With the gradual depletion of conventional oil resources, the exploitation of heavy oil is essential to alleviate the energy crisis, as fossil energy remains predominant in global energy supply. The feasibility of cyclic supercritical water (SCW) stimulation is confirmed by oil field tests, while the enhanced oil recovery (EOR) mechanisms and the dynamic characteristics of displacement are still unclear owing to the scarceness of relevant studies. In this study, an experimental system with a design temperature up to 450 degrees C and pressure up to 30 MPa was developed to simulate the cyclic SCW stimulation process. A customized two-dimensional sand pack core with equitable temperature measuring arrangement can monitor the dynamic evolution of temperature field. The results of the core experiments indicated that the injection of SCW obviously enhances oil production, with the ultimate oil recovery factor up to 75.91%, which was 18.85% higher than that of steam. The formation and expansion of the SCW gravity override was found to be one of the mechanisms for boosting oil production. At the end, the swept volume coefficient of SCW was enlarged from 5.39% to 10.53%, which was 2.99 times that of steam. The large expansion of the gravity override zone of SCW in the vertical and radial directions changes the heat and mass transfer law, raises the core temperature, and expands the swept volume. Further, the condensation of supercritical water in the soak stage caused pressure difference (up to 11.12 MPa) near the well driving distant heavy oil to flow towards. These findings have the potential to deepen the understanding of the EOR mechanisms of SCW stimulation and provide theoretical guidance for improving oil production in oilfields.

Oil reservoirs contain significant amounts of water. Therefore, the role of water in the in situ hydrocarbon generation of medium- and low-maturity organic-rich shale cannot be ignored. In this study, a self-developed reaction system was used to simulate hydrocarbon generation under supercritical water in situ conversion, examining the influence of water-shale mass ratio changes on organic carbon migration and pore evolution. The results showed that higher water-shale mass ratios were conducive to the conversion of organic carbon in shale and the migration of organic carbon to gas-phase products. As the water-shale mass ratio increased, the proportion of carbon elements in carbon dioxide from organic sources gradually decreased, while that of carbon elements from inorganic sources gradually increased. Increasing the water-shale mass ratio from 0.5 to 5, the porosity and permeability of shale were greatly improved, with porosity increasing more than threefold and permeability more than fivefold.

Pyrolysis is a significant process for the in-situ conversion and aboveground retorting of oil shale. However, the impact of inherent minerals on shale pyrolysis is still unclear. This study analyzed the effect of different inherent minerals on pyrolysis of Chang-7 oil shale, which is noted for its low carbonate, high silicate, and high pyrite content, through an integrated evaluation of kinetic and thermodynamic parameters. The pyrolysis process, arranged from 350 degrees C to 600 degrees C, was deconvoluted into three distinct processes-bitumen, kerogen, and pyrite pyrolysis-using the bi-Gaussian method. Thermodynamic results showed that pyrolysis was endothermic and non-spontaneous. Minerals significantly reduced the pyrolysis activation energy. The ratio of pyrolysis activation energies for shale to kerogen increased with the carbonate-to-silicate content ratio. Master plot analysis indicated that, mineral removal shifted the reaction model from the contraction geometry model (Rn) to the diffusion model (Dn). This transition in reaction model was due to the formation of pores from demineralization and organic decomposition, facilitating the diffusion of heat and activated molecules into the interior of particles, which has been confirmed by porosity determination. This work provides an in-depth understanding of the impact of inherent minerals on shale pyrolysis, which is conducive to the efficient development and utilization of oil shale resources.

Supercritical water upgrading (SCWU) is a promising technology for heavy oil recovery and refining, in which minerals could act as catalysts, but the effect on the upgraded product distribution remains unclear. In this study, heavy oil upgrading experiments in supercritical water (SCW) were carried out at 400 degrees C and 25 MPa to investigate the effects of reservoir minerals such as quartz, carbonate, feldspar and clay minerals on the upgrading process. The result indicated that carbonate minerals and clay-bearing minerals produced noticeable benefits to the SCWU of heavy oil process. In carbonate minerals, dolomite showed the strongest catalytic effect in promoting hydrothermal cracking of hydrocarbon macromolecules, with a 5.6 % reduction in heavy fraction and a 12.2 % increase in light fraction of the upgraded oil. Clay-bearing minerals mainly exhibited oil-enhancing and coking-inhibiting benefits, calcium montmorillonite exhibited the most significant increase in oil production of 9 %, while zeolite most significantly reduced the coke activation energy by 62 %. Regarding the catalytic mechanism, the catalytic effect of carbonates originated from the MgO and CaO sites on the surface. For clay minerals, the acidic catalytic sites exist in the interlayer domains of montmorillonite and in the pores of zeolite provided higher catalytic efficiencies in oil production. This study demonstrated the feasibility of using natural minerals as inexpensive catalysts for supercritical water upgrading of heavy oil.

