Hybrid Extraction Processes

Hybrid Extraction Processes Hybrid processes employ an extraction operation in close association with another unit operation. In these processes, the individual unit operations may not be able to achieve all the separation goals, or the use of one or the other operation alone may not be as economical as the hybrid process. Common examples include the following. 

For dilute feeds, consider options for preconcentrating the feed to reduce the volumes of feed and solvent that must be handled by the extraction operation. Consider evaporation or distillation of a high-volatility feed solvent or the use of reverse osmosis membranes to concentrate aqueous feeds. (See Hybrid Extraction Processes under Commercial Process Schemes. )... 

An improved solvent extraction process, PUREX, utilizes an organic mixture of tributyl phosphate solvent dissolved in a hydrocarbon diluent, typically dodecane. This was used at Savannah River, Georgia, ca 1955 and Hanford, Washington, ca 1956. Waste volumes were reduced by using recoverable nitric acid as the salting agent. A hybrid REDOX/PUREX process was developed in Idaho Falls, Idaho, ca 1956 to reprocess high bum-up, fuUy enriched (97% u) uranium fuel from naval reactors. Other separations processes have been developed. The desirable features are compared in Table 1. 

In simple experiments, particulate silica-supported CSPs having various cin-chonan carbamate selectors immobilized to the surface were employed in an enantioselective liquid-solid batch extraction process for the enantioselective enrichment of the weak binding enantiomer of amino acid derivatives in the liquid phase (methanol-0.1M ammonium acetate buffer pH 6) and the stronger binding enantiomer in the solid phase [64]. For example, when a CSP with the 6>-9-(tcrt-butylcarbamoyl)-6 -neopentoxy-cinchonidine selector was employed at an about 10-fold molar excess as related to the DNB-Leu selectand which was dissolved as a racemate in the liquid phase specified earlier, an enantiomeric excess of 89% could be measured in the supernatant after a single extraction step (i.e., a single equilibration step). This corresponds to an enantioselectivity factor of 17.7 (a-value in HPLC amounted to 31.7). Such a batch extraction method could serve as enrichment technique in hybrid processes such as in combination with, for example, crystallization. In the presented study, it was however used for screening of the enantiomer separation power of a series of CSPs. 

Zeitsch (303) conducted a preliminary research on the removal of acetic acid from the vapor stream of furfural reactors by means of extractive condensation. It is a hybrid vapor-phase extraction process, in which solvent (triethyl-amine, TEA) forms a high-boiling complex with acetic acid. As a result, a fog ... 

Formation of hybrid production/biotransformation - separation processes, inducting extractive processes, could enhance production and is of great interest, as shown in review papers [8, 21, 26-30]. The flowsheet of the extradive fermentation... 

In order to solve the first principles model, finite difference method or finite element method can be used but the number of states increases exponentially when these methods are used to solve the problem. Lee et u/.[8] used the model reduction technique to reslove the size problem. However, the information on the concentration distribution is scarce and the physical meaning of the reduced state is hard to be interpreted. Therefore, we intend to construct the input/output data mapping. Because the conventional linear identification method cannot be applied to a hybrid SMB process, we construct the artificial continuous input/output mapping by keeping the discrete inputs such as the switching time constant. The averaged concentrations of rich component in raffinate and extract are selected as the output variables while the flow rate ratios in sections 2 and 3 are selected as the input variables. Since these output variables are directly correlated with the product purities, the control of product purities is also accomplished. 

A suitable combination of two separation techniques like distillation and adsorption leads to a desired separation of a mixture which is either infeasible or expensive with a single technique. This combination of the different separation techniques is called hybrid separation. The techniques of hybridization are viewed as the techniques of process integration. Stankiewicz [60] presented the examples of extractive distillation, adsorptive distillation, membrane distillation, membrane absorption/stripping, and adsorptive membranes. A detailed discussion on hybrid separation processes involving distillation and one of the separation processes, namely, absorption, desorption, extraction, adsorption and membrane processes is available [61]. 

Distillation is still the most common unit operation to separate liquid mixtures in chemical and petroleum industry because the treatment of large product streams and high purities with a simple process design is possible. Despite of this the separation of azeotropic mixtures into pure components requires complex distillation steps and/or the use of an entrainer. Industrial applied processes are azeotropic, extractive or pressure swing distillation (Stichlmair and Fair, 1998). Another sophisticated method for the separation of binary or multicomponent azeotropic mixtures is the hybrid membrane process, consisting of a distillation column and a membrane unit. 

In a sense, therefore, there have been two conflicting views with respect to the suitability of formalin as a fixative, in the face of demands that biopsy tissues may be examined not only by traditional morphologic methods, but also by IHC, in situ hybridization (ISFI) and, following extraction procedures, by other molecular methods. Both views recognize that these newer methods do not perform well, or at all, on routinely processed FFPE tissues. One view advocates the development of new fixatives that are molecular friendly, the other view holds that AR-based methods may be employed to achieve accurate valid results of IHC, ISH, and other molecular methods using FFPE tissues. 

Figure 11.15 (see Plate 5 for color version) shows ideal microarray spots. However, such ideal round spots are in fact impossible to achieve. As suggested by Yang et al. [28], the imperfect spot size and shape occurs during the hybridization and printing process and is also due to the conditions of the slide surface, making it more tedious to extract the raw data. Some of the imperfect microarray spots appear in the form of a comet tail , as shown in Fig. 11.16 (see Plate 6 for color version), which is due to... 

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