scCO2 System Research Articles

Resource Recovery of Spent Lithium-Ion Battery Cathode Materials by a Supercritical Carbon Dioxide System.

The increasing global market size of high-energy storage devices due to the boom in electric vehicles and portable electronics has caused the battery industry to produce a lot of waste lithium-ion batteries. The liberation and de-agglomeration of cathode material are the necessary procedures to improve the recycling derived from spent lithium-ion batteries, as well as enabling the direct recycling pathway. In this study, the supercritical (SC) CO2 was innovatively adapted to enable the recycling of spent lithium-ion batteries (LIBs) based on facilitating the interaction with a binder and dimethyl sulfoxide (DMSO) co-solvent. The results show that the optimum experimental conditions to liberate the cathode particles are processing at a temperature of 70 °C and 80 bar pressure for a duration of 20 min. During the treatment, polyvinylidene fluoride (PVDF) was dissolved in the SC fluid system and collected in the dimethyl sulfoxide (DMSO), as detected by the Fourier Transform Infrared Spectrometer (FTIR). The liberation yield of the cathode from the current collector reaches 96.7% under optimal conditions and thus, the cathode particles are dispersed into smaller fragments. Afterwards, PVDF can be precipitated and reused. In addition, there is no hydrogen fluoride (HF) gas emission due to binder decomposition in the suggested process. The proposed SC-CO2 and co-solvent system effectively separate the PVDF from Li-ion battery electrodes. Thus, this approach is promising as an alternative pre-treatment method due to its efficiency, relatively low energy consumption, and environmental benign features.

Analysis experimental and modeling of the solubility of an antiepileptic drug, Levetiracetam, in supercritical solvent

To formulate efficient drug delivery systems by a suitable supercritical method, the solubility of drugs in the supercritical solvent like supercritical carbon dioxide (scCO2) must be determined. In this study, solubility of Levetiracetam, a well-known antiepileptic drug, in scCO2 was studied at 308 to 338 K and 120 to 300 bar. It was obtained between the mole fractions of 2 × 10−5 to 3.05 × 10−4 and 0.03 to 0.96 kg.m−3. Also, this process was modelled using various theoretical models (empirical (Chrastil, Bartle, Kumar and Johnston (KJ) and Mendez-Santiago-Teja (MST)), PC-SAFT, SRK, and modified Wilson). All the models show the acceptable results and the deviation among the experimental and model-calculated data are satisfactory. Among them, the optimized Wilson’s model (AARD% = 6.66) and the empirical model proposed by Bartle (AARD% = 13.96) show the highest and the lowest precision, respectively. Also, the total mixing, evaporation, and solvation thermal enthalpies for the Levetiracetam- scCO2 system are computed using the empirical models.

Enhancement of 6-gingerol extraction from Bentong ginger using supercritical carbon dioxide

Supercritical carbon dioxide extraction is a green technology. It was used to isolate 6-gingerol from Bentong ginger (Zingiber officinale Roscoe var. Bentong). A central composite design (CCD) was employed to investigate and optimize three process conditions, namely the extraction pressure (10–30 MPa), temperature (40–60 °C), and particle size of the sample (300–600 µm). The method was used to model the extraction of 6-gingerol, total phenolic content, total flavonoid content, and antioxidant activity determined using 2,2-diphenyl-1-picrylhydrazyl (DPPH). The optimum conditions were estimated to be a pressure of 25 MPa, a temperature of 40 °C, and a particle size of 300 µm. The highest values for 6-gingerol content (171.26 mg/g), total phenolic content (17.84 GAE mg/g), total flavonoid content (74.46 QE mg/g), and radical-scavenging activity (91.14%) of dried Bentong ginger were achieved at these optimized conditions. The good fit between predicted and experimental values shows the fitness of the model employed for estimating the optimum conditions for Bentong ginger extraction. Moreover, the scCO2 system at the conditions studied was more effective than the conventional Soxhlet method for the extraction of bioactive compounds.

