Computational Exploration of Adsorption Enhanced Haber-Bosch using MOFs and Ionic Liquid/MOFs

Abstract In this work, molecular simulation is utilized to perform the adsorption based separation of the ammonia-hydrogen-nitrogen mixture on Metal-Organic Frameworks (MOFs) operating conditions relevant to enabling low-pressure Haber-Bosch. MOFs are nanoporous structures that possess several desirable features; among them is the tunability in which one can target specific molecules through replacement or functionalization of organic linkers, metal nodes, and finally, cage decoration. This study aims to provide an efficient ammonia separation to reduce operating pressure in the ammonia reactor and highlight MOFs’ potential as material for novel applications in gas-gas separation. The pressure/temperature swing adsorption operational scheme is investigated, and the working delivered capacity and purity of ammonia are determined accordingly. Molecular simulation provides a way to examine nanomaterial potential in such applications inspecting a range of process conditions where the material is characterized based on loading, selectivity, and regeneration ability. Following an initial computational screening, Co2Cl2BBTA MOF is selected, and force field modifications have been done to fit experimental data. Besides analyzing the performance of Co2Cl2BBTA, encapsulation of ionic liquid (IL) [bmim][Tf2N] effect was analyzed from structural and adsorption properties. Interestingly, an optimum IL loading is determined based on the performance objective. Purity factor reached 93.3% at IL loading of 0.372 weight fraction. When considering capacity and purity factor, IL composition in MOF corresponding to 0.165 weight fraction revealed the best performance. Implementation of adsorption enhanced Haber-Bosch is expected to reduce immensely the amount of electrical power utilized to recycle the unreacted syngas to the ammonia synthesis reactor and produce ammonia at high pressures desirable for urea synthesis.