Comparison between the Performances of a Well-Stirred Slurry Reactor and a Spray Loop Reactor for the Alkylation of p-Cresol with Isobutene Elio Santacesaria,* Martino Di Serio, Riccardo Tesser, and Francesco Cammarota Universita ` di Napoli - Dipartimento di Chimica-Via Cinthia - Complesso Universitario di Monte S. Angelo, 80126 - Napoli - Italy The kinetics of the alkylation of p-cresol with isobutene has been studied, first of all, in a well- stirred slurry reactor. Preliminary runs of CO 2 absorption in water and of isobutene absorption in p-cresol, in the same reactor, have been made for estimating the gas-liquid mass-transfer coefficient in an independent way. The kinetic model, developed in a previous work, has been improved and the related parameters have been determined by mathematical regression analysis of many kinetic runs. Different kinetic runs have then been performed also by using a spray tower loop reactor (STLR) in similar physical conditions. These runs have been simulated in a satisfactory way by using the same kinetic model and parameters, changing only mass-transfer parameters for taking into account the different fluid dynamic conditions. The performances obtained by the two different reactors are in some conditions comparable. This work has demonstrated, therefore, the possibility and the convenience of extending the use of STLR reactors in performing gas-liquid-solid reactions. Introduction The behavior of multiphase reactors is often strongly affected by mass-transfer limitations, and different types of reactor configurations (bubble columns, jet loop reactors, spray tower loop reactors, and mechanically agitated reactors) are employed, depending on the characteristics of the reactions. Spray tower loop reac- tors (STLR) are largely employed for very fast reactions, such as neutralization reactions or pollutant abatement by absorption from gaseous mixtures. One of the main applications for spray contactors, for example, is in gas stream desulfurization. 1 It is important to point out that in STLR reactors the liquid is the dispersed phase instead of the gaseous one, as it occurs in the other mentioned reactors. The role of the mass-transfer limitations in these conditions have been poorly investigated in the literature. 2-7 In a previous work 6 we have shown that a STLR reactor can be conveniently used for some gas-liquid reactions provided that the solubility of the gaseous reagent is high enough. In particular we have studied the ethoxylation of different organic substrates, 8-11 and we concluded that, for moderately fast reactions (with Hatta no. = 1), the use of a STLR reactor can be more convenient than one of the other reactors, such as, for example bubble columns or well-stirred reactors. As a matter of fact, we have found that the gas-liquid mass- transfer rate in a STLR reactor is very high when a suitable spray nozzle is used and the behavior of the reactor can be interpreted with a mathematical model that assumes the produced droplets are internally well- mixed. 6 Moreover, we have evidence that, in some cases, the spray tower loop reactors can give better perfor- mances of the mechanically agitated reactors with the advantage of the absence of any rotating device and with the possibility of operating easily also at high pressure. A further positive aspect of the STLR reactor is the separation existing between the mass-transfer zone and the reaction one, inside the reactor, in the presence of a moderately fast gas-liquid reaction, and this is an element of greater flexibility. In the present work, we have studied the possibility of extending the use of the STLR reactor also to gas- liquid-solid reactions. No paper has been published exploring this possibility. We will consider here and discuss all the possible constraints in the use of a STLR reactor in performing gas-liquid-solid reactions, by examining also the possible advantages and drawbacks of the proposed technique. To do this, we have chosen for our investigation the alkylation of p-cresol with isobutene as a test reaction. This reaction, catalyzed by acid exchange resins, occurs in two consecutive steps, 12,13 the first giving 2-tert-butyl-p-cresol (M) and the second 2,6 di-tert-butyl-p-cresol (BHT). Isobutene can also give place to oligomers as side products and, normally, only dimerization (D) and trimerization (T) occur. In the present work, the reaction has been performed in both a well-mixed gas-liquid-solid reactor and in a spray tower loop reactor. The kinetic model developed in a previous work 12 has been improved in view of a possible scale-up, and more reliable kinetic parameters have been determined by mathematical regression analysis on many more kinetic runs performed in the slurry reactor. The same kinetic model has also been successfully used for simulating the kinetic runs per- formed in the STLR reactor. The performances of the two reactors have then been compared with particular attention devoted to the effect of mass-transfer limita- tions. A preliminary fluid dynamic characterization has been performed for both of the reactors by studying the physical absorption of CO 2 in water. Experimental Section Apparatus, Methods, and Reagents. Two different reactors have been used for studying the kinetics and * To whom correspondence must be addressed. E-mail: santacesaria@chemistry.unina.it. 9473 Ind. Eng. Chem. Res. 2005, 44, 9473-9481 10.1021/ie050221j CCC: $30.25 © 2005 American Chemical Society Published on Web 08/06/2005