Direct fluorination of carbon monoxide in microreactors Walter Navarrini a,b , Francesco Venturini a, *, Vito Tortelli c , Soubir Basak d , Ketan P. Pimparkar d , Andrea Adamo d , Klavs F. Jensen d a Dipartimento di Chimica, Materiali e Ingegneria Chimica, Politecnico di Milano, 7 Via Mancinelli, I-20131 Milano, Italy b Consorzio Interuniversitario Nazionale per la Scienza e Tecnologia dei Materiali, 9 Via G. Giusti, I-50121 Firenze, Italy c Solvay-Solexis, R&D Centre, 20, Viale Lombardia, I-20021 Bollate (MI), Italy d Chemical Engineering Department, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, United States 1. Introduction High purity COF 2 is required in many applications [1–10]. The usual approach to obtaining this compound is the direct fluorination of carbon monoxide with elemental fluorine. In general the reaction of organic substances with fluorine, in conventional reactors, is difficult to control due to the heat generated by the reaction itself [11]. The fluorination of a hydrogenated compound is a typical example where the exo- thermicity of the whole reaction is such that any carbon–carbon bond can be easily broken if the reaction is not properly controlled by dilution of reagents and by adopting a low reaction temperature and CH activation [12,13]. The improperly conducted fluorination leads invariably to several byproducts and ultimately to CF 4 and HF [14]. Attempts to obtain a clean stream of COF 2 have been carried out mainly by trying to reduce the flame temperature via massive dilution of the inlet streams or by switching to electrochemical fluorination [15,16]. The introduction of inert gases implies, at a fixed contact time, an increase of the reactor volume or, at a constant volume, a decrease in plant productivity. As a matter of fact, only a massive introduction of a dilution stream results in a lower flame temperature and hence in a higher selectivity [5,9,17]. Recently a flame-less approach has been patented [18]. It is reported that the two reactants, fluorine and carbon monoxide are continuously bubbled in a continuous stirred-tank reactor (CSTR) filled with a solvent [19]. This system has clearly some critical points, i.e. solvent stability [20] and operability. A good practice to obtain pure carbonyl-difluoride is to reduce the flame temperature by increasing the heat exchange surface. Due to the large amount of heat released during the reaction, the surface/volume ratio of the reactor has to be high, thus the use of a microreactor seems to be a suitable option. In fluorine chemistry, there is a large interest in the development of microreactors for chemical processing [21–25] due to the benefits that this technological device could provide: better reaction control, arithmetic scale-up and higher safety. Herein we report the use of a microreactor to test the highly exothermic gas phase reaction CO + F 2 with the aim of better controlling the temperature and increase the reaction selectivity. 2. Materials and methods Pure fluorine (98%, from Solvay Fluor) and pure carbon monoxide (99.8%, from Sapio) were fed in the reactor without any further dilution. The experiments were performed by setting the carbon monoxide flow-rate to 1 NL/h (44.6 mmol/h) and acting on the fluorine flow-rate in order to reproduce three experimental conditions: a lean, a stoichiometric and a rich combustion. The composition measurements of the gas produced were taken Journal of Fluorine Chemistry 142 (2012) 19–23 A R T I C L E I N F O Article history: Received 27 March 2012 Received in revised form 27 May 2012 Accepted 2 June 2012 Available online 23 June 2012 Keywords: Carbonyl-difluoride Hypofluorite Synthesis Microreactor Direct fluorination A B S T R A C T Many attempts to obtain a clean stream of COF 2 have been carried out in the past by means of the direct fluorination of carbon monoxide with elemental fluorine or by electrochemical fluorination. The reaction is highly exothermic, therefore difficult to control. It can easily develop into a thermal runaway with a poor selectivity. We have successfully circumvented these critical issues by using a stainless steel parallel channel microreactor (surface/volume ratio  1  10 4 m 1 , residence time t  0.1 s) for the direct fluorination of carbon monoxide. Its performance in terms of operability and selectivity is compared to that of a standard reactor assembly, namely a fluorine burner reactor coupled with a water cooled heat exchanger. While the microreactor assembly succeeded to control the exothermic reaction, in the same experimental conditions the standard assembly reactor underwent serious corrosion issues that lead to nozzle meltdown lack of selectivity and consequent plant shutdowns. ß 2012 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +39 02 2399 3035; fax: +39 02 2399 3080. E-mail address: francesco.venturini@chem.polimi.it (F. Venturini). Contents lists available at SciVerse ScienceDirect Journal of Fluorine Chemistry jo ur n al h o mep ag e: www .elsevier .c om /loc ate/f luo r 0022-1139/$ – see front matter ß 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jfluchem.2012.06.006