Catalytic Filter Research Articles

Development of calcium silicate-based catalytic filters for biomass fuel gas reforming

Development of calcium silicate-based catalytic filters for biomass fuel gas reforming

A new solution for destruction of PCDD/Fs by a catalytic filter system at waste incinerators

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) are emitted from high temperature combustion processes such as municipal waste incinerators, hazardous waste incinerators, medical waste incinerators, and secondary metal processing plants. Due to their extreme toxicity, stringent regulations on PCDD/Fs emissions have been in effect around the world since the early 1990s. W. L. Gore & Associates, Inc. developed a catalytic filter system in 1997 that can effectively remove and destroy PCDD/Fs in the industrial flue gases. The REMEDIATM Catalytic Filter System has been installed in various industrial facilities around the world. The dioxin emission measurements in these plants achieve more than 98% PCDD/Fs removal efficiencies and reach the European standard. In this paper, three case studies will be presented on the performance of the REMEDIA Catalytic Filter System at municipal, medical, and hazardous waste incinerators. Three cases in the paper demonstrate the efficiency and results.

Ultrasound-Assisted Deposition of Co-CeO2 onto Ceramic Microfibers to Conform Catalytic Papers: Their Application in Engine Exhaust Treatment.

The combination of the selective catalytic reduction technology with catalytic filters constitutes one of the most efficient ways for diesel engine exhaust treatment. In this paper, the development of catalytic ceramic papers as structured systems for the abatement of diesel soot particles is addressed. Ceramic papers were prepared by the dual-polyelectrolyte papermaking method, which is based on the conventional papermaking technique used for cellulosic papers, in which a portion of cellulosic fibers is replaced by ceramic ones. The deposition of Co and Ce as catalytic materials by the wet spray method on ceramic papers was studied for the development of structured catalysts using an ultrasonic nebulizer and different solvents. The use of alcohol–water solutions for the impregnation of cobalt generated smaller particles and a high dispersion of them on the ceramic fibers, greater than that obtained when pure water was employed. Temperature programmed oxidation (TPO) assays showed that the best catalytic performance was acquired with the catalysts generated with alcohol solvents, showing a maximum rate for soot combustion at a temperature close to 400 °C. The adequate soot combustion performance and the high thermal and catalytic stability make catalytic ceramic papers impregnated by the wet spray method, promising systems for their application as diesel particulate filters.

A study of modeling of flue gas patterns with number and shape variations of the catalytic converter filter

Exhaust gas in motorized vehicles is the main source of air pollution in the environment. Pollution of motor vehicle exhaust can be reduced by paying attention to the maintenance system, modern engine control concepts, fuel cleaning, and reduction of exhaust emissions. Catalytic converters are the most effective tool to fight pollutants in our environment because they reduce nearly 80 % of the harmful gases that result from incomplete combustion of the engine. To find out the flow phenomena that occur, a simulation of the pattern of exhaust gas flow is made with variations in the number and shape of the Catalytic converter filter. This research begins with the making of a Catalytic converter design which includes: filter­not­cut and filter­cut dimensions. Then design the frame dimensions of the Catalytic converter with a variety of filters: 2, 3, 4 and 5 pieces and do the simulation. The simulation results show that the increase in speed percentage is caused by the exhaust gas flow passing through the small holes in the filter so that the gas pressure changes to an increase in speed. Installation of 2 filter­not­cut pieces is recommended because there is no vacuum area. The addition of the number of filters increases the vacuum area that occurs, this is related to the durability of the Catalytic converter. The simulation results suggest using the 3 most durable filter­cut pieces compared to using filters: 2, 4 and 5 pieces. In filter­not­cut (3, 4 and 5 pieces), the random pressure distribution is caused by the non­uniform pressure. This non­uniform flow decreases the efficiency and durability of the Catalytic converter. Unlike the case with 3 filter­cut pieces that have a more regular pressure distribution, are more solid and fused

Dust Filtration Influence on the Performance of Catalytic Filters for NOx Reduction

