Supercritical Water Oxidation Process Research Articles

Effect analysis on recycling of cathode material from spent ternary lithium-ion batteries via supercritical water oxidation and acid-leaching

This study proposed a recycling method for spent batteries by combining supercritical water oxidation and acid-leaching. In supercritical water oxidation process, the cathode material was separated from the electrode plate, and 98% of lithium in the cathode was leached to achieve the separation of lithium from Ni, Co and Mn. Ni, Co and Mn were then leached during the acid leaching process. The effect of solid-liquid ratio, oxidant mass concentration, reaction time and temperature in supercritical process on metal leaching was analyzed. The leaching rate of Ni, Co and Mn was improved by increasing the mass concentration of oxidant and the reaction temperature. The effect of reaction time on metal leaching is related to the mass concentration of oxidant in the solution. Through the control of paraments, the leaching efficiencies of Ni, Co and Mn were significantly improved from 90.4%, 84.7%, 86.4–99.7%, 96.8% and 98.5%.

Energy yield from wastewater by supercritical water oxidation process: Experimental validation and simulation from the viewpoint of energy system

The degradation of high concentration organic wastewater and the recovery of energy using supercritical water oxidation (SCWO) technology have the potential to become viable in the future. High concentration organic wastewater contains a significant amount of energy. This paper focuses on utilizing high concentrated wastewater as a renewable energy source, from an energy system perspective, an experimental rig was designed to determine the optimal working conditions. The experiments were conducted with an oxidation coefficient of 1.1, a flow rate of high concentration organic wastewater of 9 ml/min, a heating temperature of 400 °C, and a reaction pressure of 25 MPa. Under these conditions, the COD and TOC removal rates of the high concentration organic wastewater were found to be 99.383 % and 99.876 % respectively. Additionally, the phenomenon of “Abnormalities in pressure sensitivity” observed during high concentration organic wastewater the experiment was further explained through additional experiments. Finally, by comparing the experimental energy recovery with the simulation results, an energy recovery efficiency of 78.95 % was achieved. The feasibility of the simulated energy recovery in practice was verified, confirming the potential to convert the previous energy-consuming wastewater treatment process into a productive one. This study provides a theoretical and experimental foundation for further related research.

Continuous Treatment of Refractory Wastewater from Research and Teaching Laboratories via Supercritical Water Oxidation–Experimental Results and Modeling

Teaching and research laboratories generate wastes of various compositions and volumes, ranging from diluted aqueous solutions to concentrated ones, which, due to milder self-regulation waste-management policies, are carelessly discarded, with little attention given to the consequences for the environment and human health. In this sense, the current study proposes the application of the supercritical water oxidation (SCWO) process for the treatment of complex refractory wastewater generated in research and teaching laboratories of universities. The SCWO, which uses water in conditions above its critical point (T > 647.1 K, p > 22.1 MPa), is regarded as an environmentally neutral process, uniquely adequate for the degradation of highly toxic and bio-refractory organic compounds. Initially, the wastewater samples were characterized via headspace gas chromatography coupled with mass spectrometry. Then, using a continuous tubular reactor, the selected operational parameters were optimized by a Taguchi L9 experimental design, aiming to maximize the total organic carbon reduction. Under optimized conditions—that is, temperature of 823.15 K, feed flow rate of 10 mL min−1, oxidizing ratio of 1.5 (50% excess over the oxygen stoichiometric ratio), and sample concentration of 30%—TOC, COD, and BOD reductions of 99.9%. 91.5% and 99.2% were achieved, respectively. During the treatment process, only CO2, methane, and hydrogen were identified in the gaseous phase. Furthermore, the developed methodology was applied for the treatment of wastewater samples generated in another research laboratory and a TOC reduction of 99.5% was achieved, reinforcing the process’s robustness. A thermodynamic analysis of SCWO treatment of laboratory wastewater under isothermal conditions was performed, using the Gibbs energy minimization methodology with the aid of the GAMS® 23.9.5. (General Algebraic Modeling System) software and the CONOPT 4 solver. Therefore, the results showed that SCWO could be efficiently applied for the treatment of wastewater generated by different teaching and research laboratories without the production of harmful gases and the addition of hazardous chemicals.

