10:15 AM - 10:30 AM
[HSC07-06] Confirmation of the effect of CNF on improving the stability of supercritical CO2 foam
Keywords:Cellulose Nano-Fiber, Foam Stabilizer, Pickering Foam, Supercritical CO2
CO2 injected into deep aquifers becomes supercritical due to the conditions in the aquifer. In typical CCS conditions, supercritical CO2 (scCO2) selectively moves to upper part of the aquifer by buoyancy force because it has a lower density and viscosity than water. It yields a reduction of CO2 storage capacity of the aquifer. Numerous efforts have been conducted to increasing viscosity of scCO2 by making a stable scCO2 foam as an injected fluid. Stability of the foam can be improved by adding solid nanoparticle, namely the Pickering effect. Various particles, such as clay minerals, silica particles, and nanocellulose, can be used as foam stabilizers. Nanocellulose is one in which cellulose, the main component of plant cell walls, is unraveled to the nanometer level. It is derived from biomass and is biodegradable, that is, an eco-friendly material for CCS. In this study, we utilize Cellulose Nano-Fiber (CNF) as a foam stabilizer. It has a large aspect ratio among nanocelluloses and other solid particles. We investigate the improvement of the stability of scCO2 foam by adding CNF and influence of the large aspect ratio.
Stability of foam is strongly influenced by the viscosity of the suspension/solution and the Pickering effect. We exclude the influence of the suspension/solution viscosity on foam stability. We prepared two different foaming agents. One contains CNF and the other contains NaCMC (Carboxymethyl Cellulose Sodium), which is a thickening agent. The two suspension/solution have the same predetermined viscosity (5, 10, 15, 20 cP). Anionic surfactant, SDS (Sodium Dodecyl Sulfate), was added at the critical micelle concentration (8 mM). Stability evaluation was conducted by measuring a half-life, which is a quantitative indicator of the foam stability. The half-life is the time it takes for half volume of the solution to be drained from the foam.
ScCO2 foam with CNF (hereafter CNF foam) show a longer half-life than scCO2 foam with NaCMC solution (hereafter NaCMC foam) at all viscosities. It is considered that CNF adsorbs on the scCO2 -liquid interface in the foam. This is a typical stabilization mechanism by adding a solid particle to foam, suppressing the collapse and coarsening. In addition, the formation of an entangled structure inside the thin liquid film of foam and the accumulation of CNF at the border between foams are other factors contributing to stabilization.
CNF foam exhibits a characteristic drainage behavior. Rapid drainage occurs immediately after stirring, and then the drainage stops, while drainage of NaCMC foam is continuous. The sheared CNF temporarily lose their viscosity due to the destruction of the entangled structure, leading to rapid drainage immediately after stirring. CNF recovers the entangled structure by the Brownian motion, strongly stabilizing the foam. In this study, we showed that CNF has a unique behavior for stabilizing scCO2 foam, comparing to other solid particles with a lower aspect ratio. It was found that the entangled structure formed by CNF breaks down and recovers due to changes in shear stress during the foaming and drainage processes, exhibiting characteristics of foam collapse and stabilization.
Stability of foam is strongly influenced by the viscosity of the suspension/solution and the Pickering effect. We exclude the influence of the suspension/solution viscosity on foam stability. We prepared two different foaming agents. One contains CNF and the other contains NaCMC (Carboxymethyl Cellulose Sodium), which is a thickening agent. The two suspension/solution have the same predetermined viscosity (5, 10, 15, 20 cP). Anionic surfactant, SDS (Sodium Dodecyl Sulfate), was added at the critical micelle concentration (8 mM). Stability evaluation was conducted by measuring a half-life, which is a quantitative indicator of the foam stability. The half-life is the time it takes for half volume of the solution to be drained from the foam.
ScCO2 foam with CNF (hereafter CNF foam) show a longer half-life than scCO2 foam with NaCMC solution (hereafter NaCMC foam) at all viscosities. It is considered that CNF adsorbs on the scCO2 -liquid interface in the foam. This is a typical stabilization mechanism by adding a solid particle to foam, suppressing the collapse and coarsening. In addition, the formation of an entangled structure inside the thin liquid film of foam and the accumulation of CNF at the border between foams are other factors contributing to stabilization.
CNF foam exhibits a characteristic drainage behavior. Rapid drainage occurs immediately after stirring, and then the drainage stops, while drainage of NaCMC foam is continuous. The sheared CNF temporarily lose their viscosity due to the destruction of the entangled structure, leading to rapid drainage immediately after stirring. CNF recovers the entangled structure by the Brownian motion, strongly stabilizing the foam. In this study, we showed that CNF has a unique behavior for stabilizing scCO2 foam, comparing to other solid particles with a lower aspect ratio. It was found that the entangled structure formed by CNF breaks down and recovers due to changes in shear stress during the foaming and drainage processes, exhibiting characteristics of foam collapse and stabilization.