Effect Of Pre-oxidation Research Articles

Effect of Pre-oxidation and SO2 Modification on Mercury Removal Performance of High Sulfur Petroleum Coke in Simulated Natural Gas

A high sulfur petroleum coke (RPC) was selected as the raw material to make mercury adsorbent used in the simulated natural gas. The effect of pre-oxidation with air at set temperature and set time and sulfurization with 20% SO2 on mercury removal in simulated natural gas was studied. The experiments were carried out on a fixed-bed experimental device. The physicochemical properties of the sorbents were characterized by surface area and porosity analysis, elemental analysis and X-ray photoelectron spectroscopy (XPS). The results show that the mercury removal performance of the sulfur-loaded petroleum coke is greatly improved through carbonthermal reduction reaction. The optimum oxidation temperature of the SO2 activated petroleum coke is 300°C, and the Hg0 removal efficiency decreases with increase of the pre-oxidation time. The three main factors such as non-oxidative sulfur functional groups, carbonyl and ester sulfur functional groups, and pore structure greatly influence the mercury removal characteristics. The pre-oxidation time and temperature play an adjustable role for getting better performance of mercury removal.

Evaluation of disinfection byproduct formation from extra- and intra-cellular algal organic matters during chlorination after Fe(vi) oxidation.

Blue-green algae commonly bloom in fresh water in summer, producing extra- and intra-cellular algal organic matters, which are important precursors for disinfection byproduct (DBP) formation. In this study, we evaluated the effect of pre-oxidation with ferrate(vi) (FeO42−, Fe(vi)) on the characterization of intracellular organic matter (IOM) and extracellular organic matter (EOM). The results indicated that soluble microbial-like products of EOM and IOM decreased and humic acid-like products of IOM increased, which would influence the DBP formation in the subsequent chlorination step. Therefore, in this study, the effect of Fe(vi) pre-oxidation on the DBP formation from IOM and EOM with subsequent chlorination was also investigated. For Chlorella sp., EOM presented no significant change, and IOM presented a reduction of THMs (8.2%) after Fe(vi) oxidation at a dosage of 16 mg L−1. For P. limnetica, EOM and IOM both exhibited reduction of trihalomethanes (THMs) and chloral hydrate (CH) after Fe(vi) oxidation. Besides, THMs had the lowest concentration at pH 8.0 in all four solutions. Haloacetonitriles (HANs) and haloketones (HKs) showed slight changes with increasing pH values. Due to the frequent detection of bromide (Br−) in surface water, the effect of bromide existence on THM formation was also investigated. The results indicated that all brominated DBPs increased, and chlorinated DBPs decreased with the increase in bromide concentration. In addition, the bromine substitution factor (BSF) of Chlorella sp. and P. limnetica both increased with the increase in Br− concentration.

Enhanced microbial degradation of benzo[a]pyrene by chemical oxidation

Chemical oxidation and microbial degradation are promising treatments to remediate soils contaminated with persistent organic pollutants. Moderate pre-oxidation is able to enhance the subsequent bioremediation of organic pollutants in soil. In this study, the effects of pre-oxidation on the subsequent biodegradation of benzo[a]pyrene (BaP) were evaluated. The tested oxidants included potassium permanganate (PP) and iron-activated sodium persulfate (PS) at the concentration of 1–40 mmol L−1. The results showed that 20 mmol L−1 PS and 10 mmol L−1 PP treatments had the highest degradation efficiency of BaP in soil, up to 98.7% and 84.2%, without inhibiting subsequent microbial degradation. 10–20 mmol L−1 of the two oxidants significantly promoted viability of microbial community. Especially, PS facilitated the occurrence of more PAHs-degrading microorganisms. The expression of PAH-degradation gene in PS treatment was significantly higher than that in PP treatment (P < 0.05), leading to 12.0–18.4% higher degradation efficiencies of BaP. In general, proper oxidants of moderate dosages were able to promote microbial bioremediation of persistent organic pollutants in soil.

Sulfidation Resistance of Porous FeCrAl Alloy

FeCrAl alloy is regarded as the optimization material for coal-gasification purification with high temperature, due to its good mechanical property, oxidation resistance and sulfide resistance. This paper focuses on the effect of preoxidation on sulfidation resistance of porous FeCrAl alloy. The continuous and dense Al2O3 film, which was formed on the surface of porous FeCrAl alloy after preoxidation, can prevent the diffusions of atom S and metal ion and improve the sulfidation resistance.

