Supercritical Carbon Dioxide Environment Research Articles

Decellularization of bone tissue in a supercritical carbon dioxide environment

The use of pig bone tissue as a graft makes it possible to obtain high-quality, relatively cheap and biocompatible ECM. This is since the mineral composition of pork bone is most similar to the mineral composition of human bone. Decellularization in SC-CO2 is a promising direction, since carbon dioxide easily diffuses into the depth of the cell and is a good solvent for lipids, it is non-flammable, non-toxic and chemically non-aggressive. In this paper, the ECM in SC-CO2 was obtained in three ways: 1) in dynamic mode with large SC-CO2 flows; 2) in static and dynamic modes with large SC-CO2 flows; 3) in static and dynamic modes with large SC-CO2 flows, with preliminary exposure in ethyl alcohol as a co-solvent. According to the histological examination, the removal of ICC by the first method is 55%. The use of a co-solvent before starting the decellularization process increases the percentage of ICC removal to 98%, which allows the use of ECM as a transplant.

Femtosecond Laser Fabrication of Silver Microstructures in Nanoporous Glasses

This paper presents the results of studying the process of laser formation of microstructures from silver nanoparticles in nanoporous quartz glasses. Glass samples were impregnated with organometallic molecules Ag(hfac)COD in a supercritical carbon dioxide environment. The formation of point and linear microstructures was carried out by high-frequency (70 MHz) femtosecond laser radiation with a wavelength of 525 nm and energy in the pulse up to 1 nJ. It was found that the formation of microstructures occurs due to photo- and thermal decomposition of precursor molecules with the formation of plasmonic silver nanoparticles. It is shown that the developed temperatures can exceed the melting point of glass, which leads to the appearance of microstructures with altered refractive index. A qualitative model explaining the individual stages of cluster formation in the glass volume under point laser impact is presented.

Corrosion Behavior of Alumina-Forming Austenitic Steel in Supercritical Carbon Dioxide Conditions: Effects of Nb Content and Temperature.

The corrosion behavior of alumina-forming austenitic (AFA) stainless steels with different Nb additions in a supercritical carbon dioxide environment at 500 °C, 600 °C, and 20 MPa was investigated. The steels with low Nb content were found to have a novel structure with a double oxide as an outer Cr2O3 oxide film and an inner Al2O3 oxide layer with discontinuous Fe-rich spinels on the outer surface and a transition layer consisting of Cr spinels and γ'-Ni3Al phases randomly distributed under the oxide layer. Oxidation resistance was improved by accelerating diffusion through refined grain boundaries after the addition of 0.6 wt.% Nb. However, the corrosion resistance decreased significantly at higher Nb content due to the formation of continuous thick outer Fe-rich nodules on the surface and an internal oxide zone, and Fe2(Mo, Nb) laves phases were also detected, which prevented the outward diffusion of Al ions and promoted the formation of cracks within the oxide layer, resulting in unfavorable effects on oxidation. After exposure at 500 °C, fewer spinels and thinner oxide scales were found. The specific mechanism was discussed.

An Experimental Investigation of Supercritical Methane Injection Characteristics in a CO2 Environment

Abstract Clean energy generation is gaining significant attention from industries, academia, and governments across the globe. The Allam cycle is one such technology that has been under focus due to its efficiency, environmental friendliness, and economics. This is a direct-fired cycle operating at supercritical conditions using carbon dioxide as a working fluid. Fuel or oxidizer jet mixing with CO2 is a vital phenomenon that governs combustion efficiency, and it is not well understood for the Allam cycle conditions. This paper experimentally investigated the jet characteristics of a methane jet injected into a subcritical to supercritical carbon dioxide environment. A wide range of injection pressures and temperatures were targeted between subcritical to supercritical conditions. Unlike previous studies, the current work focused on injecting lower-density (methane) jets into higher-density (carbon dioxide) environments. Schlieren imaging and methane absorption measurements were simultaneously performed with a CMOS high-speed camera and a 3.39 μm infrared laser. Specifically, we looked at the classical injection parameter of jet spreading angle, which was classically established to be mainly a density ratio function. Here, the jet cone angle was obtained from the postprocessed schlieren imaging. The jet cone angle is a critical characteristic parameter that describes the entrainment rate in a jet; thus, it is a crucial parameter in understanding the nature of the jet. The laser measurements were only used as an additional check to confirm the entry time of methane into the chamber filled with carbon dioxide. Notably, this paper makes a detailed comparison between the jet cone angles of jets with a density ratio. The result showed that the classical correlations, such as Abramovich's theory applied to submerged turbulent gas jets developed for low-density ratio jets, were unsuitable for higher-density ratio jets. It was also observed that the divergence angles were dependent not only on density ratio but also on other parameters such as pressure ratios and reduced pressures.

