Solubility of ibuprofen in supercritical carbon dioxide

An experimental apparatus that allows measurement of solubility of solid compounds and liquids in supercritical (SC) fluids in a wide range of temperatures and pressures using a dynamic method is constructed. Experimental data on the solubility of anthracene at 318.1 and 328.1 K and results of the solubility of ibuprofen at 313, 323, and 333 K at 10–30 MPa are obtained. The solubility of ibuprofen in SC CO₂ is described using the Peng-Robinson equation of state. Parameters of binary interactions are obtained for the ibuprofen-supercritical CO₂ system.     

Conformational lability of ibuprofen in supercritical carbon dioxide

A study of conformational equilibria of ibuprofen in vacuum and supercritical carbon dioxide (SC CO₂) was carried out using methods of quantum chemistry and molecular dynamics simulation. It was found that ibuprofen forms 12 different conformations in SC CO₂, two of them correspond to the structure of the molecule in the crystal lattice of the first and second polymorph. It was shown that the GAFF force field allows one to obtain the characteristics of conformers, almost coinciding with those obtained by quantum chemical calculations at the B3LYP/cc-pVTZ level of theory.     

S-CO2布雷顿循环转化效率分析

以超临界二氧化碳简单回热型布雷顿循环为研究对象,以核电站为应用背景,详细论述了系统循环模型与关键器部件的效率模型建立方法,并利用该模型初步分析了各类工程因素对布雷顿循环效率、系统体积的影响,分析结果表明,循环效率、系统体积对温度、压力、涡轮机械效率、回热器等参数的敏感性存在较大差异,其中增加透平入口温度对缩减系统总体积最为有效,需要建立完善的系统分析模型以进行S-CO₂系统的优化设计。     

Oxidative delignification of wood in the supercritical carbon dioxide medium. 4. Acetylization of cellulose in the supercritical carbon dioxide medium

It is shown that cellulose can be acetylated with acetic anhydride in supercritical carbon dioxide in the absence of traditional catalysts, toxic solvents, and dilutants. As substrates, three cellulose samples were tested: sulfite and sulfate cellulose and cellulose obtained by low-temperature delignification in a supercritical carbon dioxide medium. The chemical composition of the cellulose diacetate product is characterized.     

Carboxylation of aromatic compounds in a supercritical carbon dioxide medium

The reaction of direct carboxylation of benzene and its derivatives PhX (X = Me, Br, Ph, OPh, OMe), as well as mesitylene, durene, and ferrocene, in a supercritical CO₂ medium in the presence of various Lewis acids (AlCl₃, FeCl₃, ZrCl₄, and ZnCl₂) is studied. It is shown that, in all cases, secondary reactions proceed faster than the primary reaction of carboxylic acid formation. For the thoroughly studied AlCl₃-CO₂toluene system, optimal conditions of the formation of n-toluic acid are determined. For the AlCl₃-CO₂-benzene system, as an example, quantum-chemical calculations of the characteristics of the allowed pathways of the carboxylation reaction are performed.     

Extraction of hydrocarbons from carbonaceous rock in supercritical carbon dioxide

Experiments on supercritical CO₂ extraction of organic matter from carbonaceous raw material show that, regardless of its geological origin, the process is characterized by selective extraction of hydrocarbons, especially alkanes and naphthenes. The composition of the supercritical extract makes it possible to use it for manufacturing lubricants.     

Dehydration and desalination of oils using supercritical carbon dioxide

A new technology for purification of oil from water, salts, and solid impurities with supercritical (SC) CO₂ before refining at existing refineries is developed. The proposed technology, along with purifying oil from water, salts, and solid particles, accomplishes its deasphalting and demetallization. The process is implemented on a facility at a pilot plant of the Institute of Petrochemical Processes of the Azerbaijan Academy of Sciences. Preliminary technical-economical calculations show that the energy expenditures on oil extraction with SC-CO₂ are significantly lower than for the existing processes.     

Benign reduction of carbon nanotube agglomerates using a supercritical carbon dioxide process

A method was developed to deagglomerate commercially available multi-walled carbon nanotube (MWCNT) bundles while maintaining the carbon nanotube aspect ratio. The process utilizes the rapid expansion of a supercritical carbon dioxide/MWCNT mixture to separate large primary carbon nanotube agglomerates. High levels of deagglomeration of Baytubes^® C 150 P and Nanocyl? NC-7000 MWCNT bundles were observed on the macroscale and nanoscale, resulting in 30-fold and 50-fold decreases in bulk density, respectively, with median agglomerate sizes <8 μm in diameter. These results were obtained while retaining the aspect ratio of the as-received nanomaterial, irrespective of the MWCNT agglomerate morphology. It was found that a temperature and pressure of 40 °C and 7.86 MP resulted in maximum deagglomeration without damage to the MWCNTs. Thermodynamic principles were applied to describe the effect of processing variables on the efficiency of the deagglomeration. These results suggest that combining this process with a composite processing step, such as melt compounding, will result in nanocomposites with enhanced electrical properties.     

