Low temperature reduction of NO by activated carbons impregnated with Fe based catalysts

In the present study, the reduction of NO by two activated carbons without and loaded with Fe based catalysts was studied at 300 °C using a fixed-bed reactor. The activated carbon samples impregnated with and without the catalysts were characterized using TGA, SEM, gas adsorption, ICP-AES, XPS and XRD. The experimental results showed that neither of the raw activated carbons achieved the required denitrification performance. However, compared with coal derived activated carbon (C₀), biomass derived activated carbon (B₀) performed better. The denitrification efficiency improved with the O₂ content in the flue gas, achieved a maximum approximately at 3% O₂, and then decreased with further increase in the O₂ content. The effect of the metals loaded and addition amount of the catalysts was then examined in detail with the biomass derived activated carbon. At the same dosage of catalysts, the biomass derived activated carbon impregnated with K ions was apparently more efficient than it counterpart loaded with Fe ions. A higher addition rate of Fe was required in order to be efficient in NO conversion. Addition of K was further found to significantly improve the NO conversion efficiency of the biomass activated carbon loaded with 3% Fe which otherwise showed a sharp premature decrease in NO conversion efficiency immediately after the flue gas was introduced. Finally the effects contributing to the synergetic effect of Fe and K are discussed.     

Flue gas waste heat affects algal liquid temperature for microalgal production in column photobioreactors

To explore the effects of waste heat (50–170°C) from steel plant flue gas on the column photobioreactor algal liquid temperature for microalgal production, a flue gas-microalgal liquid heat transfer model was developed that simulated the microalgal growth environment for flue-gas carbon dioxide (CO₂) fixation. The simulation results showed that the influence of high-temperature flue gas weakened with the increasing microalgal liquid temperature due to enhanced evaporation and heat dissipation. Increasing the flue gas temperature and aeration rate resulted in a higher microalgal liquid temperature up to a maximum increase of 4.16°C at an ambient temperature of 25°C, an aeration rate of 2 L/min, and a flue gas temperature of 170°C. In an experiment on the effect of incubation temperature on the growth rate of microalgae, at an optimal temperature of 35°C, the Chlorella sp. PY-ZU1 growth rate exhibited a remarkable increase of 104.7% compared to that at 42.5°C. Therefore, modulating the flue gas conditions can significantly increase the microalgal growth rate for CO₂ fixation, making it a promising approach to increase biomass production for efficient carbon utilization.     

Activated carbon-supported catalyst loading of CH4N2O for selective reduction of NO from flue gas at low temperatures

Selective catalytic reduction of nitrogen oxides with loaded CH₄N₂O (low-temperature urea-SCR) is a novel and promising technology to remove nitrogen oxides from low-temperature oxygen-containing flue gas, which can avoid the problem of NH₃ escape. In the present study, a series of industrial-grade biomass-based activated carbon (AC)-supported transition metal oxide catalysts with urea loading were prepared by ultrasound-assisted impregnation, and the physicochemical properties of the catalysts were observed by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), graphite furnace atomic absorption spectroscopy (GFAAS), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) analysis, Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The influences of the AC type, reaction temperature, AC particle size, metal oxide loading, urea load level and loaded active element type on the catalytic activity were studied through experiments. Moreover, the NO adsorption capacities of the AC carrier at different temperatures were also tested and calculated. The results of NO adsorption tests show that the adsorption capacity of AC decreased with increasing temperature. The results of the catalytic performance tests indicate that the copper- and manganese-based catalysts with 6 wt% urea exhibited better activity than the other catalysts. The copper-based catalyst, in particular, yielded better than 93% NO conversion at low temperatures (50–100 °C). Finally, on the basis of the combined characterization results and thermodynamics analysis, a NO removal mechanism of the copper- and manganese-based catalysts was proposed and discussed; the electron transfers of Mn⁴⁺ ⇌ Mn²⁺ and Cu²⁺ ⇌ Cu⁰ promoted the low-temperature urea-SCR method.     

