Pyrolysis characteristics and product distribution of oil sludge based on radiant heating.

It needs to be improved the conversion efficiency and stable operation of conventional pyrolysis with high-temperature flue gas heating (HFH). Herein, a new radiative heating (RH) pyrolysis method is proposed. Experimental studies are carried out on a self-made radiation pyrolysis pilot plant to investigate the effects of different factors (pyrolysis final temperature, residence time, and carrier gas volume) on product distribution. The results show that with the increase of pyrolysis temperature, the yield of the gas phase consistently increases, and the proportion of CH4 and H2 in the pyrolysis gas reaches 62.31% at 700 °C. The yield of the liquid phase increases and then decreases. The recovery rate of pyrolysis oil achieves 68.07% when the pyrolysis temperature is 600 °C with main components of ketones and unsaturated hydrocarbon compounds. The yield of the solid phase consistently decreases. The RH in this work generates more pyrolysis gas in the pyrolysis process and alleviates the effects of fouling layers on the continuous operation of the equipment which has guiding significance for the efficient resource utilization of oil sludge.

Method of smoldering combustion for the treatment of oil sludge-contaminated soil.

There is an urgent need to globally remediate oil sludge-contaminated soil (OSS). Smoldering combustion is a new low-energy approach for the treatment of organic waste. Therefore, the feasibility of smoldering combustion for the treatment of OSS was investigated in this study using a series of laboratory-scale experiments. The effective remediation of OSS was found to be achievable when the mass ratio of oil sludge in the sample reached 1/12 and above. Experimental results showed that smoldering at peak temperatures above 500 °C was found to completely remove petroleum hydrocarbons from the samples. The mass ratio of oil sludge in the sample had little effect on the distribution of the major elements (Si, Al, and Ca) in the smoldering products, and most of the minerals in the oil sludge adhered to the surface of the soil particles after smoldering. The smoldering heating environment is detrimental to the reusability of the soil, increases soil pH and available phosphorus content, and decreases organic carbon and total nitrogen content. Moreover, the influence of the airflow rate and material height on smoldering characteristics was investigated. Matching the appropriate airflow rate can help maintain optimal smoldering conditions, and smoldering remains stable with increasing material height. The addition of recovered oil to a sample with a low mass ratio of oil sludge can help with smoldering ignition and improve the removal efficiency of petroleum hydrocarbons. This study has confirmed that smoldering can be used to treat OSS within a broad range of oil sludge concentrations without pretreatment.

Calcination of sewage sludge-based sulphoaluminate cement clinker: Mineral formation mechanism and heavy metal transition behaviors.

Utilizing sewage sludge (SS) to calcinate sulphoaluminate cement (SAC) is a promising technology for low-carbon transition of cement industry, but the unclear effects of SS-contained heavy metals limit the application of this technology. In this study, the effects of SS addition on the calcination of SAC clinker and the transformation of heavy metals were studied from the aspects of mineral phase change, microstructure evolution and heavy metal speciation respectively, covering the mineral formation temperature 900-1250 °C. The results show that the added SS will reduce the formation temperature and change the reaction pathways of mineral phases. When the content of SS increases from 10% to 25%, the compositions of mesophases CaO·Al2O3 and 4CaO·2SiO2·CaSO4 increase by 6.33% and 9.73%, respectively. Meanwhile, the formation of minerals will solidify Zn, Ni, Mn, Cu, Cr, and convert them into a more stable fraction (residual fraction), indicating a lower probability to harm the environment. Moreover, heavy metals present different migration behaviors. After calcination, Mn migrates from SS to 4CaO·Al2O3·Fe2O3 (52.48%), while Zn prefers to enter 3CaO·3Al2O3·CaSO4 (43.74%) and 4CaO·Al2O3·Fe2O3 (38.06%). This study offers new insights into the mineral formation mechanism and heavy metal transition behaviors of sewage sludge-based SAC.

Insights into the underpinning effect of graphene in Cu1Mn10 on enhancing the low-temperature catalytic activity for CO oxidation.

