CO2 Density Research Articles

Solution of the structure of the high-coverage CO layer on the Ru(0001) surface—A combined study by density functional theory and scanning tunneling microscopy

Structures formed by dense CO adsorption layers can provide information about the balance between molecule–surface and molecule–molecule interactions. However, in many cases, the structure models are not clear. Using density functional theory (DFT) and scanning tunneling microscopy (STM), we have investigated the high-coverage CO layer on the Ru(0001) surface. Previous investigations by low-energy electron diffraction (LEED) and vibrational spectroscopy led to conflicting results about the structure. In the present study, 88 models with coverages between 0.58 and 0.77 monolayers have been analyzed by DFT. The most stable structures consist of small, compact CO clusters with an internal pseudo 1×1 structure. The CO molecules in the cluster centers occupy on-top sites in an upright position, whereas the molecules farther outside are slightly shifted from these sites and tilted outward. STM data of the CO-saturated surface at low temperatures, corresponding to a coverage of 0.66 monolayers, show a quasi-hexagonal pattern of features with an internal hexagonal fine structure. Simulated images based on the cluster model agree with the experimental data. It is concluded that the high-coverage CO layer consists of the close-packed clusters predicted by DFT as the most stable structure elements. In the experiment, the sizes and shapes of the clusters vary. However, the arrangement is not random but follows defined tiling rules. The structure remains ordered, almost up to room temperature. The LEED data are re-interpreted on the basis of the Fourier transforms of the STM data, solving the long-standing conflict about the structure.

Investigation of the transferability of calibration between alternative fluids for liquid and dense phase carbon dioxide flow measurement

Carbon Capture Utilisation and Storage (CCUS) technology is pivotal for achieving global emissions reduction goals. The rise in CCUS facilities, with a near doubling of global capture capacity, indicates industry momentum. Robust flow measurement across the CCUS transport and storage networks are essential for commercial contracts, financial incentives, and regulatory compliance since these are underpinned by accurate quantification of the CO2 quantity transferred across the CCUS chain. However, a critical gap exists in verification and quality assurance of flow meters as currently there are no traceable calibration facilities that operates with liquid and/or dense phase CO2. However, globally there are many accredited traceable water and oil calibration facilities in operation, which can meet the required flow rates and meter sizes. An experimental study was then conducted at TÜV SÜD National Engineering Laboratory, UK, and at the Institute for Energy Technologies, NO, to explore the transferability of calibration between water, oil, and CO2 using five flow meter technologies with the aim of providing a preliminary assessment of whether meters calibrated in alternative fluids can accurately measure liquid and supercritical CO2. The results suggest that this approach could work for Coriolis meters. The results also suggest caution in relying solely on using Equations of State to calculate density values and a recommendation is presented to currently employing direct density measurements until a more comprehensive understanding is achieved on Equations of State performance for CO2-rich mixtures. To the best of the author's knowledge this is the first time that such experimental investigation is conducted, and the results shared publicly.

Session 3. Oral Presentation for: Analysis of an existing hydrocarbon gas pipeline for conversion to dense phase CO2 service

Session 3. Oral Presentation for: Analysis of an existing hydrocarbon gas pipeline for conversion to dense phase CO2 service

Equilibrium adsorption of diethyl ketone on activated carbon in a supercritical CO2 environment: Measurements and thermodynamic modeling

This study focuses on the equilibrium adsorption of diethyl ketone, a VOC widely used in the printing industry, on activated carbon in a supercritical CO2 environment at pressures in the range of 10 MPa to 20 MPa and temperatures between 313 K and 353 K, which provides a wider range of equilibrium adsorption data for diethyl ketone under different pressure and temperature conditions and allows a comparative analysis with other ketone VOCs. It is found that the equilibrium adsorption of diethyl ketone on activated carbon exceeds that of methyl ethyl ketone, probably due to differences in their respective affinities for activated carbon and their different volatilities in a supercritical fluid context. The Dubinin-Astakhov model was used to interpret the data and showed an average relative deviation of approximately 3.8 % between modeled and observed values. Additional analysis of the model parameters influenced by CO2 density and VOC characteristics was performed to gain a better insight into the adsorption dynamics and to contribute to the design and improvement of the activated carbon regeneration process.