Regeneration of the active aluminum oxide catalyst in supercritical carbon dioxide

The nature of the compounds inactivating the active aluminum oxide catalyst is studied. The results of the catalyst regeneration by pure supercritical carbon dioxide and by the supercritical carbon dioxide modified with a polar additive (2 wt % dimethyl sulfoxide) are presented.     

Dispersion copolymerization of methyl methacrylate and styrene in supercritical carbon dioxide

A method for producing finely dispersed powders of methyl methacrylate (MMA)-styrene copolymer by radical polymerization in a supercritical carbon dioxide medium (SC-CO₂) was proposed, studied, and experimentally implemented. The dispersing agent (surfactant), which made it possible to obtain nearly monodisperse size distribution of polymer particles, was poly(dimethylsiloxane methacrylate), a SC-CO₂-soluble substance. The copolymer, synthesized with a molecular mass of M _w ～ 36000 in the form of spherical particles with a characteristic size of ～1 μm, exhibited a higher thermal stability as compared to poly(methyl methacrylate) with a similar molecular mass. Varying the percentage ratio between MMA and styrene monomers, it was possible effectively control the integral hydrophobicity and physicomechanical characteristics of the methacrylate-styrene copolymer.     

An investigation of the dissolution of acetylsalicylic acid in supercritical carbon dioxide

The dissolution of acetylsalicylic acid in supercritical carbon dioxide (SC–CO₂) is investigated using Fourier transform IR spectroscopy. Temporal dependences of integrated intensities of the absorption band of acetylsalicylic acid (ASA) near 1199 cm^–1 are measured for various ASA charges placed into a cuvette. Molar fractions of ASA in the saturated solution in SC–CO₂ are determined at a temperature of 40°C and pressures of 10.0 and 15.0 MPa, and the components are 2.10 ± 0.25 × 10^–4 and 11.0 ± 1.5 × 10^–4, respectively.     

The ultrasonic-enhanced factor of mass-transfer coefficient in the supercritical carbon dioxide extraction

Based on several hypotheses about the process of supercritical carbon dioxide extraction, the onflow around the solute granule is figured out by the Navier-Stocks equation. In combination with the Higbie’s solute infiltration model, the link between the mass-transfer coefficient and the velocity of flow is found. The mass-transfer coefficient with the ultrasonical effect is compared with that without the ultrasonical effect, and then a new parameter named the ultrasonic-enhanced factor of mass-transfer coefficient is brought forward, which describes the mathematical model of the supercritical carbon dioxide extraction process enhanced by ultrasonic. The model gives out the relationships among the ultrasonical power, the ultrasonical frequency, the radius of solute granule and the ultrasonic-enhanced factor of mass-transfer coefficient. The results calculated by this model fit well with the experimental data, including the extraction of Coix Lacryma-jobi Seed Oil (CLSO) and Coix Lacryma-jobi Seed Ester (CLSE) from coix seeds and the extraction of Eicosapentaenoic Acid (EPA) and Docosahexaenoic Acid (DHA) from the alga by means of the ultrasonic-enhanced supercritical carbon dioxide extraction (USFE) and the supercritical carbon dioxide extraction (SFE) respectively. This proves the rationality of the ultrasonic-enhanced factor model. The model provides a theoretical basis for the application of ultrasonic-enhanced supercritical fluid extraction technique. Supported by the Major Program of the National Natural Science Foundation of China (Grant No. 10674048) and the Natural Science Foundation of Guangdong Province (Grant No. 06025714)     

Separation of low-molecular-weight fractions of ultrafine polytetrafluoroethylene with supercritical carbon dioxide

The separation of low-molecular-weight fractions of FORUM® ultrafine polytetrafluoroethylene (UPTFE) in supercritical carbon dioxide (SC-CO₂) was studied under static conditions. The experiments were performed over temperature and pressure ranges of 318–383 K and 10–70 MPa, respectively. Over the entire pressure and temperature ranges covered, a behavior typical of solid substance-SC-CO₂ systems was observed: as the pressure and temperature of the solvent increased, so did the concentrations of low-molecular-weight UPTFE fractions in it. The experimental data were interpreted within the framework of three models establishing a relationship between the solubility of a substance with the supercritical fluid density, those proposed by Chrastil, Bartle, and Mendez-Santiago. The experimental data were closely described by the Bartle and Mendez-Santiago models.     

Fabrication of highly porous bioresorbable polymer matrices using supercritical carbon dioxide

A new method for fabrication of highly porous bioresorbable polymer structures on the basis of various aliphatic polyesters for tissue engineering has been successfully designed and worked out. It has been shown that injection of polymer compositions plasticized in sub- or supercritical carbon dioxide into press forms at temperatures from 20 to 40°C through a nozzle of a certain diameter under atmospheric or elevated (up to 6 MPa) CO₂ pressure allows obtaining polymer matrices with a desired structure and morphology and mean porosity of up to 96 vol % with high reproducibility and avoiding the use of toxic organic solvents. The effect of chemical composition and molecular mass of starting polymers, as well as temperature and CO₂ pressure in the reaction cell and the receiver, on the morphology and internal structure of fabricated samples was studied using the method of scanning-electron microscopy.     