Enhanced denitrification of aniline and its derivatives by catalysts, anions, and co-fuels during supercritical water oxidation process

We investigated the denitrification performance of aniline and its derivatives (N-methylaniline and N, N-dimethylaniline) in supercritical water oxidation (SCWO) under varying conditions (temperature: 643–743 K, reaction time: 0.5–4 min, pressure: 24.0 MPa, oxidation coefficient: 300%). Cu2 + proved to be an efficient homogeneous catalyst, generating radicals via a Fenton-like reaction. Isopropyl alcohol (IPA) outperformed methanol and ethanol as a co-fuel, enhancing TN removal due to its higher heating value. Nitrogen-containing product distribution revealed that N2 generation correlated with org-N depletion, especially with Cu2 + and IPA. A denitrification mechanism was elucidated using DFT, with Fukui indices, EHOMO, and ELUMO highlighting aniline's greater susceptibility compared to MA and DMA. Our findings provide insights into optimizing SCWO denitrification using aniline derivatives, shedding light on sustainable nitrogen removal processes.

Supercritical water oxidation: a breakthrough approach for remediation TNT-contaminated pink water

ABSTRACT This study aimed to optimize the operating conditions of the supercritical water oxidation (SCWO) process for 2,4,6-trinitrotoluene (TNT)-containing pink water treatment. Lab-scale SCWO experiments were performed by varying the temperature (400–600°C), reaction time (45–180 sec), and oxidant ratio (100–300%). The performance of SCWO in terms of pink water treatment was evaluated using TNT and total organic carbon (TOC) removal efficiency, SCWO effluent toxicity, and generated by-products. The results showed that as temperature and residence time increased, the TNT and TOC removal efficiency increased due to solute-solvent reaction acceleration under SCWO conditions and long contact time between organic matter and oxidant. The optimal conditions for SCWO were identified as follows: a temperature of 500°C, a reaction time of 120 seconds, and an oxidant ratio of 150%. These conditions resulted in a TNT removal efficiency of 99.9% and a TOC removal efficiency of 93.5%. The by-products analysis results showed a relationship between operating temperature and the type of by-products produced. Various compounds such as toluene, nitrobenzene, TNT isomers, naphthalene, and simple alkane structures were formed. However, above 500°C, many of these species decomposed, giving rise to octadecanoic acid and 13- Docosenamide. The microbial toxicity test demonstrated that SCWO effluents showed no toxicity for all investigated SCWO conditions, demonstrating the superiority of the SCWO method for the toxicity removal of TNT-containing pink water.

Highly-efficient process for recovering gold from discarded mobile phones using pretreatment and mild extraction

Existing methods for recovering gold from electronic waste are based on mechanical and hydrometallurgy approaches. However, these methods usually use toxic chemicals and demonstrate low gold extraction efficiency (Ge) due to the negative influence of organic materials and other industrial metals also present in the waste. In this work, a more efficient and more environmentally friendly process is proposed that can achieve a high Ge from electronic waste by pre-treatment and pre-extraction before gold extraction. The powdered waste was first pre-treated by a supercritical water oxidation (SWO) process to remove organic materials and then pre-extracted using a mixture of FeCl3 and HCl to remove industrial metals. The solid powder thus produced was then re-extracted by a DMF-CuCl2-NaCl mild extraction system to complete the recovery of the gold content. Experimental results indicated that pre-treatment temperature, pre-treatment time, and the concentration of the FeCl3 and HCl solutions all significantly influenced the amount of gold extracted. The optimal parameters for achieving the highest Ge extraction (99.6%) using the DMF-CuCl2-NaCl extraction system were determined as follows: an extraction temperature of 65 °C, an extraction time of 70 min, a stirring speed of 420 rpm, a sample size of ≤ 850 µm, a solid/liquid (S/L) ratio of 1:12 g·mL−1, a CuCl2 concentration of 0.8 mol·L−1, and a NaCl concentration of 1.6 mol·L−1. After gold extraction, water was then used to precipitate the gold in the form of nanoparticles. Under optimal conditions (70%v/v water, 80 min), over 98.4% of the gold could be recovered in this way.

