In addition, the influences of O3/NOX and voltage on the removal of PM were analyzed. The results show that the NOX removal efficiency increases with the increasing of O3/NOX (0∼2.0), solution pH (4∼7) and L/G (2∼8), while is slightly affected by NaOH concentration (0.05∼1%). The SO2 removal efficiency increases with the increase of L/G from 2 to 8 L/Nm3, but is hardly changed by O3/NOX (0∼2.0), NaOH concentration (0.05∼1%) and solution pH (4∼10). It was found that the outlet concentration of PM (CPM) decreased with the rise of voltage ranging from 0 to 40 kV, however, slightly increases with the increment of O3/NOX at a range from 1.6 to 2.0. The optimal operating conditions can be established when taking running costs and rigorous ultra-low emission standards into consideration. Under the optimal conditions, the removal efficiencies of NOX and SO2 reached more than 75% and 98% respectively, and CPM could be also controlled within 5 mg/Nm3.

Highly porous SiC cellular ceramics for efficient high-temperature PM removal

The design and synthesis of new filtration materials for high-temperature particulate matter capture are of both technological and scientific importance but still remain a challenging task. In the current work, we presented an approach for the manufacturing of highly porous SiC cellular ceramics by combining polyether polyol-modified carbon black with polyurethane foaming method. Hydroxyl groups were introduced to the surface of carbon black to prevent agglomeration. As-obtained SiC cellular ceramic possed three-dimensional interconnected reticular architecture with the abundant micron-sized window on its cell wall. The resulting porous SiC ceramic exhibited a high removal efficiency (95.8%) with extremely low pressure drop (38 Pa). The successful fabrication of such fascinating material may provide new insights for high-temperature particulate matter filtration.

Multifunctional nickel nanofiber for effective air purification: PM removal and NO reduction from automobile exhaust

Particulate matter and NO pollution caused by automobile exhaust cause severe air pollution and respiratory diseases. Traditional gasoline particulate filter and three-way catalysts face the problem of high cost and no resistance to high temperature. Development of multifunctional filtration purification media with low cost and temperature resistance is necessary. In this paper, Ni nanofibers filter is easily fabricated by electrospinning, suitable for working environment with variable temperature. Moreover, between adjacent nanofibers, the preferable fused junction was formed which is beneficial to mechanical properties of the filter. The Ni nanofibers filter exhibits outstanding PM1 and NO gas removal ability. The PM1 filtration efficiency up to 99.86% @300 nm was achieved under wing speed of 5.3 cm/s. Moreover, the Ni nanofibers also achieve impressive NO-to-N2 and NO adsorption ability owing to the high specific surface area and activity of Ni nanofiber itself. As such, the multifunctional Ni nanofibers filter equips the potential for the actual application in automobile exhaust purification converter.

PM combustion enhancement to reduce continuous regeneration temperature of fluidized bed type PM removal device using catalyst-doped bed particle

A fluidized bed type PM removal device was developed by focusing on adhesion force as a highly efficient device for PM collection and low-temperature continuous regeneration. To further reduce the continuous regeneration temperature of this device, catalytic PM combustion was investigated. Alkaline and alkaline earth metals (potassium and calcium, respectively) are effective for PM combustion and are among the least expensive catalysts. The positive effects of these catalysts on PM combustion were compared. As their catalytic performances are almost identical, potassium was used for the continuous regeneration of this device. Potassium was doped on the bed particle via the impregnation method. Moreover, the amounts of doped potassium were compared based on the effects of PM combustion on collection efficiency, and the optimum value was determined to be 1.58 g-catalyst/kg-bed particle. Catalyst characterization was conducted via XRD and FTIR analysis of the cleaned gas. K2CO3 is detected on bed particle surface from the XRD patterns. The FTIR results show that potassium promotes PM combustion and selectively enhanced CO2 generation. CO2 is generated from the oxidation of K2CO3 and transformation of K2O2 to K2O with the consumption of PM. K2O is converted to K2CO3 with the re-absorption of CO2. The lowest continuous regeneration temperature decreases to 350 °C with maintaining the collection efficiency 100% owing to the catalytic PM combustion. Furthermore, the effect of water vapor, which is present in exhaust gas, was investigated. It promotes PM combustion and further reduces the continuous regeneration temperature to 330 °C.

