Effect of l-Tryptophan in Promoting the Kinetics of Carbon Dioxide Hydrate Formation

Carbon dioxide capture and storage (CCS) can play a vital role in overcoming global warming challenges and can help to reduce carbon footprint significantly from the environment. Carbon dioxide (CO2) hydrates are a potential option for CCS, but slow hydrate formation is a technical challenge that needs to be overcome. Kinetic promoters are often added to improve the formation rate of gas hydrates and process efficiency. In this systematic and comprehensive work, the performance of l-tryptophan, an environmentally friendly promoter, as a kinetic promoter for CO2 hydrate formation was evaluated using a stirred tank reactor. The kinetic performance of the CO2 hydrate formation process was evaluated using varying l-tryptophan concentrations (0, 100, 300, and 1000 ppm) under different experimental pressure and temperature conditions. The impact of l-tryptophan was assessed using gas uptake measurements (induction time, hydrate growth rate, and yield) coupled with visual observations through the front and top view of the reactor. With the addition of only 300 ppm l-tryptophan, an average gas uptake of 114 v/v (78% water conversion to hydrates) was achieved at 273.65 K and 3.4 MPa, which was four times that for the case without the promoter. Further increase in l-tryptophan concentration did not result in significant additional improvement. Compared to 277.65 K, experiments conducted at 273.65 and 275.65 K showed much shorter induction times and better gas uptake performance. With such an excellent enhancement effect at a low dosage and being environmentally friendly, l-tryptophan is recommended as a potential kinetic promoter for CO2 hydrate formation that could be applied for CO2 capture and storage via gas hydrate technology.