Heat Pipe‐Cooled Microstructured Reactor Concept for Highly Exothermal Ionic Liquid Syntheses

Abstract

Heat pipes used for cooling of microstructured reactors are a new approach for sustainable processing also in the lab-scale within a temperature range from ambient to more than 180°C. The main advantage of heat pipe cooling is the dynamic behavior, i.e., the cooling rate depends on the heat released. Heat pipes can also suppress thermal runaways due to their extremely short response times on momentary temperature rises. As an example, the highly exothermal synthesis of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate from the respective reactants 1-ethyl-imidazole and methyltrifluoromethanesulfonate was investigated. By transferring the protocol to continuous-flow conditions in the microscale and by applying cooling with heat pipes, an out-of-control processing can be avoided.

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

“…Continuous micro-reactors can minimise waste generation and can have very high mass and heat transfer rates due to their compact designs [54]. However, one of the challenges of microreactors is multiphase processing.…”

“…Using the heat pipe system, good thermal control was reported with a total flow rate up to 9.7 mL/min with no fan assistance, and 20 mL/min with fan-assisted forced convection cooling, demonstrating that safe operation of highly exothermic reactions under continuous conditions is possible. 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.…”

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

“…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. Production rates of 1.24 kg h −1 of the ionic liquid were feasible with this device; this corresponds to a space–time yield of 4270 tonne h −1 m −3 .…”

Ionic liquids and continuous flow processes: a good marriage to design sustainable processes

“…Hence, a production rate up to 1.24 kg h −1 of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMIM][OTf ]) can be achieved. 19,20 In a similar way, Waterkamp et al have reported an approach to intensify the synthesis of 1-butyl-3-methylimidazolium bromide ([BMIM]-[Br]) by using a continuously operating micro-reactor system. 21 The reactor set-up consists of a microstructured mixer of 450 µm channel width and a tubular reactor (inner diameter from 2 to 6 mm).…”