Novel Process Windows for the safe and continuous synthesis of tert. butyl peroxypivalate with micro process technology

Stipendiatin/Stipendiat: Dr. Tobias Illg

Since the 1950s, organic peroxides are intensively used in the industrial chemistry, especially in the polymer production [1]. Those substances easily decompose to free radicals and therefore are widely applied as initiators of free radical reactions, cross linking agents, bleaching agents, and pharmaceutical additives. Especially peroxyesters are mainly used as initiators for the polymerisation of ethylene or vinyl chloride. By varying the substituents it is possible to adjust the stability of these peroxyesters to the need of the process. The thermal instability of this class of organic peroxides can lead to a violent decomposition and under certain circumstances can cause an explosion if the heat of decomposition respectively the heat of reaction is not removed from the system. Since the common manufacturing processes are conducted in vessel reactors, the amount of reactive peroxides in the bulk moulding is enormous. On this account a lot of safety installations and measuring and control technology has to be implemented into the process. The conventional perester process is carried out in a vessel cascade and the reaction temperature is mainly controlled by step wise dosing of the reactant and mostly limited by the Self Accelerating Decomposition Temperature (SADT). Meaning that one or more components are presented in the reaction vessel and the other component is added in small portions. During these dosing steps the reaction temperature has to be strictly controlled to avoid thermal runaway, resulting in needless long reaction times and high energy costs for the cooling system. Thus an intrinsically fast reaction is deliberately slowed down for safety reasons. A common safety measure that is used to provide a sufficient temperature buffer is the dilution of the reactants. Through this, the heat of reaction is ?absorbed? and can slowly be removed. The presence of this extra solvent often influences the polymerisation process and has thus been removed before. The characteristics of this reaction make it necessary to provide good mixing to avoid mass transport limitations and also to avoid accumulation of the reactants. Also the thermal instability challenges engineering techniques. The avoidance of hot spot formation and the supply of good heat transfer are essential to guarantee a safe processing and to achieve a good conversion. The confirmed possibility to run reactions under unconventional conditions by using microstructured components should also open new process windows for the tert.-butyl peroxyester synthesis [2 - 7]. Conceivable is the boost of the process temperature up to, or above the SADT; assuming that the formation of the perester is faster than its decomposition. This will result in higher reaction rates and thus resulting in higher space-time-yields. For achieving this effect, it is essential to keep the thermal impact as short as possible. The supply of sufficient interfacial surface area in the second reaction step could also increase the conversion and additionally avoid the accumulation of reactant. The directly involved reactive volume is also reduced and can be better controlled ? in the case of process failure - than in a conventional batch process. The gained information should be beneficial for other peroxide / perester synthesis.[1] R. Dittmeyer, W. Keim, G. Kreysa, A. Oberholz, Winnacker-Küchler- Chemische Technik, Prozesse und Produkte, Band 3 Anorganische Grundstoffe, Zwischenprodukte, 5. Auflage, Wiley-VCH 2003-2005[2] V. Hessel, P. Löb, H. Löwe, Curr. Org. Chem., 2005, 9, 765-787[3] V. Hessel, C. Hofmann, H. Löwe, A. Meudt, S. Scherer, F. Schönfeld, B. Werner, Org. Proc. Res. Dev., 2004, 8, 511-523[4] V. Hessel, C. Hofmann, P. Löb, J. Löhndorf, H. Löwe, A. Ziogas, Org. Proc. Res. Dev., 2005, 9, 479-489[5] T. Schwalbe, V. Autze, M. Hohmann, W. Stirner, Org. Proc. Res. Dev., 2004, 8, 440-454[6] A. Renken, V. Hessel, P. Löb, R. Miszczuk, M. Uerdingen, L. Kiwi-Minske, Org. Proc. Res. Dev., 2007, 46, 840-845[7] DDR128663, 1976