Supercritical injection

Feed prevaporization or supercritical injection. Multiple feed injection. 

The term supercritical injection can refer to several different types of processes. There are four classes (note that is reduced absolute temperature andis reduced absolute pressure the subscript inj refers to injection, and env represents the environment) ... 

Depending on the conditions of the initial fluid and the environment, many different changes to the fluid can occur. Figure 11.1, similar to one provided by [1], illustrates the different classes of supercritical injection. 

Mayer and Telaar [13] also compared supercritical injection to gas-gas mixing. They noted that transcritical injection forms a regime that lies between subcritical spray breakup and supercritical jet breakup. 

Supercritical injection is still being studied. However, it is clear that there are many considerations that need to be accounted for when designing an injector for... 

The eluent is now supercritical. Injection is made through a loop in which the sample has been previously dissolved in the eluent. 

The WAG process has been used extensively in the field, particularly in supercritical CO2 injection, with considerable success (22,157,158). However, a method to further reduce the viscosity of injected gas or supercritical fluid is desired. One means of increasing the viscosity of CO2 is through the use of supercritical C02-soluble polymers and other additives (159). The use of surfactants to form low mobihty foams or supercritical CO2 dispersions within the formation has received more attention (160—162). Foam has also been used to reduce mobihty of hydrocarbon gases and nitrogen. The behavior of foam in porous media has been the subject of extensive study (4). X-ray computerized tomographic analysis of core floods indicate that addition of 500 ppm of an alcohol ethoxyglycerylsulfonate increased volumetric sweep efficiency substantially over that obtained in a WAG process (156). 

An on-line supercritical fluid chromatography-capillary gas chromatography (SFC-GC) technique has been demonstrated for the direct transfer of SFC fractions from a packed column SFC system to a GC system. This technique has been applied in the analysis of industrial samples such as aviation fuel (24). This type of coupled technique is sometimes more advantageous than the traditional LC-GC coupled technique since SFC is compatible with GC, because most supercritical fluids decompress into gases at GC conditions and are not detected by flame-ionization detection. The use of solvent evaporation techniques are not necessary. SFC, in the same way as LC, can be used to preseparate a sample into classes of compounds where the individual components can then be analyzed and quantified by GC. The supercritical fluid sample effluent is decompressed through a restrictor directly into a capillary GC injection port. In addition, this technique allows selective or multi-step heart-cutting of various sample peaks as they elute from the supercritical fluid... 

A schematic diagram of a chromatograph for SFC is shown in Figure 6.10. In general, the instrument components are a hybrid of components developed for gas and liquid chromatography that have been subsequently modified for use with supercritical fluids. Thus, the. fluid delivery system is a pump modified for pressure control and the injection system a rotary valve similar to components used in liquid chromatography. The column oven and... 

Figure 8.22 Schematic diagram of the Suprex MPS/225 integrated aupercritical fluid extractor, cryogenically focused interface and supercritical fluid chromatogra d>. The bold lines represent the direction of fluid flow in the load and inject positions.

If simple sample pretreatment procedures are insufficient to simplify the complex matrix often observed in process mixtures, multidimensional chromatography may be required. Manual fraction collection from one separation mode and re-injection into a second mode are impractical, so automatic collection and reinjection techniques are preferred. For example, a programmed temperature vaporizer has been used to transfer fractions of sterols such as cholesterol and stigmasterol from a reversed phase HPLC system to a gas chromatographic system.11 Interfacing gel permeation HPLC and supercritical fluid chromatography is useful for nonvolatile or thermally unstable analytes and was demonstrated to be extremely useful for separation of compounds such as pentaerythritol tetrastearate and a C36 hydrocarbon standard.12... 

Cortes, H. J., Campbell, R. M., Himes, R. P., and Pfeiffer, C. D., On-line coupled liquid chromatography and capillary supercritical fluid chromatography large-volume injection system for capillary SFC, ]. Microcol. Sep., 4, 239, 1992. 