Particle matter and NOx emission are the most significant pollutants of combustion processes, particularly so for the conversion of biomass to energy. Currently, reduction of these pollutants is addressed through particle filters and catalytic processes. Therefore, catalytic activation of filter materials seems to be a practical way to reduce NOx and fine particle emission (PM10) simultaneously at small and medium furnaces. Regularly used methods to achieve this rely on the impregnation process. However, alternatives for materials with low wettability are needed. An alternative developed and discussed in this article consists of simultaneous synthesis of filter and catalyst through hard template sintering, where the catalyst is integrated into the porous medium during the fabrication of the filter. This sintering method provides an integrated catalytic filter. Through this method, up to 2% of catalyst loading was achieved in the synthesis of four catalytic filters. The performance of these new catalysts was evaluated under downscale industrial conditions and compared with an ordinary impregnated catalyst. Finally, a dust aging treatment was applied on the catalysts in order to see the long-term influence of fine dust particles on the NOx conversion.

3D-CFD simulation of catalytic filter candles for particulate abatement and tar and methane steam reforming inside the freeboard of a gasifier

Biomass gasification is a very promising process to produce energy from agricultural wastes; however, tar and particulate have to be removed in order to make the product gas exploitable. Catalytic filter candles inserted in the freeboard of a fluidized bed gasifier, perform hot syngas cleaning from particulate and promote the steam reforming reactions of tar and methane thanks to the addition of Ni-catalyst in their inner space. In this work, a 3D-CFD model is implemented in the FLUENT software, to simulate 6 catalytic candles housing in the freeboard of a pilot scale dual bubbling fluidized bed steam gasifier (100 kWth as biomass input). Main model parameters were derived from experimental results obtained with a bench scale gasification reactor, equipped with a ceramic filtering candle containing a commercial catalyst, to allow conditioning the raw syngas produced on site. Simulations were carried out to study the conversion of tar and methane in a real case application. The temperature drop along the gasifier freeboard causes very low conversion (≈15%) of tar produced inside the gasifier fluidized bed. It was found that small injections of O2 in the freeboard can rise the temperature and increase tar conversion up to 77%. Finally, simulations with raw syngas input subjected to primary tar removal by means of Fe-olivine as fluidized bed material resulted in high conversion rates and residual tar content lower than 1 g/Nm3.

Au-promoted Ce-Zr catalytic filter for Pt/SnO2 sensor to selectively detect methane and ethanol in the presence of interfering indoor gases

Ce0.8Zr0.2O2 mixed oxide supported gold nanoparticles (Au/Ce-Zr) as a catalytic filter was synthesized through deposition-precipitation (DP) method. SnO2 as an n-type semiconductor was prepared via the precipitation method and subsequently impregnated with H2PtCl6 aqueous solution to produce Pt/SnO2 as the sensing material. BET surface area, XRD, FESEM, EDS and temperature programmed reduction (TPR) techniques were employed to characterize both the filter and the sensing material. CO, methane, ethanol, formaldehyde, acetone and toluene, as indoor pollutant gases, were selected to be studied with the sensor and the filter. The sensor response to CO (300 ppm), ethanol (300 ppm), and methane (500 ppm) were measured in the temperature range of 100–480 °C with and without Au/Ce-Zr catalytic filter. In the absence of the catalytic filter, Pt/SnO2 sensor detected all of the gases with comparable responses. In the presence of the filter however, the selectivity toward ethanol and methane occurred respectively at filter-sensor temperatures of 200–250 °C and 400–200 °C. Moreover, under exposure to the other interfering gases, the presence of the catalytic filter notably increased the selectivity of the sensor toward methane and ethanol at the corresponding temperatures. Based on these observations therefore, a temperature dependent sensor was fabricated through combination of the catalytic filter and the sensor.

Mn-Ce-Nb-Ox/P84 catalytic filters prepared by a novel method for simultaneous removal of particulates and NO