Effect of Plasma Pre-oxidation on the Cu Corrosion Inhibition in 3.5% NaCl by an Environmentally Friendly Amide

Effect of Plasma Pre-oxidation on the Cu Corrosion Inhibition in 3.5% NaCl by an Environmentally Friendly Amide

REMOCIÓN SIMULTÁNEA DE MATERIA ORGÁNICA DISUELTA, Microcystis aeruginosa Y MICROCISTINA-LR POR LOS PROCESOS DE PREOXIDACIÓN Y COAGULACIÓN-FLOCULACIÓN

The purpose of this study was to evaluate the impact of the presence of Microcystis aeruginosa (MA) and microcystin-LR (MC-LR) on the removal of dissolved organic matter (DOM) by coagulation-flocculation in optimal conditions. Additionally, we determined the effect of pre-oxidation with NaOCl on the simultaneous removal of MA, MC-LR, and DOM, using the same processes and conditions. The water used in experimental tests was prepared with distilled water, strains of MA, microcystin-LR standards, and model compounds of DOM. Once the water was prepared, the proves were carried out in jar test equipment. We used a fractional factorial design to obtain the variables of significant influence and a response surface design to attain the optimal operation conditions of each process. The DOM removal decreased 32.25% when MA and MC-LR were in the process because they were competitors for the coagulant, but the main effect was caused by MA due its high concentration and physicochemical characteristics. The dose of pre-oxidant had no significant influence in the removal of three contaminants since the contact time in tests was very short.

Effect of pre-oxidation of Si3N4 powders on the interaction between Si3N4 coating and molten Si

Si3N4 coating is widely used in the production of photovoltaic silicon ingots. This work investigates the influence of pre-oxidation of Si3N4 powders on the interaction between Si3N4 coating and molten Si based on sessile drop experiments. It is found that the surface tension and surface roughness affect the contact angle and accordingly wetting behavior. A new mechanism for the permeation of molten Si in Si3N4 coating is proposed, where the driving force for the permeation is provided by chemical reaction between SiO2 and Si instead of usual capillary force.

Pre-oxidation Effect on Oxidation Behavior of F91 in Carbon Dioxide at 550 °C

Upon exposure to CO2 at 550 °C, F91 tends to form rapidly growing scales consisting of an outer Fe oxide and an inner Fe–Cr spinel oxide. A comparative study has been carried out between the pre-oxidized and non-pre-oxidized F91, to determine the influence of pre-oxidation upon the oxidation behavior of F91 in CO2. Formation of a rapidly growing scale and carburization could be inhibited by a pre-oxidation treatment in air prior to oxidation in CO2. Although during exposure to CO2, a fast growing scale still would form locally, pre-oxidation changed its structure. Effects of pre-oxidation time on the oxidation resistance in CO2 are investigated.

Effect of Pre-Oxidation on Thermoelectric Properties of Bismuth Telluride Compacted By Spark Plasma Sintering