A Study of ibuprofen solubility in supercritical carbon dioxide by Fourier-transform infrared spectroscopy

In the work, a method of study of solubility of pharmaceutical substances in high-pressure gases and supercritical media with Fourier-transform IR spectroscopy has been developed. An investigation of the process of ibuprofen dissolution in supercritical carbon dioxide (SC CO₂) in a real-time scale has been performed. On the basis of analysis of the time dependences of the integral intensities of the selected IR-absorption bands of ibuprofen on the value of the initial weighed portion the value of solubility (molar fraction) of ibuprofen in SC CO₂ at a temperature of 35°C and pressure of 15.0 MPa was obtained, being equal to (8.9 ± 1.6) × 10^?3.     

运用液体声学理论研究超临界二氧化碳的声特性

利用液体声学模型,根据美国国家标准局提供的二氧化碳声速、密度、摩尔体积和绝热压缩系数数据,计算了气态、液态和超临界态二氧化碳在不同温度和压力条件下的摩尔声速、摩尔压缩系数及Van der Waals 常数. 分析发现,在较宽的温度和压力范围内,液体中的声学模型能够很好地运用于超临界态二氧化碳的研究. 并在液体声学模型适用范围内,计算了超临界二氧化碳在不同温度及压力状态下的表面张力、粘度、自扩散系数,为超临界流体技术提供了参考数据,并分析了这些参量的变化规律. 关键词： 超临界二氧化碳 声速 摩尔声速 摩尔压缩系数     

运用液体声学理论研究超临界二氧化碳的声特性

利用液体声学模型，根据美国国家标准局提供的二氧化碳声速、密度、摩尔体积和绝热压缩系数数据，计算了气态、液态和超临界态二氧化碳在不同温度和压力条件下的摩尔声速、摩尔压缩系数及Van der Waals 常数. 分析发现，在较宽的温度和压力范围内，液体中的声学模型能够很好地运用于超临界态二氧化碳的研究. 并在液体声学模型适用范围内，计算了超临界二氧化碳在不同温度及压力状态下的表面张力、粘度、自扩散系数，为超临界流体技术提供了参考数据，并分析了这些参量的变化规律.     

Ethylene terephthalate oligomers in the processes of modification of polyester fabrics in supercritical carbon dioxide

The influence of the conditions of processing of polyester fiber material in the supercritical carbon dioxide (SC-CO₂) medium on the localization of ethylene terephthalate cyclic oligomers on the surface of fibers is studied. It is shown that cyclic oligomers are deposited on the surface of polyester fiber materials in the form of large associates. The mechanism of migration of oligomers from the interior of polyester fibers plasticized in the SC-CO₂ medium is considered. Recommendations to minimize the amount of surface oligomers in the dyeing of polyester fiber materials in SC-CO₂ are given. It is shown that the deposition of oligomers on the surface of polyester fabric does not adversely affect the quality of their hydrophobization with ultrafine polytetrafluoroethylene in the SC-CO₂ medium.     

Hydrophobic properties of carbon fabric with Teflon AF 2400 fluoropolymer coating deposited from solutions in supercritical carbon dioxide

A method for uniform deposition of a hydrophobizing polymer from a solution in supercritical carbon dioxide (SC-CO₂) onto the surface of carbon fabric used for manufacturing gas diffusion layers of fuel cells is developed. This approach, based on using Teflon AF 2400, a SC-CO₂-soluble copolymer, is compared to the traditional method for hydrophobization of the gas diffusion layer of a fuel cell, based on the use of an aqueous dispersion of Teflon 30N. Hydrophobizing polymers were deposited on the surface of a highly rough carbon fabric (Saati), an electrically conductive gas diffusion layer material with good mechanical and resource characteristics. In one of the versions of the method of deposition from SC-CO₂, the hydrophobic film was subjected to additional annealing at a temperature above the glass transition temperature of Teflon AF 2400 amorphous copolymer. It is shown that this approach makes it possible to form a uniform thin fluoropolymer film on carbon fibers, which imparts the most stable superhydrophobic properties to the surface of the gas diffusion layer at very low amounts of deposited polymer. In this case, the contact angle reaches a value much greater than that previously reported in the literature for similar methods. Prolonged immersion in water (for 1000 h) or wash in the presence of detergent does not impair the superhydrophobicity of the gas diffusion layer. The developed gas-diffusion layer was used to prepare an electrode for phosphoric fuel cell, the current-voltage characteristic of which indicates a satisfactory performance. The results obtained show that adopted approach is promising for developing gas diffusion layers for fuel cell electrodes.