(648g) Controlled Morphology and Scale-up of Mg-MOF-74 for Direct Air Capture of Carbon Dioxide

Net-zero emissions technologies have been identified by the IPCC as an important tool to achieve the goal of a less than 2 °C global average temperature rise over pre-industrial levels. Several companies are currently working to commercialize direct-air capture (DAC) technologies to remove CO₂ directly from the atmosphere, but significant strides need to be made in the development of sorbent materials to make this an economically viable approach. Sorbent materials need to exhibit high CO2 capacity at low CO₂ concentrations (i.e. at atmospheric concentrations of ~400 ppm), rapid sorption and desorption kinetics to facilitate capture and regeneration cycles, low regeneration energy to minimize operating cost and carbon footprint, and low material capital costs. Sorbent materials also need to exhibit high stability over numerous sorption/regeneration cycles to increase the lifetime of the materials.

We have studied a series of metal organic framework (MOF) materials with the aim of optimizing and scaling them up as solid sorbents for direct air capture of CO2. Specifically, we are interested in observing the effect of synthesis scale-up and particle morphology on packed bed CO₂ sorption in DAC-relevant conditions. Previously, we evaluated the physical and CO₂ adsorption characteristics of MOF MIL-101-Cr synthesized at three different scales. Herein we will present on DAC using Mg-MOF-74.

Modulated syntheses of Mg-MOF-74 using different modulators (benzoic and salicylic acid) as well as a variety of reaction scales (100 mL, 250 mL, and 500 mL) resulted in variable and controllable particle morphologies, indicating that Mg-MOF-74 is highly favorable for morphological and size control studies relating to synthesis and gas sorption performance. The resulting MOF samples were studied using isothermal gravimetric and volumetric sorption techniques. The MOFs were also studied under multiple sorption/regeneration cycles in a packed bed sorption apparatus under dry and humid DAC operating conditions.

We found that the BET surface area and the CO₂ adsorption capacity of Mg-MOF-74 decreased significantly as the scale of the synthesis reaction increased, possibly due to differences in reactor geometry, heat distribution or flow effects between scales. The two morphologies that resulted from the use of different modulators showed differences in BET surface area and CO₂ adsorption capacity at different conditions.