首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到19条相似文献,搜索用时 62 毫秒
1.
超临界流体的共溶剂效应和混合流体研究进展   总被引:2,自引:0,他引:2  
共溶剂的出现极大地拓展了超临界流体的应用范围,推动了超临界流体科学与技术的发展。本文从相行为和分子间相互作用热力学的角度,对相行为测定、量热技术、光谱技术和分子模拟等在超临界流体中共溶剂效应的研究作了综述,主要介绍超临界流体中共溶剂的作用机理和混合流体在临界点附近热力学性质研究,并对其未来发展方向进行了展望。  相似文献   

2.
超临界流体沉积技术在纳米复合材料制备中的应用   总被引:1,自引:0,他引:1  
本文综述了超临界流体沉积法在纳米复合材料制备领域的进展,介绍了利用超临界流体的溶剂化特性、表面张力为零、性质随压力与温度的变化敏感等性质,制备高质量的纳米粒子、薄膜及多孔纳米材料,讨论了超临界流体沉积过程中的吸附、热力学平衡及扩散动力学等问题,总结了不同学者对该方法制备复合材料的机理研究,认为超临界流体沉积法是制备纳米复合材料的有效方法。最后,对深入开展此项研究工作需要努力的方向和解决的关键问题提出了建议。  相似文献   

3.
"分子模拟作为一种全新的研究手段已经在化学、化工、材料、生物等领域受到了广泛的关注。特别是在超临界流体技术方面,其应用不但可以获得许多结构、传递以及热力学信息,而且可以部分取代昂贵的超临界实验。本文从超临界流体在主体相和受限空间中的特性以及超临界萃取、反应等几个方面对现有的分子模拟方法和成果进行总结与评述,并对进一步发展的方向和面临的困难进行了讨论。  相似文献   

4.
超临界流体色谱中热力学参数最佳化和动力学最佳化同等重要。溶质的保留行为和物质对的分离受柱固定相和流动相各种参数的影响。在本研究中,使用纯CO_2作为流动相,饱和烃、芳烃、以及它们的硝基取代物作为溶质,对上述影响进行了系统地考察。结果发现影响物质对分离的(以分离系数,α,表示)最主要因素是流体的密度。而温度的影响并不明显。柱固定相的性质也有一定程度的影响。在柱固定相相同的情况下,改变操作参数,溶质峰的洗馏顺序可能出现倒置。表明在超临界流体色谱中流动相溶解能力的重要作用。实验结果为了解和优化超临界流体色谱热力学参数提供了依据。  相似文献   

5.
超临界流体技术在萃取中的应用简介   总被引:3,自引:0,他引:3  
张中一 《化学教育》2003,24(6):4-5,33
超临界流体萃取技术具有许多传统技术所没有的快速、高效、高选择性、低能耗等优点,特别是超临界流体的特性是它可以代替高毒有机溶剂做反应介质,符合绿色化学的要求。本文综述了超临界流体的特性,介绍了超临界流体萃取的原理,归纳了超临界流体萃取的应用现状,并介绍了超临界流体的其他领域应用概况。  相似文献   

6.
衍生-超临界流体萃取金属离子的技术与进展   总被引:2,自引:0,他引:2  
综述了近年来衍生-超临界流体萃取环境样品和环境模拟样品中金属离子的研究报道,结合作者的研究工作,着重评述了超临界流体萃取不同环境样品、环境模拟样品中金属离子的原理、萃取过程的动力学模型、衍生剂的选择原则、金属螫合物在超临界流体中的溶解度理论、影响萃取效率的因素、金属离子超临界流体萃取应用研究现状与进展等。利用流体与基体改性技术实现了金属离子和金属螯合物的超临界流体萃取,且在萃取体系中加入适量的表面活性剂能显著提高萃取效率。  相似文献   

7.
采用正交设计实验方法,研究了从环境模拟样品中超临界流体萃取(SFE)多环芳烃(PAH)的最佳萃取条件。着重考察了超临界流体的压力、温度和用量等对萃取效率的影响。结果表明,压力的影响居第一位,温度影响次之,超临界CO2的用量的影响居第三位。建立了选择超临界流体萃取条件的简单方法  相似文献   

8.
超临界流体中的催化反应   总被引:6,自引:0,他引:6  
介绍了近年超临界流体在催化反应中的理论研究和应用,阐述了超临界流体用于催化反应的优越性。  相似文献   