Novel mathematical and polypharmacology predictions of salicylsalicylic acid: Solubility enhancement through SCCO2 system

Over the last decades, significant drawbacks of organic solvents such as high toxicity have motivated the scientists to find more eco-friendly solvents. Supercritical fluids (SCFs), especially SCCO2, are known as a promising class of solvent, which have shown their indisputable potential of application in industrial-based pharmaceutical activities due to possessing various advantages such as high abundancy, low cost, and insignificant toxicity. Machine Learning (ML) is considered as a numerical approach to estimate drug solubility in pharmaceutical industry. The purpose of this manuscript is to estimate the solubility of salicylsalicylic acid in SCCO2 and compare it with experimental data using machine learning (ML) approach. A regression problem with 32 input vectors is the subject of this study, which is being conducted. This dataset contains two input features (P and T) and one output feature. We utilized Decision Tree (DT), K-nearest neighbor (KNN), and Multilayer perceptron (MLP) regression models as the first time for salicylsalicylic acid, which had error rates of 1.10E-01, 1.07E-01, and 7.13E-01, respectively, when using the MAPE measure. In addition, the R-squared scores for the DT, KNN, and MLP models are 0.974, 0.996, and 0.809, respectively. The third statistic is MAE, in which the error rates of models are 5.27E-05 for DT, 5.53E-05 for KNN, and 2.61E-04 for MLP. The error rates of DT, KNN, and MLP are all 5.27E-05. Finally, KNN was the most general model, with optimal values of P = 400, T = 338.0, and Y = 0.00388 being obtained.

SiO2 synergistic modification of siloxane thickener to improve the viscosity of supercritical CO2 fracturing fluid

ABSTRACT Supercritical carbon dioxide (SC-CO2) fracturing technology has the advantages of CO2 storage and waterless fracturing and has great application potential in the development of unconventional oil and gas resources. However, the low viscosity of SC-CO2 limits the development of this technology. This paper investigates the synergistic effect of nanomaterials on a developed thickener (HBD-2, high branched D4H). The research results show that among the five micro/nanomaterials Cu-BTC, SiO2, MCC, MWCNTs, and TiO2, only SiO2 has a good synergistic effect on the HBD-2/SC-CO2 system, and significantly improves its thickening, temperature resistance, temperature resistance and shear resistance. At 60s−1, 305.15 K and 10 MPa, 5 wt.% HBD-2 + 1 wt.% SiO2 increased the apparent viscosity of SC-CO2 to 5.82 mPa·s(The viscosity of 5 wt.% HBD-2 under the same conditions is 4.48 mPa·s). The apparent viscosity of SC-CO2 is positively correlated with pressure and SiO2 dosage and negatively correlated with temperature and shear rate. The SiO2/HBD-2 system can effectively avoid clay swelling and can change the water wetness on the core surface to neutral wettability. In addition, we also studied the mechanism of SiO2 in HBD-2/SC-CO2 thickening system by RDF(radial distribution function). The results show that the introduction to SiO2 shifts the peak position of the system to the left and enhances the peak intensity. The macroscopic manifestation is the enhancement of the apparent viscosity of HBD-2/SC-CO2.This paper proves the feasibility of nanomaterials to synergize SC-CO2, and provides a new thread for the research and development of SC-CO2 thickeners in the future.

Effect of process variables in supercritical carbon dioxide extraction of tocotrienols from hydrolyzed palm fatty acid distillate ( PFAD )

