Simultaneous SO x /NO x removal in a fluidized bed reactor using natural manganese ore

In this experiment, the simultaneous removal of SO₂ and NO from flue gases was investigated through the use of natural manganese ore as a sorbent‐catalyst in a fluidized bed reactor. Selective catalytic reduction behavior was determined as a function of the sulfation degree within the temperature range from 100 °C to 500 °C. The natural manganese ore showed a high activity in the production of nitrogen and water by the reaction of nitric oxide with ammonia and oxygen up to around 200 °C. At higher temperatures, the nitric oxide removal efficiency decreased due to the oxidation of ammonia by oxygen. With the increase of sulfation degree, the temperature at which the maximum selective catalytic reduction of nitric oxide appears gradually increased, however the maximum nitric oxide removal efficiency decreased. Additionally, we investigated the removal efficiency of sulfur dioxide and nitric oxide with reaction time in a batch fluidized bed reactor within a temperature range of 350 °C to 500 °C. As the reaction temperature increased, the adsorption capacity of sulfur dioxide increased, but the nitric oxide removal efficiency decreased. © 2001 Society of Chemical Industry     

Sulfur removal from coal with supercritical fluid treatment

Conversion and sulfur removal of coal in sub- and supercritical water was studied in a micro reactor in the temperature range of 340-400°C and water density 0-0.27 g/cm³ for 0-90 min under N₂ atmosphere. The experiments were conducted to investigate the effect of reaction temperature, pressure, time and density of water on the sulfur removal in gaseous and liquid effluents, respectively. The results show that supercritical condition is more effective than sub-critical condition to remove the sulfur from coal. It is possible to reduce 57.42% of the original sulfur in coal for the reaction time of 90 min at 400°C and 30 MPa. The main gas containing sulfur in the gaseous effluent is not SO₂ but H₂S, irrespective of operating condition. The sulfur removal in liquid effluents is much greater than that in gas effluents. Compared with temperature, the influence of water density and pressure is less significant.     

The Influence of Water Vapor and Sulfur Dioxide on the Catalytic Decomposition of Nitrous Oxide

In a catalysts screening for the nitrous oxide decomposition, three groups of catalysts (metals on supports, hydrotalcites, and perovskites) were studied relating to their activity in the presence of vapor or sulfur dioxide, in the temperature range from 200 to 500 °C. It was found that the water vapor strongly inhibates the nitrous oxide decomposition at T = 200–400 °C. The sulfur dioxide poisons the catalysts, in particular the perovskites. The catalysts Rh‐ZrO₂ and Ex‐Co, Rh‐Al‐HTlc are potentially suitable for the nitrous oxide decomposition in exhaust gas at around T = 500 °C.     

Temperature Effect on Removal of Sulfur Dioxide and Benzene in Humid Air by DC Corona Discharge

A DC corona discharge reactor was applied to remove sulfur dioxide (SO₂) and benzene (C₆H₆) from N₂‐O₂‐H₂O mixed gas in the temperature range from room temperature to 400 °C. When SO₂ was removed, the temperature elevation caused the decrease of the removal efficiency of SO₂. On the other hand, the removal efficiency of C₆H₆ was not significantly influenced by the temperature elevation. In the simultaneous removal of SO₂ and C₆H₆ in the relatively low temperature range below 200 °C, the removal efficiency of SO₂ is significantly inhibited by coexisting C₆H₆. When the simultaneous removal was conducted in the high temperature range, the removal efficiency of SO₂ was not sensitive against the coexisting C₆H₆. On the other hand, the removal efficiency of C₆H₆ was almost independent of coexisting SO₂ at all temperatures. A hypothesis of reaction mechanism was discussed based on radical reactions with SO₂ and C₆H₆ to explain the trend observed in the experiment.     

The Effect of Water Vapor on the Particle Structure and Size of Silica Nanoparticles During Sintering

In this article, the influence of the water vapor concentration on structural changes of SiO₂ aerosol nanoparticle agglomerates during tempering was studied. The presence of water vapor in the carrier gas was shown to strongly accelerate the kinetics of sintering. While dry sintering at temperatures between 1100°C and 1500°C generated aggregates only, the addition of water to the process yields individual, completely coalesced nanoparticles at a temperature of 1300°C. Furthermore, depending on the water vapor concentration and temperature of the process, evaporation and condensation processes could be observed, leading to bimodal size distributions. The results prove the significant role of the water concentration in high temperature synthesis of silica and may be used to improve the control over morphology and specific surface area in these processes.     