Assessment of machine learning algorithms for predicting autoignition and ignition delay time in microscale supercritical water oxidation process

With recent advancements in space technology, there is a need to develop technologies to ensure a sustainable environment for human survival. Among these, treatment of human and organic waste aboard manned space missions is a challenging task for which supercritical water oxidation using hydrothermal flames has been proposed as a possible solution. The critical step in readily adopting this technology from established ground-based setups is scaling the process to microscale. In addition to the challenge of physical realization of the microreactors at these high pressure and temperature (P>22MPa,T>350C) conditions, the need to explicitly analyze the process dynamics at microscale is inevitable owed to the size of the reactors under consideration, the physics being significantly different from meso/mini scale systems. One of the primary objectives is to identify the operating physical parameters for which formation of hydrothermal flames can be obtained. Before proceeding with an expensive computational or experimental approach to determine the exact ignition map, an initial estimate based on physical arguments can help in providing insights into the process. We address this problem using homogeneous ignition calculations to develop machine learning models to predict autoignition as well as ignition delay time. The ingenuity of the work lies in defining autoignition criteria in relation to flow time scales expected at microscale. Various classification models were trained and tested for predicting autoignition and regression models were demonstrated to predict the ignition delay time. While predicting autoignition is a straightforward process, a two-step approach is proposed for ignition delay time. Finally, how machine learning can be used more explicitly, particularly for understanding and designing efficient microreactors, is presented which highlights that machine learning approach is not merely restricted to prediction but can also have real implications on improving the process as a whole.

Catalytic supercritical water oxidation of o-chloroaniline over Ru/rGO: Reaction variables, conversion pathways and nitrogen distribution

To ascertain the reaction variables on o-chloroaniline (o-ClA) mineralization, total nitrogen (TN) removal rate, and N-species distribution, o-ClA was subjected to catalytic supercritical water oxidation (CSCWO) in a fused quartz tube reactor (FQTR). The findings demonstrated that when the temperature, reaction time, and excess oxidant were 400 °C, 90 min, and 150%, respectively, the mineralization rate of o-ClA could reach more than 95%. Moreover, potential degradation pathways of o-ClA in supercritical water oxidation (SCWO) was proposed according to the GC-MS results. TN removal rate is significantly impacted by Ru/rGO, despite the fact that its catalytic effect on the mineralization of o-ClA was not particularly noteworthy. Compared with no catalyst, the TN removal rate of o-ClA obviously increased from 44.1% to 90.3% at 400 °C, 10 wt% Ru loading, 90 min and 200% excess oxidant. In addition, N-species distribution in SCWO and CSCWO were also investigated. Results indicated that the Ru/rGO catalyst could accelerate the oxidation of ammonia-N and convert it to nitrate-N, promoting N2 generation. Finally, the possible N transformation pathway in CSCWO of o-ClA was proposed. As a result, this work offers fundamental information about o-ClA catalytic oxidation removal in the SCWO process.

Applications of Supercritical Water in Waste Treatment and Valorization: A Review

The present review deals with water applications in sub and supercritical conditions with a focus on supercritical water oxidation process (SCWO) as an example of high temperature and pressure technologies. It starts by presenting the advantages of water properties near and beyond the critical point and the major applications exploiting them. Then, it presents a review on SCWO from the description of the process, the reaction mechanism and kinetics to reactor design and modeling. It also presents the main problems and difficulties that delay the SCWO industrial application, and summarizes the main efforts and research to overcome them for a safe, efficient and economic process.