Exploring new system for chemical recycling of plastic is an effective way to convert plastic waste into energy. Herein, the use of supercritical CO2 (ScCO2) to promote the catalytic degradation of polystyrene (PS) with high yield of aromatic oils was proposed. ScCO2 provided a homogeneous environment for the reaction, which not only facilitated the swelling of PS, but also inhibited the formation of coke, beneficial for the degradation of PS to aromatic oils. In addition, CO2 as an oxidant reacted with PS or intermediates to generate new products. NiO@C catalyst prepared by doping carbon material in NiO had a simple preparation process, an abundance of porous structure and strong acidic sites, thus improving the catalytic activity. Under the co-action of ScCO2 and NiO@C, the yield of aromatic oils produced from PS was up to 89.3 +/- 0.6 wt% at 300 degrees C with a reaction time of 2 h and a catalyst loading amount of 10 wt%. Moreover, the NiO@C catalyst was used for three cycles without obvious change in the catalytic performance. The efficient catalytic degradation of PS to aromatic oils by ScCO2 promoted NiO@C catalysis provides a potential route for simultaneously recycling plastic and sequestering carbon.

In this study, a non-isothermal heating reactor was used to simulate the hydrocarbon generation process of 1-4 cm sized medium- and low-maturity organic-rich shale under the action of supercritical water. The results show that the increase in pressure had a negative effect on the utilization of organic carbon in shale. As the pressure increased, the overall conversion efficiency of organic carbon decreased. Although higher pressure inhibited both oil and gas production, the inhibition of the gas production process was more significant. The effect of reaction time on oil and gas production differed in stages. Over a 4-h reaction period, the oil and gas production rates gradually increased with longer reaction times, with oil production showing a stronger promotion effect. Beyond 4 h, further extension of reaction time mainly promoted gas production. The increase in pressure and reaction time had opposite effects on the pore structure parameters of shale. Higher pressure led to a decrease in these parameters, while longer reaction times resulted in improved and expanded parameters.

Download This Paper Open PDF in Browser Add Paper to My Library Share: Permalink Using these links will ensure access to this page indefinitely Copy URL Copy DOI

Rheological property is an important parameters in the evaluation of heavy oil and asphalt. This work studied the effect of hydrothermal reactions with CuSO4 on the rheological property. The hydrothermal reactions are used to improve the fluidity of oil and transition metal inorganic salts act as catalysts. However, when the CuSO4 concentration surpasses a certain value, the fluidity of heavy oil undergoes rapid deterioration, similar to the effect of asphalt modification. Consequently, we proposed a method modifying asphalt by hydrothermal reaction with CuSO4. Analysis of the viscoelastic results suggested that the most significant influence factors were CuSO4 concentration and reaction temperature. The presence of water is also essential. Further analysis indicated that the entry of Cu atoms into heavy oil molecules was the fundamental cause of the deterioration of rheological properties. These findings demonstrate that the hydrothermal reaction with CuSO4 can be used for asphalt modification, and the resulting product’s properties can be adjusted by manipulating reaction conditions. Furthermore, chemical reactions can lead to permanent changes that are not susceptible to separation of modifiers.

Residence time distribution (RTD) is significant for reflecting fluid mixing and materials dispersion inside continuous high-pressure hydrothermal reactor. In this work, a model is proposed to precisely fit RTD data in continuous hydrothermal reactor, and the model parameters can be used to analyze the characteristics of RTD. A series of RTD data under different working conditions are obtained by numerical simulation and analyzed by the proposed model to investigate the effects of natural convection, momentum ratio and forced flow on RTD. It is found that appropriate natural convection and momentum ratio are beneficial to fluid mixing and materials dispersion. On the other hand, excessive natural convection and too high or too low branch inflow may lead to the extension of average residence time and materials delay or stagnation. Forced flow is negatively correlated with average residence time but has little influence on materials dispersion and delay.

