Chemical Engineering Science 62 (2007) 5074 – 5077 www.elsevier.com/locate/ces Runaway prevention in liquid-phase homogeneous semibatch reactors Eugeniusz J. Molga a , ∗ , Michal Lewak a , K. Roel Westerterp b a Chemical and Process Engineering Department, Warsaw University of Technology, ul. Warynskiego 1, 00-645 Warsaw, Poland b Instituto Quimico de Sarriá, Ramon Llull University, via Augusta 390, 08017 Barcelona, Spain Received 18 June 2006; received in revised form 27 February 2007; accepted 12 March 2007 Available online 19 March 2007 Abstract A concept of the safety boundary diagram, elaborated in our previous studies for liquid–liquid heterogeneous reactions, has been developed here for liquid-phase homogeneous semibatch reactors. With the use of this boundary diagram, inherently safe-operating conditions can be easily determined without costly and time-consuming kinetic studies. A rapid procedure to estimate the dosing time and the cooling temperature appropriate for inherently safe operation of the reactor has been elaborated and proposed.  2007 Elsevier Ltd. All rights reserved. Keywords: Chemical reactors; Heat transfer; Homogeneous reactions; Thermal runaway; Reaction engineering; Safety 1. Introduction Despite a significant effort in research, design and manage- ment dedicated for many decennia by chemical engineers in the field of reactor safety, thermal runaway events in chemical reactors still occur. To prevent runaways three main lines of defence have to be considered in the design and operation of batch and semibatch reactors (Westerterp and Molga, 2006): • the choice of the right operating conditions; • the adaptation of efficient and robust early warning detection systems; • the application of a suitable system to handle and/or quench- ing reactions running away. The first line, which in a natural way is the first step in a design procedure, consists of elaboration and verification of safety cri- teria for the reactors. Numerous significant contributions to this subject can be found in the literature—a.o. see also the recent review by Westerterp and Molga (2006). From the industrial point of view, but particularly for fine chemical SMEs, the most important achievement is the determination of safety criteria for reaction systems for which kinetic information is scarce. ∗ Corresponding author. Tel.: +48 22 6606293; fax: +48 22 8251440. E-mail address: molga@ichip.pw.edu.pl (E.J. Molga). 0009-2509/$ - see front matter  2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.ces.2007.03.016 Westerterp and Molga (2004), elaborating further on the use of safety diagrams, derived previously for heterogeneous liquid–liquid reacting systems by Steensma and Westerterp (1990, 1991), demonstrated that the boundary safety diagrams can be successfully applied to determine inherently safe oper- ating conditions, even with limited kinetic information. In this study safety diagrams have been derived for homo- geneous liquid-phase semibatch reactors and for single reac- tions, described with the following stoichiometric equation:  A A +  B B →  C C +  D D. For homogeneous reactions a thermal runaway problem can occur even more rapidly than for the heterogeneous ones, due to the absence of interfacial mass transfer resistances. A fast and robust method to esti- mate safe operating conditions for such reaction systems is proposed. 2. Safety diagram and inherently safe operation Hugo and Steinbach (1986) have observed that an accumu- lation of the non-converted component dosed into a semibatch reactor may cause runaway events. They elaborated also prac- tical criteria to estimate safe operating conditions; however, these criteria are limited to a quite narrow range of operating conditions. In our study the safety diagrams have been developed for liquid homogeneous semibatch reactors within a wide range of