Impregnated carbon–ionic liquid as innovative adsorbent for H2/CO2 separation from biohydrogen

Currently, purification is a considerably important technology for biohydrogen (bioH₂) production as a renewable energy resource. Adsorption methods are promising techniques for separation of CO₂ from the H₂/CO₂ mixture of bioH₂. In this study, the adsorbent is synthesized by impregnating activated carbon (AC) with ionic liquid (IL). The ILs were prepared using choline chloride and zinc chloride at different wt% with the AC, i.e., 0.5 wt%–3 wt%. The physical and chemical properties of the synthesized adsorbents, such as surface morphology, porosity, and structures, were investigated and characterized by using scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and Brunauer–Emmett–Teller analysis (BET). To investigate the actual adsorption performances, the effects of different synthesized adsorbent types and feed gas flow rates, i.e., 0.1–1.0 L min⁻¹, were observed. Hence, a commercial gas composed of CO₂ and H₂ mixture with different compositions, i.e., 40, 50, and 60 vol%, was used as synthetic bioH₂ gas. The adsorption capacity of CO₂, i.e., adsorption capacity, were determined using single adsorber column (0.6 L) at a temperature of 300 K and pressure of 1 bar. Results showed that adsorption capacity decreased with the increased feed gas flow rate. Moreover, the carbon impregnated with 1 wt% of IL showed the most excellent adsorption capacity at 84.89 mg of CO₂/g of adsorbent. The present results are the initial findings generated for the bioH₂ separation technology for future high-purity hydrogen production.     

Biogas use in high temperature fuel cells: Enhancement of KOH-KI activated carbon performance toward H2S removal

Activated carbons (ACs) treated with KOH-KI are very effective sorbents for deep H₂S removal, as required by biogas use in high temperature fuel cell systems. For this application, the performance of a commercial KOH-KI treated AC was investigated through a systematic study based on dynamic adsorption tests. With reference to the composition of a real biogas produced in a wastewater treatment plant located in Barcelona, the present work presents a sensitivity performance analysis on singular and synergetic effects of gas matrix, humidity and oxygen on AC KOH-KI performance.The results revealed a positive role of water (up to 90% of relative humidity (R.H.)) for different gas matrices, enhanced by the simultaneous presence of small percentages of oxygen (2%_v). A relevant influence of gas matrix composition was found (except for the case of oxygen addition to dry inlet streams), specifically in terms of a marked negative effect of CO₂ and a significant sorption capacity increase for high percentage of methane. Sulfur dioxide was not detected in the outlet gas-phase for the investigated operating parameters (O₂ 2%_v, R.H. 0–90%, H₂S 100 ppm_v, temperature 45 °C). Therefore, even in the case of further oxidation of adsorbed elemental sulfur to SO₂, this product could be completely removed by AC KOH-KI.     

Removal of mercury from flue gases over iron modified activated carbon made by in situ ion exchange method

Ion exchange method was applied to synthesize iron modified activated carbon in the present study. The carbon in volatile compounds of cation-exchange resin could be fixed by ferric ion, resulting in the higher carbon yields of iron contained adsorbents. The optimal temperatures for carbonization and activation of ferric ion-exchanged resin were determined to be 800 °C. The iron modified activated carbon with (Fe/AC-800) and without (Fe/C-800) activation at 800 °C showed different mercury removal mechanisms, and they could be employed to remove mercury from flue gases at reaction temperatures of 180 and 150 °C, respectively. HgO, HgS and HgSO₄ were the mainly mercury compounds generated over spent Fe/C-800, whereas only HgO and HgS were observed over spent Fe/AC-800. The formation of HgO over spent Fe/C-800 and Fe/AC-800 were mainly due to the oxidation of mercury by chemisorbed oxygen and lattice oxygen, respectively. The HgSO₄ was derived from FeS with the aid of oxygen, and the HgS was formed through the reaction between mercury and FeS and/or elemental sulfur.     