Understanding shale oil adsorption in reservoir nanopores is essential for efficient extraction. This study used MD simulations to analyze the adsorption and diffusion of two- and multi-component hydrocarbons (Aromatics, Alkanes, Resin) on various shale surfaces (Calcite, Montmorillonite, Quartzite, Organic) at 353 K and 25 MPa. Hydrocarbons formed a bilayer adsorption structure comprising a high-concentration adsorption layer (L1, 0.35–0.90 g/cm3) and a low concentration weak adsorption layer (L2), with adsorption density ranked as Resin > Aromatics > Alkanes. Reservoir surfaces were classified as ionic (e.g., calcite, montmorillonite) and non-ionic (e.g., quartz, graphite), and polar hydrocarbons exhibited higher adsorption densities and energies on ionic surfaces due to combined electrostatic and van der Waals interactions, while non-ionic surfaces showed smaller adsorption differences. For multicomponent hydrocarbons, adsorption layer densities followed the order: graphite > MMT-SiO > quartz > calcite > MMT-Na, with competitive adsorption observed. The polar component exhibited a greater adsorption advantage on the calcite, MMT-SiO side and graphite surfaces due to electrostatic interactions and π-π interactions, and a lesser advantage on the MMT-Na side and quartz surfaces. Hydrocarbon diffusivity was influenced by molecular mass and polarity and ordered as Alkanes > Aromatics ≫ Resin. Polar molecules had a weaker diffusion than nonpolar molecules at similar molecular masses. Among the multicomponent hydrocarbons, the self-diffusion coefficient (Self-D) of Resin increased, while that of lighter components decreased compared to two-component systems. These findings offer strategies for improving shale oil recovery by tailoring injection fluids to reservoir types, anionic surfactants or chelating agents may be used to reduce electrostatic interactions in carbonate and clay reservoirs, while nonionic surfactants may be more effective in quartz reservoirs.

Download This Paper Open PDF in Browser Add Paper to My Library Share: Permalink Using these links will ensure access to this page indefinitely Copy URL Degradation of Polystyrene to Aromatic Oils with Nio@C Catalyst in Supercritical Co2 20 Pages Posted: 27 Feb 2024 See all articles by Yanbing LiuYanbing Liuaffiliation not provided to SSRNLiuhao Maoaffiliation not provided to SSRNXing Kangaffiliation not provided to SSRNYi Liaffiliation not provided to SSRNQiuyang Zhaoaffiliation not provided to SSRNHui JinXi'an Jiaotong University (XJTU)Wei MengHunan City UniversityJinwen Shiaffiliation not provided to SSRNLiejin GuoXi'an Jiaotong University (XJTU) - State Key Laboratory of Multiphase Flow in Power Engineering Abstract One of the most promising ways to dispose of plastic pollution in the future is chemical recycling of plastic, and in particular supercritical fluids with excellent fluidity and transferability have shown great attraction in the disposal of plastic. Herein, catalytic degradation of polystyrene (PS) plastic in supercritical carbon dioxide (Sc-CO2) was realized with high yield of aromatic oils. NiO with simple preparation process, and high catalytic activity and stability in Sc-CO2 was doped with carbon material to prepare NiO@C catalyst with improved catalytic performance. Compared with NiO, NiO@C catalyst had rich porous structure and strong acidic sites, resulting in higher catalytic activity. The NiO@C catalyzed degradation of PS in Sc-CO2 yielded aromatic oils as high as 89.3 ± 0.6 wt% at 300oC with a reaction time of 2 h and a catalyst loading amount of 10 wt%. Moreover, the NiO@C catalyst degraded PS in Sc-CO2 for three cycles without obvious change in the catalytic performance. Sc-CO2 not only played a favorable role in swelling PS, but also inhibited the formation of coke, beneficial for the degradation of PS. Furthermore, CO2 was be consumed as an oxidant to generate new products and reduce greenhouse gas emission. The highly efficient catalytic conversion of PS to aromatic oils in Sc-CO2 via NiO@C catalyst provides a potential route for simultaneously recycling plastic and sequestering carbon. Keywords: Carbon material, Hydrocarbon fuel, Plastic waste, supercritical fluid, carbon dioxide Suggested Citation: Suggested Citation Liu, Yanbing and Mao, Liuhao and Kang, Xing and Li, Yi and Zhao, Qiuyang and Jin, Hui and Meng, Wei and Shi, Jinwen and Guo, Liejin, Degradation of Polystyrene to Aromatic Oils with Nio@C Catalyst in Supercritical Co2. Available at SSRN: https://ssrn.com/abstract=4739644 Yanbing Liu affiliation not provided to SSRN ( email ) No Address Available Liuhao Mao affiliation not provided to SSRN ( email ) No Address Available Xing Kang affiliation not provided to SSRN ( email ) No Address Available Yi Li affiliation not provided to SSRN ( email ) No Address Available Qiuyang Zhao affiliation not provided to SSRN ( email ) No Address Available Hui Jin Xi'an Jiaotong University (XJTU) ( email ) China Wei Meng Hunan City University ( email ) China Jinwen Shi (Contact Author) affiliation not provided to SSRN ( email ) No Address Available Liejin Guo Xi'an Jiaotong University (XJTU) - State Key Laboratory of Multiphase Flow in Power Engineering ( email ) Download This Paper Open PDF in Browser Do you have negative results from your research you’d like to share? Submit Negative Results Paper statistics Downloads 0 Abstract Views 2 60 References PlumX Metrics Feedback Feedback to SSRN Feedback (required) Email (required) Submit If you need immediate assistance, call 877-SSRNHelp (877 777 6435) in the United States, or +1 212 448 2500 outside of the United States, 8:30AM to 6:00PM U.S. Eastern, Monday - Friday.