CO emission is a critical issue of industrial processes such as steel-smelting, cement manufacturing, and waste incineration. Catalytic oxidation based on Cu-Mn binary catalysts shows great potential for efficient removal of CO, whereas their practical applicability is limited by the inferior low-temperature catalytic activity and the high catalyst cost owing to a substantial quantity of Cu. In this study, doping graphene is designed to adjust the electron transfer capability to improve the low-temperature catalytic activity as well as reduce the amount of Cu, and thereby Cu1Mn10 catalysts doped with slight amounts of graphene (x%G-Cu1Mn10, x is 1∼5) were fabricated. It was found that the introduction of graphene could form effective electron transport channels to enhance the intermetallic interaction and oxygen vacancy generation, thus improving the low-temperature catalytic performance of the Cu1Mn10 catalyst. Among all the catalysts, 4%G-Cu1Mn10 exhibited the highest activity, achieving CO conversion of 92% at 110 °C at a weight hourly space velocity of 120,000 mL/(g∙h). The introduction of graphene also enabled the catalyst with excellent catalytic activity and stability at a relative humidity of 70%. Attractively, 4%G-Cu1Mn10 can be further loaded into the polyester fabric, presenting great application potentials in the effective elimination of CO during the dust removal process since the flue gas temperature in the dust collector is just around the T90% and the catalyst that is inside of fabric fiber rather than on the fabric surface can be rarely influenced by the dust. In general, doping graphene provides a facile method to enhance the low-temperature activities of the Cu-Mn binary catalysts and cut down the use of valuable Cu, showing great application potential.

Effect of temperature on the reaction path of pyrite (FeS2)-based catalyst catalyzed CO reduction of SO2 to sulfur.

To understand the physical phase structural variation and activation pathway of the active component during the catalytic reduction of pyrite (FeS2)-based catalysts, multiple methods, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and high-temperature in situ XRD, were applied to characterize the catalyst and reaction process. The reaction mechanism was simulated and verified using density functional theory. The results indicated that pyrite-based catalysts promote the CO reduction of SO2 to S through the dynamic transformation of three phases (FeS2, Fe7S8, and FeS), in which S-vacancy formation is the most important step. As the critical temperature for the reaction of FeS2 and CO was initiated at approximately 525 °C, the active component's physical phase structure and activation pathway could be controlled by adjusting the temperature.

Alkaline etched hydrochar-based magnetic adsorbents produced from pharmaceutical industry waste for organic dye removal.

A large amount of pharmaceutical industry waste (PIW) was inevitably produced every year, and the PIW can be degraded by high temperature reaction to form porous structures. The study proposed an innovative pathway to valorize PIW with hydrothermal carbonization (HTC) coupled with alkali etching (AE). Without adding any additives, magnetic hydrochar could be generated with rough surface topography and suitable specific surface area (SBET) by this method. Effects of HTC conditions and alkaline solution concentrations on the physicochemical and adsorption properties of PIW were investigated, and adsorption mechanism was explored. Based on evaluations of the magnetism, cyclic regeneration, and heavy metal leaching properties of the products, the feasibility of preparing magnetic adsorbents with solid waste by HTC coupled AE was established. The alkaline etching pharmaceutical industry waste (AEPIW) hydrochar showed the highest SBET (54.64 m2/g) after the PIW was treated by 260 °C for 2 h plus 1 mol/L KOH. The removal rate of methylene blue (MB) could exceed 90% and the saturated magnetization was ~8 emu/g. The proposed new method was able to convert the low-value solid industrial waste into high-performance hydrochar-based magnetic adsorbents, which was tested to have a capability to efficiently and sustainably remove organic pollutants from water.

A sustainable revival process for defective LiFePO4 cathodes through the synergy of defect-targeted healing and in-situ construction of 3D-interconnected porous carbon networks.

