Supercritical nitrogen dioxide

The displacing fluid may be steam, supercritical carbon dioxide, hydrocarbon miscible gases, nitrogen or solutions of surfactants or polymers instead of water. The VSE increases with lower mobility ratio values (253). A mobility ratio of 1.0 is considered optimum. The mobility of water is usually high relative to that of oil. Steam and oil-miscible gases such as supercritical carbon dioxide also exhibit even higher mobility ratios and consequent low volumetric sweep efficiencies. 

There is no doubt that these applications will grow in the future and that the range of supercritical fluids used (carbon dioxide and methanol modified carbon dioxide, nitrogen dioxide, ammonia, fluoro-hydrocarbons) will increase as will the combination of this technique with mass spectrometric identification of separated compounds. 

Langenfeld et al. [48] also compared supercritical monochlorofluoromethane, nitrogen dioxide and carbon dioxide for the extraction of polyaromatic hydrocarbons from sediments. Monochlorodifluoromethane provided the highest recoveries. 

Xantheas and co-workers [159,160] have incorporated polarization in a model scheme and have used that to provide a clear basis for the enhancement of water s dipole in ice. A model potential with polarization has been reported for the formaldehyde dimer [161]. It is an example of a carefully crafted potential, which is system-specific because of its application to pure liquid formaldehyde, but which has terms associated with properties and interaction elements as in the above models. As well, some of the earliest rigid-body DQMC work, which was by Sandler et al. [162] on the nitrogen-water cluster, used a potential expressed in terms of interaction elements derived from ab initio calculations with adjustment (morphing). Stone and co-workers have developed interaction potentials for HF clusters [163], water [164], and the CO dimer [165], which involve monomer electrical properties and terms derived from intermolecular perturbation theory treatment. SAPT has been used for constructing potentials that have enabled simulations of molecules in supercritical carbon dioxide [166]. There are, therefore, quite a number of models being put forth wherein electrical analysis and/or properties of the constituents play an essential role, and some where electrical analysis is used to understand property changes as well as the interaction energetics. 

As an extraction fluid, supercritical carbon dioxide is mostly used because its critical parameters can be rather easy obtained (Tc = 31°C, Pc = 74 bar) and is non-polluting. Other supercritical fluids are nitrogen protoxide (Tc = 36°C, Pc = 71 bar), ammonia (Tc = 132°C, Pc = 115 bar) and water (Tc = 374°C, Pc = 217 bar). The supercritical fluids can be removed at low temperatures, without any toxic wastes but the necessary high pressure can be dangerous in industrial applications. The extractors are tubular devices, pressure resistant where the (semi) solid sample is placed. 

The seventh trend is the increasing use of novel processing methods. For example, there is growing use of supercritical fluids (e.g., supercritical carbon dioxide and nitrogen gases) to foam polyolefin blends for density reduction. There is use of ultrasound to, for example, devulcanize cross-linked rubber. There is use of solid-state shear mechanical processing to break the polyolefin blend material into submicron particles to make environment friendly (water-based) polyolefin dispersions. There is use of electrospinning technique to make polyolefin fibers and in particular nanofibers. 

The increased solubilizing powers of a supercritical fluid cannot be entirely explained on the basis of an increased density of the fluid phase. Thus, supercritical carbon dioxide is a suitable solvent for SFC in terms of mobilizing a solute, but supercritical argon and nitrogen are not (116). 

Other solvents, which include organic compounds consisting of hydrogen, carbon, and atoms other than oxygen (such as chlorine or nitrogen). They also include inorganic compounds such as water or supercritical carbon dioxide. 

One approach described in the patent US 6841709 involves oxidative decomposition of the polymer by the use of chemicals such as nitrogen dioxide and/or dinitrogen tetraoxide in either an inert atmosphere or supercritical CO2. This is a method that can be applied to any... 

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