Supercritical water gasification is a clean technology for biomass conversion and utilization. In supercritical water gasification systems, H2O is often used as the transport medium. Decreases in the reaction temperature at the gasification area and in the heating rate of biomass may limit the gasification rate and efficiency. In this paper, CO2 is used as the transport medium due to its relatively low critical point and specific heat capacity. Moreover, a corn stalk gasification system with different transport media is established in this paper, and the influences of various operating parameters, such as temperature, pressure and feedstock concentration, are investigated. The results show that the gas yield in the CO2-transport system decreases by no more than 5 wt %. In addition, thermodynamic analysis reveals that a system with CO2 as transport medium consumes approximately 25% less electricity than a system with H2O as the transport medium. In addition, the reaction heat absorption decreases. The results show the superiority of CO2 to H2O as a transport medium.

Supercritical water (SCW) has gained substantial interest for shale exploitation due to its high conversion efficiency. To quantify the generated gases and the mutual conversion of gases on reaction of shale in SCW, experiments were carried out in batch reactor at 400-600 degrees C and residence time up to 480 min. The products are classified as residual solids, liquid intermediates and gases. Experimental results show that the generated gases are mainly C1, C2, C3 alkanes, H2 and CO2. The concentrations of C1 and C2 alkanes decrease with temperature and residence time but the other three are the opposite. A kinetic model of shale-intermediates-gases reaction is developed. This model can characterize the gas generation features of shale and SCW resulting from chemical reactions, and can quantitatively describe the mutual conversion between gases. The calculated results demonstrate well applicative for predicting gas concentration at various residence time within an acceptable deviation. The reaction process can be divided into three stages: pyrolysis of organic matter to generate intermediates, hydrolysis reaction and alkyl thermal cracking of intermediates to generate gases, mutual conversion between the generated gases. Reactions among gases involve methanation reaction, water-gas shift reaction and hydrocarbon gas decomposition. This study provides a potential kinetic model for the gas generation characteristics of reaction with shale and supercritical water.

In recent years, the excellent thermochemical properties of supercritical water (SCW) have been exploited in the development of supercritical water flooding (SCWF) technology as an efficient and green enhanced oil recovery (EOR) method for thick oil. The EOR method is frequently employed in the tertiary oil recovery of oilfields. However, the high water cut within the reservoir represents a main challenge to heavy oil recovery. The recovery process and recovery mechanism of SCWF technology under high water cut conditions remain unclear. This study established a novel experimental system (450 degrees C, 30 MPa) to conduct SCWF experiments for heavy oil reservoirs with high water cut. The results showed that SCWF at 400 degrees C and 25 MPa had exhibited the recovery factor efficiency up to 96.27% and the viscosity reduction factor up to 61.6% for Gudao heavy oil, compared to conventional steam flooding and subcritical water flooding. Further, the dynamic process of SCWF was divided into three stages: pressure rising drainage stage, heating and depressurization stage and miscible flooding stage. It is evident that the high diffusivity, solubility and reactivity of supercritical water play a crucial role in thermal fluid breakthrough, miscible flooding and aquathermolysis reactions, which become the key mechanisms for EOR and in situ upgrading of SCWF in heavy oil reservoirs with high water cut. This work provides a theoretical basis and experimental validation for the extraction of heavy oil in oilfields.

Bubble evolution plays a vital role in the photoelectrochemical (PEC) water-splitting process. However, quantitatively relating nucleation site distribution to bubble dynamics and reaction current remains elusive. Here, we investigate the coalescence and detachment processes of double bubbles with different nucleation site spacing (S) using electrochemical measurements and high-speed microscopic imaging. The study reveals three types of detachment mode: the periodic buoyancy-driven detachment mode, the transition mode, and the periodic coalescence-driven detachment mode. These modes are influenced by the coalescence process, which alters the S and results in changes to the bubble detachment radius and detachment frequency. Meanwhile, significant differences in the average reaction current can be obtained by changing S at the same potential. This study elucidates the fundamental relationship between bubble coalescence and detachment characteristics, which provides guidance for optimal design of the electrode morphology in a PEC water-splitting system.

