Commercial supercritical fluid extractors

In addition to the previous three commercial extractors, some authors have developed custom models [78,79], adapted in most cases from a supercritical fluid extractor [25,58,80]. For example, Heemken et al. altered a Suprex SF extractor for use in ASE [81] they disconnected the syringe pump from the COj cylinder and filled it with a suitable ASE solvent. The restrictor was replaced with a stainless steel capillary tube leading into the trapping vial and an additional nitrogen pipe was installed at the inlet valve of the extraction vessel for purging after extraction. In the extraction of PAHs from soil [79], a custom extractor and commercially available equipment provided equivalent results on the other hand, in the extraction of benzene and toluene from soil [78], the former provided even better results than the latter. 

LABORATORY-BUILT AND COMMERCIAL SUPERCRITICAL FLUID EXTRACTORS... 

Supercritical fluid extraction aroused the interest of commercial equipment manufacturers well before its potential was experimentally realized. However, the high expectations raised by this technique have not materialized — basically because of the strong dependence of the extraction efficiency on the properties of the sample matrix — as reflected in the declining interest of manufacturers in it. Thus, the number of manufacturers offering commercial supercritical fluid extractors fell by almost one half between the 1991 Pittsburgh Conference and 1997 — the year this number seemingly levelled off. 

Commercial supercritical fluid extractors have evolved in parallel with the consolidation of specific types of applications of the SFE technique [17]. By way of example of a commercial extractor and its changes over time, let us consider the one manufactured by Hewlett-Packard. This extractor has evolved from the oldest model (HP 7860 A, Fig. 7.3A), which was launched in 1992, to the present one (HP 7680 T, Fig. 7.3B). Essentially, however, the extractor continues to consist of the following elements ... 

Fig. 7.3. Commercially available supercritical fluid extractors from Hewlett-Packard. (A) HP 7680 A model. (B) HP 7680 T model. (Reproduced with permission of Hewlett-Packard.)...

FIGURE 15.12 Schematic diagram of commercial supercritical-fluid extractor. 

In these systems, the interface between two phases is located at the high-throughput membrane porous matrix level. Physicochemical, structural and geometrical properties of porous meso- and microporous membranes are exploited to facilitate mass transfer between two contacting immiscible phases, e.g., gas-liquid, vapor-liquid, liquid-liquid, liquid-supercritical fluid, etc., without dispersing one phase in the other (except for membrane emulsification, where two phases are contacted and then dispersed drop by drop one into another under precise controlled conditions). Separation depends primarily on phase equilibrium. Membrane-based absorbers and strippers, extractors and back extractors, supported gas membrane-based processes and osmotic distillation are examples of such processes that have already been in some cases commercialized. Membrane distillation, membrane... 

The Eastman process has operated in Texas (USA) with three continuous, stirred-tank reactors, a wiped-film evaporator, a distillation train and a continuous, counter-current, liquid-liquid extractor for recovery of the catalysts since 1996 (1400 metric tons per year capacity, e.g., semiworks facility), but full commercial capacity has not yet been reached. The main problem is still the formation of oligomers. Another answer to the problem of IL loss to the organic phase consists in the extraction of the products from the IL using a supercritical fluid [101], but operational costs are high. 

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