Continuous liquid interface production

Biphasic systems are composed of two continuous liquid phases the organic and the aqueous phases [13,25,27,31,36]. An interface generally separates the aqueous phase containing the biocatalyst from the organic phase containing the substrate. Moreover, the reaction product, if poorly soluble in water, can be easily separated from the biocatalyst. The use of carefully measured concentrations in hydrophobic reactants becomes facile in such systems, and substrate excess inhibition of the biocatalyst is reduced. 

Boundary conditions are 5T/0n = 0 (n is the normal to interface surface) on the gas-solid interface and on the symmetry lines as far as on the external wall surface (for case of channel with heat production in the wall) continuity both of heat flux and temperature on solid-liquid interface and the continuity of temperature on gas-liquid interface. Gauss-Zeidel iterative procedure has been used to solve the heat problem numerically. We used a non-uniform grid pattern near the vapor-liquid interface for higher computational accuracy. 

These mixed-surfactant systems are used not only for their ability to form complex condensed films at the liquid-liquid interface, enhancing the stability of the emulsion, but also because of their ability to impart body to the product, resulting in a semisolid product rather than a liquid. Mixed emulsifiers control the consistency of a cream by forming a viscoelastic network throughout the continuous phase of the emulsion. The network results from the interaction of the mixed emulsifier with water, forming a liquid crystalline phase. 

To derive the overall kinetics of a gas/liquid-phase reaction it is required to consider a volume element at the gas/liquid interface and to set up mass balances including the mass transport processes and the catalytic reaction. These balances are either differential in time (batch reactor) or in location (continuous operation). By making suitable assumptions on the hydrodynamics and, hence, the interfacial mass transfer rates, in both phases the concentration of the reactants and products can be calculated by integration of the respective differential equations either as a function of reaction time (batch reactor) or of location (continuously operated reactor). In continuous operation, certain simplifications in setting up the balances are possible if one or all of the phases are well mixed, as in continuously stirred tank reactor, hereby the mathematical treatment is significantly simplified. 

System 1 In a gas-liquid continuous-stirred tank reactor (Figure 13-If. the gaseous reactant was bubbled into the reactor while the liquid reactant was fed through an inlet tube in the reactor s side. The reaction took place at the gas-liquid interface of the bubbles, and the product was a liquid. The continuous liquid phase could be regarded as perfectly mi.xed. and the reaction rate was proportional to the total bubble surface area. The surface area of a particular bubble depended on the time it had spent in the reactor. Because of their different sizes, some gas bubbles escaped from the reactor almost immediately, while others spent so much time in the reactor that they were almost coin-... 

In particular, for the synthesis of optically pure chemicals, several immobilization techniques have been shown to give stable and active chiral heterogeneous catalysts. A step further has been carried out by Choi et al. [342] who immobilized chiral Co(III) complexes on ZSM-5/Anodisc membranes for the hydrolytic kinetic resolution of terminal epoxides. The salen catalyst, loaded into the macroporous matrix of Anodise by impregnation under vacuum, must exit near the interface of ZSM-5 film to contact with both biphasic reactants such as epoxides and water. Furthermore, the loading of chiral catalyst remains constant during reaction because it cannot diffuse into the pore channel of ZSM-5 crystals and is insoluble in water. The catalytic zeolite composite membrane obtained acts as liquid-liquid contactor, which combines the chemical reaction with the continuous extraction of products simultaneously (see Figure 11.28) the... 

Turbulence contributions for the continuous and dispersed phases have been based on a modified form of the standard multiphase k-e equations, first presented by Kashiwa et al. (1993) and described in detail by Padial et al. (2000), to calculate turbulence at the gas-liquid interface in the form of a slip-production energy term. 

When corrosion products such as hydroxides are deposited on a metal surface, a reduction in oxygen supply occurs, since the oxygen has to diffuse through deposits. Since the rate of metal dissolution is equal to the rate of oxygen reduction, a Hmited supply and limited reduction rate of oxygen will also reduce the corrosion rate. In this case the corrosion is said to be under cathodic control. In other cases corrosion products form a dense and continuous surface film of oxide closely related to the crystalline structure of metal. Films of this type prevent primarily the conduction of metal ions from metal-oxide interface to the oxide-liquid interface, resulting in a corrosion reaction that is under anodic control. When this happens, passivation occurs and metal is referred as a passivated metal. Passivation is typical for stainless steels and aluminum. 

In the liquid acid-catalyzed processes, the hydrocarbon phase and the acid phase are only slightly soluble in each other in the two-phase stirred reactor, the hydrocarbon phase is dispersed as droplets in the continuous acid phase. The reaction takes place at or close to the interface between the hydrocarbon and the acid phase. The overall reaction rate depends on the area of the interface. Larger interfacial areas promote more rapid alkylation reactions and generally result in higher quality products. The alkene is transported through the hydrocarbon phase to the interface, and, upon contact with the acid, forms an acid-soluble ester, which slowly decomposes in the acid phase to give a solvated... 

Of the analytical techniques available for process analytical measmements, IR is one of the most versatile, where all physical forms of a sample may be considered - gases, liquids, solids and even mixed phase materials. A wide range of sample interfaces (sampling accessories) have been developed for infrared spectroscopy over the past 20 to 30 years and many of these can be adapted for either near-lme/at-lme production control or on-line process monitoring applications. For continuous on-line measurements applications may be limited to liquids and gases. However, for applications that have human interaction, such as near-line measurements, then all material types can be considered. For continuous measurements sample condition, as it exists within the process, may be an issue and factors such as temperature, pressure, chemical interfer-ants (such as solvents), and particulate matter may need to be addressed. In off-line applications this may be addressed by the way that the sample is handled, but for continuous on-line process applications this has to be accommodated by a sampling system. 

---