Research on harvesting alternative energy sources has got a lot of attention to adapt human demands for energy while reducing the environmental pollution by the extensive use of fossil resources. Thermoelectricity is a technology based on the different temperature on two terminals of couples of p-n semiconductors to convert heat into electricity. By this way, waste heat can be recycled into usable and storable energy at low cost. Thus, it is esteemed as the most noteworthy technology in the field of renewable energy. However, for widespread usage, there are many challenges relating to the choice of thermoelectric materials as well as platform design for mass-production, and thus improvement of energy conversion efficiency. Among thermoelectric materials, the binary system of Bismuth and Telluride (Bi-Te) is widely used due to the high thermoelectric performance that can be obtained at a low temperature range of 300 - 500 K. However, controlling the ratio and crystallization of Bi-Te is critical. Therefore, many methods have been developed to construct thermoelectric systems based on Bi-Te with a high crystallization and in a large scale, such as chemical vapor deposition (CVD), sputtering, atomic layer deposition (ALD), spark plasma sintering (SPS), and so on. Among them, SPS is the fastest approach to produce high quality of Bi-Te systems with a low materials consumption. Therefore, we carried out the study with this approach. In other hands, the oxidation of raw Bi-Te powder can occur under ambient conditions. However, effects of the oxidation on the thermoelectric property of this system have not fully explored yet. Therefore, our work carried out to investigate the quality of the Bi-Te system compacted from their nanorized raw powders and to understand effects of pre-oxidation on the thermoelectric performance of this system. In details, the Bi-Te system has the n-type (Bi-Te alloy, Sigma Aldrich) and p-type components (Bi-Te mixed powder). The powder was prepared by mixing the raw Bi and Te powders (Sigma Aldrich) and then ground through a ball-milling process for 15 hr, resulting in a nanorized powder. After that, coin-like samples (diameter of 15 mm) were compacted through SPS by the use of the nanorized powder (p-type) and alloy (n-type). X-ray diffraction (XRD), energy dispersive spectrometry in transmission electron microscopy (TEM-EDS) and X-ray photoelectron spectroscopy (XPS) were utilized in order to analyze the structural properties of the nanorized powder, alloy, and compacted samples. Here, in XRD measurement, an insignificant change in the positions and intensities of peaks was observed in the samples with different mixing ratios of Bi-Te. Furthermore, TEM-EDS measurements showed information of the atomic arrangement and fractions of Bi-Te components that were not uniformly mixed. These hint that the pre-oxidation of these powders could occur and effect on the bonds between Bi-Te. Through the use of XPS, the intermolecular chemical bonds of the materials were revealed. As a result, the compacted samples contained a small portion of oxygen (either Bi-O or Te-O). These oxide bonds hindered Bi-Te interactions, leading to the low mixing-uniformity and small change in XRD patterns. To evaluate the thermoelectric performance of the system, its electrical conductivity depending on temperature was measured by a semiconductor parameter analyzer while its thermal conductivity was measured using the laser flash analysis (LFA). Then, Seebeck coefficient and figure of merit of the system were calculated. As a result, it is found that the increase of temperature (300 - 420 K) at one sample terminal went along with a slightly improved Seebeck coefficient but a small decrease of the figure of merit. That was because the conductivity of the n-type component increased while that of the p-type component decreased under heat. As well known, the resistance of semiconductors decreases at higher temperatures due to the increase of charge concentrations. However, our nanorized powder contained oxides that can not only hinder charge transferring pathways but also be charge trapping sites. Besides, oxygen atoms/molecules inside the powder and from the air can diffuse into the low packing crystal lattice structure of the p-type component, leading to an increase of oxide defects and charge scatterings (i.e., lower conductance) here. Generally, from the experiment observation, the pre-oxidation has a negative effect on the thermoelectric property of the Bi-Te system, especially the p-type component. Therefore, a passivation is necessary to gain better the efficiency.

Effect of pre-oxidation on the oxidation resistance of Crofer 22 APU

The ferritic stainless steel Crofer 22 APU is attractive for the use as interconnects in solid oxide fuel cell stacks. The oxidation rate of this alloy in air at 800 °C was reduced by pre-oxidation at higher temperatures in either air or N2-9%H2-1%H2O. Conversely, the oxidation rate increased when the alloy grain size was increased by heat-treating in H2 (pO2 ∼ 10−21 atm). In all cases the scale formed on Crofer 22 APU consisted of an outer (Mn,Cr)3O4 layer, an inner Cr2O3 layer and sub-scale MnCr2O4 nodules that preferentially formed at alloy grain boundaries.

Effects of Low-temperature Pre-oxidation on the Titanomagnetite Ore Structure and Reduction Behaviors in a Fluidized Bed

Effects of Low-temperature Pre-oxidation on the Titanomagnetite Ore Structure and Reduction Behaviors in a Fluidized Bed

Effect of Pre-Oxidation on the Steam Oxidation of Heat-Resistant Steel T92

Abstract Effect of pre-oxidation on the steam oxidation of T92 heat-resistant steel at 650 °C was investigated. The results show that the mass gain and the oxide thickness of T92 sample with pre-oxidation treatment were lower than that of T92 sample after exposure in steam at 650 °C. The compact and discrete Cr-rich oxide which formed on the pre-oxidized specimen hindered ion diffusion, leading to the lower oxidation rate. The effect of pre-oxidation worked at the initial stage due to the protective Cr-rich layer formed in air gas. After a long time exposure in steam, the pre-oxidation influence decreased slowly and eventually disappeared. What’s more, the adhesion property of oxide scale was improved by pre-oxidation.