Heterogeneous Catalytic and Non-Catalytic Supercritical Water Oxidation of Organic Pollutants in Industrial Wastewaters Effect of Operational Parameters

This work reports supercritical water oxidation (SCWO) of organic pollutants in industrial wastewater in the absence and presence of catalysts. To increase the efficiency of the oxidation process, the SCWO of organic compounds in industrial wastewater was performed in the presence of various iron- and manganese-containing heterogeneous catalysts (Fe-Ac, Fe-OH, and Mn-Al). The catalytic and non-catalytic SCWO of organic compounds in wastewater from PJSC “Nizhnekamskneftekhim”, generated from the epoxidation of propylene with ethylbenzene hydroperoxide in the process of producing propylene oxide and styrene (PO/SM), was performed. The effect of operational parameters (temperature, pressure, residence time, type of catalysts, oxygen excess ratio, etc.) on the efficiency of the process of oxidation of organic compounds in the wastewater was studied. SCWO was studied in a flow reactor with induction heating under different temperatures (between 673.15 and 873.15 K) and at a pressure of 22.5 MPa. The reaction time ranged from 1.8 to 4.83 min. Compressed air was used as an oxidizing agent (oxidant) with an oxidant ratio of two to four. A pseudo-first-order model expressed the kinetics of the SCWO processes, and the rate constants were evaluated. In the present work, in order to optimize the operation parameters of the SCWO process, we used the thermodynamic properties of near- and supercritical water by taking into account the asymmetric behavior of the liquid–vapor coexistence curve.

Proposal and thermo-economic analysis of a novel multi-generation system producing heating, power and clean water under energetically self-sufficient operation

ABSTRACT In this work, by using the energy released during the supercritical water oxidation process (SCWO) as the heat source, a cogeneration system producing heating, power and clean water is proposed. The system is modeled, and the performances under energetically self-sufficient operation are simulated. For the proposed system, parametric sensitivity analysis is first performed. Then the system is evaluated from exergy and economic aspects. The results show that under the given working condition, the proposed system can produce 1832.2 kW of heat and 245.2 kW of power simultaneously. The proposed system is a “heat dominant” system, for a larger part of the energy is utilized as heat, with the thermal efficiency reaching 85.9%. The exergy efficiency of the system reaches 40.1%. The total investment cost is 9053.0 k$. The equipment cost of turbines is 5703.5 k$, which accounts for 60% of the total investment cost. The electricity revenue of the system is 252.21 k$. The heat revenue is 867.94 k$. The clean water revenue is 31.73 k$. The obtained net annual income is 1124.78 k$. The dynamic payback period (DPP) is 12.31 years. While the simple payback period (SPP) is 9.03 years. This study may contribute to provide data support and theoretical basis for using the energy contained in organic wastewater.

Fate of phthalate esters in landfill leachate under subcritical and supercritical conditions and determination of transformation products

The hypothesis of this study is that the complex organic load of landfill leachate could be reduced by supercritical water oxidation (SCWO) in a single stage, but this operation could lead to the formation of some undesired by-products of phthalate esters (PAEs). In this context, the fate of selected PAEs, butyl benzyl phthalate (BBP), di-2-ethylhexyl phthalate (DEHP) and di-n-octyl phthalate (DNOP), was investigated during the oxidation of leachate under subcritical and supercritical conditions. Experiments were conducted at various temperatures (250–500 °C), pressures (10–35 MPa), residence times (2–18 min) and dimensionless oxidant doses (DOD: 0.2–2.3). The SCWO process decreased the leachate’s chemical oxygen demand (COD) from 34,400 mg/L to 1,120 mg/L (97%). Removal efficiencies of DEHP and DNOP with longer chains were higher than BBP. The DEHP, DNOP and BBP compounds were removed in the range of −35 to 100%, −18 to 92%, and 28 to 36%, respectively, by the SCWO process. Many non-target PAEs were qualitatively detected in the raw leachate apart from the selected PAEs. Besides, 97% of total PAEs including both target and non-target PAEs was mineralized at 15 MPa, 300 °C and 5 min. Although PAEs were highly mineralized during SCWO of the leachate, aldehyde, ester, amide and amine-based phthalic substances were frequently detected as by-products. These by-products have transformed into higher molecular weight by-products with binding reactions as a result of complex SCWO process chemistry. It has also been determined that some non-target PAEs such as 1,2-benzenedicarboxylic acid bis(2-methylpropyl)ester and bis(2-ethylhexyl) isophthalate can transform to the DEHP. Therefore, the suggested pathway in this study for PAEs degradation during the SCWO of the leachate includes substitution and binding reactions as well as an oxidation reaction.