The recovery of tocotrienols from palm fatty acid distillate (PFAD), a by-product of palm oil, is of economic and environmental interest. In this study tocotrienols were extracted from PFAD using supercritical carbon dioxide (scCO2) at different temperatures (40–60°C) and pressures (20–40 MPa). The optimal process conditions were estimated to be 20 MPa and 53°C for 300 min and a CO2 flow rate of 32 ± 2 g/min, with 16.45 mg/g of tocotrienols extracted. Two modifications to the extraction process were then made at the optimal conditions. First, 180 min of static extraction was added before the dynamic extraction; and second, the solvent polarity was altered by adding 0.075 ml/g ethanol to the scCO2 system. These modifications significantly increased the tocotrienol extraction, to 23.62 mg/g and 30.03 mg/g, respectively. The use of scCO2 for the extraction of tocotrienols shows great potential, which might be extended to other compounds. Novelty impact statement scCO2 extraction is capable to extract tocotrienols from palm fatty acid distillate (PFAD) at optimum condition by altering the density of CO2 through manipulating pressure and temperature. The extraction of tocotrienols can be enhanced my slight modification on the scCO2 system or modifying the polarity of the CO2 solvent. The best recovery for tocotrienols extraction from PFAD was by adding 0.075 ml/g ethanol in the scCO2 system.

High yield of reducing sugar from enzymolysis of cellulose in supercritical carbon dioxide system

High concentration of reducing sugar from enzymatic hydrolysis of cellulose is the key for utilization of cellulose nowadays. Here, in-situ homogeneous enzymolysis of cellulose in supercritical carbon dioxide (SC-CO2) system by using cellulase modified with dextran (Cell-DEX) could resolve the above question. Cell-DEX can effectively hydrolyze cellulose in SC-CO2 system, and the yield of reducing sugar reaches 242 mg/g cellulose. At the same time, the effects of the modified site, molecular weight of modifier and degree of substitution, stability of Cell-DEX were discussed. Then the enzymolysis of corn straw was also studied in this system and the efficiency has been greatly improved. Therefore, it is an effective way to use cellulose sustainably.

Parametric and kinetic study of supercritical carbon dioxide extraction on sinensetin from Orthosiphon stamineus Benth. leaves

ABSTRACT Sinensetin is a rare polymethoxyflavone that possesses strong anti-angiogenesis activity that can be obtained from Orthosiphon stamineus (O. stamineus) leaves. In this study, supercritical carbon dioxide (SC-CO2) extraction was used to improve sinensetin recovery from O. stamineus leaves. The effect of mean particle size (400–550, 550–650 and 650–750 µm), modifier ratio (0, 5 and 10%, v/v), flow rate (3, 4 and 5 mL/min), temperature (40, 60 and 80 °C) and pressure (10, 20 and 30 MPa) on the concentration of sinensetin and determine its extraction rate were investigated. Two models, viz. Patricelli and Peleg were used to evaluate the kinetic behavior of sinensetin in the SC-CO2 system. Results showed that the highest concentration of sinensetin was successfully extracted at 550–650 µm, 10% (v/v), 5 mL/min, 80 °C and 10 MPa. Also, the kinetic profile of sinensetin was well correlated with Patricelli and Peleg models with a low percentage average absolute relative deviation (AARD%) and a high coefficient of determination (R2) of <6.37% and >0.974, respectively. Thus, the fastest extraction rate of sinensetin was obtained at 9.039 × 10−3 mg/g min−1 using the Patricelli model and 8.694 × 10−3 mg/g min−1 using the Peleg model at 40 °C and 30 MPa.

Biocatalytic production of isoamyl acetate from fusel oil in supercritical CO2

Isoamyl acetate esters were enzymatically synthesized from fusel oil, a by-product generated in bioethanol industrial plants, in supercritical carbon dioxide (SC-CO2) using immobilized lipase (Lipozyme 435). Effects of enzyme load (2.5–10.0 %), substrates’ molar ratio (acetic anhydride to fusel oil; 1:1–4:1), acyl donor (acetic anhydride, ethyl acetate, and acetic acid) and solvent type (SC-CO2, n-hexane, and solvent-free system) on the biocatalytic isoamyl acetate conversion and the specific productivity were investigated. Higher volumetric expansions of the reaction medium were observed at higher temperature (60 °C) between 10 and 20 MPa. A monophasic system was observed at 15 MPa and 60 °C. Acetic anhydride and SC-CO2 were the best acyl donor and solvent, respectively. An elementary mathematical model was adjusted to the experimental data. 15 MPa, 60 °C, 2:1 substrates’ molar ratio and 2.5 % of enzyme concentration yielded the highest conversion (88.4 ± 0.5 %) and specific productivity (36.9 ± 0.2 %).