Indoor and outdoor concentration of PM10, PM2.5 and PM1 in residential building and evaluation of negative air ions (NAIs) in indoor PM removal

ABSTRACT The present work was conducted in a two-part study. In part I, the levels of indoor and outdoor PM10, PM2.5, and PM1 was measured using real time GRIMM dust monitors. In part II, the performance of NAIs method was investigated on reduction of indoor concentration of PM in these residential buildings for the first time. Hourly average concentration and standard deviation (SD) of PM10 in indoor and outdoor at residential buildings were 63.5 ± 27.4 and 90.1 ± 33.5 µg/m3, respectively. Indoor and outdoor concentrations of PM2.5 in residential buildings were 39.4 ± 18.1 and 49.5 ± 18.2 µg/m3 and for PM1 the concentrations were 4.3 ± 7.7 and 6.5 ± 10.1 µg/m3, respectively. We estimated that nearly 71.47% of PM10, 79.86% of PM2.5 and of 61.25% of PM1 in indoor of residential buildings can be removed by negative air ions.

Effect of Functional Groups of Metal-Organic Frameworks, Coated on Cotton, on Removal of Particulate Matters via Selective Interactions.

Currently, the contamination of air with particulate matters (PMs such as PM2.5 and PM10) is very severe, especially in Asian countries. Metal-organic frameworks (MOFs), with or without extra functional groups such as -NH2 and -NH-SO3H, were coated on conventional cotton to improve the efficiency of filters (composed of cotton fabric) in the removal of PMs from air. More importantly, the effect of the functional group of MOFs on the effective PM removal was analyzed quantitatively for the first time and could be interpreted via selective interactions. The removal efficiency was increased on the order: cotton < UiO-66/cotton < UiO-66-NH2/cotton < UiO-66-NH-SO3H/cotton, and the efficiency of the UiO-66-NH-SO3H-coated cotton was more than three times that of the pristine cotton. Moreover, the quality factor of cotton was more than doubled (or, 2.5-3 times) by UiO-66-NH-SO3H (only 20%) coating. The plausible mechanism for PM removal could be suggested based on the characterization of captured PM and introduced functional groups on MOFs. Based on the removal efficiency, pressure drop, and quality factor, coating of MOFs with functional groups, especially that are effective for charge separations (such as -SO3H), is one of the promising ways to improve the performance of PM filters. Moreover, the suggested strategy might be applied in capturing most of PMs composed of oxides, ammonium species, and carbons with polar outside.

Active botanical biofiltration of air pollutants using Australian native plants

Air pollutants are of public concern due to their adverse health effects. Biological air filters have shown great promise for the bioremediation of air pollutants. Different plant species have previously been shown to significantly influence pollutant removal capacities, although the number of species tested to date is small. The aims of this paper were to determine the pollutant removal capacity of different Australian native species for their effect on active biowall particulate matter, volatile organic compounds and carbon dioxide removal, and to compare removal rates with previously tested ornamental species. The single-pass removal efficiency for PM and VOCs of native planted biofilters was determined with a flow-through chamber. CO2 removal was tested by a static chamber pull down study. The results indicated that the native species were not effective for CO2 removal likely due to their high light level requirements in conjunction with substrate respiration. Additionally, the native species had lower PM removal efficiencies compared to ornamental species, with this potentially being due to the ornamental species possessing advantageous leaf traits for increased PM accumulation. Lastly, the native species were found to have similar benzene removal efficiencies to ornamental species. As such, whilst the native species showed a capacity to phytoremediate air pollutants, ornamental species have a comparatively greater capacity to do so and are more appropriate for air filtration purposes in indoor circumstances. However, as Australian native plants have structural and metabolic adaptations that enhance their ability to tolerate harsh environments, they may find use in botanical biofilters in situations where common ornamental plants may be suitable, especially in the outdoor environment.