Purification of synthetic diamond and graphite mixtures in catalytic supercritical water oxidation processes

Purifying diamonds after high-pressure and high-temperature synthesis is essential for their industrial applications, but classical purification methods usually generate a massive amount of toxic liquid wastes or cannot achieve good separation efficiency in a short time. This work proposes to utilize a catalytic supercritical water oxidation process as an environmentally friendly, fast, and highly selective alternative. To test the technical feasibility, we first examined the oxidation performance of non-catalytic and catalytic processes and discovered that potassium hydroxide and potassium carbonate accelerate oxidation kinetics. We also examine the influence of the oxidation process on the structural and surface characteristics of the synthesized diamonds. Potassium carbonate was chosen as the best homogeneous catalyst that does not deteriorate the synthesized diamond but effectively removes graphite residues. These results demonstrate that catalytic supercritical water oxidation is suitable for purifying synthesized diamonds in industrial mixtures.

Insights into carbon monoxide oxidation in supercritical H2O/CO2 mixtures using reactive molecular dynamics simulations

Carbon monoxide is an important intermediate in supercritical water oxidation processes. Carbon monoxide oxidation in supercritical H2O/CO2 mixtures was investigated using reactive molecular dynamics simulations. The results show that CO mainly converts into CO2 through the reaction CO + OH → HOCO → CO2 + H. The intermediate HOCO can also react with OH or O2 to form CO2. The overall activation energies of CO oxidation in the supercritical medium range from 125.3 ± 4.0–159.4 ± 3.6 kJ/mol, which are roughly consistent with the experimental results. Supercritical water not only provides reactive free radicals for CO conversion but also acts as a third body to induce some chemical events. The high concentration of CO2 inhibits the production of OH but highlights the oxidizing action of O and HO2. Oxygen increases the amounts of OH and HO2 through the reaction H2O + O2, thereby promoting the conversion of CO.

Management of waste printed circuit boards via supercritical water technology

In this study, the application of the supercritical water technology on the management of waste printed circuit boards (PCBs) obtained from small information technology (IT) and communication equipment was conducted. Initially, an extensive recycling-oriented characterization of waste printed circuit boards was conducted through a combination of several physicochemical analyzes such as MP-AES, XRF, TG/DTA, CHNS elemental analysis, SEM and XRD. Afterwards, at supercritical conditions of water (Tc > 374.29 °C and Pc > 22.089 MPa), the optimal conditions for the degradation of the organic polymers present in the waste PCBs were defined by a response surface methodology. A complete organic degradation rate (ODR) was achieved at 600 °C, reaction time of 60 min, waste PCBs load of 15 g and flow-rate of 5 mL min−1. After the removal of the organic polymers, the metals were liberated, and the metal recovery efficiency (MRE) reached values higher than 90% at all evaluated conditions. Then, initial insights on the subsequent treatment of the liquid decomposition by-products generated during the supercritical water (ScW) processing of waste PCBs were provided. A total organic carbon reduction of 99.88% was achieved via the ScW oxidation process using the same experimental apparatus. The treated solution was successfully re-used in the ScW processing of waste PCBs instead of clean water. Moreover, hydrogen, methane, CO2, and CO were identified as the major gaseous products associated to the supercritical water treatment of waste PCBs. Finally, a novel strategy to enhance the production of combustible gases, through the addition of ethanol and glycerol, and increase the economic feasibility of the supercritical water processing of waste PCBs was proposed.

