Liquid biphasic systems, kinetics

Joni, J., Schmitt, D., Schulz, P.S., Lotz, T.J. and Wasserscheid, P., Detailed kinetic study of cumene isopropylation in a liquid-liquid biphasic system using acidic chloroaluminate ionic liquids, J. Catal. 258, 401-409 (2008). 

To estimate costs for the liquid-liquid biphasic hydroformylation using ionic liquids, a process was designed for the production of 100,000 tons per year of nonanal. The use of ionic liquids in hydroformylation catalysis is a fairly new technology and exact kinetic data are scarce, thus the TOFs reported for the Rh-sulfoxantphos system [80] have been used to determine catalyst inventory and reactor dimensions. In a similar way the plant design for the SILP process for a production capacity of 100,000 tons per year of butanal has been derived based on preliminary literature results [68]. The process flow sheets for both process variations are shown in Figures 7.12 and 7.13. 

Biphasic systems consisting of ionic liquids and supercritical CO2 showed dramatic enhancement in the operational stability of both free and immobilized Candida antarctica lipase B (CALB) in the catalyzed kinetic resolution of rac- -phenylethanol with vinyl propionate at 10 MPa and temperatures between 120 and 150°C (Scheme 30) 275). Hydrophobic ionic liquids, [EMIM]Tf2N or [BMIM]Tf2N, were shown to be essential for the stability of the enzyme in the biotransformation. Notwithstanding the extreme conditions, both the free and isolated enzymes were able specifically to catalyze the synthesis of (J )-l-phenylethyl propionate. The maximum enantiomeric excess needed for satisfactory product purity (ee >99.9%) was maintained. The (S)-l-phenylethanol reactant was not esterified. The authors suggested that the ionic liquids provide protection against enzyme denaturation by CO2 and heat. When the free enzyme was used, [EMIM]Tf2N appeared to be the best ionic liquid to protect the enzyme, which... 

As well as biocatalysis in neat organic solvents and biphasic systems (fundamentals and synthetic applications), the present volume covers new and promising aspects of non-aqueous enzymology that have emerged in recent years, including biocatalysis with undissolved solid substrates or vaporized compounds, the use of ionic liquids as solvents, and the preparative-scale exploitation of oxynitrilases and dynamic kinetic resolutions . For the sake of completeness and comparison,... 

Therefore, important parameters such as phase transfer phenomena (i.e. solubility of the reactants in the ionic liquid phase), volume ratio of the different phases, efficiency of mixing so as to provide maximum liquid-liquid interfacial area, are key factors in determining and controlling reaction rates and kinetics. Kinetic models have been developed for aqueous biphasic systems and are continuously refined to improve agreement with experimental results. These models might be transferable to biphasic catalysis with ionic liquids, but more data concerning the solubility ofliq-uids (and gas) in these new solvents and the existence of phase equilibria in the presence of organic upper phases have still to be accumulated (see Sections 3.3 and 3.4). 

Purwanto and Delmas [10] proposed the addition of co-solvent (ethanol) to enhance the solubility of 1-octene in the aqueous phase so that the overall reaction rate was increased, and their kinetic study led to a rate model similar to that in homogeneous liquid systems consistently from the point of view of bulk reaction mechanism. Chaudhari et al. [11] reported the improvement of the hydroformylation rate by addition of a small amount of PPhj to the biphasic system to enrich the effective catalyst species at the liquid-liquid interface. Kalck et al. [12] tested two more approaches to improve the mass transfer rate of biphasic hydroformylation of 1-octene and 1-decene with catalyst precursor [Rh2(/i-S Bu)2(CO)2(TPPTS)3j use the phase-transfer agent /i-cyclodextrin to transport the substrate into the aqueous phase to react there (see Section 2.2.3.2.2), and the supported aqueous-phase (SAP) catalyst to increase the reaction area due to the high specific surface area of porous silica (see Section 2.6). The improved conversion and TOF gave informative suggestions for the reaction mechanisms. 

