Influence of the synergy between reaction, heat exchange and membrane separation on the process intensification of the dimethyl ether direct synthesis from carbon dioxide and hydrogen

ABSTRACT This work presents a comprehensible approach based on the application of characteristic times and Damkohler numbers to optimize the synergy between catalytic reaction, heat exchange and membrane separation for an exothermic balanced reaction. This approach allows the description of parameters required to reduce limitations and intensify the process, considering the DME direct synthesis from a CO2-rich feedstock as a case study. Different couplings are dealt with: reaction and heat exchange; reaction and separation; and reaction, heat exchange and separation. Coupling to a heat exchange enables to follow an optimal temperature progression and minimize the reactor volume by maximizing the reaction rate at any position, allowing the design of compact equipment adapted to delocalized production. Coupling to a membrane increases the achievable conversion at a given temperature. A trade-off between these functions is necessary to achieve the optimal conditions. Appropriate heat exchange enables proper membrane operation. Coupling to a separation improves the performance of a reactor-heat exchanger configuration. 85% of CO2 conversion may be achieved. An optimization of the catalyst distribution is proposed, reducing the total catalyst mass by 21% and hot spot intensity by about 20 °C compared to a uniform catalyst distribution for an identical outlet conversion.