Immiscible process selection method

Although blending is an easy method for the preparation of TPEs, most of the TPE blends are immiscible. Very often the resulting materials exhibit poor mechanic properties due to the poor adhesion between the phases. Over the years different techniques have been developed to alleviate this problem. One way is to alter the blending technique so that the interfacial area between the component phases can be increased. By the proper selection of the processing technique either a co-continuous or... 

Most methods of separating molecules in solution use direct contact of immiscible fluids or a sohd and a fluid. These methods are helped by dispersion of one phase in the other, fluid phase, but they are hindered by the necessity for separating the dispersed phase. Fixed-bed adsorption processes overcome the hindrance by immobilizing the solid adsorbent, but at the cost of cyclic batch operation. Membrane processes trade direct contact for permanent separation of the two phases and offer possibilities for high selectivity. 

In the previous sections, methods of qualitatively controlling the course of propagation were described. Indirect control as well as the quantitative effects caused by intentional control of the other partial processes in polymerization have still to be mentioned. The separation of initiation from propagation alters the kinetic character of the whole reaction. With ionic polymerizations, initiation can be separated from propagation by the selection of conditions suitable for rapid initiation. With radical polymerizations, this is not possible. Therefore both partial processes must be separated in space. Fortunately, radical active centres operate both in polar and in non polar media. Thus it is not difficult to confine initiation and propagation to mutually immiscible components of the medium. Emulsion polymerization remains the most important representative of quantitative control of propagation. 

Some solvent-extraction techniques are relatively difficult to effect using conventional laboratory apparatus. For example, the classical penicillin G extraction in which acidified broth is contacted with a water-immiscible solvent can only be operated effectively using continuous-flow methods because of the poor stability of the product at low pH values. This extraction can be reproduced on the bench scale using the AKUFVE apparatus, which was designed for extraction studies in the nuclear industry (12,13). Selective extraction may involve the use of a solvent in which the product has a poor partition coefficient. Countercurrent extractors are mostly process scale devices but the smallest four-stage extractor produced by Robatel could be considered a bench scale. It has a throughput of 50-100 mL/min. 

However, another criterion that needs to be considered for the selection of a suitable ISPR method is the mode of contact between the microorganisms and the separation phase that removes the product from the vicinity of the cell. Direct contact between the microorganism and a water-immiscible solvent (phase toxicity) or solid adsorbent material can have inhibitory effects on the cell [31,33]. Therefore, this direct contact limits the choice of separative aids. In addition, stability and robustness of a process is reduced if the cells are in direct... 

All methods of chromatography operate on the principle that the components of a mixture will distribute unequally between two immiscible phases, which is also the basis for separations by extraction (Chap. 5). The mobile phase is generally a liquid or a gas that flows continuously over the fixed stationary phase, which may be a solid or a liquid. The individual components of the mixture have different affinities for the mobile and stationary phases, so a dynamic equilibrium is established in which each component is selectively, but temporarily, removed from the mobile phase by binding to the stationary phase. When the equilibrium concentration of that substance in the mobile phase decreases, it is released from the stationary phase and the process continues. Since each component partitions between the two phases with a different equilibrium constant or partition coefficient, the components divide... 

Another reactive separation processes studied for ethyl lactate production is the catalytic extractive reaction (Figure 20.4.7). In this case, the esterification is performed in a biphasic liquid solvent system composed by a reactive polar liquid phase which contains the esterification constituents lactic acid, eflianol and catalyst, and an extractive organic solvent selective of the ester. Therefore, ethyl lactate should preferably be dissolved in the extractive organic phase shifting, in this way, the reaction equilibrium to ester formation. The immiscible extractive solvent is an aromatic or other solvent like toluene, benzene or diethyl ether, among others. Nevertheless, it has also been used an immiscible solvent based on fatty acid methyl ester, but in this case, the procedure represents a method to produce an organic biosolvent and not just ethyl lactate as solvent. 

---