Corrosion behavior of T91 tubing in high temperature supercritical carbon dioxide environment

The effect of stress on the corrosion behavior and mechanical properties of T91 tube exposed to high-temperature supercritical carbon dioxide (S-CO2) was investigated. Both yield strength, ultimate tensile strength, and elongation of T91 tube was decreased after being exposed to S-CO2. Besides, a large number of carbide precipitates were observed in the Fe-Cr-rich corrosion layer of T91 tube, which was attributed to higher ion diffusion and carburizing rate under the action of stress. As a result, the corrosion rate of T91 tube was significantly faster than that of T91 coupon.

Co-gasification of waste lignin and plastics in supercritical liquids: Comparison of water and carbon dioxide

Waste lignin and plastic can be converted into useful syngas by co-gasified in supercritical liquids. In this work, lignin with β-O-4 linkages and two kinds of common plastics, polyethylene and polypropylene, were simulated in the process of co-gasification. The processes in supercritical water (SCW) or supercritical carbon dioxide (SCCO2) environment at different temperatures and ratios of reactants were studied comparatively using ReaxFF molecular dynamics simulations. The composition of products has been analyzed, the co-gasification synergistic effect has been explored, and the reaction mechanisms were provided and compared. The addition of plastic increased the production of H2 in both the SCW and SCCO2 systems The effect of adding plastics on the initial pyrolysis of lignin in SCW was greater than that in SCCO2, resulting in the production of more H2 and CH4 and less CO in the SCW system.

Turbomachine Operation with Magnetic Bearings in Supercritical Carbon Dioxide Environment

In the sCO2-HeRo project, the Chair of Turbomachinery at the University of Duisburg-Essen developed, built and tested a turbomachine with an integral design in which the compressor, generator and turbine are housed in a single hermetic casing. However, ball bearings limited operation because their lubricants were incompatible with supercritical CO2 (sCO2) and they had to operate in gaseous CO2 instead. To overcome this problem, the turbomachine was redesigned built and tested in the sCO2-4-NPP project. Instead of ball bearings, magnetic bearings are now used to operate the turbomachine with the entire rotor in sCO2. This paper presents the revised design, focusing on the usage of magnetic bearings. It also investigates whether the sCO2 limits the operating range. Test runs show that increasing the density and rotational speed results in greater deflection of the rotor and greater forces on the bearings. Measurements are also analyzed with respect to influence of the density increase on the destabilizing forces in the rotor–stator cavities. The conclusion is that for the operation of the turbomachine, the control parameters of the magnetic bearings must be adjusted not only to the rotor speed, but also to the fluid density. This enabled successful operation of the turbomachine, which reached a speed of about 40,000 rpm during initial tests in CO2.

Simulation of softwood lignin gasification in supercritical carbon dioxide

Abundant renewable lignin resources have attracted increasing attention. Supercritical carbon dioxide exhibits excellent catalytic gasification properties. In this study, a molecular model for softwood lignin was established as a reactant. The ReaxFF molecular dynamics simulation method was used to simulate the gasification of softwood lignin in a supercritical carbon dioxide environment with platinum nanoparticles as catalysts. A slow temperature increase (80 K/ps) was used, and the system was studied at a constant temperature of 1700 K. The cleavage of different bonds at the initial stage of the reaction was studied, and the different gasification productions under the action of the catalyst in supercritical carbon dioxide were analysed and compared with those under non-catalyst conditions. The results showed that with the addition of the catalyst, the amount of CO2 cracking increased, the number of H2 and CO molecules produced increased, and the reaction rate increased.

Investigation on crystallization phenomena with supercritical carbon dioxide (CO2) as the antisolvent

Abstract The supercritical antisolvent (SAS) recrystallization process is one of the most promising recrystallization techniques for the particle formation of pharmaceutical compounds. In this process, a solution of active pharmaceutical ingredient (API) is sprayed into the supercritical carbon dioxide (SC CO2) environment. The mass transport of both the solvent and the antisolvent results in supersaturation followed by the crystallization of the API. In this work, a model is developed to estimate the supersaturation profile of solute in a droplet falling in the SC CO2 environment. The droplet consists of paracetamol as a solute and ethanol as a solvent. It moves down in the antisolvent (supercritical CO2) environment. Interestingly, the present model predicts a rise in supersaturation followed by a fall for a while and then a sharp increase. The competing phenomena of nucleation and growth mechanisms are used to justify this variation in the supersaturation.

Corrosion and creep behavior of a Ni-base alloy in supercritical-carbon dioxide environment at 650 °C

Creep tests were performed for a nickel-base alloy, Ni-16Cr-9Fe, in air, atmospheric CO2, and supercritical-carbon dioxide (S-CO2) at 650 °C. Creep rupture lives in S-CO2 were shorter compared to air and CO2 environments, and the difference was greater at lower applied stress. Combined effects of applied stress and high pressure caused the formation of thicker oxides, which were subjected to extensive cracking and spallation during creep tests in S-CO2. Cracks were found to propagate through the Al- and Ti-rich internal oxides formed at grain boundaries, resulting in reduced creep rupture life in S-CO2 environment.

