Supercritical Water Research Articles

Treatment of Antihypertensive and Cardiovascular Drugs in Supercritical Water: An Experimental and Modeled Approach

Pharmaceutical pollutants are considered emerging contaminants, representing a significant concern to the ecosystem. Thus, this study reports on the degradation of antihypertensive and cardiovascular drugs (atenolol, captopril, propranolol hydrochloride, diosmin, hesperidin, losartan potassium, hydrochlorothiazide, and trimetazidine) present in simulated wastewater through applying the technology of oxidation using supercritical water (SCW). The operational parameters of the treatment process, particularly the feed flow rate, temperature, and concentration of H2O2, were assessed. A central composite design of experiments associated with differential evolution was employed in the optimization. Both liquid and gaseous phase products were submitted to physical–chemical characterization. As a result, the optimized conditions for the treatment were discovered to be a feed flow rate of 13.3 mL/min, a temperature of 600 °C, and a H2O2 oxidation coefficient of 0.65, corresponding to the oxygen stoichiometric coefficient in the carbon oxidation chemical reaction. Under optimal conditions, the total organic carbon (TOC) decreased from 332 to 25 mg/L (92.1%), and the pharmaceutical molecules underwent near-complete degradation. The physical–chemical parameters also met with the main environmental regulations for wastewater disposal. The compounds determined in the gaseous phase were CO2 (97.9%), H2 (1.3%), CH4 (0.3%), and CO (0.5%.). Additionally, a modeling thermodynamic equilibrium of the system was performed, based on the experimental data. The results revealed that SCW technology has a great potential to oxidize/degrade organic matter and can be applied to treat pharmaceutical pollutants.

Simulation of Supercritical Water Gasification Reaction of Glycerol and Reactor Structure Study

The study established a reactor model with a volume of 500 ml that can withstand high temperature and high pressure, and firstly used the simulation software ANSYS FLUENT 2023R1 to simulate the process of generating H2-rich gaseous products by reacting glycerol in supercritical water at a temperature of 374°C and a pressure of 23 Mpa, and the results showed that the pressure and temperature were uniformly distributed in the fluid domain of the reactor. The results show that the pressure and temperature are uniformly distributed in the fluid domain of the reactor. Secondly, according to the pressure distribution obtained from the simulated reaction, the transient dynamics and thermo-mechanical coupling field analysis were applied to the inner wall of the reactor cavity in ANSYS Workbench to study the stress displacement. Finally, the results of the two analyses are compared to conclude that the pressure field can affect the trend of stress and displacement of the reactor structure, and the temperature field at higher temperatures can increase the values of stress and displacement.

Experimental analysis on products distribution, characterization and mechanism of waste polypropylene (PP) and polyethylene terephthalate (PET) degradation in sub-/supercritical water

Supercritical water (SCW) treatment of plastics is a clean technology in the ‘waste-to-energy’ path. In this work, PP and PET plastics were processed by sub-/supercritical water. The results showed that temperature was the most important factor of the PP and PET degradation. The influence of factors on the degradation of plastics follows the following order: temperature > residence time > plastic/water ratio. These factors influenced the yield of gas products by promoting or inhibiting various reactions (such as reverse water gas shift reaction, methylation reaction, and Fischer-Tropsch synthesis reaction). Besides, the composition of liquid oil was also analyzed. The main composition of the liquid oil produced by PET was benzoic acid and acetaldehyde, which were generated from the decarboxylation of terephthalic acid (TPA) and dehydration reaction of ethylene glycol (EG). The liquid oil from PP was mainly long-chain olefins, long-chain alkanes, cycloalkanes, etc., which were formed by the interaction of various methyl, alkyl, hydroxyl, and other free radicals. This study could build fundamental theories of plastic mixture treatment.

Direct numerical simulation of flow and heat transfer of supercritical water with different heat fluxes

The flow and heat transfer characteristics of supercritical water (SCW) are important considerations in the thermal-hydraulic design of the Supercritical Water-Cooled Reactor (SCWR). In the present study, the direct numerical simulation (DNS), developed with OpenFOAM, was utilized to investigate the effect of heat flux on the flow and heat transfer of SCW in a vertical circular pipe. The investigation involves detailed analyses of the wall temperature, velocity distribution, and turbulent statistics at various heat fluxes. It was found that buoyancy first impairs heat transfer, and then recovers heat transfer. This is attributed to the variation of buoyancy production and turbulence production, which are resulted from the buoyancy direct effect and indirect effect, respectively. As the heat flux increases, the recovery occurs earlier with higher magnitude. The vortex structures based on Q-criterion clearly illustrate the same process as well. Several heat-transfer correlations were assessed based on the DNS results. It indicates that Dittus and Boelter correlation (1930) cannot accurately predict the heat-transfer characteristics of SCW, while Chen and Fang correlation (2014) exhibits a higher level of predictive accuracy for Nusselt number. In addition, several turbulence models were evaluated against the DNS data. The results show significant deviations in predicting the heat transfer of SCW. The large discrepancy may be due to the inappropriate model coefficients, the failed predication of turbulence kinetic energy, as well as the constant turbulent Prandtl number commonly applied.

