Influence of Cr Content on the High-Temperature Oxidation Behavior and Mechanism of Low-Alloy Steels.

The high-temperature oxidation behavior of low-carbon steel (AISI 1015, AISI 8617, AISI 4115) was investigated over the temperature range from 600 to 1000 °C in humid air containing 25% water vapor. Mass gain of oxidation measurement was performed to study the oxidation kinetics. The microstructure, thickness, and composition of the oxide scale formed were investigated via optical microscope (OM), scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS), X-ray diffraction (XRD), and electron probe microanalyzer (EPMA). The oxidation process was performed from 2 to 100 min. As the oxidation time increased, the trend of mass gain per unit area switched from a linear to a parabolic law, regardless of the steel grade used. As the chromium content increased, the duration of time during which the oxidation rate followed a linear relationship decreased. In the low-alloy steel with higher chromium content, the thickness of the mixed oxide layer containing Cr increased and the oxidation rate decreased at all oxidation temperatures.

Practical approach of As(V) adsorption by fabricating biochar with low basicity from FeCl3 and lignin.

One of the main challenges of biochar application for environmental cleanup is rise of pH in water or soil due to high ash and alkali metal contents in the biochar. While this intrinsic property of biochar is advantageous in alleviating soil and water acidity, it severely impairs the affinity of biochar toward anionic contaminants such as arsenic. This study explored a technical approach that can reduce the basicity of lignin-based biochar by utilizing FeCl3 during production of biochar. Three types of biochar were produced by co-pyrolyzing feedstock composed of different combinations of lignin, red mud (RM), and FeCl3, and the produced biochar samples were applied to adsorption of As(V). The biochar samples commonly possessed porous carbon structure embedded with magnetite (Fe3O4) particles. The addition of FeCl3 in the pyrolysis feedstock had a notable effect on reducing basicity of the biochar to yield significantly lower solution pH values than the biochar produced without FeCl3 addition. The extent of As(V) removal was also closely related to the final solution pH and the greatest As(V) removal (>77.6%) was observed for the biochar produced from co-pyrolysis of lignin, RM, and FeCl3. The results of adsorption kinetics and isotherm experiments, along with x-ray spectroscopy (XPS), strongly suggested adsorption of As(V) occurred via specific chemical reaction (chemisorption) between As(V) and Fe-O functional groups on magnetite. Thus, the overall results suggest the use of FeCl3 is a feasible practical approach to control the intrinsic pH of biochar and impart additional functionality that enables effective treatment of As(V).

Valorization of plastics and paper mill sludge into carbon composite and its catalytic performance for acarbon material consisted of the multi-layerzo dye oxidation.

In this work, polyvinyl chloride (PVC) and paper mill sludge (PMS) were co-pyrolyzed under two environments of N2 and CO2. The pyrolysis process was assessed by conducting thermogravimetric analysis (TGA) and monitoring the evolution of gaseous products. The resulting solid composites were characterized using XRD, XPS, BET, and Raman analyzers, and their ability to catalytically activate persulfate (S2O82-) was tested by conducting methyl orange (MO) degradation experiments. Co-pyrolysis of PVC and PMS at the same mass ratio (1:1) in CO2 resulted in the highest production of H2 and CO (0.36 mol % H2 at 480 °C & 1.53 mol % CO at 700 °C). The characterization results revealed that the composite consisted of Fe3O4, highly graphitic carbon, and mesoporous structure. In MO oxidation experiments, the co-pyrolyzed composite actively generated OH and SO4- by activating S2O82- to achieve complete removal of 5 mg L-1 of MO during 100 min at acidic-neutral pH condition. The composite was also able to complete 3 successive cycles of MO oxidation without deactivation. Consequently, the feasibility of achieving the simultaneous production of energy resources and catalyst via industrial wastes utilization in pyrolytic process was demonstrated.

A review of recent advancements in utilization of biomass and industrial wastes into engineered biochar.

For past few years, biochar has gained a great deal of attention for its versatile utility in agricultural and environmental applications. The diverse functionality and environmental-friendly nature of biochar have motivated many researchers to delve into biochar researches and spurred rapid expansion of literature in recent years. Biochar can be produced from virtually all the biomass, but the properties of biochar are highly dependent upon the types of feedstock biomass and preparation methods. The overall performances of as-prepared biochar in treating soil and water contaminants is generally inferior to activated carbon due to its lower surface area and limited functionalities. This limitation has led to many follow-up studies that focused on improving material characteristics by imparting desired functionality. Such efforts have greatly advanced knowledge to produce better-performing engineered biochar with enhanced capability and versatility. To this end, this review was prepared to compile recent advancements in fabrication and application of engineered biochar, especially with respect to the influences of biomass feedstock on the properties of biochar and the utilization of industrial wastes in fabrication of engineered biochar.

