Effect of spray-drying and cryo-milling on the CO2absorption performance of C60cross-linked polyethyleneimine

The high CO2 capacity of PEI-C60 conjugates is impeded by a slow rate of absorption. A limiting factor to this rate is proposed to be the surface area available for the rapid contact between amine functional groups of PEI and CO2. Increasing the surface area by spray-drying a solution of reagents is proposed as a route to larger surface area products. In this work we investigate process changes to control absorption chemistry. Reagent solutions were spray-dried in different experimental conditions of concentration, drying temperature, and feed pressure. The results indicate that the rate of CO2 absorption at room temperature can be improved by a factor of 2.5 times by spray drying the product when compared to the product obtained using sonication. Given the rubbery nature of PEI-C60 the surface area, and hence CO2 capacity, could be increased using cryogenic grinding in liquid nitrogen; however, the results show that this has limited effect on the surface area of the absorbent prepared using sonication. Only compared to the hard chunks obtained via stir bar synthesis was the surface area doubled, in contrast to the rubbery product obtained using ultrasonication the area did not change significantly. Interestingly, doubling the surface area, the rate of absorption of wet CO2 at high temperature did not change, while that at low temperature doubled in rate, consistent with the presence of diffusion limitations manly at low temperature

Exceptional ammonia uptake by a covalent organic framework

Covalent organic frameworks (COFs) are porous crystalline materials composed of light elements linked by strong covalent bonds. A number of these materials contain a high density of Lewis acid boron sites that can strongly interact with Lewis basic guests, which makes them ideal for the storage of corrosive chemicals such as ammonia. We found that a member of the covalent organic framework family, COF-10, shows the highest uptake capacity (15 mol kg−1, 298 K, 1 bar) of any porous material, including microporous 13X zeolite (9 mol kg−1), Amberlyst 15 (11 mol kg−1) and mesoporous silica, MCM-41 (7.9 mol kg−1). Notably, ammonia can be removed from the pores of COF-10 by heating samples at 200°C under vacuum. In addition, repeated adsorption of ammonia into COF-10 causes a shift in the interlayer packing, which reduces its apparent surface area to nitrogen. However, owing to the strong Lewis acid–base interactions, the total uptake capacity of ammonia and the structural integrity of the COF are maintained after several cycles of adsorption/desorption.Christian J. Doonan, David J. Tranchemontagne, T. Grant Glover, Joseph R. Hunt and Omar M. Yagh