Development of aluminide diffusion coatings on ODS ferritic-martensitic steel for corrosion resistance in high temperature super critical-carbon dioxide environment

Aluminide diffusion coatings were applied on an oxide dispersion strengthened ferritic-martensitic (ODS-FM) steel as surface modification methods. Either thin layer of Al or NiAl was deposited on the ODS-FM steels, which were subjected to inter-diffusion heat treatment (IDHT) to produce Al-IDHTed or NiAl-IDHTed specimens, respectively. After corrosion test in high temperature super-critical carbon dioxide (S-CO2), both Al-IDHTed and NiAl-IDHTed specimens showed significantly improved corrosion resistance with lower weight gains and effectively supressed carburization in the matrix. The improvement in corrosion resistance was attributed to the presence of continuous alumina layer on top of surface layer. For Al-IDHTed specimen, extensive diffusion of Al from surface layer and inter-diffusion zone to substrate was observed after the S-CO2 corrosion test. However, for NiAl-IDHTed specimen, an Al-rich surface layer was well-maintained after S-CO2 corrosion as Ni acted as a diffusion barrier.

High-temperature corrosion resistance of nickel-base alloy 617 in supercritical carbon dioxide environment

Corrosion behavior of Inconel 617 in supercritical carbon dioxide at 650 °C and 15 MPa for 1000 h was investigated. X-ray diffraction, high-resolution transmission microscopy, and Raman spectrum were used to observe and analyze the corrosion products formed on Inconel 617. The results showed that the corrosion products formed on Inconel 617 were composed of a thick Cr2O3 layer, a thin Al2O3 layer and a carbon-penetrated zone from the interface between carbon dioxide and the oxide scale to the substrate. Carbon was deposited on the surface of the oxide scales, which was verified by Raman results. The oxidation of Inconel 617 suffered in supercritical carbon dioxide was more serious than the carburization of Inconel 617.

Cr diffusion coating to improve the corrosion resistance of an ODS steel in super-critical carbon dioxide environment

The surface of oxide dispersion strengthened (ODS) steel was deposited with Cr by physical vapor deposition, followed by inter-diffusion heat treatment (Cr-IDHTed) to form a thin outer Cr-rich carbide layer and inter-diffusion zone below it. When exposed to super-critical carbon dioxide (S-CO2) environment at 650 °C in 20 MPa for 500 h, a continuous and protective Cr2O3 layer was formed on Cr-IDHTed ODS steel, resulting in marked reduction in weight gain compared to the as-received one. On the other hand, thick Fe-rich oxides were formed on the as-received ODS steel, resulting in a significant weight gain. The as-received ODS steel showed near complete loss of tensile ductility after S-CO2 exposure due to extensive carburization in matrix. However, because of the presence of thin Cr-rich oxide layer on the surface, carburization was prevented and the change in tensile properties was minimized for Cr-IDHTed ODS steel.

Corrosion and Carburization Behavior of Heat-Resistant Steels in a High-Temperature Supercritical Carbon Dioxide Environment

The corrosion behavior of heat-resistant steels, including T91, VM12, Super 304H, and Sanicro 25, in high-temperature supercritical carbon dioxide at 650 °C and 15 MPa for 1000 h was investigated. X-ray diffraction, Raman spectroscopy, and glow-discharge optical emission spectrometry were employed to characterize the corrosion products. The results showed that the weight gain of the investigated steels is in the order of T91 > VM12 > Super 304H > Sanicro 25. Compared with the dual layers of Fe3O4 and FexCr3−xO4 on T91 and VM12, the chromia-rich oxide scales on Super 304H and Sanicro 25 enhanced their corrosion resistance. Internal carburization zones were found underneath the oxide scales, indicating the presence of oxidation and carburization reactions in the supercritical carbon dioxide. Moreover, the total carbon uptake into the T91 and VM12 steels approximately followed a parabolic law with experimental time but followed a linear law for the austenitic heat-resistant steel Sanicro 25. A corrosion mechanism that couples oxidation and carburization is summarized and quantified for oxidation and carburization to determine the dominant reaction.

Corrosion behaviors of four stainless steels with similar chromium content in supercritical carbon dioxide environment at 650 °C

The corrosion behavior of four stainless steels (SSs) with similar chromium content was investigated in supercritical carbon dioxide environment. Overall, weight gain was the smallest for 630 SS which formed thin and continuous Cr-rich oxide layer. Due to large Mn3O4 nodules, weight gain was larger for 430 SS. For 347H and 316LN SSs, thick duplex oxide layers were formed following the extensive oxide spallation, resulting in much greater weight gains than 430 and 630 SSs. The oxide spallation was explained by the formation of Nb-rich layer or amorphous matters at the matrix/oxide interface as well as the matrix structure.