Zirconia-Assisted Pyrolysis of Coffee Waste in CO2 Environment for the Simultaneous Production of Fuel Gas and Composite Adsorbent.

This work newly employed monoclinic zirconia (ZrO2) as a promoter to improve CO2 pyrolysis of coffee waste (CW). The CO2 pyrolysis of CW presented the high level of CO production (14.3 mol%) during two stages of non-isothermal (280 to 700 °C) and isothermal pyrolysis (kept at 700 °C). At the same condition, the incorporation of ZrO2 improved the CO generation up to about twice that of CW (29.5 mol%) by possibly inducing more conversion of pyrolytic oil into gas. The characterization results exhibited that ZrO2-impregnated biochar (ZrB) possessed the distinctive surface morphology that highly graphitic- and porous carbon layers were covered by ZrO2 nanoparticle clusters. In a series of adsorption experiments, ZrB composite showed pH-dependent As(V) adsorption and pH neutralization ability. The adsorption proceeded relatively rapid with 95% removal during 120 min in the early stage, followed by 5% removal in the remaining 240 min. The maximum adsorption capacity was found to be 25.2 mg g-1 at final pH 8. The reusability and stability of ZrB were demonstrated in the 6 consecutive cycles of adsorption/desorption. As a result, ZrO2-assisted CO2 pyrolysis can potentially produce fuel gas with high CO fraction and composite adsorbent suitable for As(V) removal in acidic wastewater.

Thermochemical conversion of cobalt-loaded spent coffee grounds for production of energy resource and environmental catalyst.

Thermochemical conversion of cobalt (Co)-loaded lignin-rich spent coffee grounds (COSCG) was carried out to find the appropriate pyrolytic conditions (atmospheric gas and pyrolytic time) for syngas production (H2 and CO) and fabricate Co-biochar catalyst (CBC) in one step. The use of CO2 as atmospheric gas and 110-min pyrolytic time was optimal for generation of H2 (∼1.6 mol% in non-isothermal pyrolysis for 50 min) and CO (∼4.7 mol% in isothermal pyrolysis for 60 min) during thermochemical process of COSCG. The physicochemical properties of CBC fabricated using optimized pyrolytic conditions for syngas production were scrutinized using various analytical instruments (FE-SEM, TEM, XRD, and XPS). The characterizations exhibited that the catalyst consisted of metallic Co and surface wrinkled carbon layers. As a case study, the catalytic capability of CBC was tested by reducing p-nitrophenol (PNP), and the reaction kinetics of PNP in the presence of CBC was measured from 0.04 to 0.12 s-1.

Reduction of Bromate by Cobalt-Impregnated Biochar Fabricated via Pyrolysis of Lignin Using CO2 as a Reaction Medium.

In this study, pyrolysis of lignin impregnated with cobalt (Co) was conducted to fabricate a Co-biochar (i.e., Co/lignin biochar) for use as a catalyst for bromate (BrO3-) reduction. Carbon dioxide (CO2) was employed as a reaction medium in the pyrolysis to induce desired effects associated with CO2; (1) the enhanced thermal cracking of volatile organic compounds (VOCs) evolved from the thermal degradation of biomass, and (2) the direct reaction between CO2 and VOCs, which resulted in the enhanced generation of syngas (i.e., H2 and CO). This study placed main emphases on three parts: (1) the role of impregnated Co in pyrolysis of lignin in the presence of CO2, (2) the characterization of Co/lignin biochar, and (3) evaluation of catalytic capability of Co-lignin biochar in BrO3- reduction. The findings from the pyrolysis experiments strongly evidenced that the desired CO2 effects were strengthened due to catalytic effect of impregnated Co in lignin. For example, the enhanced generation of syngas from pyrolysis of Coimpregnated lignin in CO2 was more significant than the case without Co impregnation. Moreover, pyrolysis of Coimpregnated lignin in CO2 led to production of biochar of which surface area (599 m2 g-1) is nearly 100 times greater than the biochar produced in N2 (6.6 m2 g-1). Co/lignin biochar produced in CO2 also showed a great performance in catalyzing BrO3- reduction as compared to the biochar produced in N2.