Association, liquid-solid extraction

This example concerns a discontinuous (batch) liquid-solid extraction process. Here, the quantity of extracted species (y, -< y >- = kgA/kg liq, A = type of species) depends on the following factors the ratio of mixing phases (mi/mg-associated to Zj -< mj/mg >-= kg liq /kg solid), the contact time (t associated to Zj, < T >-= min) the mixing rate (w = Tind -associated to Z3, -< w >-= m/s, n-rotation speed, d - mixer diameter) the mean concentration of one species carrier, which is placed in the liquid phase (Cg -associated to Z4, CgA >-= kg carrier/kg liq) the diameter of the solid particles (d-associated to Z5, d >-= m). The temperature can be another important factor in the process, but initially we can consider that it is constant. Nevertheless, it will be considered as an additional factor in a second step of this analysis. The experiments are carried out with a solid containing 0.08 kg A/kg solid. 

The most common extraction techniques for semivolatile and nonvolatile compounds from solid samples that can be coupled on-line with chromatography are liquid-solid extractions enhanced by microwaves, ultrasound sonication or with elevated temperature and pressures, and extraction with supercritical fluid. Elevated temperatures and the associated high mass-transfer rates are often essential when the goal is quantitative and reproducible extraction. In the case of volatile compounds, the sample pretreatment is typically easier, and solvent-free extraction methods, such as head-space extraction and thermal desorption/extraction cmi be applied. In on-line systems, the extraction can be performed in either static or dynamic mode, as long as the extraction system allows the on-line transfer of the extract to the chromatographic system. Most applications utilize dynamic extraction. However, dynamic extraction is advantageous in many respects, since the analytes are removed as soon as they are transferred from the sample to the extractant (solvent, fluid or gas) and the sample is continuously exposed to fresh solvent favouring further transfer of analytes from the sample matrix to the solvent. 

Mechanical methods are fairly simple. The methods may be divided into two major groups. One involves the capture of a sample of droplets on a solid surface or in a cell containing a special liquid. The captured droplets are then observed or photographed by means of a microscope, generating information on droplet size. The other involves freeze-up of droplets into solid particles and subsequent sieving to generate droplet size distribution. The major problem is associated with the extraction and collection of representative spray samples. 

Analysing volatile acids in aqueous systems, resulting mainly from the presence of water, have been reported [19]. The volatile acids high polarity as well as their tendency to associate and to be adsorbed firmly on the column require esterification prior to gas chromatographic determination. The presence of water interferes in esterification so that complex drying techniques and isolation of the acids by extraction, liquid solid chromatography, distillation, and even ion exchangers had to be used [20-23],... 

After leaving the preparation process, the flakes (or collets) are delivered to the solvent extraction operation. As this process typically uses a flammable solvent (and is classified as a hazardous flammable environment), the operation is usually somewhat removed from other facilities, and access to the controlled area is restricted. Figure 5 illustrates the typical unit operations associated with solvent extraction, which include extraction, solvent distillation, and liquid-phase recovery. Upon discharge from the extractor, solid-phase extracted material is desolventized, toasted, dried, and cooled prior to meal finishing. 

High-Level Liquid Waste (HLLW) Treatment. The high-level liquid waste is produced as a raffinate from the HA solvent extraction cycle in Purex. After generation, the HLLW is immediately transferred to the WTF via an underground pipeline without concentration or interim storage. This strategy minimizes the problems associated with solids precipitation. 

Various parameters such as adsorption and desorption isotherms, diffusion coefficients, liquid/gas, gas/solid and liquid/solid equilibrium distribution coefficients, as well as mass transfer coefficients and many other physicochemical property values have to be used in the models proposed for supercritical fluid extractions. These parameter values are either obtained from existing correlations, or from independent data sources using parameter estimation. However, in those cases where the above stated means are not sufficient to estimate the values of all parameters used in the model, the researcher(s) may be forced to use the model and the associated data to evaluate best fit or optimal values for the missing parameters. The fact is that, the number of reliable correlation s and methods for the SFE are still quite scarce. 

Samples that contain two phases present a special problem depending on the site of the materials of interest. If the substances are known to be associated with one phase only, the sample procedure is simply to separate the two phases by filtration or centrifugation and treat the sample as a liquid or solid sample depending on the phase that contains the materials to be determined. However, if the materials of interest are distributed between the two phases, some in solution and some adsorbed on the surface of the solid, then special extraction procedures will be necessary. 

Distillation is probably the most widely used separation technique in the chemical process industries, and is covered in Chapter 11 of this volume, and Chapter 11 of Volume 2. Solvent extraction and the associated technique, leaching (solid-liquid extraction) are covered in Volume 2, Chapters 13 and 10. Adsorption, which can be used for the separation of liquid and gases mixtures, is covered in Chapter 17 of Volume 2. Adsorption is also covered in the books by Suziki (1990) and Crittenden and Thomas (1998). 

Isotope fractionation between the vapor phase and the dissolved aqueous phase has been studied only for toluene and trichloroethylene (carbon only [545, 690]). Fractionation associated with adsorption has been quantified only for toluene in regard to sample extraction using a poly(dimethylsilo-xane)-coated solid-phase microextraction fiber [373] and qualified for benzene, toluene, and ethylbenzene based on high-pressure liquid chromatography analyses of isotopically labeled and unlabeled compounds (carbon and hydrogen [692]). Isotope fractionation associated with the reductive dechlorination of chlorinated ethylenes by zero-valent iron and zinc has been... 

For the determination of CCA in biological samples, methods not based on LC-MS/MS technology [39, 41-43] and methods that used LC-MS/MS [40, 52] have been reported. Most of the sample extraction methods used liquid-liquid extraction (LLE) technology, since this extraction method is simpler and able to minimize matrix effects. Consequently, LLE methods are considered to provide cleaner samples as compared to solid phase extraction (SPE) methods. Since LC-MS/MS methodology uses nonvolatile solvents or a combination of nonvolatile and volatile solvents, difficulties in the evaporation process and associated interferences when samples are injected onto the system can arise [51]. However, Bahrami as well as Souri [42,43] applied a combination of nonvolatile and volatile solvents in which the nonvolatile solvents were acidic buffers (pH 5 or less). Analytes eluted from SPE prepared samples did not undergo evaporation as applied commonly encountered in extraction procedures [37, 45]. 

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