Hydrophobization of porous ceramic materials using supercritical carbon dioxide

A process has been proposed for hydrophobizing an inorganic porous material consisting of silica fibers using fluoroalkane dissolution in supercritical carbon dioxide. The process allows one to produce thin, homogeneous polymer coatings both on the surface and in the bulk of the material, ensuring that the material has excellent hydrophobic properties, which significantly improves its performance parameters and extends its potential application field.     

Itraconazole formation using supercritical carbon dioxide

A new method of preparing Itraconazole (C₃₅H₃₈Cl₂N₈O₄), a synthetic triazole antifungal agent, was developed using supercritical carbon dioxide (SC CO₂) while eliminating the use of toxic solvents. Dissolution amounts of the product were measured in gastric fluid and compared to those of conventional drug formulations. Different operating conditions (five levels of treatment temperature ranging between 110-140°C, four levels of treatment pressure ranging between 30-400 atm, and four different treatment times ranging from 10-60 minutes) were tested in order to produce a desired Itraconazole product, which does not degrade during the product formation and has the highest extent of dissolution in gastric fluid after one hour. Itraconazole dissolution of 100% at one-hour was achieved for the drug produced at the optimum treatment condition: 135°C, 300 atm, and 30 minutes. Extent of dissolution obtained from this solvent and detergent-free process is 10% higher than that of the conventional method involving toxic organic solvents. Itraconazole produced using SC CO₂ should provide minimal side effects in human body.     

Preparation and characterization of progesterone dispersions using supercritical carbon dioxide

Context: Supercritical fluid methods offer an alternative to conventional mixing methods, particularly for heat sensitive drugs and where an organic solvent is undesirable.

Objective: To design, develop and construct a unit for the particles from a gas-saturated suspension/solution (PGSS) method and form endogenous progesterone (PGN) dispersion systems using SC-CO₂.

Materials and methods: The PGN dispersions were manufactured using three selected excipients: polyethylene glycol (PEG) 400/4000 (50:50), Gelucire 44/14 and D-α-tocopheryl PEG 1000 succinate (TPGS). Semisolid dispersions of PGN prepared by PGSS method were compared to the conventional methods; comelting (CM), cosolvent (CS) and physical mixing (PM). The dispersion systems made were characterized by Raman and Fourier transform infrared (FTIR) spectroscopies, X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), PGN recovery, uniformity and in vitro dissolution, analyzed by high-performance liquid chromatography (HPLC).

Results: Raman spectra revealed no changes in the crystalline structure of PGN treated with SC-CO₂ compared to that of untreated PGN. XRPD and FTIR showed the presence of peaks and bands for PGN confirming that PGN has been incorporated well with each individual excipient. All PGN dispersions prepared by the PGSS method resulted in the improvement of PGN dissolution rates compared to that prepared by the conventional methods and untreated PGN after 60 min (p value?Conclusion: The novel PGN dispersions prepared by the PGSS method offer the great potential to enhance PGN dissolution rate, reduce preparation time and form stable crystalline dispersion systems over those prepared by conventional methods.     

超临界二氧化碳物性参数测量方法综述

对于超临界二氧化碳(S-CO2)物性参数的获取,一般可从美国国家标准与技术研究院(NIST)直接查询,但S-CO2在临界点处物性发生剧烈变化.在实际工业应用中,S-CO2的密度、粘度和热导率这3个方面对与超临界二氧化碳布雷顿循环的研究有着很重要的作用,为了解目前S-CO2物性的测量方法,该文对当前所涉及到的S-CO2基...     

Quantitative morphology analysis of polymers foamed with supercritical carbon dioxide using Voronoi diagrams

Porous polymeric materials have a good impact strength, light weight and high porosity. Therefore, these foams are used in a wide range of applications, including insulation, separation processes and packaging. Since it is important to have an objective comparison of polymeric foams, this paper discusses a quantitative method using Voronoi diagrams, which has been developed to analyze and compare different morphologies of polymers foamed with supercritical carbon dioxide, based on the average cell area, cell area distribution and homogeneity. In contrast to SEM analysis only, different foam morphologies can be compared with this technique in an objective manner. The analysis is based on the centers of the cells and is therefore to a large extent independent of the sample preparation. Using the Voronoi-approach, it is possible to extrapolate the 2D view of the SEM picture to a 3D representation of the foam with the thickness of one cell layer.     

