Membrane filtration, advantages

In addition to the insoluble polymers described above, soluble polymers, such as non-cross-linked PS and PEG have proven useful for synthetic applications. However, since synthesis on soluble supports is more difficult to automate, these polymers are not used as extensively as insoluble beads. Soluble polymers offer most of the advantages of both homogeneous-phase chemistry (lack of diffusion phenomena and easy monitoring) and solid-phase techniques (use of excess reagents and ease of isolation and purification of products). Separation of the functionalized matrix is achieved by either precipitation (solvent or heat), membrane filtration, or size-exclusion chromatography [98,99]. 

The collection of small amounts of very fine precipitates is the basis for many chemical and biochemical analytical procedures. Membrane filtration is an ideal method for sample collection. This is of great advantage in the... 

Membrane filters have a much better separation efficiency, and oil entrainment is reduced to 40 45% (Deffense, 2000). With softer and/or less evenly sized crystals, such as the crystals that tend to be obtained in the De Smet crystallization process, membrane filters are much preferred. However, membrane filters are being used increasingly for all crystallization systems to get better separations and less oil entrainment, especially in multistep fractionation, where crystals can become more difficult to filter. An added advantage is that membrane filtration is easier to conduct under an inert gas. 

At that time, we saw the most accessible market in the pharmaceutical and food and dairy industries, because within these industries membrane filtration was so advantageous that the relatively high investment and operating costs were no impediment. 

Security in delivery is most likely best obtained by dealing with companies of a reasonable size and well introduced in the field of membrane filtration. But also here, the plate-and-frame system has an additional advantage, because membranes from other manufacturers who can cast membranes in sheet form can be used direct in our modules, though this is not something DDS is very much in favour of. 

In recent years, developing technology has led to the use of ultrafiltration and microfiltration membranes for juice clarification (1,4-13). The use of membranes has several advantages. Lower labor costs may be possible due to automation possibilities of membrane filtration (8). Filter aids such as diatomaceous earth (DE) aren t needed (9) so that product that would have been discarded with DE is saved, and DE acquisition and disposal costs are eliminated. Enzymes may be rejected by ultrafiltration membranes (4,12) causing the ultrafiltration equipment to act as an enzyme reactor (12), although some odor-active volatiles may be retained, resulting in some loss or change in flavor (8). 

For industrial biotransformations, catalyst recovery and reuse are major issues. This may be desirable either for reasons of downstream processing or for repeated use in order to reduce the specific catalyst costs per kg of product produced. A very simple method is the use of membrane filtration. Because of the increasing number of membranes from different materials (polymers, metal or ceramics) this is an attractive alternative. Whereas for whole cells microfiltration or centrifugation can be applied, for the recovery of soluble enzymes ultrafiltration membranes have to be used120-221. Often immobilization on a support is chosen to increase the catalyst s stability as well as to facilitate its recovery. The main advantages of immobilization are ... 

Alternatively, membrane filtration can be used to separate soluble metal complexes, containing polymer-attached ligands, from reactants and products [43]. A major advantage of using soluble polymer-enlarged catalysts in conjunction with membrane separation is that it is readily amenable to continuous operation. A novel example of this concept is the use of dendritic ligands [44] in combination with membrane filtration. 

Soluble polymers also can be separated by liquid/liquid separations. These liquid/liquid separations can involve membrane filtrations that use to advantage the relative size differences of macromolecules and low molecular weight substrates. Alternatively, the physical size or the phase-selective solubility of macromolecules can be used to advantage, separating a solution of a macro-molecule-bound ligand or catalyst from a low molecular weight product on the basis of size or phase-selective solubility (Fig. 2). 

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