Studies in immobilized phase transfer catalysis

Phase transfer catalysis has been in use for over three decades, but triphase catalysis, where the phase transfer catalyst is immobilized on a solid support, is of much more recent origin. Triphase catalysts offer many advantages associated with heterogeneous catalysts such as easy separation from the reaction mixture, reusability, and use in continuous reactors. These significant advantages notwithstanding, triphase catalysts have not attracted industrial attention. The main reason for the lack of industrial in triphase catalysts is their reduced activity due to diffusional limitations. Another reason is the lack of understanding of the complex diffusion-reaction problem associated with triphase catalysis.; The objective of this work is to understand the principles behind triphase catalysis to make it industrially attractive. A detailed mathematical model has thus been developed to study the diffusion-reaction problem in triphase catalysis. Also, experimental work in developing an optimal support for phase transfer catalyst has been carried out. A review of the field is given followed by the development of a mathematical model for liquid-liquid-solid triphase catalysis. Simulation studies show that the reversibility of the ion exchange reaction in the aqueous phase plays a significant role in the overall conversion.; In order to understand the effect of nonisothermality of the reaction, a dynamic model for triphase catalysis system which includes intraparticle heat transfer effects was developed. It was found that for highly exothermic reactions, catalyst effectiveness greater than unity could be obtained. Another significant observation is that in an unsteady state reactor, like the slurry reactor used in the present work, there is an optimum with respect to the reaction time.; To address the issue of reduced activity of triphase catalysts in comparison to their soluble analogs, experimental work was carried out on esterification of benzyl chloride with aqueous sodium acetate using solid supported phase transfer catalyst. Reactivities of the triphase catalysts were compared with those of comparable soluble phase transfer catalysts. The polymer bound tributylmethylammonium chloride has higher reactivity than its soluble analogs. Possible reasons for increased reactivity and the implications of this important finding in future research are discussed.