EXPERIMENT: Millipore water (18.1 Ω) was used for all experiments. NaCl(s) (Sigma-Aldrich; 99.9% purity) and CO2(g) (Praxair; 99.999% purity) were used as received. Fluidic System. Figure 1A shows a simplified diagram of the experimental setup that was designed to generate concentration profiles of CO2 in water (or in brines) as a function of time at 90 ± 2 bar and 50 ± 2 °C.
Figure 1. (A) Schematic diagram of the experimental setup used for the diffusion experiment. (B) PEEK holder that connects the capillary tubing to the fluidic system.
The fluid handling system consists of two Teledyne ISCO model 100DM pumps (pumps A and B), two Chemyx Nexus 6000 syringe pumps (pumps C and D), and stainless steel and PEEK tubing and valves to deliver and control the flow pattern at high pressure and temperature. A homemade right-angle PEEK holder (Figure 1B) connects fused silica capillaries (Polymicro Technologies; 150 or 200 μm diameter) to the fluidic system. The entire fluidic setup, with the exception of the pumps, is kept in an insulated box in which the temperature was controlled with an active PID controller (Omega Engineering, model CN8DPt)) within ±2 °C. In a typical experiment, the fluidic pathway is thoroughly flushed (to remove air in the system) and filled with water (or brines) among valves V1, V2, and V3 with pump A. Thereafter, with valve V2 closed, pumps B and C are synchronized in a “push− pull” motion to deliver and withdraw scCO2 to and from the system. This process replaces water (or brine) between V1 and V3 with scCO2 (the flow path indicated in yellow in Figure 1B) while leaving a trapped stationary water/brine column in the capillary tubing from point A to V2 (blue line). This procedure establishes a stable aqueous/scCO2 interface at point A (x = 0) in the PEEK adapter.
