Studies on The Ultrasonic Enhancement of The Catalytic Activity in The Hydrogenation of Citral

Abstract

Acoustic energy is mechanical by its nature. Cavitation bubbles are formed, provided that the intensity of ultrasonic field is sufficiently high. Cavitation close to the liquid-solid interface differs from that in pure liquid. Different mechanisms for the effects of cavitation close to the surfaces have been proposed: microjet impact and Shockwave damage (Suslick, 1990, Suslick et al. 1987). Heterogeneous catalysis involving suspended solid particles in liquid is accelerated by the use of acoustic irradiation. However, studies in the regenerating effect of acoustic irradiation in catalysts are sparse. The localized erosion and grinding caused by these phenomena are responsible for ultrasonic cleaning, generating newly exposed, highly active surface. In this work, we studied on-line acoustic irradiation in batchwise, three-phase hydrogenation of citral to citronellal and citronellol over a Raney nickel catalyst. Citral can be used in the preparation of citronellol (referred as OL hereafter) or citronellal (referred as AL hereafter), to be utilized by parfume industry etc. due to their pleasant odor (Mäki-Arvela et al, 1997; Salmi et al, 2000).