Study on cloud point pressure of [Emim][Tf2N] in supercritical carbon dioxide microemulsions based on non-ionic surfactant and role of solubilized water

We studied the solubilization effect of the supercritical carbon dioxide (scCO2) microemulsion based on non-ionic surfactants (Ls-45, Ls-54, Ls-36, Dynol-604, and TMN-6) for 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Emim][Tf2N]) ionic liquid (IL) as well as the influencing factors by analyzing the cloud point pressure (CPP) curves, which served as a function of dissolved ILs concentration. The [Emim][Tf2N]/surfactant/scCO2 microemulsion system was characterized by small-angle X-ray scattering (SAXS), which was proved to be a useful method to provide structure and size information of microemulsion. The effect of water on [Emim][Tf2N]-in-scCO2 (ILs/CO2) microemulsions was studied. The results showed that the ILs/CO2 microemulsions could be constructed by five surfactants selected in this paper, and in the Ls-mn system, the Ls-45/[Emim][Tf2N]/scCO2 system had the lowest CPP. However, the microemulsion constructed by Dynol-604 and TMN-6 surfactants had a poor solubilization effect, and the TMN-6 system was more sensitive to temperature. Besides, small amounts of water could reduce the CPP of the system to a certain extent, making the [Emim][Tf2N]/surfactant/scCO2 microemulsion system more stable, which had a positive effect on the solubilization of [Emim][Tf2N], especially the Ls-36 system. Moreover, the size of microemulsion droplets in [Emim][Tf2N]/surfactant/scCO2 systems was obtained by using the method of SAXS experiment, which also confirmed the solubilization of [Emim][Tf2N] in scCO2 microemulsion system. The structure of ILs/CO2 microemulsions constructed with a non-ionic surfactant was speculated. This study can provide a reference for the construction of ILs/CO2 microemulsions, which was helpful in understanding the microstructure and solubilities of ionic liquids in scCO2 microemulsions.

Molecular Dynamics Study on the Suitable Compatibility Conditions of a CO2-Cosolvent-Light Hydrocarbon System by Calculating the Solubility Parameters

Molecular dynamics simulations were performed to calculate the solubility parameters of oil molecules (such as straight-chain alkanes, cycloalkanes, and aromatics) and CO₂ + cosolvent systems. It was found that the solubility parameter of supercritical carbon dioxide (SC-CO₂) increases with the increase of pressure at a fixed temperature, decreases with the increase of temperature at a fixed pressure, and increases linearly with the increase of the SC-CO₂ system density. The simulated results showed that the nonbonding van der Waals interaction plays a dominant role in the solubility parameter of the SC-CO₂ system. Furthermore, adding a certain amount of cosolvent into the SC-CO₂ system can evidently improve the solubility parameters of the system. The simulated solubility parameters showed that the CO₂ + 20% ethanol molecules are more effective in extracting light hydrocarbons. When the solubility parameters of CO₂ + cosolvent systems are identical to those of alkane, cycloalkane, or aromatic systems, the linear relationship between the pressure and temperature can give the guidance for selecting the cosolvent in the SC-CO₂ system in the future. Through the simulation, we concluded that the investigations about the light hydrocarbons and CO₂ + cosolvent systems can provide a theoretical model for selecting suitable external conditions for CO₂ flooding technology.

