Microchannel reactor heat-exchangers: A review of design strategies for the effective thermal coupling of gas phase reactions

[Display omitted] •Microchannel reactors are effective heat exchangers for process intensification.•Thermal aspects of counter-, co-, and cross-flow configurations are reviewed.•Reaction coupling is dependent on flow conditions, catalysts and channel dimensions.•Wall thermal conductivity is an important parameter to control reaction heat transfer.•Spatially segregated – yet thermally coupled – experimental reactors are reviewed. The thermal coupling of endothermic and exothermic reactions is an important pathway for integrated thermal management within chemical reactors, which supports process intensification. Microchannel reactors are unique in the sense that they provide various design and operational characteristics that benefit high throughput and millisecond contact time chemical conversions. These include high microchannel aspect ratios, improved heat transfer (via thin and thermally conductive reactor substrates), and enhanced mass transfer (due to limited diffusional effects). In this review of experimental and simulated microchannel reactors, focus is put on improved designs and operating strategies to support thermal conduction across microchannel walls, yet keep chemical products from the respective reactions separate using spatially-segregated reaction chambers. Three common flow configurations (counter-current, co-current and cross-flow designs) are critically discussed as a result of their abilities to distribute ‒ and in some cases recirculate ‒ reaction heat, the steady-state temperature profiles established within them as a result of flow direction, and reactant conversions/product yields as a result of their thermal characteristics. Special attention is devoted to microchannel design aspects, including wall thermal conductivity, channel dimensions, catalyst positioning and other design strategies (distribution manifolds and heat recirculative reactor designs) to improve heat and mass flows within microchannel reactors.