Scalable Mechanochemical Synthesis of β-Ketoenamine-linked Covalent Organic Frameworks for Methane Storage

In the current scenario of increased pollution and releasing toxic gases by burning petroleum products, switching to natural gas is more promising for reducing CO₂ emissions and air pollutants. Hence, research on Liquefied Natural Gas and Compressed Natural Gas is gaining more value. However, natural gas primarily consists of CH₄ , which has less energy density than conventional fuels. Interestingly, since the C-H ratio of CH₄ gas is 1 : 4, it is easily combustible, gives less carbon footprint, and reduces unburnt hydrocarbon pollution. Hence, research on storing and transporting CH₄ has utmost importance, and porous materials are one of the suitable candidates for storing CH₄ . Herein we report the scalable synthesis of highly porous and crystalline covalent organic frameworks for storing CH₄ at room temperature and pressure. Two COFs, namely, Tp-Azo and Tp-Azo-BD(Me)₂ , synthesized in 1 kg at ∼45 g batch scale using a Planetary mixer, displayed a maximum BET surface area of around 3345 m² /g, and 2342 m² /g and CH₄ storage of 174.10 cc/cc and 151 cc/cc, respectively. A comparison of the CH₄ sorption of Tp-Azo and Tp-Azo-BD(Me)₂ COFs synthesized in different batches has a variation of only ±5 cc/cc and shows the consistency in bulk scale synthesis of COFs. The cyclic equilibrium CH₄ adsorption studies showed the COFs are stable with consistent CH₄ adsorption and desorption cycles. The present study is a step towards the scalable mechanochemical synthesis of COFs for gas storage applications.