Research Article Kinetics and Modeling of Fatty Alcohol Ethoxylation in an Industrial Spray Loop Reactor The kinetics of the ethoxylation of fatty alcohols catalyzed by potassium hydro- xide was studied to obtain the rate constants for modeling of the industrial pro- cess. Experimental data obtained in a lab-scale semibatch autoclave reactor were used to evaluate kinetic and equilibrium parameters. The kinetic model was em- ployed to model the performance of an industrial-scale spray tower reactor for fatty alcohol ethoxylation. The reactor model considers that mass transfer and re- action occur independently in two distinct zones of the reactor. Good agreement between the model predictions and real data was found. These findings confirm the reliability of the kinetic and reactor model for simulating fatty alcohol ethoxy- lation processes under industrial conditions. Keywords: Ethoxylation, Fatty alcohol, Kinetic model, Mathematical model, Spray loop reactor Received: May 03, 2011; revised: May 31, 2011; accepted: July 04, 2011 DOI: 10.1002/ceat.201100215 1 Introduction The nonionic surfactants, represented mostly by linear ethoxylated alcohols, have experienced a growing demand in the last decade. The reasons for this growth are their excellent detergency properties, along with their rapid biodegradability and low toxicity. The polyoxyethylene surfactants are commercially produced by the oligomerization reaction of ethylene oxide (EO) and/or propylene oxide with an active hydrogen-containing compound (RXH). The starter is composed of hydrophobic molecules with a polar group in their termination. The final product can be represented by the general formula RX(CH 2 CH 2 O) n H, where R can be hydrogen (for polyglycols) or a hydrophobic group (usually C1 to C12) and X represents a heteroatom such as O, S, or N [1]. The final product is formed by molecules with different numbers (n) of added EO units that can vary from 0 to 20, depending on the product desired. The chain distribution is important because it influences the product application. Short-chain products are used for oil removal whereas long-chain length products are used for liquid household detergents. The reaction is usually performed in batch reactors. Until 1990, only a few studies on ethoxylation kinetics had been published. Extensive studies on this topic were performed by the group of Santacesaria et al. [2–6]. They studied the kinetics of fatty alcohol (1-dodecanol) ethoxylation using potassium hydroxide as catalyst [3] or barium dodecanoate as catalyst [4], the products presenting different chain length distributions depending on the catalyst used. Other related studies are the kinetics of nonylphenol ethoxylation catalyzed by potassium hydroxide [2], ethoxylation and propoxylation of 1-octanol and 2-octanol catalyzed by potassium hydroxide [5], and ethoxylation and propoxylation of ethylene glycol catalyzed by potassium hydroxide [6]. The ethoxylation kinetics is described as an ionic polymerization with equilibrium between the protonated oligomers. The catalyst concentration affects the protonated oligomer concentrations and the acidity ratio between the starter and the ethoxylated oligomers, thus affecting the chain size distribution of the oligomers. The industrial catalysts can be either acid or basic; the most used basic catalysts are potassium hydroxide and sodium hydroxide. The process is carried out industrially in spray tower loop reactors [6–11] or in jet loop (buss) reactors [6, 12, 13]. In a spray tower loop reactor, presented schematically in Fig. 1, the reacting liquid containing the catalyst and fatty alcohols is sprayed into an atmosphere of gaseous EO. Mass transfer of EO occurs to the liquid phase, where the ethoxylation reaction occurs. The heat released by the exothermic reaction is counterbalanced by an external heat exchanger through which the liquid is circulated prior to injection in the spray nozzle. In a typical industrial operation, the catalyst is added to the starter and the mixture is activated by the production of a potassium salt of the starter and water in an equilibrium Chem. Eng. Technol. 2011, 34, No. 10, 1635–1644 © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.cet-journal.com Gisele M. Amaral Reinaldo Giudici Universidade de São Paulo, Escola Politécnica, Department of Chemical Engineering, São Paulo, SP, Brasil. – Correspondence: Prof. R. Giudici (rgiudici@usp.br), Universidade de São Paulo, Escola Politécnica, Department of Chemical Engineering, Av. Prof. Luciano Gualberto, travessa 3, No. 380, 05508-010, São Paulo, SP, Brasil. Ethoxylation 1635