The reutilization of spent cathode materials plays a key role in the sustainable development of Li-ion battery technology. However, current recycling approaches generally based on hydro-/pyrometallurgy fail to cater to Co-free cathodes (e.g., LiFePO4, or LFP) owing to high consumption and secondary contamination. Here, a sustainable process is proposed for the revival of defective LFP cathodes through the synergy of defect-targeted healing and surface modification. Li deficiency and Fe oxidation of cathodes are precisely repaired by solution-based relithiation; meanwhile, 3D-interconnected porous carbon networks (3dC) are in-situ constructed with the intervention of salt template during annealing, which enhances the rate performance and electronic/ionic conductivity, by providing more convenient migration channels for Li ions and controlling carbon hybridization. Nitrogen is also doped via induction of urea to fabricate advanced nanohybrid rLFP@3dC-N. New cells using rLFP@3dC-N as cathode exhibit a reversible capacity of up to 169.74 and 141.79 mAh g-1 at 0.1 and 1C, respectively, with an excellent retention rate of over 95.7% at 1C after 200 cycles. Impressively, a high capacity of 107.18 mAh g-1 is retained at 5C. This novel concepts for Li replenishment and the construction of ion-transfer channels as well as conductive networks facilitate the regeneration of spent LFP and the optimization of its high-rate performance.

Study on the synergy effect of MnOx and support on catalytic ozonation of toluene.

MnOx has received widespread attention in low-temperature catalytic oxidation of VOCs, however, the synergy effect of MnOx and support on the VOCs catalytic ozonation were rarely studied. In this study, five different MnOx/X (X: MCM-41, 13X, ZSM-5, HY, USY) were synthesized and found their support greatly affect the catalytic oxidation activity. MnOx/MCM-41 presents the largest specific surface area, pore volume and unique surface morphology, and thereby provides more sites for MnOx loading and VOCs adsorption. Moreover, MnOx/MCM-41 presents a high proportion of Mn3+, which helps to enhance the ion exchange capability, and thus promotes the regeneration of oxygen vacancies. Furthermore, a part of Mn was proved to be introduced into the MCM-41 lattice, which can promote the electron transfer between the active components and the support, and thereby effectively improve the surface electronic properties of the catalyst. The toluene catalytic experiments showed that MnOx/MCM-41 exhibited the best catalytic activity, presenting complete degradation of O3 and VOCs at room temperature. In addition, 5 wt%MnOx/MCM-41 exhibited better catalytic activity than other loading, and its higher surface oxygen species endowed it with strong water resistance and stability. In-situ DRIFTs indicated that toluene was initially oxidized into benzyl alcohol during the adsorption process, and then decomposed to intermediate products (benzaldehyde, phenolate, etc.) during the catalytic ozonation process, and finally oxidized to carbon dioxide. In conclusion, the supply of loading sites and the improvement of interfacial electron transfer are the manifestations of the synergy between the support and MnOx, leading to the promotion of the catalytic ozonation of VOCs.

Discovering the key role of MnO2 and CeO2 particles in the Fe2O3 catalysts for enhancing the catalytic oxidation of VOC: Synergistic effect of the lattice oxygen species and surface-adsorbed oxygen.

Highly active mesoporous Fe-Mn-Ce catalysts with high specific surface area (SBET) were synthesized by a modified precipitation process for catalyzing toluene oxidation. The Fe0.85Mn0.1Ce0.05 catalyst presents richer surface oxygen species (OS), a higher proportion of Mn4+ and Ce4+, a higher concentration of lattice defects and oxygen vacancies, the highest Oads/Olatt ratio, and a superior low-temperature redox property compared with the Fe-Mn binary oxide and Fe2O3 and MnO2 catalysts. The properties contribute to a high catalytic activity to achieve T90% of toluene conversion at 264 °C and 185 °C with a gas hourly space velocity (GHSV) at 180,000 and 20,000 mL/(g∙h), respectively. The introduction of a slight quantity of Ce and Mn onto the Fe2O3 catalyst is the key to enhancing the synergistic effect of the lattice OS and surface-adsorbed oxygen, contributing to the activation oxidation procedure of toluene. In-situ DRIFTS analysis reveals that the rich oxygen vacancy concentration of catalysts accelerates the key steps for the generation and activation of oxidized products. These catalysts with rich oxygen vacancies can efficiently diminish the accumulation of a small number of the intermediary species (phenolate, C6H5-OH) produced during the catalytic oxidation of toluene.

