Effect Of Pre-oxidation Research Articles

Elimination of hydrogen bonds in cellulose enables high-performance disordered carbon anode in sodium-ion batteries

Pre-oxidation remains an advantageous method to regulate the cross-linking structure of cellulose to prepare an increasingly disordered hard carbon applied in sodium-ion batteries. However, it is ambiguous how the introduction of oxygen affects the changes in the molecular structure of cellulose as well as the micro-structure of hard carbon. We herein systematically investigate the effect of air pre-oxidation on the crystallinity and cross-linking structure of cellulose macro-molecules by controlling the degree of oxidation. The findings indicate that the introduction of air can break the hydrogen bonding network of cellulose in advance and release a large number of reactive hydroxyl groups on the surface to be oxidized to form ether and ester cross-linking bonds. Ether bonds can transversely cross-link and extend the carbon layer and the bent carbon layers enclose a well-developed connective pore structure. Additionally, the breakage of oxygen-containing functional groups leads to the escape of large amounts of oxygen-containing gases to etch out more open pore structures with large pore sizes. Benefiting from these advantages, the prepared hard carbon possesses a specific capacity of 335 mAh·g‒1 and 89% of initial coulombic efficiency at 30 mA·g‒1 by pre-oxidating at 300°C for 12 h.

Effect of pre-oxidation on the rate of formation of sulfur-containing aromatic compounds during vacuum gas oil thermal cracking

It was shown that oxidation followed by heat treatment is an effective method for desulfurization of vacuum gas oil. Patterns of changes in the quantitative content of the thiophene series compounds in liquid cracking products of vacuum gas oil and liquid cracking products of pre-oxidized vacuum gas oil are described. A mixture of hydrogen peroxide and formic acid (molar ratio 3:4) was used as the oxidation system. The hypothetical mechanism for the formation of thiophene, benzo- and dibenzothiophene and their homologues from high-molecular weight components of the initial vacuum gas oil and its oxidation products is proposed. Presumably, main path of formation considerate compounds is thermal decomposition of high-molecular weight sulfur-containing components. On the basis of IR spectroscopy and structure-group analysis data, the averaged structures of such components were constructed. The influence of pre-oxidation and its conditions on the value of the rate constants for the formation of thiophene, benzo- and dibenzothiophene and their homologues during thermal cracking of initial and oxidized vacuum gas oils is studied.

Effect of pre-oxidation and cooling process on characteristics and mechanism of the coal re-ignition

Based on the engineering background that the sealed fire area is easy to reignite, the reignition characteristics of pre-oxidized coals (POC) after cooling are studied. Predecessors mainly explain this problem from the perspective of pre-oxidation affecting coals pore structure. This paper analyzes the effects of different pre-oxidation temperatures and cooling atmospheres on coal physical and chemical structure. The changes of coals during oxidation-cooling-reoxidation were studied by means of a programmed heating device, low temperature nitrogen adsorption experiment, FTIR and quantum chemical calculation. The results show that the average pore size of the coal cooled in nitrogen at the same pre-oxidation temperature is smaller than that of the coal cooled in dry air, while the spontaneous combustion characteristics of the coal cooled in nitrogen are stronger than those of raw coal, and spontaneous combustion characteristics of coal cooled in air are the opposite. The oxygen-containing functional groups of the coal cooled in nitrogen are pyrolyzed to produce active sites which can exist stably in nitrogen. Then, the rationality of “The active sites tend to be alkyl radical” is analyzed and speculated by molecular orbital theory, and it's found that alkyl radicals can release lots of heat at 30 °C.

Effect of low-temperature pre-oxidation on microstructure and reignition characteristic of water-immersion lignite

Effect of low-temperature pre-oxidation on microstructure and reignition characteristic of water-immersion lignite

Intensive coagulation of secondary effluent to mitigate reverse osmosis membrane fouling at low temperatures: Strategies of pre-oxidation and coagulant aids addition