Catalytic oxidation of NO to NO2 on activated carbon

Catalytic oxidation of NO to NO₂ over activated carbons PAN-ACF, pitch-ACF and coconut-AC at room temperature (30°C) were studied to develop a method based on oxidative removal of NO from flue gases. For a dry gas, under the conditions of a gas space flow rate 1500 h⁻¹ in the presence of oxygen of 2–20% in volume concentration, the activated coconut carbon with a surface area 1200 m²/g converted about 81–94% of NO with increasing oxygen concentration, the pitch based activated carbon fiber with a surface area 1000 m²/g about 44–75%, and the polyacrylonitriale-based activated carbon fiber with a surface area 1810 m²/g about 25–68%. The order of activity of the activated carbons was PAN-ACF<pitch-ACF<coconut-AC. However, NO conversion markedly decreased with the increases in temperature and humidity. For the dry gas, the apparent reaction rate was expressed by an equation: R=k_cP_NOP_O2^β (F/W), where β is 0.042, 0.16, 0.31 for the coconut-AC, the pitch-ACF and the PAN-ACF respectively, and k_c is 0.94 at 30°C.     

Superior catalytic effect of titania - porous carbon composite for the storage of hydrogen in MgH2 and lithium in a Li ion battery

A novel nanocomposite (0.2TiO₂ + AC) with two promising applications is demonstrated, (i) as an additive for promoting hydrogen storage in magnesium hydride, (ii) as an active electrode material for hosting lithium in Li ion batteries (surface area of activated carbon (AC): 491 m²/g, pore volume: 0.252 cc/g, size of TiO₂ particles: 20–30 nm). Transmission electron microscopy study provides evidence that well dispersed TiO₂ nanoparticles are enclosed by amorphous carbon nets. A thermogravimetry-differential scanning calorimetry (TG-DSC) study proves that the nanocomposite is thermally stable up to ∼400 °C. Volumetric hydrogen storage tests and DSC studies further prove that a 3 wt% of 0.2TiO₂+AC nanocomposite as additive not only lowers the dehydrogenation temperature of MgH₂ over 100 °C but also maintains the performance consistency. Moreover, as a working electrode for Li ion battery, 0.2TiO₂+AC offers a reversible capacity of 400 mAh/g at the charge/discharge rate of 0.1C and consistent stability up to 43 cycles with the capacity retention of 160 mAh/g at 0.4C. Such cost effective-high performance materials with applications in two promising areas of energy storage are highly desired for progressing towards sustainable energy development.     

Development and evaluation of magnetic iron-carbon sorbents for mercury removal in coal combustion flue gas

In order to get a cost effective and recyclable sorbent for mercury removal, a series of magnetic iron-carbon (Fe–C-x) sorbents was developed by co-precipitation. The physical and chemical properties of obtained sorbents were evaluated through various characterization methods. According to the results, Fe₃O₄ precipitate on carbon weakens the surface properties, but mercury removal performance in simulated flue gas is excellent. For flue gas components, HCl promotes mercury oxidation and adsorption on sorbents, O₂ has limited effect on mercury removal and SO₂ plays an inhibitive role. NO could enhance mercury oxidation with O₂ existence because of the generation of NO₂, which could react with Hg⁰ through heterogeneous reaction over iron-carbon surface. Besides, effects of temperature and regeneration performance were further researched under simulated flue gas. Apart from higher temperature will decompose mercury compounds and cause the removal efficiency decrease, Fe–C-3 sorbent shows excellent Hg⁰ removal performance at the temperature window of 100–200 °C. Exceptional regeneration performance on Hg⁰ removal indicates that spent sorbent could be regenerated.     