There are basically three methods of liquid sampling in GC direct sampling, solid-phase extraction and liquid extraction. The traditional method of treating liquid samples prior to GC injection is liquid-liquid extraction (LLE), but several alternative methods, which reduce or eliminate the use of solvents, are preferred nowadays, such as static and dynamic headspace (DHS) for volatile compounds and supercritical fluid extraction (SFE) and solid-phase extraction (SPE) for semivolatiles. The method chosen depends on concentration and nature of the substances of interest that are present in the liquid. Direct sampling is used when the substances to be assayed are major components of the liquid. The other two extraction procedures are used when the pertinent solutes are present in very low concentration. Modem automated on-line SPE-GC-MS is configured either for at-column conditions or rapid large-volume injection (RLVI). 

On-line SFE-SFC modes present several distinct advantages that are beyond reach of either technique when used separately (Table 7.13). An obvious advantage of SFE is that it is an ideal way to introduce a sample into an SFC system. Because the injection-solvent is the same as the mobile phase, in this respect the criteria for a successful coupling of different techniques are fulfilled [94], i.e. the output characteristics from the first instrument and the input characteristics of the second instrument are compatible. Supercritical fluid techniques can separate high-MW compounds are significantly faster than classical Soxhlet extractions and require less heat and solvent. SFE-SFC techniques are versatile,... 

Smith and Udseth [154] first described SFE-MS in 1983. Direct fluid injection (DFT) mass spectrometry (DFT-MS, DFI-MS/MS) utilises supercritical fluids for solvation and transfer of materials to a mass-spectrometer chemical ionisation (Cl) source. Extraction with scC02 is compatible with a variety of Cl reagents, which allow a sensitive and selective means for ionising the solute classes of interest. If the interfering effects of the sample matrix cannot be overcome by selective ionisation, techniques based on tandem mass spectrometry can be used [7]. In these cases, a cheaper and more attractive alternative is often to perform some form of chromatography between extraction and detection. In SFE-MS, on-line fractionation using pressure can be used to control SCF solubility to a limited extent. The main features of on-line SFE-MS are summarised in Table 7.20. It appears that the direct introduction into a mass spectrometer of analytes dissolved in supercritical fluids without on-line chromatography has not actively been pursued. 

Supercritical fluid-injection (SFI) Fast atom bombardment (FAB) ... 

RI(D) Refractive index (detector) SFI Supercritical fluid injection... 

Smith J.M. and Raptis, T.J., Supercritical deep well wet oxidation of liquid organic wastes, in Proc. Int. Symp. Subsurface Injection of Liquid Wastes, New Orleans, National Water Well Association, Dublin, OH, 1986, pp. 715-732. 

Corrosion-resistant cements have been developed for use in wells used to inject supercritical carbon dioxide for enhanced oil recovery (32). These are based on Portland cement and high levels (as much as 40% wt.) of additives such as fly ash. Epoxy resins have been successfully used as cements in corrosive environments... 

Doughty C., PruessK. Modeling supercritical carbon dioxide injection in heterogeneous porous media. 2004 Vadose Zone Journal 3(3) 837-847. 

Once the C02 is captured and compressed, it needs to be transported to the sequestration or utilization locations, unless the capture and sequestration processes are located at the same site. A C02 transportation infrastructure could be done with a rather conventional approach. On land, pipelines for long-distance C02 transport already exist. For example, a pipeline system more than 500 mi. long connects C02 fields in Southern Colorado to oil fields in West Texas. The C02 is purchased at about 15/ton for tertiary oil recovery. The cost of C02 transportation is a function of distance, whereas the costs of pipeline construction vary significantly by region (Doctor et al., 1997). The construction and operation of pipelines for ocean would be quite different from land-based pipelines. Generally, C02 is transported at supercritical pressures (-2000 psi). If C02 is sequestered at geological formations, the transferred C02 may require additional compression at the injection site depending on the specifics of the reservoir (Doctor et al., 1997). 

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