High yield, large-scale synthesis of calcium-based microporous metal-organic framework and examination of the long-term stability for xenon adsorption applications

Abstract

Scale-up synthesis of calcium-based microporous metal-organic framework (SBMOF-1) up to ∼400 g in a batch with a yield of >90 % was achieved by a solvothermal reaction of sulfonyldibenzoic acid (SDB) with an excess of calcium chloride. Here, we observed that recrystallization of unreacted SDB at a solvothermal condition caused a moderate reaction yield (40–50 %) at the reference condition of CCaCl2/ CSDB = 1 and CSDB/ CSDB(ref) = 1. Simply adding more reagents to the reactor did not increase the mass of product formed per unit volume due to a more pronounced loss of the yield at those conditions. By simultaneously changing the molar ratio of CaCl2 to SDB, CCaCl2/ CSDB, and the molar concentration of the SDB reagent, CSDB/ CSDB(ref), we explored %yield of the reaction. Interestingly, a linear improvement in the yield was observed from 21 % (at CCaCl2/ CSDB = 0.5) up to 78 % (at CCaCl2/ CSDB = 6) at a fixed ratio of CSDB/ CSDB(ref) = 2 and the yield leveled off after further addition. Unlike those at CCaCl2/ CSDB = 1, the yields at a high CaCl2 excess continued to improve with increasing the CSDB/ CSDB(ref). When a large pressure vessel (2500 mL EtOH, CCaCl2/ CSDB = 6, CSDB/ CSDB(ref) = 8) was used, about 415 g of SBMOF-1 with a yield of 92.3 % was produced, indicating 16 × the space yield improvement. The ability to synthesize SBMOF-1 on a large scale allowed us to examine the long-term stability of SBMOF-1 for almost 200 days in the presence of varying levels of relative humidity.