Experimental data and thermodynamic modeling of solubility of Azathioprine, as an immunosuppressive and anti-cancer drug, in supercritical carbon dioxide

The solubility of Azathioprine, as an immunosuppressive and anti-cancer drug, in supercritical carbon dioxide (SC-CO2) was measured for the first time. Under the applied conditions in terms of pressure (120–270 bar) and temperature (308–338 K), mole fractions were obtained in the range of 0.27 × 10−5 to 1.83 × 10−5. Three types of methods including (1) two equations of states (EoSs), namely Peng-Robinson (PR) and Soave–Redlich–Kwong (SRK) with vdW2 mixing rule (2) expanded liquid theory (UNIQUAC and modified Wilson models) (3) nine semi-empirical density-based models were selected to correlate the solubility data of drug. Also, two different sets were employed for obtaining critical and physicochemical properties of the solid compound. According to the results, it was found that both EoSs couple with Set1, as an estimation method for critical and physicochemical properties of Azathioprine, were capable of correlating the solubility data of drug in SC-CO2 with the higher accuracy, as compared to Set2. Also, expanded liquid theory is able to provide good predictions of solubility for Azathioprine and SC-CO2 system, this making them suitable alternatives for predicting the solubility of Azathioprine in SC-CO2. Among the semi-empirical models, Reddy and Garlapati, and Sodeifian et al. models produced the best correlation with AARD% of 7.05 and 8.04, respectively. Sodeifian et al. model competes well with Reddy and Garlapati model in solubility estimation.

Recent Advances of Supercritical CO2 in Green Synthesis and Activation of Metal–Organic Frameworks

This review considers the recent advancements of using supercritical carbon dioxide (scCO2) in the synthesis and activation of metal-organic frameworks (MOFs). The first section outlines MOF synthesis by scCO2-based methods; pure scCO2 system, and also in conjunction with a co-solvent, auxiliary ligand, expandable solvent or an ionic liquid. This is followed by elaborating on MOF activation techniques that employed scCO2, be it independently or together with thermal activation. The third section considers the effects of scCO2 on MOF and polymer structures. To conclude, projections are made for current researchers in this area to better exploit scCO2 utilization.

Study on the solubility parameter of supercritical carbon dioxide system by molecular dynamics simulation

The enhancement of the solubility parameter of supercritical carbon dioxide plays pivotal role in the application of extraction operation. The solubility parameter of supercritical CO2 solvent (SC-CO2) and supercritical CO2 with cosolvent (SC-CO2-cosolvent) system have been studied using the molecular dynamics simulations (MD). The calculated results reveal that the solubility parameters of pure SC-CO2 solvent and SC-CO2-cosolvent both reduce with the raising of temperature, enhance with the raising of pressure, and boost linearly with the raising of their density. The adding of the cosolvent (methanol, ethanol, acetone and cyclohexane) into the SC-CO2 system can enhance the solubility parameter of SC-CO2 solvent significantly, and the solubility parameter boosts with the raising of the cosolvent concentration. The cosolvent effect on solubility parameter of SC-CO2 solvent decreases in the order: methanol, ethanol, acetone, cyclohexane. The hydrogen bonding ability of the cosolvent has significant effect on solubility parameter of SC-CO2 solvent via the strengthening of the interactions among the CO2 and cosolvent molecules.

Improved respirable fraction of budesonide powder for dry powder inhaler formulations produced by advanced supercritical CO2 processing and use of a novel additive

A budesonide (BDS) suspension was obtained via advanced supercritical carbon dioxide (scCO2) processing. Thereafter, the suspension was freeze-dried (FD) to produce BDS particles for dry powder inhaler formulations (scCO2/FD processing). The scCO2/FD processed BDS powder showed low crystallinity by powder X-ray diffraction and a rough surface by scanning electron microscopy. The respirable fraction of BDS was assessed using a twin impinger and revealed that the amount of the scCO2/FD processed sample that reached stage 2 was 4-fold higher than that of the supplied powder. To extend the utility of scCO2 processing, BDS particles for dry powder inhalers were fabricated by combining the scCO2 system with various additives. When BDS was processed via scCO2/FD in the presence of the novel additive, namely, monoglyceride stearate (MGS), the residual BDS/MGS particles remaining in the capsule and devices decreased, followed by an increase in the respirable fraction of BDS 6-fold higher than with the supplied powder. The scCO2/FD processed BDS/MGS particles had a smooth surface, in contrast to the scCO2/FD processed BDS particles. A combination of BDS and an appropriate additive in scCO2 treatment may induce changes in particle surface morphology, leading to an improvement in the inhalation properties of BDS.