Drying of silica gels with supercritical carbon dioxide

Results of drying experiments of aerogels with supercritical carbon dioxide are reported. In addition to the results of experiments with a pilot extracting apparatus, a preliminary design is also given of a large-scale supercritical carbon dioxide extraction plant to be used for drying of aerogels. From the experiments it was found that crack-free aerogels could be obtained when drying with carbon dioxide under supercritical conditions. The lowest temperature and pressure at which crack-free aerogel samples were obtained was at 35 °C and 85 bar, respectively. The temperature had a minor influence on the drying time. It was also found that the diffusion of ethanol into the aerogel pores limits the drying time. This limitation implies that the thickness of the aerogel tiles will have a large influence on the cost of drying of an aerogel.     

超临界二氧化碳流动和换热研究进展

综述了国际上对超临界二氧化碳管内换热和压降特征的研究。提供了多种公开发表的超临界流体在冷却工况下的换热关联式及单相压降关联式,将实验关联式的计算结果与文献中的实验数据进行对照,在此基础上对关联式的准确性进行了讨论。同时指出了现有研究内容的不足。     

Extraction of chromated copper arsenate from wood wastes using green solvent supercritical carbon dioxide

To provide a green method to remove chromated copper arsenate (CCA) in the wood before its dumping, incineration, reuse or disposal, extraction of CCA from wood wastes using supercritical carbon dioxide (ScCO(2)) containing an organophosphorus reagent, Cyanex 302, was investigated. The majority of copper metal was removed using Cyanex 302 in supercritical fluid extraction (SFE). The order of extraction efficiency was found to be Cu>As>Cr. Factors that affected SFE efficiencies, such as matrices, oxidation state of metal species [Cr(III), Cr(VI), As(III), and As(V)], and SFE pressure, were studied. Using this in situ chelation/SFE technique to remove leachable metals from the CCA-treated wood was found to significantly reduce the risk of leaching metals into the environment during storage, or waste disposal.     

Synthesis of manganese oxide electrocatalysts in supercritical carbon dioxide

In this work, a novel method of preparing manganese oxide nanoparticles from an organometallic precursor dissolved in supercritical carbon dioxide (sc CO₂) was presented. Using the new approach, nanomaterials mostly consisting of manganese oxides in β-MnO₂ and ε-MnO₂ phases with small-sized (~?40 nm) grains and low polydispersity index (~?0.12) can be synthesized, which was consistently proved by means of thermogravimetric and X-ray diffraction analysis, scanning and transmission electron microscopy. Moreover, reasonable electrocatalytic activity of the obtained materials was detected by a rotating disk electrode method.     

Derivatization of chiral amino acids in supercritical carbon dioxide

A new method is proposed to perform the derivatization of chiral amino acids occurring in complex samples using supercritical carbon dioxide as both the reaction medium and the agent used to extract the obtained derivatives prior to accomplishing the subsequent enantiomeric chromatographic analysis. The derivatization step under supercritical conditions involves the esterification of the carboxyl group and the acylation of the amino group of the amino acids without using a catalyst. A Chirasil-L-Val capillary column enabled the separation of the D- and L-forms of the amino acids as their N(O)-pentafluoropropionyl 1-propyl esters. Relative standard deviation values obtained from the gas chromatographic analysis for the derivatized amino acids ranged from 5 to 15%.     

Synthesis of epoxy ferrite nanocomposites in supercritical carbon dioxide

A series of epoxy ferrite nanocomposites (EFNCs) was synthesised through dispersing ferrite nanoparticles (5.0 phr, parts per hundred of resin) into diglycidylether of bisphenol A (0.1 mol) in supercritical carbon dioxide at 85 ± 1°C, 1600 psi over 1 h followed by curing with triethylene tetramine (15 phr) at 40 ± 1°C. For this purpose, ferrite nanoparticles were synthesised through size-controlled precipitation method. The size of ferrite nanoparticles was calculated through XRD and further verified through transmission electron microscopy. The synthesised EFNCs were characterised through UV-Vis, FT-IR, laser-induced breakdown spectra, X-ray diffraction, scanning electron microscopy and vibrational sample magnetometry. The results showed that, with the decrease in size, the concentration of ferrite nanoparticle in EFNCs was increased ranging 3.843–4.042 phr. This resulted in a substantial increase in the compression, tensile, impact strength and Rockwell hardness of EFNCs. The effect of particle size on wear behaviour of EFNCs was investigated at various combinations of hydraulic end load ranging 1.0–3.0 bar and disc speed 230 rpm, which showed that a decrease in the size of ferrite nanoparticles imparts a remarkable reduction in wear volume over epoxy composite. All such EFNCs showed superparamagnetic behaviour with saturation magnetisation ranging 15.8–39.91 emu g^?1.     