The potential for CO2 storage in residual oil zones in onshore Australian basins

Geoscience Australia and CSIRO have collaborated to investigate whether residual oil zones (ROZs), sometimes associated with conventional Australian hydrocarbon plays, could provide a carbon dioxide (CO2) storage resource and enhance the storage capacity of depleted fields. Our petrophysical study demonstrates that ROZs occur in Australia’s hydrocarbon-rich regions, particularly in the Cooper-Eromanga Basin. ROZs with more than 10% residual oil saturation are uncommon, likely due to small original oil columns and lower residual saturations retained in sandstone reservoirs than in classic, carbonate-hosted North American ROZs. Extensive, reservoir-quality rock is found below the deepest occurring conventional oil in many of the fields in the Eromanga Basin, potentially offering significant CO2 storage capacity. Multiphase compositional flow modelling was used to estimate the CO2 storage efficiency of typical Australian ROZs. We developed a novel modelling methodology that first captures oil migration events leading to the formation of ROZs. Modelling CO2 storage over a 20-year injection period demonstrates that CO2-oil interactions increase the density and viscosity of CO2, enhancing CO2 sweep efficiency and lateral flow, improving storage efficiency. The extent of these effects depends on the quantity and spatial distribution of residual oil in place and the miscibility of CO2 at reservoir conditions.

Analysis of an existing hydrocarbon gas pipeline for conversion to dense phase CO2 service

Esso Australia is investigating the feasibility of a carbon capture and storage (CCS) project in East Gippsland, Victoria. Known as the South-East Australia Carbon Capture and Storage (SEA CCS) Hub, the project aims to re-purpose existing infrastructure and offshore depleted hydrocarbon reservoirs to store carbon dioxide (CO2). The project aims to reduce greenhouse gas emissions from Esso’s Longford Gas Conditioning Plant, and to unlock future CCS opportunities for Australia. One option identified as part of the SEA CCS feasibility was to convert part of the existing onshore section of the Barracouta 450 mm gas pipeline to Longford Gas Plant (BTA450-LFD), Licence PL/1 under the Victorian Pipeline Act, to dense phase CO2 service. This paper documents the initial findings of the potential for the onshore section of the BTA450 for conversion, with particular emphasis on brittle and ductile fracture control considerations. In summary, when attempting to convert existing hydrocarbon gas pipelines for CO2 service, operators need to undertake an appropriate assessment of fracture control considerations. The insights of this paper may serve as a useful guide document for assessing other existing onshore pipelines for CO2 service conversion. Due to the thermal modulation effect of the surrounding water for subsea pipelines, this guidance does not apply to subsea pipeline sections.

Investigating the influence of oxygen doping in modulating product distribution for electrocatalytic CO2 reduction reaction

Efficient carbon recycling hinges on a comprehensive understanding of the mechanics behind electrocatalytic carbon dioxide reduction reactions (ECO2RR). Here, we have engineered, in-situ growth of CuO featured on O-doped gCN (COG) and ex-situ growth of CuO on bare gCN (CG) respectively, functioned as platforms fordisengaging the fundamental of ECO2RR. The COG holds substantial capacity compared to CG for efficient conversion of CO2 into hydrocarbons and initiated the C2 product pathway with enlarged faradaic efficiency (FE). The experimental results indicate that the COG enhanced the product conversion of CH3OH (FE = 61.5% ± 0.5), C2H5OH (FE = 24.7% ± 0.5), and HCOO– (FE = 6.1% ± 0.5) at −1.1 V Vs RHE. Meanwhile, the CG exhibited the maximum conversion of CO2 into CH3OH (FE = 56.4% ± 0.5) at the same potential range. For the CG, the partial current density of CH3OH (JCH3OH) is −1.8 mA cm−2, whereas COG exhibited −4.9 mA cm−2. Interestingly, in this ECO2RR, the study of oxygen doping demonstrated that feasible CO2 conversion, due to its affinity towards CO2 and high donor density.

