Superabsorbent polymer for improved CO2 hydrate formation under a quiescent system

Abstract

The hydrate formation rate and conversion yield are essential factors for hydrate-based gas storage and accordingly various thermodynamic and kinetic promoters have been extensively investigated. However, for hydrate-based CO2 capture, carbonate ions induced from dissolved CO2 in water hinder the performance of kinetic promoters (e.g., sodium dodecyl sulfate (SDS)). In this work, we introduce a superabsorbent polymer (SAP) matrix that provides an extremely high interfacial area between a sorbed tetrahydrofuran (THF) solution and gaseous CO2. The SAP enhanced the formation rate of binary THF-CO2 hydrate, despite the absence of mechanical agitation. We varied the concentration of THF, temperature, reactor volume, and the ratio of solution to the reactor for a systematic study and explored their effects on the CO2 storage capacity and the induction time. We observed that highly concentrated THF and a larger reactor with a high gas-liquid contact area enhanced the CO2 storage capacity and formation rate. Raman and PXRD spectroscopic analyses were employed to investigate the guest distribution and crystalline structure of the THF-CO2 hydrates synthesized under various conditions. All the binary hydrates were structure-II (sII) hydrates, and there was no pure structure-I (sI) CO2 hydrate. Based on the spectroscopic results, we developed a theoretical model that could calculate the amount of enclathrated CO2 and dissolved CO2 in liquid phases separately. This work reveals that SAP has excellent potential for rapid CO2 capture in hydrate media with a high water-to-hydrate conversion ratio.