Improvement of biohydrogen production from biomass using supercritical water gasification and CaO adsorption

Producing biohydrogen is a promising alternative to fossil fuels, sourced from renewable energy like wind, solar, and biomass, known for its eco-friendliness and minimal greenhouse gas emissions. This study focuses on the process design and simulation of producing biohydrogen from biomass (bagasse) gasification. New integration of the water gas shift reactor and CaO adsorption process is connected to biomass gasification with the steam/supercritical water agents for improving the hydrogen production process. Simulations show that steam gasification integrated with CaO adsorption (SG-CaO) is optimized at specific conditions, resulting in high-purity hydrogen at 99.95 %. Similarly, the supercritical water gasification integrated with CaO adsorption (SCWG-CaO) requires specific conditions, achieving exceptionally pure hydrogen at 99.99 %. In terms of energy analysis, SCWG-CaO outperforms SG-CaO, with higher hydrogen yield (14.16 % vs. 14.12 %) and greater energy efficiency (42.32 % vs. 40.26 %). It shows that the SCWG-CaO is a suitable and efficient approach for biohydrogen production, considering factors such as hydrogen purity, yield, and energy efficiency.

Corrosion behavior of 304 stainless steel in supercritical water

Supercritical water (SCW) has strong reactivity and the ability to fuse non-polar substances, but it requires higher corrosion resistance of structural materials. To select reliable candidate materials for a supercritical water system, this study investigated the corrosion behavior of 304 stainless steel (304 SS) in supercritical water (798 K/24 MPa). After soaking 304 SS in supercritical water for 200 h, the oxidation kinetics, surface morphology, and element diffusion were studied by weight measurement, scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersion spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The surface of 304 SS shows an isolated and discontinuous oxidation deposition. It is determined that the oxide layer is a single layer, mainly composed of Fe-Cr-rich spinel, with a small amount of magnetite attached to the surface of the oxide layer. Besides, the oxidation mechanism was also studied since some pores were found on the surface due to pitting.

Reaction characteristics of homogeneous and heterogenous reactions for glucose gasification in supercritical water using ruthenium catalyst supported on carbon nanotube

In this study, a spherical, Ru-based catalyst with a Carbon nanotube (CNT) support was used in a continuous-flow system, where homogeneous and heterogeneous reactions occurred simultaneously. Therefore, determining the homogeneous and heterogeneous reaction rates is important. Glucose (5 and 10) wt%, a typical model biomass compound, was chosen as the feedstock, and the reaction temperature was set at (500 and 600) ℃. The weight hourly space velocity was changed (40, 80, or 160) h−1 by maintaining the catalyst loading at 0.15 g and altering the flow rate (2, 4, or 8) mL/min. A reaction model where homogeneous and heterogeneous reactions proceed in parallel was developed, and the reaction rates were determined. The homogeneous reaction rate constants were (0.00968 and 0.0194) /s for (500 and 600) ℃, respectively, and the heterogeneous ones for Ru-based catalyst with a CNT support were (0.0137 and 0.0420) m3/(kg s) for (500 and 600) ℃, respectively.

Numerical simulation of thermal hydraulics of supercritical pressure water with 2×2 rod assembly wrapped differently with a wire

Through the use of CFD, a thermal-hydraulic analysis was carried out on a set of 4 rod assemblies. The common wire-wrapped spacers on the fuel assemblies are wound in the same direction for all rods. Because of this design, it is anticipated that there would be an adverse flow in all of the sub-channels. In the course of this analysis, this flow was demonstrated to be real. In order to achieve desirable flow characteristics for coolant mixing, a novel configuration for wire-wrapped spacers is proposed here. This pattern designates a group of 4 rods, the rods have the wrapping system of clockwise and anticlockwise pattern. It was determined that this pattern had an exceptional mixing effect as well as a uniform flow. This pattern has a maximum temperature area that is approximately 8.5 °C lower than that of the conventional wire-wrapped fuel bundle arrangement. When compared to the regular pattern, the pressure drop caused by the new arrangement was approximately 1.9% less severe. The redesigned layout of the rod assembly improves heat transfer while also reducing the amount of pressure loss that occurs.