Conventional coagulation-sedimentation, typically used as a pretreatment for ultrafiltration-reverse osmosis, is ineffective in solving the problem of reverse osmosis membrane fouling at low temperatures. In this study, the coagulation enhancement effect of pre-oxidation and the addition of coagulant aids on conventional coagulation with polyaluminum chloride as a coagulant was investigated. The results showed that the addition of fly ash, powdered activated carbon, or diatomite as coagulant aids improved the reduction of turbidity, dissolved organic carbon (DOC), and ultraviolet absorbance at 254 nm (UV254), and also reduced the residual content of dissolved aluminum ions. Among them, diatomite was superior. Pre-oxidation before conventional coagulation increased the reduction of turbidity and UV254 by about 50 % and doubled the removal of proteins, polysaccharides, and DOC compared to conventional coagulation. Ozone was superior to sodium hypochlorite. The combination of ozone pre-oxidation and diatomite addition with conventional coagulation further increased the pollutant removal rate, with the removal rates of turbidity, UV254, polysaccharides, proteins, and DOC reaching 82.20 %, 52.35 %, 26.34 %, 24.89 %, and 26.38 %, respectively. In addition, the residual content of dissolved aluminum ions decreased to 0.84 mg/L. The reverse osmosis filtration simulation test showed that pretreating the feed water with the enhanced coagulation by the combination of ozone pre-oxidation and diatomite addition resulted in a slower decrease in membrane flux, reduced foulant content on the membrane surface, and the smallest increase in contact angle. The results of this research may offer a viable pretreatment method to reduce fouling in reverse osmosis membranes operating at low temperatures.

Response of petroleum-contaminated soil to chemical oxidation combined with biostimulation

In this study, a microcosm experiment was conducted to investigate the effects of Na2S2O8 preoxidation combined with biostimulation on petroleum-contaminated soil remediation. The response of microbial community during this process was explored using BIOLOG ECO microplate carbon utilization method and 16 s rDNA high-throughput sequencing. The results showed that use of 10 mg/g Na2S2O8 removed 19.8 % of the petroleum hydrocarbons, reduced soil biotoxicity and did not affect soil microbial activity compared to other concentrations. Therefore, sodium persulfate of ca. 10 mg/g was used to oxidize petroleum in soil before the biostimulation experiment with organic and inorganic fertilizers. Our finding showed that the content of total petroleum hydrocarbons (TPHs) in soil was reduced by 43.3 % in inorganic fertilizer treatment after 60 days. The results of BIOLOG ECO microplate carbon utilization analysis and 16 S rDNA high-throughput sequencing further confirmed that biostimulation quickly restored the microbial activities in oxidant treated soil. The main marker bacteria in chemical oxidation combined with biostimulation remediation were Arthrobacter and Paenarthrobacter, and their relative abundances were both significantly negatively correlated with the content of petroleum hydrocarbons in soil.

Co-pyrolysis characterization of pre-oxidized lignite and corn stover

In this paper, low-rank lignite and corn stover were pre-oxidized at 200 °C with varying oxygen concentrations (0 %, 6 %, 21 %). The study investigated the effects of pre-oxidation on the physical and chemical properties of lignite and stover, including composition, functional group structure, etc. Subsequently, co-pyrolysis experiments were conducted on the pre-oxidized lignite and stover at 700 °C. The study examined the characteristics of the co-pyrolysis of lignite and corn stover under different oxygen concentrations. The results showed that pre-oxidation could effectively increase the content of fixed carbon in the raw materials, elevate the content of carbonyl and carboxyl groups in the raw materials, and reduce the number of aliphatic hydrocarbon side chains as well as hydroxyl groups. The degree of aromatization of the co-pyrolysis char produced from pre-oxidized lignite and corn stover was enhanced. The 6 % O2 pre-oxidation promoted the pyrolysis degree of the raw materials and intensified the progression of the reaction. The CO2 content of the co-pyrolysis tar was at a minimum of 23.028 % with 0 % O2, and the gas had a maximum calorific value of 11.651 MJ∙Nm−3 at this point. Pre-oxidation had an inhibitory effect on the production of co-pyrolysis tar, and the inhibitory effect became more pronounced with higher concentrations of O2. The higher the oxygen concentration, the more pronounced the inhibition. The addition of oxygen promotes the generation of phenols and ketones in the tar, reducing the content of acids and aldehydes. This improves the quality of the tar but also results in a reduction of aromatic hydrocarbons to some extent.