The Mn-Ce-Nb-Ox/P84 catalytic filter for removal of particulates and NO simultaneous was prepared by a novel method (foam coating method). The process parameters including the concentrations of PTFE emulsion, particle size of catalyst and calcination temperature for preparation of catalytic filters were analyzed. In addition, the physical properties and performance for removal of NO (NH3-SCR) and particulates of Mn-Ce-Nb-Ox/P84 catalytic filter prepared under the optimized parameters, were also systematic studied. Results show that the process parameters had significant influences on stability and performance of catalytic filter. The Mn-Ce-Nb-Ox/P84 catalytic filter prepared by foam coating method under the optimized parameters, has satisfactory physical properties and catalytic performance for removal of NO and particulates at 140–220 °C. The NO removal efficiency of catalytic filter can reach 95.3% at 200 °C as the catalyst loading amount is 450 g/m2. Moreover, the dust removal efficiency of Mn-Ce-Nb-Ox/P84 catalytic filter reaches as high as 99.98%, and the PM2.5 removal efficiency also reaches 99.98%. The anti-sulfur performance of Mn-Ce-Nb-Ox catalytic filter is also attractive, after injecting 150 ppm SO2, the NO removal efficiency still retains up to 85%. It is indicated that the foam coating method can not only make a bond of high strength between catalyst and filter, but also make the catalytic filter possessing an excellent and stable performance for removal of NO and particulates.

Ligand-Free Nano-Au Catalysts on Nitrogen-Doped Graphene Filter for Continuous Flow Catalysis.

In this study, the authors rationally designed a high-performance catalytic filter for continuous flow catalysis. The catalytic filter consisted of ligand-free nanoscale gold (nano-Au) catalysts and nitrogen-doped graphene (N-rGO). The Au catalyst was fabricated in situ onto a pre-formed N-rGO support by the NaBH4 reduction of the Au precursor, and the size of the nano-Au was fine-tuned. A hydrothermal pretreatment of graphene oxide enriched nitrogen-containing species on the surface of two-dimensional graphene supports and enhanced the affinity of Au precursors onto the support via electrocatalytic attraction. The nano-Au catalysts acted as high-performance catalysts, and the N-rGO acted as ideal filter materials to anchor the catalysts. The catalytic activity of the as-designed catalytic filter was evaluated using 4-nitrophenol (4-NP) hydrogenation as a model catalytic reaction. The catalytic filters demonstrated superior catalytic activity and excellent stability, where a complete 4-nitrophenol conversion was readily achieved via a single pass through the catalytic filter. The as-fabricated catalytic filter outperformed the conventional batch reactors due to evidently improved mass transport. Some key operational parameters impacting the catalytic performance were identified and optimized. A similar catalytic performance was also observed for three 4-nitrophenol spiked real water samples (e.g., surface water, tap water, and industrial dyeing wastewater). The excellent catalytic activity of the nano-Au catalysts combined with the two-dimensional and mechanically stable graphene allowed for the rational design of various continuous flow catalytic membranes for potential industrial applications.

Integration of Biomass Gasification and Hot Gas Cleaning Processes

In the near future, most of the world population will live in the developing countries, and it is plausible that biomass will be one of the main renewable energy sources of the future. Fluidized bed reactors should be the best solution to transform biomasses having different physical properties in energy and chemical vectors through gasification, due to its possibility to operate continuously, at high temperatures, and to utilize catalysts into the reactor and downstream of it, in order to reduce tar, NH3 etc. in the product gas.Catalytic filter candles are an innovative solution for hot gas cleaning & conditioning. It has been demonstrated that catalytic ceramic filters inserted in the freeboard of a fluidized bed gasifier, allow the complete removal of particulate by means of their anisotropic porous filtering structure, and furthermore act as catalyst to remove tar and ammonia, thanks to the Ni based catalyst contained into the filter itself (Rapagna, Gallucci and Foscolo, 2017).To by-pass the preparation of the catalytic ceramic filters and to render the overall process more feasible in practice, ceramic filters filled with commercial steam reforming catalyst pellets have been located in the freeboard of a 0.1 m ID fluidized bed reactor, where olivine particles act as bed inventory.Experimental tests were carried out to check the values of the gas pressure drop through the plain filter and through the filter containing catalyst pellets, at different temperatures and gas filtration velocities. It has been found that at the highest temperature and filtration velocity (T 800°C and v 140 m/h) the pressure drops are around 48 mbar, while at the operating conditions (T 800°C and v 100 m/h) the total pressure drops are only 35 mbar. Furthermore it was observed that there is an almost negligible difference between the pressure drops in the case of empty and filled candle; it was thus deduced that the catalyst pellets do not cause relevant additional losses compared to the empty filter. The trends of pressure drops were fitted with the empirical Darcy-Forchheimer relation and with the Ergun equation, and it was found that the major contribution is given by the viscous term of the relation. Furthermore an additional contribution of concentrated pressure drops was identified and ascribed to the outer Al2O3 membrane of the candle characterized by very fine pores.

