Extraction operation design considerations

This chapter provides a state-of-the-art review of HFMST including a general review of hollow fiber membrane contactors, operating principles, design consideration, commercial availability of hollow fiber membrane, and module for scale-up and large-scale studies. Application of HFMST in pharmaceutical, biotechnological, gas absorption and stripping, wastewater treatment, and few latest studies of metal ion extraction are described in detail. 

Many rubber products must operate in contact with fluids of various types. An important part of compound design is formulation for resistance to fluids. Selection of suitable polymer is important, (e.g., use of a polar rubber for oil resistance), while for minimal swelling it is desirable to have a high crosslink density. Other design considerations are also important, such as the effect of the liquid on the filler and plasticiser systems. Plasticisers will often be extracted by fluids and occasionally replaced by the fluid within the compound. Filler effects are discussed in Section 7.6.3.5. 

Ezrin et al [980] developed a direct dynamic headspace device for use in GC-MS in which the sample (5-25 mg) is placed in the hot zone directly on the GC column head. The method is adequate even for very high boiling compounds. The design of the DHS-GC-MS device probably contributes to this capability, there being no transfer lines and the sample tube being located directly at the head of the GC column. It is capable of isolating trace level compounds that would have been much more difficult to determine by extraction methods. Analysis time is much shorter than by extraction. Identification of compounds is based on GC retention times, mass spectrometry and reference compounds. Alternate methods of analysis, such as SFE and SFC, which use CO2 for extraction and as the carrier in SFC, operate at considerably lower temperature than in DHS-GC-MS. Possibly the aromatics can be extracted more readily and completely by SFE than by heat alone (headspace). 

Centrifugation to aid an operation has found considerable use in the General Medical Science/Atomic Energy Commission approach to automation pioneered hy Anderson [S], and was also used hy Bartels et al. [6], in the design of a sohd-hquid extraction system. 

Although considerable studies on the use of centrifugal fields in chemical processing have been reported for lab- and pilot-scale operations, little information is public on scale-up criteria for either performance parameters or equipment design. Three examples of commercial use of centrifugal fields are available for review. These include liquid-liquid extraction, water deaeration, and reactive stripping for hypochlorous acid production. 

Calculations of multicomponent liquid-liquid equilibrium are needed in the design of liquid (solvent) extraction systems. Since these operations take place considerably below the bubble point, it is not necessary to consider the equilibrium-vapor phase. The equations to be solved are ... 

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