Liquid Separation Applications

Zeolite/polymer mixed-matrix membranes have been investigated for liquid separations such as purification ofp-xylene [76], separation of ethanol-water mixtures [93-96] and water desalination [83]. 

The new concept of using mixed-matrix membranes with commercially attractive thin-film composite geometry for desalination of water has been demonstrated by Jeong and coworkers [83]. 

Another potential application for zeolite/polymer mixed-matrix membranes is the separation of various liquid chemical mixtures via pervaporation. Pervapora-tion is a promising membrane-based technique for the separation of liquid chemical mixtures, especially in azeotropic or close-boihng solutions. Polydime thy 1-siloxane (PDMS), which is a hydrophobic polymer, has been widely used as the continuous polymer matrix for preparing hydrophobic mixed-matrix membranes. To achieve good compatibility and adhesion between the zeolite particles and the PDMS polymer, ZSM-5 was incorporated into the PDMS polymer matrix, the resulting ZS M -5/ P DM S mixed-matrix membranes showed simultaneous enhancement in selectivity and flux for the separation of isopropyl alcohol from water. It was demonstrated that the separation performance of these membranes was affected by the concentration of the isopropyl alcohol in the feed [96]. 

Another type of mixed-matrix membranes for alcohol/water pervaporation applications was developed utilizing hydrophiUc poly(vinyl alcohol) (PVA) and ZSM-5. The ZSM-5/PVA mixed-matrix membranes demonstrated increased selectivity and flux, compared to pure PVA, for the water/isopropyl alcohol separation [97]. This type of mixed-matrix membranes, however, may have membrane swelling issue due to the hydrophilic nature of the PVA polymer. Mixed-matrix membranes comprising modifled poly(vinyl chloride) and NaA zeolite have shown both enhanced flux and selectivity for the ethanol/water separation at high NaA loadings [98]. 

1 Singh, R. (1998) Industrial membrane separation processes. Chemtech, 28 (4), 33 4. 

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For derivations that are more complex and a more detailed description of solid-liquid separation applications, the reader is referred to specialist texts e.g. Coulson and Richardson (1991), Purchas (1981), Purchas and Wakeman (1986), Matteson and Orr (1987), Wakeman (1990a,b), Cheremisinoff (1998), Sinnott (1999) and Svarovsky (2000). Several types of drier and associated drying theory are considered in detail in a number of texts, including Nonhebel and Moss (1971), Keey (1972, 1978, 1991), Masters (1985) and Coulson and Richardson (1991). 

The use of KnitMesh in a coalescer for liquid-liquid separation applications is illustrated in Figure 13.27 where an oil-water mixture enters the unit and passes through the coalescer element. As it does so, the water droplets coalesce and separation occurs between the oil and the water. After passing through the KnitMesh, the two phases are readily removed from the top and bottom of the unit. 

Much equipment for the separation of liquids and finely divided solids was invented independently in a number of industries and is of diverse character. These developments have occurred without benefit of any but the most general theoretical considerations. Even at present, the selection of equipment for specific solid-liquid separation applications is largely a process of scale-up based on direct experimentation with the process material. 

The relative suitability of the common kinds of solid-liquid separation applications is summarized in Table 11.3. Filtration is the most frequently used operation, but sedimentation as a method of pretreatment and centrifugation for difficulty filterable materials has many applications. Table 11.14 gives more detail about the kinds of filters appropriate to particular services. 

The reliability of separation/permeation performance is coupled with (a) fouling problems and (b) the stability of the micro(pore) structure of the membrane system. Fouling is a problem in almost all liquid separation applications. Strategies have been developed to cope with this problem, usually in a satisfactory way. 

In liquid separation applications interesting fields with micro- and ultrafiltration are ... 

In the biomedical applications outlined by Ward et al. (7 ), more so than in any other separation application of synthetic polymeric membranes, the goal is to mimic natural membranes. Similarly, the development of liquid membranes and biofunctional membranes represent attempts by man to imitate nature. Liquid membranes were first proposed for liquid separation applications by Li (46-48). These liquid membranes were comprised of a thin liquid film stabilized by a surfactant in an emulsion-type mixture. Wtille these membranes never attained widespread commercial success, the concept did lead to immobilized or supported liquid membranes. In... 

FIGURE 3.2-19 Vapor-liquid separator application range. 

The subroutine is well suited to the typical problems of liquid-liquid separation calculations wehre good estimates of equilibrium phase compositions are not available. However, if very good initial estimates of conjugate-phase compositions are available h. priori, more effective procedures, with second-order convergence, can probably be developed for special applications such as tracing the entire boundary of a two-phase region. 

Separation applications Separation cell Separation, liquid-liquid Separation, low energy Separation, magnetic Separation nozzle Separation of fatty acids Separations... 

Modification of Process Conditions Relatively small changes in process conditions often markedly affect the performance of specific solids-liquid separators, makiug possible their application when initial test results indicated otherwise or vice versa. Flocculating... 

L., and Thew M. T., (eds.). Hydrocyclones Analysis and Applications, p. 95, Kliiwer Academic Publishers, Dordrecht, The Netherlands, 1992. Dahlstrom D. A., Fundamental of Solid-Liquid Separation, Mnlar A. L., and Anderson,... 

Even though surtace-property-based liquid-solid-liquid separation techniques have yet to be widely used in significant industrial applications, several studies which demonstrate their effectiveness have appeared in literature. 

There are a large number of processes in the chemical industries that handle a variety of suspensions of solid particles in liquids. The application of filtration techniques for the separation of these heterogeneous systems is sometimes very costly. If, however, the discrete phase of the suspension largely contains settleable particles, the separation can be effected by the operation of sedimentation. The process of sedimentation involves the removal of suspended solid particles from a liquid stream by gravitational settling. This unit operation is divided into thickening,... 

Crystals suspended in liquors emerging from crystallizers are normally passed to solid-liquid separation devices such as gravity settlers or thickeners that may subsequently feed filters to remove yet more liquid prior to drying. Here the transport processes of particle motion and the flow of fluids through porous media are important in determining equipment size, the operation of which may be intensified by application of a centrifugal force. 

Crystallization-based separation of multi-component mixtures has widespread application. The technique consists of sequences of heating, cooling, evaporation, dilution, diluent addition and solid-liquid separation. Berry and Ng (1996, 1997), Cisternas and Rudd (1993), Dye and Ng (1995), Ng (1991) and Oyander etal. (1997) proposed various schemes based on the phase diagram. Cisternas (1999) presented an alternate network flow model for synthesizing crystallization-based separations for multi-component systems. The construction... 

L. J. Brice, W. H. Pirkle, Enantioselective transport through liquid membranes in Chiral separations, applications and technology, S. Ahuja (Ed.), American Chemical Society, Washington... 

The Sylvan Chart [2] of Figure 4-3 is useful in preliminary equipment selection, although arranged primarily for dust separations, it is applicable in the appropriate parts to liquid separations. Perry [23] presents a somewhat similar chart that is of different form but contains much of the same information as Figure 4-1 and 4-lA. 

Two other major factors determining module selection are concentration polarisation control and resistance to fouling. Concentration polarisation control is a particularly important issue in liquid separations such as reverse osmosis and ultrafiltration. Hollow-fine-fibre modules are notoriously prone to fouling and concentration polarisation and can be used in reverse osmosis applications only when extensive, costly feed solution pretreatment removes all particulates. These fibres cannot be used in ultrafiltration applications at all. 

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