Protic ionic liquids as thermodynamic methane hydrates inhibitors

Abstract

Hydrates are highly unwanted solids in the oil/gas industry. They can be formed by water and gas molecules present in oil/gas production when pressure and temperature conditions are favorable to their precipitation. This can lead to flow obstruction, which is why chemicals able to inhibit their formation are desirable. In the last 15 years there has been interest in finding Ionic Liquids (ILs) able to inhibit hydrate formation. However, Protic Ionic Liquids (PILs), an inexpensive class of ILs, have been neglected in the published literature on ILs as thermodynamic hydrates inhibitors (THIs). In this work four PILs were experimentally tested as THIs in a high-pressure cell using the isochoric method with stepwise temperature increase. The PILs 2-hydroxyethylammonium formate ([2-HEA][Of]), 2-hydroxyethylammonium acetate ([2-HEA][Ac]), bis(2-hydroxyethyl)ammonium formate ([BHEA][Of]), and bis(2-hydroxyethyl)ammonium acetate ([BHEA][Ac]) were tested at 10 wt% and 20 wt% in water within a pressure range of 5.06 MPa–11.70 MPa. The possibility of synergy with ethylene glycol (MEG) was also considered by testing solutions of [2-HEA][Of] + MEG and [2-HEA][Ac] + MEG at 10 wt% total THI content in water. From the thermodynamically consistent data obtained, it was possible to verify that these PILs are powerful THIs, with suppression temperatures comparable to or higher than MEG at the same mass content. Therefore, progress in finding alternative chemical hydrates inhibitors has been made with this study. In particular, [2-HEA][Ac] at 20 wt% was capable of dislocating the hydrate equilibrium curve by 6.8 K. Additionally, it was possible to verify that the effect of adding PIL to MEG in an aqueous media is purely additive as THI.