Supercritical Water Conditions Research Articles

Evaluation of the reaction order and kinetic modeling of Domanic oil shale upgrading at supercritical water conditions

Two different kinetic models were developed for the kinetic study of Domanic oil shale conversion in the supercritical water. The oil shale reaction order was evaluated with a three-lump reaction scheme taking into account oil shale, gases, and synthetic oil. Contrary to the commonly reported first-order, it was found that a higher order (2.5) is more suitable for the conversion of oil shale at supercritical water conditions. The main reaction mechanism and predictions were obtained using a more detailed reaction network (five-lump model), which precisely estimates the experimental yield of all compounds contemplated. The statistical analysis suggested that the estimated kinetic parameters were suitably optimized, as well as the sensitivity analysis confirmed that these are the optimal values. The conversion of organic matter into gas and coke through free radical reactions exhibits larger rates using supercritical water. Low temperature (380 °C) and short reaction times favor the yield of synthetic oil because when these conditions are exceeded secondary cracking reactions provoke the generation of gases. Gas production is mainly carried out by the conversion of organic matter for brief reaction times and the transformation of carbonates for extended periods.

Kinetic insights into heavy crude oil upgrading in supercritical water

Heavy crude oil upgrading in a supercritical water environment is a promising technology owing to diverse advantages such as heteroatom removal, high yields of low molecular weight fractions, and inhibition of coke production. In order to increase the performance of this process, some challenges need to be overcome by researching the reaction mechanisms and developing proper numerical models. Therefore, the kinetic studies reported in the literature for hydrothermal upgrading of heavy crude oil under supercritical water conditions and their results were systematically analyzed and discussed to achieve a better understanding of the diverse approaches considered to determine the distribution of reaction products and limitations. Additionally, fundamental aspects of the kinetic models, including experimental considerations and numerical methodologies applied for kinetic parameter estimation, are reviewed to obtain representative information about the reactant system that can be subsequently integrated into reactor design models or reservoir simulations.

Enhancing oil production via radical reactions during hydrothermal coliquefaction of biomass model compounds and plastics: A molecular dynamic simulation study

Recently, hydrothermal coliquefaction of biomass and plastic waste has attracted considerable research interest. However, there is a notable gap in understanding the fundamental reaction mechanisms between biomass and plastics during coliquefaction. This study focused on the coliquefaction of biomass model compounds and plastic polymers using ReaxFF molecular dynamics simulations under both subcritical and supercritical water conditions. Molecular-level tracking and probing of the reaction mechanisms between biomass model compounds and plastics were conducted to purposefully enhance oil production. The study observed related radical reactions between by-product molecules, with detailed mechanisms primarily involving (1) ▪OH radicals released by aqueous phase molecules from biomolecules, transferring as H2O molecules and facilitating plastic depolymerization, and (2) C1–C4 radicals in the gaseous phase, emitted from biomolecule and plastic, colliding and subsequently recombining to form oil molecules. Moreover, the yield of multiple products from various mixtures were evaluated by considering the key reaction parameters including reaction temperature and feedstock blended ratio. An exploration into the effect of coliquefaction on oil yield was conducted to precisely identify the optimal coliquefaction conditions. The positive effect of coliquefaction was more pronounced between biomass model compounds and aromatic polymers compared to aliphatic polymers. Analysis of reaction mechanisms and product outcomes has shown that hydrothermal coliquefaction is a viable approach to improving oil production from multi-source organic solid waste.

Molecular Dynamics Simulations Guide the Gasification Process of Carbon-Supported Nickel Catalysts in Biomass Supercritical Water.

In this study, the Density Functional Theory (DFT) Calculations for Molecules and Clusters-ADF module is employed to model carbon-supported nickel catalysts and lignin monomers, integrating the ReaxFF module to simulate molecular dynamics under supercritical water conditions, with a focus on lignin decomposition reactions. Molecular dynamics models for supercritical water gasification are established under various conditions such as catalyst presence, water molecule quantities, and reaction temperature. By comparing simulation systems under different conditions, the yields of and variations in combustible gases (hydrogen and carbon monoxide) are summarized. Introducing heteroatoms into the lattice of the carbon support can alter the electronic structure within graphene, thereby influencing its electrical and electrochemical properties, increasing the number of active sites, and significantly enhancing electrocatalytic activity. Simulation results indicate that carbon-supported nickel metal catalysts can promote the cleavage of C-C bonds in lignin monomers, thereby increasing the rate of water-gas shift reactions and boosting hydrogen production in the system by 105%. Increasing water molecule quantities favored water-gas shift reactions and hydrogen generation while lowering carbon monoxide formation. Moreover, elevating reaction temperatures led to increased hydrogen and carbon monoxide production rates, which were particularly pronounced between 2500 K and 3500 K. These findings offer crucial theoretical insights for advancing efficient hydrogen production through biomass supercritical water gasification.