Directional transformation and migration pathways of nitrogen during pig manure supercritical water gasification

Nitrogen is a valuable nutrient element in pig manure. This work focuses on investigating the distribution, directional transformation, and migration pathways to facilitate the recovery of nitrogen from supercritical water gasification products. Results indicated that no nitrogen-containing gas was detected and 12.65 % of nitrogen remained in solid products. 82.49 % of nitrogen migrated into liquid products, which are predominated by ammonia. Catalysts were employed to promote the conversion of solid nitrogen to liquid nitrogen and organic nitrogen to ammonia. Finally, 85 % of nitrogen is enriched into liquid products and ammonia predominated the liquid nitrogen. The percentage of ammonia increased to 97.51 % at 620 °C in the presence of potassium carbonate. The migration pathways indicated that nitrogen was transformed into ammonia by various intermediates such as indole. The rest of the nitrogen remained in solid products with stable quaternary-nitrogen. These findings provide valuable insights into nitrogen management and recovery.

Intermediate temperature of supercritical water enhances the dispersion of cohesive particles

Supercritical water gasification represents a promising technology for the clean conversion of coal to hydrogen, so that it is expected to replace the traditional use of coal by burning. However, the flocculation of cohesive coal particles significantly reduces the contact area between particles and supercritical water, which limits the chemical reaction that produces hydrogen. Based on Lifshitz theory, we propose a cellular flow model for numerically reproducing the flocculation of cohesive particles in supercritical fluid turbulence. Cohesion, lubrication, and direct contact forces between particles are fully accounted for, so that the model allows us to conduct a detailed analysis of the translation, rotation, growth, and breakage of flocs in supercritical fluid turbulence. The results show a transient flocculation phase of cohesive particles characterized by an increasing average floc size, followed by a statistically steady equilibrium phase. Increasing the density ratio between particles and supercritical water significantly accelerates the flocculation of dispersed cohesive particles. Higher temperature of the fluid yields faster flocculation and larger flocs when the temperature is below the critical value of 660 K. Upon raising the temperature above 660 K, the flocculation rate and floc size first decrease, and then increase again, yielding an optimal temperature around 750 K where the primary particles are most effectively dispersed by the supercritical water turbulence.

Experimental and molecular dynamics simulation study on solubility characteristics of chloride and sulfate salts in supercritical water

Supercritical water gasification (SCWG) shows great potential in converting organic waste into hydrogen-rich gas with low environmental impacts and significant economic benefits. However, a comprehensive analysis of the solubility of inorganic salts in supercritical water is still scarce, hindering the application of SCWG high-salt organic waste. In this work, solubility characteristics of chloride and sulfate salts in the range of 673 K to 773 K and 22 MPa to 30 MPa are explored using both experimental and molecular dynamics simulation methods. The results indicate that salt solubility in supercritical water increases with decreasing temperature and increasing pressure. The solubility of cations and anions follows the order of K+ > Na+ > Ca2+ and Cl- > SO42-, respectively. The addition of type I salt significantly enhances type II salt solubility in the ternary system. This work is expected to offer a reference for the optimization design of SCWG reactors.

Experimental and kinetic modeling study of acetic acid oxidation and hydrolysis in supercritical water

The oxidation and hydrolysis of 0.11–0.14 M acetic acid in supercritical water (SCW) have been investigated at temperatures of 773–873 K and a pressure of 25.0 MPa in a flow reactor. CO and CO2 were the main products at oxygen-rich conditions. For hydrolysis experiments, CH4 and CO2 were produced in nearly equal amounts while the yield of CO was negligibly small. A detailed chemical kinetic model was developed by revising the kinetic parameters of key elementary reactions. The model performance was evaluated by comparison to the present data as well as data from literature. The model predicted the kinetic behavior of acetic acid oxidation fairly well, despite of slight underprediction of CO and overprediction of CH4. It also reproduced satisfactorily the species concentrations during acetic acid hydrolysis at high temperatures. Based on the model, kinetic analyses were further conducted to identify important elementary steps and to infer reaction mechanisms.