Performance of thin-film composite hollow fiber nanofiltration for the removal of dissolved Mn, Fe and NOM from domestic groundwater supplies

Groundwater (GW) is one of the most abundant water resources and around 1.5 billion people rely on GW as their main water supply. Manganese (Mn) and iron (Fe) are very common GW contaminants. Even though their presence is considered mainly as an organoleptic and operational nuisance, water with elevated Mn content may also lead to adverse health impacts. Amongst the most common treatment processes currently used to treat domestic GW supplies: catalytic filtration may lead to Mn leaching if improperly maintained; while ion exchange consumes a considerable amount of salt and produces a brine waste which pollutes the environment. Thus, it is proposed to design a simple, yet robust treatment system which can be implemented in small/remote communities or even domestic applications. To this end, the main objective of this investigation was to assess the potential application of novel outside-in sulfonated polyethersulfone thin-film composite hollow fiber nanofiltration (HFNF) membranes to remove dissolved Mn, Fe and natural organic matter (NOM) from domestic GW supplies. Of particular interest was the impact of GW matrix on performance of the HFNF membranes. Our experimental findings demonstrated that, in absence of hardness and the cumulative throughput of 1.9 L/m2, above 90% of Mn, Fe and NOM were retained by the examined HFNF membranes (MWCO ∼ 200 Da) regardless of their initial concentrations in the feed solution (250–1000 μ g/L). In contrast, increasing the hardness level reduced the removal of Mn and Fe ions. XPS analysis revealed that the surface properties of the HFNF membranes were altered when the membranes were exposed to calcium and magnesium salts. These observations were attributed to the propensity for Ca and Mg ions to bind to the sulfonic groups present on the surface of the HFNF membranes which, subsequently, weakens rejection by charge exclusion. On the other hand, in the absence of GW hardness, charge exclusion was mainly responsible for rejection of dissolved Mn and Fe. It was also found that GW hardness had no marked impact on the NOM rejection as the later was mostly removed by size exclusion.

Low Temperature Microwave Regeneration of Catalytic Diesel Particulate Filter

Diesel particulate filter (DPF), consisting in alternately plugged parallel square channels with porous walls that trap the soot particles, must be periodically regenerated. In this work, a new procedure for the preparation of microwave susceptible catalytic DPFs based on a preliminary controlled chemical erosion of the porous structure was optimized, so obtaining catalytic filters with higher catalyst load (30 %wt CuFe2O4). The filters showed pressure drop values very similar to that pertaining to the uncatalysed filters and a higher regeneration activity: consequently their microwave assisted regeneration phase, compared to the traditional fuel post-injection, allowed an energy saving of about 60 %.

Free-standing hierarchical α-MnO2@CuO membrane for catalytic filtration degradation of organic pollutants

Catalytic membrane, due to its compact reactor assembling, high catalytic performance as well as low energy consumption, has proved to be more attractive for wastewater treatment. In this work, a free-standing α-MnO2@CuO membrane with hierarchical nanostructures was prepared and evaluated as the catalytic membrane to generate radicals from peroxymonosulfate (PMS) for the oxidative degradation of organic dyes in aqueous solution. Benefiting from the high mass transport efficiency and the hierarchical nanostructures, a superior catalytic activity of the membrane was observed for organic dyes degradation. As a typical organic dye, more than 99% of methylene blue (MB) was degraded within 0.23 s using dead-end filtration cell. The effects of flow rate, PMS concentration and buffer solution on MB degradation were further investigated. Besides MB, the catalytic membrane also showed excellent performance for the removal of other dyes, such as congo red, methyl orange, rhodamine B, acid chrome blue K and malachite green. Moreover, the mechanism study indicated that OH and SO4- generated from the interaction between PMS and Mn/Cu species with different oxidation states mainly accounted for the dyes degradation. The catalytic filtration process using α-MnO2@CuO catalytic membrane could provide a novel method for wastewater purification with high efficiency and low energy consumption.