MSW landfill biogas desulfurization

Biogas utilization in MCFC systems requires a high level of gas purification in order to meet the stringent sulfur tolerance limits of both the fuel cells and the reformer catalysts. In this study, two commercial activated carbons (ACs) have been tested for H₂S removal from the biogas produced at the Montescarpino Municipal Solid Waste landfill in Genoa, Italy. The performed analyses show a low selectivity of activated carbon towards the adsorption of only sulfur species. This represents a drawback for the use of this type of system, however, the use of mixed beds of different ACs has demonstrated to be advantageous in improving the removal efficiency of H₂S. Thus, the adsorption treatments with AC can ensure the high level of gas desulfurization required for fuel cell application. Nevertheless, the low adsorption capacity observed using landfill biogas would lead to high operative costs that suggest the application of a preliminary gas-scrubbing stage.     

Characterization of products evolved from supercritical water gasification of xylose (principal sugar in hemicellulose)

The catalyst decomposition of xylose (the principal sugar in hemicellulose) was examined in supercritical water for temperature from 400 to 600°C. Experiments were performed in the absence and presence of three main types of catalysts [alkali catalysts (K₂CO₃ and KOH) and metal impregnated activated carbons (Ni/AC) and (Ru/AC)] with a reaction time of 1h. Gasification yield reaches maximum values by using K₂CO₃ and KOH at the highest temperature of 600°C. The highest H₂ yield and the highest CH₄ yield were obtained by using Ru/AC and Ni/AC, respectively. Acetic acid and 5-methyl furfural were determined as the main aqueous products and reached maximum value by using Ru/AC.     

Hydrogen adsorption on modified activated carbon

The aim of this work is to investigate hydrogen adsorption on prepared super activated carbon (AC). Litchi trunk was activated by potassium hydroxide under N₂ or CO₂ atmosphere. Nanoparticles of palladium were impregnated in the prepared-AC. Hydrogen adsorption was accurately measured by a volumetric adsorption apparatus at 77, 87, 90 and 303 K, up to 5 MPa. Experimental results revealed that specific surface area of the prepared-AC increased according to KOH/char ratio. The maximum specific surface area reached up to 3400 m²/g and total pore volume of 1.79 cm³/g. The maximum hydrogen adsorption capacity of 2.89 wt.% at 77 K and under 0.1 MPa, was obtained on these materials. The hydrogen adsorption capacity of the 10 wt.% Pd-AC was determined as 0.53 wt.% at 303 K and under 6 MPa. This amount is higher than that on the pristine AC (0.41 wt.%) under the same conditions.     

Adsorptive removal of H2S in biogas conditions for high temperature fuel cell systems

Desulfurization represents a crucial step in fuel processing for high temperature fuel cells, because of catalysts stringent requirements. Moreover, when fuel cell stacks are used in micro-CHP applications, it is necessary to build an efficient and compact system. The use of biogas from anaerobic digestion could have a significant impact in terms of fossil fuels saving and environmental conservation. Biogas contains different impurities, among which H₂S represents one of the most harmful components.Adsorption tests for H₂S removal were carried out in biogas conditions, using commercial adsorbents, defining the materials characterized by the best performance and resulting in a predominance of impregnated activated carbons. The influence on adsorption capacity of operating parameters, such as gas hourly space velocity, gas matrix composition (N₂, CH₄ and CO₂), humidity, temperature (30–150 °C), H₂S concentration (50–1000 ppmv) and filter geometry, was investigated. The aim of the study was the functional parameters optimization to obtain a compact filter with high removal activity.     