Leaf morpho-anatomical adjustments in a Quercus pubescens forest after 10 years of partial rain exclusion in the field.

In the Mediterranean region, a reduction of annual precipitation and a longer and drier summer season are expected with climate change by the end of the century, eventually endangering forest survival. To cope with such rapid changes, trees may modulate their morpho-anatomical and physiological traits. In the present study, we focused on the variation in leaf gas exchange and different leaf morpho-anatomical functional traits of Quercus pubescens Willd. in summer using a long-term drought experiment in natura consisting of a dynamic rainfall exclusion system where trees have been submitted to amplified drought (AD) (~-30% of annual precipitation) since April 2012 and compared them with trees under natural drought (ND) in a Mediterranean forest. During the study, we analyzed net CO2 assimilation (An), stomatal conductance (gs), transpiration (E), water-use efficiency (WUE), stomatal size and density, density of glandular trichomes and non-glandular trichomes, thickness of the different leaf tissues, specific leaf area and leaf surface. Under AD, tree functioning was slightly impacted, since only An exhibited a 49% drop, while gs, E and WUE remained stable. The decrease in An under AD was regulated by concomitant lower stomatal density and reduced leaf thickness. Trees under AD also featured leaves with a higher non-glandular trichome density and a lower glandular trichome density compared with ND, which simultaneously limits transpiration and production costs. This study points out that Q. pubescens exhibits adjustments of leaf morpho-anatomical traits which can help trees to acclimate to AD scenarios as those expected in the future in the Mediterranean region.

The Influence of CO2 Physical Properties on Casing and Its Prediction Method

In order to reveal the physical properties of CO2 under actual formation conditions, this paper establishes a mathematical model of the temperature field and pressure field in the wellbore under CO2 injection conditions, optimizes the state equation of CO2 physical-property parameters, calculates the change trend of CO2 density, viscosity, and compression factor along the wellbore, and obtains the influence law of CO2 corrosion on the casing and interface. The viscosity showed a downward trend along the well depth; the compression factor showed an upward trend. The surfaces of the three casings were smooth and flat without obvious defects, the cement structure was dense, and there was no obvious pore structure. After corrosion, with the increase of Cr content, the change of interfacial corrosion decreases. The morphology of the Q125 and 3Cr interface is loose after corrosion, while there is no obvious change in the 13Cr interface. With the prolongation of corrosion time, low wellbore internal pressure easily causes casing yield, and high wellbore internal pressure easily causes cement-sheath compression failure. The circumferential stress of the casing increases with the corrosion time extension, and the radial stress of the casing and cement sheath decreases first and then increases with the corrosion time. The compressive strength of the cement sheath does not exceed the compressive strength.

ASSESSMENT OF HEAT BALANCE IN THE FSRU REGASIFICATION CYCLE ALIGNS WITH IMO’S DECARBONISATION STRATEGY

In 2023, the International Maritime Organization revised its greenhouse gas strategy, striving to reduce annual emissions from international shipping by at least 70% by 2040. The Mediterranean Sea will become an emission control area for sulphur oxides and particulate matter from May 2025, and the EU will include shipping in its Emission Trading System from 2024. Liquid natural gas is expected to become a cleaner marine fuel, but it alone cannot meet emission reduction goals. The cryogenic carbon capture process can separate CO2 from exhaust gases, compress it, and store it in a liquid state with high density. This study aims to integrate an energy balance equation model to analyse the energy exchange in the regasification process and identify potential areas for improvement and targeted solutions to enhance performance and comply with IMO emission regulations. Based on a mathematical model, the energy balances are calculated and yield the following results: steam heater (26,999 kW), R-290 preheater (5,837 kW), trim heater (3,290 kW), R-290 evaporator (13,322 kW), and LNG vaporiser (23,118 kW). A report also determined that within a temperature range between -56.6℃ and 31℃ and a pressure range of greater than 5.2 bar (absolute) and less than 74 bar (absolute), the CO2 is in a liquid phase. Due to CO2 density which fluctuates in liquid at 1032 kg/m3 and in solid phase at 1562 kg/m3 the physical condition is compatible with the storage stage of capture emission.