Development of high performance catalytic filter of V2O5-WO3/TiO2 supported-SiC for NOx reduction

Fabrication of V2O5-WO3/TiO2 supported-SiC catalytic filters has been developed by using rotational coating method and discussed their NO conversion performances at different reaction temperature (150–380°C). M3C catalytic filter (coated with the grinded catalyst solution of catalyst with particle size of 1.0μm) showed the 99.9% NO conversion with the Nx-slip concentration below 15ppm with the optimal temperature range from 230–350°C, which is very satisfactory with the value approaching to the case of powder catalyst. The concentration of the catalyst coating solution optimized to 10wt% (M310) to achieve the better NO conversion >99.5%. An effect of ball milling on the catalytic coating solution has investigated to achieve the 99.9% NO conversion. The effect of varied V2O5 content on NO conversion has been studied. The activation temperature for >99% conversion of 700ppm NO gas shifted towards the lower one with the increase of the V2O5 content of V2O5-WO3/TiO2 supported SiC filter. M3V3 (3wt% V2O5) is the best catalyst composition showed 100% NO conversion with the reaction temperature window 280–320°C with less N2O formation below 20ppm. However, M3V6 (6wt% V2O5) showed the lowest reaction temperature as 240°C for >99% NO conversion.

Properties of catalyst for iron and manganese oxidation in filter materials

The aim of this work is to determine the properties of contact layers of grain of different type of filter media in term of their suitability for catalytical manganese oxidation and auto-activation for manganese removal from groundwater. The following oxidative filtration materials were investigated: auto-activated silica sand taken from full-scale filters (oxide coated filter media), Pyrolox – manganese ore – natural material and Hydrolit – artificially activated material. As a reference two natural not chemically active materials were tested: clean silica sand and clean chalcedonite. The investigation resulted in chemical composition and microstructure parameters of catalyst contact layers of grains. The modern analytical methods were used: EDAX, Raman spectroscopy, mercury and helium porozymetry. The data indicated that catalyst from autoacivated filtration material has better chemical composition and porosity parameters in comparison to tested catalytic filtration materials, making it more suitable for adsorption and catalytic manganese oxidation.

3D reconstruction and pore-scale modeling of coated catalytic filters for automotive exhaust gas aftertreatment

This paper introduces a newly developed methodology for the pore-scale simulation of flow, diffusion and reaction in the coated catalytic filter. 3D morphology of the porous filter wall including the actual distribution of catalytic material is reconstructed from X-ray tomography (XRT) images and further validated with the mercury intrusion porosimetry (MIP). The reconstructed medium is then transformed into simulation mesh for OpenFOAM. Flow through free pores in the substrate as well as through the coated zones is simulated by porousSimpleFoam solver, while an in-house developed solver is used for component diffusion and reactions. Three cordierite filter samples with different distribution of alumina-based coating ranging from in-wall to on-wall are examined. Velocity, pressure and component concentration profiles are calculated enabling the prediction of permeability and component conversion depending on the actual microstructure of the wall. The simulation results suggest that the gas predominantly flows through remaining free pores in the filter wall and cracks in the coated layer. The mass transport into the coated domains inside the filter wall is enabled mainly by diffusion. Large domains of compact catalytic coating covering complete channel wall result in a significant increase of pressure drop as the local permeability of the coating is two orders of magnitude smaller than that of bare filter wall.

Combined effects of soot load and catalyst activity on the regeneration dynamics of catalytic diesel particulate filters

The combined effects of soot load and catalyst activity on the regeneration dynamics of a catalytic diesel particulate filter have been investigated through transient CFD‐based simulations of soot combustion in a single‐channel configuration. The soot load was changed by varying the amount of soot accumulated as cake layer, while keeping the amount of soot trapped inside the catalytic wall constant. Substantially uniform soot combustion that allows reasonably fast regeneration of the filter under controlled temperature conditions has been simulated only in the absence of cake and at relatively low catalyst activity. Conversely, in the presence of cake, numerical predictions have shown that, regardless of both soot load and catalyst activity, fast regeneration always occurs by propagation of sharp reaction fronts that result in high temperature rises. These findings highlight the importance of avoiding the cake formation, while properly optimizing the catalyst activity, to conduct a safe and effective regeneration of catalytic filters. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1714–1722, 2018

MnO2-Fe2O3 catalysts supported on polyphenylene sulfide filter felt by a redox method for the low-temperature NO reduction with NH3

MnO2-Fe2O3 catalysts were successfully deposited on the surface of polyphenylene sulfide (PPS) filter felt by a redox method, and the as-obtained catalytic filter material was tested in the low-temperature NH3-SCR. NO conversions in the 79.8–99.2% range at 140–180°C and a gas hourly space velocity (GHSV) of 120,000cm3g−1h−1 were obtained, result which is attributed to the presence of amorphous MnO2 and Fe2O3 catalytic phases. The formation mechanism of the MnO2-Fe2O3 catalyst decorated on the polyphenylene sulfide filter felt is discussed.