Study of heavy crude oil upgrading in supercritical water using diverse kinetic approaches

Heavy crude oil upgrading under a supercritical water environment has demonstrated to have diverse advantages. For commercial applications, it is necessary to develop mathematical models that can predict the reactive behavior of the different components of crude oil under these operating conditions. However, the consideration of different experimental and modeling approaches can significantly influence the determination and evaluation of reaction rates, which complicates providing essential insights into the reaction system and thus generates numerical simulations and strategies that allow for increasing the efficiency of these processes. Therefore, this study analyzes the effect of the supercritical water atmosphere on the diverse reactions among oil components as well as different kinetic modeling approaches reported in the literature to predict the yields of reactive compounds. Complex kinetic models were developed using proposed reaction schemes and experimental data obtained during the upgrading of heavy crude oil under supercritical water conditions. The predictions with the models show good agreement concerning the experimental data. In addition, it was shown that the conversion of asphaltenes to resins and gas compounds under supercritical conditions presents a significant increase in reaction rates compared with experiments under non-catalytic and catalytic thermal cracking conditions.

Partial upgrading of bitumen with supercritical water— liquid products characteristics, gas composition and coke morphology

The study aimed to investigate the partial upgrading of bitumen in the absence of water (non-water) and the presence of supercritical water (SCW). Partial upgrading experiments were conducted at the target temperature of 420 °C, with the reaction time varying from zero to 60 min in a batch reactor. The liquid products were analyzed for density, viscosity, composition, total acid number (TAN), olefin content, and elemental analysis. The gas composition and morphology of solid products were also studied. The experimental results revealed that while partial upgrading of bitumen with SCW could accelerate improvement in oil quality, particularly in terms of API and viscosity, it concurrently led to elevated gas and coke formation levels. Moreover, the difference in the distribution of oil fractions between the two environments (absence and presence of SCW) tends to diminish with an extended residence time. Additionally, as the residence time increases, the efficiency of TAN reduction under SCW conditions is less pronounced compared to the non-water conditions. Liquid products obtained in an SCW environment exhibited higher olefin content (between 3 and 4 wt %) compared to non-water conditions (between 1.8 and 2.7 wt %). In both environments, the olefin content was initially increased up to a residence time of 20 min and then decreased. Regarding heteroatoms, the sulphur (S) and nitrogen (N) contents decreased up to 36 % and 72 %, respectively, while a greater reduction was observed in the presence of SCW. More non-hydrocarbon gases (H2S, CO2 and CO) were produced in the presence of SCW. SEM images showed that an extended residence time led to a shift in coke morphology towards a more uniform and compact structure, regardless of the upgrading environment. However, the porous structures of coke samples obtained under SCW are distinguished from those formed without water, which is attributed to the phase inversion of precursors. The findings of this study confirm that SCW plays a beneficial role as a solvent in the partial upgrading of bitumen, expediting the process. However, the increased level of coke formation and olefin contents suggest that it may not function effectively as a hydrogen donor in the process.

Chemical Transformations of Fatty Acids in the Hydrolysis of Triglycerides. Selective Isolation of Oleic Acid from Rapeseed Oil under Sub- and Supercritical Water Conditions

Chemical Transformations of Fatty Acids in the Hydrolysis of Triglycerides. Selective Isolation of Oleic Acid from Rapeseed Oil under Sub- and Supercritical Water Conditions

Understanding the conversion mechanisms in supercritical water conditions of PET as a model compound of plastic wastes