Particulate Matter Emission Reduction from Marine Diesel Engines by Electrohydrodynamic Methods

Abstract Particulate matter (PM) and gaseous compounds (SO2, NOx, VOC) emitted by diesel engines causes serious global environmental problems and health impact. Despite numerous evidences about the harmfulness of diesel particles, the PM emission by diesel engines used by ships, cars, agricultural machines, or power generators is still unregulated, and the efficient removal of PM from diesel exhausts is still the major technological challenge. In order to comply with the International Maritime Organization regulation, the NOx emission is reduced by using selected catalytic reactor, and sulphur oxide emission has been reduced by using fuels of low sulphur content. However, both of those measures cannot be used for the reduction of PM emission produced during combustion of marine fuels. The lack of appropriate regulations results from insufficiently developed technology, which could remove those particles from exhaust gases. Conventional scrubbers currently available on the market remove only sulphur oxide with required collection efficiency, but the collection efficiency for PM2.5 is below 50%. The article discusses the technical means used for the removal of PM from marine diesel engines via applying electrohydrodynamic methods, in particular electrostatic agglomeration, as a method of nanoparticles coagulation to larger agglomerates, which could operate in two-stage electrostatic precipitation systems, and electrostatic scrubbers, which remove particles by electrically charged water droplets. The experimental results were obtained for a 2-stroke 73 kW diesel engine fuelled with marine gas oil (MGO). The agglomerator allowed increasing the collection efficiency from diesel exhausts for PM2.5 particles by about 12%, compared to electrostatic precipitator operating without agglomerator, and the total mass collection efficiency was above 74%. The collection efficiency of electrostatic scrubber was higher than 95wt.%. The advantage of using the electrostatic scrubber is that it can also reduce the SO2 emission by more than 90%, when HFO is used.

A new cyclone design with adjustable inlet angle and external geometry for optimal PM10 removal

In this study, a 2D2D cyclone layout was used as the base structure for the design of a new cyclone with an adjustable inlet angle and vortex finder height. The optimal conditions for the removal of fine particles were studied analytically and experimentally in the laboratory. The purpose of this study is to optimize the performance of the cyclone with different inlet angles to enhance particulate matter PM10 removal efficiency. The ASTM_D3685 method was used for sampling and testing the main factors. To determine the relationship between the variables and the study purpose, the data were analyzed using Minitab software (19). The results showed that the efficiencies of the removal of PM and particles with diameters of 10 μm, 4.7 μm, and 1 μm were 73.5%, 90%, 75%, and 60%, respectively. The cyclone was effective under a low suction pressure and 90° inlet angle, and a vortex finder height $$h_{\text{vf}} = \frac{1}{2}D$$. By optimizing the geometric structure, cyclones can be used as the main device to remove particulates, especially those of 1–10 μm, in a variety of industries and in particular sensitive industries.

Design and evaluation of a sintered metal fiber filter for gasoline direct injection engine exhaust aftertreatment

A novel metal fiber gasoline particulate filter (GPF) is designed and evaluated as a potential improvement to the traditional automotive wall flow substrate. A procedure based on single fiber efficiency theory and the Kuwabara flow model for fibrous filter media is developed to optimize filter design. The prototype design is derived from two constraints, namely to maximize PM removal efficiency while minimizing filter backpressure. Metal fibers are chosen that tolerate gasoline engine exhaust temperatures and pleating is used to fulfill size limits dictated by vehicle space constraints. Two prototypes are evaluated by vehicle and engine dynamometer testing. These tests reveal PM filtration efficiencies of greater than 78% for both the FTP and US06 drive cycles, with an average backpressure of approximately 1 kPa over a US06 drive cycle on a 2.0 L GDI light duty vehicle. Measured PM removal efficiencies at constant exhaust temperature and flowrate agree well with model predictions. Backpressure predictions agree withs measurements after accounting for GPF entrance and exit effects. The metal fiber GPF performance is discussed relative to the current state of the art wall flow filters and the limited literature data on metal foam filters. Whereas the fibrous media offers excellent efficiency and backpressure penalty, achieving surface areas comparable to wall flow substrates remains a challenge for practical implementation.