Recovery of CaO from CaSO4 via CO reduction decomposition under different atmospheres.

CaSO4 reduction decomposition for CaO preparation provides a theoretical basis for the utilization of the industrial byproduct, gypsum. In this study, the effects of temperature (950 °C-1150 °C), CO2/CO partial-pressure ratio (1-15), CO concentration (1%-5%), and O2 concentration (1%-7%) on the preparation of CaO from CaSO4 by CO reduction decomposition under different reaction atmospheres were investigated. The physical properties of CaO prepared by the decomposition of CaSO4 and CaCO3 were analyzed and compared. Finally, the reaction mechanism of the reduction decomposition of CaSO4 to CaO by CO was studied. The findings reveal that CaSO4 can be completely decomposed into CaO when the reaction temperature exceeds 1000 °C, CO% ≥ 2%, and P(CO2)/P(CO) ≥ 8. Furthermore, the addition of an appropriate amount of O2 can improve the yield of CaO in the products. In an O2-CO-N2 atmosphere, where O2% = 7% and CO% = 16%, CaSO4 can be completely decomposed into CaO without the addition of CO2. The physical properties of CaO prepared by the reduction and decomposition of CaSO4 are better than those prepared by the calcination of CaCO3. An analysis of the reaction mechanism of the reduction decomposition of CaSO4 by CO reveals that CaSO4 generates CaO and CaS simultaneously. In addition, CaS can react with unreacted CaSO4 to form CaO. Furthermore, it can react with CO2 to produce CaO if an appropriate amount of CO2 is added to the reaction atmosphere. The secondary interactions of CaS with CaSO4 and CO2 can significantly improve the yield of CaO in the product.

Effect of additives on the distribution of three-phase products of oily sludge subjected to microwave pyrolysis.

This study aimed to explore the influence of activated carbon, oily sludge pyrolysis residue, and biochar and their contents on the distribution of three-phase products of oily sludge subjected to microwave pyrolysis. A microwave reaction system, refinery gas analyzer, and chromatography-mass spectrometry were used to carry out the experiment and analyze the results. The results showed that all three additives reduced the yield of solid products and increased the yield of gas products. With an increase in the additive content, the volatile matter and moisture content in the pyrolysis residue greatly reduced. The content of CH4 and H2 in the pyrolysis gas increased with an increase in the additive content. When the amount of activated carbon was 20%, the H2 content reached a maximum (39.7%), and when the amount of biochar was 20%, the CH4 content reached a maximum (44.5%). All three additives increased the content of small molecules in the pyrolysis oil; when 10% activated carbon was added, the oil recovery rate reached up to 78.5%. The results of this study can guide the industrial application of microwave pyrolysis oily sludge.

Desorption of CO2, SO2, and NH3 in the vacuum evaporation of desulfurization wastewater.

Mechanical vapor compression and multi-effect evaporation have been widely used in achieving zero discharge of desulfurization wastewater as they are energy-saving and efficient technologies. Solubilized weak ions, such as CO32-, SO32-, and NH4+, in the desulfurization wastewater are partly converted into CO2, SO2, and NH3, respectively, during the vacuum evaporation process, thus affecting the heat exchange and compressor performance. In this study, the migration and coupling mechanism of CO2, SO2, and NH3 desorption in desulfurized wastewater under vacuum evaporation were analyzed. The effects of temperature, pressure, reaction time, and other factors on the migration process were discussed. The hydrolysis and electrolytic equilibrium constants of the related ions were obtained for temperatures between 70 and 90 °C. The results demonstrate the relationship between the desorption capacities of CO2, SO2, and NH3 and the hydrolysis constants of their respective ions. The desorption of CO2 and NH3 increased significantly when CO32- and NH4+ coexisted, whereas the SO2 desorption capacity remained low under the same experimental conditions. The experimental results indicate that the desorption of CO2, SO2, and NH3 is controlled by chemical reactions and can be described by first-order reaction kinetics.