Syngas production by gasification of aquatic biomass with CO2/O2 and simultaneous removal of H2S and COS using char obtained in the gasification

Applicability of gulfweed as feedstock for a biomass-to-liquid (BTL) process was studied for both production of gas with high syngas (CO + H₂) content via gasification of gulfweed and removal of gaseous impurities using char obtained in the gasification. Gulfweed as aqueous biomass was gasified with He/CO₂/O₂ using a downdraft fixed-bed gasifier at ambient pressure and 900 °C at equivalence ratios (ER) of 0.1–0.3. The syngas content increased while the conversion to gas on a carbon basis decreased with decreasing ER. At an ER of 0.1 and He/CO₂/O₂ = 0/85/15%, the syngas content was maximized at 67.6% and conversion to gas on a carbon basis was 94.2%. The behavior of the desulfurization using char obtained during the gasification process at ER = 0.1 and He/CO₂/O₂ = 0/85/15% was investigated using a downdraft fixed-bed reactor at 250–550 °C under 3 atmospheres (H₂S/N₂, COS/N₂, and a mixture of gases composed of CO, CO₂, H₂, N₂, CH₄, H₂S, COS, and steam). The char had a higher COS removal capacity at 350 °C than commercial activated carbon because (Ca,Mg)S crystals were formed during desulfurization. The char simultaneously removed H₂S and COS from the mixture of gases at 450 °C more efficiently than did activated carbon. These results support this novel BTL process consisting of gasification of gulfweed with CO₂/O₂ and dry gas cleaning using self-supplied bed material.     

Nitrogen-doping activated biomass carbon from tea seed shell for CO2 capture and supercapacitor

Activated carbon is a promising material that has a broad application prospect. In this work, biomass (tea seed shell) was used to prepare activated carbon with KOH activation (referred to as AC), and nitrogen was doped in activated carbon using melamine as the nitrogen source (referred to as NAC-x, where x is the mass ratio of melamine and activated carbon). The obtained activated biomass carbon (activated bio-carbon) samples were characterized by Brunauer–Emmett–Teller (BET)-specific surface area analysis, ultimate analysis, X-ray photoelectron spectroscopy (XPS) analysis, Raman spectrum analysis, and X-ray diffraction (XRD) patterns. The specific surface areas of activated bio-carbons were 1503.20 m²/g (AC), 1064.54 m²/g (NAC-1), 1187.93 m²/g (NAC-2), 1055.32 m²/g (NAC-3), and 706.22 m²/g (NAC-4), revealing that nitrogen-doping process leads to decrease in specific surface area. XPS analysis revealed that the main nitrogen-containing functional groups were pyrrolic-N and pyridinic-N. The capacity of CO₂ capture and electrochemical performance of activated bio-carbon samples were investigated. The CO₂ capturing capacity followed this order: AC (3.15 mmol/g) > NAC-2 (2.75 mmol/g) > NAC-1 (2.69 mmol/g) > NAC-3 (2.44 mmol/g) > NAC-4 (1.95 mmol/g) at 298 K at 1 bar, which is consistent with the order of specific surface area. The specific surface area played a dominant role in CO₂ capturing capacity. As for supercapacitor, AC-4 showed the highest specific capacitance (168 F/g) at the current density of 0.5 A/g, but NAC-2 showed the best electrochemical performance (89 F/g) at 2 A/g. Nitrogen-containing functional groups and specific surface area both had an important impact on electrochemical performance. In general, NAC-3 and NAC-2 produced excellent electrochemical performance. Compared with NAC-3, less melamine was used to prepare NAC-2; therefore, NAC-2 was considered as the best activated bio-carbon for supercapacitor for 141 F/g (at 0.5 A/g), 108 F/g (at 1 A/g), and 89 F/g (at 2 A/g) in this work.     

Nitrogen oxides reduction by liquid petroleum gas over Co–Ce–Ti catalysts in a simulated rotary reactor

Hydrocarbons could be used as the reductant for elimination of NO_x emissions. Liquid petroleum gas, with higher carbon hydrocarbons and cheaper costs, may be of practical value as reducing agents. Due to the consumption of hydrocarbons by oxygen, the NO_x reduction efficiency is significantly inhibited by oxygen in the flue gas. In this research, a novel rotary reactor, realizing the alternating cycle of adsorption zone and reduction zone, was proposed to overcome this negative effect. Co–Ce–Ti mixed oxide catalysts synthesized by a sol–gel method were tested in a simulated rotary reactor for NO_x removal by liquid petroleum gas and characterized by SEM, BET, XRD and XPS. The results showed that catalysts exhibited better NO conversion efficiency at higher temperature but were highly susceptible to oxygen. Catalysts achieved nearly full removal of NO_x from flue gas at 300 °C in a simulated rotary reactor, and 300 °C is considered to be the most optimum temperature with lower energy consumption and excellent flue gas purification performance.     