Effect of Permanganate Preoxidation to Natural Organic Matter and Disinfection by-Products Formation Potential Removal

Laboratory scale experiments was conducted to examine effect of permanganate (KMnO4) peroxidation in characterizing and to remove natural organic matter (NOM) in source water. The experimental results shows that increasing permanganate dosage could decreased aromatic matter, as indicated by decreasing UV254 and SUVA value about 23% and 28%, respectively. It seems that permanganate preoxidation caused the breakdown of high molecular weight (MW) organics into low MW ones, as represented by increasing NPDOC about 10%. Further, disinfection by-products formation potential (DBPFP) in terms of trihalomethanes formation potential (THMFP) and haloacetic acid formation potential (HAAP) decreased about 15% and 23%, respectively. HAAFP removal is higher than THMFP removal and that DPBFP removal is consistent with UV254 and NPDOC removal.

Impact of ClO2 pre-oxidation on the formation of CX3R-type DBPs from tyrosine-based amino acid precursors during chlorination and chloramination

ClO2 is frequently used as a pre-oxidant in water treatment plants. However, the effects of ClO2 pre-oxidation on disinfection by-product (DBP) formation, especially the highly toxic nitrogenous DBPs, during subsequent chlor (am)ination have not been studied thoroughly. There is also limited information about DBP formation from combined amino acids (AAs), which are more abundant than free AAs in source waters. Many typical DBPs (including representative N-DBPs) have a similar structure of “CX3R” (X = H, Cl, Br or I). In the study, tyrosine and forms representing its reactivity in combined AAs (tyrosine tert-butyl ester and Boc-tyrosine) were selected as model precursors. The formation of various regulated and unregulated CX3R-type DBPs from ClO2 pre-oxidation and subsequent chlor (am)ination were studied at a wide-range of ClO2 and chlor (am)ine doses (ClO2/precursors and chlor (am)ine/precursors are at the range of 0–2.5 and 1–20 [Mol/Mol], respectively). Chloroform and chloral hydrate (CH) yields increased with chlorine dose, while haloacetonitrile and haloacetamide maximized at median chlorine dose (Cl2/Precursors = 10). All DBP yields increased with chloramine dose. ClO2 pre-oxidation increased chloroform, haloacetonitrile, trichloronitromethane and CH yields during chlorination, but ClO2 increased chloroform, CH, trichloroacetamide while decreased dichloroacetonitrile and trichloronitromethane yields during chloramination. The overall toxicity of the formed DBPs was evaluated by cytotoxicity index (CTI). ClO2 pre-oxidation increased CTI from all precursors during post-chlorination while reduced it during post-chloramination. Results imply that ClO2 is probably more suitable for use in combination with chloramination disinfection, rather than chlorination, in the integrated control of CX3R-type DBPs from source waters abundant in AAs.

Effect of pre-oxidation on the carbothermic reduction of ilmenite concentrate powder

The carbothermic reduction behavior of original ilmenite and pre-oxidized ilmenite concentrates were investigated by a non-isothermal method using a thermogravimetry facility. The reaction degree was calculated using the tail gas composition and the Starink method to analyze the activation energy of the reduction. The results demonstrated that trends of different reaction degree curves are similar under the same conditions. The average activation energy of the pre-oxidized ilmenite concentrate was less than that of the original form by approximately 25%, and the starting reduction temperature was lower by 67K than that of the original ilmenite concentrate. However, the reduction time of the pre-oxidized ilmenite concentrate was longer than that of the original ilmenite concentrate for the same reaction degree; therefore, a slow reduction rate for the oxidization sample was observed. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersion spectroscopy (EDS) were used to characterize the phase and micro-morphology of the two raw materials and compare the reduction products.