Study on sulfur migration in activated carbon adsorption-desorption cycle: Effect of alkali/alkaline earth metals.

Activated carbon (AC) has been widely used in the removal of SO2 from flue gas owing to its well-developed pore structure and abundant functional groups. Herein, the effect of alkali/alkaline earth metals on sulfur migration was investigated based on the dynamic adsorption and temperature programmed desorption experiment. The adsorption and desorption properties of six types of AC (three commercial and three laboratory-made) were carried out on a fixed-bed experimental device, and the physical and chemical properties of samples were determined by X-ray fluorescence, X-ray diffraction, scanning electron microscopy/energy dispersive X-ray, and X-ray photoelectron spectroscopy analysis. The experimental results showed that the adsorbed SO2 cannot be completely desorbed by increasing the regeneration temperature (350 - 850°C), while the SO2 fixed in the AC combines with the Ca-based minerals in the ash to form a stable sulfate. For different samples, higher ash content, higher CaO content in the ash and a more developed pore structure lead to a higher SO2 fixation rate. Moreover, the multiple adsorption-desorption cycles experiment showed that the effect of SO2 fixation is mainly reflected in the first cycle, after which the adsorption and desorption amount are approximately the same. This study elucidates the effect of alkali/alkaline earth metals on the adsorption-desorption cycle of AC, which provides a deeper understanding of sulfur migration in the AC flue gas desulfurization process.

Current status of applying microwave-associated catalysis for the degradation of organics in aqueous phase - A review.

Interactions between microwaves and certain catalysts can lead to efficient, energy-directed convergence of a relatively dispersed microwave field onto the reactive sites of the catalyst, which produces thermal or discharge effects around the catalyst. These interactions form "high-energy sites" (HeS) that promote energy efficient utilization and enhanced in situ degradation of organic pollutants. This article focuses on the processes occurring between microwaves and absorbing catalysts, and presents a critical review of microwave-absorbing mechanisms. This article also discusses aqueous phase applications of relevant catalysts (iron-based, carbon-based, soft magnetic, rare earth, and other types) and microwaves, special effects caused by the dimensions and structures of catalytic materials, and the optimization and design of relevant reactors for microwave-assisted catalysis of wastewater. The results of this study demonstrate that microwave-assisted catalysis can effectively enhance the degradation rate of organic compounds in an aqueous phase and has potential applications to a variety of engineering fields such as microwave-assisted pyrolysis, pollutant removal, material synthesis, and water treatment.

Fe-rich biomass derived char for microwave-assisted methane reforming with carbon dioxide.

Microwave-assisted methane reforming with carbon dioxide was dealt with in this work, using a Fe-rich biomass-derived char by one-step preparation. The main factors on the reforming reaction and stability of this catalyst were evaluated, together with a series of characterization on the produced gas and the used char. The char obtained from biomass pyrolysis with Fe2O3 addition of 10% exhibited the best performance on dry reforming reaction. A target CH4 conversion of 95% over this char was realized at 800 °C. Moreover, H2/CO ratio achieved with this char was prone to approach the stoichiometric value. Compared to CO2 conversion, CH4 conversion was more promoted with the increase of CO2/CH4 ratio. The variation of CO2/CH4 ratio also leaded to a noticeable changes on H2/CO ratio. More importantly, the selected char presented a satisfied stability, evidenced by the total decrease of 4.8% for CH4 conversion and 3.1% for CO2 conversion in the test of 160 min. This was contributed to a depressed in-situ carbon consumption and a moderate deterioration of porous structure. Gaseous products obtained with the appropriate char in a long run had a syngas content of 88.79% and H2/CO ratio of 0.92 on average.

