Magnesium hydroxide – expanded graphite composite pellets for a packed bed reactor chemical heat pump

•An expanded graphite/Mg(OH)2 composite was developed for a packed bed reactor chemical heat pump.•The expanded graphite/Mg(OH)2 composite (EM) was compressed in figure of pellets.•Higher reaction rates were observed for the dehydration and hydration of EM pellets.•EM pellets showed better performance in terms of heat storage and heat output.•EM pellets were able to withstand repetitive cyclic reactions without significant failures.

The chemical heat pump is a promising technology for the recovery of waste heat from industrial processes or cogeneration systems. It can be used for storing the surplus heat during low demand periods and release it for shaving the peaks of heat demand, with a benefit for the overall system efficiency. In this work, a packed bed reactor chemical heat pump based on the dehydration and hydration of magnesium hydroxide has been investigated. Due to its high thermal conductivity, expanded graphite was mixed with magnesium hydroxide to enhance heat transfer. The composite material, named EM, was developed and tested experimentally in order to understand the effects of expanded graphite on the chemical reactions occurring in the packed bed reactor.