Synthesis and characterization of a host–guest complex based on acetylated-β-cyclodextrin and its application in improving the viscosity of supercritical carbon dioxide

The development of carbon (CO 2 ) dioxidecapture, utilization, and storage methods is crucial to achieving carbon neutrality. The use of supercritical CO 2 (sc-CO 2 ) in enhanced oil recovery applications offers a promising carbon utilization route; however, its application in petroleum exploration and production is limited by its low viscosity. Here, a host–guest complex was synthesized based on acetylated-β-cyclodextrin (ACD) and polyphthalamide (PPA) to enhance the viscosity of sc-CO 2 , and various techniques were used to characterize its structure. The results showed that adding 2.0 wt% ACD-PPA/10 wt% ethanol at an ACD/PPA molar ratio of 1:3 increased the viscosity of sc-CO 2 to 4.36 mPa·s, an increase of ∼ 109 times compared with pure sc-CO 2 . The mechanism for viscosity enhancement involves the building of a large number of C O bonds between the ACD and CO 2 molecules, contributing to the polymer’s high solubility in sc-CO 2 . Meanwhile, a strong hydrogen bond network is formed between the hydroxyl groups of the PPA terminal groups. Hence, a supramolecular system is developed through interactions of the host and guest molecules, which dramatically improves the viscosity of sc-CO 2 . Increasing the viscosity of sc-CO 2 allows it to be used in underbalanced drilling, anhydrous fracturing, thick oil extraction, etc., as well as being valuable in the field of carbon capture and storage.