In this work, polyethylene terephthalate (PET) was used as a model compound for understanding the conversion mechanism of plastic wastes through supercritical water gasification (SCWG) for producing: i) a gas rich in methane/hydrogen; and ii) for obtaining valuable molecules to be recycled in chemical processes (e.g., benzoic and acetic acids).The experiments were conducted at two different temperatures (above the critical point of water): 450 °C and 600 °C, in order to study the influence of this parameter on the conversion yield. The holding time in the reactor was set at 30 min for all trials. The experimental data were compared to the thermodynamic equilibrium calculations and the results showed that increasing the temperature from 450 °C to 600 °C, the total gas yield is highly improved (from 8.6 mol gas/kg of dried feedstock to 22 mol gas/kg of dried feedstock). The experiments with Raney-nickel catalyst indicated a significant improvement of the carbon conversion yield, which led to a higher gas production from mild to higher temperatures. The maximum total gas yield obtained with this catalyst was 63.4 mol gas/kg of dried feedstock at 600 °C, which is almost 3 times higher than that obtained at the same operating conditions without catalyst. The HHV of the obtained gas at 600 °C with the catalyst was 64.7 MJ/kg gas and 57.9 MJ/kg gas at 450 °C. Additionally at mild operating temperatures (450 °C), the obtained performance with the catalyst was even higher than that obtained at 600 °C without catalyst (50 mol gas/kg dried feedstock and 22 mol gas/kg dried feedstock, respectively), which is the major contribution of this work. At mild temperatures (450 °C) the methane production is highly favored, meanwhile at 600 °C the hydrogen production is enhanced. The methane yield obtained at 450 °C was 21.3 mol CH4/kg dried feedstock and the hydrogen yield obtained at 600 °C was 20.6 mol H2/kg dried feedstock. In the aqueous phases obtained from the experiments performed without catalyst at 450 °C, it was found valuable intermediate species such as benzoic and acetic acids (at a concentration of 4462 mg/L and 946 mg/L, respectively). This study represents a sustainable approach for valorizing plastic wastes by catalytic SCWG process.

The effect of different surface treatments of 310S austenitic stainless steel on the corrosion behavior in supercritical water using slow positron methods

AbstractThe corrosion behavior of 310S austenitic stainless steel, subjected to different surface treatments machined (MA), sandblasting (SB), and polishing (PO), was exposed to a 550°C supercritical water (SCW) environment. The aged samples were analyzed using variable‐energy slow positron beam techniques. The obtained results revealed that the plastic deformation of the near‐surface region of the MA and SB samples was substantially recovered in the SCW conditions. At least two distinct oxide layers formed, and the oxidation process created a Fe/Cr depletion zone in the inner layer. Various surface treatments, however, led to different corrosion profiles. The depth profile of slow positron beam characterization suggests that significant residual stress and deformation zones on the surfaces of the sandblasted samples probably provided a diffusion path for the oxidation of the 310S. Only the SB samples exhibited a negative weight change after SCW exposure. At the same time, the SB samples showed the highest concentration of the positron traps in this region, which was explained by open‐volume defects associated with the microcracks introduced by sandblasting.

Preparation and Characterization of Multielement Composite Oxide Nanomaterials Containing Ce, Zr, Y, and Yb via Continuous Hydrothermal Flow Synthesis.

The synthesis of multielement composite oxide nanomaterials containing Ce, Zr, Y, and Yb was investigated using a micro confined jet mixer reactor operated in continuous mode under supercritical water conditions. The obtained nanoparticles were characterized using ICP-AES, SEM-EDS, FTIR, Raman spectroscopy, XRD, and TEM. All samples exhibited a uniform particle shape and a narrow particle size distribution. An analysis of the d-spacing results using selected electron area diffraction (SAED) patterns confirmed the production of cubic-phase crystals. A BET test was employed to determine the specific surface area of the prepared nanoparticles. OSC and TPR techniques were utilized to characterize the oxygen storage capacity and reduction performance of the obtained samples, with an analysis conducted to determine how the different proportions of elements affected the performance of multielement mixed oxides. The ionic conductivity of multielement composite oxide was measured using alternating current impedance spectroscopy (EIS), and the impact of Y, Ce, and Yb on the electrolyte material's ionic conductivity was analyzed.

The utilization of lathe waste as a catalyst for the treatment of landfill leachate in supercritical water conditions

The utilization of lathe waste as a catalyst for the treatment of landfill leachate in supercritical water conditions

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.

Measurement system for in-situ estimation of instantaneous corrosion rate in supercritical water

Current research of cladding and in-core materials for the supercritical water reactor concept is focused on Fe-Cr-Ni alloys (e.g. 800 H, 310 S). Along the standard measurements of general corrosion rate of materials by exposure testing in autoclaves, where poor reproducibility is an issue, especially when comparing results from different experimental facilities, a good alternative may be the use of in-situ electrochemical measurements. The use of electrochemical methods is, however, more challenging due to complicated instrumentation as well as due to the supercritical water conditions. This paper is focused on the design of an experimental facility for in-situ electrochemical testing at supercritical water conditions, i.e. main circulating loop with autoclave, including the design of the electrode system, electrode leads and their surface insulation coating. Stability of electrochemical measurements has been tested using 2- and 3-electrode set-ups. Finally, surface insulation coating of the electrode leads with the best chemical and mechanical stability during experiment has been chosen for the presented application.