Early environmental sustainability guidance on supercritical water gasification technologies for sugarcane bagasse management

The sugar industry is considered a high-energy-demand and wasteful industrial sector in many developing countries. Such a high energy demand can undermine the sugar industry's economic and environmental aspects. Shifting from a linear economy model to a circular economy (CE) can help this industrial sector solve the current economic and environmental crises, decrease dependencies on fossil-based energies, increase circularity, and save considerable resources. However, such a transition necessitates comprehensive pre-feasibility studies to avoid problem shifts. Herein, we compared some novel waste-to-energy (WtE) technologies from a life cycle assessment (LCA) point of view; (a) integrated supercritical water gasification (SCWG) at 700 °C with solid oxide fuel cell (SOFC), (b) integrated SCWG at 700 °C with combined cycle gas turbine (CCGT), (c) cogeneration (Boiler), (d) integrated fixed-bed gasification combined cycle (IFXBGCC), and (e) integrated fluidized-bed gasification combined cycle (IFLBGCC). Iran, as a developing country with high dependencies on fossil resources and less CE implementation, was selected as a case study. Scenarios were compared using a functional unit (FU) of thermal management of 1 tonne of bagasse. SCWG is found to be an environmentally superior approach when hydrogen production is the primary function of the system. Otherwise, using boiler and steam turbine is is still the best approach to generate heat and electricity from bagasse. Direct combustion in the boiler showed considerable savings in climate change, i.e., 469 kg CO2 eq saving/FU. The LCA results showed that bagasse to energy throughout direct combustion is a promising pathway to generating clean energy; in addition to helping industries earn more income, and contribute to sustainable development.

Theoretical Study of Raman Intensities of p-Nitroaniline in Different Solvent Conditions by Using a Reference Interaction Site Model Self-Consistent Field Explicitly Including Constrained Spatial Electron Density Distribution.

Raman spectroscopy is one of the most powerful tools to understand and characterize the states and structures of systems in several environments. To obtain highly accurate changes in Raman intensities of systems in solution, theoretical treatment, which can deal with not only the states and structures of systems but also the environment around molecules, proves to be significant. Hence, in this study, we developed the calculation of changes in Raman intensities of systems in different solvent conditions by using the reference interaction site model self-consistent field study explicitly including constrained spatial electron density distribution; this model is designed based on elements from both quantum mechanics and statistical mechanics. We showed that our calculation method could reproduce the changes in Raman intensities of p-nitroaniline (pNA) under different solvent conditions, including supercritical water, which has been observed in previous experimental studies. Based on the analysis of the calculation results, we observed that the ratio of the Raman intensity change of pNA in different solvent conditions is strongly correlated with the charge-transfer character of pNA.

In-situ hydrogen production and battery electrode materials from metal effluent and biomass

Supercritical water gasification (SCWG) is an effective technique for the conversion of biomass into hydrogen-rich fuel gas. This work addresses two important aspects of the SCWG process by employing the concept of waste to wealth: first, the requirement of heterogeneous catalysts for better efficiency, and second, the safe disposal of byproducts of the process. Metal-contaminated aqueous effluent (Zn-EPW) is used as the reaction medium with the catalyst for single-step hydrothermal conversion of banana pseudo-stem (BPS) to synthesize multi-dimensional value-added products such as H2-rich fuel gas, nano metal–carbon hybrids (NCH), and treated aqueous phase. This study demonstrates the enhanced conversion of biomass into hydrogen-rich gas and recovery of heavy metals (HMs) in the form of nanometal carbon hybrids, which can be utilized to fabricate carbon-based electrodes in Li-S batteries. A comparative study of feedstock, such as a combination of Zn-EPW adsorbed on BPS (MA-BPS) with Millipore water, direct treatment Zn-EPW with BPS, and Millipore water with BPS (without HMs), was performed. The results inferred the catalytic effect of heavy metals increased the yield of hydrogen about ∼2.9 times with Zn-EPW and BPS and ∼1.7 times with MA-BPS and Millipore water over the non-catalytic operation. Furthermore, the obtained NCH were characterized to evaluate their performance for electrodes in energy storage devices. The electrochemical performance of NCH obtained after multi-step SCWG of MA-BPS with Millipore water and single-step treatment of Zn-EPW with BPS at 600 °C, have specific capacity of 610 and 615 mAh.g−1 at 0.1C respectively.

Experimental Investigation on the Pyrolysis and Conversion Characteristics of Organic-Rich Shale by Supercritical Water.

Organic-rich shale oil reservoirs with low-medium maturity have attracted increasing attention because of their enormous oil and gas potential. In this work, a series of experiments on pyrolysis of the particle and core samples were carried out in a self-made supercritical water pyrolysis apparatus to evaluate the feasibility and benefits of supercritical water in promoting the transformation efficiency and oil yield of the low-medium maturity organic-rich shale. Core samples had a mass loss of 8.4% under supercritical water pyrolysis, and many microcracks were generated, which increased the pyrolysis efficiency substantially. The oil yield of shale pyrolysis could reach 72.40% under supercritical water conditions at 23 MPa and 400 °C, which was 53.02% higher than that under anhydrous conditions. In supercritical water conditions, oxygen-containing compounds are less abundant than in anhydrous conditions, suggesting that supercritical water can inhibit their formation. Also, supercritical water conditions produced higher yields for light fraction, medium fraction, and heavy fraction shale oil than those under anhydrous conditions. These results indicate that supercritical water pyrolysis is feasible and has excellent advantages for low-medium maturity organic-rich shale.

