Heat Pipe-Mediated Control of Fast and Highly Exothermal Reactions

Abstract

The synthesis of 1-ethyl-3-methylimidazolium ethyl-sulfate ([EMIM]EtSO 4 ) from 1-methyl-imidazole and diethyl sulfate suffers from highly exothermal behavior. Once the activation energy barrier is reached (E A = 89 kJ mol À1 ), the bimolecular reaction accelerates with a high reaction enthalpy (ΔH = À130 kJ mol À1 ). 1À3 The excess of heat has to be concurrently dissipated to avoid hot spots or thermal runaways. Depending on the volume flow velocity of the reactants and the applied reactor temperature, the reaction zone can be shifted inside the reactor from the inlet to the outlet and vice versa. Therefore, a sophisticated thermal control, oscillating between providing activation energy and intense cooling of the reaction mixture, is required. Heat pipes intrinsically allow both fast dynamic bidirectional heating and cooling. A stainless steel chiplike setup equipped with an externally heated, modified heat pipe system was used. 4 Independently from the reactant volume flow, a colorless and 1 H NMR clean product could be obtained by setting a self-controlled optimal operating temperature of about 100 °C.

Rapid process development using oscillatory baffled mesoreactors – A state-of-the-art review

“…Since then, Löwe et al (2010) [54] have commented that the very fast thermal response times and passive heat transfer of the heat pipe can suppress thermal runaways, as any heat transfer fluctuations can be removed at a maximum velocity corresponding to sonic conditions, or a Mach number of 1 for the working fluid. Ehm and Löwe (2011) [77] also used the same heat pipe micro-reactor for ionic liquid synthesis. By rapidly increasing/decreasing the operating temperature in discrete steps, the authors demonstrated that the maximum temperature spike from the reaction could be shifted within the reactor.…”

Novel Process Windows for Enabling, Accelerating, and Uplifting Flow Chemistry

“…Towards this end, heat pipes were used for dynamic cooling of microstructured reactors by Löwe et al. in the synthesis of 1‐ethyl‐3‐methylimidazolium trifluoromethane sulfonate (Scheme ) 58. 59 With this reactor setup, the cooling rate could be automatically adjusted, depending on the released heat, thereby avoiding the formation of hot spots and thermal runaways.…”

“… Flow synthesis of 1‐ethyl‐3‐methylimidazolium trifluoromethanesulfonate with heat‐pipe dynamic cooling 58…”