4-lump kinetic model for non-catalytic oil shale upgrading at sub- and supercritical water conditions

The kinetics of non-catalytic oil shale conversion at sub- and supercritical water conditions was studied. All experiments were carried out in a batch reactor at 300–400 °C and 1–48 h. A four-lump reaction scheme is proposed, where oil shale produces synthetic oil, gas and coke, and some other reactions take place between products (coke to gas, synthetic oil to gas and synthetic oil to coke). Low average absolute error (<6.5%) was obtained, which corroborates the accuracy of estimated parameters of the developed kinetic model. The reaction rate was found to depend more on synthetic oil yield than on oil shale conversion according to the calculated reaction orders. The sensitivity analysis of the kinetic parameters showed that all values of the obtained reaction rate coefficients are the optimal. At temperatures near the critical point of water (350 and 400 °C), lowest values for asphaltenes and highest light fractions contents in synthetic oil were obtained.

Development of a detailed kinetic model for high-pressure ethanol oxidation in gas phase and supercritical water

The present study aims to develop a detailed chemical kinetic model for high-pressure ethanol oxidation in the gas phase and supercritical water (SCW). Kinetic parameters for key elementary reactions involving HO2 and CH3OO radicals were updated, deriving from a careful analysis of ignition delay data or analogy. The model performance is validated comprehensively by comparison to a wide variety of recent experimental data from both gas-phase and SCW conditions. The model predicted ignition delay times and speciation measurements (15–60 bar) in the gas phase fairly well. Additionally, the model showed satisfactory performance in reproducing the species concentration profiles at SCW conditions. A comparative kinetic analysis was further conducted to investigate the characteristic differences and similarities of ethanol oxidation at the two conditions. The results indicated SCW lowered the onset temperature for ethanol ignition and facilitated the ethanol oxidation rate, but did not introduce additional oxidation pathways.

Study on Hydrothermal Cracking of Heavy Oil under the Coexisting Conditions of Supercritical Water and Non-condensate Gas.

This study looked at the effects of temperature, water-oil ratio, and the addition of non-condensable gas on the thermal cracking of extra-heavy oil in the lab. The goal was to learn more about the properties and reaction rates of deep extra-heavy oil under supercritical water conditions, which are not well understood. The changes in the composition of the extra-heavy oil were analyzed with and without the presence of non-condensable gas. The reaction kinetics of the thermal cracking of extra-heavy oil were quantitatively characterized and compared between the two conditions of supercritical water alone and supercritical water mixed with non-condensable gas. The results showed that (1) under supercritical water conditions, the extra-heavy oil underwent significant thermal cracking, which led to a significant increase in the amount of light components, the release of CH4, and the formation of a new component, coke, which led to a noticeable decrease in the viscosity of the oil; (2) increasing the water-oil ratio could promote the thermal cracking of extra-heavy oil and led to a significant decrease in oil viscosity, indicating a more complete thermal cracking reaction. Moreover, increasing the water-oil ratio was found to facilitate the flowability of the cracked oil; (3) the addition of non-condensable gas intensified the conversion of coke but inhibited and slowed down the thermal cracking of asphaltene, which is detrimental to the thermal cracking of extra-heavy oil; and (4) the kinetic analysis showed that the addition of non-condensable gas resulted in a decrease in the thermal cracking rate of asphaltene, which is detrimental to the thermal cracking of heavy oil.

Biochemical and biohythane production from anaerobically digested water plant by hydrothermal liquefaction/gasification

Water hyacinth (Eichhornia crassipes) was anaerobically digested with waste sludge in a batch system at varying total solid (TS) contents (3.3–8.3%) and temperatures (35–55 °C). Then, the high organic content of digested biomass was utilized for hydrothermal liquefaction/gasification in the batch reactor system at different temperatures (200–600 °C) to yield biofuels and biochemicals. Hydrothermal liquefaction/gasification was performed in sub- and super-critical water (above 374 °C and 221 bar) conditions. Prevailing products are some biochemical compounds (carboxylic acids, furfurals, aldehyde/ketones, phenols etc.) at lower temperatures (200–300 °C) while biohythane (total of hydrogen and methane) gaseous fuel are produced at higher temperatures (400–600 °C). The highest carbon gasification efficiency (73 g C in product/g C in feed) was obtained at 600 °C with the sample that has a high anaerobic digestion efficiency (digested at 6.3 TS% at 35 °C). The highest carbon liquefaction efficiency (37.2 g C in product/g C in feed) was obtained at 200 °C with the sample which has a low anaerobic digestion yield (digested at 8.3 TS% at 35 °C).