Rapid degradation of malachite green by CoFe2O4-SiC foam under microwave radiation.

This study demonstrated rapid degradation of malachite green (MG) by a microwave (MW)-induced enhanced catalytic process with CoFe2O4-SiC foam. The catalyst was synthesized from CoFe2O4 particles and SiC foam by the hydrothermal method. X-ray diffraction and scanning electron microscopy techniques were used to confirm that CoFe2O4 particles were settled on the surface of SiC foam. In this experiment, a novel fixed-bed reactor was set up with this catalyst for a continuous flow process in a MW oven. The different parameters that affect the MW-induced degradation rate of MG were explored. The MW irradiation leads to the effective catalytic degradation of MG, achieving 95.01% degradation within 5 min at pH 8.5. At the same time, the good stability and applicability of CoFe2O4-SiC foam for the degradation process were also discussed, as well as the underlying mechanism. In brief, these findings make the CoFe2O4-SiC foam an excellent catalyst that could be used in practical rapid degradation of MG.

Experimental study of destruction of acetone in exhaust gas using microwave-induced metal discharge.

Volatile organic compounds (VOCs) are air pollutants that pose a major concern, and novel treatment technologies must be continuously explored and developed. In this study, microwave-induced metal discharge was applied to investigate the destruction of acetone as a representative model VOC compound. Results revealed that metal discharge intensity largely depended on microwave output power and the number of metal strips. Microwave metal discharge exerted the distinct combined effects of intense heat, strong light, and plasma. In the case of MW without metal discharge, the decrease in acetone at 200 ppm was remarkably limited (approximately 5.5% (mol/mol)). By contrast, in the case of microwave-induced metal discharge, a considerably high destruction efficiency of up to 65% (mol/mol) was obtained at low concentrations. This finding highlights the potential of microwave-induced discharge for VOC removal. Initial assessment indicated that energy consumption can be acceptable.

Process of CH4-CO2 reforming over Fe/SiC catalyst under microwave irradiation.

In this work, the properties of the CH4-CO2 reforming reaction over the Fe/SiC catalyst during the whole process were studied under microwave irradiation and the reaction process was analyzed by mass spectrometry and Fourier transfer infrared spectrometry in real time. The effects of microwave power on the gas composition, conversion of reactants, and selectivity of products in the reaction were investigated. It was found that the microwave dry reforming reaction can be divided into a rapid reaction stage, slow reaction stage, and reaction equilibrium stage. The conversion of reactants and selectivity of products in the slow reaction stage were both higher than 95% under 90 W/g. In the long-term (~50 h) stability test, a combination of SEM, XRD, BET, and TG analyses found that the catalyst activity did not reduce significantly and the amount of carbon deposits (which was mainly Cγ) was negligible (~0.78 wt%). The results indicate that the cheap Fe-based catalyst has good catalytic activity and stability under microwave irradiation and hence has a promising application.

Pyrolysis of tyre powder using microwave thermogravimetric analysis: Effect of microwave power.

The pyrolytic characteristics of tyre powder treated under different microwave powers (300, 500, and 700 W) were studied via microwave thermogravimetric analysis. The product yields at different power levels were studied, along with comparative analysis of microwave pyrolysis and conventional pyrolysis. The feedstock underwent preheating, intense pyrolysis, and final pyrolysis in sequence. The main and secondary weight loss peaks observed during the intense pyrolysis stage were attributed to the decomposition of natural rubbers and synthetic rubbers, respectively. The total mass loss rates, bulk temperatures, and maximum temperatures were distinctively higher at higher powers. However, the maximum mass loss rate (0.005 s-1), the highest yields of liquid product (53%), and the minimum yields of residual solid samples (43.83%) were obtained at 500 W. Compared with conventional pyrolysis, microwave pyrolysis exhibited significantly different behaviour with faster reaction rates, which can decrease the decomposition temperatures of both natural and synthetic rubber by approximately 110 °C-140 °C.