An Electrically Renewable Air Filter with Integrated 3D Nanowire Networks

AbstractParticulate matter (PM) is a major pollutant in air and filtration at the source and on‐site is an effective approach to remedy PM pollution. Filters integrated with nanowires are advantageous for their high PM removal efficiency and low resistance to airflow. In this work, carbon nanowires are directly grown as 3D networks on a 304 stainless steel mesh to form a robust air filter. The growth of the carbon nanowires is initiated by exposing the stainless steel substrate to the vapor generated from the thermal decomposition of a silicone. The stainless steel is attacked by the carbon supersaturated vapor and releases metal nanoparticles, which catalyze the growth of carbon nanowires. The air filter with integrated 3D nanowire networks achieves a high PM removal efficiency with a low pressure drop. Moreover, the filter is heat resistant and can be renewed by electrical resistive heating to burn off the captured PM. After electrical renewal treatment, the filter recovers the low pressure drop while still maintaining a high PM removal efficiency. This air filter is promising for applications requiring on‐site renewal and will be useful for treating high temperature emissions.

Removal of PM2.5 and secondary inorganic aerosols in the North China Plain by dry deposition

The North China Plain (NCP) has experienced heavy air pollution in the past several decades featured by high levels of fine particulate matter (PM2.5). PM2.5 removal from the atmosphere in the NCP by dry deposition was estimated from 1999 through 2013 using the inferential method, which combined PM2.5 air concentrations retrieved from satellite remote sensing and dry deposition velocities (Vd) calculated using a bulk particle dry deposition model. Dry deposition of the three major inorganic ions in PM2.5, namely NH4+ (ammonium), NO3− (nitrate), and SO42− (sulfate), with their concentrations in 2000 and 2010 obtained from WRF-Chem model simulations, were also investigated considering their important roles in PM2.5 formation and ecosystem health. High levels of modeled and satellite-retrieved PM2.5 air concentrations, the secondary inorganic aerosols (the sum of NH4+, NO3−, and SO42−), and their respective deposition fluxes were identified from the southern NCP to Beijing-Tianjin metropolitans. The deposition fluxes derived from the inferential method and WRF-Chem increased considerably in the 2000s due to rising PM2.5 atmospheric levels across the NCP. The enhancement of dry deposition velocities of PM2.5 and three aerosol species in the NCP were associated nicely with increasing vegetation coverage and wind speed. We show that both air concentrations of PM2.5 and secondary inorganic aerosols and rising dry deposition velocities related to extensive afforestation activities contributed to their deposition fluxes and an inclining trend of PM2.5 removal from the atmosphere.

SiC@TiO2/Pt Catalytic Membrane for Collaborative Removal of VOCs and Nanoparticles

A SiC@TiO2/Pt catalytic membrane was fabricated to simultaneously remove volatile organic compounds (VOCs) and nano particulate matter (nano-PM) from industrial fumes. The TiO2 transition layer and Pt nanoparticles were prepared by soaking SiC membrane into the corresponding precursor and then high temperature sintering, respectively. The TiO2 layer decorated on the pore surface of SiC was found to be essential for the effective loading of Pt nanoparticles and improving of catalytic activity. Meanwhile, this modification process has no effect on the gas permeation of the membrane. The mesitylene degradation and PM removal efficiency of SiC@TiO2/Pt catalytic membrane were evaluated. Complete conversion could be obtained for mesitylene with the inlet concentration of 300, 600, and 800 ppm at the residence time of 1.0 s, reaction temperature of 240, 251, and 263 °C, respectively. In the dust and mesitylene coexistence system, the catalytic membrane can completely degrade mesitylene and remove 99.98% of Al2O3...

Fe-doped LaCoO3 perovskite catalyst for NO oxidation in the post-treatment of marine diesel engine’s exhaust emissions

New post-treatment process for marine diesel engine exhaust emissions was proposed by combining NO oxidation and wet scrubbing technology for the simultaneous removal of SOX, NOX and PM. NO, insoluble in aqueous scrubbing absorbent, is preferentially oxidized to NO2, which then turns fully soluble in it. Fe substituted LaCo1-xFexO3 perovskite catalysts were developed for NO oxidation to NO2. The catalysts were prepared by co-precipitation method and analyzed with XRD, XRF, BET, FT-IR, NO-TPD and XPS techniques. Crystal structure change from rhombohedral to orthorhombic was observed with the increased amount of Fe substituted in the B site of the perovskite by XRD analysis. From FT-IR and NO-TPD analysis, nitrate on perovskite species was found to be the active species for NO oxidation. Quantitative analysis was performed within the prepared catalysts. Catalytic activity was measured using a packed bed reactor operated at 150–400 °C, atmospheric pressure and with gas hourly space velocity (GHSV) of 20,000 h-1 using a simulated exhaust gas composed of NO 400 ppm, O2 10% balanced with N2. Formation of Fe4+ cation enhanced the redox property as well as the mobility of the lattice oxygen present in the perovskite catalysts, confirmed by XPS analysis. Reaction mechanism of NO oxidation on Fe substituted LaCo1-xFexO3 was discussed based on Mars-van Krevelen mechanism.

