Permeation-Based Products

Rubber-based products permeate our lives, forming part of the many materials used for personal, domestic and industrial purposes. Rubber may be natural, synthetic or a mixture of the two. Since the vast majority of rubberized materials are unlabeled, it is difficult to determine whether a product contains natural or synthetic rubber. The overlap between rubber and plastic further complicates the matter, especially since plastics contain many of the same catalysts, stabilizers, antioxidants and pig-ments/dyes that are present in rubber products. Fregert (1981) listed a number of naphthylamines, substituted para-phenylenediamines, alkylphenols and hydroquinone derivatives, which are utilized in the manufacturing of both rubber and plastic. Although completely cured plastics are rare sensitizers, fully cured rubber products produce allergic reactions as the sensitizers in rubber can leach out or bloom over time. 

A) Adsorption selectivity (from CCMC simulations for binary mixtures taking /j = 0.5 MPa at the upstream face), (B) diffusion selectivity sei/ 2seif> evaluated at the total mixture loading at the upstream face), and (C) resulting permeations selectivity (=product of the adsorption and diffusion selectivities) [2]. The graphs were constructed based on the data from [8]. 

Pervaporation is a membrane-based product recovery technique. In this process, membrane is used to selectively separate volatile compounds (eg, ethanol and butanol). Volatile compounds in the liquid diffuse through the membrane and evaporate into vapor, and are collected by condensation (Yang and Lu, 2013). A partial pressure difference across the membrane is required to volatilize permeates into vapor. Polydimethylsilox-ane (PDMS) membrane has been extensively used for pervaporation separation of acetone, butanol, and ethanol (Liu et al., 2005). 

The hydrophobic macroporous polystyrene beads are exceptionally chemically stable and are used for organic phase gel permeation chromatography products, Styragel (Waters) and PLgel (Polymer Laboratories) and reversed phase HPLC separations, PRP (Hamilton) and PLRP-S (Polymer Laboratories). It is possible to surface modify the particle to mask the hydrophobicity of the base polymer and produce ion exchange and hydrophilic materials, PI SAX, PL-GFC (Polymer Laboratories). In the microporous form after derivatisation to form strong cation exchangers these materials are commonly used for carbohydrate and amino acid separations, Aminex (BioRad). 

Table 5 presents typical operating conditions and cell production values for commercial-scale yeast-based SCP processes including (63) Saccharomjces cerevisae ie, primary yeast from molasses Candida utilis ie, Torula yeast, from papermiU. wastes, glucose, or sucrose and Klujveromjces marxianus var fragilis ie, fragihs yeast, from cheese whey or cheese whey permeate. AH of these products have been cleared for food use in the United States by the Food and Dmg Administration (77). 

In a very recent study, it has been demonstrated116 that zinc 5,15-bis(3,5-di-tert-butylphenyl)-porphyrin (13) without any activating halogen atoms at the chromophore can be directly linked in a very simple oxidative coupling reaction with silver(I) hexafluorophosphate to a mixture of porphyrin dimers, trimers and tetramers. The separation of the product mixture was achieved by gel-permeation chromatography based on the molecular weights of the oligomers. The dimer when re-exposed to the same reaction conditions yielded 25% of the tetramer.116... 

Plastics packaging and contained food products are chemically related in four distinct ways. This relationship is based largely on the permeation property of the plastic material. Direct chemical reaction between plastic and product is seldom a problem when inert plastics such as polyethylene are used. However, polyethylene can transmit minute amounts of product to the outside. This paper examines the effect of permeation through the plastic wall and the direct effects of the plastic on the food product. Specific food packaging applications and methods of testing are discussed. 

The system area A needed for batch or fed-batch operation can be calculated by using the formulas in Table 20-19 for production rates V(/t based on feed volume Vq and average fluxes during process steps. The final retentate batch volume Vr = Vq/X or permeate batch volume Vp = Vo(l — l/X + N/X) can be used to restate the production rate on other bases. Although experience can be used to estimate solute passage and process fluxes, they should be determined e3q)erimentally for each application. 

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