The buckwheat-derived hard carbon as an anode material for sodium-ion energy storage system

Biomass-derived hard carbon (HC) has attracted much attention as a promising electrode material for sodium-ion batteries (SIBs) due to its unique properties such as high porosity, large surface area and adjustable pore size distribution. This work presents the results of electrochemical studies of HC derived from buckwheat seeds. The HCs were preoxidized at 300 °C and synthesized using a pyrolysis method in the range 600–1400 °C. It was found that the electrochemical characteristics of the HC anodes are strongly dependent on the morphology and structure. Furthermore, the positive effect of preoxidation on the porosity of HC was confirmed. Although all buckwheat-derived HC-based anodes showed stable cyclability over 100 cycles with CE of approximately 97–98 %, the preoxidized HCs pyrolyzed at 1400 °C achieved the highest reversible capacity of 330.23 mAh g−1 with excellent stability. Additional study using “single particle” measurement of HC1400 and HCox1400 showed that the preoxidation may significantly contribute to the improvement of the mass transfer.

Synergistic effect of spinning drawing and preoxidation stretching on the orientation structure of mesophase pitch carbon fibers

Mesophase pitch carbon fiber has shown remarkable prospects in specialty carbon material. The mechanical properties of mesophase pitch carbon fiber (CF) cannot be precisely controlled because of the difficulty of forming process regulation. The early forming of carbon fiber (precursor fiber (PF) and pre-oxidation fiber (OF)) is difficult to regulate, such as carbon microcrystal and carbon layer texture, while cause the irreversible growth of carbonization process. Herein, a synergy strategy of spinning drawing and preoxidation stretching is developed to optimize orientation structure, eliminate morphology defects and improve mechanical properties. A synergistic effect of superior spinning drawing and suitable preoxidation stretching is beneficial to adjust the more order rearrangement of carbon microcrystals. The tensile strength of carbon fibers with spinning drawing and preoxidation stretching is increased by 1.7 times, and their defects are reduced by 40%. The results show that the excellent mechanical property of carbon fiber is contributed by the extrusion stress caused by high oxidation crosslinked surface layer under tension, and the micro-flow and rearrangement of carbon microcrystals induced by extrusion stress. A mechanical strengthening mechanism of carbon fiber is proposed, which provides guidance for high-performance mesophase pitch carbon fiber.

Promotion of lignin depolymerization and cellulose utilization via the coupling effects of DDQ pre-oxidation and HCOOH extraction

The full utilization of biomass plays an important role in the environment and energy. In this study, the coupling pretreatment of DDQ pre-oxidation and HCOOH extraction was employed to realize the separation and modification of three components of sugarcane bagasse for full utilization. Especially, the modified lignin was depolymerized to obtain aromatic monomers, and cellulose-rich residue was used to prepare lignocellulose straws. Furthermore, the coupling effects between DDQ pre-oxidation and HCOOH extraction on chemical and physical properties of modified lignin and lignocellulose straws were studied. In addition, the mechanism of lignin depolymerization and lignocellulose straw synthesis were explored as well as the mass balance of the biorefinery process. The results showed that the total yield of aromatic monomers increased by nearly 2 times and the conversion of lignin was 95.1 % after DDQ pre-oxidation. The mechanism showed that DDQ selectively oxidized Cα-OH bond of lignin to Cα = O bond, which not only avoided the formation of carbocation, but also reduced the bond dissociation energy of β-O-4 bond. Moreover, the tensile strength of hydrophobic lignocellulose straw increased by nearly 2 times and its flexural strength was 10.36 MPa. Modified lignin and modified cellulose were connected via hydrogen bonds, which enhanced the intermolecular crosslinking of molecules, thus improving the mechanical properties of lignocellulose straws. Besides, the maximum xylose relative content and concentration of xylose were 61.16 % and 17.57 g/L, respectively. This study provides a method for high-value and green utilization of sugarcane bagasse.

