Date of Award
Doctor of Engineering Science in Chemical Engineering
Chemical Engineering and Chemistry
Saul I. Kreps
Dimitrios P. Tassios
The effect of ultrasonic vibrations on the vapor phase decomposition of cumene to benzene and propylene was investigated employing silica-aluminum cracking catalyst.
The catalytic reactor consisted of a 1 cm. diameter stainless steel tube containing a 20 in. long preheater and a 4 in. long catalyst chamber. The catalyst bed was irradiated from above by means of an ultrasonic horn which transmitted acoustical energy directly into the vapor.
The reactor was run at temperatures of 650°F. and 1050°F., frequencies of 26,000 cps and 39,000 cps, feed rates of 20 to 600 gms./hr., power outputs of 0.5 to 1.3 watts/cm.2, and catalyst loadings of approximately 1 to 6 grams.
At temperatures and flow rates where external bulk diffusion controlled the rate of reaction, the application of ultrasound resulted in increases in the mass transfer coefficient up to 40%. In the area where surface reaction and internal pore diffusion controlled, the combined catalyst effectiveness factor - surface reaction rate constant was increased by up to 160%.
Confidence intervals were calculated for the coefficients of the equations expressing log kg as a function of T and log εLk2 as a function of 1/T . The analysis of variance indicated that the increases in mass transfer coefficients and combined catalyst effectiveness factor - surface reaction rate constants were significant at ultrasonic frequencies of 39,000 cps. The increases obtained between frequencies of 26,000 cps and no ultrasound were of lesser significance.
It is postulated that ultrasound causes acoustic streaming within the reactor tube and catalyst pores, resulting in higher transport rates caused by the combined effect of diffusion and forced convection as compared to the effect of diffusion alone in the absence of ultrasound. In addition, acoustic energy may cause localized heating within the catalyst bed, thereby increasing the rate of surface reaction.
Lintner, William, "The effect of ultrasonic vibrations on heterogeneous catalysis" (1973). Dissertations. 1288.