2-Chlorobenzoylthiourea-modified MCM-41 for Drug Delivery

Mesoporous 2-Chlorobenzoylthiourea-modified MCM-41 was prepared and loaded with ibuprofen in a supercritical carbon dioxide (sC-CO2) environment. 2-chloro-benzoythiourea modified MCM-41 was prepared and also characterized via XRD, FT-IR, SEM and BET techniques. The (100) and (110) reflections observed at low angle XRD show the mesoporous SiO2 structure. The paticule size of non-uniform spheres were observed at a range of 250-305 nm. BET surface areas were calculated as 1506 m2 / g for MCM-41 and 306 m2/g 2-chloro-benzoythiourea modified MCM-4, respectively. The absorption and releasing studies of ibuprofen were caried out in simulated body fluid. The result revealed that high adsorption capacity for drug with 2-chloro-benzoythiourea modified MCM-41 and slower drug release rate was achieved.

Oxidation behavior of high-strength FeCrAl alloys in a high-temperature supercritical carbon dioxide environment

The oxidation behavior of three high-strength FeCrAl alloys was investigated in supercritical carbon dioxide environment at 650 °C. After exposure for 500 h, the weight gains of the FeCrAl alloys gradually decreased with increasing Al content. The oxide scales are primarily composed of α-Al2O3 and spinel oxides. With increasing Al content, the amount of α-Al2O3 increases and the C content decreased in the oxide scale and sub-scale matrix. Moreover, larger (Nb,Mo)C carbides formed in the sub-scale matrix and their number decreased with the increase of Al content.

Surface modification of Kevlar fiber by nanoSiO2 deposition in supercritical fluid

ABSTRACTIn this work, we modified Kevlar fiber first by depositing nano SiO2 on its surface from sol-gel reaction of tetraethylorthosilicate (TEOS) and formic acid using supercritical carbon dioxide (scCO2) as the solvent. The results showed that the Kevlar fiber surface can be successfully deposited with nano SiO2 in this manner while its properties were hardly affected by the supercritical carbon dioxide environment. However, special attention needs to be given to an optimal scCO2 pressure for the purpose of enhancing the interfacial adhesion and shear strength between Kevlar fiber and epoxy resin as too low or too high pressures result in certain morphologies of deposited nano SiO2 particles that give rise to insufficient penetration of the resin into the fiber surface. Plasma treatment was found to provide a significant surface etching effect that is more effective than nano SiO2 deposition alone. Moreover, it has such a synergistic effect with nano SiO2 deposition that when they were employed sequentially, the interface between the Kevlar fiber and the epoxy resin has the strongest adhesion and shear strength, which are 83.6% higher than those in the original composite with no surface treatment.

Surface modification of austenitic stainless steel for corrosion resistance in high temperature supercritical-carbon dioxide environment

Surface-modification was applied to austenitic stainless steel 316LN in order to improve the corrosion resistance in high temperature supercritical-carbon dioxide (S-CO2) environment. The surface-modification methods consisted of deposition of either a single Al layer or a NiAl bi-layer on the surface, followed by inter-diffusion heat treatments. The former resulted in formation of a surface layer composed of a mixture of NiAl and ferrite phases, and the latter resulted in formation of a continuous NiAl surface layer. Surface-modified 316LN showed reduced weight gains than the as-received 316LN alloy after exposure to S-CO2 at 650 °C (20 MPa) for 500 h. Pre-oxidation in helium at 900 °C before S-CO2 exposure further improved corrosion resistance by forming inner α-Al2O3 layer. On the other hand, the extent of inter-diffusion zone was less for the specimen with a continuous NiAl surface layer before and after S-CO2 exposure.

Characterization of Alloy 600 joints exposed to a high-temperature supercritical-carbon dioxide environment

Two types of Alloy 600 joints, such as diffusion-bonded joint and Alloy 182 fusion-weld, were exposed to supercritical-CO2 environment at 550 and 650 °C (20 MPa) for 1000 h. The diffusion-bond region showed similar oxidation characteristics as parent Alloy 600, but the migration of diffusion bond line below oxide layer was observed due to the Cr-depletion induced recrystallization. For Alloy 182 fusion-weld, outer Mn-rich oxides (Mn3O4 and MnCr2O4) and a small amount of inner SiO2 mixed with chromia were formed due to high Mn and Si contents. The presence of SiO2 in chromia suppressed carburization at the oxide/matrix interface, which resulted in the formation of an amorphous C layer between the outer Mn-rich oxide and inner Cr-rich oxide. For Alloy 182 fusion-weld, tensile property changes after exposure to supercritical-CO2 environment were negligible.