Significantly enhanced electrochemical hydrogen storage performance of biomass nanocomposites from Pistacia Atlantica modified by CuO nanostructures with different morphologies

Pistacia Atlantica biomass was utilized as an activated carbon precursor for the preparation of copper oxide/activated carbon (CuO/AC) nanocomposites and the electrochemical hydrogen storage (EHS) capacities of copper oxide with different morphologies and provided nanocomposites were studied. Further, the influence of copper oxide pores size upon the EHS capacity was studied through chronopotentiometry system. Under 1 mA current, the discharge capacities of CuO nanoflowers (CuO_nf), CuO nanoparticles (CuO_np), Pistacia Atlantica activated carbon (AC), copper oxide nanoflower/activated carbon (CuO_nf/AC), and copper oxide nanoparticle/activated carbon (CuO_np/AC) were reached to 650, 850, 1200, 2000, and 3000 mAh/g after 25 cycles, respectively. Outcomes reveal that the coating of copper oxide upon the AC with different pores size leads to get better discharge capacity. Therefore, produced nanostructures with inexpensive and simple manner can be utilized for EHS and can be applied as Renew. Energy to reduce the use of fossil fuels.     

Posidonia Oceanica and Wood chips activated carbon as interesting materials for hydrogen storage

The goal is to investigate the feasibility to use a local biomass (Posidonia Oceanica and Wood chips), as a raw precursor, to the production of activated carbons (AC) with a high surface area and remarkable hydrogen (H₂) adsorption properties.Biomasses (particle size of 0.3–0.4 mm) were pyrolyzed at 600 °C with a heating rate of 5 °C/min under an argon atmosphere. The biochar obtained from the carbonization step was chemically activated with KOH. The activation methodology induces a considerable improvement of the properties of the porous carbon in terms of carbon content (from 58 to 69 wt% to 93–96 wt%), surface area (from 41 to 425 m²/g to 2810–2835 m²/g) and H₂ adsorption in cryogenic condition (from 0,1 wt% to over 5 wt%).All porous carbons were characterized in terms of elemental analysis (CHNS–O), textural properties and H₂ adsorption measurements.     

Hydrogenation properties of MgH2- x wt% AC (x=0, 5, 10, 15) nanocomposites

Magnesium is considered as a promising candidate for hydrogen storage due to its high storage capacity (theoretical value ~ 7.6 wt%). Nanocomposites of Magnesium hydride and activated charcoal (AC) were prepared using ball milling method. These nanocomposites were characterized by XRD, TGA, DSC and SEM techniques. The TGA analysis show that the MgH₂-5 wt% AC nanocomposite exhibits dehydrogenation capacity of 7.45 wt% (which is very close to the storage capacity of MgH₂) and starts release of hydrogen at 140 °C temperature. The results from the Kissinger plot from DSC result showed that the activation energy for hydrogen desorption of MgH₂ with 5 wt% AC was reduced compared to those of as-received.     

ESP飞灰和FF飞灰脱汞特性的试验研究

采用汞渗透管产生的汞蒸气和其它主要烟气成分,在小型多功能固定床试验台上开展静电除尘器( ESP)飞灰和布袋除尘器(FF)飞灰脱除单质汞的试验研究.结果表明:O2、SO2、NO对Hg0的氧化均有一定的作用,尤其SO2对Hg0的氧化效果最为显著.飞灰对汞的吸附与飞灰中Fe2O3、Al2O3等化学成分的催化氧化有一定的相关性...