Algal-Rich Drinking Source Water: Effects of Chlorine Pre-oxidation on Algal Growth, Algal Organic Matter, and the Potential of Disinfection By-Products

Algal-Rich Drinking Source Water: Effects of Chlorine Pre-oxidation on Algal Growth, Algal Organic Matter, and the Potential of Disinfection By-Products

Pool boiling heat transfer: Thermal performance for alternating and extended operational conditions

Oxide formation on metallic heat transfer surfaces poses a risk parameter in high-power thermal systems maintained by multi-phase cooling. In spite of the significance for practical applications, the potential change in chemistry and morphology on the surfaces exposed to continuous or alternating boiling process plays a vital role in heat transfer efficiency. In this comprehensive study, the effect of heat flux rate, boiling crisis, operation time, surface roughness, and pre-oxidation by the system calibration on oxide layer formation and its inevitable effect on boiling heat transfer (BHT) have been evaluated separately. A sort of experimental scenarios rather representing real operating conditions encountered in phase-change cooling apparatuses were carried out on smooth and rough copper substrates in saturated de-ionized water at atmospheric pressure. In order to practice the scenarios, a series of subsequent critical heat flux (CHF) runs and continuous boiling operations at certain heat flux levels ranging between 15 and 60 W/cm2 were performed within different numbers and sequences as a part of the Design of Experiments (DOE). Each operating scenario was analyzed and compared individually, while questions regarding the effect of the number of CHF runs, heat flux level during long-term operation, surface roughness, pre-oxidation, and rigorous long-term stability operation on boiling heat transfer were examined exhaustively. As a result, CHF and maximum heat transfer coefficient (HTC) of all surfaces exposed to boiling processes considerably enhanced at different rates corresponding to applied scenarios. The rate of heat flux level applied on heating surfaces was not determined to be a significant factor, whereas the HTC and CHF enhanced as the number of subsequent boiling crises (CHF runs) ultimately raised. On the other hand, HTC of the surface non-exposed to CHF runs demonstrated a drastic enhancement by 45% after 24 h of continuous boiling exposure at 45 W/cm2 compared to initial performance with 1.0 W/cm2K. The heat transfer from the surfaces exposed to extended long-term operations showed a final stable thermal behavior, while CHF values doubled from an initial value of approximately ∼73 W/cm² to 144.7 W/cm2 as exposure time increased. X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and scanning electron microscope (SEM) analyses were executed to evaluate the influence of micro-nano-scale oxide particles/layers developed on the heater surfaces and to interpret the changes in heat transfer performance.

Enhancing short-chain fatty acids production via acidogenic fermentation of municipal sewage sludge: Effect of sludge characteristics and peroxydisulfate pre-oxidation.

This study first employed a combined pretreatment of low-dose peroxy-disulfate (PDS) and initial pH 10 to promote short-chain fatty acids (SCFAs) production via acidogenic fermentation using different types of sewage sludge as substrates. The experimental results showed that the yield of maximal SCFAs and acetate proportion after the combined pretreatment were 1513.82±28.25mg chemical oxygen demand (COD)/L and 53.64%, and promoted by 1.28 and 1.56 times higher, respectively, compared to the sole initial pH 10 pretreatment. Furthermore, in terms of the disintegration degree of sewage sludge, it increased by more than 18% with the combined pretreatment compared to the pretreatment of sole initial pH 10. Waste-activated sludge (WAS) from A2/O and Bardenpho processes were more biodegradable, explained by the 1.47- and 1.35-times higher disintegration rate than those from oxidation ditch and they favored acetate dominant fermentation. Correlation analysis revealed a strong correlation (p ≤ 0.01) between SCFAs production and soluble COD, total proteins, proteins in soluble-extracellular polymeric substances (SEPS), total polysaccharides, and polysaccharides in SEPS. Mechanism explorations showed that preoxidation with PDS enhanced the solubilization and biodegradability of complex substrates, and altered the microbial community structure during the fermentation process. Firmicutes and Tetrasphaera were proven to play a key role in improving SCFA production, especially in promoting acetate production by converting additional SCFAs into acetate. Additionally, the addition of PDS greatly promoted sulfur and iron-related metabolic activities. Finally, the combined pretreatment was estimated to be a cost-effective solution for reutilizing and treating Fe-sludge.