Decoding wettability in coal-water-CO2 system for enhanced sequestration security

The injection of CO2 into deep unminable coal seam is a most promising carbon storage method that can simultaneously achieve the dual objectives of mitigating CO2 emission and enhancing coalbed methane recovery. In this context, the wettability of the coal-water-CO2 system plays an important role in the CO2 injection rate, storage capacity, and sequestration security. However, the factors affecting wettability alternation in the coal-water-CO2 system are still unclear until now. In this study, the sessile drop method was used to measure the contact angle (CA) in the coal-water-CO2 system under different pressures (3 – 8 MPa) and temperatures of (40–70 °C) with four different rank coals. Results indicate that with increasing pressure, the CA shows a steady increase below 5 MPa followed by a rapid increase at 5 – 8 MPa. The CA decreases with increasing temperature and coal rank. The CA is negatively correlated with the mes- and macro-pores, but positively correlated with micropores. It was found that these relationships are attributed to the CO2 density and CO2 adsorption capacity of coal. As the CO2 density increases, the coal-CO2 interaction force intensifies, leading to a tendency towards CO2 wetting for the coal-water-CO2 system. The adsorption capacity illustrates the strength of the coal-CO2 interaction, where the affinity of polar adsorption sites for CO2 molecules exceeds that of nonpolar adsorption sites. Finally, we conducted a comprehensive assessment of the wettability of the coal-water-CO2 system as it varies with burial depth by developing an integrated model that considers four influential factors, including pressure, temperature, coal rank, and pore structure. The findings of this study can be utilized to determine the optimal CO2 injection pressure in CO2-ECBM projects and enhance sequestration safety.

Adsorption and Diffusion Properties of Functionalized MOFs for CO2 Capture: A Combination of Molecular Dynamics Simulation and Density Functional Theory Calculation.

The capture of carbon dioxide (CO2) from fuel gases is a significant method to solve the global warming problem. Metal-organic frameworks (MOFs) are considered to be promising porous materials and have shown great potential for CO2 adsorption and separation applications. However, the adsorption and diffusion mechanisms of CO2 in functionalized MOFs from the perspective of binding energies are still not clear. Actually, the adsorption and diffusion mechanisms can be revealed more intuitively by the binding energies of CO2 with the functionalized MOFs. In this work, a combination of molecular dynamics simulation and density functional theory calculation was performed to study CO2 adsorption and diffusion mechanisms in five different functionalized isoreticular MOFs (IRMOF-1 through -5), considering the influence of functionalized linkers on the adsorption capacity of functionalized MOFs. The results show that the CO2 uptake is determined by two elements: the binding energy and porosity of MOFs. The porosity of the MOFs plays a dominant role in IRMOF-5, resulting in the lowest level of CO2 uptake. The potential of mean force (PMF) of CO2 is strongest at the CO2/functionalized MOFs interface, which is consistent with the maximum CO2 density distribution at the interface. IRMOF-3 with the functionalized linker -NH2 shows the highest CO2 uptake due to the higher porosity and binding energy. Although IRMOF-5 with the functionalized linker -OC5H11 exhibits the lowest diffusivity of CO2 and the highest binding energy, it shows the lowest CO2 uptake. Accordingly, among the five simulated functionalized MOFs, IRMOF-3 is an excellent CO2 adsorbent and IRMOF-5 can be used to separate CO2 from other gases, which will be helpful for the designing of CO2 capture devices. This work will contribute to the design and screening of materials for CO2 adsorption and separation in practical applications.