Carbon nanofibers prepared by electrospinning accompanied with phase-separation method for supercapacitors: Effect of thermal treatment temperature

Abstract

Effect of pre-oxidation on the kinetics of reduction of ironsand

The kinetics of reduction raw and pre-oxidized ironsand with hydrogen was studied using a combination of thermogravimetric analysis technique and microstructural characterization. Temperature range of 1073–1273 K (800–1000 °C) and H2 partial pressure of 0.1–1.0 atm were covered. It was found that the reaction is first order with respect to pH2 at 1173 K (900 °C). The reduction reaction was considerably faster for the pre-oxidized ironsand, owing to the presence of micro-cracks in the particles. The extent of reduction was quantified against time at different temperatures and the results were analyzed using both conventional kinetic models, as well as an iso-conversional method. The results indicated that for the raw ironsand, the reduction rate is first limited by nucleation and growth of products and later by first order chemical reaction. At last, it is controlled by three-dimensional diffusion of reactants. The apparent activation energy of reduction increased from ∼50 to 105 kJ mol−1 when the conversion degree increased from 0.2 to 0.6. On the other hand, the activation energy for the pre-oxidized ironsand remained stable at 67.2 kJ mol−1 over the entire process, following a first order chemical reaction control step. The diffusion-limited step does not appear to be limiting the rate for the pre-oxidized ironsand reduction process due to the micro-cracks formed in this material, facilitating the gas access to solids.

Hot corrosion behaviour of single-phase platinum-modified aluminide coatings: Effect of Pt content and pre-oxidation

Hot corrosion behaviour of nickel-based aluminide coatings with different thicknesses of initial Pt plating was evaluated in the Na2SO4/NaCl (75:25, wt./wt.) salt mixture at 900°C. Compared to plain aluminide, the Pt-modified coatings showed better hot corrosion resistance by hindering the outward diffusion of undesirable elements from the substrate alloy. Pre-oxidation was confirmed to be capable of preventing molten salt from accessing the alloy surface and reversibly dissolving the oxide scale. Oxide growth and dissolution, acting as two competitive processes, occurred simultaneously and had an important impact on the entire performance of the Pt-modified aluminide coatings in hot corrosion.

Chlorine decay and trihalomethane formation following ferrate(VI) preoxidation and chlorination of drinking water

This paper presents the effect of preoxidation with ferrate(VI) (FeVIO42−, Fe(VI)) prior to chlorination on chlorine decay and formation of disinfection by-products in filtered raw water from a full-scale drinking water treatment plant. The rate of chlorine decay became significantly faster as the concentration of ferrate(VI) increased. Chlorine degradation followed two first-order decay reactions with rate constants k1 and k2 for fast and slow decay, respectively. Kinetic modeling established the relationships between k1 and k2 and varying dosages of chlorine and ferrate(VI). When ferrate(VI) was used as a pre-oxidant, the levels of trihalomethanes (trichloromethane (TCM), dichlorobromomethane (DCBM), dibromochloromethane (DBCM), and tribromomethane (TBM)) in water samples decreased as the ferrate(VI) concentration increased. The concentrations of these trihalomethanes followed the order TCM > DCBM ≈ DBCM > TBM.

Effects of pre-oxidation and adsorption on haloacetonitrile and trichloronitromethane formation during subsequent chlorination.

In this study, the effects of pre-oxidants permanganate (PM), persulfate (PS), hydrogen peroxide (PO), and ozone (OZ)) and/or adsorption on pseudoboemite-chitosan shell magnetic nanoparticles (ACMNs) on haloacetonitrile (HAN) and trichloronitromethane (TCNM) formation from aspartic acid (Asp; positive charge) and/or histidine (His; negative charge) were compared. Asp and His apparently do not interact in aqueous solution during chlorination. Asp and/or His can undergo partially oxidation by PM, but are recalcitrant to direct oxidation by PS and PO. Pre-oxidation with OZ decreases the formation of HANs but increases the formation of TCNM. ACMN prefers to adsorb Asp over His in the competitive sorption of coexisting Asp and His because of attractive electrostatic interactions. The rank order for the effect of the pre-oxidants and ACMN adsorption on dichloroacetonitrile and trichloroacetonitrile formation is OZ and ACMN adsorption > PM and ACMN adsorption > PS and ACMN adsorption > PO and ACMN adsorption; that for the effect of the pre-oxidants and ACMN adsorption on TCNM formation is PM and ACMN adsorption > PS and ACMN adsorption > PO and ACMN adsorption > OZ and ACMN adsorption. The favored adsorption of Asp over His by ACMN is weakened by pre-oxidation.