The effect of HCl and H<Subscript>2</Subscript>O on the H<Subscript>2</Subscript>S removing capacities of Zn-Ti-based desulfurization sorbents promoted by cobalt and nickel oxide

The sulfur removing capacities of various Zn-Ti-based sorbents were investigated in the presence of H₂O and HCl at high-(sulfidation, 650 °C; regeneration, 800 °C) and medium-(sulfidation, 480 °C; regeneration, 580 °C) temperature conditions. The H₂O effect of all sorbents was not observed at high-temperature conditions. At mediumtemperature conditions, the reaction rate of ZT (Zn/Ti : 1.5) sorbent decreased with the level of H₂O concentration, while modified (ZTC, ZTN) sorbents were not affected by the water vapor. HCl vapor resulted in the deactivation of ZT sorbent with a cycle number at high-temperature due to the production of ZnCl₂ while the sulfur removing capacities of ZTC and ZTN sorbents were maintained during 4–5 cyclic tests. In the case of medium-temperature conditions, ZT sorbent was poisoned by HCl vapor while cobalt and nickel added to ZT sorbent played an important catalytic role to prevent from being poisoned by HCl due to providing heat, emitted when these additives quickly react with H₂S even at medium-temperature conditions, to the sorbents     

Electrochemical desulfurization of geothermal fluids under high temperature and pressure

Electrochemical removal of sulfide ions was achieved in salt water using graphite anodes in an autoclave under high temperatures and pressures, simulating geothermal fluids. The reaction products were characterized using microscopy and X-ray photoelectron spectroscopy (XPS). At low temperatures the reaction rate is quite small. It decreases rapidly with time down to a negligibly small value, which increases only slightly with temperature. The reaction produces elemental sulfur, which was seen under the microscope and identified using XPS. It passivates the electrode and hence diminishes its activity. Above about 115 °C, much higher removal rates can be sustained for much longer times, while the increase of temperature has a much stronger effect on the reaction rate. Under this condition, elemental sulfur was no longer detected among the reaction products, while the electrode retained its activity for continuous operation. The XPS spectra at high temperatures reveal the presence of oxygen bearing sulfur species, such as sulfates. The melting of sulfur (at 115 °C) has a much stronger effect on the efficiency of the process than the transition of orthorhombic to monoclinic sulfur (at 95 °C). A Clausius-Clapeyron’s analysis reveals that the melting point of sulfur inside the autoclave is nearly equal to its normal melting point.     

Hydrogen production via solar‐aided water splitting thermochemical cycles with nickel ferrite: Experiments and modeling

Water splitting — thermal reduction cyclic studies with NiFe₂O₄ redox materials were performed in a differential fixed‐bed laboratory reactor in the temperature range 700–1,400^°C to quantify the effects of operation temperatures and steam mole fraction on hydrogen and oxygen yields. Hydrogen yield increased drastically by an increase of the water splitting temperature from 800 to 1,000^°C reaching a plateau at 1,100^°C. In parallel, a simple mathematical model was formulated describing the water splitting process via the heterogeneous surface reactions of water vapor with the redox powder material, from which, in conjunction to the aforementioned experiments, the kinetic parameters of the water splitting and thermal reduction reactions were extracted. The water splitting kinetic constants exhibited weak temperature dependence between 700 and 1,100^°C suggesting the existence on the redox material of more than one type of oxygen storage sites with respect to ease of exposure and accessibility to the gas phase. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1213–1225, 2013     

Plasma-Assisted Diesel Oxidation Catalyst on Bench Scale: Focus on Light-off Temperature and NOx Behavior

The effect of a non-thermal plasma reactor over a commercial Diesel oxidation catalyst (DOC) was investigated. Studies have been focused on the gas treatment efficiency together with lowering light-off temperature when a DOC catalyst was connected downstream to plasma reactor in test bench scale. Experiments have been conducted using multi-DBDs (dielectric barrier discharge) reactor in planar configuration driven by a HV AC generator (11 kV–15 kHz). The specific input energy was set to 57 and 85 J/L. Experiments were performed in gas composition simulating Diesel exhaust. Commercial DOC, monolith-supported Pt–Pd/Al₂O₃, was used at gas hourly space velocities of about 55,000 and 82,000 h^?1. CO and hydrocarbons light-off curves were determined for DOC, plasma, and plasma-DOC systems by temperature programmed surface reaction from 80 to 400 °C. Particular attention has been paid to the gas temperature between the plasma reactor and the DOC. Results show that the plasma-catalyst system provides the lowest light-off temperatures for CO and HCs. Under conditions of this study, light-off temperature improvement by about 57 °C was obtained and the plasma reactor totally oxidized NO to NO₂ at low temperature.     

