Higher Fatty Acid-Based CO2-Controllable Dual-Circulation Approach for Oil Recovery

Advances in CO2-switchable surfactants towards the fabrication and application of responsive colloids

CO₂-switchable surfactants have selective surface-activity, which can be activated or deactivated either by adding or removing CO₂ from the solution. This feature enables us to use them in the fabrication of responsive colloids, a group of dispersed systems that can be controlled by changing the environmental conditions. In chemical processes, including extraction, reaction, or heterogeneous catalysis, colloids are required in some specific steps of the processes, in which maximum contact area between immiscible phases or reactants is desired. Afterward, the colloids must be broken for the postprocessing of products, solvents, and agents, which can be facilitated by using CO₂-switchable surfactants in surfactant-stabilized colloids. These surfactants are mainly cationic and can be activated by the protonation of a nitrogen-containing group upon sparging CO₂ gas. Also, CO₂-switchable superamphiphiles can be formed by non-covalent bonding between components at least one of which is CO₂-switchable. So far, CO₂-switchable surfactants have been used in CO₂-switchable spherical and wormlike micelles, vesicles, emulsions, foams, and Pickering emulsions. Here, we review the fabrication procedure, chemical structure, switching scheme, stability, environmental conditions, and design philosophy of such responsive colloids. Their fields of application are wide, including emulsion polymerization, catalysis, soil washing, drug delivery, extraction, viscosity control, and oil transportation. We also emphasize their application for the CO₂-assisted enhanced oil recovery (EOR) process as a promising approach for carbon capture, utilization, and storage to combat climate change.

CO2-Repurification Microemulsion Detergent for Oil-Based Slurry Cleaning

In order to solve problems such as environmental pollution and pipeline blockage caused by oily wastewater after washing, N,N-dimethylcyclohexylamine (DMCHA) with CO₂ response was selected as the oil phase, and an O/W microemulsion wellbore cleaning fluid with CO₂ switching characteristics was successfully prepared with erucamide propyl betaine (EAB-40), sodium dodecyl benzene sulfonate (SDBS), n-butanol, silicone defoamer, and water. The water content of the microemulsion was 89.99%, and it had good stability at 40 and -5 °C. The emulsion was rapidly demulsified after being injected with CO₂ in the CO₂-repurification microemulsion detergent, and CO₂ was removed with a N₂ detergent. The emulsion was restored to its original state, which demonstrated the CO₂/N₂ switching properties of the emulsion. It is proven that the switching microemulsion has a good wetting transformation ability by cleaning the steel sheet and quartz sheet contaminated by oil-based slurry. The switching microemulsion system can clean the simulated wellbore contaminated by oil-based slurry, and the cleaning efficiency is above 99%. CO₂ can be used at room temperature to separate oil and water from oily wastewater after cleaning.