9.
当流体的温度和压力处于它的临界温度和临界压力以上时,称该流体处于超临界状态,为超临界流体.超临界流体表现出许多不同于一般气体和液体的特性,如溶质在超临界流体中的溶解度可较同温常压下溶质在同种气体中的溶解度大很多,超临界流体密度与液体的密度相近,其粘度却比液体小近百倍,导热系数比常压气体大得多等.由于超临界流体具有这些不同寻常的特性,因而以超临界萃取为代表的超临界流体已有广泛的工业应用.近年来超临界流体在聚合物加工中的应用逐渐受到重视,如超临界分级、造粒、气体辅助注塑成型、发泡成型等[1~3].  相似文献   

10.
白术挥发性成分的超临界流体萃取及其分析   总被引:5,自引:0,他引:5  
采用超临界流体萃取白术挥发油成分,对萃取条件进行优化,并用气相色谱、气相色谱-质谱分析鉴定出超临界流体萃了的挥发油中22个化合物。最佳的超临界流体萃取条件为压力22.0MPa,温度60℃,0.5mL乙醇作改性,先静态萃取10min(CO2用量2.0mL),再动态萃取40min(CO2流速为0.3mL/min)。将超临界流体萃取与水蒸气蒸馏进行对比,水蒸气蒸馏5h的油收率仅为超临界流体萃取1h油收率的10.32%,证明超临界流体萃取替代传统萃取的必要性。  相似文献   

11.
可调变流体与绿色化工过程   总被引:14,自引:1,他引:13  
介绍了可调变流体特性及其在绿色化工过程中的应用。重点介绍了利用超临界流体(主要是超临界C02)、亚临界水和气体(主要是CO2)膨胀的流体这三类可调变流体进行绿色化工过程设计的特点与途径。  相似文献   

12.
A study of the kinetics and mechanism of chemical reactions in supercritical fluids is considered. An experimental procedure was proposed for examining reversible chemical reactions in supercritical water. The reaction kinetics of 2-propanol dehydration in supercritical water was studied. It was found that the uncatalyzed reactions of olefin hydrogenation by hydrogen dissolved in supercritical water occur at high rates near the critical point of water. The experimental data on the dehydration of 2-propanol in supercritical water are adequately described by first-order reaction rate equations. The rate constants and activation energies of 2-propanol dehydration near the critical point of supercritical water were found.  相似文献   

13.
Supercritical fluids:Clean solvents for green chemistry   总被引:2,自引:0,他引:2  
Supercritical fluids are becoming increasingly attractive as environmentally acceptable replacement for organic solvents in chemical reactions and material processing. This paper highlights some of the properties of supercritical fluids, especially supercritical CO2, which offer particular advantages for the handling of polymers, metal complexes and the environmentally more friendly synthesis and manufacture of chemicals. The paper includes some of the researches in University of Nottingham and a number of recent reviews which together provide a comprehensive introduction.  相似文献   

14.
超临界流体技术在绿色化工过程中的应用范围不断拓宽。由于超临界甲醇具有独特的物理和化学性质,它既是反应介质,也是反应物,因此,超临界甲醇下的化学反应研究得到人们广泛的关注。本文在介绍超临界甲醇独特的物理化学特性的基础上,综述了近年来超临界甲醇体系在有机合成、生物柴油的制备、生物质处理和高聚物的降解等方面的应用研究进展,重点对超临界甲醇下各种反应的影响因素进行了分析讨论。最后,展望了超临界甲醇在甲醇化工中的应用前景。  相似文献   

15.
Malick RE  Dorsey JG  Chester TL  Innis DP 《Talanta》1993,40(12):1951-1959
Since flow injection (FI) is a dilution technique, efforts have been undertaken to minimize online dilution or dispersion. Solutes in supercritical fluids exhibit increased diffusion coefficients which have been shown to decrease dispersion of the sample zone. This work investigates the use of supercritical fluids (or CO2 modified fluids) as carrier streams for FI. Both a non-reacting tracer and an online chemical reaction were employed to investigate the behavior of solutes in supercritical and near critical systems. Further, these results are compared to those obtained in the system studied with a conventional carrier stream. Plots of peak response vs% CO2 modifier increase with a sharp break at moderate modifier composition (20–30%). Plots of peak variance vs% CO2 modifier show decreased variance with increasing % modifier. The system was also optimized with regards to temperature and pressure. The optimized system displayed improved limits of detection and decreased variance relative to 0% CO2 modifier carrier streams.  相似文献   

