Chemical Engineering and Processing 46 (2007) 840–845 Ionic liquid synthesis in a microstructured reactor for process intensification A. Renken b,∗ , V. Hessel a,c , P. L¨ ob a , R. Miszczuk b , M. Uerdingen d , L. Kiwi-Minsker b a Institut f ¨ ur Mikrotechnik Mainz GmbH, Carl-Zeiss-Str. 18-20, D-55129 Mainz, Germany b Ecole Polytechnique F´ ed´ erale de Lausanne, SB-ISIC-GGRC-Station 6, CH-1015 Lausanne, Switzerland c Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands d Solvent Innovation GmbH, Nattermannallee 1, D-50829 K¨ oln, Germany Received 24 May 2007; accepted 28 May 2007 Available online 15 June 2007 Abstract Ionic liquids (IL) are the focus of growing interest over the last few years due to their low vapour pressure being beneficial for replacing common organic solvents with high vapour pressure. IL synthesised via alkylation are produced in batch or semi-batch stirred tank reactors. The reaction is highly exothermic and the kinetics was shown to be fast. The heat management during the reactor operation is a crucial point leading to high quality IL product and avoiding thermal runaway. This study reports the use of a microstructured reactor (MSR) system for the production of ethylmethylimidazole ethylsulfate by a solvent-free alkylation reaction. A combination of MSR and two tubular capillary reactors operating at two different cooling temperatures has been proposed. The save and stable operation of this reactor system is proven experimentally rendering the IL of high quality. The specific reactor performance was about 4 kg m -3 s -1 being ca. 3 orders of magnitude higher as compared to more traditional reactors. © 2007 Elsevier B.V. All rights reserved. Keywords: Microreactor; Process intensification; Novel chemistry; Ionic liquids 1. Introduction Ionic liquids (IL) have gained an enormous interest over the past years due to their unique low vapour pressure being beneficial for the replacement of traditional organic solvents in organic synthesis and extraction [1,2]. The potential appli- cations of IL may lead to an increasing demand. Therefore, appropriate methods allowing their production on industrial scale are warranted. Traditionally, IL synthesised via alkyla- tion are produced in batch or semi-batch stirred tank reactors. The reaction is highly exothermic and the kinetics was shown to be fast. The heat management is of major concern to attain high quality product and to avoid thermal runaway. Therefore, it is difficult to increase the specific reactor performances by using traditional reactors. In the present study, we report the use of microstructured reactors (MSR) for the production of ∗ Corresponding author. E-mail address: albert.renken@epfl.ch (A. Renken). an ethylmethylimidazole ethylsulfate ([EMIM][EtSO 4 ] under solvent-free conditions via alkylation of methylimidazole with diethylsulfate. Organic synthesis under solvent-free conditions leads to more benign processes and is an important factor for process intensification. The scheme of the chosen reaction is presented in Fig. 1. Chemical microstructured reactors (MSR) are devices containing open paths for fluids with dimensions in the sub- millimeter range. Mostly MSR have multiple parallel channels with diameters between 10 and several 100 m where the chem- ical transformations occur. This gives a high specific surface area in the range of 10,000–50,000 m 2 m -3 and allows an effec- tive mass and heat transfer compared to traditional chemical reactors. Another important feature of MSR is that the heat exchange and the reaction are often performed in the same gadget. MSR are operated under laminar flow with the heat transfer coefficient for liquids about 10 kW m -2 K -1 . This is one order of magnitude higher than in the traditional heat exchang- ers and allows: to avoid hot-spot formation, to attain higher reaction temperatures and to reduce reaction volumes. This in 0255-2701/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.cep.2007.05.020