Characterization of chromia scales formed in supercritical carbon dioxide

Abstract

Initial experimental work at 700°–800 °C is in progress to develop a lifetime model for supercritical CO₂ (sCO₂) compatibility for a 30-year lifetime of a >700 °C concentrated solar power system. Nickel-based alloys 282, 740H and 625 and Fe-based alloy 25 are being evaluated in 500-h cycles at 1 and 300 bar, and 10-h cycles in 1 bar industrial grade CO₂. The alloys showed similar low rates of oxidation in 1 and 300 bar CO₂ in 500-h cycles at 750 °C. However, in 10-h cycles, alloy 25 showed accelerated attack at 700° and 750 °C. Transmission electron microscopy scale cross-sections on alloy 25 after 1000 h at 700 °C in sCO₂ and in air only showed a small row of carbides beneath the scale in the former environment. Similar characterisation was performed on alloys 625 and 282 after sCO₂ exposure at 750 °C.     

Solubility of supercritical carbon dioxide in polyethylene glycol 4000

We present the experimental results on the solubility of supercritical carbon dioxide in polyethylene glycol of molecular weight 4000, namely, the isotherms at T = 313, 323, and 333 K in the pressure range of P = 10–35 MPa. Based on the Sanchez–Lacombe lattice model, the results of solubility are described and the empirical parameters of the binary intermolecular interaction in the system of supercritical CO₂-polyethylene glycol 4000 are obtained.     

Preparation and characteristics of water-free coating particles of PMMA/modified nano-CaC03 in supercritical carbon dioxide

以超临界流体法制备聚甲基丙烯酸甲酯（PMMA）-CaCO3粉末涂料,应用于纸张表面干法处理技术。为了解决无机颜料与有机胶黏剂界面结合、均匀分散等问题,探究了用硅烷偶联剂KH-570对纳米碳酸钙进行改性。实验考察了反应温度和改性CaCO3用量对制备的无水相涂料性能的影响,通过FT-IR、TG等对改性后CaCO3进行表征,利用GPC-十八角度激光光散射联用技术、TG、SEM等对制备的粉末涂料进行表征。实验表明,与未改性的纳米Ca-CO3相比,改性CaCO3与PMMA粉末涂料颗粒分布均匀,界面结合和分散状况基本能满足纸张表面干法处理的要求。     

超声强化超临界二氧化碳除锈除油污

结合超声清洗的优势与超临界二氧化碳的特性,设计出超声强化超临界二氧化碳复合清洗实验平台,超声换能器最大发射声功率为1 200 W,换能器每工作10 s停止20 s,即一个工作周期为30 s。利用实验平台开展了CD03钢片表面除锈实验,使用ZEISSMerlin高分辨率热场发射扫描电镜对CD03钢片表面进行扫描电子显微镜(Scanning Electronic Microscopy, SEM)和能谱(Energy Dispersive Spectrometer, EDS)分析,实验结果表明,随着清洗时间的延长,铁锈在超声作用下逐渐剥落,超声作用适当的工作周期数后,清洗效果达到最佳,超声作用时间太长会造成对钢片基体的损伤。利用实验平台开展了碳钢片表面油污清除实验,使用徕卡光学显微镜对清洗后的碳钢片做表面形貌观察,利用JA2003电子天平等手段对清洗效果进行了计算分析,同样,超声强化超临界二氧化碳油污清洗也存在一个最佳清洗时间。但是,不同污染所需的最佳清洗时间不同,甚至可以相差很大。在实际的清洗中要先根据污染物的类别确定最佳清洗时间,然后进行清洗。     

Polymer synthesis and characterization in liquid / supercritical carbon dioxide

The use of carbon dioxide as an inert solvent has emerged recently as an important development in polymer chemistry. The past year has seen major advances in the synthesis of a variety of polymeric materials in carbon dioxide. At the same time complementary studies have successfully elucidated the physical behavior of a range of polymers in carbon dioxide solution. Herein we review both synthetic and physical studies that are defining the scope of this approach.     

Solubility parameters and solubilities of metal dithiocarbamates in supercritical carbon dioxide

The solubilities of Cu, Hg, and Zn complexes with seven different dithiocarbamate ligands in supercritical fluid CO(2) at 60 °C and two pressures (100 and 230 atm) are reported. In each metal chelate system, the solubility of the metal-dithiocarbamate complex shows a strong correlation with the solubility parameters of the ligands, calculated using a group contribution method. Dithiocarbamate ligands with smaller solubility parameter values form metal complexes with higher solubilities in supercritical CO(2). The solubility parameter value may provide a general guideline for selecting effective ligands for metal extraction in supercritical CO(2).