Experimental Measurement of Phase Equilibrium of Hydrate in Water plus Ionic Liquid + CH4 System

With the goal of discovering a more effective type of thermodynamic hydrate inhibitors (THIs), the phase equilibrium conditions of CH4 hydrates were examined in the presence of morpholinium and piperidinium ionic liquids (ILs) at a mass fraction of 0.1. It was observed that the addition of ILs shifted the hydrate equilibrium conditions toward higher pressure and lower temperature compared with those of hydrates formed from pure water. Both cationic and anionic species influenced the equilibrium conditions of the CH4 hydrate. The piperidinium ILs showed better inhibition effect than did the morpholinium ILs at the same species of counteranions. The result may be due to the more hydrophobic nature of piperidinium ILs, which have a higher affinity for CH4 molecules. It was also seen that the inhibition effect of BF4- ions was stronger than that of Br- ions for both piperidinium and morpholinium ILs. Thus, the inhibition effect became stronger in the order: N-ethyl-N-methylpiperidinium tetrafluoroborate ([EMPip][BF4]) > N-ethyl-N-methylpiperidinium bromide ([EMPip][Br]) > N-ethyl-N-methylmorpholinium tetrafluoroborate ([EMMor][BF4]) > N-ethyl-N-methylmorpholinium bromide ([EMMor][Br]). The best among these ILs had inhibition effectiveness comparable with ethylene glycol and triethylene glycol, which are used commercially as THIs.