Pulsation effects on mixing behaviour of binary particles with different densities in supercritical water fluidized bed reactors: A CFD-DEM study

A coupled computational fluid dynamics - discrete element method (CFD-DEM) model for simulating supercritical water fluidized bed reactors (SCWFBR) is established and verified using the previous correlations based on experimental data. The CFD-DEM model is then adopted to investigate the pulsation effects on the mixing behaviour of binary particles with different densities in the SCWFBR. Numerical results show that external energy pulses can be effective in promoting the mixing of binary particle systems with different densities in SCWFBR which cannot be achieved by simply increasing the flow rate constantly. Within the current parameter range: low-frequency pulses are favored to promote particle mixing rather than high-frequency pulses, and an optimal frequency exists. The role of low amplitudes in influencing mixing degree is slight, but the particle mixing degree can be greatly enhanced by increasing the pulse amplitude beyond a certain value. The mechanism that pulsed inlet fluid promotes particle mixing is to raise the heavy particles which are inclined to stay at low positions during the fluidization. The Fast Fourier Transform (FFT) method to predict the optimal frequency established for size-induced segregation can be applicable to solve the problem of the density-induced segregation.

REMOTE MONITORING OF RADIATION TEST TEMPERATURE REGIME AT A HIGH-CURRENT ELECTRON ACCELERATOR

Methods for evaluating the radiation resistance of structural materials of nuclear reactors have been developed and research is being carried out in NSC KIPT. As a part of these studies, a supercritical water convection loop with a chamber for irradiation of the tested samples by electron beam of the accelerator LU-10 (beam energy of 8…10 MeV, beam power up to 10 kW) was developed. A pyrometric system based on a DSLR camera (Digital Single-Lens Reflex Camera) has been created for the remote continuous non-intrusive control of the surface temperature of the irradiation cell in the range of 350…550°С. The work presents the results of calibration and use of the developed system in the conditions of a 500-hour run of sample irradiation in the loop.

Thermodynamic and environmental analysis of an integrated multi-effect evaporation and organic wastewater supercritical water gasification system for hydrogen production

Organic wastewater poses significant environmental and human health risks. Supercritical water gasification (SCWG) presents a promising approach for converting organic waste into hydrogen-rich mixed gases. Nevertheless, the high moisture content present in organic wastewater hampers the energy efficiency of the SCWG process. To tackle this challenge, we have designed and developed an organic wastewater SCWG hydrogen production system incorporating a multi-effect evaporator. The developed system demonstrates the ability to achieve autothermal conditions for the treatment of swine wastewater with a solids concentration of 4.3%. Notably, this system exhibits impressive energy efficiency, reaching a maximum value of 44.88%, along with an exergy efficiency of 33.90% when processing 7% swine wastewater. Exergy analysis further reveals that the incorporation of a multi-effect evaporator leads to a reduction in exergy destruction within the gasification unit, oxidation unit, and heat exchanger. These improvements highlight the positive impact of the multi-effect evaporator on the overall performance of the supercritical water gasification system. Sensitivity analysis indicated that suitable concentrated concentration and an appropriate amount of preheated water can improve hydrogen production. The system minimum GWP reaches 5.27 kgCO2-eq/kgH2 after adding the CCUS. This work expands the range of applicable feedstocks for the autothermal SCWG process.

Effect of exposure temperature on the corrosion behavior of a FeNiCrCuAl high entropy alloy in supercritical water

The corrosion behavior of a FeNiCrCuAl high entropy alloy exposed to supercritical water at 380–650 °C and 25 MPa was investigated. The weight gain exhibited a nearly parabolic kinetics. At 380 °C, Al2O3 precipitated on Fe3O4 particles in FeCr-rich regions and intensified as the temperature increased to 650 °C, eventually resulting in an Al2O3 particle. A mixed Fe3O4 and NiAl2O4 outer layer developed on NiAl-rich regions at 380 °C, whereas an Al2O3 layer formed at 650 °C. Cu2O formed along the boundaries of NiAl-rich regions, regardless of exposure temperatures. The corrosion mechanism at different temperatures was elucidated.