Treatment of wet electrostatic precipitators wastewater by supercritical water oxidation

ABSTRACT The most commonly used method for treating gas emissions generated during the drying process in chipboard production plants is the Wet Electrostatic Precipitator (WESP). The wastewater generated from the WESP process is considered hazardous due to high pollutants loads and cannot be treated efficiently using conventional treatment methods, such as chemical and biological treatment, sedimentation, and various separation processes. Therefore, there is an urgent need to investigate a novel and efficient treatment method for WESP wastewater. Supercritical water oxidation (SCWO) has recently gained attention as a powerful technique that can remove organic pollutants from wastewater in a short time. In this study, the removal of pollutants from real WESP wastewater was investigated using the SCWO process. The effects of operating conditions; oxidation rate, reaction temperature, and process reaction time, were studied under different experimental conditions. For the SCWO process, optimum conditions 99%, the reaction time of 166 seconds, oxidant ratio of 1.78 and 600°C were determined for 95% yield of total organic carbon (TOC) and total nitrogen (TN). The overall results showed that the TOC and TN removal efficiencies increased with the increase of temperature, oxidant dosage, and reaction time. The result from this study indicated that SCWO is a promising and innovative technique for the treatment of WESP wastewater.

Supercritical water oxidation of coal pyrolysis wastewater: Effects of main operating parameters and reaction pathways of 2-(N-Morpholino)ethanesulfonic acid

Coal pyrolysis wastewater has high chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) contents, which seriously endanger human health and environment. In this work, supercritical water oxidation attempted to dispose coal pyrolysis wastewater. The results showed that the removal rates of COD and NH3-N were significantly improved with the increase of reaction temperature, oxidation coefficient, residence time and initial COD concentration. Residence time and reaction temperature played more important roles in organic matter degradation, and their extremum differences in orthogonal tests were 6.8% and 2.6%, respectively. The supercritical water oxidation processes of the N-containing compound 2-(N-Morpholino)ethanesulfonic acid in coal pyrolysis wastewater were speculated to mainly include two reaction pathways, in which large amounts of hexadecane, heptadecane and butyramide were found in the second pathway.

Hybridization of supercritical water oxidation and gasification processes at pilot plant scale

The combination of SCWO with SCWG forms a unique system that has been tested in the present study at pilot plant scale using a single reactor with a flowrate of up to 150 kg/h. SCWO of a highly concentrated ethanol solution takes place in the first section of the tubular reactor, rising temperature. Then, an isopropanol solution is gasified into the second section to prevent any further increments of the temperature and producing hydrogen. The effect of different flowrates, the addition of different oxidant amounts and the preheating temperature of the gasification feed have been evaluated obtaining a gas effluent containing 10.7% H2 and 17.2% CH4 in the best conditions that have could tested, although better results would be obtained if processes could be carried out at more extreme conditions based on literature evidences.

Treatment of Organic Wastewater by Supercritical Water Oxidation

Supercritical water oxidation (SCWO) is a robust process in removing the hazardous organic wastes. Therefore, it is necessary to improve the SCWO process to eliminate the organic hazardous wastes. In present work, SCWO process used cyclohexylamine (CHA) as the organic chemical model. The co-oxidizers consisted of propylene glycol (PG), methanol and the oxygen source was hydrogen peroxide. The experiments were conducted using at a laboratory scale. A plug-flow reactor was utilized at different operating temperatures ranging from 425 to 525 ºC, the critical pressure was 25 MPa. At working temperatures, the co-oxidizer and the oxidant ratios were also investigated . The results indicated that the temperature had an impact on the removal efficiency of cyclohexylamine. The maximum total organic carbon removal (TOC) in the presence of propylene glycol was achieved with 98% at 525 ºC and the residence time was 14 s.

Naphthalene mineralization by supercritical water oxidation and determination of by-products using non-target analysis

Abstract In this study, the fate of naphthalene was investigated with a supercritical water oxidation process (SCWO). Also, the effectiveness of different operating conditions including pressure, temperature, residence time and oxidant dose on the formation of by-products was determined. The experimental sets were determined by the experimental design program and the effect of the selected variables on the removal of the naphthalene was associated statistically. According to obtained results, naphthalene by SCWO process was mineralized up to 98.5%. Removal efficiencies in sub- and supercritical conditions were between 94 and 100%. Derivatives of aldehyde, propanoic acid, benzene acetic acid and benzofuran were detected as by-products at many experimental conditions and also, some intermediates with a molecular weight higher than naphthalene were determined.