A Novel Process for Renewable Methane Production: Combining Direct Air Capture by K<Subscript>2</Subscript>CO<Subscript>3</Subscript>/Alumina Sorbent with CO<Subscript>2</Subscript> Methanation over Ru/Alumina Catalyst

CO₂ methanation over supported ruthenium catalysts is considered to be a promising process for carbon capture and utilization and power-to-gas technologies. In this work 4% Ru/Al₂O₃ catalyst was synthesized by impregnation of the support with an aqueous solution of Ru(OH)Cl₃, followed by liquid phase reduction using NaBH₄ and gas phase activation using the stoichiometric mixture of CO₂ and H₂ (1:4). Kinetics of CO₂ methanation reaction over the Ru/Al₂O₃ catalyst was studied in a perfectly mixed reactor at temperatures from 200 to 300 °C. The results showed that dependence of the specific activity of the catalyst on temperature followed the Arrhenius law. CO₂ conversion to methane was shown to depend on temperature, water vapor pressure and CO₂:H₂ ratio in the gas mixture. The Ru/Al₂O₃ catalyst was later tested together with the K₂CO₃/Al₂O₃ composite sorbent in the novel direct air capture/methanation process, which combined in one reactor consecutive steps of CO₂ adsorption from the air at room temperature and CO₂ desorption/methanation in H₂ flow at 300 or 350 °C. It was demonstrated that the amount of desorbed CO₂ was practically the same for both temperatures used, while the total conversion of carbon dioxide to methane was 94.2–94.6% at 300 °C and 96.1–96.5% at 350 °C.     

Hydrodesulfurization of diesel in a slurry reactor

The need for more complete removal of sulfur from fuels is due to the lower allowable sulfur content in gasoline and diesel, which is made difficult by the increased sulfur contents of crude oils. This work reports an experimental study on the hydrodesulfurization (HDS) of diesel in a slurry reactor. HDS of straight-run diesel using a NiMoS/Al₂O₃ catalyst was studied in a high-pressure autoclave for the following operating conditions: 4.8–23.1 wt% catalyst in the reactor, 320–360 °C, 3–5 MPa pressure, and 0.56–2.77 L/min hydrogen flow rate. It was found that the reaction rate was proportional to the catalyst amount and increased with temperature, pressure and hydrogen flow rate. The reaction kinetics for the HDS reaction in the slurry reactor was obtained. As compared with HDS in a fixed bed reactor, HDS in a slurry reactor is promising because of the uniform temperature profile, high catalyst efficiency, and online removal and addition of catalyst.     

Product composition of the dynamic conversion of brown coal in supercritical water

The product composition of the dynamic conversion of brown coal, which was continuously supplied as a water-coal slurry to a flow reactor at 30 MPa, was studied. The temperature of water and coal particles was increased from room temperature to 400°C (top part of the reactor). The conversion of the organic matter of coal was ～48%, and the products collected at the reactor outlet consisted of solid tar components, substances dissolved and emulsified in water, and volatile substances, whose major constituent was CO₂. The composition of solid tar components and oils was determined.     

Optimal temperature of fixed-bed reactor for high temperature removal of hydrogen sulfide

To find optimal temperature of the reaction between H₂S gas and ZnO-5 at% Fe₂O₃ sorbent, the effluent gas from a fixed-bed reactor was analyzed by gas chromatography. The experimental results showed that H₂S removal efficiency of sorbent was maximum at 650°C and EDX data were in accordance with this feature. XRD analysis exhibited intriguing phenomenon in that different mechanisms were observed at different temperatures. Chemisorption and chemical reaction was considered to be the main mechanism of H₂S removal at 600 C and 650°C, respectively. SEM photographs supported this interesting phenomenon, but unfortunately TGA and DTA results could not distinguish it. To investigate the effect of sorbent deactivation on the reaction rate, deactivating factor was considered.     

Performance of a coal gasification pilot plant with hot fuel gas desulfurization

A coal gasification pilot plant operation with hot fuel gas desulfurization (HGD) was performed taking two coals (Indonesian ABK and MSJ) that differ in their carbon and sulfur contents. A dry-feeding entrained-bed type gasifier was used for gasification with oxygen and capable of operating at 30 bar pressure and 1,550 °C. The HGD unit consisted of a transport desulfurizer, a bubbling regenerator and a multi-cyclone. Attention was focused on attaining high carbon conversion and cold gas efficiency in the entrained bed reactor and the sulfur removal efficiency of the hot fuel gas desulfurization unit. The optimum conditions for achieving high performance of the operation are reported.     

Effect of moisture on the oxidation behavior of ZrB2

Oxidation studies of ZrB₂ were performed under wet air and dry air conditions at 1200°C, 1400°C, and 1500°C for 1, 4, and 10 h. Compared to dry air, the presence of water vapor was found to enhance the oxidation kinetics by a factor of 7 to 30, depending on the temperature. Thermodynamic calculations suggested that water vapor promoted the formation of additional volatile species such as boric acid (HBO₂), in addition to boria (B₂O₃) produced in dry air, which increased the evaporation rate of B₂O₃. Compared to dry air, the presence of water vapor leads to more rapid evaporation of boria and the transition from parabolic oxidation kinetic behavior (ie, rate controlled by diffusion through boria) to linear (ie, underlying ZrB₂ is directly exposed to the oxidizing environment) at shorter times and lower temperatures.     