Hydrogen donation is the key to supercritical water upgrading of heavy oil, because it benefits light distillate production and inhibits condensation, but the mechanism is still unclear. In this work, an isotope tracing method, combined with Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy analyses, was used to elucidate the hydrogen donation mechanism in supercritical water upgrading of asphaltenes. In asphaltenes upgrading, it was found that the aliphatic carbon at the end of the side chain of asphaltene macromolecules could capture deuterium from supercritical heavy water via free radical reactions, and the deuteration ratio at this position was 11 %. For supercritical water upgrading of vacuum residue which is generally considered as a system of asphaltenes dissolved in maltenes, the existing maltenes enhanced hydrogen donation to asphaltenes. Further, a possible hydrogen donation pathway was proposed. This work provides an in-depth understanding of the hydrogen donation mechanism for supercritical water upgrading.

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 hydro-carbon 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 degrees C, 21 MPa subcritical water and 400 degrees 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 investi-gated. 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 su-percritical 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 su-percritical 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.

High-temperature steam injection is a common means of thermal recovery of thick oil. Although the steam injection boiler currently used for thick oil injection can achieve fast start-stop control, the power consumption of the pump is large, and the boiler control is demanding. Besides, a large amount of fossil fuel is needed to supply the heat required for steam heating. Using solar thermal to realize the transformation of solar energy-molten salt heat energy-steam energy can effectively reduce the burning of fossil fuels and realize clean thermal recovery of thick oil. To ensure the actual demand of thermal recovery of thick oil, it is necessary to determine a reasonable steam evaporation volume and vapor phase fraction. This paper simulates a solar thermal heat exchange system for molten salt-steam based on Aspen Plus. The simulation results show that the heat load and required solar panel area of all heat exchangers rise when the evaporation volume increases. However, the superheater grows most slowly. When the vapor phase fraction at the evaporator outlet rises to 1, there is no phase change heat transfer in the superheater, and its heat load plummets to 230 kW.

Multi-component supercritical thermal fluid (mcSCTF) has been recently recognized as a promising media for enhancing heavy oil recovery. For its economic application, an efficient mcSCTF generation should be studied. In this work, a novel experimental system with various units is being first introduced for mcSCTF generation and theoretically modelled for the energy and exergy analysis as the two contributions of this work. Based on the results, optimal retrofit strategy is proposed as the coming improvement. Starting with a specific experimental setup, theoretical modeling methods including Gibbs free energy minimization and mass balances are employed to predict the output of the core unit of reactor. The models are validated using measured experimental data. Then, energy and exergy analysis are conducted to quantify the energy and exergy losses in each unit. The reactor, heat exchanger and compressor are found to contribute for the major exergy losses accounting for 40.1%, 39.4% and 12.3%, respectively. With this, sensitivity analysis of three key factors (i.e., reactor heat dissipation rate, heat exchanger efficiency, and compressor isentropic efficiency) as well as their combinations are performed to identify potential solutions for improving efficiency. Finally, a retrofit design with around 10% efficiency enhancement is proposed.

Supercritical water conversion of low-maturity shale is a promising method to produce oil and gas. Hydrocarbon generation from kerogen is influenced by inorganic minerals in shale. This study aims to clarify hydrocarbon generation characteristics of pure kerogen in supercritical water by removing inorganic minerals by acid-pickling. A series of experiments on hydrocarbon generation of kerogen in the temperature range of 300-700 degrees C were carried out in a batch reactor, and the produced oil and gas were quantitatively analyzed. The results showed that when the temperature increased, the oil yield had experienced a variation of first an increase and then a decrease with a peak value of 0.19 g/gTOC at 380 degrees C, while the gas yield continued to increase to 0.88 g/gTOC at 700 degrees C. By increasing the temperature from 300 to 500 degrees C, it would favor producing high quality oil with more light distillates (70% at 500 degrees C) and less asphaltene (5% at 500 degrees C). The main gas products were methane, hydrogen, and carbon dioxide as well as C2+ hydrocarbons. The proportion of hydrogen increased with temperature (30% at 700 degrees C), while the proportion of methane peaked to 51% at 600 degrees C. Elevated temperatures in a supercritical water atmosphere increase ring-opening processes and the cleavage of branched side chains, boosting the maturation of the kerogen.