16.
Kurnik, R.T. and Reid, R.C., 1982. Solubility of solid mixtures in supercritical fluids. Fluid Phase Equilibria, 8: 93-105Supercritical fluids are receiving widespread attention as possible extraction agents for relatively non-volatile solids and liquids. Previous studies of the solubility of solids in supercritical fluids have been limited to pure solids. These pure-component data are interesting and indicate novel properties of supercritical fluids in this respect. The more general problem, however, lies in determining the solubility of multicomponent solids in supercritical fluids. Experimental data have now been obtained on the solubilities of binary, solid hydrocarbon mixtures in both supercritical carbon dioxide and supercritical ethylene. Most of the behavior exhibited by pure solids in supercritical fluids still exists for multicomponent solid solute systems (e.g., retrograde solidification, solubility extrema), but new phenomena were also found. The most interesting finding is that the solubility of a solid component when in a multicomponent solute system can be as much as 300% higher than the component solubility in a pure solid system at the same operating conditions. The multicomponent-solid-fluid data usually correlate well with thermodynamic theory.  相似文献   

17.
The results of fundamental studies performed by the author on the reactivity of supercritical fluid solvents are systematized and generalized; practical applications of these solvents are considered. Methods for performing kinetic and physicochemical experiments, processing the data, constructing kinetic models, and calculating the thermodynamics of nonideal supercritical fluids (the parameters of critical points, binodal and spinodal lines, and critical point drifts; the thermophysical properties of reaction mixtures under supercritical conditions; etc.) are described. Attention is focused on the effect of supercritical fluid pressure on the rate constants of chemical reactions. The kinetics and mechanisms of the reactions of 2-propanol dehydration and decomposition of aliphatic nitro compounds in supercritical water and the isomerization of terpene compounds (α-pinene, β-pinene, and turpentine) in supercritical lower alcohols are studied. The formation of nanoparticles in supercritical fluid solvents and the treatment of ultradisperse diamonds in supercritical water are considered. The results formed the basis for the simulation and calculation of acetic acid and phenol oxidation processes in supercritical water and the Fischer-Tropsch synthesis in a supercritical solvent and for the development of a pilot plant for the complete oxidation of trinitroglycerol and diethylene glycol dinitrate in supercritical water.  相似文献   

18.
Supercritical fluids are beginning to be used widely in chemistry. Applications range from extraction and chromatography in analytical chemistry to solvents for reaction chemistry and preparation of new materials. Spectroscopic monitoring is important in much of supercritical chemistry, and vibrational spectroscopy is particularly useful in this context because the vibrational spectrum of a given molecule is usually quite sensitive to the environment of that molecule. Thus, vibrational spectra are excellent probes of conditions within the fluid. In this review, we describe a variety of techniques and cells for IR and Raman spectroscopy in supercritical fluids and illustrate the breadth of applications in supercritical fluids. The examples include: the use of supercritical Xe as a spectroscopically transparent solvent for chemistry and for supercritical fluid chromatography with FTIR detection of analytes; Raman spectroscopy as a monitor for gases dissolved in supercritical CO2; the effect of solvent density on hydrogen bonding in supercritical fluids and the formation of reverse micelles; IR as a monitor for the supercritical impregnation/extraction of polymers and the reactions of organometallic compounds impreganated into polymers; reactions of organometallic compounds in supercritical fluids; and finally, the use of miniature flow reactors for laboratory-scale preparative chemistry. Overall, our aim is to provide a starting point from which individual readers can judge whether such measurements might usefully be applied to their own particular problems.  相似文献   

19.
The time evolution of the density fluctuation of molecules is investigated by dynamic light scattering in six neat fluids in supercritical states. This study is the first to compare the dynamics of density inhomogeneity between hydrogen- and non-hydrogen-bonded fluids. Supercritical methanol and ethanol are used as hydrogen-bonded fluids, whereas four non-hydrogen-bonded fluids were used: CHF(3), C(2)H(4), CO(2), and Xe. We measure the time correlation function of the density fluctuation of each fluid at the same reduced temperatures and densities and investigate the relationship between the dynamic and static density inhomogeneities of those supercritical fluids. In all cases, the profile of the time correlation function of the density fluctuation is characterized by a single-exponential function, whose decay is responsible for the dynamics characterized by hydrodynamic conditions. We obtain correlation times from the time correlation function and discuss dynamic and static inhomogeneity using the Kawasaki theory and the Landau-Placzek theory. While the correlation times in the six fluids show noncoincidence, those values agree well with each other except for the supercritical alcohols when scaled to a dimensionless parameter. Although the principle of corresponding state is observed in the non-hydrogen-bonded fluids, both the supercritical methanol and ethanol deviate from that principle. This deviation is attributed to the presence of hydrogen bonding among alcohol molecules at high temperature and low density. The average cluster size of each fluid is estimated under the same thermodynamic conditions, and it is shown that the clusters of supercritical alcohols are on average 1.5-1.7 times larger than those of the four non-hydrogen-bonded fluids. Moreover, the thermal diffusivity of each neat fluid is obtained over wide ranges of density and temperature.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号