Synthesis, characterization and activity evaluation of Cu-based catalysts derived from layered double hydroxides (LDHs) for DeNOx reaction

Catalytic filter for DeNOx reaction composed of practical ceramic filter and catalytic active component enables simultaneous removal of dusts and NOx and therefore is of great potential for industrial application. To find out catalytically active components for DeNOx reaction and concurrently which can be grown on ceramic filter by an in-situ method, the Cu-based catalysts derived from LDHs precursor with different promoters (Co, Ni, Zn, Mg) were synthesized. The results of catalytic activity evaluation showed Zn is the most suitable promoter. Then, the effect of the Cu/Zn ratio on the catalytic performance was examined. It was found that the (CuxZny)2Al-MMO with an Cu/Zn ratio of 4 exhibited the maximum NOx conversion of 80% at 240°C and a NH3/NO ratio of 0.8. The addition of Zn could weaken the catalytic oxidation of ammonia (NH3-SCO) and then improve turnover frequency (TOF) of NOx reduction per Cu atom. The characterizations of the TEM and H2-N2O titration to catalysts reveal that the addition of Zn helps the dispersity of CuO on the surface of the support. The H2-TPR results further demonstrates that the added Zn species facilitate the reducibility of CuO species at low temperature. At last, in-situ growth of Cu-Zn-Al-LDHs on a practical ceramic filter for DeNOx reaction was first successfully carried out and the resulted catalytic filter showed a reasonably high DeNOx activity and strong bonding strength between catalyst and filter.

Optimized microwave susceptible catalytic diesel soot trap

The wall-flow diesel particulate filter (DPF) is currently the usual post-treatment system in diesel engines for soot particle abatement in passenger, heavy-duty and non-road vehicles. It consists in alternately plugged parallel square channels, in order to force the exhaust gases to flow through the porous inner walls: soot is so collected on the surface and in the porosity of the channel walls, progressively blocking the pores, making mandatory the filter regeneration. In this work we realised a specific pre-treatment procedure in order to modify the porosimetric characteristics of the bare support, with the aim of increasing the active species load and simultaneously keeping the pressure drop and the filtration efficiency of the final catalytic system in the same range of an uncatalysed DPF. The pre-treatment is based on a controlled chemical erosion of the SiC porous structure with a HF:HNO3 acid solution. The results showed that, if compared with the analogues prepared without acid treatment, the pre-treated samples resulted with a modified pores distribution, with an increased average pore diameter. This important result allowed us to obtain new catalytic filters with higher catalyst load, higher regeneration activity and simultaneously keeping the pressure drop at similar values of the uncatalysed filters. As a consequence of these improved performances, a decrease in the frequency and duration of the regeneration step will be possible without affecting the filtration efficiency, as verified from the deposition and on-line microwave assisted regeneration tests. In particular, the results showed that the simultaneous porosity modification and the higher catalyst loading (30%wt of copper ferrite) allowed to decrease the threshold catalyst temperature to about 350°C, but more importantly allowed to decrease the regeneration step duration from about 22 to about 15min. Moreover, the addition of K to the catalyst formulation had the important effect of further decreasing the regeneration time to about 8min, even if it had no effect on the threshold temperature. So, very positive effects on the performances of the final catalysed filter prepared on the carrier with a modified porosity with the proposed procedure are observed on the energy needed to regenerate the filter: the comparison of the microwave energy supplied, considering the same filter volume (about 0.35liters), during the microwave assisted regeneration phase of all the filter typologies considered in this work, compared to the traditional fuel post-injection, showed that just the addition of the catalyst allows an energy saving of about 60%, that increased up to 75% after the K addition to copper ferrite to a filter with modified porosity.