Effect of Direct and Indirect Pre-Oxidation of Gold Ore from Doup North Sulawesi using Ozone Gas on the Gold Extraction in the Cyanidation Process

Refractory gold ore is a type of gold ore that is difficult to process when treated through a conventional cyanidation process. Pre-oxidation using ozone gas is one of the pre-treatment methods that can be used to improve gold recovery from sulfide-type refractory ore. This study used gold ore samples from Doup, North Sulawesi, Indonesia, to study the effect of direct and indirect pre-oxidation using ozone gas on gold recovery and subsequently treated by a cyanidation process. Direct and indirect pre-oxidation experiments were carried out at different pHs and using two raw materials for ozone generation (air and O2). The slurry obtained from the pre-oxidation experiments was filtered, and the filtrate was analyzed for the concentration of dissolved Cu, Fe, and Zn using atomic absorption spectroscopy (AAS); meanwhile, the residue from each pre-oxidation experiment was leached by cyanidation to obtain a pregnant leaching solution (PLS), which was analyzed for its gold concentration using AAS. The percentages of dissolved Cu, Fe, and Zn during pre-oxidation increased with the pre-oxidation time when the acidity was maintained at pH 2, using pure O2 as the ozone raw material. The direct pre-oxidation process at pH 2 using air as the ozone raw material increased gold extraction from 79.08% to 82.78% in the cyanidation process. The pre-oxidation experiments performed without controlling the pH resulted in lower gold dissolutions than the pre-oxidation conditions at pH 2. Possible causes of the lower gold dissolution were discussed.

Effect of pre-oxidation and sea salt on the hot corrosion behavior of MCrAlY coatings and Al[sbnd]Si coatings

This paper investigated the hot corrosion behavior of two types of coatings, namely NiCoCrAlYHfSi and AlSi coatings, used in gas turbines operating in a moderate-temperature sea salt environment. Prior to the corrosion experiment, pre-oxidation treatment was employed to generate a continuous α-Al2O3 thin layer on the surface of the coatings, leading to a significant reduction in coating roughness. The results demonstrated distinct failure behaviors of the two coatings in the presence of sea salt, providing insights into the mechanism of hot corrosion. The NiCoCrAlYHfSi coating effectively resisted corrosion through a mixed oxide layer consisting of Al2O3 and Cr2O3, while the AlSi coating utilized the continuous formation of Al2O3 to combat corrosion. In comparison to the NiCoCrAlYHfSi coating, the AlSi coating exhibited superior resistance to sea salt erosion. In addition, pre-oxidation is able to effectively reduce the erosion of the coating by sea salt, thereby extending the lifespan of the NiCoCrAlYHfSi coating and the AlSi coating by 40 % and 30 % respectively.

Effect of preoxidation on fouling mitigation in a low-pressure membrane system with clean-in-place (CIP) treatment

The study investigates the impact of biological (soluble microbial products), organic (humic acid), and inorganic foulants (Al, Mn, and Fe) on the structure of polyvinylidene fluoride (PVDF) and polyethersulfone (PES) membranes during filtration processes. While different forms of Al, including mononuclear (Ala), colloidal (Alc), and polymeric (Alb) species, were also analyzed and a chlorination dose of 1.5 mg.L−1 was used as pretreatment for the feed water. The results revealed that the PES membranes exposed to the untreated feed solution were more vulnerable to severe structural deterioration as compared to PVDF membranes, in the presence of organic/biological foulants and complex mixtures of organic and inorganic foulants. Presence of carbonate (O-C=O) and carboxylic groups on PES membranes and the reduction of hydrophilic additives on PVDF membranes after exposure to the feed streams was observed. Moreover, the pore size of the PES and PVDF membranes increased to 1308.1 nm and 287.8 nm, respectively, at the end of study. The PVDF membranes exhibited severe fouling than PES membranes due to strong adsorption potential for the foulants. Moreover, Alb had stronger fouling effect that Ala and Alc, while pre-chlorination increased charge neutralization and reduced fouling due to weaker binding with the organic foulants. Results from Hermia's fouling model confirmed the occurrence of complete blocking, followed by the formation of a cake layer and intermediate fouling.

Hydrogen peroxide preoxidation as a strategy for enhanced antimicrobial photodynamic action against methicillin-resistant Staphylococcus aureus.