Experimental investigation on hydrocarbon generation of organic-rich shale with low maturity in sub- and supercritical water

Sub- and supercritical water, as solvents for organic matters, are promising for hydrocarbon generation of low maturity organic-rich shale. However, there is still no noteworthy study on the difference of dynamic hydrocarbon generation of low maturity organic-rich shale between sub- and supercritical water conditions. In this study, a non-isothermal heating reactor was used to simulate the hydrocarbon generation experiment of low maturity organic-rich shale at 360 °C, 21 MPa subcritical water and 400 °C, 25 MPa supercritical water within the range of 2–12 h. The differences of the hydrocarbon generation performance, product distribution, mineral composition and pore size distribution evolution between sub- and supercritical water condition were investigated. The results showed that the utilization degree of organic carbon and gas yield under supercritical water conditions were higher than that under subcritical water conditions at any given time within 2–12 h. The supercritical water condition had the advantage of an oil yield before 10 h, which was surpassed by subcritical water condition after 10 h. The relative content of saturated hydrocarbon and aromatic hydrocarbon were higher than resin and asphaltene under both sub- and supercritical water condition. The oil produced under subcritical water condition had more aromatic hydrocarbons. The selectivity of supercritical water for H2, CH4, C2H4 and C2H6 was higher than that of subcritical water, and the selectivity of subcritical water for CO2 was higher than that of supercritical water within the range of 0–12 h. The pyrite removing and pore expansion effects of supercritical water were greater than subcritical water. The mechanism of supercritical water to enhance the utilization degree of organic carbon mainly includes the enhancement of thermal efficiency, solubility, diffusion in terms of physical property effect, and the promotion of free radical reaction in terms of chemical property effect. We hope that the results will provide technical and theoretical support for in-situ hydrocarbon generation of low-mature organic-rich shale.

Characteristics of products of thermal and catalytic cracking of heavy oil asphaltenes under supercritical water conditions

This work deals with the reactivity and structural changes of asphaltenes during cracking in supercritical water using water-soluble salts Co and Ni. Cracking of the asphaltenes was carried out in an autoclave with a volume of 12 cm3 at a temperature of 450 °C, the process time was 80 min and the pressure was ≈ 29–30,8 MPa. The reactivity and structural changes of the asphaltenes were evaluated based on the yield and composition of the products (gas, maltenes, and coke) and the characteristics of the residual asphaltenes obtained by the method of structural group analysis based on elemental analysis, the values of molecular weight and 1H nuclear magnetic resonance (1H NMR), and XRD. Under supercritical water conditions, coke formation reactions are slowed down, with increasing diameter of the carbon stack structure. It is found out that the cobalt-containing catalyst promotes the formation of additional amounts of lower molecular weight components, i.e. maltenes and gas. In this case, the structure of secondary asphaltenes refers to the "island", and the number of packs and the total height in the asphaltene cluster increase.

Hydrothermal co-liquefaction of biomass and plastic wastes into biofuel: Study on catalyst property, product distribution and synergistic effects

This study reports an efficient conversion route for prosopis juliflora (PJ) biomass into high-quality bio-oil through catalytic hydrothermal liquefaction (HTL) process with systematically substituted hydrogen-rich plastic waste ‘polypropylene (PP)’, and using alumina supported metal oxide (Mo, Ni, W, and Nb) catalysts. The HTL treatments of PJ with PP (0-75 wt.%) were investigated in both sub and supercritical water conditions. An excellent synergy between PP and PJ was observed even in subcritical conditions (97.6% synergy at 340 °C at 25% PP to PJ), while efficient liquefaction of PP alone was observed only in the supercritical conditions. The optimum temperature, and PP substitution were found to be 420 °C and 25% respectively, with 46.5% bio-oil yield, high deoxygenation (65.1%), and carbon recovery (78.9%) when using Nb/Al2O3 as the catalyst. An in-depth analysis of physicochemical properties and the bio-oil product distribution with respect to each catalyst and PP/PJ substitution ratio are discussed in detail. Among all, the Nb/Al2O3 catalyst performed well with remarkable recyclability up to 10 cycles. The produced bio-oil mixture due to its low oxygen content is very promising to be upgraded to precursors for chemicals and transportation biofuels.