Modeling of Pressure Dependence of Interfacial Tension Behaviors of Supercritical CO2 + Crude Oil Systems Using a Basic Parachor Expression

Parachor based expressions (basic and mechanistic) are often used to model the experimentally observed pressure dependence of interfacial tension (IFT) behaviors of complex supercritical carbon dioxide (sc-CO2) and crude oil mixtures at elevated temperatures. However, such modeling requires various input data (e.g. compositions and densities of the equilibrium liquid and vapor phases, and molecular weights and diffusion coefficients for various components present in the system). In the absence of measured data, often phase behavior packages are used for obtaining these input data for performing calculations. Very few researchers have used experimentally measured input data for performing parachor based modeling of the experimental IFT behaviors of sc-CO2 and crude oil systems that are of particular interest to CO2 injection in porous media based enhanced oil recovery (EOR) operations.This study presents the results of parachor based modeling performed to predict pressure dependence of IFT behaviors of a complex sc-CO2 and crude oil system for which experimentally measured data is available in public domain. Though parachor model based on calculated IFT behaviors shows significant deviation from the measured behaviors in high IFT region, difference between the calculated and the experimental behaviors appears to vanish in low IFT region. These observations suggest that basic parachor expression based calculated IFT behaviors in low IFT region follow the experimental IFT behaviors more closely.An analysis of published studies (basic and mechanistic parachor expressions based on modeling of pressure dependence of IFT behaviors of both standard and complex sc-CO2 and crude oil systems) and the results of this study reinforce the need of better description of gas-oil interactions for robust modeling of pressure dependence of IFT behavior of these complex systems.

Application of combinational supercritical CO2 techniques to the preparation of inhalable particles

This study describes a supercritical CO2 (scCO2) system, which combines supercritical antisolvent (SAS) and rapid expansion from supercritical to aqueous solution (RESAS) processes, enabling the preparation of a poorly water-soluble drug (ONO-2921) as a dry powder for inhalable formulations. The SAS unit disperses the drug solution in scCO2 and the RESAS unit sprays the drug dispersion into water. Dispersing the ethanolic drug solution into a vessel purged with scCO2 practically eliminated crystallization of ONO-2921 when the CO2 pressure was more than 15 MPa at 40 °C. In contrast, a suspension containing submicron-sized particles was obtained when the scCO2-drug mixture was sprayed into water using a RESAS device. Suspensions were freeze-dried to create powdered samples for determining in vitro inhalation properties. Freeze-dried particles processed with 25 MPa of CO2 at 40 °C showed 24-fold greater deposition in the stage 2 fraction of the twin impinger than raw ONO-2921. The fine particle fraction value (aerodynamic diameter <4.7 μm) of its processed sample was 48.7% ± 0.6%. As this scCO2 approach does not require additives or excipients to prepare the particles, the pulmonary delivery of large amounts of ONO-2921 as an inhalable dry powder represents an attractive drug delivery system.

Green biodiesel production: a review on feedstock, catalyst, monolithic reactor, and supercritical fluid technology

The advancement of alternative energy is primarily catalyzed by the negative environmental impacts and energy depletion caused by the excessive usage of fossil fuels. Biodiesel has emerged as a promising substitute to petrodiesel because it is biodegradable, less toxic, and reduces greenhouse gas emission. Apart from that, biodiesel can be used as blending component or direct replacements for diesel fuel in automotive engines. A diverse range of methods have been reported for the conversion of renewable feedstocks (vegetable oil or animal fat) into biodiesel with transesterification being the most preferred method. Nevertheless, the cost of producing biodiesel is higher compared to fossil fuel, thus impeding its commercialization potentials. The limited source of reliable feedstock and the underdeveloped biodiesel production route have prevented the full-scale commercialization of biodiesel in many parts of the world. In a recent development, a new technology that incorporates monoliths as support matrices for enzyme immobilization in supercritical carbon dioxide (SC-CO2) for continuous biodiesel production has been proposed to solve the problem. The potential of SC-CO2 system to be applied in enzymatic reactors is not well documented and hence the purpose of this review is to highlight the previous studies conducted as well as the future direction of this technology.