Ultra‐Fast Kelvin Wave Packets in Mars' Atmosphere and Their Interactions With Tides as Viewed by MAVEN/NGIMS and MRO/MCS

AbstractA key element of successful aerobraking operations at Mars is accurate thermospheric density predictions. Evidence suggests that much of the longitude variability in Mars' aerobraking region is associated with atmospheric tides, and the day‐to‐day variability is connected with tidal modulation by longer‐period global‐scale waves. Specifically, ultra‐fast Kelvin waves (UFKWs) and their modulation of the tidal spectrum play a key role in coupling Mars' lower (<∼80 km) and middle (∼80–100 km) atmosphere with the aerobraking region above. In this study, over 5 years of Mars Atmosphere and Volatile Evolution Neutral Gas and Ion Mass Spectrometer CO2 density observations are employed to reveal prominent, frequent, and persistent 2.5‐ to 4.5‐day UFKW packets in the whole Martian middle and upper thermosphere (ca. 150–200 km), and large secondary waves arising from their nonlinear interactions with the tidal spectrum. Detailed analyses focusing on a prominent ∼2.5‐day UFKW event in late 2015 demonstrate primary and secondary wave amplitudes growing twofold with altitude from ∼7%–14% near 150 km to ∼12%–25% near 200 km and their combined effects to account for ∼60%–80% of the altitude‐longitudinal variability of Mars' thermospheric density. Concurrent temperature measurements from Mars Reconnaissance Orbiter Mars Climate Sounder reveal consistent wave signatures near 80 km altitude suggesting propagation of both primary and secondary waves from the lower atmosphere. This study demonstrates that UFKWs and secondary waves from UFKW‐tide interactions are sources of significant altitude‐longitude variability in the Mars' aerobraking region that should be accounted for when analyzing satellite observations and nonlinear models.

Enhanced oil recovery via dissolution of low molecular weight PDMS in CO2 during immiscible gas injection in matrix-fracture system

Oil recovery in natural fracture reservoirs can be improved by reducing the capillary force during the gravity drainage process in matrix-fracture system. In the current study, a modified gas was generated via dissolution of low molecular weight poly(dimethyl siloxane) (PDMS, average Mw 3780 g/mol, 10000 – 50000 ppm) in CO2 to enhance oil recovery at 50 °C or 70 °C and 3000 psi. Cloud point measurements indicated that PDMS dissolved in CO2 at pressures less than 3000 psi, which was below the minimum miscibility pressure (MMP) of ∼3600 psi at 70 °C determined with the vanishing interfacial technique. The solution density increased from 669.6 kg/m3 for pure CO2 to 780.3 kg/m3 for CO2/PDMS (50000 ppm) at 70 °C and 3000 psi, thereby reducing the density difference between the CO2-rich fluid and crude oil (ρo=865.2 kg/m3) in matrix-fracture system. Also, CO2-oil interfacial tension (IFT) was reduced from 65 to 15 dyn/cm via the dissolution of 50000 ppm PDMS in CO2. Therefore, it led to the CO2 diffusion coefficient increased in both reservoir-fluid saturated porous media and bulk oil scenarios 3–4 fold and 4–7 fold respectively in comparison to pure CO2 injection. These PDMS-induced changes reduced the capillary effects in gas-invaded zone, which consequently led to an increase in oil recovery of 25% points (from 31% to 56%) compared to pure CO2 injection in the case of capillary continuity during gravity drainage tests. For the field-scale, because the PDMS can dissolve in CO2 at pressures and temperatures which are commensurate with CO2 EOR, it is a promising CO2-philic chemical for increasing CO2 density and improving CO2 diffusion coefficient in gas invaded zone compared to conventional CO2 injection.

Molecular CO2 Storage: State of a Single-Molecule Gas.

