Triphase catalysis: mass transfer and kinetic studies

The importance of phase transfer catalysis (PTC) in the production of high value chemicals has grown immensely over the past few years. PTC may be a suitable method to synthesize a product whenever each reactant is miscible in a different phase. By addition of a PT catalyst, which functions as a ferrying agent between the phases, significant rate enhancements can be achieved;The PT catalyst (e.g. a quaternary ammonium salt) is usually used in soluble form. Alternatively, it can be bound to a solid support. The latter technique is called triphase catalysis (TPC). It has operational advantages over conventional PTC due to its potential use in continuous processes. However, the solid support (usually a porous polymer) induces diffusional limitations and consequently reduces overall reaction rates;The objective of the present research is to develop a method to determine external mass transfer coefficients since many TPC systems may be film diffusion limited under typical reaction conditions. A rotating disk contactor (RDC) has been specifically designed for this purpose. From the data obtained from this unit, it is possible to calculate mass transfer coefficients of several reaction systems and to suggest a general equation that correlates the Sherwood number to the Reynolds and Schmidt numbers;In view of conflicting reports on the efficacy of supported PTC, a comparative assessment of heterogeneous and homogeneous catalysts has been made for different mechanistic categories of PTC systems. It is possible to identify conditions under which the supported catalyst performs distinctly better than its soluble counterpart. The solubility of the homogeneous catalyst in the organic phase is found to be the most important factor in determining catalytic activity. Under certain conditions, polarity changes of the organic bulk phase induces autocatalytic behavior, an observation not hitherto made. In conclusion, it can be stated that certain categories of heterogenized catalysts perform better than their soluble counterparts for some reactions, notwithstanding their natural predilection to hinder reaction by diffusional limitation. This fact, coupled with the operational advantages of triphase catalysis, opens up the distinct possibility of its acceptance by industry