Physical and numerical simulations of the presence of a forsterite transitional zone at high temperature and pressure: insight for scCO2 geological storage

ABSTRACTGeological sequestration is one of the most effective ways to reduce greenhouse gases, such as carbon dioxide (CO2). The deep oceanic crust dominated by ultrabasic rock could store CO2 permanently. However, the storage mechanism has not been thoroughly understood because of the limited amount of research and experiments conducted. This study explored the reactive mechanisms of water–rock–gas in an ultrabasic system under different conditions. Forsterite, the most dominant mineral found in ultrabasic reservoirs, was used to conduct laboratory physical simulation experiments. Two experimental systems were designed including an scCO2–forsterite–water system and an N2–forsterite–water system. All experiments were performed for 1000 h at an experimental temperature of 150°C and a pressure of 150 bar, respectively, to mimic the geological conditions. The liquid products from the experiments were analysed by inductively coupled plasma-optical emission spectrometry, whereas the solid samples were analysed by scanning electron microscopy with energy disperse spectroscopy. Results showed that: (1) in the early stage during scCO2/N2–forsterite–water interaction, forsterite was dissolved with a reactive transitional zone forming on the surface, which caused H+ to enter into the silicate framework and accelerated the reaction; (2) in the N2 system, the dissolution of forsterite was inhibited by the Mg2+ concentration after reaching its saturation in the late stage; and (3) in the scCO2 system, magnesite was precipitated as a secondary mineral during the late stage, which promoted the dissolution of forsterite. As a result, the degree of dissolution of forsterite in the scCO2 system was far higher than in the N2 system. The experimental results are consistent with the numerical simulation using TOUGHREACT, a geochemical simulation procedure, which showed that CO2 promotes the dissolution of forsterite greatly at high temperature and pressure.

Formation of Insulating Oxide Films with Hydrolysis Reactions of Alkoxide Precursors in Supercritical Fluid CO2: Chemistry, Morphology, Characterization and Film Thickness

ABSTRACTInsulating silicon dioxide (SiO2) films can be produced by hydrolysis of metal alkoxide tetraethylorthosilicate (TEOS) in the presence of an acid catalyst in supercritical fluid CO2 (sc-CO2). In this study, SiO2 films are formed on different substrates using TEOS as a source of silicon, and acetic acid (HAc) as a catalyst. Water required for the hydrolysis reaction is from in situ generation of esterification and condensation reactions involving HAc and the alcohol produced. The acid catalyzed deposition reaction actually starts at room temperature but produces decent films in sc-CO2 at moderately high temperatures (e.g. 50 °C). Supercritical fluid CO2 is known to have near zero surface tension and provides an ideal medium for fabrication of SiO2 films. Formation of SiO2 films via hydrolysis reaction in sc-CO2 is more rapid compared to the traditional hydrolysis reaction at room temperature. In general, metal alkoxide hydrolysis reactions carried out in a closed sc-CO2 system is not affected by moisture in air compared with traditional open-air hydrolysis systems. Using sc-CO2 as a reaction medium can eliminate undesirable organic solvents utilized in traditional alkoxide hydrolysis reactions.X-ray diffraction (XRD) and electron diffraction (ED) measurements demonstrated that the SiO2 films produced are amorphous. Energy dispersive spectroscopy (EDS), attenuated total reflectance-Fourier transform infrared (ATR-FTIR) and X-ray photoelectron (XPS) spectroscopy show elemental compositions of the films formed on the substrate surfaces to be SiO2. Film thickness formation by controlling the amount of the catalyst is discussed.