CO2 evolution is one of the urgent global issues; meanwhile, understanding of sorptive/dynamic behavior is crucial to create next-generation encapsulant materials with stable sorbent processes. Herein, we showcase molecular CO2 storage constructed by a [60]fullerenol nanopocket. The CO2 density reaches 2.401 g/cm3 within the nanopore, showing strong intramolecular interactions, which induce nanoconfinement effects such as forbidden translation, restricted rotation, and perturbed vibration of CO2. We also disclosed an equation of state for a molecular CO2 gas, revealing a very low pressure of 3.14 rPa (1 rPa = 10-27 Pa) generated by the rotation/vibration at 300 K. Curiously enough, the CO2 capture enabled to modulate an external property of the encapulant material itself, i.e., association of the [60]fullerenol via intercage hydrogen-bonding.

Distribution of the adsorbed density of supercritical CO2 onto the anthracite and its implication for CO2 geologic storage in deep coal

CO2 geological storage in deep coal has been a research hotspot in carbon capture and storage under the background of carbon neutrality. Understanding supercritical CO2 adsorption onto coals has been significant for accurately evaluating deep coal's CO2 geological storage capacity and further determining the deployment of a CO2-ECBM project. The supercritical CO2 adsorption experiments on dry Qinshui anthracite coal were conducted. The adsorbed CO2 density and average number of adsorbed molecule layers were calculated. The effects of temperature, pressure, and pore size on the density of the adsorbed phase were discussed using the simplified local density (SLD) adsorption model, and the distribution of adsorbed CO2 on the coal surface was disclosed. Finally, the modified method for calculating CO2 geological storage in coal was proposed. The results show that: (1) The average adsorbed density of supercritical CO2 onto the anthracite at the experimental temperatures ranged from 1.073 to 1.088 g/cm3, and the average number of adsorbed molecular layer ranged from 1.15 to 1.26, indicating the coexistence of micropore filling and multilayer adsorption. (2) The SLD theory demonstrated that the distribution of the adsorbed CO2 density is jointly controlled by temperature, pressure, pore size, and CO2 phase. The supercritical CO2 can form a second layer of adsorbed molecules. The minimum pore size to keep the adsorbed CO2 density unchanged on the pore wall is around 0.82 nm for subcritical CO2 and 3 nm for supercritical CO2. (3) The real average adsorbed CO2 density is always lower than that of the first adsorbed molecular layer and the density under extreme pressure. There are four different distributions of free and adsorbed CO2 on the surface of the coal with the changes in temperature and pressure, consisting of subcritical, gas-like supercritical, liquid-like supercritical, and extreme states. (4) The modified method of CO2 storage capacity for coal, based on excess adsorption and equivalent free CO2 in the total pore, avoids the error caused by the uncertainty of adsorbed CO2 density and free space volume. It is recommended that this method should be preferentially adopted during the selection of the potential target area for CO2 geological storage in deep coal. The study aims to provide a new idea for the mechanism of supercritical CO2 adsorption on coal and the assessment of supercritical CO2 geologic storage capacity in deep coal.

A near-infrared spectroscopic study of the conformational equilibria of lidocaine molecules in a highly concentrated lidocaine solution in supercritical CO2

In this work, we studied conformational equilibria of molecules of lidocaine in its highly concentrated solutions in scCO2 at the CO2 density values ranging from ∼1.5 to ∼2.0 of the critical value along the isotherm of 35 °C. The study was based on analyzing the spectral band related to the first overtone of the stretching vibrations of the lidocaine molecule N–H fragment. To determine the key factor affecting the formation of intermolecular hydrogen bonds between the lidocaine molecules in the solution we divided our experiment into two stages. First, in the pressure range of 100–180 bar we analyzed the spectra evolution associated with an increase in the concentration of the saturated solution. Then, in the pressure range of 180–300 bar we analyzed the spectra evolution for a solution, where the lidocaine concentration, which was reached at 180 bar, remained constant.We found that the probability of intermolecular hydrogen bond formation considerably increased with lidocaine concentration growth, which, in turn, led to a rise in the population of lidocaine molecules without an intramolecular hydrogen bond. We concluded that the formation of intermolecular hydrogen bonds caused redistribution of the conformer fractions with and without an intramolecular hydrogen bond. Finally, we showed that the key factor affecting the formation of intermolecular hydrogen bonds between the molecules of lidocaine in its solution in scCO2 is the solute concentration rather than the pressure.

