Effect of sodium tripolyphosphate (STPP) and tetrasodium pyrophosphate (TSPP) on the formation kinetics of CO2 hydrate in bulk and porous media in the presence of pure water and seawater relevant for CO2 sequestration

Abstract

Enhanced kinetics of carbon dioxide (CO2) hydrate formation will assist in developing technologies for CO2 gas storage, carbon capture and sequestration (CCS), and potentially for methane production from natural gas hydrates. The present work is focused on understanding the kinetics of CO2 hydrate formation in both bulk and porous media with pure water and seawater under the influence of non-toxic and low-cost inorganic emulsifiers or builders. Sodium tripolyphosphate (STPP) and tetrasodium pyrophosphate (TSPP) was used in a very low concentration of 0.2 wt.% to promote its economic viability. The experiments were carried out in a 300 mL stirred tank reactor and 100 mL porous bed reactor with an initial pressure of 3.5 MPa and 274.65 K with pure water and seawater, respectively. The porous bed was made with 0.15 mm silica sand with 70% water saturation. Both STPP and TSPP showed significant improvement in induction time for CO2 hydrate formation. Moreover, STPP showed reasonable enhancement in CO2 gas uptake compared to TSPP in both bulk and porous bed with both pure water and seawater. The average rate of hydrate formation was also better for STPP with multiple growth peaks. The results obtained will enhance hydrate-based technologies for efficient CO2 sequestration in shallow subsea sediments.