Oxidation of low concentrations of hydrogen sulfide over activated carbon

The oxidation of low concentrations of hydrogen sulfide with air over activated carbon was studied over the temperature range 24-200°C using both fixed and fluid bed reactors. The predominant reaction, H₂S + ½ O_a → H₂O + S, was found to have an order of 0.5 with respect of H₂S concentration. Activity of the catalyst decreased as the amount of sulfur deposited on it increased. Indirect evidence suggests that adsorption of water by the carbon also decreases its activity as a catalyst at lower temperatures. Values of the activation energy and the frequency factor were determined for various sulfur loadings using the fixed bed reaction system. Regeneration of the carbon loaded with sulfur was studied at temperatures between 150 and 500°C using steam as a carrier gas. Bright yellow sulfur was recovered. The regenerated carbon was shown to have its original activity.     

A kinetic study of gaseous potassium capture by coal minerals in a high temperature fixed-bed reactor

The reactions between gaseous potassium chloride and coal minerals were investigated in a lab-scale high temperature fixed-bed reactor using single sorbent pellets. The applied coal minerals included kaolin, mullite, silica, alumina, bituminous coal ash, and lignite coal ash that were formed into long cylindrical pellets. Kaolin and bituminous coal ash that both have significant amounts of Si and Al show superior potassium capture characteristics. Experimental results show that capture of potassium by kaolin is independent of the gas oxygen content. Kaolin releases water and forms metakaolin when heated at temperatures above 450 °C. The amounts of potassium captured by metakaolin pellet decreases with increasing reaction temperature in the range of 900–1300 °C and increases again with further increasing the temperature up to 1500 °C. There is no reaction of pre-made mullite with KCl at temperatures below 1300 °C. However, the weight gain by mullite is only slightly smaller than that by kaolin in the temperature range of 1300–1500 °C. A simple model was developed for the gas–solid reaction between potassium vapor and metakaolin pellet at 900 °C.     

Fourier transform infrared analysis of plasma-polymerized hexamethyldisiloxane

The plasma-induced polymerization of hexamethyldisiloxane onto solid surfaces is studied by FTIR. An inductively coupled RF reactor was used to produce the thin polymer coatings. Analysis of the plasma polymer indicates a long chain polysiloxane structure resulting from the removal of some methyl groups from the monomer structure. Increasing the plasma power level from 30 to 100 W increased the chain length in the resultant polymer as indicated by the widening and splitting of the Si–O stretching absorptions. Thermal aging of the vapor phase polymer at 120°C for 1 h in vacuum and at 410°C for 30 min in a nitrogen atmosphere revealed the removal of some methyl groups from the polymer structure with temperature. TGA runs on the vapor phase polymer at 20°C/min in air showed the polymer retaining almost 65% of its weight at 1000°C. The residue remaining after the TGA run had very little organic content and may represent a glass type silicate network. Wettability values determined on coated glass slides revealed the hydrophobicity of the coatings with water contact angle values > 100°. SEM micrographs showed uniform and featureless coating on glass fibers which was etched by boiling water and was attributed to the loss of vapor phase polymer on the surface.     

The behavior of silver particles supported on graphite in various gaseous environments

Controlled atmosphere electron microscopy has been used to continuously follow the behavior of silver particles supported on graphite when heated in the presence of various gases including helium, hydrogen and water vapor. In dry systems particles were observed to exhibit mobility over the range 320°–515°C. When water vapor was introduced either continuously or as a pulse injection particle motion was suppressed. At higher temperatures all systems showed similar behavior irrespective of the nature of the gas. Silver particles tended to collect into large globular islands at 615°C, and in this form showed characteristics of the bulk metal rather than those associated with small discrete particles. When the temperature was raised to 960°C discrete particles re-formed and once again exhibited mobility. This sequence of events and possible reasons for the inhibition of particle movement by water vapor is discussed.     

Manufacture of Granular Polysilicon from Trichlorosilane in a Fluidized‐Bed Reactor

Manufacturing of polysilicon by chemical vapor deposition from SiHCl₃ in a fluidized‐bed reactor was studied. The effects of reaction temperature, H₂/SiHCl₃ ratio, gas velocity, and seed particle loading were evaluated. The outlet gas composition was analyzed by gas chromatography. The physical features of the product particles were determined by scanning electron microscopy and laser particle size analyzer. Well‐grown product particles were obtained. The temperature and H₂/SiHCl₃ ratio significantly affected conversion, yield, and selectivity, which were less affected by gas velocity and seed particle loading at higher temperatures. The surface reaction kinetics determined the product yield only at lower temperatures, and thermodynamic equilibrium was approached at temperatures above 900 °C.