Quaternary salts can form semiclathrate hydrates with vacant cages to capture gas molecules, such as CO2. To study the effect in the formation process of CO2 hydrates, the formation kinetics of tetrabutylphosphonium bromide (TBPB) + CO2 hydrate were investigated in this work. The study was conducted by employing an isobaric method with salt mass fraction and subcooling degree ranging from (0.10 to 0.60) and from (8 K to 10 K), respectively. The kinetic performance of TBPB was evaluated by the induction time, normalized gas consumption, and normalized gas consumption rate. The results showed that the induction time decreased with the increase of subcooling degree as well as the salt mass fraction. When salt mass fraction exceeded 0.20, the average induction times were particularly short and almost the same. In addition, the salt mass fraction had a great impact on the normalized gas consumption rather than the normalized gas consumption rate. (C)2016 Elsevier B.V. All rights reserved.