Biphasic hydroformylation is a typical and complicated gas-liquid-liquid reaction. Although extensive studies on catalysts, ligands, and catalytic product distributions have appeared, the reaction mechanism has not been understood sufficiently and even contradictory concepts of the site of hydroformylation reaction were developed [11, 13, 20]. Studies on the kinetics of hydroformylation of olefins are not only instructive for improvement of the catalytic complexes and ligands but also provide the basic information for design and scale-up of novel commercial reactors. The kinetics of hydroformylation of different olefins, such as ethylene, propylene, 1-hexene, 1-octene, and 1-dodecene, using homogeneous or supported catalysts has been reported in the literature. However, the results on the kinetics of hydroformylation in aqueous biphasic systems are rather limited and up to now no universally accepted intrinsic biphasic kinetic model has been derived, because of the unelucidated reaction mechanism and complicated effects of multiphase mass transfer (see also Section 2.4.1.1.2). 

Several experiments using different organic solvents in different biphasic media are necessary to find the adequate distribution of the reaction components. A series of experiments are essential for the choice of a process and for scaling-up. Experiments using Lewis cells [44] may yield useful results for understanding equilibrium, kinetics, and interactions between organic solvent-substrate and/or organic solvent-biocatalyst. A study of two-liquid phase biotransformation systems is detailed below in Sections II-IX. 

Amiali et al. (2005) inactivated S. enteritidis and/or E. coli 0157 H7 in liquid whole egg using a continnous PEF system in combination with heal The bacteria were treated at 10°C, 20°C, or 30°C using EF intensity of either 20 or 30kV cm". A biphasic instant reversal PEF waveform with np to 105 pulses of 2ps in pulse width was applied. The maximum reduction of 3.9 and 3.6 log cycles were obtained for E. coli 0157 H7 and S. enteritidis, respectively. Higher kinetic constant value was obtained for S. enteritidis (0.043 ps ), representing the more heat-PEF-sensitive bacteria compared to E. coli 0157 H7. 

This chapter describes our recent advances on the utilization of polymer-modified laccase complexes in aqueous systems towards the oxidation/polymerization of naturally hydro-phobic steroidal compounds, Equilin (EQ) and 17-P-estradiol (P-EST). We elucidate the kinetic and synthetic aspects of the process with the model compoimd 5,6,7,8-tetrahydro-2-naphthol (THN). The nano-reactor system is composed of linear poly(ethylene oxide)-dendritic poly(benzyl ether) diblock copolymer (G3-PE013k) and laccase isolated from Trametes versicolor. Other advantages of the complex in comparison to the native enzyme are its recyclability, enhanced stability, activity, and overall simplicity in product harvesting and isolation. A principle of action of the complex is suggested based on these findings and is further supported by the biphasic solid-liquid nature of the reaction medium, which exhibits continuous influx of starting material and steady solid product expulsion. Comparative experiments with linear-linear poly(styrene)-Woc -poly(ethylene oxide) copolymer under identical conditions do not evince formation of a... 

The biphasic hydroformylation of 1-octene was studied in the presence of ethanol as a co-solvent and a proposed kinetic rate expression was nearly identical to that of the homogeneous system [10, 23]. A further kinetic study of this biphasic hydroformylation system was conducted by Lekhal et al. [6] to analyze the experimental data by coupling kinetics to a pseudo-homogeneous gas-liquid-liquid macroscopic conservation model the authors proved that gas-hquid mass transfer was the only limitation. 

Liquid-liquid-solid reactors are commonly used for biphasic reactions catalyzed by immobilized phase-transfer catalysts (which form the third, solid phase). Certain basic aspects of such reactors were considered in Chapter 19. Three-phase reactions of this type are also encountered in biological reactions, for example, the enzymatic synthesis of amino acid esters in polyphasic media (Vidaluc et al., 1983), and the production of L-phenylalanine utilizing enzymatic resolution in the presence of an organic solvent (Dahod and Empie, 1986). Predictably, the performance of these reactors is influenced by the usual kinetic and mass transfer aspects of heterogeneous systems (see Lilly, 1982 Chen et al., 1982 Woodley et al., 1991a,b). Additionally, performance is also influenced by the complex hydrodynamics associated with the flow of two liquids past a bed of solids (Mitarai and Kawakami, 1994 Huneke and Flaschel, 1998). It is noteworthy, for instance, that phase distribution within the reactor is different from that in the feed and is also a function of position within the reactor and within the voids of each pellet in the bed. More intensive research is needed before these reactors can be rationally designed. 

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