Antimicrobial photodynamic treatment (aPDT) is a photooxidative process based on the excitation of a photosensitizer (PS) in the presence of molecular oxygen, under specific wavelengths of light. It is a promising method for advanced treatment of water and wastewater, particularly targeting disinfection challenges, such as antibiotic-resistant bacteria (ARB). Research in improved aPDT has been exploring new PS materials, and additives in general. Hydrogen peroxide (H2O2) a widely applied disinfectant, mostly in the food industry and clinical settings, present environmentally negligible residuals at the usually applied concentrations, making it friendly for the water and wastewater sectors. Here, we explored the effects of preoxidation with H2O2 followed by blue light-mediated (450 nm) aPDT using curcumin (a natural-based PS) against methicillin-resistant Staphylococcus aureus (MRSA). Results of the sequential treatment pointed to a slight hampering in aPDT efficiency at very low H2O2 concentrations, followed by an increasing cooperative effect up to a deleterious point (≥7 log10 inactivation in CFU mL-1), suggesting a synergistic interaction of preoxidation and aPDT. The increased performance in H2O2-pretreated aPDT encourages studies of optimal operational conditions for the assisted technology and describes potentials for using the described strategy to tackle the issue of ARB spread.

Molecular insight of dissolved organic matter and chlorinated disinfection by-products in reclaimed water during chlorination with permanganate preoxidation

Permanganate is a common preoxidant applied in water treatment to remove organic pollutants and to reduce the formation of disinfection by-products. However, the effect of permanganate preoxidation on the transformation of dissolved effluent organic matter (dEfOM) and on the formation of unknown chlorinated disinfection by-products (Cl-DBPs) during chlorination remains unknown at molecular level. In this work, the molecular changes of dEfOM during permanganate preoxidation and subsequent chlorination were characterized using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Permanganate preoxidation was found to decrease the DBE (double bond equivalent) and AImod (modified aromaticity index) of the dEfOM. The identity and fate of over 400 unknown Cl-DBPs during KMnO4-chlorine treatment were investigated. Most Cl-DBPs and the precursors were found to be highly unsaturated aliphatic and phenolic compounds. The Cl-DBPs precursors with lower H/C and lower O/C were preferentially removed by permanganate preoxidation. Additionally, permanganate preoxidation decreased the number of unknown Cl-DBPs by 30% and intensity of unknown Cl-DBPs by 25%. One-chlorine-containing DBPs were the major Cl-DBPs and had more CH2 groups and higher DBEw than Cl-DBPs containing two and three chlorine atoms. 60% of the Cl-DBPs formation was attributed to substitution reactions (i.e., +Cl–H, +2Cl–2H, +3Cl–3H, +ClO–H, +Cl2O3–2H). This work provides detailed molecular level information on the efficacy of permanganate preoxidation on the control of overall Cl-DBPs formation during chlorination.

Improving repair performance for damaged C/C composites via heat-treatment temperature optimization and surface pretreatment

A Ni-based solder BNi-5 was adopted as the repair agent to repair the prefabricated defects on the carbon/carbon (C/C) composites. The effects of different heat-treatment (HT) temperatures and pre-oxidation on the chemical composition, microstructure, and mechanical behavior of the repaired C/C composites were investigated, and the repair mechanism was studied by finite element analysis methods. The repair agent and C/C composites were tightly bonded through mechanical interlocking and chemical reactions, and the flexural properties of the damaged C/C composites were significantly improved after repair. The products at the interface formed a gradient distribution structure of the thermal expansion coefficient when the HT temperature was 1300 °C, which is beneficial to relieve the residual thermal stress at the interface. Meanwhile, the porosity of the surface of the C/C composites was higher after pre-oxidation, which led to more diffusion channels for the repair agent and enhanced the interface bonding ability. The flexural strength was the highest with a recovery rate of 85.2% when the C/C composites were pre-oxidized at 600 °C and the HT temperature was 1300 °C. This work provides a strategy for the engineering application of the damage repair of C/C composites.

Early stages of liquid-metal corrosion on pre-oxidized surfaces of austenitic stainless steel 316L exposed to static Pb-Bi eutectic at 400 °C

The effect of pre-oxidation in air at 300–500 °C on the initiation and development of liquid metal corrosion attack on 316L austenitic steel in static lead-bismuth eutectic (LBE) with ∼10−10 – 10−9 mass% dissolved oxygen at 400 °C for 1200 h is investigated. General dissolution with preferential attack along twin boundaries was observed on polished surfaces with native oxide films. Fe/Cr-based oxide films pre-formed in air at 300 and 400 °C protect surfaces against dissolution. Localized corrosion was observed on surfaces pre-oxidized at 500 °C. Thermal oxide degradation rate depends on its composition rather than thickness.