Advanced Materials for Capturing Particulate Matter: Progress and Perspectives

AbstractParticulate matter (PM) of different sizes is the prominent air pollutant that causes severe health issues. Despite source control, the removal of PM by porous materials is believed to be the most effective way of air purification. Extensive effort has been made toward the construction of advanced materials with both a high filtration efficiency and low pressure drop across them. Weight, transparency, thermal stability, and comfort in different environments are also key parameters for the practical use of such materials. Here, progress in the state of the art of materials for capturing particulate matter is summarized. Their structure, properties, and filtration mechanism are discussed. In addition, some possible directions for the future development of air filters, with regard to materials selection and structural design, are suggested.

Simple fabrication of a multifunctional inorganic paper with high efficiency separations for both liquids and particles

An inorganic paper with simultaneous emulsion separation, PM removal and dye adsorption characteristics has been prepared by a facile and environmentally-friendly method.

Adsorption and Agglomeration Characteristics of Ash Particles after Reducing Flue Gas Temperature below the Acid Dew Point

In order to develop suitable low-low temperature flue gas system for China and determine its operation parameters, the adsorption characteristics of ash particles for sulfuric acid mist need to be investigated, as well as the adhesion characteristics of ash particles after the adsorption. In this paper, experiments were conducted on a laboratory-scale fixed bed adsorption reaction system. The adsorption characteristic curves of different particle sizes and adsorption temperature were obtained. The results show that adsorption temperature has a larger influence on the adsorption process compared with particle size. And there exists an adsorption limit in the adsorption process. In addition, the ultimate D/S (Dp/Sp) of ash particle is defined, which means the ratio of ash particle weight (mg) to adsorbed H2SO4 weight (mg) when ash particle reaches the adsorption limit. It is an inherent attribute of ash particle, only influenced by the particle constituents and sizes, representing the ultimate adsorption capacity of ash particle for sulfuric acid. The experiment results show that the chemical constituents of ash are the main determinate factors of adsorption limit and the Dp/Sp. And the Dp/Sp could be used cooperatively with D/S when people design the parameters of low-low temperature flue gas system for different types of coal. Furthermore, there was a significant agglomeration phenomenon between ash particles after the adsorption reaction, and it can increase the average size of particles which is conducive to the removal of PM.

Adsorption Characteristics of Sulfuric Acid Mist on Fly Ash in Low-low temperature Flue Gas System

Low-low temperature flue gas system which also called MHI high efficiency system developed by Mitsubishi Corporation has gained comprehensive attention in Japan, European countries and American. However, the applications of this system in China are facing several sever problems about corrosion and ash fouling. This paper focuses on the adsorption characteristics of sulfuric acid mist on fly ash during the flue gas cooling process in the exchanger before the electrostatic precipitator. The experimental results indicate that there is an optimum adsorption temperature for the adsorption of sulfuric acid mist, and this temperature is about 30 ℃ lower than the acid dew point. The process of adsorption is mainly dominated by chemical reactions rather than physical reactions, and the alkali metals (Na, K) and alkaline earth metals (Mg, Ca) are the main factors which influence the chemical reaction rate, especially the Na element. Besides, with the D/S increasing, the adsorption efficiency increases and it is independent of the adsorption temperature. Ash particle size also has large influence on the adsorption efficiency, the smaller the particle size is, the larger the adsorption efficiency is. And when the flue gas speed rose, gas residence time correspondingly reduced and the adsorption efficiency dropped. However, since gas residence time is short in engineering applications, the influence of gas residence time is quite moderate. Furthermore, the adsorption of the sulfuric acid mist will cause a significant agglomeration between ash particles, and it has great significance to the removal of PM.