Modeling solid solute solubility in supercritical carbon dioxide by machine learning algorithms using molecular sigma profiles

Supercritical carbon dioxide (ScCO2) is a solvent used in industries due to its non-toxic, non-flammable nature and unique liquid–gas properties. To predict the solubility of different solid solutes in ScCO2 for extraction or pharmaceutical process design, machine learning (ML) has been widely used to correlate the thermodynamics parameters with solubility. This work presents an investigation of the solubility of 116 drug-like solutes (comprising 2791 data points) in ScCO2 using machine learning models. Deep neural network (DNN) and random forest (RF) methods were employed with temperature, pressure, CO2 density, molecular weight, and sigma profile (σ-profile) as input features for predicting solubility. Results indicate strong ML model capabilities with R2 and ALD-x values of DNN being 0.9911 and 0.090 and those of RF being 0.9892 and 0.087, though DNN showed slightly higher errors. The effect of reducing input features of σ-profile on prediction accuracy revealed a negligible increase in error but maintained overall performance. This demonstrates that using a reduced number of σ-profile features offers practical estimation with limited computational resources. This work shows the robust potential of machine learning in accurately predicting the solubility of solids in ScCO2 using σ-profiles.

Effects of CO2 variable thermophysical properties and phase behavior on CO2 geological storage: A numerical case study

CO2 injection into the reservoir can effectively reduce greenhouse gas emissions. The thermophysical parameters and phase behavior of CO2 are highly sensitive to pressure and temperature, resulting in drastic change in wellbore and reservoir, and thus affecting the CO2 storage effect. To study the impact of CO2 thermophysical properties and phase behavior on CO2 geological storage, we established a fully coupled 1D+3D wellbore coupled 3D reservoir model. Based on the analysis of non–isothermal flow characteristics, CO2 thermophysical properties and phase behavior, the influence of engineering parameters on the key factors of CO2 geological storage is discussed. The findings indicate that the density and thermal capacity of CO2 are the most important thermophysical parameters that affect wellhead pressure and bottomhole temperature respectively. The efficiency of CO2 storage is greatly influenced by the density and viscosity of CO2, more so than any other thermophysical parameters. CO2 phase behavior and permeability change increase CO2 seepage capacity by 3.50 % and 8.79 % respectively. Engineering parameters will affect the thermophysical properties and permeability of bottom–hole CO2, thereby affecting the injectability and storage efficiency of CO2. This research can offer suggestions and theoretical groundwork for the improved design of CO2 geological storage.

Efficient supercritical carbon dioxide extraction of astaxanthin from Hematococcus pluvialis at high pressure

Astaxanthin derived from Hematococcus pluvialis (H. pluvialis) exhibits potent capacity in scavenging free radicals and quenching active oxygen. However, the conventional extraction of Astaxanthin from H. pluvialis involves the use of a substantial amount of organic reagents, leading to environmental pollution and low extraction efficiency. In this work, a high-pressure supercritical CO2 extraction (H-SFE) was applied to extract astaxanthin from H. pluvialis. Influential parameters of H-SFE were optimized by single factor, orthogonal test and kinetics experiments. Extraction pressure is a critical component influencing the extraction efficiency of SFE. Increased pressure results in increased supercritical CO2 density and thus increased solubility of substances and enhanced component extraction. The extraction yield of astaxanthin at 65MPa was 1.25 times and 2.32 times higher than that at 45MPa and 25MPa, respectively. The H-SFE extraction yield of astaxanthin was 20%-70% higher than that of ultrasonic-assisted extraction (UAE) and organic solvent extraction (OSE).