Screen additives for CH4/CO2 separation by gas hydrate technique: Investigating the effect of pyrrolidine, piperidine, 1-methylpiperidine, and 4-methylpiperidine on phase boundary and induction time of CO2 hydrate

Background

This study investigates the effect of four cyclic secondary amine additives, pyrrolidine, piperidine, 1-methylpiperidine, and 4-methylpiperidine, on CO₂ hydrate formation to advance gas hydrate techniques for CH₄/CO₂ separation.

Methods

The equilibrium dissociation conditions were collected at 1.7–3.4 MPa with 5 and 10 wt% additive concentrations by an isochoric method. The Clausius–Clapeyron analysis and the Østergaard-Masoudi-Tohidi-Danesh-Todd model were used to speculate the CO₂ hydrate structure and to correlate the dissociation data, respectively. In addition, the effects of pyrrolidine and piperidine at 5 and 10 wt% concentrations on the induction time of CO₂ hydrate formation were determined.

Significant findings

Cyclic secondary amines, particularly pyrrolidine, exhibited the strongest inhibition compared to previously reported thermodynamic hydrate inhibitors (THIs), such as amines, alcohols, and ionic liquids. In addition, pyrrolidine and piperidine also significantly prolonged the induction time of CO₂ hydrate and kinetically inhibited CO₂ hydrate formations. In summary, this study suggests that pyrrolidine and piperidine act as dual-function additives, promoting CH₄ hydrate formation while inhibiting CO₂ hydrate formation from both thermodynamic and kinetic perspectives. This unique characteristic presents a strong potential for CH₄/CO₂ separation via HBGS technology through the selective formation of CH₄ hydrate, as such additives have not been previously reported.